geological survey of denmark and greenland bulletin 28, 2013, 25-28 25 terrain subsidence detected by satellite radar scanning of the copenhagen area, denmark, and its relation to the tectonic framework peter roll jakobsen, urs wegmuller, ren capes and stig a. schack pedersen in the european union (eu) project terrafirma, which is supported by the european space agency to stimulate the global monitoring environment system, we are using the latest technology to measure terrain motion on the basis of satellite radar data. the technique we employ is known as persistent scatterer interferometry (psi); in denmark, it was previously used to map areas of subsidence susceptible to f looding in the danish part of the wadden sea (vadehavet) area (pedersen et al. 2011). that study was part of the f looding risk theme under the terrafirma extension project. another coastal protection monitoring activity in the eu seventh framework project subcoast followed, in which the low-lying south coast of lolland, prone to f looding, was studied. the geological survey of denmark and greenland (geus) is also involved in the three-year eu collaborative project pangeo in which geus is one of 27 eu national geological surveys. the objective of pangeo is to provide free and open access to geohazard information in support of the global monitoring environment system. this will be achieved by providing a free, online geohazard information service for the two largest cities in each eu country, i.e. 52 towns throughout europe with c. 13% of eu’s population. the danish cities selected for investigation under terrafirma are copenhagen and aalborg. capitals have first priority, and aalborg was chosen because of good satellite data. in this paper, psi data for copenhagen are presented together with interpretations of terrain displacement (fig. 1). psi processing of satellite radar data for copenhagen the satellite data covering copenhagen were obtained from the descending track d480 ers satellite in the period 1992–2000. the psi processing was carried out by gamma remote sensing ag, using a method that was carefully qualified and validated in the terrafirma project (crosetto et al. 2008). geus carried out the analysis using the program arcgis, in which geological and topographical data provide the basis for interpretation. based on the psi data, nine areas were outlined in which subsidence had occurred over the period 1992–2000. the areas are between 0.1 and 2.2 km2 and here we present two of them. apart from those mentioned above, minor subsidence differences of regional extent have been recognised; these are interpreted as tectonic. the copenhagen area that was processed has a size of 960 km2 with a reference point at 55.685668°n, 12.493937°e. a total of 419  660 psi points were identified, corresponding to 437 points per km2. the majority of the points (94.5%) show small rates of vertical motion, i.e. between –1.5 and +1.5 mm/year. a small number of points (1.6%) show subsidence rates of 3.5 to 1.5 mm/year, and a few (0.2%) show subsidence rates of more than 3.5 mm/ year. a few points (0.4%) show uplift rates between 1.5 and 3.5 mm/year; these are regarded as scattered uncertainties in relation to the average annual motion rate of 0.35 mm/ fig. 1. map of greater copenhagen showing the area covered by psi data. vertical movements are represented in a raster grid showing the average movement in 100 × 100 m squares. the concentrations of yellow-red colours show areas with maximum rates of subsidence. note the regional difference in light and dark green colours which might be caused by tectonic subsidence east of the carlsberg fault zone. © 2013 geus. geological survey of denmark and greenland bulletin 28, 25–28. open access: www.geus.dk/publications/bull carlsberg fault zone rate of change (mm/year) −10 to −4 −4 to −3 −3 to −2 −2 to −1 −1 to −0.5 −0.5 to 0.5 0.5 to 1 1 to 2 2 to 3 3 to 4 4 to 5 5 km 55°40´n 12°28´e øresund sjælland amager furesø airport harbour 2626 year for the entire area, with a standard deviation of annual motion rate amounting to 0.74 mm/year. the geology of copenhagen and its relation to subsidence areas copenhagen is located on the east coast of the island of sjælland, which is separated from sweden by the strait of øresund (fig. 1). part of the city extends onto the smaller, neighbouring island of amager, and the strait between the two islands is the site of copenhagen harbour. the airport of copenhagen, kastrup, is situated on the southern part of amager. most parts of copenhagen are lowland, i.e. a few metres above sea level, but the terrain rises northwards and westwards where it reaches heights of 50 m a.s.l. the bedrock of copenhagen is dominated by danian limestone. two units are found: the stevns klint formation that comprises bryozoan limestone rich in chert beds (surlyk et al. 2006) and the københavn kalk formation which is dominated by calcarenitic, calcilutitic limestone with chert beds (stenestad 1976). an important tectonic feature is the carlsberg fault zone (stenestad 1976; jakobsen et al. 2002) that can be followed from the south coast of amager northwestwards to furesø (figs 1, 2). the quaternary deposits of copenhagen comprise ice age and postglacial deposits. the latter consist of terrestrial sediments that accumulated in streams and bogs, and marine sand and gravel which accumulated along the coasts (fig. 2b). the ice-age deposits are dominated by a widespread young till unit overlying meltwater sand and gravel, and more local, older till units and meltwater clay. tunnel valleys, depressions in hummocky moraine and stream valleys form wetlands around copenhagen, where freshwater deposits, mainly peat, accumulated in the holocene. the western part of amager is reclaimed sea f loor with marine and coastal deposits. areas with dump and fill deposits occur along the coasts or in peat-dominated depressions and may be characterised by high rates of subsidence. examples of areas with subsidence based on the geology and records of man-made ground, there are three types of areas with potential risk of subsidence, namely areas underlain by postglacial peat deposits (amounting to 70 km2), large areas of man-made ground (53 km2) and small areas of reclaimed land (19.4 km2). one of the areas with subsidence identified from the psi data in the period 1992–2000 is lersøparken (figs 2, 3) with fig. 2. correlation between ground stability and surficial deposits in greater copenhagen. a: map of classified soft ground areas in greater copenhagen. the rectangles show the location of two examples of subsiding areas described in the text. b: geological map of surficial deposits. the fill and reclamation areas did not exist when the region was mapped in 1899 (rørdam 1899). ]] amager a b furesø 10 km fig. 3 fig. 4 55°40´n 12°30´e observed psi, natural ground movement observed psi, anthropogenic artificial ground potential instability, natural ground potential instability, anthropogenic artificial ground clayey till meltwater sand meltwater gravel aeolean sand peat freshwater sand freshwater clay unmapped marine sand marine gravel marine clay fill and land reclamation 27 a subsidence rate between 2 and 5 mm/year. the 0.22 km2 subsiding area is situated in a ne–sw-trending valley where postglacial peat has accumulated above clay in an elongated depression (fig. 3). the depression was used as a dump site in the period from 1880 to 1920. peat is easily compressed, and compaction of the waste is an additional factor accounting for the high subsidence rate. kalveboderne with valbyparken and tippen along the coast of southern copenhagen is another example of an area with subsidence (figs 2, 4). a considerable number of psi points show subsidence of more than 4 mm/year. this area of 1.4 km2 was used as a dump from 1913 to 1960 when waste was dumped on the beach and in the adjacent shallow sea. in 1961, the area was extended with fill to the present artificial shoreline. compaction of the soft, natural sediments and waste followed by fill deposits lead to subsidence. subsidence related to tectonic features the most important tectonic feature in the subsurface of copenhagen is the se–nw-striking carlsberg fault zone (fig. 1). the fault is part of a number of relay faults related fig. 3. detailed map of lersøparken (red frame). a: orthophotograph of the area with psi points representing areas of subsidence. b: geological map of the area showingt clay and peat in the ne–sw-striking valley. for location see fig. 2. fig. 4. detailed map of the kalveboderne area where waste and fill have been deposited on holocene marine and coastal deposits. a: orthophotograph with psi data points. b: an old topographical map showing the same area prior to deposition of waste and fill. for location see fig. 2. ! ! !! ! !! !!! ! !! !!!!! ! ! ! ! ! !!! !!! ! ! ! !!! ! !!! !! ! ! ! ! ! !! !! ! ! !! !!! ! !!! !!!!! velocity clayey till peat freshwater clay500 m > –5 –4 to –5 –3 to –4 –2 to –3 –2 to –0.75 0.75 to –0.75 0.75 to 2 55°43´n 12°34´erate of change (mm/year) aa bb 55°37´37´´n 12°31´e tippen 500 m > –5 –4 to –5 –3 to –4 –2 to –3 –2 to –0.75 0.75 to –0.75 0.75 to 2 a b valbyparken rate of change (mm/year) 2828 to the tornquist–sorgenfrei wrench fault zone. a seismic cross-section of the carlsberg fault zone shows that it can be classified as a negative f lower structure with a mean vertical offset of 50–100 m of the limestone deposits. the hanging block is found north-east of the fault zone (fig. 5; fallesen 1995; jakobsen et al. 2002). the limestone in the fault zone itself is strongly fractured as documented by low seismic velocity in the fault-affected zone (nielsen et al. 2005). there is clear evidence of weak, regional subsidence east of the fault zone, i.e. the area of the down-thrown fault block (fig. 1). the carlsberg fault zone can be followed north-westwards to furesø, which is the deepest lake in denmark, and we suggest that the shape of the lake is governed by displacement along the fault zone. this would be an alternative explanation of the origin of the lake, which has hitherto been regarded as formed from a combination of tunnel valleys and kettle holes. the subsidence recorded by the psi points may correspond to subsidence rates in the copenhagen area recorded from traditional levelling (mark & jensen 1982). groundwater extraction may also inf luence subsidence, which could have been the case for amager. however, the groundwater level on amager was stable during the period of the satellite data acquisition. references crosetto, m., monserrat, o., adam, n., parizzi, a., bremmer, c., dortland, s., hanssen, r.f. & van leijen, f.j. 2008: validation of existing processing chains in terrafirma stage 2, final report, 15 pp., http://www. terrafirma.eu.com/validation/valproj/final%20reports/valproj _ final_report.pdf. fallesen, j. 1995: stratigraphy and structure of the danian limestone on amager, examined with geophysical investigations – especially with regard to the carlsberg fault. unpublished msc thesis, university of copenhagen, denmark jakobsen, p.r., fallesen, j. & knudsen, c. 2002: strukturer i den københavnske undergrund – folder, forkastninger og sprækker. dansk geoteknisk forening bulletin 19, 19–29. mark, a. & jensen, j.e. 1982: niveauændringer i københavn bestemt ud fra gentagne præcisionsnivellementer. landinspektøren 32, 10–21. nielsen, l., thybo, h. & jørgensen, m.i. 2005: integrated seismic interpretation of the carlsberg fault zone, copenhagen, denmark. geophysical journal international 162, 461–478. pedersen, s.a.s., cooksley, g., gaset, m. & jakobsen, p.r. 2011: detection of terrain changes in southern denmark using persistent scatterer interferometry. geological survey of denmark and greenland bulletin 23, 41–44. rørdam, k. 1899: beskrivelse til geologisk kort over danmark, (i maalestok 1:100,000). kortbladene kjøbenhavn og roskilde. danmarks geologiske undersøgelse i. række 6, 88 pp. stenestad, e. 1976: københavnsområdets geologi især baseret på citybaneundersøgelserne. danmarks geologiske undersøgelse iii. række 45, 149 pp. (with summary in english). surlyk, f., damholt, t. & bjerager, m. 2006: stevns klint: uppermost maastrichtian chalk, cretaceous–tertiary boundary, and lower danian bryozoan mound complex. bulletin of the geological society of denmark 54, 1–48. top cretaceous 100 m sw ne top cretaceous 0 100 200 300 tw ow ay t ra ve l t im e (m se c) fig. 5. seismic cross-section of the carlsberg fault zone (from jakobsen et al. 2002). maastrichtian chalk is found at the top of the western block, whereas danian limestone is present at the top of the eastern block. authors’ addresses p.r.j. & s.a.s.p, geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: prj@geus.dk u.w., gamma remote sensing, worbstrasse 225, ch-3073 gümligen, switzerland. r.c., npa satellite mapping, crockham park, edenbridge, kent tn8 6sr, uk. http://www.terrafirma.eu.com/validation/valproj/final reports/valproj_final_report.pdf http://www.terrafirma.eu.com/validation/valproj/final reports/valproj_final_report.pdf http://www.terrafirma.eu.com/validation/valproj/final reports/valproj_final_report.pdf geological survey of denmark and greenland bulletin 31, 2014, 47-50 47 stormwater management: methods for measuring near-surface infiltration capacity in clayey till britta bockhorn, marina bergen jensen and knud erik s. klint glacial till forms a major proportion of the surface deposits in northern europe, and in denmark more than 40% of the land surface is covered by clayey till. at the same time the majority of densely populated areas are situated on this fertile sediment type. in urban areas, one of the major tools in adaptation to climate change are sustainable drainage systems (suds). their function is to manage the increasing amounts of stormwater on site, often by direct infiltration into the sediment. accordingly, a realistic estimate of nearsurface hydraulic properties is required when dimensioning suds for infiltration. clayey tills are generally believed to have a low-bulk hydraulic conductivity and thus a low infiltration capacity. however, clayey tills can be very heterogeneous and especially their bulk hydraulic properties can vary significantly depending on the distribution of permeable structures such as macropores (e.g. earthworm holes and fractures) and sand lenses within the till matrix (klint & gravesen 1999; nilsson et al. 2001; kessler et al. 2012). the saturated hydraulic conductivity (ksat) of clayey tills varies from c. 1.0 × 10–10 to c. 1.0 × 10–4 m/s and thus covers a significant span (fredericia 1990; mckay et al. 1993). assessment of this value is a major challenge when considering the variability of this sediment type. it is therefore important to determine how representative standard infiltration tests are, specifically in tills, when used to formulate infiltration strategies. goals and scope in this study we compare three different methods for measuring ksat close to the surface: the double ring infiltrometer, the guelph permeameter and infiltration tests in a small excavation. each of these methods represents different scales and depths using different flow mechanisms. the goal of the study is to: 1. evaluate the suitability of these methods to return realistic ksat values in tills, taking into account the geological heterogeneity of a clayey till from infiltration scale (0.5 m × 0.5 m) to field scale (100 m × 100 m), and 2. suggest relevant scales and strategies for infiltration tests in future experiments. © 2013 geus. geological survey of denmark and greenland bulletin 28, 47–50. open access: www.geus.dk/publications/bull fig. 1. a: map of denmark showing the location of the test site. b: map of the test site showing the distribution of various sediment types and the locations of the infiltration tests. a b10°e 57° 57°n 55° 50 km 20 m 55°39.5´n 12°16.6´e postglacial clay clayey till sandy clayey till sandy till postglacial sand fill deeper borehole auger test guelph permeameter measurement double ring infiltrometer measurement shallow (2.5 and 4 m) monitoring borehole infiltration hole høje tåstrup 4848 field experiments the infiltration tests were conducted on former agricultural land next to the technological institute in høje taastrup, denmark (fig. 1). the area represents a site with a typical danish clayey till. the geological setting is dominated by two basal till beds overlying glaciofluvial deposits and flow tills deposited in a supraglacial environment. the glacial deposits overlie highly fractured limestone bedrock c. 14–16 m below the ground surface. the primary groundwater table is located in the limestone bedrock at depths greater than 16 m and a secondary groundwater table is found in the upper till unit. the latter is located around 3 m below the surface during summer and around 1.0 to 0.5 m below the surface during winter. an area of c. 100 m × 100 m was mapped in great detail using a hand auger ( jakobsen et al. 2011) with sampling in a 10 × 10 m grid. shallow boreholes were cored to depths of 2.5 –4 m and used for monitoring the annual fluctuation of the secondary groundwater table. two deeper boreholes were cored to a depth of c. 16 m. two large holes were excavated to 5 and 8 m below the ground surface and used for detailed mapping of fractures and collection of large, intact samples for hydraulic tests in the laboratory. the guelph permeameter method measures the steadystate rate of water flow required to maintain a constant depth of water in a 40 cm deep and 8 cm wide cylindrical borehole. water flows out of the outlet tube through a perforated section located above the permeameter tip. the guelph reynolds & elrick (1985) 60 cm infiltration holedouble ring infiltrometerguelph permeameter direction of measured water flow expenditure of time (time required to achieve full saturation) 3-dimensional 1-dimensional 3-dimensional effect on soil structure smearing during excavation causing potential underestimation of k. counteraction: careful removal of smearing with knife non-invasive highly invasive suitability to represent geological heterogeneity 1–2 hours depending on soil moisture 1–2 hours depending on soil moisture poor good degree of disturbance 1.5 hours to several hours depending on soil moisture 8 cm 5–10 cm 30.5 cm 60.5 cm minimally invasive rather poor counteraction: conduct at least a triplet of measurements counteraction: conduct as many measurements as possible 100 cm 200 cm literature on estimation of ksat reynolds et al. (2002) 40 cm formation of cracks during insertion of cylinders into the soil creation of preferential flow routes causing potential overestimation of k. counteraction: sealing of contact with clay on the outside of the inner cylinder smearing during excavation of hole causing potential underestimation of k. counteraction: careful removal of smearing with knife or use of excavation technologies that prevent or minimise smearing, e.g. chain excavator fig. 2. overview and principle of the different techniques used in this study. the blue arrows represent water f low. k: hydraulic conductivity. 49 permeameter method is based on the assumption of threedimensional steady-state infiltration from a cylindrical test hole into the sediment. two concentric metal cylinders with diameters of 30.5 and 60.5 cm were used for the double ring infiltrometer method. after removal of the sward, the cylinders were carefully pressed 5–10 cm into the sediment. water was poured into the inner cylinder, and also into the outer cylinder to prevent lateral movement of water beneath the inner cylinder, thus maintaining one-dimensional flow conditions. the amount of cumulative infiltration with time under fallinghead conditions was recorded and ksat values determined. the infiltration holes were excavated to a depth of 60 cm with an inner area of 100 × 200 cm. smearing caused by the excavation process was carefully removed with a knife. the holes were filled with water and when a steady state was attained, the infiltration rate from the hole into the sediment was measured directly. a total of 41 infiltration tests were conducted across the site: 19 guelph permeameter measurements, 18 double ring infiltrometer measurements and four infiltration tests in the excavated holes. more information on the methods is provided in fig. 2. results and discussion the application of conventional infiltration technologies indicates that the saturated hydraulic conductivity (ksat) of tills is a spatially highly variable property. in two guelph permeameter measurements no infiltration at all was observed, which might be due to smearing during preparation of the borehole or compaction by heavy machines as the field site is former agricultural land. compaction might also be the reason for one no-flow measurement in the double ring infiltrometer. the results are presented in table 1 and fig. 3. the guelph permeameter and the double ring infiltrometer average values are lower than those from the infiltration holes. this is probably due to not fully saturated conditions around the holes as the area is rather large compared to the area used for the guelph permeameter and double ring infiltrometer measurements, where saturated conditions are attained reasonably quickly. the fact that the holes involve a much larger area than the guelph permeameter and the double ring infiltrometer means that they involve more than one sediment type and accounts best for macro-pores, confirming that geological heterogeneity on clayey till plains influences the hydraulic conductivity even at infiltration plot scales. a realistic estimate of hydraulic conductivity is crucial when planning how to manage stormwater infiltration. the present field-based study shows that hydraulic conductivity values are strongly influenced by the physical scale of the field measurements. this is mainly due to the local distribution of macro-pores and how well the geological heterogeneity is represented. the importance of scale-dependent variability of ksat has also been demonstrated in previous studies (e.g. jenssen 1990; ronayne et al. 2012), but is still widely neglected when hydraulic conductivity values are used for stormwater management practices. due to the large variation of grain-size distribution in tills, it is not recommended to apply methods that define ksat based on grain-size distribution. neither is it recommended 1 × 10–9 1 × 10–8 1 × 10–7 1 × 10–6 1 × 10–5 guelph permeameter double ring infiltrometer infiltration holes sa tu ra te d hy dr au lic c on du ct iv ity (m /s ) fig. 3. box and whisker diagram illustration of the range of saturated hydraulic conductivity values obtained using the guelph permeameter, double ring infiltrometer and infiltration hole techniques. the scale is logarithmic. whiskers are plotted at the maximum and minimum values, however, the minimum value for the double ring infiltrometer test is below the scale and not shown. guelph permeameter 19 9.12 × 10–8 6.18 × 10–6 1.44 × 10–6 double ring infiltrometer 18 7.43 × 10–13 9.7 × 10–6 8.26 × 10–7 infiltration holes 4 1.4 × 10–6 1.46 × 10–5 7.25 × 10–6 table 1. summary statistics of saturated hydraulic conductivity values method number mininum maximum arithmetic mean 5050 to use ksat values obtained with a double ring infiltrometer or a guelph permeameter alone as they can vary by several orders of magnitude already on a infiltration plot scale. in our study we found a variable of more than two orders of magnitude. data from infiltration holes give more realistic values. however, they are highly invasive and it may be difficult to excavate adequate holes in densely populated areas. instead of using highly invasive infiltration holes, we recommend to carry out combined hydrogeological investigations where double ring infiltrometer and guelph permeameter measurements are supported by geological information from maps of near-surface deposits and borehole descriptions. in that less-destructive way, small-scale geological heterogeneity can be revealed and the most suitable areas for stormwater infiltration can be selected to enhance work efficiency of infiltration devices. acknowledgement the work was conducted as part of the innovation consortium cities in waterbalance (byer i vandbalance) financed by the danish council for technolog y and innovation. references fredericia, j. 1990: saturated hydraulic conductivity of clayey tills and the role of fractures. nordic hydrolog y 21, 119–132. jakobsen, p.r., hermansen, b. & tougaard, l. 2011: danmarks digitale jordartskort. danmarks og grønlands geologiske undersøgelse rapport 2011/40, 28 pp. jenssen, p.d. 1990: methods for measuring the saturated hydraulic conductivity of tills. nordic hydrolog y 21, 95–106. kessler, t.c., klint, k.e.s., nilsson, b. & bjerg, p.l. 2012: characterization of sand lenses embedded in tills. quaternary science reviews 53, 55–71. klint, k.e.s. & gravesen, p. 1999: fractures and biopores in weichselian clayey till aquitards at flakkebjerg, denmark. nordic hydrolog y 30, 267–284. mckay, l.d., cherry, j.a. & gillham, r.w. 1993: field experiments in a fractured clay till. 1. hydraulic conductivity and fracture aperture. water resources research 29, 1149–1162. nilsson, b., sidle, r.c., klint, k.e., bøggild, c.e. & broholm, k. 2001: mass transport and scale-dependent hydraulic tests in a heterogeneous glacial till–sandy aquifer system. journal of hydrolog y 243, 162–179. reynolds, w.d. & elrick, d.e. 1985: in situ measurement of field-hydraulic conductivity, sorptivity, and the alpha-parameter using the guelph permeameter. soil science 140, 292–302. reynolds, w.d., elrick, d.e., youngs, e.g., amoozegar, a., booltink, h.w.g. & bouma, j. 2002: saturated and field-saturated water flow parameters. in: dane, j.h. & topp, g.c. (eds): methods of soil analysis, part 4, physical methods, 797–878. madison, wi: soil science society of america. ronayne, m.j., houghton, t.b. & stednick, j.d. 2012: field characterization of hydraulic conductivity in a heterogeneous alpine glacial till. journal of hydrolog y 458–459, 103–109. authors’ addresses b.b. & m.b.j., department of geosciences and natural resource management, university of copenhagen, rolighedsvej 23, dk-1958 frederiksberg, denmark. e-mail: bboc@ign.dk.ku k.e.s.k., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. geological survey of denmark and greenland bulletin 28, 2013, 37-40 37 evaluation of total groundwater abstraction from public waterworks in denmark using principal component analysis brian lyngby sørensen and rasmus rønde møller in denmark water abstraction data have been collected since the late 1970s. initially the purpose was to monitor and assess the groundwater resources available for future local water abstraction. for this reason, abstraction data were collected not only from waterworks, but also from irrigation, industry etc. today water abstraction data are used for several purposes, for instance in water -balance calculations to estimate the available resource to wetlands, streams and lakes or to calculate the f low of chemical substances in the water environment. the role of climatic changes in the future hydrological cycle is subject to increasing attention. apart from a small reserve of surface water, all drinking water in denmark comes from groundwater. when precipitation changes in the future the amount of groundwater available for abstraction will also change. hence, for reasons of security of supply and environmental impact, it is important to know the amount and trend of abstraction each year. at national level, it is a statutory objective to abstract groundwater in a way that does not obstruct the general water-environmental objectives outlined in the european union’s water framework directive (the european parliament and the council of the european union 2000). the purpose of this paper is to present a method to evaluate the errors in the overall national groundwater abstraction dataset and describe how to correct erroneous data. for the sake of overview the national data are typically presented as an overall sum in million cubic metres per year (e.g. thorling et al. 2012). public groundwater abstraction in denmark drinking water in denmark comes from approximately 2500 waterworks, abstracting about 400 million m3 of groundwater per year. there is a pronounced decentralised water supply structure with many small waterworks spread across the country. approximately 72% of the waterworks each abstract less than 0.1 million m3 water per year, amounting to a total of 56.5 million m3 per year. at the other end of the fig. 1. an example of a time series for a specific municipality before (a) and after (b) correction of the abstraction data. data from 2011 are included in the graph for clarity. © 2013 geus. geological survey of denmark and greenland bulletin 28, 37–40. open access: www.geus.dk/publications/bull m ill lo n m 3 of g ro un dw at er a bs tr ac te d m ill lo n m 3 of g ro un dw at er a bs tr ac te d 0 5 10 15 20 25 1990 2000 2010 year corrected 0 5 10 15 20 25 1990 2000 2010 year a b uncorrected 3838 scale, 3% of the waterworks each abstract more than 1 million m3 per year, totalling 154 million m3 per year. according to danish legislation it is mandatory for waterworks and other users abstracting groundwater to report the amount abstracted once a year to the municipalities. the municipalities check for mistyped data and forward them to the national danish database on geology, groundwater and drinking water (the jupiter database at the geological survey of denmark and greenland). municipal reform in 2007, a major municipal reform took place in denmark. thirteen former counties (amter) were replaced by five socalled regions and most municipalities (kommuner) were merged into fewer and larger units, resulting in a drop from 271 to 98 municipalities. as part of this reform the new municipalities took over the responsibility to manage the water resources including abstraction licensing. this involved transferring employees from the former counties, new distribution of responsibilities and introduction of new computer systems and new procedures; all of which inf luenced the overall quality of the abstraction data. for instance, the new municipalities were responsible for submitting the 2006 water abstraction data to jupiter, although they were not operative before 1 january 2007. data preparation the water abstraction data used in this study were extracted from the jupiter database for the period 1989–2010. based on the extracted data, a date table was compiled with the sum of groundwater abstraction per year within each municipality. a time series for each municipality was plotted and visually inspected. at municipality level, small year-toyear changes and thus a smooth curve are expected, because fig. 2. total water abstraction in denmark for uncorrected (a) and corrected (b) data. the dashed lines show varexp – the correlation between the pca score of the first primary component (pc1) and the input data, expressed in million m3 per year. problem cause action no data were reported at all from the municipality an expected average was calculated based on data from 1–2 years before and after the year with missing data. evidently missing data no data from one or more waterworks. typing errors double registration from one or more waterworks. typing errors an expected average was calculated for the individual waterworks, or in case of typing errors a more probable value was estimated. evidently too high amount quoted evident double registrations were subtracted from the sum. in case of typing errors a more probable value was estimated. table 1. typical problems associated with registration of water abstraction data no data other apparent error unidentified no action taken. uncorrected corrected 300 350 400 450 500 550 600 1990 1995 20052000 2010 year a 300 350 400 450 500 550 600 1990 1995 20052000 2010 year b m ill lo n m 3 of g ro un dw at er a bs tr ac te d m ill lo n m 3 of g ro un dw at er a bs tr ac te d 39 on average the waterworks abstract almost the same amount each year. after initial inspection, 22 municipalities with unexpected data pattern were selected for detailed examination. four types of main problems were identified (table 1); the causes for three of the types could be identified and relevant action taken. correction of abstraction data for a single municipality an example of a time series for a selected municipality is shown in fig. 1a. the water abstraction from a specific waterworks was erroneously reported three times in the years 2006–2008 and twice in the years 2009–2010. thus, the water abstraction in the municipality was overestimated by 16.7 and 7 million m3, respectively, in the two periods. with the extra registrations removed, the time series shows a behaviour similar to what is expected (fig. 1b). a similar inspection was made of the time series from the 21 other municipalities. finally, a new data table was compiled by merging the corrected data with the data from the uncorrected time series from the remaining 76 municipalities. principal component analysis and pearson’s correlation coefficient principal component analysis is a mathematical procedure introduced by pearson (1901) and widely used to visualise multivariate data by dimension reduction (garcia & filzmoser 2011). according to garcia & filzmoser, the main problems of multivariate data can be avoided by using the principal component analysis to transform “. . . the original variables into a smaller set of latent variables which are uncorrelated”. each new variable (principal component or pc) can then be interpreted independently. there are several ways to perform principal component analysis, some of which are described in wikipedia (2013). the method used here is singular value decomposition (svd) using the ‘prcomp’ function of the base package of r (r core team 2012). the time series for the individual municipalities were used as objects (rows) and the years were used as variables (columns). for each year the pearson’s correlation coefficient ρ between the scores of the first principal component (pc1) and the corrected and uncorrected datasets d, was calculated and expressed in terms of million m3 (varexp) using the formula: where t is the total national abstraction. the correlation was done using the default settings of the ‘cor’ function of r (r core team 2012). the magnitude of ρ shows the strength of the linear dependence between the score of pc1 and d. status of water abstraction and comparison of uncorrected and corrected data figure 2 shows the total groundwater abstraction from public waterworks in million m3 per year from 1989 to 2010 with uncorrected and corrected data. both diagrams show the pearson’s correlation coefficient expressed in million m3 (varexp, dashed lines), according to the formula above. the variance explained ranges between 90 and 98% of the total yearly water abstraction. the remaining 2–10% can be perceived as ‘noise’ in the sense that this part of the variance is due to errors, short-term but large extra deliveries of water, abrupt changes in water needs, new or closed down waterworks etc. before the municipal reform (the period from 1989 to 2005) the unexplained variance on average corresponds to 16 million m3 for the uncorrected data and 12.7 million m3 for the corrected data. the improvement of the explained variance by correcting the data is thus 3.3 million m3. after the reform (2006–2010) the unexplained variance on average corresponds to 45.3 million m3 for the uncorrected data and 20.8 million m3 for the corrected data, leading fig. 3. locally weighted average (loess) of uncorrected and corrected groundwater abstraction data. uncorrected (data point / loess) corrected (data point / loess) 300 350 400 450 500 550 600 1990 1995 20052000 2010 year m ill lo n m 3 of g ro un dw at er a bs tr ac te d 4040 to an average improvement of 24.5 million m3 by correcting the data. because of the errors mentioned above the amount of groundwater abstracted in denmark by the waterworks is only known with some uncertainty. in fig. 3 a locally weighted regression (loess) is calculated for corrected and uncorrected abstraction data in order to yield a ‘best guess’ of the total water abstraction. the curves show an overall trend with a large decline in the first half of the 1990s when abstraction decreased c. 20% from c. 550 million m3 in 1990 to c. 460 million m3 in 1996. later, the abstraction dropped to just over 400 million m3 in 2005. from fig. 3 it is clear that when corrected data are used, the abstraction f lattens out at around 400 million m3 per year from 2005 onwards. if uncorrected data are used the abstraction level seems to decrease even further to below 400 million m3 per year over the same period. therefore the interpretation of trends depends to a large degree on whether the data are corrected or not. the main reasons for the large decline after 1989 are adoption of new legislation, increased water taxes and water saving campaigns (stockmarr & thomsen 2006). conclusions after the municipal reform in 2007 water abstraction data reported to the jupiter database show increased levels of errors due to changes in the way data are treated and reported. this means that national trends and levels are blurred which can lead to misinterpretations. by carefully examining data from the individual waterworks, it is often possible to determine the causes of errors and thereby correct them. the combined use of pca and pearson’s correlation coefficient is a useful way to provide an overall check on how well the data are corrected. this study shows that after the municipal reform the improvement is on average equivalent to 24.5 million m3 or c. 6%. on regional and local scales the impact of erroneous data can be severe. the example in fig. 1 shows that the abstraction can be overestimated by a factor 2.5 if no action is taken to investigate and correct erroneous data. it is crucial to correct and improve such data before they are used in waterbalance calculations, hydrological modelling, abstraction licensing and projections of water use in denmark. references garcia, h. & filzmoser, p. 2011: multivariate statistical analysis using the r package chemometrics, 71 pp. vienna: vienna university of technolog y, department of statistics and probability theory. thorling, l., hansen, b., langtofte, c., brüsch, w., møller, r.r. & mielby, s. 2012: grundvandsovervågning 2012 – grundvand. status og udvikling 1989–2011. teknisk rapport, http://www.geus.dk/publications/grundvandsovervaagning/1989_2011.htm pearson, k. 1901: on lines and planes of closest fit to systems of points in space. philosophical magazine, series 6, 2, 559–572. r core team 2012: r: a language and environment for statistical computing. vienna: r foundation for statistical computing, http://www.rproject.org/ stockmarr, j. & thomsen, r. 2006: water supply in denmark. the danish action plan for promotion of eco-efficient technologies – danish lessons, 18 pp. copenhagen: miljøstyrelsen. the european parliament and the council of the european union 2000: establishing a framework for community action in the field of water policy. http://eur-lex.europa.eu/lexuriserv/lexuriserv. do?uri=celex:32000l0060:en:html wikipedia, the free encyclopedia 2013: principal component analysis. accessed 7 february 2013. http://en.wikipedia.org/wiki/principal_component_analysis authors’ addresses b.l.s. & r.r.m.* geological survey of denmark and greenland, lyseng allé 1, dk-8270 højbjerg, denmark. e-mail: bls@geus.dk * present address: horsens kommune, rådhustorvet 4, 8700 horsens, denmark. http://www.geus.dk/publications/grundvandsovervaagning/1989_2011.htm http://www.geus.dk/publications/grundvandsovervaagning/1989_2011.htm http://www.r-project.org/ http://www.r-project.org/ http://www.ecoinnovation.dk/nr/rdonlyres/e4d4bd37-82e9-413d-87d8-d6aecd6b7e79/0/vandforsyning_artikel.pdf http://eur-lex.europa.eu/lexuriserv/lexuriserv.do?uri=celex:32000l0060:en:html http://eur-lex.europa.eu/lexuriserv/lexuriserv.do?uri=celex:32000l0060:en:html http://en.wikipedia.org/wiki/principal_component_analysis http://en.wikipedia.org/wiki/principal_component_analysis mailto:tvp@geus.dk geological survey of denmark and greenland bulletin 17, 2009, 1-8 geological survey of denmark and greenland ministry of climate and energy geologic al survey of denmark and greenland bulletin 17 • 2009 review of survey activities 2008 edited by ole bennike, adam a. garde and w. stuart watt rosa_2008:rosa-2008 01/07/09 15:47 side 1 geological survey of denmark and greenland bulletin 17 keywords geological survey of denmark and greenland, survey organisations, current research, denmark, greenland. cover photographs from left to right 1. inspection of cores in jameson land, east greenland. photo: john boserup. 2. field work in west greenland. photo: denis schlatter. 3. investigations and sampling of an outcrop at conde, bahia, brazil. photo: peter japsen. 4. field experiments with remediation of contaminated soil in vadsby, west of copenhagen. photo: knud erik s. klint. frontispiece: facing page visit at the automatic weather station ‘lower nuuk’ on 30 july 2008 for data retrieval and maintenance. the station is located on the gla cier qamanaarsuup sermia near the margin of the greenland ice sheet, east of godthåbsfjord (64º29´n, 49°31´w). it collects weather information and data about the local ablation and was established in 2007 as part of the promice project (www.promice.org). photo: søren nielsen. chief editor of this series: adam a. garde editorial board of this series: john a. korstgård, department of earth sciences, university of aarhus; minik rosing, geological museum, university of copenhagen; finn surlyk, department of geography and geology, university of copenhagen scientific editors: ole bennike, adam a. garde and w. stuart watt editorial secretaries: jane holst and esben w. glendal referees: (dk = denmark; numbers refer to first page of reviewed article): anonymous (29, 29, 33, 45, 49, 77, 77, 81); lars christiansen, dk (41); finn dalhoff, dk (13); gregers dam, dk (53); edward f. duke, usa (69); ida fabricius, dk (17); henrik friis, dk (25); mariejosé gaillard, s (37); ole graversen, dk (81); karen hanghøj, usa (61); bent hasholt, dk (45); jens havskov, n (9); ole humlum, n (74); paul martin holm, dk (61); jens konnerup-madsen, dk (65); john a. korstgård, dk (57); nicolaj krog larsen, s (33); poul-henrik larsen, dk (53); christoph mayer, g (74); florence mazier, s (37); klaus mosegaard, dk (9); john myers, australia (49); allan aasbjerg nielsen, dk (69); henrik olsen, dk (41); graham pearson, uk (65); asger ken pedersen, dk (57); gunver krarup pedersen, dk (21); jan audun rasmussen, dk (21); martin sønderholm, dk (25); morten gjetting stage, dk (13); ole v. vejbæk, dk (17). illustrations: stefan sølberg, with contributions from benny m. schark lay-out and graphic production: henrik klinge pedersen and annabeth andersen printers: schultz grafisk, albertslund, denmark manuscripts submitted: 23 january – 27 march 2009 final versions approved: 25 may 2009 printed: 8 july 2009 issn 1603-9769 (review of survey activities) issn 1604-8156 (geological survey of denmark and greenland bulletin) isbn 978-87-7871-250-9 citation of the name of this series it is recommended that the name of this series is cited in full, viz. geological survey of denmark and greenland bulletin. if abbreviation of this volume is necessary, the following form is suggested: geol. surv. den. green. bull. 17, 84 pp. available from geological survey of denmark and greenland (geus) øster voldgade 10, dk-1350 copenhagen k, denmark phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: geus@geus.dk © de nationale geologiske undersøgelser for danmark og grønland (geus), 2009 for the full text of the geus copyright clause, please refer to www.geus.dk/publications/bull rosa_2008:rosa-2008 01/07/09 15:47 side 2 rosa_2008:rosa-2008 01/07/09 15:47 side 3 4 7 review of survey activities 2008 f.g. christiansen 9 earthquake in southern sweden wakes up denmark on 16 december 2008 p.h. voss, t.b. larsen, l. ottemöller and s. gregersen 13 the potential for large-scale, subsurface geological co2 storage in denmark p. frykman, l.h. nielsen, t. vangkilde-pedersen and k.l. anthonsen 17 increased oil recovery from halfdan chalk by flooding with co2-enriched water: a laboratory experiment d. olsen 21 ladinian palynofloras in the norwegian– danish basin: a regional marker reflecting a climate change s. lindström, h. vosgerau, s. piasecki, l.h. nielsen, k. dybkjær and m. erlström 25 fingerprinting sediments along the west coast of jylland: interpreting provenance data c. knudsen, t. kokfelt, t. aagaard, j. bartholdy and m. pejrup 29 structural development of maglevandsfald: a key to understanding the glaciotectonic architecture of møns klint, se denmark s.a.s. pedersen and p. gravesen 33 fracture valleys in central jylland – a neotectonic feature p.r. jakobsen and s.a.s. pedersen 37 soil erosion and land-use change during the last six millennia recorded in lake sediments of gudme sø, fyn, denmark p. rasmussen and j. olsen thailand laos pdr ghana uganda tanzania mozambique vietna greenland kenya spain chile germany the netherlands denmark brazil zambia yemen cambodia mali sudan bahrain geus working areas 2008. orange areas are covered in this volume. for further information on other working areas please refer to our website: www.geus.dk/international rosa_2008:rosa-2008 01/07/09 15:47 side 4 5 41 geophysical methods and data administra tion in danish groundwater mapping i. møller, v.h. søndergaard and f. jørgensen 45 water budget of skærsø, a lake in south-east jylland, denmark: exchange between groundwater and lake water b. nilsson, p. engesgaard, j. kidmose, s. karan, m.c. looms and m.c.s. frandsen 49 geological observations in the southern west greenland basement from ameralik to frederikshåb isblink in 2008 n. keulen, a. scherstén, j.c. schumacher, t. næraa and b.f. windley 53 shallow core drilling and petroleum geology related field work in east and northeast greenland 2008 j.a. bojesen-koefoed, m. bjerager and s. piasecki 57 the bedrock geology under the inland ice: the next major challenge for greenland mapping p.r. dawes 61 developing a 3-d model for the skaergaard intrusion in east greenland: constraints on structure, mineralisation and petrogenetic models t.f.d. nielsen, s.d. olsen and b.m. stensgaard 65 diamonds and lithospheric mantle properties in the neo proterozoic igneous province of southern west greenland a. steenfelt, s.m. jensen, t.f.d. nielsen, k.k. sand and k. secher 69 using spectral mixture analysis of hyperspectral remote sensing data to map lithology of the sarfartoq carbona tite complex, southern west greenland e. bedini and t. tukiainen 73 glaciological investigations at the malmbjerg mining prospect, central east greenland m. citterio, r. mottram, s.h. larsen and a. ahlstrøm 77 holocene climate variability in southern greenland: results from the galathea 3 expedition n. nørgaard-pedersen, n. mikkelsen, m.d. poulsen and a.s. simonsen 81 post-rift landscape development of northeast brazil j.m. bonow, p. japsen, p.f. green, p.r. cobbold, a.j. pedreira, r. lilletveit and d. chiossi thailand laos pdr uganda tanzania mozambique vietnam kenya phillipines mark zambia yemen cambodia sudan bahrain rosa_2008:rosa-2008 01/07/09 15:47 side 5 rosa_2008:rosa-2008 01/07/09 15:47 side 6 7 following a number of years with major changes of the scientific environment in denmark and also within the management of the geological survey of denmark and greenland (geus), 2008 was a year of stability and consolidation, a situation that will hopefully continue. many new projects have been initiated and many previous projects have been completed at a time with strong focus on geus’ activities politically, commercially and from the media. this sixth annual issue of review of survey activities describes selected projects that geus and its partners carry out in denmark, greenland and internationally. together with the previous five published issues (also available at www.geus.dk), it provides a good overview of the survey’s many different types of research and advisory activities. it contains a total of 19 four-page papers: ten on denmark, eight on greenland and one on international work. geology was on the lips of most of the danish population an early morning in december 2008 when one of the strongest earthquakes recorded in scandinavia woke up hundreds of thousands of people in southern sweden and on sjælland. one paper in this issue describes the background and details of the earthquake, including input from the public that contacted geus through its website. reduction of the emission of co2 is high on the political agenda in denmark and internationally. one of the possibilities to reduce co2 emission from large point sources is to use carbon capture and storage (ccs). the danish subsurface has a high potential to store co2, and structures such as the vedsted structure in northern jylland could be among the first dozen storage facilities utilised in europe, and thereby become a key area for detailed research and monitoring for many years to come. the background for ccs and geological possibilities in denmark are described in one paper. oil and gas exploration and production are still very important for the economy of denmark, and geus has a strong emphasis on research within this field. two papers concentrate on petroleum geology. one of them is based on laboratory flooding experiments and describes the possibility of increasing oil recovery from reservoirs in chalk using injection of co2-enriched water; the other provides a detailed biostratigraphic correlation of the late triassic succession in the norwegian–danish basin. most surface features in denmark have been formed by glacial and coastal processes during the quaternary. several papers in this issue describe such processes; one of them demonstrates the use of sophisticated analytical techniques such as computer-controlled, scanning electron microscopy of heavy minerals and laser ablation, inductively coupled mass spectro metry of zircon grains to describe erosion and re-deposition of sand along the west coast of jylland. the structural development of the famous møns klint geosite is dealt with in one paper, and the occurrence of neotectonic fracture valleys in central jylland in another. a third paper describes soil erosion and land use change during the last six millennia as recorded in lake sediments from gudme sø on fyn. groundwater mapping and management have a very high priority in denmark. one paper describes the many different geophysical methods that are used in hydrogeological mapping, as well as the administration of the geophysical data that are archived in a major database hosted at geus. another paper describes the exchange between lake water and groundwater of lake skærsø in jylland. in 2008 there was a high level of field activities in green land. the two largest campaigns in southern west green land and eastern greenland are described in individual papers. the west greenland field work was a follow-up on earlier projects focused on updating previous maps and thereby creating a better understanding of the potential distribution of mineral occurrences. the field work in eastern greenland is the start of a major oil industry sponsored programme that has been launched to support and promote petroleum exploration within the coming five-year period. it includes shallow core drilling. one paper addresses a question often raised by scientists and explorers: what is the bedrock geology under the inland ice that covers 81% of the total area of greenland? available review of survey activities 2008 flemming g. christiansen deputy director © geus, 2009. geological survey of denmark and greenland bulletin 17, 7–8. available at: www.geus.dk/publications/bull rosa_2008:rosa-2008 01/07/09 15:47 side 7 geological and geophysical data are shortly reviewed and ideas for future studies presented. another paper introduces a 3-d modelling of one of the best studied intrusions in the world, the paleocene skaergaard intrusion in east greenland. identification of significant platinum group and gold occurrences in this intrusion has lead to detailed investigations and exploration drilling over many years. the last decade of diamond exploration in west greenland has provided a wealth of data on the dykes of kimberlite and ultramafic lamprophyres that may host diamonds. one paper summarises new data on petrology and age distribution of the dykes that have important implications for future diamond exploration. in a large country like greenland, use of remote sensing data is important and cost-effective in mapping and exploration. one paper presents an analysis of hyperspectral data from the sarfartoq carbonatite complex in west greenland. the paper illustrates that such data can be applied to mapping of individual rock types. the most recent processes and climate development in greenland are described in two papers of which one stresses the importance of applied glaciology for the exploitation of the malmbjerg molybdenum deposit in east greenland, because the site of a possible future mine is located between two glaciers. future access to the mining site and removal of ore and waste rock are highly dependent on the movement of the glaciers. the second paper addresses holocene climate variation and marine history in south greenland, based on a number of samples collected in bredefjord and narsaq sund during the galathea 3 expedition. a final paper on landscape development in brazil employs the same methods of landscape mapping and apatite fission track analysis that were used to study the uplift history of the margins of greenland and scandinavia. 8 rosa_2008:rosa-2008 01/07/09 15:47 side 8 geological survey of denmark and greenland bulletin 20, 2010, 75–78 75 establishment of robust reservoir models and estimates of subsurface hydrocarbon volumes in relatively unknown subsurface settings can be improved by using data from field analogues. the discovery of the rosebank oilfield in the faroe–shetland basin showed that intrabasaltic sandstones can form important hydrocarbon reservoirs in volcanic basins (helland-hansen 2009). the sødalen region in southern east greenland (fig. 1) forms an excellent field analogue to the rosebank oilfield where contemporaneous palaeogene sediments interbedded with lava units can be studied and sampled (larsen et al. 1999). in this area many of the exposures are located along steep, inaccessible cliffs with excellent exposures that are ideal for 3-d photogeological studies based on digital high-resolution photographs taken from a helicopter. the analogue study reported on here has integrated results from a wide range of spatial scales. on a large scale (kilometre to metre), 3-d photogeology was used to study the extent, geometry and interfingering of volcanic and intrabasaltic sedimentary units. photogeology was also used to map faults, dykes and sills, which may lead to compartmentalisation (division) of reservoirs. on an intermediate scale (metre to millimetre), sections are logged in the field, sedimentary and volcanic facies are mapped and depositional environments are interpreted. three-dimensional photogeology is also applied on an intermediate scale to map lateral variations of sedimentary units between logged sections. on a small scale (millimetre to micrometre), mineral-chemical, petrographical and zircon age determinations provide information on sediment source, provenance area and diagenetic inf luences on reservoir properties. the analogue study has resulted in a large database, which can form an important source of estimates of reservoir size, geometry and connectivity, and of vertical and lateral variations in the sandstone content of reservoirs. ultimately this may improve estimates of the actual volumes and recoverable volumes of hydrocarbons in intrabasaltic subsurface sediments. the 3-d photogeological method the 3-d photogeological method used in this study was developed at the geological survey of denmark and greenland (geus) and builds on earlier work by dueholm et al. (1993) and dueholm & olsen (1993). the method allows the acquisition of geological data from vertical and oblique aerial photographs, with a three-dimensional overview of the outcrops. the oblique photographs (1:15  000–1:17 000 scale) are triangulated with coloured, vertical, aerial photographs (1:27 000 scale) using a 3-d stereo-plotter coupled with stereo-mirror technology. the mapping of geological features includes determination of strata thickness, strike direction and dip values working on a 3-d high resolution vision of the cliffs. the resolution of volcanic and sedimentary beds and geological features is c. 10 cm. all the mapped features are stored in a gis database and 3-d polylines can be exported study of a palaeogene intrabasaltic sedimentary unit in southern east greenland: from 3-d photogeology to micropetrography henrik vosgerau, pierpaolo guarnieri, rikke weibel, michael larsen, cliona dennehy, erik v. sørensen and christian knudsen sø d ale n ‘sødalengletscher’ 68°15´n 31°w miki fjord j.c. jacobsen fjord greenland mainly palaeogene volcanic rocks palaeogene gabbro mesozoic–palaeogene sedimentary rocks precambrian basement 10 km fig. 2a fig. 1. map of the sødalen area in southern east greenland. the red line shows the location of the profile in fig. 2a. © geus, 2010. geological survey of denmark and greenland bulletin 20, 75–78. open access: www.geus.dk/publications/bull 7676 a. large scale b. intermediate scale c. small scale 0 1 2 3 4 5 6 7 lava unit invasive lava lower–middle shoreface lower–middle shoreface lav a u nit 8 9 10 m cl si sand gnl 5 m 20%10090%80706050403020100 1 1 2 2 upper shoreface dyke 20 μm b volcanics volcanics chlorite quartz feldspar volcanic fragments mica heavy minerals sphene rock fragments quartz feldspar calcite illite chlorite detrital composition authigenic phases b 200 m bedding dyke fault intrabasaltic unit nwnw sesenw se 77 as shape files suitable for 3-d modelling using, for example, petrel reservoir engineering software. moreover, using 3-d feature databases in arcgis, geological cross-sections can be generated automatically to obtain real representations of outcrops, and then projected onto a topographic profile, where the accuracy is as high as the resolution in the photographs. the oblique photographs used here were small-frame colour photographs taken from a helicopter f lying close to the cliff faces (<800 m) and at a constant altitude along straight lines approximately parallel to the cliffs. the photographs were taken with a 60 to 80% overlap using a 22 megapixel digital camera. on a large scale (kilometre to metre) on a large scale, 3-d photogeology is used to study the lateral extent and geometry of the intrabasaltic sediments and volcanic rocks and boundary relationships. evidence of compartmentalisation of the intrabasaltic reservoir analogues, caused for example by dykes, sills or faults, are mapped. figure 2a shows an oblique view of a 1.2 km section on the eastern side of sødalen, which is an 8 km long u-shaped valley, orien tated se–nw from miki fjord to ‘sødalengletscher’ (fig. 1). the photograph focuses on the stratigraphically lowest intrabasaltic, whitish sedimentary unit, which dips gently to the south-east. the geological cross-section in fig. 2a is projected on the cliff view, and is obtained from 3-d polylines created during the 3-d photogeological work. figure 2a illustrates several large-scale features relevant to the analogue study such as: (1) top and bottom geometry of the sandstone unit, (2) density of dykes and faults, which has a large impact on the lateral extension of the layers due to offsetting and (3) an evaluation of reservoir compartmentalisation. on an intermediate scale (metre to millimetre) on an intermediate scale, sedimentary and volcanic sections are logged in the field. facies types are identified, their lateral distribution and vertical stacking patterns are mapped and the boundaries between sedimentary and volcanic units are studied in detail. the 3-d photogeology is also useful on this intermediate scale because the high resolution of the digital photographs allows enlargement to study decimetre-sized features. photogeology can therefore be very helpful in mapping sedimentary facies assemblages between logged sections as well as key surfaces separating the different facies, such as sequence boundaries and marine-f looding surfaces. the overall depositional environments and the governing mechanisms for facies distribution, such as sediment transport directions, relative sea-level variations and palaeotopography can be interpreted from these studies. an example of a study on an intermediate scale is illustrated in fig. 2b where the photograph is an enlargement of a small area on the digital photograph (fig. 2a). the log of the sedimentary unit of shallow marine sandstone is shown on the left side of the figure. the lower, exposed part of the unit consists of crudely and irregularly bedded sandstones, locally with vertical burrows, interpreted as deposited in the upper shoreface zone. the lower part is overlain by wellsorted, fine to medium-grained, laterally extensive sandstone sheets and wedge-shaped sandstone beds with a large variety of sedimentary structures including local vertical burrows, cross-stratification and parallel bedding. these sandstones are interpreted as deposited in the lower to middle shoreface zone, which implies that the boundary to the underlying upper shoreface sandstones represents a minor f looding surface. on the photograph (fig. 2b) it is seen that the upper and lower to middle shoreface facies assemblages can be followed laterally for tens of metres. it is also seen that the boundary between the lava units and the sedimentary unit is slightly undulating, and that the invasive lava bed can be followed into the overlying lava to the right. the dyke that cuts through both the sedimentary unit and the lava units may have led to a possible compartmentalisation of the sandstone reservoir. fig. 2. ( facing page) a: oblique photograph (upper) and derived geological cross-section (lower) of the eastern side of sødalen, an 8 km long u-shaped glacial valley, extending se–nw from ‘sødalengletscher’ to miki fjord. for location see fig.1. the photograph focuses on the lowest intrabasaltic sediments (whitish colour) that dip gently to the south-east. faults and dykes are also seen. the geological cross-section below is a projection of 3-d polylines along a n–s-oriented profile, slightly different from the nw–se orientation of the photograph. b: close-up view of the white square in fig. 2a. a field log of the section (left) labels the sedimentary facies assemblages which can be followed laterally on the photograph. other important observations include an invasive lava bed and a dyke cutting through both lavas and intrabasaltic sediments. c: detrital and authigenic mineralogical composition of the facies in the sedimentary unit.  the larger amount of authigenic phases in the lower-middle shoreface sandstones compared to the upper shoreface sandstones, ref lect that these sandstones originally had a larger content of unstable, glass-rich volcanic fragments. the positions of the two samples are shown on fig. 2b. 7878 on a small scale (millimetre to micrometre) on a small scale, petrography is used to understand diagenetically induced reductions in porosity and permeability to understand the inf luence of provenance, sedimentary facies and surrounding ‘hot’ units on diagenetic processes. based on intensive sampling in a well-described geological framework controlled by 3-d photogeology and logged sedimentary sections, diagenetic changes are compared with detrital composition, depositional environment and effects from overlying and underlying lava units as well as dykes and sills. provenance variations are revealed from heavy mineral analysis using computer-controlled scanning electron microscopy, zircon age distributions and petrography. geochemistry is applied to distinguish different intrabasaltic units. the intrabasaltic sedimentary rocks consist of a mixture of detrital siliciclastic (quartz, feldspar, mica etc.) and volcaniclastic input (fig. 2c). the upper shoreface facies is richer in volcanic fragments than the lower-middle shoreface facies, yet it has a lower content of authigenic phases (fig. 2c). this is unexpected as volcanic fragments traditionally have been associated with intensive alteration thereby liberating elements for extensive authigenic phases. however, the type of volcanic fragments is also crucial for the degree of diagenetic alteration. glass-rich volcanic fragments are common in the lower-middle shoreface facies, whereas relatively stable volcanic fragments (lath-shaped plagioclase with little interstitial glass matrix) are more abundant in the upper shoreface. glass-rich volcanic fragments, which are easily altered, result in extensive authigenic formation, including chlorite as shown in fig. 2c. the stable volcanic fragments behave as plagioclase grains during diagenesis and have less inf luence on the authigenic phases than the glass-rich volcanic fragments. consequently, the upper shoreface sandstones show better reservoir properties than the lower-middle shoreface facies. conclusions the field analogue project at sødalen integrated the three disciplines of 3-d photogeology, sedimentology and petrography, and gave detailed information from kilometre to micrometre scale. petrographical investigations revealed the diagenetic inf luence on the reservoir properties. when the diagenetic changes were related to the sedimentary facies, the information on the reservoir properties could be scaled up to sedimentary bodies. the geometry of the sedimentary bodies and the probability of compartmentalisation are defined from 3-d photogeology and logged sedimentary sections. integration and up-scaling of several types of geological data resulted in a more complete understanding of the geology of the area and can form the basic input for reservoir modelling and as field analogue for hydrocarbon discoveries in a similar, inaccessible geological setting in offshore areas. acknowledgements chevron and sindri group are thanked for their financial contribution to the field work in greenland. references dueholm, k.s. & olsen, t. 1993: reservoir analog studies using multimodel photogrammetry; a new tool for the petroleum industry. aapg bulletin 77, 2023-2031. tulsa, oklahoma: american association of petroleum geologists. dueholm, k.s., garde, a.a. & pedersen, a.k. 1993: preparation of accurate geological and structural maps, cross-sections and block diagrams from colour slides, using multi-model photogrammetry. journal of structural geolog y 15, 933–937. helland-hansen, d. 2009: rosebank – challenges to development from a subsurface perspective. in: varming, t. & ziska, h. (eds): faroe islands exploration conference: proceedings of the 2nd conference. annales societatis scientarium faeroensis, supplementum 50, 241–245. larsen, m., hamberg, l., olaussen, s., nørgaard-pedersen, n. & stemmerik, l. 1999: basin evolution in southern east greenland; an outcrop analog for the cretaceous–paleogene basins on the north atlantic volcanic margin. aapg bulletin 83, 1236–1261. tulsa, oklahoma: american association of petroleum geologists. authors’ addresses h.v., p.g., r.w., e.v.s. & c.k., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: hv@geus.dk m.l., dong energy a/s, agern alle 24–26, dk-2970 hørsholm, denmark. c.d., chevron upsteams europe, chevron north sea ltd., chevron house, hill of rubislaw, aberdeen ab15 6xl, uk. geological survey of denmark and greenland bulletin 20, 2010, 71–74 71 an airborne hyperspectral survey was organised by the geological survey of denmark and greenland (geus) and carried out in 2000 to test the use of spectral analysis in mineral exploration under arctic conditions. the hyperspectral data were acquired by using the hymap imaging system consisting of sensors that collect ref lected solar radiation in 126 bands covering the 440–2500 nm wavelength range (bedini & tukiainen 2008). the spatial resolution was 4 × 4 m (tukiainen 2001). eight sites underlain by caledonian or post-caledonian rocks with known mineral occurrences (fig. 1) were tested. the project was financially supported by the greenland bureau of minerals and petroleum and the data were analysed by geus. here we provide a summary of the results. field work 2005–2009 ground checks were undertaken in 2005, 2008 and 2009 by geus (thomassen & tukiainen 2008). the field work by the authors was carried out from light-weight camps in co-operation with international molybdenum ltd. that explored the malmbjerg molybdenum deposit, and with other geus activities. the aim was to investigate hyperspectral anomalies and known mineral occurrences. the field work comprised ground measurements of rocks, minerals and their weathering products with a portable spectro-radiometer in order to determine their spectral character and to compare this information with the airborne data. in 2005 and 2008, a pima ii portable instrument was borrowed from other institutions, but for the 2009 season geus purchased an advanced spectro-radiometer, model fieldspec 3 hires. our investigations showed that there is good correlation between the airborne spectra and the field spectra, thus confirming the quality and stability of the airborne hyperspectral data. in general, sulphide minerals have poor to weak spectral response in the visible and near-infrared (vnir) and shortwave infrared (swir) spectral regions whereas their alteration products, such as malachite, cerussite, smithsonite and jarosite, are distinctly swir-active. however, apart from jarosite, these minerals are virtually non-existent in the region. in contrast, it appears from our study that the hyperspectral detection of typical hostand wall-rock alteration minerals (jarosite, white micas, phengite, kaolinite, dolomite etc.) provides an effective method to outline potential exploration targets. main results below we present some results that are of relevance for mineral exploration in the region. the reader is referred to harpøth et al. (1986) for a description of the mineral occurrences of the region and to henriksen et al. (2009) for a description of the regional geology. the locations of the described areas are shown in fig. 1. area 1 – wegener halvø. this horst-like peninsula exposes a complex pattern of fault blocks involving neoproterozoic to triassic sedimentary rocks, with stratabound base-metal mineralisation occurring in the permo-triassic section. disseminated mineralisation hosted by triassic sandstone and shale could not be detected by the airborne hyperspectral survey due to lack of alteration minerals. however, a close association of dolomitisation with upper permian, carbonate-hosted base-metal mineralisation is confirmed by our investigations, making the dolomite map a valuable exploration tool (fig. 2). area 2 – werner bjerge. a well-known porphyry molybdenum deposit is hosted in the malmbjerg granite stock, which is a unit of the palaeogene werner bjerge alkaline intrusive complex. the alteration zones surrounding the deposit constitute an important target for our investigation. conspicuous high-temperature, potassic and siliceous hydrothermal alteration outlined by muscovite and phengite is well displayed in the hyperspectral data. the high-temperature alteration apparently culminated in greisenisation of the malmbjerg granite stock, as exemplified by topaz-muscoviteenriched rocks in the stock roof and in the roofing permocarboniferous sandstone (fig. 3). in addition, the hyperspectral mapping of typical alteration minerals outlines a large number of potential exploration targets with low-temperature argillitic and propylitic alteration elsewhere in the alkaline intrusive complex. the hyperspectral mapping also defined a locality c. 1 × 1.5 km in size immediately south of werner bjerge, which displays many spectral similarities to malmbjerg. the accessible part of this anomaly at 1300 m was found to host a significant number of pyriteand f luorite-bearing trachytic application of airborne hyperspectral data to mineral exploration in north-east greenland tapani tukiainen and bjørn thomassen © geus, 2010. geological survey of denmark and greenland bulletin 20, 71–74. open access: www.geus.dk/publications/bull 7272 dykes and sheets a few metres thick in permo-carboniferous sandstone. the intrusive trachytic rocks host abundant wallrock fragments and are highly enriched in potassium and show elevated concentrations of tungsten (max. 35 ppm), molybdenum (max. 21 ppm) and thorium (max. 226 ppm). these rocks may represent the top of a porphyry system with an unexposed granite at a lower level. area 3 – mestersvig. the permo-carboniferous sandstones of this area host epithermal lead–zinc-bearing quartz veins, including the mined-out blyklippen deposit. the min100 km werner bjergewerner bjerge blyklippenblyklippen tnathorst land trailltraill øø j a m e s o n l a n d constable pynt gåseland malmbjergmalmbjerg milne land hinks land charcot land hudsonhudson landland claveringclavering ø ø wollastonwollaston forlandforland t canning land wegener halvø devondal kap simpson mestersvig werner bjerge p d m f malmbjerg blyklippen daneborg ’lauge koch’s gold mine’ parkinson bjerg traill ø ymer ø hold with hope clavering ø wollaston forland hudson land kong o scar fjord kejser franz joseph fjord i n l a n d i c e greenland post-caledonian caledonian orogen ice quaternary, undifferentiated intrusive complexes palaeogene volcanic province sedimentary basins allochthonous thrust sheets structures boundary/unconformity thrust post-devonian main fault normal fault base, abandoned mine area with airborne hyperspectral data extensional fault and detachment separating thrust units basaltic sills and dykes basaltic plateau lavas jurassic–palaeogene triassic upper permian permo-carboniferous devonian granites (sensu lato) early neoproterozoic metamorphosed rocks mesoproterozoic metasediments palaeoproterozoic crystalline basement complexes archaean crystalline basement complexes neoproterozoic – lower palaeozoic sediments 4 pdmf 72°n 73°n 74°n 25°w 20° 1 4 2 3 5 6 7 8 fig. 1. geological map of north-east greenland showing areas covered by airborne hyperspectral data. the numbers refer to the areas discussed in the text. modified from henriksen & higgins (2008). 73 eralisation is accompanied by silicification and kaolinisation of the wall rocks, but this association did not clearly define the veins in the airborne survey. however, the airborne data reveal a distinct, c. 500 m wide zone of pervasive kaolinisation of the arkosic sandstone some 3 km north-east of the old mine. this could be related to unknown base-metal mineralisation of the blyklippen type. area 4 – kap simpson. the palaeogene kap simpson alkaline intrusive complex hosts a caldera structure displaying widespread and intensive hydrothermal alteration. pyrite is common and traces of molybdenite are known, with basemetal and niobium-bearing quartz and calcite veins in the host mesozoic sediments. the hyperspectral survey distinguished between low-temperature, fumarole-related alteration (montmorillonite-illite-jarosite and iron oxides) and high-temperature alteration (muscovite-phengite) associated with subvolcanic intrusions. high-temperature potassic alteration and greisen-like spectral signatures on a granite in the north-western part of the intrusive complex define a new exploration target with potential for porphyry-type mineralisation. area 5 – ymer ø. ymer ø hosts a number of e–w-striking, epithermal tungsten, antimony, gold, base-metal-bearing quartz veins in neoproterozoic sediments. samples from the antimonite-bearing veins returned up to 23.4% sb and 4.7 ppm au. these veins give a weak hyperspectral response, due to the presence of low-temperature argillitic minerals (kaolinite, illite and alunite) in the quartzitic wall rock. however, known scheelite-antimonite-bearing veins are not detected by the hyperspectral survey. this is due to lack of distinct alteration minerals other than quartz in the carbonate wall rock. distinct linear anomalies detected in the airborne data turned out to originate from 3–5 m thick, e–w-striking, unmineralised rhyolitic veins with kaolinite alteration or weathering products, probably related to the mineralising system. area 6 – hudson land. central hudson land exhibits various types of mineralisation in a complex pattern of proterozoic to palaeogene rocks transsected by a regional, n–strending structure, called the post-devonian main fault. quartz veins 0.1–1.0 m thick with greisen mineralisation returned up to 1.4% sn and 0.5% cu but were not depicted in the airborne data due to their modest size. in contrast, extensive, low-temperature, hydrothermal alteration with associated epithermal baseand noble-metal-bearing veins along the post-devonian main fault is clearly seen in the hyperspectral data. special attention was paid to a devonian granite stock at parkinson bjerg, which is surrounded by geochemical sn-w-mo-nb anomalies. the granite was found to have a pegmatitic core rich in quartz, f luorite and tourmaline, corresponding to a distinct tourmaline and phengite response in the airborne data. this granite is a potential source for the geochemical anomalies. rock samples returned up to 0.4% sn, 0.17% be and 0.1% y. area 7 – clavering ø. extensive rust zones caused by hydrothermal alteration and epithermal base-metal mineralisation along faults occur in proterozoic metasediments on clavering ø. the mineralisation was investigated in the 1930s when a test adit was excavated at the so-called ‘lauge koch’s gold mine’, which transpired to host a pyrite vein without anomalous gold. the mineralised structures are distinct in the hyperspectral mapping as lineaments with lowtemperature alteration minerals such as illite and jarosite. samples of massive, brecciated pyrite ‘ore’ with minor f luorite and galena returned <2 ppb au. area 8 – wollaston forland. prior to 2000, no mineralisation had been reported from wollaston forland, and the area was included in the airborne survey for biological reasons. the survey showed hyperspectral anomalies caused by jarositeand muscovite/sericite-rich zones or lithologies in the north-western part of the area, which is underlain by proterozoic metasedimentary rocks. a scree sample of pyritiferous paragneiss below an anomaly returned 4.1 ppm ir while another loose block returned 0.38 ppm au. surrounding blocks of ultramafic rocks indicate a magmatic component in the area with potential for platinum group mineralisation. cu-pb-(zn)cu-pb-(zn) cu-pbcu-pb cu-pbcu-pb cu-pbcu-pb cu-pbcu-pbcu-pb-(zn) cu-pb cu-pb cu-pb cu-pb fig. 2. perspective view from the south-east of the north slope of devondal showing dolomitic alteration (red) of upper permian limestone. the scree aprons enhance the surface impression of dolomite. known occurrences of cu-pb-(zn) mineralisation are indicated. background image is a colour composite of hymap bands 27(r), 18(g) and 4(b). no vertical exaggeration, relief is 600 m. 7474 concluding remarks the present study demonstrates that the hyperspectral method is well suited for mineral exploration in remote and mountainous arctic regions. the most obvious target for future use of this method in greenland seems to be the palaeogene igneous province that stretches for 1100 km along the east coast. this province should be investigated for hostand wall-rock alteration indicative of subvolcanic porphyry-type molybdenum mineralisation. references bedini, e. & tukiainen, t. 2008: using spectral mixture analysis of hyperspectral remote sensing data to map litholog y of the sarfartoq carbonatite complex, southern west greenland. geological survey of denmark and greenland bulletin 17, 69–72. harpøth, o., pedersen, j.l., schønwandt, h.k. & thomassen, b. 1986: the mineral occurrences of central east greenland. meddelelser om grønland, geoscience 17, 139 pp. henriksen, n. & higgins, a.k. 2008: caledonian orogen of east greenland 70°n–82°n: geological map at 1:1 000 000 – concepts and principles of compilation. in: higgins, a.k., gilotti, j.a. & smith, m.p. (eds): the greenland caledonides: evolution of the northeast margin of laurentia. geological society of america memoir 202, 345–368. henriksen, n., higgins, a.k., kalsbeek, f. & pulvertaft, t.c.r. 2009: greenland from archaean to quaternary. geological survey of denmark and greenland bulletin 18, 126 pp. thomassen, b. & tukiainen, t. 2008: ground check of airborne hyperspectral anomalies in the greater mesters vig area, central east greenland. danmarks og grønlands geologiske undersøgelse rapport 2008/14, 85 pp. tukiainen, t. 2001: projects mineo and hypergreen: airborne hyperspectral data acquisition in east greenland for environmental monitoring and mineral exploration. geolog y of greenland survey bulletin 189, 122–126. malmbjerg granite stock b a fig. 3. perspective view from the south-west of the malmbjerg granite stock, no vertical exaggeration, relief is 500 m. the digital terrain model is based on lidar data from international molybdenum ltd. (re-sampled at 1 × 1 m resolution). a: minimum noise fraction transformed shortwave infrared data draped on the detailed digital terrain model. note the compositional zoning of the granite stock and intensive high-temperature alteration of the roofing rocks (hues of yellow and orange). b: orthoscopic lidar image draped on the detailed digital terrain model. the pixels mapped as topaz/tourmaline-bearing greisen are shown in red. the boundaries of the granite stock are indicated. authors’ addresses t.t., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: tt@geus.dk b.t., present address: avannaa resources ltd., dronningens tværgade 48, dk-1302 copenhagen k, denmark. geological survey of denmark and greenland bulletin 31, 2014, 39-42 39 ribbed moraines formed during the retreat of the scandinavian ice sheet from eastern himmerland, ne jylland, denmark hans lerche, peter roll jakobsen and stig a. schack pedersen the glacial geology of himmerland in the north-eastern part of jylland, south of limfjorden (fig. 1) has never received any special attention. however, the occurrence of parallel ridges south of torup was mentioned by milthers (1948) who interpreted them as marginal moraines. the ridges were recently studied during mapping of eastern himmerland. systematic geological mapping of the area north and south of mariager fjord started in 2009 and was completed in 2013 (map sheet 1316 iii; pedersen et al. 2013). this was followed by the map sheet to the north (1316 iv). during the recent mapping the extent of the terrain with parallel ridges was determined (fig. 2); the western boundary is found in rold skov (pedersen & jakobsen 2005) and the eastern boundary follows an ancient coastline in eastern himmerland. the most impressive parallel ridges occur in a forested area east of madum sø where the top level of the ridge crests reaches an elevation of 95 m a.s.l. however, the majority of the crests are at 60–70 m a.s.l. and most of the ridges are c. 10–15 m high. the sediments in the ridges are dominated by coarse-grained sand and gravel, and accumulations of erratic boulders are found on the surface of the ridges. after completion of the mapping of the area, we decided to make a detailed investigation of the ridges using groundpenetrating radar (gpr) to map the internal structures of the ridges. we also studied sections in a small gravel pit at the northern boundary of siem skov (figs 3, 4). the aim of this paper is to describe the terrain with parallel ridges, which we interpret as ribbed moraines. we discuss the geological setting of the ridges in relation to the data acquired during the systematic geological mapping and the accompanying gpr survey. a glaciodynamic model for the formation of the ridges is proposed related to the recession of the ice that had its source area in south central sweden. © 2014 geus. geological survey of denmark and greenland bulletin 31, 39–42 . open access: www.geus.dk/publications/bull himmerland vendsyssel 10°e limfjorden lille vildmose kongerslev rebild bakker støvring hobro aalborg torup kirke rold skov hellum skov mariager fjord fig. 2 56°50´n hadsund 5 km denmark 50 km kattegat fig. 1. map of the north-eastern part of himmerland where systematic geological mapping has been conducted over the past five years. the area with moraine ridges is indicated by a rectangle. the locations of place names mentioned in the text are shown. 0–10 10–20 20–30 30–40 40–50 50–60 60–70 70–80 80–90 90–100 2 km elevation (m a.s.l.) ridge fig. 4 madum sø fig. 2. lidar-based digital elevation model of the study area showing moraine ridges. most of the ridges are found in three separate areas. the most densely spaced and largest ridges occur in the central area. 4040 geological setting the bedrock in himmerland is dominated by maastrichtian chalk which is exposed in pits throughout the region. an erosional unconformity separates chalk from quaternary deposits. major parts of the region between mariager fjord and limfjorden are covered by glaciofluvial sand that reaches a thickness of c. 40 m at hadsund. in the small gravel pit at the northern boundary of siem skov, the succession begins with a glaciolacustrine unit, which increases in thickness towards the east. this unit is interpreted as a palaeo-kattegat deposit and may correlate with the lønstrup klint formation in vendsyssel (pedersen 2005). it is overlain by glaciofluvial sand and gravel that may correlate with the rubjerg knude formation (pedersen 2005). these proglacial deposits of the glaciodynamic sequence (according to the concept of pedersen 2012) are overlain by c. 3 m of till. the till is classified as a sandy till; it contains indicator boulders from the oslo fjord region and its fabric indicates an ice-flow direction from north to south. based on this ice movement direction the till is correlated with the kattegat till formation (houmark-nielsen & kjær 2003; pedersen 2005). the top of the till is at 56 m a.s.l. in siem skov where it forms the base of the 10–25 m high ridges. meltwater related to the swedish ice advance only played a small role in the region with the parallel ridges. to the west, glaciofluvial deposits from the swedish ice advance are found in the upper part of the rebild bakker (pedersen & jakobsen 2005). after the parallel ridges had formed, depressions were created in the landscape due to melting of bodies of stagnant ice that were left from the retreating ice front. during the early holocene valleys were eroded when the relative sea level was low. geomorphology of the parallel ridges the elongate ridges cover an area of 15 × 8 km. most of them are n–s-oriented, but there are nw–se-oriented ridges in the north-western part of the area. the ridge density is highest in the central part of the area, in hellum skov and siem skov (fig. 4) where the ridges reach elevations of 70 m a.s.l. and are c. 10 m high. the mean spacing between the ridges is 48 m in hellum skov and siem skov and the longest ridges are c. 2500 m long. towards the east and south, ridges may still be recognised but are somewhat obscured. in these areas, ridge crests are at c. 30 m a.s.l. and the ridges are 5–10 m high. georadar survey of the parallel ridges in september 2013, ground penetrating radar (gpr) surveys were carried out in hellum skov where the most pronounced ridge terrain is found. an ekko 100tm device mounted on a cart was used, and six lines perpendicular to the ridges were recorded; five lines in the northern part of the forest and one line c. 1 km to the south. transmitter voltage was 400 v and antenna frequency was centered at 100 mhz. the antennas were oriented broadside to the survey direction and separated by 1 m. traces were recorded every 20 cm and consist of stacks of eight. two representative profiles, line0007 and line0014, illustrate the internal architecture of the ridges (fig. 5). assuming a mean velocity of 0.1 m/ns, 1 m equals 20 ns. in line0014 the layers below the ridges are predominantly a west east 1 m torup kirke small gravel pit madum sø line0007 line0014 siem skovhellum skov 1 km fig. 3. exposure in a small gravel pit located c. 1.2 km ssw of torup kirke showing a section through one of the ridges. west of the anticline (a) dipping layers of glaciaof luvial sand and gravel are seen, and east of the anticline layers of f low till occur. the architecture can be compared to the structures seen in the gpr profiles (fig. 5). photograph: elina kamla. fig. 4. hill shade image of the central part of the ridge terrain. the ridges are almost parallel, mainly n–s-oriented but nw–se-oriented in the north. the locations of the two gpr profiles (fig. 5) are also shown. line0007 was acquired in a spruce plantation across relatively smooth ridges, whereas lin0014 was acquired along a gravel road crossing 11 steep-sided ridges. 41 subparallel anticlines, whereas layers below depressions are dominantly subparallel synclines. in both profiles two types of faults are found: (1) small, dominantly eastward-dipping faults and (2) larger, possibly superimposed folded thrust faults, which can be traced from near the surface down to 7–10 m below the surface (fig. 5). formation of the ridges the small e-dipping faults recognised in the gpr profiles are interpreted as thrust faults caused by pushing from the east. small w-dipping faults may indicate landslides on steep ridge flanks. large thrust faults are interpreted as listric faults with décollement surfaces c. 7–10 m below the ground. the folded lower layers of line0014 suggest ductile deformation within the ridges and the depressions. gpr data indicate that the ridges were formed by ice pushing from the east under non-permafrost conditions. we suggest that the ridges reflect a net ice recession with a mean rate of c. 50 m/year, but with a number of small advances (fig. 6). the east–west extent with ridges is almost 10 km wide, corresponding to a period of c. 200 years. a similar magnitude of recession rate of the scandinavian ice sheet has been suggested for vendsyssel, where recession from the coastal area along kattegat north of limfjorden is estimated to have occurred in the interval from 19 to 18.5 ka (sandersen et al. 2009). we suggest that shortly after termination of the last glacial maximum temperature increased rapidly, which lead to a significant recession of the ice margin. the moraines show some similarities to de geer moraines (de geer 1940; lundquist 1986; lundquist & viborg 1998; lindén & möller 2005). however, de geer moraines formed in water depths of 150–250 m, during retreat of a grounding line with a calving glacier front. in contrast, the himmerland moraines formed on dry land. west east line0007 line0014 western part line0014 western part line0014 eastern part line007 0 200 400 0 200 20 m 0 200 400 0 200 bedding fault 0 200 400 0 200 400 tw ow ay t ra ve l t im e (n s) groundwater? west east fig. 5. two examples of processed ground-penetrating radar records and their interpretations (line0014 is divided into two parts). the gpr data were processed using ref lex2dquick analysis. the following steps were followed prior to the interpretation of the data: (1) x-axis f lip, (2) move start time to –45.2 ns, (3) normal move-out, 1 m separation, (4) dewow noise filtered, time window 10 ns, (5) bandpass frequency, 20/187 mhz, (6) topographic migration, summation width 50 traces, (7) divergence compensation gain, scaling value 1 and (8) topographic correction, square interpolation. our knowledge of radar-wave velocity variations in the survey area is limited, and hence we refrained from converting the recorded two-way travel time to depth. however, hyperbola velocity adaptions provided approximate mean velocities for each survey line. 4242 conclusions as part of the systematic mapping of eastern himmerland, a detailed investigation was made of a terrain with parallel ridges located in a 120 km2 large area centred on siem skov. the individual ridges are up to c. 2.5 km long. the ridges are 10–25 m high, and the spacing between the ridge crests varies from 50 to 100 m. the parallel ridges are interpreted as ribbed moraines that formed during recession of the ice margin at c. 19 ka. the detailed architecture of the ridges was investigated by gpr surveys which show an integrated depositional and deformational dynamic picture with narrow and steep-sided depressions filled with flow-till materials contemporaneous with fold-push and up-thrusting. references de geer, g. 1940: geochronologia suecica, principles. kungliga svenska vetenskapsakademiens handlingar ser. iii 18(6), 367 pp. houmark-nielsen, m. & kjær, k.h. 2003: southwest scandinavia, 40–15 kyr bp: palaeogeography and environmental change. journal of quaternary science 18, 769–786. lindén, m. & möller, p. 2005: marginal formation of de geer moraines and their implications to the dynamics of grounding-line recession. journal of quaternary science 20, 113–133. lundqvist, j. 1986: late weichselian glaciation and deglaciation in scandinavia. quaternary science reviews 5, 269–292. lundqvist, j. & viborg, l. 1998: isavsmältning och israndlinjer i sverige and lokaler i sverige. in: andersen, s. & pedersen, s.a.s. (eds): israndslinier i norden, 61–81 and 161–215. copenhagen: nordisk ministerråd. milthers, v. 1948: det danske istidslandskabs terrænformer og deres opstaaen. danmarks geologiske undersøgelse iii. række 28, 234 pp. (with summary in english). pedersen, s.a.s. 2005: structural analysis of the rubjerg knude glaciotectonic complex, vendsyssel, northern denmark. geological survey of denmark and greenland bulletin 8, 192 pp. pedersen, s.a.s. 2012: glaciodynamic sequence stratigraphy. in: huuse, m. et al. (eds) 2012: glaciogenic reservoirs and hydrocarbon systems. geological society (london) special publication 368, 29–51. pedersen, s.a.s. & jakobsen, p.r. 2005: geologisk kortlægning af statsskovarealerne i rold skov. systematisk geologisk kartering af statsskovarealerne i rold skov, som udgør dele af 1:25 000 kortbladene 1216 i sø og 1216 ii nø, nordlige jylland. danmarks og grønlands geologiske undersøgelse rapport 2005/81, 28 pp. pedersen, s.a.s., jakobsen, p.j., tougaard, l. & gravesen, p. 2013: geological map of denmark 1:50  000, map sheet mors, nw denmark. geological survey of denmark and greenland bulletin 28, 29–32. sandersen, p.b.e., jørgensen, f., larsen, n.k., westergaard, j.h., & auken, e. 2009: rapid tunnel-valley formation beneath the receding late weichselian ice sheet in vendsyssel, denmark. boreas 38, 834– 851. authors’ addresses h.l., department of geosciences and natural resource management, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: hans_lerche@hotmail.com p.r.j. & s.a.s.p., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. + + + + + + + + + + ++ west east + + + + + + a b c d basal till fig. 6. conceptual model showing the formation of moraine ridges in north-eastern himmerland. a: in winter the glacier front advances, pushing up and deforming deposits in front of the glacier. b: in summer the mass balance of the glacier is negative and the glacier front recedes. the proximal part of the deformed deposits collapses and a ridge is formed. a new outwash fan forms between the glacier margin and the ridge. c: the next winter the new outwash fan is pushed up and deformed. syntectonic deposition in the form of f low till and alluvial sediments also occurs. d: the next summer another outwash fan is formed. geological survey of denmark and greenland bulletin 26, 2012, 69-72 69 methane and possible gas hydrates in the disko bugt region, central west greenland naja mikkelsen, troels laier, tove nielsen, antoon kuijpers and niels nørgaard-pedersen current climate models predict an annual temperature increase in the arctic between 4° and 6°c by the end of the 21st century with widespread impact on the arctic environment. warming will lead to thawing of the widespread, permanently frozen, high-latitude peat-lands and to degradation of marine gas hydrates, both of which may increase the rate of methane release to the atmosphere. this will inf luence global climate as methane is a potent greenhouse gas with a large global warming potential. marine gas hydrates are found worldwide on continental margins and frequently occur in the arctic. interpretation of seismic profiles has also indicated their presence in the disko bugt region in western greenland. in june 2011 a scientific cruise was undertaken in the disko bugt region (fig. 1) to investigate the occurrence of methane and possible gas hydrates in the region. the cruise was part of a multidisciplinary scientific project impact on permafrost, gas hydrates and periglacial processes following climate changes in greenland (permagas). the project studies the impact of global climate warming on permafrost and gas hydrates in the disko bugt region. the aim of the project is to link marine and terrestrial occurrences of gas emissions. marine gas hydrates gas hydrate is a crystalline solid consisting of gas molecules, usually methane, with each gas molecule surrounded by a frame of water molecules. marine gas hydrates form under high pressure and low temperature in sediments below the seabed (fig. 2). depending on the bottom water temperature methane hydrate is typically stable in sea-f loor sediments on the continental slope, but in high-latitude regions with low bottom water temperatures, the top of the gas hydrate stability zone may occur at shallower depths. gas hydrates are a potential energy resource as well as a potential risk for geohazards and the safe exploitation of sea bed resources (kvenvolden & rogers 2005). the worldwide amount of carbon bound in gas hydrates is conservatively estimated to total twice the amount of carbon found in all fig. 1. map of the disko bugt region. the black dots show core sites in egedesminde dyb (a, b), on the shelf off aasiaat (c), in southern vaigat (d) and off jakobshavn isfjord (e). methane was encountered at sediment sites a and b, and traces of methane occurred at site c. at sites d and e, where pockmarks have been mapped during previous surveys, evidence of upwelling freshwater was found. contours: 100, 200 and 500 m. the red line that crosses the core location at site c shows the position of the seismic profile in fig. 3. fig. 2. phase diagram showing the boundary between free methane (no colour) and gas hydrate (blue). vaigat 69° 54°w 25 km 56° 68°30´n 200 500 50 0 disko disko bugt jakobshavn isfjord aasiaat a b c e d greenland 2 0 0 20 0 2 4 6 8 10 temperature (°c) 5 10 150 p re ss u re ( m p a) site b egedesminde dyb gas hydrate the general water depth in disko bugt is 200–400 m, corresponding to c. 2–4 mpa methane + water © 2012 geus. geological survey of denmark and greenland bulletin 26, 69–72 . open access: www.geus.dk/publications/bull 7070 known fossil fuels on earth, and methane bound in hydrates amounts to approximately 3000 times the volume of methane in the atmosphere. in a warming world, methane from the dissociation of large and dynamic gas hydrate reservoirs therefore has the potential to inf luence oceanic and atmospheric carbon pools and thus inf luence global climate. gas hydrate may be recognised on seismic profiles by the presence of a so-called bottom-simulating ref lector that marks the base of the gas hydrate stability zone (mackay et al. 1994). the ref lector is caused by the impedance contrast between the solid gas hydrate layer and free gas accumulations beneath. however, bottom-simulating ref lectors are also found in areas without gas hydrates. the disko bugt region since the discovery of extensive oil seeps north of disko in 1992 (christiansen et al. 1996), marine geologists’ interest in the disko bugt region has increased significantly. however, little is known about the possible existence of gas hydrates on the continental margin, offshore west greenland. the presence of pockmarks in disko bugt (weinrebe et al. 2008) provides evidence of upwelling gas or f luid from the sea bottom. the bottom water temperature is c. 3°c in the disko bugt region and gas hydrates can be expected to occur at water depths exceeding 400 m, provided that methane occurs in high concentrations. during collection of a piston core in central disko bugt high gas content was demonstrated by the sudden escape of large amounts of strongly expanding gas that disrupted the sediment (kuijpers et al. 2001). in addition, bottom-simulating ref lectors have been observed on a number of seismic profiles from the area (fig. 3). material and methods during the cruise, up to 6 m long gravity cores and up to 2 m long cores, taken with a max planck institute rumohr lot corer, were retrieved from five sites above and within the gas hydrate stability zone. the cores were sub-sampled for analysis of sediments and pore f luids (fig. 4; nielsen et al. 2011). the sediment cores were subjected to a number of geochemifig. 3. ref lection seismic profile from site c (fig. 1). the bottom-simulating ref lector (yellow) at 75 msec two-way travel time below the seabed may indicate the occurrence of an up to 70 m thick gas hydrate zone. pockmarks and seabed mounds (red) overlying faults in the shallow sub-seabed unit may be caused by seepage of free gas from beneath the gas hydrate zone. the seismic profile is part of released data acquired for the company nunaoil in 1998. fig. 4. plastic liners with 10 cm diameter cores sampled for pore water. the samples were analysed during the cruise for concentrations of methane, sulphate and dissolved sulphide. the r hizon samplers were inserted into pre-drilled holes in the gravity core sections and pore water extracted by applying vacuum to the sampler when pulling the syringe piston. fig. 5. total inorganic carbon (tic), total sulphur (ts) and total organic carbon (toc) in a sediment core from site b in egedesminde dyb (after kuijpers et al. 2001). 1 km 0.5 1.0 t w o -w ay t ra ve l ti m e ( se c ) sw ne tic (%) ts (%) toc (%) 0 1 2 3 0 300 600 900 d e p th ( c m b e lo w c o re t o p ) 71 cal analyses, including measurements of methane concentrations and concentration of pore-water solutes (particularly sulphate), which aimed at providing data that could confirm the presence of gas hydrates. geochemical results and discussion in the cores collected in egedesminde dyb at sites a and b (fig. 1), which are situated within the gas hydrate stability zone, high pore-water methane concentrations were noted. however, the maximum methane concentration measured (c. 16 mm) is much below what is expected for methane saturation at 800 m depth in the egedesminde dyb (147 mm; yamamoto et al. 1976). this is probably due to partial degassing during core retrieval. a pressure core barrel was not available during the cruise and the large drop in pressure during retrieval of the sediment cores would inevitably lead to loss of methane. therefore it was not possible to prove the existence of small amounts of methane hydrate that may have formed as a result of in situ methane supersaturation. we did not observe any diagnostic features of hydrates either, such as trends in the chloride concentration or soupy sediment textures. the methane is most likely microbial in origin and formed in situ as a result of organic matter degradation below the sulphate zone c. 0.5 m below the sea f loor. this assumption is supported by the high content of organic matter in the sediment (total organic carbon = 1.9–2.3%; fig. 5). methane production is also promoted by the relatively high sedimentation rate in the area, 0.4–0.5 cm/year at site b (moros et al. fig. 6. pore-water concentration profiles of dissolved methane, sulphate and chloride from sediment cores retrieved from egedesminde dyb (sites a (842 m) and b (865 m)), off aasiaat (site c, 544 m) and from vaigat (site d, 469 m). yellow symbols: short rumohr lot cores, black symbols: gravity cores. concentrations are in mm (millimoles per litre). 440 480 520 560 gravity core rumohr lot core 440 480 520 560 cl mm 440 480 520 560 440 480 520 560 0 10 20 30 0 10 20 30 0 10 20 30 so4 mm 0 10 20 30 0 100 200 300 400 500 600 0 0.1 0.2 0 100 200 300 400 500 600 0 5 10 15 20 0 100 200 300 400 500 600 d e p th ( c m b e lo w c o re t o p ) 0 5 10 15 20 0 100 200 300 400 500 600 ch4 mm 0 5 10 15 20 site a site b site c site d sulphate-methane transition zone sulphate-methane transition zone 7272 2006) that allows for a high proportion of easily degradable organic matter to enter the zone of methanogenesis (henrichs & reeburgh 1987). at site c in the area west of aasiaat the much lower methane concentration than at sites a and b may be explained by the high sulphate concentration (figs 1, 6), which generally excludes the presence of methane (iversen & jørgensen 1985). still the concentration of methane is significantly above background values for other sulphate pore-water concentrations in the disko bugt region. this may suggest upward migration of methane from gas hydrates as indicated by seismic data from the area (fig. 3). the slight decrease in pore-water chloride concentrations with depth (fig. 6) may further sustain the assumption of an upward migration of f luids depleted in chloride from below. pore-water sulphate in sediment cores from site d located in the southern end of the strait vaigat is almost exhausted at approximately 5 m below the sea f loor (figs 1, 6). however, the low sulphate concentration is presumably not entirely due to in situ microbial sulphate reduction, as the decrease in pore-water chloride concentration with depth indicates a considerable contribution of freshwater from submarine groundwater discharge (fig. 6). additional field work was conducted during the cruise in an area off the mouth of jakobshavn isfjord (site e). pockmarks observed during an earlier multibeam survey in that area (weinrebe et al. 2008) were suspected to have formed due to upward gas migration (hovland & svendsen 2006). however, the absence of methane together with the sediment texture observed in sediment cores from the area indicate that the pockmarks form from upwelling water and not from gas seepage. concluding remarks the geochemical data obtained as a result of the 2011 cruise to the disko bugt region indicate that gas hydrates may occur in the region. further investigation of the possible gas hydrates will continue during a new cruise in the area in 2012. acknowledgements the 2011 cruise was supported by a grant from geocenter denmark to the project permagas. the success of the cruise depended very much on the operational skills of the captain and crew of the r/v paamiut and the smooth co-operation during the cruise with a scientific team from the greenland institute of natural resources. references christiansen, f. g., bate, k.j., dam, g., marcussen, c. & pulvertaft, t.c.r. 1996: continued geophysical and petroleum geological activities in west greenland in 1995 and the start of onshore exploration. bulletin grønlands geologiske undersøgelse 172, 15–21. henrichs, s.m. & reeburgh, w.s. 1987: anaerobic mineralization of marine sediments organic matter: rates and role of anaerobic processes in the oceanic carbon economy. geomicrobiolog y journal 5, 191–237. hovland, m. & svendsen, h. 2006: submarine pingoes: indicators of shallow gas hydrates in a pockmark at nyegga, norwegian sea. marine geolog y 228, 15–23. iversen, n. & jørgensen, b.b. 1985: anaerobic methane oxidation rates at the sulphate–methane transition in marine sediments from kattegat and skagerrak (denmark). limnolog y oceanography 30, 944–955. kvenvolden  k.a. &  rogers  b.w.  2005:  gaia’s breath – global methane exhalations. marine and petroleum geolog y 22, 579–590. kuijpers, a., lloyd, j.m., jensen, j.b., endler, r., moros, m., park, l.a., schulz, b., jensen, k.g. & laier, t. 2001: late quaternary circulation changes and sedimentation in disko bugt and adjacent fjords, central west greenland. geolog y of greenland survey bulletin 189, 41–47. mackay, m.e., jarrard, r.d., westbrook, g.k. & hyndman, r.d. 1994: origin of bottom-simulating ref lectors: geophysical evidence from the cascadia accretionary prism. geolog y 22, 459–462, http://dx.doi. org/10.1130/0091-7613(1994)022%3c0459:oobsrg%3e2.3.co;2 moros, m., jensen, k.g. & kuijpers, a. 2006: midto late-holocene hydrological and climatic variability in disko bugt, central west greenland. the holocene 16, 357–367. nielsen, t., laier, t., mikkelsen, n. & kristensen, j.b. 2011: permagas project: sampling gas hydrates in the disko bay area. cruise report – r/v paamiut 20 to 26 june 2011. danmarks og grønlands geologiske undersøgelser rapport 2011/105, 40 pp. weinrebe, w., kuijpers, a., klaucke, i., fink, m., jensen, j.b. & mikkelsen, n. 2008: high-resolution bathymetry of disko bay and ilulissat icefjord, west greenland. american geophysical union fall meeting, san fransisco, california, 15–19 december 2008 (abstract c31e0563). yamamoto, s., alcauskas, j.b. & crozier, t.e. 1976: solubility of methane in distilled water and seawater. journal of chemical and engineering data 21, 78–80. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: nm@geus.dk geological survey of denmark and greenland bulletin 31, 2014, 55-58 55 estimating thermal conductivity from lithological descriptions – a new web-based tool for planning of ground-source heating and cooling claus ditlefsen, inga sørensen, morten slott and martin hansen it is the overall policy of the danish government that by 2050 electricity, heating and transport will be 100% based on renewable energy. in order to reach this goal a number of different green technologies will have to interact. in areas with no district heating, ground-source heating by heat pump technology (sanner 2011) could well be one of the solutions. the potential energy extraction from closed-loop boreholes for ground-source heating depends to a large degree on the thermal conductivity of the surrounding geological formations, although other parameters such as the thermal gradient and the extent of groundwater flow also affect the transport of heat to the borehole. initial estimates indicate that in denmark there may be as much as 40% difference between the most and the least favourable geological conditions, determined by the thermal conductivity of the different sediment or rock types alone (vangkilde-pedersen et al. 2012). therefore specific knowledge of the thermal conductivity of the geological formations is essential when estimating the optimal drilling depth and the number of boreholes required for a specific plant. in co-operation with research and industrial partners, the geological survey of denmark and greenland is conducting a three-year project with the title ‘geoenergy, tools for ground-source heating and cooling based on closed-loop boreholes’ (www.geoenergi.org). the objective of the project is to acquire knowledge and develop tools and best practices for the planning, design and installation of shallow geothermal energy systems. this paper describes a web-based tool developed to estimate the thermal conductivity in the area surrounding a potential new plant. the tool was developed within the geoenergy project and can be used by administrators, energy planners and drillers of closed-loop boreholes. thermal conductivity of shallow danish sediments the thermal conductivity of sediments or rocks depends on their mineral composition, the texture, and the water content. above the water table, where air is present in the pore spaces, sediments generally have a low thermal conductivity. hence information about the position of the water table in the borehole is important when planning a new site. relatively few investigations of thermal properties of danish sediments have been carried out (balling et al. 1981; porsvig 1986) and thermal conductivity values published in international literature show broad ranges for the individual sediment types (e.g. banks 2008; vdi 2010). this is generally the case for clayey sediments and particularly for glacial till, see vangkilde-pedersen et al. (2012) for details. therefore a programme was initiated to investigate the thermal properties of common shallow sediments. the work focused on determining the thermal conductivity of prevalent watersaturated sediments. the range of the thermal conductivities within common sediment types was determined from measurements of 51 samples from well-characterised exposures at different localities (figs 1, 2). the samples were water saturated in the laboratory and placed in a thermal cupboard at 20°c for at least 16 hours before measurements were made. the thermal conductivity was determined using the needle probe method (wechsler 1992; hukseflux 2003). detailed © 2014 geus. geological survey of denmark and greenland bulletin 31, 55–58. open access: www.geus.dk/publications/bull 10°e 14°e 55° 57°n 50 km bornholm denmark sweden fig. 3 germany fig. 1. map showing sample locations. one sample from northern germany was kindly provided by reinhard  kirsch, landesamt  schleswigholstein. for sample details see ditlefsen & sørensen (2014). the arrow shows the location of the map included in fig. 3. http://www.geoenergi.org 5656 descriptions of sampling and laboratory procedures, as well as data analysis and statistical analysis were published by ditlefsen & sørensen (2014) and sørensen et al. (in press). a summary of the results is provided in table 1. each sample has been measured 2 to 5 times and an average value representing the sample was calculated. the variation amongst samples of the same sediment type is given as one standard deviation using the average values of each sample. the results indicate that the different sediment types have thermal conductivities within characteristic ranges with one standard deviation corresponding to approximately 20% of the mean. this further implies that it will be possible to estimate the thermal conductivity around a specific borehole from thorough descriptions of borehole samples alone. the national borehole database jupiter the geological survey of denmark and greenland has acquired data on boreholes since 1926 in accordance with the danish water supply legislation. the data include information about location, construction, geology, water table and groundwater chemistry (hansen & pjetursson 2011). samples from approximately one third of the boreholes have been described and interpreted by geologists; the rest have been described by drillers in the field. since 1969, drillers have also been obliged to submit representative borehole samples to the survey where they are described according to strict standards as outlined by larsen et al. (1995). in addition, geological interpretations of age and depositional environment are made (gravesen & fredericia 1984). the data are stored in the national borehole database, jupiter, which can be accessed on the internet free of charge (www.geus.dk). the database includes data on more than 270 000 boreholes, corresponding to about six boreholes per  square kilometre. in 2001, training and certification of drillers operating in denmark became mandatory, including instruction in making a simple but rigorous description of borehole samples. this allows for an overall assessment of the character and possible origin of samples that have been described in the field by drillers. all in all, the national borehole database provides planners, drillers and administrators with a unique possibility to evaluate local geological conditions at a given site. estimating thermal conductivity values from sediment descriptions as described above, it has been possible to establish a relationship between lithology and thermal conductivity for a number of common danish sediment types. the national database holds a large number of lithological descriptions from throughout the country, and by combining the lithological and thermal conductivity data the borehole database can be used in a new way. to do this it has been necessary to develop a routine that could relate a lithological description to one of the sediment groups in table 1. this task was facilitated by the structure of the lithological table in jupiter, where different components of the lithological description e.g. rock type, minor components, mineralogy, grain size, overall interpretation etc. are stored with unique codes a b fig. 2. a: sampling of clayey till. b: a sediment sample with a needle probe installed. gyttja 3 0.68 0.58–0.86 0.15 smectite-rich clay 3 0.98 0.80–1.14 0.17 silty clay 10 1.15 0.90–1.42 0.17 chalk* 4 1.62 1.49–1.80 0.13 mica-rich, fine-grained sand 8 1.81 1.48–2.19 0.27 till 19 1.89 1.40–2.66 0.30 glacial sand, gravelly 4 2.24 1.98–2.43 0.19 pure quartz sand 3 2.75 2.41–3.34 0.51 table 1. thermal conductivity of some common, shallow, danish sediments * selected data from balling et al. (1981). measurements were conducted with a needle probe (hukseflux 2008) using water-saturated samples. sediment type number of samples average thermal conductivity range one standard deviation w mk–1 w mk–1 w mk–1 57 in individual data fields, which makes rigorous queries into the lithological data possible. in this way most samples described and interpreted by geologists could fairly easily be assigned to one of the sediment groups in table 1. in addition granite, gneiss and sedimentary rocks found near the surface on the island of bornholm (fig. 1) are tentatively ascribed thermal conductivities in accordance with vdi (2010). water-lain sediments consisting of alternating layers of sand and clay are tentatively ascribed an average thermal conductivity of 1.5 w mk–1 in accordance with the values for sand and clay (table 1). for samples where only the overall sediment type was noted by the driller, interpretations had to be made (table 2). finally, to compensate for the fact that sediments which are not water saturated have reduced thermal conductivities (vdi 2010), all deposits above the water table in the borehole are tentatively ascribed a conductivity of 1.0 w mk–1. table 2. interpretation of thermal conductivity * sediment type according to driller. § the values are based on measurements of thermal conductivity (table 1) and our interpretations of sediment types. $ clay deposits with sand, gravel or stones are interpreted as till. other clay deposits are interpreted as clay deposited in water. sediment type* supplementary information from driller suggested thermal conductivity (w mk–1)§ sand 2.24 limestone 1.62 clay 1.15 clay$ containing, sand, gravel or stones 1.89 clay, sand, and stones$ 1.89 fig. 3. results from the web application shown in a standardised report window. http://geuskort.geus.dk/termiskejordarter/ –2 print 1.47 1.20 1.95 2.18 alternating sand and clay d ep th (m ) water table n u m b er o f b o re h o le s estimated thermal conductivity (w mk–1) 2 2 1 1 1 sediment distribution (%) 0 25 50 75 100 125 1.65 1 2 3 1000 glacial till mica-rich sand smectite-rich clay chalk and limestone gyttja and peat dry sediment above water table 1.00 1.81 1.50 0.98 1.62 0.68 1.15 1.89 silty clay granite, gneiss and sandstone quartz sand shale sand and gravel 2.75 2.20 2.24 3.00 89.257 89.90 56°8.7´n 10°8.1´e 100 m http://geuskort.geus.dk/termiskejordarter/ 5858 it is the intention of the web application to show the expected thermal conductivity in a new project area from existing lithological descriptions and further to show the variation in thermal conductivity with depth as a function of the lithological variations. the calculations include all available boreholes within a user-defined rectangle, and the estimated thermal conductivity is calculated in depth intervals of 25 m from the available lithological descriptions. furthermore, it is required that at least 80% of the interval is covered by descriptions that can be related to a thermal conductivity value. if this requirement is not met, the borehole is excluded from the calculations for the specific depth interval. within each interval the percentage of each sediment type is then calculated and from this distribution the resulting thermal conductivity of the interval is estimated from the reference values for water-saturated sediments or rocks (fig. 3). furthermore, the average depth to the water table is calculated from the most recent soundings in each borehole. above this depth a reduced thermal conductivity of 1 w mk–1 is estimated overruling the thermal conductivity related to the water saturated sediment. the web application is available at http://geuskort.geus. dk/termiskejordarter/. from the initial map, the user can zoom in on the relevant project area and see all boreholes. by using the box search button and clicking on the individual boreholes, a standard lithological report appears and the quality of the individual borehole data can be accessed. by dragging a rectangle over one or more boreholes, calculations based on the selected boreholes are made as described above. in order to obtain a reliable estimate of the thermal conductivity, it is important that the selected boreholes represent the geology at the new site, and a rectangle size of not more than 1 km2 is recommend unless an initial data inspection indicates otherwise. the results are shown in a standardised report window (fig. 3). the report shows the average lithological composition of each 25 m interval as bars and a plot of expected thermal conductivity values versus depth. a plot of the depth to the water table calculated from soundings in the area is shown to the left. the report also contains a locality map that shows the boreholes in the area and a legend that includes average thermal conductivities of different sediment and rock groups. the properties of the different groups can easily be adjusted or more groups can be added by the web administrator when more information about the thermal conductivity of different sediments and rocks becomes available. so far, the web application has been tested and released. the next step will be to introduce it to different end users such as administrators, drillers and energy planners. we also plan to conduct a number of interviews to get feedback, which may lead to adjustment of the system. acknowledgement the eudp programme of the danish energ y agency is thanked for financial support of the geoenerg y project. references balling, n., kristiansen, j.i., breiner, n., poulsen, k.d., rasmussen, r. & saxov, s. 1981: geothermal measurements and subsurface temperature modelling in denmark. geoskrifter 16, 176 pp. banks, d. 2008: an introduction to thermogeolog y: ground source heating and cooling, 351 pp. oxford: blackwell publishing. ditlefsen, c. & sørensen, i. 2014: d6 overfladenære jordarters termiske egenskaber (in danish with english summary), 30 pp. http://geoenergi. org/xpdf/d6_ jordarters_termiske_egenskaber.pdf gravesen, p. & fredericia, j. (eds) 1984: zeus-geodatabase system. borearkivet. databeskrivelse, kodesystem og sideregistre. danmarks geologiske undersøgelse serie d 3, 259 pp. hansen, m. & pjetursson, b. 2011: free, online danish shallow geological data. geological survey of denmark and greenland bulletin 23, 53–56. hukseflux 2003: tp02 non-steady-state probe for thermal conductivity measurement. tp02 manual v1209. delft: hukseflux. hukseflux 2008: tpsys02  thermal conductivity measurement system user manual tpsys02 manual v0806.doc. delft: hukseflux. larsen, g., frederiksen, j., willumsen, a., fredericia, j., gravesen, p., foged, n., knudsen, b. & baumann, j. 1995: a guide to engineering geological soil description. danish geotechnical society bulletin 1e, 130 pp. porsvig, m. 1986: varmeovergangsforhold omkring jordslanger. energiministeriets varmepumpeforskningsprogram 33, 56 pp. sanner, b. 2011: concept and feasibility studies. in: mc corry, m. & jones, g.l. (eds): geotrainet training manual for designers of shallow geothermal systems, 21–24. brussels: geotrainet. sørensen, i., palola, m.a. & ditlefsen, c. 2014: d8 guidelines for equipment, methods and calibration, part 1: measurement of thermal conductivity. geoenerg y report, 37 pp. www.geoenergy.dk vangkilde-pedersen, t., ditlefsen, c. & højberg, a.l. 2012: shallow geothermal energ y in denmark. geological survey of denmark and greenland bulletin 26, 37–40. vdi (verein deutscher ingenieure) 2010: thermische nutzung des untergrundes: grundlagen, genehmigungen, umweltaspekte. richtlinie 4640, blatt 1, 33 pp. düsseldorf: verein deutscher ingenieure. wechsler, a.e. 1992: the probe method for measurement of thermal conductivity. in: maglic, k. d., cezairliyan, a. & peletsky, v.e. (eds): compendium of thermophysical property measurement methods 2, recommended measurement techniques and practices, 161–185. new york: plenum press. authors’ addresses c.d., geological survey of denmark and greenland, lyseng allé 1, dk-8270, højbjerg, denmark. e-mail: cd@geus.dk m.s. & m.h., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. i.s., via university college, campus horsens, chr. m. østergaards vej 4, dk-8700 horsens, denmark. http://geuskort.geus.dk/termiskejordarter/ http://geuskort.geus.dk/termiskejordarter/ http://geoenergi.org/xpdf/d6_jordarters_termiske_egenskaber.pdf http://geoenergi.org/xpdf/d6_jordarters_termiske_egenskaber.pdf http://www.geoenergy.dk geological survey of denmark and greenland bulletin 17, 2009 carbon capture and storage (ccs) is increasingly considered to be a tool that can significantly reduce the emission of co2. it is viewed as a technology that can contribute to a substantial, global reduction of emitted co2 within the timeframe that seems available for mitigating the effects of present and continued emission. in order to develop the ccs method the european union (eu) has supported research programmes for more than a decade, which focus on capture techniques, transport and geological storage. the results of the numerous research projects on geological storage are summarised in a comprehensive best practice manual outlining guidelines for storage in saline aquifers (chadwick et al. 2008). a detailed directive for geological storage is under implementation (european commission 2009), and the eu has furthermore established a programme for supporting the development of more than ten large-scale demonstration plants throughout europe. geological investigations show that suitable storage sites are present in most european countries. in denmark initial investigations conducted by the geological survey of denmark and greenland and private companies indicate that there is significant storage potential at several locations in the subsurface. the danish perspective in storage capacity the ten largest point sources of co2 emission in denmark account for 21 mega-tonnes per year (mt/year). from preliminary investigations of the danish subsurface the co2 storage capacity in selected subsurface structures is estimated to 2500 mt (geocapacity 2009a). this corresponds to more than 100 years of storage from the ten largest emission point sources. the critical parameters of this analysis are the size of the structure, thickness, continuity and quality of the reservoir and the amount of formation water that may be displaced by the injected co2. the estimate is calculated assuming a surrounding aquifer volume displacement of formation water, which is limited to 50 times the trap volume (geocapacity 2009b). these estimates of storage capacity are uncertain and have not yet been tested in real physical storage operation. therefore it is difficult to evaluate to what degree the volume calculations are realistic. when a specific structure is selected for storage, a number of investigative steps are necessary, including acquisition and interpretation of new 2-d or 3-d seismic data, drilling of new wells, geological and reservoir modelling and flow simulation studies. for each step of incorporating new geological data, the site model of the reservoir is updated in the process of maturing the structure towards a storage site. this stepwise approach to site characterisation gradually leads to a research-based and relatively certain capacity estimate and an evaluation of the safety and behaviour of the site under simulated conditions, including the uncertainties of the estimates. assessment of geological and environmental risks can be carried out at various stages in the process. similarly, establishment of baseline studies and monitoring strategies need to be considered along with the progress of the characterisa© geus, 2009. geological survey of denmark and greenland bulletin 17, 13–16. available at: www.geus.dk/publications/bull the potential for large-scale, subsurface geological co2 storage in denmark peter frykman, lars henrik nielsen, thomas vangkilde-pedersen and karen lyng anthonsen 13 �� �� �� �� �� �� �� �� �� �� vedsted structure stenlille structure jylland fyn sjælland ålborg large point sources structures �� 50 km fig. 1. map of denmark showing the most important point sources of co2 emission and prospective structures for geological storage of co2. the stenlille structure is presently used for storage of natural gas; it serves to moderate seasonal fluctuations in consumption. the vedsted structure is currently investigated for possible storage of co2. rosa_2008:rosa-2008 01/07/09 15:47 side 13 tion of the storage site in order to make sure that the necessary background information is obtained before storage is initiated. in order to be reliable and operational, the baseline studies should preferably focus on measurement of conditions and properties that are stable and only show limited seasonal variations. such studies may include groundwater-flow models and groundwater chemistry, pore water and pore gas analyses from deep wells, surface topography and natural seismicity. a site study site investigations have recently been initiated of the vedsted structure by vattenfall a/s, with the intention of using the structure for storage of co2 from a nearby coal-fired power plant in ålborg (fig. 1; sørensen et al. 2009). existing data from oil exploration activities in the 1950s include one well in the centre of the structure and sparse 2-d seismic line data. the main target layer is the triassic–jurassic gassum for mation at around 1800 m depth. the formation is widely distributed in the danish basin and has good reservoir properties (fig. 2). it is currently used for storage of natural gas in the stenlille structure on sjælland and for geothermal energy in the thisted area in northern jylland. detailed sedimentological and sequence stratigraphic interpretations and correlations of the well logs and cores have established a robust stratigraphic framework for the upper triassic – jurassic succession (nielsen 2003). this framework forms the basis for the interpretation of the vedsted-1 well section as well as predictions regarding the lithology of the potential reservoirs and seals in the vedsted area (fig. 3). the process has also underlined the necessity of acquisition of new data and more detailed modelling at several different scales. at site scale, the optimal positioning of injection wells, as well as injectivity and capacity can be modelled and analysed, and the coupling between the operation of the power plant and the capture facility can be studied. the specific geological properties of the storage reservoir layers have consequences for the propagation and distribution of the injected co2 and for the storage mechanisms in the specific reservoir. most reservoirs show both vertical and horizontal heterogeneities that will influence the distribution of the co2. the preliminary reservoir model for the vedsted structure has been investigated by simulating an injection well on its south-eastern flank and using injection rates realistic for power-plant supply rates (frykman et al. 2009). after ten years of constant injection, the co2 distribution is as seen in fig. 4, which clearly shows the subdivision of the migrating front into several sub-layers due to intraformational sealing layers with low permeability that also have high capillary entry pressures. the layering in the model has maximum lateral continuity, which probably overestimates the segregation to be found in real cases, but any intra-reservoir sealing layers will have such an effect on the distribution. since this filling pattern influences the capacity, it is necessary to analyse further the properties and the continuity of the intraformational sealing layers. co2 can be trapped by several mechanisms, including structural trapping under an overlying sealing formation, dissolution of co2 in formation water, capillary trapping in the pore network and mineral trapping by reactions between co2 and mineral phases in the reservoir rock. these trapping mechanisms work on different scales both in space and time and need to be studied by designing appropriate models and experiments. for large-scale injection of co2 displacing saline porewater, the propagation of the pressure field during injection outside the immediate site area is of interest. modelling of this pressure distribution will serve to predict the amount of overpressure building up locally within the storage site, and can be used to suggest possible means of management. 14 50 km fig. 2. distribution of the triassic–jurassic gassum formation in the subsurface at depths between 800 m and 2400 m (yellow), the depth interval in which co2 exists as a supercritical phase and where burial dia genesis has not yet provoked significantly lowered porosity. at the supercritical phase the volume of co2 is much less than that of the co2 gas at the surface. rosa_2008:rosa-2008 01/07/09 15:47 side 14 the scale of the challenge and future perspective the first detailed pan-european assessment of co2 storage capacity in the framework of the eu research project geo capacity has resulted in a geographic information system (gis) database of co2 emissions, storage capacity estimates and geological information. the database includes information on reservoirs with a total storage capacity of 360 000 mt co2, with 326 000 mt in deep saline aquifers, 32 000 mt in depleted hydrocarbon fields and 2000 mt in unmineable coal beds: 116 000 mt are onshore, and 244 000 mt offshore (geocapacity 2009a). some of the estimated storage capacity is associated with structural traps, but a very large part is in regional deep saline aquifers without identified specific traps. almost 200 000 mt of the total storage capacity in the database are located offshore norway. these estimates date back to 2003 and have not been updated within the geocapacity project. an attempt to provide a more cautious and conservative european estimate has yielded a storage ca pacity of 117 000 mt with 96 000 mt in deep saline aquifers, 20 000 mt in depleted hydrocarbon fields and 1000 mt in coal beds, and with approximately 25% located offshore norway. this must be compared to a total of 2000 mt of co2 emission from large point sources, i.e. point sources emitting more than 0.1 mt/year within europe. in order to illustrate the scale of the technology and infrastructure that has to be established if ccs is to become an active industry, we can look at the amount of co2 produced by the ten largest point sources in denmark. there are 43 large point sources emitting 28 mt co2/year, the ten largest of which are responsible for 21 mt/year. at surface condi15 fig. 3. sw–ne-oriented cross-section across the danish basin, the sorgenfrei–tornquist zone and the skagerrak–kattegat platform (red line on the index map). the panel shows the lower part of the gassum reservoir which comprises fluvial, estuarine and shallow-marine deposits interbedded with offshore mudstones and some lacustrine mudstones. shoreline fluctuations have caused interfingering of these different facies types and given rise to pronounced vertical variability. informations from the four wells in the section about sedimentary facies have been interpreted and correlated into a sequence-stratigraphic framework. at a local site, this framework must be confirmed from detailed investigations of material from new wells drilled, and supplemented with new seismic data. modified from nielsen (2003). 4 ce rl rl skagerrak–kattegat platform sorgenfrei–tornquist zone 37 km 5 km 41 km 30 km 20 km børglum fault ation pt pt ts 7 danish basin sæby-1 vedsted-1rødding-1 sp hyllebjerg-1farsø-1 gr flyvbjerg-1 nesw 32 50 m 50 km sorgenfrei–tornquist zone danish basin skagerrak–kattegat platform fyn high ringkøbing – fluvial estuarine lacustrine lagoonal shoreface offshore depositional environments rosa_2008:rosa-2008 01/07/09 15:47 side 15 tions this corresponds to 11 billion (11 × 109) m3 co2 gas. the annual production of natural gas from the danish part of the north sea amounts to 10 billion (10 × 109) m3 (danish energy agency 2008), which is transported in pipe lines and tankers and processed at plants and refineries. the comparable size of the potential volume of co2, to be moved around at surface and injected into the subsurface (although compressed to smaller volumes at depth), points to the large scale at which a ccs-related processing and transporting industry has to be established. concluding remarks the ccs activities described here related to large-scale storage operations will involve significant physical resources and manpower. fortunately, the work with storage-related items does not have to begin from first principles, because much of the experience already exists in the oil and gas industry, which can provide methods and tools for immediate use. the skills of geoscientists and engineers are needed in the investigation and characterisation of the sites and the subsurface conditions for storage of co2, and a whole new infrastructure and industry may be established. geoscience and geo-engineering will play a major role in the analysis of the geological foundation, the assessment of site performance, and will be critical in securing the safety of the operations. initial investigations of the danish subsurface indicate that suitable structural traps with a significant storage potential are present at several locations, and that the structures can accommodate the co2 produced from several or most of the large danish point sources. thus, geological storage of co2 may contribute considerably to the reduction of the danish co2 emission, if we can be assured about safety issues, and if political and public acceptance can be obtained. references chadwick, a., arts, r., bernstone, c., may, f., thibeau, s. & zweigel, p. 2008: best practice for the storage of co2 in saline aquifers – observations and guidelines from the sacs and co2store projects. british geological survey occasional publication 14, 267 pp. danish energy agency 2008: oil and gas production in denmark 2007, 98 pp. copenhagen: danish energy agency. european commission 2009: directive of the european parliament and of the council on the geological storage of carbon dioxide, 84 pp. brussels: european union. frykman, p., bech, n., sørensen, a.t., nielsen, l.h., nielsen, c.m., kristensen, l. & bidstrup, t. 2009: geological modelling and dynamic flow analysis as initial site investigation for large-scale co2 injection at the vedsted structure, nw denmark. 9th international conference on greenhouse gas control technologies, washington d.c., 16–20 no vember, 2008. ghgt9 energy procedia 1, 2975–2982. geocapacity 2009a: geocapacity wp 2 report, storage capacity. eu geocapacity deliverable d16, 162 pp. eu geocapacity consortium, brussels. geocapacity 2009b: geocapacity wp 4 report, capacity standards and site selection criteria. eu geocapacity deliverable d26, 45 pp. eu geocapacity consortium, brussels. nielsen, l.h. 2003: late triassic – jurassic development of the danish basin and the fennoscandian border zone, southern scandinavia. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and green land. geological survey of denmark and greenland bulletin 1, 459–526. sørensen, a.t., klinkby, l., christensen, n.p., dalhoff, f., biede, o. & noer. m. 2009: danish development of a full-scale ccs demonstration plant in a saline aquifer. first break 27, 79–83. 16 authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: pfr@geus.dk fig. 4. vertical nw–se section in the gassum reservoir model through the injection well, showing co2 saturation sg (free gas-phase supercritical co2) after 10 years of injection. although the model is constructed in a fairly coarse grid, the intra-reservoir sealing layers are clearly reflected and influence the spatial distribution of the injected co2. the sedimentary layering causes filling of the individual layers of porous sand with the injected co2, whereas the interbedded mudstone layers with much lower reservoir quality are not filled and also limit the vertical movement of co2. model thickness 300 m, length 4800 m, vertical exaggeration 5 times. (modified from frykman et al. 2008). 0.55 sg 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 rosa_2008:rosa-2008 01/07/09 15:47 side 16 geological survey of denmark and greenland bulletin 28, 2013, 45-48 45 the norite belt in the mesoarchaean maniitsoq structure, southern west greenland: conduit-type ni-cu mineralisation in impact-triggered, mantle-derived intrusions? adam a. garde, john pattison, thomas f. kokfelt, iain mcdonald and karsten secher with the recent discovery of the giant, deeply eroded, 3 ga maniitsoq impact structure in southern west greenland (garde 2010), an enigmatic, c. 75 by 15 km large, curvilinear belt of undeformed norite intrusions with ni-cu mineralisation was re-interpreted as representing crustally contaminated melts derived from the mantle in the wake of the impact (fig. 1; garde et al. 2012). the norite belt (nielsen 1976; secher 1983) was discovered in the early 1960s by the mining and exploration company kryolitselskabet øresund a/s, and more than one hundred shallow exploration holes were drilled by the company in the period 1965–1971. the mineralisation has subsequently been investigated by cominco ltd., falconbridge ltd. and nunaminerals a/s. in 2011, the re-interpretation of the norite belt, and recent availability of improved airborne geophysical exploration tools, prompted the canadian company north american nickel inc. (nan) to resume exploration. © 2013 geus. geological survey of denmark and greenland bulletin 28, 45–48. open access: www.geus.dk/publications/bull d = 100 km d = 50 km d = 150 km 2 5 4 d = 100 km ‘spotty hill’ ‘imiak hill’ sillisissannguit nunaat ‘fossilik’ 65°n 10 km maniitsoq al an ng ua toqqusap nunaa ? ? ? 52°w greenland jurassic / archaean carbonatite surficial cover c. 3 ga cataclasis >3 ga rocks palaeoproterozoic mafic dykes norite belt, ni mineralisation postkinematic diorite intrusions granitic plutons archaean, c. 3 ga rocks approx. melt zone (extent revised from garde et al. 2012) metavolcanic belts and related rocks finnefjeld domain (cataclastic rocks) ttg orthogneiss fig. 1. geological map of the central part of the maniitsoq impact structure with the cataclastic finnefjeld domain in its centre, currently known distribution of norites and postkinematic diorites, and three labelled diamond drilling sites from 2012. reference circles with 50 and 100 km diameters are shown. 4646 this contribution gives a short description of the norite belt, outlines its ni-cu mineralisation and presents a preliminary interpretation. it is well known that the 1.85 ga sudbury impact structure in canada hosts a group of worldclass ni-cu deposits at the base of the impact melt sheet (eckstrand & hulbert 2007). the ni-cu mineralisation of the norite belt in west greenland is profoundly different as it is located in lower-crustal mafic intrusions, but we suggest here that also this was governed by impact-related magmatic processes. the maniitsoq structure the maniitsoq structure (garde et al. 2012) constitutes the deeply eroded, deep-crustal remains of a giant extraterrestrial impact that struck an active magmatic arc 3 ga ago in the north-central part of the north atlantic craton (fig. 1). the visible remains of the structure comprise a core measuring 35 by 50 km of thoroughly crushed, mechanically mixed and subsequently welded fragments of orthogneiss and amphibolite (together constituting the finnefjeld domain), surrounded by an up to c. 75 km wide, annular melt zone variably affected by both crushing and melting, and a peripheral, less damaged zone with a diameter of approximately 150 km. large parts of the entire structure have been affected by intense hydrothermal alteration and related, f luid-induced, partial melting. these features, and their large geographical extent, suggest that the original maniitsoq crater was larger than all previously known terrestrial impact structures. the norite belt and postkinematic diorites the norite belt (see above) and associated postkinematic diorites in the southern part of the impact structure (berthelsen 1960; garde 1991) collectively comprise numerous mafic to ultramafic intrusions ranging in size from small dykes to inclined, elongate bodies up to several square kilometres in outcrop size, hosted by mesoarchaean orthogneisses and mafic, metavolcanic belts. they were emplaced close to 3.0 ga ago (see garde et al. 2012), and their undeformed state and occasional xenoliths of crushed orthogneiss and f luidised microbreccia document that they post-date the impact. the intrusions are locally cut by few centimetres thick, white, undeformed pegmatites. most intrusions display inclined hostrock contacts, and the exposed bodies may thus represent open-ended magma conduits. the hybridised contact zones are diffuse, up to about 10 m wide and commonly hydrated (fig. 2). the known extent of the norite belt is shown on fig. 1, but at least a few additional, unmapped bodies are known to occur east and west of the main belt. the postkinematic diorites have a more random distribution and extend up to c. 70 km south and east of the centre of the impact structure. they have only been mapped systematically south of 65°n. the noritic and dioritic rocks typically form dark brown, crumbly weathering, mediumto coarse-grained, mostly structureless masses. they largely consist of variable proportions of orthopyroxene and andesine plagioclase with mediumto coarse-grained, granular textures. rhythmic magmatic layering is rare, but has been observed, e.g. at sillisissannguit nunaat (fig. 1; secher 1983). both small and large intrusions locally display proto-orbicular quench textures comprised of skeletal, rounded to ellipsoidal plagioclase crystals up to about 10 cm in size, and interstitial orthopyroxene (fig. 3), and locally display metre-scale layering. bulk compositions cover a large range from dioritic to fig. 2. typical homogeneous, undeformed norite outcrop with diffuse, hybridised contact zones to quartzo-feldspathic orthogneiss. from garde et al. (2012). fig. 3. proto-orbicular texture in norite, with rounded, skeletal plagioclase crystals and interstitial hypersthene. the hammer is 45 cm long. 47 noritic, but display a broadly uniform trace element distribution pattern; high mgo, cr and ni contents (≤21 wt%, 3685 ppm and 909 ppm, respectively) coupled with low nb and ta suggest an ultramafic precursor affected by abundant crustal contamination (garde 1991; garde et al. 2012). ni-cu mineralisation more than 50 sulphide-mineralised norite localities with uniform characteristics have been investigated over time (nielsen 1976; unpublished company reports). in typical, two-dimensional outcrops, the mineralised rocks form isolated, rusty weathered spots and lenses that rarely exceed 25 m in length (secher 1983). the sulphide paragenesis in fresh samples is almost invariably pyrrhotite-pentlanditechalcopyrite-pyrite, with accessory magnetite and ilmenite. the sulphide minerals form interconnected, semi-massive networks with inclusion-bearing, breccia-like textures characterised by rounded, centimetre-sized and larger lumps of the host rock (fig. 4). these textures closely resemble those found in magmatic, conduit-type ni deposits such as noril’sk in russia and lynn lake and voisey’s bay in canada (eckstrand & hulbert 2007). all significant nickel occurrences discovered to date at maniitsoq are entirely contained within norite intrusions. based on nan’s diamond drilling, combined with historical drill-hole information and three-dimensional modelling of airborne geophysical and down-hole electromagnetic data, the mineralisation can typically be described as steeply to vertically dipping pipeand sheet-like bodies comprised of heavily disseminated to near massive sulphide, often with abundant 0.2–5.0 cm subangular to subrounded inclusions of norite. in most cases, strongly mineralised zones are surrounded by a broad halo of weaker, disseminated mineralisation; however, in some places the contact between near solid sulphide and barren norite host rock is extremely sharp. diamond drilling in 2012 was performed at ‘imiak hill’, ‘spotty hill’ and ‘fossilik ii’ (cf. fossilik in fig. 1); the following, generalised figures of metal contents are solely intended to characterise the type of mineralisation without addressing economic aspects. the mineralisation has a high, uniform ni tenor averaging 6–9% ni recalculated to 100% sulphide, both at localities previously drilled by kryolitselskabet øresund a/s and also in new cores drilled by nan at ‘imiak hill’ and ‘spotty hill’ in 2012. typical ni contents in wt% of the total rock vary between 1 and 2% over several to many metres, with additional 0.1–0.6% cu, 0.01–0.07% co, up to 0.2 ppm pt and pd, and au in the ppb range (data from www.northamericannickel.com and secher 2001). these relatively low platinum-group element tenors are similar to the voisey’s bay deposit (lightfoot et al. 2012). discussion and interpretations origin of the noritic and dioritic intrusions garde (1991) and garde et al. (2012) interpreted the noritic and almost all of the dioritic intrusions as highly unusual, mantle-derived, crustally contaminated ultrabasic melts. this interpretation is based on (1) the wide, hybrid contact zones and (2) proto-orbicular interior textures of skeletal plagioclase and orthopyroxene, showing that the magmas were chilled by their hosts and crystallised rapidly (and thus indicating a very high emplacement temperature), (3) highly variable chemical compositions combined with (4) broadly similar overall element spectra consistent with mantle-crust mixtures, (5) ultramafic trace element signatures with very high cr, ni and v contents, and (6) mantle-like, strongly suprachondritic ru/ir, rh/ir, pt/ir and pd/ir ratios similar to high-mg basalts. fig. 4. inclusion-bearing, breccia-like texture of ni-cu mineralisation at ‘imiak hill’ (north american nickel inc. 2012 drill core mq-12-002 at 66.55 m). fig. 5. magmatic open-conduit model for the ni-cu mineralisation in the norite belt. schematic vertical section. modified from maier et al. (2001). ni-cu sulphides norite orthogneiss-amphibolite complex upper chamber lower chamber present-day erosion level 4848 interpretation of the ni-cu (-pge) mineralisation magmatic ni-cu-pge deposits are governed by several different factors (e.g. li et al. 2001; maier et al. 2001) including a fertile source (typically the mantle), where a significant ni contribution comes from interstitial sulphide minerals in addition to olivine. a high degree of melting is also required in order to ensure a complete dissolution of the sulphides with their metals into the primary magma. on the ascent of the magma, segregation of immiscible, sulphidic melt from the silicate melt must then occur in order to recapture the chalcophile elements of interest. in general terms, such segregation in response to sulphur saturation can be brought about by either fractional crystallisation in large magma chambers (potentially leading to pge-dominated deposits), or by crustal contamination in dynamic magma channels of restricted volume, potentially leading to ni-cu-dominated deposits (li et al. 2001). in the latter case, a suitable physical mechanism to separate and concentrate the exsolved, high-density sulphide liquid from the f lowing magma is also required. the essential features of the sulphide occurrences in the norite belt are all compatible with an interpretation as magmatic, open-source mineralisation systems. these features include high-temperature ultramafic host rock melts, abundant field and chemical evidence of crustal contamination, inclusion-bearing, breccia-like textures in the mineralised rocks, a high ni tenor in the sulphides, and ni/cu and (ni + cu)/pge ratios characteristic of this type of mineralisation. the three-dimensional shapes of the mineralised volumes and mechanism(s) of physical extraction of the exsolved sulphide melt phase are currently poorly known, but a schematic section of a possible scenario is shown in fig. 5. concluding remarks widespread ultramafic magmatism, such as in the norite belt, does not belong in convergent orogenic systems (garde 1991; garde et al. 2012), although ultramafic intrusions can occur under special plate-tectonic circumstances of ridge subduction or delamination of the lower crust, for which there is no evidence at maniitsoq. furthermore, the protoorbicular textures and very high degrees of contamination in the norite belt and postkinematic diorites are highly unusual even for ultramafic melts. the possibility of impact-induced mantle melting associated with giant impacts has previously been discussed in the literature ( jones et al. 2002), but no examples have been found prior to the case at maniitsoq (see garde et al. 2012). we conclude that the ni-cu occurrences in the norite belt are likely an impact-induced mineralisation. however, unlike sudbury they are not part of a differentiated impact melt sheet, but constitute a special variety of open-conduit systems, which are otherwise known from magmatic settings of non-impact origin. references berthelsen, a. 1960: structural studies in the pre-cambrian of western greenland. ii. geolog y of tovqussap nunâ. bulletin grønlands geologiske undersøgelse 25, 223 pp. eckstrand, o.r. & hulbert, l.j. 2007: magmatic nickel-copper-platinum group element deposits. in: goodfellow, w.d. (ed.): mineral deposits of canada: a synthesis of major deposit types, district metallogeny, the evolution of geological provinces, and exploration methods. geological association of canada special publication 5, 205–222. garde, a.a. 1991: post-kinematic diorite intrusions in archaean basement rocks around outer fiskefjord, southern west greenland. bulletin of the geological society of denmark 39, 167–177. garde, a.a. 2010: the 2975 ma maniitsoq impact structure in west greenland: the oldest and most deeply exposed meteorite crater on earth. abstracts and proceedings of the geological society of norway 1, 57–58. garde a.a., mcdonald, i., dyck, b. & keulen, n. 2012: searching for giant, ancient impact structures on earth: the mesoarchaean maniitsoq structure, west greenland. earth and planetary science letters 337–338, 197–210. jones, a.p., price, g.d., price, n.j., de carli, p.s. & clegg, r.a. 2002: impact induced melting and the development of large igneous provinces. earth and planetary science letters 202, 551–561. li, c., maier, w.d. & de waal, s.a. 2001: magmatic ni-cu versus pge deposits: contrasting genetic models and exploration implications. south african journal of geolog y 104, 309–318. lightfoot, p.c., keays, r.r., evans-lamswood, d. & wheeler, r. 2012: saturation history of nain plutonic suite mafic intrusions: origin of the voisey’s bay ni-cu-co sulfide deposit, labrador, canada. mineralium deposita 47, 23–50. maier, w.d., li, c. & de waal, s.a. 2001: why are there no major ni-cu sulfide deposits in large layered mafic–ultramafic intrusions? canadian mineralogist 39, 547–556. nielsen, b.l. 1976: economic minerals. in: escher, a. & watt, w.s. (eds): geolog y of greenland, 460–487. copenhagen: geological survey of greenland. secher, k. 1983: noritic rocks and associated nickel-copper-sulphide occurrences in sukkertoppen district, central west greenland. rapport grønlands geologiske undersøgelse 115, 30–34. secher, k. 2001: the pd+pt dispersion in noritic and undifferentiated mafic rocks of the archaean craton east of maniitsoq, southern west greenland. danmarks og grønlands geologiske undersøgelse rapport 2001/123, 22 pp. authors’ addresses a.a.g., t.f.k. & k.s., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: aag@geus.dk j.p., north american nickel inc., 301–260 w. esplanade, north vancouver, bc v7m 3g7, canada. i.mcd., school of earth and ocean sciences, cardiff university, p.o. box 914, cardiff cf10 3ye, uk. http://discovery.ucl.ac.uk/8800/ http://discovery.ucl.ac.uk/8800/ e2019430106-01 the brackish water baltic sea and the more saline kattegat in the north are connected by three straits, lillebælt, storebælt and øresund (fig. 1). storebælt (the great belt) is the deepest and widest of the straits. the strait is characterised by deeply incised channels that are partly filled by sediments. the water depth in major parts of storebælt is about 20 m, though in some areas the channels are more than 50 m deep. the formation of the channels has been subject to discussion. andersen (1927) suggested that the channels formed due to strong currents that are still active today or by f luvial erosion during the so-called continental period (fastlandstiden) in the early holocene. at this time, the relative sea level in the region was lower than at present and a huge lake, the ancylus lake, which occupied the baltic basin, may have drained via storebælt. andersen dismissed the idea that the channels were formed by subglacial erosion by meltwater during the last deglaciation. more recently, mathiassen (1997) interpreted some of the deposits in the channels as late glacial, a viewpoint followed by bennike et al. (2004). however, the age of the late glacial deposits in the channels are poorly constrained. the first studies of sediment cores from storebælt were carried out by krog (1973), winn (1974) and mathiassen (1997), but these studies concentrated on the holocene development from mires to lakes to brackish and marine environments. wiberg-larsen et al. (2001) documented the presence of early holocene river deposits. here we report on some new ages of macrofossils from late glacial deposits in the storebælt channels. in the late 1970s, the danish state began to map deposits of sand and gravel in storebælt and several potential aggregate resources were identified east of romsø. in this part of storebælt there are two parallel south–north-orientated incised channels. in 2017, new vibrocores were collected by the geological survey of denmark and greenland (geus) as part of a mapping programme of submarine aggregates the channels in storebælt, denmark: implications of new radiocarbon ages ole bennike*1, niels nørgaard-pedersen1 and jørn bo jensen1 geus bulletin is free to individuals and institutions in electronic form. the author(s) retain copyright over the article contents. r esearch article | open access geus bulletin vol 43 | e2019430106 | published online: 24 june 2019 https://doi.org/10.34194/geusb-201943-01-06 10°e 14°e 56°n 57°n sweden denmark germany kattegat storebælt femer bælt baltic sea kielerkieler lillebælt øresundfig. 2 50 km jylland fyn 55°n fig. 1. map of denmark and the surrounding area showing the location of the study area. fig. 2. bathymetry of the storebælt region showing the locations of the cores discussed in this paper. water depth: 0 to c. 50 m. water depth at core site 544001-1 is 38.5 m, and at core site 544002-1 it is 33.6 m. 10°40'e 11°10'e 55°40' 55°30'n 5 km 544001-1 544002-1 544001-1 fyn sjælland 544002-1 romsø https://doi.org/10.34194/geusb-201943-01-06 e2019430106-02 for the danish environmental protection agency. coring positions were selected from interpretations of shallow seismic data acquired during the initial mapping projects. two of the new cores from storebælt contained remains of plants that are typical of late glacial deposits from denmark. three samples were submitted for radiocarbon dating, and here we report on the results. methods an innomar parametric sub-bottom profiler was used to acquire high-resolution seismic data. vibrocoring was carried out with a 6 m long, 10 cm diameter vibrocorer (vkg-6) from the vessel skoven. differential gps was used to determine coring locations. the cores were cut into 1 m long sections onboard the ship and sent to geus. in the laboratory, the core was split, photographed and described. half of the cores were archived and the other half were subsampled. samples for palaeoecological analyses and radiocarbon dating were wet sieved and the residue left on the sieves was analysed using a dissecting microscope. ages were determined by accelerator mass spectrometry (ams) radiocarbon dating and calibrated to calendar years before present (1950 ce) according to the intcal13 data (table 1). results core 544001-1 was collected on the western f lank of the western storebælt channel (fig. 2). a shallow seismic east– west profile obtained at the coring site shows thin holocene marine deposits underlain by late glacial deposits (lomholt et al. 2017). the core is 557 cm long and contains fine-grained sand overlain by silt with granules. these lower units do not contain any macrofossils (fig. 3). then follows an almost 400 cm thick unit of heterolithic laminated mud and clay with plant and animals remains. plant remains include the land plants betula nana, betula pubescens, dryas octopetala, selaginella selaginoides and distichium sp., the reed plant scirpus lacustris and the water plants ranunculus hyperboreus, hippuris vulgaris, eleocharis palustris, potamogeton natans, p. perfoliatus, p. praelongus, stuckenia pectinata and s. filiformis. animal remains comprise piscicola geometra, candona sp., cytherissa lacustris, valvata cristata, v. piscinalis, pisidium sp. and cristatella mucedo. the assemblage is typical of late glacial lake deposits in the region, with the exception of scirpus lacustris and stuckenia pectinata ( jensen 1985; bennike et al. 2004). the warmth-demanding scirpus lacustris (schoenoplectus lacustris) is rare in late glacial deposits, though it has been recorded in sediments from the arkona basin in the south-western baltic sea, where it was dated to c. 12 800 cal. years bp, corresponding to the end of the allerød chronozone. to our knowledge, there are no previous finds of stuckenia pectinata from late glacial deposits in denmark. these plants probably spread northwards by rivers in storebælt during the bølling and allerød chronozones. a sample of betula nana twigs from a depth of 447 cm was dated to 14 070–14 560 cal. years bp, corresponding to the bølling chronozone, and a sample of scirpus lacustris was dated to 13 094–13 315 cal. years bp, corresponding to the allerød chronozone (table 1). the upper 1.5 m consists of marine bioturbated clay and mud with shells of marine gastropods, bivalves and barnacles, such as turritella communis, arctica islandica and balanus crenatus. core 544002-1 is 500 cm long and contains sandy diamicton at its base, which is interpreted as glacial till (figs 3, 4). the till is overlain by laminated mud and homogenous finegrained sand with plant and invertebrate remains. remains of land plants are dominated by betula nana but also include dryas octopetala, salix sp., empetrum nigrum, rumex acetosella and selaginella selaginoides. water plants include ranunculus sect. batrachium sp., menyanthes trifoliata, stu ckenia pectinata and s. filiformis. the fauna includes candona sp., cytherissa lacustris, lepidurus sp., gyraulus rossmaessleri, pisidium sp. and cristatella mucedo. a sample of betula nana and dryas octopetala remains was dated to 13 130–13 340 cal. years bp, which corresponds to the allerød chronozone. the f lora and fauna are typical of late glacial deposits in the region, except for gyraulus rossmaessleri, which table 1. new radiocarbon ages from storebælt, denmark * below core top. † calibrated to calendar years before present according to the intcal13 dataset. 11 374 ± 54 9294 ± 33 core n. lat. e. long. laboratory species depth age (14c calibrated no. no. b.c.t. (cm)* years bp) age (years bp)† 12 310 ± 40 11 405 ± 44 9455 ± 38 544001-1 55.571° 10.828° aar-29105 scirpus lacustris 201 13 094–13 315 544001-1 beta-481723 betula nana 447 14 070–14 560 544002-1 55.538° 10.823° aar-29106 phragmites australis 214 10 433–10 561 544002-1 aar-29107 phragmites australis 229 10 604–10 741 544002-1 beta-481724 b. nana, dryas octopetala 375 13 130–13 340 e2019430106-03 is rarely recorded, and stuckenia pectinata as mentioned above. the heterolithic sediments are overlain by a layer of homogenous fine-grained sand with betula nana remains. the minerogenic sediments are overlain by a thin layer of peat and gyttja with a rich f lora that includes pinus sylvestris, betula sect. albae sp., populus tremula, cladium mariscus, stachys palustris, ceratophyllum demersum, najas marina and a fauna with bithynia tentaculata and perca f luviatilis. we also found a fragment of a lower jaw of sorex minutus (pygmy shrew). the fossil assemblage is typical of early holocene peat and gyttja deposits in the region (bennike et al. 2004), but sorex minutus is new to the early holocene fauna of denmark (aaris-sørensen 2009). the lower part of the peat was dated to 10 604–10 741 cal. years bp and the upper part to 10 433–10 561 cal. years bp (table 1). the upper 2 m of the sediment core consists of bioturbated mud with shells of marine species such as ammonia beccarii, balanus crenatus, tritia reticulata, nucula tenuis, arctica islandica, abra alba, corbula gibba and echinocardium cordata. fig. 3. sedimentological logs based on sediment cores from storebælt. radiocarbon ages are calibrated to calendar years bp (mean probability ages). vf: very fine-grained. f: fine-grained. m: medium-grained. c: coarse. vc: very coarse. 1 0 2 3 4 5 cl ay sil t vf sand f m c vcd ep th (m ) 0 d ep th (m ) li th ol og y li th ol og y 544001-1; water depth 38.5 m 14 244 cal. years bp 1 2 3 4 544002-1; water depth 33.6 m 13 242 cal. years bp 13 215 cal. years bp 10 499 cal. years bp 10 691 cal. yrs bp glacial till homogenous marine holocene mud with shells homogenous fine-grained sand peat homogenous marine holocene clay with shells alternating layers of mud and clay homogenous fine-grained sand silt with pebbles layered mud homogenous marine holocene mud with shells cl ay sil t vf sand f m c vc fig. 4. selected part of sub-bottom innomar profile, with the position of sediment core 544002-1 indicated. the red line separates till from late glacial non-marine sediments. the blue line separates late glacial sediments from marine sediments. d ep th b el ow s ea le ve l ( m ) 40 42 44 38 36 34 32 30 core 544002-1 late glacial marine till 500 mnnw sse e2019430106-04 discussion the old age of c. 14 200 cal. years bp from core 544001-1 is noteworthy, because only a few plant remains of this age have previously been radiocarbon dated from late glacial deposits in denmark. active glacier ice disappeared from the region between 18 000 and 17 000 years bp (houmarknielsen et al. 2012). stagnant ice lingered on in many parts of denmark and at the same time, temperatures were low in the region until the abrupt warming at the start of the bølling chronozone at 14 700 years bp. the widespread existence of stagnant glacier ice and low temperatures likely delayed the migration and spread of terrestrial plants and animals in the region. in core 544002-1, a layer of sand is found below the peat deposit. such sand layers are commonly found below early holocene peat layers in the region. in some cores the sand layers contain in situ roots that can be related to the peat layers. in a few cases, the sand layers contain an increasing amount of plant remains in the upper part, and the boundary between the sand layer and the peat layer is often gradual. however, in most cases the sand layers contain no plant macrofossils and the sand–peat boundary is sharp. the sand layer probably ref lects a low stand, and the following peat formation can be seen as a consequence of increasing temperatures and more stable soil conditions at the beginning of the holocene. we interpret the sand layer as late glacial because it contains some remains of betula nana, but usually such sand layers do not contain plant macrofossils (bennike et al. 2004). conclusions the radiocarbon ages discussed in this paper indicate that the deeply incised channels in storebælt were formed by meltwater during the last deglaciation, as the ice margin receded southwards and huge amounts of meltwater f lowed northwards. the channels were probably eroded by water below the ice, near the ice margin. the fossil f lora and fauna are typical of late glacial deposits in the region, except for the warmth-demanding reed plant scirpus lacustris and the water plant stuckenia pectinata. these species likely colonised the storebælt area due to northward f lowing rivers and grew in the area during the warm bølling and allerød interstadials. the ages show that the late glacial deposits in the incised channels are at least in part of bølling and allerød age. acknowledgements this study was supported by geocenter denmark. kristian gregersen from the zoological museum in copenhagen kindly identified the jaw fragment of sorex minutus. we are grateful to journal referees jacob yde and jakob qvortrup christensen for comments on the manuscript. references aaris-sørensen, k. 2009: diversity and dynamics of the mammalian fauna in denmark throughout the last glacial–interglacial cycle, 115–0 kyr bp. fossils and strata 57, 59 pp. andersen, s.a. 1927: storebælt i nutid og fortid. geologiska föreningens i stockholm förhandlingar 49, 427–437. https://doi. org/10.1080/11035892709444582 bennike, o., jensen, j.b., lemke, w., kuijpers, a. & lomholt, s. 2004: lateand postglacial history of the great belt, denmark. boreas 33, 18–33. https://doi.org/10.1111/j.1502-3885.2004.tb00993.x houmark-nielsen, m., linge, h., fabel, d., schnabel, c., xue, s., wilcken, k.m. & binnie, s. 2012: cosmogenic surface exposure dating the last deglaciation in denmark: discrepancies with independent age constraints suggest delayed periglacial landform stabilization. quaternary geochronolog y 13, 1–17. https://doi.org/10.1016/j.quageo.2012.08.006 jensen, h.a. 1985: catalogue of lateand post-glacial macrofossils of spermatophyta from denmark, schleswig, scania, halland, and blekinge dated 13,000 b.p. to 1536 a.d. danmarks geologiske undersøgelse, serie a 6, 95 pp. krog, h. 1973: the early holocene development of the store belt as ref lected in a former fresh water basin. danmarks geologiske undersøgelse, årbog 1972, 37–47. lomholt, s., leth, j.o., nørgaard-pedersen, n., witt, n.h. & bennike, o. 2017: rapportering af 150 boringer udført i spekulative ressourcer. danmarks og grønlands geologiske undersøgelse rapport 2017/34, 248 pp. mathiassen, d.r. 1997: the changing landscapes of the storebælt from the retreat of the ice to the sea f lood. in: pedersen, l., fischer, a. & aaby, b. (eds): the danish storebælt since the ice age: man, sea and forest. a/s storebæltsforbindelsen, copenhagen, 22–28. wiberg-larsen, p., bennike, o., jensen, j. b. & lemke, w. 2001: trichoptera remains from early holocene river deposits in the great belt, denmark. boreas 30, 299–306. https://doi.org/10.1111/j.1502-3885.2001. tb01049.x winn, k. 1974: present and postglacial sedimentation in the great belt channel (western baltic). meyniana 26, 63–101. how to cite bennike, o., nørgaard-pedersen, n. & jensen, j.b. 2019: the channels in storebælt, denmark: implications of new radiocarbon ages. geological survey of denmark and greenland bulletin 43, e2019430106. https://doi.org/10.34194/geusb-201943-01-06 *corresponding author: ole bennike | e-mail: obe@geus.dk 1 geological survey of denmark and greenland (geus), c.f. møllers allé 8, dk-8000, aarhus c, denmark. https://doi.org/10.1080/11035892709444582 https://doi.org/10.1080/11035892709444582 https://doi.org/10.1111/j.1502-3885.2004.tb00993.x https://doi.org/10.1016/j.quageo.2012.08.006 https://doi.org/10.1016/j.quageo.2012.08.006 https://doi.org/10.1111/j.1502-3885.2001.tb01049.x https://doi.org/10.1111/j.1502-3885.2001.tb01049.x https://doi.org/10.34194/geusb-201943-01-06 mailto:obe@geus.dk geological survey of denmark and greenland bulletin 20, 2010, 99–102 99 in the c. 40 000 km2 large phu quoc basin south-west of vietnam reflection seismic data suggest a thin-skinned thrust-fault complex concealed by neogene marine sediments (fig. 1; fyhn et al. 2010). the deformed sedimentary succession in the complex is of early cretaceous age, which is documented by biostratigraphical studies of outcrops and a 500 m deep well on the phu quoc island. a model for the thrust-fault deformation suggests that piggy-back basins were formed during displacement along the thrust faults. the translation was 3–8 km from east to west. the model is based on detailed structural analyses of 36 seismic sections that cover the phu quoc basin (fig. 1). the main structural elements in the complex are f lats and ramps with hanging-wall anticlines developed above the ramps. the crests of the hanging-wall anticlines occur as remnants of partially eroded structural highs. this paper describes the thin-skinned thrust-fault structures that form the basis for the interpretation of the concealed fold-belt complex in the phu quoc basin. architectural framework of the fold belt along the west coast of vietnam folded and thrust-deformed mesozoic and palaeozoic sedimentary rocks form a n–sstriking fold belt referred to as the kampot fold belt (fyhn et al. 2010). to the north the fold belt continues into a hilly area at the border between vietnam and cambodia, where it forms a mountain range. to the south, offshore the west coast of vietnam, the fold belt is concealed below neogene marine sediments. from west to east the fold belt is divided into a distal, intermediate and proximal part (fig. 1). the distal part is a frontal wedge that passes into the foreland about 100 km west of the vietnam coast. the intermediate part is characterised by moderately folded, hanging-wall anticlines with thrust displacements in the order of a few kilometres. the transition from the intermediate to the proximal parts is located close to the nam du archipelago (pedersen et al. 2009). two interpreted, representative seismic sections have been selected to illustrate the architectural style in structural cross-sections perpendicular to the main trend of the thrustfault belt (figs 2, 3). phu quoc p ro x im al i m b ri c at e p ar t 104˚00'103˚40' 104˚20'e20 km ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 9˚20' fig. 3 fig. 2 9˚00' 8˚40' 10˚00'n ▲ ■■ distal part intermediate part proximal part thrust fault footwall syncline flexure on ramp dip conventional seismic lines high resolution seismic lines enreca-2 well hanging-wall anticline 500 km laos thailand cambodia vietnam nam du fig. 1. map of the study area off sw vietnam, showing the seismic grid which formed the basis for the study of the phu quoc basin. on the map the main structural elements are shown with the trends of anticlines and thrust faults interpreted from the seismic sections. the location of the 500 m deep well enr eca-2 on the phu quoc island and the position of the two cross-sections in figs 2 and 3 representing the distal and the intermediate parts of the deformation complex are also shown. the inset map shows the location of the investigated area in se asia. © geus, 2010. geological survey of denmark and greenland bulletin 20, 99–102. open access: www.geus.dk/publications/bull thin-skinned thrust-fault tectonics offshore south-west vietnam stig a. schack pedersen, lars ole boldreel, emil bach madsen, mette bjerkvig filtenborg and lars henrik nielsen 100100 the distal part of the tectonic complex the distal part of the complex passes gradually into the undeformed foreland where almost horizontally bedded cretaceous sediments occur, which are separated from overlying neogene marine sediments by a distinct unconformity. thrust-faults dipping <2° are found from the foreland towards the intermediate part. a number of minor ramps are present until the main décollement zone passes into a deeper level along a moderately dipping ramp, above which the westernmost, major hanging-wall anticline is seen (fig. 2). the main décollement zone is located below 2.5 km of sediments in the distal area, west of the foreland-near, hanging-wall anticline. the ramp takes the décollement zone down to 3 km below surface. at this depth the resolution of the seismic data becomes low, so no further interpretations are carried out. the hanging-wall anticline is relatively f lat-topped, which corresponds well with a model for hanging-wall anticlines where the displacement is about half the thickness of the thrust-faulted sedimentary rock unit (pedersen 2006). the western limb of the hanging-wall anticline dips c. 25°w, and the uppermost depositional unit below the neogene unconformity on-laps the dipping limb. the beds in this unit are gently tilted towards the west due to the main, gentle dip of the depositional wedge in the frontal part of the thrust system. therefore this uppermost depositional unit may be regarded as a piggy-back basin, which was formed during the translation of the frontal part of the thrust-fault complex. interpretations of the seismic sections north of the presented cross-section show additional examples of piggyback basins. the most important of these is a basin found south-east of the phu quoc island. it formed between two hanging-wall anticlines during their fold and translation development. in addition, we have interpreted the gently deformed lower cretaceous deposits that were penetrated by the enreca-2 well on the phu quoc island to continue into the deformed succession offshore. in our tectonic model the environment surrounding phu quoc island is regarded as located at the transition from the distal to the intermediate part of the tectonic complex. the intermediate part of the tectonic complex two or more levels of thrust faults with f lats and ramps have developed in the intermediate part of the complex (figs 1, 3). the number of ramps increases eastwards, which leads to an increasing number of hanging-wall anticlines, some of which are interpreted to have developed into antiformal stacks. the appearance of duplex structures initially lifted the top of the tectonic complex to a higher level. however, this is only recognised as a deeper level of erosion into the tectono-stratigraphic units. the displacement increases to 3–8 km resulting in some variation in the structural style of neogene marine sediments lower décollement surface pre-cretaceous deposits neogene unconformity lower cretaceous terrestrial deposits thrust fault hwr fwr 1 km cretaceous forela nd-basin unconfor mity 0 500 1000 1500 2000 2500 3000 3500 0 500 1000 1500 2000 2500 3000 3500 ww ew e t w o -w ay t ra ve l ti m e ( m se c ) t w o -w ay t ra ve l ti m e ( m se c ) c . 1 k m fig. 2. seismic section representing the distal part of the tectonic complex. in the western part of the cross-section the most distally appearing hanging-wall anticline is seen, and to the west the almost planar horizontal bedding extends into the foreland basin. beds in the youngest phu quoc unit onlap the moderately dipping beds on the western limb of the hanging-wall anticline, and these beds as well as the top of the hanging-wall anticline are truncated by the neogene unconformity. hwr: hanging-wall ramp, fwr: footwall ramp. blue lines: prominent bedding surfaces. red lines: thrust faults. purple line: the main neogene unconformity that truncates the structures in the tectonic complex. for location see fig. 1. 101 the hanging-wall anticlines. at the transition from the intermediate to the proximal part, erosional remnants of the hanging-wall anticlines are preserved as scattered islands rising a few hundred metres above sea level. the easternmost island in the nam du archipelago provides an example of this. on this island the thrust deformation elevated permian rhyolitic hyaloclastics to a surface-near position (pedersen et al. 2009). the proximal part of the tectonic complex the proximal part of the tectonic complex is only covered by seismic data only in the south-eastern part of the study area (fig. 1). here steeply dipping imbricate structures with 200–500 m thick thrust sheets occur. the depth to the décollement zone is more than 3 km. onshore the imbricate structures in the proximal part are exposed in the mountain range at the border between vietnam and cambodia. in this area the general dip of the thrust sheets is about 30°, and the deformed sedimentary rocks comprise upper palaeozoic sandstones and shales, permian carbonates and triassic sandstones, arkoses and conglomerates. in the thrust-fault zones, shearing and low-grade metamorphism have altered the sediments with recrystallisation of albite and formation of chlorite and biotite, corresponding to lower to medium greenschist facies. no minerals indicating higher metamorphic grades have been recognised. one of the small islands c. 50 km north-north-east of nam du is located in the proximal part. on this island, permian carbonates are thrustfaulted over jurassic shales and sandstones. a granitic plug occurs in the middle part of the island and granitic sills have intruded the jurassic succession. the intrusions are of lower cretaceous age (pedersen et al. 2009). cretaceous granitic intrusions occur on the mainland east of the proximal part of the tectonic complex. they form a cretaceous magmatic arc in the hinterland zone of the kampot fold belt (fyhn et al. 2010). the intrusive age of the granites is based on radiometric dating, and the dating of the uplift and erosion is based on fission-track studies that indicate exhumation during the eocene (fyhn et al. 2010). discussion the timing of the deposition of the basin fill and the deformation of the phu quoc basin are addressed by the tectonic model. the structural interpretation of the thrust-fault structures implies that the piggy-back basins formed in the cretaceous, which in turn suggests that the deformation started in the cretaceous. however, according to the apatite fission-track analysis the sedimentary rocks in the phu quoc basin and the kampot fold belt were buried to a depth where the temperature exceeded 100°c (fyhn et al. 2010). this indicates burial below 2–3 km of sediments that were entirely eroded away in the early eocene when the main exhumation 0 500 1000 1500 2000 2500 3000 3500 0 500 1000 1500 2000 2500 3000 3500 fwr fwr fwr lower cretaceous deposits neogene unconformity hwr hwr hwr neogene marine sediments pre-cretaceous deposits c . 1 k m 1 km t w o -w ay t ra ve l ti m e ( m se c ) t w o -w ay t ra ve l ti m e ( m se c ) lower décollement ww ew e fig. 3. seismic section representing the intermediate part of the tectonic complex. this part is characterised by increasing numbers of hangingwall anticlines and thrust faults. the upper thrust fault constitutes an upper f lat to the west, an upper footwall ramp (fwr) that connects the upper f lat to an intermediate f lat, and a lower footwall ramp that continues into the lower f lat to the east. each footwall ramp corresponds to a hanging-wall anticline above a displaced hangingwall ramp (hwr). due to the presence of two footwall ramps a prominent syncline developed between the two hanging-wall anticlines. blue lines: prominent bedding surfaces. red lines: thrust faults. purple line: the main neogene unconformity that truncates the structures in the tectonic complex. for location see fig. 1. 102102 of the region occurred (fyhn et al. 2010). it is suggested that the compressional deformation was caused by subduction of the westernmost part of the pacific ocean plate (metcalfe 1996). erosion of the up-thrust, pre-cretaceous rock units in the kampot fold belt supplied sediments for the cretaceous deposits in the phu quoc basin. the progressing compression led to deformation of the proximal part of the basin. a crosssection of the tectonic complex indicates a 200 km wide zone and the shortening of the complex is roughly estimated to be 50%. assuming a compressional orogenic translation in the order of 5 cm/y, the deformation lasted c. 4 million years. following the deformation, granites were intruded into the fold belt as the subducted sedimentary rocks below the fold belt began to melt. the age of the intrusions corresponds with the cretaceous deformation in the distal part of the tectonic complex. the crucial issue is to understand the mechanism that caused uplift in the eocene and subsidence in the neogene. we suggest that the subducted slab with a top layer of granitic composition was less dense than the base of the overlying lithosphere, and that this could cause a regional but orogenically passive uplift. the uplift was followed by eocene–miocene erosion and denudation before the raised granitic lithosphere cooled, which led to the neogene subsidence that created new accommodation space in the area above the phu quoc basin. conclusion the deposits in the phu quoc basin off south-west vietnam were affected by a late mesozoic orogeny. the tectonic complex at nam du archipelago is characterised by thin-skinned thrust-fault deformation with a distal part to the west, an intermediate part around the nam du archipelago, and a proximal part, which includes a hilly area in the onshore part of the kampot fold belt. the hinterland of the tectonic complex includes a magmatic arc represented by granitic plutons exposed in the south-western part of vietnam. the orogenic deformation of the complex is interpreted to be of early–middle cretaceous age. the complex was successively buried by a more than two kilometres thick package of sediments that was removed by erosion during uplift in the early eocene. finally subsidence in the neogene resulted in sedimentation that covered the mid-tertiary unconformity. acknowledgements we thank vietnam petroleum institute and petrovietnam for permission to use the commercial seismic data and permission to publish figs 2 and 3. the company landmark is thanked for a university grant to the department of geography and geolog y at copenhagen university. the enr eca programme of danida is thanked for financial support. references fyhn, m., pedersen, s.a.s., boldreel, l.o., nielsen, l.h., green, f.p., dien, p.t., huyen, l.t. & frei, d. 2010: palaeocene – early eocene inversion of the phuquoc-kampot som basin: se asian deformation associated with the suturing of luconia. journal of the geological society (london) 167, 281–295. metcalfe, i. 1996. pre-cretaceous evolution of se asian terranes. in: hall, r., blundell, d. (eds.): tectonic evolution of southeast asia. geological society special publication (london) 106, 97–122. pedersen, s.a.s.2006: strukturer og dynamisk udvikling af rubjerg knude glacialtektoniske kompleks, vendsyssel, danmark. geologisk tidsskrift 2006, 1, 46 pp. pedersen, s.a.s., fyhn, m. dien, p.t., boldreel, l.o., nielsen, l.h., green, f.p., huyen, l.t. & mai, l.c. 2009: structural geolog y of the nam du island and neighbouring areas in the phu quoc basin, sw vietnam. danmarks og grønlands geologiske undersøgelse rapport 2009/7, 47 pp. authors’ addresses s.a.s.p. & l.h.n., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: sasp@geus.dk l.o.b., e.b.m. & m.b.f., department of geography and geology, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. geological survey of denmark and greenland bulletin 17, 2009, 33-36 geomorphological indications of tectonic activity in the danish glacial landscape were pointed out already by milthers (1916, 1948). he described a conspicuous system of n–s-trending, narrow valleys in central jylland and interpreted them as fault-generated features (fracture valleys). the valleys occur in the area between ulstrup and hammel and in a smaller area near skjød (fig. 1). the most significant valley system is found near hvorslev, and it is here referred to as the hvorslev lineaments (fig. 1). an alternative interpretation of the genesis of the hvorslev lineaments was presented by hansen (1970). he argued that the n–s-trending valleys were formed by backward erosion from e–w-orientated erosional valleys in a former drainage system related to former higher groundwater table. however, milther’s interpretation that the valleys have a tectonic origin was later supported by larsen & kronborg (1994) and torp (2001). former interpretations of the lineaments were primarily based on morphological studies and arguments. recently the area with the hvorslev lineaments was mapped as part of the systematical geological mapping of denmark by the geolo gi cal survey of denmark and green land. the mapping of the surface li tho logy has added new information, and along with available seismic data it provides a frame work for a well-found ed interpretation of the elongated valleys, which is presented in this paper. we conclude that the fracture valleys are tectonic features, based on their morphology and because they are situated above a fault zone. geological setting the highest levels in the region are covered by a till unit, mainly a clayey till, but with patches of sandy till (fig. 2). on fracture valleys in central jylland – a neotectonic feature peter roll jakobsen and stig a. schack pedersen © geus, 2009. geological survey of denmark and greenland bulletin 17, 33–36. available at: www.geus.dk/publications/bull 33 bbjbjbjebjebjeeeebjeebjebjebjebjebbjbjebjebjebjebjebjejbjejbjebjebjebjebjeebjebjebjebjebjeebjebjeejebjbbbjjjjjj rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrirrrrrrrrrrrrrrrrrrrrrrrrirrrrrrrrrrrirrrrrrrriririrr bngbngbbnggbgbngbbbbbbbngbngbbbngbngbngbgbbbbbbbbbbbngbgbbbbgbbbngbbbngbngbbbbngbnnngbn bngbngbngbbngbbngbngbngbngbngbgngbg roororororroroorrroroooorororoorrororoorororooroooroorobjerringbro hvohvohvohvohvohvohvovohvovohvohvohvohhhvohvohvohvohvohvovohvovohvohvohvohvoohvhvoovoovvvvvhvovvovhvvohvov rrrrrsrsrrsrsrsrrrsrsrssssrsrsrrrrrr vevevevevvevevevevevevvve uuluuuluuuuuululuuluuuuuululsu suuuulsuuulsulssuulsuulsuuuulsssstttttrutrutrtttrut uttrutrut uttrtrutrutrtrurrrutrtrtrutrutrtrutrurupppppppppppppppppppppppppppppppppppppp hhamhhahamhamhamhamhhhhamhamhamhamhamhamhhahamhamhamhamhhamhhamhamhhhammmhh mmmmemememmemememememmemmmm hinhinhhhhinhinhinininnnhinh nnhhh nh nhinhhhh nhhhhhhhhhhhhhhhhhhhhhhhinhhhhinnnernenenernenerenerererrreerneererererrrruuuupupupupupuupppuupupppuppp ttthothothothohothoththothothothothooootthothohoootthoothotththohotththoothtthohththhhh rrsrsrsørsrssøsørsørsørsørsørsørsrsøørsørsøøøørrrrr skjskjskjkjskjskjkskjkskjkjskjskjskskjskjskjskkskjskskskjskjskskjskjskjskjskjjskjkjjsk ødødødødødødødødødødødøddøddød udgudguddgudgududddudgudgududdguddgudgudguddggudggudgudguudggudddgudddddduddddududddenåenåenåenenåenenåennåenåeenåenåenåenenånånånåenånenånånenåenååenånenååennånånnåneenåenåååå hvorslev ulstrup hammel hinnerup thorsø skjød gudenå 5 km fig. 1. digital elevation model of the hvorslev region with place names mentioned in the text. the focus area is the northern part of the valley system between ulstrup and hammel near hvorslev. the difference in elevation from the valleys to the highest areas is around 90 m. the rectangle shows the location of fig. 3, and the inset map of denmark shows the location of the model. fig. 2. geological map of the hvorslev area (extract from the digital map, see jakobsen & hermansen (2007). contour interval 5 m. the location of the seismic line 73203 is shown with dots, which indicate the position of every 10th geophone. 60 m sandy till gravelly till clayey till gravel sand clay gravel sand postglacial freshwater deposits peat sand, clay extra-marginal deposits glaciofluvial deposits glacial deposits built-up areas2 km ulstrup bjerringbro hvorslev 1080 1100 11201090 1110 rosa_2008:rosa-2008 01/07/09 15:48 side 33 the steep slopes of the gudenå valley, glaciofluvial deposits are found below the till unit. smaller outcrops of glaciofluvial sand appear in the till unit representing erosional windows in the till surface. thus the uppermost lithostratigraphy in the region comprises a glaciofluvial unit overlain by a till. this succession is also recorded in boreholes in the region (gravesen 1991). in most wells a clayey till is present at the top below which the glaciofluvial sand has a thickness of up to 20 m. the sand rests mainly on oligocene mica clay and in a few places on oligocene quartz sand. the glaciofluvial unit is correlated with the teppestrup formation (larsen et al. 1977; pedersen & petersen 1997), which was deposited on an outwash plain in front of the ice advancing from the north-east. the clayey till is interpreted as deposited by the ice advance from the north-east that reached the main stationary line in jylland. the till is correlated with the mid danish till of houmark-nielsen (1987) and its correlative the fårup till of kronborg et al. (1990), which date to around 23 000–21 000 years before present in this part of denmark (houmark-nielsen & kjær 2003). morphology the parallel alignment of valleys in the ulstrup–hammel area suggests that they can be characterised as fracture valleys (fig. 1). the length of the valley system between ulstrup and hammel is about 17 km. the most prominent part of the system is located at hvorslev, where the valleys trend n–s with a spacing of 125 m to 250 m. the individual valleys are up to about 9 km long and 6 m deep. the width of the zone with fracture valleys is 800–1100 m wide (figs 1, 3). the valleys cut hills and erosional valleys without any change of direction and are therefore not controlled by the general landscape morphology. even one of the highest hills in the area is cut at the top by one of the valleys. the individual valleys show an undulating floor in the longitudinal direction, occasionally with small depressions containing bogs and lakes. most cross-sections of the individual valleys display a u-shaped morphology; in some places an asymmetrical shape is seen with a steep eastern slope and a gently dipping western slope. the trends of the westernmost valleys south of hvorslev are concave towards the west, curving around a depression which is filled with postglacial freshwater deposits. downhill towards this depression, and almost perpendicular to the hvorslev lineaments, a system of erosional valleys cuts into the surface with a gentle fall towards the west. the most pro minent erosional valley system is first order valleys with branching second order valleys. the major first order valley cuts through the hvorslev lineaments and a stream starts in its lower part where one of the n–s-trending valleys intersects the erosional valley. the second order valleys are not as deep as the first order valleys, and are cut by the hvorslev lineaments. some of them are hanging valleys on the sides of the n–s-trending valleys. the e–w-trending erosional valleys were generated shortly before the hvorslev lineaments. most of them are dry valleys that formed at a time when surface drainage was greater than now, most likely shortly after deglaciation. ero sion within the first order valleys was so strong that it sustained the effect of the formation of the hvorslev lineaments, which were apparently almost penecontemporaneous with the erosional valleys. seismic records the seismic section 73203 shows an e–w cross-section across the hvorslev lineaments south-east of bjerringbro (fig. 4). the features between geophone positions 1090 and 1112 are inter34 s n 500 m 50 m fig. 3. block diagram of the hvorslev lineaments. the inferred faults are drawn on the frontal south-facing side of the block diagram. the arrows mark some of the erosional valleys. 1080 1100 1120 1140 0 0.5 1.0 1.5 2.0 2.5 3.0 tw o -w ay t ra ve l t im e (s ec ) geophone positions eeww ew base chalkbase chalk 2 km fig. 4. part of the seismic section 73203 in the hvorslev region (for location see fig. 2). the fault zone is situated between geophone positions 1090 and 1112, and the faults are marked with black lines. the height of the section corresponds to c. 3000 m. rosa_2008:rosa-2008 01/07/09 15:48 side 34 preted as faults. they occur over a zone c. 2.5 km wide situated directly below the hvorslev lineaments. the overall struc ture is interpreted as a negative flow er structure, where extension caused downfaulting of seg ments into a minor graben bounded by marginal faults. across the inferred fault zone downfaulting towards w predominates. the largest normal fault displacement is 0.05 second at 1.4 second two-way travel time measured on the re flec tor of the base chalk, which corresponds to a downthrow of c. 50 m at 1400 m depth. east of the fault zone the reflector is horizontal, and to the west it dips weakly towards w. indications of faulting at the surface most of the area around the hvorslev lineaments is covered by till. along the steepest slopes of the asymmetrical valleys, glaciofluvial sand is recorded below clayey till and on the gently dipping slopes clayey till drapes the surface all the way to the bottom of the valley (fig. 5). our interpretation of this distri bution of the lithological units is that the upper till unit has been displaced by a normal fault down to the floor of the valley, whereby the glaciofluvial sand is exposed in the footwall (fig. 5). the fault planes dip steeply w with a vertical displacement of c. 6 m. discussion the correlation between the hvorslev lineaments and the faults inferred from the seismic section indicates that the lineaments are surface traces of deep-seated faults. the hvorslev lineaments strike n–s, which most likely corresponds to the orientation of the faults. the himmerland graben is located to the north of the hvorslev lineaments (fig. 6; vejbæk 1990). it is a deep-seated structure outlined by two major n–s-trending basementattached faults, which is associated with the sorgenfrei– tornquist zone (fig. 6). dextral strike-slip faulting in the sorgenfrei–tornquist zone has resulted in e–w extension across the himmerland graben and led to normal faulting. the major tectonic events which caused syn-rift subsidence within the himmerland graben occurred during the triassic and in the late cretaceous. the hvorslev lineaments are situated south of the eastern fault of the himmerland graben and probably form a southern continuation of this fault. the indication of downthrow to wards w within the hvorslev lineaments corroborates this assumption. this implies that the fault activity in the him merland graben continues to the south into the central part of jylland. the fault-related valleys formed after deposition of the young est till in the area, because the till is cut by faults (fig. 5). the youngest glaciation of the area was during the main weichselian ice advance, during which the mid danish till was deposited. because the fracture valleys and the erosional valleys were formed at the same time, the faulting probably occurred shortly after the recession following the main weich selian ice advance. the deglaciation of the region occurred around 21 000 years ago, which gives a maximum age for the formation of the fracture-valley system in central jylland. two different causes can be suggested for the generation of the faults. either the fault activity was a response to the glaciostatic rebound after the last deglaciation, or the faulting is related to the neotectonic extension responsible for the general graben subsidence in the danish basin. this question cannot be answered unambiguously on the basis of the available data, but the trend of the lineaments and graben faults are oblique to the general trend of the postglacial marine limit in the region (mertz 1924) and hence are probably not linked to postglacial isostatic movements. the fact that the asymmetrical valleys show a downthrow towards w indicates that the valleys were formed in connection with tectonic activities in the him merland graben. moreover, the long length of the fault-related valleys also supports a tectonic origin. 35 fig 5. photograph of one of the asymmetric valleys (viewed southwards). in the westfacing, steep slope, glaciofluvial sand is present below a clayey till. the height of the steep slope is 6 m. on the gently dipping slope clayey till drapes the surface down to the bottom of the valley. the inserted block diagram illustrates the interpretation of the valley as generated by faulting. till till glaciofluvial sand c. 10 m w till glaciofluvial sand fa ult e rosa_2008:rosa-2008 01/07/09 15:48 side 35 in addition to the fracture-valley system between ulstrup and hammel, another system of similar valleys occurs near skjød, as pointed out by milthers (1916, 1948). fracture valleys are also found farther to the east near hinnerup (fig. 1; czakó 1994). morphologically they are similar to the hvorslev lineaments, although they are more curved. nevertheless, we suggest that they are fault-controlled. conclusions we suggest that the system of long, straight and narrow valleys in central jylland is related to a fault zone recognised on a seismic section across the valley system. hence the valleys are regarded as surface traces of a deep-seated fault zone. the faulting resulted in downfaulting of the surface-forming till along normal faults with downthrow mainly to w. the faulting occurred at a time when surface drainage was greater than at present, shortly after the last deglaciation that occurred around 21 000 years ago. the deformation is consequently a neotectonic activity. the fracture valleys indicate that the him merland graben continues farther to the south than previously outlined, and that crustal deformation related to this tectonic feature took place during the late quaternary. fault-related valleys as described in this paper are geomorphological elements that characterise some parts of the danish landscape. it is important to consider their potential implications for geological and hydrological models developed for the quaternary deposits. references czakó, t. 1994: the photogeological map and the map of surface water flow net of grundfør. explanations, preliminary results. dgu datadokumentation 3, 18 pp. gravesen, p. 1991: geological map of denmark, 1:50 000. map sheet bjerringbro. geological basic data map. danmarks geologiske under søgelse kortserie 32. hansen, k. 1971: de miltherske spaltedale i jylland. dansk geologisk forening, årsskrift for 1970, 47–53. houmark-nielsen, m. 1987: pleistocene stratigraphy and glacial history of the central part of denmark. bulletin of the geological society of denmark 36, 1–189. houmark-nielsen, m. & kjær, k. 2003: southwest scandinavia, 40–15 kyr bp: palaeogeography and environmental change. journal of quaternary science 18, 769–786. jakobsen, p.r. & hermansen, b. 2007: danmarks digitale jordartskort 1:25 000, version 3.0. danmarks og grønlands geologiske under søgelse rapport 2007/84, 27 pp. kronborg, c., bender, h., bjerre, r., friborg, r., jacobsen, h.o., kristiansen, l., rasmussen, p., sørensen, p.r. & larsen, g. 1990: glacial stratigraphy of east and central jutland. boreas 19, 273–287. larsen, g., jørgensen, f.h. & priisholm, s. 1977: the stratigraphy, structure and origin of glacial deposits in the randers area, eastern jutland. danmarks geologiske undersøgelse ii. række 111, 36 pp. larsen, g. & kronborg, c. 1994: geologisk set, det mellemste jylland. en beskrivelse af områder af national geologisk interesse. 272 pp. odense: geografforlaget. mertz, e.l. 1924: oversigt over de senog postglaciale niveau forandringer i danmark. danmarks geologiske undersøgelse ii. række 41, 49 pp. milthers, v. 1916: spaltedale i jylland. danmarks geologiske under søgelse iv. række 1(3), 16 pp. milthers, v. 1948: det danske istidslandskabs terrænformer og deres opstaaen. danmarks geologiske undersøgelse iii. række 28, 234 pp. pedersen, s.a.s. & petersen, k.s. 1997: djurslands geologi, 96 pp. copen hagen: geological survey of denmark and greenland. sigmond, e.m.o. 2002: geological map, land and sea areas of northern europe, scale 1:4 million. trondheim: geological survey of norway. torp, s. 2001: de miltherske spaltedale – landskabsdannelse og laserscanning i midtjylland. geologisk nyt 3(1), 28–29. vejbæk, o.v. 1990: the horn graben, and its relationship to the oslo graben and the danish basin. tectonophysics 178, 29–49. 36 authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: prj@geus.dk 56°30´n 10°e himmerland graben danish basin sorgenfrei–tornquist zone 25 km lineamentsfaults fig. 6. map of central jylland showing the tectonic outline of the region. fault-related valleys (red box) after milthers (1916) are located in the continuation of the eastern boundary fault of the himmerland graben. faults after vejbæk (1990) and sigmond (2002). rosa_2008:rosa-2008 01/07/09 15:48 side 36 geological survey of denmark and greenland bulletin 26, 2012, 85-88 85 rock phosphate and lime for small-scale farming in tanzania, east africa per kalvig, niels fold, jesper bosse jønsson and elisante elisaimon mshiu poor soils are a major cause of poverty in sub-saharan africa, and thus restoration of soil fertility is a significant challenge for sustainable agriculture. some of the main resources required, e.g. phosphate and lime, are present in many african countries and can be used by smallholder farmers in a relatively unprocessed form instead of expensive commercial fertilisers. here we present a small study of the mbeya region in tanzania, which locally has both phosphate and lime. most soils in sub-saharan africa are losing nutrients necessary for sustainable agriculture. this is mainly due to intensive farming and the fact that the nutrients are not replaced adequately. further reasons for nutrient losses are leaching, soil erosion and fixation by iron and aluminium oxides. vast areas experience moderate to acute phosphorus deficiency (vanlauwe & giller 2006). the mbeya region in south-western tanzania (fig. 1) is characterised by intensive smallholder plots along with several local sources of phosphate-bearing rocks and limestone. the former were examined in the 1980s (chesworth et al. 1988, 1989), but have never been utilised (kalvig et al. 2010). phosphates and lime – opportunities and constraints soils may become acid for many reasons and high rainfall may lead to washing out the nutrients needed for healthy plant growth. thus phosphorus and calcium deficiencies are common factors that restrict plant growth in highly leached tropical soils. the majority of smallholders cannot afford to use adequate quantities of commercial fertilisers and lime, resulting in low yields. an alternative is to use local sources, which can improve agricultural productivity by slowly releasing essential elements and raising the ph value of the soil. phosphates, lime, potassium-rich minerals, clay, zeolite and mica are common locally, but lacking awareness of their effects, very few smallholders use them. if such an awareness could be fostered and local resources made available at affordable prices, it would give farmers an opportunity to improve their crop yields (van straaten 2002; mitchell 2005). the phosphate potential in tanzania was outlined twenty years ago by mchihiyo (1991). the study presented here shows that local phosphate can be made available at affordable costs. phosphate minerals. natural fertilisers are available and can be used untreated. they comprise organic fertilisers such as manure, leaf litter and sludge, and rock fertilisers such as marl, rock phosphate, volcanic rock and mica. in contrast to natural fertilisers, artificial fertilisers are readily soluble and contain guaranteed total, active nutrient concentrations. the practical challenges and potential benefits involved in the use of rock phosphate have been widely discussed (mchihiyo 1991; appleton 2002; van straaten 2002, 2006; vanaluwe & giller 2006). the general view is that the use of rock phosphate for local agriculture is justified, provided its addition is managed in accordance with the type of crop and the conditions of the soil. usually, crop yields only show a slow response over 2–3 years after the addition of rock phosphates, which makes it difficult to generate interest among local farmers. the solubility of phosphate-bearing rocks differs widely depending on the mineralogy and chemistry of the rock i i i i i i i i i i i i i i i i i i i i i i i i i i rukwa rift 33°e kenya tanzania 400 km major road minor road railway regional capital district capital international boundary prospects 25 km river 9°s 33°e panda hills songwe scarp mbeya mbalizi lake rukwa njelenje sukumavera muvwa lake nyasa 9°s nanyala fig. 1. map of south-western tanzania showing the mbeya region with its main towns, roads and railway. the prospects indicated are known carbonatite occurrences which were considered potential phosphate resources by previous studies. © 2012 geus. geological survey of denmark and greenland bulletin 26, 85–88. open access: www.geus.dk/publications/bull 8686 type, and not all of them are therefore effective when applied directly to the soil. some important factors for the successful use of rock phosphate are: (1) the type of phosphatic rock, with apatite as the most common phosphate mineral containing 34–42% p2o5, (2) the reactivity of the phosphate rock, (3) the soil, where in particular ph, cation exchange capacity, phosphorus and calcium concentration, and phosphorus-fixing capacity of the soil play important roles, (4) the type of crop, because the ability to use h2po4, which dominates at low ph, differs from crop species to crop species, and (5) fertiliser management (van straaten 2002). lime. the primary reason for increasing the soil ph by liming is to reduce the aluminium toxicity to plants, and to ensure that ca, mg, k and p are available to the plant. raising the ph value to 5.2–5.5 is adequate for increasing crop yields, whereas higher values reduce the breakdown of rock phosphate (mitchell 2005). phosphate and lime resources in the mbeya region geological setting. in tanzania, a central archaean craton is surrounded by proterozoic fold belts (fig. 2). the mbeya region lies south-west of the archaean craton in the nw–sestriking 2000–1800 ma old ubendian fold belt. this fold belt is dominated by gneisses and amphibolitic rocks, intruded by 730 ma old syenite-gabbro complexes, all of which have been intruded by carbonatite complexes of cretaceous to late palaeogene age. during the late phanerozoic, rifting and faulting occurred in connection with the formation of the east african rift valley. the occurrence of neogene sediments such as conglomerate, clay and chert as well as volcanic rocks is related to the rift valley. phosphate in the mbeya region. the most promising phosphate occurrence is the songwe scarp carbonatite, which is a 20 km long, 50 m wide, nw–se-striking, 100 ± 10 ma old ferrocarbonatite (miller & brown 1963; brown 1964). mchihiyo et al. (1992) provide an overview of the exploration history of this carbonatite, which took place in the 1950s. the exploration focussed on uranium and comprised geological mapping of anomalous zones of the carbonatite some 2 km north-west of the village njelenje (fig. 1; brown 1964). in the 1990s, the phosphate was assessed as a potential source of fertiliser (van straaten 2002). the exploration led to the recognition that several parts of the songwe scarp carbonatite are relatively rich in apatite. it was also discovered that areas with elevated concentrations of radioactive elements, yttrium and other rare-earth elements occur near njelenje (fig. 3). the highest phosphate concentrations were found in limonitic residual soils overlying the carbonatite, with up to 20% p2o5 and 6% k 2o. these soils can be used as phosphate fertilisers (chesworth et al. 1989; appletorn 2002; van straten 2002). in addition to the songwe scarp carbonatite, the region holds several other occurrences of phosphate. one is the panda hills carbonatite where c. 1 mt of residual phosphates with a p2o5 concentration up to 10.3% have been mapped (van straaten 2002). another is the mbalizi carbonatite where weathered parts locally form a 0.5 m thick limonitic crust with up to 30% p2o5 (mchihiyo 1991; mchihiyo et al. 1992). this phosphate is under exploration as a potential source of niobium and other rare-earth elements. a third possibility of phosphate is guano from bats around sukumavera, but the amount is far too small to play any role, even for smallholders (van straaten 2002). limestone in the mbeya region. calcareous sedimentary rocks, mainly travertine in the songwe valley, are mined for (1) dimension stones using a yellowish travertine near nanyala in the mbozi district, (2) carbonate for calcination and (3) cement production. hochstein et al. (2000) and roberts et al. (2004) provided geological details of this limestone unit and estimated that it covers an area of c. 13 km2 with a thickness of 5–70 m, equivalent to >150 000 000 m3. an example of a weathered occurrence is shown in fig. 4. bukobau supergroup cenozoic cretaceous proterozoic 200 km 30°e 10°s 10°s tanzania craton mbeya sediments neogene volcanics proterozoic fold belts carbonatites archaean craton victoria lake lake kenya tanganyika zambia rwanda fold belt u bendian fig. 2. simplified geological map of tanzania (based on van straaten 2002). the mbeya region (framed) is located in south-western tanzania. 87 proposals for feasibility studies small-scale phosphate operation to supply local smallholders. the songwe valley area holds two potential sources for the production of local rock phosphate: carbonatite and apatite-rich residuals of carbonatite. given that previous studies indicate that enrichment of phosphorus has taken place in the residual apatite-rich soil (mchihiyo et al. 1992) and that a production based on such soil is technically relatively straightforward, the present study only considers this source. in the vicinity of the village of njelenje, the p2o5 concentration reaches 18–20% and the k2o concentration 6% (mchihiyo et al. 1992). a pilot study was conducted in march 2010. the purpose was to learn from smallholding farmers what their local cultivation practices are and get their views on requirements on and limits to the use of locally produced phosphate fertilisers.   the study also aimed at clarifying the availability of local labour for small-scale phosphate extraction. the village of muvwa, located in the mbeya region, was chosen due to its proximity to the phosphate resources of the songwe scarp carbonatite (fig. 3). the study area encompassed 420 households corresponding to 1768 inhabitants of whom 331 persons were capable of working. twenty-one households were interviewed in order to learn about the general pattern of cultivation practices. the low number means that the results are only indicative (kalvig et al. 2010). as no geological data on the survey area are available, the data from njelenje, situated c. 5 km to the north of the interview area, may serve to indicate the total available phosphorus content of the soils in the survey area. a feasibility study of a potential rock phosphate production is warranted and, based on a labour intensive concept producing rock fertiliser for local consumption, should (1) assess the phosphate resource (grade and tonnage estimates – and the potential content of harmful elements), (2) propose a suitable set-up for the production and (3) assess the distribution and market prospects. at this stage, no calculations of the required amount of local rock phosphate per hectare can be made, because a number of technical data are not yet available: the actual fertility of the soils of the trial area; depletion rate of phosphorus; fixation rate of phosphorus; identification of the most phosfig. 3. landscape around the village of njelenje in the song we valley, looking east and showing the song we scarp carbonatite. fig. 4. small section of limestone in the nanyala area of the mbeya region showing the boundary between topsoil and weathered rock. 8888 phorus demanding crops; the average phosphorus content of the potential rock phosphate. small-scale extraction of lime to supply local smallholders. in the village of nanyala, some hundred people are involved in small-scale mining of a weathered, whitish travertine accompanied by a semi-mechanised production of hydrated lime. more than ten mining licences cover the lime producing area. the limestone resource in the songwe valley consists of various grades of quaternary to recent travertine deposits. it is dominated by poorly consolidated, partly weathered, whitish rock, of which neither the quantity nor the quality has ever been thoroughly investigated as regards lime for agricultural use. the ideal agricultural lime is a ground dolomite or dolomitic limestone with a particle size <2 mm; 60% <400 μm and up to 50% <150 μm (mitchell et al. 1997). labour intensive production of agricultural lime is a relatively straightforward process (mitchell & mwanza 2005). the march 2010 survey included interviews with some of the operators in the neighbouring nanyala area (kalvig et al. 2010). hydrolime has been produced for several years in this area. there is a potential for diversifying the existing hydrolime production to include lime products for local use and particularly for sale to local smallholders cultivating coffee. in tanzania, agricultural lime is mainly produced in the tanga district located c. 800 km from the mbeya region. a feasibility study on how to extend the on-going production of hydrolime to include lime for agricultural use seems warranted. it should include all steps from quarrying and marketing to testing the products and should be based on a labour intensive concept. acknowledgements geocenter denmark is thanked for financial support, and the tanzania commission for science and technolog y for permission to conduct field work. references appleton, j.j. 2002: local phosphate resources for sustainable development in sub-saharan africa. british geological survey report cr/02/121/n, 134 pp. brown, p.e. 1964: the song we scarp carbonatite and associated feldspathization in the mbeya range, tanganyika. quarterly journal of the geological society 120, 223–240. chesworth, w., semoka, j.m.r., van straaten p., mnkeni, p.m.s., kamasho, j.a.m. & mchihiyo, e.p. 1988: tanzania–canada agrogeolog y project: report on completion of the first phase, 93 pp. ontario, canada: university of guelph. chesworth, w., van straaten, p. & semoka, j.m.r. 1989: agrogeolog y in east africa: the tanzania–canada project. journal of african earth sciences 9, 357–362. hochstein, m.p., temu, e.p. & moshy c.m.a. 2000: geothermal resources of tanzania. world geothermal congress 2000, kyushu–tohoku, japan, 28 may to 10 june 2000. proceedings 1233–1238. kalvig, p., fold, n., jønsson, j.b. & mshiu, e.e. 2010: local use of agrominerals. untapped resources for farming communities in sub-saharan africa. appraisal study on the agromineral potential in the mbeya area, tanzania. danmarks og grønlands geologiske undersøgelse rapport 2010/107, 58 pp. mchihiyo, e.p. 1991: phosphate potential in tanzania. fertilizer research 30, 177–180. mchihiyo, e.p., kiranga, o.w. & mbasha, m.z. 1992: tanzania –canada agromineral project. report on completion of second phase (madini group). unpublished report, madini group, tanzania. miller, j.a. & brown, p.e. 1963: the age of some carbonatite activity in south-west tanganyika. geological magazine 100, 276–279. mitchell, c.j. 2005: farm lime: low cost lime for small-scale farming. british geological survey technical report cr/03/066n, 138 pp. mitchell, c.j. & mwanza, m. 2005: manual for small-scale production of agricultural lime. british geological survey commissioned report cr/05/092n, 31 pp. mitchell, c.j., inglethorpe, s.d.j., tawodzera, p., bradwell, s. & evans, e.j.m. 1997: local development of affordable lime in southern africa. british geological survey technical report wc/94/20, 120 pp. roberts, e.m., o’connor, p.m., gottfried, m.d., stevens, n., kapalima, s. & ngasal, s. 2004: revised stratigraphy and age of the red sandstone group in the rukwa basin, tanzania. cretaceous research 25, 749–759. van straaten, p. 2002: rocks for crops. agrominerals of sub-saharan africa, 338 pp. nairobi, kenya: international centre for research in agroforestry. van straaten, p. 2006: farming with rocks and minerals: challenges and opportunities. anais da academia brasileira de ciências 78, 731–747. vanaluwe, b. & giller, k.e. 2006: popular myths around soil fertility management in sub-saharan africa. agriculture, ecosystems and environment 116, 34–46. authors’ addresses p.k., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: pka@geus.dk n.f., department of geography and geology, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. j.b.j., school of geographical & earth sciences, university of glasgow, glasgow g12 8q q, scotland, uk. e.e.m., department of geology, university of dar es salaam, p.o. box 35052, dar es salaam, tanzania. geological survey of denmark and greenland bulletin 20, 2010, 83–86 83 the greenland ice sheet is one of the most significant contributors to the rising global sea level with a contribution of 0.5 mm per year (rignot & kanagaratnam 2006). evidence is emerging that rising temperatures of subsurface ocean currents play a vital role in the recent acceleration of large fast f lowing glaciers such as jakobshavn isbræ in west greenland (holland et al. 2008) and helheimgletscher in south-east greenland (straneo et al. 2010). important questions are whether these incursions of warmer water are part of a recurrent phenomenon and indeed exactly how they inf luence the glaciers. the geocenter denmark project sedimice (linking sediments with ice-sheet response and glacier retreat in greenland) investigates past ice f luctuations in the helheimgletscher region in south-east greenland with regard to magnitude, possible causes and effects. one of the main tasks in this project is to analyse sedimentary deposits in the main fjord sermilik (fig. 1), which is inf luenced by the tidally affected helheimgletscher that has a short f loating tongue. by combining sediment studies with modern climate studies we aim to extrapolate meteorological data back in time. in august 2009 the geological survey of denmark and greenland collected short sediment cores in sermilik near tasiilaq (fig. 1). to select core sites and to understand the sedimentary processes, we also acquired data on the bathymetry and conducted shallow seismic profiling. this paper presents some results of the seismic survey, preliminary sediment core data and bathymetrical data from the fjord. apart from a few isolated depth values, the bathymetry of sermilik was unknown before the 2009 survey. setting sermilik is about 80 km long and 7–13 km wide. the terrain around the fjord is alpine with elevations of 300–600 m near the coast and up to 1000 m inland. frequent glacial and geologically controlled fissure valleys dissect the area in a criss-cross pattern. the northern end of sermilik branches into three fjords with calving glaciers. the westernmost – helheimgletscher – is a fast f lowing glacier and the third most prolific iceberg producer in greenland (rignot & kanagaratnam 2006). the climate of the region is low arctic and the weather conditions are inf luenced by lows moving north along the coast. the fjord is covered by sea ice from december to may. the hydrographic conditions in the fjord are inf luenced by a 10– 20 m thick layer of glacial water, underlain by 100–150 m of bathymetry, shallow seismic profiling and sediment coring in sermilik near helheimgletscher, south-east greenland camilla snowman andresen, niels nørgaard-pedersen, jørn bo jensen and birger larsen fig. 1. study area and bathymetrical data from sermilik based on data collected in 2009. depth data on the shelf south of the fjord mouth are from clausen (1998) and this survey. the positions of the seismic lines a, b and c are indicated by black lines and sediment core sample sites are shown. 37°0´w toqqulertivit imiat shelf trough tasiilaq sill er07 c b a er15 er13 er11 10 km bank 700 m 200 m helheimgletscher 38°w 66°n se rm ili k greenland 3–100 101–200 201–300 301–400 401–500 501–600 601–700 701–800 801–900 901–1000 1001–1100 sample site bathymetry depth (m) depotø © geus, 2010. geological survey of denmark and greenland bulletin 20, 83–86. open access: www.geus.dk/publications/bull 8484 polar water. below the polar water towards the bottom warmer atlantic water of subtropical origin with temperatures of 3.5–4°c is found (straneo et al. 2010). the inf low of warmer waters into sermilik takes place via deep troughs in the shelf. glacial history of the region a study from the toqqulertivit imiat valley (fig. 1) shows that a glacier f lowed through this valley and most likely coalesced with a glacier f lowing south in sermilik and out over the continental shelf during the last glacial maximum (roberts et al. 2008). exposure ages of 11.8–9.9 ka (kilo-annum, 103 years bp) from bedrock surfaces at high elevations (683–740 m a.s.l.) provide minimum ages for the last deglaciation (roberts et al. 2008). these ages from toqqulertivit imiat support the ‘maximum’ model of a large last glacial maximum ice sheet extending to the shelf break in southeast greenland (stein et al. 1996; kuijpers et al. 2003). evidence from the shelf south of sermilik indicates that the ice margin retreated to the inner shelf around 15.7–14.6 calibrated (cal.) ka (kuijpers et al. 2003). in the kangerlussuaq region farther north the ice-sheet margin retreated from the outer shelf around 15.5 cal. ka and reached the present outer coast around 13.6–10 cal. ka ( jennings et al. 2006). this is in accordance with surface exposure ages from lower toqqulertivit imiat indicating that ice retreated to the mouth of sermilik between 11.1 and 9.7 ka (roberts et al. 2008). these data are further supported by a minimum age of 11 cal. ka for the formation of the local marine limit (at 69 m) and thereby local ice retreat near tasiilaq (long et al. 2008). methods we used the locally hired motor boats erik den røde and puite for the work. an innomar ses-2000 medium sub-bottom echo sounder from innomar tecnologies, rostock, germany, was used for bathymetrical and sub-bottom sediment profiling. this parametric device is designed for water depths down to about 2000 m and has the ability to resolve sediment layers a few decimetres thick and penetrate down to about 50 m below the sea f loor. the transducer was mounted on a vertical steel tube attached to the side of the boat and a motion sensor was used to compensate for movements of the boat. additional bathymetrical data were recorded in the inner fjord from the echo sounder of erik den røde during the sediment coring cruise. comparisons of depth recordings obtained by the two methods showed that the results are compatible to within a few metres. sediment coring was performed with a rumohr lot corer with up to 1.5 m long core liners. bathymetrical data from sermilik the southern part of sermilik fjord is an up to 920 m deep and f lat basin (fig. 1). the bathymetry of the fjord mouth can be described as terminating into a se-directed trough and a sw-directed trough separated by a broad bank with water depths of less than 200 m. the bathymetry of the swdirected trough is very uncertain. the shallowest part of the se-directed trough forms a c. 550 m deep sill between the deep fjord and the 800–900 m deep trough that stretches the entire shelf towards the irmiger sea. the deep fjord basin extends up to 40 km northward from the fjord entrance into the middle part of sermilik where several bathymetrical highs (400–550 m) narrow the connection to the northern part of the fjord. towards the northern part of sermilik, the basin f loor rises steadily to a depth of about 600–650 m just south of depotø. the fjord bottom in the inner part is more irregular with channel systems more than 100 m wide and up to 20 m deep. during the survey we could not measure water depths in the inner east– west-trending fjord arm leading up to helheimgletscher due to semi-permanent sea ice extending tens of kilometres er15 er13 er11er07 5 cm fig. 2. selected examples of x-ray radiographs from core er15 (600 m water depth), er13 (660 m water depth), er07 (525 m water depth) and er11 (600 m water depth) that document different sedimentation regimes. note the dark sand layer in core er13 with a lower erosive boundary; this unit is interpreted to be a turbidite. core sites are shown in fig.1. 85 from the helheimgletscher calving front. however, according to the skipper of erik den røde (sigurdur petursson), water depths up to 800 m are found north-west of depotø. sediment cores altogether 19 cores with lengths ranging from 30 to 150 cm were retrieved during the sediment coring cruise. the full sediment core data (sedimentology, geochemistry and chronology) will be presented elsewhere. however, preliminary inspection of cores er07, er11, er13 and er15 documents the variable sediment regimes that characterise the fjord (figs 1, 2), and x-ray radiography of the cores show diamicton facies, laminated mud facies and sand layers with erosive lower boundaries. these lithofacies are similar to lithofacies described from sediment cores from kangerlussuaq (smith & andrews 2000) and scoresby sund (dowdeswell et al. 1994; ó cofaigh & dowdeswell 2001). for example, core er15 consists of laminated mud with variable content of pebbles, which is interpreted as ice-proximal glaciomarine sediments mainly deposited by suspension settling from turbid overf low plumes and turbidity currents and occasional iceberg rafting. in contrast, cores er07 and er11 are characterised by massive diamicton facies with abundant pebbles, which is interpreted as the result of iceberg rafting. core er13 has a unit of diamicton facies above a unit of laminated mud facies. this may ref lect an environmental change from a long-lasting sea-ice cover in the fjord prohibiting iceberg passage to a period with increased passage and melting of icebergs. as also suggested by jennings & weiner (1996) variable inf low of atlantic water may inf luence the melting and traversing of icebergs. 210pb dating of the upper decimetres of the cores show sedimentation rates >1 cm/yr in er15, 0.4 cm/yr in er13 and 0.2 cm/yr in er11. the decreasing sedimentation rates with increasing distance to the present front of the calving glaciers ref lect the decreasing inf luence from meltwater plume sedimentation. seismic profiles the seismic profile (fig. 3a) shows an outer f lat, deep basin in sermilik with an upper 4–6 m thick, transparent seismic unit overlying a well-stratified section (>15 m thick) that is characterised by strong, continuous, parallel ref lectors. there is no distinct boundary between the two seismic units, as weak, discontinuous, parallel ref lectors characterise the uppermost c. 2 m of the stratified section. on vertically extremely exaggerated sections, wide lenticular units and stratigraphical onlap structures are visible in some parts of the lower seismic unit. to the north, the transparent upper unit disappears and well-stratified sediments, with some channel features, dominate the seismic profiles (fig. 3b). the profiles of the bathymetrical highs in the middle part of the fjord are dominated by overlapping diffraction hyperbolae. the inner, shallower part of the fjord is characterised by large channel and levee structures, and broad f lank units showing well-stratified sediments in the north-western part of the seismic survey area (fig. 3c). formation of fjord-bottom sediment structures the sediment unit with a transparent pattern in the outer fjord basin indicates a uniform lithology that possibly originwnw sese nwnw sese nw se nw se nn ssn s c b a 1 km10 m 1 km5 m 1 km 5 m fig. 3. representative seismic sections that illustrate different structures in different parts of sermilik (see text for description and fig. 1 for location). 8686 nates from suspension sedimentation (meltwater plumes) and ice-rafting during the main part of the holocene (fig. 3a). the lower stratified section is interpreted as glaciomarine sediments consisting of turbidites and mass-transport deposits interbedded with suspension-deposited sediments. the lower unit was possibly deposited during the final deglaciation of the main part of sermilik at about 10 ka (cf. roberts et al. 2008). turbidite sedimentation typically creates very f lat fjord basins with ref lectors onlapping basin margins and structural highs. it is possible that the structural highs in the middle part of sermilik could serve as anchor points for the retreating glacier, causing a stagnation of the fjord glacier front during the last deglaciation. the inner basin with its apparent active channel and levee sedimentation and over-all fill geometry (fig. 3c) can be characterised as a progradational–aggradational wedge of sediments with possibly very high sedimentation rates from turbidites and mass f lows, as well as plume sedimentation. it is an open question whether the channel systems are directly fed by the helheimgletscher source, or whether bedrock thresholds in the innermost fjord system prohibit bed transport of glaciogenic sediments. if a deeper sub-basin exists north of depotø, we can only explain the seismic signature and large channel-levee systems of the inner basin by a very advanced position of helheimgletscher to near depotø during the late holocene. hopefully, future exposure ages from the land terrain near depotø by our collaborators can show if the front of helheimgletscher had a standstill near depotø during the little ice age. in conclusion, the seismic survey has revealed a rather complex pattern of sub-bottom sediment structures (down to 50 m) in sermilik ref lecting the early holocene retreat of helheimgletscher, probably followed by a holocene ice advance – perhaps during the little ice age. preliminary results from analyses of the sediment cores support the interpretation that the glaciomarine sediments in sermilik is related to settling from meltwater plumes and iceberg rafting. knowledge of the sediment depositional regime on the fjord bottom from seismic investigations is highly relevant for retrieval of sediment cores suitable for holocene palaeoclimatic reconstructions. we hope to collect more and longer sediment cores in the fjord in coming years. acknowledgements geocenter denmark is thanked for financial support. we would also like to thank our two skippers bendt josvassen of m/v puite and sigurdur petursson of m/v erik den røde. rineke gieles at the royal netherlands institute for sea research is thanked for x-ray radiography of sediment cores. references clausen, l. 1998: the southeast greenland glaciated margin: 3d stratal architecture of shelf and deep sea. geological society special publications (london) 129, 173–203. dowdeswell, j.a., whittington, r.j. & marienfeld, p. 1994: the origin of massive diamicton facies by iceberg rafting and scouring, scoresby sund, east greenland. sedimentolog y 41, 21–35. holland, d.m., thomas, r.h., de young, b., ribergaard, m. h. & lyberth, b. 2008: acceleration of jakobshavn isbræ triggered by warm subsurface ocean waters. nature geoscience 1, 659–664. jennings, a.e. & weiner, n.j. 1996: environmental change in eastern greenland during the last 1300 years: evidence from foraminifera and lithofacies in nansen fjord, 68°n. the holocene 6, 179–191. jennings, a.e., hald, m., smith, m. & andrews, j.t. 2006: freshwater forcing from the greenland ice sheet during the younger dryas: evidence from southeastern greenland shelf cores. quaternary science reviews 25, 282–298. kuijpers, a., troelstra, s.r., prins, m.a., linthout, k., akhmetzhanov, a., bouryak, s., bachmann, m.f., lassen, s., rasmussen, s. & jensen, j.b. 2003: late quaternary sedimentary processes and ocean circulation changes at the southeast greenland margin. marine geolog y 195, 109–129. long, a.j., roberts, d.h., simpson, m.j.r., dawson, s., milne, g.a. & huybrechts, p. 2008: late weichselian relative sea-level changes and ice sheet history in southeast greenland. earth and planetary science letters 272, 8–18. ó cofaigh, c. & dowdeswell, j.a. 2001: laminated sediments in glacimarine environments: diagnostic criteria for their interpretation. quaternary science reviews 20, 1411–1436. rignot, e. & kanagaratnam, p. 2006: changes in the velocity structure of the greenland ice sheet. science 311, 986–990. roberts, d.h., long, a.j., schnabel, c., freeman, s.p.h.t. & simpson, m.j.r. 2008: the deglacial history of southeast sector of the greenland ice sheet during the last glacial maximum. quaternary science reviews 27, 1505–1516. smith, l.m. & andrews, j.t. 2000: sediment characteristics in iceberg dominated fjords, kangerlussuaq region, east greenland. sedimentary geolog y 130, 11–25. stein, r., nam, s.i., grobe, h. & hubberten, h. 1996: late quaternary glacial history and short-term ice-rafted debris f luctuations along the east greenland continental margin. in: andrews, j.t. et al. (eds): late quaternary paleoceanography of the north atlantic margins. geological society special publications (london) 111, 135–151. straneo, f., hamilton, g.s., sutherland, d.a., stearns, l.a., davidson, f., hammill, m.o., stenson, g.b. & rosing-asvid, a. 2010: rapid circulation of warm subtropical waters in a major glacial fjord in east greenland. nature geoscience 3, 182–186. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: csa@geus.dk geological survey of denmark and greenland bulletin 28, 2013, 53-56 53 fingerprinting of corundum (ruby) from fiskenæsset, west greenland nynke keulen and per kalvig since the late 1960s, it has been known that pink and red corundum occur in the area near fiskenæsset (qeqertarsuatsiaat) in southern west greenland. corundum is hosted in the fiskenæsset complex, which is part of the archaean basement of the north atlantic craton. to date, c. 40 corundum localities with a wide range of quality are known in the area – a few localities yield stones of gem quality. the most promising locality, aappaluttoq, is likely to be mined in the foreseeable future by the canadian company true north gems (figs 1, 2a). red corundum of gem quality is called ruby; gem quality corundum of other colours (e.g. pink, yellow or blue) is called pink sapphire, yellow sapphire etc., while the blue gem corundum is sapphire. red, pink and blue corundum are also known in smaller quantities from other areas in greenland. the fiskenæsset complex the fiskenæsset complex (fig. 1) comprises a series of intrusive sheets of anorthosite, leucogabbro, gabbro and ultramafic rocks (myers 1985), and is interpreted as derived from a supra-subduction setting, while the associated amphibolites stem from a mid-oceanic ridge to island arc basalt precursor (polat et al. 2009). the greater fiskenæsset region was metamorphosed c. 2.85–2.80 ga ago at midto upper amphibolite-facies temperatures and pressures, reaching granulite facies conditions near the village of fiskenæsset (mcgregor & friend 1992; schumacher et al. 2011). at least one generation of the c. 2.71 ga felsic pegmatite sheets cuts the anorthosite, ultramafic rocks, amphibolite and gneisses and created reaction zones that developed aluminium-rich mineral assemblages derived from the aluminium in the anorthosite rocks (schumacher et al. 2011; fig. 2b). these reaction zone assemblages, associated with pegmatitic felsic sheets and the ultramafic bodies, include very coarse-grained, radial anthophyllite ± green pargasite ± green or red spinel ± sapphirine ± cordierite (up to 30 cm single crystals) ± pink corundum, and ± phlogopite (schumacher et al. 2011). this study is a first attempt to find geochemical and mineralogical characteristics that can be used to tie the greenlandic rubies to their area of origin. this may have practical implications if an operation of rubies and pink sapphires is established in greenland. here, we present laser ablation inductively coupled plasma mass spectrometry (la-icpms) trace-element geochemical and oxygen isotope data of samples from the fiskenæsset area and other known localities in greenland (storø, maniitsoq, kapisillit and nattivit). © 2013 geus. geological survey of denmark and greenland bulletin 28, 53–56. open access: www.geus.dk/publications/bull fig. 1. simplified geological map of the fiskenæsset area in southern west greenland showing the investigated pink and red corundum (ruby) localities in the fiskenæsset complex. map after keulen & kokfelt et al. (2011). m: maniitsoq, s: storø, k: kapisillit, f: fiskenæsset, n: nattivit. ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; 63°n63°n greenlandgreenland nnkkss mm ff 50°w50°w 10 km10 km qororssuaq eastqororssuaq east piqinikpiqinik rubin ø (tasiusarsuaq)rubin ø (tasiusarsuaq) qaqat aquleritqaqat aqulerit bjørnesund 2008bjørnesund 2008 qaqqatsiaqqaqqatsiaq siggartartuliksiggartartulikkigutilikkigutilik lower annertusoqlower annertusoq upper annertusoqupper annertusoq aappaluttoqaappaluttoq bjø rne sun d bjø rne sun d fiskenæ sfjorde n fiskenæ sfjorde n grædefjordgrædefjord gneissgneiss amphiboliteamphibolite granitegranite doleritedoleriteanorthosite (fiskenæsset complex)anorthosite (fiskenæsset complex) fiskenæssetfiskenæsset 5454 trace-element geochemistry corundum has the chemical formula al2o3 and like most other minerals usually includes very small quantities of other elements in its crystal structure. the amounts of these trace elements and their ratios may depend on the geological conditions during the formation of the corundum and therefore usually vary between individual corundum deposits. twenty-four different elements were analysed for by means of laicp-ms; however most of them were not detected, including sn, nb, and ta. our investigations of the greenlandic corundum were concentrated on the elements mg, si, ti, v, cr, fe, and ga, as these elements are present in significant amounts and are also the most widely documented. we used fig. 2. a: aappaluttoq, fiskenæsset, seen from a helicopter towards the north. the white-grey rock is anorthosite. b: rubies in their host rock at tasiussarsuaq, fiskenæsset, greenland. fig. 3. normalised trace-element distributions for a: ti-cr-ga, b: fe-cr-ga, c: fe-si-ga and d: fe-cr-ti in corundum from fiskenæsset. the data are compared with data on international and greenlandic corundum occurrences (calligaro et al. 1999; del castillo et al. 2009; kalvig & frei 2010; pornwilard et al. 2011; rakontondrazafy et al. 2008; schwarz et al. 2008; thirangoon 2008). different colours show different countries. initials of the authors’ names were used where more than one study of the same locality exist. diagrams were created with wxternary (keulen & heijboer 2011). a b aappaluttoq upper annertusoq lower annertusoq bjørnesund 2008 siggartartulik rubin ø kigutilik intex qororssuaq east qaqqatsiaq aappaluttoq (t) aappaluttoq (kf) annertusoq (kf) qaqat aqulerit (kf) bjørnesund 2008 (kf) rubin ø (kf) siggartartulik (kf) piqinik (kf) maniitsoq storø kapisillit nattivit winza umba tunduru sahabano zazafotsy jagdalek jaipur & mysore john saul tsavo ratnapura luc yen macedonia 80% fiskenæsset best aappaluttoq soamiakatra ilakaka andilamena pailin (p) pailin (c) bo rai chanthaburi mong hsu mogok ti* fe* cr* ga* cr* ga* si* fe* ga* 80 ti* fe* cr* 60 40 20 80 60 40 20 80 60 40 20 80 60 40 20 80 60 40 20 80 60 40 20 80 60 40 20 80 60 40 20 80 204060 80 20406080 204060 80 204060 a b c d 55 the laser ablation sector-field inductively coupled plasma mass spectrometer (la-sf-icp-ms) at the geological survey of denmark and greenland (frei & gerdes 2009), employing an element 2 instrument from thermo-fisher scientific and a up213 frequency-quintupled nd:yag solid state laser system from new wave research. data reduction and determination of concentrations were calculated off-line through the software iolite using the trace_elements_is routine (hellstrom et al. 2008). further details on the methods are found in keulen & kalvig (2013). results on the trace-element investigations of corundum grains separated from 21 hand specimens from ten localities in the fiskenæsset complex are shown with red symbols in the ternary diagrams of fig. 3. the data for corundum from the fiskenæsset complex are in good concordance with earlier data from the area (kalvig & frei 2010; thirangoon 2008). in fig. 3 they are compared with data from other localities in greenland and from internationally, well-known, ruby occurrences. samples from fiskenæsset show a considerably higher amount of cr (up to 14000 ppm) than samples from other areas in greenland and most international samples. the fiskenæsset rubies are relatively rich in fe and si, but relatively poor in ti and ga, while v and mg do not show very distinctive values compared to samples from other areas (kalvig & keulen, 2011). in order to use trace-element investigations as a fingerprinting tool for rubies it is necessary to investigate the amount of overlap between samples from fiskenæsset and other localities. the blue lines in fig. 3 include 80% (26 out of 32) of the samples from the fiskenæsset area, based on sample distribution density contouring. most samples from other localities plot outside the blue line, but an overlapping chemistry is found with samples from soamiakatra, ilakaka, and andilamena in madagascar, bo rai and chanthaburi in thailand, pailin in cambodia and winza in tanzania. rubies from all these localities are hosted by ultramafic to mafic rocks or are found as placer deposits. this indicates that the trace elements in the rubies derive from the ultramafic rocks that are associated with the anorthosite. however, if only the four handspecimens with the most transparent and most intensively red-coloured corundum grains from aappaluttoq, fiskenæsset, are taken into account, no overlap between these handspecimens and samples from other known ruby occurrences is seen. corundum from these handspecimens is closest in transparency and colour to the stones that would be sold from a potential mine and therefore represent the aappaluttoq signature. as these corundum grains have a distinct composition, it can be concluded that trace-element geochemistry with icp-ms is a helpful tool in fingerprinting rubies from greenland. oxygen isotope geochemistry oxygen isotopic composition measurements were performed on ten samples from greenland at the university of lausanne, switzerland using an isotope ratio mass spectrometer, employing a method similar to that described by kasemann et al. (2001), see kalvig & keulen (2011) for details. six of the samples come from the fiskenæsset complex. their δ18o values vary between 1.62 and 4.20‰ for the fiskenæsset area, which is low compared to the other areas in greenland (up to 10.03‰ for maniitsoq) with the exception of one sample from nattivit (2.41‰; fig. 4). the δ18o values are also low compared to most other investigated corundum deposits worldwide (giuliani et al. 2007). the lowermost values (δ18o <3‰) are nearly diagnostic for the fiskenæsset area – worldwide only the placer deposits at andilamena and ilakaka in madagascar and gem-corundum in a cordieritite from iankaroka, madagascar have lower reported δ18o values. low δ18o values (≤4‰) generally ref lect rock types such as mafic rocks, mafic gneiss, basalts, and desilicated pegmatite in mafic rocks (giuliani et al. 2005), which is in excellent agreement with the mafic to ultramafic setting of the fiskenæsset rubies. the values for samples from nattivit, kapisillit and storø are also low (2.4, 4.5 and 6.0‰ respectively) and also plot in the mafic–ultramafic field. unfortunately, no further geological information is available for these specimens and the data can thus not be validated fig. 4. δ18o values for six samples from fiskenæsset and four other localities in greenland. the values are relative to vsmow (vienna standard mean ocean water). colours indicate the approximate colour of the stones. red boxes and classification as mafic-ultramafic, john saul mine, and marble after giuliani et al. (2007). mafic-ultramafic john saul mine aappaluttoq annertusoq bjørnesund 2008 rubin ø siggartartulik pikiniq nattivit maniitsoq kapisillit storø marble δ18o corundum (‰, v-smov) 497395 078667 513743 497393 497392 497383 497397 289933 224779 497396 0 6 16108 18 202 4 221412 24 ggu no. 5656 against field observations. the value for maniitsoq with δ18o =10.03‰ is typically related to skarns in marble, or to biotitite in gneiss related to shear zones with high f luid activity. the rubies in the investigated sample are assumed to stem from sapphirine-bearing hornblendite. the hornblendite was probably formed in a shear zone with high f luid activity (like the biotitites in madagascar). the low δ18o values are a potentially useful tool for fingerprinting greenlandic rubies, especially the very low values for the fiskenæsset complex and nattivit, as only few other international occurrences have such low values. conclusions high confidence fingerprinting of rubies requires a combination of independent analytical methods such as traceelement analyses, oxygen isotope analyses and other studies. the two methods discussed here are efficient in characterising the fiskenæsset rubies. the ongoing research focuses on optical and physical characteristics, spectroscopy methods and scanning xrf. acknowledgements this study is part of a collaboration project between the bureau of minerals and petroleum in nuuk, greenland and the geological survey of denmark and greenland. the authors wish to thank kerstin bauer and torsten vennemann for help with the oxygen isotope analyses. references calligaro, t., poirot, j.-p. & querré, g. 1999: trace element fingerprinting of jewellery rubies by external beam pixe. nuclear instruments and methods in physics research b 150, 628–634. calvo del castillo, h., deprez, n., dupuis, t., mathis, f., deneckere, a., vandenabeele, p., calderón, t. & strivay, d. 2009: towards the differentiation of non-treated and treated corundum minerals by ion-beaminduced luminescence and other complementary techniques. analytical and bioanalytical chemistry 394, 1043–1058. frei, d. & gerdes, a. 2009: precise and accurate in situ u-pb dating of zircon with high sample throughput by automated la-sf-icp-ms. chemical geolog y 261, 261–270. giuliani, g., fallick, a.e., garnier, v., france-lanord, c., ohnenstetter, d. & schwarz, d. 2005: oxygen isotope composition as a tracer for the origins of rubies and sapphires. geolog y 33, 249–252, http://dx.doi. org/10.1130/g21261.1. giuliani, g. et al. 2007: oxygen isotope systematics of gem corundum deposits in madagascar: relevance for their geological origin. mineralium deposita 42, 251–270. hellstrom, j., paton c., woodhead j. & hergt j. 2008: iolite: software for spatially resolved la(quad and mc) icpms analysis. in: sylvester p. (ed.): laser ablation icp–ms in the earth sciences: current practices and outstanding issues, 343–348. mineralogical association of canada short course series 40, 343–348. kalvig, p. & frei, d. 2010: testing the use of geochemical characteristics of corundum from greenland as a tool for geographical typing. danmarks og grønlands geologiske undersøgelse rapport 2010/68, 36 pp. kalvig, p. & keulen, n. 2011: aktiviteter i rubinprojektet 2011 – samarbejdsprojekt med råstofdirektoratet. danmarks og grønlands geologiske undersøgelse rapport 2011/138, 41 pp. kasemann, s., meixner, a., rocholl, a., vennemann, t., schmitt, a. & wiedenbeck m. 2001: boron and oxygen isotope composition of certified reference materials nist sr m 610/612, and reference materials jb-2g and jr-2g. geostandards newsletter 25, 405–416. keulen, n. & heijboer, t. 2011: the provenance of garnet: semi-automatic plotting and classification of garnet compositions. geophysical research abstracts 13, egu 2011-4716. keulen, n. & kalvig, p. 2013: report of the activities in the ruby project 2012 – a joint project with the bureau of minerals and petroleum. danmarks og grønlands geologiske undersøgelse rapport 2013/09, 25 pp. keulen, n., kokfelt, t.f. & the homogenisation team 2011: a 1:100 000 seamless, digital, internet-based geological map of south-west and southern west greenland, 61°30´–64°n, http://geuskort.geus.dk/gisfarm/gis_ svgreenland.jsp. copenhagen: geological survey of denmark and greenland. mcgregor, v.r. & friend, c.r.l. 1992: late archean prograde amphiboliteto granulite-facies relations in the fiskenæsesset region, southern west greenland. the journal of geolog y 100, 207–219. myers, j.s. 1985: stratigraphy and structure of the fiskenæsset complex, southern west greenland. bulletin grønlands geologiske undersøgelse 150, 72 pp. polat a., appel, p.w.u., fryer, b., windley, b., frei, r., samson, i.m. & huang, h. 2009: trace element systematics of the neoarchean fiskenæsset anorthosite complex and associated meta-volcanic rocks, sw greenland: evidence for a magmatic arc origin. precambrian research 175, 87–115. pornwilard, m.-m., hansawek, r., shiowatana, j. & siripinyanond, a. 2011: geographical origin classification of gem corundum using elemental fingerprint analysis by laser ablation inductively coupled plasma mass spectrometry. international journal of mass spectrometry 306, 57– 62. rakontondrazafy, a.f.m. et al. 2008: gem corundum deposits of madagascar: a review. ore geolog y reviews 34, 134–154. schumacher, j.c., van hinsberg, v.j. & keulen, n. 2011: metamorphism in supracrustal and ultramafic rocks in southern west greenland and south-west greenland 64°–61.5°n. danmark og grønlands geologiske undersøgelse rapport 2011/6, 29 pp. schwarz, d. et al. 2008: rubies and sapphires from winza, central tanzania. gems & gemolog y 44, 322–347. thirangoon, k. 2008: ruby and pink sapphire from aappaluttoq, greenland. status of on-going research. unpublished report for true north gems co. (in archives of geological survey of denmark and greenland, geus report file 23642, 18 pp.). authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: ntk@geus.dk mailto:ksv@geus.dk characterising brines in deep mesozoic sandstone reservoirs, denmark research article characterising brines in deep mesozoic sandstone reservoirs, denmark   hanne d. holmslykke*1, niels h. schovsbo1, lars kristensen1, rikke weibel1 and lars henrik nielsen1 *corresponding author: hanne d. holmslykke | e-mail: hdh@geus.dk 1geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350, copenhagen k, denmark geus bulletin vol 43 | e2019430104 | published online: 17 july 2019 https://doi.org/10.34194/geusb-201943-01-04   the danish subsurface contains several sandstone units, which represent a large geothermal resource (vosgerau et al. 2016). currently, only three geothermal plants are operating in denmark, but several exploration licences are expected to be awarded in 2019. geothermal energy is exploited from deeply buried porous sandstones by bringing warm formation water (brine) to the surface, extracting the heat and returning the cooled water to the same sandstones. the reduced temperature of the brine during this process implies a risk of scaling, which may reduce reservoir permeability and hence injectivity. predicting the chemical composition of formation waters, however, could help to reduce the risk associated with scaling in planned geothermal facilities. here, we present a regional overview of the geochemistry of brines from deep mesozoic sandstones in the danish basin and north german basin that supplements previous studies, notably by laier (2002, 2008). the brine composition at shallow burial typically reflects the original (connate) formation water chemistry, which is determined by the original depositional environment of the sandstone, for example fluvial or marine. however, the mineralogical composition of the sandstone changes during burial, whereby some minerals may dissolve or precipitate when exposed to higher temperatures. these mineral changes are reflected in the brine composition, which typically becomes more saline with increased burial (e.g. laier 2008; kharaka & hanor 2003). the brine chemistry reported here shows a distinct depth trend, which reflects original connate formation waters that are modified through burial diagenesis. we have classified the brines into brine types, which are shown to be related to their depositional environment, depth, geological formation and geographical domains. methods we collected new samples from the production wells at each of the three danish geothermal sites (margretheholm, sønderborg and thisted) in 2017. the samples were analysed for ph, anions, cations and trace elements. cations were analysed by icp-ms (perkinelmer elan6100drc quadrupol) with a standard deviation of 3–15% depending on the element measured. samples for anion analysis were frozen for ion-chromatography (lc50-cd50, dionex, ca, usa) with a quantification limit of 0.05 mg/l. total dissolved species (tds) were calculated as the weight sum of analysed ions per weight of saltwater. these new data are combined with previously published data from the northern north german basin (tønder-4, -5 wells, sønderborg-1a, -2 wells) and from the danish basin (fig. 1, farsø-1, aars-1, stenlille-1, -19 wells, thisted -2, -3 wells, margretheholm-1, -2 wells; laier, 2002, 2008; hjuler et al. 2019). collectively, these samples span the triassic skagerrak, bunter sandstone and falster formations, the upper triassic – lower jurassic gassum formation and the jurassic fjerritslev and haldager sand formations (fig. 2). contaminated samples picked during test pumping were deselected and only samples in the late phase with stable water chemistry (notably k+ and cl-) were used. a principal component analysis (pca) was conducted on the combined dataset to classify the formation water chemistry into one of three brine types (table 1). altogether, the new samples and the samples from the literature total 39 samples (fig. 3). in the pca, present day vertical depth is used with no correction for cenozoic uplift. table 1.  brine type characteristics. brine type depth cl– br– so42– na+ k+ ca2+ mg2+ ca:cl tds ph sr2+ fetot mntot nh4 + zn2+ ba2+ li+ sio2 m ppm ppm ppm ppm ppm ppm ppm mol/mol ppm ppm ppm ppm ppm ppm ppm ppm ppm 1a 1250 97 264 310 869 53 382 502 4372 1167 0.04 157 866 6.6 196 19 6 0 1 2 1b 1376 105 000 372 26 56 667 421 8033 1480 0.08 171 998 6.3 498 39 15 27 11 15 10 13 3 1769 195 250 1275 595 115 000 1425 8750 1400 0.04 323 695 2b 2511 177 667 993 163 77 333 1838 27 950 2820 0.16 288 765 5.9 815 281 80 20 28 9 28 2a 2565 135 407 824 261 53 758 717 22 276 2820 0.16 216 064 6.3 862 6 20 21 5 11 11 6 tds: total dissolved species. fetot: total iron. mntot: total manganese. fig. 1.  location of the wells used for brine type characterisation and distribution of geothermal reservoirs: skagerrak (yellow – orange), bunter sandstone (red), and gassum (blue) formations. modified from weibel et al. (2017a). fig. 2.  stratigraphy of reservoirs and location of brine types. brine types are defined in fig. 3. the broken line indicates present-day depth of 2 km below surface. tø: tønder. sø: sønderborg. aa: aars. fa: farsø. ti: thisted. st: stenlille. ma: margretheholm. palaeo.: palaeozoic. cen.: cenozoic. fig. 3.  principal component analysis (pca). a: score plot. b: loading plot of pca on regional data. the plots model 85% of the total data variance. variance proportions are shown along each component axis. brine types are classified according to their groupings in a. results and discussion to classify the brine types we applied a pca, which transforms a matrix of measured data (x; comprised of n samples and p variables) into sets of projection subspaces delineated by principal components. each component is a linear combination of all p variables, which displays variance-maximised interrelationships between the variables (schovsbo et al. 2016). pca results are presented as a score plot (fig. 3a), which displays groupings, or clusters, of samples based on compositional similarities, alongside a loading plot (fig. 3b), which shows the variable correlations. finally, we quantify the proportion of the total dataset variance that can be modelled by each component (as shown in each of the axes in fig. 3). brine type classification in the pca model, the first two principal component axes resolve 85% of the total data variance (fig. 3). the main trend expressed on the pca-1 axis is high ion concentrations in water from deeply buried reservoirs, expressed as high positive pca-1 loadings at depth (fig. 3a) for all ions except so42– (fig. 3b). the pca-2 axis displays high positive loadings of na+, cl–, k+, so42– and br–, as well as high negative loadings of elements like mg2+, ca2+ and also at depth (fig. 3b). from the pca, three main brine types can be identified based on natural groupings in the pca-2 versus pca-1 plot (fig. 3a). the characteristics and occurrence of each type are presented below. brine type 1 plots with negative pca-1 and with slightly positive (type 1a) or negative (type 1b) pca-2 score (fig. 3a) and is characterised by relative low chloride content (cl– < 110 000 ppm) and low tds (table 1). type 1a is so42– enriched, and type 1b is so42– depleted (table 1). type 1 occurs mainly in gassum reservoirs from the stenlille, thisted (type 1b) and sønderborg wells (type 1a). these three reservoirs are buried between 1.2 and 1.6 km depth. brine type 2 is characterised by positive pca-1 and negative (type 2a) or neutral (type 2b) pca-2 scores and can be characterised compositionally by medium to high salinities (cl– >130 000 ppm), and high to very high ca2+ and mg2+ concentrations (fig. 3). type 2a is cl– and k+ depleted relative to 2b, whereas type 2b is k+ enriched (table 1). brine type 2 occurs at depths greater than 2 km in a broad range of reservoirs belonging to the haldager sand, gassum, bunter sandstone and skagerrak formations. type 2a occurs exclusively in the margretheholm area (fig. 3a). brine type 3 has intermediate pca-1 and highly positive pca-2 scores (fig. 3a), reflecting high salinities (cl– >190 000 ppm, table 1). type 3 waters are restricted to the bunter sandstone reservoir in the tønder area overlying a zechstein salt dome. in addition, halite (nacl) is also present in the triassic sequence at tønder (laier & nielsen 1989). the brine is halite saturated and it is estimated that c. 5 g/l halite has precipitated at surface conditions during production tests (hjuler et al. 2019). saturation index from phreeqc simulations to further interpret the brine types, we performed a chemical speciation analysis using the numerical code phreeqc and its pitzer database. the in situ reservoir temperature was estimated from the regional temperature gradient (e.g. balling et al. 1981). the fluid pressure of the reservoirs was assumed to be hydrostatic (9.79 kpa/m) assuming a water density of 1.1 g/cm3). the saturation state of the brines with respect to selected minerals is indicated by the saturation index (si) whereby positive and negative values indicate super-saturation and undersaturation, respectively. equilibrium with respect to the mineral is assumed for –0.4 ≤ si ≤ +0.4. this accounts for the uncertainties associated with the difficulties of sampling brines at high temperature and pressure, the analytical uncertainty and the application of thermodynamic equilibrium constants on mineral phases in saline systems. formation water with a si within this band is assumed to be saturated, and thus in equilibrium for this mineral. carbonate minerals are not included in table 2, due to the difficulty of correctly measuring components of the carbonate system (ph, hco3etc.) in heated pressurised samples. table 2.  saturation index (si) for selected minerals calculated with phreeqc. brine type depth (m) anhydrite halite barite celestite 1a 1250 –0.42 –0.90 0.40 0.08 1b 1376 –1.69 –0.79 –0.06 –1.08 3 1769 0.35 0.39 2b 2511 –0.29 0.03 –0.20 –0.09 2a 2565 –0.20 –0.55 0.03 0.04 minerals with a saturation index in the band –0.4 ≤ si ≤ 0.4 are assumed to be in equilibrium, within the uncertainties of analyses and thermodynamic parameters in the phreeqc database. the salinity of the brine types increases with the average depth (e.g. cl– in brine types 1a, 1b, 2b, table 1). this relationship was previously explained by the diffusion of cl– from the underlying zechstein salt deposits occurring in most of the danish basin and the north german basin (laier 2002). for the deepest reservoirs (type 2b) the brine is saturated with respect to halite (si = 0.03; table 2). even though types 2a and 2b are sampled from the same depth, type 2a has a significantly lower cl-concentration and is undersaturated with respect to halite (si = –0.55, table 2). this may be because brine type 2a, from margretheholm geothermal plant, was sampled from reservoir sandstones at the basin margin, where zechstein salt deposits are absent. brine type 3, sampled in tønder has a high salt content compared to deeper brines (types 2a and b), and the brine is saturated with respect to halite. brine type 3 is the only sample located in an area where halite-cemented sandstone intervals are present and salt deposits exist both above (röth salt) and below (zechstein salt). brine type 3 is saturated with respect to anhydrite (caso4 si = 0.35; table 2), which makes sense as anhydrite is a common mineral in the bunter sandstone formation (weibel & friis 2004). despite a high si for barite (baso4) in brine type 1a (si = 0.40, table 2), we did not observe any barite precipitation in the margretheholm geothermal plant. the high saturation index probably reflects the uncertainties associated with sampling and analysing from deep reservoirs and most likely the formation water is in equilibrium with barite in the reservoir. the ca:cl ratio (table 1) is significantly higher in the deeper types (2a and 2b) compared to the shallower brines (types 1a, 1b and 3). calcite (caco3) is common in the shallow part of the gassum formation, but ankerite (ca(mg, fe, mn)(co3)2) is more abundant in the deeper parts (weibel et al. 2017b). hence, replacement of calcite with a fe and mgrich carbonate would liberate ca2+ to the formation water. similarly, ca2+ may be liberated to the pore fluid, as dolomite (camg(co3)2) becomes more stable than calcite in the deeply buried parts of the skagerrak formation (weibel et al. 2017a). the k+ content generally increases with burial depth in the gassum formation (table 1). k+ may have been liberated by albite (naalsi3o8) replacement (albitisation) of k-feldspar (kalsi3o8), which has been documented in gassum sandstones from both the aars-1 and farsø-1 cores (weibel et al. 2017b). formation water from the bunter sandstone formation generally has a similarly high or higher k+ content as the deeply buried gassum formation. this may relate to a generally higher abundance of k-feldspar and rock fragments (weibel & friis 2004), or it may originate from kcl in the under or overlying evaporites. conclusions here, we have identified and characterised three brine types present in danish geothermal reservoirs. reservoir depth and the occurrence of salt in the subsurface layer appear to be a dominant control. brine type 1 occurs in reservoirs shallower than 2 km, whereas brine type 2 occurs in both jurassic and triassic sandstones buried to more than 2 km. among the deeply buried reservoirs, type 2a brine is only found in the margretheholm wells and is interpreted to reflect the absence of salt in the subsurface around these wells in contrast to all other analysed deep wells. brine type 3 is highly saline and occurs at less than 2 km depth in the tønder area. classification of brine types according to chemical composition, highlights variable risks in potential scale and scale types and shows that local conditions must be considered prior to any new planned geothermal facility. geological information, depth and geographical domains can serve as a rough predictive tool, and will be further refined as additional data are collected from new geothermal wells. acknowledgments this contribution is part of the project geotherm (“geothermal energy from sedimentary reservoirs – removing obstacles for large scale utilization”) (no. 6154-00011b) funded by the innovation fund denmark (ifd). we thank the two reviewers, ida fabricius and nicolas marty, for their comments, which improved the manuscript. references balling, n., kristensen, j.i., breiner, n., poulsen, k.d., rasmussen, r. & saxov, s. 1981: geothermal measurements and subsurface temperature modelling in denmark. geoskrifter 16, 173 pp. hjuler, m.l., olivarius, m., boldreel, l.o., kristensen, l., laier, t., mathiesen, a., nielsen, c.m. & nielsen, l.h. 2019: multidisciplinary approach to assess geothermal potential, tønder area, north german basin. geothermics 78, 211–223. https://doi.org/10.1016/j.geothermics.2018.12.001 kharaka, y.k. & hanor, j.s. 2003: deep fluids in the continents: i. sedimentary basins. in: drevor, j.i. (ed.): treatise on geochemistry 5, 499–540. https://doi.org/10.1016/b0080437516/05085-4 laier, t. 2002: vurdering af udfældningsrisici ved geotermisk produktion fra margretheholmboringen mah-1a. beregning af mætningsindeks for mineraler i saltvand fra danmarks dybere undergrund. danmarks og grønlands geologiske undersøgelser rapport 2002/95. 48pp laier, t. 2008: chemistry of danish saline formation waters relevant for core fluid experiments. fluid chemistry data for lab experiments related to co2 storage in deep aquifers. danmarks og grønlands geologiske undersøgelser rapport 2008/48. laier, t. & nielsen, b.l. 1989: cementing halite in triassic sandstone (tønder southwest denmark) as a result of hyperfiltration of brines. chemical geology 76, 353–363. https://doi.org/10.1016/0009-2541(89)90103-4 schovsbo, n.h., hedegaard, k., holmslykke, h.d., kjøller, c., kristensen, l., thomsen, e. & esbensen, k.h. 2016: formation water and produced water types in danish oil and gas fields: implications for enhanced oil recovery by “smart” water. geological survey of denmark and greenland bulletin 35, 43–46. vosgerau, h. et al. 2016: a webgis portal for exploration of deep geothermal energy based on geological and geophysical data. geological survey of denmark and greenland bulletin 35, 23–26. weibel, r. & friis, h. 2004: opaque minerals as keys for distinguishing oxidising and reducing diagenetic conditions in the lower triassic bunter sandstone, north german basin. sedimentary geology 169, 129–149. https://doi.org/10.1016/j.sedgeo.2004.05.004 weibel, r. et al. 2017a. the influence of climate on early and burial diagenesis of triassic and jurassic sandstones from the norwegian – danish basin. the depositional record 3, 60–91. https://doi.org/10.1002/dep2.27 weibel, r., olivarius, m., kristensen, l., friis, h., hjuler, m.l., kjøller, c., mathiesen, a. & nielsen, l.h. 2017b: predicting permeability of low enthalpy geothermal reservoirs: a case study from the upper triassic − lower jurassic gassum formation, norwegian – danish basin. geothermics 65, 135–157. https://doi.org/10.1016/j.geothermics.2016.09.003 how to cite holmslykke, h.d., schovsbo, n.h., kristensen, l., weibel, r. & nielsen, l.h. 2019: characterising brines in deep mesozoic sandstone reservoirs, denmark. geological survey of denmark and greenland bulletin 43, e2019430104. https://doi.org/10.34194/geusb-201943-01-04 geological survey of denmark and greenland bulletin 31, 2014, 67-70 67 combining exploration and multivariate techniques to detect the bjørnesund west gold occurrence, southern west greenland denis martin schlatter and bo møller stensgaard gold exploration in the bjørnesund region has been carried out since the early 1990s, and gold was found in the central part of the bjørnesund east area by nunaoil and the geological survey of denmark and greenland (geus). records of stream sediment samples with elevated gold concentrations up to several hundred parts per billion led to the recognition that amphibolites in the central part of the bjørnesund east could be a promising target and work in 1996 led to the discovery of hydrothermally altered amphibolites with up to several hundred ppb gold. however, exploration work was limited to grassroots prospecting and none of the targets were drilled. the aim of new field work was to target areas in the bjørnesund supracrustal belt which mainly consists of amphibolites but also comprises significant proportions of diorite, anorthosite, leucogabbro, granitoid rocks and ultramafic to mafic rocks that occur as relatively thin slivers in the amphibolite. we tested if the targeted areas were favourable for gold mineralisation and investigated the relationship between the mineral potential mapping and the actual geology. here we demonstrate that based on older data we located new gold mineralising systems in the western part of the bjørnesund supracrustal belt, identified platinum-enriched mafic to ultramafic rocks and located new occurrences of corundum at amphibolite-anorthosite contacts (schlatter © 2014 geus. geological survey of denmark and greenland bulletin 31, 67–70. open access: www.geus.dk/publications/bull fig. 1. geological map of the bjørnesund west and east areas showing the location of the newly discovered gold occurrence in bjørnesund west. prior to field work by geus in 2009, no gold occurrences were reported here. black outlines indicate the sampled areas of bjørnesund west, regarding sampling density see fig. 3. camp 1 bjørnesund west62°54´n bjørnesund east 62°56´n camp 2 1 km 50°03´w layers comprising garnet-rich amphibolite extensive surface staining new gold occurrence, bjørnesund west gold occurrence, bjørnesund east, 80 ppb fig. 3b fig. 3a bjørnesund dolerite granitic aplite/pegmatite trondhjemite (2.84 ga) trondhjemite with amphibolite inclusion ttg-gneiss (2.87–2.89 ga) migmatised ttg-gneiss ttg-gneiss with pl, bt and ep agmatitic ttg-gneiss ttg-gneiss with hbl and bt anorthosite ultramafic to mafic rock amphibolite amphibolite lens (hosted in gneiss) quartz-dioritic gneiss (2.919 ga) quaternary not digitised 50°18´w greenland 6868 & stensgaard 2012). we also show how lithogeochemical studies were useful to define the main rocks types, chemostratigraphic relations and hydrothermal alteration of the newly discovered gold mineralisation. based on our study, we encourage the use of artificial neural network analysis and data interpretation prior to field work in greenland in areas where only relatively little geological and mineral exploration work has been conducted and where the field season is relatively short. geology of the bjørnesund area the bjørnesund supracrustal belt (keulen et al. 2010) is of mesoarchaean age, c. 50 km long and a few hundred metres to 3 km wide (fig. 1). amphibolites dated to 2947 ± 47 ma are bounded towards the north and south by 2920–2810 ma tonalite-trondhjemite-granodiorite (ttg) gneisses (keulen et al. 2010; kolb et al. 2013) that are interpreted to have been intruded into the amphibolites. sheets of leucogabbro, gabbro and anorthosite are interpreted to have been intruded into the amphibolites at about 2950 ma and were in turn intruded by quartz dioritic protoliths at 2920 ma (keulen et al. in press). finally, late granites were intruded into the sequence of quartz-diorite amphibolite and anorthositegabbro between 2860 and 2830 ma (kolb et al. 2013). the rocks were affected by f1 folding into an isoclinal synform and f2 folding at 2850–2830 ma with an e–w-trending fold axis, which is the most dominant structural feature in the bjørnesund area (keulen et al. in press). the f2 folding is associated with thrusting that caused shearing with only minor displacement. finally, f3 nnw–sse-trending folds have bent the regional foliation slightly. methods a total of 116 rock samples (900 g) and 56 stream sediment samples (200 g) were collected during the field work and used for geochemical and petrographic investigations. rock samples were crushed and milled by actlabs laboratory in ontario, canada, and stream sediment samples were sieved at geus using a 0.18 mm sieve. the fine-grained fraction was sent to actlabs for analysis. gold was analysed by instrumental neutron activation whereas major and trace elements were analysed using actlabs package ‘4lithoresearch’. the u-pb ages of zircon grains from four plutonic rock samples were also determined by keulen et al. (in press). an artificial neural network is a mathematical and computational structure simulating the human neural network (the brain). information, in the form of input data, which are presented to the network causes the network to learn and recognise patterns in the data. for instance, when a network is shown multiple datasets for known gold occurrences, it is able to identify and memorise possible patterns in the datasets associated with the occurrences which can be regarded as training points for the network. afterwards, when the network is shown datasets from areas without any known gold occurrences, the network applies what it has learned and looks for patterns in the datasets that are similar to those recognised for the known gold occurrences. in that way, areas can be classified and mapped according to how similar their data patterns are to the patterns from the known gold occurrences. these areas can be regarded as potential to host gold occurrences. mineral potential mapping artificial neural network analysis (stensgaard 2013) was used for mineral potential mapping (fig. 2) together with ni/mg ratios from analysed stream sediment samples. this led to the identification of portions of the western and eastern parts of the bjørnesund supracrustal belt as the most favourable for gold occurrences. areas with anomalously high levels of fe3+ were identified using aster satellite images, and correspond to ultramafic dunitic and pyroxenitic rocks (schlatter & stensgaard 2012). the most favourable areas, as identified from artificial neural network analysis, coincide with areas of stream sediments with elevated ni/mg ratios. based on these detailed analyses, the bjørnesund west and east areas were selected for field work with the aim to characterise the geological environment and evaluate the gold potential. a new detailed and geo-referenced digital geological map was compiled after the new field work (fig. 1) and a new interesting gold occurrence was found in a hydrothermally altered shear zone in the amphibolites of the bjørnesund bjø rne su nd 5 km 50°10´w 62°55´n 2.1 3.2 3.9 4.9 6.2 7.5 fig. 2. neural network analysis for gold favourable areas in the bjørnesund west and east areas. top 8.5% most favourable areas for gold in seven coloured intervals according to the neural network analysis of as, cs, rb, sb and u stream sediment geochemistry and lineaments. a geological map is placed beneath the neural network analysis result, which is transparent. 69 west area. this several tens-of-metres wide ne–sw-trending shear zone (figs 1, 3a) dips 80° se. it can be followed over several hundred metres along strike and contains a 50 cm yellow-brownish, rusty-stained amphibolite, which hosts parallel quartz-carbonate-feldspar veinlets. chip samples collected over this altered unit yielded 569 ppb au (fig. 3a), and alteration related to this gold occurrence was identified to be of the garnet-biotite-iron oxide-hydroxide type (kolb et al. 2013). these new findings, together with elevated gold concentrations in stream sediment and rock samples along the same ne–sw-trending shear zone, indicate that the bjørnesund supracrustal belt may host undiscovered gold occurrences and confirm that stream sediment sampling is a powerful exploration tool (fig. 3a). furthermore, nickel and platinum-group elements could also constitute a target as pentlandite was identified in an ultramafic rock sample with elevated concentrations of ni, cr, co and pge from bjørnesund east (fig. 1; schlatter & stensgaard 2012). chemostratigrapy and hydrothermal alteration based on lithogeochemical immobile-element-ratio classification (barrett & maclean 1994) seven types of amphibolite and three different types of other mafic to ultramafic rocks (high mg-cr-ni-co, ni-rich and high-ti-zr basalt) were distinguished (figs 1, 3b). the gold horizon was located at the contact of basalt a and basalt e (fig. 3b). amphibolites with elevated gold concentrations (less than 100 ppb) were also located in bjørnesund east (fig. 1, c. 2 km north-east of camp 2) where the ore horizon is also located at the contact of basalt a and basalt e (schlatter & stensgaard 2012). it appears that this basalt a – basalt e contact represents a good geochemical marker horizon in the bjørnesund supracrustal belt. changes were calculated for 35 basalt samples from the bjørnesund area using the single precursor approach (maclean & barrett 1993). the results show that the richest gold-bearing basalt with 569 ppb au from bjørnesund west (fig. 3b, encircled in white) is characterised by strong additions of feo and silica (fig. 4a) and by gain of cao and loss of k2o (fig. 4b). in contrast, a basalt sample from bjørnesund east with 80 ppb au (fig. 1) shows only a small loss of silica, no change of iron, gain of k2o and loss of cao (fig. 4). we conclude that favourable alteration associated with gold mineralisation is characterised by silicification combined with addition of feo and cao. discussion and conclusions mineral potential mapping was successful because it indicated areas containing gold-mineralised rocks and pinpointed unusual mafic to ultramafic rocks where elevated concentrations of nickel and platinum-group metals were subsequently identified. extensive rust zones were identified from aster satellite data, some of which correspond to the mafic to ultramafic rock units with elevated ni, cr, co and pge contents; several of the ultramafic to mafic rocks fall into the komatiite field and pentlandite was identified by microprobe analysis in one sample (schlatter & stensgaard 2012). fig. 3. a: gold anomaly plot of sediment and rock samples from the bjørnesund west area. a several tens-of-metres wide shear zone (dashed line) with gold-mineralised portions was discovered at 62°54.4´n, 50°16.2´w and at 555 m a.s.l. legend below figure. b: chemostratigraphic relation seen from the bjørnesund west area. a rock unit which comprises mainly basalt a and a unit comprising mainly basalt c can be identified based on lithogeochemical immobile element techniques. the gold occurrence is found in rocks of basalt e type, and have basalt a and c in the structural footwall. for legend see fig. 1. quaternary granite amphibolite amphibolite of extrusive origin diorite and tonalite trondhjemite with amphibolite inclusion gneiss ultramafic rocks anorthosite b 31 122 16 16 21 569 9 50 11 71 6 11 134 6 au content in ppb rock sample stream/scree sediment sample 1 km 1 km gabbro basalt a field of basalt a field of basalt c ni-rich basalt basalt d basalt d basalt d basalt c basalt c high ti-zr basalt basalt c basalt x basalt a basalt f basalt f basalt b basalt e basalt e au mineralisation basalt a ttg gneiss amphibolite-gneiss anorthosite high mg-cr-ni-co basalt high mg-cr-ni-co basalt ca mp 1 bjørnesund westa 97 7070 chemostratigraphic interpretations show that the au horizon is located at the contact between basalt a and basalt e and can be followed along the bjørnesund supracrustal belt for at least 10 km (figs 1, 3) so that this horizon represents an exploration target for gold and provides evidence of an e–w continuation. alteration related to au mineralisation is of garnet-biotite-iron oxide-hydroxide type and quartz-carbonate-feldspar veinlets occur in an amphibolite-hosted thrustshear zone between quartz-dioritic gneiss and gneiss. masschange calculations show that favourable ‘au-alteration’ is characterised by gains of feo, sio2 and cao and enrichment of as, sb and zn (schlatter & stensgaard 2012). the spatial association of gold occurrences and granite-trondhjemite rocks (fig. 1) possibly indicates that the granitoids played a role in the emplacement of the gold. the association of gold and nickel is intriguing (schlatter & steensgaard 2013) and could be related to deep structures which might have been activated during events similar to those described by fiorentini et al. (2012) from the highly nickel-enriched agnew-wiluna greenstone belt in western australia where felsic and komatiitic magmas are related to deep crustal conduits. with respect to the timing of events of the bjørnesund supracrustal belt, we suggest that ultramafic rocks, leucogabbro and anorthosite were intruded into amphibolites (fig. 1). this event may have been coeval with orthomagmatic nickel-platinum group-element mineralisation and isoclinal f1 folding. it is suggested that gold was then orogenically emplaced between 2860 and 2830 ma (kolb et al. 2013) at peak regional metamorphism. finally, late f3 deformation events created faulting in a staircase-like outcrop pattern at 2710–2700 ma (keulen et al. in press). this study represents a coupled effort of artificial neural network analysis and targeted field exploration and shows that such an approach can be efficient and successful in identifying new exploration targets of gold, nickel-platinum group elements and corundum. references barrett, t.j. & maclean, w.h. 1994: chemostratigraphy and hydrothermal alteration in exploration for vhms deposits in greenstones and younger volcanic rocks. in: lentz, d.r. (ed.): alteration and alteration processes associated with ore-forming systems. st. john’s: geological association of canada. short course notes 11, 433–467. fiorentini, m., beresford, s., barley, m., duuring, p., bekker, a., rosengren, n., cas, r. & hronsky j. 2012: district to camp controls on the genesis of komatiite-hosted nickel sulfide deposits, agnew-wiluna greenstone belt, western australia: insights from the multiple sulfur isotopes. economic geolog y 107, 781–796. keulen, n., kokfelt, t.f. & scherstén, a. 2010: notes on the common legend to the 1:100 000 digital geological map of southern west and south-west greenland, 61°30´–64°n. danmarks og grønlands geologiske undersøgelse rapport 2010/119, 41 pp. keulen et al., in press: mesoand neoarchaean geological history of the bjørnesund supracrustal belt, southern west greenland: settings for gold enrichment and corundum formation. precambrian research. kolb, j., dziggel, a. &. schlatter, d.m. 2013: gold occurrences of the archean north atlantic craton, southwestern greenland: a comprehensive genetic model. ore geolog y reviews 54, 29–58. maclean, w.h. & barrett t.j. 1993: lithogeochemical techniques using immobile elements. journal of geochemical exploration 48, 109–133. schlatter, d.m. & stensgaard, b.m. 2012: evaluation of the mineral potential in the bjørnesund greenstone belt combining mineral potential mapping, field work and lithogeochemistry. danmarks og grønlands geologiske undersøgelse rapport 2012/60, 60 pp. schlatter, d.m. & stensgaard, b.m. 2013: evaluation of the mineral potential in the bjørnesund greenstone belt, southern west greenland, combining multivariate studies, field work and geochemistry. 11th swiss geoscience meeting, lausanne, 15–16 november 2013. abstracts, 74–75. stensgaard, b.m. 2013: analysis of regional data sets: predictive gold potential using neural network analysis. danmarks og grønlands geologiske undersøgelse rapport 2013/15, 27–81. authors’ addresses d.m.s.* & b.m.s., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. * present address: helvetica exploration services gmbh, carl-spitteler-strasse 100, ch-8053 zürich, switzerland. e-mail: denis.schlatter@helvetica-exploration.ch a b ∆cao (wt%)∆sio2 (wt%) ∆ fe o (w t% ) –10 0 10 20 30 40 50 60 –20 –10–40 0 20 0 1040 high ti-zr basalt (n=4) chemical rock types: basalt a (n=10) basalt c (n=2) basalt d (n=5) basalt e (n=10) basalt f (n=4) silicification addition of feo and silica removal of k2o and cao gain of cao and loss of k2o addition of k2o and loss of cao addition of feo and loss of silica silica removed au=569 ppb au=97 ppb au=97 ppb a u= 56 9 pp b au=80 ppb au=80 ppb au=134 ppb au=134 ppb ∆ k 2 o (w t% ) –2 –1 1 2 0 fig. 4. hydrothermal alteration based on mass-change calculations for 35 rocks from the bjørnesund west and east areas. a: δsio2 versus δ feo. b: δcao versus δk2o. mass changes were calculated using the method described by barrett & maclean (1994). mass changes are reported in wt% change (δ) relative to the precursor rock. geological survey of denmark and greenland bulletin 17, 2009, 25-28 the danish north sea coast is a dynamic sedimentary environment experiencing erosion, transport and re-deposition of sand along the coast. because of the natural and economic value of the coastal zone expensive protection measures such as nourishment of the coast are undertaken. the present study utilises provenance analysis techniques developed at the geological survey of denmark and greenland (geus) to characterise the coastal sand bodies by fingerprinting the heavy minerals in the sand. the aims of the study are to test these new methods in an active sedimentary environment and to develop an understanding of transport pathways along the coast. a total of c. 40 samples have been collected and analysed as part of the project. this paper gives an outline of the project and provides examples of the methods used based on six samples from the husby profile on the west coast of jylland (fig. 1). the study is a collaboration project involving geus and the department of geography and geology (dgg) at copenhagen university; geus is responsible for the analyses and dgg for sample collection. provenance analysis based on modal abundance and composition of heavy minerals is used to understand the dispersal of sand in ancient siliciclastic systems, with focus on problems relevant to the petroleum industry (e.g. larsen et al. 2006; morton et al. 2007). investigation of present-day processes and sedimentary environments may provide a key to understand how provenance indicators can be used to describe and interpret fossil clastic sedimentary systems. it is well known that properties such as grain shape and density are important factors in the processes controlling transport and deposition of mineral grains. as the heavy minerals used in provenance analysis have a wide range of densities and shapes, it is important to include these properties in studies of their dynamics in the environment. therefore geus has focused on developing computer-controlled scanning electron microscopy (cc sem), which provides information on mineralogy and mineral chemistry together with grain size and shape (keulen et al. 2008). furthermore, the development of laser ablation inductively coupled mass spectrometry (la-icp-ms) analysis has focused on a single, robust mineral species, zircon. these analyses also yield information on the age of the zircon mineral grains, and the age distribution of zircon grains is used to fingerprint the sand (knudsen et al. 2005; frei et al. 2006). saye & pye (2005) have described variations in the bulk chemical composition and particle size of coastal sands in denmark. the work outlined here is a continuation of this work, but using different methods focusing on the modal mineralogy of the heavy minerals in the sand as well as the age distribution of detrital zircon grains. sample sites samples have been collected from three settings. (1) from coastal cliffs that are being actively eroded and accordingly supply sediment to the littoral drift system along the coast of jylland. the sampling aims at fingerprinting some of the potential sources of sand mainly from till beds and glacio-fluvial sediments. (2) from four profiles orientated perpendicular to the coast; the samples represent lower shoreface, upper shoreface, beach and dunes (profiles at bovbjerg, husby, vejers and skallingen; fig. 1). the aim is to study the variation of the sediment fingerprint between the different sedimentary facies along the coast as well as the variation within identical sedimentary environments. the profiles are situated along the southward-directed net littoral drift of sand that exists between bovbjerg and skallingen. (3) from the vejers/ skallingen/grå dyb area samples will be analysed to investigate if the littoral drift sediment bypasses horns rev and to characterise the sedifingerprinting sediments along the west coast of jylland: interpreting provenance data christian knudsen, thomas kokfelt, troels aagaard, jesper bartholdy and morten pejrup © geus, 2009. geological survey of denmark and greenland bulletin 17, 25–28. available at: www.geus.dk/publications/bull 25 fig. 1. map of western denmark showing the location of the husby area (red box) and place names mentioned in the text. the map to the right shows the husby area with sample sites marked. skallingen grådyb vejers horns rev husby jylland bovbjerg 50 km vadehavet n orth sea husby 8°9’e 56°17’n 70248/70249 (black till) 70230 (dune) 70231 (swash zone) 70228 (–6 m) 70229 (–3 m) sea beach dunes other land roads ditches 1 km north sea rosa_2008:rosa-2008 01/07/09 15:48 side 25 ment exchange between the north sea and vadehavet (danish wadden sea) relative to other sources and sinks in the area. here we present data from the profile at husby. computer-controlled scanning electron microscopy (ccsem) ccsem is used at geus to analyse the composition and properties of detrital mineral grains. sediment samples are sieved and the fraction between 45 and 710 µm analysed. the samples are separated using heavy liquid (2.89 g/cm3) and the heavy mineral fraction is used for analysis. the grains are mounted in epoxy in such a way that the grains do not touch one another. the mount is polished and analysed by ccsem to determine the chemical composition of c. 1200 individual heavy mineral grains, together with their size and shape. the result of the chemical analysis of each grain is compared with a library of mineral compositions. the results are stored in a database and properties such as modal mineralogy, mineral chemistry and grain-size distributions of the individual species can be displayed (figs 2, 3). the ccsem analytical procedure is described in further detail by knudsen et al. (2005), keulen et al. (2008) and bernstein et al. (2008). la-icp-ms fingerprinting of zircon when using the modal proportions of heavy minerals for characterising the provenance of the sand, it is important to recognise potential hydrodynamic effects due to, e.g. grain density. in addition, the size and shape characteristics of the grains of the different heavy mineral species may influence their response to sedimentary processes. further more, the relative sensitivity of the heavy mineral species to 26 the 63–125 µm fraction contains c. 60% of the zircon c. 40% of the ilmenite c. 35% of the garnet c. 20% of the mafic silicates the 63–125 µm fraction contains c. 80% of the zircon c. 80% of the ilmenite c. 80% of the garnet c. 75% of the mafic silicates grain diameter (µm) 10 1006345 125 710 1000 0 50 100 50 100 c um ul at iv e w t% c um ul at iv e w t% husby –6 m husby –3 m garnet ilmenite mafic silicates zircon fig. 2. grain-size distribution curves for zircon, garnet, ilmenite and mafic silicates in two samples from husby taken at 3 and 6 m water depth. note that if only the 63 to 125 µm fraction of the heavy mineral fraction was analysed, the modal proportions of the heavy mineral species would not represent the actual proportions in the sand. fig. 3. the heavy mineral proportions in the six samples from husby recorded by ccsem. the samples from the shoreface (–3, –6 m) are characterised by low contents of garnet (c. 7%) in contrast to the samples from the beach and dune that are characterised by high garnet contents (c. 20%). 0 20 40 60 80 100 beach dune ti magnetite magnetite silicates, other mafic silicates staurolite sillimanite garnet zircon rutile leucoxene ilmenite fr ac ti o n (% ) –6 m –3 m till 1 till 2 rosa_2008:rosa-2008 01/07/09 15:48 side 26 chemical and physical decomposition depends on the stability of the different minerals. to overcome these problems, it is advisable in provenance analysis to focus analysis on one mineral species because differences in hydrodynamic behaviour or weathering can thereby be discounted. for this purpose the extremely stable mineral zircon is very well suited. a key property of zircon in provenance analysis is the relatively high content of uranium, which makes the mineral well suited for dating. at geus the measurements are carried out on a laser ablation inductively coupled mass spectrometer (la-icp-ms; frei et al. 2006; frei & gerdes 2009). the sand is physically separated using a shaking table to concentrate the very heavy minerals. from this concentrate, the zircon is picked out and mounted (c. 150 zircon grains per sample) in epoxy. the mount is polished and introduced to the laser ablation system. a c. 30 µm diameter spot is ablated with the laser in the core of each zircon grain, and the ablated material is introduced into the icp-ms, in which the ratios between the different u and pb isotopes are measured. results from husby some results of analyses of six samples collected near husby (fig. 1) are discussed here. two samples are from till beds exposed in the coastal cliff, one is from a dune, one is from the active swash zone and two samples are from the shoreface, at water depths of 3 and 6 m. the grain-size distribution varies among the different heavy mineral species (fig. 2). zircon with the highest density is finer-grained than lighter minerals such as ilmenite and garnet, and the mafic silicates (amphibole, pyroxene and epidote) are the most coarse-grained of the heavy minerals. this is in close accordance with that predicted by stokes’ law, and implies that grain-size sorting has acted according to grainfall velocity. the steepness of the grain-size distribution curves also varies among the different minerals. the garnet curve is steeper and narrower than that of, for example, 27 0 500 1000 1500 2000 2500 3000 3500 4000 age (ma) 0 5 10 15 20 25 30 fr eq ue nc y 70249 husby (till 2) n = 91/113, 90–110% conc. r el at iv e pr o ba bi lit y 0 5 10 15 20 fr eq ue nc y 70248 husby (till 1) n = 108/139, 90–110% conc. r el at iv e pr o ba bi lit y 0 5 10 15 20 fr eq ue nc y 70230 husby (dune) n = 92/92, 90–110% conc. r el at iv e pr o ba bi lit y 0 5 10 15 20 25 30 35 fr eq ue nc y 70231 husby (swash zone) n = 123/124, 90–110% conc. r el at iv e pr o ba bi lit y 0 10 20 30 40 fr eq ue nc y 70229 husby (–3 m) n = 146/147, 90–110% conc. r el at iv e pr o ba bi lit y 0 5 10 15 20 25 fr eq ue nc y 70228 husby (–6 m) n = 129/129, 90–110% conc. r el at iv e pr o ba bi lit y fig. 4. age distribution of zircons in the samples from husby. the frequency (red histograms) indicates the number of zircons in the age brackets (100 ma). the green area indicates the content of concordant grains whereas the yellow area indicates the discordant grains (only present in the till samples). the samples from the shoreface (–3, –6 m) are characterised by two main populations, one with ages between 1000 ma and 1300 ma and one with ages between 1400 ma and 1900 ma, the latter being the most abundant. samples from the beach and dune contain the same populations, but are characterised by more equal proportions of the two populations. it can also be noticed that the samples from the till in the cliff behind the beach are characterised by a pattern similar to the samples from the shoreface. rosa_2008:rosa-2008 01/07/09 15:48 side 27 ilmenite or mafic silicates. this could be caused by differences in grain shape, and one of the aims of the project is to investigate how the grain-size distribution varies among the different sedimentary environments along the west coast of jylland. in provenance analysis it is often assumed that ratios between the heavy mineral species can be used as provenance indicators. due to analytical constraints, or chosen standard procedures, a given size-fraction (typically 63 to 125 µm; hallsworth & chisholm 2008; yang et al. 2009) is often used for such analysis, regardless of the fact that the sands which are compared have different overall grain-size distributions. as can be seen on fig. 2, for example, the modal proportions of the heavy minerals would not reflect the true values if only the fraction between 63 and 125 µm was analysed. the sample husby –6 m would be characterised by its finer part, with zircon being over-represented whereas the sample husby –3 m would be close to the modal value. in fig. 3, the modal proportions of the heavy minerals show that the composition of the heavy mineral fraction in the shoreface sands (–6 and –3 m) is similar but different to the beach sand and dune sands, which in turn resemble each other. the main difference between these two pairs is that garnet is more abundant in the beach and dune sands than in the shoreface sand. the heavy mineral assemblages from the tills exposed in the cliff are different to the beach and dune sands, but similar to the sand from the shoreface. figure 4 shows the age distributions of the zircon grains in the six samples. the samples show roughly the same spectra: a few archaean (>2500 ma) grains, an early proterozoic maximum (c. 2000–1500 ma), a middle proterozoic maximum (c. 1400–900 ma) and a caledonian peak (c. 400–300 ma). it is a characteristic feature of the shoreface sands and the till samples that early proterozoic zircons are more abundant than middle proterozoic zircons. in contrast, the two populations are equally represented in the beach and dune samples. the middle proterozoic zircons were probably de rived from the sveco-norwegian orogen in southern norway and western sweden to the north of jylland whereas the early proterozoic zircons were probably derived from jotnian and sveco-fennian sources to the east. both the mineral paragenesis data and the zircon age distributions suggest that the shoreface sands have a provenance that is distinct from the beach and dune sands at husby. this is surprising, and further work will concentrate on explaining these patterns, with the aim of understanding the processes responsible for the observed distribution of these sands. in addition, the distribution of heavy mineral assemblages along the shore will be analysed. references bernstein, s., frei, d., mclimans, r.k., knudsen, c. & vasudev, v.n. 2008: application of ccsem to heavy mineral deposits: source of high-ti ilmenite sand deposits of south kerala beaches, sw india. journal of geochemical exploration 96, 25–42. frei, d., hollis, j.a., gerdes, a., harlov, d., karlsson, c., vasquez, p., franz, g., johansson, l. & knudsen, c. 2006: advanced in situ geo chronological and trace element microanalysis by laser ablation techniques. geological survey of denmark and greenland bulletin 10, 25–28. frei, d. & gerdes, a. 2008: precise and accurate in situ u-pb dating of zircon with high sample throughput by automated la-sf-icp-ms. chemical geology 261, 261–270. hallsworth, c.r. & chisholm j.i. 2008: provenance of late carboniferous sandstones in the pennine basin (uk) from combined heavy mineral, garnet geochemistry and palaeocurrent studies. sedimentary geology 203, 196–221. keulen, n.t., frei, d., bernstein, s., hutchison, m.t., knudsen, c. & jensen, l. 2008: fully automated analysis of grain chemistry, size and morphology by ccsem: examples from cement production and diamond exploration. geological survey of denmark and greenland bulletin 15, 93–96. knudsen, c., frei, d., rasmussen, t., rasmussen, e. s. & mclimans, r. 2005: new methods in provenance studies based on heavy minerals: an example from miocene sands in jylland, denmark. geological survey of denmark and greenland bulletin 7, 29–32. larsen, m., knudsen, c., frei, d, frei, m., rasmussen, t. & whitham, a.g. 2006: east greenland and faroe–shetland sediment provenance and palaeogene sand dispersal systems. geological survey of denmark and greenland bulletin 10, 29–32. morton, a.c., herries, r. & fanning, c.m. 2007: correlation of triassic sandstones in the strathmore field, west of shetland, using heavy mineral provenance signatures. in: mange, m. & wright, d.t. (eds): heavy minerals in use. developments in sedimentology 58, 1037–1072. saye, s.e. & pye, k. 2006: variations in chemical composition and particle size of dune sediments along the west coast of jutland, denmark. sedimentary geology 183, 217–242. yang, s., wang, z., guo, y., li, c. & cai, j. 2009: heavy mineral compositions of the changjiang (yangtze river) sediments and their provenance-tracing implication. journal of asian earth sciences 35, 56–65. authors’ addresses c.k. & t.f.k., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: ckn@geus.dk t.a., j.b. & m.p., department of geography and geology, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. 28 rosa_2008:rosa-2008 01/07/09 15:48 side 28 geological survey of denmark and greenland bulletin 26, 2012, 9-12 9 nano-quartz in north sea danian chalk holger lindgreen and finn jakobsen the main oil reservoir in the central graben in the north sea is chalk of the maastrichtian tor formation, which has high porosity and relatively high permeability. the chalk of the danian ekofisk formation is an additional reservoir, but with highly variable porosity and permeability. whereas the tor formation is almost pure calcite primarily consisting of coccolith debris, the ekofisk formation also comprises significant proportions of phyllosilicates (clay minerals) and quartz in addition to coccolith debris. for decades the quartz was assumed to be a normal crystalline α-quartz such as is present in quartz sand, and the clay fraction was assumed to consist predominantly of phyllosilicates. however, maliva & dickson (1992) reported the presence of presumably authigenic submicron-size quartz crystals arranged in clusters, and suggested that these clusters were transformed opal-ct lepispheres. investigations by nano-structural methods (xray diffraction and atomic force microscopy (afm)) revealed that the prevailing quartz component in the north sea chalk comprises α-quartz appearing as nano-size quartz spheres ( jakobsen et al. 2000; lindgreen et al. 2010). nano-quartz spheres were first observed in indurated chalk in the ekofisk formation in the ekofisk field and later in the south arne field. subsequent analyses of the ekofisk formation in different chalk fields showed that the content of nano-quartz varies throughout the chalk succession and to some degree ref lects the cyclic development of the chalk. the proportion of dispersed nano-quartz in the chalk is highly variable, from 10% to more than 80% in the lower danian (lindgreen et al. 2010). this paper describes the nano-quartz, its formation and structure and presents a model for the formation of f lint from nano-quartz in the north sea ekofisk chalk. material and methods we have investigated core samples from the ekofisk formation in the south arne field wells sa-1 and rigs-1, in the halfdan field wells sif-1 and nana-1 and in the gorm field well n-22 (fig. 1). most samples contained large amounts of calcite, so calcite-free residues were prepared by dissolving the calcite in an acetate-acetic acid buffer at ph 4.5–5. in this buffer, non-calcite minerals and especially fine-grained nano-quartz and clay minerals are not corroded or dissolved. scanning electron microscopy (sem) is routinely used for investigations of chalk minerals and in special cases micronsized particles can be identified (hjuler & fabricius 2009). however, rock samples dominated by nano-sized quartz are at the limit of resolution in the sem and generally give poor sem images due to poor current transmission in the fine-grained matrix. we used x-ray diffraction and afm to characterise the ultra-fine particles in the chalk, such as nano-quartz and clay minerals. x-ray diffraction scanning using 10 s/0.1 °2θ was applied routinely to determine the mineralogical composition of both core piece samples and of non-calcite residues. high statistic scanning using 100 s/0.02 °2θ was used to characterise the nano-quartz. afm (binnig et al. 1986) generates topographic images by scanning a sharp tip across a surface and can produce images at atomic resolution of both conductors and nonconductors. for afm we used a rasterscope 3000 instrument under room conditions with a force of 0.175 nn and a scanning speed of 500 nm/s. in the present investigation of the topography of raw surfaces, afm was run in non-contact r in gkø b in g– fyn h igh gas in chalk oil in chalk field at other level 4°e 5°e 56°n c entral g raben 25 km national border rigs-1 sa-1 sif-1 nana-1 n-22 uk nl n dk 200 km g fig. 1. map of the danish central graben showing the locations of the investigated wells. © 2012 geus. geological survey of denmark and greenland bulletin 26, 9–12 . open access: www.geus.dk/publications/bull 1010 mode. intact rock samples of small pieces of chalk or f lint were glued onto gold-coated sample holders. in chalk samples, non-calcite minerals were identified and imaged from the insoluble residue. for such samples, the residue was dispersed ultrasonically in distilled water and the samples prepared by leaving a drop of the suspension to dry under room conditions on a block of highly oriented pyrolytic graphite. structure of the nano-quartz particles afm of non-calcite residues deposited on graphite showed that the nano-quartz consists predominantly of rather uniform, c. 600 å large spherical particles (fig. 2a). afm images of intact f lint surfaces showed that the f lint consists of similar spherical particles with a diameter of c. 500 å or more (fig. 2b) and some irregularly shaped particles. x-ray diffraction showed that the non-calcite residues and the f lint and quartz layers are composed of α-quartz having practically identical patterns and resembling the pattern of standard quartz (fig. 3). it is remarkable that the quartz in all the examined samples of dispersed quartz and f lint have almost identical unit cell a and c parameters and sizes of coherent scattering domains (lindgreen et al. 2011). at high angles peak broadening was pronounced for the nano-quartz particles and careful recording revealed a broad and distorted pattern of the (212), (203) and (301) ref lections compared to the ref lection from standard quartz (fig. 4). these distortions are due to larger a and c parameters compared to those of normal quartz (lindgreen et al. 2011). the nano-quartz spheres had colloidal properties and f locculated in suspensions with sufficient ionic strength, such as sea water (fig. 5). formation of quartz particles the nano-quartz spheres are anticipated to be of a type that might crystallise in a marine environment which is slightly enriched in silicon (williams & crerar 1985). the source of silicon was probably opal-a from radiolarians, which were the main silica-bearing organism in the chalk sea (maliva & dickson 1992). it is important that the non-crystalline si in radiolarians will dissolve at the low concentration of si, which is sufficient to precipitate fine quartz, and that the quartz will be the first silica phase to crystallise. a b 200 nm200 nm standard merck quartz sa 3344.15 m quartz in matrix nana 2135.7 m quartz in flint 80 81 °2θ 82 2 1 2 α 1 2 0 3 α 1 2 0 3 α 2 3 0 1 α 1 3 0 1 α 2 2 1 2 α 2 a b c fig. 3. a: x-ray diffraction pattern of standard merck quartz. b: of calcitefree residue from chalk, south arne field, well sa-1, 3344.15 m, c: and of f lint layer in halfdan field, well nana-1, 2135.7 m. co-k α radiation, 5% si added as internal standard. fig. 4. x-ray diffraction patterns. a: region of (212), (203) and (301) ref lections of standard merck quartz. b: the same region for calcite-free residue from chalk, south arne field, well sa-1, 3344.15 m. c: the same region for f lint layer in halfdan field, well nana-1, 2135.7 m. co-k α radiation. fig. 2. atomic force microscopy images of spherical grains of quartz. noncontact mode, room conditions, force 0.175 nn, scanning speed 500 nm/s. a: calcite-free residue deposited on graphite from well sa-1, 3344.15 m. b: intact f lint from nana-1, 2135.7 m. 20 30 40 50 60 70 80 90 standard merck quartz sa 3344.15 m quartz in matrix nana 2135.7 m quartz in flint si si si °2θ a b c 11 data from williams et al. (1985) indicate that the c. 500 å diameter quartz spheres observed in the chalk and in the f lint of the north sea danian chalk can form at sio2 concentrations of c. 12 ppm. the north sea chalk is a deep water deposit and present-day deep sea water has a concentration of 1–10 ppm sio2 (millot 1970; calvert 1974). we think that only a minor increase in si concentration would result in crystallisation of nano-quartz spheres. the colloidal quartz spheres could then have f locculated and been deposited on the sea f loor mixed with coccolith ooze. flocculation is important for sedimentation of silica and the rate of sedimentation for the formation of layers rich in quartz. chemical environment in the water column as described above, we assume that silica was not deposited as biogenic opal-a. therefore the variation in proportion of nano-quartz cannot be caused by changes in the supply of silicon to the sea as such changes would be ref lected in changes in size and mineralogy of the silica. an alternative is variation in the sedimentation of coccoliths. such variation may be due to a decrease in ph which may cause coccoliths to be partly or totally dissolved in the water column. such a decrease in ph requires significant amounts of an acidifier. this acidifying agent was most probably atmospheric co2 , which by mixing with sea water has been found to decrease the calcification of marine plankton (riebesell et al. 2000; feely et al. 2004). co2 released in large quantities during volcanic eruptions (holmes 1965; zimmer & erzinger 2003; frondini et al. 2004; schuiling 2004; self et al. 2006) could be a cause of the dissolution of the coccoliths in parts of the danian chalk deposits in the north sea. sensitivity analysis has indicated that only massive and short-lived volcanism could cause the caco3 undersaturation of seawater (berner & beerling 2007). age determinations of lavas from the british tertiary igneous province have yielded ages of 63–65 ma (saunders et al. 1997), corresponding to a danian age. we therefore propose that the pronounced quartz enrichment in the danian chalk of the north sea was associated with frequent volcanic eruptions in this period at and after the cretaceous–tertiary boundary. our model implicates that the degree of dissolution of the coccoliths in the sedimentary environment determines the proportion between calcite and nano-quartz in the chalk. theories for flint formation the new theory for the formation of f lint and dispersed nano-quartz in the north sea by crystallisation of nano-quartz in the marine environment is totally different from the generally accepted theory for f lint formation in chalk based on studies of chalk from onshore outcrops (bromley & ekdale 1986; clayton 1986; zijlstra 1987; madsen & stemmerik 2010). according to the current theory for f lint formation, opaline tests and sponge spicules in the sediment are dissolved during burial and the si is recrystallised as opal-ct and quartz in hollows and by replacement of calcite. however, the generally accepted theory does not agree with our results obtained for the silica in the investigated north sea chalk. we support our point of view by observing that the type of α-quartz dispersed in chalk is identical with the type constituting the f lint nodules and f lint horizons and with the type constituting the α-quartz horizons in the chalk. we find it highly unlikely that the same size and shape of particles will crystallise in the chalk and in the hollows during dissolution or reprecipitation, whereas the particles are of the type which can possibly crystallise in the marine environment that is slightly enriched in silicon (williams & crerar 1985). a sedimentary origin of the silica-rich chalk layers is supported by the presence of a f lint bed in well n-22. the f lint layer includes a calcite-filled burrow within fig. 5. flocculation of nano-quartz particles. residue from well sa-1, 3353.0 m. left: quartz dispersed in distilled water. right: quartz dispersed in 0.2 m cacl2 . dispersed in distilled water dispersed in 0.2m cacl2 1212 a matrix comprising nano-quartz spheres. the occurrence of a burrow in rather pure α-quartz sediment shows that the α-quartz was soft when biological activity took place. a sedimentary origin of the f lint fits well with our results for the north sea tertiary chalk, which is a deposit in relatively deep water. however, it cannot be generally applied to other areas and deposits in different settings without further investigations. conclusions we have proposed a new model for the formation of f lint in north sea chalk: (1) the nano-quartz in the f lint, like the nano-quartz in the chalk matrix, has crystallised in the marine chalk-sea environment. the colloidal quartz particles have then f locculated and have been deposited on the sea f loor mixed with coccolith ooze. (2) regional variations in the concentration of nano-quartz particles in the sediment ref lect different degrees of acidification of the chalk sea. (3) this resulted in areas with a high concentration of nanoquartz spheres that could form f lint layers. in areas with lower concentration of nano-quartz spheres, indurated chalk with abundant nano-quartz particles are now preserved. (4) the acidification may have been caused by enhanced atmospheric co2 linked to massive volcanic eruptions. references berner r.a. & beerling d.j. 2007: volcanic degassing necessary to produce a caco 3 undersaturated ocean at the triassic–jurassic boundary. palaeogeography, palaeoclimatolog y, palaeoecolog y 244, 368–373. binnig, g., quate, c.f. & gerber, ch. 1986: atomic force microscope. physics revue letters 56, 930–933. bromley r.g. & ekdale, a.a. 1986: flint and fabric in the european chalk. in: sieveking, g.d.g. & hart, m.b. (eds): the scientific study of f lint and chert, 71–82. cambridge: cambridge university press. calvert s.e. 1974: deposition and diagenesis of silica in marine sediments. international association of sedimentologists, special publication 1, 273–300. clayton c.j. 1986: the chemical environment of f lint formation in upper cretaceous chalk. in: sieveking, g.d.g. & hart, m.b. (eds): the scientific study of f lint and chert, 43–54. cambridge: cambridge university press. feely, r.a., sabine c.l., lee, k., berelson, w., kleypas, j., fabry, v.j. & millero, f. j. 2004: impact of anthropogenic co 2 on the caco 3 system in the oceans. science 305, 362–366. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: hl@geus.dk frondini, f., chiodini, g., caliro, s., cardellini, c., granieri, d. & ventura, g. 2004: diffuse co 2 degassing at vesuvio, italy. bulletin of volcanolog y 66, 642–651. hjuler, m.l. & fabricius, i.l. 2009: engineering properties of chalk related to diagenetic variations of upper cretaceous onshore and offshore chalk in the north sea area. journal of petroleum science and engineering 68, 151-170. holmes, a. 1965: principles of physical geolog y, 1288 pp. london: nelson. jakobsen, f., lindgreen, h. & springer, n. 2000: precipitation and f locculation of spherical nano silica in north sea chalk. clay minerals 35, 175–184. lindgreen, h., jakobsen, f. & springer, n. 2010: nano-size quartz accumulation in reservoir chalk, ekofisk formation, south arne field, north sea. clay minerals 45, 171–182. lindgreen, h., drits, v.a., salyn, a.l., jakobsen, f. & springer, n. 2011: formation of f lint horizons in north sea chalk through marine sedimentation of nano-quartz. clay minerals 46, 525-537. madsen, h.b. & stemmerik, l. 2010: diagenesis of f lint and porcellanite in the maastrichtian chalk at stevns klint, denmark. journal of sedimentary research 80, 578–588. maliva, r.g. & dickson, j.a.d. 1992: microfacies and diagenetic controls of porosity in cretaceous/tertiary chalks, eldfisk field, norwegian north sea. a apg bulletin 76, 1825–1838. millot, g. 1970: geolog y of clays, 429 pp. new york: springer. riebesell, u., zondervan, i., rost, b., tortell, p.d., zeebe, r.e. & morel, f.m.m. 2000: reduced calcification of marine plankton in response to increase atmospheric co2 . nature 407, 364–367. saunders, a.d., fitton, j.g., kerr, a.c., norry, m.j. & kent, r.w. 1997: the north atlantic igneous province. in: mahoney, j.j. & coffin, m.f. (eds): large igneous provinces. geophysical monograph series 100, 45–97. schuiling, r.d. 2004: thermal effects of massive co 2 emissions associated with subduction volcanism. comptes rendus geoscience 336, 1053–1059. self, s., widdowson, m., thordarson, t. & jay, a.e. 2006: volatile f luxes during f lood basalt eruptions and potential effects on the global environment: a deccan perspective. earth and planetary science letters 248, 518–532. williams, l.a. & crerar, d.a. 1985: silica diagenesis, ii. general mechanisms. journal of sedimentary petrolog y 55, 312–321. williams, l.a., parks, g.a. & crerar, d.a. 1985: silica diagenesis, i. solubility controls. journal of sedimentary petrolog y 55, 301–311. zijlstra, h.j.p. 1987: early diagenetic silica precipitation, in relation to redox boundaries and bacterial metabolism, in late cretaceous chalk of the maastrichtian type locality. geologie en mijnbouw 66, 343–355. zimmer, m. & erzinger, j. 2003: continuous h 2 o, co 2 , 222rn and temperature measurements on merapi volcano, indonesia. journal of volcanolog y and geothermal research 125, 25–38. geological survey of denmark and greenland bulletin 31, 2014, 91-94 91 surface albedo as a proxy for the mass balance of greenland’s terrestrial ice william colgan, jason e. box, robert s. fausto, dirk van as, valentina r. barletta and rene forsberg satellite observations are critical to understanding the mass balance of greenland’s terrestrial ice (fig. 1). the gravity recovery and climate experiment (gr ace) satellite constellation provides monthly gravimetry observations that can directly assess mass balance. temporal data gaps have begun to appear in the gr ace record due to declining satellite function. in anticipation of further deterioration in the coverage of gr ace, we have explored an empirical relation between ice-surface albedo (or reflectance) and ice-mass balance to fill the gaps in the gravimetry record of greenland’s ice-mass balance. as surface albedo observed by the moderate-resolution imaging spectroradiometer (modis) aboard the terra satellite is available in near real-time, employing a modisderived proxy permits near real-time estimates of greenland ice-mass balance. the geological survey of denmark and greenland has begun employing the albedo – mass-balance relation described here to issue near real-time estimates of greenland ice-mass balance during the summer melt season at www.polarportal.org. data and method we employ ice-mass balance data for greenland as assessed by the technical university of denmark monthly gr ace rl05 solutions from the 2003 to the 2012 summer melt seasons (may to september; barletta et al. 2013). monthly mass balance, calculated by node-centred finite differencing of this solution time series, is available for 44 out of 50 study-period months. single, missing monthly solutions ( jun 2003, jun 2011 and jul/aug 2012) prevent resolving mass balance for the months preceding and following the missing solutions (may/jul 2003, may/jul 2011 and jun/sep 2012; tedesco et al. 2013). the 1σ uncertainty associated with monthly mass balance calculated in this way ranges from 45 to 149 gt, with an average of 91 gt over the study period. we take this average value as representative of the uncertainty in gr acederived monthly mass balance. we employ the greenland ice-surface albedo observed by terra modis mod10a1 during clear sky conditions. clear sky conditions vary both temporally and spatially, especially in south greenland, where c. 25% of the modis scenes show clear sky. eleven-day running statistics are used to identify and reject <5% of the values within a given scene that exceed 2σ from the running multi-scene mean. to prevent rejecting potentially valid cases, data within 0.04 of the running multi-scene median are not rejected (box et al. 2012). mean monthly albedo is generated from these clear sky and filtered scenes for the melt-season months from 2003 to 2012. we compared the modis monthly albedo with in situ observations from the programme for monitoring of the greenland ice sheet (promice; van as et al. 2013) and the greenland climate network (steffen & box 2001), and found that the root mean squared error reached a minimum of 0.039 in may and a maximum of 0.085 in september. the bias between modis and in situ albedo, which was less than the root mean squared error in all months, ranged from –0.027 in june to 0.022 in september. we therefore take the 1σ uncertainty associated with the ice-sheet-wide modis monthly albedo to be 0.059 during the summer melt season, the average may © 2014 geus. geological survey of denmark and greenland bulletin 31, 91–94. open access: www.geus.dk/publications/bull 50°w 70°n 60°n albedo (no unit) 0.90 0.45 mass balance (kg/m2/a) 150 –1000 65°n 75° a b fig. 1. a: mean annual mass balance of greenland’s terrestrial ice, derived by an inversion of mass loss observed by satellite gravimetry that is constrained by satellite altimetry and fractional ice-coverage information (colgan et al. 2014). b: june to august mean albedo, derived by averaging all available clear sky albedo scenes, each of which has been filtered using running statistics to reject invalid data (box et al. 2012). both datasets span the period from 2004 to 2010 and share a common ice mask where the local ice fraction exceeds 0.5 at 26 km resolution. colour bars saturate at maximum and minimum values. 9292 through september root mean squared error between local in situ and modis observations. a portion of this apparent discrepancy likely results from footprint differences between in situ (c. 10 m2) and modis (c. 500 m2) albedo samples. using these gr ace-derived mass-balance and modisderived albedo records, we evaluate a single variable regression model to estimate monthly mass balance as a function of monthly albedo. monthly albedo (α) is strongly correlated with monthly mass balance (∂m/∂t) during the summer melt months within the study interval (r = 0.899, p <0.01; fig. 2a). this implies that the greenland ice-mass balance can be statistically approximated by t m a c 2 2 a= + where a is a coefficient equal to 1650 gt/month, and c is a constant of –1340 gt/month. a is the apparent sensitivity of mass balance to albedo (e.g. a 0.01 decrease in monthly average albedo corresponds to a 16.5 gt decrease in monthly mass balance), while c would be the theoretical minimum monthly mass balance when all solar radiation is absorbed (e.g. when α = 0). application two sources of error arise when estimating the greenland ice-mass balance via ice-surface albedo: the statistical uncertainty associated with albedo as a proxy for mass balance, and the underlying measurement uncertainty associated with resolving monthly mass balance. the monthly greenland ice-mass balances predicted by single variable albedo regression agree with the monthly mass balances observed by gr ace within a root mean squared error of ±32 gt/month. combining, in quadrature, this statistical uncertainty with the characteristic measurement uncertainty in the gr ace-derived greenland ice-mass balance (±91 gt/month), yields a total uncertainty in albedo-regressed mass balance of ±96 gt/month. we calculate uncertainty in, and assess stationarity of, a and c by calculating their values in overlapping four-year subsets of the ten-year study period. this subset analysis yields 1σ uncertainties associated with best-fit a and c parameters of 1650 ±400 and –1340 ±300 gt/month, respectively. an apparent increase in a and decrease in c over time are suggestive of an increase in mass-balance sensitivity to albedo over time. this is consistent with indications that surface mass balance is now the dominant mechanism of greenland ice loss (enderlin et al. 2014). the drift in both a and c, however, is statistically insignificant over the satellite record length presently available for analysis. within associated statistical uncertainty, we therefore suggest that average monthly ice-surface albedo is a stationary proxy for the monthly greenland ice-mass balance during the 2003 to 2012 melt seasons. 0.65 0.7 0.75 0.8 0.85 –350 –300 –250 –200 –150 –100 –50 0 50 100 albedo (no unit) m as s ba la nc e (g t/ m on th ) 0.4 0.5 0.6 0.7 0.8 –3000 –2500 –2000 –1500 –1000 –500 0 500 albedo (no unit) m as s ba la nc e (k g/ m 2 /a ) y = 1650x – 1340 r = 0.899 n = 44 y = 2230x – 1850 r = 0.694 n = 2615 a b fig. 2. mass balance versus albedo in time and space. a: greenland ice monthly mass balance derived from satellite gravimetry (barletta et al. 2013) versus monthly average albedo derived from satellite imagery (box et al. 2012), during may to september over the period from 2003 to 2012. b: local mean annual mass balance derived from an inversion of satellite gravimetry (colgan et al. 2014) versus local june to august mean albedo derived from satellite imagery (box et al. 2012), averaged over the 2004 to 2010 period and across the domain shown in fig. 1. solid and dashed lines denote ordinary least squares regression (2σ uncertainty envelope). 93 the utility of ice albedo as a proxy for ice-mass balance may be evaluated by comparing gr aceand modis-derived cumulative mass-balance anomalies and monthly massbalance rates. the albedo-regressed cumulative anomaly captures both the rate and magnitude of mass loss in each melt season between 2003 and 2012 (fig. 3a). albedo-regressed mass-balance rates, however, generally overestimate mass loss early in the melt season (–26 gt/month on average in may and june), and underestimate mass loss late in the melt season (+13 gt/month on average in august and september). the single largest residual is a mass-loss overestimate of –92 gt in june 2009 (fig. 3c). precipitation is recognised to decrease with air temperature, as a function of temperaturedependent absolute humidity. promice weather data suggest the june 2009 outlier is most likely due to anomalously cold air temperatures and little snowfall after the initiation of spring melt, which resulted in an anomalously low june surface albedo and melt rate. while cumulative anomalies compound any systematic biases over the course of a season, the magnitude and associated uncertainty of the albedo regressed, monthly mass-balance rates appear reasonable in the context of analogous gr ace values (fig. 3b). discussion and summary the mass balance of greenland’s ice reflects a combination of surface mass balance and underlying ice dynamic processes. the physical basis for surface albedo being a skilful proxy of surface mass balance is straightforward; albedo increases with fresh snowfall and decreases with melt or snowpack removal (fig. 2b). albedo therefore integrates the competing surface mass-balance processes of accumulation and ablation. snow or ice albedo directly influences meltwater profig. 4. understanding the relation between surface albedo and mass balance: a schematic overview of previously recognised linkages between increased meltwater runoff and enhanced ice loss in greenland (box & colgan 2013). many intermediate processes convert increased meltwater runoff into increased ice loss via either iceberg discharge or surface or basal mass balance. some processes involving ice-surface albedo and crevasses form positive feedback loops, potentially amplifying mass loss (colgan et al. 2011). a b c –2000 –1500 –1000 –500 0 500 1000 a no m al y (g t) grace modis –300 –200 –100 0 100 2003 2005 2007 2009 2011 ra te ( g t/ m on th ) grace modis 2003 2005 2007 2009 2011 2003 2005 2007 2009 2011 2013 2013 2013 ra te ( g t/ m on th ) year –100 –50 0 50 100 may june july august september fig. 3. a: cumulative mass balance anomaly for greenland’s ice observed by gr ace satellite gravimetry over the period from january 2003 to october 2012 (barletta et al. 2013), and the analogous albedo-regressed anomaly for may to september melt periods derived from modis satellite imagery. in each year, cumulative albedo-regressed mass loss is applied to the april anomaly assessed by barletta et al. (2013). b: melt season ice-mass balance rate (barletta et al. 2013), and the analogous albedoregressed rate when gr ace-derived values are not available. c: residual (modis-derived minus gr ace-derived) in monthly ice-mass balance during the may to september melt season. climate forcing enhanced process mass loss increased runoff marine convection cryo-hydrologic warming basal lubrication crevasse formation lake drainage submarine ablation terminus instability deformational velocity surface albedo sliding velocity albedo feedback crevasse feedback balance surface mass iceberg discharge balance basal mass 9494 duction and mass loss via runoff (hock 2005). the indirect links between decreased surface albedo (and increased meltwater runoff ) and enhanced mass loss via ice discharge from marine-terminating glaciers are numerous and diverse (fig. 4; box & colgan 2013). similar to surface-balance processes, however, processes enhancing ice dynamics, such as crevasses and supraglacial lakes, also generally decrease albedo with increasing mass loss. for example, as crevassed ice absorbs approximately twice as much solar radiation as non-crevassed ice, small changes in crevasse extent can substantially modify albedo. a >10% increase in crevasse extent since c. 1998 within a west greenland study area has been attributed to the acceleration of jakobshavn isbræ (colgan et al. 2011). crevasses can facilitate dynamic mass loss via enhanced terminus instability, as well as enhanced deformational velocity resulting from cryo-hydrologic warming. similarly, a low-albedo ‘dark zone’ forms in the elevation band where meltwater accumulates, both within the snow and firn, as well as in supraglacial lakes. within this ‘dark zone’, up to 40% of variability in annual mass balance is due to variability in summer ice-surface albedo (greuell 2000). in high-melt years, lakes form at higher elevations and have a higher probability of rapidly draining large water volumes to the subglacial hydrological system (liang et al. 2012). albedo ‘dark zone’ width is therefore directly proportional to the delivery of water to the ice–bed interface. given previously recognised strong links between albedo and surface mass balance (hock 2005), the high correlation between greenland ice albedo and mass balance that we have explored supports the notion that the majority of recent greenland ice-mass loss has occurred via meltwater runoff (enderlin et al. 2014). given the numerous and diverse previously postulated links between increased meltwater runoff and enhanced ice-dynamic mass loss, we suggest that a substantial portion of variability in dynamic mass loss is ultimately modulated by surface albedo and meltwater runoff (box & colgan 2013). the overarching inference from our preliminary data exploration is that a strong relation exists between greenland’s ice-surface albedo and mass balance, both through time and across space, and this merits further examination (fig. 2). as near real-time albedo monitoring has proved successful in qualitatively forecasting extreme greenland ice-mass loss events (box et al. 2012), the geological survey of denmark and greenland has begun employing the albedo regression described here to issue near real-time estimates of greenland ice-mass balance during the melt season at www.polarportal.org (fausto et al. 2013). acknowledgement this work is supported by the danish council for independent research, natural sciences (11-115166) and promice. references barletta, v.r., sørensen, l.s. & forsberg, r. 2013: scatter of mass changes estimates at basin scale for greenland and antarctica. the cryosphere 7, 1411–1432. box, j., fettweis, x., stroeve, j.c., tedesco, m., hall, d.k. & steffen, k. 2012: greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers. the cryosphere 6, 821–839. box, j. & colgan, w. 2013: greenland ice sheet mass balance reconstruction. part iii: marine ice loss and total mass balance (1840–2010). journal of climate 26, 6990–7002. colgan, w., steffen, k., mclamb, w.s, abdalati, w., rajaram, h., motyka, r.j., phillips, t. & anderson, r.s. 2011: an increase in crevasse extent, west greenland: hydrologic implications. geophysical research letters 38, l18502. colgan, w., abdalati, w., citterio, m., csatho, b., fettweis, x., luthcke, s., moholdt, g. & stober, m. 2014: hybrid inventory, gravimetry and altimetry (higa) mass balance product for greenland and the canadian arctic. the cryosphere discussions 8, 537–580. enderlin, e.m., howat, i.m., jeong, s., noh, m.-j., van angelen, j.h. & van den broeke, m.r. 2014: an improved mass budget for the greenland ice sheet. geophysical research letters 41, 866–872. fausto, r.s., colgan, w. & langen, p.l. 2013: real-time changes in arctic ice presented in online portal. eos, transactions of the american geophysical union 94, 397–398. greuell, w. 2000: melt-water accumulation on the surface of the greenland ice sheet: effect on albedo and mass balance. geografiska annaler 82a, 489–498. hock, r. 2005: glacier melt: a review of processes and their modelling. progress in physical geography 29, 362–391. liang, y.-l., colgan, w., qin, l, steffen, k., abdalati, w., stroeve, j., gallaher, d. & bayou, n. 2012: a decadal investigation of supraglacial lakes in west greenland using a fully automatic detection and tracking algorithm. remote sensing of environment 123, 127–138. steffen, k. & box, j. 2001: surface climatolog y of the greenland ice sheet: greenland climate network 1995–1999. journal of geophysical research 106, 33 951–33 964. tedesco, m., fettweis, x., mote, t., wahr, j., alexander, p., box, j.e. & wouters, b. 2013: evidence and analysis of 2012 greenland records from spaceborne observations, a regional climate model and reanalysis data. the cryosphere 7, 615–630. van as, d., fausto, r.s., colgan, w.t., box, j.e. and the promice project team 2013: darkening of the greenland ice sheet due to the meltalbedo feedback observed at promice weather stations. geological survey of denmark and greenland bulletin 28, 69–72. authors’ address es w.c., j.e.b., r.s.f. & d.v.a., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: wic@geus.dk v.r.b. & r.f., technical university of denmark dk-2800 kgs. lyngby, denmark. geological survey of denmark and greenland bulletin 35, 2016, 71-74 71© 2016 geus. geological survey of denmark and greenland bulletin 35, 71–74. open access: www.geus.dk/publications/bull in recent years, the greenland ice sheet has been losing mass at an average rate of 262 ± 21 gt yr–1 (2007–2011; andersen et al. 2015). part of this mass loss was due to increases in melt, reducing the surface mass budget (enderlin et al. 2014). also, the acceleration of many marine-terminating outlet glaciers increased the dynamic mass loss (rignot et al. 2008). both mass-loss mechanisms are linked to recent increases in atmospheric and oceanic temperatures (dutton et al. 2015). for instance, in summer 2012 greenland experienced exceptionally warm atmospheric conditions, causing nearly the entire ice-sheet surface to melt for two periods of several days (nghiem et al. 2012) and contributing to the largest annual ice-sheet mass loss on record (khan et al. 2015). this is in contrast to a return to more average conditions in 2015 (tedesco et al. in press). in 2007 the programme for monitoring of the greenland ice sheet (promice) was initiated to monitor both the surface mass budget and dynamic contributions to mass change. for the monitoring, c. 20 automatic weather stations were distributed over eight regions of the greenland ice sheet (fig. 1), primarily in the ablation area where surface melting is most prominent (van as et al. 2011). these stations record a suite of meteorological and radiative variables that allow for surface-energy budget closure, and reveal the relative importance of the different energy fluxes contributing to melting. each station also monitors ablation by sonic height rangers, pressure transducers and ablation stakes (fausto et al. 2012). table 1 shows that the 2015 melt season yielded ablation totals below the promice average (i.e. reduced surface mass loss) in all regions except the two northernmost ones: kpc and thu. along the south-western ice sheet margin the 2015 ablation anomalies appear to be one third below average. however, what has to be accounted for in the interpretation is that the promice observational period contained several warm years and summers. figure 2 illustrates that there have been considerable fluctuations in atmospheric temperatures at greenland coastal sites with continuous records dating back to the 19th century. the promice observational period distinctly classifies as one with aboveaverage temperatures, both in the relatively warm south and colder north (fig. 2). this is also likely to imply above-average ablation, and thus biased promice ablation anomalies. it is therefore more insightful to evaluate recent ablation measurements in the context of a more representative placing greenland ice sheet ablation measurements in a multi-decadal context dirk van as, robert s. fausto, john cappelen, roderik s.w. van de wal, roger j. braithwaite, horst machguth and the promice project team* * charalampos charalampidis, jason e. box, anne m. solgaard, andreas p. ahlstrøm, konstanze haubner, michele citterio and signe b. andersen fig. 1. map of greenland with 2015 ablation anomaly values referenced to the 1961–1990 period at the lower (suffix l) promice weather station sites. black dots indicate dmi weather stations selected for this study. 250 km qas_l nuk_l kan_l thu_l upe_l kpc_l tas_l station nord tasiilaq pituffik upernavik kangerlussuaq nuuk qaqortoq 14% sco_l ittoqqortoormiit –13% 184% –18% –1% 56% 67% 20% 7272 climate. greenland studies often use the 1961–1990 period, during which the ice sheet is assumed to have been in nearsteady state (e.g. braithwaite et al. 1992; rignot et al. 2008). the main aim of this study is to reference promice-measured ablation to this 1961–1990 ‘climate normal’. present-day temperatures in a multidecadal perspective in order to determine the 1961–1990 reference climate, we need observational records spanning that period and recent years. the only continuous and (on these time scales) relevant greenland data series that exist have been recorded in coastal areas, by weather stations of the danish meteorological institute (dmi). for this study we selected those dmi time series that were gathered closest to the promice weather station sites and were initiated before 1961 (fig. 1). the earliest measurements (primarily of air temperature) were taken in the 1700s; several continuous records date back to the mid to late 1800s (fig. 2). ice sheet surface melting occurs predominantly in summer, so for the purpose of this study we calculated the average june–july–august (jja) temperature for each year, following e.g. braithwaite et al. (1992). temperature anomalies were calculated by subtracting the 1961–1990 jja average. we obtained monthly average data from the dmi technical report 15-04 (cappelen 2015) and supplemented these with 2015 data. table 1 shows that at all selected dmi sites the jja temperature during the promice observational period is higher than in the reference period. the smallest difference is found at qaqortoq in south greenland (0.8°c), and the largest at ittoqqortoormiit in the east (2.4°c). for the years with promice annual ablation values (2008–2015), only three out of a total of 64 station years (5%) had negative jja temperature anomalies indicative of conditions colder than during the reference period, emphasising the need for a well-defined context. measurements of ice ablation along the ice-sheet margin the first promice weather stations were established in 2007 (van as et al. 2011), thus providing annual net-ablation values since 2008 (i.e. end of melt season 2007 until end of melt season 2008). at any given site five to eight years’ worth of ablation data exist. in this study we only make use of the eight weather stations that are located closest to the ice-sheet margin (all with suffix ‘l’ for ‘lower’). at these elevations, summer ablation is much larger than winter accumulation, resulting in stronger correlations between net ablation and atmospheric temperature anomalies than higher on the ice sheet where ablation becomes an increasingly small contributor to the surface-mass budget. selecting the ‘lower’ promice stations provides us with a total of 56 ablation years. table 1. temperature and ablation statistics for the promice weather station sites temperature jja 1961–1990 (°c) 1.7 2.7 5.5 6.5 5.5 9.2 4.1 3.9 temperature jja 2008–2015 (°c) 2.8 5.0 6.7 7.3 7.5 10.5 6.3 5.3 annual net ablation promice (m ice eq.) 2.2 3.2 3.6 6.4 5.5 3.8 2.6 1.8 2015 ablation anomaly ref. to the promice average (%) 7 –1 –14 –20 –31 –34 –12 30 annual net ablation 1961–1990 (m ice eq.) 1.4 2.7 2.7 5.1 4.4 3.1 1.5 0.8 temperature sensitivity (line slope) (m ice eq. °c–1) 0.71 0.25 0.79 1.23 0.64 0.63 0.55 0.89 correlation of linear fit (r) 0.59 0.50 0.60 0.75 0.83 0.71 0.81 0.94 rmsd* of linear fit (m ice eq.) 0.5 0.3 0.6 0.9 0.6 0.5 0.3 0.2 uncertainty ablation calculation (m ice eq.) 0.6 0.4 0.7 0.9 0.6 0.6 0.5 0.4 2015 ablation anomaly referenced to 1961–1990 (%) 67 ± 40 20 ± 15 14 ± 25 –1 ± 18 –13 ± 15 –18 ± 19 56 ± 31 184 ± 43 kpc_l sco_l tas_l qas_l nuk_l kan_l upe_l thu_l * rmsd: root mean squared differences −12 −9 −6 −3 0 3 1860 1880 1900 1920 1940 1960 1980 2000 2020 t e m p e ra tu re ( °c ) year upernavik nuuk qaqortoq promice period reference period fig. 2. annual (dots) and five-year (lines) running-mean temperatures at the three longest-running dmi measurement sites used in this study. arrows indicate the 1961–1990 reference period and the promice period (2007–present). 73 we supplement the promice data with older ablation observations gathered in close proximity to the current station locations, at identical elevations, and covering the entire ‘hydrological’ year, i.e. referenced to the end of the melt season. at four station sites, such measurements from before 2008 exist, namely at qas_l for 2001–2007 (e.g. podlech et al. 2004), at nuk_l for 1981–1987 (e.g. braithwaite et al. 1992), at k an_l since 1991 (van de wal et al. 2012) and at thu_l in 1954 (schytt 1955). these 40 historical measurements bring our grand total to 96 ablation years. present-day ablation in a multi-decadal perspective in this study we relate annual net-ablation values to jja temperatures following e.g. braithwaite et al. (1992), but without precipitation due to lacking dmi data. besides, differences in precipitation at the dmi and promice sites can be large due to spatial heterogeneity. in fig. 3 we plotted the annual net-ablation values against the temperature anomalies calculated from dmi weather stations in the region. at all sites, the ablation totals typically increase with temperature, as indicated by the linear least-squares fit lines. the slopes of these lines are the regional temperature sensitivities, which is relatively low at the sco_l site with 0.25 m ice equivalent (eq.) °c–1, and high for qas_l where roughly an additional 1.2 m of ice would ablate for every degree jja temperature increase (table 1). we find an average temperature sensitivity of the ice-marginal area of 0.71 ± 0.28 m ice eq. °c–1 (standard deviation given), rather similar to the value of 0.5 m water eq. °c–1 mentioned in e.g. braithwaite et al. (1992). a key element in this study is the ablation value at which the fitted lines intercept the 0°c temperature anomaly line, which for some sites requires extrapolation. the intercept values represent net ablation in the reference climate. most promice ablation values exceed the intercept values specific to their sites: ablation is larger in recent years than in the reference period. table 1 shows that the largest relative increase is found at thu_l, where we estimate annual net ablation to have increased by c. 120%. the reference period adjustment for promice ablation values is substantial at all sites (0.6–1.2 m ice eq., table 1). we need to be cautious in the interpretation of these results as the number of data points is still rather small. furthermore, one cannot expect a perfect correlation between ablation and temperature because: (1) melt is the result of a surplus in energy at the ice-sheet surface, of which only part is provided by atmospheric heat content, (2) the horizontal and vertical distances between the dmi and promice observation sites are considerable, and (3) winter accumulation is part of the net ablation signal but not a function of jja temperatures. as a measure of uncertainty of reference-period ablation due to the above, we calculate the root mean squared differences (rmsd) between the measured and calculated values. these range from 0.2 to 0.9 m ice eq. (table 1). to this we add a conservatively chosen measurement uncertainty in the annual net-ablation values of 0.3 m ice eq. (fausto et al. 2012), resulting in total uncertainties ranging from 0.4 to 0.9 m ice eq. the largest uncertainty is found for qas_l, likely due to interannual variability in winter accumulation and the station’s positioning in an irregular, crevassed terrain prior to its 1.5 km relocation in 2009. through the above re-referencing procedure the 2015, ablation anomalies become considerably larger (table 1, fig. 1). after reference adjustment, we find positive 0 2 4 6 8 −2 −1 0 1 2 3 4 a b la ti o n ( m i c e e q .) temperature anomaly (°c) kpc_l sco_l tas_l qas_l nuk_l kan_l upe_l thu_l fig. 3. measured annual net ablation from promice (dots) and other projects (circles) plotted against the regional temperature anomaly referenced to the 1961–1990 period. lines illustrate linear least-squares fits. 0 2 4 6 8 1860 1880 1900 1920 1940 1960 1980 2000 2020 a b la ti o n ( m i c e e q .) year kpc tas nuk upe sco qas kan thu fig. 4. estimated yearly (dots) and five-yearly (lines) net ablation for sites currently instrumented by promice. 7474 2015 anomalies for all sites except qas_l, nuk_l and k an_l, though these do not exceed their uncertainty ranges. the largest anomaly still occurs at thu_l, but is 184 ± 43% when referenced to the 1961–1990 climate, six times larger than the 30% value when referenced to the promice average. approximating past ablation the relations found between jja temperature and annual net ablation in fig. 3 can be used to estimate ablation from temperature in any year. in fig. 4 we used these functions for all summers for which dmi temperature data are available – though some of the earlier data were discarded to maintain continuity. we assume the uncertainties listed in table 1 to apply for these calculations as well, although it should be noted that the derived functions are less well constrained in the range with negative temperature anomalies (fig. 3). we conclude that at our study sites annual net ablation is likely to be larger in recent years than during any previous period in the instrumental era, covering up to 150 years. especially at the more northern locations we find that ablation increases in recent years are large. yet fig. 4 suggests that in southern greenland ablation peaked significantly around 1930. while most of greenland underwent relatively warm (summer) conditions in the 1930s (cappelen 2015), this was most notable at the more southern locations, resulting in amplified ablation values according to our estimates. jja temperatures were higher in 1928 and 1929 than in any other year of the qaqortoq record, both attaining values of 9.2°c. this suggests that ablation in those years may have exceeded the largest net ablation measured on the greenland ice sheet (9.3 m ice eq. at qas_l in 2010), although this is not beyond the uncertainty that accounts for important factors such as winter accumulation. acknowledgements this is a publication in the framework of the dancea-funded programme for monitoring of the greenland ice sheet (promice), in collaboration with several other projects. the k an stations are funded by the greenland analogue project (gap). stake measurements by utrecht university are funded through the nwo polar programme. references andersen, m.l. et al. 2015: basin-scale partitioning of greenland ice sheet mass balance components (2007–2011). earth and planetary science letters 409, 89–95. braithwaite, r.j., olesen o.b. & thomsen h.h. 1992: calculated variations of annual ice ablation at the margin of the greenland ice sheet, west greenland, 1961–1990. journal of glaciology 38 (129), 266–272. cappelen, j. (ed.) 2015: greenland – dmi historical climate data collection 1784–2014. danish meteorological institute technical report 15–04, 97 pp. dutton, a., carlson, a.e., long, a.j., milne, g.a., clark, p.u., deconto, r., horton, b.p., rahmstorf, s. & raymo, m.e. 2015: sealevel rise due to polar ice-sheet mass loss during past warm periods. science 349 (6244) aaa4019. enderlin, e.m., howat, i.m., jeong, s., noh, m.-j., van angelen, j.h. & van den broeke, m.r. 2014: an improved mass budget for the greenland ice sheet. geophysical research letters 41 (3), 866–872. fausto, r.s., van as, d., ahlstrøm, a.p. & citterio, m. 2012: assessing the accuracy of greenland ice sheet surface ablation measurements by pressure transducer. journal of glaciology 58 (212), 1144–1150. khan, s.a., aschwanden, a., bjørk, a.a.,wahr, j., kjeldsen, k.k. & kjær, k.h. 2015: greenland ice sheet mass balance: a review. reports on progress in physics 78, 046801. nghiem, s.v. et al. 2012: the extreme melt across the greenland ice sheet in 2012. geophysical research letters 39, l20502. podlech, s., mayer, c. & bøggild, c.e. 2004: glacier retreat, mass-balance and thinning: sermilik glacier, south greenland. geografiska annaler 86a, 305–317. rignot, e., box, j.e., burgess, e. & hanna e. 2008: mass balance of the greenland ice sheet from 1958 to 2007. geophysical research letters 35, l20502. schytt, v. 1955: glaciological investigations in the thule ramp area. report snow, ice, and permafrost research establishment 28, 88 pp. corps of engineers, u.s. army. tedesco, m. et al. in press: greenland ice sheet [in ‘state of the climate in 2015’]. bulletin of the american meteorological society 97(7). van as, d., fausto, r.s. & promice project team 2011: programme for monitoring of the greenland ice sheet (promice): first temperature and ablation records. geological survey of denmark and greenland bulletin 23, 73–76. van de wal, r.s.w., boot, w., smeets, c.j.p.p., snellen, h., van den broeke, m.r. & oerlemans, j. 2012: twenty-one years of mass balance observations along the k-transect, west greenland. earth systems science data 4, 31–35. authors’ addresses d.v.a., r.s.f., h.m., c.c., j.e.b., a.m.s., a.p.a., k.h., m.c. & s.b.a., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: dva@geus.dk h.m. also at department of geography, university of zurich, winterthurerstrasse 190, 8057 zürich, switzerland. k.h. also at natural history museum, copenhagen university, øster voldgade 5, dk-1350 copenhagen k, denmark. j.c., danish meteorological institute, lyngbyvej 100, dk-2100 copenhagen ø, denmark. r.s.w.v.d.w., institute for marine and atmospheric research, utrecht university, princetonplein 5, 3584 cc utrecht, the netherlands. r.j.b., school of environment, university of manchester, oxford road, manchester m13 9pl, uk. geological survey of denmark and greenland bulletin 31, 2014, 75-78 75 earthquake swarms in greenland tine b. larsen, peter h. voss, trine dahl-jensen and hans peter rasmussen two earthquake swarms have been detected in greenland. one occurred on the island of disko in august 2010, the other one was active from january 2008 to june 2009 near the south-east greenland coast c. 200 km south of tasiilaq. an earthquake swarm is defined as a series of earthquakes of similar magnitude located within a small area. the magnitude of the largest earthquakes in a swarm is typically less than 4 (ma & eaton 2009). swarm activity is distinctly different from the more common mainshock–aftershock activity, which is characterised by one large earthquake (mainshock) followed by a series of smaller aftershocks. earthquake swarms mainly occur in areas with tectonic and/or volcanic activity (stykes 1970), but intraplate swarms are also found in otherwise stable environments (gregersen 1979; atakan et al. 1994; uski et al. 2006; ma & eaton 2009). geological boundaries and old fault zones appear to be a common setting for intraplate earthquake swarms. earthquake swarms have previously been detected in north and north-east greenland (gregersen 1979) at a time when the seismograph coverage was very sparse. it was concluded that the earthquake swarms were caused by tectonic stresses in and around old sedimentary basins near the continental margin. in this study we take advantage of the recently improved network of digital broadband seismographs in greenland (dahl-jensen et al. 2010). the shorter distance between seismograph stations and the high quality digital data enable us to better detect small earthquakes. we have focused on the last decade during which the digital network has gradually been established (fig. 1). we revisited the two regions where swarms have previously been detected, in north greenland and in north-east greenland (gregersen 1979). searching the geus earthquake database for recent earthquakes showed nothing in the area of the north greenland swarm. the swarm described by gregersen (1979) was primarily detected using data from a canadian station (ale) and a temporary station on the ice sheet, supplemented with data from station nord (nor) for the largest earthquakes in the swarm. this particular region has not experienced an increase in station coverage in recent years. it is therefore impossible to distinguish whether the lack of recent detections is due to a lack of activity in that area. the location of the north-east greenland earthquake swarm has also been searched without finding any new swarm activity in the last decade. only two small earthquakes have been detected in the area, one in 2008 and another in 2011. in this area the station coverage has improved since 1974, so the lack of detections reflects that the area is currently seismically quiet. two new localities with earthquake swarms were uncovered in this study (fig. 1). both are areas with regular seismic activity. one swarm is located on the island of disko near the disko gneiss ridge (fig. 2) where a fault zone runs n–s through the island (chalmers et al. 1999). this is a very distinct swarm with its main activity concentrated on two days © 2014 geus. geological survey of denmark and greenland bulletin 31, 75–78. open access: www.geus.dk/publications/bull dag sco sfjd nrs nuuk sumg angg (in tasiilaq) dy2g dbg soeg nor ale iluli kullo tuleg isog ivi nuug icesg upnv fig. 2 fig. 3 250 km 60°n 60° 50° 40° 30° 20° 10° 0° 40°w 80°n 70° disko umiivik archaean volcanic rocks palaeozoic fold belts sedimentary basins and intrusions reworked archaean palaeoproterozoic precambrian shield neem fig. 1. geological map of greenland with seismograph stations marked by triangles. the locations of the swarms found by gregersen (1979) are marked with red circles. the locations of the swarms presented in this study are marked with black boxes. 7676 in late august 2010, followed by slightly increased seismicity during the following two months. the other swarm is located in a remote area near the south-east greenland coast, c.  200 km south of tasiilaq (fig. 3). this swarm is less distinct with two main pulses of activity in january 2008 and spring 2009. this area had increased seismicity for a year and a half, before it tapered off. the objective of this paper is to describe the two newly discovered earthquake swarms and how they relate to the local geology. data and analysis seismographs have been continuously operating in greenland since 1927 (hjelme 1996). originally the instruments were large, difficult to install and labour intensive to maintain. it was only possible to operate a few stations in greenland. this changed with the development of digital instruments, and during the last decade a network of 20 digital broadband seismographs with real-time data transmission has been installed in greenland (fig. 1). this massive undertaking is a result of the international collaboration in the greenland ice sheet monitoring network (glisn) project with funding from around the world (dahl-jensen et al. 2010). the latest seismological station was installed in upernavik in 2013 by the korean polar research institute (see upnv fig. 1). data from the real-time network of seismographs are processed daily at geus using the seisan analysis software (ottemöller et al. 2013). earthquake phases are manually identified and combined to form earthquake locations when possible. locations and phase readings are kept in the geus database for future reference. this includes phase readings not associated with an earthquake location. all the raw waveform data are also stored. the new earthquake swarms were discovered by performing a search in the database around locations, where clustering of seismicity was observed on a map of all earthquakes in greenland. the search results were then examined for possible clustering of events in time. two earthquake clusters fulfilled the criteria defining an earthquake swarm. despite the improved station coverage, it is still challenging to determine the focal mechanism of most earthquakes in greenland. particularly the small swarm earthquakes that are only registered on one to four seismographs, which is insufficient for reliable focal mechanism calculations. earthquake swarm at the island of disko disko and the surrounding areas are frequently shaken by small earthquakes, some large enough to be felt by the locals. disko is also known for its warm springs formed where circulating surface water penetrates into the subsurface through deep cracks and is heated by the higher temperatures at depth. the flow of a warm spring is sometimes changed by a small earthquake, indicating that the earthquake sources are shallow. there are thousands of springs with constant temperature on disko. the temperatures in individual springs vary between 1°c and 18.5°c (kristensen 2006). the number of earthquakes detected near the southern end of the disko gneiss ridge per year for 2006–2013 varies between one and ten (fig 4a). however, 2010 stands out with 27 detected earthquakes. the earthquake activity was particularly intense on 22 and 23 august (fig 4b). the earthquakes ranged in magnitude from 1.9 to 3.2 with most lower tertiary basalts upper cretaceous and lower precambrian basement tertiary sediments fault10 km 69°30´ storbræen disko fjord 55°w fig. 2. the calculated epicentres for the swarm earthquakes on disko, west greenland. the disko gneiss ridge runs along the fault line on the map. reworked archaean archaean 64°30´ 10 km umiivik 42°w 64°n 64°30´n 64°n 40°w 40°w fig. 3. the calculated epicentres for the swam earthquakes near umiivik, on the south-east greenland coast. 77 clustering in the magnitude range between 2.2 and 2.8. the earthquake epicentres were spread out over a small area with the largest distance between two events being about 30 km. this distance is within the uncertainty on the locations. the uncertainty on the epicentres is in the order of 10 km in n–s direction and at least 50 km in e–w direction. this is caused by the geometry of the network relative to the events with seismographs primarily located north and south of the epicentres. as fig. 2 shows, the scatter in the epicentres was indeed largest in e–w direction. the closest seismograph where all earthquakes were registered is located in ilulissat (iluli) 110–120 km away. the earthquakes were also registered in nuugaatsiaq (nuug) c. 220 km to the north, in kangerlussuaq (sfjd) 320 km to the south and at the summit ice camp (sumg) 650 km towards the north-east. a few earthquakes were registered on a total of eight seismographs in greenland, but most of them were registered in just four locations. the depth of the earthquakes is poorly determined, but appears to be shallow. a major challenge in determining the depth is the limited knowledge of the crustal velocity structure. the depth to moho is known from receiver function studies (dahl-jensen et al. 2003), and the crustal density structure in the disko area has been modelled from seismic and potential field data (chalmers et al. 1999). relocating the earthquakes with a fixed depth of 5 km does not reduce the distance between the epicentres significantly. however, the variation in time difference between the p-wave arrival and the s-wave arrival was less than 1.5 sec. indicating a small source region. the north–south-oriented fault along the disko gneiss ridge is a known zone of weakness, and the area is characterised by a moderate earthquake activity with no seasonal variation. in se finland earthquake swarms are observed to be related to the intrusion of water and gas into fractures working in concert with the local stress field (uski et al. 2006). a similar mechanism is likely on disko. as warm water is circulating in deep cracks all year round a seasonal variation is not expected. some of the warm springs on disko are radioactive (kristensen 2006) containing radon from the basement. radon is also observed near earthquake swarms in finland, and radon gas is believed to play a minor role in triggering earthquake swarms in se finland (uski et al. 2006). earthquake swarm in south-east greenland the east coast of greenland is frequently shaken by small earthquakes. in tasiilaq earthquakes are felt almost every year. many small earthquakes are registered farther down the coast, but it is not known if any of these events can be felt as the area is not populated. earthquake swarm activity was detected in january 2008 and in the spring of 2009 just off the coast near umiivik. the earthquakes in the swarm range in magnitude from 1.8 to 3.8. in the years before and after the swarm period, the level of earthquake activity in the area range between 12 and 21 earthquakes per year (fig. 5a). however, in 2008 and 2009 respectively 71 and 114 earthquakes were registered. the earthquakes occurred primarily in january and april 2008 and again from january to july 2009 (fig. 5b). the uncertainty on most of the epicentres is several hundred kilometres in both the n–s and e–w directions. this is a consequence of the earthquakes being detected primarily by only two seismographs (four phases in total) in kangerlussuaq (sfjd) and at summit (sumg) 550 km and 1000 km from the epicentres. the distance between the seismographs and the epicentres is well-determined, but the direction is poorly constrained. after improvements had been made to the seismograph network, a larger earthquake with a magnitude of 3.6 occurred in the area on 13 october 2009. this earthquake was well-recorded at four locations: narsarsuaq (nrs), kangerlussuaq (sfjd), ilulissat (iluli) and summit (sumg) with an uncertainty of less than 10 km in n–s direction and less than 20 km in e–w direction. this earthfig. 5. a: number of earthquakes per year for the period 2006–2013 around the location of the earthquake swarm at the se greenland coast. b: number of earthquakes per month from january 2008 to july 2009 in the same area. 0 1 2 3 4 5 20 /0 820 10 21 /0 820 10 22 /0 820 10 23 /0 820 10 24 /0 820 10 25 /0 820 10 26 /0 820 10 27 /0 820 10 28 /0 820 10 29 /0 820 10 30 /0 820 10 0 5 10 15 20 25 2006 2008 2010 2012 year date n um be r of e ar th qu ak es n um be r of e ar th qu ak esa b disko fig. 4. a: number of earthquakes per year for the period 2006–2013 around the location of the earthquake swarm on disko. b: number of earthquakes per day from 20 to 30 august 2010 in the same area. ja n ja n m ar m ay ju l se p n ov m ar m ay ju l2006 2008 2010 2012 year month (2008 and 2009) n um be r of e ar th qu ak es n um be r of e ar th qu ak es 0 20 40 60 80 100 0 5 10 15 20 a bse greenland 7878 quake is located near the centre of the cloud of epicentres, and it can be used to evaluate the relative locations of the swarm earthquakes. the waveforms for the small earthquakes are very noisy, making a direct comparison difficult. instead we examine the variation in time difference between the p-wave and swave arrival for individual earthquakes. despite the epicentres being scattered over almost 100 km in n–s direction and c. 50 km in e–w direction, the variation in s–p time (i.e. the distance to the earthquake) at each seismograph station fluctuated only in rare cases by more than 1.5 sec. relative to the 13 october 2009 earthquake. the large scatter in epicentres is probably an artefact of the focal depth being unconstrained. the umiivik area marks a major geological transition between the relatively unreworked archaean rocks to the south and rocks highly deformed in the proterozoic to the north (henriksen et al. 2009). offshore the existence of a failed rift arm was proposed by hopper et al. (1998). the earthquake swarm was thus located close to two old geological boundaries. this is in good accordance with the general observations by stykes (1978) that intraplate earthquakes indeed occur in old zones of weakness. conclusion as shown by this initial search for earthquake swarms, the improvements to the seismograph network in greenland enable us to better uncover and analyse swarms in the future. the swarms presented in this paper could not have been detected a decade ago. intraplate earthquake swarms can contribute to the understanding of geological processes currently at work near old geological boundaries in remote areas. both swarms presented here were active near old geological boundaries. the swarm on disko is located at the southern end of the disko gneiss ridge where a large fault runs through the island. circulating water in deep cracks may possibly play a role. the se greenland swarm is located close to a major geological boundary between reworked and unreworked archaean rocks. furthermore, the swarm is close to the proposed location of a failed rift arm in the atlantic. finding earthquake swarms close to old, major, geological boundaries is well in accordance with the literature. the earthquake swarms presented in this paper are not associated with known sedimentary basins such as the swarms described in gregersen (1979). this indicates a diversity of swarm sources in greenland. further work will be carried out on the earthquake swarms in greenland and data from temporary and canadian seismographs will be included in the analysis. acknowledgement the data were collected and distributed by the glisn project and its members, www.glisn.info. references atakan, k., lindblom, c.d. & havskov, j. 1994: earthquake swarm in steigen, northern norway: an unusual example of intraplate seismicity. terra nova 6, 180–194. chalmers, j.a., pulvertaft, t.c.r., marcussen, c. & pedersen, a.k. 1999: new insight into the structure of the nuussuaq basin, central west greenland. marine and petroleum geolog y 16, 197–224. dahl-jensen, t. et al. 2003: depth to moho in greenland: receiver function analysis suggests two proterozoic blocks in greenland. earth and planetary science letters 205, 379–393. dahl-jensen, t., larsen, t.b., voss, p.h. & the glisn group 2010: greenland ice sheet monitoring network (glisn): a seismological approach. geological survey of denmark and greenland bulletin 20, 55–58. gregersen, s. 1979: intraplate earthquake swarms in greenland and adjacent continental regions. nature 281, 661–662. henriksen, n., higgins, a.k., kalsbeek, f. & pulvertaft, t.c.r. 2009: greenland from archaean to quaternary. descriptive text to the geological map of greenland 1:2 500 000. 2nd edition. geolog y of greenland survey bulletin 18, 126 pp. hjelme, j. 1996: history of seismological stations in denmark and greenland. in: wahlström, r. (ed.): seismograph recording in sweden, norway – with arctic regions, denmark – with greenland, and finland. proceedings from the uppsala wiechert jubilee seminar, 49–57. uppsala: seismological department, uppsala university, sweden. hopper, j.r., lizarralde, d. & larsen, h.c. 1998: seismic investigations offshore south-east greenland. geolog y of greenland survey bulletin 180, 145–151. kristensen, r.m. 2006: de varme kilder. in: bruun, l. et al. (eds): arktisk station 1906–2006, 310–315. copenhagen: r hodos. ma, s. & eaton, d.w. 2009: anatomy of a small earthquake swarm in southern ontario, canada. seismological research letters 80, 214– 223, http://dx.doi.org/10.1785/gssrl.80.2.214 ottemöller, l., voss, p.h. & havskov, j. 2011: seisan earthquake analysis software for windows, solaris, linux and macosx. university of bergen. stykes, l.r. 1970: earthquake swarms and sea-floor spreading. journal of geophysical research 75, 6598–6611. stykes, l.r. 1978: intraplate seismicity, reactivation of pre-existing zones of weakness, alkaline magmatism, and other tectonism postdating continental fragmentation. reviews of geophysics and space physics 16, 621–688. uski, m., tiira, t., korja, a. & elo, s. 2006: the 2003 earthquake swarm in anjalankoski, south-eastern finland. tectonophysics 422, 55–69. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark; e-mail: tbl@geus.dk geological survey of denmark and greenland bulletin 28, 2013, 61-64 61 calibration of spectral gamma-ray logs to deltaic sedimentary facies from the cretaceous atane formation, nuussuaq basin, west greenland gunver krarup pedersen, niels h. schovsbo and henrik nøhr-hansen gamma-ray logs are widely used as a lithology indicator in wells as part of standard petrophysical interpretations. in cored wells, gamma-ray logs should always be calibrated to the lithology in order to correct the petrophysical model. gamma radiation is emitted from three elements, k, th and u (potassium, thorium and uranium) which occur in minerals such as feldspar, mica, glauconite, clay minerals, zircon, titanite and apatite as well as in organic complexes. organicrich mudstones usually have high gamma-radiation values and quartz-rich sandstones low values. in many places, upward-coarsening successions are recognisable from the gamma log. the gamma log records the sum of radiation from k, th and u, and their relative contributions are measured in a spectral gamma-ray log. the present case study focuses on spectral gamma-ray characterisation of the deltaic atane formation which shows well-developed, upward-coarsening delta-front deposits in outcrops (fig. 1c). geological setting the nuussuaq basin is a rift basin, which contains the only exposures of cretaceous and paleocene sediments along the west coast of greenland. the siliciclastic sediments are overlain by a thick pile of volcanic rocks (chalmers et al. 1999; dam et al. 2009). during late cretaceous, greenland was characterised by a warm and probably humid climate. the sediments range from alluvial fans overlying deeply weathered precambrian basement through marginally marine deposits to marine deep-water deposits, all referred to the nuussuaq group (dam et al. 2009). the f loodplains and delta plains had a rich f lora, recorded in well-preserved plant fig. 1. a: geological map of central west greenland showing the location of ataata kuua on the south coast of nuussuaq. b: the atane formation is erosionally overlain by the kangilia formation in the western slope of ataata kuua. the yellow dot marks the drilling site of borehole 247801, d: dyke. height of section c. 500 m. the frame shows the position of fig. 1c. c: the atane formation with depositional environments indicated. note the distinct coarsening-upward successions (triangles). height of section c. 100 m. © 2013 geus. geological survey of denmark and greenland bulletin 28, 61–64. open access: www.geus.dk/publications/bull greenland 70° disko 50 km nuussuaq 53° volcanics ataata kuua precambrian cretaceous sediments atane formationatane formation a c b c kangilia formation 13 0 m d d d 247801 delta front delta plain shoreface channel 60 m 6262 fig. 2. data from borehole 247801: a simplified sedimentological log of the entire core (566 m), a gamma log measured in the borehole to a depth of 320 m, and the new range chart for the dinof lagellate cysts in core samples. api: american petroleum institute units. ggu 247801 is located at 70°19.87´n, 52°55.8´w. the framed interval is shown in fig. 3. the drill site is shown in fig. 1b. d ep th (m ) 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 500 525 550 c hr on o. la te c re ta ce ou s pe ri od /e po ch ea rl y c on ia ci an – e ar ly s an to ni an a ge sa m pl es 23.70 43.90 54.35 91.50 118.05 138.55 149.70 182.40 219.00 239.60 256.65 290.85 336.20 360.45 391.00 405.30 433.60 464.00 485.70 519.60 545.70 cl ei st os ph ae rid iu m m ul tif ur ca tu m isa be lid in iu m s pp . o do nt oc hi tin a sp p. ra ph id od in iu m fu ca tu m tr ith yr od in iu m s us pe ct um ch at an gi el la d iti ss im a ch at an gi el la g ra nu lif er a ci rc ul od in iu m d ist in ct um h et er os ph ae rid iu m d iff ici le la cin ia di ni um a rc tic um o do nt oc hi tin a op er cu la ta o lig os ph ae rid iu m a lb er te ns e o lig os ph ae rid iu m s pp . pa la eo hy st ric ho ph or a in fu so rio id es sp in id in iu m c f. ec hi no id eu m sp in id in iu m s pp . sp in ife rit es s pp . ta ny os ph ae rid iu m s pp . isa be lid in iu m m ag nu m fr om ea fr ag ilis isa be lid in iu m c oo ks on ia e pa la eo pe rid in iu m p yr op ho ru m ch at an gi el la s pp . tr ith yr od in iu m s pp . ex oc ho sp ha er id iu m s pp . su rc ul os ph ae rid iu m lo ng ifu rc at um h et er os ph ae rid iu m h et er ac an th um pa ra le ca ni el la in de nt at a al te rb id in iu m s pp . ch at an gi el la m cin ty re i se ne ga lin iu m s pp . pa la eo cy st od in iu m s pp . ? dinoflagellate cysts ru gu bi ve sc icu lit es ru go su s ru gu bi ve sic ul at es re du ct us ap pe nd ici sp or ite s cf . in sig ni s ? ? ? ? ? ? ? ???? ?? ?? ? ?? ? ? ? ? ? ? sp events chatangiella mcintyrei heterosphaeridium difficile palaeoperidinium pyrophorum spinidinium cf. echinoideum, chatangiella ditissima, chatangiella granulifera, heterosphaeridium difficile trithyrodinium suspectum, rugubivesciculites rugosus, isabelidinium spp. 0 100 200 api base top 200 250 300 350 400 450 500 550 tr tr tr tr tr tr 50 100 20 m 150 tr tr tr core from borehole ggu 247801 a ta ne f or m at io n q ila ki ts oq m em be r delta front channel delta plain coal shoreface 63 macrofossils and abundant comminuted plant debris. a huge volume of non-marine to shallow marine deposits constitutes the cretaceous atane formation, which is well exposed along 65 km of the south coast of nuussuaq from sea level to altitudes of 500–800 m. seismic data indicate a minimum thickness of 3000 m for the formation (dam et al. 2009). ataata kuua – a narrow f luvial valley at ataata kuua, on the south coast of nuussuaq (fig. 1), shows the deltaic atane formation erosively truncated and overlain by the turbiditic, paleocene kangilia formation (dam et al. 2009). in 1980, the geological survey of greenland drilled a 566 m deep borehole (ggu 247801) at ataata kuua as part of a regional study of the composition and distribution of coal in the atane formation. the entire succession was cored, with 100% recovery, and a gamma log was measured in the upper 320 m of the borehole. this gamma log as well as a simplified sedimentological log of the entire core are shown adjacent to the new biostratigraphical range chart in fig. 2. biostratigraphy – in recent studies of 21 delta-front mudstone samples from core 247801, palynomorphs have been examined (fig. 2). the diversity and density of dinof lagellate cysts, spores and pollen are very low, but the presence of chatangiella granulifera, heterosphaeridium difficile and spinidinium cf. echinoideum in the lower part and chatangiella mcintyrei and spinidinium cf. echinoideum in the middle to upper part indicates an early coniacian age or younger. an early santonian minimum age of the upper part of the core is indicated by the presence of rugubivesciculites spp., the absence of campanian marker species and by the presence of heterosphaeridium difficile, laciniadinium arcticum and spinidinium cf. echinoideum in a sample from the ataata kuua 2004-3 section situated immediately above the site of borehole 247801. the relatively uniform dinof lagellate assemblage recorded throughout the core (fig. 2) supports the interpretation of a relatively high sedimentation rate. sedimentology – the delta deposits of the atane formation represent four depositional environments: delta front, distributary channel, delta plain and shoreface (figs 1c, 2, 3). the delta-front deposits include mudstones, heterolithic sandstones with wave-generated sedimentary structures and wellsorted sandstones, all with comminuted plant debris. the distributary channel deposits are mostly cross-bedded, mediumto coarse-grained sandstones with some feldspar grains. the delta-plain mudstones are interbedded with coal beds or thin sandstone beds. the thin shoreface sandstones contain abundant marine trace fossils and overlie erosive surfaces. the delta-front deposits and the overlying f luvial sandstones form distinctly upward-coarsening units (figs 1c, 2, 3), interpreted as formed during delta progradation. the shoreface sandstones are interpreted as deposited during a transgression. a detailed log of the core is shown in dam et al. 2009 (fig. 43). the dominant minerals in the mudstones are quartz and kaolinite, neither of which contain more than traces of k. small amounts of k-feldspar and mica result in a k content about 1.3–1.8% k2o, significantly lower than the 2.7% k2o of average mudstones (rider 1990). all mudstones and many sandstones in the atane formation contain comminuted debris from higher land plants. total organic carbon (toc) values of the non-marine delta-plain mudstones range from 3 to 15% and include thin coal beds with 50–65% toc (pedersen et al. 2006). the marine delta-front mudstones contain 6–14% toc, with the highest values in the finegrained, lower part, which includes a f looding surface and had a low sedimentation rate. despite this, marine organic particles, such as dinof lagellate cysts, only form a small part compared to terrestrial organic matter. the gamma log obtained in the borehole shows, as expected, low values for the f luvial sandstones whereas the mud-dominated delta-front and delta-plain deposits are difficult to identify from the gamma log alone (fig. 2). in order to document the contributions of k, th and u to the total gamma radiation we measured the spectral gamma radiation (fig. 3). k is mainly located in feldspar, mica and glauconite; th and u are hosted in zircon, titanite, and apatite. clay minerals may contain small amounts of th, and organic complex compounds may contain u. spectral gamma-ray characterisation core scanning – the core interval was scanned at the core laboratory at the geological survey of denmark and greenland using a set-up which allows simultaneous spectral gamma-ray and density measurements. the spectral gamma-ray analysis is carried out using two 15 cm nai (tl) crystals and the bulk density is determined using a caesium source. the scanning speed was 1 cm/min., corresponding to a vertical resolution of approximately 2 cm for the density log. the scanning data thus supply high resolution data to support sedimentary and geochemical data from the core, as exemplified in fig. 3. results – the upward-coarsening successions, which are clearly seen in the field and in the core (figs 1c, 2, 3), are difficult to identify on the total readings of the spectral gamma log (fig. 3). the grain-size trends are, however, ref lected in the th and k logs, which are negatively correlated. the mudstones have high th and low k contents, whereas the sandstones have high k and low th contents. no distinct 6464 relationship between high u content and mudstone grainsize is seen. ruffell et al. (2003) presented a model for the f lux of k, u and th in different weathering systems at basin scale. one of their scenarios is a basin with a low-relief hinterland and a humid climate, which applies to the depositional setting of the atane formation. the model predicts that chemical weathering dominates and that k and u are removed in solution to sea water, while th is concentrated in detrital clay. this model may explain the relatively high th radiation in the detrital mudstones of the atane formation. k-feldspar is a minor constituent of the sandstones but contributes significantly to the k-radiation in the sandstones. the model further predicts that k and u are enriched in authigenic minerals in the basin. such enrichment of u is not observed in the atane formation, possibly due to the relatively high sedimentation rate. the low u content may also ref lect the predominance of land plants (type iii kerogen) that generally contain small amounts of u in organic complexes compared to marine organic material. a comparison of sedimentological logs from delta-front successions with their total gamma radiation in a case study from ireland also indicates that the delta-front successions are difficult to identify from the gamma log alone (davies & elliott 1996). summary the present study demonstrates the importance of calibrating petrophysical logs to core data. the cyclicity which characterises the atane formation in outcrops and cores (figs 1, 2), and which would be a means of identifying the atane formation in an un-cored well, is obscured in the total gammaray log. this fails to resolve the grain-size variation in the atane formation because the presence of k-poor kaolinite, despite enrichment by th, provides a ‘cleaner’ signature of the mudstones while the presence of sand-sized k-feldspar gives a ‘dirtier’ signature of the sandstones. the th log can, to some degree, resolve the lithological variation but the energy is too small to be ref lected in the total gamma-ray signal. the high sedimentation rate and the predominance of terrestrial organic material precluded the development of a characteristic u signature in the marine mudstones. the gamma log thus shows the variations in elements which occur in small amounts, because the bulk of the sediment (quartz, kaolinite and terrestrial coal debris) contributes very little to the gamma-ray radiation. references chalmers, j.a., pulvertaft, t.c.r., marcussen, c. & pedersen, a.k. 1999: new insight into the structure of the nuussuaq basin, central west greenland. marine and petroleum geolog y 16, 197–224. dam, g., pedersen, g.k., sønderholm, m., midtgaard, h.m., larsen, l.m., nøhr-hansen, h. & pedersen, a.k. 2009: lithostratigraphy of the cretaceous–paleocene nuussuaq group, nuussuaq basin, west greenland. geological survey of denmark and greenland bulletin 19, 171 p. davies, s.j. & elliott, t. 1996: spectral gamma ray characterisation of high resolution sequence stratigraphy: examples from upper carboniferous f luvio-deltaic systems, county clare, ireland. in: howell. j.a. & aitken, j.f. (eds): high resolution sequence stratigraphy: innovations and applications. geological society (london), special publications 104, 25–35. pedersen, g.k., andersen, l.a., lundsteen, e.b., petersen, h.i., bojesenkoefoed, j.a. & nytoft, h.p. 2006: depositional environments, organic maturity and petroleum potential of the cretaceous coal-bearing atane formation at qullissat, nuussuaq basin, west greenland. journal of petroleum geolog y 29, 3–26. rider, m.h. 1990: gamma-ray log shape used as a facies indicator: critical analysis of an oversimplified methodolog y. in: hurst, a., lovell, m.a. & morton, a.c. (eds): geological applications of wireline logs. geological society special publications (london) 48, 27–37. ruffell, a.h., worden, r.h. & evans, r. 2003: palaeoclimate controls on spectral gamma-ray radiation from sandstones. international association of sedimentologists special publication 34, 93–108. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: gkp@geus.dk fig. 3. spectral gamma logs from 40 m of the core from borehole 247801. note the difficulty in interpreting the total gamma radiation log, the negative correlation between k and th content, and the absence of maxima on the u log. the core section is located in fig. 2. yellow: sandstone, grey: mudstone, black: coal or plant debris, black stars: pyrite. cps: counts per second. the total gamma radiation (gr) may be compared to the radiation measured in the borehole (fig. 2). 145 140 120 125 110 115 130 135 105 0 1 2 3 4 0 0 5 10 151 2 3 4 gr total (cps) k (%) 0 5 10 15 20 25 th (ppm)u (ppm) ★ ★ vf clay silt sand f m c mailto:tl@geus.dk geological survey of denmark and greenland bulletin 28, 2013, 69-72 69 darkening of the greenland ice sheet due to the meltalbedo feedback observed at promice weather stations dirk van as, robert s. fausto, william t. colgan, jason e. box and the promice project team* fig. 1. map of greenland showing the locations of the 21 promice weather stations in eight regions. the blue colours show mean satellite (modis) derived albedo for the months of june, july and august for 2008–2012. the contour lines show elevations (m) of the ice-sheet surface. © 2013 geus. geological survey of denmark and greenland bulletin 28, 69–72 . open access: www.geus.dk/publications/bull * andreas p. ahlstrøm, signe b. andersen, morten l. andersen, charalampos charalampidis, michele citterio, karen edelvang, trine s. jensen, signe h. larsen, horst machguth, søren nielsen, martin veicherts and anker weidick the greenland ice sheet is losing mass (barletta et al. 2012) and at least half of this loss is caused by an increase in surface melt (e.g. tedesco et al. 2013). the other part is caused by increased dynamic mass loss, as marine-terminating glaciers lose resistive stresses (nick et al. 2009) due to both retreat and meltwater lubrication at the bed (sasgen et al. 2012). in 2007, the programme for monitoring of the greenland ice sheet (promice) was initiated with the aim of gaining an insight into the causes of the ice-mass budget changes based on quantitative observations. this is primarily done by assessing how much mass is gained as snow accumulation on the surface versus how much is lost by calving and surface ablation (ahlstrøm et al. 2008). promice monitors the surface mass balance by means of automatic weather stations (awss) designed to quantify accumulation and ablation, as well as the specific energy sources contributing to ablation. these observations are vital to interpreting the physical mechanisms for ice-sheet response to climate change and for the calibration and validation of both satellite observations and climate models. in the wake of several record-breaking warm summers – increasing surface melt rate and extent (nghiem et al. 2012) – interest in greenland’s surface mass balance has increased (tedesco et al. 2013). observations of net ablation at promice stations provided in situ confirmation of extreme massloss events in 2010 (fausto et al. 2012) and 2012, primarily documented by other workers through satellite data. in this paper, we present atmospheric temperatures and surface solar ref lectivity (known as albedo) of the greenland ice sheet in the promice period. albedo modulates the absorption of solar radiation, which is the primary source of melt energy. it is reported to be decreasing in greenland in recent years (box et al. 2012), causing the monitoring of albedo variability to be increasingly important. air temperatures, besides being strongly correlated to surface melt rates, affect surface albedo by controlling the rate of snow-grain metamorphism and the fraction of summer precipitation falling as rain versus snow. to elucidate the so-called melt-albedo feedback, whereby increased melt darkens the ice sheet and further enhances melt, the relationship between albedo and air temperature, observed at promice stations, is examined in this study. 1500 200 0 2500 20 00 0.8 1.0 albedo 0.7 0.75 0.5 0.6 0.4 0.3 25 00 20 00 15 00 kan scoupe thu kpc tasnuk qas 3000 500 km 7070 promice measurements the original promice network consisted of 14 awss in the regions kronprins christian land (kpc), scoresbysund (sco), tasiilaq (tas), qassimiut (qas), nuuk (nuk), upernavik (upe) and thule (thu), each region monitored with a lower (l) and an upper (u) station in the ablation area (fig. 1). promice has both contributed to and received contributions from other projects in the kangerlussuaq, nuuk and tasiilaq regions, leading to the installation of seven additional stations. the promice study regions were selected to best complement the spatial distribution of existing ice-sheet weather stations, such as in the greenland climate network (steffen et al. 1996), by providing data from the under-represented ablation area (ahlstrøm et al. 2008). the promice awss measure meteorological variables including air temperature (at c. 2.7 m above the surface), pressure and humidity, wind speed, downward and upward solar (shortwave) and terrestrial (longwave) radiation. the awss also record temperature profiles in the upper 10 m of the ice, gps-derived location and diagnostic parameters such as station tilt angles. a pressure transducer and two sonic rangers measure snow and surface-height change associated with ablation and accumulation (fausto et al. 2012). most variables are measured every ten minutes, with the data stored locally awaiting collection during maintenance visits. hourly averages of the most transient variables are transmitted via satellite between days 100 and 300 of each year, while the remaining variables are transmitted at six-hour intervals. transmissions have a daily frequency in the remaining (winter) period. all data and metadata including sensor specifications are archived in the promice database and made freely available for display and download at www.promice.dk. in this study, we present monthly mean measurements of air temperature and surface albedo. to obtain the temperature averages, we first calculate daily mean air temperatures for all days in which data coverage of hourly mean values exceeds 80%. subsequently, we calculate monthly mean air temperature for all months in which data coverage of daily mean values exceeds 24 days. to calculate surface albedo, we divide instantaneous values of upward shortwave radiation by the downward component before averaging. however, instrument tilt induces significant errors in the measurement of shortwave radiation (van den broeke et al. 2004), which is a common problem in the ice-sheet ablation area due to irregular melting of the ice surface on which the aws stands. therefore we employ the tilt correction method as described by van as (2011) that uses the measured aws tilt to correct downward shortwave radiation. in contrast to the temperature averaging, a minimum of one successful hourly mean albedo is sufficient to produce a daily mean, provided that the direct solar radiation (which occurs when skies are not overcast) hits the upper dome of the radiometer at angles exceeding 30°, where measurements are more precise. the low sun angle in winter prevents calculation of albedo values. atmospheric temperature all promice sites record a distinct annual cycle in air temperature (fig. 2a). as is common for arctic climates, temporal variability is largest in winter due to a more vigorous atmospheric circulation. the amplitude in the annual air temperature cycle is largest for stations at high latitudes or high elevations since above-freezing temperatures and thus a melting ice surface capable of local thermo-regulation, are least common at these stations. the more northerly stations also show a larger annual temperature cycle due to the increasing contrast in the lengths of polar day and night with increasfig. 2. a: monthly mean air temperatures at the 18 promice sites installed on the ice sheet and before 2012. b: same but for albedo. c: albedo versus temperature. black lines: kpc stations, green: sco, orange: tas, light blue: qas, dark blue: nuk, red: k an, purple: upe, yellow: thu. year 20082007 2009 2010 2011 2012 a b c 20082007 2009 2010 2011 2012 a ir t em pe ra tu re ( °c ) 10 0 –10 –20 –30 su rf ac e al be do 0.8 0.6 0.4 0.2 –25 –20 –15 –10 –5 0 5 10 air temperature (°c) su rf ac e al be do 0.8 0.6 0.4 0.2 71 ing latitude. the smallest amplitude in the annual temperature cycle is seen at qas_l, the most southerly promice site. here, free-atmospheric temperatures can exceed 20°c, leading to strong melt. in 2010, the large heat content of the atmosphere, low summer albedo and anomalously low winter accumulation combined to yield a long net-ablation season and the largest ever recorded ablation in greenland in a single melt season (9 m of ice; fausto et al. 2012). as the greater part of mass loss by melt takes place during the summer, we calculated the fouror five-year trends in combined mean air temperature for the months of june, july and august, for eight stations with a sufficiently long coverage. given the relatively short promice record length, these trends are not free from the inf luence of inter-annual, natural climatic variability and thus not climatological trends. the data show that at all except two sites the summers have become warmer over the promice period. most noteworthy is that the warming is most pronounced (c. 0.6°c/year) at the high latitude/elevation sites, where the inf luence of a melting ice surface is spatially and temporally limited. at the sites that experience the highest temperatures and strongest melt, interannual variability of free-atmospheric temperatures has had limited effect on air temperatures over the nearly permanently melting ice-sheet surface in summer. the inter-annual temperature variability is shown in an anomaly plot (fig. 3a). it is seen that 2010 was a warm year, especially in west greenland, and mostly early and late in the year, with anomalies exceeding 5°c. the widespread and large melt in 2012 (nghiem et al. 2012) was the result of high temperatures in july, as seen from positive air temperature anomalies at all promice sites. the record-warm years/summers of 2010 and 2012 (e.g. tedesco et al. 2013), following the warmest decade in greenland’s instrumental temperature record, are consistent with persistent warming observed globally, but are suggested to be a consequence of north atlantic oscillation variability affecting atmospheric heat transport (fettweis et al. 2013). atmospheric warming has been reported to be highest in south and west greenland. this is confirmed by the promice observations in west greenland, but observations at kpc_u in north-eastern greenland show a similar rate of short-term warming. these observations provide in situ indications that the atmospheric warming may be spatially pervasive. darkening ice-sheet surface the surface albedo is generally high in the cold, snow-covered interior of the ice sheet (>0.75), and lower along the ice-sheet margin where melting occurs in summer (fig. 1). in winter, the ice sheet is fully snow covered except where wind erosion dominates. depending on the location of each aws in the ablation area, snow melt starts in april or may as seen from air temperatures and decreasing albedo (fig. 2b). thereafter, albedo drops throughout the melt season until snowfall occurs in autumn, yielding a distinct annual cycle which is largest at the high-melt sites. surface melt causes this annual darkening of the ice-sheet surface as snow undergoes heatdriven metamorphosis, or completely melts to expose darker bare ice. the ice-sheet surface may also darken as impurities collect on the ice surface or supraglacial meltwater-filled features become more abundant. we find that on average surface albedo drops below fresh snow values as monthly mean temperatures exceed c. –2°c (fig. 2c). the hyperbolic shape of the scatter plot is primarily a consequence of the annual cycle in albedo (α) and can be approximated by where t is near-surface air temperature and maximum (αmax) and minimum albedo (αmin) are prescribed as 0.8 and 0.2, respectively. t0 and c, taken as 2 and 1°c respectively, are empirical constants characterising a melting point offset and the exponential scaling length of α(t). fig. 3. a: monthly mean air temperature anomalies, i.e. after subtracting the mean annual cycle for stations with data series spanning a minimum of three years. b: albedo versus temperature anomalies plotted for months with mean temperatures exceeding –2°c in order to extract melt-season values only. year –4 –2 0 2 4 air temperature anomaly (°c) a ir t em pe ra tu re a no m al y (° c ) 5 0 –5 –10 su rf ac e al be do a no m al y 0.2 0 –0.4 –0.2 r = –0.59 a b 20082007 2009 2010 2011 2012 7272 though there are exceptions, taken as a whole the promice data indicate that albedo has decreased over the past five years while temperature has increased. this is most notable at the higher-elevation sites; the lower sites are completely snow-free in every summer and thus exhibit little change. by calculating the temporal correlations between temperature and albedo for all individual stations for the months of june, july and august separately (minimum four-year time series), we isolate the inter-annual variability by eliminating the annual cycle. we observe 36 out of 39 correlation coefficients to be negative, implying a widespread association of temperature-induced melt with surface albedo on the ice sheet. mean correlation is strongest in june (–0.76 ± 0.28), followed by august (–0.54 ± 0.39) and july (–0.43 ± 0.45). the surface albedo at most awss was relatively low in 2010 and 2012, coincident with the warm summers of the past years. in order to assess the impact of atmospheric warming on ice-sheet darkening at any given site on the greenland ice sheet, we plot the albedo anomalies versus the temperature anomalies in fig. 3b for monthly temperatures exceeding –2°c, hereby isolating the melt season. the correlation of –0.59 between the plotted variables is statistically significant. a linear fit yields that one degree of warming in the near-surface air temperature will lead to an average albedo reduction of 0.043. this value is sensitive to the temperature cut-off value (here taken at –2°c) and will become more accurate with longer aws time series. since the promice stations measure close to the ice surface where temperature variability is dampened over a melting surface, a stronger correlation could be expected between albedo and local freeatmospheric temperatures, although the regions with low temperature variability are also associated with low albedo variability (fig. 3b). as mentioned, this darkening is likely due to an increase in surface melt, which cannot be linked to changes in solar radiation in recent years and thus may very well be directly and indirectly caused by changes in air temperature. although absorbed solar radiation is the primary source of melt energy, the melt-albedo feedback is initiated by the energy f luxes that respond to changes in temperature, such as downward longwave radiation and the turbulent heat f luxes. since both atmospheric warming and ice-sheet darkening increase surface melt intensity and melt area, the anticipated future warming will result in a self-reinforcing ice sheet mass-loss contribution from the melt-albedo feedback. while increased surface melt is a primary mechanism for ice loss in greenland, an increase in meltwater may also enhance mass loss due to ice dynamics, through processes such as basal lubrication and warming of the ice matrix. acknowledgements promice is funded by the danish ministry of climate, energ y and building. the awss in the kangerlussuaq region are funded by the greenland analogue project, while partner awss in the nuuk region are co-funded by the greenland climate research centre. several other projects also contributed to promice. references ahlstrøm, a.p. & the promice project team 2008: a new programme for monitoring the mass loss of the greenland ice sheet. geological survey of denmark and greenland bulletin 15, 61–64. barletta, v.r., sørensen, l.s. & forsberg, r. 2012: variability of mass changes at basin scale for greenland and antarctica. the cryosphere discussions 6, 3397–3446. box, j.e., fettweis, x., stroeve, j.c., tedesco, m., hall, d.k. & steffen, k. 2012: greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers. the cryosphere 6, 821–839. fausto, r.s., van as, d. & the promice project team 2012: ablation observations for 2008–2011 from the programme for monitoring of the greenland ice sheet (promice). geological survey of denmark and greenland bulletin 26, 73–76. fettweis, x., hanna, e., lang, c., bellef lamme, a., erpicum, m. & gallée, h. 2013: important role of the mid-tropospheric atmospheric circulation in the recent surface melt increase over the greenland ice sheet. the cryosphere 7, 241–248. nghiem, s.v., hall, d.k., mote, t.l., tedesco, m., albert, m.r., keegan, k., shuman, c.a., digirolamo, n.e. & neuman, g. 2012: the extreme melt across the greenland ice sheet in 2012. geophysical research letters 39, l20502, http://dx.doi.org/10.1029/2012gl053611. nick, f.m., vieli, a., howat, i. & joughin, i. 2009: large-scale changes in greenland outlet glacier dynamics triggered at the terminus. nature geoscience 2, 110–114. sasgen, i., van den broeke, m.r., bamber, j.l., rignot, e., sørensen, s.l.s., wouters, b., martinec, z., velicogna, i. & simonsen, s.b. 2012: timing and origin of recent regional ice-mass loss in greenland. earth and planetary science letters 333, 293–303. steffen, k., box, j.e. & abdalati, w. 1996: greenland climate network: gc-net. in: colbeck, s.c. (ed.): glaciers, ice sheets and volcanoes: a tribute to mark f. meier. crr el special report 96-27, 98–103. tedesco, m., fettweis, x., mote, t., wahr, j., alexander, p., box, j. & wouters, b. 2013: evidence and analysis of 2012 greenland records from spaceborne observations, a regional climate model and reanalysis data. the cryosphere 7, 615–630. van as, d. 2011: warming, glacier melt and surface energ y budget from weather station observations in the melville bay region of northwest greenland. journal of glaciolog y 57(202), 208–220. van den broeke, m., van as, d., reijmer, c. & van de wal, r. 2004: assessing and improving the quality of unattended radiation observations in antarctica. journal of atmospheric and oceanic technolog y 21, 1417–1431. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: dva@geus.dk geological survey of denmark and greenland bulletin 28, 2013, 17-20 17 a baltic ice lake lowstand of latest allerød age in the arkona basin, southern baltic sea ole bennike and jørn bo jensen after the last deglaciation, the baltic sea underwent a complex salinity history and dynamic shore-level development with several lacustrine and marine stages: the baltic ice lake, the yoldia sea, the ancylus lake and the littorina sea (björck 1995). in connection with shallow seismic profiling in the south-western baltic sea, two marked and widespread erosional unconformities have been identified ( jensen et al. 1997, 1999; lemke et al. 1998; larsen 2004). the older unconformity occurs within sediments deposited in the baltic ice lake, whereas the younger one separates baltic ice lake sediments from holocene lake and mire deposits. the latter unconformity is dated to the transition between the younger dryas and the holocene, corresponding to c. 11.7 cal. ka bp and formed due to a sudden drop in the level of the icedammed baltic ice lake of around 25 m, caused by ice recession from mt. billingen in south central sweden. the age of the older erosional unconformity is poorly constrained. however, it has been suggested that the level of the baltic ice lake also experienced a sudden drop during the allerød chronozone. the temperature increased during the allerød, and it is possible that the margin of the fennoscandian ice sheet also receded from the mt. billingen area at this time. if so, the older erosional unconformity may have formed in connection with an early drainage of the baltic ice lake. the question about such an early lake-level fall was discussed by björck (1995), who listed a number of arguments for and against it. one of the arguments for drainage is that evidence of a rapid lake-level fall is seen in both south-eastern sweden and in other baltic countries. a study in southwestern sweden indicates a high discharge of freshwater, and data from south central sweden indicate a significant glacial recession west of mt. billingen during the allerød, which could have led to drainage of the baltic ice lake. it has been suggested that drainage happened around 13 cal. ka ago (uścinowicz 2006; andrén et al. 2011). in connection with sediment coring in the arkona basin, firm evidence of an early lowstand was for the first time identified in a sediment core. an organic-rich sediment which can be referred to this lowstand was found, and material was submitted for 14c dating. the aim of this paper is to report on the age and its implications. the location of the coring site in the arkona basin is shown in fig. 1. the basin is up to 49 m deep and the surface of the till is found at a depth of 30 to 70 m (moros et al. 2002). material and methods sediment coring was carried out using a 10 cm diameter vibrocorer with a 6 m long steel tube. normally, coring positions are selected from high-resolution, shallow seismic profiles, but in the deeper parts of the arkona basin, gas-bearing, organic-rich, holocene marine sediments are widespread and hamper the use of seismic data. hence the core described here was collected at a site with poor seismic data. the core was sampled at a water depth of 39.5 m, at 54°45.005́ n, 13°45.876́ e. the core was collected c. 5 km ene of the northern end of a seismic profile published by lemke et al. (1998), where the unconformity is clearly seen. the lower unconformity is also seen on seismic data collected in the region during the baltic pipe survey (larsen 2004). we collected two cores at the site, designated 258000-1 and 258000-2. the first core was collected in plastic foil, split lengthwise in the ship laboratory and described and subsampled for palaeoecological analysis. the second core was collected in a pvc tube and cut into 1 m sections for storage. however, the second core penetrated somewhat deeper than the first core, and in the core catcher, clay was found with abundant plant remains underlain by clay-rich, mediumgrained sand. ten 1 kg samples from core 258000-1 and from © 2013 geus. geological survey of denmark and greenland bulletin 28, 17–20. open access: www.geus.dk/publications/bull 14°e 14°e 55°n 55° 54°30´n 13°e 13°e 55–60 50–55 45–50 40–45 35–40 75–80 70–75 65–70 60–65 30–35 25–30 20–25 15–20 10–15 5–10 depth (m) 20 km 0–5 54°30´n 258000 skåne bornholm møn rügen fig. 1. bathymetrical map of the arkona basin. the red dot shows the location of the studied sediment core. the core site is also shown on fig. 5. 1818 the core catcher of 258000-2 were brought to the geological survey of denmark and greenland, where the samples were wet sieved shortly after the cruise. fruits of cladium mariscus (a reed plant) were dried and shortly after submitted for accelerator mass spectrometry (ams) radiocarbon age determination at the leibniz laboratory for radiometric dating and isotope research in kiel, germany. results and discussion core 258000-1 consists of olive-grey mud from the core top down to a depth of 412 cm (fig. 2). some shells of macoma balthica and mytilus edulis were noted, which shows that the mud is marine and of holocene age. from 412 to 473 cm, clay without carbonate is found; this succession was divided into three units according to variations in colour and texture. shells and head shields of chydoridae (cladocerans, water f leas) are common, head capsules of larvae of chironomidae (non-biting midges) are present but rare, egg cocoons of the fish leach piscicola geometra were found in two samples, and statoblasts of the bryozoan cristatella mucedo in four samples (fig. 3; table 1). these invertebrate remains show that the clay was deposited in a lake. the presence of rare remains of betula sect. albae (tree birch) and pinus sylvetris (pine) indicates an early holocene age. the lower part was rich in radicells (tiny roots) of reed plants, which show that the shoreline was not far away from the coring site. the clay was probably deposited in the ancylus lake and perhaps in the yoldia sea. d ep th b el ow c or e to p (c m ) holocene marine mud indistinct layering holocene marine mud homogeneous fineto medium-grained sand late glacial clay late glacial clay with plant remains late glacial sand holocene lacustrine clay 0 100 200 300 400 500 fig. 2. composite lithological log of core 258000 from the arkona basin. the two lower units were only found in core 258000-2. the core numbers refer to the system used at the department of marine geolog y at the institute for baltic sea research in warnemünde. fig. 3. macrofossil diagram of the lower parts of cores 258000-1 and 258000-2 from the arkona basin. the hollow bars show remains not counted. 2 1 50 10 100 20 1 200 1 5 10 400 420 440 460 480 500 520 540 560 580 600 d ep th (c m ) be tu la s ec t. al ba e sp . pi nu s s ylv es tri s ph ra gm ite s a us tra lis cl ad iu m m ar isc us ca re x sp . co m ar um p al us tre ci cu ta v iro sa r ad ic el ls c ha ra ce ae in de t. a m bl ys te gi ac ea e in de t. m en ya nt he s t rif ol ia ta n ym ph ae a sp . pi sc ico la g eo m et ra c la do ce ra c hi ro no m id ae in de t. cr ist at el la m uc ed o pi sc es in de t. sc irp us la cu st ris rare common abundant terrestrial telmatic lacustrine li th ol og y 19 the clay is underlain by 2 cm of fineto medium-grained grey sand. this thin sand layer may have been deposited at or after the final drainage of the baltic ice lake. below the sand layer and down to the bottom of the core at 570 cm, grey clay is found. this unit is rich in carbonate and barren of fossils and it is interpreted as late-glacial clay deposited in the baltic ice lake during the younger dryas. from the deeper core 258000-2, a sample rich in plant remains was analysed for macrofossils. the plant remains were dominated by fruits and seeds of the telmatic plants menyanthes trifoliata and fruits of carex, mainly carex vesicaria, cladium mariscus, scirpus lacustris, comarum palustris and cicuta virosa (fig. 3). limnic plants and animals were represented by a seed of nymphaea sp., common stems of amblystegiaceae (mosses, not shown), rare shells and head shields of chydoridae and rare head capsules of larvae of chironomidae. the fossil assemblage and in particular the occurrence of abundant remains of telmatic plants show that the sediment was deposited in shallow water near the shore of a lake, probably just outside the reed belt. the presence of fruits of betula sect. albae indicates that the land was covered by birch forests. the sample of cladium mariscus fruits yielded an age of 10  980 ± 55 14c years bp (kia-21680). this is calibrated to 12.674–13.069 cal. ka bp, according to the intcal09 dataset, which corresponds to the youngest part of the allerød chronozone or the oldest part of the younger dryas. an age corresponding to the warm allerød chronozone was expected from the fossil assemblage, because cladium mariscus and scirpus lacustris are thermophilous plants. cladium mariscus was recorded from late-glacial deposits in south-eastern denmark by bennike & jensen (1995), but its presence was probably due to down-core contamination, and there are no secure records of it from late-glacial deposits in denmark (iversen 1954; jensen et al. 1997; bennike et al. 2004). its northern geographical limit during the allerød may thus have been located near the coring site. as the core was collected at a water depth of 39.5 m and the sample comes from a core depth of c. 5.8 m, the dated sample comes from a depth of c. 45.3 m below present sea level. the sediment is fine-grained and was probably deposited at a water depth of several metres, and we suggest that the shore level during deposition was around 40 m lower than at present. both before and after this lowstand episode, the relative shore level was around 20 m below the present sea level according to jensen et al. (1997). this implies that the shore-level fall towards the end of the allerød chronozone was of the same magnitude as the fall at the younger dryas – holocene transition, i.e. considerably more than 5–10 m as suggested by björck (1995). the new data allow us to modify the shore-level model proposed by bennike & jensen (1998) and extend it back in time. figure 4 shows a new model for relative shore-level changes in the arkona basin from the last deglaciation to the present. it is seen that transgressions were interrupted by sudden regressions. south of the arkona basin, late-glacial sediments reach elevations lower than 20 m (lampe 2005). however, the relationship between these sediments and the regional shore level of the southern baltic basin is uncertain. some of the sediments are glaciof luvial and were deposited above shore level, other late-glacial sediments may have been deposited in local basins, perhaps in part dammed by bodies of stagnant ice. at present, the most enigmatic stage in the history of the baltic basin is that of the early holocene ancylus lake; the shore-level curve for this stage has been drawn as a dashed line on fig. 4. it has been suggested that the ancylus regresfig. 4. tentative curve showing relative shore-level changes in the arkona basin during the late-glacial and the holocene. ka: kilo-annum (1000 years), bil: baltic ice lake, ys: yoldia sea, all: allerød, yd: younger dryas. modified from bennike & jensen (1998). table 1. macrofossils in core 258000 r: rare, c: common. 412–420 – – – – – – – – – – – c r – 420–430 – – – – – – – – – – – c r – 430–440 3 – – – – – – – – – – c r 4 440–449 2 – – – – – – – – – – c – 10 449–454 – – – – – – – – – – – c – 1 454–459 – – – – – – – – – – 5 c r 8 459–463 2 r – – – – – c – – 1 c r – 463–468 – – – – – – – c – – – c r – 468–473 1 r – – – – – c – 1 – c r – c. 580 3 – 50 15 150 20 1 c 200 1 – r r – be tu la s ec t. al ba e sp . d ep th (c m ) pi nu s sy lve st ris cl ad iu m m ar isc us sc irp us la cu st ris ca re x sp p. co m ar um p al us tre ci cu ta v iro sa ra di ce lls m en ya nt he s tr ifo lia ta n ym ph ae a sp . pi sc ico la g eo m et ra c hy do ri da e in de t. c hi ro no m id ae in de t. cr ist at el la m uc ed o d ep th (m b .s. l.) 12 10 8 6 4 2 0 age (cal. ka bp) 0 10 20 30 40 littorina seaancylus lakeysbil focus of this paper holoceneydall 2020 sion was around 20 m (björck 1995), but more recently figures of 5 m and 10 m were also proposed (björck et al. 2008; rosentau et al. 2013). no erosional unconformity has been reported from the south-western baltic basin that formed during this regression ( jensen et al. 1999). figure 5 shows a model of the palaeogeography of the baltic basin after the late allerød drainage. although the baltic basin was now at the same level as the sea, it probably remained a freshwater lake. the connection to the sea was narrow, and we suggest that the outf low of huge amounts of fresh water coming from rivers and from the melting ice sheet hindered seawater from entering the baltic basin. concluding remarks the rich occurrence of remains of reed plants at a depth of 45  m below sea level in the arkona basin provides firm evidence of a lowstand. a radiocarbon age shows that it occurred at the end of the allerød chronozone. we suggest that the shore level fell about 20 m, similar to the shore-level fall at the younger dryas – holocene boundary. acknowledgements the captain and crew of the former r/v alexander von humboldt from the institute for baltic sea research in warnemünde are thanked for their help during the marine cruise. this paper is dedicated to the memory of wolfram lemke, who invited us to take part in the cruise during which cores 258000-1 and 258000-2 were collected. references andrén, t., björck, s., andrén, e., conley, d., zillén, l. & anjar, j. 2011: the development of the baltic sea during the last 130 ka. in: harff, j. et al. (eds): the baltic sea basin, 75–97. berlin: springer verlag. bennike, o. & jensen, j.b. 1995: near shore baltic ice lake deposits in fakse bugt, southeast denmark. boreas 24, 185–195. bennike, o. & jensen, j.b. 1998: lateand postglacial shore level changes in the southwestern baltic sea. bulletin of the geological society of denmark 45, 27–38. bennike, o., jensen, j.b., lemke, w., kuijpers, a. & lomholt, s. 2004: lateand postglacial history of the great belt, denmark. boreas 33, 18–33. björck, s. 1995: a review of the history of the baltic sea, 13.0–8.0 ka bp. quaternary international 27, 19–40. björck, s., andrén, t. & jensen, j.b. 2008: an attempt to resolve the partly conf licting data and ideas on the ancylus–littorina transition. polish geological institute special papers 23, 21–26. iversen, j. 1954: the late-glacial f lora of denmark and its relation to climate and soil. danmarks geologiske undersøgelse ii. række 80, 87–119. jensen, j.b., bennike, o., witkowski, a., lemke, w. & kuijpers, a. 1997: the baltic ice lake in the southwestern baltic: sequence-, chronoand biostratigraphy. boreas 26, 217–236. jensen, j.b., bennike, o., witkowski, a., lemke, w. & kuijpers, a. 1999: early holocene history of the southwestern baltic sea: the ancylus lake stage. boreas 29, 437–453. lampe, r. 2005: lateglacial and holocene water-level variations along the ne german baltic sea coast: review and new results. quaternary international 133–134, 121–136. larsen, c.s. 2004: sequence stratigraphy based on vibrocore description and shallow seismic data from the south-western baltic sea. danmarks og grønlands geologiske undersøgelse rapport 2004/53, 28 pp. lemke, w., endler, r., tauber, f., jensen, j.b. & bennike, o. 1998: late and postglacial sedimentation in the tromper wiek (western baltic). meyniana 50, 155–173. moros, m., lemke, w., kuijpers, a., endler, r., jensen, j.b., bennike, o. & gingele, f. 2002: regression and transgressions of the baltic basin ref lected by a new high-resolution deglacial and postglacial lithostratigraphy for arkona basin sediments (western baltic sea). boreas 31, 151–162. rosentau, a. et al. 2013: stone age settlement and holocene shore displacement in the narva-luga klint bay area, eastern gulf of finland. boreas. http://dx.doi.org/10.1111/bor.12004 uścinowicz, s. 2006: a relative sea-level curve for the polish southern baltic sea. quaternary international 145–146, 86–105. wohlfarth, b., björck, s., funder, s., houmark-nielsen, m., ingólfsson, ó., lunkka, j.-p., mangerud, j., saarnisto, m. & vorren, t. 2008: quaternary of norden. episodes 31, 73–81. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: obe@geus.dk fig. 5. generalised palaeogeographical map of the baltic region after the drainage at the end of the allerød. modified from björck (1995) and wohlfahrt et al. (2008). b: billingen. 250 km ice sea lake land b 258000 http://dx.doi.org/10.1111/bor.12004 mailto:prj@geus.dk geological survey of denmark and greenland bulletin 4, 2003, pp 9-12 9 in an oil reservoir, the geometry of the interface between water and oil is critical in determining the volume of oil trapped below the top seal. if the interface is planar and horizontal, the volume calculation is fairly simple, but if the interface is tilted or undulating, estimation of the volume of the trapped oil is complex as it depends on the combined structural and fluid contact geometry. since accumulation of the oil may take place over a time span of several million years, while the reservoir is experiencing burial and compaction, the charge history must be studied using dynamic methods that account for these changes and for flow in both the oil and water phases. these processes have been studied quantitatively at the geological survey of denmark and greenland (geus) in a project that has combined the burial model with a fluid flow simulator. the modelling study shows that filling of a chalk reservoir can have a very long and complex history dominated by very low fluid flow rates (cm/year). the resulting modelled present-day situation exhibits a very irregular oil distribution and a non-planar geometry of the fluid contacts, and shows marked similarities to that shown by the field data. oil–water contact and free water level the positions of the oil–water contact (owc), the gas–oil contact (goc) and the associated free water level (fwl) in an oiland gas-field are some of the most important factors in estimating the in-place hydrocarbon volumes of a given field. thus it is important to be able to analyse and predict tilted or irregular fluid contacts (dennis et al. 2000; moss et al. 2003; dennis et al. in press; vejbæk et al. in press). the fluid contact can be defined in two radically different ways: the owc is defined by setting a threshold for the oil saturation, whereas the fwl is defined where the pressures the history of hydrocarbon filling of danish chalk fields peter frykman, ole v. vejbæk, niels bech and carsten m. nielsen fig. 1. map showing top chalk depth structure for the danish north sea area. producing chalk fields are shown, with oil fields green, and gas fields red. colour interval is 100 m and contour interval 50 m. the red line on the kraka field shows location of the profile studied (see fig. 3). full black lines are major faults. dashed black lines are offshore sector boundaries. modified from vejbæk et al. (in press). geological survey of denmark and greenland bulletin 4, 9–12 (2004) © geus, 2004 10 in the water and the oil phases are equal. in the chalk reservoirs in the north sea, the relationship between the owc and the fwl can be described in simple cases by the capillary characteristics of the reservoir rock. in the central north sea (fig. 1), the fluid contacts in the chalk can be naturally tilted by hydrodynamic activity due to a regional flow of water in the chalk. a regional pressure gradient in the chalk aquifer has been described from available pressure measurements (megson 1992), and later refined using more data (dennis et al. in press). the regional lateral pressure gradient reflects differential compaction caused by rapid neogene deposition with the highest burial rates in the central ekofisk area (japsen 1998). the water therefore migrates laterally away from this area and towards the periphery of the north sea. analysis of burial history by backstripping and decompaction shows that this pressure was probably caused mainly by rapid deposition in the time interval from latest miocene to recent times, as the magnitude of the pressure corresponds to the thickness of these deposits (japsen 1998). this is consistent with a very low regional permeability of the chalk (and adjacent sedimentary packages) probably not exceeding 1 md. the flow of water and the accompanying pressure differences will influence the position of the fwl (fig. 2a). if the oil is also flowing due to either buoyancy equilibration or active migration, it will affect both the fwl and the goc (fig. 2b, c). factors that modify the position of the fwl include tilting due to structural movements, and the presence of oil migrating from the underlying source rocks into the reservoir. the reason that these processes influence the present geometry of the fwl is that both oil and water flow take place at very low velocities (cm/year), due to the low permeability of the chalk. even though structural movements are very slow, the flow is not able to respond quickly enough to equilibrate the system, even on a scale of millions of years. the petrophysical properties of the north sea chalk reservoirs are mainly governed by their high-porosity/low-permeability aspect with porosities usually around 20–40% and average permeability of 1 md. case study the kraka field in the southern danish north sea (fig. 1) has been chosen as the subject of a case study of primary oil charging and remigration. to study the interaction of the different processes, reservoir fluid flow simulation techniques have been applied in combination with burial modelling, including compaction (vejbæk 2002). the results show that a time span in the order of 2 ma is required for the hydrocarbons to reach the top of the reservoir in an approximately equilibrium state, if they enter the reservoir section from a flank position. however, not even dynamic equilibrium can be fully obtained in this time span if re-perturbation by structural movements leads to changing water-zone pressure gradients. the study is focused on a 2d section from the crestal part through the south-eastern flank of the kraka field (figs 1, 3). since porosity is the main cause for changes in seismic impedance (japsen et al. in press), detailed porosity profiles can be achieved by converting acoustic impedance derived by seismic inversion. these porosity profiles have been modified by backstripping to reconstruct geometry and porosity. as flow simulation has only been applied to the chalk group layers, fig. 2. possible dynamic equilibrium situations that may fit a tilted oil–water contact. arrows show direction of pressure drop corresponding to flow direction. 1 and 2 represent wells where the pressure depth plots shown to the left are generated: (a) only the water phase is dynamic; (b) both oil and water are flowing, but the tilt is maintained due to a higher lateral pressure gradient in the water phase; (c) the tilt is maintained only by an oil phase gradient. the situations are physically distinguishable by the dip of the gas–oil contact. modified from vejbæk et al. (in press). 11 detailed porosity profiles have only been constructed for these layers. the simulation of flow processes in chalk reservoirs is characterised by the need for end-point scaling and hysteresis, in order to account for the marked influence from the high capillary forces in this low-permeability medium. since the dominant process during the filling history is a drainage process (i.e. oil replacing water), the saturation functions must also be derived for this type of process. there is a general lack of relative permeability analyses for drainage, and therefore imbibition curves have been the guide for establishing the drainage saturation functions for relative permeability. for each rock type (danian and maastrichtian), the irreducible water saturation (swi) and capillary entry pressure (pce) are assumed to depend upon the porosity (φ) through relatively simple relationships. using these relationships, the primary drainage capillary pressure is described by means of the eqr model (engstrøm 1995). the simulation of the filling history uses 8 million years before present as the starting point, and the entry of hydrocarbons from an underlying source rock is assumed to occur on the south-eastern flank (fig. 3). the flow simulation of the filling dynamics of the kraka chalk reservoir has a complex geometry due to the high capillary entry pressures in the low-permeability chalks. these internal barriers re-direct hydrocarbons, such that oil flows in the maastrichtian layers for some time before it is able to penetrate upwards into the overlying danian chalk (fig. 3a). if oil supply is stopped after 1 million years, the oil continues to move towards the crest, but leaves immobile residual oil on the migration route. hydrocarbon charging is slow and equilibration of hydrocarbons with respect to pressure gradients therefore occurs very slowly. after two million years, the oil is seen to be nearly in equilibrium even though the fwls are still slightly inclined and do not coincide for the two reservoir units (fig. 3b). after 4 million years, equilibrium is more obvious (fig. 3c). between 2 million years before present and the present, a fig. 3. modelled oil saturation in the kraka field profile at different times during the simulated filling history. top structures of the ekofisk (maastrichtian) and tor (danian) formations are shown as thin green and red lines, respectively. calculated free water levels (fwls) for these two reservoir units are shown in thicker green and red lines, respectively. charging of the reservoir starts at 8 ma b.p. by injecting oil at a very low rate at the flank position shown with an arrow. a: the situation after 250 000 years, where the injected oil is preferentially moving in the maastrichtian reservoir unit. b: oil distribution after 2 ma, where the charging has been sustained over the first 1 ma, accompanied by equilibration during continued burial. c: oil is near-equilibrium at 4 ma b.p. d: tilted fwls resulting from a lateral pressure gradient of 3.5 psi/km (24.1 kpa/km) applied for 1 ma (from 2 to 1 ma b.p.) within the water phase. this causes a water-flow south-eastwards in the aquifer, and accordingly a tilting of the fwl in that direction, which is further accentuated until the modelled present-day situation shown in e. modified from vejbæk et al. (in press). 12 pressure gradient is imposed in the water zone in order to allow for the regional pressure distribution during that period. as a result, the oil is forced south-eastwards towards the flank (fig. 3d), which is further accentuated through time as the water gradient is sustained (fig. 3e). again a zone with residual oil is left behind. conclusions the modelling reported here demonstrates that oil accumulations in chalk may require several million years to equilibrate following perturbations resulting from primary migration or reservoir tilting, if matrix permeability governs fluid flow. since naturally occurring disequilibrium oil accumulations dominate the danish chalk fields, it must be concluded that matrix flow dominates fluid dynamics. the modelled filling scenarios are intended to illustrate the general aspects of geological timescale oil–water dynamics in chalk reservoirs. the scenarios are not considered to represent actual filling histories, as they are constrained by relatively simple model assumptions, but they are geologically plausible. due to the long equilibration times, it can be dangerous to interpret tilted contacts as reflecting only dynamic equilibrium, as they may be fully dynamic and still actively flowing. this is revealed locally by non-equilibrium between danian and maastrichtian oil where they are seen to have different fwls. it is important to try to understand fluid dynamics during exploration work, since this strongly affects trap definition and volumes. the project shows that with simple and geologically based assumptions, a reasonable filling history can be modelled quantitatively. a reasonable end-result can be produced that has many similarities with present-day hydrocarbon configurations. with the methods developed in the project, even a fully dynamic system (with both oil and water moving), as for example in the dan–halfdan field system, may be explained. acknowledgement the work presented in this paper was partly funded by the danish energy authority (grant no. 1313/01-0004). references dennis, h., baillie, j., holt, t. & wessel-berg, d. 2000: hydrodynamic activity and tilted oil–water contacts in the north sea. in: ofstad, k., kittilsen, e.-j. & alexander-marrack, p. (eds): improving the exploration process by learning from the past. norwegian petroleum society (npf), special publications 9, 171–185. dennis, h., bergmo, p. & holt, t. in press: tilted oil–water contacts – modelling the effects of aquifer heterogeneity. in: doré a.g. & vining, b. (eds): petroleum geology: north-west europe and global perspectives. proceedings of the 6th petroleum geology conference. london: geological society. engstrøm, f. 1995: a new method to normalize capillary pressure curves. 1995 international symposium of the society of core analysts, san francisco, ca, usa, september 12–14, 1995, sca-9535, 12 pp. japsen, p. 1998: regional velocity-depth anomalies, north sea chalk; a record of overpressure and neogene uplift and erosion. american association of petroleum geologists bulletin 82(11), 2031–2074. japsen, p., bruun, a., fabricius, i.l., rasmussen, r., vejbæk, o.v., pedersen, j.m., mavko, g. & mogensen, c. in press: influence of porosity and pore fluid on acoustic properties of chalk: avo-response from oil, south-arne field, north sea. petroleum geoscience. megson, j.b. 1992: the north sea chalk play: examples from the danish central graben. in: hardman, r.f.p. (ed.): exploration britain: geological insights for the next decade. geological society (london) special publication 67, 247–282. moss, b., barson, d., rakhit, k., dennis, h. & swarbrick, r. 2003: formation pore pressures and formation waters. in: evans, d. et al. (eds): the millenium atlas: petroleum geology of the central and northern north sea, 317–329. london: geological society. vejbæk, o.v. 2002: a 1, 2 and 3d backstripping procedure with application to the kraka field. danmarks og grønlands geologiske undersøgelse rapport 2002/44, 35 pp. vejbæk, o.v., frykman, p., bech, n. & nielsen, c.m. in press: the history of hydrocarbon filling of chalk fields. in: doré, a.g. & vining, b. (eds): petroleum geology: north-west europe and global perspectives. proceedings of the 6th petroleum geology conference. london: geological society. authors’ addresses p.f., o.v.v. & n.b., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: pfr@geus.dk c.m.n., danish energy authority, amaliegade 44, dk-1256 copenhagen k, denmark. << /ascii85encodepages false /allowtransparency false /autopositionepsfiles true /autorotatepages /all /binding /left /calgrayprofile (dot gain 20%) /calrgbprofile (srgb iec61966-2.1) /calcmykprofile (u.s. web coated \050swop\051 v2) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.4 /compressobjects /tags /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjdffile false /createjobticket false /defaultrenderingintent /default /detectblends true /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true 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<feff4f7f752890194e9b8a2d5b9a5efa7acb76840020005000440046002065874ef65305542b8f039ad876845f7150cf89e367905ea6ff0c4fbf65bc63d066075217537054c18cea3002005000440046002065874ef653ef4ee54f7f75280020004100630072006f0062006100740020548c002000520065006100640065007200200035002e0030002053ca66f465b07248672c4f86958b555f3002> >> >> setdistillerparams << /hwresolution [2400 2400] /pagesize [595.000 842.000] >> setpagedevice e2019430101-01 between 1850 and 2006 global mean sea level rose by 24 ± 18 cm. it is projected to rise a further 52 ± 21 cm under the representative concentration pathway (rcp) 4.5 scenario, which approximates the carbon emissions reductions of the ‘paris agreement’ climate pathway. it is projected to rise 74 ± 28 cm under the rcp8.5 scenario, which represents a ‘business-as-usual’ climate pathway (box & colgan 2017). these rates of recent and future sea-level rise are faster than those reconstructed for previous warm intervals, such as the medieval climatic optimum (c. 1000 to 1400 ce) and the holocene thermal maximum (c. 7000 to 3000 bce) (gehrels & shennan 2015). moreover, palaeo reconstructions indicate a global sea-level sensitivity of two metres per degree of warming (levermann et al. 2013). the forces driving global sea-level change are complex. the global sea-level budget includes the transfer of land ice into the ocean, thermal expansion of seawater, changes in land water storage, and changes in ocean basin volume (church et al. 2013). at the local scale, the evolving planetary gravity due to shifting water and ice masses, shifting oceanic and atmospheric currents and persistent tectonic and glacial isostatic adjustment processes can also be important. sea-level changes around the globe are therefore far from uniform ( jevrejeva et al. 2016). here, we highlight the value of combining palaeo reconstructions of sea level, the measured tide gauge record, and projections of future sea level. this allows us to understand local sea-level changes from the recent past in the context of global projections for the near future (0 to 2100 ce). we explore the strong differences in local sea-level histories and future projections at three danish cities: skagen and esbjerg, as they have contrasting glacio-isostatic adjustment histories, and copenhagen, where we also compare local and global drivers of present-day sea-level rise based on previously published research. data we employ the standardised permanent service for mean sea level annual tide gauge records at copenhagen (psmsl site 21), esbjerg (psmsl site 80) and skagen (psmsl site 89) since c. 1880 (holgate et al. 2013). while psmsl data are formatted as sea-level elevation relative to the geoid, we instead express local sea-level elevations as relative to the 1901–1950 baseline elevation throughout this study (fig. 1). for each city, we characterise a centennial (1900–1999) rate of sea-level change using a linear trend to the annual psmsl data. we estimate uncertainty in this centennial sea-level trend using a monte carlo envelope that assumes ± 10 cm uncertainty in annual elevations. the dating of raised beach sequences, wind-blown sand deposits, and salt-marsh sediments has permitted sea level to be reconstructed since the last glaciation at skagen (hauerbach 1992; clemmensen et al. 2001) and esbjerg (gehrels et al. 2006; szkornik et al. 2008). at esbjerg, the palaeo records of relative sea level overlap with the observed record of tide gauge data, revealing some discrepancies between the two datasets during this overlapping period. for example, gehrels et al. (2006) suggest palaeo-sea-level at esbjerg in the 1880s was –24 cm below the c. 2000 level, while the tide gauge record suggests it was –5 cm below the 1901–1950 baseline. some of this apparent discrepancy is likely attributable to differing baseline periods in the two datasets. to minimise such discrepancies, we shift the relative sea levels reported in gehrels et al. (2006) and szkornik et al. (2008) by +19 and –8 cm, respectively. at skagen, there is no overlap of measured tide gauge data and reconstructed sea levels. we therefore assume the relative sea levels reported in hauerbach (1992) and clemmensen et al. (2001) are characteristic of the 1901–1950 reference period. analogous palaeo reconstructions of sea-level elevation are not readily available in the immediate vicinity of copenhagen, ref lecting the relative paucity of palaeo data within urbanised sjælland. sea-level rise in denmark: bridging local reconstructions and global projections william colgan*1, jason e. box1, sofia ribeiro1 and kristian k. kjeldsen1 geus bulletin is free to individuals and institutions in electronic form. the author(s) retain copyright over the article contents. r esearch article | open access geus bulletin vol 43 | e2019430101 | published online: 01 july 2019 https://doi.org/10.34194/geusb-201943-01-01 https://doi.org/10.34194/geusb-201943-01-01 e2019430101-02 the projections of future sea-level rise are based on simulations of global sea-level budget terms under the rcp4.5 and rcp8.5 climate pathways (box & colgan 2017). we translate this 1850–2100 global eustatic sea-level budget into local sea-level budgets by applying a linear trend to the global budget that makes it fit the linear trend of a local budget during the 20th century (1900–1999). this yields global-to-local scaling terms of 0.4 mm/year at esbjerg, –1.8 mm/year at skagen and 1.1 mm/year at copenhagen. these terms capture the site-specific processes causing deviations from the global mean – including the net effects of glacioisostatic adjustment and persistent changes in atmospheric and oceanic currents – during the 20th century. these linear scaling terms are also applied to the projections. calendar year 1900 1950 2000 2050 2100 se a le ve l r el at iv e 19 01 -1 95 0 (m ) -0.2 0 0.2 0.4 0.6 0.8 1 1.2 calendar year 0 500 1000 1500 2000 se a le ve l r el at iv e 19 01 -1 95 0 (m ) -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 clemmensen2001 hauerbach1992 holgate2013 box2017:rcp4.5 box2017:rcp8.5 b calendar year 1900 1950 2000 2050 2100 se a le ve l r el at iv e 19 01 -1 95 0 (m -0.2 0 0.2 0.4 0.6 0.8 1 1.2 calendar year 0 500 1000 1500 2000 se a le ve l r el at iv e 19 01 -1 95 0 (m ) -3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 szkornik2008 gehrels2006 a holgate2013 box2017:rcp4.5 box2017:rcp8.5 fig. 1. sea level, relative to the 1901–1950 period, at esbjerg (a) and skagen (b) between 0 and 2100 ce, derived from palaeo reconstructions (hauerbach 1992; clemmensen et al. 2001; gehrels et al. 2006; szkornik et al. 2008), tide gauge measurements (holgate et al. 2013) and projections (box & colgan 2017). for palaeo reconstructions, uncertainty is depicted with xand y-whiskers. for projections, uncertainty is depicted with dashed lines bounding solid line best estimates. linear best fit and associated uncertainty is shown for the tide gauge records. e2019430101-03 past millennial-scale sea-level change in the past 2000 years, local relative sea level has risen 1.5 ± 0.5 m (0.8 ± 0.3 mm/year) at esbjerg and fallen 4.0 ± 0.5 m (2.0 ± 0.3 mm/year) at skagen (table 1). these contrasting sea-level histories are primarily due to local differences in glacio-isostatic adjustment. at skagen, the earth’s crust is still rebounding upwards following the relatively rapid removal of the scandinavian ice sheet during the last glaciation c. 17  000 years ago (morén et al. 2018). at esbjerg, the earth’s crust is still sinking due to the collapse of the crustal forebulge that once ringed the scandinavian ice sheet (stuhne & peltier 2015; fig. 2). local relative sea-level rise ref lects the net effect of changes in land and ocean elevation. during the 20th century, skagen was rebounding faster than eustatic sea level was rising. as a result, while global average sea level rose 1.5 ± 0.4 mm/year during 1900–1999 (box & colgan 2017), the relative sea level measured at skagen fell 0.3 ± 0.4 mm /year (holgate et al. 2013). at esbjerg, sea level did rise, but less than the global mean (1.1 ± 0.4 mm/ year). these local departures from the global pattern ref lect our global-to-linear scaling terms described above. assessing the magnitude and spatial distribution of recent sea-level rise across denmark therefore requires – among other things – constraining present-day glacio-isostatic adjustment rates resulting from deglaciation following the last glacial period. present-day sea-level rise components land ice was responsible for c. 51% of global mean sea-level rise during 2004–2010 (box & colgan 2017). as large ice and water masses shift around the planet, they modify the planetary gravity field. where land ice diminishes under climate change, local gravitational fields weaken and nearby sea level falls. in this process, the ocean water previously held near land ice is redistributed to raise distant sea levels, elsewhere. in this way, greenland land ice contributes four times as much to global mean sea-level rise (c. 24%) than it does to local sea-level rise at copenhagen (c. 6%; fig. 3). conversely, antarctic land ice is slightly more important to local sea-level rise at copenhagen (c. 11%) than the global mean (c. 7%). this is because copenhagen lies within the gravitational weakening anomaly associated with greenland, but lies outside the analogous gravitational weakening anomaly associated with antarctica (larour et al. 2017). notably, while scandinavian land ice contributes just c. 1% global mean sea-level rise, it actually provides a c. 1% sealevel fall at copenhagen due to the associated weakening of gravity within scandinavia (larour et al. 2017). non-land ice processes, including the thermal expansion of seawater, changes in land water storage (i.e. groundwater and dams) and – at the local scale – shifts in atmospheric and oceanic currents, are relatively more important to local sea-level rise at copenhagen (c. 69%) than the global mean (c. 49%). post1993 satellite altimetry indicates that sea level is increasing in the gulf of bothnia, between finland and sweden, more than three times faster than in the north sea (fig. 2). moreover, appreciable local glacio-isostatic adjustment rates mean that global sea-level budget terms cannot be neatly translated into local sea-level budget terms (nielsen et al. 2014). sea-level rise projections while the city-specific sea-level projections we present here are less physically-based than those derived from more complex downscaling approaches ( jevrejeva et al. 2016), they are informative within their respective one standard deviation longitude (°e) 5 1 0 1 5 2 0 2 5 la tit ud e (° n ) 52 54 56 58 60 62 64 66 fig. 2 a: trend in mean sea-level elevation (in mm/year) measured by satellite altimetry during the january 1993 and july 2016 period for which data was freely available (nerem et al. 2010). b: present-day (c. 2015) glacioisostatic rebound (in mm/year) simulated by one of the many geodynamic models for which data was freely available (stuhne & peltier 2015). c: relative sea-level change calculated as a minus b, without accounting for geoid differences between both datasets. a longitude (°e) 5 1 0 1 5 2 0 2 5 la tit ud e (° n ) 52 54 56 58 60 62 64 66 n/a < -7 -7 to -5 -5 to -3 -3 to -1 -1 to 1 1 to 3 3 to 5 5 to 7 > 7 b longitude (°e) 5 1 0 1 5 2 0 2 5 la tit ud e (° n ) 52 54 56 58 60 62 64 66 c fig. 2 a: trend in mean sea-level elevation (in mm/year) measured by satellite altimetry during the january 1993 and july 2016 period for which data were freely available (nerem et al. 2010). b: present-day (c. 2015) glacio-isostatic rebound (in mm/year) simulated by one of the many geodynamic models for which data were freely available (stuhne & peltier 2015). c: relative sea-level change calculated as a minus b, without accounting for geoid differences between both datasets. e2019430101-04 uncertainties. the distance between esbjerg and skagen – 280 km – highlights a considerable spatial gradient in sealevel rise. due to ongoing glacio-isostatic rebound at skagen, 21st century sea-level rise relative to 1901–1950 will be limited to 64 ± 28 cm under rcp8.5 and 39 ± 21 cm under rcp4.5 (table 1). at esbjerg, where there is instead ongoing glacio-isostatic subsidence, 21st century sea-level rise will consequently be c. 25 cm greater; 89 ± 28 cm under rcp8.5 and 63 ± 21 cm under rcp4.5. the year 2100 sea-level rise projected for esbjerg under rcp4.5 is therefore similar to that projected for skagen under rcp 8.5. the sea-level forecast for copenhagen is between that of these two endmember case studies. at all three cities, rates of 21st century sea-level rise will be ten times more rapid than rates of 20th century sea-level rise. at esbjerg, the sea-level change over the next century will be approximately equivalent in magnitude to the sea-level change that has occurred there over the past millennium. outlook this study translates the global sea-level projections compiled by the geological survey of denmark and greenland (geus) in support of the 2017 snow, water, ice and permafrost assessment of the arctic monitoring (swipa 2017) and assessment program into local sea-level rise projections at esbjerg, skagen and copenhagen. these danish case studies highlight strong differences in local sea-level histories and projections, as well as marked differences in the drivers of present-day sea-level rise relative to the global average. there is a multi-centennial to millennial lag in the global sea-level response to global climate, which can introduce transient local sea-level responses. contextualising near-term change with long-term perspectives can therefore substantially improve local sea-level projections. contemporary sea-level change is variable across the earth. this study supports ongoing efforts by the department of glaciology and climate at geus to communicate emerging sea-level science to the danish public in a local and regional context, especially with regard to the role of the changing greenland ice sheet (colgan et al. 2018). here, we show that the year 2100 differences in projected sea-level rise between two danish cities under a single climate scenario is approximately equivalent to the differences projected for one city under two climate scenarios. communicating presentday and future sea-level changes throughout the kingdom of denmark – including greenland and the faroe islands – therefore remains a challenging task. references box, j. & colgan, w. 2017: sea level rise contribution from arctic land ice: 1850–2100. in: snow, water, ice and permafrost in the arctic (swipa) 2017, 219–229. arctic monitoring and assessment programme (amap), oslo, norway. church, j. et al. 2013: sea level change. in: climate change 2013: the physical science basis. contribution of working group i to the fig. 3. highlighting the present-day land ice contribution to sea-level rise at copenhagen (a) and the global mean (b) (box & colgan 2017; larour et al. 2017). the slight difference in pie chart size ref lects sea-level rise at copenhagen (2.9 ± 0.4 mm/year; holgate et al. 2013) versus the global mean (2.8 ± 0.3 mm/year; nerem et al. 2010) during the 1993–2012 period. non-land ice processes include thermal expansion of seawater, changes in land water storage and shifts in atmospheric and oceanic currents at the local scale. a b russian arctic land ice scandinavian land ice alaskan land ice canadian arctic land ice other land ice antarctic land ice greenland land ice non-land ice processes year skagen copenhagen esbjerg table 1. sea level (m) relative to the 1901–1950 mean at skagen, copenhagen and esbjerg between 0 and 2100 ce based on palaeoreconstructions, tide gauge measurements and projections. uncertainties denote one standard deviation. c. 0 4.0 ± 0.5 n/a –1.5 ± 0.5 1980 –0.01 ± 0.01 0.01 ± 0.01 0.06 ± 0.01 2010 –0.02 ± 0.01 0.02 ± 0.01 0.10 ± 0.01 2040 rcp4.5 0.12 ± 0.08 0.21 ± 0.08 0.28 ± 0.08 rcp8.5 0.15 ± 0.09 0.23 ± 0.09 0.31 ± 0.09 2070 rcp4.5 0.27 ± 0.15 0.37 ± 0.15 0.47 ± 0.15 rcp8.5 0.37 ± 0.18 0.47 ± 0.18 0.57 ± 0.18 2100 rcp4.5 0.39 ± 0.21 0.51 ± 0.21 0.63 ± 0.21 rcp8.5 0.64 ± 0.28 0.77 ± 0.28 0.89 ± 0.28 e2019430101-05 fifth assessment report of the intergovernmental panel on climate change, 1137–1205, cambridge, cambridge university press. https:// doi.org/10.1017/cbo9781107415324.026 colgan, w., grinsted, a., box, j. & macferrin, m. 2018: the mind-bending physics of scandinavian sea-level change. popular science article for sciencenordic.com and videnskab.dk: http://sciencenordic.com/ mind-bending-physics-scandinavian-sea-level-change clemmensen, l., richardt, n. & andersen, c. 2001: holocene sea-level variation and spit development: data from skagen odde, denmark. the holocene 11, 323–331. http://dx.doi. org/10.1191/095968301667877044 gehrels, w., szkomik, k., bartholdy, j., kirby, j., bradley, s., marshall, w., heinemeier, j. & pedersen, j. 2006: late holocene sea-level changes and isostasy in western denmark. quaternary research 66, 288–302. http://dx.doi.org/10.1016/j.yqres.2006.05.004 gehrels, w. & shennan, i. 2015: sea level in time and space: revolutions and inconvenient truths. journal of quaternary science 30, 131–143. http://dx.doi.org/10.1002/jqs.2771 hauerbach, p. 1992: skagen odde – skaw spit. an area of land created between two seas. folia geographica danica 20, 119 pp. holgate, s. et al. 2013: new data systems and products at the permanent service for mean sea level. journal of coastal research 29, 493–504. http://dx.doi.org/10.2112/jcoastres-d-12-00175.1 jevrejeva, s., jackson, l., riva, r., grinsted, a. & moore, j. 2016: coastal sea level rise with warming above 2°c. proceedings of the national academy of sciences 113, 13342–13347. https://doi.org/10.1073/ pnas.1605312113 larour, e., ivins, e. & adhikari. s. 2017: should coastal planners have concern over where land ice is melting? science advances 3, p.e1700537. http://dx.doi.org/10.1126/sciadv.1700537. levermann, a., clark, p., marzeion, b., milne, g., pollard, d., radic, v. & robinson, a. 2013: the multimillennial sea-level commitment of global warming. proceedings of the national academy of sciences 110, 13745–13750. https://doi.org/10.1073/pnas.1219414110 móren, b., sejrup, h., hjestuen, b., borge, m. & schaüble, c. 2018: the last deglaciation of the norwegian channel – geomorpholog y, stratigraphy and radiocarbon dating. boreas 47, 347–366. http://dx.doi. org/10.1111/bor.12272 nerem, r., chambers, d., choe, c. & mitchum, g. 2010: estimating mean sea level change from the topex and jason altimeter missions. marine geodesy 33, 435–446. http://dx.doi.org/10.1080/0149 0419.2010.491031 nielsen, l., hansen, j., hede, m., clemmensen, l., pejrup, m. & noenygaard, n. 2014: simultaneous estimation of lithospheric uplift rates and absolute sea level change in southwest scandinavia from inversion of sea level data. geophysics journal international 199, 1018–1029. http://dx.doi.org/10.1093/gji/ggu290 permanent service for mean sea level (psmsl) 2018: tide gauge data. retrieved 10 november 2018 from http://www.psmsl.org/data/obtaining. stuhne, g. & peltier, w. 2015: reconciling the ice-6g_c reconstruction of glacial chronolog y with ice sheet dynamics: the cases of greenland and antarctica. journal of geophysical research: earth surface 120, 1841–1865. http://dx.doi.org/10.1002/2015jf003580 szkornik, k., gehrels, w. & murray, a. 2008: aeolian sand movement and relative sea-level rise in ho bugt, western denmark, during the ‘little ice age’. the holocene 18, 951–965. https://doi. org/10.1177/0959683608091800 how to cite colgan, w., box, j.e., ribeiro, s. & kjeldsen, k.k. 2019: sea-level rise in denmark: bridging local reconstructions and global projections. geological survey of denmark and greenland bulletin 43, e2019430101. https://doi.org/10.34194/geusb-201943-01-01 *corresponding author: william colgan | e-mail: wic@geus.dk 1 geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350, copenhagen k, denmark. https://doi.org/10.1017/cbo9781107415324.026 https://doi.org/10.1017/cbo9781107415324.026 http://sciencenordic.com http://videnskab.dk: http://sciencenordic.com/mind-bending-physics-scandinavian-sea-level-change http://sciencenordic.com/mind-bending-physics-scandinavian-sea-level-change http://dx.doi.org/10.1191/095968301667877044 http://dx.doi.org/10.1191/095968301667877044 https://dx.doi.org/10.1016/j.yqres.2006.05.004 http://dx.doi.org/10.1002/jqs.2771 http://dx.doi.org/10.2112/jcoastres-d-12-00175.1 https://doi.org/10.1073/pnas.1605312113 https://doi.org/10.1073/pnas.1605312113 http://dx.doi.org/10.1126/sciadv.1700537 https://doi.org/10.1073/pnas.1219414110 http://dx.doi.org/10.1111/bor.12272 http://dx.doi.org/10.1111/bor.12272 http://dx.doi.org/10.1080/01490419.2010.491031 http://dx.doi.org/10.1080/01490419.2010.491031 http://dx.doi.org/10.1093/gji/ggu290 http://www.psmsl.org/data/obtaining http://dx.doi.org/10.1002/2015jf003580 https://doi.org/10.1177/0959683608091800 https://doi.org/10.1177/0959683608091800 https://doi.org mailto:wic@geus.dk geological survey of denmark and greenland bulletin 20, 2010, 91–94 91 a number of sedimentary basins of various ages are located on and offshore vietnam (fig. 1). some of them have significant petroleum resources and have thus attracted interest from industry and academia (rangin et al. 1995; matthews et al. 1997; lee & watkins 1998; lee et al. 2001). moreover, vietnam is located in a position central to the understanding of the geological development of south-east asia (hall & morley 2004). the structural style and the stratigraphy of the vietnamese basins thus provide a valuable record about the development of south-east asia throughout the phanerozoic and the subsequent eocene as well as younger deformation associated with the collision and indentation of india into eurasia and the opening of the south china sea (fyhn et al. 2009a, 2010a). the geological survey of denmark and greenland has worked in vietnam since 1995 to assess the geology and petroleum potential of the vietnamese basins. since 2002 the work has been carried out in cooperation with the department of geography and geology, university of copenhagen, as part of the enreca project (enhancement of research capacity in developing countries). an integrated part of the project is its training of vietnamese msc and phd students incorporating both training courses at the department of geography and geology and courses held in vietnam. so far, 10 msc and 4 phd students have completed their training under the auspices of the enreca project and another 10 are expected to complete their education within the next phase of the project. the enreca project has already completed two phases and a third and final phase has recently started. the initial phase focused on the phu khanh and the song hong basins located in the south china sea offshore north and central vietnam and the smaller onshore song ba trough (fig. 1; bojesen-koefoed et al. 2005; nielsen et al. 2007; fyhn et al. 2009a, b, c). during the second enreca phase, completed in 2009, attention shifted towards the malay – tho chu and phu quoc basins located in the gulf of thailand, ssw of vietnam (petersen et al. 2009, in press; fyhn et al. 2010a, b). the phu quoc basin continues onshore to the north to form part of the mountainous area between vietnam and cambodia. in the recently started third phase of the project, the focus remains on the phu quoc basin in addition to a revisit to the song hong basin on the north vietnamese margin and onshore beneath the song hong (red river) delta. the phu quoc basin the phu quoc basin stretches in a 100–150 km broad belt from the central part of the gulf of thailand c. 500 km northwards to central cambodia. the basin is late jurassic to cretaceous in age but is one of the least explored basins in the region and remains to be drilled offshore (fyhn et al. 2010a). in order to assess the geological evolution and the petroleum potential of the basin, regional seismic analyses of the vietnamese part of the basin were carried out in combination with drilling of the fully cored, 500 m deep enreca-2 well on the phu quoc island. data from the enreca-2 well were complemented by data from outcrop studies on phu quoc and in cambodia. vietnamese sedimentary basins: geological evolution and petroleum potential michael b.w. fyhn, henrik i. petersen, anders mathiesen, lars h. nielsen, stig a.s. pedersen, sofie lindström, jørgen a. bojesen-koefoed, ioannis abatzis and lars o. boldreel phu khanh basin phu khanh basingulf of thailand gulf of thailand � � � � � � � � � �� red river shear z one ? m ae ping shear z one w. natuna basin w. natuna basin penyu basin mtcbmtcb mergui basin mergui basin pattani basin pattani basin malay basin malay basin fig.2 andaman sea three pagodas shear z one malaysia cambodia vietnam laos myanmar thailand sedimentary basin major thrust fault oceanic crust shear zone with main cenozoic strike-slip direction 100°e 110°e 15°n s again f au lt w . a n d am an f au lt ? ? ? nam con son basin nam con son basin cuu long basin cuu long basin phu quoc basin song hong basin song hong basin ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ india south china sea china borneo australia ▲ ▲ ▲ ▲ ▲ ▲ ▲ 2000 km khorat basin khorat basin song ba trough song ba trough phu quoc basin 250 km phu quoc basin © geus, 2010. geological survey of denmark and greenland bulletin 20, 91–94. open access: www.geus.dk/publications/bull fig. 1. map of south-east asia showing the locations of sedimentary basins and areas underlain by oceanic crust. strike-slip arrows illustrate the prevailing eocene–recent offset directions. mtcb: malay – tho chu basin. the inset map shows a simplified structural outline of the region. modified from fyhn et al. (2010b). 9292 alluvial sandstones with an average of c. 10% rhyolitedominated lithic fragments make up the greater part of the up to c. 4 km thick sediments filling the phu quoc basin. only a few, minor, shallow marine sandstone beds have been encountered in the terrestrially dominated succession. the sandstone-dominated succession is intercalated with subordinate alluvial plain and lacustrine siltand mudstone intervals. coal fragments are abundant at specific stratigraphic levels but do not contribute to any source potential. the thicknesses of the deposits are not affected by synsedimentary faulting, but gradually increase towards the east, where a coeval, jurassic–cretaceous, magmatic arc parallels the eastern basin f lank (fig. 2). this is compatible with a retroarc–foreland basin setting associated with the growth of the magmatic arc located east of the basin that also served as a primary source of sediments for the basin. a distinct basin inversion is indicated by a prominent angular unconformity that caps the mesozoic basin fill and is associated with spectacular thrust faulting and folding (fig. 3). the structural complexity increases towards the deeply eroded and hitherto undescribed fold belts that confine the basin to the east and west. the stratigraphic level of erosion increases towards these orogenic belts. palaeozoic and lower mesozoic igneous and sedimentary rocks therefore crop out on small islands and onshore, or subcrop towards the base of the cenozoic within the kampot fold belt f lanking the basin to the east. the inversion unconformity is underlain by lower cretaceous deposits and overlain by middle eocene and younger deposits, which provide only modest information on the age of the orogenic event. in order to constrain the age of inversion more precisely, apatite fission track analysis (afta) was carried out on rock samples from the kampot fold belt collected on islands and in mainland vietnam. the afta samples demonstrate a distinct cooling event that affected the region during the period from late paleocene to early eocene (fyhn et al. 2010a). the cooling corresponds to uplift and denudation of the area in response to the thrust faulting and basin inversion and thus confines the age of the orogenic event controlling the deformation. the malay – tho chu basin the malay – tho chu basin constitutes the vietnamese north-eastern part of the malay basin that was initiated somewhere between the middle and late eocene (fyhn et al. 2010b). the malay – tho chu basin is situated in the central part of the gulf of thailand and is therefore superimposed on the southernmost part of the phu quoc basin. rifting in the area took place between middle?–late eocene and oligocene time and resulted in the creation of a series of deep grabens filled by continental to shallow marine deposits (fig. 4; fyhn et al. 2010b). a set of nnw-trending rifts are the dominating structures in the area; they are often distinguished from other, wnw-trending rifts by their downwards steepening, their great depth and their linearity. the nnw-trending rifts seem to have accommodated leftlateral transtension. large-scale eocene–oligocene rifting associated with strike-slip faulting in the region is viewed as a response to the indian–eurasian collision that forced the neighbouring parts of south-east asia away from the collision zone through a series of lateral shear zones (e.g. tapponnier et al. 1986; fyhn et al. 2009a, 2010b), although n k h m e r f o ld b e lt k a m p o t f o ld b e lt ju r a s s ic – c r e t a c e o u s m a g m a t ic a r c u. jurassic – l. cretaceous strongly deformed u. jurassic – l. cretaceous pre-u. jurassic mainly mesozoic igneous rocks middle to upper cenozoic extensional fault subcrop concealed under thick cenozoic cover lower cenozoic contractional fault 50 km phu quoc enreca-2 vietnam m a la y – t h o c hu basin cambodia phu quoc basin fig. 3 fig. 4 10°s 104°e fig. 2. subcrop map towards the base cenozoic top / mesozoic unconformity outlining the southern part of the phu quoc basin. fold belts confine the basin to the east and west. onshore pre-quaternary outcrops are indicated, outlining the onshore continuation of the phu quoc basin, the kampot fold belt and the se indochina jurassic–cretaceous magmatic arc. for location see fig. 1. modified from fyhn et al. (2010a). 93 other theories exist (morley 2002; hall & morley 2004; watkinson et al. 2008; hall 2009). around the onset of the miocene, rifting declined and thermal sagging came to dominate throughout the neogene. this resulted in broadening of the subsiding area and increasing marine inf luence. deltaic and shallow marine siliciclastics therefore prevail in the neogene succession of the basin. petroleum exploration in the malay – tho chu basin began during the early 1970s, encouraged by successful exploration immediately south of vietnamese territory. the first well was drilled in 1994. since then, significant gas, condensate and oil discoveries have been made in several wells drilled in this basin, but only a few discoveries are as yet considered commercial. a re-evaluation of the existing exploration strategies is therefore desirable in order to optimise and focus future exploration. exploration has mainly aimed at early to middle miocene f luviodeltaic sand reservoirs with late neogene structural trapping mechanisms. potential source rocks have been interpreted as alginite-bearing lacustrine shales and humic coals situated in the palaeogene synrift and in the lowermost post-rift sections. the few potential source-rock levels penetrated by wells have shown remarkably low vitrinite ref lectance (vr) values compared to vr values obtained from overlying neogene coals (data presented in petersen et al. 2009). the maturity trends of such vr data sets are not well constrained as they produce suspiciously low thermal maturity gradients. however, suppressed vr values may occur in algenite-rich rocks. vr suppression is therefore particularly common in lacustrine shales with high hi (hydrogen index) values. the f luorescence alteration of multiple macerals (famm) technique is an accurate method to determine thermal maturity in rocks including those containing vitrinite with suppressed and enhanced vr values (willkins et al. 1992). by combining conventional vr measurements and the famm technique a revised, higher and more reliable thermal maturity gradient has been established (petersen et al. 2009). 2-d modelling of the maturation history of the basin was carried out based on the revised thermal maturity gradient, detailed seismic mapping, borehole information and new custom kinetics for petroleum generation; the latter was determined from lacustrine source rock samples and a terrestrially inf luenced mudstone collected from wells (petersen et al. in press). maturation modelling indicates that most of the syn-rift succession in the vietnamese malay basin is located in, or has passed through, the main oil and gas windows. carbonaceous 0 1 2 3 5 km t w o -w ay t ra ve l ti m e ( se c ) 4 5 sw l. pliocene u. miocene m. miocene pr ec en oz oi c eo ce ne l. miocene u. oligocene ne wnw-trending normal fault wnw-trending normal fault nnw-trending transtensional faults dhisdhi fig. 4. seismic transect across a nnwtrending palaeogene graben bounded by steep transtensional faults and half grabens confined by more gently dipping w nw-trending normal faults that link up with the steep faults at depth. deposition broadened across basement highs following the palaeogene synrift period due to regional thermal sagging. dhis (direct hydrocarbon indicators) within the miocene succession are frequently associated with structural traps formed during the late neogene. modified from fyhn et al. (2010b). 0 1 2 inversion unconformity ? sea neogene u. jurassic – l. cretaceous pre-jurassic t w o -w ay t ra ve l ti m e ( se c ) 10 km w e fig. 3. offshore stratigraphic profile across the phu quoc basin. jurassic–cretaceous subsidence was most intense simultaneous with the magmatic arc developing to the east. a prominent inversion unconformity separates the mesozoic thrust-faulted strata from the truncating unconformity of the base of the neogene deposits. modified from fyhn et al. (2010a). 9494 syn-rift deposits have therefore undergone adequate maturation and may have produced and expelled significant quantities of hydrocarbons. the oldest deposits in the deepest part of syn-rift depressions entered the oil window during the palaeogene syn-rift period but the main oil generation generally took place during early and middle miocene times. 2-d modelling of the hydrocarbon generation therefore indicates that the main risks in the tested play types are (1) the timing of petroleum generation relative to trap formation completed in the late neogene, (2) the pervasive faulting, which may have complicated petroleum migration to the structures and breached charged traps and (3) the distribution and amount of matured source rocks in smaller grabens. based on the above-mentioned criteria and the presence of direct hydrocarbon indicators (dhi), an untested alternative play type is proposed relying on syn-rift sandstones located up-dip from and near source-rock intervals with palaeogene structural and stratigraphic trapping mechanisms that did not experience subsequent neogene deformation. acknowledgements the enr eca project is funded by the danish ministry of foreign affairs through danida. geocenter denmark provided additional financial support. vietnam petroleum institute (petrovietnam) is thanked for providing data and permission to publish this paper. references bojesen-koefoed, j.a., nielsen, l.h., nytoft, h.p., petersen, h.i., dau, n.t., hien, l.v., duc, n.a. & quy, n.h. 2005: geochemical characteristics of oil seepages from dam thi nai, central vietnam: implications for hydrocarbon exploration in the offshore phu khanh basin. journal of petroleum geolog y 28, 3–18. fyhn, m.b.w., boldreel, l.o. & nielsen, l.h. 2009a: geological development of the central and south vietnamese margin: implications for the establishment of the south china sea, indochinese escape tectonics and cenozoic volcanism. tectonophysics 478, 184–204. fyhn, m.b.w., boldreel, l.o. & nielsen, l.h. 2009b: tectonic and climatic control on growth and demise of the phanh rang carbonate platform offshore south vietnam. basin research 21, 225–251. fyhn, m.b.w. et al. 2009c: geological evolution, regional perspectives and hydrocarbon potential of the northwest phu khanh basin, offshore central vietnam. marine and petroleum geolog y 26, 1–24. fyhn, m.b.w., pedersen, s.a.s., boldreel, l.o., nielsen, l.h., green, p.f., dien, p.t., huyen, l.t. & frei, d. 2010a: palaeocene – early eocene inversion of the phuquoc – kampot som basin: se asian deformation associated with the suturing of luconia. journal of the geological society of london 167, 281–295. fyhn, m.b.w., boldreel, l.o. & nielsen, l.h. 2010b: escape tectonism in the gulf of thailand: paleogene left-lateral pull-apart rifting in the vietnamese part of the malay basin. tectonophysics 483, 365–376. hall, r. 2009: hydrocarbon basins in se asia: understanding why they are there. petroleum geoscience 15, 131–146. hall, r. & morley, c.k. 2004: sundaland basins. in: clift, p. et al. (eds): continent–ocean interactions within east asian marginal seas. geophysical monograph 149, 55–85. lee, g.h. & watkins, j.s. 1998: seismic sequence stratigraphy and hydrocarbon potential of the phu khan basin, offshore central vietnam, south china sea. aapg bulletin 82, 1711–1735. tulsa, oklahoma: american association of petroleum geologists. lee, g.h., lee, k. & watkins, j.s. 2001: geological evolution of the cuu long and nam con son basins, offshore southern vietnam, south china sea. aapg bulletin 85, 1055–1082. tulsa, oklahoma: american association of petroleum geologists. matthews, s.j., fraser, a.j., lowe, s., todd, s.p. & peel, f.j. 1997: structure, stratigraphy and petroleum geolog y of the se nam con son basin, offshore vietnam. in: fraser, a.j., matthews, s.j. & murphy, r.w. (eds): petroleum geolog y of southeast asia. geological society special publications (london) 126, 89–106. morley, c.k. 2002: a tectonic model for the tertiary evolution of strikeslip faults and rift basins in se asia. tectonophysics 347, 189–215. nielsen, l.h., petersen, h.i., thai, n.d., duc, n.a., fyhn, m.b.w., boldreel, l.o., tuan, h.a., lindstrøm, s. & hien, l.v. 2007: a middle– upper miocene f luvial–lacustrine rift sequence in the song ba rift, vietnam: an analogue to oil-prone, small-scale continental rift basins. petroleum geoscience 13, 145–168. petersen, h.i., sherwood, n., mathiesen, a., fyhn, m.b.w., dau, n.t., russell, n., bojesen-koefoed, j.a. & nielsen, l.h. 2009: application of integrated vitrinite ref lectance and famm analyses for thermal maturity assessment of the northeastern malay basin, offshore vietnam: implications for petroleum prospectivity evaluation. marine and petroleum geolog y 26, 319–332. petersen, h.i., mathiesen, a., fyhn, m.b.w., dau, n.t., bojesen-koefoed, j.a., nielsen, l.h. & nytoft, h.p. in press: modeling of petroleum generation in the vietnamese part of the malay basin using custom kinetics. aapg bulletin. tulsa, oklahoma: american association of petroleum geologists. rangin, c., klein, m., roques, d., le pichon, x. & trong, l.v. 1995: the red river fault system in the tonkin gulf, vietnam. tectonophysics 243, 209–222. tapponnier, p., peltzer, g. armijo, r. 1986: on the mechanics of the collision between india and asia. in: coward, m.p. & ries, a.c. (eds): collision tectonics. geological society special publications (london) 19, 115–157. watkinson, i., elders, c. & hall, r. 2008: the kinematic history of the khlong marui and ranong faults, southern thailand. journal of structural geolog y 30, 1554–1571. wilkins, r.w.t., wilmshurst, j.r., russell, n.j., hladky, g., ellacott, m.v. & buckingham, c.p. 1992: fluorescence alteration and the suppression of vitrinite ref lectance. organic geochemistry 18, 629–640. authors’ addresses m.b.w.f., h.i.p., a.m., l.h.n., s.a.s.p., s.l., j.a.b-k. & i.a., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: mbwf@geus.dk l.o.b., department of geography and geology, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. geological survey of denmark and greenland bulletin 20, 2010, 103–106 103 in the following we describe the result of the titan project, an interactive web application (titan) developed at the geological survey of denmark and greenland (geus) together with dupont titanium technologies. the main aim of titan is to make computer-controlled scanning electron microscopy (ccsem) data, generated at geus, available via the internet. in brief, ccsem is a method automatically to detect particles with a scanning electron microscope (sem), and based on computer-controlled imagery to measure the chemistry and grain morphology of each particle in a given sample (knudsen et al. 2005; bernstein et al. 2008); keulen et al. 2008. titan makes data available on-line so that the user can interact with the data sets and analyse them using a web browser. in addition to ccsem data, titan contains a global database of titanium deposits and various reports. the web application is customised, such that the functionality and amount of data available for a given user depend on the privileges of that user. data a prerequisite for making titan available on the internet is that the data are stored in a relational database allowing for fast querying and retrieval. a detailed description of the data model is not given here, but we will make a short overview of the different data types and how the data are inserted and managed in the database. the data are stored in an oracle 10g database that is housed and maintained by geus (tulstrup 2004). ccsem data ccsem data are uploaded to the jupiter database via a desktop program developed with the delphi software tool at geus (fig. 1). typical ccsem samples consist of roughly one thousand grains. for each grain c. 30 analytical parameters are measured including elemental composition, grain size and grain shape. all parameters are stored in the database including the energy dispersive x-ray spectrum for each grain (from which the elemental composition of the grain is determined) as well as backscatter-mode sem images of the sample. the number of measurements currently stored in the database exceeds 54 million (fig. 2), and the number continues to grow at a rate of c. 15 million per year. once data are uploaded, each grain is classified according to a mineral classification scheme that is implemented using oracle database pl/sql procedures. the mineral classification scheme is based on the measured concentration of elements, and different schemes are available depending on the type of sample. for example, there is a mineral classification scheme for heavy mineral concentrates, while another scheme is applied for soil samples. titanium deposits and reports data on titanium deposits can be entered directly into the database through titan, and at present it contains detailed information about more than 600 deposits around the world. interactive web analysis and presentation of computer controlled scanning electron microscopy data peter riisager, nynke keulen, uffe larsen, roger k. mclimans, christian knudsen and jørgen tulstrup © geus, 2010. geological survey of denmark and greenland bulletin 20, 103–106. open access: www.geus.dk/publications/bull fig. 1. entry of sample metadata and uploading of ccsem data to the database using a desktop programme. the energ y dispersive x-ray spectrum for each grain and backscatter-mode sem images of the sample are also uploaded. 104104 reports and report metadata are uploaded to the database via the web application. the option to create, read, update, and delete deposits and reports is restricted to certain users and managed by strict user control. web interface the web application is based on open-source software, mainly java, and is running in an open-source jboss application server housed and maintained by geus. access to titan requires login with username and password. once logged in, the system assigns the user a specific role with specific priviliges allowing certain analytical functions. the user control is also extended to the individual ccsem samples so that each group of users can see and interact with only a restricted subset of ccsem samples. the ccsem data can be accessed using an interactive geological map web page (fig. 3) or by alphanumeric search criteria. when a sample is found, various recalculated data for that sample are available in table formats, and back-scatter mode sem images or other files, such as outcrop pictures related to the sample, can be viewed or downloaded. if users want to work with the data off-line, data can be exported to microsoft excel format or a customised pdf report can be generated. most importantly, the user has the option to visualise and interact with the data using various plots. for example, the elemental composition of all the mineral grains in a given sample can be presented in a scatter plot (fig. 4), where the user defines the elements assigned to the x and y axes and which minerals should be plotted. the user can select which minerals to be plotted for analysis and comparison of apparent grain sizes (fig. 5). this gives the user quick and easy access to make the desired analyses and plots. the on-line access has the added benefit that users around the world always have live access to the database, meaning that as soon as new data are uploaded the users can start interacting with them. 2002 2003 2004 2005 2006 2007 2008 2009 2010 10 000 000 20 000 000 30 000 000 40 000 000 50 000 000 year 0 n u m b e r o f an al y se s fig. 2. number of measurements in the titan database as a function of time. currently the database contains c. 54 million measurements. fig. 3. the titan web application includes an interactive map that allows the user to search for ccsem samples based on their geographic sampling coordinates. clicking on a sample on the map takes the user to other screen images where one can interact with the actual data (figs 4, 5). 105 examples of applications titan has successfully delivered data to scientists working at geus as well as various external end-users. in the following we will give some short examples of the use of titan. tracing kimberlite-indicator minerals for diamond prospection the elemental compositions of megacrystal and xenocrystal phases within kimberlitic rocks are used as an important diamond exploration tool. preliminary studies have demonstrated the excellent potential of ccsem to determine the elemental composition of minor elements in these minerals in a reliable and more cost-efficient manner than conventional electron microprobe analysis (keulen et al. 2009). exploration and ore deposit evaluation mineralogical characterisation of sediments is a prerequisite for exploration and exploitation of valuable sediment occurrences, such as heavy mineral deposits. with titan we have characterised individual mineral particles in heavy mineral sands, with the aim of detecting heavy mineral ore deposits (knudsen et al. 2005; bernstein et al. 2008). soil sample mineralogy for the cement industry cement manufacture causes emission of large quantities of airborne pollutants including greenhouse gases. with titan we have studied the raw materials used in cement production to optimise the performance of the grinding mill and the sintering process, with the ultimate aim to lower energy consumption at high temperatures (keulen et al. 2008). sediment provenance studies for oil exploration and sedimentary basin analysis sediment provenance studies are an important aspect in the evaluation of possible sandstone reservoirs. titan has served as an indispensable tool to determine source, compositional fig. 4. analysis of ccsem data with an interactive scatter plot using titan. the user defines the elements assigned to the x and y axes, and which minerals are plotted. 106106 variation and sedimentary pathways of several sedimentary deposits relevant for oil exploration (knudsen et al. 2005; bernstein et al. 2008). concluding remarks earth science is becoming an increasingly more quantitative science with new insights, more often than not, derived from detailed measurements. the titan project represents an example where advanced geoscientific instrumentation has allowed us to design projects that were not previously feasible, thereby opening new scientific research areas (e.g. bernstein et al. 2008; keulen et al. 2008, 2009). it is, however, important to underline that this progress does not only include the scientific instruments and analyses themselves, it also represents a major challenge to store and analyse the huge quantities of data generated (fig. 2). in this paper we have demonstrated that information technology plays a central role in facilitating the storage, retrieval and analysis of large geoscientific datasets. storing and distributing geological data are important aspects of national geological surveys, and it is important that geus follows in the footsteps of other national surveys in order to take full advantage of the new opportunities offered by the revolution of information technology. the titan project demonstrates that geus has the in-house expertise to develop technologies that address the full life cycle of geoscientific data from the raw instrument output, to store data securely in a database, analyse and reduce data, and finally distribute the data providing on-line and interactive access to the data. the know-how from the titan project is currently being applied to other similar projects at geus. finally, we would like to point out that besides the scientific and societal rationale of titan, it continues to be used by commercial partners. in fact, the application itself has almost exclusively been financed by industrial partners. references bernstein, s., frei, d., mclimans, r.k., knudsen, c. & vasudev, v.n. 2008: application of ccsem to heavy mineral deposits: source of high-ti ilmenite sand deposits of south kerala beaches, sw india. journal of geochemical exploration 96, 25–42. keulen, n., frei, d., bernstein, s., hutchison, m.t., knudsen, c. & jensen, l. 2008: fully automated analysis of grain chemistry, size and morpholog y by ccsem: examples from cement production and diamond exploration. geological survey of denmark and greenland bulletin 15, 93–96. keulen, n., hutchison, m.t. & frei, d. 2009: computer-controlled scanning electron microscopy: a fast and reliable tool for diamond prospecting. journal of geochemical exploration 103, 1–5. knudsen, c., frei, d., rasmussen, t., rasmussen, e.s. & mclimans, r. 2005: new methods in provenance studies based on heavy minerals: an example from miocene sands in jylland, denmark. geological survey of denmark and greenland bulletin 7, 29–32. tulstrup, j. 2004: environmental data and the internet: openness and digital data management. geological survey of denmark and greenland bulletin 4, 45–48. authors’ addresses p.r., n.k., u.l., c.k. & j.t., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: pri@geus.dk r.k.mcl., dupont titanium technologies, experimental station, e352/217, route 141 and henry clay, wilmington, de 19808, usa. fig. 5. analysis and comparison of the apparent grain size distributions of the various mineral fractions in the sample using titan. the plot is interactive, allowing the user to choose which minerals are plotted. geological survey of denmark and greenland bulletin 20, 2010, 79–82 79 greenland is receiving unprecedented international attention, both in scientific and political circles. characterised by a central ice sheet up to 3.4 km thick (inland ice), numerous ice caps and hundreds of outlet glaciers debouching into the surrounding oceans, greenland supports the second largest ice mass in the world. analysis of glacier movements, melt rates and ice loss to the sea, provide data with which to assess mass balance changes and thereby predict global sealevel rise. thus greenland plays a central role in the current worldwide debate on climate change. present-day dynamic ice loss is invariably advertised by the fast moving glaciers of western greenland with their spectacular calf ice production, such as the ice streams around disko bugt reviewed by weidick & bennike (2007). this tends to overshadow ice stability and expansion seen in the form of stationary and advancing glaciers elsewhere in greenland (modis 2009). while the seawards acceleration of glacier f low and retreat in frontal positions can be readily attributed to a shift in atmospheric and oceanic conditions (global warming), the same explanation can hardly be used for glaciers with contrasting movement histories. aim of this paper we focus on three west coast, marine-terminating glaciers between 75° and 78°n (fig. 1) to elucidate the retreat–advance paradox referred to above. steenstrup gletscher and tracy gletscher are chosen to illustrate the regional pattern of ice recession, including massive ice wasting on a broad front in melville bugt, whereas berlingske bræ defies this trend by long-lasting advance. the receding glaciers steenstrup and tracy are known from regional surveys (e.g. kollmeyer 1980; rignot & kanagaratnam 2006), but the advancing glacier berlingske bræ has only been cursorily mentioned in map descriptions (dawes 1992, 2006). we present maps showing the terminus f luctuations of the three glaciers based on historical records (figs 2–4) but the paper’s four-page limit prohibits discussion of the early sources. this aspect, climatic records and their relation to ice f luctuations, and comparisons with other greenland glaciers, will be dealt with in a forthcoming paper. historical sources and the 2009 database t.c. chamberlin and r.d. salisbury were the first to investigate glaciers in the region in 1894–95 when they reached as far north as inglefield bredning, the location of our northern glacier (tracy gletscher). the next milestone was the regional mapping by geologist and cartographer lauge koch between 1916 and 1923 who surveyed and described glaciers throughout the region. the 1940s heralded a new era of research with the incoming of aerial photographs and such images are available from the period 1948–1985. finally in the last decades, satellite images have assured a continual record of the areas covered and uncovered by greenland glaciers (weidick 1994). in this paper we make use of such imagery from the period 1963–2009. table 1 summarises our data sources. an advancing glacier in a recessive ice regime: berlingske bræ, north-west greenland peter r. dawes and dirk van as fig. 1. map of north-west greenland showing the locations of the three studied glaciers featured in figs 2–4. © geus, 2010. geological survey of denmark and greenland bulletin 20, 79–82. open access: www.geus.dk/publications/bull greenland 60°w 70°w 76°n 77°n 100 km fig. 4 tracy gletscher fig. 3 berlingske bræ fig. 2 steenstrup gletscher harald moltke bræ prudhoe land 78°n inland ice melville bugt baffin bay wolstenholme fjord l a u g e k o c h k y s t steensby land pituffik (thule air base) qaanaaq kap york 8080 steenstrup gletscher, melville bugt steenstrup gletscher is the widest glacier of the impressive ice front that characterises lauge koch kyst and that calves into melville bugt (figs 1, 2). stretching from the kap seddon peninsula to red head, where steenstrup gletscher borders the fairly stable kjer gletscher, the glacier has an irregular and crevassed f loating tongue more than 30 km wide. ice production from the central part is spectacular, both as regards the number of calved bergs and their size. koch (1928) noted that large portions of the 25 m high f loating tongue become detached and move seawards before being broken up, while kollmeyer (1980) described the calving of ‘ jigsaw puzzle type’ icebergs in excess of 1 km in length. as illustrated by fig. 2, the main f luctuations affected the central part of the f loating tongue where drawback since 1916 is almost 25 km. melville bugt is noted for its ice-infested waters during summer months and the records show that the nature and position of the ice front can change seasonally depending on the degree of ice congestion. in five months, from spring to autumn 1916, the central part of the front had moved westwards by c. 1 km while in 1920, after a summer when melville bugt was free of ice, there was recession of more than 6 km (koch 1928). in contrast, the northern segment of the terminus was stationary between 1916 and 1923. fig. 2. satellite image of steenstrup gletscher and neighbouring glaciers, southern melville bugt, showing eight frontal positions from 1916 to 2009. thin, white line: coastline. for sources, see table 1. fig. 3. satellite image of berlingske bræ, granville fjord showing seven frontal positions from 1922 to 2009. thin, white line: coastline. for sources, see table 1. table 1. data for north-west greenland glacier fluctuations year type/medium source 1892 field/map peary (1892) 1916 field/map koch (1922) 1922 field/map koch (1932) 1949* oap † /map geodetic institute § 1953 vap ‡ u.s. military 1963 satellite zhou & jezek (2003) 1971 vap ‡ greenarctic consortium 1985 vap ‡ geodetic institute 1975 1999 landsat nasa and u.s. 2007 satellite geological survey 2009 *photography 1948–1950; § 1st edition map 1954 † oblique aerial photography; ‡ vertical aerial photography red head kap seddon 10 km sverdrup gletscher d ie tr ich so n g l. steenstrup gletscher kjer gletscher 1916 1949 1963 1975 1985 1999 2007 2009 5 km 1916 1949 gr an vil le f jo rd berlingske bræ po liti ke n b ræ 1963 1975 1985 2007 2009 81 the shrinkage shown in fig. 2 has produced new bedrock exposures, and red head, which was a semi-nunatak in 1916, became an island in 2005. berlingske bræ, granville fjord berlingske bræ f lows westwards into the head of granville fjord from the major ice cap of steensby land that has a bridge connection with the inland ice (figs 1, 3). it is the only glacier of several draining into granville fjord that currently reaches the sea. the glacier has a rather low gradient and its f low pattern can be traced for about 25 km before being lost to the ice cap. the glacier trunk is 3–4 km wide, and today the terminus is irregular, rather slender and crevassed, and over 2 km across. it is unknown whether the snout is af loat, but the apparent lack of iceberg production suggests it is grounded. an unnamed tributary originating from a more westerly ice cap joins the northern f lank of berlingske bræ contributing to its westerly f low into granville fjord. the terminus positions shown in fig. 3 illustrate a continuous ice advance in excess of 4 km in the last 85 years that has changed the glacier front from being terrestrial to marine. as opposed to when the glacier terminated on land, its tongue now is strongly tapering. the glacier has overrun the entire alluvial gravel plain that in the early 20th century extended beyond its snout and separated it from the fjord, and it has also engulfed bedrock exposures on its southern f lank that were mapped by the first author in 1974. tracy gletscher, inglefield bredning tracy gletscher is the second largest of six outlet glaciers that debouch into the headwaters of inglefield bredning (figs 1, 4). it is about 5 km wide with a steep front that has a regular concave trace which is probably af loat. the f low pattern of the glacier is recognisable over 30 km before being lost to the east to the inland ice proper. the 115-year record (fig. 4) shows substantial ice wasting amounting to frontal recession of c. 15 km. the terminus positions show that for a century (1892–1985) tracy gletscher was coalesced with farquhar gletscher. in 1923 the seaward front of the f loating conf luent ice embracing melville gletscher was a cliff 20 m high and 19 km long (koch 1928). over the past century the glacier tongue has lost about 100 km2 of ice, which represents at least 20 km3 based on koch’s observation. recession with the impressive break-up of the conf luent ice mass has led to striking landscape changes. for example, longtime nunataks lee bjerg and field bjerg are now lapped by the sea, while josephine peary ø finally lives up to its name as an island being eventually released from the ice around 1960 (inûterssuaq uvdloriaq, personal communication 1971). recent glacial history: retreat versus advance the glaciers of north-west greenland and their marginal deposits are shown on the thule 1:500 000 scale geological sheet, and a summary of glacial history is given in the map description (dawes 2006). the regional pattern of spatial change seen in terms of terminal positions between 1948–50 and 1985 is shown on the maps of dawes (1988). this information, plus the early records summarised by koch (1928), the regional analysis of davies & krinsley (1962) and satellite data of the last decades, demonstrate that the general recession of the inland ice and its outlet glaciers is regional in character and persistent for more than a century. the drastic deglaciation of melville bugt has brought the ice limit there close to the early holocene position (bennike 2008). harvard øer lee bjerg tracy gletscher smithson bjerge heilprin gletscher inglefield bredning josephine peary ø m el vi lle g l. field bjerg sh a rp g le ts ch er fa rq u h a r g le ts ch er 5 km 1892 1922 1949 1963 1975 1985 2007 2009 fig. 4. satellite image of tracy gletscher and neighbouring glaciers, inglefield bredning, showing eight frontal positions from 1892 to 2009. thin, white line: coastline. for sources, see table 1. 8282 the overall pattern is that glaciers with f loating tongues, like steenstrup and tracy, have shown by far the largest retreat and ice wastage. the most extensive ice withdrawal has been along the heavily glaciated lauge koch kyst, where the lowering ice surface is being pierced by its rock substratum and where nunataks have become shoreline, and ice-rooted peninsulas insular. however, some glaciers show current fast retreat after decades of stability (e.g. sverdrup gletscher; fig. 2). in general, land-based glaciers show relatively sluggish movement, and some have been almost stationary or only show minor retreat (e.g. prudhoe land glaciers; dawes 2006). it is clear that given the existence of a detailed database, the general recession can be seen to have been interrupted by short periods of comparative stability and even advance (e.g. harald moltke bræ; mock 1966). in contrast to this regional recessive regime, berlingske bræ shows continual advance for at least 85 years. an explanation of this deviant behaviour must be sought in the fact that the glacier originates from an independent ice cap that responds to changes in temperature and precipitation differently than the inland ice. the glacier advance can be a response to increased precipitation on the ice cap or increased basal sliding, both of which could be related to the observed increase in atmospheric temperatures. no matter which, the advance of berlingske bræ over such a long period is unexpected in a warming climate. conclusions, relevance to global climate research and future work berlingske bræ is located between steenstrup gletscher and tracy gletscher that are 340 km apart. the two receding glaciers compare with others in melville bugt (and in other areas of greenland) indicating changed mass balance of their source: the inland ice. the main causes of this long-lasting change – documented in our data back to 1892 – must be regional, and thus the present warming climate must affect the process. however, whatever the fundamental cause (or causes) controlling regional meltdown, it has been a subordinate factor at berlingske bræ where there is long-standing advance. seen in terms of the regional, recessive ice regime in which it is located, berlingske bræ is anomalous and thus outside mainstream research concerning analysis of dwindling ice masses and their response to global warming. however, if we are to understand the underlying complex processes, and ultimately the effect of climate change on the regional recessive regime, attention should also be paid to such glaciers. among other things, this research should be directed to discovering why receding and expanding glaciers with century-long contrasting histories occur side by side. this paper is a contribution to international promotion of this aspect of glacioclimatic research in progress at the survey, both in our study region and elsewhere in greenland (e.g. weidick 2009). references bennike, o. 2008: an early holocene greenland whale from melville bugt, greenland. quaternary research 69, 72–76. davies, w.e. & krinsley, d.b. 1962: the recent regimen of the ice cap margin in north greenland. international association of scientific hydrolog y 58, 119–130. dawes, p.r. 1988: geological map of the thule district, north-west greenland. 1:100 000 sheets 1–6 and 1:200 000 sheets 7–11. unpublished maps, geological survey of denmark and greenland, copenhagen. dawes, p.r. 1992: new geological map of the thule region, north-west greenland. rapport grønlands geologiske undersøgelse 155, 42–47. dawes, p.r. 2006: explanatory notes to the geological map of greenland, 1:500 000, thule, sheet 5. geological survey of denmark and greenland map series 2, 97 pp. koch, l. 1922: note to maps of melville bay from wilcox point to cape york and of north greenland from 81°–83°35́ n, 38°–56°w. meddelelser om grønland 64(2), 77–88. koch, l. 1928: contributions to the glaciolog y of north greenland. meddelelser om grønland 65(2), 183–464. koch, l. 1932: map of north greenland, scale 1:300,000. copenhagen: geodetic institute, 19 sheets. kollmeyer, r.c. 1980: west greenland outlet glaciers: an inventory of the major iceberg producers. cold regions science and technolog y 1, 175–181. mock, s.j. 1966: fluctuations of the terminus of the harald moltke bræ, greenland. journal of glaciolog y 6(45), 369–373. modis 2009: modis studies of greenland. moderate resolution imagery spectroradiometer, nasa and byrd polar research center, http//bprc.osu.edu/modis/?p=61. peary, r.e. 1892: the north greenland expedition of 1891–92. journal of american geographical society 24, 536–558. rignot, e. & kanagaratnam, p. 2006: changes in the velocity structure of the greenland ice sheet. science 311, 986–990. weidick, a. 1994: satellite image atlas of glaciers of the world. greenland. united states geological survey professional paper 1386–c, 141 pp. weidick, a. 2009: johan dahl land, south greenland: the end of a 20th century glacier expansion. polar record 45(235), 337–350. weidick, a. & bennike, o. 2007: glaciation history and glaciolog y of jakobshavn isbræ and the disko bugt region, west greenland: a review. geological survey of denmark and greenland bulletin 14, 78 pp. zhou, g. & jezek, k. 2003: disp yearly satellite photographic mosaics of greenland 1962–1963. national snow and ice data center, boulder, colorado. digital media. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: prd@geus.dk geological survey of denmark and greenland bulletin 28, 2013, 33-36 33 assessing urban groundwater table response to climate change and increased stormwater infiltration mark t. randall, lars troldborg, jens christian refsgaard and jacob b. kidmose the global climate is expected to show continued warming throughout the coming century. as a direct consequence of higher temperatures, the hydrological cycle will undergo significant changes in the spatial and temporal distribution of precipitation and evapotranspiration. in addition to more frequent and severe droughts and f loods, climate change can affect groundwater recharge rates and groundwater table elevation (bates et al. 2008). some previous studies of climate change impact on groundwater have suggested alarming reductions in groundwater recharge and lowering of water tables. other studies, especially those focusing on regions of higher latitudes, have indicated a potential rise in water tables due to increased precipitation and recharge (scibek & allen 2006; woldeamlak et al. 2007). in addition to changes in precipitation patterns, a shift in stormwater infrastructure design may also alter the hydrologic cycle of urban areas. in recent years, there has been a growing trend towards adoption of low-impact development practices managing stormwater runoff. these practices aim to mitigate the impacts of urbanisation such as increased runoff volume, higher peak runoff f lows, lowered water tables and reduced water quality (prince george’s county 1999). in contrast to conventional stormwater infrastructure, which is designed to rapidly collect and convey runoff, low-impact development practices are designed to slow runoff, remove pollutants and evapotranspirate and infiltrate runoff locally. in recent years, numerous modelling studies have investigated the potential impact of stormwater infiltration on groundwater levels. gobel et al. (2004) used a combination of models (gwneu, hydrus-2d, spring) to demonstrate that the installation of infiltration practices across an urban catchment area in germany could raise the groundwater surface by up to 2.3 m in some locations. in another catchment scale study, maimone et al. (2011) used the modelling code dynflow to show that the future groundwater table may eventually stabilise up to 1.5 m higher than its current level in parts of philadelphia, if the city’s plan to alter 40% of its impervious areas into so-called ‘green’ stormwater recharge areas is completed. thompson (2010) used hydrus-2d to demonstrate that a stormwater infiltration basin could cause up to 1.3 m of localised groundwater mounding. in yet another study, endreny & collins (2009) used modflow to show that rain gardens installed throughout a residential catchment area could raise the steady-state groundwater table by up to 1.1 m. the studies mentioned above have investigated groundwater level response to either changes in climate or stormwater management infrastructure. however, to the authors’ knowledge no studies have investigated the concurrent effects of both alterations on the urban hydrologic cycle. in urban areas, it is necessary to determine the potential magnitude of the combined impact, as a steep rise in groundwater level can damage building foundations and subsurface infrastructure due to f looding and buoyancy forces (gobel et al. 2004; vázquez-suñé et al. 2005). this study aims to assess the potential changes in groundwater response caused by both increased precipitation and widespread instalment of stormwater infiltration infrastructure in the city of silkeborg, denmark, using the mike she model. change of groundwater level at the planned location of a new motorway in silkeborg is the focus of this study as portions of the config. 1. the silkeborg study area and the proposed course of the motorway. inset: the location of silkeborg in jylland. © 2013 geus. geological survey of denmark and greenland bulletin 28, 33–36. open access: www.geus.dk/publications/bull 1 kmend of pipe recharge area pervious area impervious area motorway jylland silkeborg c. 9°40´e c. 56°11´n 3434 struction are expected to come critically close to the present high groundwater table in that area. knowledge of the magnitude of potential groundwater changes is essential because improved drainage measures and increased use of concrete will significantly raise the costs of the new motorway. study area the city of silkeborg has a population of c. 43 000 inhabitants and is located in the central part of jylland, denmark (fig. 1). the focus of this study is just north of the river gudenåen, where a portion of the new motorway will be constructed c. 6 m below the present terrain surface. the surficial geology is dominated by coarse-grained, postglacial, sandy sediments that form an upper unconfined aquifer with a vertical extent of 10–15 m. the average precipitation in silkeborg during the period 1961–1990 was 903 mm per year, and the average potential evapotranspiration was 546 mm per year. the average monthly temperature during that period was 15.2°c in july/august and −0.3°c in january/ february (kidmose et al. 2013). methods hydrological models – mike she is a deterministic, fullydistributed and physically based model software capable of simulating surface and subsurface hydrological processes. the danish national water resources model (dk-model) is based on mike she and incorporates national data on geology, soil type, land use, topography, river network geometry, water abstraction and climate. the silkeborg model is a 100 m grid local model using hydraulic head boundary conditions from the 500 m grid dk-model. a 9.2 km2 area within the 103 km2 silkeborg model, which encompasses the new motorway construction and the greater part of the urbanised surroundings, was chosen for the current study (fig. 1). details on the development, calibration and validation of the dk-model and the silkeborg model are found in højberg et al. (2013) and kidmose et al. (2013), respectively. six different model scenarios have been evaluated (table 1). stormwater infiltration modelling – the silkeborg study area consists of 65.5% pervious and 34.5% impervious cover. in the scenarios with conventional drainage stormwater infrastructure (i.e. the ‘cd’ scenarios), 100% of the precipitation on impervious cells was routed directly to the river system (fig. 2a). precipitation on impervious cells had one time step (i.e. one day) to infiltrate or evapotranspirate. at the end of the time step, any water in excess of a detention storage of 4.7 mm (based on calibration results) was routed overland to adjacent cells based on topography. it is assumed that the cd-2010 scenario is representative of silkeborg’s current climate and stormwater conditions. in the end of pipe recharge (epr) scenarios (fig. 2b), it was assumed that 10.7% (34 ha) of the city’s pervious area has been turned into end of pipe stormwater infiltration ponds (figs 1, 2). model cells which were assumed to contain infig. 2. three model scenarios for stormwater drainage infrastructure. scenario name climate data input stormwater infrastructure cd-2010 recorded 1991–2010 conventional drainage to river system epr-2010 recorded 1991–2010 end of pipe infiltration ponds lar-2010 recorded 1991–2010 local area recharge cd-2100 projected 2081–2100 conventional drainage to river system epr-2100 projected 2081–2100 end of pipe infiltration ponds lar-2100 projected 2081–2100 local area recharge table 1. summary of model scenarios a b c conventional drainage end of pipe recharge local area recharge 35 filtration ponds were assigned detention storage of 500 mm to represent the storage depth of the pond. in the epr scenarios, precipitation which would normally be applied to impervious cells was reduced to zero, and the equivalent volume of precipitation was instead evenly distributed over the infiltration pond cells via an increase in precipitation applied to those cells. in the epr scenarios there were 9.3 times as much impervious drainage area as infiltration pond area, so the infiltration pond model cells had 1030% (i.e. 100% + 9.3 × 100%) of the actual rainfall applied to them. this method of manipulating precipitation to simulate the collection of stormwater in specialised infiltration areas on a city-wide scale is similar to the modelling strategy used by holmandodds et al. (2003). the local area recharge (lar) scenarios represent a system where stormwater is managed at the level of individual plots through any combination of infiltration practices, each no more than tens of metres across. it was assumed that infiltration possibilities are numerous and located in close proximity so that at the scale of the model, each cell effectively behaves as a pervious cell. therefore, all paved areas were given properties identical to the pervious areas with infiltration rates controlled by the underlying soils. climate input – precipitation, temperature and evapotranspiration data from the danish meteorological institute from 1991 to 2010 were used as input to the ‘2010’ model scenarios. the input climate data for the ‘2100’ scenarios were generated by applying correction factors based on nine climate model projections from the ensembles project (christensen et al. 2009) to present-day climate data. further information on the delta change downscaling method used can be found in seaby et al. (2013). to generate the results for each of the three ‘2100’ infrastructure scenarios, the model was run nine times (once for each of the nine climate model projections), and the results averaged. results water table elevation – average groundwater elevations along the area planned for the motorway construction were extracted from the mike she model results (fig. 3). areas where the solid black line (i.e. the motorway surface) drops below the water table indicate portions of the motorway which could be f looded by groundwater. in the cd-2010 scenario, a stretch of 160 m of motorway is below the average water table. in the cd-2100 scenario, the average groundwater table elevation is raised by 0.08 m, and the length of motorway surface at risk is extended to 180 m. hundreds of metres of the proposed motorway are potentially f looded in the lar-2010 and the lar-2100 scenarios where the average water table rose 0.48 and 0.55 m above cd-2010 levels, respectively. the highest average water tables of 1.15 and 1.19 m above cd-2010 occur in the epr-2010 and epr-2100 scenarios, which would both put a stretch of nearly 1 km of the proposed motorway at risk. the results indicate that the impact of climate change (i.e. the difference between the ‘2010’ and the ‘2100’ scenarios) is small compared to the impact of extensive implementation of either local area or end of pipe stormwater infiltration practices. only average water tables are presented here to compare the relative impacts of different model scenarios. however, maximum water tables could put much longer sections of the motorway at risk and will therefore be considered in the final design of the motorway. water balance – average yearly volumes of precipitation, evapotranspiration, recharge and overland f low were calculated for the 1991–2010 time period for each stormwater infig. 3. average modelled groundwater table elevations along the 2000 m of projected motorway at silkeborg. the results are relative to cd-2010. model scenario mean (mm/year, 1991–2010) precipitation evapotranspiration recharge overland flow baseflow cd 911 319 304 292 8 lar 911 441 463 11 15 epr 911 311 588 19 29 table 2. catchment water balances for different stormwater infrastructure scenarios lar-2010 lar-2100 epr-2010 epr-2100 motorway surface cd-2100 nw se –0.5 0.5 1.0 1.5 3.0 2.5 2.0 0.0g ro un dw at er t ab le ( m ) 0 500 1000 1500 2000 distance along subsurface motorway stretch (m) 3636 frastructure scenario using mike she’s water balance tool (see table 2). evapotranspiration was greater in the lar scenario, due to the much larger evaporation surface available. recharge was much higher in both infiltration scenarios than in the cd scenario. overland f low, or the volume of water which f lows directly into the river system, was very small in both the infiltration scenarios in comparison to the cd scenario which routed all water from impervious areas into the nearest stream. basef low was highest in the epr scenario, followed by the lar scenario and finally the cd scenario, as would be expected based on the relative recharge volumes in these scenarios. summary and conclusions previous studies have reported groundwater level rise due to either climate change (scibek & allen 2006; woldeamlak et al. 2007) or stormwater infiltration practices (gobel et al. 2004; maimone et al. 2011). however, these two changes to the urban hydrologic cycle are typically not assessed in an integrated way as in this study. the modelling results presented in this paper are within the ranges of the above studies, i.e. tens of centimetres due to climate change and potentially more than 1 m due to the widespread adoption of stormwater infiltration practices. however, these results are specific to the silkeborg motorway and it is expected that the relative magnitude of the impact due to climate change and stormwater infiltration could vary greatly under different climatic and geological regimes. stormwater infiltration practices are often regarded as a form of climate change adaptation in the field of stormwater management as they can help to accommodate the higher intensity and larger volume precipitation events expected in the future. however, as the results of this study indicate, these same practices amplify other problems associated with climate change (i.e. groundwater table rise). the study clearly shows the need for integrated research of urban hydrology, and communication between hydrogeologists, stormwater engineers, planners and policy makers. acknowledgement we thank the danish road directorate for funding this study. references bates, b., kundzewicz, z., wu, s. & palutikof, j. 2008: climate change and water. intergovernmental panel on climate change, technical paper 6, 200 pp. geneva: ipcc. christensen, j.h., rummukainen, m. & lenderink, g. 2009: formulation of very-high-resolution regional climate model ensembles for europe [research theme 3]. ensembles: climate change and its impacts: summary of research and results from the ensembles project, 47–58. exeter, uk: meteorological office hadley centre. endreny, t. & collins, v. 2009: implications of bioretention basin spatial arrangements on stormwater recharge and groundwater mounding. ecological engineering 35, 670–677. gobel, p. et al. 2004: near-natural stormwater management and its effects on the water budget and groundwater surface in urban areas taking account of the hydrogeological conditions. journal of hydrolog y 299, 267–283. højberg, a.l., troldborg, l., stiesen, s., christensen, b.b.s. & henriksen h.j. 2013: stakeholder driven update and improvement of a national water resources model. environmental modelling & software 40, 202–213. holman-dodds, j.k., bradley, a.a. & potter, k.w. 2003: evaluation of hydrologic benefits of infiltration based urban storm water management. journal of the american water resources association 39, 205–215. kidmose, j., refsgaard, j.c., troldborg, l., seaby, l.p. & escrivà, m.m. 2013: climate change impact on groundwater levels: ensemble modelling of extreme values. hydrolog y and earth system sciences 17, 1619–1634. maimone, m., o’rourke, d.e., knighton, j.o. & thomas, c.p. 2011: potential impacts of extensive stormwater infiltration in philadelphia. environmental engineer 14, 29–39. prince george’s county 1999: low-impact development design strategies: an integrated design approach, 150 pp. prince george’s county, md: department of environmental resources. http://water.epa.gov/polwaste/green/upload/lidnatl.pdf scibek, j. & allen, d. 2006: comparing modelled responses of two highpermeability, unconfined aquifers to predicted climate change. global and planetary change 50, 50–62. seaby, l.p., refsgaard, j.c., sonnenborg, t.o., stisen, s., christensen, j.h. & jensen, k.h. 2013: assessment of robustness and significance of climate change signals for an ensemble of distribution-based scaled climate projections. journal of hydrolog y, http://dx.doi.org/10.1016/j. jhydrol.2013.02.015 thompson, a., nimmer, m. & misra, d. 2010: effects of variations in hydrogeological parameters on water-table mounding in sandy loam and loamy sand soils beneath stormwater infiltration basins. hydrogeolog y journal 18, 501–508. vázquez-suñé, e., sanchez-vila, x. & carrera, j. 2005: introductory review of specific factors inf luencing urban groundwater, an emerging branch of hydrogeolog y, with reference to barcelona, spain. hydrogeolog y journal 13, 522–533. woldeamlak, s., batelaan, o. & de smedt, f. 2007: effects of climate change on the groundwater system in the grote-nete catchment, belgium. hydrogeolog y journal 15, 891–901. authors’ addresses m.t.r., computational hydraulics international, 147 wyndham street north, suite 202, guelph, ontario, n1h 4e9 canada. e-mail: mark@chiwater.com l.t., j.c.r. & j.b.k., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. http://dx.doi.org/10.1016/j.jhydrol.2013.02.015 http://dx.doi.org/10.1016/j.jhydrol.2013.02.015 geological survey of denmark and greenland bulletin 13, 2007, 73-76 a series of cenozoic basins fringes the vietnamese coastal margin, often characterised by more than 10 km of sedimentary infill (fig. 1). greater parts of the margin are still in an early explorational state, although significant petroleum production has taken place in all but the southern song hong and the phu khanh basins. this has increased the need for a fundamental understanding of the processes behind the formation of the basins, including analyses of potential source rocks. the basins fringing the indochina block provide excellent evidence of the geological evolution of the region, and the basin geometries reflect the collision of india and eurasia and the late cenozoic uplift of south indochina (rangin et al. 1995a; fyhn et al. in press). in addition, the basins provide evidence of regional palaeogene rifting and subsequent late palaeogene through early neogene sea-floor spreading in the south china sea. apart from the regional cenozoic tectonic record, the basins contain a high-resolution climatic record of south-east asia due to the high depositional rates, changing depositional styles and large hinterland of the basin (clift et al. 2004). background since 1995 the geological survey of denmark and greenland (geus) and the department of geography and geo logy, university of copenhagen, have operated jointly in vietnam aiming to improve the local geoscientific capa city. the work is part of the enreca project (enhancement of research capacity in developing countries), funded by the danish international development agency (danida). this part of the enreca project focuses on an assessment of the hydrocarbon potential of the vietnamese continental margin, and has led to basin evaluations of the song hong and the phu khanh basins (fig. 1), and to a series of both vietnamese and danish m.sc. projects (nielsen et al. 1999; nielsen & abatzis 2004; andersen et al. 2005; boldreel et al. 2005; fyhn et al. in press). the ongoing second phase of the project focuses both on training vietnamese m.sc. and ph.d. students and on evaluating the hydrocarbon potential of the vietnamese part of the malay and khmer basins, as well as cenozoic evolution of the vietnamese coastal margin michael b.w. fyhn, lars henrik nielsen and lars ole boldreel © geus, 2007. geological survey of denmark and greenland bulletin 13, 73–76. available at: www.geus.dk/publications/bull 73 fig. 1. map showing major cenozoic basins and oceanic crust and simplified cenozoic structural features. a: cross-section shown in fig. 3. b: cross-section shown in fig. 4. modified from fyhn et al. (in press). the mesozoic strata underneath and shoreward of these basins. sampling of source rocks and oil seeps and drilling of two 500 m deep, fully cored wells (enreca-1 and 2, fig. 1) as well as acquisition of shallow seismic data have been carried out as part of the basin evaluations (bojesen-koefoed et al. 2005; petersen et al. 2005). furthermore, a broader analysis of the structure and stratigraphy of the entire vietnamese margin is being carried out as a separate ph.d. study funded by the university of copenhagen. tectonic models the indochina block is situated immediately south-east of the eastern himalayan syntaxis. the himalayan orogeny thus had a major impact on the structural evolution of indo china, leading to major north-west–south-east crustal shortening in the north and to significant lateral movements along shear zones transecting and bordering the indochina block (fig. 1; morley 2002). some of the largest shear zones are the north-west-trending red river, mai ping and three pagodas shear zones. south-eastward displacement and rotation of indochina and adjacent areas produced a total left-lateral offset of several hundreds of kilometres along the three shear zones (hall 2002). tapponnier et al. (1982) suggested that the south china sea and its marginal basins formed due to complex pull-apart mechanisms in response to these left-lateral displacements (fig. 2a). alternatively, taylor & hayes (1983) suggested that the formation of the south china sea was a result of a southward subduction of ocean crust beneath borneo (fig. 2b). one of the major differences between the two models is that the subduction model predicts right-lateral displacement across a large part of the vietnamese margin, whereas the pull-apart model is associated with a left-lateral transform along the margin. the offshore red river shear zone the most extensive of the indochinese left-lateral shear zones is the red river shear zone that passes through south china and northern vietnam into the song hong basin. seismic studies of the almost 20 km deep song hong basin indicate that the basin formed in response to major palaeogene leftlateral offset along the seaward continuation of the red river shear zone (rangin et al. 1995a; nielsen et al. 1999; ander sen et al. 2005). recent studies show that the shear zone continues along the vietnamese coast in the phu khanh basin further south (fig. 1; fyhn et al. in press). the shear zone runs along the western boundary of the phu khanh basin 74 fig. 2. conceptual models of the two basic theories initially proposed for the formation of the south china sea (tapponier et al. 1982; taylor & hayes 1983). later studies have suggested various integrations of the two models (hall 2002; morley 2002; fyhn et al. in press). a: the pullapart model suggests rifting and subsequent sea-floor spreading as a result of a complex left-lateral pull-apart mechanism. b: the subduction model suggests rifting and subsequent sea-floor spreading as a result of the subduction of old oceanic lithosphere beneath borneo. note that both models infer a transform zone along the central and south vietnamese margin but with opposite relative sense of motion. modified from tapponier et al. (1982) and taylor & hayes (1983). fig. 3. cross-section of the northern phu khanh basin transecting the offshore continuation of the red river shear zone. timing of the deformations shows palaeogene left-lateral movement followed by moderate right-lateral inversion during the early neogene. the structural cut-off of the pre-rift sequence towards the shear zone is interpreted to be a result of the large left-lateral movement along the zone (see fig. 1 for location). forming a major rift structure filled by thick palaeogene synrift deposits (fig. 3). left-lateral transtension ended during latest oligocene time in the phu khanh basin, but was followed by earliest miocene structural inversion. this is interpreted to reflect a change from intense left-lateral trans tension to modest right-lateral movements along the seaward extension in the red river shear zone in the basin, corroborated by a study by rangin et al. (1995b) showing that left-lateral, coast-parallel wrench faults onshore have been inverted by right-lateral movements. the latest palaeogene termination of left-lateral movement along the offshore part of the red river shear zone in the phu khanh basin does not support neogene sea-floor spreading in the south china sea as a result of left-lateral pull-apart. consequently, neogene seafloor spreading cannot have been caused by left-lateral pullapart, but was probably forced by subduction of older oceanic crust beneath borneo. palaeogene rifting along the vietnamese margin was, on the other hand, greatly influenced by left-lateral transtension. the offshore three pagodas shear zone rifting in the malay and khmer basins south-west of vietnam was originally linked to left-lateral transtension across a seaward extension of the three pagodas shear zone (fig. 1; tapponnier et al. 1982). later models suggested right-lateral faulting along the fault zone as the forcing mechanism (polachan & sattayarak 1989), or a combination of forces related to the indochina extrusion and extension caused by subduction roll-back (morley 2001), or mantle plume emplacement (ngah et al. 1996). seismic structural analysis of the vietnamese part of the malay and khmer basins indicates that rifting mainly took place during the palaeogene, and was controlled by a steep, north-north-west-trending, downward steeping master fault, which is flanked by smaller north-west-trending conjugate normal faults (fig. 4). the master fault offsets the basement with up to more than 2 sec. twt and transects the entire study region striking towards the point at which the three pagodas shear zone enters the gulf of thailand. the master fault is therefore interpreted as an offshore fault strand of the three pagodas shear zone. the fault characteristics indicate palaeogene left-lateral transtension and thus support a close relation between extrusion of indochina and rifting in the two basins. depositional trends sea-floor spreading in the south china sea did not start until the middle oligocene, and palaeogene syn-rift sedimentation was therefore dominated by alluvial and lacustrine deposition. in the song hong basin a gradual marine transgression of the margin started after the onset of sea-floor spreading. during initial transgression siliciclastic deposition in estua ries and narrow marine pathways dominated larger parts of the basins, and carbonate growth took place on inundated highs. open marine conditions prevailed in most basins during neogene times as sea-floor spreading propagated to its max imum south-western extension. extensive carbonate growth took place on many intraand interbasinal highs south of and along the vietnamese margin up to c. 16°n during the neo gene, favoured by the open marine environment and climatic conditions. in contrast, sediment supply kept pace with subsidence in most parts of the malay and song hong basins, preventing long-lasting periods of open marine sedimentation. during late neogene time, central and southern indo china were thermally uplifted, thus significantly increasing the siliciclastic input to the marginal basins. the increased terrigenous sediment supply inhibited widespread carbonate growth off southern and central vietnam and resulted in the progradation of a distinct shelf slope, which has led to the present outline of the margin. source rocks one of the main risk factors regarding petroleum exploration in the vietnamese offshore basins is the presence of adequate source rock intervals. onshore data from the enreca-1 core through the song ba trough in central vietnam show, however, that thick intervals of excellent oiland gas-prone lacustrine mudstone and humic coals may develop even in 75 fig. 4. cross-section of the vietnamese part of the malay basin which transects a fault strand of the seaward continuation of the three pagodas shear zone. the main offset along the major fault occurred during palaeogene times as left-lateral transtension forced by the indentation of india into eurasia (see fig. 1 for location). small basins characterised by high sediment input. although the song ba trough is an order of magnitude smaller than the vietnamese offshore basins, seismic data in the latter show apparent depositional similarities suggesting the presence of similar high-quality source rocks in the offshore basins (nielsen et al. 2007; fyhn et al. in press). in addition, seismic facies analysis as well as oil and gas compositions indicate that other source rock types, such as neogene fluvio-deltaic coals, carbonaceous shales and fore-reef marls are present in some of the basins and thus testify to the great petroleum potential of the vietnamese margin (bojesen-koefoed et al. 2005; fyhn et al. in press). acknowledgements this study is a ph.d. project funded by the faculty of natural science at the university of copenhagen to the first author. funding to the enreca project was given by the danish ministry of foreign affairs through danida. vietnam petroleum institute (petrovietnam) is thanked for providing the seismic reflection and well data and giving permission to publish these. references andersen, c., mathiesen, a., nielsen, l.h., tiem, p.v., petersen, h.i. & diem, p.t. 2005: evaluation of petroleum systems in the northern part of the cenozoic song hong basin (gulf of tonkin), vietnam. journal of petroleum geology 28, 167–184. bojesen-koefoed, j.a., nielsen, l.h., nytoft, h.p., petersen, h.i., dau, n.t., hien, l.v., duc, n.a. & quy, n.h. 2005: geochemical characteristics of oil seepages from dam thi nai, central vietnam: implications for exploration in the offshore phu khanh basin. journal of petroleum geology 28, 3–18. boldreel, l.o. et al. 2005: the phu khanh basin – aspects of structural evolution and hydrocarbon potential. science-technology conference: 30 years vietnam petroleum industry – new challenges and opportunities, 24–25 august 2005. hanoi, vietnam: petrovietnam (cd-rom). clift, p.d., layne, g.d. & blusztajn, j. 2004: marine sedimentary evidence for monsoon strengthening, tibetian uplift and drainage evolution in east asia. in: clift, p.d. et al. (eds): continent–ocean interactions within east asian marginal seas. geophysical monograph series 149, 235–254. fyhn, m.b.w. et al. in press: geological evolution, regional perspectives and hydrocarbon potential of the northwest phu khanh basin, offshore central vietnam. marine and petroleum geology. hall, r. 2002: cenozoic geological and plate tectonic evolution of se asia and the sw pacific: computer-based reconstructions, model and animations. journal of asian earth sciences 20, 353–431. morley, c.k. 2001: combined escape tectonics and subduction rollback–back arc extension: a model for the evolution of tertiary rift basins in thailand, malaysia and laos. journal of the geological society (london) 158, 461–474. morley, c.k. 2002: a tectonic model for the tertiary evolution of strikeslip faults and rift basins in se asia. tectonophysics 347, 189–215. ngah, k., madon, m. & tjia, h.d. 1996: role of pre-tertiary fractures in formation and development of the malay and penyu basins. in: hall, r. & blundell, d. (eds): tectonic evolution of southeast asia. geological society special publication (london) 106, 281–289. nielsen, l.h. & abatzis, i. 2004: petroleum potential of sedimentary basins in vietnam: long-term geoscientific co-operation with the vietnam petroleum institute. geological survey of denmark and greenland bulletin 4, 97–100. nielsen, l.h., mathiesen, a., bidstrup, t., vejbæk, o.v., dien, p.t. & tiem, p.v. 1999: modeling the hydrocarbon generation in the cenozoic song hong basin, vietnam: a highly prospective basin. journal of asian earth sciences 17, 269–294. nielsen, l.h., petersen, h.i., thai, n.d., duc, n.a., fyhn, m.b.w., boldreel, l.o., tuan, h.a., lindstöm, s. & hien, l.v. 2007: a middle–upper miocene fluvial-lacustrine rift sequence in the song ba rift, vietnam: an analogue to oil-prone, small-scale continental rift basins. petroleum geoscience 13, 145–168. petersen, h.i., tru, v., nielsen, l.h., duc, n.a. & nytoft, h.p. 2005: source rock properties of lacustrine mudstones and coals (oligocene dong ho formation), onshore song hong basin, northern vietnam. journal of petroleum geology 28, 19–38. polachan, s. & sattayarak, n. 1989: strike-slip tectonics and the development of tertiary basins in thailand. in: thanasuthipitak, t. (ed.): proceeding of the international symposium on intermountain basins: geology and resources, 243–253. chiang mai, thailand: university press. rangin, c., klein, m., roques, d., le pichon, x. & trong, l.v. 1995a: the red river fault system in the tonkin gulf, vietnam. tectonophysics 243, 209–222. rangin, c., huchon, p., le pichon, x., bellon, h., lepvrier, c., roques, d., hoe, n.d. & quynh, p.v. 1995b: cenozoic deformation of central and south vietnam. tectonophysics 235, 179–196. tapponier, p., peltzer, g., le dain, a.y., armijo, r. & cobbold, p. 1982: propagating extrusion tectonics in asia: new insights from simple experiments with plasticine. geology 10, 611–616. taylor, b. & hayes, d.e. 1983: origin and history of the south china sea basin. in: hayes, d.e. (ed.): the tectonic and geologic evolution of southeast asian seas and islands 2. geophysical monograph series 27, 23–56. authors’ addresses m.b.w.f. & l.o.b., department of geography and geology, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: fyhn@geol.ku.dk l.h.n., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. 76 geological survey of denmark and greenland bulletin 28, 2013, 21-24 21 late glacial to early holocene development of southern kattegat carina bendixen, jørn bo jensen, ole bennike and lars ole boldreel the kattegat region is located in the wrench zone between the fennoscandian shield and the danish basin that has repeatedly been tectonically active. the latest ice advances during the quaternary in the southern part of kattegat were from the north-east, east and south-east (larsen et al. 2009). the last deglaciation took place at c. 18 to 17 ka bp (lagerlund & houmark-nielsen 1993; houmark-nielsen et al. 2012) and was followed by inundation of the sea that formed a palaeo-kattegat (conradsen 1995) with a sea level that was relatively high because of glacio-isostatic depression. around 17 ka bp, the ice margin retreated to the øresund region and meltwater from the retreating ice drained into kattegat. over the next millennia, the region was characterised by regression because the isostatic rebound of the crust surpassed the ongoing eustatic sea-level rise, and a regional lowstand followed at the late glacial to holocene transition (mörner 1969; thiede 1987; lagerlund & houmark-nielsen 1993; jensen et al. 2002a, b). major parts of kattegat are characterised by thick successions of late weichselian and holocene sediments (mörner 1969; bergsten & nordberg 1992; gyldenholm et al. 1993). at around 9.6 ka bp, a large lagoon–estuary environment in southern kattegat was partly blocked by transgressive, coastal barrier islands and spits (bennike et al. 2000; jensen et al. 2002a). the aim of this paper is to describe the late glacial and early holocene development of southern kattegat, based on a recent study (bendixen 2012). the study area covers 1696.5 km2 and is located south of the island of anholt in the southern part of kattegat (figs 1, 2). the south-western part of the area is shallow but water depths increase to the north-east where depths over 40 m are found (fig. 2). two distinct submarine channels running nearly n–s and ne– sw were probably formed by subglacial meltwater erosion; these channels are partly filled by late glacial and holocene sediments. the area can be seen as a transitional shallow water area at the entrance to the baltic sea (bennike et al. 2000). detailed 2d seismic work will be conducted in the region over the next years, which will improve the basis for interpretations in the coming years. methods the data used in this study consist of shallow single-channel seismic profiles and sediment cores. the seismic data comprise boomer data acquired by r/v alexander von humboldt from 1997 to 1999 and sparker data acquired in 2011 using m/v laura. navigation was based on differential gps. the sediment cores were collected with a 6 m long vibrocorer fig. 1. map of denmark showing the location of the study area of fig. 5 in southern kattegat. fig. 2. bathymetric map of the study area in southern kattegat showing the two incised palaeo-channels from storebælt (arrows) that drained into the kattegat and the location of the shallow seismic profile shown in fig. 3. the white areas to the east are swedish territorial waters. © 2013 geus. geological survey of denmark and greenland bulletin 28, 21–24. open access: www.geus.dk/publications/bull 10°e 14°e 55°n 57°n kattegat storebælt baltic sea kielerkieler fig. 2 fig. 5 øresund fennoscandian shield danish basin 50 km jylland fyn djursland anholt 11°e 12°e 56°40´n 56°20´n anholt djursland 20 km fig. 3 fig. 5 0 10 20 30 40 50 60 70 80 water depth (m) 2222 from laura in 2011. the cores were cut into 1 m long sections that were shipped to the geological survey of denmark and greenland where they were split, photographed, described and subsampled in the laboratory. prior to interpreting the seismic profiles, promax seismic data processing software was used to optimise the data quality. the boomer data were subjected to frequency filtering and the sparker data were subjected to the kirchhoff time-migration method. interpretation of the seismic data was carried out using the program seisvision. results and discussion two late glacial units (lg1 and lg2) have been identified (fig. 3); they show high variability in thickness in the area studied. the sediments were deposited during a sea-level highstand period, which can be seen from the internal seismic pattern. the older lg1 unit shows draping parallel ref lections of low amplitude whereas the lg2 unit shows parallel ref lections of high amplitude (fig. 3). the units are divided by an erosional unconformity in the north-eastern parts of the study area, whereas continued deposition occurred in the west where no unconformity is found. a single radiocarbon dating of a shell of hiatella arctica from lg1 gave an age of 16.1–16.6 cal. ka bp, and dating of shells from lg2 gave ages of 13.3–15.5 cal. ka bp ( jensen et al. 2002a). distinct normal faults cut the late glacial deposits. detailed interpretations of the seismic profiles show that faulting occurred during the last stage of the deposition of the lg2 unit. this is evident because the uppermost part was not affected by the faulting whereas the lower-lying sediments are cut by the faults. this finding is consistent with the conclusions of jensen et al. (2002b). the nw–se-orientated sparker profile r3_021a (fig. 3) shows major bounding faults that cut the late glacial sediments to the north-west and south-east and hence limit the distribution of the younger sediments. within the late glacial units, two major faults are interpreted as strike-slip faults. the faulting postdates the uppermost part of the lg2 unit and was possibly a result of the deglaciation of the katfig. 3. a: selected part of shallow seismic profile r3_021a obtained by a boomer. b. preliminary interpretation. for location see fig. 2. compaction fault normal fault older late glacial sediments lg1 younger late glacial sediments lg2 late glacial lowstand sediments early holocene sediments h1 holocene sediments h2 glacial sediments nw se 30 40 50 60 depth (m) sea floor multiple 30 40 50 60 500 m sea floor multiple a b deformed deformed 23 tegat region that led to isostatic uplift and reactivation of older faults. this tectonic event may have contributed to the opening of storebælt. the late glacial units between the faults show an internal pattern with contorted ref lectors. the late glacial deposits have been reworked by faulting and a significant erosional unconformity is found between the late glacial and the holocene sediments. this unconformity formed during the late glacial – early holocene lowstand period. above the erosion surface, two holocene units can be separated on the basis of their difference in ref lection pattern and infill direction, with h1 showing infill from the south-east and h2 from the north-east. two lithological units presumably of holocene age were also found in sediment core no. dgu 561118.10 collected at 56°23.165́ n, 11°22.0´e from a water depth of 38.0 m (fig. 4). the core was 518 cm long and consisted of 136 cm sand with abundant shells of the common blue mussel mytilus edulis that is characteristic of shallow water, overlain by 328 cm of mud with shells of turritella communis, arctica islandica, pecten s.l. sp. and other marine molluscs that are characteristic of deeper water. the marked lithological change 382 cm below the core top probably corresponds to the boundary between units h1 and h2 (bendixen 2012). we suggest that the sand was deposited during the early holocene when sea level was low, whereas the mud was deposited after the relative sea level had increased. radiocarbon dating of holocene sub-littoral sand deposits in the region has yielded ages of c. 11–10 cal. ka bp (bennike et al. 2000; jensen et al. 2002a). a palaeogeographic map of the region illustrates northward coastal progradation with spits and barriers with backbarrier-enclosed environments in which finer-grained sediments were deposited (fig. 5). fig. 4. sedimentological log of vibrocore dgu 561118.10. for location see fig. 5. fig. 5. palaeogeographic map of the area south of anholt in kattegat in early holocene showing glacial deposits to the south and west, coastal sandy deposits formed by prograding shorelines and a barrier island. the present-day form of anholt is included to show the location of the map. mud cl ay sil t vf sand f m c vcli th ol og y thin clay layer with organic material carbonate present carbonate present arctica islandica cerastoderma, turritella dark grey colour a few thin clay layers pecten s.l. sp. dark olive grey colour olive grey colour turretella communis abundant mytilus edulis a few stones up to 3 cm 100 200 300 400 500 d ep th b el ow c or e to p (c m ) glacial deposits coastal deposits sea profile r3_021a (fig. 3) barrier island core 561118.10 10 km anholt 11°49´e 56°31´n 56°40´n 2424 conclusions the late glacial sediments in southern kattegat consist of a lower and an upper sequence deposited during relatively high sea level; the boundary between the sequences shows an erosional surface towards the north-east. the distribution of the sediments is limited by major faults which were initiated during deposition of the uppermost part of the youngest late glacial unit. major faults bounding the late glacial sediments were active during the deposition of the uppermost part of the youngest late glacial unit. we suggest that strike-slip movements occurred due to isostatic reactivation of the fennoscandian border zone and upward movement of the late glacial sediments. an early holocene lowstand level is identified as an erosional surface, underlying units h1 and h2. initial transgression resulted in coastal progradation and back-barrier-enclosed environments with deposition of finergrained sediments (h2) in the former incised valleys. acknowledgement the danish nature agency (naturstyrelsen) funded the work. references bendixen, c. 2012: interpretation of shallow seismic and sediment cores from the area stretching from the southern part of kattegat to the great belt in the period late-weichselian to early holocene 1, 2, 74 pp + 102 pp. unpublished m.sc. thesis, university of copenhagen, denmark. bennike, o., jensen, j.b., konradi, p.b., lemke, w. & heinemeier, j. 2000: early holocene drowned lagoon deposits from the kattegat, southern scandinavia. boreas 29, 272–286. bergsten, h. & nordberg, k. 1992: late weichselian marine stratigraphy of the southern kattegat, scandinavia: evidence for drainage of the baltic ice lake between 12,700 and 10, 300 years bp. boreas 21, 223–252. conradsen, k. 1995: late younger dryas to holocene palaeoenvironments of the southern kattegat, scandinavia. the holocene 5, 447– 456. gyldenholm, k.g., lykke-andersen, h. & lind, g. 1993: seismic stratigraphy of the quaternary and its substratum in southeastern kattegat, scandinavia. boreas 22, 319–327. houmark-nielsen, m., linge, h., fabel, d., schnabel, c., xu, s., wilcken, k.m. & binnie, s. 2012: cosmogenic surface exposure dating the last deglaciation in denmark: discrepancies with independent age constraints suggest delayed periglacial landform stabilisation. quaternary geochronolog y 13, 1–17. jensen, j.b., kuijpers, a., bennike, o. & lemke, w. 2002a: balk at – the baltic sea without frontiers (english version). geologi, nyt fra geus 2002(4), 20 pp. jensen, j.b., petersen, k.s., konradi, p., kuijpers, a., bennike, o., lemke, w. & endler, r. 2002b: neotectonics, sea-level changes and biological evolution in the fennoscandian border zone of the southern kattegat sea. boreas 31, 133–150. lagerlund, e. & houmark-nielsen, m. 1993: timing and pattern of the last deglaciation in the kattegat region, southwest scandinavia. boreas 22, 337–347. larsen, n.k., knudsen, k.l., krohn, c.f., kronborg, c., murray, a.s. & nielsen, o.b. 2009: late quaternary ice sheet, lake and sea history of southwest scandinavia: a synthesis. boreas 38, 732–761. mörner, n.-a. 1969: the late quaternary history of the kattegatt sea and the swedish west coast. déglaciation, shorelevel displacement chronolog y, isostasy and eustasy. sveriges geologiska undersökning ser. c, 63(3), 487 pp. thiede, j. 1987: the late quaternary skagerrak and its depositional environment. boreas 16, 425–432. authors’ addresses c.b., j.b.j., o.b. & l.o.b.*, geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: cb1@geus.dk * also: department of geosciences and natural resource management, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. mailto:jbj@geus.dk geological survey of denmark and greenland bulletin 13, 2007, 69-72 las tablas de daimiel, together with other wetlands in la mancha, spain, situated in the upper guadiana basin (fig. 1), has been catalogued as a biosphere reserve area since 1981 as part of the unesco man and the biosphere programme. between the mid-1970s and late 1980s, over 150 000 hectares of new irrigation areas were established, mainly as a result of private initiative. the average recharge rate of groundwater in the western la mancha aquifer in the upper guadiana basin is estimated to be between 200 and 500 million m3 per year, in dry and wet years respectively. re charge also depends on the depth of the water table (martínez-cortina & cruces 2003). abstraction reached 600 million m3 per year by the end of the 1980s. up to this time a total of 3000–5000 million m3 of the upper gua diana basin aquifer’s water reserves was withdrawn (bromley et al. 2000; lopéz-geta et al. 2006). the intensive use of groundwater has been a main factor for the improvement of the social and economic situation in this region, with a population of about half a million people, and where the agricultural sector is very important (llamas et al. 2006). water-table drawdown due to the intensive abstraction of groundwater for irrigation has caused severe negative impacts on wetlands, streams and rivers, and has resulted in a lowering of groundwater levels by up to 50 m. the main conflicts in the area are between farmers and conservationists, between central, regional and local government water agencies, and between small farmers and big farmers. the conflicts began about three decades ago (llamas 1988) and have not yet been settled. in 2001 the spanish parliament asked the govern ment to present a hydrological plan for the upper guadiana basin within one year. more than 20 draft proposals have been presented, the last one in 2006 with a budget of almost four billion euros. this proposal has been met with strong opposition from most farmer lobbies. the guadiana basin is one of seven transboundary case studies of the eu newater research project (new approaches for adaptive water management under uncertainty). the prin cipal water-management issues in the project are addressed by adaptive and integrated water-resource manage ment. this includes uncertainty and risk mitigation, gov er n ance, crosssectoral integration, scale analysis, information management, stakeholder participation, financial aspects, system resilience and vulnerability. one work block in the newater project has the task of translating research outputs into tools for practitioners and end-users. as part of this effort, bayesian belief networks (bns) were selected as one possible tool to be developed as an aid to stakeholder participation in integrated assessment of gaps, being a suitable tool for dialogue in order to identify gaps in water-resource management functions, gaps to meet the goals of the eu water framework directive and to analyse management potentials and constraints. the purpose of this paper is to describe the testing of bns as a tool for participatory integrated assessment and adaptive and integrated water-resource management in the upper guadiana basin. participatory integrated assessment participatory integrated assessment can be considered a form of participatory policy analysis, which aims to support the policy process by designing and facilitating policy debate and argument. assessment is integrated when it draws on a broader set of knowledge domains than are represented in the bayesian belief networks as a tool for participatory integrated assessment and adaptive groundwater management: the upper guadiana basin, spain hans jørgen henriksen, per rasmussen, john bromley, africa de la hera portillo and m. ramón llamas © geus, 2007. geological survey of denmark and greenland bulletin 13, 69–72. available at: www.geus.dk/publications/bull 69 fig. 1. location of the guadiana basin in spain. the upper guadiana basin includes las tablas daimiel and upstream areas in the castilla-la mancha region. major rivers indicated. research product of a single discipline. assessment is distinguished from disciplinary research by its purpose: to inform policy and decision-making, rather than to advance knowledge for its intrinsic value (hisschemöller et al. 2001). a wide range of methods and techniques can be drawn from social psychology, policy sciences, decision analysis and anthropology (hisschemöller et al. 2001) for high-level participatory integrated assessment. some of these, like brainstorming or decision seminars, although well established, are of limited value for integrated water-resource management because a proper understanding of the spatial and temporal variation and the complexity within river basins requires a modelling approach (croke et al. 2007). according to jakeman & letcher (2003) the tools for participatory integrated assessment must: 1. be problem-focussed, using an iterative, adaptive ap proach that links research to policy; 2. possess an interactive, transparent framework that en hances communication; 3. be enriched by stakeholder involvement and dedicated to adoption; 4. connect complexities between the natural and human en vironment, recognising spatial dependencies, feedbacks and impediments; and 5. attempt to recognise essential lacking knowledge. jakeman & letcher (2003) list several tools for participatory integrated assessment, e.g. system dynamics, bns, metamodels, risk assessment approaches, coupled component models, agent-based models and expert systems. here bns are in focus as a tool for adaptive and integrated water management in the upper guadiana basin test case. bayesian belief networks a bayesian belief network (bn) is a type of decision support system based on probability theory which implements bayes’ rule of probability (jensen 2002; bromley 2005). this rule shows mathematically how existing beliefs can be modified with the input of new evidence. bns organise the body of knowledge in a given area by mapping out relationships among key variables and encoding them with numbers that represent the extent to which one variable is likely to affect another. bns have gained a reputation for being a powerful technique to model complex problems involving uncertain knowl edge and uncertain impacts of causes. ideally, bns are a technique to assist decision-making that is especially helpful when there is scarcity and uncertainty in the data used in making the decision and the factors are highly interlinked, all of which makes the problem very complex. the graphical nature of bns facilitates formal discussion of the structure of the proposed model. furthermore, the ability of bns to describe the uncertain relationships between variables is ideal to describe the relationship between events, which may not be well understood. bns help water managers, stakeholders and scientists (1) to visualise and recognise, in the face of complexity and uncertainty, the relationships between different actions and consequences; (2) to make learning about water-resource systems more efficient; and (3) to encourage the involvement of social and political values in water-resource management (e.g. henriksen et al. 2007a, b). furthermore, it has been judged that bns are an excellent tool for integrating different domains, e.g. socio-economy, hydrology and groundwater quality data of different knowledge types (monitoring data, models and expert opinions; henriksen et al. 2007a). here the guidelines from the merit project (bromley 2005) can help support a successful and efficient involvement of stakeholders in the participatory integrated assessment process, a process which is demanding to run due to multiple frames and opposing interests. design for testing the enhanced bayesian belief network tool a test of an enhanced bn tool is being undertaken in the upper guadiana basin as part of the newater project. the test involves the construction of a bn to represent the management of groundwater levels in the region, taking into account the social, economic, hydrological and ecological consequences of alternative irrigation and groundwater management scenarios (table 1). in november 2006, an initial workshop was held at the geological survey of spain (igme) in madrid with participants from the case study group. during this workshop a preliminary bn for the upper guadiana basin was developed by bn experts from igme, the university complutense de madrid, the geological survey of denmark and greenland, and the centre of ecology and hydrology, wallingford, uk, 70 together with a representative of the water managers of the basin responsible for water planning in relation to implementation of the eu water framework directive. a joint workshop with all stakeholders to finalise the network has been planned for the first half of 2007. the process and method for constructing the bn in the upper guadiana basin test will follow the merit guidelines (bromley 2005). in the following we present the preliminary bn and the hypotheses relating to the use of the tool in participatory integrated assessment and adaptive management in the guadiana basin. results of testing bayesian belief networks for adaptive water management the initial step in network design was to establish the space and time boundaries of the system being modelled. it was agreed to restrict the model to the upper guadiana basin, and a one-year time period for groundwater level and socioeconomic consequences was decided. the pilot bn for the upper guadiana basin case which emerged from this process is shown in fig. 2. the network deals with the way in which different management actions influence irrigation water use, groundwater level, crop pattern, farmers’ income, wetland recovery, productivity and employment in the region (fig. 2). included among the potential actions that might be taken are: (1) acquisition of water rights; (2) law enforcement; (3) common agricultural programmes (cap) subsidies; and (4) annual management plans. climate and the initial state of the aquifer are included as control factors. the indicators (objectives) in the network include: (1) groundwater levels; (2) impact on wetland recovery; (3) agricultural productivity; (4) farmers’ income; and (5) levels of employment in the region. when running the bn, combinations of actions can be selected and calculated. it is hypothesised that bns fully support four of the five requirements proposed by jakeman & letcher (2003) for participatory integrated assessment (table 2). one requirement, the representation of spatial dependencies, is only partly supported (e.g. input to the decision-making about which specific wetlands that will be recovered by a certain increase in groundwater level has to be evaluated using a groundwater model). however, as stated by pascual (2005): “the beauty of bns lies in their explanatory power: observations about any node generates knowledge about all other nodes, providing one with a tool to draw transparent, ration al inferences in a probabilistic world”. this illustrates that the tool can be used for diagnosis and social learning. bns allow targeted modelling, participatory integrated assessment and strong support for sense and decision-making in cases with multiple frames (e.g. when stakeholders perceive their environment differently, and frame and construct their world in different ways) that create ambiguous situations and conflicting interests hindering sustainable solutions for man71 fig. 2. preliminary bayesian network for the upper guadiana basin. the objectives of the bayesian network are to analyse the way in which different management actions will influence irrigation water use, change in groundwater level, crop pattern, farmers’ income, wetland recovery, productivity and employment. agement of the environment. the tool and the probability tables (numbers) are not easily understood if not properly explained. thus, training and introduction to the tool and the statistical background behind bns is important (table 2). acknowledgements the work reported from the newater project has been financially supported by the european commission under contract number 511179 (goce). integrated project in priority 6.3 global change and ecosystems in the 6th eu framework programme. references bromley, j. 2005: guidelines for the use of bayesian networks as a participatory tool for water resource management, 117 pp. wallingford: centre for ecology and hydrology. bromley, j., cruces, j., acreman, m., martinez, l. & llamas, m.r. 2000: groundwater over-exploitation in the upper guadiana catchment, central spain: the problems of sustainable groundwater resources man agement. international water resources development 17, 379–396. croke, b.f.w., ticehurst, j.l., letcher, r.a., norton, j.p., newham, t.t.h. & jakeman, a.j. 2007: integrated assessment of water resources: australian experiences. water resource management 21, 351–373. henriksen, h.j., rasmussen, p., brandt, g., bülow, d.v. & jensen, f.v. 2007a: engaging stakeholders in construction and validation of baye sian belief network for groundwater protection. in: castelletti, a.e.r. & soncini-sessa, r. (eds): topics on system analysis and integrated water resource management, 49–72. amsterdam: elsevier. henriksen, h.j., rasmussen, p., brandt, g., bülow, d.v. & jensen, f.v. 2007b: public participation modelling using bayesian networks in management of groundwater contamination. environmental modell ing & software 22, 1101–1113. hisschemöller, m., tol, r.s.j. & vellinga, p. 2001: the relevance of participatory approaches in integrated environmental assessment. inte grated assessment 2, 57–72. jakeman, a.j. & letcher, r.a. 2003: integrated assessment and modelling: features, principles and examples for catchment management. envi ronmental modelling and software 18, 491–501. jensen, f. 2002: bayesian networks and decision graphs: statistics for engineering and information science, 296 pp. new york: springerverlag. llamas, m.r. 1988: conflicts between wetland conservation and groundwater exploitation: two case histories in spain. environmental geol ogy and water sciences 11, 241–251. llamas, m.r., martínez-santos, p. & hera, a. de la 2006: dimensions of sustainability in regard to groundwater resources: an overview. pro ceedings of the international symposium on groundwater sustain ability, alicante, spain, 24–27 january 2006, 1–13. madrid: instituto geológico y minero de españa. lópez-geta, j.a., fornés, j.m., ramos, g. & villarroya, f. 2006: groundwater. a natural underground resource, 107 pp. madrid: insti tuto geológico y minero de españa, unesco and fundación mar celino botín. martínez-cortina, l. & cruces, j. 2003: the analysis of the intensive use of groundwater in the upper guadiana basin (spain) using a numerical model. in: llamas, m.r. & custodio, e. (eds): intensive use of groundwater, challenges and opportunities, 285–294. london: taylor and francis. pascual, p. 2005: wresting environmental decisions from an uncertain world. environmental law institute news and analysis 8-2005, 10539–10549. authors’ addresses h.j.h. & p.r., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: hjh@geus.dk j.b., oxford university centre for the environment, south parks road, oxford ox1 3qy, uk. a.d.l.h.p., geological survey of spain, 23 rios rosas, itge-e 28003 madrid, spain. m.r.l., university of complutense, ciudad universitaria, 28040 madrid, spain. 72 geological survey of denmark and greenland bulletin 17, 2009, 29-32 the møns klint glaciotectonic complex (fig. 1) exposed in the n–s-trending chalk cliff on the east coast of the island of møn in south-east denmark is one of the most famous glaciotectonic geosites in the world. people of all nationalities are attracted to the site, which has more than 300 000 visitors per year. many of them may not realise the uniqueness of the glaciotectonic framework, and are probably more fascinated by the spectacular view of the white cliff and chalk peaks separated by the deep green gorges. however, without the glaciotectonic deformation the cliffs would never have formed. instead the cretaceous chalk would still have been resting horizontally below the seabed, covered by glaciofluvial sand, gla ciolacustrine clay and clayey till. in the summer 2007, a new natural science exhibition centre, geocenter møns klint, was opened. the exhibition fo cuses on the geology of denmark with special reference to the chalk cliffs of møns klint. prior to the decision to build the centre, the geological survey of denmark and greenland was asked to provide an evaluation of the landslide risk for the site, because landslides regularly occur along the cliff section (pe dersen 2003). a detailed structural analysis was consequently carried out at the planned site of the centre just above the maglevandsfald gorge (fig. 1). during this investigation it became obvious that understanding the glaciotectonic framework was a prerequisite for the geological risk analysis. thus the structural details at maglevandsfald became a key point for the glaciotectonic model of møns klint which we present in this paper. geological setting of møns klint the cretaceous chalk represents the oldest bedrock affected by glaciotectonic thrusting in denmark. the chalk consists of a fine-grained matrix of coccoliths and remains from invertebrates (surlyk & håkansson 1999). the chalk at møn is correlated with the upper part of the tor formation in the north sea and the danish basin (surlyk et al. 2003). an erosional unconformity on top of the chalk represents a hiatus of about 60 million years. due to erosion, the unconformity is found at gradually lower and lower levels towards the southern part of the cliff, which indicates that the pre-qua ternary relief probably contributed to the formation of glaciotectonics in the area. in some parts of møn the pre-qua ternary unconformity is overlain by a saalian till, marine eemian clay and three weichselian tills intercalated by glaciolacustrine and glaciofluvial deposits (houmark-nielsen 1994). however, at møns klint an old weichselian till is the oldest quaternary deposit recognised at present (pedersen & gravesen 2006). this till is a grey and reddish sandy till that grades up into a gravelly, stone-rich top surface indicating terrestrial conditions. we tenta tively correlate this unit with the ristinge klint till (houmarknielsen 1987, 1994), which was deposited by a baltic ice stream in the early part of the weichselian (c. 60 000 years bp) from a source area in the baltic sea. when the baltic ice stream melted back the depression became occupied by a huge lake, in which dark glaciolacustrine mud rich in dropstones was deposited (houmark-nielsen 1994; houmark-nielsen & kjær 2003). structural development of maglevandsfald: a key to understanding the glaciotectonic architecture of møns klint, se denmark stig a. schack pedersen and peter gravesen © geus, 2009. geological survey of denmark and greenland bulletin 17, 29–32. available at: www.geus.dk/publications/bull 29 fig. 1. aerial photograph of møns klint. the highest cliff in the centre is dronningestolen. to the left the maglevandsfald gorge leads from the location of geocenter møns klint down to the beach. at the left side of dron ningestolen a wedge-shaped structure is seen (red arrow), which was formed in the first deformation phase of the glaciotectonic complex. the thrust structures to the right of dronningestolen were thrust to the sw during the last deformation phase. the location of møns klint is shown on the inset map of denmark. dronningestolenmaglevandsfald geocentre rosa_2008:rosa-2008 01/07/09 15:48 side 29 the unit is informally called the elephant clay due to its characteristic erosion features. at the late weichselian glacial maximum the swedish ice advanced over the eastern part of the danish basin onto the main stationary line depositing the mid danish till on møn (fig. 2; houmark-nielsen 1987; pedersen & gravesen 2006). at about 18 000 years bp the young baltic ice stream reached møn (houmark-nielsen & kjær 2003). the pressure from the ice was directed away from the central axis of the ice stream towards both north and south, where it thrust up the chalk sheets at møns klint. the glaciotectonic structures at møns klint can be divided into three architectural elements. in the southern part the thrust sheets form an imbricate fan with thrust faults striking e–w, in the central part the structures form an antiformal stack, and farthest to the north the thrust sheets dip gently to the south in the foreland regime of the thrust deformation (fig. 3; pedersen 2000). towards the end of the weich selian the scandinavian ice sheet melted back. however, a re advance from southern sweden reached møn from eastnorth-east at a time between 17 000 and 15 000 years bp, which was responsible for superimposed deformation of the glaciotectonic complex (pedersen 2000). photogrammetric mapping and a borehole investigation a 3-d terrain model of the area was developed for the risk evaluation. the data for the model were provided by a photo grammetric survey and a digital model was constructed, in which the trace of the glacial deposits, interbedded between the unconformity on top of the chalk and the base of an overthrust chalk sheet, was positioned (fig. 4). in addition, a borehole was drilled to investigate whether karst cavities or an unforeseen thrust-fault zone with dip towards the cliff and beach were present. if a fault zone exists below the location it could be a candidate for a landslip similar to the one that destroyed the store taler chalk peak in january 2007 (fig. 5). the borehole was placed on top of the cliff 100 m above sea level close to the old hotel store klint (fig. 6). the uppermost 16.3 m consist of glacial sediments resting upon the chalk unconformally. the oldest unit in the glacial succession is a 1 m thick till that is correlated with the ristinge klint till. this formation is overlain by 2.3 m glaciolacustrine mud, which grades into the nearly 2 m thick mid danish till. a 7.7 m thick unit of glaciofluvial sand and gravel overlies the mid danish till; the upper part of the glacial succession is a 3.5 m thick, sandy till that was deposited by the young baltic ice. below the unconformity the drilling penetrated 48 m of cretaceous chalk, after which the drilling was 30 s n 100 m sea le vel glaciofluvial sand mid danish till glaciolacustrine clay ristinge klint till maastrichtian chalk thrust fault 10 0 m fig. 2. stratigraphical and structural framework of the southern imbricate fan at møns klint. the thickness of the lithological units is variable, and especially the glaciofluvial sand above the mid danish till increases in thickness, where the sand was deposited in piggyback basins during the thrust-fault deformation. from pedersen & gravesen (2006). imbricate fan antiformal stack ramp slotsgavle foreland thrust dronningestolen antiformal stack maglevandsfald ramp gråryg imbricate ene jydelejet superimposed thrusting sse young baltic ice advance fig. 3. principal structural framework of the møns klint glaciotectonic complex. blue: chalk; brown and orange: quaternary deposits. red lines outline the thrust faults. to the south the e–w-trending ridges represent an imbricate fan, and in the central part an antiformal stack is responsible for the formation of dronningestolen. two principal sketches of the structures are shown in the top left corner. in the distal part of the complex to the north a gently dipping imbricate fan was formed in the nearforeland regime. the structures from the distal regime to maglevandsfald were strongly affected by superimposed deformation caused by a re advance of ice from skåne. after pedersen (2000). rosa_2008:rosa-2008 01/07/09 15:48 side 30 unfortunately stopped for logistic reasons. it would have been perfect if the borehole had reached the level of the lower thrust fault and the underlying glacial succession. however, the data demonstrate that neither a karst cavity nor an eastward dipping thrust-fault zone was present. thrust-fault tectonics and superimposed deformation the structures in the møns klint glaciotectonic complex are directly comparable to structures in thin-skinned thrustfault belts formed by gravity spreading (pedersen 2005). the geomorphological expression of a mountain range is clearly seen in the parallel-ridged landscape of høje møn (the eastern, hilly part of møn). for detailed structural analysis five cross-sections were constructed across the maglevandsfald (figs 6, 7). the data for the cross-sections were taken from the photogrammetric survey combined with a structural investigation of the cliff section immediately south of maglevandsfald. in the cross-sections two horizons of glacial successions are shown (fig. 7). the lower glacial horizon rests on the unconformity on top of the chalk. the top of the glacial deposits is bordered by a thrust fault, where the base of the chalk sheet can be classified as a hanging-wall flat related to the earliest glaciotectonic deformation. farther to the south this flat can be followed into a hanging-wall ramp, which dips into the subsurface below the beach. this ramp strikes e–w, indicating that it is part of the antiformal stack structure (fig. 3). as the décollement zone must be situated at the base of the chalk unit, which in fig. 7 can be seen to be about 60 m thick, the depth to this zone must be of similar magnitude, probably about 75 m below sea level. therefore the chalk below the lower glacial unit is also interpreted as a thrust sheet lifted up from the décollement zone. the lower glacial unit is folded in a sw-verging overturned structure, which has been deformed by the second glaciotectonic event. the structure is partly hidden by soil and vegetation in the maglevandsfald gorge, but the upper limb of the structure is exposed at the cliff edge of magle vandsnakken (fig. 7), where the unit continues into the wedge-shaped feature in the southern part of the dron ningestolen cliff section (fig. 1). the wedge-shaped feature was formed during the foreland-dipping thrusting of the antiformal stack (compare with fig. 3). the thrust-fault flat 31 fig. 4. 3-d model of the maglevandsfald gorge. the position of the ex ploratory borehole dgu 228.84 is indicated with a dot, located be tween the exhibition centre and the old hotel. the upper and lower bound aries of the glacial succession are shown with a brown line. contour interval 10 m. steps to the beach 100 m a.s.l. glacial succession dgu 228.84 n fig. 5. the landslide at store taler took place at the end of january 2007. a volume of more than 100 000 m3 was displaced along an inherited thrust-fault surface formed during the last phase of deformation at møns klint. store taler is located in the northern part of møns klint. location of cross-sections dronningestolen dgu 228.84dgu 228.84 parking place parking place 1 2 3 4 5 hotel geocentre hotel geocentre 100 m thrust unconformity n 10 20 30 50 60 4050 60 708090 95 100 130 120 110 100 90 80 70 10 20 30 50 60 4050 60 708090 95 100 130 120 110 100 90 80 70 fig. 6. the maglevandsfald area with location of the exploratory borehole mentioned in the text and the cross-sections applied in the structural analysis. rosa_2008:rosa-2008 01/07/09 15:48 side 31 32 above the glacial unit is folded in the maglevandsfald gorge structure with a fold axis trending nw–se, which demonstrates the superimposed deformation. a similar wedge-shaped structure is present just below the edge of the dronningestolen cliff, which may indicate that a thrust sheet existed even higher in the antiformal stack before the young baltic ice truncated the structure during the advance towards nnw. final remarks møns klint is one of the most famous glaciotectonic localities in the world. the structures in the møns klint glacio tec tonic complex are comparable to structures in thinskinned thrust-fault belts formed by gravity spreading. the glaciotectonic complex is responsible for the parallel-ridge landscape known as høje møn, where aborre bjerg (143 m) represents the highest hill in eastern denmark. a combination of an imbricate fan and an antiformal stack is respon sible for the impressive tectonic complex. its main architecture was formed during the young baltic ice stream advance dated to about 18 000 years bp, but a readvance of ice from southern sweden from 17 000 to 15 000 years bp is responsible for the superimposed deformation of the complex. the most impressive unit forming the thrust sheets is the maastrichtian chalk. the chalk is part of the huge carbonate platform that spread over northern europe during the late cretaceous. the top surface of the chalk, the pre-quaternary unconformity, was originally situated more than 20 m below sea level, and the décollement zone for the thrusting is probably located about 80–100 m below sea level in a marl-rich variety of the chalk. references houmark-nielsen, m. 1987: pleistocene stratigraphy and glacial history of the central part of denmark. bulletin of the geological society of denmark 36, 1–189. houmark-nielsen, m. 1994: late pleistocene stratigraphy, glacial chronology and middle weichselian environmental history from klintholm, møn, denmark. bulletin of the geological society of denmark 41, 181–202. houmark-nielsen, m. & kjær, k. 2003: southwest scandinavia, 40–15 kyr bp: palaeography and environmental change. journal of quaternary science 18, 769–786. pedersen, s.a.s. 2000: superimposed deformation in glaciotectonics. bulletin of the geological society of denmark 46, 125–144. pedersen, s.a.s. 2003: vurdering af skredrisiko for området oven for magle vandsfaldet på møns klint. strukturel undersøgelse af de glacialtektoniske forhold i klintområdet ved hotel storeklint, møns klint, møn. danmarks og grønlands geologiske undersøgelse rapport 2003/50, 31 pp. pedersen, s.a.s. 2005: structural analysis of the rubjerg knude glaciotectonic complex, vendsyssel, northern denmark. geological survey of denmark and greenland bulletin 8, 192 pp. pedersen, s.a.s. & gravesen, p. 2006: geological map of denmark, 1:50 000, møn. copenhagen: geological survey of denmark and greenland. surlyk, f. & håkansson, e. 1999: maastrichtian and danian strata in the southeastern part of the danish basin. in: pedersen, g.k. & clemmensen, l.b. (eds): ias field trip guidebook. contribution to geology, 29–58. copen hagen: geological museum, university of copenhagen. surlyk, f., dons, t., clausen, c.k. & higham, j. 2003: upper cretaceous. in: evans, d. et al. (eds): the millennium atlas: petroleum geology of the central and northern north sea, 213–233. london: the geological society of london. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: sasp@geus.dk 140 120 100 80 60 40 20 0 140 120 100 80 60 40 20 h ei g h t (m a .s .l. ) h ei g h t (m a .s .l. ) h ei g h t (m a .s .l. ) 140 120 100 80 60 40 20 0 maglevandsfald maglevandsfald cross-section 1 cross-section 3 maglevandsfald maglevandsnakken maglevandsnakken glacial succession on top of upper thrust sheet thrust fault glacial succession at the base of the cliff cross-section 5 dronningestolen nesw 1000 200 300 400 1000 200 300 400 1000 200 300 400 distance (m) borehole 228.84 fig. 7. three of the cross-sections across the maglevandsfald gorge (for location see fig. 6). the cross-sections were constructed perpendicular to the fold axis of the last deformation, which created a recumbent anticline and syncline pair below a thrust fault with a displacement of 20 m. the folding is outlined in the glacial units below the thrust-fault flat of the first deformation, which is responsible for the wedge-shaped feature in the top of the fold. the strike of the first deformation thrust is oblique to the second phase fold axis, and therefore the position of the wedge changes from cross-section to cross-section. in cross-section 5 the tip of the thrust wedge touches the cliff edge, which corresponds to the exposure of the wedge seen in fig. 1 immediately to the right of magle vandsfald. rosa_2008:rosa-2008 01/07/09 15:48 side 32 geological survey of denmark and greenland bulletin 17, 2009, 9-12 a moderately strong earthquake struck southern sweden 5 km south-west of the town of sjöbo, 60 km east of malmö, in the early morning at 6:20 a.m. local time on 16 december 2008. the epicentre was located in skåne, a region that is known for its extremely low seismicity, and its location was determined to be 55.5°n and 13.6°e with an uncertainty of about 6 km. a depth of 9 km with an uncertainty of 3 km was obtained from teleseismic observations at the yellowknife seismic array, usa. since waveform data from the swedish national seismic network are not yet available, depth estimation using local stations has so far not been attempted. dur ing the period 1970–2008, only three small earthquakes were detected in the region; the largest measured 2.8 on the local richter scale. to our knowledge none of these previous earthquakes were felt by people. the historical archives dating back to 1375 show that 14 other earthquakes have been felt in the area. the largest of these, recorded in 1894, was felt over an area of 7300 km2 and had an epicentre 50 km east of the 16 december 2008 earthquake (scandinavian earthquake archive 2003). the activity in southern sweden is similar to that of northern sjælland and north-western jylland, and confirms the low seismicity of the region (gregersen et al. 1991). even though the earthquake was unusual, the event was not totally unexpected. northern europe is un der constant pressure from the mid-atlantic ridge, and the resulting stress is released in small to moderate size earthquakes. the local stress field is further modified by postglacial rebound. earthquakes in denmark and southern sweden occur where there are weaknesses or faults in the subsurface. in some cases the earthquakes occur where there are no mapped faults (gregersen et al. 1996). shaking from the earthquake was felt widely in denmark. strong shaking and low-frequency earthquake sounds frightened many people and caused them to abruptly leave their houses. authorities such as the police and the geological survey of denmark and greenland (geus) were flooded with phone calls and e-mails from concerned citizens. fortunately the earthquake did not cause any real damage, and no one was in danger at any time. macroseismic effects in denmark the basic physical earthquake parameters are determined from instrumental recordings. however, the effects of the earthquake on people, buildings, and nature require human inter© geus, 2009. geological survey of denmark and greenland bulletin 17, 9–12. available at: www.geus.dk/publications/bull earthquake in southern sweden wakes up denmark on 16 december 2008 peter h. voss, tine b. larsen, lars ottemöller and søren gregersen 9 6˚e 8˚e 10˚e 12˚e 14˚e 16˚e 58˚n 57˚n 56˚n 200 km 55˚n fig. 1. map showing the epicentre of the 16 december 2008 earthquake (yellow circle) and the locations of the first 3000 macro seismic reports received (red circles) from denmark. known faults are also shown. rosa_2008:rosa-2008 01/07/09 15:47 side 9 action to be delineated. immediately following the earthquake, geus requested input from the public through the news media and our own web page. our earthquake questionnaire was placed on www.geus.dk and a paper copy was mailed to those who had no internet access or who felt uncomfortable about reporting electronically. after a few days, geus had received more than 3000 earthquake reports (fig. 1), and after a month the number exceeded 4000 reports. this is a large increase compared to the last widely felt earthquake in den mark in 2001, where we received little more than 400 reports (larsen et al. 2008) and the one in 1985 in kattegat, which was almost as large as the 16 december 2008 earthquake, where we received a total of around 500 reports from sweden and denmark. in denmark alone the area where the earthquake was felt covers about 50 000 km2 (fig. 1). earthquakes in scandinavia are felt over much larger areas than in california, where c.f. richter worked when he invented the richter magnitude scale. thus the attenuation in scandinavia is lower than that in california. a comparison of local observations of 25 earthquakes in different regions and their magnitude suggests that the affected area this time will exceed 100 000 km2 (fig. 2). reports from the population are an important tool to assess the impact of an earthquake and to identify locations that are particularly vulnerable to ground shaking. this is still of great interest as earthquakes can be compared to historic events predating the era of instrumental recording. this information is used in seismic hazard studies, for example in connection with large construction projects. the geus questionnaire comprises the address of the observer, information about the building in which the observer was located and detailed information about shaking and other effects caused by the earthquake. shaking is strongly amplified in tall buildings, and the euro pean macroseismic scale (grünthal et al. 1998) recommends that shaking observations above the 5th floor are not taken into account when determining the intensity of an earthquake. a detailed study of the 4000 current reports has not yet been completed, but the reports will provide valuable shake information especially for sjælland. in many locations the earthquake was felt strongly. some examples, with locations shown on fig. 3, are: copenhagen: “walls, closet and bed were shaking”, gilleleje: “the chair i was sitting in was shaking”, humlebæk: “it was as if the bed was shaken – it felt very terrifying”, ålborg: “it felt as if someone was shaking my bed gently”, kettinge: “as when a large truck is just outside”. some reports claim that the earthquake caused a road in helsingør to crack. inspection of the road confirms the presence of cracks, but it is not obvious that the cracks opened during the earthquake. new asphalt was added to the road a year earlier, and the small cracks are located in the weak zone where new asphalt overlaps with old. the road is exposed to heavy traffic and the cracks could have opened at any time. they do not look any different from other asphalt cracks. the euro pean-mediterranean seismological centre has also received information (a photo) of cracked asphalt in sweden, but it has not been confirmed that these cracks formed during the earthquake. 10 6 10 00 2 3 4 magnitude 5 10 00 0 00 10 0 00 0 10 0 00 a re a (k m 2 ) intensity 3 uk noshel nor kads fig. 2. perceptibility areas for 25 selected earthquakes (area of intensity 3) correlated with their magnitudes. the red squares are for the shield region in kaliningrad, denmark and sweden (kads) compared to the 16 december 2008 earthquake. these areas are larger than those in norway (nor), on the norwegian continental shelf (noshel) and in the united kingdom (uk). the 16 december earthquake (preliminary result shown by a circle) seems to confirm the trend. sjöbo helsingør malmö jylland sjælland copenhagen humlebæk kettinge ålborg holbæk skåne skagerrak kattegat øresund gilleleje fig. 3. map of denmark and south-western sweden showing the location of place names mentioned in the text. rosa_2008:rosa-2008 01/07/09 15:47 side 10 earthquake magnitude determining the magnitude of an earthquake is not straightforward. many different definitions of magnitude are in use at seismological data centres around the world. they measure fundamentally different parameters in the seismograms, all with the intention to reproduce c.f. richter’s original magnitude measure from 1935 (richter 1935), which is in widespread use for public information and in engineering in earthquake regions. the earthquake hazards program at the united states geological survey (usgs) calculates up to six different magnitude values for each registered earthquake. at geus, two different magnitudes are calculated: our own computation of local magnitude (ml), which should give the classical richter number (richter 1935) for local earthquakes, and the moment magnitude (hanks & kanamori 1979), which reflects the size of the fault area and the slip during the earthquake. at geus, the ml is calculated from the maximum amplitude of the earthquake signal on the vertical component of the seismograph (usually the (surface) lg wave) taking into account the distance between the earthquake and the seismograph station. when the lg wave is observed at several seismographs, we calculate the ml as the average of the separate ml values. it requires little data to calculate and it can be calculated shortly after the earthquake. when the data quality is low, as is often the case with weak, local earthquakes, the ml is the only magnitude that can be calculated. the calculation of ml builds on experience of how effectively the shaking propagates in the area. the variations in the ml value calculated at different seismograph stations can be large. following the earthquake on 16 december 2008, several european agencies reported ml values for their stations. the values ranged from 4.6 to 5.8 even though the local corrections are supposed to ensure similar values for all stations (fig. 4). ideally the ml values estimated at seismographs map the energy released in different directions from the earthquake, but the uncertainty in the correction of damping is large, so the pattern is only determined with some uncertainty. at geus, a ml value of 4.8 was calculated, identical to the ml value reported by the usgs. university of bergen reported 4.7, university of helsinki 4.9 and helmholtz-zentrum potsdam deutsches geoforschungszentrum 5.4. the moment magnitude is based on the seismic moment of the earthquake, a physical parameter that is proportional to the area of the fault multiplied by its slip. the moment can be determined from seismological measurements, and in special cases from geodetic measurements. a large number of clear signals on seismographs surrounding the epicentre are needed to obtain a well constrained moment magnitude, using moment tensor inversion. the moment magnitude is determined by searching for the earthquake source parameters that produce synthetic seismograms that have the best possible fit to the observed seismograms. we have determined the moment tensor and a moment magnitude of 4.2 using the method by dreger (2003). university of uppsala, usgs and istituto nazionale di geofisica e vulcanologia reported a moment magnitude of 4.3. fault plane solutions determined in this preliminary study and by others all show a strike-slip movement with a normal component. the corresponding compressional stress field is orientated in a nnw–sse direction as shown by the focal mechanisms (fig. 4). 11 fig. 5. seismograms of the 16 december 2008 earthquake showing the vertical component of the broadband seismometers at copenhagen and bornholm, located 65 and 108 km from the epicentre, respectively. fig. 4. map showing magnitudes and focal mechanisms from various agencies. each circle shows the ml estimated from the data from each seismograph. ml values are from university of bergen, university of helsinki, geoforschungszentrum in postdam and geus. the 2008 epicentre is shown by a star. the focal mechanisms in the upper left corner were determined by this (preliminary) study, cmt (the global cmt project; ekström & nettles 2008) and ingv (the mednet network; morelli et al. 2000). 400 km 5.8 5.6 5.4 5.2 5.0 4.8 4.6 10°e0°10°w 64°n 60°n 56°n 52°n 48°n 20°e this study cmt ingv 20 21 copenhagen bornholm minutes rosa_2008:rosa-2008 01/07/09 15:47 side 11 tectonic setting the epicentre is located in the sorgenfrei–tornquist zone, which is part of a major transition zone in europe between (1) the old precambrian shield of fennoscandia and eastern europe and (2) the younger lithosphere of central europe (pharaoh 1999). the earthquake activity in the sor gen frei–tornquist zone is limited, with kattegat being the most active region. the most active area in denmark is from north-western jylland into skagerrak (gregersen et al. 1998). recent studies show that many of the earthquakes cannot be referred to known faults in the sor genfrei–tornquist zone (gregersen et al. 1996). this is the case even though the uncertainties in the earthquake locations are large. faults in the top pre-zechstein rocks have been mapped in the area where the earthquake occurred (fig. 1). however, the location uncertainty (6 km) means that one cannot link the 16 december 2008 earthquake to a known fault. this is a general problem as small earthquakes occur at depth where as faults are mostly mapped near the surface. a re-analysis of the data recorded by the danish seismological network shows that no foreshocks or aftershocks were observed in the months before or after the 16 december earthquake. seismograms of the earthquake are shown in fig. 5. concluding remarks to feel an earthquake in denmark is rare but not unlikely. earthquakes felt in denmark are generally small and felt in north-western jylland or northern sjælland (gregersen et al. 1998; larsen et al. 2008). large earthquakes with epicentres located outside denmark have also been felt in denmark, like the earthquakes in lissabon in 1755, oslo in 1904 and kaliningrad in 2004 (gregersen et al. 2007). the perceptibility area in denmark of the 16 december 2008 earthquake is comparable to the perceptibility area of the holbæk earthquake in 2001 (larsen et al. 2008), where the earthquake was felt mostly in northern sjælland. also, the area is not much dif ferent from that shaking in 1930 by a small earthquake in øresund. the shaking from the oslo earthquake in 1904 was felt in the north-eastern part of denmark. the kaliningrad earthquake in 2004 was felt by many in copenhagen and in northern sjælland, but only marginally in the rest of den mark. the coincidence of the perceptibility areas must be included in future evaluations of the earthquake hazard of denmark. denmark is located in an area of low earthquake hazard (giardini et al. 2003) and the danger of any damage or injury caused by an earthquake is insignificant compared to other hazards. acknowledgements university of bergen, university of helsinki, university of uppsala, deutsches geoforschungszentrum in postdam and usgs provided data for this study. references ekström, g. & nettles, m. 2008: the global cmt project, http:// www. globalcmt.org. dreger, d.s. 2003: tdmt_inv: time domain seismic moment tensor inversion. in lee, w.h.k., kanamori, h., jennings, p.c. & kisslinger, c. (eds): international handbook of earthquake and engineering seismology 81b, 1627 only. london: academic press. giardini, d., jiménez, m.-j. & grünthal, g. (eds) 2003: europeanmediterranean seismic hazard map. european seismological com mission. gregersen, s. 1992: crustal stress regime in fennoscandia from focal mechanisms. journal of geophysical research 97, 11,821–11,827. gregersen, s., korhonen, h. & husebye, e.s. 1991: fennoscandian dynamics: present-day earthquake activity. tectonophysics 189, 333–344. gregersen, s., leth, j., lind, g. & lykke-andersen, h. 1996: earthquake activity and its relationship with geologically recent motion in denmark. tectonophysics 257, 265–273. gregersen, s., hjelme, j. & hjortenberg, e. 1998: earthquakes in denmark. bulletin of the geological society of denmark 44, 115–127. gregersen, s., wiejacz, p., debski, w., domanski, b., assinovskaya, b., guterch, b., matyniemi, p., nikulin, v., pacesa, a. & puura, v. 2007: the exceptional earthquakes in kaliningrad district, russia on september 21, 2004. physics of the earth and planetary interiors 164, 63–74. grünthal, g., musson, r.m.w., schwarz, j. & stucchi, m. (eds) 1998: european macroseismic scale 15, 99 pp. luxembourg: cahiers du centre européen de géodynamique et de séismologie. hanks, t.c., & kanamori, h. 1979: a moment magnitude scale. journal of geophysical research 84(b5), 2348–2350. larsen, t.b., gregersen, s., voss, p.h., bidstrup, t., & orozova-bekkevold, v. 2008: the earthquake that shook central sjælland, denmark, november 6, 2001. bulletin of the geological society of denmark 56, 1–11. morelli, a., ekström, g., mazza, s., pondrelli, s., boschi, e. & dziewonski, a.m. 2000: surface-wave centroid moment tensors in the mediterranean region: the mednet-harvard project. orfeus electronic newsletter 2, p. 4. pharaoh, t. 1999: palaeozoic terranes and their lithospheric boundaries within the trans-european suture zone (tesz): a review. tectono physics 314, 17–41. richter c.f. 1935: an instrumental earthquake magnitude scale. bulletin of the seismological society of america 25, 1–32. scandinavian earthquake archive 2003: cd with scanned reports for icg project no. 3. icg 3-2003-3. authors’ addresses p.h.v., t.b.l. & s.g., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: pv@geus.dk l.o., british geological survey, murchison house, west mains road, edinburgh eh9 3la, uk. 12 rosa_2008:rosa-2008 01/07/09 15:47 side 12 geological survey of denmark and greenland bulletin 20, 2010, 87–90 87 small-scale mining is extraction of metals, precious stones, industrial minerals and other commodities using simple technologies. at a worldwide scale, an estimated 100 million people depend on income from small-scale mining (hinton 2006). in tanzania, there are more than half a million active small-scale miners, most of whom extract gold from placer and hard-rock deposits. apart from providing a livelihood for thousands of households, small-scale mining reduces migration from rural to urban areas. however, small-scale mining is associated with a number of negative effects, because mining activities have severe impacts on both the local environment and the miners’ health. most significantly the widespread use of mercury for gold extraction results in polluted environments and serious health hazards for the miners themselves and for the population in the vicinity of smallscale gold mining settlements (bose-o’reilly et al. 2008a, b; 2010; jønsson et al. 2009). large amounts of mercury are transferred to the environment from small-scale gold mining activities in tanzania (taylor et al. 2005). the mercury remains in the environment and constitutes a severe health hazard, also for generations to come. thus, it is of paramount importance to reduce or, even better, stop the release of mercury from small-scale gold mining. a number of alternative methods have been suggested and tested with limited degrees of success (hilson & van der horst 2002). in 2009 geocenter denmark financed a project to test the feasibility of using borax as a replacement for mercury in small-scale gold extraction in tanzania. gold extraction small-scale gold mining of rock deposits in tanzania is done by sinking shafts and digging tunnels along gold reefs. the mined ore is crushed to walnut size manually or using a jaw crusher and ground in metal drums with hard steel balls or rods, the so-called ball mills. the pulverised material is f lushed down a water channel, the bottom of which is covered by a piece of cloth. the heavy particles are caught in the cloth and the light particles end as tailings. this is called sluicing. the heavy fraction from the cloth is treated with mercury (fig. 1). the gold particles amalgamate with mercury and can thus be separated from other heavy minerals. the amalgam is placed in a small iron cup over a fire, the mercury evaporates and the gold is left behind. this gold extraction method is not efficient, so the tailings from sluicing and amalgamation are reprocessed up to ten times in order to recover more gold. the amalgamation method is easy to learn and swift. however, as mentioned above, the method causes serious environmental and health problems and is not particularly efficient with respect to gold recovery. borax – an alternative to mercury for gold extraction by small-scale miners: introducing the method in tanzania peter w.u. appel and jesper bosse jønsson fig. 1. about 100 g of mercury are added to about 5 kg of concentrate from the sluicing. © geus, 2010. geological survey of denmark and greenland bulletin 20, 87–90. open access: www.geus.dk/publications/bull 8888 mercury toxicity during amalgamation the metallic mercury evaporates. some of the vapour is inhaled by people working in the vicinity and may over time cause irreparable damage to their brains. the rest of the mercury vapour gradually precipitates on the ground and enters the drainage system, where it is transformed to methylated mercury by bacteria. methylated mercury is water soluble and enters the food chain causing serious damage to humans who are at the top of the food chain. methylated mercury is extremely harmful to the central nervous system, where it causes tremors, difficulty in walking, tunnel vision, psychological problems and eventually death. there is no cure for permanent mercury poisoning (clarkson et al. 2003). unborn babies are especially prone to damage from methylated mercury. if a pregnant mother has mercury in her body, the foetus ‘sucks’ mercury from her. the nervous system of the foetus is much more sensitive to mercury than that of an adult. a mother with even a low concentration of mercury in her body thus has a high risk of giving birth to mentally or physically disabled children (davidson et al. 1998). gold extraction with borax the use of chemical borax, also known as sodium borate, appears to be one of the more viable ways that have been proposed to reduce or stop the use of mercury by small-scale miners (spiegel & veiga 2010). borax is used for cleaning purposes and is therefore commonly available. the reason for using borax in the smelting process of ore material is that borax reduces the melting point of metals and minerals. under normal field circumstances small-scale miners cannot smelt gold, as they cannot create the high temperature required to smelt the ore. by adding borax to their concentrate, however, they can extract and smelt their gold. gold purchasers already use borax to purify gold with a high content of mercury; however, the method has only recently been applied by small-scale miners. in the benguet area of the northern philippines, around 15 000 small-scale gold miners currently mix their gold concentrate with borax, followed by heating and smelting (leoncio na-oy, personal communication 2010). as a consequence, the mercury usage in the area is minimal and the gold recovery rate quite impressive. the process works as follows: the gold ore is crushed, ground and concentrated as in the case of mercury-based extraction. however, the final product needs to have a very high gold concentration, above 90%, for the borax method to work. this requires skill, practise, and not least time. during testing of the borax method in tanzania, two ways of smelting gold were applied. the first one involved using charcoal and a blower, the second one the use of acetylene gas. charcoal and blower. the gold concentrate is mixed with borax and placed in a plastic bag in a small ceramic bowl filled fig. 2. vigorous burning of charcoal is achieved with a hand-powered blower. fig. 3. molten gold in the centre of the glowing clay bowl and charcoal. 89 with charcoal and some borax, with the recommended ratio between gold concentrate and borax being 1 to 3. the charcoal is ignited and vigorous burning is achieved by using a hand-powered blower (fig. 2). after about 30 minutes the metals and minerals in the concentrate begin to smelt and small drops of gold coalesce at the bottom of the bowl (fig. 3) and can be picked up with the tip of a knife. the advantage of the blower is that it is inexpensive; the disadvantage is that it takes up to half an hour to smelt the gold. acetylene gas. the gold concentrate is mixed with borax and placed in a small plastic bag in a ceramic bowl lined with borax. the gold concentrate –borax mixture is melted with the gas f lame and after about 10 minutes the gold melts and coalesces (fig. 4). the advantage of using acetylene gas is that the miners get their gold fast; the disadvantage is that acetylene is expensive and that the gas bottles are heavy to transport. what does it take for the miners to accept the borax method? changing a well-established habit is difficult and requires very good reasons. the habit of using mercury for gold extraction is clearly such a case, because the mercury method is easy to learn and carry out. obviously, this makes the introduction of a new and healthier method a challenge, especially because the borax method requires skill and patience. depending on the skills of the person who prepares the concentrates, the borax method may take between half an hour and an hour longer than the mercury method. the immediate advantage of using borax is that it does not harm the environment or the people within or close to the mining sites, in the quantities necessary for gold extraction. in addition, borax is cheaper than mercury and produces purer gold than that produced with mercury (fig. 5). as small-scale miners are often paid according to the gold content in their gold, the gold produced with borax is likely to provide a better price. however, the question still remains whether these advantages are sufficient to make small-scale gold miners swap from mercury to borax. considering the embedded culture of using mercury, a change from mercury to borax extraction is not likely to come easy. an additional incentive for the miners to convert to the borax method may be needed. the geocenter denmark project that was conducted in two small-scale mining communities in tanzania in may 2009 demonstrated that abandoned tailings from small-scale gold mining may contain a very high gold content, with up to 100 ppm of gold. the average gold grade in the ore mined by the small-scale miners is in the order of 3 to 50 ppm. it was a puzzle how the miners could loose so much gold in spite of repeated processing. the techniques used by small-scale miners are not sophisticated and in general it is believed that around 50% of the gold is lost. nevertheless, tailings with up to 100 ppm gold require an explanation. when small-scale miners treat their concentrate with mercury, they do not recover all the mercury which instead ends up in the tailings. miners know that they are incapable of recovering all the gold in one go and therefore reprocess the tailings in the ball mills, where the mercury becomes pounded to an extent where it looses its ability to coalesce; it turns into what may be termed mercury f lour. this f lour cannot easily be recovered, which also goes for the gold amalgamated with it. as a result, all the mercury–gold f lour is lost to the tailing dumps. awareness by the miners that they lose substantial quantities of gold and income as a result of 1 cm fig. 5. gold extracted by borax (left) is pure, whereas gold extracted by mercury (right) contains up to 10% mercury giving it a paler colour. fig. 4. gold smelting in borax with an acetylene burner. 9090 the mercury technique could be what is needed to facilitate a shift from mercury-based to borax-based gold extraction. lessons learned in rural tanzania the borax method was tested and demonstrated in the two small-scale gold-mining communities londoni and itumbi in tanzania. the tests were carried out by a small-scale miner from the philippines, who uses the borax method on a daily basis. in londoni, a demonstration using charcoal and a blower proved successful and produced a gold tablet of 2.4 grams with a high purity. in itumbi, the test was carried out by using acetylene gas. the test was successful, a tablet of 3 grams was produced, and the project demonstrated that the method is feasible for small-scale gold miners. the small-scale miners from itumbi, a permanent and well-established community, seemed more keen to learn about the mercury-free method than those from londoni, which is a gold-rush settlement, where most residents come from elsewhere. after the demonstration in itumbi, the miners expressed their opinion about the method at a small workshop. on the one hand, most miners recognised the potential of using the borax method, as it would significantly reduce mercury usage and improve the purity of their gold. on the other hand, they mentioned the high price of acetylene gas, the fact that borax is not readily available in the region (this is true and ways of making borax available in that part of the country are needed), the longer time required for preparing the concentrate, and the fact that many miners need to process small quantities of gold (e.g. 0.3 gram) on a daily basis to get food on the table, and that the borax method seemed a bit too advanced for such small quantities. finally, they requested additional instruction and demonstrations in which they could take part before they would be prepared to adopt the new method. conclusions the borax method was received with interest in both smallscale gold-mining communities, but the attitude was more positive in the more permanent settlement of itumbi where people are more concerned about the environment. the following points must be taken into account before borax has a chance of replacing mercury: (1) locally produced, inexpensive blowers or acetylene gas must be easily available, as well as access to the necessary expertise, (2) borax must be readily available, (3) a substantial training programme has to be carried out, (4) a link must be established between the small-scale miners and advisers, preferably the local mining authorities, who can guide the miners when technical problems occur and (5) small-scale miners need to understand the link between the borax method and a higher gold recovery rate. acknowledgements the authors would like to thank the small-scale miners who participated in the testing of the borax method. financial assistance for the research was provided by geocenter denmark. references bose-o’reilly, s., lettmeier, b., gothe, r.m., beinhoff, c., siebert, u. & drasch, g. 2008a: mercury as a serious health hazard for children in gold mining areas. environmental research 107, 89–97. bose-o’reilly, s., lettmeier, b., roider, g., siebert, u. & drasch, g. 2008b: mercury in breast milk – a health hazard for infants in gold mining areas? international journal of hygiene and environmental health 211, 615–623. bose-o’reilly, s., drasch, g., beinhoff, c., tesha, a., drasch, k., roider, g., taylor, h., appleton, d. & siebert, u. 2010: health assessment of artisanal gold miners in tanzania. science of the total environment 408, 796–805. clarkson, t.w., magos, l. & myers, g.j. 2003: the toxicolog y of mercury – current exposures and clinical manifestations. new england journal of medicine 349, 1731–1737. davidson, p.w. et al. 1998: effects of prenatal and postnatal methylmercury exposure from fish consumption on neurodevelopment: outcomes at 66 months of age in the seychelles child development study. journal of american medical association 280, 701–707. hilson, g. & van der horst, r. 2002: technolog y, managerial, and policy initiatives for improving environmental performance in small-scale gold mining industry. environmental management 30, 764–777. hinton, j.j. 2006: communities and small scale mining: an integrated review for development planning, 413 pp. washington: world bank group. jønsson, j.b., appel, p.w.u. & chibunda, r. 2009: a matter of approach: the retort’s potential to reduce mercury consumption within small-scale gold mining settlements in tanzania. journal of cleaner production 17, 77–86. spiegel, s.j. & veiga, m.m. 2010: international guidelines on mercury management in small-scale gold mining. journal of cleaner production 18, 375–385. taylor, h., appleton, j.d., lister, r., smith, b., chitamweba, d., mkumbo, o., machiwa, j.f., tesha, a.l. & beinhoff, c. 2005: environmental assessment of mercury contamination from the rwamagasa artisanal gold mining centre, geita district, tanzania. the science of the total environment 343, 111–133. authors’ addresses p.w.u.a., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: pa@geus.dk j.b.j., department of geography and geology, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. geological survey of denmark and greenland bulletin 28, 2013, 49-52 49 geochemistry and petrology of gold-bearing hydrothermal alteration zones on qilanngaarsuit, southern west greenland martin koppelberg, annika dziggel, denis martin schlatter, jochen kolb and franz michael meyer during field work in 2008, the geological survey of denmark and greenland investigated the gold potential of hydrothermal vein systems in the nuuk region of the archaean north atlantic craton. a new gold occurrence was discovered on the island of qilanngaarsuit, 35 km south of nuuk. two cross sections through hydrothermal alteration zones, that locally contain up to 672 ppb au, were mapped and sampled in detail. in this study, we present petrological and geochemical data in order to constrain the conditions for ore formation and transport of elements during f luid–rock interaction. geological setting qilanngaarsuit in southern west greenland (fig. 1) is situated in the godthåbsfjord gold province, a c. 20 km by 150 km wide, ne-trending sector along the ivinnguit fault system. several gold occurrences such as storø, qussuk, bjørneøen and sw isua have been described from this sector (garde et al. 2012; scherstén et al. 2012; kolb et al. 2013). the ivinnguit fault, situated north of the island, is a deep-crustal shear zone, which formed during terrane amalgamation and it represents the border between the færingehavn and akia terranes (nutman & friend 2007). qilanngaarsuit island is dominated by eoarchaean tonalite-trondhjemite-granodiorite (ttg) gneisses of the færingehavn terrane, which are overlain by amphibolites and aluminous cordierite-orthoamphibole gneisses that originated from c. 2840 ma old protoliths (nutman & friend 2007). four deformation events can be distinguished, involving north-vergent thrusting, isoclinal folding and the formation of late, upright, open to tight folds (e.g. kolb et al. 2013). the gold-bearing quartz veins are hosted by amphibolites in the central part of the island and surrounded by approx. 8 m wide hydrothermal alteration zones. the foliation-parallel, c. 10–20 cm wide, quartz veins can be followed over several hundred metres along strike. structural data indicate that they formed in response to f lexural, slip folding during the late-tectonic evolution of the region (kolb et al. 2013). one sample from a hydrothermal alteration zone surrounding the veins contains up to 672 ppb au and several other vein and alteration zone samples have elevated au contents (> 20 ppb au; kolb et al. 2009). © 2013 geus. geological survey of denmark and greenland bulletin 28, 49–52 . open access: www.geus.dk/publications/bull 50°w 64°n 63°n s q b 50 km eoarchaean gneiss anorthosite-gabbro complexes orthogneiss and granitic rocks (mesoto neoarchaean) tonalitic to granodioritic plutons (mesoto neoarchaean) granite (mesoto neoarchaean) quaternary cover ice cover granulite facies qôrqut granite complex fault qilanngaarsuit fisk efjo rd f ault go dt hå bs fjo rd fisk efjo rd amer alik amer alik ser mili k bjørnesund block færingehavn terrane tasiusarsuaq terrane akia terrane tre brødre terrane tre brødre terrane isukasia terrane bu kse fjord bjør nes un d grædefjord godthåbsfjord– ameralik belt ivinnguit fault sermilik block nuuk færingehavn kapisilik terrane terrane or block boundary supracrustal belts (undifferentiated) greenland fig. 1. geological map of the nuuk region (modified from allaart 1984). b: bjørneøen, q: qussuk, s: storø. 5050 petrology and geochemistry two profiles from the unaltered wall rocks through the hydrothermal alteration zones were investigated (fig. 2). two types of amphibolite can be distinguished: homogeneous amphibolite in the footwall and compositionally layered amphibolite in the hanging wall of the hydrothermal vein system. their protoliths were low-k tholeiites depleted in light rare-earth elements (lree), geochemically similar to other amphibolites in the buksefjord region (chadwick 1981). generally, the amphibolites are fineto medium-grained and consist of hornblende (40 vol.%), plagioclase (30  vol.%), clinopyroxene (20   vol.%) and clinozoisite/zoisite/epidote (10  vol.%). metamorphic garnet is locally present in the layered amphibolite. retrogression is indicated by the transformation of plagioclase to a fine-grained assemblage of zoisite and quartz, and by the replacement of amphibolite and clinopyroxene by epidote and clinozoisite. within the alteration zone, the amphibolite-facies mineral assemblages are replaced by a high temperature alteration assemblage of garnet, quartz, plagioclase, biotite, and sillimanite (figs 2, 3). in contact with the veins, the hydrothermal alteration zone consists of up to 50   vol.% garnet, 15  vol.% plagioclase, 15  vol.% quartz, 10  vol.% biotite and 10   vol.% sillimanite (fig. 2). relict amphibole facies minerals such as hornblende and clinopyroxene are locally preserved, indicating that these minerals formed during regional metamorphism prior to the mineralisation. ore minerals make up ≤1 vol. % of the rocks; they include pyrite, pyrrhotite and chalcopyrite. mass-balance calculations based on whole-rock, majorand traceelement data (kolb et al. 2009; koppelberg 2011) and using the method of gresens (1967) indicate that the ore f luid was enriched in si, k, lree, au, cr, cu, zn, mo and as (fig. 4). in si-rich, vein-dominated samples, the hydrothermal overprint was associated with a volume increase of 14–62%. in contrast, the sillimanitebearing samples record a significant volume loss of 15–50%, and are depleted in si (fig. 4). this suggests that at least some of the si in the quartz veins was leached from the surrounding wall rocks. garnet in the alteration zones is rich in almandine (koppelberg 2011). most grains are essentially unzoned and have fig. 2. lithological logs of profiles a and b (modified from schlatter 2009). amphibolite with weak grt-bt alteration (pl (xab0.22-0.45), hbl, qtz, cpx, bt, grt (alm46-62, prp20-39,grs80-12) unaltered amphibolite (hbl, pl, cpx, qtz, ttn) retrogressed amphibolite (pl (xab0.49-0.61), hbl, zo, cpx ± qtz, ttn, ep, bt, cal unaltered amphibolite with grt (alm53-59,prp13-20, grs20-22), hbl, pl (xab0.19-0.29), cpx, qtz grt-bt alteration, vein-dominated, without sil: pl (xab0.59-0.65), qtz, grt (alm53-64-prp10-33-grs3-28), bt, hbl, cpx, chl ± sil grt-bt alteration with sil: grt (alm54-69-prp13-31-grs3-23), pl (mainly andesine, locally an), qtz, bt, sil grt-bt alteration without sil: (pl (xab0.56–0.57), grt (alm53-75-prp13-31-grs4-13), qtz, bt, chl) unaltered amphibolite, slightly retrogressed (hbl, pl (xab0.31-0.35), cpx, czo) 508405 508406 <2 ppb 23 ppb 508407 508408 508409 508410 508411 <2 ppb 12 ppb 4 ppb <2 ppb <2 ppb 508412 508413 508414 508415<2ppb <2ppb 508381 508382 508383 508384 508385 508386 508387 508388 508389 508390 508391 <2 ppb <2 ppb 3 ppb <2 ppb 46 ppb 34 ppb 20 ppb 38 ppb 672 ppb <2 ppb <2 ppb 508392 grt-bt-pl thermobarometry: 540°–620°c 4.5 ± 1 kbar profile aprofile b(cliff profile) 4 ppb <2 ppb 3 ppb 20 ppb <2 ppb 5 m petrographical sample (polished thin section) geochemical sample (fa gold)38 ppb 67 ppb sillimanite garnet sulphides qtz vein / qtz-blebs pegmatite silicified (schist) grt-rich schist bt-rich schist layered amphibolite (type 1) homogeneous amphibolite (type 2) lithogeochemical sample (whole-rock + trace elements + inaa gold) legend 51 a composition of alm53–69, prp21–31, grs3–12, depending on bulk composition. in some of the larger grains, the rims have slightly higher fe concentrations (alm62–72, prp20–25, grs3–10). metamorphic garnet in the unaltered wall rocks is unzoned and enriched in grossular (alm53–59, prp13–20, grs17–21). both types of garnet have very low ree contents (<2 ppm), and are depleted in lree. biotite in the alteration zone has aliv contents between 2.4 and 2.65 atoms per formula unit and mg/(fe+mg) ratios between 0.25 and 0.45. the composition of plagioclase from the amphibolites varies from andesine to anorthite; most grains can be classified as labradorite and bytownite. plagioclase in the hydrothermal alteration zone is depleted in ca and is mostly andesine. in order to achieve reliable pressure–temperature (p–t) estimates, only mineral cores of neighbouring minerals were used for geothermobarometry. due to the presence of retrograde reaction rims in some of the garnet grains, it was assumed that the mineral cores ref lect the equilibrium mineral composition and were not altered by retrograde processes. p–t estimates on the alteration assemblage using the garnetbiotite-plagioclase-quartz geothermobarometer of wu et al. (2004) give conditions of c. 540–620°c and 4.5 ± 1 kbar (fig. 5). p–t pseudosection models using the computer program perplex developed by connolly (1990) confirm these conditions (koppelberg 2011). 500 µm hbhb grtgrt btbt btbt btbt silsil silsil silsil cr cu zn mo as au ni co sc la ce pr nd sm eu gd tb dy ho er tm yb lu –100 –50 0 50 100 150 200 –100 –50 0 50 100 150 200 –100 –50 0 50 100 150 200 a b c quartz-vein dominated alteration zone (vf: 1.14–1.62) silimanite-bearing alteration zone (vf: 0.5–0.85) g ai n/ lo ss (% ) g ai n/ lo ss (% ) g ai n/ lo ss (% ) sio2 al2o3 tio2 fe2o3 mgo mno cao na2o k2o fig. 3. photomicrograph illustrating the replacement of the regional metamorphic amphibolite facies mineral assemblages by hydrothermal garnet, biotite and sillimanite in sample ggu 508405. fig. 4. results of mass-balance calculations for quartz-vein dominated and sillimanite-bearing alteration zones. vf: volume factor – the change of volume of altered rock relative to unaltered rock. a: major elements, b: trace elements, c: rare-earth elements (r ee). fig 5. thermobarometry results (see main text). the al2sio5 diagram is from holdaway & mukhopadhyay (1993). red: sample ggu 508384, green: 508385, blue: 508386, yellow: 508405. the al2sio5 triple point is at 500°c and 3.75 kbar. kyanite silimanite andalusite ky ky sil si l an d an d 200 300 500400 600 700 800 900 2 1 3 4 5 6 7 8 9 temperature (°c) pr es su re (k ba r) 5252 discussion and conclusion the majority of the world’s gold deposits formed in the archaean (c. 2.7 ga) as a result of crust-forming processes during collision events of converging continental plates (groves et al. 2005). these epigenetic deposits are called orogenic gold deposits, and occur in metamorphic terranes that mainly show greenschist facies metamorphism (groves et al. 1998). other orogenic deposits are known to have formed at amphibolite-facies metamorphic grades, and these are termed hypozonal deposits (groves et al. 1998). the replacement of regional, metamorphic, amphibolite-facies mineral assemblages by hydothermal minerals surrounding the goldbearing quartz veins as well as the late timing of quartz-vein formation by ductile, f lexural slip folding (kolb et al. 2009), indicate that the gold mineralisation and associated hydrothermal alteration formed late in the metamorphic evolution on qilanngaarsuit. the low-pressure amphibolite-facies metamorphism in the surrounding amphibolites has been dated to c. 2715 ma (nutman & friend 2007), while the mineralisation probably occurred between 2660 and 2600 ma (kolb et al. 2013). the qilanngaarsuit mineralisation is, therefore, interpreted to represent a new example of hypozonal orogenic gold mineralisation in the godthåbsfjord gold province. the origin of other gold prospects (storø, qussuk) is still a matter of debate, and both metamorphosed epithermal and orogenic models have been proposed (garde et al. 2012; scherstén et al. 2012; kolb et al. 2013). the alteration systematics, timing and conditions of the gold mineralisation on qilanngaarsuit are, however, similar to those of other gold occurrences, in particular storø, in the godthåbsfjord gold province. the deposits are spatially closely associated with a major terrane boundary, the ivinnguit fault, suggesting that this shear zone may have acted as a major pathway for the gold-bearing f luids between c. 2660–2600 ma. acknowledgements the professor dr. karl-heinrich heitfeld-stiftung is thanked for financial support. the work benefited from valuable comments and discussions with susan giffin and nicolas stoltz. references allaart, j.h. 1982: geological maps of greenland 1:500 000. map sheet no. 2, frederikshåb isblink – søndre strømfjord. copenhagen: geological survey of denmark and greenland. chadwick, b. 1981: field relations, petrography and geochemistry of archaean amphibolite dykes and malene supracrustal amphibolites, northwest buksefjorden, southern west greenland. precambrian research 14, 221–259. connolly j.a.d. 1990: multivariable phase diagrams: an algorithm based on generalised thermodynamics. american journal of science 290, 666–718. garde, a.a., whitehouse, m. & christensen, r. 2012: mesoarchean epithermal gold mineralisation preserved at upper amphibolite-facies grade, qussuk, southern west greenland. economic geolog y 107, 881–908. gresens, p.l. 1967: composition-volume relationships of metasomatism. chemical geolog y 2, 47–65. groves, d.i., goldfarb, r.j., gebre-mariam, m., hagemann, s.g. & robert, f. 1998: orogenic gold deposits: a proposed classification in the context of their crustal distribution and relationship to other gold deposit types. ore geolog y reviews 13, 7–27. groves, d.i., condie, k.c., goldfarb, r.j., hronsky, j.m.a. & vielreicher, r.m. 2005: secular changes in global tectonic processes and their inf luence on the temporal distribution of gold-bearing mineral deposits. economic geolog y 100, 203–224. holdaway, m.j. & mukhopadhyay, b. 1993: a re-evaluation of the stability relations of andalusite: thermochemical data and phase diagram for the aluminum silicates. american mineralogist 78, 298–315. kolb, j., stensgaard, b.m., schlatter, d.m. & dziggel, a. 2009: controls of hydrothermal quartz vein mineralization and wall-rock alteration between ameralik and sermilik, southern west greenland. danmarks og grønlands geologiske undersøgelse rapport 2009/25, 76 pp. kolb, j., dziggel, a. & schlatter, d.m. 2013: gold occurrences of the archean north atlantic craton, southwestern greenland: a comprehensive genetic model. ore geolog y reviews 54, 29–58. koppelberg, m. 2011: geochemische und petrologische charakterisierung einer goldführenden hydrothermalen alterationszone auf der insel qilanngaarsuit, sw grönland, 70 pp. unpublished diploma thesis, institut of mineralogy and economic geology, rwth aachen university. nutman, a.p. & friend, c.r.l. 2007: adjacent terranes with c. 2715 and 2650 ma high-pressure metamorphic assemblages in the nuuk region of the north atlantic craton, southern west greenland: complexities of neoarchaean collisional orogeny. precambrian research 155, 159–203. scherstén, a., szilas, k., creaser, r.a., næraa, t., van gool, j.a.m. & østergaard, c. 2012: re-os and u-pb constraints on gold mineralisation events in the mesoto neoarchaean storø greenstone belt, storø, southern west greenland. precambrian research 200-203, 149-162. schlatter, d.m. 2009: petrographic and lithogeochemical surface data from the new gold occurrence on qilanngaarsuit island, southern west greenland. in: kolb, j & kokfelt, t.: annual workshop on the geolog y of southern west greenland realted to field work: abstract volume 1, geus rapport 2009/94, 18–21. wu, c.-m., zhang, j. & ren, l.-d. 2004: empirical garnet-biotite-plagioclase-quartz (gbpq ) geobarometry in mediumto high-grade metapelites. journal of petrolog y 45, 1907–1921. authors’ addresses m.k., a.d., f.m.m., institute of mineralogy and economic geology, rwth aachen university, wüllnerstraße 2, 52056 aachen, germany; e-mail: koppelberg@iml.rwth-aachen.de d.m.s., helvetica exploration services gmbh, carl spitteler strasse 100, ch-8053 zürich, switzerland. j.k., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. geological survey of denmark and greenland bulletin 31, 2014, 71-74 71© 2014 geus. geological survey of denmark and greenland bulletin 31, 71–74. open access: www.geus.dk/publications/bull integrating 3d photogeology with aeromagnetic data as a tool for base-metal exploration in east greenland anaïs brethes, pierpaolo guarnieri and thorkild m. rasmussen an 800 km long basin system developed along the east greenland margin since the late palaeozoic in which the jameson land basin forms the southern part of the system. along the margins of the jameson land basin there are occurrences of barite, copper, lead, zinc and silver, which are particularly abundant in the northern part of the basin’s eastern margin in the wegener halvø area (fig. 1). structures and stratigraphic architecture play important roles in the mineralisation distribution, so detailed mapping is essential. we used 3d photogeology combined with geophysical data to map the different stratigraphic units, faults and dykes in three dimensions. geological setting of jameson land basin the east greenland basin began to develop during the devonian following the caledonian orogeny. in the late carboniferous and early permian rotational block faulting took place (surlyk 1990). the faults were reactivated during the late permian and early triassic and synsedimentary faulting occurred at the same time (seidler 2000). the resulting fault blocks were peneplained before transgression and onset of sedimentation in the late permian. on wegener halvø the up to 300 m thick upper permian sequence unconformably overlies deformed and peneplained devonian sediments (fig. 1). the sequence is dominated by karstified dolomitic limestone of the karstryggen formation, by carbonate buildups which developed on palaeotopographic highs (the wegener halvø formation) and by bituminous dark shale of the upper permian ravnefjeld formation. these filled up the deepest and karstified parts of the previous formations and locally contain calcareous concretions and fossils derived from the carbonate buildups. the unconformable to conformable permian–triassic boundary is locally incised by submarine canyons (seidler 2000). laterally variable, the triassic stratigraphic architecture was controlled by tectonics and rapid asymmetric subsidence. this entire sequence is mainly composed of continental deposits with some shallow marine incursions. in the tertiary the jameson land basin was covered by flood basalt and intruded by a complex of sills and e–w to nw–se-trending dykes. the intrusions that are dated to the latest paleocene to earliest eocene (soper et al. 1976) affect the entire sequence of basin fill. in miocene time the northern part of the basin was uplifted more than 1 km (mathiesen et al. 2000; hansen et al. 2001). base-metal mineralisation on wegener halvø the first rock samples were collected in east greenland in 1822 and during the three-year expedition to east greenland from 1931 to 1934 copper-, leadand silver-bearing minerals were discovered on wegener halvø (fig. 1), in the upper permian carbonates of the wegener halvø formation. subsequent investigations by nordisk mineselskab a/s (nordmine) led to the discovery in 1968 of base-metal occurrences in the black shale of the ravnefjeld formation. min5 km greenland 22°45´2.5 km precambrian to lower permian upper permian triassic jurassic quaternary fault 22°30´ 71°35´ 71°40´ nordenskiöld bjerg buch bjerg quensel bjerg tait bjerg fle min g f jord na tho rst fjo rd pe rm dal de von dal w eg en er h al vø ss jl ll fig. 1. simplified geological map of the wegener halvø area (modified from perch-nielsen et al. 1983). ss: scoresby sund. jl: jameson land. ll: liverpool land. contour interval 200 m. 7272 eral exploration ceased because the ore was too low grade, but the oil industry became interested in the hydrocarbon source-rock potential of the upper permian shale. harpøth et al. (1986) reviewed more than a century of these sporadic field campaigns and since 2011 avannaa resources ltd has explored the area for base metals. mineral occurrences are particularly abundant along the eastern margin of the jameson land basin, especially in the wegener halvø area where they occur in three of the upper permian formations and three of the triassic formations. one of the most interesting ore-bearing formations is the limestone buildups of the wegener halvø formation. as described by harpøth et al. (1986), cu, pb and zn sulphides are scattered throughout the whole peninsula. they are also found as fine-grained material in inter-reef black-shale occurrences in the ravnefjeld formation. base-metal minerals are mainly found in the upper part of the carbonates and in the lower part of the shales (upper permian formations), but stratiform occurrences occur in triassic sediments. early triassic alluvial conglomerate and arkosic sandstone are mineralised with argentiferous chalcocite-covellite, and galena occurs as cement. according to soil sample geochemical analyses, the highest grades appear to be concentrated at the contact between two facies, in a trend perpendicular to the palaeocurrents (harpøth et al. 1986). in the late triassic playa-lake mudstone and sandstone, fine-grained cu sulphides are found over an area of 1000 km2. 3d photogeology the geological survey of denmark and greenland is equipped with a 3d stereoplotter to carry out multi-model photogrammetry that can be used to accurately map geological features from vertical and oblique aerial photographs. the instrument is equipped with two polarised monitors set one above the other with an angle of 110° separated by a halfmirror (vosgerau et al. 2010). each polarised screen displays one photograph of an overlapping stereopair. the half-mirror allows the viewer to see two photographs as one image with 3d polarised glasses getting a depth perception of the geological features that, in turn, can be digitised as 3d polylines. the geologic features and the database are automatically imported into a geographic information system where they can be edited. the photographs used for the present work were taken during a combined hyperspectral and lidar survey in 2012 (thorning et al. in press). the spacing between the flight lines was c. 500 m and the pixel size in the centre of each image is 27 × 27 cm. on wegener halvø, an area of 100 km2 comprising devondal and nordenskiöld bjerg was mapped on a scale of 1:1000 (fig. 1). more than 5000 features were digitised, including bedding, stratigraphic boundaries as well as fractures and dykes (fig. 2). together with the digitised 3d polylines it is possible to calculate strata thicknesses and measure strike and dip of bedding of faults and dykes. the overall fig. 2. 3d view from the south towards nordenskiöld bjerg created with orthophotographs draped on a digital elevation model developed from lidar data. the geological features collected from aerial photographs are: faults and fractures (red lines) and triassic bedding (black lines). 400 m 73 stratigraphic succession is based on the published geological map (perch-nielsen et al. 1983). more than 900 faults, fractures and dykes were digitised in the wegener halvø area and the majority shows a n–s and nnw–sse-orientation. the structures are steep and occur as flower structures affecting the entire succession. the vertical offset is small and decreases from south to north along the strike of the faults that in some cases have a strike-slip component. integrated 3d photogeology and aeromagnetic data the dataset from the interpretation of the photographs has been combined with a new structural interpretation of airborne magnetic data from the aem greenland 1997 survey (rasmussen et al. 2001). different maps were obtained from the calculation of the magnetic gradient tensor elements to highlight structures in different directions (pedersen & rasmussen 1990). the total magnetic intensity anomalies of the structures of interest have small amplitudes (around 3 nt) that are close to the detection limit of c. 0.5 nt of an airborne survey. as differentiation works as a high-pass filter, the second vertical derivative of the total magnetic intensity was also calculated to emphasise the linear features. this processing provides a better dynamic range for visualising the structures than the measured field. to attenuate the short wavelength noise features generated by this differentiation, an upward continuation of the magnetic field to 100 m was applied. lineaments defined by negative magnetic anomalies and interpreted as major structures were digitised on the resulting map (fig. 3a). these features are n–s to nnw–sse-trending and several kilometres long and they fit with the faults in the geological map (fig. 1) and with the fault segments mapped with the 3d stereo-plotter (fig. 3b). the accurate fault segments mapped by photogeolog y were integrated with the magnetic lineaments highlighted at a larger scale. thus, an identified structure can be prolongated on the map using geophysical data and constrained in its precise location and dip using 3d photogeolog y. one of the n–s-trending faults mapped by 3d photogeolog y and visible on the magnetic data coincides with the so-called vimmelskaft lineament defined by pedersen (1997). this lineament corresponds to a zone where a n–s-trending fault and a n–s-running dyke cut through upper permian shales and karstified carbonates. important mineral occurrences with high base-metal content are found along this lineament and the concentration decreases away from the lineament. fig. 3. a: second vertical derivative of the total magnetic intensity (tmi) from the aem greenland 1997 survey (pixel size is 50 × 50 m) continued upward to 100 m and draped on the shaded elevation model. the negative magnetic lineaments are digitised and shown as black lines. b: correlation between magnetic data and the faults, fractures and bedding collected from aerial photographs. note the presence of eroded strata parallel to positive magnetic anomalies and faults and fractures related to negative anomalies. lineament 2nd vertical derivative tmi (nt/m2) –1.2 × 10–5 1.5 × 10–5 b a 71°28´ 22°48´ 4 km -0.3.10 -5 [nt.m -2] 0.5.10 -5 fleming fjord fm. gipsdalen fm. pingodal fm. faults and fractures beddings: fleming fjord fm gipsdalen fm pingo dal fm faults and fractures bedding: 0.5 × 10–5 –0.3 × 10–5 500 m 71°34´ 22°30´b 2nd vertical derivative tmi (nt/m2) 7474 the positive magnetic anomalies are not linear and appear to be associated with magnetic domains in the triassic formations (fig. 3b). the contours of these domains are parallel to the stratification collected from 3d photogeology (edges of eroded beds) and are mostly located on crests. concluding remarks using 3d photogeology we mapped a 100 km2 area with good exposures on a scale of 1:1000. formation boundaries and dip of strata are well constrained. new structures were mapped and the resulting dataset forms a good starting point for further studies of the stratigraphy or tectonic evolution using 3d modelling. the combination of 3d photogeology with new processing of the magnetic data has shown a good match between n–s-trending magnetic lineaments and n–s-trending normal steep faults. structures of this type were highlighted by pedersen (1997) for their possible role as pathways for mineralising fluids. the structures mapped during this study that affect the upper permian carbonates and shales, should be checked in the field. furthermore, although mineral occurrences found in the triassic formations are stratiform, remobilised sulphides are concentrated in cross-cutting fractures. the mapped faults and fractures that cut through triassic formations could also be interesting targets for exploration. detailed studies of structures and stratigraphic architecture are key points for mineral exploration. accurate mapping using 3d photogeology combined with geophysical data can be efficient tools for this, especially in areas with difficult access and excellent outcrops. references hansen, k., bergman, s.c. & henk, b. 2001: the jameson land basin (east greenland): a fission track study of the tectonic and thermal evolution in the cenozoic north atlantic spreading regime. tectonophysics 331, 307–339. harpøth, o., pedersen, j.l., schønwandt, h.k. & thomassen, b. 1986: the mineral occurrences of central east greenland. meddelelser om grønland, geoscience 17, 139 pp. mathiesen, a., bidstrup, t. & christiansen, f.g. 2000: denudation and uplift history of the jameson land basin, east greenland – constrained from maturity and apatite fission track data. global and planetary change 24, 275–301. pedersen, m. 1997: investigation of ore potential in black shales of the upper permian ravnefjeld formation in scoresby land and on traill ø, central east greenland. danmarks og grønlands geologiske undersøgelse rapport 1997/124, 17 pp. pedersen, l.b. & rasmussen, t.m. 1990: the gradient tensor of potential field anomalies. some implications on data collection and data processing of maps. geophysics 55, 1558–1566. perch-nielsen, k., henriksen n. & stemmerik, l. 1983: geological map of greenland, 1:100 000, fleming fjord, 71 ø.1 nord. copenhagen: geological survey of greenland. rasmussen, t.m., thorning, l., stemp, r.w., jørgensen, m.s. & schjøth, f. 2001: aem greenland 1994–1998 – summary report. danmarks og grønlands geologiske undersøgelse rapport 2001/58, 46 pp. seidler, l. 2000: incised submarine canyons governing new evidence of early triassic rifting in east greenland. palaeogeography, palaeoclimatolog y, palaeoecolog y 161, 267–293. soper, n.j., downie, c., higgins, a.c. & costa, l.i. 1976: biostratigraphic ages of tertiary basalts on the east greenland continental margin and their relationship to plate separation in the northeast atlantic. earth and planetary science letters 32, 149–157. surlyk, f. 1990: timing, style and sedimentary evolution of late palaeozoic – mesozoic extensional basins of east greenland. in: hardman, r.f.p. & brooks, j. (eds): tectonic events responsible for britain’s oil and gas reserves. geological society, special publication (london) 55, 107–125. thorning, l., christensen, n.n., olsen, s., riisager, p., sørensen, l.l., sørensen, e.v. & tukiainen, t. in press: high resolution airborne hyperspectral imaging spectroscopy in central east greenland 2012 – data acquisition and pre-processing. danmarks og grønlands geologiske undersøgelse rapport. vosgerau h., guarnieri p., weibel r., larsen m., dennehy, c., sørensen, e.v. & knudsen, c. 2010: study of a palaeogene intrabasaltic sedimentary unit in southern east greenland: from 3-d photogeolog y to micropetrography. geological survey of denmark and greenland bulletin 20, 75–78. authors’ addresses a.b. & p.g., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: aib@geus.dk t.m.r., division of geosciences and environmental engineering, luleå university of technology, s-971 87 luleå, sweden. geological survey of denmark and greenland bulletin 31, 2014, 95-98 95 to what extent is denmark vulnerable to mineral supply shortage? per kalvig, rune j. clausen, niels fold and karen hanghøj mineral resources are building blocks of modern society and essential for progress and prosperity. mankind has always depended on access to mineral raw materials, which have been a key factor for wealth, culture and development. modern societies are characterised by a rapidly increasing demand for specialised mineral raw materials, determined by their stage of technological development, the number of consumers, and their standard of living. generally, the availability of mineral raw materials has not, until recently, been considered an issue by the average consumer or by companies in the downstream end of the value chains, and mineral resources have not been part of the political agenda. in this context china’s control over rare-earth elements (ree) has been an eye opener to both industry and politicians worldwide, and has subsequently led to discussions about the possible exhaustion of finite resources and potential threats to the availability of raw materials caused by geopolitical tension and market restrictions. the increased concern has lead to several attempts to assess the risk of supply shortage which are however still at a rather qualitative stage. inadequate knowledge about the current and future demand for mineral raw materials prevents political and industrial decision-makers from taking the necessary actions to predict and mitigate the national and industrial vulnerability to supply shortage. thus, most modern societies, including denmark, are vulnerable to mineral raw materials scarcity, but unaware of where and how it may appear, and how to prevent and address the problem. scarcity issues scarcity issues have been discussed since thomas malthus in 1798 initially predicted problems of food shortage due to increasing population and later also in relation to mineral resources. a number of organisations and individuals (e.g. club of rome, gro harlem bruntland) have taken the lead in these discussions and emphasised that natural resources are finite and limited and that the global economy is growing disproportionately. at the summit meeting in rio de janeiro in 1992, all nations were encouraraged to adopt the so-called bruntland principles to ensure sufficient resources for future generations. the term sustainability was introduced to the mining industry. however, no clear effects can be identified neither in the policies nor in the overall mineral consumption, and global and national concern on how to secure raw material supply is increasing. terms such as critical minerals were introduced, reflecting the risk of scarcity of some raw materials. the us national research council quantitatively addressed scarcity issues related to minerals in 2008 (national research council 2008), and since then a substantial number of reports have focused on the topic (e.g. rosenou-tornow et al. 2009; european commission 2010; undp 2010; graedel et al. 2012). the decoupling of wealth and mineral resource consumption remains to be seen. why are minerals important? mineral-based materials are present everywhere in our daily life – in houses, cars, computers, cooking utensils, paint, tiles, paper, plastic, batteries, wind turbines, roads, pipes etc. for each and all of these ‘end products’ the choice of raw materials – and thus the minerals that need to be mined – depends on the required physical and chemical properties of the products. in some cases more than one material may fulfil the product requirements and the choice will then be based on price and availability. all societies need mineral resources for their development, but exactly which minerals and metals are in demand and how they are used depend on the stage of development of the particular society. during historic time the trend has been very clear; innovation and new technologies require an increasing number of specialised raw materials. consequently, we need to explore for new types of minerals to meet new demands. the demand for minerals is fueled by a number of drivers demographics – the united nations has estimated that the world population will increase from currently 7 billion to 9 billion by 2050 and that about 6.5 billion people will © 2014 geus. geological survey of denmark and greenland bulletin 31, 95–98. open access: www.geus.dk/publications/bull 9696 live in cities in 2050. this trend creates a need to develop new infrastructure to support the fast-growing urbanisation, which in turn creates an increased demand for minerals, in particular sand, gravel, iron and copper. numerous other raw materials are also needed for basic infrastructure. wealth – the economic growth in some of the emerging markets – e.g. brazil, russia, india, indonesia, china, the republic of korea, south africa – creates millions of new customers for products like houses, household machines, bicycles, cars, computers, etc. these are all manufactured from raw materials which have to be mined and processed. an example of this is china that has the world’s largest population and is globally the largest consumer of copper, aluminium and iron. however, the consumption of copper in china is still only 3 kg/person/year, much lower than in europe where the consumption is 16 kg/person/year (bogner 2012). however, it is expected that china’s copper consumption will increase substantially mainly as a result of growing wealth, rather than just the growing population. technology – the introduction of new materials, for example in houses and vehicles, in new electronic communication equipment and in new ‘green’ energy technology, changes the desired physical and chemical properties of materials, which in turn creates demand for new mineral raw materials. emerging technologies and new materials have created a rapidly growing demand for certain commodities such as indium and gallium used in light-emiting diode lamps; lithium, copper, neodymium and dysprosium used in electric cars; indium, cadmium and tellurium in photovoltaic thin-film and dysprosium and neodymium in magnets. concurrently, the need for some traditional materials has been reduced. for example, light, strong materials such as aluminium and magnesium have reduced the amount of steel required to build car frames. critical minerals and vulnerability to supply restrictions during the past decade mineral resource shortage has made headlines in the media, especially with regard to the ree. in response, a number of institutions have developed lists of mineral criticality on regional and national levels. for example, the european union has defined 14 raw materials as critical to the eu (european commission 2010). typically, the studies have used a two-fold approach: (1) assessment of the supply risk and (2) assessment of the impact of an actual shortage. the term critical minerals is frequently used in this context. critical minerals are those which are important to su pp ly r isk geological, technological, and economic social and regulatory geopolitical national vulnerability to supply restriction importancesubstitutabilitysusceptibility 1 3 2 4 fig. 1. diagram of vulnerability to the supply risk and restriction (modified from graedel et al. 2012). in the diagram element 1 has a low supply risk and even if a supply shortage occurs, this will not have a great impact on society; element 4 has a high supply risk and society is vulnerable to supply restictions; element 2 possesses a high supply risk but low vulnerability to supply restrictions; and for element 3 the opposite situation occurs, the supply risk is low, but in the event of a supply risk the national vulnerability is high. 97 society and subject to a specific availability or supply risk, e.g. at the corporate, national, regional or global industry level. scarcity is the potential outcome of criticality if a supply risk is not effectively mitigated. scarcity can be a result of several factors such as political conflicts, embargos, cartels, natural disasters, sudden increases in demand, inadequate investment in new mines and processing facilities or resource depletion. resource depletion causing significant shortages of mineral commodities has not yet been documented except in the case of cryolite, but it may pose a long-term threat. based on longand medium-term supply risk graedel et al. (2012) assessed the vulnerability to supply shortage and identified three general components, namely (1) geology, technology and economy; (2) social and regulatory factors and (3) geopolitical factors. each of these were specified by six indicators, forming the ‘supply risk axis’. the ‘vulnerability to supply restrictions axis’ is composed of another set of factors such as (1) importance, (2) substitutability and (3) susceptibility specified in eight indicators (see figs 1, 2). graedel et al. (2012) suggested that vulnerability should also include the environmental impact. forecasting and creating possibilities for adequate policies the value chains for mineral raw materials include all stages of mineral exploration, mining and the processes transforming the minerals into intermediate goods applicable for manufacturing by industrial end users. however, most of the companies in the chain may be unaware of shortor long-term market constraints or opportunities. this prevents the industry itself from responding to sudden changes in demand. the exploration that targets new raw materials is therefore driven by commodity prices. globally, 2556 companies spent 20.5 billion us$ on mineral exploration in 2012, of which 49% was spent on gold, 32% on base metals and the remaining 19% on all other commodities (wilburn & stanley 2013). this illustrates that the exploration sector is decoupled from the end user demand. furthermore, there is a mismatch between the time scales of action in different parts of the value chain. industrial demand for new raw materials and markets for raw materials fluctuate on short-time scales, whereas the time needed to adjust the supply is much longer; it typically takes more than ten years to open a new mine, and sometimes even substantially longer. scrap supplies for recycling, secondary raw materials, are insufficient and usually too expensive to handle in order to bridge the gap between short-term demand and supply. individual governments and their institutions need updated assessment data on the national vulnerability to supply restrictions of mineral raw materials in order to develop and implement policies to avoid scarcity of particular critical minerals. for example, the general conditions for europe may not necessarily be accurate and relevant for the danish industrial and agricultural sectors. so far, only very limited data on vulnerability to supply restrictions are available for substitutability susceptibilityimportancecomponent indicator 87.5 (75–100) 62.5 (50–75) 37.5 (25–50) 12.5 (0–25) national economic importance net import reliance ratio net import reliance global innovation index substitute performance substitute availability environmental impact ratio see equation in si score for percentage of population utilising percentage of population utilising supply risk score of substitute see equation in si see equation in si see equation in si see equation in si poor adequate good exemplary sc or e fig. 2. components of the valuation methodolog y for the vulnerability to supply restriction, detailing the x-axis in fig. 1 (from graedel et al. 2012). supporting information (si) is detailed in: http://pubs.acs.org/doi/suppl/10.1021/es203534z/suppl_ file/es203534z_ si_001.pdf 9898 public and private stakeholders in denmark. in 2013, the geological survey of denmark and greenland (geus) established the center for minerals and materials (mima) to identify and study the most important raw material value chains. the danish government subsequently decided to strengthen the knowledge about criticality, vulnerability and scarcity of raw materials and have requested mima to carry out a three-year research programme to complete a vulnerability analysis for denmark. mima is currently identifying an adequate approach for this programme. danish industry is characterised by an advanced downstream sector that depends on many imported components in end-product assemblages, while manufacturing of upstream products based on primary raw materials is of lesser importance. however, regardless of where the danish manufacturing activities belong in the value chains, they are all based on mineral raw materials, some of which may be classified as critical minerals. it is important to examine and map the extent to which denmark is subject to supply restrictions and to understand the implications of such vulnerability. danish consumers may not be aware of a product’s requirements with regard to raw materials, and thus remain unaware of a potential supply problem attached to the product. statistically, denmark monitors export and import of all goods in compliance with international categories for goods and industries, but there is a need for more knowledge about the amount and types of processed raw materials in these goods and components used by danish industry. mima and its partners will investigate these issues further and disseminate results, analyses and forecasts. conclusions denmark, like all other countries, depends on mineral raw materials – domestic and imported – to sustain and develop society and is thus vulnerable to mineral raw materials scarcity. however, most consumers and companies in the downstream parts of the value chains as well as decision makers in the administration and industry are relatively unaware of this. it is the aim of the center for minerals and materials, mima, to build knowledge and disseminate information for the danish society about mineral resource supply risks and vulnerability to supply restrictions. references bogner, s. 2012: the commodity megatrend. resource investor (www.resourceinvestor.com/2012/05/09/the-commodity-megatrend). european commission 2010: critical raw materials for the eu. report of the ad-hoc working group on defining critical raw materials, 84 pp. brussels: european commission. graedel, t.e. et al. 2012: methodolog y of metal criticallity determination. environmental science & technolog y 46, 1063–1070. malthus, t.r. 1798: an essay on the principle of population, 388 pp. london: j. johnson. national research council 2008: minerals, critical minerals, and the u.s. economy. washington, dc: the national academies press. rosenau-tornow, d., buchholz, p., riemann, a. & wagner, m. 2009: assessing the long-term supply risks for mineral raw materials – a combined evaluation of past and future trends. resources policy 34, 161–175. undp 2010: human development report 2010 – 20th anniversary edition. the real wealth of nations: pathways to human development, 238 pp. published for the united nations development programme. basingstoke: palgrave macmillan. wilburn, d.r. & stanley, k.a. 2013: exploration review. annual review 2012. mining engineering, may 2013, 22–42. authors’ addresses p.k., r.j.c. & k.h., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark; e-mail: pka@geus.dk n.f., department of geosciences and natural resource management, øster voldgade 10, dk-1350 copenhagen, k, denmark. http://www.resourceinvestor.com/2012/05/09 http://www.resourceinvestor.com/2012/05/09 mailto:pka@geus.dk geological survey of denmark and greenland bulletin 31, 2014, 59-62 59 six years of petroleum geological activities in north-east greenland (2008–2013): projects and a view of the future jørgen a. bojesen-koefoed, peter alsen and flemming g. christiansen the deadline for applications to the first licence round for petroleum exploration offshore north-east greenland was 15 december 2012. the round was restricted, allowing only members of the kanumas consortium to be operators (bp, chevron, exxon, jogmeg, shell and statoil). nunaoil is also part of kanumas, but it is a carried, non-operator partner. an ordinary licensing round followed shortly after with a deadline on 15 october 2013. at the end of 2013, pre-round licences were awarded and the results of the ordinary round are expected in 2014. irrespective of the outcome of future exploration activities, this milestone marks an important step in greenland’s long way towards becoming an oil nation. it also offers an opportunity to summarise petroleum-directed activities in northeast greenland since 2008, through which the geological survey of denmark and greenland (geus) has provided crucial knowledge to both the industry and the greenland bureau of minerals and petroleum (bmp) in their preparations for the licence rounds. background almost a decade ago, a licence round offshore north-east greenland, including the danmarkshavn basin (figs 1, 2), was discussed between the k anumas partners and the bmp, and the details of timing and block locations were negotiated over several years. in keeping with this, geus initiated discussions with the petroleum industry to clarify its needs in order to be able to provide optimal service to both companies and authorities when required. concurrently, the united states geological survey’s (usgs) ‘circum arctic resource appraisal’ directed focus to subjects that required further study. the north-east greenland part was carried © 2014 geus. geological survey of denmark and greenland bulletin 31, 59–62 . open access: www.geus.dk/publications/bull fig. 1. map of north-east greenland, showing the offshore licence area, onshore field work areas (colour-coded according to year) and the locations of core holes. inland ice danmarkshavn basin store koldewey wollaston forland hold with hope jameson land wandel sea basin 2012 2008 2013 2009 2011 2010 18 15 14 19 17 16 13 11 12 10 9 8 4 2 3 1 7 6 5 kilen tertiary basalts wandel sea basin carboniferous–cretaceous sed. jameson land basin devonian basin palaeozoic shelf sediments palaeozoic trough sediments proterozoic sediments and volcanics caledonian fold belt proterozoic basement 7 core hole block number onshore field work awarded block greenland sea peary land 6060 out in collaboration with geus (christiansen et al. 2006; gautier 2007; gautier et al. 2011; christiansen 2011). the seismic coverage of the north-east greenland shelf is scattered and there are no wells. therefore an understanding of the onshore geology is indispensable to construct analogues for the offshore basins. geologists from danish research institutions have worked in ne greenland for over a century, and the accumulated sample and knowledge base at geus is the largest existing geological database for greenland. in 2008, a project was set up at geus to systematise relevant available data and samples from this database, which contains results from onshore field work, core drilling and subsequent analyses. the aim was to use this material as a starting point for addressing key risks and uncertainties for future offshore exploration. risks for offshore ne greenland petroleum exploration include in broad terms: (1) the distribution, quality and correlation of the main upper jurassic – lower cretaceous source rock units, which have an important bearing on the nature of the petroleum products generated, (2) the nature and stratigraphic distribution of potential reservoir and seal rocks (and possible source rocks), primarily in the rather poorly known cretaceous succession, which is very thick according to the only published seismic interpretation of the danmarkshavn basin (hamann et al. 2005) and (3) the subsidence and exhumation history of north-east greenland. project portfolio in late 2007, a collaboration project, ‘petroleum geological studies, services and data in east and north-east greenland’, was initiated between geus and a number of oil companies. from the start, only little more than a handful of companies chose to participate, but soon the number grew to approximately twenty. the activity was designed with an open end, i.e. to continue for as long as industry interest would last, and it is now entering its seventh year. participation is open to all companies that actively explore for and exploit petroleum. upon entry into the group of partners, each company gets: (1) a gis compilation summarising all available relevant information from north-east greenland, including geological and palaeogeographical maps, data on >17 000 samples, photographs, logs, potential field data, etc. from onshore north-east greenland from 70° to 82°n, (2) three reports on ‘petroleum systems’, ‘uplift’ and ‘seabed features’ mainly based on existing knowledge but including some new and reprocessed data, (3) invitation to semi-annual workshops at geus of which the 12th took place in november 2013, (4) access to data, results, power point presentations, etc. in addition, project partners are invited to participate in a number of projects dedicated to specific topics defined by geus. at the end of 2013, nine such projects, including a field excursion to north-east greenland have been carried out, and an additional four new projects have recently been proposed (table 1). field work and shallow core drilling onshore field work, often including shallow core drilling down to approximately 235 m, has been carried out every summer since 2008 (fig. 1). each year’s field campaign in north-east greenland lasted 3–6 weeks and comprised 20–30 participants. an overview of the 2008 field season, including preliminary results of the drilling of the blokelv-1 core hole was presented by bojesen-koefoed et al. (2009). a principal target for shallow core drilling was the upper jurassic – lower cretaceous source rock succession, which is the local equivalent of the deposits that have generated the main part of the petroleum found in the north sea and its northward extension. the imperfect knowledge of this succession was one of the key problems for assessment of the petroleum potential offshore north-east greenland (greenland sea), and based on available outcrop samples the potential seemed surprisingly poor. three cores with nearly 100% recovery and a total length of more than 600 m were fig. 2. aerial view of kilen, a key area for understanding the geolog y of the wandel sea basin with exposures of triassic to cretaceous sediments. kilen is approximately 10 × 30 km large and is surrounded by glaciers except to the south-east that faces the northeast water polynya. view towards the south. for location see fig. 1. 61 collected, covering the full stratigraphy from the oxfordian to the ryazanian (blokelv-1, rødryggen-1 and brorson halvø-1). more than 600 samples were analysed for petroleum potential and numerous biological marker and isotopic analyses carried out. integrated with detailed stratigraphic and sedimentological studies they provide a unique insight into the character and development of the succession. based on these studies, it has been demonstrated that the petroleum potential is 2–3 times higher than expected from initial data and that the succession, contrary to previous beliefs, is complete with only local hiatuses in specific tectonic settings. core drilling has also been carried out in unexposed intervals of the cretaceous (store koldewey-1, nanok-1), and in the triassic (dunken-1, 2) and permian successions (kim fjelde-1) of peary land. traditional onshore field work focused on solving predefined problems related to the overall key risks and uncertainties listed in the foregoing. each season, individual field teams dedicated most of their efforts to one of the various projects (table 1), while also contributing to other projects where needed. for instance, although both sand provenance and uplift studies were carried out with dedicated field teams, all teams collected samples for mineralogical analysis, apatite fission track analysis (afta) and vitrinite reflectance analysis (ro), ensuring proper geographical and stratigraphic coverage. a small degree of overlap between some projects exists. for instance, the store koldewey study was concentrated in a restricted geographical area, but included deposits ranging from caledonian basement to pleistocene mud and elements of uplift studies, sand provenance, etc. as integral parts of the study. in contrast, the cretaceous study concerned a specific, poorly known, portion of the stratigraphic column with scattered outcrops over a huge area (including store koldewey). the study was divided into sub-projects such as the erection of a formal and consistent lithostratigraphy, an integrated biostratigraphy that included macrofossils, microfossils (palynomorphs), reservoir model studies, petroleum source rock studies and more. published research generally, all results produced during the course of the project are subject to a five-year confidentiality clause that must expire before geus can publish detailed results. however, general observations of little or no relevance for the proprietary studies have been published and more are under way. these include studies of igneous rocks (larsen et al. 2013, in press), coal deposits (bojesen-koefoed et al. 2012; petersen et al. 2013), palaeogene sediments (nøhr-hansen et al. 2011), stratigraphy and palaeoenvironments (alsen & mutterlose 2009; nøhr-hansen 2012; pauly et al. 2012a, b, 2013) and integrated studies (fyhn et al. 2012). a large number of pathe triassic of the wandel sea basin pending also highly relevant for barents sea geology the jurassic–cretaceous of the pending also highly relevant for barents sea geology wandel sea basin the tectonic evolution of the pending also highly relevant for barents sea geology wandel sea basin northern east greenland uplift history pending extension of previous uplift studies to 83°n and northwards – focus on the wandel sea basin table 1. overview of completed and proposed projects project title initiated completed comments data package, blokelv-1 core, oct. 2008 dec. 2009 oxfordian–volgian portion of u. jurassic – l. cretaceous source jameson land rock succession. comprehensive sedimentological, stratigraphic and source rock study provenance study of possible oct. 2008 dec. 2010 based on zircon ages and provenance sensitive minerals. reservoir sandstone units in east comprehensive study of potential reservoir sandstone units, and north-east greenland >200 samples data package, rødryggen-1 core, mar. 2010 dec. 2010 kimmeridgian–ryazanian portion of u. jurassic – l. cretaceous source wollaston forland rock succession. comprehensive sedimentological, stratigraphical and source rock study north-east greenland uplift history mar. 2010 nov. 2011 extension of initial uplift study to 78°n phase ii the cretaceous of north-east jun. 2010 jun. 2012 comprehensive study of the entire exposed and mostly poorly greenland known cretaceous succession geology of store koldewey dec. 2010 mar. 2012 important area for understanding the danmarkshavn basin. gis compilation, including core-hole data data package, brorson halvø-1 core, apr. 2011 dec. 2011 kimmeridgian–ryazanian portion of u. jurassic – l. cretaceous wollaston forland source rock succession in different tectonic settings. comprehensive sedimentological, stratigraphic and source rock study data package, nanok-1 core, nov. 2011 nov. 2012 poorly exposed cenomanian–turonian succession hold with hope comprehensive sedimentological, stratigraphic and source rock study 6262 pers by geus scientists are expected in the coming years as confidentiality expires. impact on offshore petroleum exploration and perspectives for the future a better understanding of numerous critical parameters has been achieved, and many of the results have had a strong influence on the development of offshore exploration models. in particular, based on the onshore work a better understanding of source rock distribution, thickness and quality as well as the timing and magnitude of subsidence and uplift have been obtained. in addition, a detailed understanding of the cretaceous succession will be very important for evaluating future prospects and for correlation when offshore core holes and wildcat wells are eventually drilled. in recent years, the focus of onshore field activities has shifted northwards, where the deposits of the wandel sea basin (fig. 1) are important for the understanding of the geology of the northernmost portion of the licence area off north-east greenland. the northern region is also important for understanding the geology of the barents sea shelf, which is an area under intense exploration. hence, a gradual shift of focus towards the conjugate margin is expected to take place in the coming years. the nature of the collaboration with the industry in north-east greenland must be expected to change after allocation of licences. companies holding licences may change their focus whereas others not holding licences are expected to downgrade their interests in the region. however, geus sees an obvious interest in a continued collaboration, since it provides a platform for studies that would otherwise be beyond the economic capacity of the institution, but which are nonetheless important elements of the raison d’être of a geological research institution. references alsen, p. & mutterlose, j. 2009: the early cretaceous of north-east greenland: a crossroads of belemnite migration. palaeogeography, palaeoclimatolog y, palaeoecolog y 280, 168–182. bojesen-koefoed, j.a., bjerager, m. & piasecki, s. 2009: shallow core drilling and petroleum geolog y related field work in north-east greenland 2008. geological survey of denmark and greenland bulletin 17, 53–56. bojesen-koefoed, j.a., kalkreuth, w., petersen, h.i. & piasecki, s. 2012: a remote coal deposit revisited: middle jurassic coals at kulhøj, western germania land, northeast greenland. international journal of coal geolog y 98, 50–61. christiansen, f.g. 2011: greenland petroleum exploration: history, breakthroughs in understanding and future challenges. memoir of the geological society (london) 35, 647–661. christiansen, f.g., gautier, d.l., stemmerik, l., bidstrup, t., bojesenkoefoed, j.a. & sørensen, k. 2006: petroleum resource potential of the east greenland shelf. aapg hedberg research conference on understanding world oil resources, colorado springs, colorado, usa, 12–17 november 2006. extended abstract, poster. fyhn, m.b.w., rasmussen, t.m., dahl-jensen, t., weng, w.l., bojesenkoefoed, j.a. & nielsen, t. 2012: geological assessment of the east greenland margin. geological survey of denmark and greenland bulletin 26, 61–64. gautier, d.l. 2007: assessment of undiscovered oil and gas resources of the east greenland rift basins province. u.s. geological survey fact sheet 2007-3077, 4 pp. gautier, d.l., stemmerik, l., christiansen, f.g., sørensen, k., bidstrup, t., bojesen-koefoed, j.a., bird, k.j., charpentier, r.r., houseknecht, d.w., klett, t.r., schenck, c.j. & tennyson, m.e. 2011: assessment of ne greenland: prototype for development of circum-arctic resource appraisal methodolog y. memoir of the geological society (london) 35, 663–672. hamann, n.e., whittaker, r.c. & stemmerik, l. 2005: geological development of the northeast greenland shelf. in: doré, a.g. & vining, a.a. (eds): petroleum geolog y: north-west europe and global perspectives. proceedings of the 6th petroleum geolog y conference, 887–902. london: geological society. larsen, l.m., pedersen, a.k., sørensen, e.v., watt, w.s. & duncan, r.a. 2013: stratigraphy and age of the eocene igtertivâ formation basalts, alkaline pebbles and sediments of the kap dalton group in the graben at kap dalton, east greenland. bulletin of the geological society of denmark 61, 1–18. larsen, l.m., pedersen, a.k., tegner, c. & duncan, r.a. in press: eocene to miocene igneous activity in ne greenland: northward younging of magmatism along the east greenland margin. journal of the geological society (london), http://dx.doi.org/10.1144/jgs2013-118 nøhr-hansen, h. 2012: palynostratigraphy of the cretaceous – lower palaeogene sedimentary succession in the kangerlussuaq basin, southern east greenland. review of palaeobotany and palynolog y 178, 59–90. nøhr-hansen, h., nielsen, l.h., sheldon, e., hovikoski, j. and alsen, p. 2011: palaeogene deposits in north-east greenland. geological survey of denmark and greenland bulletin 23, 61–64. pauly, s., mutterlose, j. & alsen, p. 2012a: lower cretaceous (upper ryazanian–hauterivian) chronostratigraphy of high latitudes (northeast greenland). cretaceous research 34, 308–326. pauly, s., mutterlose, j. & alsen, p. 2012b: early cretaceous palaeoceanography of the greenland–norwegian seaway evidenced by calcareous nannofossils. marine micropaleontolog y 90–91, 72–85. pauly, s., mutterlose, j. & alsen, p. 2013: depositional environments of lower cretaceous (ryazanian–barremian) sediments from wollaston forland and kuhn ø, north-east greenland. bulletin of the geological society of denmark 61, 19–36. petersen, h.i, øverland, j.a., solbakk t., bojesen-koefoed, j.a. & bjerager, m. 2013: unusual resinite-rich coals found in northeastern greenland and along the norwegian coast: petrographic and geochemical composition. international journal of coal geolog y 109–110, 58–76. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: jbk@geus.dk. geological survey of denmark and greenland bulletin 28, 2013, 73-76 73 titanium minerals in cameroon christian knudsen, joseph penaye, martin mehlsen, roger k. mclimans and feiko kalsbeek the mineral rutile (tio2) is a major ore of titanium, which is used in products such as white pigment and titanium metal. the global consumption of titanium minerals in 2011 was c. 6.7 million tonnes of which 0.7 million tonnes were rutile and 6 million tonnes ilmenite (tifeo3). rutile is almost pure tio2 and therefore more valuable than ilmenite (c. 1500 $/t and 300$/t, respectively). compared with ilmenite, rutile can be processed with lower consumption of chemicals and yields less waste products. rutile was mined in cameroon between 1935 and 1955 when a total of 15 000 tonnes of rutile were extracted from alluvial deposits. the french bureau de recherches géologiques et minières conducted a drilling programme in cameroon in the 1980s which identified c. 2.6 million tonnes of rutile in discontinuous occurrences with concentrations of c. 1%. most of the occurrences are located in smallto medium-sized riverbeds with a thickness of 1.5–4.5 m. the main alluvial rutile area is located around the town of akonolinga, 80 km east of yaoundé, the capital of cameroon (fig. 1). the rutile in the alluvial deposits was derived from the bedrock by weathering, and at some sites major, residual rutile deposits are reported from quaternary lateritic deposits. the geological survey of denmark and greenland conducted a project together with the institut de recherches géologiques et minières in cameroon to gain a better understanding of how rutile formed in the bedrock before it was weathered out and try to tie the rutile in the alluvial deposits to its source rocks. this is done by studying the compositional variation of the rutile in the alluvial deposits and comparing it with possible bedrock sources. the compositional variation of ilmenite and monazite ((la,ce)po4)) and the age distribution of zircon (zrsio4) in alluvial sand and bedrock were also investigated. the chemical compositions of minerals in the sediments are used to infer the bedrock source of the minerals. this has particular application in many areas of cameroon, such as the southern part of the country which is characterised by low relief and dense rain forest with bedrock outcrops that are sparse and difficult to find. cameroon is a country in west central africa (fig. 1) and is called ‘africa in miniature’ because of its cultural, geological and landscape diversity. the landscape includes beaches, deserts, mountains, rain forests and savanna. the highest point is the active volcano mount cameroon (4095 m), and the country is home for over 200 different linguistic groups with french and english as the official languages. compared with other african countries, cameroon is politically and socially stable. the country covers an area of 475  442 km2 with a population of c. 20 million of which 70% are christians and 20% muslims. geochronology of the yaoundé group stendal et al. (2006) suggested that the rutile in southern cameroon is associated with the neoproterozoic yaoundé group that primarily consists of garnet-bearing metamorphosed sediments such as shale and sandstone. these fig. 1. simplified geological map of cameroon. © 2013 geus. geological survey of denmark and greenland bulletin 28, 73–76. open access: www.geus.dk/publications/bull central african republic tchad nigeria gulf of guinea equatorial guinea gabon congo yaoundé tertiary to recent volcanics phanerozoic sediments neoproterozoic sediments neoproterozoic plutonic rocks neoproterozoic metamorphic volcanics yaoundé group neoproterozoic metasediments undifferentiated gneiss palaeoproterozoic gneiss archaean gneiss fig. 4 nyo ng rive r akonolinga 100 km 4°n national border 10°e africa http://en.wikipedia.org/wiki/central_africa http://en.wikipedia.org/wiki/mount_cameroon http://en.wikipedia.org/wiki/french_language http://en.wikipedia.org/wiki/english_language 7474 sediments are believed to have been deposited on the passive margin of the congo craton (nzenti et al. 1988), and available isotope data suggest that the sediments that formed the precursor of the yaoundé group were deposited during late neoproterozoic time. toteu et al. (2004) interpreted some of the sediments as deposited between 626 and 600 ma. in order to elucidate the timing of deposition and metamorphism of the yaoundé group, zircons from three samples of the yaoundé group have been dated by laser ablation inductively coupled plasma mass spectrometry at the geological survey of denmark and greenland (kalsbeek et al. 2013; for analytical procedures see frei et al. 2006). the results for one of the samples, a garnet-kyanite gneiss (ggu 512411), are shown in fig. 2. zircon grains from this sample have wide metamorphic rims which surround cores that are interpreted to represent remnants of originally detrital grains (inset in fig. 2). the rims yielded a weighted mean age of 635 ± 10 ma (n = 41, mswd = 0.48). most of the cores are of neoproterozoic age (mainly 650–1100 ma); a small number of palaeoproterozoic zircon grains are also present. in contrast to ggu 512411, two other samples from the yaoundé group (ggu 512401 and 512415) did not yield zircon ages younger than c. 950 ma. most zircon grains from these samples are of palaeoproterozoic age, but some mesoproterozoic and archaean grains are also present. the different detrital zircon age distributions indicate different source areas of the yaoundé group sediments. one source area may have been dominated by either palaeoproterozoic or neoproterozoic zircon grains, and another source area showed diverse age distribution patterns with archaean to neoproterozoic zircon grains. the rutile-forming event the metamorphic event that affected the sediments was related to the pan-african orogeny and the formation of the gondwana supercontinent. in cameroon, the pan-african orogeny was caused by the collision of the congo craton to the south with the nigerian shield to the north. in the areas where placer rutile deposits are found, the bedrock often consists of kyanite-bearing mica schist, indicating high-pressure, metamorphic conditions during this orogeny. rutile occurs together with garnet and kyanite and was formed by breakdown of titanium-bearing minerals such as ilmenite, biotite and muscovite. in cameroon, the rutile is commonly located within kyanite and garnet crystals (fig. 3) fig. 2. 207pb/206pb age distribution (sircombe 2004) of zircons from sample ggu 512411 from the yaoundé group. the inset shows a zircon grain with a distinct metamorphic rim. ages of cores and rims are shown separately; for simplicity no distinction is made between concordant and discordant analyses. 2 mm almandine quartz muscovite plag-na kyanite biotite rutile 33.78% 18.85% 17.35% 11.21% 10.02% 4.04% 2.07% 0 10 20 30 0 1 2 3 n um be r of a na ly se s core 1918 ± 29 ma rim 652 ± 42 ma 41 analyses of metamorphic rims mean age 635 ± 10 ma 72 analyses of detrital cores rims cores 207pb/206pb age (ga) fig. 3. mineral liberation analysis (mla) image of a kyanite garnet gneiss sample (ggu 512921) in which the rutile is enclosed in both garnet and kyanite; this indicates that the rutile was formed during prograde metamorphism – i.e. during increasing pressure and temperature. mla is a scanning electron microscope-based method where a polished, mounted part of the sample is divided into 10 × 10 µm pixels. the beam of electrons generates an x-ray spectrum, which is subsequently compared with a library of spectra representing different minerals. in this way, the instrument can recognise the minerals in the sample and generate an image of the mineralog y. the mla technique was described by fandrich et al. (2007). http://en.wikipedia.org/wiki/gondwana http://en.wikipedia.org/wiki/supercontinent 75 that formed during high-pressure metamorphism, and thus rutile must have formed during the same episode when pressure and temperature were rising (prograde metamorphism). however, it is possible that some of the rutile grains in the rocks of the yaoundé group are inherited from older rocks, as suggested by stendal et al. (2006). the temperature of rutile formation can be inferred from the rutile geothermometer (zack et al. 2004; tomkins et al. 2007). eighteen rutile-bearing rock samples from the yaoundé group were studied. as shown in fig. 4, the temperature during formation of the rutile varies significantly. the geographical distribution of the temperatures appears to show a pattern with a core area around yaoundé characterised by high temperatures in the 700–900°c range with areas to the north-east and south-west characterised by temperatures of 600–700°c. both east and west of the core area, the estimated temperatures of formation are lower, mainly in the range 500–700°c. it is not known if there was only one episode of rutile formation. geochronological work on the rutile is planned to test if it is possible to tie the formation of the rutile in the area to the pan-african orogeny. sediment sampling and analysis a programme combining collection of sediment samples from modern rivers and sampling of older river deposits was initiated in an area in the southern part of cameroon (figs 1, 4). the samples from streams were collected as heavy mineral concentrates, and the alluvial deposits were sampled using either a light auger driven by a small engine mounted on a tripod or a hand auger (fig. 5). the samples were analysed for major and trace elements using x-ray f luorescence and inductively coupled plasma mass spectrometry, respectively. the ratio between tio2 and fe2o3 was used to identify areas where the titanium is primarily located in rutile. the results show that areas with a tio2/fe2o3 ratio > 2 in stream sediments and alluvial deposits coincide with areas where yaoundé group sediments are found below the surficial deposits. in order to study the texture of the titanium mineral grains in stream sediments and alluvial sand, samples were subjected to ‘mineral liberation analysis’ (fig. 6). the analysis shows that the detrital rutile grains often have a rim of ilmenite. this is also seen in rock samples from the area fig. 4. pie diagrams showing temperatures during formation based on the zr content in rutile from 18 rock samples from the yaoundé group. the calculation of the temperature t (in °c) = 127.8 × ln (zr in rutile in ppm) –10 is based on zack et al. (2004). yg: yaoundé group. for location see fig. 1. fig. 5. two sampling methods being tested. left: a light auger driven by a small engine mounted on a tripod; right: a hand auger. at this location, the hand auger was superior as it penetrated 4.5 m in 30 minutes whereas the engine-driven auger penetrated 2 m during the same time. 12°e 3°n 100 km tertiary to recent volcanics phanerozoic sediments neoproterozoic sediments neoproterozoic plutonic rocks high-grade metamorphosed sediments of the yg low-grade metamorphosed sediments of the yg undifferentiated gneiss palaeoproterozoic gneiss archaean gneiss temperature (°c) legend to pies, 201–300 301–400 401–500 501–600 601–700 701–800 801–900 yaoundé 7676 where rutile is overgrown by ilmenite. this is caused by recrystallisation of the rock under lower-grade metamorphic conditions, probably retrogression during the late part of the pan-african orogeny. conclusions the titanium mineral rutile was formed by high-grade metamorphism of sedimentary rocks of the neoproterozoic yaoundé group during the pan-african orogeny c. 635 ma ago. the temperature of the rutile-forming event has been estimated using the ‘rutile geothermometer’ based on the zr content in the rutile, and it is found that the highest temperatures (c. 750 ± 100°c) are found in the area from yaoundé towards the north-east. both north-west and south-east of this area the rutile geothermometer indicates lower metamorphic temperatures (c. 600 ± 100°c). acknowledgements we thank j.v. hell, director of institut de recherches géologiques et minières in cameroon for enthusiastic support and permission to use vehicles from the institute during the field work. j. boserup constructed the small tripod drillrig and alfons berger assisted with the electron microprobe analyses at the department of geosciences and natural resource management, university of copenhagen. we thank j.z. johansen, j.m.u.o. njel and b. kankeu for help during field work in cameroon. dupont titanium technologies, wilmington, delaware, usa, provided financial support. references fandrich, r., gu, y., burrows, d. & moeller, k. 2007: modern sembased mineral liberation analysis. international journal of mineral processing 84, 310–320. frei, d., hollis, j.a., gerdes, a., harlov, d., karlsson, c., vasques, p., franz, c., johansson, l. & knudsen, c. 2006: advanced in situ geochronological and trace element microanalysis by laser ablation techniques. geological survey of denmark and greenland bulletin 10, 25–28. kalsbeek, f., ekwueme, b.n., penaye, j., de souza, z.s. & thrane, k. 2013: recognition of early and late neoproterozoic supracrustal units in west africa and north-east brazil from detrital zircon geochronolog y. precambrian research 226, 105–115. nzenti, j.p., barbey, p., macaudière, j. & soba, d. 1988: origin and evolution of the late precambrian high-grade yaoundé gneisses (cameroon). precambrian research 38, 91–109. sircombe, k.n. 2004: agedisplay: an excel workbook to evaluate and display univariate geochronological data using binned frequency histograms and probability density distributions. computers & geosciences 30, 21–31. stendal, h., toteu, s.f., frei, r., penaye, j., njel, u.o., bassahak, j., nni, j., kankeu, b., ngako, v. & hell, j.v. 2006: derivation of detrital rutile in the yaoundé region from the neoproterozoic pan-african belt in southern cameroon (central africa). journal of african earth sciences 44, 443–458. tomkins, h.s., powell, r. & ellis, d.j. 2007: the pressure dependence of the zirconium-in-rutile thermometer. journal of metamorphic geolog y 25, 703–713. toteu, s.f., penaye, j. & djomani, y.p. 2004: geodynamic evolution of the pan-african belt in central africa with special reference to cameroon. canadian journal of earth sciences 41, 73–85. zack, t., moraes, r. & kronz, a. 2004: temperature dependence of zr in rutile: empirical calibration of a rutile thermometer. contributions to mineralog y and petrolog y 148, 471–488. authors’ addresses c.k., f.k. & m.m., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: ckn@geus.dk j.p., institut de recherches géologiques et minières, rue mgr vogt, p.o. box 4110 nlongkak, yaoundé, cameroon. r.k.mcl., dupont titanium technologies, experimental station, e352/217, route 141 and henry clay road, wilmington, de 19808, usa. 500 µm rutile ilmenite fe-oxides zircon leucoxene titanite silicates accessories pseudorutile titanomagnetite monazite fig. 6. mineral liberation analysis image of detrital grains from nyong river in cameroon (ggu 517615). the purple coloured parts are rutile and the blue is ilmenite. the orange grains are altered ilmenite grains (leucoxene). http://www.sciencedirect.com/science/article/pii/s0301926812003105 http://www.sciencedirect.com/science/journal/03019268 http://www.sciencedirect.com/science/journal/03019268/226/supp/c mailto:ckn@geus.dk geological survey of denmark and greenland bulletin 28, 2013, 65-68 65 a new seamless digital 1:500 000 scale geological map of greenland mikael pedersen, willy l. weng, nynke keulen and thomas f. kokfelt for around 40 years, the geological survey of greenland (ggu) and later the geological survey of denmark and greenland (geus) conducted systematic geological overview mapping of greenland, leading to the production of 14 printed map sheets on a scale of 1:500 000 which covers the entire country (fig. 1). the mapping was completed in 1999 and the map sheets were published between 1971 and 2004. revised 2nd editions of two of the sheets have been published (table 1). as a result of the development of the internet, the publication platform for geological maps has increasingly moved from traditional paper sheets to digital publications for most geological surveys worldwide. this tendency has changed the requirements to the underlying production, storage and publication platforms for map data. for the same reason, it has over the past decade been a strategy of geus to bring the 1:500  000 geological maps of greenland together as a seamless, digital product with a homogeneous legend. this has been further motivated by the increasing number of geographic information system (gis) and web applications to which such a map would provide a valuable background, as well as to many international projects such as onegeology. the harmonisation of the geological maps was carried out by a project team at geus comprising both geological and gis expertise. the first version of the new seamless map was finished in 2012 and will be released in various web applications in 2013. digitisation the production of a seamless, digital product makes new demands on the underlying map data. most importantly, all data have to be in vector form in a gis environment. only the three most recent of the 14 original map sheets mentioned above were produced digitally (sheets 6, 9, and 11; fig. 1, table 1). as part of the project thematic maps and data of north and northeast greenland: geology, mineral occurrences and hydrocarbons (mikkelsen et al. 2005; christoffersen & jepsen 2007) four of the printed map sheets (sheets 7, 8, 10 and 12) were vectorised. of the remaining seven sheets, two sheets (1 and 3) were up for revision, and new editions were produced digitally in 2007 and 2010. the last five (sheets 2, 4, 5, 13 and 14) were vectorised in order to create full digital coverage. the vectorisation was done from scanned versions of the published maps. in this process, the geological information was taken from the maps and integrated with the best available topographic base-map data, which in most cases were photogrammetric data derived from 1:150 000 aerial photographs (based on aerotriangulations of varying quality). some of the topography from printed maps was taken from g/250 vektor data from the danish geodata agency and used in map sheets 1, 4 and 5. due to the nature of the mapping technique and the geodetic control, the old geological paper maps had a much better local than absolute accuracy: the geometric relations between a geological feature and 6 7 9 10 11 12 13 14 500 km1 2 3 4 5 8 fig. 1. index map of greenland showing the boundaries of the 14 geological map sheets on a scale of 1:500 000 covering greenland. © 2013 geus. geological survey of denmark and greenland bulletin 28, 65–68. open access: www.geus.dk/publications/bull 6666 the nearby topographic features, such as shore lines and rivers, are usually correct even if the location of such features is quite wrong (as indicated for example by the geographic grid). during vectorisation in the gis environment, it was therefore constantly necessary to shift the scanned geological map in order to fit the printed map topography to the new digital topography, which in some cases was rather different from that on the printed map. the digitisation included boundaries between exposed geological units and structural elements, all of which were attributed with type and source information. subsequent to the vectorisation, polygons were formed and encoded according to their geological type. as the gis data were stored in a single seamless database, geometric ambiguities across map-sheet boundaries had to be corrected. the geometric quality of the final map varies substantially. in areas with well-defined topographic features and the best possible photogrammetry, mean errors around 50 m can be expected. however, in areas where topography from paper maps was used as reference during digitisation, errors fig. 2. geological map of the mestersvig area in central east greenland. a, c: examples of how mapping inconsistencies between two printed map sheets are displayed, where the same unit is shown with different colours across the former map-sheet boundary. b: an example of a geometrical problem where a boundary between two units shows a ‘ jump’. these small inconsistencies remain on the new digital map. no name compilers published edition cartographic topography technique source 1 sydgrønland a.a. garde 2007 2 digital mixed 2 frederikshåb isblink – søndre strømfjord j.h. allaart 1982 analog photogr. 3 søndre strømfjord – nuussuaq a.a. garde & m. marker 2010 2 digital photogr. 4 upernavik isfjord j.c. escher 1985 analog paper map 5 thule p.r. dawes 1991 analog paper map 6 humboldt gletscher p.r. dawes & a.a. garde 2004 digital photogr. 7 nyeboe land n. henriksen 1989 analog (d) photogr. 8 peary land h.-j. bengaard & n. henriksen 1986 analog (d) photogr. 9 lambert land h.f. jepsen 2000 digital photogr. 10 dove bugt n. henriksen 1997 analog (d) photogr. 11 kong oscar fjord j.c. escher 2001 digital photogr. 12 scoresby sund h.-j. bengaard & n. henriksen 1984 analog (d) photogr. 13 kangerdlugssuaq j.s. myers, p.r. dawes & t.f.d. nielsen 1988 analog photogr. 14 skjoldungen j.c. escher 1990 analog photogr. table 1. data on the greenlandic bedrock maps 1:500 000 d: vectorised as a part of the project thematic maps and data of north and northeast greenland (mikkelsen et al. 2005; christoffersen & jepsen 2007) greenland a b 10 km c 67 are probably around 250 m. the position of the ice margin shown on the paper maps is even worse. in the baffin bay region for example, the ice-margin position in the 1950s is used. another important part of the geographic data set is the place names. although not all of the place names on the printed maps have been digitised yet, the current data set already contains more than 2500 place names. the concept of map scale also remains when data are being used digitally. the target 1:500  000 scale has governed the selection of features and their degree of detail; it also applies to the base topography that was duly generalised, typically from 1:100 000 originals. geological harmonisation the 14 map sheets that form the basis of the new seamless 1:500 000 scale map were published between 1982 and 2010. the original maps all have their own way of presenting the geology, depending on the map compilers and the individual mapping geologists. the maps vary greatly in degree of detail ref lecting the amount of time spent during the original mapping, and the availability of helicopter support in the different areas. furthermore, the maps show an evolution in the understanding of the geology, and changes in mapping philosophy from older to younger maps. an important issue was to implement a uniform geological nomenclature to the entire map, so that a single, harmonised legend for all of greenland could be developed. since no geological remapping was done, the level of detail displayed in different areas remains uneven. therefore, boundaries between mapping areas of individual mapping parties, both within former map areas and across former map boundaries, to a large extent remain visible. an example of this is shown in fig. 2. the homogenised legend for the thematic maps of north and northeast greenland at 1:250  000 (christoffersen & jepsen 2007) was used used as a basis for further harmonisation; the harmonisation process was started by combining the adjacent four map sheets (sheet 5, 6, 12 and 13), where similar geological units occur, into a common legend. the north-western, northern, north-eastern and eastern parts of greenland largely consist of palaeoproterozoic to paleogene sedimentary basins. the sediments are divided into groups, formations and members described in variable, although generally high degrees of detail. the western, southern and south-eastern parts of greenland mainly consist of metamorphosed archaean and palaeoproterozoic fig. 3. the colours on the digital map follow the colour scheme of the original 1:500 000 scale maps, but have been updated to modern standards where necessary. an example from south-east greenland (map sheet 14). a: the new digital map. b: the same area on the printed version that was published in 1990 (table 1). a b 10 km greenland 6868 basement rocks. in line with the original, printed 1:500 000 maps, the rock units in these parts of greenland are mainly divided by their age and petrography. in cases where archaean rocks have undergone later reworking, e.g. archaean gneisses deformed and metamorphosed in the palaeoproterozoic, the entry in the legend is placed under the time of formation and not under the time of reworking, as on the original paper map sheets. the legends of most of the printed map sheets contain a number of rock types with generic names such as orthogneiss, amphibolite, mica schist, granite and ultramafic rocks. these units have been pooled into broader units that cover all of the corresponding rock types of similar age. however, if the original map sheet showed similar rock units with special features as separate types (e.g. the welldescribed, pyroxene-bearing ilivertalik granite), these have been retained in order not to loose information compared with the original map sheets. legend the link between geological features on a digital geological map and the corresponding legend is ensured by the use of codes. each polygon on the map has a code, which is translated into a colour and a descriptive text by the gis program. in the course of geological harmonisation, the codes from the various input maps were translated into a new, homogeneous encoding scheme so that, e.g. an ‘undifferentiated gneiss’ in one area got the same code as a corresponding unit in another area. this work was carried out using a combination of translation tables and python scripts, and resulted in a total list of 443 unique codes each representing a geological unit. the geological units were subsequently compiled in a legend organised by age and region. rock units that belong to a supergroup, a sedimentary basin, an igneous province or a metamorphic complex have been grouped together, even if they cover more than one time period. the grouping by age starts with quaternary deposits and ends with eoarchaean rocks of the isua complex. each original 1:500 000 map sheet legend had its own style, therefore a harmonisation of rock descriptions was also necessary. where the nomenclatures are obsolete, rock names have been adopted to modern nomenclature. we mainly followed the principles by the british geological survey (gillespie & styles 1999; hallsworth & knox 1999; robertson 1999). a data set containing as many different feature types as described requires careful symbolisation. the one currently used tries to stay as close as possible to the tradition of the printed maps of ggu and geus. however, some colours – mainly for igneous rocks – have been adapted to colours that are more common on modern maps (fig. 3). the new digital compilation is to a large degree intended for viewing on a computer screen. for that reason, the first version of the new map has only been assigned rgb colours. another colour scheme for map-sheet printing using cmyk colours will be developed at a later stage. publication platforms compared to a printed map, a digital geological map has more potential applications. first of all, it is well suited for gis work where users can zoom in on areas of interest and examine the geology e.g. by clicking on geological features and receive detailed information from the underlying databases. the new seamless map has been integrated in such a web-gis application which can be found at http://data. geus.dk/map2/geogreen. the seamless map is furthermore an important geus contribution to the global onegeology portal (http://portal.onegeology.org). this portal aims to put geological maps from all countries in the world together on a scale of 1:1 million or better, by using distributed web map services (wms). the geological map of greenland on this portal is currently a 1:2 500 000 scale map. the new 1:500 000 map will fulfil geus’ participation in this important international initiative. references christoffersen, m. & jepsen, h.f. 2007: geological maps of north and north-east greenland 1:250  000. copenhagen: geological survey of denmark and greenland. gillespie, m.r. & styles, m.t. 1999: bgs rock classification scheme 1. classification of igneous rocks. british geological survey research report r r 99-06, 52 pp. hallsworth, c.r. & knox, r.w.o’b. 1999: bgs rock classification scheme. classification of sediments and sedimentary rocks. british geological survey research report r r 99-03, 44 pp. mikkelsen, n., jepsen, h.f., ineson, j.r., piasecki, s., von platen-hallermund, f., schøjth, f., thomassen, b. & weng, w.l. 2005: thematic maps and data of north and northeast greenland: geolog y, mineral occurrences and hydrocarbons. danmarks og grønlands geologiske undersøgelse rapport 2005/28, 56 pp. robertson, s. 1999: bgs rock classification scheme 2. classification of metamorphic rocks. british geological survey research report r r 99-02, 24 pp. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark; e-mail: mp@geus.dk geological survey of denmark and greenland bulletin 26, 2012, 73-76 73 ablation observations for 2008–2011 from the programme for monitoring of the greenland ice sheet (promice) robert s. fausto, dirk van as and the promice project team* recent estimates from the glaciological community agree that the greenland ice sheet is losing mass at an accelerated pace due to climate change (velicogna 2009; khan et al. 2010; rignot et al. 2011). this has caught the attention of the public and policy makers due to the potential impact on sea-level rise (dahl-jensen et al. 2009). the mass loss can be attributed approximately equally to increases in meltwater runoff from surface melt and iceberg production (van den broeke et al. 2009). the robustness of mass-balance predictions relies heavily on observational data from the greenland ice sheet and in recent years the need for frequent, reliable surface mass-balance measurements has increased (ipcc 2007; dahl-jensen et al. 2009). in anticipation of this need, the programme for monitoring of the greenland ice sheet (promice) was initiated in 2007, delivering in situ data from a network of automatic weather stations (aws) covering eight different regions of the ice sheet (fig. 1; van as et al. 2011). apart from the direct insight into the surface mass balance provided by these stations, the in situ data are also valuable for calibrating and validating melt estimates from remote sensors and surface mass-balance models (dahl-jensen et al. 2009). in this paper, we present the ablation records for the promice awss for 2008–2011, and the impact of the extraordinary atmospheric conditions on ablation in 2010 (tedesco et al. 2011) are compared to the other years. promice automatic weather stations the promice network in greenland currently consists of eight sites with two (or three) awss placed at different elevations (fig. 1; table 1; ahlstrøm et al. 2008) with a total of 18 stations. at each site, one station is typically located in the lower ablation zone close to the margin and the other in the upper ablation zone. exceptions are station kan_u, which is placed in the lower part of the accumulation zone, and station tas_u, which is placed well below the equilibrium-line altitude for reasons of accessibility. each station measures all relevant meteorological parameters and ice and snow ablation (fig. 2). it measures and stores data every ten minutes * andreas p. ahlstrøm, signe b. andersen, morten l. andersen, michele citterio, karen edelvang, signe h. larsen, horst machguth, søren nielsen and anker weidick. 80°n 75°n 70°n 65°n 60°n 80°w 60°w 40°w 50°w 40°w 20°w 20°w 0°w 225 0 3000 2750 2500 100 0 150 0 175 0 20 0022 50 2 7 5 0 2 5 0 0 2 2 5 0 1 7 5 0 1 5 0 0 1 2 5 0 200 0 greenland 500 km qas nuk upe thu kpc sco tas kan fig. 1. map of greenland showing the locations of the promice automatic weather stations. each dot represents two or three stations. station names are found in table 1. dashed lines: elevation contours. © 2012 geus. geological survey of denmark and greenland bulletin 26, 73–76. open access: www.geus.dk/publications/bull 7474 with the exception of the wind-speed observations that give the mean wind speed since the last measurement cycle, and the gps measurements, which follow the transmission schedule. during winter (day 301 to day 99 of the year) the acquired data are transmitted once a day at midnight to limit power consumption when solar power is not available. during summer (day 100 to day 300) the data are transmitted hourly. the transmissions consist of daily or hourly average values of the more variable quantities such as temperature or radiation. values of less variable quantities, such as surface height and station tilt are appended once every six hours in summer and once a day in winter for all daily transmissions. instrumentation and accuracy the promice awss are equipped with an ørum & jensen nt1400 pressure transducer assembly and two campbell scientific sr50a sonic rangers that monitor surface-height change caused by accumulation and ablation. the pressure transducer assembly consists of a (non-freezing) liquid-filled hose with a pressure transducer located at its end/bottom. the hose is drilled into the ice. the pressure signal registered by the transducer is that of the vertical liquid column over the sensor, which can be scaled to depth using the density of the liquid. the free-standing aws tripod (fig. 2) moves down with the ablating surface and the hose melts out of the ice, reducing the hydrostatic pressure from the vertical liquid column in the hose. the reduction in pressure provides the ablation totals. the assembly was first constructed and implemented by bøggild et al. (2004). since the first successful tests in 2001, we have developed the system and now use a larger diameter hose and have changed from relative to absolute pressure transducers. we also use an ethylene-glycol solution, instead of alcohol and secure the upper reference level of the assembly (in the form of a bladder) to the mast instead of leaving it exposed on the ice surface. by measuring on a (sub-)daily timescale, the pressure transducer assembly is well suited to monitor ice ablation in remote regions, with clear advantages over other well-established methods. for instance, the stake readings providing information about surface-height change are done at every maintenance visit, so the records are limited to the visits. the accuracy of the sr50a sonic ranger is given by the manufacturer (campbell scientific) to be ±1 cm or ±0.4% of the measuring height after temperature correction. this was confirmed over 2.3 months of a virtually accumulation-free wintertime period at sco_u, during which time standard deviations of 1.7 cm and 0.6 cm were found (after spike removal), corresponding to 0.7% and 0.6% of the distance measured by the two sonic rangers, respectively. however, the precision of the readings from these sensors may reduce over time as the sensors degrade due to continuous cycles of moisture freezing on and melting off them. a major problem with sonic rangers in surface-mass balance studies is that they need to be mounted on the stake assemblies drilled into station latitude longitude elevation start date name (°n) (°w) (m a.s.l.) kpc_l* 79°55´ 24°05´ 380 17 july 2008 kpc_u 79°50´ 25°10´ 870 17 july 2008 sco_l 72°14´ 26°49´ 470 21 july 2008 sco_u 72°24´ 27°15´ 1000 21 july 2008 tas_l 65°38´ 38°54´ 270 23 august 2007 tas_u 65°42´ 38°52´ 580 15 august 2007 qas_l 61°02´ 46°51´ 310 24 august 2007 qas_u 61°11´ 46°49´ 890 7 august 2008 nuk_l 64°29´ 49°32´ 560 20 august 2007 nuk_u 64°30´ 49°16´ 1140 20 august 2007 nuk_n 64°57´ 49°53´ 930 26 july 2010 kan_l 67°60´ 50°70´ 670 1 september 2008 kan_m 67°40´ 48°49´ 1280 1 september 2008 kan_u 67°00´ 47°10´ 1830 4 april 2009 upe_l 72°54´ 54°18´ 230 17 august 2009 upe_u 72°53´ 53°32´ 980 17 august 2009 thu_l 76°24´ 68°16´ 570 9 august 2010 thu_u 76°25´ 68°09´ 770 9 august 2010 table 1. promice automatic weather station metadata (status 2011) *l: lower station, m: middle station, u: upper station, n: new station. 1 2 3 4 5 7 8 5 9 7 6 10 11 fig. 2. the promice automatic weather station upe _l photographed on 17 august 2009. 1: radiometer. 2: inclinometer. 3: satellite antenna. 4: anemometer. 5: sonic rangers. 6: thermometer and hygrometer. 7: pressure transducer. 8: solar panel. 9: data logger, barometer and gps. 10: battery box with 4 × 28 ah batteries. 11: 8-level thermistor string. 75 the ice. during a single melt season, these stake assemblies can melt out several metres, often causing them to move or even collapse during strong winds. in comparison, the pressure transducer assembly is operational until it has melted out of the ice, which can take several years depending on drill depth and the local ablation rate. this reduces the need for annual station visits, and thereby the considerable expenses associated with logistics in greenland. the measurement uncertainty of the pressure transducer sensor given by the manufacturer is 2.5 cm. the mean standard deviation of the upe and sco pressure transducer readings outside the ablation season is found to be ±1 cm, indicating a small random error comparable to that of the sonic ranger. the precision of the pressure transducer readings falls over time as the transducer degrades due to the continuous pressure on the sensor. sensitivity drift defines the amount by which an instrument’s sensitivity varies as ambient conditions change. calibration tests of the pressure transducer show that the sensor sensitivity drift amounts to 1.6% on average for a four-year measuring period (0.4% per year), suggesting that drift is not a large source of error. the pressure transducer is especially suitable for high ablation areas of >3 m per year because it is independent of the stakes drilled into the ice (fig. 2). ablation records for 2008–2011 the promice ablation records presented in table 2 are based on measurements by sonic rangers and pressure transducers, supplemented by stake readings. the net ablation values are calculated as the height difference between the end-of-melt-season surface level in the given year and the year before. the geographical distribution and annual net ablation records in table 2 show that for all station pairs, the lower stations measure larger ablation totals than the upper ones, because the temperature decreases with elevation and the seasonal averaged surface albedo decreases towards the ice margin. there are considerable latitudinal differences as well, as the greenland ice sheet is more than 2000 km long. ablation totals in the southern part of greenland typically amount to 3–7 m (at the lower tas, qas and nuk stations), whereas ablation totals at the more northerly sco_l and upe_l stations only amount to 2–3 m at low altitudes (<500 m a.s.l.). the ablation totals (negative value is net accumulation) from the upper stations (>500 m a.s.l.) typically amount to –0.3 to 4 m in the south (tas, qas, nuk, kan) and –0.1 to 3 m in the north (kpc, sco, upe). the record-warm year 2010 (in most regions of greenland) showed the largest ablation at most aws sites, followed by 2008, 2011, and lastly 2009 in the four-year promice record. the 2010 ablation year was characterised by relatively low winter accumulation and a long period of positive air temperatures, which are both important for net ablation (tedesco et al. 2011; van as et al. 2012). however, as the energy from solar radiation is the main contributor to the melting of snow and ice, the direct impact on ablation of inter-annual variability of temperature may be small. it was the combination of low winter accumulation and high temperatures, causing low albedo in large sections of the greenland ice sheet in 2010, that resulted in large net ablation records (tedesco et al. 2011; van as et al. 2012). the southern (qas) and south-western (nuk and kan) parts of greenland experienced a particularly anomalous ablation season, with ablation totals of up to 3 m more than in other years. even more significant was the melt response at stations close to the equilibrium-line altitude (zero net ablation) in the south and west; qas_u went from a 0.3 m surface rise in 2009 to a 3.4 m surface lowering in 2010, and at kan_m ablation increased from 0.3 m to 2.6 m during the same years. even in normal years, the kan_u station, which is placed in the accumulation zone, showed a surface lowering due to melt over the year 2010. on the other hand, the northern kpc_u station did not show anomalous ablation, as temperatures did not exceed their normal summer values (table 2). north-east greenland did not experience the anomalous circulation pattern that, in particular, southern and western greenland experienced (tedesco et al. 2011). fifteen out of 18 promice stations were successful in obtaining ablation station\year 2008 2009 2010 2011 kpc_l –* – † – † – † kpc_u –* –0.1 ‡ 0.1 ‡ 0.2 ‡ sco_l –* 2.6 3.5 3.1 sco_u –* 1.4 2.5 2.1 tas_l 3.6 7.4 ** 3.4 ‡ tas_u 3.3 1.5 ‡ 3.9 $ 2.9 qas_l 7.3 – 9.3 5.5 qas_u –* –0.3 ‡ 3.4 0.8 nuk_l 5.3 4.8 7.2 – nuk_u 2.2 1.5 2.5 2.3 nuk_n – – –* 5.1 kan_l –* 3.5 5.4 4.0 kan_m –* 0.3 ‡ 2.6 ‡ 1.7 ‡ kan_u – –* – –0.2 ‡ upe_l – –* 3.2 2.9 upe_u – –* 2.7 2.6 thu_l – – –* † – † thu_u – – –* † – † table 2. yearly ablation totals, given as the difference between the surface height at end of the melt season and that of the previous years, in metres snow/ice equivalent per year * partial data coverage due to station establishment that year. † data may become available after the next maintenance visit. ‡ sonic ranger measurement. $ sonic ranger and stake measurements. ** sonic ranger and stake measurements for both 2009 and 2010. 7676 totals up until 2011. the remaining three stations (kpc_l, thu_l, and thu_u) did not transmit any data, but data may become available during the next maintenance visit. we obtained 42 interannual ablation totals for all the stations out of 50 possible totals. when disregarding the three stations that did not transmit, the number would be 45. this gives a success rate of 84% for all 18 stations, or 93% when disregarding the 3 non-transmitting stations. conclusions ablation totals at low altitudes (<500 m a.s.l.) typically amount to 3–7 m in the southern part of greenland, with an ablation total at the more northerly stations of 2–3 m. the ablation totals from the upper stations above 500 m a.s.l., typically amount to –0.3 to 4 m in the south (tas, qas, nuk, kan) and –0.1 to 3 m in the north (kpc, sco, upe). the interannual ablation totals show that 2010 was a year with large melt when compared to the other years. the 2010 season showed record-setting ablation totals for the southern (qas) and south-western stations (nuk and kan), however, a longer time series is needed to quantify the anomalous 2010 ablation totals (van as et al. 2012). the promice station network has successfully obtained ablation totals at the end of 2011 for 15 out 18 stations. the interannual success rate was 84% for all 18 stations and 93% if the three non-transmitting stations (kpc_l, thu_l, and thu_u) are omitted. acknowledgements the programme for monitoring of the greenland ice sheet (promice) is funded by the geological survey of denmark and greenland (geus) and the danish ministry of climate, energ y and building under danish cooperation for environment in the arctic (dancea), and is conducted in collaboration with the national space institute (dtu space) and asiaq (greenland survey). the nuk and k an stations are (co-)funded by the greenland climate research centre (gcrc) and the greenland analogue project (gap), respectively. references ahlstrøm, a.p. & promice project team 2008: a new programme for monitoring the mass loss of the greenland ice sheet. geological survey of denmark and greenland bulletin 15, 61–64. bøggild, c.e., olesen, o.b., ahlstrøm, a.p. & jørgensen, p. 2004: automatic glacier ablation measurements using pressure transducers. journal of glaciolog y 50(169), 303–304. dahl-jensen, d. et al. 2009: the greenland ice sheet in a changing climate: snow, water, ice and permafrost in the arctic (swipa), 115 pp. oslo: arctic monitoring and assessment programme (amap). ipcc 2007: intergovernmental panel on climate change (ipcc) fourth assessment report (ar4), climate change 2007. 4 volumes. cambridge: cambridge university press. khan, s.a., wahr, j., bevis, m., velicogna, i. & kendrick, e. 2010: spread of ice mass loss into northwest greenland observed by gr ace and gps. geophysical research letters 37, l06501, http://dx.doi. org/10.1029/2010gl042460 rignot, e., velicogna, i., van den broeke, m.r., monaghan, a. & lenaerts, j. 2011: acceleration of the contribution of the greenland and antarctic ice sheets to sea level rise. geophysical research letters 38, l05503, http://dx.doi.org/10.1029/2011gl046583 tedesco, m., fettweis, x., van den broeke, m.r., van de wal, r.s.w., smeets, c.j.p.p., van de berg, w.j., serreze, m.c. & box, j.e. 2011: the role of albedo and accumulation in the 2010 melting record in greenland. environmental research letters 6, 014005, http://dx.doi. org/10.1088/1748-9326/6/1/014005 van as, d., fausto, r.s. and the promice project team 2011: programme for monitoring of the greenland ice sheet (promice): first temperature and ablation records. geological survey of denmark and greenland bulletin 23, 73–76. van as, d., hubbard, a.l., hasholt, b., mikkelsen, a.b., van den broeke, m.r. & fausto, r.s. 2012: large surface meltwater discharge from the kangerlussuaq sector of the greenland ice sheet during the recordwarm year 2010 explained by detailed energ y balance observations. the cryosphere 6, 199–209. van den broeke, m., bamber, j., ettema, j., rignot, e., schrama, e., van de berg, w.j., van meijgaard, e., velicogna, i. & wouters, b. 2009: partitioning recent greenland mass loss. science 326, 984–986. velicogna, i. 2009: increasing rates of ice mass loss from the greenland and antarctic ice sheets revealed by gr ace. geophysical research letters 36, l19503, http://dx.doi.org/10.1029/2009gl040222 authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: rsf@geus.dk geological survey of denmark and greenland bulletin 28, 2013, 41-44 41 seismic activity in denmark: detection level and recent felt earthquakes trine dahl-jensen, peter h. voss, tine b. larsen and søren gregersen the geological survey of denmark and greenland (geus) records seismological data at six locations in denmark (fig. 1) and all data from these stations are manually reviewed for events like earthquakes and explosions. the identified events are analysed and located, in many cases using supporting data from stations outside denmark. seismic events have been recorded instrumentally in denmark since 1929, but earthquakes felt in denmark have been reported as far back as 1515 (lehmann 1956; gregersen et al. 1998; geus 2012). this article reports on the developments in detection level of both man-made events and natural earthquakes within the danish exclusive economic zone (eez) from 2000 to 2012. changes in detection level are mainly due to the availability of data from new seismic stations in sweden and norway as well as from a geus test station at gøttrup in nw jylland. as a case study, the list of events on and around bornholm is reviewed. also described here are the reported intensities at two recent felt events in denmark (north sea magnitude 4.3 on 19 february 2010 and kattegat magnitude 4.1 on 6 august 2012). development in detection level and completeness from 2000 to 2012 the events from 2000 to 2012 located within the danish eez (fig. 1) are divided into known explosions (pink), events recorded only on one or two stations which are typically small events (yellow), events where a magnitude could not be calculated (grey) and events which possibly are earthquakes (red) and recorded on three or more stations. many of the ‘possibly earthquakes’ events occur in areas where explosions are known to take place, and many of these events are suspected to have a man-made origin. many explosions are reported to the seismological service at geus, and are tagged as such, but many more are not reported and only some are tagged as possible explosions. the north sea is the only area with no explosions known to the seismological service but with many probable earthquakes. for example, the earthquake felt in february 2010, described below, is located in this area. however, earthquakes do occur in other areas of denmark; for example the felt earthquake that occurred in august 2012 in kattegat. fig. 1. seismic events within the danish exclusive economic zone (eez). among the recorded events are un-identified explosions, particularly in the area where many identified explosions are marked (in pink). the two felt events described in this paper are marked in blue. k = kattegat on 6 august 2012 and n = north sea on 19 february 2010. seismological stations are green triangles. the events are divided into events seen on three or more stations with defined magnitude (red), events seen on only one or two stations with defined magnitude (yellow), events where no magnitude has been calculated (grey) and known (or probable) explosions (pink). inset: the eez around bornholm after revision of the database. © 2013 geus. geological survey of denmark and greenland bulletin 28, 41–44. open access: www.geus.dk/publications/bull magnitude 1 2 3 4 station known explosions 1 or 2 stations no magnitude bsdbsd snart homb mud goet n k lldlld gidgid copcop bsdbsd 15˚e10˚e5˚e 59˚n 57˚n 55˚n 55˚n 15˚e 4242 in the years 2000–2005, fewer than 15 events (either earthquakes or non-reported explosions) observed on three or more stations were recorded each year, with an additional c. 20 known explosions. only large events were seen outside the danish network of stations (at the time bsd, cop, mud, lld and gid) (fig. 1). the number of events rose dramatically in 2006 (fig. 2), as a result of the installation of the norwegian seismological station snart (nnsn 2012). the addition of this station has aided in locating events, as it provides a much improved geometry of the station network (fig. 1). the increase in the number of events recorded is also due to a change in policy in 2006; since then events located by azimuthal analysis when only one or two stations have recorded the events (fig. 2) are included. for events seen on three or more stations, the increase is most pronounced for the smaller events, under magnitude 2, but also events with magnitudes between 2 and 3 are more numerous. the next large step up in event detections occurred in 2010 (fig. 2). this is due to data from the large swedish network (snsn 2012) becoming available, and also data from the new norwegian station homb. many of the additional events, only recorded on the snsn stations, have no magnitude due to missing calibration information from the new snsn. in 2012 the number of events with no magnitude declined, while the total number of events is fairly constant, as a result of snsn becoming established and complete metadata becoming available. in denmark we added goet as a test station in 2012, and data came online in november 2012. together with mud and the norwegian stations the azimuth coverage for the many events in the danish north sea is highly improved. explosions in the database far from all activity recorded within the danish eez are natural earthquakes. the seismological service at geus is frequently notified by the danish navy of upcoming or recent blasts. following world war ii, numerous unexploded mines and ammunition are still present in danish water; the largest neutralised in 2012 was equivalent to 800 kg tnt. the navy searches for the mines and detonates them on site. many are seen as signals on the seismic stations, and if known to be explosions they are logged as such in the database. on fig. 1 the known explosions are marked with pink, and are present in large parts of danish waters. known explosions also occur on land – for example in controlled-source scientific projects (thybo et al. 2006) and on rare occasions a house demolition. however, not all explosions are known by the seismological service. natural earthquakes are distributed evenly throughout the 24 hours of the day, while manmade events such as explosions mainly take place during the daytime. the navy usually blasts in the early afternoon. figure 3 illustrates the distribution of recorded events sorted by of day, and it is clear that the distribution is heavily skewed towards events in daytime hours. the known explosions are, as expected, concentrated during daytime hours; the exception being urgent blasts when a find of undetonated explosives endangers the surroundings. scientific blasts often take place during the quiet night hours. in the period 2000–2005 the events are evenly distributed through all 4 hour intervals, while the events in both the 2006–2009 and the 2010–2012 periods have a large overrepresentation in daytime. in total fig. 3. seismic events seen on three or more stations sorted by time of day. the events are sorted into 4 hour intervals in utc time. denmark is one hour ahead of utc (two hours in summertime). for each series of years, the number of events within a 4 hour interval is calculated as per year, so the three periods (2000–2005; 2006–2009 and 2010–2012) can be compared. in addition the number of known explosions in the entire period (2000–2012) is sorted in the same manner for comparison. inset: events in the area in the danish north sea with many events recorded but no known explosions. fig. 2. statistics on event detection from 2000–2012 within the danish exclusive economic zone. known or probable explosions are not included. 100 80 60 40 20 0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 1–2 stations magnitude > 4 magnitude 3–4 magnitude 2–3 magnitude 1–2 magnitude <1 no magnitude no. of events 0–4 4–8 8–12 12–16 16–20 20–24 0 10 20 30 40 known explosions 2000–2012 2000–2005 2006–2009 2010–2012 0 1 0–4 4–8 8–12 12–16 16–20 20–24 north sea 2000–2012 no. of events per year 43 426 events are included. assuming that the night-time level of events is correct, and the natural earthquakes are evenly distributed, a simple calculation shows that at least half the events are probably not natural earthquakes. not all explosions are reported to geus, for example explosions carried out by foreign naval vessels participating in exercises in danish waters or mines or ammunition neutralised by our neighbouring countries but erroneously located into danish waters. the only area where no known explosions are located is within the group of events in the danish north sea. for events in this area there is no concentration in daytime (fig. 3 – inset), and they are assumed to be natural earthquakes. case study bornholm a revision of the entire database of seismic events is in its initial phase, and for 2000 to 2012 the revision has been carried out on bornholm and within the eez around the island. here quarry blasts add to the man-made events recorded, as bornholm granit blasts several times a week at set times (paul ebbesen, rønne granit, ncc, pers. communication). by logging all events known or strongly suspected to be explosions, excluding small events seen only on one or two stations (and with a large uncertainty in location) and events so small that no magnitude could be calculated in spite of all necessary station information, only two events remain as probable natural earthquakes. the original list contained 129 events within the eez around bornholm, of which 25 were seen on three or more stations (of these three without magnitude). the remaining 104 events were seen only on one or two stations, and many with no magnitude. seventy events are suspected quarry blasts. in all 23 events had a magnitude of 2 or higher. ten previously known explosions make an original total of 139 events recorded. the two ‘surviving’ events are marked on the inset on fig. 1 and are a magnitude 2.0 event in 2006 and a very small magnitude 0.8 event in 2011. recent felt earthquakes it is rare for denmark to experience an earthquake which can be felt. however, it does happen and the two most recent felt earthquakes are brief ly described below. north sea, 19 february 2010, magnitude 4.3 at 21:08 utc (22:08 local time) on 19 february 2010, a magnitude 4.3 earthquake occurred 45 km offshore the north-western danish coast at a depth of 39 km (fig. 4a). the focal mechanism indicates a reverse fault overthrusting to the west, in agreement with earlier earthquakes in the area. this is the most active area in denmark, with many known earthquakes. from the instrumental era, table 1 lists fig. 4. reports of observed intensity from the public. the earthquakes are marked by blue stars scaled by size. a: north sea on 19 february 2010 magnitude 4.3. geus received 344 reports from people who felt the earthquake. seven small aftershocks (magnitude 1.9 to 2.8) were observed during four weeks after the main event. b: kattegat on 6 august 2012 magnitude 4.1. in addition to reports received by geus (441), we have reports from the united states geological survey (in all 76 reports of which more than half are from sweden (30 in halmstad and 13 in falkenberg)) marked with diamonds scaled to the number of individual reports, and from the swedish national seismic network (snsn) (16 reports) – marked with dots in sweden – are included. the insets in both a and b are all known, instrumentally recorded events over magnitude 3.5 in the two areas. a 2010-02-19 intensity 2 3 4 5 6 57˚n 8˚e t magnitude 5.0 4.5 4.0 3.5 56°n 10°e kattegat fyn sjælland sweden jylland 2012-08-06 b 2 13 7 2 30 3 3 4 2 6 intensity 2 3 4 5 6 12°e57˚n 56˚n magnitude 5.0 4.5 4.0 3.5 56°n 10°e anholt 4444 earthquakes in the area over magnitude 3.5 (see also inset in fig. 4 a). earlier earthquakes are also known historically (gregersen et al. 1991). geus received 344 macroseismic reports with observations of the 2010 earthquake from the public. the earthquake was mainly felt in north-western denmark, with a few reports from northern sjælland and fyn. all observations were classified according to the european macroseismic scale (grünthal 1993), and ranged from 2 to 6, including three instances of slight damage to houses in the form of cracks in walls. kattegat, 6 august 2012, magnitude 4.1 early morning at 02:57 utc (03:57 local time) on 6 august 2012, a magnitude 4.1 earthquake occurred in kattegat, 26 km from the island of anholt, at a depth of 22 km. the focal mechanism indicates a dextral strike-slip movement in a nw–se direction, aligning with the general fault direction in the area including the tornquist zone. also in this area earthquakes are known, both historically (gregersen et al. 1991) and instrumentally recorded (events over magnitude 3.5 in table 1 and inset in fig. 4b). geus received 441 macroseismic reports with observations of the 2012 earthquake from the public. the earthquake was felt mainly in northern sjælland – where the population density is high, and where many people also experienced the magnitude 4.8 earthquake in southern sweden in 2008 (voss et al. 2009). but the earthquake was also felt in north-eastern jylland and northern fyn – and of course on anholt. furthermore, this event was widely felt in sweden, and on fig. 4b observations from snsn (snsn 2012) and usgs (usgs 2012) in usa are included. all observations were classified according the european macroseismic scale (grünthal 1993), and ranged from 2 to a single occurrence of intensity 6 where small cracks had opened in the façade of a house. acknowledgement reynir bodvarsson at university of uppsala kindly supplied us with the macroseismic reports in sweden from the kattegat event. references geus 2012: seismological service. registrerede jordskælv, http://www. geus.dk/departments/geophysics/seismolog y/seismo_reg-dk.htm gregersen, s., korhonen, h. & husebye, e.s. 1991: fennoscandian dynamics: present-day earthquake activity. tectonophysics 189, 333–344. gregersen, s., hjelme, j. & hjortenberg, e. 1998: earthquakes in denmark. bulletin of the geological society of denmark 44, 115–127. grünthal, g. (ed.) 1993: european macroseismic scale 1992 (updated msk scale). pp. luxemborg: european seismological commision, subcommision of engineering seismolog y, working group macroseismic scales. lehmann, i. 1956: danske jordskælv. bulletin of the geological society of denmark 13, 88–103. nnsn 2012: norsk nasjonalt seismik nettverk, http://www.geo.uib.no/ seismo/nnsn/index.shtml snsn 2012: svenska nationella seismiska nätet, http://snsn.geofys.uu.se/ thybo, h., sandrin, a., nielsen, l., lykke-andersen, h. & keller, g.r. 2006: seismic velocity structure of a large mafic intrusion in the crust of central denmark from project estrid. tectonophysics 420, 105– 122. usgs 2012: national earthquake information center – neic, http:// earthquake.usgs.gov/regional/neic/ voss, p.h., larsen, t.b., ottemüller, l. & gregersen, s. 2009: earthquake in southern sweden wakes up denmark on 16 december 2008. geological survey of denmark and greenland bulletin 17, 9–12. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: tdj@geus.dk table 1. all instrumentally recorded events over 3.2 on the richter scale in the areas around the north sea and kattegat earthquakes y/m/d-t position depth stamagnitude (utc) (degree) (km) tions (ml) north sea area 1954 / 10 / 18 16:44 56.85n 8.29e 25.5 4 4.6 1964 / 07 / 14 05:33 57.03n 7.20e 36.0 4.0 1969 / 04 / 05 19:09 57.16n 6.76e 0.1 23 4.2 1975 / 11 / 12 06:00 57.10n 7.14e 40.0 37 3.7 1978 / 04 / 26 12:32 56.75n 7.81e 40.0 18 3.4 1981 / 09 / 06 04:11 57.03n 6.88e 40.0 84 5.2 1981 / 09 / 07 14:03 57.06n 7.12e 30.3 13 3.6 1982 / 05 / 24 03:10 56.64n 8.21e 41.4 25 3.7 1987 / 03 / 01 06:42 57.00n 6.98e 40.1 26 3.5 1997 / 11 / 15 16:11 56.86n 7.62e 6.6 56 3.6 1997 / 12 / 04 22:03 56.91n 7.69e 8.5 48 3.4 2001 / 06 / 02 00:44 56.80n 7.80e 59.3 39 3.5 2010 / 02 / 19 21:08 56.89n 7.52e 22.0 111 4.3 kattegat area 1970 / 03 / 12 16:05 56.54n 12.69e 0.0 12 4.0 1980 / 01 / 21 07:41 56.27n 12.16e 10.2 29 3.9 1982 / 11 / 01 02:48 56.28n 11.82e 3.4 17 3.5 1985 / 06 / 15 00:40 56.61n 12.19e 9.1 44 4.7 1986 / 04 / 01 09:56 56.54n 12.18e 7.2 37 4.1 1990 / 05 / 24 09:51 56.48n 11.93e 10.0 15 3.2 1995 / 10 / 04 20:49 56.78n 12.08e 9.9 31 3.8 1997 / 09 / 20 14:21 56.94n 12.42e 15.0 4 3.8 2012 / 08 / 06 02:57 56.60n 11.95e 22.1 31 4.1 mailto:sg@geus.dk geological survey of denmark and greenland bulletin 35, 2016, 63-66 63© 2016 geus. geological survey of denmark and greenland bulletin 35, 63–66. open access: www.geus.dk/publications/bull in the rinkian belt of west greenland, reworked archaean gneisses are overlain by supracrustal successions of the palaeoproterozoic karrat group, defined by henderson & pulvertaft (1967) as comprising two formations: the qeqertarssuaq formation and the nûkavsak formation. the group was later extended to include the mârmorilik formation (henderson & pulvertaft 1987) originally considered to be of archaean age (henderson & pulvertaft 1967) but later shown to be palaeoproterozoic, resting with a depositional unconformity on archaean gneiss (garde 1978). henderson & pulvertaft (1987) suggested that the carbonatedominated mârmorilik formation in the south was laterally equivalent to the siliciclastic-dominated qeqertarssuaq formation in the north, the two subbasins being separated by a basement topographic high. the karrat group and the archaean basement were metamorphosed and folded during the rinkian orogeny (henderson & pulvertaft 1987; grocott & pulvertaft 1990). during shipand helicopter-supported fieldwork in 2015, the kangerluarsuk–maarmorilik area (fig. 1) was visited to sample the zn-pb-mineralised horizons found by rtz mining and exploration ltd. (coppard et al. 1992) along the basement-cover boundary and to obtain oblique photographs of the contact that was described as faults on the mârmorilik geological map sheet (scale 1:100  000, henderson & pulvertaft 1987). the aim of this paper is to show preliminary new results on the geometry and type of unconformity between the palaeoproterozoic karrat group and the underlying gneisses, and to describe a new stratigraphic unit representing here the lowermost sedimentary sequence above the unconformity. this unit is of particular relevance as it controls the distribution of the zn-pb mineralisation. palaeoproterozoic palaeovalleys as a result of unconformity one of the best localities to characterise the basal unconformity of the palaeoproterozoic karrat group is along a cliff face of qaarsukassak at the head of kangerluarsuk (fig. 1). the more than 1800 m high cliff face exposes archaean basement rocks (umanak gneiss) and greywackes of the nûkavsak formation (henderson & pulvertaft 1987). the contact between the archaean basement and the karrat group was originally mapped as a series of faults, probably based on binocular observations from a boat in the 1960s, and from the black and white aerial photographs that were available at that time. the detail of our new oblique photographs clearly shows that this contact corresponds to a nonconformity with incised valleys into archaean basement gneiss filled by palaeoproterozoic siliciclastic rocks of the karrat group (figs 2, 3). the palaeotopography that is preserved below the palaeoproterozoic sedimentary cover appears deeply excavated with highs and lows representing an ancient palaeodrainage system with a topographic relief of 300–400 m (fig. 3). qaarsukassak represents one of the domal structures described by henderson & pulvertaft (1987), and the palaeotopography is accentuated by this fold structure. the south-eastern and north-western limbs of this wide upright anticline were visited and the basal unit was sampled (fig. 2). palaeovalleys at the basal unconformity of the palaeoproterozoic karrat group, west greenland pierpaolo guarnieri, camille a. partin and diogo rosa tornit 'discovery’ qaarsukassak alfred wegener halvø maarmorilik 51°30' w 52° w 7 1 °2 0 ' n 7 1 °1 0 ' n tornit ice nûkavsak fm metavolcanic rocks quaternary qaarsukassak fm umanak gneiss mârmorilik fm figs 2, 3 'discovery’ qaarsukassak alfred wegener halvø maarmorilik 51°30' w 52° w 7 1 °2 0 ' n 7 1 °1 0 ' n 5 km kangerluarsuup sermia ka ng erl ua rsu k k greenland fig. 1. simplified geological map of the central karrat group area (modified from escher & pulvertaft 1995). k: kangerlussuakassak. 6464 the overall geometry of the archaean–palaeoproterozoic unconformity displays important regional differences. in the maarmorilik sector to the south the palaeosurface appears to be a peneplain covered by the basal quartzites of the mârmorilik formation described by garde (1978); in the central kangerluarsuk sector described here, it is represented by well-developed incisions filled with a new stratigraphic unit and local occurrences of lava flows. to the north of the studied area, in the karrat isfjord sector, the unconformity is represented by an undulated palaeosurface covered by thick metavolcanic rocks that were also noted by henderson & pulvertaft (1987). qaarsukassak formation here we describe a new stratigraphic unit in the karrat group, informally named the qaarsukassak formation, which occurs locally below the nûkavsak formation in the kangerluarsuk fjord area (fig. 1). this sequence was previously described at the so-called ‘discovery’ showing by coppard et al. (1992). the report describes a 30–66 m thick quartzite-carbonate succession with a mineralised zone occurring dominantly in calcite-bearing dolostone, and bounded by the archaean basement gneiss and the nûkavsak formation. the measured section from the base to the inferred stratigraphic top (fig. 4) reveals that its stratigraphic thickness prior to structural repetition is less than 20 m. the lower contact with the archaean basement gneiss is a planar to undulating erosional surface that preserves a depositional contact. laminated to massive quartzite fines upward into fine-grained metamorphosed sandstones and sandy mudstones, including calcite-cemented and graphitic quartzites (unit 1). these siliciclastic rocks are overlain in sharp contact by light grey to white metacarbonate rocks with pods of massive tremolite and in some horizons, minor graphite (unit 2). this is succeeded by another quartzite unit (unit 3), followed by dark grey, laminated metacarbonate rocks with possible slump folds and minor tremolite veining (unit 4). the overlying, rusty weathering metasedimentary rocks including graphitic, metamorphosed mudstones and siliciclastic rocks represent the ore zone (unit 5). the upper contact of the qaarsukassak formation with the nûkavsak formation is not well-exposed. also of note is a thin re-sedimented calcitic marble horizon within the basal part of the nûkavsak formation, which might be derived from contemporaneous erosion of the qaarsukassak formation. all metacarbonate rocks in the qaarsukassak formation at the ‘discovery’ section described here are calcitic. the mârmorilik formation, by contrast, contains both calcitic and dolomitic marble (garde 1978). the primary occurrence of calcitic marble in the upper mârmorilik formation suggests possible correlation with the qaarsukassak formation. the presence of tremolite in some outcrops of qaarsukassak kangerlussuakassak 1850 m nw nukavsak fm (palaeoproterozoic) qaarsukassak fm (palaeoproterozoic) umanak gneiss (archaean) oblique photo (fig. 3) se 0 m 1000 2000 ‘discovery’ 569813 569816 fig. 2. geological cross-section of qaarsukasak showing the palaeoproterozoic unconformity with the incised palaeovalleys into the archaean umanak gneiss infilled by the qaarsukassaq formation at the bottom and the nûkavsak formation on top. the locations along the cross-section of two analysed samples (fig. 5) are also shown. qaarsukassak 1710 m 1140 m 960 m 1200 m nûkavsak fm umanak gneiss nw se u nconformity u nconformity fig. 3. the geometry of valleys and onlap of palaeoproterozoic greywackes of the nûkavsak formation at qaarsukassak, photographed from a helicopter. the difference between bottom and top of the palaeorelief is about 240 m. position of image shown on fig. 2. 65 the qaarsukassak formation, though, suggests the former presence of dolomite or high-mg calcite. unit 1 of the qaarsukassak formation could represent a fluvial environment, but outcrops lack the sedimentary structures to confirm this. instead, the qaarsukassak formation was likely deposited in a shallow marine environment. the qaarsukassak formation shows minor thickness variations along strike, suggesting that its deposition infilled pre-existing topographical lows in the archaean basement gneiss. in addition to the main section in the ‘discovery’ area, similar rocks also occur at two other localities, namely at tornit on the south side of kangerluarsuk and along kangerluarsuup sermia (fig. 1), although exposures are not laterally continuous. at tornit the orientation of the qaarsukassak formation is vertical and forms part of the overturned limb of the kigarsima nappe (henderson & pulvertaft 1987). at this outcrop the formation occurs between a thin amphibolite unit and the nûkavsak formation as a c. 10 m thick section comprised of calcitic marble and rusty metasedimentary rocks, with quartzite, a possible quartz-pebble conglomerate and siliceous marble. the section might be repeated by folding and therefore only less than 10 m thick. at kangerluarsuup sermia an overturned 30–40 m section of dark grey, tremolite-bearing dolomitic marble with black layers of metamudstone occurs structurally below archaean basement gneiss, which is thrust over the marble. the qaarsukassak formation extends to the north-west side of the section shown in fig. 2 on the northwestern limb of the wide anticline at kangerlussuakassak. mineralisation carbonate-hosted zn-pb mineralisation is common in the calcitic marble of the upper mârmorilik formation and was exploited at the black angel mine between 1973 and 1990 (thomassen 1991). additionally, coppard et al. (1992) identified intermittent stratabound zn-pb mineralisation of the ‘discovery’ and kangerluarsuup sermia occurrences, hosted within a carbonate and siliciclastic sequence. this sequence was considered to be the basal sequence of the mârmorilik formation by coppard et al. (1992). here, we allocate this succession to the qaarsukassak formation, since it is not in contact with the mârmorilik formation and the two units are separated by the basement topographic high. the recognition and understanding of the distribution of this formation are important as the formation controls the distribution of the regional zn-pb mineralisation, which should be distinguished from rusty* ** * * * * * * * * * 0 5 m 10 m 15 m 20 m unit 1 unit 2 unit 3 unit 4 ore zone u m an ak gn e is s q aa rs u k as sa k f m massive to laminated quartzite unconformity orthogneiss calcite-cemented quartzite graphitic quartzite metapelite carbonate rock pb-zn ore zone tremolite in carbonate rock slump folds palaeoproterozoic qaarsukassak fm archaean * fig. 4. stratigraphic section of the qaarsukassak formation at the type locality of qaarsukassak at head of kangerluarsuk (fig. 2 for location). fe 10(zn+pb) s sph py gn base metal mineralisation, hosted by carbonates (mârmorilik and qaarsukassak fms) barren, pyritic and/or pyrrhotitic mineralisation (nûkavsak fm) m et as ed im en t, p yr it ic c h er t/ sh al e g o ss an s 569807 569813 569816 fig. 5. fe–s–10(zn+pb) ternary diagram with discriminant compositional areas of base-metal mineralisation hosted by carbonates of the mârmorilik and qaarsukassak formations (right) and the rusty-weathering zones hosted by the nûkavsak formation (left). py: pyrite. gn: galena. sph: sphalerite. 6666 weathering, pyritic or pyrrhotitic, but barren horizons located in the nûkavsak formation. a ternary diagram (fig. 5) discriminates the signatures of the base-metal mineralisation hosted by carbonate rocks of the mârmorilik or qaarsukassak formations, and of the rusty-weathering horizons hosted by the nûkavsak formation. the latter are dominated by pyrite or pyrrhotite and lack significant amounts of base metals (fig. 5). due to the effects of weathering, resulting in gossanous horizons, compositions of the sulphides in exposed rocks can depart from pyrite and become enriched in iron and depleted in sulphur. the former have variable amounts of iron sulphide, but can also have significant sphalerite or galena contents. the two samples closest to the metal corner were collected at the previously established ‘discovery’ and ‘south lakes glacier’ occurrences, samples 569813 and 569807, respectively. a third sample (569816, fig. 5) was collected c. 10 km to the north-west (fig. 2) where mineralisation was not previously seen. although the absolute base-metal content of this sample is not high, it is elevated relative to sulphur (akin to the tenor concept in nickel exploration). its presence supports potential correlation with the mârmorilik formation and the proposed continuation of the qaarsukassak formation, hosting base-metal mineralisation, to the north-western limb of the wide anticline of the cross section shown in fig. 2. discussion and conclusion henderson & pulvertaft (1987) proposed a palaeoproterozoic structural high of archaean basement gneiss exposed on alfred wegener halvø, bounding the carbonate-dominated mârmorilik basin to the south and separating it from the qeqertarssuaq and nûkavsak formations in the north. our new observations show that such archaean basement gneiss in the kangerluarsuk area is heavily incised, and that palaeoproterozoic palaeovalleys were filled in with siliciclastic and carbonate rocks of the qaarsukassak formation (new informal unit) that correlates well with the mârmorilik formation and is conformably overlain by the nûkavsak formation. its intermediary, mixed siliciclasticcarbonate sedimentation could have been marginal marine and transitional into sedimentation of the turbiditic greywackes of the nûkavsak formation. the palaeovalleys observed at qaarsukassak seem to reflect an erosional event prior to the deposition of a sedimentary cycle represented by a carbonate-rich basin in the maarmorilik area and an area rich in volcanic components in the north, separated by a continental shelf area. the erosion may have been related to a re-organisation of the basin structure, where uplift in some areas created the observed palaeotopography beneath the nûkavsak formation. the observations in the kangerluarsuk area described here, coupled with new observations from the qeqertarssuaq formation in the north which will be described elsewhere, may suggest that the karrat group comprises more than one sedimentary cycle separated by erosion and possibly deformation. an ongoing geochronological study of detrital zircon from different units within the karrat group is expected to yield new information about the depositional ages of its individual formations. acknowledgments this work was carried out within the framework of an ongoing project financed by the geological survey of denmark and greenland (geus) and the ministry of mineral resources of greenland (mmr). references coppard, j., swatton, s. & harris, c.j. 1992: karrat exclusive exploration licence. 1992 year-end report, 19 pp. unpublished report, rtz mining and exploration limited (in archives of the geological survey of denmark and greenland, geus report file 21297). escher, j.c. & pulvertaft, t.c.r. 1995: geological map of greenland, 1:2 500 000. copenhagen: geological survey of greenland. garde, a.a. 1978: the lower proterozoic marmorilik formation, east of mârmorilik, west greenland. meddelelser om grønland 200(3), 71 pp. grocott, j. & pulvertaft, t.c.r. 1990: the early proterozoic rinkian belt of central west greenland. in: lewry, j.f. & stauffer, m.r. (eds) the early proterozoic trans-hudson orogen of north america. geological association of canada special paper 37, 443–463. henderson, g. & pulvertaft, t.c.r. 1967: the stratigraphy and structure of the precambrian rocks of the umanak area, west greenland. meddelelser fra dansk geologisk forening 17, 1–22. henderson, g. & pulvertaft, t.c.r. 1987: geological map of greenland, 1:100 000. mârmorilik 71 v.2 syd, nûgâtsiaq 71 v.2 nord, pangnertôq 72 v.2 syd. lithostratigraphy and structure of a lower proterozoic dome and nappe complex. descriptive text. 72 pp. copenhagen: geological survey of greenland. thomassen, b. 1991: the black angel lead-zinc mine 1973–90. rapport grønlands geologiske undersøgelse 152, 46–50. authors’ addresses p.g. & d.r., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. email: pgua@geus.dk c.a.p., department of geological sciences, university of saskatchewan, 114 science place, saskatoon, sk s7n 5e2, canada. e2019430301-01 the amount of provenance information available for onshore and offshore sedimentary deposits in the north atlantic region is substantial and rapidly increasing. these data provide an improved understanding of reservoir geology (quality, diagenetic issues, regional source-to-sink relations and local stratigraphic correlations), and thereby can reduce hydrocarbon exploration risk. as such, the number of proprietary, industry-related and public research provenance studies has increased considerably in recent years, and the development and use of new analytical techniques has also caused a surge in the number of grains, isotopes and chemical elements analysed in each study. as a result, it is today close to impossible for the individual researcher or petroleum geologist to draw on all existing provenance data. and the vast expansion of data availability demands new and better methods to analyse and visualise large amounts of data in a systematic way. to this end, the geological survey of denmark and greenland (geus) and the norwegian petroleum directorate (npd) have established a web-based database of provenance data for the north atlantic area: the north atlantic provenance database. construction of the database was funded jointly by geus and npd. future maintenance and further development will be funded by the petroleum industry by subscription to the database. the database was launched in march 2019 and can be accessed at https://data.geus.dk/provenance. access to the database is granted via application to the steering committee, comprised of staff at geus, npd and sponsoring petroleum companies. the aims of the database are three-fold: • assemble provenance data from onshore and offshore greenland, faroe islands, norway and neighbouring areas. • make the data easily assessable to the petroleum industry and research institutions for visualisation and statistical analysis through a web application. • facilitate research as well as development of new provenance tools and techniques that can reduce exploration risk. the north atlantic provenance database: an introduction christian knudsen*1, martin sønderholm1, tjerk heijboer1, jeppe ågård kristensen2 and dag bering3 geus bulletin is free to individuals and institutions in electronic form. the author(s) retain copyright over the article contents. r esearch article | open access geus bulletin vol 43 | e2019430301 | published online: 22 july 2019 https://doi.org/10.34194/geusb-201943-03-01 fig. 1. output map from the database showing the detrital zircon age distributions available as of july 2019. each data point (sample) is marked by either a yellow or a blue dot representing a sandstone sample or a present-day drainage sample, respectively. the rosette visualises the age distribution histogram where ‘north’ is 0 ma and ‘south’ is 1.8 ga with clockwise increasing ages. the length of each bar represents the frequency in 100 ma bins. inset: area shown in fig. 2. https://data.geus.dk/provenance https://doi.org/10.34194/geusb-201943-03-01 e2019430301-02 here, we provide a brief introduction to the database and its future development and expansion. we highlight the current capabilities with an example from east greenland. database contents, development and application the north atlantic provenance database is a spatiotemporal, object-rational database in postgresql. it consists of two main packages: • a database for storage of: – detrital zircon age data and other types of provenance data – metadata with information about the samples and the analytical procedure used • an analytical module allowing users to compile, compare and analyse the datasets. data at the time of publication ( july 2019), the database consists of 1659 sandstone samples and 413 stream sediment samples, each containing detrital zircon u-pb ages, together with metadata such as coordinates, stratigraphic data, analytical data and a reference to where the data are published. the database contains more than 170 000 detrital zircon u-pb ages. the detrital zircon u-pb age data available in the database ( july 2019) are summarised in fig.1. at present, detrital zircon u-pb age data constitute by far the main part of the existing provenance data in the north atlantic provenance database. other provenance data types, such as detrital rutile, monazite and apatite u-pb age data as well as stable heavy mineral distributions and heavy mineral chemistry, will be included at later stages. the analytical capabilities and possibilities are under constant change and the database structure is therefore f lexible, to accommodate parameters that are not yet part of standard provenance analysis. most of the data from greenland that are stored in the database are comprised of onshore outcrop samples, but also include shallow core wells and samples from present-day drainage systems. in eastern greenland, c. 500 samples have been analysed for provenance properties. of these, more than 400 were analysed by geus. the database contains the age distribution of these detrital zircon grains as well as their heavy mineral distribution and compositions. in addition, the database also contains results from various studies n a f d e g c b 20 km fig. 2. geological map (1:500  000) of ymer ø in the kong oscar fjord area, east greenland (output directly from the database; location marked in fig.1). locations of stream sediment (blue) and sandstone samples (yellow) are marked, see fig. 1 for further details. inset: sampling locations of the seven samples (a–g; see fig. 3) discussed in the text. 0 1000 2000 3000 g f e d c b a ma 8307751 8105181 8105150 8105153 473730 473731 473729 n=58/135 n=121/154 n=115/140 n=109/143 n=101/148 n=79/121 n=37/54 fig. 3. detrital zircon age distribution histograms of the seven samples (a–g) selected in fig. 2. (rehnström et al. 2010). the histograms are generated according to thomsen et al. (2016). e2019430301-03 in east greenland: some are published (e.g. røhr et al. 2008; kirkland et al. 2009; sláma et al. 2011; olivarius et al. 2018), and others are to be found in unpublished theses and company reports. a wealth of offshore and onshore data is available for norway. some data have been extracted from published work, but the vast majority of the data are yet to be recovered from either unpublished academic work or company reports. on the norwegian shelf, a large number of samples have been analysed for their detrital zircon age distribution and heavy mineral content. again, some of these data are published (e.g. morton et al. 2005; lorenz et al. 2013; fleming et al. 2016) and others are yet to be extracted from unpublished theses and company reports. data from neighbouring territories such as west greenland, arctic russia and canada, the faroe islands, denmark and the uk are also accessible in the database. analytical module users can query the database via the analytical module interface, where they can view and analyse the relevant datasets for a given number of samples. from here, users can generate various visualisations of the data and export them as figures in pdf format. note that the data belong to the institutions that produced them and so they are not directly available to download from the database. however, the database contains full bibliographic information and links to where the data can be found. a more detailed description of the database architecture will be published alongside the database at a later date. here, we simply demonstrate some of functionality, using seven samples from gunner andersen land, ymer ø in kong oscar fjord, east greenland (rehnström et al. 2010; location in fig. 2). stream sediment samples from present-day drainage systems and proterozoic and devonian sandstones were chosen for further analysis. visual inspection of the detrital zircon age distribution rosettes (fig. 2) and histograms (fig. 3) show distinct modal variation between the seven samples. this is confirmed by the kolmogorov-smirnov (ks) dissimilarity test (fig. 4 and table 1). some of the metadata available in the database for these samples are shown in table 2. sample 473729 (fig. 3a) represents the sandertop formation of the upper proterozoic lyell land group, part of the eleonore bay supergroup. detrital zircon ages span the palaeoproterozoic–mesoproterozoic eras, with a few archaean grains. samples 473730 (fig 3c) and 473731 (fig. 3b) represent the devonian kap kolthoff group consisting of immature sandstone and conglomerate. the detrital zircon age distributions are dominated by a palaeoproterozoic a b fig. 4. kolmogorov-smirnov (ks) dissimilarities of the seven selected samples. a: cumulative age distributions. b: hierarchical clustering. table 1. kolmogorov-smirnov (ks) dissimilarity matrix of the seven selected samples. x473729 x473730 x473731 x8105150 x8105153 x8105181 x8307751 x473729 0.631 0.585 0.190 0.126 0.344 0.268 x473730 0.631 0.064 0.647 0.631 0.328 0.620 x473731 0.585 0.064 0.622 0.610 0.330 0.589 x8105150 0.190 0.647 0.622 0.176 0.369 0.127 x8105153 0.126 0.631 0.610 0.176 0.343 0.163 x8105181 0.344 0.328 0.330 0.369 0.343 0.330 x8307751 0.268 0.620 0.589 0.127 0.163 0.330 e2019430301-04 peak around 1980 ma, which is well known from the tonalitic gneiss that occur in the basement northeast of the area (kalsbeek et al. 2008). samples 8105153, 8105150 and 8307751 (figs 3d, e, f) represent stream sediments collected from the present-day drainage system on ymer ø. they have very similar detrital zircon age distributions that resemble those of the upper proterozoic eleonore bay supergroup bedrock (see sample 473729; fig 3a). this supports the view that stream sediment offers a good representation of the catchment bedrock geology. stream sample 8105181 (fig. 3g) from the mainland has a very complex detrital zircon age distribution suggesting a fundamental difference in the bedrock geology in the catchment area of this sample. the analytical module allows users to calculate and visualise cumulative age distributions and kolmogorov-smirnov dissimilarities (fig. 4) – a widely used method for comparing mineral age distributions. this is enabled through a plugin between the database and the freely available statistical programming software r (r development core team 2008). these functionalities are part of the ‘provenance’ package’ developed specifically for detrital sediment provenance analysis (vermeesch et al. 2016). the similarities between e.g. samples 473730 and 473731 are clearly seen in figures 4a and 4b, and in table 1. outlook compiling the large amount of available provenance data into a regional, cross-border, web-database will make these types of data much more accessible and applicable to industry and the research community. in doing so, we hope to promote the use of these data in studies of the north atlantic region. with an extensive database covering both sides of the atlantic ocean more comprehensive source-to-sink analyses can be made, resulting in an improved understanding of onshore–offshore provenance relationships. in the long-term, we hope to include more data from neighbouring geographic areas such as the russian and canadian arctic, since detrital material in the north atlantic may have been derived from these areas. it is envisaged that more than 100 000 detrital zircon grains from the north atlantic region have been dated, and the aim is to capture the majority of these in the database, making them available for data comparison (e.g. with statistical tools) and visualisation to enhance the understanding of the regional reservoir geology. users are expected to upload their own provenance data in return for using the database. it is also possible to restrict access to certain data in the database, so that they are kept confidential for a time. this is an important feature for these types of datasets, many of which are funded by private companies and have confidentiality clauses imposed for a finite period. for more information contact the lead-author. references fleming, e.j., flowerdew, m.j., smyth, h.r., scott, r.a., morton, a.c., omma, j.e., frei, d. & whitehouse m. j. 2016: provenance of triassic sandstones on the southwest barents shelf and the implication for sediment dispersal patterns in the northwest pangea. marine and petroleum geolog y 78, 516–535. https://doi.org/10.1016/j.marpetgeo.2016.10.005 kalsbeek, f., thrane, k., higgins, a.k., jepsen, h.f., leslie, a.g., nutman, a.p. & frei, r. 2008: polyorogenic history of the east greenland caledonides. in: higgins et al. (eds): memoir 202: the greenland caledonides: evolution of the northeast margin of laurentia. boulder, colorado: geological society of america, 55–72. https://doi. org/10.1130/2008.1202(03) kirkland, c.l., pease, v., whitehouse, m.j. & ineson, j.r. 2009: provenance record from mesoproterozoic-cambrian sediments of peary land, north greenland: implications for the ice-covered greenland shield and laurentian paleogeography. precambrian research 170, 43–60. https://doi.org/10.1016/j.precamres.2008.11.006 lorenz, h., gee, d.g., korago, e., kovaleva, g., mcclelland, w.c., gilotti, j.a. & frei, d. 2013: detrital zircon geochronolog y of palaeozoic novaya zemlya – a key to understanding the basement of the barents shelf. terra nova 25, 496–503. https://doi.org/10.1111/ter.12064 morton a.c., whitham, a.g. & fanning c.m. 2005: provenance of late cretaceous to palaeocene submarine fan sandstones in the norwegian sea: integration of heavy mineral, mineral chemical and zircon age data. sedimentary geolog y 182, 3–28. https://doi.org/10.1016/j. sedgeo.2005.08.007 olivarius, m., bjerager, m., keulen, n., knudsen, c. & kokfelt, t.f. 2018: provenance of basinal sandstones in the upper jurassic hareelv formation, jameson land basin, east greenland. in: ineson, j. & bojesentable 2. example metadata available for the seven samples in fig. 2 storage sample type lithology lithostratigraphy base age top age reference number 473729 rock sample sandstone lyell land group sandertop formation tonian tonian rehnstrøm et al. 2010 473730 rock sample sandstone kap kolthoff group givetian famennian rehnstrøm et al. 2010 473731 rock sample sandstone kap kolthoff group givetian famennian rehnstrøm et al. 2010 8105150 stream sediment sample rehnstrøm et al. 2010 8105153 stream sediment sample rehnstrøm et al. 2010 8105181 stream sediment sample rehnstrøm et al. 2010 8307751 stream sediment sample rehnstrøm et al. 2010 https://doi.org/10.1016/j.marpetgeo.2016.10.005 https://doi.org/10.1016/j.marpetgeo.2016.10.005 https://doi.org/10.1130/2008.1202(03) https://doi.org/10.1130/2008.1202(03) https://doi.org/10.1016/j.precamres.2008.11.006 https://doi.org/10.1111/ter.12064 https://doi.org/10.1016/j.sedgeo.2005.08.007 https://doi.org/10.1016/j.sedgeo.2005.08.007 e2019430301-05 koefoed, j.a. (eds): petroleum geolog y of the upper jurassic – lower cretaceous of east and north-east greenland: blokelv-1 borehole, jameson land basin. geological survey of denmark and greenland bulletin 42, 39–64. r development core team 2008. r: a language and environment for statistical computing. r foundation for statistical computing, vienna, austria. isbn 3-900051-07-0, ur l http://www.r-project.org. rehnström, e.f., thrane, k., kokfelt, t.f. & frei, d. 2010: age distribution of detrital zircon grains in sandstones and stream sediments from east greenland north of 70°n. geological survey of denmark and greenland report 2010/130. 125 pp røhr, t. s., andersen, t. & dypvik, h. 2008: provenance of lower cretaceous sediments in the wandel sea basin, north greenland. journal of the geological society 165, 755–767. https://doi.org/10.1144/001676492007-102 sláma, j., walderhaug, o., fonneland, h., kosler, j. & pedersen, r.b. 2011: provenance of neoproterozoic to upper cretaceous sedimentary rocks, eastern greenland: implications for recognizing the sources of sediments in the norwegian sea. sedimentary geolog y 238, 254–267. https://doi.org/10.1016/j.sedgeo.2011.04.018 thomsen, t.b., heijboer, t., & guarnieri, p. 2016: jagedisplay: software for evaluation of data distributions in u-th-pb geochronolog y. geological survey of denmark and greenland bulletin 35, 103–106. vermeesch, p., resentini, a. & garzanti, e. 2016: an r package for statistical provenance analysis. sedimentary geolog y 336, 14–25. https:// doi.org/10.1016/j.sedgeo.2016.01.009 how to cite knudsen, c., sønderholm, m., heijboer, t., kristensen, j.å. & bering, d. 2019: the north atlantic provenance database: an introduction. geological survey of denmark and greenland bulletin 43, e2019430301. https://doi.org/10.34194/geusb-201943-03-01 *corresponding author: christian knudsen | e-mail: ckn@geus.dk 1 geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350, copenhagen k, denmark. 2 department of physical geography and ecosystem science, lund university, sölvegatan 12, s-223 62 lund, sweden. 3 norwegian petroleum directorate, professor olav hansens vei 10, postboks 600, 4003 stavanger, norway. http://www.r-project.org https://doi.org/10.1144/0016-76492007-102 https://doi.org/10.1144/0016-76492007-102 https://doi.org/10.1016/j.sedgeo.2011.04.018 https://doi.org/10.1016/j.sedgeo.2016.01.009 https://doi.org/10.1016/j.sedgeo.2016.01.009 https://doi.org/10.34194/geusb-201943-03-01 mailto:ckn%40geus.dk?subject= geological survey of denmark and greenland bulletin 31, 2014, 51-54 51 a multidisciplinary study of a geothermal reservoir below thisted, denmark morten leth hjuler, henrik vosgerau, carsten møller nielsen, peter frykman, lars kristensen, anders mathiesen, torben bidstrup and lars henrik nielsen the first geothermal plant in denmark was established in 1984 near the town of thisted (fig. 1). for nearly 30 years the plant has successfully produced c. 43°c hot water (surface temperature) from a highly permeable sandstone reservoir in the late triassic to early jurassic gassum formation and used the heat from the geothermal water for district heating. the 45°c hot water (formation temperature) is pumped up from a vertical production well, thisted-2, from a depth of c. 1250 m and the cooled water (c. 12°c) is re-injected into the formation through a vertical injection well, thisted-3, located 1.5 km east of the production well. in order to increase the capacity of the plant the supplier of district heating, thisted varmeforsyning, plans to add a new well to the current configuration. in 2013 the geological survey of denmark and greenland was assigned the task to propose suitable sites for a new well. the sites will be proposed based on the quality, continuity and temperature of the reservoir(s) within the gassum formation. three possible well sites (thisted-5a–c) were considered (fig. 1). well-log information and core-analysis data from four existing wells, thisted-1–4, indicate significant variations in reservoir properties and spatial extent of the reservoir bodies within the gassum formation. in order to establish a robust geological reservoir model that covers all reservoir-qualifying aspects it was decided to conduct the evaluation as a multidisciplinary study that included: (1) seismic interpretation and mapping, (2) determination of reservoir temperature, (3) petrophysical interpretation of well logs and (4) sedimentological description of well cores. two possible well configurations were considered: (1) the new thisted-5 is used as an injection well and thisted-2 continues as a production well. production can be increased with additional injection capacity, and by using thisted-5 as the principal injection well the breakthrough of cold injection water is postponed. (2) the new thisted-5 is used as a production well with thisted-2 and -3 as injection wells. thisted-5 will be located downflank of the thisted salt structure and will produce geothermal water from greater depths and expectedly with higher temperature than the existing production well. geological setting and seismic mapping thisted is located in the central to northern part of the norwegian–danish basin in an area characterised by numerous salt pillows and diapirs. the upper permian – mesozoic suc© 2014 geus. geological survey of denmark and greenland bulletin 31, 51–54. open access: www.geus.dk/publications/bull possible site for new well contour line 1500 land sea town thisted existing well geothermal plant seismic line 1 km 1000 thisted-3 thisted-4 thisted-2 thisted-1 thisted-5c thisted-5b thisted-5a 750 1250 fig. 2 fig. 1. depth structure map of near top gassum formation (contour interval: 50 m) of the thisted area showing seismic lines, well locations and possible locations of the planned thisted-5 wells. base upper cretaceous mid-cimmerian unconformity near top gassum formation near base gassum formation near top skagerrak formation near top zechstein near base zechstein 0 1 2 3 2 km nw se tw ow ay t ra ve l t im e (s ec ) fig. 2. seismic section (pr kl7374a no 74249) across the thisted salt pillow. 5252 cession consists of 5–5.5 km of sediments (vejbæk & britze 1994). thick zechstein salt layers are overlain by triassic sandstone, mudstone, carbonate and salt, followed by lower jurassic mudstone, middle jurassic sandstone, upper jurassic – lower cretaceous mudstone and siltstone with few sandstone beds. this succession is overlain by thick layers of chalk and limestone. thisted is situated over the southern part of a gently sloping salt pillow and the strata above the salt pillow in the area of the thisted-2 and 3 wells dip towards the south. thisted-1 and 4 are located on top of the structure. all relevant 2d seismic profiles in the thisted area were interpreted in order to map the presence and variations of the reservoirs including depth, changes in thickness and the occurrence of faults which may affect the lateral continuity of the reservoirs. due to low resolution of the seismic data near the potential sites of thisted-5, it was difficult to map faults and lateral changes in lithology and to trace seismic horizons. however, seven horizons could be identified, including the near top and near base of the gassum formation (fig. 2). mapping of single reservoir intervals within the gassum formation was impossible and no faults were identified. based on the seismic interpretation, four depth structure maps were compiled, including one of the near top gassum formation (fig. 1). from this map the depth of the gassum formation at the three suggested well sites can be estimated. relative to the thisted-2 well, the thisted-5a site is located downflank of the thisted structure whereas the thisted5b and 5c are situated upflank. due to deeper burial and expected higher temperature of the geothermal target, the thisted-5a site is suitable as a production well, whereas thisted-5b and 5c are injection well candidates. reservoir temperature temperature data from danish onshore wells are limited and include values from different depths and different formations, thus the geothermal gradient covers a wide range of 28–20°c/km. in the thisted-2 production well, c. 43°c warm water (surface temperature) is produced from a depth of 1250 m (formation temperature 45°c). the geothermal target in thisted-5a is estimated to be located at a depth of c. 1450 m, which corresponds to a temperature up to 52°c, if extrapolated from a continuation of the regional gradient and the temperature data from the thisted-3 well. the geothermal target in the thisted-5b and 5c injection sites is located at a depth of c. 1150 m corresponding to a reservoir temperature of 41°c using thisted-3 data. 6 260 ms/ft dt 60 cali 16 prs g as su m f or m at io n fj er ri ts le v fm vi nd in g fm 1130 1140 1150 1160 1170 1180 1190 1200 1210 1220 1230 1240 1250 1260 1270 1280 1290 1300 1310 1320 gr api0 250 inches phie 0 % 40110000 md perm_log 1 rhob 1.7 g/cm3 2.7 nphi 0.6 v/v dec 0 depth (m) sandstone siltstone shale marlstone potential reservoir sand production interval fig. 3. petrophysical evaluation of the gassum formation in the thisted-2 well, including a lithological interpretation. 0 1 10 100 1000 10 000 100 000 0 5 10 15 20 25 30 35 40 45 50 a ir p er m ea bi lit y (m d ) porosity (%) all wells thisted-3: low-permeability group thisted-3: high-permeability group regional trend (all wells) trend (thisted-3: low-perm. group) trend (thisted-3: high-perm. group) fig. 4. porosity–permeability plot based on conventional core analysis data from the gassum formation. 53 well-log interpretation and core description the evaluation of the reservoir quality of the gassum formation is primarily based on wireline logs and core-analysis data from thisted-1–4 (fig. 3). the quality of the logs is fairly good, but at certain intervals indications of caving lead to uncertain porosity estimates. lithology, clay content, porosity and permeability are evaluated from combined analyses of log data, lithological descriptions of cores and core analysis data. high, well test-based, porosities and permeabilities for the thisted wells were validated by gas permeability measurements from core analysis and are possibly caused by the relatively shallow depth of the gassum formation (hjuler et al. 2013). the regional porosity–permeability trend (fig. 4) significantly underestimates the actual (well test) permeability and was therefore calibrated to more closely approximate the well test results. evaluation of the sandstones indicates high average porosities exceeding 28% for the thisted-1 and 3 wells (table 1). the interpreted porosity of 25.3% for the thisted-2 well seems too low considering the fairly high test permeability of 3670 md; this is possibly due to erroneous log data. despite considerable variation of the assessed net sand thickness within the study area all thicknesses are considered sufficient for geothermal exploitation (table 1). detailed sedimentological descriptions and interpretations of the cores from the thisted-3 well indicate that the reservoir sandstones were mainly deposited in fluvial and estuarine environments (nielsen 2003; hjuler et al. 2013). considerable lateral and stratigraphical variations of the logs from the thisted wells indicate spatial and temporal variations of the sedimentary environment, which must have a significant influence on reservoir distribution and quality. it is thus important for the mapping of reservoir intervals to sb9 sb7 sb6 sb3 sb5 sb4 sequence boundary thisted-1 thisted-4 thisted-2 thisted-3 sandstone siltstone shale marlstone limestone dolomite coal gr dt gr caliper dt nphi rhob prs perm_log phie gr caliper dt nphi rhob prs perm_log phie core 2 core 3 core 4 core 5 datum line 1 g as su m f or m at io n fluvial estuarine shoreface offshore 1 4 2 3 5 g as su m f or m at io n g as su m f or m at io n g as su m f or m at io n depth (m) 750 800 850 900 depth (m) 1150 1200 1250 1300 depth (m) 1100 1150 1200 depth (m) 750 800 850 gr caliper dt rhob prs perm_log phie fig. 5. log correlation of sedimentary units within the gassum formation in the four thisted wells. 1–5: sequences, red lines: sequence boundaries (corresponding to incised valley f loors), prs: potential reservoir sand. the sediments of the incised valleys are f luvial and estuarine. thisted-1 137 94.4 84.4 0.62 28.3 2500 3125 thisted-2 135 94.9 70.3 0.52 25.3 1300 1625 thisted-3 115 67.4 54.5 0.47 28.6 3500 4375 thisted-4 114 36.6 – – – – – table 1. reservoir parameters for net sand from the gassum formation* well formation gross sand net sand n/g† average estimated estimated no. thickness (m) thickness (m) thickness (m) porosity (%) gas perm. (md) reservoir perm. (md)‡ * shale and porosity cut-off applied, net sand is defined as sandstone with <30% shale and porosity >15%. † n/g: net sand thickness divided by formation thickness. ‡ estimated reservoir permeability: estimated gas permeability multiplied by 1.25 (upscaling factor). 5454 understand the variations in the sedimentary environment. hence the logs of the four wells have been correlated (fig. 5). five periods of sea-level rises and falls were identified within the gassum formation. during sea-level falls, incised valleys formed which were filled with fluvial and estuarine sediments during subsequent rises in sea level. the extent of reservoir sandstone deposits is limited by the extent of the valleys. to estimate the dimensions of sandstone bodies in the thisted area the extent of present-day estuaries has been studied. it was found that the width of estuarine sediment bodies exceeds 8 km and the lengths are probably several tens of kilometres. in the late triassic – early jurassic the overall shoreline was nw–se oriented. the seismic data do not allow the determination of the relief and extent of the incised valleys, but an overall ne–sw-orientation of the estuarine sediment bodies is assumed. the reservoir lithology is limited to fluvial and estuarine sandstones with the fluvial sandstones being c. 20 times more permeable than the estuarine sandstones because detrital clay clogs the pores of the latter. as expected, the reservoir properties of clayand siltstones outside the estuaries are poor and thus fluvial sandstones in the valleys may be hydraulically separated from each other. log correlation implies that the estuarine deposits may coalesce into larger reservoir units, or may be partly separated by layers of low permeability. in a more landward position towards the ne fluvial reservoir sandstones may amalgamate into more coherent reservoir units, leading to improved reservoir continuity. a reservoir model petrel® software was used to establish a reservoir model that covers an area of 11 × 13.5 km; flow simulations and dynamic modelling were performed using the eclipse® 100 software (fig. 6). input data for the reservoir model were prepared by integration of interpreted seismic data, depth structure maps, temperature assessment, petrophysical evaluation, core description and log correlations as described above. comparison with historic data was not possible as no pressure data of the thisted-2 and 3 wells are available; the simulated response from the dynamic modelling could only be adjusted because no significant temperature drop has been recorded in the production water since 1984. hence the model results are uncertain and should be evaluated with caution due to lack of calibration data. with this limitation in mind, and using the current well configuration, the model simulations indicate another 15 years of production with no alarming decrease in water temperature (less than 1°c). with thisted-5a as a new production well situated downflank of the existing well pair, the production could benefit from a higher temperature with no sign of cooler water arriving during an operational time of 30 years (uncertainty in modelling results as above). with thisted-5b or -5c as a new injection well situated at shallower depth than the existing well pair, and with thisted-2 still used as production well, the new injection well can benefit from higher permeability. concluding remarks by integrating data from geological, geophysical and petrophysical disciplines, a detailed geological model was established that provides a structural framework and demonstrates how depositional environment controls the lateral extent, continuity and quality of reservoirs. a detailed reservoir model was also established, which can simulate the remaining lifetime of the geothermal plant with the current well configuration, or the lifespan of the plant with the addition of a new production or injection well. the combination of geological and reservoir models provides indications of the best sites for additional production or injection wells. references hjuler, m.l., vosgerau, h., nielsen, c.m., frykman, p., kristensen, l., mathiesen, a., bidstrup, t. & nielsen, l.h. 2013: assessment of potential capacity increase of the geothermal plant at thisted by adding a new geothermal well. danmarks og grønlands geologiske undersøgelse rapport 2013/80, 90 pp. nielsen, l.h. 2003: late triassic – jurassic development of the danish basin and fennoscandian border zone, southern scandinavia. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 459–526. vejbæk, o.v. & britze, p. 1994: geological map of denmark 1:750 000. top pre-zechstein (two-way traveltime and depth). danmarks geologiske undersøgelse kortserie 45, 8 pp. fig. 6. permeability model that crosses the thisted-2 and 3 wells. thisted-2 thisted-3 top gassum fm base gassum fme 1000 100 10 1 permeability (md) 1 km w authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark; e-mail: mlh@geus.dk geological survey of denmark and greenland bulletin 31, 2014, 79-82 79 outlet glacier dynamics and bathymetry at upernavik isstrøm and upernavik isfjord, north-west greenland camilla s. andresen, kristian k. kjeldsen, benjamin harden, niels nørgaard-pedersen and kurt h. kjær during the past decades, the greenland ice sheet has experienced a marked increase in mass loss resulting in an increased contribution to global sea-level rise. the three largest outlet glaciers in greenland have increased their discharge, accelerated, thinned and retreated between 1996 and 2005. after 2005 most of them have slowed down again although not to previous levels. geodetic observations suggest that rapid increase in mass loss from the north-western part of the ice sheet occurred during 2005–2010 (kjeldsen et al. 2013). warming of the subsurface water masses off greenland may have triggered the acceleration of outlet glaciers from the ice sheet (straneo & heimbach 2013). the north atlantic subpolar gyre, which transports water to south-east and west greenland via the warm irminger current, warmed in the mid-1990s. increased inflow of warm subpolar waters likely led to increased submarine melting of tidewater glaciers. climate, glacier configuration and fjord bathymetry play fundamental roles for outlet glacier dynamics and thus knowledge of these parameters is warranted. in particular, the bathymetry of a fjord gives important information about the exchange between fjord waters close to marine-terminating glaciers and the shelf and ocean. however, only sparse bathymetric data are available for the majority of fjords in greenland. the international bathymetry chart for the arc© 2014 geus. geological survey of denmark and greenland bulletin 31, 79–82 . open access: www.geus.dk/publications/bull a 73°n glacier 1 glacier 2 glacier 3 glacier 4 55°w 5 km potential temperature (°c) salinity (psu) 1 2 3 32 33 34 35 100 200 300 400 500 600 700 d ep th (m ) 73°n 56°w upernavik isstrøm b upernavik isfjord 10–100 101–200 201–300 301–400 401–500 501–600 601–700 701–800 801–900 901–1000 1001–1100 water depth depth (m) greenland hg mb fig. 1. a: landsat 8 satellite image from august 2013 of the upernavik isfjord region with recorded water depths in the fjord. b: temperature and salinity profiles at a mid-fjord site (white diamond). data acquired in 2013 by oceanographers from woods hole oceanographic institution. mb: melville bugt. hg: helheimgletscher. 8080 tic ocean (ibcao) does not provide adequate data for the fjords and gives the impression that water depths in fjords are typically <200 m. here we present the first detailed bathymetric data from upernavik isfjord in north-west greenland, which were obtained during a cruise led by the geological survey of denmark and greenland in august 2013. the purpose of the cruise was to retrieve sediment cores, collect hydrographic data and map the bathymetry of the fjord. in this paper, we also estimate retreat rates of the upernavik isstrøm since 1849 and evaluate them in the context of climate variability, glacier setting and fjord bathymetry. upernavik isstrøm and upernavik isfjord upernavik isstrøm consists of four main ice streams (glaciers 1–4, fig. 1) that had a total mass loss of 53.5 ± 12.8 gt during the period 2005–2010 (khan et al. 2013). the four glaciers terminate in the c. 80 km long upernavik isfjord. glaciers 1 and 2 are the most productive and the fjord in front of these glaciers is packed with icebergs throughout the year. the bathymetric data (fig. 1) show that most of the fjord is over 900 m deep, but water depths of 600–800 m are found near its head. due to ice conditions, water depths could only be measured near glacier 4 where there is an area with water depths around 200 m. local fishermen report water depths of 600–700 m at a distance of c. 5–10 km from the fronts of glaciers 1–3. the survey ended slightly west of the fjord mouth and there was no indication of a sill. the hydrographic measurements show a c. 2°c warm, lowsalinity, 50 m thick surface layer. from 50 to 150 m cold polar water with a temperature of 0.5–1.5°c is found, and below this the water gradually warms from 1 to 3°c and becomes more saline, which shows that atlantic water penetrates into the fjord (fig. 1). this also indicates that there is no shallow sill at the entrance to the fjord. radar-based surveys suggest grounding line depths of 400–700 m for glaciers 1–3 and 100 m for glacier 4 (morlighem et al. 2014). this suggests that atlantic water comes into contact with the fronts of glaciers 1–3, whereas the front of glacier 4 is in contact with polar water. this finding has implications for understanding the history of glacier retreat. glacier retreat and climate change frontal positions of upernavik isstrøm were compiled for the period from 1849 to 1953 by weidick (1958; fig. 2). along with satellite images from 1966 and 1976 (this study) and more continuously since 1985 (khan et al. 2013) these compilations provide a 150 years long record of glacier retreat since the little ice age maximum position. using the centre flow-line we estimate average annual retreat rates between glacier margin positions (fig. 3c). from the little ice age until c. 1931, the four glaciers were merged into one and retreated relatively slowly. the frontal retreat rate accelerated around 1931 and glaciers 1 and 2 and glaciers 3 and 4 started to split into two separate arms, and after 1946 glaciers 3 and 4 were decoupled from each other. the relatively high retreat rates lasted until the mid-1940s and were followed by lower retreat rates. glaciers 1 and 2 decoupled from each other after 1966. three subsequent episodes of increased retreat rates are seen: (1) between 1966 and 1985 (glaciers 1, 2 and 4), (2) late 1990s (glaciers 1, 2 and 4) and (3) 2005–2009 (all glaciers). during the latter period, the retreat rate of glacier 1 was exceptionally high. the temporal resolution of the data does not allow us to detect earlier similar rapid retreat events. in a recent study, data on frontal changes, thinning, and glacier velocity since 1985 were obtained from aerial photos and sat73°n 54°w 54°w55°w 55°w 5 km upernavik isfjord 1849 1886 1931 1937 1942 1946 1949 1953 1966 1976 1985 1991 1996 2000 2005 2010 fig. 2. glacier frontal positions based on maps from historical expeditions, aerial photographs and satellite images (weidick 1958; khan et al. 2013), supplemented with a corona satellite image from 1966 and a landsat mss image from 1976. the black and white lines show the tracks used for calculating single-point distances from the glacier margin. 81 ellite data and used to estimate dynamic mass loss (khan et al. 2013). glacier 4 experienced a marked mass loss episode, including >100 m thinning, prior to 1991. at the same time no marked changes were recorded for glaciers 1–3. in contrast, between 2005 and 2009, glacier 1 sped up, retreated and thinned markedly, whereas glaciers 2–4 were relatively stable. kjær et al. (2012) documented two events of dynamic mass loss along the melville bugt coast but also noted a spatially variable pattern in the magnitude of these events. the extended retreat data presented here may indicate that the marked dynamic mass loss prior to 1991 of glacier 4 was preceded by an even more marked event between 1966 and 1985 affecting not only glacier 4 but also glaciers 1 and 2. care should be taken in comparing magnitude and timing of retreat rates from merged and decoupled glaciers due to their different and temporally variable tributary sizes, glacier tongue widths and flow rates. moreover, the estimated frontal positions are based on single points and may be subject to seasonal fluctuations and are thus only approximate. however, the timing of accelerated retreat rates in the different glaciers is fairly synchronous over inter-annual time scales. the onset of increased retreat rates in the 1930s of glaciers 1 + 2 and 3 + 4 as well as the increased retreat rates of glaciers 1 + 2 around 1966 may have been initiated by their decoupling from the merged glacier and glaciers 1 + 2 at this time. this would suggest that topographical constraints are important for retreat rates. alternatively, a common climate change may have forced accelerated retreat and in this way caused the decoupling of glaciers. the marked retreat episodes in 1931–1946 (of the merged glacier), in the late 1990s (glaciers 1, 2, 4) and in 2005–2009 (all glaciers, but most markedly glacier 1) occurred at times of marked warming near upernavik and entire greenland (chylek et al. 2006). marked retreat from 1930 to the 1940s has also been documented elsewhere in greenland, specifically for helheimgletscher in south-east greenland (andresen et al. 2012; figs 1, 3d) and has been ascribed to variations in the atlantic multi-decadal oscillation (amo). the amo is a mode of variability with its main expression in sea-surface temperatures in the north atlantic ocean and influencing circum-atlantic climate, including coastal greenland. the amo has a periodicity of c. 60 years, and a positive amo fig. 3. a: atlantic multi-decadal oscillation (amo) index (schlesinger & ramankutty 1994). b: annual average air temperature for upernavik (data from the danish meteorological institute). c: calculated changes in rate (m yr–1). negative values and colour-filled boxes: glacier retreat. positive values and white boxes: glacier advance. episodes characterised by increased retreat rates by upernavik are highlighted with yellow boxes. d: marine sediment-based proxy data from south-east greenland. relative variability in calving from helheimgletscher based on sand f luxes (andresen et al. 2012) and shelf sea-surface temperatures based on analyses of core er07 from sermilik fjord (andresen et al. 2013). yellow boxes highlight warm episodes with increased dynamic mass loss in south-east greenland. 1860 1880 1900 1920 1940 1960 1980 2000 year amo+ amo– glaciers 1–4 merged glacier 1 glacier 2 glacier 4 glacier 3 1+2 merged se greenland 1+2 merged 3+4 merged 3+4 merged glaciers 1–4 merged glaciers 1–4 merged glaciers 1–4 merged upernavik isstrøm –2293 g la ci er r et re at r at e (m /y ea r) 12 calving helheimgletscher te m p. (° c ) a b c d –10 –6 –2 te m pe ra tu re (° c ) 0 –400 –800 400 0 –400 –800 400 0 –400 –800 0 –500 8 10 8282 index is linked with higher sea-surface temperatures. the accelerated retreat episodes of upernavik isstrøm from 1930 to the 1940s, late 1990s and 2005–2009 could be associated with warming of subsurface waters during periods with positive amo indexes (fig. 3). however, since air temperatures co-vary with the amo index on multi-decadal timescales (figs 3a, b) it is not possible to differentiate directly between influence from increased air versus water temperatures on mechanisms that could lead to retreat of the glacier margin. as noted the increased retreat rates of glaciers 1 and 2 between 1966 and 1985 may have been triggered by changed topographical constraints such as loss of pinning points as the combined glacier front widened considerably (figs 2, 3c). however, due to the synchronous, high retreat rates of glacier 4 within its own tributary, as well as continued high retreat rates long after decoupling of glaciers 1 and 2, we speculate that climate forcing is also involved. the increased retreat differs from the other retreat episodes because it occurred during a negative amo index. however, even though average sea-surface temperatures in the source region of atlantic waters were generally low between the early 1960s and the mid-1990s and annual air temperatures in upernavik decreased slightly, air temperatures increased between the early 1970s and 1980. interestingly, sediment-based proxy glacier and ocean data document a marked warming of atlantic waters in south-east greenland at this time along with a marked increase in calving from helheimgletscher (fig. 3d). the concurrency between this climate warming and glacier instability in south-east greenland supports the theory that the increased retreat rates of glaciers 1, 2 and 4 between 1976 and 1985 were forced by climate warming. the front of glacier 4 has been located in a 200 m shallow area since the 1950s (fig. 1) and the front of this glacier is not in direct contact with the deeper warm subsurface layer in the fjord. although warming or increased thickness of the atlantic water layer may increase the temperature of the polar water layer, we suggest that the accelerated retreat rates of glacier 4, including the 1985–1991 episode of marked thinning (khan et al. 2013), may be linked with increased air temperatures. it has been suggested that meltwater percolating down the glacier being released as subglacial discharge may have a considerable influence on the submarine melt rates and thus glacier stabilisation. we emphasise that the retreat record is not fully representative of glacier changes. not only are the determined frontal positions rather sporadic and do not represent a continuous record of change, but in addition we need to assess thinning and flow-rate changes to obtain a more comprehensive picture of glacier changes since the little ice age. one way to overcome this will be to analyse sediment cores to obtain a continuous proxy record of calving variability. this will add information on dynamic changes and can subsequently be linked to digital elevation models and mass-balance modelling to estimate mass loss. our results also show that bathymetric conditions may partly explain asynchronous glacier responses to climatic warming. it is therefore important to incorporate bathymetric data when trying to understand and predict outlet-glacier behaviour. hopefully future campaigns to collect and pool bathymetric data will provide improved bathymetric maps of the greenland fjords. acknowledgements the ‘upernavik glacier project’ is funded by geocenter danmark. we thank arctic station on disko for the use of the vessel porsild and hans karl petersen from upernavik who was pilot during the survey of glacier 4 and provided water-depth information by glaciers 1–3. references andresen, c.s. et al. 2012: rapid response of helheim glacier in greenland to climate variability over the past century. nature geoscience 5, 37–41. andresen, c.s., sicre, m.-a., straneo, f., sutherland, d.a., schmith, t., ribergaard, m.h., kuijpers, a. & lloyd, j.m. 2013: a 100-year record of alkenone-derived sst changes by southeast greenland. continental shelf research 71, 45–51. chylek, p., dubey, m.k. & lesins, g. 2006: greenland warming of 1920– 1930 and 1995–2005. geophysical research letters 33, l11707. khan, s.a., et al. 2013: recurring dynamically induced thinning during 1985 to 2010 on upernavik isstrøm, west greenland. journal of geophysical research: earth surface 118, 111–121. kjær, k.h. et al. 2012: aerial photographs reveal late-20th-century dynamic ice loss in northwestern greenland. science 337, 569–573. kjeldsen, k.k., et al. 2013: improved ice loss estimate of the northwestern greenland ice sheet. journal of geophysical research: solid earth 118, 698–708. morlighem, m., rignot, e., mouginot, j., seroussi, h.& larour, e. 2014: deeply incised submarine glacial valleys  beneath the greenland ice sheet. nature geoscience 7, 418–422. schlesinger, m.e. & ramankutty, n. 1994: an oscillation in the global climate system of period 65–70 years. nature 367, 723–726. straneo, f. & heimbach, p. 2013: north atlantic warming and the retreat of greenland’s outlet glaciers. nature 504, 36–43. weidick, a. 1958: frontal variations of upernaviks isstrøm in the last 100 years. meddelelser fra dansk geologisk forening 14, 52–60. authors’ addresses c.s.a. & n.n.p., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: csa@geus.dk k.k.k. & k.h.k., natural history museum of denmark, university of copenhagen, øster voldgade 5-7, dk-1350 copenhagen k, denmark. b.h., woods hole oceanographic institution, woods hole, ma 02543, usa. geological survey of denmark and greenland bulletin 28, 2013, 57-60 57© 2013 geus. geological survey of denmark and greenland bulletin 28, 57–60. open access: www.geus.dk/publications/bull lineament mapping and geological history of the kangerlussuaq region, southern west greenland knud erik s. klint, jon engström, andrew parmenter, timo ruskeeniemi, lillemor claesson liljedahl and anne lehtinen how could future ice ages affect deep nuclear waste repositories in crystalline basement rocks? deep repositories may be affected by a number of glacially induced processes including, but not limited to, (1) fault activation or re-activation and associated seismicity, (2) changing hydraulic and chemical groundwater dynamics and (3) enhanced erosion. such processes are likely to affect not only man-made barriers in spent fuel repositories such as copper canisters and bentonite clay buffers, but also the rock masses that contain and isolate the repositories. in order to increase our understanding of this problem, an international study (the greenland analogue project) was set up in 2008. the aim of the study was to use crystalline bedrock at the margin of the inland ice near kangerlussuaq airport in west greenland as an analogue for future nuclear fuel waste repositories affected by glaciation in fennoscandia and canada. accordingly, a wide range of field surveys were conducted for the analogue project (fig.  1). this paper describes a detailed structural investigation of lineament zones and the establishment of an event succession for fault and fracture zone evolution in central parts of the study area (figs 1b, 2), as well as an interpretation of the distribution of fracture and fault zones with potentially increased permeability. three deep holes were drilled in the study area, and instruments were installed in two of them for subsequent down-hole sampling and monitoring of groundwater to a depth of c. 600 m. the cores were used to compare the subsurface fracture patterns with those established on the basis of surface mapping. fig. 1. a: map of greenland showing the extent of the nagssugtoqidian orogen and the location of fig. 1b (rectangle). b: regional geolog y of southern west greenland, modified from garde & hollis (2010) and garde & marker (2010). cno, nno and sno are central, northern and southern nagssugtoqidian orogen, respectively. c: lineament map of the area around kangerlussuaq airport. areas a and b were mapped in detail. sisimiut disko bugt lineament systems 1 2 3 5 6 4area a area b (fig. 2)10 km c proterozoic reworked gneiss, mainly granodioritic or quartz dioritic with basic schlieren and lenses of metadolorite dykes orthogneiss late archaean granite early archaean gneiss syntectonic granite suite arfersiorfik igneous suite sisimiut charnockite kangâmiut mafic dykes archaean palaeoproterozoic undifferentiated supracrustal rocks granite amphibolite quaternary pegmatite fault51°w51°w 67°n67°n steep belt shear zone ‘flat b elt’nort hern cno c 52°w a greenland ice sheet 67° 66°n b 50 km southern archaean foreland nagssugtoqidian nno cno sno kangerlussuaqkangerlussuaq nord re iso rtoq ikert ôq thrus t zon e nord re st rømf jord 5858 geological setting the kangerlussuaq area is located close to the southern margin of the c. 1.85 ga old collisional nagssugtoqidian orogen (van gool et al. 2002). the study area covers a 100 × 50 km large area in front of and below the western margin of the inland ice (fig. 1). detailed geological mapping was carried out along a transect from kangerlussuaq airport to the margin of the inland ice, and of a smaller area around the three drilling sites in the valley in front of the inland ice (fig. 2). the bedrock is mainly reworked archaean orthogneiss with minor palaeoproterozoic metavolcanic amphibolite and metasedimentary rocks that were deformed under highgrade metamorphic conditions during the nagssugtoqidian orogeny (van gool et al. 2002). the nagssugtoqidian structures are generally ductile and include a penetrative gneissic fabric, macroscale folds and pronounced shear zones. occasional, deformed mafic dykes also occur, mainly members of the rift-related nagssugtoqidian kangâmiut dyke swarm that preceded the nagssugtoqidian orogeny (mayborn & lesher 2006). brittle structures such as faults and fractures are abundant and were probably formed in a younger, shallower, colder and hence more rigid environment. regional lineament mapping and geology of the study area most lineaments in crystalline rocks represent structural features such as faults and shear zones, rock fabrics and lineaments that were created at discontinuities due to differences in rheology or competence. our lineament mapping comprised four steps. first, lineaments were identified using remotely sensed gis-data compiled from aerial photographs, fig. 2. aerial image of area b (fig. 1c) with mapped and inferred rock fabric (foliation), rock types and structural elements. local event stratigraphic models were developed for locations a–f. the macro-scale structures outline large-scale ductile folds overprinted by various shear and fault zones. three deep holes were drilled (dh-gap01, dh-gap03 and dh-gap04). !! !! !! ! ! (( (( (( (( (( (( (( ( 65° 14 mafic dyke intr f1 f2 kang. dyke intr 74° 60 ° dh-gap01 dh-gap03 dh-gap04 78° 82° décollement f2 folding? dyke intr ( 74 85 8080 79 79 84 84 85 79 86 76 62 70 88 67°08´n kang. dyke intr 1 km fold strike slip fault dip slip fault thrust fault fault foliation fold axis rock fabric banded felsic gneiss mafic gneiss structures syncline hinge line anticline hinge line 1 2 3 4 5 6 kan gerlu ssua q–r usse ll fau lt lin e lineament system peg intr + 50°09´w lithology: f1 f2 f2 f2 a b c peg intr f2 peg intr peg intr d e peg intr + d f2 f 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 61 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 russell glacier 59 topographical and geological maps and geophysical data. the second step was a descriptive and kinematic field analysis of the remotely detected lineaments. in the third step, a local event succession model was developed by determination of overprinting relationships. finally, the local geological history of the kangerlussuaq area was interpreted and correlated with the regional geological evolution (van gool et al. 2002; garde & hollis 2010). in order to provide an overview of the geological framework of the study area, the measured and interpreted structures (foliation, fold hingeline, fault and shear zone traces) are shown on a high-resolution aerial image (fig. 2). close to the margin of the inland ice in the north-eastern part of the area, the bedrock is characterised by folded mafic gneiss that defines an open, nnw-trending and shallowly plunging (c. 14°) f1 fold structure. this structure gradually turns into a tight to isoclinal fold that can be traced southward and westward around an open, steeply-plunging, kilometre-scale f2 fold structure with a nwto n-trending axial surface (figs 1c, 2). five general lineament systems were outlined from the gis analysis, and a sixth, subhorizontal system was identified by the field work, during which also the curvilinear nature of the foliation traces became apparent and highlighted the superposition of the f1 and f2 fold phases. on a regional scale, system 1 lineaments are generally distributed between the system 2 steep belts (fig 1). these lineaments dominate in some parts of the southern study area and consist of ductile, e–w-trending, 10–100 m wide, foliation-parallel, steeply inclined and steeply n-dipping dextral shear zones (figs 1c, 2). these shear zones may have acted as décollement planes for the f2 folding (see below). system 2 lineaments constitute the most pronounced linear feature and represent regional, sw-trending shear zones, including the zone outlining søndre strømfjord itself and especially the northern margin of sandf lugtdalen that extends from kangerlussuaq to russell glacier, hereafter named the kangerlussuaq–russell fault line. other lineaments farther north with similar orientations (fig. 1b) comprise the ikertôq zone (van der molen 1984), the nordre isortoq steep belt and the nordre strømfjord shear zone (van gool et al. 2002). along the kangerlussuaq–russell fault line this lineament is dominated by sinistral strike-slip movement overprinting elements of thrust faulting dipping towards the north. large boudins of deformed kangâmiut mafic dykes (mayborn & lesher 2006) are included in this zone, which is therefore younger than the intrusion of the kangâmiut dykes. system 3 lineaments are a major nw-trending system along pronounced valleys and extend all the way up to aassiaat and disko bugt (fig. 1a). locally within the study area they form semi-brittle, sinistral strike-slip fault zones that displace the system 1 shear zones. system 4 lineaments form oblique to sub-horizontal fracture systems trending nne and are not represented by any pronounced topographic lineaments. these structures may also be related to a population of normal faults and younger, age general tectonic events in central west greenland correlation to the kangerlussuaq area table 1. event succession of the kangerlussuaq area compared with the general history of central west greenland* * based on van gool et al. (2002) and garde & hollis (2010) † kangerlussuaq–russell fault line >2.5 ga (archaean) formation of ‘banded gneiss’ protoliths f1 folding + multiple healed structures c. 2.04 ga continental rifting coupled with mafic dyke intrusions intrusion of kangâmiut mafic dykes 1.92–1.75 ga nagssugtoqidian orogen. continental collision. reworking, system 1 dextral, strike-slip shear and f2 folding folding and thrusting of gneiss/mafic rocks followed by system 2 wsw–ene-trending faulting (k–r fl†) peak metamorphism and large-scale folding during n–s reactivation of kangerlussuaq–russell fault sinistral contraction. finally formation of steep belts with sinistral strike slip movements system 3 sinistral strike-slip shear zones c. 1.78 to present day various stress conditions. formation and reactivation system 4 normal faults with shallow dip towards of open mode fractures at more shallow depths during se and nw accompanied by pegmatite intrusions 20–25 km uplift 1.2 ga diamond-bearing, ultramafic lamprophyre intrusions s and w of kangerlussuaq 600 ma kimberlite intrusions s and w of kangerlussuaq 100–50 ma faulting related to sea-floor spreading during the system 5 sinistral strike-slip faults trending ne–sw opening of labrador sea and baffin bay. nne–ssw system 6 dextral strike-slip faults trending n–s sinistral strike-slip faulting and conjugate dextral strike slip faulting at least the last 2 ma repeated glaciations resulting in erosion, glacier-induced reactivation of existing fault zones reactivation of fractures during glacial subsidence and rebound of the basement 6060 nne-trending pegmatites orientated parallel with the normal faults. they overprint the system 1 and 3 lineaments, but no cross-cutting relations to system 2 lineaments have been noticed. system 5 lineaments are semi-brittle, sinistral, strike-slip faults trending ne and dipping to the nw. this system outlines the pronounced escarpment in the central to northeastern part of the study area (fig. 2). local zones of wswstriking thrust faults with both northerly and southerly dips are regarded as representing local transpression in a wrench fault system related to the overall system 5 lineaments. system 6 lineaments consist of n–s-trending, brittle, dextral, strike-slip faults. this system may be conjugate with system 5. lineaments with this orientation near the outer coast of central west greenland have been related to the rifting between greenland and canada during the last 100 ma (wilson et al. 2006). preliminary geological history as demonstrated by its structural complexity (fig. 2), the study area has undergone several episodes of deformation. these episodes have been compiled into a local event history that recognises seven types of structural overprint (table 1). two stages of folding (f1 and f2) are identified. f1 may be of archaean age, while f2 seems to be nagssugtoqidian and contemporary with the system 1 shear zones, since the kangâmiut dykes were folded during this event. the kangerlussuaq–russell fault line of system 2 lineaments has been reactivated with sinistral, strike-slip movement, during which the kangâmiut dykes were deformed, but a clear, cross-cutting relation with systems 1 and 3 has not yet been documented. the system 3 lineaments clearly overprint system 1 and the f2 folds. the normal faulting and nne trending pegmatites of system 4 either indicate a general, extensional stress regime or local transtension during strikeslip movements. the timing of this event is highly speculative. the youngest geological events are related to the type 5 and 6 lineaments that form two, generally brittle, strike-slip fault systems. these are also regarded as the primary hydraulic zones in the kangerlussuaq area. the absolute ages of the different types of ductile and brittle deformation are uncertain because of lack of radiometric ages. however, in relative terms, it is suggested that the kangerlussuaq–russell fault line and most other semi-ductile shear zones are ancient features related to the nagssugtoqidian orogeny (van gool et al. 2002). the system 3 and 4 semi-brittle lineaments may be of intermediate ages related to postorogenic tectonic events, whereas the youngest and most brittle deformations may be related to the opening of the north atlantic ocean, the labrador sea and the baffin bay over the last 100 ma (wilson et al. 2006). acknowledgement the study was funded by the swedish, finnish and canadian nuclear waste management organisations. references garde, a.a. & hollis, j.a. 2010: a buried palaeoproterozoic spreading ridge in the northern nagssugtoqidian orogen, west greenland. geological society special publications (london) 338, 213–234. garde, a.a. & marker, m. 2010: geological map of greenland, 1:500 000, søndre strømfjord – nuussuaq. copenhagen: geological survey of denmark and greenland. mayborn, k.r. & lesher, c.e. 2006: origin and evolution of the kangâmiut mafic dyke swarm, west greenland. in: garde, a.a. & kals beek, f. (eds): precambrian crustal evolution and cretaceous–palaeogene faulting in west greenland. geological survey of denmark and greenland bulletin 11, 61–86. van gool, j.a.m., connelly, j.n., marker, m. & mengel, f.c. 2002: the nagssugtoqidian orogen of west greenland: tectonic evolution and regional correlations from a west greenland perspective. canadian journal of earth sciences 39, 665–686. van der molen, i. 1984: dykes and deformation in the ikertôq zone of the nagssugtoqidian at søndre strømfjord airport, west greenland. bulletin of the geological society of denmark 32, 101–106. wilson, r.w., klint, k.e.s., van gool, j.a.m., mccaffrey, k.j.w., holdsworth, r.e. & chalmers, j.a. 2006: faults and fractures in central west greenland: onshore expression of continental break-up and seaf loor spreading in the labrador – baffin bay sea. geological survey of denmark and greenland bulletin 11, 185–204. authors’ addresses k.e.s.k., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: kesk@geus.dk j.e. & t.r., geological survey of finland, p.o. box 96, sf-02151 espoo, finland. l.c.l., swedish nuclear fuel and waste management co, box 250, se-101 24, stockholm, sweden. a.p., nuclear waste management organization, 22 st. clair avenue east, sixth floor, toronto, m4t 2s3, canada. a.l., posiva oy olkiluoto, sf-27160 eurajoki, finland. mailto:kesk@geus.dk geological survey of denmark and greenland bulletin 31, 2014, 43-46 43 arctic plant remains of weichselian age from the danish north sea ole bennike, jørgen o. leth, jørn bo jensen, niels nørgaard-pedersen and steen lomholt the north sea is a large, shallow epicontinental sea dominated by a sandy bottom that reflects a high-energy environment. little is known about the environmental history of the danish part of this large area during the weichselian, the last ice age. parts of it were glaciated during the last glacial maximum and probably also during older glaciations. shallow parts were dry land, and deeper parts were covered by the sea during ice-free intervals. large, partly ice-dammed lakes also existed. three remains of walrus (odobenus rosmarus) have been radiocarbon dated (möhl 1985; kim aaris-sørensen, unpublished). one of the finds was dated to c. 35 cal. ka bp, whereas the two others finds gave somewhat younger ages of c. 30 cal. ka bp (table 1). knudsen (1985) described the stratigraphy of sediment cores from the western part of the danish north sea. from the roar 41 core, she reported on eemian deposits overlain by weichselian marine deposits with an arctic or boreoarctic foraminiferal fauna. an age of 30–50 cal. ka bp was suggested for this deposit by larsen et al. (2009, fig. 8h). leth (1998) obtained three radiocarbon ages of 43–45 cal. ka bp on marine bivalve shells from two vibrocores from jyske rev. in connection with mapping of sand and gravel deposits in 2012, a number of 6 m long vibrocores were collected by the geological survey of denmark and greenland (geus). during description of the sediment cores, remains of plants were noted; most of them were early holocene. however, a few samples from two sediment cores contained macrofossils of arctic plants and two samples were dated. the aim of this paper is to report on these ages and their implications. the locations of the coring sites are shown in fig. 1. material and methods sediment coring was carried out with a vibrocorer with a 6 m long, 10 cm wide steel core barrel with a pvc tube mounted. coring positions were selected from high-resolution, shallow seismic profiles. the cores were collected in pvc tubes and cut into 1 m long sections and shipped to geus, where they were split and described. a few 1–2 kg samples with plant remains were wet sieved and the residue left on the sieves was analysed using a dissecting microscope. two samples of terrestrial plant remains were dried and dated by radiocarbon accelerator mass spectrometry. a late weichselian deposit lithological logs of the cores are shown in fig. 2. ns 12-213 consists of 100 cm of holocene marine silt and very finegrained sand, underlain by 178 cm indistinctly laminated clay and silt, 180 cm of alternating layers of fine-grained sand, medium-grained sand and silt, 15 cm silt and 71 cm of alternating layers of fine-grained sand, medium-grained sand and silt. the deposits below the marine unit were interpreted as late glacial. plant remains were noted near the bottom of the core. remains of terrestrial plants include leaves of salix herbacea, a leaf of salix phylicifolia, a leaf of betula nana, seeds of empetrum nigrum, a seed of lychnis flos-cuculi, a megaspore of selaginella selaginoides and a stem of distichium sp. © 2014 geus. geological survey of denmark and greenland bulletin 31, 43–46. open access: www.geus.dk/publications/bull 0° 100 km scotland 5°e 0° 5°e 58°n 58°n 56°n 54°n 56°n 54°n denmark norway england the netherlands united kingdom germany 09 13 41 jr >500 200–500 100–200 50–100 40–50 30–40 20–30 10–20 0–10 depth (m) fig. 1. bathymetrical map of the north sea. the dots show the locations of the studied sediment cores (13 = ns 12-2-13, 09 = ns 12-3-09). the green dot shows the location of core roar 41 discussed by knudsen (1985). jr: jyske rev. 4444 (table 2). freshwater plants are represented by potamogeton filiformis, and freshwater invertebrates are represented by cristatella mucedo and fredericella indica. stems of scorpidium scorpioides and drepanocladus s.l. sp. are common; these mosses as well as carex spp. probably grew in wet areas. a sample of salix herbacea leaves gave an age of c. 12.6 cal. ka bp, corresponding to a younger dryas age (table 1). younger dryas deposits are common in denmark, and several submarine deposits from inner danish waters have also been found (e.g. bennike et al. 2004; bennike & jensen ns 12-2-13 56°15.862´ 7°27.819´ lus-10493 salix herbacea 542 12 554–12 746 ns 12-2-09 56°28.478´ 6°27.794´ lus-10494 s. herbacea, d. octopetala 495 33 957–35 010 562026 56°39.3´ 7°39.9´ aar-3291 spisula subtruncata 230 41 136–44 666 562026 56°39.3´ 7°39.9´ aar-3292 macoma balthica 550 42 298–47 250 562028 56°46.3´ 7°33.2´ aar-3293 donax vittatus 310 40 807–45 085 off esbjerg k-3727 odobenus rosmarus 27 033–29 417 table 1. pre-holocene radiocarbon ages from the danish north sea c. 56°30´ c. 7° k-3726 odobenus rosmarus 31 578–36 9401110 ‡ c. 57°12´ c. 8°28´ k-5746 odobenus rosmarus 27 616–33 475a * below core top. † calibrated according to the calib 7.0 program. ‡ core numbers refer to the numbering system used by the marine geologists at geus. § leth (1998). ¶ möhl (1985). a k. aaris-sørensen, unpublished data. § ¶ ¶ § § 1270+ – 10 730 ± 75 24 380 ± 620 39 300 ± 1300 41 500 ± 1450 39 200 ± 1100 30 530 ± 300 30 880 26 700 ± 1500 core n. lat. e. long. laboratory species depth age (14c calibrated no. no. b.c.t. (cm)* years bp) age (years bp)† 1 2 3 4 5 cl ay sil t vf sand f m d ep th (m ) li th ol og y d ep th (m ) li th ol og y ns 12-2-13 ns 12-3-09 1 2 3 4 5 cl ay sil t vf sand f m c vc gravel gr an pe bb table 2. macrofossils of weichselian age from the north sea r: rare, c: common. plants cenococcum geophilum sclerotia 3 15 distichium sp. stems – 1 ditrichum sp. stem – 4 bryum sp. stems – r paludella squarrosa stem – 1 drepanocladus revolvens stems – 2 drepanocladus s.l. sp. stems c r scorpidium scorpioides stems c r polytrichum sp. leaves 1 3 selaginella selaginoides megaspores 1 1 ranunculus sp. achene 1 – betula nana leaf fragment 1 – salix herbacea leaves 7 16 salix phylicifolia leaves 2 – dryas octopetala leaves – 11 empetrum nigrum endocarps 4 – juncus sp. seed – 1 carex spp. achenes 6 14 potamogeton filiformis achenes – 3 animals cladocera indet. shells – r staphylinidae indet. wing 1 – chironimidae indet. head capsules – r trichoptera indet. sclerite – 1 oribatida indet. skeletons – r fredericella indica statoblast 1 – cristatella mucedo statoblast 1 – ns 12-2-13 ns 12-3-09 c. 12.6 ka c. 35 ka fig. 2. lithological logs of core ns 12-2-13 and ns 12-3-09. ns 12-2-13 was sampled at a water depth of 32.0 m and core ns 12-3-09 was sampled at a water depth of 43.5 m. blue: marine holocene. yellow: non-marine pre-holocene. 45 2011; mortensen et al. 2014). however, the present article is the first that reports on a younger dryas deposit from the danish part of the north sea. the deposit shows that the coring site had not yet been transgressed by the sea. a middle weichselian deposit core ns 12-3-09 consists of 75 cm of holocene marine finegrained sand, underlain by 10 cm of holocene marine gravel, 145 cm clay and silt, 238 cm fineand medium-grained sand, 87 cm fine-grained sand with plant remains and 15 cm gravel. remains of terrestrial plants include leaves of salix herbacea, leaves of dryas octopetala, a megaspore of selaginella selaginoides, 2 stems with leaves of ditrichum sp., 1 stem with leaves of distichium sp. and sclerotia of cenococcum geophilum (table 2). wetland species are represented by carex sp., juncus sp., scorpidium scorpioides, drepanocladus revolvens and paludella squarrosa. lake or pond species are represented by potamogeton filiformis, and freshwater invertebrates are represented by cladocerans, chironomid larvae and trichoptera. a sample of s. herbacea and d. octopetala leaves gave an age of c. 35 cal. ka bp, corresponding to a middle weichselian age – prior to the last glacial maximum (table 1). most of the species are known from middle weichselian deposits in denmark, and indicate an open, treeless, tundralike environment with wetlands and lakes. s. herbacea grows in areas with a long-lasting snow cover, whereas d. octopetala prefers areas with little snow cover. the presence of both of these dwarf shrubs indicates that wind-swept hills and places where snow could accumulate were present in the area. non-marine middle weichselian deposits with organic remains are rare in denmark. deposits of broadly the same age as the deposit from the north sea have been discussed by bennike et al. (1994, 2007) and houmark-nielsen et al. (1996); in addition, a number of re-deposited mammal bones and teeth, especially of mammoth (mammuthus primigenius) have been found. the flora and fauna from the other danish sites are similar to those from the north sea. the ålesund interstadial in south-west norway, dated to 28–35 cal. ka bp, is characterised by an arctic vertebrate fauna. pre-holocene bivalve shells and bones as mentioned in the introduction, dating of pre-holocene marine shells from two cores from jyske rev gave ages of 43–45 cal. ka bp (table 1; leth 1998). two of the dated species are boreal and warmth-demanding, which contrasts with indications of arctic conditions during the same time period, as seen in other records from the region. a number 0 50 100 150 200 250 300 350 400 450 500 550 d ep th (c m ) m yt ilu s e du lis ce ra sto de rm a ed ul e ar ct ica is la nd ica sp isu la su bt ru nc at a m ac om a ba lth ica d on ax v itt at us m ya tr un ca ta ba la nu s c re na tu s ba la nu s b al an us tu rit el la c om m un is lu na tia a ld er i ac te on to rn at ili s re tu sa tr un ca tu la n uc ul a ni tid os a ch la m ys v ar ia o str ea e du lis m ys el la b id en ta ta ac an th oc ar di um e ch in at um en sis e ns is fa bu lin a fa bu la ab ra a lb a ch am el ea s tr ia tu la d os in ia e xo le ta co rb ul a gi bb a ec hi no ca rd iu m c or da tu m z on e 1 2 fig. 3. simplified macrofossil diagram of core 562028 from jyske rev (see fig. 1 for location). blue: holocene marine fine-grained sand. yellow: preholocene mediumand coarse-grained sand with pebbles. 4646 of samples from the two cores were analysed in connection with this study. the studied fauna includes a number of boreal species (fig. 3, zone 1). in addition to donax vittatus and spisula subtruncata reported by leth (1998), boreal species are also represented by arctica islandica and cerastoderma edule. these four species are known from holocene and eemian deposits in the region, but not from weichselian deposits. the fauna from the cores also comprises macoma balthica, macoma calcarea, mytilus edulis, hiatella arctica, mya truncata, balanus crenatus and balanus balanus that are boreal and arctic. no species that are confined to the arctic were found, and the fauna can be characterised as of interglacial type. the fauna in zone 2 is typical for holocene fine-grained deposits in the region. there are no reports of interglacial-type deposits from the region from the middle weichselian. for example, in france where the nearest continuous weichselian deposits are found, the middle weichelian was characterised by open vegetation with cold-adapted beetles. hence we suggest that the pre-holocene fauna from jyske rev is of eemian age. that means that the radiocarbon dates should be considered minimum ages. there are numerous examples in the literature of interglacial shells that have yielded non-finite radiocarbon ages which are usually assigned to post-mortem recrystallisation. the deposits with the pre-holocene shells consist of mediumand coarse-grained sand and fine-grained gravel. during periods of low relative sea level, these sandy deposits may have been subject to groundwater flow, which could lead to recrystallisation and introduction of younger carbon. in some areas of the dutch sector of the north sea, bones of cold-adapted mammals are common. the fauna includes terrestrial species such as mammoth (mammuthus primigenius), musk-ox (ovibos moschatus) and reindeer (rangifer tarandus), but also marine species such as walrus, white whale (delphinapterus leucas) and bearded seal (erignatus barbatus). radiocarbon dating of bones from marine mammals yielded middle weichselian ages and non-finite ages (post 2005). we suggest that the finite ages should also be regarded as minimum ages, because we find it doubtful that the sea extended this far south during the middle weichselian, when the global sea level was much lower than at present. we consider it likely that arctic marine mammals lived in the southern north sea during the early weichselian. summary during parts of the weichselian, parts of the danish north sea were land with an open, treeless, tundra-like environment with wetlands and lakes. two radiocarbon-dated arctic floras are dated to the younger dryas and the middle weichselian. a marine fauna from jyske rev gave non-finite middle weichselian ages and we conclude that it is an interglacial-type fauna probably of eemian age. acknowledgement the mapping of sand and graval deposits was funded by the danish nature agency. references bennike, o. & jensen, j.b. 2011: postglacial, relative shore-level changes in lillebælt, denmark. geological survey of denmark and greenland bulletin 23, 37–40. bennike, o., houmark-nielsen, m., böcher, j. & heiberg, e.o. 1994: a multi-disciplinary macrofossil study of middle weichselian sediments at kobbelgård, møn, denmark. palaeogeography, palaeoclimatolog y, palaeoecolog y 111, 1–15. bennike, o., jensen, j.b., lemke, w., kuijpers, a. & lomholt, s. 2004: lateand postglacial history of the great belt, denmark. boreas 33, 18–33. bennike, o., houmark-nielsen, m. & wiberg-larsen, p. 2007: a middle weichselian interstadial lake deposit on sejerø, denmark: macrofossil studies and dating. journal of quaternary science 22, 647–651. houmark-nielsen, m., bennike, o. & björck, s. 1996: terrestrial biotas and environmental changes during the late middle weichselian in north jylland, denmark. bulletin of the geological society of denmark 43, 169–176. knudsen, k.l. 1985: foraminiferal stratigraphy of quaternary deposits in the roar, skjord and dan fields, central north sea. boreas 14, 311–324. larsen, n.k., knudsen, k.l., krohn, c.f., kronborg, c., murray, a.s. & nielsen, o.b. 2009: late quaternary ice sheet, lake and sea history of southwest scandinavia – a synthesis. boreas 38, 732–761. leth, j.o. 1998: late quaternary geolog y and recent sedimentary processes of the jutland bank region, ne north sea, 173 pp. unpublished phd thesis, university of aarhus, denmark. möhl, u. 1985: the walrus, odobenus rosmarus (l.), as a “danish” faunal element during the weichsel ice age. bulletin of the geological society of denmark 34, 83–85. mortensen, m.f., henriksen, p.s. & bennike, o. 2014: living on the good soil: relationships between soils, vegetation and human settlement during the late glacial. vegetation history and archaeobotany 23, 195–205. post, k. 2005: a weichselian marine mammal assemblage from the southern north sea. deinsea 11, 21–27. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: obe@geus.dk geological survey of denmark and greenland bulletin 4, 2003, pp 17-20 17 the geological survey of denmark and greenland (geus) has for many years been involved with research, advisory and consultancy services concerning the assessment of the geothermal energy potential in denmark, in close cooperation with private and public partners. the survey’s particular responsibility has been the development of geological models to describe and predict the distribution of sandstone reservoirs suitable for geothermal exploitation. danish geothermal resources in known sandstone aquifers are estimated to be sufficient to cover household heating requirements in denmark for more than a century (sørensen et al. 1998). background utilisation of geothermal energy is a well-established technology with more than one hundred plants currently operating in europe. concerns with respect to co2 emission to the global atmosphere have led to increased interest in the utilisation of geothermal energy as one possible way of reducing the consumption of fossil fuels. in 1983, dansk olie & naturgas a/s (dong a/s) was granted a sole concession for the exploration and production of geothermal energy in the entire land area in denmark. in fig. 1. map of denmark showing the regional geothermal potential of possible aquifer formations, based on a burial depth of 1000–2500 m and a sand thickness of more than 25 m. white areas in denmark indicate that the reservoir is not present (ringkøbing–fyn high), too shallow (northernmost jutland), or too deeply buried (central part of danish basin). the locations of the thisted geothermal plant and the new geothermal site at margretheholm in copenhagen are shown. geological survey of denmark and greenland bulletin 4, 17–20 (2004) © geus, 2004 geothermal energy in denmark lars henrik nielsen, anders mathiesen and torben bidstrup 1993 and 2003, selected parts of the concession area were returned to the state in accordance with the licensing terms. the first comprehensive study of danish geothermal resources was presented by michelsen et al. (1981), which incorporates seismic and well data from the danish onshore areas, with a focus on sandstone aquifers between 2000 and 3000 m depth. the survey’s contributions to the two volumes of the atlas of geothermal resources published by the euro-pean commission (haenel & staroste 1988; hurter & haenel 2002) have presented data and information that identify areas of interest for further geothermal exploration. initially it was believed that geothermal heat could be produced from deep, hot aquifers, and in the early 1980s sandstones of the upper triassic gassum formation were tested at depths of c. 3000 m in three wells in northern jutland (fig. 1). thick sandstones were encountered, but permeability was insufficient and the results were discouraging. however, technological innovation during the past decade has shifted interest from deep and hot, but high-risk reservoirs, towards shallower aquifers with good porosity and permeability and thus the potential of producing large volumes of warm water. following heat extraction, the cold water is re-injected into the aquifer at some distance from the producing well via an injection well, in order to maintain reservoir pressure and avoid mixing the cold return water with the warm formation water. areas of potential interest four major structural features – the danish basin, the sorgenfrei–tornquist zone, the ringkøbing–fyn high and the north german basin – exert the overall control on the geothermal prospectivity of denmark. they essentially determine the distribution, thickness, facies types and burial depths of the stratigraphic units with potential reservoirs (fig. 1). the danish basin is bounded by the ringkøbing–fyn high to the south and the sorgenfrei–tornquist zone to the north-east. the upper permian – cenozoic basin-fill is 5–6.5 km thick along the basin axis, increasing locally to more than 9 km in the sorgenfrei–tornquist zone. the triassic – lower cretaceous succession has a relatively uniform thickness in most of the basin with some thinning towards the ringkøbing–fyn high. due to uplift of most of the basin and the ringkøbing–fyn high in early middle jurassic time, the triassic – lower jurassic succession is truncated by the ‘base middle jurassic unconformity’, which shows a progressively deeper truncation towards the ringkøbing–fyn high (fig. 2). on the high the lower jurassic, and in places parts of the triassic, have been eroded. regional subsidence gradually took over again in late middle – early late jurassic time and became more widespread, as shown by a progressively younger upper jurassic – lower cretaceous onlap onto the unconformity towards the high. these events have great influence on the distribution of reservoirs and the thickness of the overburden. thus, the lower triassic reservoirs may be found at moderate depths on the ringkøbing–fyn high and along the northern and southern (north german basin) flanks of the high. the sorgenfrei–tornquist zone crosses northern jutland, kattegat, the northern part of øresund and southern sweden. it is a strongly block-faulted zone with tilted palaeozoic fault blocks overlain by thick mesozoic deposits (fig. 1). this zone experienced continuous, but slow, subsidence during the middle jurassic regional uplift that affected the danish basin and the ringkøbing–fyn high, and thick paralic sandstones were deposited in the zone; these sandstones 18 fig. 2. generalised stratigraphic scheme of the danish onshore area along a nw–se-trending cross-section. the formations with potential aquifers are indicated in yellow and brown. note the pronounced erosion surfaces at the base of the middle jurassic and lower cretaceous and the progressive onlap to these surfaces. these features have a major influence on the regional distribution and burial depths of potential reservoirs. ag, stratigraphic position of the arnager grønsand formation; ngb, north german basin; rkf, ringkøbing–fyn high; skp, skagerrak platform; stz, sorgenfrei–tornquist zone. form excellent reservoirs (haldager sand formation; fig. 2). the zone is further characterised by pronounced late cretaceous – early tertiary tectonic inversion with the uplift of potential reservoirs. potential reservoirs the most promising reservoirs occur within the triassic – lower cretaceous succession (fig. 2). this succession has been the target of hydrocarbon exploration since 1935, and is thus known from about 60 deep wells and seismic data acquired over many years, although with a very variable data quality and coverage. based on regional geological studies (e.g. bertelsen 1978, 1980; michelsen et al. 2003; nielsen 2003) a number of stratigraphic units with a regional geothermal potential have been identified. these include the lower–upper triassic bunter sandstone and skagerrak formations, the upper triassic – lower jurassic gassum formation, the middle jurassic haldager sand formation and the upper jurassic – lower cretaceous frederikshavn formation. other formations may locally contain potential aquifers, such as the fine-grained sandstones of the f-ii member of the fjerritslev formation on the skagerrak– kattegat platform, and the arnager grønsand formation in easternmost zealand. the bunter sandstone formation is present south of the ringkøbing–fyn high, on parts of the high and in the danish basin. it grades into the skagerrak formation towards the north-eastern basin margin (bertelsen 1978, 1980). the bunter sandstone formation is dominated by fine-grained sandstones, mainly deposited in an arid continental environment dominated by fluvial channels, aeolian dunes and marginal marine facies. the skagerrak formation is less well known, but its marginal distribution along the northern and north-eastern basin margin, and the coarsegrained, often poorly sorted sandstones interbedded with claystones, suggest deposition in alluvial fans and lakes. the gassum formation is present in almost the entire danish area, and shows a remarkable lateral continuity with thickness generally between 100 and 150 m with a maximum of about 300 m in the sorgenfrei–tornquist zone (michelsen et al. 2003; nielsen 2003). the formation consists of fineto medium-grained, locally coarse-grained, sandstones interbedded with heteroliths, claystones and thin coals. the laterally continuous shoreface sandstones were deposited by repeated shoreline progradation. fluvial and estuarine sandstones dominate the lower–middle part of the formation in the sorgenfrei–tornquist zone. the haldager sand formation is up to 200 m thick in the sorgenfrei–tornquist zone, and shows a marked thinning towards the south-west and north-east (michelsen et al. 2003; nielsen 2003). it consists of thick, fineto coarsegrained sandstones alternating with thin siltstones, claystones and coals, deposited in shallow marine, estuarine, fluvial and lacustrine environments. the frederikshavn formation is present in the northern part of the danish area, and shows marked thickness variations (75–235 m), reaching a maximum in the sorgenfrei–tornquist zone (michelsen et al. 2003). the formation consists of siltstones and fine-grained sandstones interbedded with claystones. temperature and salinity of the formation water in these potential reservoirs increase with increasing depth. the temperature–depth relation is well established, and is rather uniformly developed over the danish area with a general gradient of about 30°c per km. the salinity shows a general increase of about 10% per km burial depth, but great variations are found. porosity and permeability decrease with increasing depth due to mechanical compaction and the formation of diagenetic minerals that reduce pore volume and pore connections. permeability is very critical, but difficult to predict since very large variations are found depending on depositional facies, provenance, mineralogical composition, burial history and position in the basin. these relationships and their mutual dependency are not fully understood, which weakens the predictive strength of the current geological models used for identifying areas of interest. however, combining the distribution of the above-described formations with an estimate of where sand thickness of the formations exceeds 25 m at depths of 1000–2500 m provides a useful indication of regional geothermal potential. figure 1 displays the potential for the land area of denmark in a general manner, and indicates which formations may warrant further investigation for geothermal energy production. existing and planned geothermal facilities the thisted plant in northern jutland is the only working geothermal plant in denmark, although a second plant is currently under construction in copenhagen (fig. 1). the thisted plant has produced heat from the gassum formation for almost 20 years without notable production or injection problems. a study of the geothermal potential in the copenhagen–malmö region was initiated in the year 2000 on behalf of dong a/s encouraged by financial support from the danish government and technological developments that make the utilisation of relatively low temperature formation water possible. the subsurface of the greater copenhagen area was previously poorly known, as no deep wells existed and seismic data coverage was very poor. new seismic data were acquired in 2001, and the survey has carried out a 19 20 geological evaluation of the geothermal potential at seven localities in the greater copenhagen area, based on integration of the new data with existing well and seismic data from denmark, øresund and southern sweden. the evaluation indicated the presence of several possible sandstone aquifers, including the gassum and bunter sandstone formations. the margretheholm location close to the centre of copenhagen was selected for further investigations, and a vertical well was drilled to about 2700 m in 2002 (fig. 3). the well encountered a promising aquifer in the bunter sandstone formation, and a second, deviated well was drilled to the same aquifer in 2003. the test results were promising, and a geothermal power plant is now under construction based on the utilisation of c. 70°c geothermal water. when established, the plant is expected to produce around 400 tj heat annually, corresponding to 1% of the total heating demand of the copenhagen area, with an option for future expansion. as a direct result of the successful efforts in copenhagen, geothermal exploration has now been resumed in other parts of the onshore danish area. geus is currently cooperating with dong a/s on the identification and assessment of several prospective sites. references bertelsen, f. 1978: the upper triassic – lower jurassic vinding and gassum formations of the norwegian–danish basin. danmarks geologiske undersøgelse serie b 3, 26 pp. bertelsen, f. 1980: lithostratigraphy and depositional history of the danish triassic. danmarks geologiske undersøgelse serie b 4, 59 pp. haenel, r. & staroste, e. (eds) 1988: atlas of geothermal resources in the european community, austria and switzerland. commission of the european communities, publication eur 11026, 74 pp., 110 plates. hurter, s. & haenel, r. (eds) 2002: atlas of geothermal resources in europe. european commission, publication eur 17811, 92 pp., 89 plates. michelsen, o. et al. 1981: kortlægning af potentielle geotermiske reservoirer i danmark. danmarks geologiske undersøgelse serie b 5, 28 pp. michelsen, o., nielsen, l.h., johannessen, p.n., andsbjerg, j. & surlyk, f. 2003: jurassic lithostratigraphy and stratigraphic development onshore and offshore denmark. in: ineson, j.r & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 147–216. nielsen, l.h. 2003: late triassic – jurassic development of the danish basin and the fennoscandian border zone, southern scandinavia. in: ineson, j.r & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 459–526. sørensen, k., nielsen, l.h., mathiesen, a. & springer, n. 1998: geotermi i danmark: geologi og ressourcer. danmarks og grønlands geologiske undersøgelse rapport 1998/123, 24 pp. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: lhn@geus.dk fig. 3. the drilling of two deep wells at margretheholm, central copenhagen. << /ascii85encodepages false /allowtransparency false /autopositionepsfiles true /autorotatepages /all /binding /left /calgrayprofile (dot gain 20%) /calrgbprofile (srgb iec61966-2.1) /calcmykprofile (u.s. web coated \050swop\051 v2) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.4 /compressobjects /tags /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjdffile false /createjobticket false /defaultrenderingintent /default 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potential storage sites. based on data from the energ y, environment and economy research institute, tsinghua university; institute of geolog y and geophysics, chinese academy of sciences; china university of mining and technolog y; research institute of petroleum exploration and development, petrochina and the china university of petroleum (cup). the outline of the shengli oilfield complex and the pipeline data are from ‘energ y map of china 2008’, © the petroleum economist ltd, london. © british geological survey. british geological survey produced the gis map. the challenge of climate change demands reduction in global co2 mission. carbon dioxide capture and storage (ccs) technology can be used to trap and store carbon dioxide gas emitted by coal-burning plants and this can reduce the world’s total co2 emission by about one quarter by 2050 (iea 2008, 2009; ipcc 2005). experience from the storage sites of sleipner in the norwegian north sea, salah in algeria, nagaoka in japan, frio in usa and other sites shows that geological structures can safely accommodate co2 produced and captured from large co2 point sources. ccs is regarded as a technology that will make power generation from coal sustainable, based on cost-effective co2 capture, transport and safe geological storage of the released co2 . china has large coal reserves (delaquil et al. 2003), and is not about to give up on this reliable source of fossil fuel. hence a large production of co2 can be expected to continue for many years. china also has a large theoretical geological carbon dioxide storage capacity in onshore areas with deep saline formations (dahowski et al. 2009). in an extensive collaborative research effort between chinese and european scientists, the coach project (cooperation action within ccs china-eu) was successful in building the expertise, developing the capture technologies and mapping transportation routes for co2, and it produced two scenarios for geological storage of co2 in china. the aim of the coach project was to initiate a durable cooperation between europe and china in response to china’s rapidly growing energy demand. the project ran from november 2006 to october 2009 and was set up and funded by the european commission under the memorandum of understanding on near zero emissions coal, to build demonstration plants in china. twenty partners consisting of eight chinese and twelve european partners evaluated the feasibility of establishing ccs in china (coach 2009). coach had four work packages dealing with (1) knowledge sharing and capacity building, (2) capture technologies, (3) permanent geological storage of co2 and (4) recommendations and guidelines for implementation. three tasks were carried out under the potential for permanent geological storage of co2 in china: the coach project niels e. poulsen © geus, 2010. geological survey of denmark and greenland bulletin 20, 95–98. open access: www.geus.dk/publications/bull 9696 third work package: (a) capacity estimates at regional level, (b) mapping of the geology and emission point sources and (c) improving methods for storage capacity assessment and site selection criteria. the geological survey of denmark and greenland and tsinghua university in beijing shared the leadership of the third work package. this short article presents the results of the work conducted on the potential for geological storage of co2 in china. background and methods aims of the carbon sequestration leadership forum the aim of co2 storage is the permanent removal of co2 from the atmosphere. the european union has supported current research on co2 capture and storage methods for more than a decade, with emphasis on capture techniques, transport and geological storage. the results of the research on geological storage are summarised in a comprehensive manual by chadwick et al. (2008). internationally recognised standards for capacity assessments were established by the carbon sequestration leadership forum (cslf) in 2004–2005 and a task force on capacity estimation standards has been active since presenting comprehensive definitions, concepts and methods (bachu et al. (2007a, b). these capacity standards were reviewed for the coach project by poulsen et al. (2009) and were used for the work on permanent co2 storage estimates in china (zeng et al. 2009). comparison of methods various methods are available for calculation of co2 storage capacity in a geological environment (koide et al. 1992, 1995; tanaka et al. 1995; shafeen et al. 2004) . the methods used in the coach project (poulsen et al. 2009) were based on bachu et al. (2007a, b) and used in the coach database to estimate the storage capacity of hydrocarbon fields. estimates made by the china university of petroleum applied tanaka et al.’s (1995) method for computing the storage capacity in the shengli oilfield complex (zeng et al. 2009). the two methods proposed by the cslf task force and tanaka et al. (1995) are basically identical in their approach. both methods are based on a volumetric approach and are applicable to site, regional and basin-scale co2 storage capacity estimates. both can be considered as ‘simple’ equation models, which try to calculate an ‘approximation’ of a possible storage capacity. the methods gave almost identical results when applied to the shengli oilfield complex (table 1). there are, however, some differences in the approach to co2 behaviour in the storage site. the cslf method works with replacement of oil, gas or formation water but does not incorporate dissolution of co2 in formation water. the method of tanaka et al. (1995), on the other hand, operates with a free phase of co2 and takes into account dissolution of co2 in the formation water, but it does not considerer the time period needed for the dissolution (poulsen et al. 2009). long term behaviour of co2 in a storage site the long term behaviour of co2 in a storage site depends on (1) a number of reservoir parameters (temperature, pressure, capillary pressure, porosity, permeability, and the cap rock permeability and capillary entry pressure), (2) the co2 composition, (3) the formation water and (4) time (chadwick et al. 2008). the solubility of co2 in formation water varies with salinity, temperature and pressure of the formation water (the brine). the dissolution of co2 in pure water increases with increasing pressure (and thus increasing depth) up to approximately 7 mpa. on the other hand, the co2 solubility in a brine decreases with increasing temperature and salinity and thus in most cases decreases with depth (bachu & adams 2003). the fig. 2. an example of a shengli oilfield production site. 97 result is that in general, the solubility of co2 in the brine decreases with increasing salinity (shafeen et al. 2004). the buoyancy of injected supercritical co2 leads to an upward gravity-driven f low of co2 towards the top of the formation where it forms a plume below the cap rock. co2 (liquid or supercritical) and water are immiscible, but co2 can dissolve to a certain extent in water. due to the slow solubility of co2 in brine, a large volume of brine is necessary to dissolve a given amount of co2. the density of the brine increases with increasing co2 dissolution and a downward gravity-driven f low will be induced by the increased density of the co2-saturated brine. on the initiation of storage, before the plume of saturated brine has reached the bottom, the overall dissolution rate is essentially constant due to rapid convective overturn (ennis-king & paterson 2007). at a later stage during storage the saturated brine forms a gravity current propagating outwards from the co2 source. activities and results the main purpose of the coach project was to prepare the way for co2 capture and storage in china. in order to achieve this, the coach partners developed an integrated gasification combined cycle capture technique. this is a coal-based energy system with hydrogen production using coal gasification, electricity generation from a combined cycle hydrogen turbine and fuel cell system, and capture of the co2. the partners have mapped emission sources and investigated potential co2 storage sites in eastern china (fig. 1, table 1). the storage potential of the selected sites was evaluated using published data or data provided by the research institute of petroleum (petrochina). particular oilfields, saline aquifers and un-exploitable coal beds were investigated. several test sites are available in some of the oilfields. the storage potential in oilfields is 10–500 mt, (pilot scale level; fig. 1, table 1). following this, a co2 transport infrastructure based on connecting co2 sources and storage sites by pipeline or ship has been suggested (fig. 1; table 1). the saline jiyang aquifers in the huimin sub-basin show storage capture at an industrial scale (around 50 gt; fig. 1, table 1), but further geological investigations are required. the security of energy supply is a key consideration in china, and enhanced oil recovery (eor) could be an option. some of the oilfields in the dagang and shengli oilfield complexes may be suitable for an enhanced oil recovery pilot project. injecting co2 into oilfields approaching depletion will not only store co2, but may also enhance or prolong oil recovery (coach 2009). the coals of the kailuan coalfield have low permeability and probably low injectivity, but a high theoretical ability to adsorb co2 (fig. 1, table 1). in general, however, the storage capacity in coal seams is uncertain. on the other hand, it has been demonstrated that injection of co2 into coal beds can lead to methane production (enhanced coal bed methane recovery; yu et al. 2007). at the same time it is a very attractive option for geological co2 storage as co2 is strongly absorbed onto the coal. two scenarios for possible co2 capture and storage demonstration projects have been proposed by work package 4, based on the mapping of emission point sources, geology, and capacity estimates by work package 3 together with economic analyses. the first scenario is for a pilot scale site with 0.1–1 mt co2/year stored in the dagang or shengli oilfield complexes. the second scenario is intended for industrialscale storage at 2–3 mt co2/year, which could be accommodated in the shengli oilfield complex or potentially in the saline formations in the huimin sub-basin. the pilot scale scenarios focus initially on enhanced oil recovery for storage where this is feasible. the large-scale option could begin with enhanced oil recovery but would need to switch to saline 472 mt using cslf methodology and 463 mt using cup method table 1. summary of geological sites assessed for geological storage of co2 after zeng et al. (2009) storage site capacity injectivity seal dagang oilfield complex selected 7 fields 22 mt largest gangdong field 10 mt 1000 md some compartmentalisation by faulting and stratigraphy mudstones shengli oilfield complex 1000–2500 md some compartmentalisation by faulting and stratigraphy lower jurassic mudstones huimin sag aquifers (jiyang) for huimin sub-basin 50 gt for selected troughs in sub-basin 0.7 gt permeability around 1600 md in neighbouring oilfields mudstones of minghuanzhen fm kailuan coalfield 504 gt adsorbed onto coal and 38 100 mt void capacity permeability generally low 3.7 md in taiyuan formation and 0.1 md in shanxi and xiashihezi fm mudstones 9898 aquifer storage once the potential reservoir and sealing formations have been adequately investigated. both scenarios are based on capture of co2 from the tianjin greengen power plant (coach 2009). final remarks in 2005 construction began of the coal-based tianjin greengen power plant (fig. 1) and electricity production started in 2009. it will be the first near-zero emission power plant in china. research over the next decade is expected to develop and demonstrate the efficiency of coal-based power generation, mostly by recycling energy lost in the process. the goal is to achieve sustainability of coal-based power generation. the project concludes that there is significant potential to develop carbon dioxide capture and storage technologies in china and to make major reductions in co2 emissions over the next century. experience from the storage sites sleipner in the norwegian north sea, in salah in algeria, nagaoka in japan, frio in usa and other sites shows that geological structures can safely accommodate co2 produced and captured from large point sources. thus, geological storage of co2 can contribute considerably to the reduction of co2 emission in china and other countries. acknowledgements coach was funded as part of the 6th framework programme for research by the european commission (project no. 038966). nikki smith from the british geological survey is thanked for producing the map used in fig. 1. references bachu, s., & adams, j. j. 2003: sequestration of co2 in geological media in response to climate change: capacity of deep saline aquifers to sequester co2 in solution. energ y conversion and management 44, 3151–3175. bachu, s., bonijoly, d., bradshaw, j., burruss, r., christensen, n.p. holloway, s., & mathiassen, o.m. 2007a: estimation of co2 storage capacity in geological media – phase 2. work under the auspices of the carbon sequestration leadership forum (www.cslforum.org). final report from the task force for review and identification of standards for co2 storage capacity estimation, 43 pp. washington: carbon sequestration leadership forum. bachu, s., bonijoly, d., bradshaw, j., burruss, r., holloway, s., christensen, n.p. & mathiassen, o.m. 2007b: co2 storage capacity estimation: methodolog y and gaps. international journal of greenhouse gas control 1, 430–443. chadwick, a., arts, r., bernstone, c., may, f., thibeau, s. & zweigel, p. (eds) 2008: best practice for the storage of co2 in saline aquifers – observations and guidelines from the sacs and co2stor e projects. british geological survey occasional publication 14, 267 pp. coach 2009: project n° 038966: coach, cooperation action within ccs china-eu, executive report, 38 pp. dahowski, r.t., li, x., davidson, c.l., wei, n., dooley, j.j. & gentile, r.h. 2009: a preliminary cost curve assessment of carbon dioxide capture and storage potential in china. energ y procedia 1, 2849–2856. delaquil, o., wenying, c., & larson, e.d. 2003: modeling china’s energ y future. energ y for sustainable development 7, 40–56. ennis-king, j. & paterson, l. 2007: coupling of geochemical reactions and convective mixing in the long-term geological storage of carbon dioxide. international journal of greenhouse gas control 1, 86–93. iea (international energ y agency) 2008: energ y technolog y perspectives: scenarios and strategies to 2050, 650 pp. paris, france. iea (international energ y agency) 2009: technolog y roadmap. wind energ y, 52 pp. paris: international energ y agency. koide, h., tazaki, y., noguchi, y., nakayama, s., iijima, m., ito, k., & shindo, y. 1992: subterranean containment and long term storage of carbon dioxide in unused aquifers and in depleted natural gas reservoirs. energ y conversion management 33, 619–626. koide, h., takahashi, m., tsukamoto. h. & shindo, y. 1995: self-trapping mechanism of carbon dioxide in aquifer disposal. energ y conversion management 36, 505–508. metz, b. et al. (eds) 2005: carbon dioxide capture and storage. ipcc 2005, 431 pp. cambridge university press. poulsen, n.e., chen, w., dai, s., ding, g., kirk, k., li, m., zeng, r., vangkilde-pedersen, t., vincent, c.j. & vosgerau, h.j. 2009: d3.3. improving methodologies for storage capacity assessment and site selection criteria. eu project no. 038966. coach work package 3 report. eu deliverable d3.3, 45 pp. eu coach project, brussels. shafeen, a., croiset, e., douglas, p.l. & chatzis, i. 2004: co2 sequestration in ontario, canada. part i: storage evaluation of potential reservoirs. energ y conversion and management 45, 2645–2659. tanaka, s., koide, h. & sasagawa, a. 1994: possibility of underground co2 sequestration in japan. energ y conversion and management 36, 527–530. yu, h., zhou, g., fan, w. & ye, j. 2007: predicted co2 enhanced coalbed methane recovery and co2 sequestration in china. international journal of coal geolog y 71, 345–357. zeng, r., li m., dai, s., zhang, b., ding, g. & vincent, c. 2009: assessment of co2 storage potential in the dagang oilfield, shengli oilfield and kailuan coalfield. coach work package 3 report. eu deliverable d3.1, 45 pp. eu coach project, brussels. author’s address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: nep@geus.dk geological survey of denmark and greenland bulletin 31, 2014, 35-38 35 palynological and microfossil biostratigraphy and palaeoecology over the paleocene–eocene transition, femern bælt, northern germany patrick alexander richardt and emma sheldon a palynological and micropalaeontological biostratigraphic and palaeoecological investigation has been carried out on the paleocene–eocene transition of core 10.a.057 from the femern bælt (fig. 1). initial investigations of boreholes from the femern bælt indicated that core 10.a.057 included a thick succession of upper paleocene – lower eocene clay (sheldon & nøhr hansen 2010; rambøll arup jv 2011; fig 2). complete paleocene–eocene sections have been described from jylland and the storebælt (heilmann-clausen 1985, laursen & andersen 1997; laursen & king 2000, nielsen et al. 1986), but no detailed studies have been published on these successions from the femern bælt. boreholes were drilled on lolland in denmark, under the femern bælt and on fehmarn island, germany from 2009 to 2011 as part of geological and geophysical investigations performed in preparation for the construction of a fixed road and rail link connecting denmark and germany. the boreholes penetrated campanian – upper eocene strata, overlain by quaternary deposits. borehole 10.a.057 is located in the southern part of the femern bælt (figs 1, 2). geology and palaeoecology the femern bælt is located in the german basin south of the ringkøbing–fyn high. during the late cretaceous, the danish area was characterised by an epicontinental sea resulting in chalk deposition. the sea became more restricted in the early–middle paleocene and several highs bordered the marine area (clausen & huuse 2002). transgression during the selandian resulted in clastic marine sedimentation and the north sea, denmark and the german basin formed a partially enclosed shelf area. during the late paleocene and early eocene, sediment deposition occurred in a relatively deep marine basin, at some distance from the shore. intense volcanic activity caused by the opening of the north atlantic resulted in deposition of ash and tuff layers during this period. the present distribution of the upper part of the palaeogene sediments is a result of erosion and glaciotectonic deformation during the quaternary (fig. 2). in the 10.a.057 core, the very fine-grained clays of the upper paleocene holmehus formation and østerrende clay (informal lithostratigraphic unit of nielsen et al. 1986) are overlain by the lower eocene ølst formation, which is characterised by dark grey clay with abundant layers of black volcanic ash (heilmann-clausen et al. 1985). © 2014 geus. geological survey of denmark and greenland bulletin 31, 35–38. open access: www.geus.dk/publications/bull ringkøbing–fyn high 100 km 14°e 57°n 55° sweden denmark germany german basin norway lolland fehmarn femern bælt 10°e 10.a.057 viborg-1 bovlstrup jylland storebælt north sea stolle klint fig. 1. map of denmark and northern germany showing the location of the planned fixed road and rail link across the femern bælt and the location of borehole 10.a.057 at 54°31.8´n, 11°15.9´e. fehmarn lolland10.a.057 3 km 0 m 50 100 150 quaternary deposits folded and faulted palaeogene clay palaeogene cretaceous fig. 2. sketch south–north cross-section of the femern bælt area showing the location of borehole 10.a.057. 3636 biostratigraphy a total of 19 samples were analysed for dinocysts, diatoms, foraminifers and radiolarians (figs 3, 4). the danish paleocene–eocene zonation of the viborg-1 cored borehole (heilmann-clausen 1985) and the north sea zonation of mudge & bujak (1996) were used for the dinoflagellate cyst stratigraphy. the north sea cenozoic zonation of king (1989) was used for microfossils. dinocysts the samples from 100.49 to 90.31 m are assigned to the areoligera gippingensis acme subzone p5a (mudge & bujak 1996; fig. 3). this subzone represents the uppermost part of zone v4 (heilmann-clausen 1985) and is equivalent to the uppermost part of the holmehus formation (mudge & bujak 1996). p5a is characterised by an acme of a. gippingensis and the presence of eisenackia margarita. the top of p5a is defined by the top of the a. gippingensis acme. nielsen et al. (1986) found low abundances of deflandrea oebisfeldensis in v4 in a borehole from the storebælt but heilmann-clausen (1985) did not find this species in v4. the boundary between v4 and the overlying v5 is tentatively placed, since relatively high abundances of a. gippingensis continue into v5. the samples from 90.31 to 79.42 m are assigned to the e. margarita subzone p5b (v5) based on the last occurrence (lo) of e. margarita (mudge & bujak 1996). e. margarita has its lo in the østerrende clay (nielsen et al. 1986). zone v6, which is characterised by a dominance of the warm-water genus apectodinium and an acme of apectofig. 3. range chart showing the distribution (number of specimens) of dinocysts, diatoms, foraminifers and radiolarians from borehole 10.a.057. p: pyrite, a: ash layer. observed outside counting very rare (1) rare (2–4) common (5–14) abundant (15–49) dominant (>50) c hr on os tr at ig ra ph y ea rl y eo ce ne la te p al eo ce ne li th os tr at ig ra ph y ø lst f or m at io n h ol m eh us f or m at io n ø st er re nd e c lay d an ish v ib or g di no cy st z on at io n v7 e1 b v5 v4 p5 a p5 b n or th s ea m ic ro fo ss il zo ne s m ud ge & b uj ak 1 99 4, b uj ak & m ud ge 1 99 6 n sp 4 / n sa 2 n sp 3 / n sa 1b ac ho m os ph ae ra s pp . co rd os ph ae rid iu m s pp . d ef la nd re a oe bi sfe ld en sis d in oc ys t s pp . m icr od in iu m c f. or na tu m pa la eo te tra di ni um m in us cu lu m sp in ife rit es ra m os us sp in ife rit es s pp . h ys tr ich os ph ae rid iu m tu bi fe ru m im pa gi di ni um s pp . o lig os ph ae rid iu m c om pl ex th al as sip ho ra d el ica ta ac ho m os ph ae ra c ra ss ip el lis gl ap hy ro cy st a or di na ta gl ap hy ro cy st a sp p. gl ap hy ro cy st a di va ric at a h ys tr ich os ph ae rid iu m tu bi fe ru m b re vis pi nu m al iso cy st a sp . 2 cr ib ro pe rid in iu m s pp . o pe rc ul od in iu m s pp . cr ib ro pe rid in iu m te nu ita bu la tu m u ni nd en tif ie d pe ri di no id c ys ts ac ho m os ph ae ra a lci co rn u ar eo lig er a gi pp in ge ns is ac hi lle od in iu m la tis pi no su m ei se na ck ia m ar ga rit a pa la eo cy st od in iu m li di ae ar eo lig er a sp p. dinoflagellate cysts d ia to m s pp . fe ne st re lla a nt iq ua co sc in od isc us m or sia nu s m oe lle ri th al as sio rir op sis w itt ia na au la co di sc us a llo rg ei d ia to m s pp . f la t s ilic eo us h em ia ul us s pp . tr in ac ria re gi na d ia to m s pp . f la t p yr iti se d fe ne st re lla a nt iq ua (s m al l) diatoms sp iro pl ec ta m m in a sp ec ta bi lis sp iro pl ec ta m m in a sp p. ag gl ut . f or am in ife ra in de t am m od isc us c re ta ce us gl om os pi ra c ha ro id es rh ab da m m in a sp p. ba th ys ip ho n m icr or ha ph id us ba th ys ip ho n sp p. cy cla m m in a am pl ec te ns cy cla m m in a ro tu nd id or sa ta cy st am m in a pa uc ilo cu la ta h ap lo ph ra gm oi de s sp p. h ap lo ph ra gm oi de s wa lte ri h or m os in a sp p. la br os pi ra s cit ul a m ar ss on el la o xy co na re cu rv oi de s sp p. re op ha x sp p. rh ab da m m in a ro bu st a agglutinating benthic foraminifers ra di ol ar ia ns ce no di sc us s pp . 100 95 90 85 80 75 70 65 60 55 p p p p p p p p p p a a a p d ep th (m ) 37 dinium augustum, was not found in this study. a missing core section from 79.42 to 73.36 m could represent zone v6, but v6 has not been observed previously in the femern bælt area (c. heilmann-clausen & h. nøhr-hansen, personal communication 2013). however, v6 is present in the stolle klint clay, north-western jylland. the base of the apectodinium acme in the earliest eocene is a global event and is coupled with a carbon isotope excursion denoting the start of the paleocene–eocene thermal maximum (petm). the samples from 73.36 to 51.81 m are referred to early eocene d. oebisfeldensis acme subzone e1b (upper v7; bujak & mudge 1994). the interval from 66.18 to 51.81 m is characterised by a minor acme of glaphyrocysta divaricata and a high abundance of microdinium cf. ornatum (fig. 3). zone v7 is found in the upper part of the ølst formation (heilmann-clausen 1985). foraminifers and diatoms the assemblages mainly consist of poorly preserved agglutinating benthic foraminifers and diatoms. samples from 100.49 to 79.42 m are assigned to zone nsa1b. most samples only contain few foraminifers, but two samples from the upper c. 2 m contain rich faunas with spiroplectammina spectabilis, labrospira scitula, ammodiscus cretaceus, glomospira charoides, marsonella oxycona, cystammina pauciloculata, recurvoides spp., hormosina spp., rhabdammina robusta, cyclammina rotundidorsata, haplophragmoides walteri, bathysiphon spp. and cyclammina amplectens. this assemblage is known as the ‘rhabdammina biofacies’. the shift from low to higher diversity benthic assemblages in nsa1b was also noted in the bovlstrup borehole, eastern jylland (laursen & andersen 1997) and was interpreted as a shift from very poor to slightly improved life conditions on the sea floor. a low-diversity diatom flora with pyritised fenestrella antiqua (var. small) and diatom spp. (flat) is also present, in addition to sponge debris and radiolarians (cenodiscus spp.). nsa1 is assigned to the holmehus formation in denmark (king 1989). samples from 73.36 to 51.81 m are assigned to zone nsp4. the assemblages are dominated by resting spores of centric diatoms, comprising coscinodiscus morsianus moelleri, fenestrella antiqua, diatom spp. (flat), thalassiophora wittiana, trinacria regina, aulacodiscus allorgei and hemiaulus spp. from 66.18 to 56.87 m pyritised and translucent diatoms occur in equal numbers; above and below this level only pyritised specimens occur. this difference in preservation is probably due to variations in the oxygen level in the water column and the amount of sulphide present in the sediment (de jonghe et al. 2011). zone nsp4 also includes bryozoan fig. 4. selected fossils: a–c and f–i: foraminifers, d, e, j, k: diatoms, l–r: dinocysts. a: ammodiscus cretaceous. b: cyclammina amplectens. c: cystammina pauciloculata. d: coscinodiscus morsianus moelleri. e: fenestrella antiqua. f: glomospira charoides. g: haplophragmoides walteri. h: labrospira scitula (front). i: labrospira scitula (side). j: trinacria regina. k: trinacria regina (siliceous). l: microdinium cf. ornatum. m: piece of dinocyst. n: areoligera gippingensis. o: def landrea oebisfeldensis. p: eisenackia margarita. q: hystrichospharidium tubiferum. r: unidentifiable peridinoid cyst. scale bars: 100 µm (a–k), 20 µm (l–r). a b c d e f g h i j k m n o p l q r 3838 fragments, fish teeth, inoceramus fragments, sponge spicules and rare agglutinating foraminifers. nsp4 is assigned to the early eocene ølst formation (king 1989). discussion and conclusions a dominance of agglutinating foraminifers of the ‘rhabdammina biofacies’ in subzone nsa1b suggests a middle to lower bathyal palaeoenvironment characterised by restricted water circulation, with low oxygen levels and a reducing environment at the sea floor ( jones & charnock 1985; king 1989). the low oxygen level may have led to decreasing degradation of organic matter by bacteria and benthic organisms, giving rise to the dark grey colour of the holmehus formation compared with those described by heilmann-clausen et al. (1985). a relatively high abundance of the supposed heterotrophic dinoflagellate deflandrea oebisfeldensis and the rich diatom flora in the ølst formation may be due to increased productivity in the surface layers perhaps due to enhanced upwelling in coastal areas. the rich diatom flora, preserved as resting spores, also suggests stressed sea-surface and seabed conditions, perhaps due to volcanic ash falls and periods of anoxia (bidgood et al. 1999). the scarcity of agglutinating foraminifers is probably due to reducing conditions at the sea floor. schiøler et al. (2007) suggested that the balder formation (the north sea equivalent of the ølst formation) was deposited in a restricted marine environment at upper bathyal depths with dysoxic to anoxic bottom conditions. in core 10.a.057, palynological biostratigraphy indicates that zone v6 is absent, either due to erosion or non-deposition, therefore the paleocene–eocene thermal maximum is not preserved at this location. a hiatus with v6 missing was noted in the lillebælt area (heilmann-clausen et al. 1985), supporting the femern bælt data. however it is possible that zone v6 is found in the missing core interval between 79.42 and 73.36 m. references bidgood, m.d., mitlehner, a.g., jones, g.d. & jutson, d.j. 1999: towards a stable and agreed nomenclature for north sea tertiary diatom floras – the ‘coscinodiscus’ problem. in: jones, r.w. & simmons, m.d. (eds): biostratigraphy in production and development geolog y. geological society (london) special publications 152, 139–153. bujak, j. & mudge, d. 1994: a high-resolution north sea eocene dinocyst zonation. journal of the geological society 151, 449-462. clausen, o.r. & huuse, m. 2002: mid-paleocene palaeogeograhpy of the danish area. bulletin of the geological society of denmark 49, 171–186. de jonghe, a., hart, m.b., grimes, s.t., mitlehner, a.g., price, g.d. & smart c.w. 2011: middle eocene diatoms from whitecliff bay, isle of wight, england: stratigraphy and preservation. proceedings of the geologists’ association 122, 472–483. heilmann-clausen, c. 1985: dinoflagellate stratigraphy of the uppermost danian to ypresian in the viborg 1 borehole, central jylland, denmark. danmarks geologiske undersøgelse serie a 7, 69 pp. heilmann-clausen, c., nielsen, o.b. & gersner, f. 1985: lithostratigraphy and depositional environments in the upper paleocene and eocene of denmark. bulletin of the geological society of denmark 33, 287–323. jones r.w. & charnock, m.a. 1985: ‘morphogroups’ of agglutinating foraminifera: their life positions, feeding habits and potential applicability in (paleo)ecological studies. revue de paléobiologie 4, 311–320. king, c. 1989. cenozoic of the north sea. in: jenkins, d.g. & murray, j.w. (eds): stratigraphical atlas of fossil foraminifera, 418–489. chichester: ellis horwood. laursen, g.v. & andersen, s.b. 1997: a late palaeocene–early eocene benthic foraminiferal record from bovlstrup, denmark, showing a remarkable agglutinated fauna. journal of micropalaeontolog y 16, 19–29. laursen, g.v. & king, c. 2000: preliminary results of a foraminiferal analysis of a core from østerrende, denmark. geologiska föreningen i stockholm förhandlingar (gff) 122, 92 only. mudge, d.c. & bujak, j.p. 1996: palaeocene biostratigraphy and sequence stratigraphy of the uk central north sea. marine and petroleum geolog y 13, 295–312. nielsen, o.b., baumann, j., zhang, d., heilmann-clausen, c. & larsen, g. 1986: tertiary deposits in store bælt. the tertiary section of borehole d.g.i. 83101, østerenden, storebælt, denmark. in: møller, j.t. (ed.): twentyfive years of geolog y in aarhus. geoskrifter 24, 237-249. department of geoscience, aarhus university, denmark. rambøll arup jv 2011: summary of geological conditions. geotechnical data report 01.3-002, 53 pp. virum: femern a/s. schiøler, p. et al. 2007: lithostratigraphy of the palaeogene – lower neogene succession of the danish north sea. geological survey of denmark and greenland bulletin 12, 77 pp. sheldon, e. & nøhr-hansen, h. 2010: fehmarn belt fixed link pre-quaternary biostratigraphy – a final status report for ramboll arup joint venture. danmarks og grønlands geologiske undersøgelse rapport 2010/134, 53 pp. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: par@geus.dk geological survey of denmark and greenland bulletin 17, 2009, 21-24 the triassic – lower cretaceous sedimentary succession of the norwegian–danish basin has for a long time been of exploration interest, and numerous studies have been carried out. however, high-resolution correlation within the basin remains necessary, especially between the danish and nor we gian parts of the basin. a variety of lithoand biostratigraphic schemes have been applied to the succession over the years, but lack of consistency in terminology has often led to confusing interpretations of the geological development. in this study a sequence stratigraphic scheme has been developed for the danish basin and a compiled palynological event stratigraphy is applied to a number of wells connecting the danish and norwegian parts of the basin and new marker horizons are identified. one of the aims of this study is to reach consistency in order to facilitate correlation within the basin and we also emphasise the recognition of a potentially important mid-triassic event in the basin. geological setting the intracratonic permian–cenozoic norwegian–danish basin is bounded to the south by the ringkøbing–fyn high and to the north by the strongly faulted sorgenfrei–tornquist zone (fig. 1). the basin was formed by late carboniferous – early permian crustal extension followed by thermal sagging, local faulting and salt tectonics. the syn-rift succession consists of rotliegendes volcaniclastic rocks, alluvial conglomerates and sandstones as well as lacustrine mudstones. the overlying zechstein–cenozoic post-rift succession consists of two major sequences separated by an early middle jurassic unconformity that reflects regional uplift and erosion (nielsen 2003). the lower sequence comprises zechstein salt, triassic sandstones, mudstones, marls and carbonates and lower jurassic claystones, while the upper sequence encompasses middle jurassic – lower cretaceous clastic rocks, ladinian palynofloras in the norwegian–danish basin: a regional marker reflecting a climate change sofie lindström, henrik vosgerau, stefan piasecki, lars henrik nielsen, karen dybkjær and mikael erlström © geus, 2009. geological survey of denmark and greenland bulletin 17, 21–24. available at: www.geus.dk/publications/bull 21 100 km land redbeds sea fault a-2 höllviken-2 ffc-1/2 8/11-1 felicia-1 100 m 8/11-1 west 9/11-1 10/7-1 11/10-1 inez-1 f-1x east k-1x felicia-1 børglum fm flyvbjerg fm haldager fm fj er ri ts le v fm gassum fm vinding fm oddesund fm skagerrak fm f-iii f-iv f-ii f-i gr sonic gr sonicgr sonic gr sonic gr sonic gr sonic gr sonic gr sonicflyvbjerg fm gassum fm marine mudstones shallow marine sandstones and siltstones, offshore mudstones paralic and non-marine sandstones, mudstones and coals alluvial conglomerates, sandstones and lacustrine mudstones marine calcareous claystones, carbonates ladinian palynofloras sabkhas and lacustrine calcareous, evaporitic mudstones danish wellsnorwegian wells fyn high ringkøbing – norwegian–danish basin sorgenfrei–tornquist zone fig. 1. correlation of middle triassic to upper jurassic strata along a transect. the map shows the location of the wells and the middle triassic palaeogeography. gr, gamma ray log; sonic, sonic log. rosa_2008:rosa-2008 01/07/09 15:48 side 21 upper cretaceous chalk and cenozoic clastic rocks. large parts of the lower sequence are difficult to date accurately by biostratigraphy owing to the predominantly continental strata deposited during a hot and arid climate, whereas the upper sequence is dominated by marine fossiliferous de po sits, which are easier to date. the investigated succession and the stratigraphic approach the principal reservoir rocks and potential source rocks of the basin were formed during late triassic – late jurassic times (petersen et al. 2008). different lithostratigraphic terminologies are used for the norwegian and danish areas (fig. 2). an inconsistent mixture of lithostratigraphic names from both norwegian and danish schemes is commonly used by the operators in well reports, and in some cases, lithostratigraphic names normally applied to units in the norwegian central graben further contribute to the confusion. a robust sequence stratigraphic scheme established in the danish basin by nielsen (2003) and a compiled palynostratigraphic event scheme are applied to a number of wells (felicia-1, k-1, f-1, inez-1, 11/10-1, 10/7-1, 9/11-1 and 8/11-1) situated along an e–w trending transect from the fjerritslev fault nw of jylland to the border of the norwegian central graben (fig. 1). based on characteristic well-log patterns supported by lithological descriptions from well reports, formation tops and sequence stratigraphic surfaces were identified and integrated with palynological events identified in this study. the latter events are based on established spore–pollen and dinoflagellate cyst stratigraphies for the triassic – early cretaceous of western europe. selected im portant palynostratigraphic events and sequence stratigraphic surfaces are shown in fig. 2. 22 oddesund fm se ri es sy st em stage ju ra ss ic t ri as si c norwegian–danish basin børglum formation flyvbjerg formation haldager sand formation gassum formation vinding formation skagerrak formation muschelkalk fm frederikshavn formationvolgian kimmeridgian oxfordian callovian bathonian bajocian aalenian toarcian pliensbachian sinemurian hettangian rhaetian norian carnian ladinian fjerritslev fm sauda fm tau fm egersund fm sandness fm bryne fm u pp er m id dl e m id dl e lo w er u pp er mfs 15 sb 19 sb 20 sb 21 sb 22 sb 23 sb 24 sb 15 sb 11 mfs 7 mfs 1 sb 5 ts 1 ts 22 ts 23 sb 9 paralic and non-marine sandstones, siltstones, mudstones and coals marine mudstones and siltstones unconformity shallow marine sandstones and siltstones, offshore mudstones alluvial sandstones and lacustrine mudstone marine calcareous claystones, carbonates hiatus sequence boundary maximum flooding surface transgressive surface danish part norwegian part selected key surfaces last occurrence datums gassum fm skagerrak formation smith bank formation mfs ts sb fjerritslev formation oligosphaeridium patulum gleicheniidites conspiciendus nannoceratopsis gracilis mancodinium semitabulatum kekryphalospora distincta parvocysta spp. endoscrinium luridum gonyaulacysta jurassic glossodinium dimorphum, dichadogonyaulax pannea chasmatosporites hians quadraeculina anellaeformis mendicodinium reticulatum neoraistrickia gristhorpensis liasidium variabile dapcodinium priscum rhaetipollis germanicus rhaerogonyallax rhaetica illinites chitinoides enzonalasporites vigens vallasporites ignaciii camerosporites secatus, duplicisporites granulatus triadispora verrucata fig. 2. stratigraphical scheme showing upper tri assic and jurassic litho stratigraphic units, selected sequence strati graphic boundaries and selected last occurrence datums of selected taxa in the norwe gian–danish basin. rosa_2008:rosa-2008 01/07/09 15:48 side 22 the results of the correlation show that lithostratigraphic units and key sequence stratigraphic surfaces can be followed across the danish and norwegian areas indicating that the general depositional development along the transect largely follows the pattern described by nielsen (2003). hence, the sequence stratigraphic and lithostratigraphic schemes established for the danish part were successfully applied to the norwegian wells, as exemplified in figs 1, 2. however, the lack of readily recognisable sequence stratigraphic key surfaces and biostratigraphic events within the middle – upper triassic succession is a major problem for reliable stratigraphic analyses. the middle triassic – an unsuitable climate for palynomorph preservation during the middle triassic the norwegian–danish basin was situated around 35°n. the arid to semi-arid conditions that had prevailed during the early triassic continued, as signified by mainly fluvial and lacustrine, heterogeneous, siliciclastic rocks of the skagerrak formation (michelsen & clausen 2002). marine calcareous mudstones and carbonates of the muschelkalk formation in the north german basin ex panded northwards during a transgressive event in the anisian to early ladinian (michelsen & clausen 2002). arid to semi-arid climatic conditions continued during early late triassic times, with deposition of variegated, calcareous, anhydritic and pyritic mudstones in sabkhas and ephemeral lakes. in the deep central part of the basin more permanent lakes were established. the deposits are included in the oddesund (danish area) and smith bank (norwegian area) formations. towards the basin margins in the north and north-east these deposits pass into alluvial fans and fluvial sediments of the skagerrak formation. the combination of large lateral variations in depositional environment and the absence of extensive marine-flooding surfaces and marked unconformities hinder identification of reliable and regional sequence stratigraphic key surfaces. whereas middle to lower upper triassic successions of the arctic, alpine and tethys regions show evidence of fairly rich and diverse vegetation, the pre-rhaetian triassic redbeds of the norwegian–danish basin only contain sparse palyno morphs. however, this does not necessarily mean that there were no plants growing in the area at the time of deposition. most arid areas today host some vegetation adapted to such a hostile climate, but conditions for preservation of palynomorphs are generally poor due to oxidation of the sediments. nevertheless, the present study indicates that during a restricted interval in the latest middle triassic the area hosted a relatively rich vegetation and the climatic conditions in the area were better suited for palynomorph preservation. ladinian spore–pollen floras well-preserved, typical middle triassic palynofloras were found in ditch cuttings from the lowermost part of the oddesund formation in the felicia-1 well, and in the lower part of the skagerrak formation in k-1 and 11/10-1. these assemblages are distinguished from caved rhaetian–creta ceous material by their generally darker colour. all the assemblages contain illinites chitonoides, a pollen species that has a last appearance datum at the top of the ladinian in northern europe, and within the carnian in the arctic region (de graziansky et al. 1998). the assemblage from felicia-1 is dominated by the bisaccate pollen ovalipollis ovalis /pseudoalatus, which has its first common appearance datum at the base of the late ladinian (de graziansky et al. 1998). in addition, members of protodiploxypinus, e.g. p. fastidioides and p. macroverrucosus, and triadispora, mainly t. crassa, t. plicata, t. verrucata, are common constituents of the palynofloras. the co-occurrence of angustisulcites klausii, kuglerina meieri, podosporites amicus, staurosaccites quadrifidus, rimaesporites aquilonalis, ara tri sporites spp., camerosporites secatus, c. verrucatus, dupli ci sporites granulatus and enzonalasporites vigens also suggests a late ladinian age (de graziansky et al. 1998; schulz & heu nisch 2005). the presence in felicia-1 of the typical triassic chlorococcalean coenobium plaesiodictyon mosellanum with a known stratigraphical range from late anisian to latest norian indicates brackish to freshwater conditions. in the easternmost parts of the norwegian–danish basin comparable palynofloras are present in core samples from the höllviken-2 well and two other wells in southern sweden. the höllviken-2 palynoflora is dominated by monolete (ara trisporites spp.) and trilete (e.g. calamospora spp. and ana pi culatisporites spp.) spores, but bisaccate pollen are also abun dant and diverse. both abundant aratrisporites spores and species of protodiploxypinus suggest a latest muschelkalk – early keuper (i.e. ladinian) age, and this range is further limited to early keuper by the presence of retisulcites perforatus (last appearance datum in earliest carnian), nevesisporites lubricus, and ovalipollis brutus. a banana-shaped acritarch, dactylofusa sp., is present in the palynoflora from fcc-1. comparable palynofloral assemblages were found in well a-2 in the danish central graben containing e.g. aratri sporites saturni, angustisulcites klausii, illinites chitonoides, tria dispora spp., protodiploxypinus fastidioides, p. granulatus, pro to diploxy pinus spp., and striatoabieites aytugii (bertelsen 1975). thus, typical ladinian palynofloras appear to be present with in a relatively restricted time interval along the northern margin of the mid-triassic muschelkalk sea. 23 rosa_2008:rosa-2008 01/07/09 15:48 side 23 24 remarks on stratigraphy, environment and climate the höllviken-2 assemblages are recorded in a succession of dark, fine-grained sediments (maglarp-c member) with fossiliferous intervals containing fossil fish, ostracods and characean algae. previous biostratigraphy based on the latter correlates the succession with late muschelkalk to early keuper, i.e. mainly of ladinian age (kozur 1974). the characean algae suggest lim nic to possibly brackish environments, while the fish fauna vary from limnish-brackish (e.g. paleobates spp.) to fully marine (e.g. birgeria spp. and hybodus spp.). the ostracods (bairdia spp.) indicate warm, shallow littoral environments. hence, the combined macrofossil evidence suggests a shallow marine environment with brackish to limnic lagoons behind the coast. the palynoflora recorded in the höllviken-2 core supports a ladinian age. all the contemporaneous palynofloras described here contain several elements typical of warm and dry conditions. for instance, aratrisporites is a common constituent in arid to semi-arid triassic palynofloras worldwide. the parent plants, pleuromeiacean lycopsids, appear to have been opportunistic and saline-tolerant inhabitants of intertidal environments (retallack 1975). the taeniate bisaccates, e.g. lunatisporites and striatoabieites, are generally regarded to have been produced by pteridosperms, and adapted to warm and dry conditions. the bisaccate pollen of triadispora, protodiploxypinus, ovalipollis, illinites and staurosaccites, as well as the monosaccate pollen enzonalasporites, and pollen of the circumpolles group, i.e. duplicisporites and camerosporites, are all believed to come from conifers. the circumpolles group is only recorded in some of the investigated assemblages. they are regarded as relatives to the cheirolepids, a group of conifers often associated with warm and dry conditions. in palynofloras of similar age from central and south europe, pollen of the circumpolles group tend to be much more abundant. the diverse ladinian spore–pollen flora described above indicates a generally warm and dry climate, but the diversity and preservation suggest a change towards more humid conditions favouring preservation of palynomorphs during this interval. in germany and poland the uppermost ladinian, known as the lettenkeuper, is interpreted as reflecting more humid conditions. it seems plausible that the palynofloras recorded in this study reflect the same change to more humid conditions. conclusions the recorded ladinian palynofloras from the maglarp-c member in southern sweden, the lowermost oddesund formation in denmark, and from the middle skagerrak formation in both denmark and norway, enable correlation between these units in the otherwise poorly dated triassic succession in the norwegian–danish basin. the fact that the palynofloral assemblages are recognisable even in ditch cutting material of exploration wells makes them very useful markers. the palynoflora contains many elements indicating a warm and dry climate, and deposition in fresh to brackish water in coastal environments. the preservation of the palynoflora probably reflects a climatic event with a change to more humid conditions, similar to that recorded in northern and central europe. acknowledgement we thank talisman energy norway a/s for allowing us to publish results from the norwegian wells. references bertelsen, f. 1975: triassic palynology and stratigraphy of some danish north sea boreholes. danmarks geologiske undersøgelse årbog 1974, 17–32. de graziansky, p.-c., hardenbol, j., jacquin, t. & vail, p.r. (eds) 1998: mesozoic and cenozoic sequence stratigraphy of european basins. society for sedimentary geology (sepm) special publication 60, 786 pp. kozur, h. 1974: biostratigraphie der germanischen mitteltrias. freiberger for schungshefte c280 paläontologie, teil i, ii & anlagen, 56 pp. + 71 pp. michelsen, o. & clausen, o.r. 2002: detailed stratigraphic subdivision and regional correlation of the southern danish triassic succession. marine and petroleum geology 19, 563–587. nielsen, l.h. 2003: late triassic – jurassic development of the danish basin and the fennoscandian border zone, southern scandinavia. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 459–526. petersen, h.i., nielsen, l.h., bojesen-koefoed, j.a., mathiesen, a. & dalhoff, f. 2008: evaluation of the quality, thermal maturity and distribution of potential source rocks in the danish part of the nor wegian–danish basin. geological survey of denmark and greenland bulletin 16, 66 pp. retallack, g.j. 1975: the life and times of a triassic lycopod. alcheringa 1, 3–29. schulz, e., & heunisch, c. 2005: palynostratigraphische glieder ungs möglichkeiten des deutschen keupers. courier forschungsinstitut sen c kenberg 253, 43–49. authors’ addresses s.l., j.h.v., l.h.n., s.p., & k.d., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: sli@geus.dk m.e., geological survey of sweden, kiliansgatan 10, s-223 50 lund, sweden. rosa_2008:rosa-2008 01/07/09 15:48 side 24 e2019430202-01 the greenland ice sheet has been losing mass in response to increased surface melting (khan et al. 2015; van den broeke et al. 2017) as well as discharge of ice from marine terminating outlet glaciers (van den broeke et al. 2009; box et al. 2018). marine terminating outlet glaciers f low to the ocean where they lose mass by e.g. iceberg calving. currently, the mass loss from the greenland ice sheet is the largest arctic contributor to global sea-level rise (van den broeke et al. 2009, 2017; box et al. 2018). therefore, monitoring changes in the greenland ice sheet is essential to provide policy makers with reliable data. there is a consensus that most marine terminating outlet glaciers have retreated in recent decades, and that the increased calving rates are a response to recent atmospheric and oceanic warming (e.g. box et al. 2018; moon et al. 2018). the rate of dynamic mass loss is determined by changes of the glacier calving front (i.e. its terminus) position, ice thickness and changes in ice f low. ocean temperature and fjord circulation also inf luence the calving front stability by melting the glacier below the water line, thinning the ice that is in contact with water (moon et al. 2014). change in calving front position is therefore an important indicator for monitoring the dynamic behaviour of the upstream area of the ice sheet, which is further modulated by local topographic features and buttressing effects (rignot & kanagaratnam 2006; nick et al. 2009). the programme for monitoring of the greenland ice sheet (promice) is dedicated to monitoring changes in the mass budget of the greenland ice sheet, including monitoring of the calving front lines of marine terminating outlet glaciers. here, we present an updated collection of annual measurements of end-of-melt-season calving front lines for 47 marine terminating outlet glaciers in greenland between 1999 and 2018. we also present an example application of update of annual calving front lines for 47 marine terminating outlet glaciers in greenland (1999–2018) jonas k. andersen1, robert s. fausto*1, karina hansen1, jason e. box1 and the promice project team** **signe b. andersen1, andreas p. ahlstrøm1, dirk van as1, michele citterio1, william colgan1, nanna b. karlsson1, kristian k. kjeldsen1, niels j. korsgaard1, signe h. larsen1, kenneth d. mankoff1, allan ø. pedersen1, christopher l. shields1, anne solgaard1 and baptiste vandecrux1 geus bulletin is free to individuals and institutions in electronic form. the author(s) retain copyright over the article contents. r esearch article | open access geus bulletin vol 43 | e2019430202 | published online: 26 june 2019 https://doi.org/10.34194/geusb-201943-02-02 daugaard jensen kangerdlugssuaq fenris helheim midgaard tingmjarmiut ikertivaq qajuuttap sermilik kangiata nunata sermia jakobshavn sermeq avannarleq store lille kangigdleq sermeq silardleq perdlerfiup sermia kangerdluarssup sermia rinkumiamako ingia upernavik nunatakavsaup sermia nunatakassaap sermia hayes steenstrup kong oscars docker smith humboldt petermann nioghalvfjerdsfjorden zachariae storstrømmen academy ryder hagen ostenfeldsteensby fig. 1. location of each of the surveyed outlet glaciers (table 2). https://doi.org/10.34194/geusb-201943-02-02 e2019430202-02 the data set, in which we estimate area changes for this group of glaciers since 1999. the greenland calving front lines were measured from optical satellite imagery obtained from landsat, aster, and sentinel-2 (table 1). the promice calving front product is freely available for download as esri shapefiles (https://doi.10.22008/promice/data/calving _front_lines). methodology calving front lines were digitised through manual delineation in optical satellite images at the end of melt season every year from 1999 to 2018. the end of melt season was determined for each glacier by comparing a series of images from july–november (dependent on latitude) and selecting the one in which the glacier is at its minimum position. prior to 2018, calving front lines were digitised primarily using landsat-7 and landsat-8 images. in 2018, front lines were digitised solely using sentinel-2 imagery. we used mainly the panchromatic band to identify front line positions in landsat-7 images, a combination of three visible/nir bands in landsat-8 images and the nir band in sentinel-2 images (table 1). the resulting product is a collection of shapefiles, containing a polyline for each glacier for each year in the measurement period (1999–2018). the product comprises 47 of the largest greenland marine terminating outlet glaciers in the standard wgs-84 (epsg:4326) projection (see the glacier location map; fig. 1 and table 2). while the total number of glaciers is arbitrary, the ensemble of glaciers was selected to include the largest marine terminating outlet glaciers (measured in width) and to comprise glaciers from all along the greenland coast. table 1: overview of images used in the mapping of calving front lines satellite sensor band resolution image coverage (%) landsat 5 tm 3 30 m 0.8 landsat 7 etm+ 8 15 m 62.1 landsat 7 etm+ 3–5 30 m 4.9 landsat 8 oli 8 15 m 0.4 landsat 8 oli 4–6 30 m 22.0 terra aster 1–3 15 m 4.5 sentinel-2 msi 8 10 m 5.3 image coverage indicates the number of images used from each sensor as a percentage of the total number of images used. auxiliary images used in cases of distortion due to clouds or missing data bands in landsat 7 images are not counted. landsat images can be obtained from the usgs (https://earthexplorer.usgs.gov/), while sentinel-2 data can be obtained from the copernicus open access hub (https://scihub.copernicus.eu/). image coverage indicates the number of images used from each sensor as a percentage of the total number of images used. auxiliary images used in cases of distortion due to clouds or missing data bands in landsat 7 images are not counted. landsat images can be obtained from the usgs (https:// earthexplorer.usgs.gov/). sentinel-2 data can be obtained from the copernicus open access hub (https://scihub.copernicus.eu/). glacier name lat. long. width net area average area (°n) (°e) (km) change change (km2) (km2 a-1) zachariae 78.90 –20.14 24.6 –409.6 –21.6 petermann 80.10 –61.17 17.4 –289.5 –15.2 humboldt 79.50 –64.61 89.0 –259.4 –13.7 hagen 81.53 –28.50 9.1 –172.8 –9.1 jakobshavn 69.18 –49.73 11.4 –137.0 –7.2 storstrømmen 76.71 –22.47 31.9 –99.5 –5.2 nunatakassaap sermia 74.62 –56.34 5.4 –70.5 –3.7 steensby 81.20 –53.90 4.5 –69.5 –3.7 ostenfeld 81.60 –45.20 7.0 –65.0 –3.4 79 fjorden 79.60 –20.17 42.2 –51.7 –2.7 steenstrup 75.28 –57.89 16.2 –50.8 –2.7 kangerdlugssuaq 68.61 –32.93 6.0 –45.9 –2.4 midgaard 66.45 –36.73 3.8 –40.9 –2.2 upernavik a 73.00 –54.47 7.3 –40.4 –2.1 helheim 66.36 –38.12 5.8 –34.6 –1.8 inngia 72.03 –52.61 4.0 –31.7 –1.7 kong oscars 75.98 –59.79 4.2 –21.5 –1.1 sermeq silardleq 70.80 –50.80 3.3 –19.7 –1.0 academy 81.50 –32.65 8.8 –14.2 –0.7 umiamako 71.72 –52.44 2.9 –13.3 –0.7 ikertivaq a 65.67 –39.60 3.2 –13.1 –0.7 docker–smith 76.24 –61.00 5.1 –13.1 –0.7 upernavik b 72.94 –54.38 3.8 –12.4 –0.7 tingmjarmiut 62.76 –43.18 2.5 –11.3 –0.6 ikertivaq d 65.49 –40.06 7.9 –10.6 –0.6 daugaard–jensen 71.92 –28.57 5.3 –10.1 –0.5 sermeq avannarleq 69.36 –50.31 4.4 –9.5 –0.5 hayes 74.92 –57.00 9.6 –9.0 –0.5 perdlerfiup sermia 70.99 –50.92 2.7 –9.0 –0.5 ikertivaq c 65.58 –39.96 5.3 –7.3 –0.4 fenris 66.36 –37.54 2.8 –7.1 –0.4 sermilik 61.00 –45.95 1.5 –6.3 –0.3 kangia nunata sermia 63.33 –49.62 7.8 –6.2 –0.3 ikertivaq b 65.63 –39.64 4.5 –3.6 –0.2 kangerdluarssup sermia 71.25 –51.47 3.2 –3.4 –0.2 upernavik d 72.79 –54.22 2.3 –3.4 –0.2 upernavik e 73.00 –54.65 2.0 –3.4 –0.2 lille 70.43 –50.51 2.1 –2.8 –0.1 upernavik c 72.85 –54.33 6.3 –2.7 –0.1 ryder 81.30 –49.90 8.0 –2.3 –0.1 rink 71.75 –51.64 5.1 2.0 0.1 upernavik f 73.03 –54.84 1.8 –1.9 –0.1 kangigdleq 70.72 –50.64 2.9 –0.8 0.0 qajuuttap 61.32 –45.78 3.2 0.7 0.0 nunatakavsaup sermia 73.22 –55.14 3.6 0.5 0.0 kangerdlugssup sermerssua 71.46 –51.36 4.9 –0.1 0.0 store 70.40 –50.55 5.2 –0.1 0.0 table 2: overview of net area change, average annual area change, and width for the 47 tidewater glaciers monitored between 1999–2018. the table is sorted by magnitude net area change. https://earthexplorer.usgs.gov/ https://earthexplorer.usgs.gov/ https://scihub.copernicus.eu/ e2019430202-03 area change estimates since 1999 visualising annual calving front lines is a useful tool for identifying glacier retreat, advance or stable calving front lines (as shown in fig. 2). comparing sequential annual lines enables annual area change assessment for individual glaciers and for the whole ensemble, by selecting a constant reference line upstream of the glacier. the reference line is somewhat arbitrary, but when combined with each calving front line, we can generate a series of annual polygons. annual area changes are then estimated as the area difference between consecutive polygons. for a thorough presentation of the methodology, see jensen et al. (2016). measuring the polygon area change is arguably a more robust method than measuring a one-dimensional change in glacier length, since it accounts for non-uniform changes to the shape of the calving front. figure 2 shows an example, where the 2012 and 2013 calving front lines of hayes glacier have each been combined with the same reference line, generating two polygons. the 2012–2013 area change is then computed as the 2013 polygon area minus the 2012 polygon area. sources of uncertainty the two main sources of uncertainty in the promice calving line product are the manual delineation of front lines and the timing of front-line mapping. in principle, a front line can be delineated from a given satellite image with the precision of a single image pixel. however, in practice such precise digitisation is not feasible as the exact position of the calving front line is often obstructed by shadows or thin clouds. consequently, an uncertainty of about two image pixels is inherent in the manual digitisation process. on the ground, one pixel represents either 10 m or 15–30 m for the utilised sentinel-2 and landsat bands, respectively. for example, the error associated with the petermann glacier area change is estimated to be around 1 km2 in a 15 m resolution image, or 0.7 km2 using a 10 m resolution image. this rough estimate is computed as four times the image pixel size multiplied by the glacier width (which is about 17.4 km, cf. table 2), representing an uncertainty of ±2 image pixels for each point in the front-line delineation process. the end of the melt season for a given glacier is defined as the time at which the glacier is at its minimum position, i.e. when it has retreated the farthest. however, satellite coverage is limited, and a subset of images are unusable due to the presence of clouds, potentially causing the timing of the end of the melt season to be overor under-estimated. such a mistiming introduces uncertainty when computing annual area change, as area measurements are compared at different points in the season. the final uncertainty depends strongly on how many images are available, and whether the image is obstructed by clouds. jensen et al. (2016) estimated the error due to mistiming to be within 1 km2 and highlighted image availability as the dominant source of error. the problem is somewhat alleviated by the availability of data from sentinel-2, which provides images more frequently due to its short repeat pass time of five days. another source of error arises from an instrument failure on landsat 7’s enhanced thematic mapper plus (etm+) sensor, resulting in bands of missing data across all landsat 7 images from 2003 onwards. in images where one of these bands aligned with the calving front line in parallel, obstructing a major part of the front line, other images from within a few weeks were used to approximate the front-line glacier name lat. long. width net area average area (°n) (°e) (km) change change (km2) (km2 a-1) zachariae 78.90 –20.14 24.6 –409.6 –21.6 petermann 80.10 –61.17 17.4 –289.5 –15.2 humboldt 79.50 –64.61 89.0 –259.4 –13.7 hagen 81.53 –28.50 9.1 –172.8 –9.1 jakobshavn 69.18 –49.73 11.4 –137.0 –7.2 storstrømmen 76.71 –22.47 31.9 –99.5 –5.2 nunatakassaap sermia 74.62 –56.34 5.4 –70.5 –3.7 steensby 81.20 –53.90 4.5 –69.5 –3.7 ostenfeld 81.60 –45.20 7.0 –65.0 –3.4 79 fjorden 79.60 –20.17 42.2 –51.7 –2.7 steenstrup 75.28 –57.89 16.2 –50.8 –2.7 kangerdlugssuaq 68.61 –32.93 6.0 –45.9 –2.4 midgaard 66.45 –36.73 3.8 –40.9 –2.2 upernavik a 73.00 –54.47 7.3 –40.4 –2.1 helheim 66.36 –38.12 5.8 –34.6 –1.8 inngia 72.03 –52.61 4.0 –31.7 –1.7 kong oscars 75.98 –59.79 4.2 –21.5 –1.1 sermeq silardleq 70.80 –50.80 3.3 –19.7 –1.0 academy 81.50 –32.65 8.8 –14.2 –0.7 umiamako 71.72 –52.44 2.9 –13.3 –0.7 ikertivaq a 65.67 –39.60 3.2 –13.1 –0.7 docker–smith 76.24 –61.00 5.1 –13.1 –0.7 upernavik b 72.94 –54.38 3.8 –12.4 –0.7 tingmjarmiut 62.76 –43.18 2.5 –11.3 –0.6 ikertivaq d 65.49 –40.06 7.9 –10.6 –0.6 daugaard–jensen 71.92 –28.57 5.3 –10.1 –0.5 sermeq avannarleq 69.36 –50.31 4.4 –9.5 –0.5 hayes 74.92 –57.00 9.6 –9.0 –0.5 perdlerfiup sermia 70.99 –50.92 2.7 –9.0 –0.5 ikertivaq c 65.58 –39.96 5.3 –7.3 –0.4 fenris 66.36 –37.54 2.8 –7.1 –0.4 sermilik 61.00 –45.95 1.5 –6.3 –0.3 kangia nunata sermia 63.33 –49.62 7.8 –6.2 –0.3 ikertivaq b 65.63 –39.64 4.5 –3.6 –0.2 kangerdluarssup sermia 71.25 –51.47 3.2 –3.4 –0.2 upernavik d 72.79 –54.22 2.3 –3.4 –0.2 upernavik e 73.00 –54.65 2.0 –3.4 –0.2 lille 70.43 –50.51 2.1 –2.8 –0.1 upernavik c 72.85 –54.33 6.3 –2.7 –0.1 ryder 81.30 –49.90 8.0 –2.3 –0.1 rink 71.75 –51.64 5.1 2.0 0.1 upernavik f 73.03 –54.84 1.8 –1.9 –0.1 kangigdleq 70.72 –50.64 2.9 –0.8 0.0 qajuuttap 61.32 –45.78 3.2 0.7 0.0 nunatakavsaup sermia 73.22 –55.14 3.6 0.5 0.0 kangerdlugssup sermerssua 71.46 –51.36 4.9 –0.1 0.0 store 70.40 –50.55 5.2 –0.1 0.0 table 2: overview of net area change, average annual area change, and width for the 47 tidewater glaciers monitored between 1999–2018. 57°15’w 74°57’n 74°55’n 8 km4 620 57°15’w 57°15’w reference line 2013 calving front line 2012 calving front line 2013 polygon 2012 polygon fig. 2: example image from hayes glacier showing how area change is estimated from two consecutive calving front lines. the green line indicates the reference line. the calving front lines in 2012 and 2013 are depicted by blue and red lines, respectively. the glacier area change is computed as the area difference between the 2012 and 2013 polygons. the satellite image is an eu copernicus sentinel-2a image from 14 august 2018. e2019430202-04 position. if a band of missing data crossed the calving front line in a roughly perpendicular way, only obstructing a short stretch of the calving front line, the front line was simply digitised in a straight line across the missing data band. again, this problem is alleviated by the use of sentinel-2 or landsat 8 data. results and discussion as an example of the database, we present the calving front changes of greenland’s fastest f lowing glacier, jakobshavn isbræ (sermeq kujalleq; fig. 3). in 2017 the calving front advanced after more than 10 km of retreat between 1999 and 2016. the 2017 advance and stability into 2018 occurred in the faster f lowing southern branch of the glacier. a time series of the cumulative net area change for the period 1999–2018, estimated from the calving front line product of 47 glaciers, shows a net area loss of about 2100 km2 (fig. 4). this equates to an average annual area loss of c. 110 km2 for these 47 glaciers since 1999, which corresponds to an area roughly the size of paris. the rate of area change varies substantially through time. the period 2007–2012 underwent a rapid loss of glacier area, compared to 2013–2018, in which glacier area was relatively stable, associated with a small area change. the year 2017–2018 stands out as the only period with net area gain (+4.1 km2). table 2 provides the net area change as well as the average annual area change for each of the 47 surveyed glaciers. nearly all of the investigated marine terminating outlet glaciers show a negative net area change since 1999, indicating a retreat. only three glaciers (rink, nunatakavsaup sermia and qajuuttap) show a positive net area change. there is substantial variation between the glaciers in the ensemble, but a few of the large glaciers, such as humboldt, petermann, zachariae, and jakobshavn, are responsible for a considerable amount of the total ensemble net area change observed in fig. 4. other glaciers such as store and nunatakavsaup sermia show a net area change very close to zero. the area change of two glaciers is not directly comparable; a wider glacier will tend to show larger area changes than a narrower one. alternatively, to compare 69°14’n 50°15’w 50°0’w 49°45’w 49°30’w 69°7’n year 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 fig. 3: evolution of the calving front position of jakobshavns isbræ from manually delineated end-of-melt-season calving front lines spanning 1999 to 2018. the background image is from the eu copernicus sentinel-2b satellite from 4 september 2018. it is the same image that was used to delineate the 2018 front line. e2019430202-05 the area change of two glaciers, one could compute an estimate of the one-dimensional movement of each glacier as the obtained area change normalised (i.e. divided) by the glacier width. we anticipate the updated promice front line data set to be a useful addition to statistical investigations of glacier behaviour in greenland. questions remain as to the sensitivity of glacier area change to various climate parameters such as atmospheric forcing, sea-surface temperature, sea-ice concentration and the north atlantic oscillation (nao). jensen et al. (2016) found significant correlations between glacier area change and climate parameters for the period 1999–2013, dependent on geographical region. the reduction in ice-area loss in jakobshavn isbræ in 2017–2018 (fig. 3) coincides with anomalously low melt-season temperatures, but kazendar et al. (2019) pointed to colder ocean waters as the primary cause. bevis et al. (2019) supported the notion of inter-annual variations in surface melting, driven by the nao, as an indicator of variability in greenland mass loss. a physical mechanism linking summer air temperature and the front area of marine terminating outlet glaciers is the so-called hydrofracture, in which increased air temperature increases the supply of meltwater. more meltwater increases the availability and weight of water filling surface depressions. water being denser than ice, adds an additional stress that can disaggregate the ice, especially along fractures (e.g. weertman 1973; van der veen 1998). with the promice calving front line product, the time series of calving front line measurements is extended and five more glaciers are added to the ensemble, which serves to improve the accuracy of such statistical investigations performed by jensen et al. (2016). the calving front line product can also be used to compute ice velocity along a glacier f low line. ice velocity products are typically generated by cross-correlation of synthetic aperture radar (sar) images, and do not distinguish between glaciers and sea ice. knowing the position of the calving front line allows a f low line to be constructed based on the glacier alone, thus eliminating this problem. the calving front line product can thus act as an auxiliary data set in cases where annual movement of calving front lines must be taken into account. conclusions the promice calving front line product provides a useful data set of calving front lines at the end of each melt season since 1999. area change estimates generated from earlier versions of the data set have been used in international climate status reporting, for example in the arctic monitoring and assessment programme (amap 2017), in the state of the climate series (e.g. tedesco et al. 2016) and the arctic report card (tedesco et al. 2018). the updated and extended data set now provides annual end-of-melt-season calving front lines for 47 greenland marine terminating glaciers between 1999 and 2018. the data have been added to the list of promice products, which are publicly available at www. promice.dk. acknowledgements we thank one anonymous reviewer and mette kusk gillespie for constructive reviews. the programme for monitoring of the greenland ice sheet (promice) is funded by the geological survey of denmark and greenland (geus) and the danish ministry of energ y, utilities and climate under danish cooperation for environment in the arctic (dancea), and is conducted in collaboration with the national space institute (dtu space) and asiaq (greenland survey). we would also like to thank the eu copernicus program and esa for sentinel-2 data, nasa/usgs for landsat data, and nasa/usgs/jss ( japans space systems) for aster products. references amap 2017: snow, water, ice and permafrost in the arctic 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https://doi.org/10.1002/2014gl061836 https://doi.org/10.1007/s40641-018-0107-0 https://doi.org/10.1007/s40641-018-0107-0 https://doi.org/10.1038/ngeo394 https://doi.org/10.1126/science.1121381 https://doi.org/10.1126/science.1121381 https://doi.org/10.1175/2016bamsstateoftheclimate.1 https://doi.org/10.1175/2016bamsstateoftheclimate.1 https://arctic.noaa.gov/report-card/report-card-2018/artmid/7878/articleid/781/greenland-ice-sheet https://arctic.noaa.gov/report-card/report-card-2018/artmid/7878/articleid/781/greenland-ice-sheet https://arctic.noaa.gov/report-card/report-card-2018/artmid/7878/articleid/781/greenland-ice-sheet https://doi.org/10.1126/science.1178176 https://doi.org/10.1007/s40641-017-0084-8 https://doi.org/10.1007/s40641-017-0084-8 https://doi.org/10.1016/s0165-232x(97)00022-0 https://doi.org/10.34194/geusb-201943-02-02 geological survey of denmark and greenland bulletin 3, 98-112 98 the skagen well the skagen well – perspectives the perspectives of the drilling of the skagen well can be seen by describing the sedimental changes observed in the succession of strata penetrated. however, for the first 30 m of skagen well iii, only wash-samples were taken, in order to establish the well for further drilling down to the prequaternary. therefore, the first drilling segment, composed of sand and gravel, was later repeated elsewhere in order to obtain core samples also from the topmost part. this was done in a nearby position – the so-called skagen iv well – and consequently the full record of shell material and sediments can be given from the core samples obtained from the well, representing all the strata met with in the skagen area from the quaternary, the skagen iii well dgu file no. 1.287. the skagen wells iii and iv are considered to represent one well and are therefore listed together. however, also the wash-samples obtained throughout the quaternary are represented, but only as qualitative analyses with the first occurrences of macrofossils – especially the molluscs – indicated (appendix 2). thirty metres below surface (+ 1 m a.s.), the sediment is well-sorted fine sand. for the following 10 m to 40 m b.s., the average grain size falls within the coarse silt fraction which is consistent down to 75 m b.s. as shown from 11 interjacent measurements, appendix 3. from the depth of 75 m b.s. the average diameter falls within that of medium silt, down to the level of 100 m b.s., still well sorted. at the following levels to a depth of 133 m b.s., the material is fine silt and clay. at a depth of 135 m b.s., fine sand with poor sorting occurs, and at 136–137 m b.s., with very poor sorting and quartiles 40% / 90% of 54.099, which shows a diamict material with a content of stones and only allochthonous shell material, in contrast to the superjacent 130 m. at a depth of 179 m, the well produced a fine-grained material of medium silt, moderately sorted, which is close to what was found above the diamict sequence. with some rise in the average diameter to fine sand and a lowering of the sorting, the next remarkable shift happens at a depth of 187 m b.s., where a new diamict sequence is found down to 195 m b.s. here the boundary to the prequaternary deposits is met with, most probably belonging to the lower cretaceous, according to skagen ii, dgu file no. 1, 43 (sorgenfrei & buch 1964). from the above-mentioned strata in the cored sections, the well can be divided into two parts from the point of view of the present investigation on macrofossils. a sandy to gravelly, clayey to silty wellsorted material found in the upper 130 m of the well and in a smaller interval of almost 10 m at a depth of 179 to 187 m b.s. between these two parts, diamict and well-sorted clayey layers without an in situ macrofauna are found. as the main characteristic feature of the 140 m finegrained and well-sorted material, its content of shellbearing marine molluscs is considered. however, also other marine macrofossils have been recognised but not referred to species level, although recorded on a higher taxonomic level in appendix 3, which represents the finds in the skagen well. also the sedimental data are all shown in appendix 3, allowing a direct comparison between the finds of faunal elements and lithology sensu lato. the organic compound is shown with loss on ignition (550°c) and the occurrences of concretions such as pyrite and iron compounds. also allochthonous shell materials are figured. in consequence of the quantitative analyses of molluscs, diversity and number of specimens are given for the marine strata throughout the whole sequence. it is shown that these figures are very greatly according to the different facies met with. on the basis of the dating within the limits of the carbon-14 method (heier-nielsen et al. 1995), appendix 4 and fig. 3, it is seen that the 130 m thick upper sequence of the well is dated to the last 15 000 14c years. this comprises the whole of the holocene with its boreal sea deposits and the late weichselian with the arctic younger yoldia deposits. but also from 140–150 m b.s., measurements on gas compounds of marine origin (t. layer, personal communication 1999) and shell fragments have been dated, giving ages around 36 000 b.p. 14c years. this means that the diamictic sequence occurring between the two marine strata has taken up material which in age is equivalent to the younger part of the older yoldia clay sediments. the deposition of the diamictic geus bulletin no 3.pmd 28-06-2004, 08:4598 99 sediments is referred to the time of the late weichselian ice advance to the main stationary line in jylland. molluscan shells (macoma calcarea) from the younger part of the older yoldia clay (the macoma calcarea zone, sensu petersen in bahnson et al. (1974)), has recently been dated by the ams method to be in 14c years around 32 000 – 33 000 b.p. (aar-1410 and aar-1411). consequently, it is likely that the older marine strata in the lower marine part of the skagen well can be correlated to part of the sequence demonstrated in the skærumhede well (jessen et al. 1910; bahnson et al. 1974) covering the eemian and the main part of the weichselian. regarding the 130 m thick upper sequence, this is from results of the 14c dates related to the time of the younger yoldia sea and the holocene, and as it appears from the dates of the sediments here is for the first time within the danish area found in a continuous marine succession. this can be explained on the basis of the hitherto unsurpassed thickness of late weichselian–holocene marine strata. therefore, while most of the danish area has a continental period in the time span 11 000 – 7500 b.p. in 14c years (petersen 1985b), the skagen area was so low-lying that it was continuously covered by the sea. this is a reflection of a lesser glacial deposition and the glacio-isostatic down-pressing – the latter amounting to up to 200 m, as seen from the amount of isostatic rebound after the waning of the ice cap over northern denmark (petersen 1990). however, when only holocene dates are used, the estimated rebound of 200 m seems to be greater than the present dates allow when also late weichselian dates are used (petersen 1999). so the low stand of sea level during the latest part of the weichselian and early holocene was not to be overtaken by the isostatic uplift at any time in this area. after the final large eustatic rise in the early atlantic, the marine sedimentation is a dominating factor in raising the levelled sea bottom, compared to a decreasing isostatic rebound up to the subatlantic when the isostatic rebound in denmark expired (petersen 1990). here the formation of the skagen spit takes over, so that the last event of changing depth depends on the large quantities of sand and gravel deposited as the skagen spit grows to the north. the pre-late quaternary deposits in the deeper part of the skagen well, the base of the quaternary is found resting on pre-quaternary deposits of lower cretaceous sand. in the following description, appendix 3 should be consulted. the pre-quaternary strata consist of quartz sand and gravel. from a depth of 195.15–195.30 m b.s., which is the upper part of the pre-quaternary stratum, a mean grain size of fine sand, poorly sorted, is found (lab. no. 789.93). at a depth of 194.35–194.48 m b.s., the sediment is poorly sorted and the mean grain size is within medium sand, and this sediment also contains much quartz, but has another component in the form of stones of granitic composition. the cumulative curve shows an even distribution of all grain sizes, which refers this sediment to be a till (lab. no. 788.93). this is also true for the overlying strata up to around 189 m b.s. the mean grain size is here within fine sand; however, more fine-grained parts are found. the sediment contains siderite(?) concretions with pyrite, in which imprints of cyrena sp. are found. this might show that jurassic deposits have been eroded. some traces in pyrite were found as well. the whole sequence can be regarded as till. the sediment analyses from 188.57 to 187.18 give a badly sorted sediment sustaining that this is a till. also this level contains shell fragments, one of which can be shown to be a nuculana pernula. the late pleistocene eemian deposits the granulometric composition is shown from sample lab. no. 800.93. at a depth of 185.37 m b.s. the sediment is very fine-grained but contains only fragmented bivalves. at 185.0 m b.s. the marine sediment can be demonstrated by the occurrences of dentalium vulgare in many specimens and the bivalve kelliella miliaris also in many specimens and with connected valves. the granulometric composition can be seen from the two levels 182.65 and 180.57 m b.s., samples nos 784.93 and 797.93 respectively. it appears that the sediment is very fine-grained clay to fine silt and moderately sorted in the 180.57 m level. accessory finds of spatangids and ophiorids occur at the 185.0 m level, and pyrite formed in former burrows in the clayey material. also finds of fish occur, as found at the 182 m level, geus bulletin no 3.pmd 28-06-2004, 08:4599 100 and under the name of other fossils also crustacean remains have been listed. the third mollusc species found at this level is the ophistobranch limacina retroversa, which is found in large numbers (11 specimens in one sample) together with kelliella miliaris (also of a number of 15 in one sample). the samples here referred to are all from the heavy weight separation of the foraminifer samples. the species diversity and number of specimens in the sediment appear from the sample at 182.24 m b.s. in which 25 specimens of kelliella miliaris are found – most of them with connected valves and in some parts kept in pyrite. trace fossils in pyrite are found in great quantities recorded in the table from all levels. an expression of the grade of fine-grained sediment occurring at this level can be seen from the fact that only a biogene residue occurs here including the pyritiferous biogene traces – lebenspuren. the limpid delectopecten vitreus also appears at this level. as mentioned in the chapter on the molluscan species, the two sedentary species which today are known from the deeper part of the skagerrak are delectopecten vitreus and kelliella miliaris. the latter is also found in the turritella terebra zone in the skærumhede well. from 183.4 m b.s. hiatella arctica is found, which occurs also at the greater depths and furthermore is a species widely extended. the occurrence of entalina tetragonia at 183.6 m b.s. goes together with the occurrence of delectopecten vitreus, both of which are found in the deeper part of the skagerrak today, where they are part of the amphilopsis norwegica/delectopecten vitreus community. to this can be added cadulus jeffreysi found at the 184.4 m level. this species is widely extended in the northern part of the atlantic down to the bay of biscay and into the mediterranean. however, a single find of siphonodentalium lobatum at 184.6 m b.s. points to a more arctic environment. such shells are found in glaciation deposits according to muus (1959). however, the species may extend into the lusitanian region. from the 182 m level and up to 180 m b.s. still with a fine-grained and well-sorted sediment, yoldiella frigida appears, which is also known from the deeper part of the skagerrak today. this species can be referred to the same environment as has been mentioned above – the amphilopsis norwegica/delectopecten vitreus community. yoldiella frigida is known from the turritella terebra zone in the skærumhede sequence and the portlandia arctica zone according to jensen & spärck (1934). kelliella miliaris and limacina retroversa, which have been very frequent in marine layers met with under 180 m b.s., are no longer found above 180 m b.s. the early/middle weichselian, marine and glacigene deposits regarding the sediment which is to follow at the levels above, between 179.65 and 179.74, it appears that the mean grain size is somewhat bigger medium sand, moderately sorted. but the most significant is found in the cumulative curve showing two maxima on the frequency curve (fig. 91). this points to the effects of two sedimentation agents which might be a drop till effect besides the general marine sedimentation. during the examination of the samples from this level, sand and fine gravel occur, in contrast to the levels below, where only biogene remains were found, including the pyritiferous biogeneous traces. the coarser minerogene elements are found higher up in the series to the level 175.30–175.50 m where a fine-grained sediment with a median grain size of 0.002 mm reveals arctic marine molluscs. this is the first appearance of portlandia arctica, which as the name tells is the characteristic mollusc of the portlandia arctica zone in the skærumhede sequence. however, also the presence of yoldia hyperborea, which is known today from the arctic and down to the lofoten area is characteristic. this species is also found in the portlandia arctica zone together with nuculana pernula and palliolum greenlandicum. the occurrence of macoma sp. has been added from cumulated weight per cent frequency per cent grain size distribution older yoldia sea sediment sample id: 179.65 – 179.74 m 100 90 80 70 60 50 40 30 20 10 0 0. 00 20 0. 00 28 0. 00 39 0. 00 55 0. 00 78 0. 01 10 0. 01 56 0. 02 21 0. 03 12 0. 04 42 0. 09 00 0. 12 50 0. 18 00 0. 25 00 0. 35 50 0. 50 00 0. 71 00 1. 00 00 0. 06 30 w ei gh t pe r ce nt , % grain size, mm fig. 91. the granulometric composition with two maxima on the frequency curve (lab. no. 483.93) at the 179.65–179.74 m level. geus bulletin no 3.pmd 28-06-2004, 08:45100 101 the 177.8 m level but not on species level because of the fragmentary state of the shell. both spatangids and ophiorids are found and a fragment of cirriped at the 177.8 m level. at 174.4 m b.s. a single find of yoldia hyperborea occurs. the granulometric composition found at the 173.67–173.85 level (lab. no. 781.93) shows bad sorting in a clayey sediment with a median grain size within clay to fine silt. in this sediment fragments of arctica islandica are found that can be regarded as being part of the redeposited material which can be found also higher up in the core. at a level of 166.5 m b.s. the sediment is well-sorted fine sand and regarded as fluvial. in the following 16 m up to 151.50 m b.s. the sediment is coarser, being a moderately sorted medium sand also regarded as fluvial sand. from here only some shell fragments are found and no record of fossilia varia (other fossils in appendix 3). in the next metres to the level of 143.83–144.00 m b.s. the mean grain size is within the medium silt grade. this is found to be a fine-grained fluvial material forming part of a glacigene complex. also here, fragmentary molluscs are found. the late weichselian marine and glacigene deposits the first molluscs regarded as autochthonous above the glacigene complex are found at the 130.2 m level, so this is regarded as the upper limit of the glacigene sequence. in the interval from 141.00 and up to 130.2 m b.s. more shell fragments have been found – all showing signs of transport and wear. finds of pyrite (137.8 m level), concretion (132.6 m level), and glacial stria on a stone (137.44 m level) all reflect typical features for a till deposit. the marine shell material taken up by the glacier occurs in a fragmentary state, which is typical for redeposited material. however, it is from these strata that the absorption of gases from marine deposits has been dated. these dates form as mentioned a parallel to the age determination of the shells (macoma calcarea) from the skærumhede sequence where the older yoldia clay fauna has been studied (madsen et al. 1908; bahnson et al. 1974). the ages found on macoma calcarea shells from the skærumhede ii well give for the first time, on the basis of molluscs, the absolute age of around 32 000 – 33 000 (14c years) of the younger part of the older yoldia clay. compared with the dating of the marine gases from the skagen well, there is a good correlation to the stratigraphically now well-established skærumhede sequence, so that the two cored sections found on skagen and at skærumhede can be regarded as deposited during the same time in the weichselian. the skagen sequence, however, has been strongly eroded by the ice sheet advancing during the late weichselian. however, the thick packet of up to 50 m glacial sediments consequently contains the traces (gases) of that marine environment, which has been eroded, but is hereby dated to give the maximum age of the glaciation. this age points to the glaciation event in the late weichselian around 20 000 – 18 000 b.p. (petersen & kronborg 1991). however, here the upper marine sequence found in the skagen well will be described. from the 131.63–131.73 m level and up the core the sediment is extremely fine-grained with a medium grain size of fine silt which stays as such a size up to 100 m b.s. it should be noted that throughout the first 15 m of the core from the above-mentioned level finds of coarser material occur. this is seen at the 125.89–126.00 m level (lab. no. 526.93), where the granulometric composition reflects two maxima on the frequency curve (fig. 92). this is taken as a typical sign of a supplementary sedimentation which might have been caused by the melting of floating ice with the coarser sediment imbedded – a drop till effect, as found deeper in the core (fig. 91). this suspected arctic influence is sustained by the occurrences of arctic molluscs up to the 114.0–115 m level, where both portlandia arctica and bathyarca glacialis are present. cumulated weight per cent frequency per cent grain size distribution younger yoldia sea sediment sample id: 125.89 – 126.00 m 100 90 80 70 60 50 40 30 20 10 0 0. 00 20 0. 00 28 0. 00 39 0. 00 55 0. 00 78 0. 01 10 0. 01 56 0. 02 21 0. 03 12 0. 04 42 0. 09 00 0. 12 50 0. 18 00 0. 25 00 0. 35 50 0. 50 00 0. 71 00 1. 00 00 0. 06 30 w ei gh t pe r ce nt , % grain size, mm fig. 92. the granulometric composition with two maxima on the frequency curve (lab. no. 526.93) at the 125.9–126.0 m level. geus bulletin no 3.pmd 28-06-2004, 08:45101 102 furthermore, species such as nuculana pernula, nuculana minuta and yoldiella lenticula occur, which are known from the older yoldia clay in the skærumhede sequence. yoldiella frigida is the first to occur at the 130.2 m level in the skagen well. from this level several finds of ophiuroids (fragments), cirripeds and remains of pisces. however, no finds of spatangoids have been demonstrated within the whole sequence referred to the arctic marine deposits, but they are found all the way up in the boreal sequence (fig. 93e; fold-out, back cover). in the upper part of the arctic sequence siphonodentalium lobatum occurs at the 116.0–114.6 m level and a single find of entalina tetragona. occurrences of nucula sp. and macoma sp. are also recorded in the arctic part, but in such a fragmented state that the species cannot be given. from the recorded faunal composition it appears that it is a deeper-water fauna. this is also supported by the fact that forms reflecting an arctic macoma calcarea community are not present, and the fine-grained sediment points in the same direction. as a comment to the sedimentary environment it should be mentioned that magnetic spherical concretions have been found all through the arctic sequence. from five levels: 117.69–117.85, 124.34–124.50, 127.39– 127.50, 128.13–128.33 and 132.69–132.77 m b.s. a high content of griegite (fe 3 s 4 ), which explains their magnetic quality, has been found by x-ray analysis together with quartz, calcite, feldspar and clay. griegite has been reported as a constituent of reduced sediments. the occurrences in the skagen well are of interest in so far as the spherical magnetic concretions have been recorded only from the arctic sequence. this arctic sea deposit has been dated on material from the cores both foraminifers and macrofossils (heier-nielsen et al. 1995). from this it is seen that the actual time span ranges over 5000 14c years from 15 000 to 10 000 b.p. the sudden change in the macrofauna, or better the abrupt stop of the occurrences of arctic species, at the level of 114.2 to 114.00 m b.s. gives the pleistocene– holocene boundary. the transition from the pleistocene younger yoldia sea to the holocene marine deposits is here recorded for the first time within the danish realm with a whole series of ams datings supporting the chronostratigraphic position, see appendix 4. the dates are highly significant because the molluscan finds in the older part of the marine holocene are extremely poor. this, however, is not caused by the lack of samples from this core section, but is as will be shown dependent on the type of facies following the deposition of the youngest yoldia sea, which was a deeper-water deposit, followed by a boreal deeperwater facies in the older part of the holocene. the change from arctic to boreal conditions is regarded as influenced by a new current system from the atlantic bringing in the new temperate fauna replacing the arctic fauna of late weichselian age. the change in fauna is, however, not reflected in the sedimentary record (appendix 3, pp. 17, 21), which shows a very homogeneous clayey grain size distribution with nothing coarser than fine sand. only in one sample (appendix 3, p. 21, 115 m b.s.) at the sharp boundary between late weichselian and holocene medium sand, coarse sand and gravel are observed. on this homogeneous sequence of clay to fine sand measurements of magnetic susceptibility and thermoluminescence sensitivity have been conducted. it is worth noticing that in a diagram of magnetic susceptibility versus tl sensitivity the two samples forming the peak in the last part of the late weichselian also represent the more immature sediment (high susceptibility and high tl sensitivity). in contrast, the whole series of samples from the lower part of the holocene seems more mature (low susceptibility and low tl sensitivity). so, in this way the peak can also be connected with the sudden break through of the water from the baltic ice lake at mt. billingen, whereas the mature sediments from the holocene may reflect the long-transported sediments introduced by the new current system from the atlantic, bringing in the new temperate fauna in the early part of the holocene and replacing the arctic fauna of late weichselian age (unpublished data, k.l. rasmussen and k.s. petersen). the holocene as mentioned earlier, the transition from the arctic younger yoldia sea to the oldest holocene marine deposits is not to be seen from the sediment analyses except for the occurrences of griegite and some coarser material in the arctic part. this appears when the cumulative curves from the 125.89–126.0 and 113.60– 113.70 m levels from the arctic and boreal part (figs 92, 94, lab. nos 526.93 and 522.93 respectively) are compared. the median grain size is for both samples fine silt, see appendix 3, p. 21. considering the many samples analysed within the geus bulletin no 3.pmd 28-06-2004, 08:45102 103 lower part of the holocene up to the 100 m level, which is dated to be around the boreal–atlantic boundary, only very few molluscan species have been found; also the number of specimens is low. the preboreal–boreal 10 000 – 8000 14c years b.p. in the preboreal–boreal sequence only parvicardium minimum has been found in more than a single find together with mysella bidentata. however, three other genera are recorded: cardium, abra and lyonsia. parvicardium minimum is known from the deeper part of the skagerrak today and is found up to a depth of 30 m in the kattegat. it is recorded also from the eemian in the skærumhede series. compared with the occurrences of mysella bidentata also in this core level at skagen one can imagine a deeper-water environment, because mysella bidentata is also found to great depth (600 m) today in the skagerrak. spatangoids, apparently in great quantities – considering the many fragments – are found and in a lesser degree fragments of ophiuroids, which were also recorded from the arctic part. from the family spatangidae, five genera are known in nordic waters. from the skagen well at a depth of 108.34–108.56 m b.s. a well-preserved species of brissopsis lyrifera (forbes) has been collected (fig. 95). this species lives only on pure muddy bottoms and totally embedded in the sediment. as seen from the grain-size distribution from the level of 107.90–108.00 m b.s., this part is a fine-grained sediment. from the 109.39–109.50 m level the core section revealed a cut through the traces of a spatangoid similar to those that brissopsis lyrifera could leave, with the typical backfilling (bromley 1990, fig. 5.11; see fig. 96). brissopsis lyrifera can be found in great quantities in the northern part of the kattegat and skagerrak, while it might be found in the øresund but not in the bælt sea, the baltic and the limfjord region, according to mortensen (1924). cumulated weight per cent frequency per cent grain size distribution early holocene sediment sample id: 113.60 – 113.70 m 100 90 80 70 60 50 40 30 20 10 0 0. 00 20 0. 00 28 0. 00 39 0. 00 55 0. 00 78 0. 01 10 0. 01 56 0. 02 21 0. 03 12 0. 04 42 0. 09 00 0. 12 50 0. 18 00 0. 25 00 0. 35 50 0. 50 00 0. 71 00 1. 00 00 0. 06 30 w ei gh t pe r ce nt , % grain size, mm fig. 94. the cumulative curve from the 113.60–113.70 m level, lab. no. 522.93. fig. 95. the well-preserved brissopsis lyrifera (forbes) from the 108.34–108.56 m level. mguh 25404. fig. 96. trace from the 109.39–109.50 m level. might be similar to that of brissopsis lyrifera. geus bulletin no 3.pmd 28-06-2004, 08:45103 104 also other spatangoids might be found in the skagen cores in the huge material of fragments. from the older strata the genus echinocardium has been recorded earlier from the skærumhede series by the author, and echinocardium cordatum has been found in the cyprina clay from the eemian (madsen et al. 1908). so poor in molluscan species this community from the early holocene appears to be, one may pay attention to the abundant of remains of starfishes and echinoids which can be seen as a dominating element in this environment. in this way the sea bottom of those days was controlled by the echinoderms eating up most of the larvae of molluscs, as described by thorson (1961). if one should be compared with a present-day community, it must be the maldane-ophiura sarsi community in which besides ophiura sarsi, brissopsis lyrifera is found as the only often found larger animal (thorson 1968). the maldane-ophiura sarsi community replaces the amphiura community at depths of around 150 m and deeper in the skagerrak. a single find of pisces (100.3–100.5 m) has been recorded and a few finds of plant remains and pyritified traces (chondrites?). these rare finds of marine deeper-water facies from the very last part of the pleistocene and the earliest holocene will contribute to our knowledge of the land and sea configuration during the so-called continental period (petersen 1985b). considering the sedimentation rate during the first 2000 years of the holocene, viz.: through the preboreal and the boreal from which there have been only a few records earlier within the danish area, it is seen to be around 7.5 m per 1000 years. this is higher than the sedimentation rate for the younger yoldia sea, as found also in the skagen well record of 3 m per 1000 years. when this is given in calendar years, the differences are even bigger, because then the sedimentation of 15 m in the younger yoldia sea took about 6000 calendar years and still about 2000 calendar years in the preboreal and boreal seas within the skagen area (petersen & rasmussen 1995a, b). regarding the sediment, 50% is found to be clay in the younger yoldia sea – and in some parts at the level of 117.29–117.40 m b.s. around 63% – while during the preboreal–boreal the clay content has fallen from around 40% at the 113.60–113.70 m level to 20– 30% at the 100 m level. the atlantic 8000–5000 14c years b.p. from the dates (heier-nielsen et al. 1995) the atlantic covers the cored section from 100 to 80 m b.s. here the sediment in the oldest part has 30–20% clay, falling to a content of 15% clay in the youngest part at the 80.60–80.70 m level (see fig. 93a). throughout the atlantic the echinoids still dominate the samples and among these the spartangoids, as in the preboreal and boreal. however, here small gastropods occur: melanella lubrica, odostomia umbilicaris, and eulimella scillae. melanella lubrica is regarded as an ectoparasite on holothuroids, and odostomia umbilicaris is often found together with mytilus adriaticus. however, the latter bivalve has not been found in the skagen well material. it should be mentioned that the odostomia species are difficult to determine (fretter et al. 1986, p. 605) and no less so in subfossil material. furthermore, onoba vitrea and aclis minor are found in the younger part of the atlantic, where the determination of onoba vitrea is taken with some reservation because the three other species odostomia semicostata, odostomia aculeus, and odostomia proxima are very much alike and difficult to tell apart on shell features alone. aclis minor belongs to a large group of predatory gastropods that mostly and perhaps always (cf. fretter & graham 1962) are associated with echinoderms. from the atlantic single finds of parvicardium minimum from the 96 m level and spisula subtruncata at the 86 m level occur. spisula subtruncata is found next at the 73 m level in the subboreal, but becomes the dominating bivalve at the 30 m level, which can be referred to the younger part of the subatlantic. this depth is also within the range where this bivalve is found in large amount in the present-day danish seas. from the atlantic the predatory gastropod lunatia alderi occurs. this species is most probably the one which has bored into the many molluscs found in the overlying strata, but has not been recognised by its traces in the sparse material from the atlantic. fragments of abra sp. and macoma sp. occur in the cored section from the atlantic, and from the 80.60– 80.70 m level also finds of pisces and crustaceans have been recorded, as seen in appendix 3. it appears that also in the atlantic the sampling reveals a deposit with low diversity and few specimens of molluscs, where the echinoderms dominate as in the preboreal and the boreal sequence. however, considering the older holocene deposits which were tengeus bulletin no 3.pmd 28-06-2004, 08:45104 105 tatively referred to the maldane-ophiura sarsi community, the one from the atlantic can on the basis of the molluscs and the still dominating echinoderms be regarded as another of the deeper-water communities found in the present-day deeper water in skagerrak. here it should be the amphiura community, which as mentioned earlier is found above depths of 150 m. the subboreal 5000–2500 14c years b.p. the following 20 m of the skagen well cover the subboreal, 80 to 60 m b.s. the sedimentation rate can be estimated to be 8 m per 1000 years, a slight rise from the 6.6 m per 1000 years found during the atlantic. the clay content falls in this part to below 10%, and the coarse silt and fine sand fractions become the dominating grain sizes. the material is well sorted. fig. 93a, c. in all the sampled cores within this section fragments of echinoderms occur – mostly spatangoids as found earlier – but the diversity of mollusc species is higher, up to 10 different species in one sample and several with five to seven species in each. however, the number of specimens is still low and most of the finds are of single specimens. only onoba vitrea is found in a number of eight specimens in one sample (the 67.0 m level). among the other species, only lunatia alderi can be mentioned occurring in a number of eight within the whole section. from the 73.0 m level turritella communis occurs with boring of predatory gastropods – probably lunatia alderi. furthermore, eulimella scillae and retusa truncatula are found from the 67 m level and mysella bidentata together with corbula gibba at the 65.6 m level. the latter will be more common in the above-lying strata belonging to the subatlantic. from the subboreal sequence, one of the very few finds of polyplacophora occurs sitting in the sediment, represented, however, only by one plate which does not allow further determination by the author. within the interval from 75.0 m to 72.0 m three finds of turritella communis have been recorded. this is one of the characteristic species on the level muddy bottoms. nuculana minuta which has been found also in the arctic younger yoldia clay is here recorded for the first time in the holocene in the skagen well. there are several finds of nuculana minuta from the subboreal, and it is found in the present-day kattegat on muddy bottoms at depths of more than 20 m. this fits very well with the occurrences of turritella communis. acanthocardia echinata is also found for the first time and here recorded from 78.0 m. this species occurs on mixed bottoms and clay bottoms at depths of from 10 to 150 m. also phaxas pellucidus occurs for the first time in the skagen well during the subboreal. this mollusc occurs in general at depths of between 10 and 50 m, often together with abra alba, also found in this section of the well. the first occurrences of chamelea striatula and corbula gibba are in the skagen well during the subboreal. chamelea striatula is one of the most common of the danish marine bivalves but is connected to the sandy bottoms. according to jensen & spärck (1934), it is not found in the kattegat at depths greater than 50 m, because the sandy bottom in this region goes no further out and the species is rarely taken on clayey bottoms. in this connection it should be noticed that just around the 75 m level, where chamelea striatula occurs for the first time in the skagen well, the sediment changes to coarse silt with more than 50% fine sand. finally, at 61.09–61.14 m, is the first occurrence of tellimya ferruginosa. this species will also be more common in the subatlantic from the 30 m level. tellimya ferruginosa is often connected with the occurrence of echinocardium cordatum but can also be found free living (jensen & spärck 1934). the many new species – new through time in the skagen well – introduced in the subboreal point to water depths around 50 m with characteristic species from the present-day community such as turritella communis and chamelea striatula – the venus community. the changes to a more sandy sediment are perhaps the background for the occurrences of the new species. however, the echinoids have also decreased – and this may explain the more prolific mollusc faunas, for the toll of eaten molluscan larvae taken by the echinoderms is no longer so high (cf. thorson 1961). the subatlantic 2500– 14c years b.p. the uppermost 60 m of the skagen well belongs to the subatlantic. in general the 60 m cored section that falls within the subatlantic can be divided into two parts of an equal length of 30 m: the lower 30 m with geus bulletin no 3.pmd 28-06-2004, 08:45105 106 a clay content of 30–40% of well-sorted sediment, and the upper 30 m mainly consisting of fine to medium sand with few intercalations of gravel. regarding the dated part of this upper sequence (heier-nielsen et al. 1995, table 1) – from 30.25 to 12.75 m b.s. the sedimentation is 17.50 m during 210 years from a.d. 950 to a.d. 1160. this gives a sedimentation rate of about 80 m per 1000 years. in this case showing a fine example of the building up of the skagen spit, where the coarser material occurs as part of the long-shore transport, and deposited in foreset beds. the older subatlantic the older part of the subatlantic covers the interval from 60 to 30 m b.s. this section shows a slight coarsening upwards and a sedimentation rate of 30 m per 1000 years. the faunal composition can be analysed on the basis of 50 samples with a higher species diversity than found in the subboreal. some of the species are new to the record from the skagen well. hinia pygmaea appears for the first time at the 42 m level, as well as hinia reticulata. they both belong to the sublittoral zone and are found on muddy bottoms. mangelia brachystoma, which first occurred at the 58 m level, also belongs to the sublittoral fauna, but it occurs on sand and sandy muddy bottoms. polygireulima sinuosa is an ectoparasite on echinoderms which are still common and constitute a part of every one of the samples, but it has been found only within the level 38.19–38.24 m. the first littoral species, mytilus edulis, occurs at 49.14–49.24 m, and from this level it occurs regularly upwards, but only in small numbers until the 31 m level, where it is found in greater quantities. this species can be found out to 40 m depth, but must nevertheless be considered an eulittoral species where its occurrence is most abundant. the young specimens are often found on the vegetation. also chlamys varia is common in the coastal zone and occurs at the 32.85–32.90 m level. heteranomia squamula is epifaunal on hard substrates but also on algae and crustaceans. it has a wide occurrence from the littoral zone out to a depth of 100 m. in the skagen well it is confined to the subatlantic part. thyasira flexuosa is today a common bivalve on clayey bottoms from 20 m to 100 m, but it has been found only in two samples from the older subatlantic. this is hard to explain, as it has a wide extension within the whole of the north atlantic area (jensen & spärck 1934), and in numbers it is one of the most dominant species on the muddy bottoms which according to the sediment analysis have been prevalent for most of the holocene in the skagen area. turtonia minuta, belonging to the species from the coastal zone, is found in a single specimen at 39.85– 40.02 m. it is not recorded from the recent danish fauna, but lives off the norwegian west coast and is found subfossil in the limfjord region. at 47.30–47.35 m is the youngest record of parvicardium minimum, which was one of the few species occurring in the older holocene reflecting deeper water. a single find of angulus tenuis is at 55.30–55.35 m. the common occurrence of this species starts at the 30 m level. also donax vittatus occurs at 35.90–36.00 m level which must be seen as outside the general occurrence of this species, which is from littoral to around the 20 m depth donax vittatus is found within the high energy zone. a single find of abra prismatica at 49.90–42.00 m is within the general depth interval for this species (20– 60 m). in connection with the depth indications given in the well in metres below surface and the common depth intervals indicated by various authors for the molluscan species, it is possible to use the actual depth recorded in the well as the living depth for the subfossil fauna found in the skagen well during the younger part of the holocene. this because of the expiring isostatic movement and only little eustatic changes during the late holocene (petersen 1991b). corbula gibba, which was also found during the subboreal has in the subatlantic an even occurrence through the older part. barnea candida, normally only found out to a depth of 30 m, occurs in the well already at the 51.54–51.59 m level, although only found in fragments. cochlodesma praetenue which was found in the eemian at 183.77–184.00 m b.s. is also found in the subatlantic at 43.19–43.24 m. this species is rare in danish waters and has been taken alive only once north-east of the island of læsø. however, shells have been found elsewhere in the kattegat region, jensen & spärck (1934). it has a wide occurrence from the littoral zone and out to 110 m on different bottom types. finally thracia phaseolina shall be mentioned. this species occurs to depths around 50 m on clayey bottoms. as mentioned above, the echinoderms are also found geus bulletin no 3.pmd 28-06-2004, 08:45106 107 in the subatlantic represented by the fragments of spatangoids. also cirripeds occur in still higher quantities up towards the 30 m level (appendix 3, p. 6). furthermore, there are single finds of pisces and other fossil remains such as crustaceans (other fossils in appendix 3). however, also serpulae are found and may have settled on the shells of the other animals as the crustacean carapax. the younger subatlantic the increasing number of cirripeds in the upper 30 m should probably be regarded as allochthonous, since they occur together with the coarser material during the formation of the advancing skagen spit. the change in the upper 30 m to coarser material also introduces new forms of molluscs that are characteristic of the littoral facies and high-energy coastal situation still prevailing in this area today. the description of the upper 30 m is, as mentioned earlier, based on the skagen iv well 50 m away from the skagen iii well and at the same level (+ 1 m). this was done because only washed samples were obtained from the upper 30 m of the skagen iii well, and such samples could not form the best basis for a uniform description of the whole sequence – especially the necessary quantitative treatment of the molluscan faunas could not be fulfilled in that way. furthermore, a total of 29 grain-size analyses have been made within this part of the column, showing two sequences of well-sorted sediment coarsening upwards, with a sorting coefficient lower than 2 (fig. 97). in order to control the degree of transported shell material, size analyses and counts on right and left valves have been considered relevant with such a highenergy near shore sedimentation (fig. 98). especially the most prevalent bivalve within these uppermost 30 m, spisula subtruncata, has been counted. also observed borings have been figured in appendix 3, to be seen in connection with the actual finds of the predatory gastropods. this is done in order to show the degree of mutual connection in the molluscan assemblages, between predatory elements and their prey. the building-up of the upper 30 m took place within a very short period of time, and the sedimentation rate of this interval is estimated to be around 70 m per 1000 years. this high sedimentation rate has a serious effect on animal life. the dates on the building-up of the skagen spit lead to the conclusion that the extension of the coast line to the place where the wells have been sunk took place around a.d. 1400. taking into account that the final history of the coastal development takes place as a near-shore and littoral deposition history, the actual development on a west coast site similar to the skagen area has been analysed. this has been done by way of several van veen grab samples – altogether 61 outside the agger tange complex in the westernmost part of the limfjord (petersen 1994a). these investigations focused on the bivalves, evaluating their degree of being autochthonous from the preservation with both valves together, one valve but whole, a fragmented state or a rolled fragment. these observations have been summarised in appendix 5. the newcomers of molluscs from the skagen well will be mentioned. these also represent the species earlier known to live close to the recent danish waters and species new compared to what is known to be part of the recent danish fauna. this part of the record has the highest diversity and number of specimens compared to other sections of the skagen well. the mean species diversity per sample shows a rise compared to the older part and reflects the new sedimentary facies. however, the near to shore situation also puts forward the question of whether part of the faunas, if not all, may have been reworked. eliminating the uppermost ten samples covering the 5 m which can be regarded as the medieval shore. first the species represented by only few finds that are commonly found in great quantities will be discussed. lacuna pallidula occurs only as a single find at 30.0– 30.5 m level. this species occurs on fucus serratus and in great quantities from the littoral and to a depth of 70 m. hydrobia ulvae occurs normally in high numbers in shallow water. in the skagen well it has been recorded from only two levels (11.70–11.80 m and 25.0– 25.5 m) and with few specimens. rissoa violacea is connected with seaweeds and found from the tidal zone to a depth of 50 m. here the only finds are from the 27.0–27.5 and 28.0–28.5 m levels. also bittium reticulatum appears not to be part of the environment, since this species has only one occurrence at the 22.0– 22.5 m level. this species lives on zostera, as do other of the above-mentioned species. it can be concluded that the upper 30 m section of the well lacks the normal abundance of epifaunal elements connected with vegetation. this is also in good accordance with the high rate of sedimentation. geus bulletin no 3.pmd 28-06-2004, 08:45107 108 0 10 20 30 40 50 60 70 80 90 100 weight per cent, % d ep th b el o w s ur fa ce , m la bo ra to ry n um be r clay/silt medium sand gravelfine sand coarse sand 2.2 20.8 3.6 4.6 5.6 6.6 7.6 8.6 9.6 10.6 11.6 12.6 13.6 14.6 15.6 16.6 17.6 18.6 19.6 21.6 22.6 23.6 24.6 25.6 26.6 27.8 28.4 29.8 30.6 295.93 296.93 297.93 298.93 299.93 300.93 301.93 302.93 303.93 304.93 305.93 306.93 307.93 308.93 309.93 310.93 311.93 312.93 313.93 314.93 315.93 316.93 317.93 318.93 319.93 320.93 321.93 323.93 324.93 histogram of 29 grain-size analyses from the upper 30 m of the skagen well 4 among the gastropods occurring in the upper part of the well, aporrhais pespelicani occurs in the interval from 22.0–22.5 m to the 11.0–11.5 m level. this species is regarded as sublittoral from depths of 10– 180 m on a sandy muddy bottom or muddy bottom. however, it has been found in large quantities as empty shells on the shore of the east coast of skagen. this was rather puzzling until it was explained that the hermit crab might have been the actual agent bringing the shells on shore (g.h. petersen, personal communication 1998). the occurrence of lunatia montagui is restricted to the 20.0–20.5 m level, while lunatia alderi is rather frequent in the core samples. the impact of these predatory gastropods on the fauna – 15 species have been recorded with such borings, including some of the lunatia species themselves – has been quantified in appendix 3. the high number of lunatia alderi in the upper 30 m is in accordance with the preferred environment of clean sand of this species. a new neogastropod to the fauna of the well is the buccinum undatum from the 11.0–11.5 m level, while hinia pygmaea now becomes common, occurring in most of the samples from the 28.0–28.5 m level to 6.0– 6.5 m b.s. and represented in many specimens – some of them bored by predatory gastropods, as seen in appendix 3. the small gastropod oenopota turricula has a wide depth range (20–200 m), so the single finds at the 23.5– fig. 97. histogram of 29 grain-size analyses from the upper 30 m of the skagen well 4, showing two coarsening-upwards sequences. geus bulletin no 3.pmd 28-06-2004, 08:45108 109 21.0 m level most probably reflect that only in this part of the well does the clean sandy bottom occur which is preferred by oenopota turricula. of the heterogastropod newcomers in the upper section, graphis albida from the 25.0–25.5 m level can be mentioned. this species is not recorded among the recent danish molluscs (jensen & knudsen 1995). it is found sublittorally out to a 30 m depth. hemiaclis ventrosa occurs at the 30.0–30.5 m and 11.0– 11.5 m levels, but it is recorded in recent waters at a much deeper level: 100–200 m. neither this nor the species mentioned above is recorded from danish waters. vitreolina philippii, occurring within the interval from 29.5 to 7.0 m with seven specimens, is known from the recent danish fauna and is noted as sublittoral to a depth of 200 m. this gastropod is a parasite on echinoderms, as the other eulimidae. echinoderms are still present in the material as seen from appendix 3. from the 15.0–15.5 m level, finds of chrysallida decussata occur, which is also recorded by jensen & knudsen (1995). this species occurs at the depth interval of 14–40 m. turboniella acuta has been recorded from danish waters by jensen & knudsen (1995) although rare. the occurrence of this species in the skagen well is at the 21.0–21.5 m and 20.0–20.5 m levels with, two wellpreserved specimens. among the ophistobranchs there are some fragmentary finds which have not been identified to species ratio 1:1 rightleft > 4.0> 0.5 > 2.0 > 6.5 > 8.0 size, mm 125 48 109 147 311 321 442 569 278 1129 4332 1201 113 85 166 826 98 68 59 14 0 79 75 92 39 5.0–5.5 6.0–6.5 7.0–7.5 8.0–8.5 9.0–9.5 10.0–10.5 11.0–11.5 12.0–12.5 13.0–13.5 14.0–14.5 15.0–15.5 16.0–16.5 17.0–17.5 18.0–18.5 19.0–19.5 20.0–20.5 21.0–21.5 22.0–22.5 23.0–23.5 24.0–24.5 25.0–25.5 26.0–26.5 27.0–27.5 28.0–28.5 29.0–29.5 depth below surface, m number of valves relative size distribution left/right valves ratio valves: spisula subtruncata fig. 98. size histograms for spisula subtruncata in the upper part of the subatlantic sequence, the 29.0–29.5 m level to the 5.0–5.5 m level, with ratio on left and right valves from the 29.0–29.5 m level to the 11.0–11.5 m level. geus bulletin no 3.pmd 28-06-2004, 08:45109 110 level, but species such as retusa truncatula and cylichna alba are found also in the upper part of the well. a fragmentary scaphopod from the 15.0–15.5 m level has not been referable to species level. among the bivalves, many are new to the already mentioned fauna from the well, and the number of specimens is for many of the species very high in comparison to what has been recorded from the older strata. of palaeotaxodonta, nucula nitidosa is found and represented all through the interval from 29.5 to 13.0 m b.s., occurring on sand bottom, which is the preferred substrate. also nucula nucleus is found within the interval from 30.5 to 8.0 m b.s. with many (13) specimens, part of them bored as the presiding species by the predatory gastropods. in the subclass pteriomorphia, species from mytiloida and pterioida such as musculus discors at the 28.0– 28.5 level and mytilus edulis in large quantities (113 specimens) are found, albeit most of the latter as juveniles. from the 28.0–29.5 m level individuals are found (with both valves). this latter species is typical in the littoral zone, but may occur at depths out to 40 m. pectinidae have been found, but all in fragments, in the interval 25.5–12.0 m b.s. ostrea edulis occurs in the interval 28.5–7.0 m b.s. – mostly as juveniles. the subclass heterodonta, from where most of the found bivalves come also includes the species most often found and characteristic of the youngest part of the marine sequence. mysella bidentata is recorded from the entire holocene, although only a few specimens are present in the early holocene. in the latest holocene as the present 30 m, 125 specimens have been found. the closely related tellimya ferruginosa occurs apart from a single find at the 61.09–61.14 m level, from the 29.5 m level where it is common up to 8.0 m b.s. both of these species have specimens bored by the predatory gastropods. tellimya ferruginosa is a commensal on echinocardium cordatum, but can also be found on its own in the sediment. mactra stultorum has been found only in the upper part of the cored section and can be seen as connected with the clean sand that is the type of bottom preferred by this species. on a suitable bottom it may be found out to a depth of 60 m. spisula subtruncata, which has a wide distribution from the littoral zone and out to a depth of 200 m, can be found both on muddy and on sandy bottoms. it dominates the uppermost part of the sequence, with 11085 specimens! in recent waters on sandy bottoms this species is one of the most common bivalves in the kattegat at depths between 20 and 30 m (jensen & spärck 1934). on the cored material from the skagen well size histograms and counts on left and right valves have been made in order to ascertain from such measurements whether the shell material is autochthonous/ parautochthonous. as seen from the figures in fig. 98, it appears that there is an even representation of the left and right valves, and the size histograms reflect a life assemblage which also might appear from the wellpreserved gracile valves. the borings counted on valves of this species make it clear that spisula subtruncata must have been the preferred victim of the predatory gastropods in this molluscan assemblage. at the 15.0–15.5 m level around 10% of the specimens are bored (2723 individuals out of which 268 have been bored). individuals (with both valves) have been found up to the 21.0–21.5 m level, where also other bivalves have been found with closed valves. however, the most even occurrence of left– right valves also at the 15.0–15.5 m level (2147–2105 respectively) may speak in favour of an autochthonous state also at this depth. the size histogram from the same level points to the same conclusion (see fig. 98). by way of the same kind of measurements it is possible to extend the possible life-assemblages up to a level of 10.0–10.5 m b.s., where the material still is present in such quantity that the measurements can be taken as bearing. investigations performed on nearshore deposits off the west coast of jylland in the agger tange area given in appendix 4 support the view that lifeassemblages can be found near to shore at depths of up to 6–7 m. almost all the ams datings in the upper part of the well have been based on spisula subtruncata, and these datings all fall within the right relative age according to their respective levels. this is not the case with the date on donax vittatus, which has also been dated within the upper 30 m interval. as shown on the dating diagram (heier-nielsen et al. 1995; appendix 3), the donax vittatus age clearly appears as an older element in a younger part of the section. however, donax vittatus will be commented upon later in the text. solenidae species often occur in the upper part of the sequence, but often in a fragmentary state. however, phaxas pellucidus is common in the interval between the 30.5 and 20.0 m level, where it is found in several specimens in some of the samples. it lives on different bottom types from the sublittoral at a depth of 4 m out to a depth of 150 m. however, in the skagen well there is only a single occurrence at 73.39–73.44 m b.s. geus bulletin no 3.pmd 28-06-2004, 08:45110 111 one of the dominating bivalves is fabulina fabula, which only occurs within the interval 28.5–4.0 m b.s. some of the specimens have been the victims of the predatory gastropods. this species prefers a bottom type of fine sand, which might explain the interval of occurrence in the skagen well, where there are sandy layers only in the uppermost 30 m. on a suitable bottom this species goes out to a depth of 50 m. also tellina pygmaea and angulus tenuis occur in the upper part of the sequence and only there, with the exception of a single find of angulus tenuis at the 55.30–55.35 m level. this is outside the general occurrence of this shallow-water species normally found from the intertidal zone out to a depth of 10 m. donax vittatus, which is found regularly in the interval from the 27.5–4.0 m level, but often in a fragmentary state, is a typical high-energy coastal form on a sandy bottom. as already mentioned in connection with the dates, donax vittatus also occurs as an allochthonous element, which can be seen from the many rolled fragments of this sturdy shell. its occurrence out to a depth of 20 m off high-energy shores characterises in the best way the situation by the building up of the skagen spit system. the species is not found in the kattegat region and is absent from the inner part of the limfjord. gari fervensis is found only in this upper part of the skagen well from the 27.5 to 23.0 m level. accordingly, in danish waters it is known from a depth of 15–40 m on mixed bottoms and sometimes on sandy bottoms. through most of the holocene, fragments of the genus abra have been found. abra nitida, which has a wide depth distribution from the sublittoral zone out to a depth of 200 m, has been found through the last part of the holocene from the 71.89–72.00 m level to the 10.70–10.80 m level mostly in single specimens. this species has its main distribution today in the deeper parts of the skagerrak and the kattegat on muddy bottoms. a single find of a rolled fragment of arctica islandica occurs at 14.70–14.80 m, which is the only find besides the fragment from the glacial series at the 173.67– 173.85 m level. however, the washed samples have given another specimen also from the subatlantic (appendix 2). chamelea striatula is the characteristic animal of the venus community on a sandy bottom in the north sea and the kattegat. at skagen it occurred already at the 76.34–76.50 m level (late subboreal). at this depth a change of weight per cent of clay takes place (from 13.7% to 7.8%), and the fine sand component becomes the dominating grain size with a weight per cent of 54.9. from the 30 m level, chamelea striatula is more common, and specimens with connected valves occur up to 21.0–21.5 m b.s., many of them bored by predatory gastropods, as shown in appendix 3. from the point of view that also other bivalve species have been found as whole individuals up to the 20 m level, it can be regarded as the well-established limit for an autochthonous occurrence of the molluscs. however, as seen from the observations off the agger tange area given in appendix 5, there will always be an element of allochthonous material in such a high-energy coastal environment which should be taken into account also for the skagen area regarding the uppermost part of the sequence from the skagen well. a single find of timoclea ovata is also found in the upper part of the section at the 27.0–27.5 m level. this species is today found at a greater depth than chamelea striatula, but is not very numerous. within the order myoida, corbula gibba is also well represented in the upper section, with individuals found up to a level of 27.0–27.5 m b.s. this species also shows many specimens killed by predatory gastropods. corbula gibba is found in the sublittoral zone out to a depth of 250 m. at skagen its first occurrence is at 74.89–75.00 m, in the early subboreal, but it becomes common in the subatlantic and occurs in high numbers only in the last part of the subatlantic from the 30 m level, often bored. finally, two single finds of saxicavella jeffreysi and pholas dactylus occurred at the 20.0–20.5 m level. saxicavella jeffreysi is in recent danish waters not very abundant at depths between 25 and 50 m, while pholas dactylus would only be expected to be found at depths less than 10 m. pholas dactylus is a boring form found in hard substrates, which is far from the actual sediment occurring at this level in the skagen well. the fragmentary pholas dactylus can be regarded as one of the allochthonous elements that can be seen in connection with the accessory finds mentioned in appendix 3 and commented upon below. among the accessory finds the barnacles and sea urchins dominate. also fish remains are found, often in the form of vertebrae, but an otolith appears as well. other fossil remains are serpulids, bryozoans, crustaceans, and plant and insect remains, which taken as a whole very well characterise the near-shore environment. on the other hand, no concretions are found like the ones from the younger yoldia sea, or pyrite as found at the base of the holocene and the eemian. although these accessory elements cannot be quantigeus bulletin no 3.pmd 28-06-2004, 08:45111 112 fied, they offer some additional information when considered together with the sedimentological and mollusc records. conclusive remarks on the skagen well in the description given above, the faunal record is the basis for understanding the climatic changes in the skagen well, supplemented by the observation on the changes in the sediments. however, the changes found during the holocene are most likely to be connected with changes in facies, and here the changing depth is the most prominent agent, ending up with the last event represented by the depositional history of the skagen spit. based on the dating of the holocene and the late weichselian, the descriptions have been given in terms of episodes. especially the holocene strata points to a development from deeperto shallow-water facies from preboreal to subatlantic. in this development there appears to be a facies change that can be compared to the bottom communities as known from the skagerrak–kattegat region when going from the deeper-water communities of the present day, the so-called maldane-ophiura sarsi community, to the venus community of the more shallow seas. the mollusc assemblages in the skagen sequence indicate a deeper-water facies during the eemian, the weichselian and the older holocene in contrast to what hitherto was known in other parts of the danish area during the late quaternary. the skagen well has a record of the changing seas during the late quaternary, from the eemian through the weichselian (although only in parts) and the holocene. for the first time within the danish area, the full record of the marine environmental transition from the late pleistocene to the holocene can be demonstrated on the basis of molluscs. however, not all the episodes known from the skagen well can be found in marine facies of the other regions, but thanks to the new records from the north sea around the jydske rev area, a near to full holocene marine record is at hand, including part of the preboreal (petersen 1998). the environmental changes through time in the seven sectors based on the molluscan records the recorded mollusc species within each area are given in appendix 6. regarding the environmental changes through time within the danish realm, the seven sectors will be considered from the eemian, starting in the south within the classical area where forchhammer named the deposits the cyprina clay. eemian species sorted after climatic affinities the bælt sea age: eemian climatic regions: asbl class bivalvia subclass heterodonta order myoida mya truncata linnaeus 1758 total for climatic regions asb. : 1 (1.7%) climatic regions: .sb. class bivalvia subclass heterodonta order veneroida arctica islandica (linnaeus 1767) order myoida zirfaea crispata (linnaeus 1758) total for climatic regions .sb. : 2 (3.4%) climatic regions: .sbl class bivalvia subclass pteriomorpha order mytiloida mytilus edulis linnaeus 1758 order pterioida geus bulletin no 3.pmd 28-06-2004, 08:45112 e2019430201-01 the programme for monitoring of the greenland ice sheet (promice) has measured ice-sheet elevation and thickness via repeat airborne surveys circumscribing the ice sheet at an average elevation of 1708 ± 5 m (sørensen et al. 2018). we refer to this 5415 km survey as the ‘promice perimeter’ (fig. 1). here, we assess ice-sheet mass balance following the input-output approach of andersen et al. (2015). we estimate ice-sheet output, or the ice discharge across the ice-sheet grounding line, by applying downstream corrections to the ice f lux across the promice perimeter. we subtract this ice discharge from ice-sheet input, or the area-integrated, ice sheet surface mass balance, estimated by a regional climate greenland ice sheet mass balance assessed by promice (1995–2015) william colgan*1, kenneth d. mankoff1, kristian k. kjeldsen1,2, anders a. bjørk2, jason e. box1, sebastian b. simonsen3, louise s. sørensen3, s. abbas khan3, anne m. solgaard1, rene forsberg3, henriette skourup3, lars stenseng4, steen s. kristensen5, sine m. hvidegaard3, michele citterio1, nanna karlsson1, xavier fettweis6, andreas p. ahlstrøm1, signe b. andersen1, dirk van as1 and robert s. fausto1 geus bulletin is free to individuals and institutions in electronic form. the author(s) retain copyright over the article contents. r esearch article | open access geus bulletin vol 43 | e2019430201 | published online: 08 july 2019 https://doi.org/10.34194/geusb-201943-02-01 fig. 1. a the promice perimeter and nineteen ice sheet sub-sectors (zwally et al. 2012). major glaciers ( jakobshavn ( jak), humboldt (hum), zachariae (zac), kangerlussuaq (k an) and helheim (hel)) are shown for reference. b average surface mass balance (smb) in mm of water equivalent (we) per year over the 1980–1999 period from four mar3.5.2 simulations (fettweis et al. 2017). c satellite-derived ice-surface velocity during winter 2008/2009 (rignot & mouginot 2012). both surface mass balance and ice-surface velocity data are only shown within the promice ice-sheet mask, excluding independent ice caps and glaciers (citterio & ahlstrøm 2013). 300 km 50ow 75on 70on 65on 60on 40ow 70ow 50ow 30ow 10ow 0o 1000 100 10 velocity (m/yr) 10ow30ow 40ow50ow 50ow70ow 0o 300 km smb (mmwe/yr) 2000 –2000 0 70ow 50ow 30ow 10ow 0o a b c 300 km 50ow 80on 75on 70on 65on 60on 40ow 1.1 1.2 1.3 1.4 2.1 2.2 3.1 3.23.3 4.1 4.2 4.3 5 6.1 6.2 7.1 7.2 8.1 8.2 hum zac jak kan hel km 0 km 5415 https://doi.org/10.34194/geusb-201943-02-01 e2019430201-02 model. while andersen et al. (2015) assessed ice-sheet mass balance in 2007 and 2011, this updated input-output assessment now estimates the annual sea-level rise contribution from eighteen sub-sectors of the greenland ice sheet over the 1995–2015 period. input-output method ice discharge is calculated as the ice f lux across the promice perimeter, corrected for downstream mass changes due to surface mass balance and changing ice volume (fig. 2). ice f lux (f) across the promice perimeter within a given ice-sheet sub-sector is calculated as: f = ∑li=0 vpi hi ρf ∙ ∆l where vp is gate-perpendicular, or perimeter-perpendicular, ice-surface velocity, h is the ice thickness, ρ is bulk ice-sheet density (assumed to be 915 ± 2 kg/m3) and f is the ratio of surface-to-depth-averaged ice velocity (assumed to be 0.93 ± 0.05; thomas et al. 2001). ice f lux is summed along the promice perimeter length (l) within a given ice-sheet sub-sector in increments (δl) of 30 m. gate-perpendicular velocity is calculated as: vp= v cos ϑ where v is the absolute surface velocity and ϑ is the difference between ice f low and gate-perpendicular azimuths. when ϑ exceeds 90°, gate-perpendicular velocity becomes negative, indicating ice f low into the perimeter (fig. 3). this reverse ice inf low occurs along 5.1% of the entire promice perimeter (275 km), primarily in east greenland. grounding-line ice discharge (d) is calculated as the sum of ice f lux across the promice perimeter (f) and two downstream corrections that account for changing ice volume and surface mass balance: d = f – v .ds + b . ds where v .ds is the area-integrated observed rate of change in ice volume downstream of the perimeter, and b . ds is the areaintegrated modelled surface mass balance downstream of the perimeter. the rate of change in downstream ice volume captures changes due to both surface mass balance and ice dynamics. this requires the secondary surface mass balance correction to isolate the ice dynamic contribution to grounding-line ice discharge. subtracting a negative downstream volume change increases ice f lux, while adding a negative downstream surface mass balance decreases ice f lux. we assess mass balance (m. ) within a given ice-sheet subsector as: m. = b . – d where b . is area-integrated modelled surface mass balance and d is calculated grounding-line ice discharge. we assess mass balance in eighteen of nineteen ice-sheet sub-sectors delineated by zwally et al. (2012) using the promice ice-sheet mask (citterio & ahlstrøm 2013). these eighteen minor sub-sectors are aggregated into eight major sectors (fig. 1a). we do not assess mass balance in sector 3.2 (geikie plateau). we propagate the uncertainties following andersen et al. (2015), whereby we employ quadratic sums for terms with common units and quadratic fractional sums for terms with differing units. datasets we interpolate satellite-derived synthetic aperture radar ice velocity (v) along the promice perimeter from a spatially complete and temporally constrained winter 2008/2009 velocity mosaic of 150 m spatial resolution (rignot & mouginot 2012). where possible – along 67% of the promice perimeter – we derive temporal trends in ice velocity from overlapping winter 2008/2009 and winter 2014/2015 velocity mosaics ( joughin et al. 2010). we apply these temporal trends within each sub-sector to estimate annual perimeter velocity profiles during the 2000–2015 period. this approach is meant to complement the spatial completeness of the rignot & mouginot (2012) annual mosaic with the temporal repeat of the joughin et al. (2010) data. we assume the perimeter velocity profile in the year 2000 is characteristic of the 1995–1999 period, on the basis that the ice-sheet interior was near equilibrium mass balance prior to 2000 (thomas fig. 2. schematic representation of calculating ice discharge using the promice perimeter. ice discharge (d) at the grounding line is derived from downstream rate of change in ice volume (v .ds ) and surface mass balance (b . ds) corrections applied to the ice f lux (f) observed through the promice perimeter (andersen et al. 2015). e2019430201-03 et al. 2001). these simplifications overlook pre-2008 ice f low variability, such as the acceleration and deceleration of south-east greenland glaciers during 2000–2007 (enderlin et al. 2014). while pre-2008 ice-sheet velocity maps are available, their quality decreases inland from the ice-sheet margin, which results in poor sampling along the promice perimeter (fig. 3). we estimate ice thickness (h) along the promice perimeter using ice surface and bed elevation data. where possible, ice thickness is calculated from promice airborne campaign laser and radar altimetry measurements in 2007, 2011 and 2015 (sørensen et al. 2018). promice airborne radar surveys have measured bedrock elevation along 79% of the perimeter. bedrock elevations are interpolated along the remaining 21% of the perimeter from bedmachine v3 (morlighem et al. 2017). promice laser altimetry surveys each measured ice-sheet surface elevation along 74 to 79% of the perimeter. along 15% of the perimeter never surveyed by airborne altimetry, ice-sheet surface elevations are interpolated from a digital elevation model representative of 2007 (howat et al. 2014). when and where required, independent altimetry-derived rates of elevation change are used to derive annual elevation profiles along the perimeter during 2000–2015 (khan et al. 2016). we interpolate area-integrated rate of change in ice volume observed downstream of the promice perimeter (v . ds) annually within each ice-sheet sub-sector during the 1995–2015 period from the same independent airand satellite-borne altimetry product (khan et al. 2016). these rates of volume change have been corrected for firn compaction when and where necessary. we estimate rates of change in ice volume in each sub-sector by area-integrating this altimetry product, and associated uncertainties, at 500 m spatial resolution, over the ice-sheet area downstream of the promice perimeter (citterio & ahlstrøm 2013). fig. 3. a: satellite-derived annual winter icevelocity data availability along the promice perimeter within the combined joughin et al. (2010) and rignot & mouginot (2012) datasets during winters 1995–2015. b: 2008/2009 ice f low and gate-perpendicular azimuths around the promice perimeter (rignot & mouginot 2012). c: dimensionless scale factor (cos ϑ) of velocity magnitude. d: absolute and gate-perpendicular surface velocity around the promice perimeter. e: changes in gate-perpendicular ice velocities surveyed in 2008/2009 and 2014/2015 ( joughin et al. 2010). in all subplots vertical dashed lines denote major glaciers (fig. 1). e2019430201-04 we use surface mass balance simulated by the mar3.5.2 regional climate model for both downstream surface mass balance correction (b . ds) and assessing ice-sheet wide surface mass balance input (b . ). this permits us to assimilate the runoff and snowfall rates of a four-simulation ensemble ref lecting four different climate forcings (er a-20c, er a-interim, ncepv1 and 20crv2c) into an annual surface mass balance time series that spans 1980–2015 at 500 m spatial resolution. we remove relative anomalies between these four simulations during the common 1980–1999 period (fettweis et al. 2017). the promice ice-sheet mask we employ has a more extensive ice-sheet ablation area than the native mar3.5.2 ice mask (citterio & ahlstrøm 2013). relative to the native 25 km mar ice mask, the more extensive ice-sheet ablation area of the 500 m promice ice mask decreases ice-sheet integrated surface mass balance by c. 30 gt/yr. the ice-sheet integrated downscaled surface mass balance we interpolate is within the range of independently elevationdependent downscaled mar2 simulations (franco et al. 2012). ice sheet mass loss our updated input-output assessment gives a total 1995– 2015 ice-sheet mass loss of 3028 ± 711 gt (fig. 4). this is equivalent to a eustatic sea-level rise contribution of 8.4 ± 1.9 mm. we assess all eight major ice-sheet sectors as within uncertainty of equilibrium balance at the start of the surfig. 4. annual surface mass balance, ice discharge and mass balance in eight major ice-sheet sectors (1–8), as well as for the entire ice sheet, over the 1995– 2015 period. vertical spread denotes associated uncertainty. map: spatial distribution of the average 1995–2015 mass balance (mb) within the promice ice-sheet mask (citterio & ahlstrøm 2013; khan et al. 2016). black lines denote the eight major ice-sheet sectors (zwally et al. 2012). 1995 2000 2005 2010 2015 (g t/ yr ) -100 0 100 1 1995 2000 2005 2010 2015 (g t/ yr ) -100 0 100 2 1995 2000 2005 2010 2015 (g t/ yr ) -100 0 100 3 1995 2000 2005 2010 2015 (g t/ yr ) -100 0 100 4 1995 2000 2005 2010 2015 (g t/ yr ) -100 0 100 5 1995 2000 2005 2010 2015 (g t/ yr ) -100 0 100 6 1995 2000 2005 2010 2015 (g t/ yr ) -100 0 100 7 1995 2000 2005 2010 2015 (g t/ yr ) -100 0 100 8 1995 2000 2005 2010 2015 (g t/y r) -600 -400 -200 0 200 400 600 ice sheet ice discharge surface mass balance mass balance 0°10°w30°w 40°w50°w 50°w70°w 80°n 75°n 75°n 70°n 70°n 65°n 65°n 60°n 60°n300 km mm/yr mb 2000 0 -2000 2 3 7 6 4 5 1 8 e2019430201-05 vey period (c. 1995). negative mass balance years, however, have clearly become more common towards the end of the survey period (fig. 4). in particular, marine-terminating sectors with substantial ice discharge (central west (7), southeast (4) and north-east (8)) transitioned to persistent mass loss c. 2002, 2004 and 2005, respectively. land-terminating sectors with substantial meltwater runoff (south (5), southwest (6)) subsequently transitioned to persistent mass loss c. 2006. at the ice-sheet scale, the total mass loss we assess over the 1995–2011 period agrees, within uncertainty, with that assessed by the ice sheet mass balance inter-comparison exercise (imbie) (fig. 5; shepherd et al. 2012). the apparent discrepancy between imbie and promice mass loss estimates is approximately equivalent to independent estimates of peripheral glacier mass loss (noël et al. 2017). adding the promice mass loss estimate for the ice sheet proper with the peripheral glacier mass loss estimate of noël et al. (2017) suggests that peripheral glaciers were responsible for 17 ± 7% of greenland’s contribution to sea level change during 2004–2013. peripheral glaciers account for < 5% of greenland’s ice-covered area (citterio & ahlstrøm, 2013), making their specific, or per unit area, sea-level contribution disproportionately greater than the ice sheet. our linear extrapolation of pre-2008 ice velocities, under-sampling f low variations in south-east greenland glaciers in 2000–2007, likely contributes to some discrepancy with the imbie sealevel contribution curve (enderlin et al. 2014). ice discharge increased from 1995 (350 ± 72 gt/yr) to 2009 (487 ± 71 gt/yr), before decreasing slightly to 2015 (465 ± 74 gt/yr). persistently increasing trends in iceberg calving are more readily apparent in sectors 7 and 8 than in sectors 3 (central east) and 4 (fig. 4). the trend in ice f lux across the promice perimeter ( 1.5 gt/yr/yr) was small in comparison to the trend in ice discharge across the grounding line ( 7.2 gt/yr/yr) during 2000–2015. the majority of the inter-annual variability in grounding-line ice discharge therefore results from the downstream surface mass balance and ice volume corrections we apply to the perimeter f lux. ice-sheet wide ice discharge during 2000–2015 (432 ± 74 gt/yr) is c. 45 gt/yr (10%) lower than that assessed by king et al. (2018) (479 ± 20 gt/yr) for the same period. during 2000–2010, our ice discharge (422 ± 74 gt/yr) is c. 90 gt/yr (21%) lower than that assessed by enderlin et al. (2014; 511 ± 30 gt/yr) during the same period. the formal uncertainty of a given study can therefore be substantially smaller than inter-study discrepancies. trends and variability in mar-simulated ice-sheet wide surface mass balance have been widely discussed (fettweis et al. 2017). the ice-sheet wide annual surface mass balances we employ are consistent with the relatively extensive ablation area of the 500 m resolution promice ice mask and the average surface mass balance we interpolate over the 1990–2010 period (382 ± 58 gt/yr) is within the sensitivity range of the elevation-dependent downscaled product of mar2 simulations from their native 25 km resolution to 15 km resolution during the same period (franco et al. 2012). as virtually the entire ice-sheet ablation area is downstream of the promice perimeter, the ice discharge we assess is fundamentally dependent on simulated surface mass balance. a more positive surface mass balance simulation would result in greater ice discharge and vice versa. differences in downstream surface mass balance correction are primarily responsible for the c. 55 gt/yr (12%) decrease in the ice discharge assessed here (460 ± 75 gt/yr) in comparison to that originally assessed by andersen et al. (2015; 515 ± 57 gt/yr) during 2007 and 2011. programme outlook this report updates the contribution of the greenland ice sheet to annual sea-level rise assessed by promice, using the andersen et al. (2015) input-output approach. we assess an ice-sheet mass loss of 3028 ± 711 gt over the 1995–2015 period, which is equivalent to a eustatic sea-level rise contribution of 8.4 ± 1.9 mm. combining our estimate of ice-sheet mass loss with a previous estimate of peripheral glacier mass loss yields a total greenland ice loss (ice sheet plus peripheral fig. 5. cumulative sea-level equivalent (sle) contribution from this promice study shown in comparison to the greenland mass balance inter-comparison exercise (imbie; shepherd et al. 2012). as imbie surveys both the ice sheet and peripheral glaciers, we also sum this study with the independent peripheral glacier contribution estimate of noël et al. (2017) for context. 1995 2000 2005 2010 2015 se ale ve l c on tr ib ut io n (m m ) 0 2 4 6 8 10 12 imbie promice (this study) promice + noël2017 e2019430201-06 *corresponding author: william colgan | e-mail: wic@geus.dk 1 department of glaciology and climate, geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350, copenhagen k, denmark. 2 natural history museum, university of copenhagen, copenhagen, denmark 3 department of geodynamics, technical university of denmark, lyngby, denmark 4 department of geodesy, technical university of denmark, lyngby, denmark 5 department of microwave and remote sensing, technical university of denmark, lyngby, denmark 6 department of geography, university of liège, liège, belgium glaciers) that is consistent with the most recent consensus of total greenland ice loss (shepherd et al. 2012; noël et al. 2017). digital versions of the area-integrated calendar year mass balance that we assess in eighteen ice-sheet sub-sectors, as well as underlying components, are available on the www. promice.dk website. as a result of the relatively high-elevation and inland location of the promice perimeter, virtually the entire icesheet ablation area resides downstream. this makes interannual variability in grounding-line ice discharge estimated by andersen et al. (2015), highly sensitive to inter-annual variability in downstream corrections. future promice mass balance products will therefore adopt new approaches where ice f lux is estimated across gates near the grounding lines of individual outlet glaciers. the sustained effort of the programme for monitoring of the greenland ice sheet (promice) will continue to provide danish and international stakeholders open access to policy-relevant estimates of ice-sheet mass loss and sea-level rise. acknowledgements this work is a product of the programme for monitoring of the greenland ice sheet (www.promice.dk), which is funded by the danish cooperation for environment in the arctic (dancea) through the danish ministry of climate, energ y and utilities. we thank the reviewers, rachel carr and ellyn enderlin, for their comments, which improved the manuscript. references andersen et al. 2015: basin-scale partitioning of greenland ice sheet mass balance components (2007–2011). earth and planetary 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http://icesat4.gsfc.nasa.gov/cryo_data/ant_grn_drainage_systems.php https://doi.org/10.34194/geusb-201943-02-01 geological survey of denmark and greenland bulletin 42, 2018, 1-5 petroleum geology of the upper jurassic – lower cretaceous of east and north-east greenland: blokelv-1 borehole, jameson land basin edited by jon r. ineson and jørgen a. bojesen-koefoed geologic al survey of denmark and greenland ministry of energy, utilities and climate geological survey of denmark and greenland bulletin 42 • 2018 22 geological survey of denmark and greenland bulletin 42 keywords jameson land, central east greenland, blokelv-1, borehole, petroleum geolog y cover recovery of the excellent blokelv-1 core, on which this bulletin is based, was thanks to the professional expertise of the drilling team (faxe kalk a/s, geus), depicted here erecting the drilling rig. photograph: annette ryge. frontispiece: facing page the flat-topped hills in the foreground are formed by the hareelev formation, the subject of this bulletin, viewed here in central jameson land with a backdrop to the east of the snow-clad mountains of liverpool land. photograph: jørgen bojesen-koefoed. chief editor of this series: adam a. garde editorial board of this series: john a. korstgård, department of geoscience, aarhus university; minik rosing, geological museum, university of copenhagen; finn surlyk, department of geosciences and natural resource management, university of copenhagen scientific editors of this volume: jon ineson and jørgen bojesen-koefoed editorial secretary: jane holst referees (numbers refer to first page of reviewed article): morten smelror, no & william wimbledon, uk (15); michael larsen & finn surlyk, dk (39); jens therkelsen, dk & knut bjørlykke, no (65); erdim idiz & iain c. scotchmann, uk (85); jiri slama, cz & martin sønderholm, dk (115); christian tegner, dk & godfrey fitton, uk (127); andrew carter & andrew whitham, uk (133); finn surlyk, dk & rikke bruhn, no (149) illustrations: jette halskov and stefan sølberg layout and graphic productions: jacob lind bendtsen printers: rosendahls, søborg, denmark submission/acceptance dates of manuscripts: see end of individual articles printed: 28 december 2018 issn (print) 1604-8156 issn (online) 1904-4666 isbn (print) 978-87-7871-508-1 isbn (online) 978-87-7871-509-8 citation of the name of this series it is recommended that the name of this series is cited in full, viz. geological survey of denmark and greenland bulletin. if abbreviation of this volume is necessary, the following form is suggested: geol. surv. den. green. bull. 42, 168 pp. available from geological survey of denmark and greenland (geus) øster voldgade 10, dk-1350 copenhagen k, denmark to buy bulletin in printed form please contact bogsalg@geus.dk and at www.geus.dk/bulletin42 (open access) © de nationale geologiske undersøgelser for danmark og grønland (geus), 2018 for the full text of the geus copyright clause, please refer to www.geus.dk/bulletin mailto:bogsalg@geus.dk http://www.geus.dk/bulletin42 http://www.geus.dk/bulletin 44 contents preface jørgen a. bojesen-koefoed ................................................................................................................................................................ 5 the upper jurassic blokelv-1 cored borehole in jameson land, east greenland – an introduction morten bjerager, stefan piasecki and jørgen a. bojesen-koefoed ............................................................................................... 7 biostratigraphy of the hareelv formation (upper jurassic) in the blokelv-1 core, jameson land, central east greenland peter alsen and stefan piasecki ....................................................................................................................................................... 15 sedimentology, geochemistry and reservoir properties of upper jurassic deep marine sediments (hareelv formation) in the blokelv-1 borehole, jameson land basin, east greenland morten bjerager, claus kjøller, mette olivarius, dan olsen and niels h. schovsbo .............................................................. 39 diagenesis of upper jurassic sandstones of the blokelv-1 core in the jameson land basin, east greenland mette olivarius, rikke weibel, niels h. schovsbo, dan olsen and claus kjøller ................................................................... 65 petroleum potential of the upper jurassic hareelv formation, jameson land, east greenland jørgen a. bojesen-koefoed, morten bjerager, h. peter nytoft, henrik i. petersen, stefan piasecki and anders pilgaard ............................................................................................................................................... 85 provenance of basinal sandstones in the upper jurassic hareelv formation, jameson land basin, east greenland mette olivarius, morten bjerager, nynke keulen, christian knudsen and thomas f. kokfelt ........................................... 115 igneous intrusions in the cored upper jurassic succession of the blokelv-1 borehole, jameson land basin, east greenland lotte melchior larsen ..................................................................................................................................................................... 127 burial and exhumation history of the jameson land basin, east greenland, estimated from thermochronological data from the blokelv-1 core paul f. green and peter japsen ...................................................................................................................................................... 133 late jurassic evolution of the jameson land basin, east greenland – implications of the blokelv-1 borehole morten bjerager, peter alsen, jørgen a. bojesen-koefoed, tove nielsen, stefan piasecki and anders pilgaard ............................................................................................................................................. 149 5 preface this bulletin presents a series of nine papers dealing with the succession of upper jurassic – lower cretaceous sedimentary rocks penetrated by the fully cored blokelv-1 borehole, drilled in western jameson land, central east greenland in august 2008. the borehole was drilled as the first of three boreholes that in combination were designed to provide full coverage of the upper jurassic – lower cretaceous petroleum source-rock succession in eastern greenland. the remaining two boreholes, rødryggen-1 and brorson halvø-1, were drilled on wollaston forland in 2009 and 2010, respectively, and the results from these boreholes will be published in a companion volume. the objectives of the drilling campaign were fulfilled, demonstrating that continuous sedimentation of oil-prone petroleum source rocks took place in eastern greenland over a period of c. 13 million years from the oxfordian to the ryazanian, with the blokelv-1 succession representing the older, oxfordian– volgian part of this interval. the drilling campaign was carried out as one of a number of projects within the framework of a multi-client collaborative programme between geus and a long list of petroleum companies entitled petroleum geological studies, services and data in east and northeast greenland. this collaboration was initiated in 2007 and is ongoing at the time of writing with more than 20 participant companies, a subset of which sponsored the studies presented herein; for contractual reasons, these companies cannot be named. the geus–industry collaboration was initiated in recognition of the need for new and better data on many aspects of the petroleum geolog y of eastern greenland prior to an anticipated licensing round of offshore north-east greenland. the circum-arctic resource appraisal (cara), undertaken by the united states geological survey (usgs), also played an important role in defining the priorities of the collaborative agreement by directing attention towards specific subjects in need of investigation. licensing rounds in 2012 and 2013 resulted in the award of five licences. based on the results of these activities in eastern greenland, a large number of scientific papers have been published since 2008, and more are expected as confidentiality clauses expire. this volume is, however, the first geus bulletin to be published as a direct consequence of the geus–industry collaboration. jørgen a. bojesen-koefoed © geus, 2018. geological survey of denmark and greenland bulletin 42 , 5. available at: www.geus.dk/bulletin42 http://www.geus.dk/bulletin42 geological survey of denmark and greenland bulletin 35, 2016, 13-16 13© 2016 geus. geological survey of denmark and greenland bulletin 35, 13–16. open access: www.geus.dk/publications/bull the subsurface material in urban areas comprises the original geological succession together with anthropogenic modifications and deposits. the geological survey of denmark previously performed geological mapping in selected danish cities (e.g. mertz 1974), but this practice stopped in the mid-1980s. the lack of recent systematic mapping in urban areas is apparent not only in denmark but also in most other european countries (cost 2015). however, there is a growing demand for knowledge of the subsurface beneath our cities for a number of reasons: increased urbanisation, infiltration of excess surface water and other climate-change related measures, thermal storage, groundwater cooling and abstraction, subsurface infrastructure, infrastructure projects, etc. the physical properties of the subsurface material are in constant change due to urban growth and infrastructure development. this can strongly influence the geotechnical properties and handling of excess surface water. in order to manage both challenges and opportunities of the ground beneath the cities there is a growing need for 3d hydrogeological models that can encompass all relevant parts of the physical subsurface system and act as operational tools in its management. with the main focus on hydrogeology and the urban water cycle, the municipality of odense, the local waterworks (vandcenter syd), the geological survey of denmark and greenland (geus) and two consultants (alectia and i-gis) have made a joint effort to systematically map the subsurface layers and build a 3d hydrogeological model of the subsurface of the city of odense (fig. 1). this paper provides an overview of the project rationale and an outline of the major results. the sedimentary succession beneath odense the uppermost 50 to 100 m of the subsurface of odense is dominated by weichselian clay till with intervening sand layers (e.g. jørgensen & piotrowski 2003, mertz 1974), which form three groundwater reservoirs of varying extent and thickness. there are also lateto postglacial, nearsurface, sandy outwash plains and heterogeneous infill of erosive channels and depressions (sandersen et al. 2015). historical maps from the late 1800s show that postglacial bogs and wetland areas have also earlier been present. the urban development of odense has mainly taken place within the past 200 years (fig. 1). the switch to the industrial era increased its population and led to expanding residential and paved areas, installation of water supply and sewage systems, creation of waste dumps and an accelerated abstraction of groundwater. the drainage and lowering of the groundwater table dried out some of the former wetlands and created new agricultural and urbanised land, and in other areas caused subsidence due to the decay of organic matter. since the 1980s, a growing environmental awareness and increased taxes have resulted in a marked decrease in groundwater abstraction, and former 3d hydrogeological modelling for urban subsurface management in odense, denmark susie mielby, tom martlev pallesen and peter b.e. sandersen 1717 1839 1892 1928 1977 urban plan 2009–2021 odense municipality odense o de nse fjo rd 5 km fig. 1. urban development of odense municipality (laursen & mielby 2016). 1414 wetland areas are beginning to return to their original wet state. the urban activities within the last 200 years created a heterogeneous man-made layer consisting of backfill of excavations, modified terrain, landfill, waste dumps, etc. parts of this anthropogenic layer rest on top of the original geological formations, whereas other parts replace them. building the 3d model the man-made modifications of the urban subsurface, along with the ongoing climate change, affect the urban water cycle and must therefore be carefully evaluated. for instance, in areas with sustainable urban drainage systems (suds), the local infiltration potential and its consequences on the hydraulic heads in adjacent areas must be known (jeppesen 2014; mielby et al. 2015a), and this implies a need for a close integration of regional and local geological information. in order to build a comprehensive subsurface model for odense both the natural and man-made layers were mapped, but due to their different nature, different mapping and modelling approaches were needed. a standard framework-model approach where layer boundaries were mapped all the way to the surface was employed for the original geology, primarily using borehole data, geophysical data and high-resolution digital elevation models (sandersen et al. 2015). the man-made layers shown in fig. 2 were mapped using data from boreholes about the thickness and character of infill, and from excavations around subsurface infrastructures. the latter requires detailed information about the age, character and spatial extent of the individual parts of the infrastructure and access to current standards for excavation back-fill (fig. 3; pallesen & jensen 2015). the digital information about the anthropogenic layer is generally abundant, but also rapidly changing compared with the traditional geological data. because the elements of the anthropogenic layers change over time, a tool for the modelling of the anthropogenic layers was established in the modelling software geoscene3d to make a sequential handling of the infrastructure data possible (pallesen & jensen 2015). the need for a high degree of detail is most relevant in the uppermost parts of the 3d model, where the scale of the urban infrastructure typically is counted in metres or tens of metres. mapping of the man-made layers should therefore be done with a corresponding level of detail. in the deeper parts of the subsurface, the number of boreholes that reach depths of 20 m or more is very limited (kristensen et al. 2015), meaning that the deeper geological succession typically cannot be resolved better than 100 m horizontally (sandersen et al. 2015). after mapping of the original geological layers and the man-made components the two parts are merged, whereby the latter component replaces the model part of the original geological layers (fig. 4). in this way, two models are combined into one 3d model. however, due to the above-mentioned scale difference, it is important to choose a common resolution that meets the required need for detail but does not exceed computational capability. the major part of the geological information in the urban area comes from relatively short boreholes drilled in connection with geotechnical and environmental projects. the geotechnical borehole information is very important, as it provides information about both the original geology and the composition of the man-made fill. data from many of these boreholes are stored in the national jupiter database, but its quality is variable because upload of this type of borehole data is not mandatory. in addition, many boreholes have not found their way to the national database at all, because the data were collected by private companies, considering the information their private property. therefore, the readily available digital geological information does not necessarily reflect all of the existing data, and this problem must be addressed before a 3d model is constructed. fig. 2. simplified picture of the subsurface elements in the man-made urban layer, where the original geological sediments (light grey) are replaced by infill (yellow), basements of buildings, wells, pipes, sewers, etc. forming the anthropogenic layer. 15 results the project resulted in a 3d geological municipality model, and detailed anthropogenic and combined hydrogeological models were made for a chosen site in order to test the modelling in a typical situation. in addition to the models and the model tool in geoscene3d, descriptions, workflows and recommendations for data acquisition, management and updating procedures were also developed. in the project, a systematic and comprehensive collation of available data was established within the borders of odense municipality. in 2015, the geological model concept provided the ‘best so far‘ foundation for the management of the urban hydrogeology in odense. the resulting model and its tools were proven to be valuable, as they were quickly taken into use in several new hydrological modelling projects such as modelling of hydrological climatechange effects and detailed infiltration possibilities, as well as the evaluation of the natural protection of drinkingwater well fields. the data and information density proved variable, and therefore information on the data background is important for the municipal decision-making. detailed studies in odense showed that in many areas the data coverage is insufficient for the purpose required. therefore, the geological basis for planning and water management has to be improved, and this requires a dynamic model that can benefit from both existing and new data. if all additional geological data are to be accessible for future planning, the authorities must ensure that all geological and geotechnical data are reported and available. the investigations in the current project proved that open access to better geotechnical and geological data and modelling would also benefit a wider range of users such as archaeologists, engineers, architects, entrepreneurs and other professionals working with e.g. road and railway construction (laursen et al. 2015). if the 3d model is regularly updated in the future, odense will also obtain an increasingly robust foundation for the hydrological modelling and management of the urban water cycle. detailed recommendations and experience from the current project (mielby et al. 2015b), urban data modelling tools in geoscene3d and data storage facilities for geotechnical information in the jupiter database (hansen et al. 2015) are available for the benefit of other areas. a b fig. 3. a: large sewer in an excavation to be filled with gravel. image source: vandcenter syd. b: anthropogenic model of sewers with other implemented data elements (roads, pipes and buildings). 1616 acknowledgements the foundation for development of technology in the danish water sector (vtufonden; ans-7497.2012) is thanked for financial support. the project partners knud søndergaard and gert laursen, odense municipality, christian ammitsøe and johan linderberg, vcs denmark, martin hansen and margrethe kristensen, geus and jan jeppesen, alectia are acknowledged for fruitful collaboration. references cost 2015: http://www.cost.eu/cost_ actions/tud/actions/tu1206. suburban – a european network to improve understanding and use of the ground beneath our cities. hansen, m., wiese, m.b., gausby, m. & mielby, s. 2015: udvikling af en 3d geologisk/hydrogeologisk model som basis for det urbane vandkredsløb. delrapport 6 – teknisk håndtering og lagring af bygeologiske data og modeller, 22 pp. københavn: de nationale geologiske undersøgelser for danmark og grønland. jeppesen, j. 2014: udvikling af en urban-hydrologisk model til simulering af nye innovative lar-løsninger til lokal håndtering af både regn-vand og grundvand (larg). afrapportering af vtu-projekt 29. december 2014. jørgensen, f. & piotrowski, j.a. 2003: signature of the baltic ice stream on funen island, denmark during the weichselian glaciation. boreas 32, 242–255. kristensen, m., sandersen, p. & mielby, s. 2015: udvikling af en 3d geologisk/hydrogeologisk model som basis for det urbane vandkredsløb. delrapport 2 – indsamling og vurdering af data, 82 pp. københavn: de nationale geologiske undersøgelser for danmark og grønland. laursen, g. & mielby, s. 2016: odense. tu1206 cost sub-urban wg1 report. laursen, g., mielby, s. & kristensen, m. 2015: udvikling af en 3d geologisk/hydrogeologisk model som basis for det urbane vandkredsløb. delrapport 3 – geotekniske data til planlægning og administration, 32 pp. københavn: de nationale geologiske undersøgelser for danmark og grønland. mertz, e.l. 1974: odense og omegns jordbundsforhold: en ingeniørgeologisk beskrivelse. danmarks geologiske undersøgelse rapport 9, 37 pp. mielby, s., laursen, g., linderberg, j., sandersen, p. & jeppesen, j. 2015a: udvikling af en 3d geologisk/hydrogeologisk model som basis for det urbane vandkredsløb. delrapport 1 – 3d-modellen som basis for håndteringen af det urbane vandkredsløb, 66 pp. københavn: de nationale geologiske undersøgelser for danmark og grønland. mielby, s., jespersen, c.e., ammitsøe, c., laursen, g., jeppesen, j., linderberg, j., søndergaard, k., kristensen, k., hansen, m., jensen, n.-p. & sandersen, p. 2015b: udvikling af en 3d geologisk/hydrogeologisk model som basis for det urbane vandkredsløb. synteserapport, 57 pp. københavn: de nationale geologiske undersøgelser for danmark og grønland. pallesen, t.m. & jensen, n.-p. 2015: udvikling af en 3d geologisk/ hydrogeologisk model som basis for det urbane vandkredsløb. delrapport 5 – interaktiv modellering af antropogene lag, 58 pp. københavn: de nationale geologiske undersøgelser for danmark og grønland. sandersen, p., kristensen, m. & mielby, s. 2015: udvikling af en 3d geologisk/hydrogeologisk model som basis for det urbane vandkredsløb. delrapport 4 – 3d geologisk/hydrostratigrafisk modellering i odense, 106 pp. københavn: de nationale geologiske undersøgelser for danmark og grønland. a b c fig. 4. elements of the geological modelling. a: buildings and pipes. b: man-made ground with fill. c: combined model showing man-made features and the underlying geological model. authors’ addresses s.m. & p.s., geological survey of denmark and greenland, c.f. møllersvej 8, building 1110, dk-8000 aarhus c, denmark. e-mail: smi@geus.dk. t.m.p., i-gis, voldbjergvej 14, dk-8240 risskov, denmark. 51 lithological mapping using remote sensing depends, in part, on the identification of rock types by their spectral characteristics. chemical and physical properties of minerals and rocks determine their diagnostic spectral features throughout the electromagnetic spectrum. shifts in the position and changes in the shape and depth of these features can be explained by variations in chemical composition of minerals. detection of such variations is vital for discriminating minerals with similar chemical composition. compared with multispectral image data, airborne or spaceborne hyperspectral imagery offers higher spectral resolution, which makes it possible to estimate the mineral composition of the rocks under study without direct contact. arctic environments provide challenging ground for geological mapping and mineral exploration. inaccessibility commonly complicates ground surveys, and the presence of ice, vegetation and rock-encrusting lichens hinders remote sensing surveys. this study  addresses the following objectives: 1. modelling the impact of lichen on the spectra of the rock substrate; 2. identification of a robust lichen index for the deconvolution of lichen and rock mixtures and 3. multiscale hyperspectral analysis of lithologies in areas with abundant lichens. modelling the impact of lichen cover spectral mixing of lichens and bare rock can shift the wavelength positions of characteristic absorption features and complicate the spectral mapping of minerals and lithologies. salehi et al. (2017) investigated how surficial lichen cover affects the characteristics of shortwave infrared mineral absorption features and the efficiency of automated extraction of absorption features. for this purpose, mixed spectra were synthetically generated from laboratory spectra of common rock-forming minerals and lichens. wavelength displacements of characteristic absorption features for each mixed spectrum were then analysed as a function of lichen cover percentage (see an example in fig. 1). by quantifying lichen hyperspectral analysis of lithologies in the arctic in areas with abundant lichen cover sara salehi 2000 2100 2200 2300 2400 wavelength (nm) 0.15 0.02 0.25 0.30 0.35 0.40 re fle ct an ce kimberlite lichen hull a b quotient 2240 2260 2280 2300 2320 2340 wavelength (nm) 0.85 0.90 0.95 1.00 h ul l q uo tie nt 0 kimberlite / 100 lichen 50 kimberlite / 50 lichen 100 kimberlite / 0 lichen fig. 1. a: averaged spectra of pure rock and lichen for a kimberlite substrate in shortwave infrared range. b: the corresponding hull quotient (clark & roush 1984) and band centres of mixed spectra associated with the antigorite absorption feature. the 10% spectral intervals used to investigate the main absorption features are highlighted. x: wavelength positions of local minima (salehi et al. 2017). © 2018 geus. geological survey of denmark and greenland bulletin 41, 51–55. open access: www.geus.dk/bulletin http://www.geus.dk/bulletin 5252 cover effects on mineral absorption features, this study highlights the importance cautious interpretation in areas characterised by abundant, lichen-covered outcrops. this can be of significant importance for mineral and deposit identification, because slightly shifted features for a given spectrum caused by lichen cover can be erroneously identified as a path to a deposit. salehi et al. (2017) showed that spectral shifts caused by lichens are not constant, i.e. each mineral spectral feature may be affected differently depending on the shape of the lichen spectrum. for example, the absorption feature related to the chlorite mineral group around 2254 nm is shifted towards longer wavelength, while the one around 2320 nm is shifted towards shorter wavelength and the 2380 nm band maintains its spectral characteristics. spectral shifts are not only related to rock/lichen proportions but also to the modal abundance of minerals in certain rock types. background minerals and associated overlapping features will have an effect on the related absorption depth and play a critical role in the scale of wavelength displacement. identification of a robust lichen index the ability to distinguish a lichen cover from its rock/mineral substrate is important, and decomposition of a mixed pixel into a collection of pure ref lectance spectra can improve the use of hyperspectral methods for mineral exploration. in order to identify spectral indices that can directly ref lect the ratio of the rock and lichen in hyperspectral data, a number of index structures were assigned to an optimisation algorithm, which was tasked to find the best values for the location of the bands along the ref lectance spectra measured in the laboratory (salehi et al. 2016). in order to further investigate the functionality of the indices for the airborne platform, the spectra were resampled to hymap resolution. the indices proposed by salehi et al. (2016) proved robust to the type of the substrate rock and permitted an estimate of the lichen cover with acceptable, albeit varying, levels of error. the results revealed that the ratio between r 894-1246 and r 1110 explains most of the variability in the hyperspectral data at the original laboratory resolution (r 2=0.769). however, the normalised index incorporating r 1106-1121 and r 904-1251 yields the best results for the hymap resolution (r 2=0.765). re fle ct an ce (o ffs et fo r cl ar ity ) wavelength (nm) wavelength (nm) olivine (usgs) talc (usgs) anthophyllite (usgs) hornblende (usgs) hornblende (hymap) antigorite-anthophyllite (hymap) talc-olivine/pyroxene (hymap) actinolite (hymap) serpentine-olivine (hymap) serpentine (usgs) actinolite (usgs) actinolite-hornblende (hymap) a b 500 1000 1500 2000 2200 2300 2400 fig. 2. spectra of extracted end members compared with selected minerals from the usgs spectral library in envi software. a: full spectral range. b: shortwave infrared range. 53 the proposed methodology has the advantage of not requiring a priori knowledge about the exact effects of lichens – or any other substance – on the ref lectance of the mixtures. instead, this information is obtained by an automated trial and error process. therefore, this technique can also be beneficial for identification of sensitive bands and indices for deconvolution of any other mixed spectra, whether synthetic as in this case, or obtained directly from the samples. multiscale hyperspectral analysis of lithologies with abundant lichen cover two sets of hyperspectral data acquired by airborne hymap (350–2500 nm) and light-weight rikola (500–900 nm) sensors were chosen to investigate the potential of visible near infrared and shortwave infrared spectral range for detailed lithological mapping in the nagssugtoqidian orogen of west greenland, where an ultramafic rock unit with abundant lichen cover is exposed. the extent to which geological information derived from airborne data is retained in the rikola serpentine + pyroxene 0 end-member abundance (%) serpentine + olivine/pyroxene amphibole (actinolite/hornblende) lichen vegetation 0.25 0.50 0.75 1 0 0.25 0.50 0.75 1 0 0.25 0.50 0.75 1 0 0.25 0.50 0.75 1 0 0.25 0.50 0.75 1 66 °4 4' 38 ''n 66 °4 4' 10 ''n 52°31'26'' w 52°30'22'' w 500 m fig. 3. the result of unmixing analysis and the abundance of mafic-ultramafic minerals using hymap data. masked pixels are indicated by black colour. ricola vnir b a b c d fig. 4. a: supracrustal rocks in the innarsuaq region comprising a kilometre-sized body of mafic-ultramafic, looking north. b: bright green and black amphibole and biotite at the corner (alteration zone). c: host ultramafic rock; green amphibole to the left and white talc vein in the middle. d: 50 cm long asbestos fibres. 5454 hyperspectral data, is examined as an insight to future dronebased hyperspectral mapping capabilities and the possibility of extracting valuable mineralogical and lithological information using such platforms. the airborne hyperspectral dataset is corrected for abnormal pixels and removal of bad bands (such as water vapour absorption features and noisy bands) prior to atmospheric correction. dark pixels, snow, clouds and water were filtered out. next, the spatial–spectral end-member extraction method (rogge et al. 2007) is used to derive an image end-member set. this makes an assessment of subtle lithological variability across a given study area possible. these end members are then sorted based on expert knowledge of known spectral features (water, snow, vegetation, lichen and geological materials) followed by a more detailed sorting into individual classes within each category. subtle shortwave infrared features related to key minerals in the geological materials are particularly important. the resulting sorted end-member classes are subsequently averaged to produce a final end-member set. a final set of six geological end members (fig. 2), and two end members related to vegetation and lichens are deducted from expert-based analysis. figure 2 mafic lichen and vegetation 500 m 50 m ultramafic a b c w e 0 0.25 0.50 0.75 1 0 0.25 0.50 0.75 1 0 0.25 0.50 0.75 1 0 0.25 0.50 0.75 1 0 0.25 0.50 0.75 1 actinolite serpentine/olivine talc anthophyllite lichen and vegetation legend (c). end-member abundance (%) fig. 5. a: true-colour hyperspectral image mosaic generated using the rikola camera. b: minimum noise fraction false-colour image: red: band 6. green: band 2. blue: band 1. c: result of spectral unmixing analysis and the abundance of mafic-ultramafic minerals. 55 shows a plot of the extracted end members using the spatial– spectral end-member extraction method and the corresponding signatures from the united states geological survey (usgs) spectral library (kokaly et al. 2017). the shortwave infrared spectral characteristics of the ultramafic rocks studied here were controlled by amphibole minerals as exemplified by hornblende, actinolite and anthophyllite (fig. 3). the absorption features in the shortwave infrared region are located at 2320 and 2380 nm and are of the same order of magnitude. the shortwave infrared spectrum of olivine-rich rocks clearly ref lects a mixture of antigorite serpentine with a characteristic stronger absorption feature at 2320 nm. a less distinct absorption feature at 2310 nm is present for rocks enriched in talc. fractional abundances of the end members within the scene are determined using an iterative implementation of spectral mixture analysis method (rogge et al. 2007). the interpretation of hymap data revealed a number of mafic and ultramafic complexes in the border area between the parautochthonous and allochthonous zones of the nagssugtoqidian orogen. one such complex occurs to the east of the head of the fjord kangerluarsuk, here referred to as innarsuaq (see fig. 1 of salehi & thaarup 2018, this volume). as can be seen from fig. 3, the predictive map from the innarsuaq area displays a complex distribution of exposed bedrock, a feature confirmed during a brief field visit. the results were validated using expert knowledge of spectral characteristics of lichens and mineralogy, as well as spectral measurements of field samples and associated xrd results. the rikola camera was operated in ground-based mode and panned stepwise to acquire a set of five overlapping images. the images were corrected for geometric, radiometric and topographic effects and stitched to a continuous mosaic (figs 4, 5). the distribution of lithological  units  were then mapped using the minimum noise fraction method (kruse et al. 1993).the information regarding mineral abundances were retrieved using the spectra unmixing procedure (fig. 5). conclusions 1. lichen effects on the spectra of their rock substrate have important implications for the geological analysis of airborne/spaceborne hyperspectral data where rock-encrusting lichens partially obscure exposed bedrock. 2. analysis of airborne hyperspectral data can result in highquality regional mapping products capable of discriminating geological materials of interest based on subtle spectral differences. the map product generated from the rikola scenes in this study captures the broad geological patterns and many of the lithologies generated from the airborne data, although some spectral and lithological discrimination is lost due to its more limited wavelength range. 3. the performance of hyperspectral data acquired from different platforms and at various scales is investigated for qualitative mapping of arctic mineral resources in the presence of abundant lichens. the application of such technologies to extract detailed geological information from complex inaccessible regions of greenland certainly has a very low cost/benefit ratio in comparison to traditional geological fieldwork. future space-borne hyperspectral sensors will offer new possibilities to expand the scale of mapping in greenland. integration with other remote sensing datasets such as magnetic data will simplify mineral exploration and geological mapping in the arctic. acknowledgments the helmholtz institute freiberg is thanked for the use of rikola hyperspectral imager. references clark, r.n. & roush, t.l. 1984: ref lectance spectroscopy: quantitative analysis techniques for remote sensing applications. journal of geophysical research: solid earth 89(b7), 6329–6340. kokaly, r.f., clark, r.n., swayze, g.a., livo, k.e., hoefen, t.m., pearson, n.c., wise, r.a., benzel, w.m., lowers, h.a., driscoll, r.l.& klein, a.j. 2017: usgs spectral library version 7. u.s. geological survey data series 1035, 61 pp., http://dx.doi.org/10.3133/ds1035 kruse, f.a., lef koff, a., boardman, j., heidebrecht, k., shapiro, a., barloon, p. & goetz, a. 1993: the spectral image processing system (sips) – interactive visualization and analysis of imaging spectrometer data. remote sensing of environment 44, 145–163 rogge, d.m., rivard, b., zhang, j., sanchez, a., harris, j., & feng, j. 2007: integration of spatial–spectral information for the improved extraction of endmembers. remote sensing of environment 110, 287–303. salehi, s. & thaarup, s. 2018: mineral mapping by hyperspectral remote sensing in west greenland using airborne, ship-based and terrestrial platforms. geological survey of denmark and greenland bulletin 41, 47–50 (this volume). salehi, s., karami, m. & fensholt, r. 2016: identification of a robust lichen index for the deconvolution of lichen and rock mixtures using pattern search algorithm (case study: greenland). international archives of the photogrammetry, remote sensing & spatial information sciences xli-b7, 973–979. salehi, s., rogge, d., rivard, b., heincke, b.h. & fensholt, r. 2017: modeling and assessment of wavelength displacements of characteristic absorption features of common rock forming minerals encrusted by lichens. remote sensing of environment 199, 78–92. author’s address s.s., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: ssal@geus.dk. http://dx.doi.org/10.3133/ds1035 mailto:ssal@geus.dk geological survey of denmark and greenland bulletin 41, 2018, 75-78 75 initial field activities of the camp century climate monitoring programme in greenland william colgan, allan pedersen, daniel binder, horst machguth, jakob abermann and mike jayred fig. 1. location of camp century that was constructed by the us army corps of engineers in 1959 in the greenland ice sheet. camp century was abandonned in 1967. 500 km camp century thule air base camp century was a military base constructed by the us army corps of engineers in 1959 in the near-surface layers of the greenland ice sheet at 77.13°n, 61.03°w and 1886 m above sea level (clark 1965; fig. 1). the base housed up to 200 military personel and was continuously occupied until 1964. after three years of additional seasonal operation, the base was abandoned with minimal decommissioning in 1967. recent danish scholarship has documented the political and military history of camp century in detail (nielsen & nielsen 2016). in 2016, the geological survey of denmark and greenland (geus) participated in a multi-nation study that presented regional climate simulations that suggested the icesheet surface mass balance at camp century may change from net accumulation to net ablation by 2100 under the un intergovernmental panel on climate change rcp8.5 ‘business-as-usual’ climate scenario. however, according to colgan et al. (2016), net accumulation would persist beyond 2100 at camp century under the climate-change mitigation characterised by rcp4.5, an approximately ‘paris agreement’ climate scenario. in 2017, in response to concerns from the government of greenland over the potential to remobilisation of contaminants from camp century within the next century, the government of denmark established a programme for long-term climate monitoring and detailed one-time surveying of the debris field at camp century (colgan et al. 2017). this report describes the initial field activities of the camp century climate monitoring programme in the context of the four programme goals: 1. to continuously monitor relevant climate variables, including the depth to which meltwater percolates, at the camp century site. 2. to regularly update annual likelihoods of meltwater interacting with abandoned materials at the camp century site over the next century. 3. to map the estimated spatial extent and vertical depth of abandoned wastes across the camp century site. 4. to publicly report all findings from the camp century climate monitoring programme in a timely manner. field logistics field activities of the camp century climate monitoring programme were initiated in summer 2017, when a six-person team spent two weeks at the camp century site (19 july to 3 august). there is no abandoned infrastructure visible at the ice-sheet surface at camp century (fig. 2). debris field location, as well as zones of restricted drilling depth, were estimated prior to field work (fig. 3). this was done by georeferencing a historical site map using a single tie-point, the location of the original drill tower, corrected for motion since its last precise survey in 1986 (gundestrup et al. 1987). the 2017 summer camp, which consisted of three common © 2018 geus. geological survey of denmark and greenland bulletin 41, 75–78. open access: www.geus.dk/bulletin http://www.geus.dk/bulletin 7676 tents and six personal tents, was established within the debris field, approximately aligned with the location of post-closure summer camps (kovacs 1970). although decamped entirely, the footprint of the 2017 summer camp will likely be visible in subsequent ice-penetrating radar surveys due to the formation of massive wind-sculpted snowdrifts around it. during field work, there was persistent cloud cover with frequent storm conditions. the mean wind speed was 8.8 m/s, and the maximum 1 hour mean wind speed was 18.3 m/s (beaufort 8). thule air base, located approximately 200 km west, served as logistical base for the field work. a ski-equipped twin otter aircraft was used to transport 3200 kg of equipment and supplies to and from the ice sheet. field work consisted of installing three automated instrument stations, drilling boreholes for instrument installation and firn sampling, surveying velocity stakes, and collecting ice-penetrating radar profiles. of the 175 m firn core drilled, 135 m were analysed in the field and 40 m were transported to copenhagen for more detailed radionuclide analysis by the center for nuclear technologies at the technical university of denmark. instruments and data climate measurements were initiated using automated weather station technology previously developed by geus. the automatic weather station design has a proven record of more than 175 station-years of deployment in greenland since its introduction in 2007 (citterio et al. 2015). the primary weather station at camp century (cen) measures air temperature and humidity, wind speed and direction, atmospheric pressure, upward and downward shortwave and longwave radiation, subsurface (snow/ice) temperatures to 10 m s6 s5 cen-com b62 500 m b73 cen cen-gps cen-thm s7 instrument tower borehole ice velocity stake 2017 camp ice-penetrating radar 25 m drill zone 10 m drill zone 545250 545750 546250 546750 547250 547750 548250 85 66 50 0 85 67 00 0 85 67 50 0 85 68 00 0 85 68 50 0 85 69 00 0 projection: wgs84, utm 20n s2 s3 s4 fig. 3. overview of initial field activities at camp century. recently constructed instrument towers refer to the primary weather station (‘cen’), the supplementary thermistor station (cen-thm), the supplementary compaction station (cen-com) and the supplementary global positioning system station (cen-gps; to be installed). boreholes refer to the 73 (b73) and 62 (b62) m firn cores. restricted drill zone depths were assessed based on georeferencing of a historical as-built site map (kovacs 1970). fig. 2. the temporary ice-sheet camp at 1600 utc on 20 july 2017. the camp consisted of three common tents and six personal tents. there was persistent cloud cover with frequent storm conditions and a mean wind speed of 8.8 m/s. no abandoned infrastructure is visible at the ice-sheet surface; the entire debris field is now subsurface as a result of net snow accumulation since closure. 77 fig. 4. left: near-surface firn density profiles measured both inside (b73) and outside (b62) the debris field. the high-density layer between 32 and 35 m depth within the debris field likely ref lects enhanced compaction during the c. 1960–1964 active period. r ight: near-surface snow/ice temperatures at b73 inside the debris field. the annual temperature cycle penetrates to c. 12 m depth, with year-round firn temperatures remaining c. –24°c below this depth. density (kg/m )3 400 600 800 d ep th (m ) 0 10 20 30 40 50 60 70 b62 b73 temperature (°c) –30 –20 –10 0 0 10 20 30 40 50 60 70 aug sep oct nov dec jan feb mar apr depth, and snow depth, as well as diagnostic parameters such as battery voltage. the temperature of the relatively porous near-surface ice-sheet layer known as firn is also measured by a supplementary thermistor station (cen-thm) to a depth of 73 m, which approximates local pore close-off depth (fig. 3). ice-sheet structure was analysed with 73 and 62 m deep firn cores, hereafter referred to as b73 and b62. firn density and melt percentage were measured to a minimum depth of 62 m at locations inside and outside the debris field (fig. 4). a third automatic station was deployed to measure the compaction rate of snow into ice, or vertical strain, over the 0 to 5 m, 0 to 20 m and 1 to 62 m depth ranges. this third automatic station, the supplementary compaction station (cen-com), is located outside the debris field. all three automatic stations satellite-transmit their measurements in near-real-time to www.campcenturyclimate.dk. a fourth station that records observations from the global positioning system (cen-gps) will be installed to continuously monitor ice f low. these climate and ice data will be used to calibrate and validate future simulations of firn evolution. preliminary interpretation the measurements from the automated weather station (cen) record that midday air temperature exceeded 0°c for three days during the operational period of the 2017 summer camp. the maximum one-hour mean air temperature was 1.8°c. under these warm conditions, surface melt quickly froze to moving drill parts when the drill was lowered into cold winter firn. this necessitated a two-day suspension of drilling. preliminary analysis of the b73 deep thermistor measurements, located within the debris field, indicates that the annual temperature cycle in near-surface snow and ice temperatures penetrates to c. 12 m depth (fig. 4). beyond this depth, year-round firn temperatures appear to remain c. –24°c. in summer 2017, there was limited meltwater production and refreezing, with no apparent change in firn temperature beyond this annual diffusion cycle. preliminary analysis of near-surface firn structure indicates that refrozen meltwater layers are readily identifiable in the uppermost 15 m of the firn. the largest of these layers is c. 8 cm thick, which represents the melt-and-refreeze of c. 25% of annual snowfall (buchardt et al. 2012). the firn cores suggest that meltwater movement beyond the annual layer is unlikely. near-surface firn densities are similar both inside and outside the debris field to 32 m depth (fig. 4). between 32 and 35 m depth, firn density is significantly greater within the debris field. this high-density layer is slightly discoloured in appearance and likely ref lects enhanced compaction and pollution during the c. 1960–1964 active period. below this active layer, firn densities are similar inside and outside the debris field. after drilling b73 through the highdensity active layer, pressurised hydrocarbon vapours vented from the borehole until it was backfilled. mobile hydrocarhttp://www.campcenturyclimate.dk 7878 bon vapours were not anticipated, and vapour-tight equipment was not available on-site to opportunistically sample these vapours. radar survey data from the one-time summer 2017 radar survey are being analysed to perform a detailed assessment of the horizontal extent and vertical range of the debris field. 100 and 250 mhz ice-penetrating radar data were collected by crosscountry skiing in a dense grid pattern over the camp century debris field (fig. 3). the radar profiles, each tagged with global positioning system coordinates, will be available on the programme website. a preliminary field analysis of the ice-penetrating radar data shows that the sub-surface debris field is c. 2 km in diameter, with debris ranging between c. 20 and 100 m depth. this ice-penetrating radar data will permit improved geo-referencing of historical as-built site maps, via precisely positioning key subsurface infrastructure features, which will facilitate delineating the debris field beyond the extent recorded by as-built site maps. programme outlook this report describes the initial field activities of the camp century climate monitoring programme in the context of programme goals. near-real-time climate and ice measurements from automated stations, ice-penetrating radar profiles, as well as programme outreach materials and publications, can be accessed at www.campcenturyclimate.dk. subsequent field work at camp century will be undertaken, as needed, to service deployed instrumentation. during these subsequent site revisits, ice-velocity stakes will be resurveyed to precisely measure the relatively slow (<5 m/yr) ice velocity over several years. data analysis, in support of observationally-constrained numerical simulations of the evolution of meltwater and firn, is the major programme focus. while climate change now gives camp century previously unanticipated social significance, the sustained effort of the camp century climate monitoring programme will continue to provide danish and greenlandic stakeholders open access to relevant in situ measurements and model projections. refined knowledge of the spatial extent and vertical range of the debris field, as well as the changes in firn structure and meltwater production anticipated under climate change, will inform science-based discussions of the shifting fate of camp century. acknowledgements the camp century climate monitoring programme is jointly funded by geus and the danish cooperation for environment in the arctic (dancea) within the danish ministry for energ y, utilities and climate. j.a. was supported by the greenlandic ministry of independence, foreign affairs and agriculture. the 2017 field team (w.c., a.p., d.b., h.m., j.a. and m.j.) warmly thank danish liaison officers kim marchuard mikkelsen and jens alsing for logistical assistance at thule air base. references buchardt, s., clausen, h., vinther, b. & dahl-jensen, d. 2012: investigating the past and recent δ18o-accumulation relationship seen in greenland ice cores. climate of the past 8, 2053–2059. clark, e.f. 1965: camp century evolution of concept and history of design, construction and performance. cold regions research and engineering laboratory. technical report 174, 69 pp. citterio, m. et al. 2015: automatic weather stations for basic and applied glaciological research. geological survey of denmark and greenland bulletin 33, 69–72. colgan, w., machguth, h., macferrin, m., colgan, j.d., van as, d. & macgregor, j.a. 2016: the abandoned ice sheet base at camp century, greenland, in a warming climate. geophysical research letters 43, 8091–8096. colgan, w., andersen, s.b., van as, d., box, j.e. & gregersen, s. 2017: new programme for climate monitoring at camp century, greenland. geological survey of denmark and greenland bulletin 38, 57–60. gundestrup, n.s., clausen, h.b., hansen, b.l. & rand, j. 1987: camp century survey 1986. cold regions science and technolog y 14, 281– 288. kovacs, a. 1970: camp century a pictorial overview june 1969. cold regions research and engineering laboratory, special report 150, 59 pp. nielsen, h. & nielsen, k. 2016: camp century – cold war city under the ice. in: doel, r., harper, k. & heymann, m. (eds): exploring greenland: cold war science and technolog y on ice, 195–216. new york: palgrave macmillan us. authors’ addresses w.c., a.p., d.b., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: wic@geus.dk. h.m., university of fribourg, avenue de l ’europe 20, sx 1700 fribourg, switzerland. j.a., asiaq greenland survey, qatserisut 8, dk 3900 nuuk, greenland. m.j., university of wisconsin, madison, wisconsin 53706, usa. http://www.campcenturyclimate.dk mailto:wic@geus.dk e2019430208-01 the landslide of 17 june 2017 at karrat fjord, central west greenland, triggered a tsunami that caused four fatalities. the catastrophe highlighted the need for a better understanding of landslides in greenland and initiated a recent nation-wide landslide screening project led by the geological survey of denmark and greenland (geus; see also svennevig (2019) this volume). this paper describes an approach for compiling freely available data to improve geus’ capability to monitor active landslides in remote areas of the arctic in near real time. data include seismological records, spaceborne synthetic aperture radar (sar) data and multispectral optical satellite imagery. the workf low was developed in 2018 as part of a collaboration between geus and scientists from the technical university of denmark (dtu). this methodology provides a model through which geus will be able to monitor active landslides and provide relevant knowledge to the public and authorities in the event of future landslides that pose a risk to human life and infrastructure in greenland. we use a minor event on 26 march 2018, near the site of the karrat 2017 landslide, as a case study to demonstrate 1) the value of multidisciplinary approaches and 2) that the area around the landslide has continued to be periodically active since the main landslide in 2017. geological setting and description of the landslide area the geology of the karrat area (fig. 1) predominantly consists of reworked archaean gneiss interfolded with supracrustal rocks of the palaeoproterozoic karrat group (henderson & pulvertaft 1967). locally, around the landslide and surrounding unstable areas, the succession consists of archaean gneiss overlain by palaeoproterozoic semipelitic to pelitic schist. the geology of the karrat 2017 landslide has not been mapped in detail; however, an ongoing mapping project aims to update the geological maps of the area (e.g. sørensen & guarnieri 2018). during the landslide of 17 june 2017, 35–58 million m3 of material were mobilised (bessette-kirton et al. 2017; gauthier et al. 2018). a preliminary examination of the karrat 2017 landslide shows that a number of precursor events took place in the years prior to the main landslide. unstable areas that may fail in the future have also been identified. of these, two principal areas (marked with y and z in fig. 2a) west of the scarp of the main slide (marked by ‘x’ in fig. 2a) a multidisciplinary approach to landslide monitoring in the arctic: case study of the march 2018 ml 1.9 seismic event near the karrat 2017 landslide kristian svennevig*1, anne munck solgaard1, sara salehi1, trine dahl-jensen1, john peter merryman boncori2, tine b. larsen1 and peter h. voss1 geus bulletin is free to individuals and institutions in electronic form. the author(s) retain copyright over the article contents. r esearch article | open access geus bulletin vol 43 | e2019430208 | published online: 01 july 2019 https://doi.org/10.34194/geusb-201943-02-08 fig. 1 overview map of the uummannaq fjord area showing the location of the 26 march 2018 1.9 ml seismic event (ellipse) along with the position of the 17 june 2017 landslide at karrat and the nearby instabilities. the size of the landslide and nearby instabilities are slightly exaggerated for clarity on the small map scale. seismic stations in uummannaq and nuugaatsiaq are shown along with settlements in the area. fig. 2 71°30’n 71°00’n 51°w u u m m a n n a q f j o r d s i g g n u p n u n a a n u u s s u a q nuugaatsiaq illorsuit ukkusissat marmorilik qaarsut niaqornat uummannaq saattut g r e e n l a n d i c e s h e e t 53°w fig. 1 k a r r a t f j o r d seismic station location of event ml 1.9 (26 march 2018) landslide of 17 june 2017 instability settlement g re en la nd 25 km https://doi.org/10.34194/geusb-201943-02-08 e2019430208-02 show signs of significant deformation both before and after the 2017 landslide. this activity is observable in both optical satellite images and in the results derived from remotely sensed differential synthetic aperture radar (sar) interferometry (dinsar; y and z in figs 2a, d, e). data the various data sources used here have different temporal and spatial resolutions. individually, they provide unique information for landslide monitoring, but their value increases significantly when combined. as such, integration of data from seismograms, dinsar and optical images can provide a more complete understanding of the geological processes contributing to landslide activity. seismic events the present greenland ice sheet monitoring network (glisn) of seismographs consists of 21 stations, situated about 200 km or more apart (clinton et al. 2014). given this large distance, the uncertainty associated with the horizontal location of detected earthquakes or other types of seismic events in greenland can be up to 50 km. differentiation of tectonic and non-tectonic events is based on the judgement of an experienced seismologist. for example, the main seismic features associated with tectonic earthquakes are clearly separated body waves, higher frequency content and a well-located hypocentre at depth, whereas non-tectonic events are not dominated by higher frequencies. these can be caused in several ways. glacial events, such as those caused by calving ice, have an epicentre located near an outlet glacier and often contain a low frequency component (ekström et al. 2003; nettles et al. 2008). large landslides can also generate seismic signals, but these are often of longer duration than those caused by tectonic earthquakes, such as the seismic signals caused by the 2000 paatuut (dahljensen et al. 2004) and the 2017 karrat (clinton et al. 2017) landslides. for smaller landslide events (e.g. events without catastrophic failure and rock avalanche activity), the duration will be shorter and the amplitude smaller, and it may be difficult to distinguish them with seismic data alone from other non-tectonic seismic sources, e.g. signals generated by moving sea ice or glaciers. integration of other data sources are thus necessary. optical satellite images sentinel-2a and -2b are multispectral optical satellite imaging systems that cover 13 spectral bands at various spatial resolutions: 4 bands at 10 m resolution (including visual light), 6 bands at 20 m and 3 bands at 60 m. the revisit frequency of sentinel-2a and -2b over the karrat fjord area is 1–2 days at around 15:30–16:00 utc (12:30–13:00 local time). however, no images are collected between the end of october and the start of march as it is too dark. the present study is limited to visual interpretation of sentinel-2 images as change detection algorithms have not been implemented. dinsar dinsar (rosen et al. 2000) was applied to sentinel-1a and sentinel-1b synthetic aperture radar (sar) data acquired between 24 february and 13 april 2018. this method provides one-dimensional ground motion measurements in the satellite line-of-sight direction, i.e. towards and away from the radar. the main acquisition mode of sentinel-1 over land is the interferometric wide (iw) swath mode,  which provides 250 km × 250 km images at a 5 m × 20 m spatial resolution in the ground range and f light-path directions, respectively. the karrat area is covered by two satellite tracks: descending track 25 and ascending track 90. however, on ascending passes in track 90, the area of interest slopes towards the radar, leading to significant radar foreshortening (and in some locations even to layover). in turn, this causes geometric decorrelation of the radar signal even for small interferometric baselines, due to the horizontal spreading of the scatterers within each resolution cell (i.e. due to the poor line-of-sight resolution). for this reason, we used data from track 25 only in this analysis. unlike optical data from e.g. sentinel-2, sar has the advantage of being insensitive to cloud cover and solar illumination, and imagery can therefore be acquired year-round. dinsar can be applied to data collected along the same radar track, which are available every six days for the sentinel1a/b constellation on the greenland ice sheet margin. one of the main requirements of dinsar is a sufficient level of coherence (i.e. statistical similarity) between the two acquisitions. in practice, this limits the number of good interferograms collected during the winter season, as snowfall may change the surface morphology between two acquisitions and cause loss of coherence. for this study, both 6 and 12 day differential interferograms were constructed. topographic contributions to the interferometric phase were removed using arcticdem version 2.0 (porter et al. 2018) and additional corrections (courtesy of e.v. sørensen, geus) were e2019430208-03 plot start time: 2018 26 march 21:20 56 21:21 seconds time (utc) 100 20 30 40 50 nuug hhz nuug hh1 nuug hh2 a b c fig. 2 x y z 2018 26 march 15:29 41 1 km 2018 27 march 15:48 59 250 m x y z x y z d e march 20 to 26 2018 march 26 to april 1 2018 fig. 2 composite figure with the different datasets used to constrain the event. a: sentinel-2a rgb image from 26 march 2018 15:29 41 utc. dashed line at x shows the scar of the 17 june 2017 landslide and y shows the outline of the active area to the sw. z indicates the position of a large older landslide with periodic activity in the toe. b: sentinel-2b rgb image from 27 march 2018 15:48 59 utc. red arrows show rock fall at the unstable area y and the green arrow shows rock fall at the back scarp of the karrat 2017 event. the dotted black line shows the outline of the area affected by the event, as observed in the inset image. c: the 26 march 2018 21:21 utc 1.9 ml seismic event as recorded on the nuugaatsiaq seismograph (fig. 1). d: sentinel-1 differential interferogram from before the event, (20180320-20180326), the latter interferogram was acquired only hours prior to the event. x, y and z refer to the same areas in a. e: sentinel-1 differential interferogram spanning the event from (20180326-20180401). x, y and z refer to the same areas in a. e2019430208-04 made to account for the height variations associated with the june 2017 landslide. the 26 march 2018 ml 1.9 event on 26 march 2018 at 21:21 utc (18:21 local west greenland time) a shallow, low frequency non-tectonic ml 1.9 seismic event was recorded on several seismographs in west greenland (figs 1, 2c; see the earlier discussion of tectonic vs. non-tectonic event features). the event was located to an ellipsoid of c. 100 by 20 km covering an area of known landslide activity near the 2017 karrat landslide. the time between the p and s wave arrivals corresponded to the distance between the seismic station in nuugaatsiaq, and the karrat landslide area. the ellipsoid also encompassed two glacial outlets (fig. 1). to investigate the source of the seismic signal, we acquired sentinel-2a and 2b images from 26 march 15:29 utc and 27 march 15:48 utc. comparison of the two images show dark colouration of the snow (fig. 2b) indicating rock fall from the known active area (red arrows in fig. 2b) and the whole length of the headscarp of the karrat 2017 landslide (green arrow in fig 2b). the rock fall was only observed very locally on the coast and a screening of neighbouring slopes and glacial outlets showed no changes between the two images. temperatures were well below freezing during the whole period. images from the week before and after the event were also screened and showed no increased rock fall activity. in the period leading up to the event, the 6 day pairs of sar images are coherent in the whole slope area, and the differential interferograms show activity constrained to the 2017 landslide area and areas y and z to the west (fig. 2). these areas, or subareas within them, show incoherence in all studied interferograms back to the spring of 2015. an example of this is given in fig. 2d where the last image in the pair is from just hours prior to the seismic event. the image pairs (both 6 and 12 day) spanning the seismic event have a low coherence, resulting in noisy interferograms (fig. 2e). inspection of optical images from approximately the same time as the sar images suggests that the observed loss of coherence is due to changes in snow cover over most of the slope likely due to redistribution by wind. it is thus not possible to observe this event in the interferograms as, for example, an increase in decorrelated area of the continuous active areas. instead, we have to rely on observations from the optical imagery for interpretation. this emphasises the importance of using multiple independent methods for observing landslides. possible cause of the event it is clear that the localised rock fall occurred across the time span of the shallow ml 1.9 non-tectonic seismic event. however, the interferograms spanning this event are noisy and thus we cannot yet confirm the exact cause of the event. however, by compiling all three independent datasets together, we suggest that landslide movement along a fracture could have generated the seismic signal and triggered localised rock fall near the epicentre. the landslide movement could have been either a rapid acceleration in creep of the unstable area west of the 2017 karrat landslide scar (y in fig. 2a), or the propagation of an unknown fracture related to landslide activity – potentially the westward migration of the fracture that forms the headscarp of the 2017 landslide – or both. this appears to be supported by the fact that no catastrophic mass wasting was observed in the sentinel-2 images, which might otherwise have indicated that the event was a true landslide like the 2017 karrat landslide. moreover, no large-scale calving events were observed in the two nearby glacial outlets, suggesting that glacial activity was not the cause of the seismic event. the differential interferogram prior to the event (fig. 2d) shows that areas on the slope were moving before the event, but there are no seismic signals present during this period. other similar seismic and rock fall events have been observed episodically throughout 2018 and eyewitnesses have reported activity in the area since the 2017 karrat landslide took place. the area continues to be active. outlook the approach described here has the potential to serve as a model contingency plan to gather the relevant information in the event of a landslide. this information could then be disseminated to the public and relevant authorities in the form of express reports. these methods can also be applied to quantify the temporal evolution of past landslides using archive data. sentinel-2 images are available from mid-2015 and for older events, more coarse-scale landsat images can be used back to the early seventies. sentinel-1a sar data are available from october 2014, whereas both sentinel-1a and 1b data are available from october 2016. the current glisn seismic network is available back to summer 2010 (clinton et al. 2017). the first stations were installed in greenland in 1928, and until the 1990s the network consisted of only 3–4 stations, increasing to 5–8 stations before the glisn network. prior to 2010, only very large landslides would have been observed by the seismic stations, for example the 2000 paatuut landslide (dahl-jensen et al. 2004), which also coincided with e2019430208-05 a research network station deployment (dahl-jensen et al. 2003). a similar approach could also be implimented to quantify activity in other remote areas that are prone to landslides. an obvious candidate is the south coast of the nuussuaq peninsular where several catastrophical historical and prehistorical landsides are known to have occurred (pedersen et al. 2002; dahl-jensen et al. 2004; svennevig 2019). in the future, a denser network of seismographs on a regional scale would greatly improve our capability to locate earthquakes in the area more precisely and help us to determine the cause of non-tectonic events. for example, an event that is far from a glacier terminus is less likely to be caused by glacial activity. a local seismic network around the landslide coast at karrat would further help to determine the cause of these earthquakes by pinpointing exactly where on the slope they occur relative to known structures. a similar network could also be applied to the vaigat coast where non-tectonic seismic events are also suspected to be caused by landslide activity, and where there is a historical record of landslides (pedersen et al. 2002; dahl-jensen et al. 2004). automation of the sar and optical data processing (change detection; e.g., lacroix et al. 2018) could also aid the workf low. while we are unable to precisely identify the cause of the ml 1.9 seismic event, it is clear that the combination of the various datasets is key to understanding the process involved in such events and demonstrates the benefit of a multidisciplinary approach. acknowledgments we thank the reviewers, andrée blais-stevens and erin bessette-kirton, whose comments and suggestions improved the manuscript. references bessette-kirton, e., allstadt, k., pursley, j. & godt, j. 2017: preliminary analysis of satellite imagery and seismic observations of the nuugaatsiaq landslide and tsunami, greenland. https://www.usgs.gov/ natural-hazards/landslide-hazards/science/preliminar 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nettles, m. & abers, a.g. 2003: glacial earthquakes. science 302, 622–624. https://doi.org/ 10.1126/science.1088057 gauthier, d., anderson, s.a., fritz, h.m. & giachetti, t. 2018: karrat fjord (greenland) tsunamigenic landslide of 17 june 2017: initial 3d observations. landslides 15, 327–332. https://doi.org/10.1007/ s10346-017-0926-4 henderson, g. & pulvertaft, t.c.r. 1967: the stratigraphy and structures of the precambrian rocks of the umanak area, west greenland. meddelelser dansk geologisk forening 17, 1–20. lacroix, p., bièvre, g., pathier, e., kniess, u. & jongmans, d. 2018: use of sentinel-2 images for the detection of precursory motions before landslide failures. remote sensing of environment 215. 507–516. https:// doi.org/10.1016/j.rse.2018.03.042 nettles, m. et al. 2008: step-wise changes in glacier f low speed coincide with calving and glacial earthquakes at helheim glacier, greenland. geophysical research letters 35, 1–5. https://doi. org/10.1029/2008gl036127 pedersen, s.a.s., larsen, l.m., dahl-jensen, t., jepsen, h.f., krarup, g., nielsen, t., pedersen, a.k., von platen-hallermund, f. & weng, w.l. 2002: tsunami-generating rock fall and landslide on the south coast of nuussuaq , central west greenland. geolog y of greenland survey bulletin 191, 73–83. porter, c. et al. 2018: arcticdem v2, https://doi.org/10.7910/dv n/ ohhukh, harvard dataverse. rosen, p.a., hensley, s., joughin, i.r., li, f.k., madsen, s.n., rodriguez, e. & goldstein, r. 2000: synthetic aperture radar interferometry. proc. of the ieee 88, 333–382. https://doi.org/10.1109/5.838084 sørensen, e.v. & guarnieri, p. 2018: remote geological mapping using 3d photogrammetry: an example from karrat, west greenland. geological survey of denmark and greenland bulletin 41, 63–66. svennevig, k. 2019: preliminary landslide mapping in greenland. geological survey of denmark and greenland bulletin 43, e2019430207. https://doi.org/10.34194/geusb-201943-02-07 how to cite svennevig, k. solgaard, a.m., salehi, s., dahl-jensen, t., merryman boncori, j.p., larsen t.b., & voss, p.h. 2019: a multidisciplinary approach to landslide monitoring in the arctic: case study of the march 2018 ml 1.9 seismic event near the karrat 2017 landslide. geological survey of denmark and greenland bulletin 43, e2019430208. https://doi.org/10.34194/ geusb-201943-02-08 *corresponding author: kristian svennevig | e-mail: ksv@geus.dk 1 geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350, copenhagen k, denmark. 2 dtu space, national space institute, technical university of denmark, ørsteds plads, 2800 lyngby, denmark. https://www.usgs.gov/natural-hazards/landslide-hazards/science/preliminary-analysis-satellite-imagery-and-seismic?qt-science_center_objects=0#qt-science_center_objects https://www.usgs.gov/natural-hazards/landslide-hazards/science/preliminary-analysis-satellite-imagery-and-seismic?qt-science_center_objects=0#qt-science_center_objects https://www.usgs.gov/natural-hazards/landslide-hazards/science/preliminary-analysis-satellite-imagery-and-seismic?qt-science_center_objects=0#qt-science_center_objects https://www.usgs.gov/natural-hazards/landslide-hazards/science/preliminary-analysis-satellite-imagery-and-seismic?qt-science_center_objects=0#qt-science_center_objects https://doi.org/10.1002/2014eo020001 https://ds.iris.edu/ds/nodes/dmc/specialevents/2017/06/22/nuugaatsiaq-greenland-landslide-and-tsunami/#seismic-observations-from-nuugatsiaq-slidetsunami https://ds.iris.edu/ds/nodes/dmc/specialevents/2017/06/22/nuugaatsiaq-greenland-landslide-and-tsunami/#seismic-observations-from-nuugatsiaq-slidetsunami https://ds.iris.edu/ds/nodes/dmc/specialevents/2017/06/22/nuugaatsiaq-greenland-landslide-and-tsunami/#seismic-observations-from-nuugatsiaq-slidetsunami https://doi.org/10.1016/s0012-821x(02)01080-4 https://doi.org/10.1016/s0012-821x(02)01080-4 https://doi.org/10.1023/b:nhaz.0000020264.70048.95 https://doi.org/10.1023/b:nhaz.0000020264.70048.95 https://doi.org/10.1126/science.1088057 https://doi.org/10.1007/s10346-017-0926-4 https://doi.org/10.1007/s10346-017-0926-4 https://doi.org/10.1016/j.rse.2018.03.042 https://doi.org/10.1016/j.rse.2018.03.042 https://doi.org/10.1029/2008gl036127 https://doi.org/10.1029/2008gl036127 https://doi.org/10.7910/dvn/ohhukh https://doi.org/10.7910/dvn/ohhukh https://doi.org/10.1109/5.838084 https://doi.org/10.34194/geusb-201943-02-07 https://doi.org/10.34194/geusb-201943-02-08 https://doi.org/10.34194/geusb-201943-02-08 mailto:rsf%40geus.dk?subject= geological survey of denmark and greenland bulletin 42, 2018, 127-131 127 igneous intrusions in the cored upper jurassic succession of the blokelv-1 borehole, jameson land basin, east greenland lotte melchior larsen the fully cored upper jurassic succession in the blokelv-1 borehole in the jameson land basin, east greenland, is intersected by igneous intrusions at four levels; the intrusions comprise a c. 15 cm thick dyke and three sills with thicknesses of 0.7, 1.2 and 1.9 m. the sills consist of fine-grained, sparsely plagioclase-olivine-phyric basalt with chilled contacts to the sediments. analyses of two sills gave very similar results. the sills are tholeiitic basalts with compositions similar to the main group of dykes and sills in the jameson land basin, and the blokelv-1 sills are thus considered to belong to this group which has been dated at c. 53 ma. the intrusions form part of a 55–51 ma suite of tholeiitic basalt intrusions that was emplaced over an area extending for over 500 km north-to-south within the sedimentary basins of east and north-east greenland. keywords: east greenland, dykes, cenozoic __________________________________________________________________________ l.m.l., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: lml@geus.dk the fully cored blokelv-1 borehole was drilled in 2008 through upper jurassic sediments in the jameson land basin, east greenland (bojesen-koefoed et al. 2009), in order to study the sedimentary succession (fig. 1a). the sediments in jameson land are intruded by many cenozoic dykes and sills (e.g. noe-nygaard 1976; hald & tegner 2000), and one of the site selection criteria was to minimise the risk of encountering thick igneous intrusions during drilling. although major intrusions were avoided, the 233.8 m succession in the blokelv-1 core is cut by intrusive igneous rocks at four levels with a combined thickness of 4.1 m (fig. 1b). the purpose of this paper is to present descriptions and analyses of these intrusions and compare them with other cenozoic dyke and sill intrusions in northern east greenland. intrusions in the blokelv-1 core the core is cut by igneous intrusions at four levels in the upper half of the section: 102.04–100.1 m (thickness 1.9 m), 56.4–55.2 m (thickness 1.2 m), 27.10–26.40 m (thickness 0.70 m) and 7.35–7.05 m (thickness 0.3 m). the uppermost intrusion has oblique boundary contacts, dipping at 60°, and is accordingly described as a dyke; its true thickness must be c. 15 cm. the three lower intrusions show boundary contacts that are broadly parallel to bedding in the host rock and thus appear to be sills. the two thickest sills have caused prominent alteration of the surrounding sediments (see olivarius et al. 2018, this volume). the thin dyke uppermost in the section (fig. 1b) is thoroughly altered and was not studied further. the remaining three sills are lithologically similar and consist of fine-grained, sparsely plagioclase-olivine-phyric basalt. at the chilled contacts, they are very fine-grained to aphanitic, altered, and cut by carbonate veins. in the middle sill, a fracture is filled with biodegraded oil (bojesenkoefoed et al. 2018, this volume). © geus, 2018. geological survey of denmark and greenland bulletin 42 , 127–131. available at: www.geus.dk/bulletin42 mailto:lml@geus.dk http://www.geus.dk/bulletin42 128128 petrography the 1.9 m thick lower sill (fig. 1b, 102.04–100.1 m) has a lower chilled margin that is aphanitic with many plagioclase microlites, sparse 0.1–0.2 mm plagioclase microphenocrysts, and a few plagioclase-olivine glomerocrysts with up to 2 mm plagioclase laths and 0.8 mm olivine crystals. plagioclase is fresh but the olivine is completely altered. the groundmass is extensively replaced by carbonate, but plagioclase phenocrysts are fresh. the rock is cut by 0.1–0.5 mm wide veins of ankerite with patches of pyrite which cut both sill and sandstone at the contact (fig. 2; see olivarius et al. 2018, this volume). the veins are thickest at the contact. the veins in the sandstone appear to fill tension cracks. the 1.2 m thick middle sill (fig. 1b, 56.4–55.2 m) has a very fine-grained upper chilled margin with sparse 0.5 mm plagioclase microphenocrysts and tiny <0.5 mm euhedral olivine crystals; all olivine crystals are altered to clay. the groundmass is intersertal with numerous plagioclase microlites. the central part of the sill is finegrained with sparse <1 mm plagioclase phenocrysts and sparse c. 0.5 mm fresh olivine microphenocrysts, often assembled in glomerocrysts. the groundmass is intergranular with plagioclase, clinopyroxene, fe-ti oxide, olivine, and abundant mesostasis. the 0.7 m thick upper sill (fig. 1b, 27.10–26.40 m) is a fine-grained, nearly aphyric rock with scattered vugs filled with colourless minerals. the lower contact is not preserved. the rock becomes slightly finer grained towards the upper contact and there is possibly a thin glass chill at the top. there is no visible influence on the overlying sediments. 70°30'n 50 km blokelv-1 mudstone sandstone a igneous intrusion 25°w 24°w 23°w 22°w 71°30'n 71°n 24°w 23°w 22°w 10 depth (m) 20 30 40 50 60 70 80 90 100 110 b h urry inlet j a m e s o n l a n d liverpool land bk s lml 1 s c o r e s b y s u n d upper jurassic – lower cretaceous middle jurassic upper triassic – lower jurassic devonian – middle triassic crystalline rock normal fault fig. 1. a: map of central and southern jameson land showing the location of the blokelv-1 borehole (70°45.305́ n, 23°40.430´w, wgs84 coordinates); inset shows the location of the study area in east greenland. bk: blosseville kyst. s: shannon. b: simplified log of the upper part (0–110 m) of the blokelv-1 core (ggu no. 511101). 129 chemical compositions two samples from the centres of the lower and middle sills have been analysed for major and trace elements. major elements were analysed by n. odling at university of edinburgh by x-ray fluorescence spectrometry (xrf) and procedures as described by fitton et al. (1998). trace elements were analysed in geus’ rock geochemical laboratory using a perkinelmer elan 6100 drc quadrupole inductively coupled plasma mass spectrometer (icp-ms). sample dissolution followed a modified version of the procedure used by turner et al. (1999) and ottley et al. (2003). calibration was done using two certified ree solutions and three international reference standards. results for reference samples processed and run simultaneously with the unknowns are normally within 5% of the reference value for most elements with concentrations >0.1 ppm (results are shown in table 1). the two sills consist of tholeiitic basalt with 6–7 wt% mgo and 2.1–2.3 wt% tio 2 . losses on ignition are low and the samples appear to be fresh. measured values of tantalum (ta) are high (1.1–1.4 ppm) where only c. 0.8 ppm ta is expected; this may be contamination from the tungsten carbide crushing vessel and the data are not included in table 1. the lower sill has 5.6 ppm pb which is very high, indicating contamination with pb either during emplacement or from the drilling process; there is no evidence of additional contamination. 5 mm fig. 2. lower contact towards sandstone of the 1.9 m thick lower sill at 102.04 m in the core. two ankerite veins cross both sill and sandstone. note plagioclase-olivine glomerocryst in the very fine-grained basalt matrix between the two veins. thin section 511101.246; plane-polarised light. major elements, wt% (xrf analyses) sio2 47.84 48.43 48.34 48.30 tio2 2.30 2.11 2.35 2.33 al2o3 13.71 12.87 13.79 13.80 fe2o3 14.07 12.95 14.07 14.07 mno 0.21 0.26 0.20 0.20 mgo 6.85 6.24 6.99 6.96 cao 11.23 12.08 11.52 11.47 na2o 2.23 2.03 2.39 2.37 k2o 0.22 0.40 0.29 0.30 p2o5 0.20 0.19 0.24 0.23 loi 0.47 1.84 -0.27 0.14 sum 99.33 99.40 99.91 100.17 trace elements, ppm (icp-ms analyses) sc 38 36 40 38 v 374 345 371 362 cr 190 179 259 249 co 55 50 53 52 ni 99 90 121 109 cu 240 218 256 249 zn 108 100 114 115 ga 21.0 20.0 rb 3.4 8.7 5.3 6.3 sr 217 230 237 228 y 31.1 30.5 32.1 31.7 zr 145 135 159 159 nb 12.1 11.7 12.6 12.8 cs 0.52 0.20 0.48 0.12 ba 130 110 71.6 71.9 la 10.5 11.6 10.7 10.9 ce 27.2 29.9 28.0 28.0 pr 4.10 4.27 4.16 4.17 nd 19.7 20.1 19.1 19.2 sm 5.09 5.01 5.15 5.27 eu 1.68 1.64 1.77 1.74 gd 6.07 5.79 5.42 5.30 tb 0.99 0.91 0.94 0.93 dy 5.78 5.45 5.49 5.36 ho 1.14 1.07 1.13 1.10 er 3.09 2.95 2.91 2.87 tm 0.47 0.44 0.43 0.43 yb 2.77 2.69 2.65 2.61 lu 0.41 0.39 0.36 0.38 hf 3.77 3.47 3.60 3.57 ta 0.84 0.84 pb 0.91 5.61 1.29 1.71 th 0.84 1.25 0.9 0.89 u 0.26 0.29 0.31 0.31 depth (m) 55.2–56.4 100.1–102 ene dyke thin sill ggu no 511101.230 511101.229 407203 403021 table 1. chemical analyses of two sills in the blokelv core, with comparisons from jameson land total iron is reported as fe2o3. loi is loss on ignition. data for jameson land from hald & tegner (2000). middle sill lower sill jameson land lml table 1 130130 discussion the two analysed sills have very similar compositions and are considered to have been intruded during the same magmatic event. the tholeiitic basalt represents a magma type that is known from widespread sills and dykes in the jameson land basin (larsen et al. 1989; hald & tegner 2000). hald & tegner (2000) recognised five different magma types represented by sills and dykes, and by far the most common group is the one found in the blokelv sills. this group was called the ‘high-ti group’ by hald & tegner (2000), but as the ti contents are not high, it is referred to here as the ‘main group’. figure 3 shows geochemical patterns for the blokelv sills compared with similar patterns for the jameson land sills and dykes. the close similarity of the blokelv sills with the main group of tholeiitic sills and dykes in jameson land is clear. the blokelv intrusions are poorly suited for 39ar/40ar dating because of the low k 2 o content and few and small plagioclase phenocrysts. however, hald & tegner (2000) dated a sill and a dyke from the main group by the 39ar/40ar method. the sill yielded a 5-point isochron age of 52.7 ± 1.2 ma, and the dyke yielded a four-point isochron age of 53.3 ± 1.4 ma; the two ages are within the uncertainty of each other (the ages are here recalculated to an age of 28.201 ma for the fish canyon tuff standard). it is therefore most probable that the two blokelv sills were emplaced at c. 53 ma. the intrusions in the jameson land basin were emplaced after the plateau lavas of the blosseville kyst at 56.4–55.3 ma (storey et al. 2007) and after or just concomitantly with the plateau lavas in north-eastern greenland at 56–53 ma (larsen et al. 2014). they are within the age range of 55–51 ma obtained for tholeiitic sills and dykes intruded into the sediments from jameson land in the south to the island of shannon in the north (hald & tegner 2000; larsen et al. 2014). most intrusion ages are in the interval 54–52 ma and magma production at that time must have been very extensive. these intrusions cover a stretch of least 500 km which is close to the entire onshore extent of the mesozoic basins. the intrusions are older than the igtertivâ formation at kap dalton on the blosseville kyst which comprises two parts dated at 49.1 ± 0.5 ma and 43.8 ± 1.1 ma (larsen et al. 2013). larsen et al. (2013) found significant geochemical differences between the igtertivâ formation basalts and the underlying 55 ma lavas of the skrænterne formation, in particular in the rare-earth element (ree) ratios. as seen in fig. 4, the intrusions at 55–51 ma retained the geochemical characteristics of the older plateau lavas, indicating that the conditions of magma generation were unchanged, probably mainly governed by the relatively thick lithosphere beneath the continent away from the developing oceanic rift (hald & tegner 2000). conclusions the two analysed sills in the blokelv-1 core are compositionally similar to the main group (high-ti group) of tholeiitic basalt sills and dykes that occur frequently in the jameson land basin, of which two have been dated at c. 53 ma. the blokelv sills are considered to belong to this group. the group shares trace element characteristics 1 10 100 1000 1 10 100 1000 la ce pr nd pm sm eu gd tb dy ho er tm yb lu rb ba th u nb ta k la ce pb pr sr nd sm zr hf eu ti tb dy y ybgdp sa m pl e/ c ho nd ri te sa m pl e/ pr im iti ve m an tle alkaline main group blokelv sills low-ti lml 2 lml3 fig. 3. multi-element patterns for the blokelv sills compared with sills and dykes in the jameson land basin (data from hald & tegner 2000). alkaline and low-ti basalt are two other basalt groups defined by hald & tegner (2000). note the close similarity between the main group of intrusions and the blokelv sills. the high pb in one of the blokelv samples must be due to contamination. 131 with the older blosseville kyst lavas and the 55−51 ma tholeiitic sills and dykes in east greenland, but not with the younger 49−54 ma igtertivâ formation lavas. the older magmas were probably generated under similar conditions beneath relatively thick lithosphere. acknowledgements the referees, godfrey fitton and christian tegner, are thanked for their constructive comments. references bojesen-koefoed, j.a., bjerager, m. & piasecki, s. 2009: shallow core drilling and petroleum geolog y related field work in east and north-east greenland 2008. geological survey of denmark and greenland bulletin 17, 53–56. bojesen-kofoed, j., bjerager, m., nytoft, h.p., petersen, h.i., piasecki, s. & pilgaard, a. 2018: petroleum potential of the upper jurassic hareelv formation, jameson land, east greenland. in: ineson, j. & bojesen-koefoed, j.a. (eds): petroleum geolog y of the upper jurassic – lower cretaceous of east and north-east greenland: blokelv-1 borehole, jameson land basin. geological survey of denmark and greenland bulletin 42, 85–113 (this volume). fitton, j.g., saunders, a.d., larsen, l.m., hardarson, b.s. & norry, m.j. 1998: volcanic rocks from the southeast greenland margin at 63°n: composition, petrogenesis and mantle sources. in: saunders, a.d., larsen, h.c. & wise, s.w., jr. (eds): proceedings of the ocean drilling program, scientific results 152, 331−350. college station, tx. hald, n. & tegner, c. 2000: composition and age of tertiary sills and dykes, jameson land basin, east greenland: relation to regional flood volcanism. lithos 54, 207–233. larsen, l.m., watt, w.s. & watt. m. 1989: geolog y and petrolog y of the lower tertiary plateau basalts of the scoresby sund region, east greenland. bulletin grønlands geologiske undersøgelse 157, 164 pp. larsen, l.m., pedersen, a.k., sørensen, e.v., watt, w.s. & duncan, r.a. 2013: stratigraphy and age of the eocene igtertivâ formation basalts, alkaline pebbles and sediments of the kap dalton group in the graben at kap dalton, east greenland. bulletin of the geological society of denmark 61, 1–18. larsen, l.m., pedersen, a.k., tegner, c. & duncan, r.a. 2014: eocene to miocene igneous activity in ne greenland: northward younging of magmatism along the east greenland margin. journal of the geological society (london) 171, 539–553. noe-nygaard, a. 1976: tertiary igneous rocks between shannon and scoresby sund, east greenland. in: escher, a. & watt, w.s. (eds): geolog y of greenland, 386–402. copenhagen: geological survey of greenland. olivarius, m., weibel, r., schovsbo, n.h., olsen, d. & kjøller, c. 2018: diagenesis of upper jurassic sandstones of the blokelv-1 core in the jameson land basin, east greenland. in: ineson, j. & bojesen-koefoed, j.a. (eds): petroleum geolog y of the upper jurassic – lower cretaceous of east and north-east greenland: blokelv-1 borehole, jameson land basin. geolog y of denmark and greenland survey bulletin 42, 65 –84 (this volume). ottley, c.j., pearson, d.g. & irvine, g.j. 2003: a routine method for the dissolution of geological samples for the analysis of ree and trace elements via icp-ms. in: holland, j.g. & tanner, s.d. (eds): plasma source mass spectrometry: applications and emerging technologies, 221–230. cambridge: royal society of chemistry. storey, m., duncan, r.a. & tegner, c. 2007: timing and duration of volcanism in the north atlantic igneous province: implications for geodynamics and links to the iceland hotspot. chemical geolog y 241, 264–281. turner, s.p., platt, j.p., george, r.m.m., kelly, s.p., pearson, d.g. & nowell, g.m. 1999: magmatism associated with orogenic collapse of the betic–alboran domain, se spain. journal of petrolog y 40, 1011–1036. 1.0 1.5 2.0 2.5 0.0 0.5 1.0 1.5 2.0 2.5 (la/sm)n (g d/ lu ) n igtertivâ fm lavas skrænterne fm lavas ne greenland sills and dykes jameson land sills and dykes blokelv intrusions, jameson land 55–51 ma 49–44 ma lml 4 fig. 4. rare-earth element (r ee) ratios for older (55–51 ma) lavas and intrusions (blosseville kyst to shannon) and younger (49–44 ma) igtertivâ formation lavas on blosseville kyst, east greenland. data from hald & tegner (2000), larsen et al. (2013), larsen et al. (2014) and unpublished geus data (2008–2010). a few crustally contaminated samples are not plotted. la/sm is the light r ee ratio and gd/lu is the heavy r ee ratio; n designates chondrite-normalised concentrations. _________________________________________________________________________________________ manuscript received 17 december 2015; revision accepted 29 august 2017 geological survey of denmark and greenland bulletin 41, 2018, 13-16 13 this study is based on a feasibility study for the danish energinet.dk to identify potential formations for brine storage near the gas storage facility at lille torup, northern jylland, denmark (fig. 1; hjuler et al. 2017). located on top of a salt structure, the gas storage facility comprises seven caverns, which have been washed out by circulating water in the salt dome. one cavern contains c. 520.000 m3 of intrusive brine that must be disposed of in order to increase the storage volume for gas. one option is to inject the brine into the subsurface if a target with appropriate storage properties can be identified, but it is a prerequisite that the stored brine does not compromise freshwater reservoirs. due to cost considerations, the brine storage should be situated within a radius of 50 km of the gas storage facility and at a depth not exceeding 2000 m. based on the national geothermal research conducted during the last decade, a number of sandy formations are considered potential storage reservoirs (fig. 2; e.g. mathiesen et al. 2009; vosgerau et al. 2016). around lille torup, these include the bunter sandstone/skagerrak, gassum, haldager sand and frederikshavn formations where the two former formations are discarded due to present-day burial depths exceeding 2000 m. in addition, the chalk group is considered a potential storage formation due to its importance as a hydrocarbon reservoir in the north sea, however, due to risk of leakage to the younger sediments and risk of environmental issues, the chalk was discarded as potential storage zone. geological background the lille torup area is located centrally in the danish basin, where the upper permian–mesozoic succession is 5–5.5 km thick. the basin was formed in the late carboniferous–early permian with basal rotliegendes coarse-grained clastic sediments and thick zechstein salts overlain by triassic sandstone, mudstone, carbonate rocks and salt (nielsen 2003). these are followed by lower jurassic mudstone, middle jurassic sandstone, upper jurassic–lower cretaceous mudstone and siltstone with few sandstone layers. the mesozoic succession terminates with c. 1200 m thick carbonate deposits. the salt structure at lille torup consists of mobilised zechstein salt penetrating the mesozoic succession. its top point is c. 250 m below the present-day surface. the haldager sand formation in the northern part of the basin is 2–150 m thick, but may exceed 200 m in rim synclines of salt structures, where sandstone commonly dominates the lithology. the frederikshavn formation is primarily present in the northern part of the basin and frequently includes sandstone layers. its thickness decreases southwards from 150–300 m to a few metres. the more than 1000 m thick chalkand limestone-dominated chalk group constitutes the topmost pre-quaternary formation in large parts of the danish basin. potential for brine storage near the gas storage facility at lille torup, northern jylland, denmark morten leth hjuler, morten sparre andersen, carsten møller nielsen, anders mathiesen, lars kristensen, nina skaarup and lars henrik nielsen r i n g k ø b i n g f y n h i g hn o r t h g e r m a n b a s i n n o r w e g i a n d a n i s h b a s i n 50 km lille torup gas storage facility salt diapir fault selected storage area 2d seismic line aarhus silkeborg randersviborg hobro skive aalborg holstebro 1 2 3 4 5 erslev-1 erslev-2 hyllebjerg-1 aars-1 farsø-1 kvols-1 hobro-1 gassum-1 skive-1 skive-2 mors-1 rødding-1 15 km fig. 1. the study area and selected storage areas within a radius of 50 km of the lille torup gas storage facility. © 2018 geus. geological survey of denmark and greenland bulletin 41, 13–16. open access: www.geus.dk/bulletin http://www.geus.dk/bulletin 1414 methods the subsurface within a radius of 50 km of the lille torup storage facility was screened for potential sandstone reservoirs suitable for storage. the local database comprises 11 vertical deep wells and an open grid of regional 2d seismic profiles of variable quality and resolution (fig. 1). some wells were excluded from the database due to location on top of salt structures (erslev-1–2 and skive-1–2), uncertain data quality (aars-1) or separation from the lille torup storage facility by fjord water (mors-1). the danish geothermal webgis application (vosgerau et al. 2016) provided maps of formation depth, formation thickness and potential reservoir sandstone thickness as well as reservoir parameters of relevant wells. the potential reservoir sandstone thickness map was developed for assessment of the geothermal potential and is used in this study as an indicator for injection capacity. reservoir properties derived from well logs include the depths of formation top and base, formation thickness, gross sand thickness (i.e. cumulated thickness of all sandstone layers), potential reservoir sandstone thickness (i.e. cumulated thickness of sandstone layers with a shale content <30% and a porosity >15%), as well as averaged values of porosity, permeability and transmissivity of the potential reservoir sandstone. for uncertainty considerations, see http://dybgeotermi.geus.dk/. potential formations for brine storage five potential storage areas were defined based on reservoir quality assessments obtained by integration of well-log data and webgis data improved with locally refined seismic interpretations. injectivity assessments were performed using eclipse 100 reservoir simulation software and petrel software. see hjuler et al. (2017) for details. the haldager sand formation (figs 3a–c) is presently buried more than 2000 m in large parts of the study area, but more shallow occurrences exist. the generally 50–150 m thick formation is dominated by sandstone known to be quartz-rich, which points to good reservoir properties. in areas of relatively shallow burial (<2000 m), the haldager sand formation may constitute a storage formation. the frederikshavn formation (figs 3d–f) is buried less than 2000 m and generally more than 100 m thick; it is thickest east of lille torup. several potential storage reservoirs with sufficient lateral extent can be identified. the frederikshavn formation constitutes a storage option. the chalk group (figs 3g, h) is buried at 100–700 m depth and is more than 1 km thick. on top of the lille torup salt structure, the salt movements may have fractured the c. 250 m of chalk, and increased permeability and thus reservoir quality. however, the overlaying quaternary deposits are not expected to possess sealing qualities and brine storage in the chalk could lead to environmental issues. the chalk group is therefore discarded as a potential storage formation. potential seals the chalk group outside the top of the lille torup salt structure is expected to effectively seal off pore water from the sandy formations beneath it due to its low permeability and great thickness. in addition, the clayey lower cretaceous unit is assumed to be of sufficiently low permeability to prevent pressure and pore-water propagation from below. reservoir parameters of the formations the haldager sand formation mainly comprises sandstone layers with porosities in the 18–22% range and permeabilities in the 140–360 md range (table 1). disregarding burial depth, the haldager sand formation is assumed to provide suitable storage properties. the sandstone layers of the frederikshavn formation have porosities in the 17–30% range, permeabilities in the 110–1500 md range and the thickness of potential reservoir sandstone in the 6–66 m range (table 1). in the kvols-1 well, however, the formation seems to have little or no storage potential, assumedly because clay minerals reduce both pore quaternary system lithostratigraphic unit post chalk group chalk group lower cretaceous unit reservoir reservoir reservoir reservoir assumed seal assumed seal assumed seal frederikshavn fm børglum fm flyvbjerg fm haldager sand fm fjerritslev fm gassum fm vinding fm oddesund fm tønder fm falster fm ørslev fm bunter sandstone fm zechstein group cretaceous jurassic triassic permian fig. 2. lithostratigraphic chart showing potential reservoirs (yellow) and assumed seals (brown). 15 space and permeability. the thickness of potential reservoir sandstone decreases from east to west (fig. 3f). suggested areas for brine storage the webgis-based maps (fig. 3) are suitable for assessing reservoir quality trends on a regional scale of tens of kilometres, but not on a local scale of up to a few kilometres as uncertainties will be significant. thus, the areas suggested for brine storage cover several square kilometres (fig. 1). area 1 includes the hyllebjerg-1 and farsø-1 wells (figs 1, 3), in which the haldager sand formation is evaluated to provide the better storage reservoir, with higher porosities and permeabilities than the frederikshavn formation (table 1). the two formations offer two storage options within a narrow depth interval. area 2 is situated above the rim syncline next to the salt structure beneath lille torup (figs 1, 3), where the frederikshavn and haldager sand formations may be up to 300–400 m thick (figs 3a, d) and include potential reservoir sandstone units more than 15 m thick at depths shallower than 1400 m. however, existing seismic data are insufficient to confirm these thickness estimates and the formation depths may be closer to 2000 m due to deposition in the rim synm below mean sea level thickness thickness h al da ge r sa nd f m fr ed er ik sh av n fm c ha lk g ro up hy-1 a-1f-1 k-1 ho-1 g-1 m-1 hy-1 a-1f-1 k-1 ho-1 g-1 m-1 hy-1 a-1f-1 k-1 ho-1 g-1 m-1 hy-1 a-1f-1 k-1 ho-1 g-1 m-1 hy-1 a-1f-1 k-1 ho-1 g-1 m-1 hy-1 a-1f-1 k-1 ho-1 g-1 m-1 hy-1 a-1f-1 k-1 ho-1 g-1 m-1 hy-1 a-1f-1 k-1 ho-1 g-1 m-1 hy-1 a-1f-1 k-1 ho-1 g-1 m-1 hy-1 a-1f-1 k-1 ho-1 g-1 m-1 hy-1 a-1f-1 k-1 ho-1 g-1 m-1 hy-1 a-1f-1 k-1 ho-1 g-1 m-1 hy-1 a-1f-1 k-1 ho-1 g-1 m-1 hy-1 a-1f-1 k-1 ho-1 g-1 m-1 hy-1 a-1f-1 k-1 ho-1 g-1 m-1 hy-1 a-1f-1 k-1 ho-1 g-1 m-1 r-1 s-1 s-2r-1 s-1 s-2 r-1 s-1 s-2r-1 s-1 s-2 r-1 s-1 s-2r-1 s-1 s-2 r-1 s-1 s-2r-1 s-1 s-2 r-1 s-1 s-2r-1 s-1 s-2 above sea level ≥ 15 m 0–100 100–200 200–300 300–400 400–500 500–600 600–700 700–800 1200–1300 1300–1400 1400–1500 1500–1600 800–900 900–1000 1000–1100 1100–1200 not present 0–50 m 50–100 100–150 150–200 200–250 250–300 300–350 350–400 400–450 450–500 500–550 550–600 600–650 > 700 650–700 not present at 800–3000 m below mean sea level 50 km lille torup gas storage facility salt diapir fault wells: study area e-1 erslev-1 e-2: erslev-2 f-1: farsø-1 g-1: gassum-1 ho-1: hobro-1 hy-1: hyldebjerg-1 k-1: kvols-1 m-1: mors-1 r-1: rødding-1 s-1: skive-1 s-2: skive-2 a-1: aars-1 depth to formation formation thickness potential reservoir sand thickness a b c d e f g h fig. 3. webgis-generated maps of potential brine storage formations in the study area. reservoir quality is assessed based on depth to formation top, formation thickness and potential reservoir sand thickness. 1616 cline. thus, the estimated reservoir parameters are based on average values of the nearby wells, hyllebjerg-1, farsø-1, hobro-1 and kvols-1. area 3 includes the hobro-1 well (figs 1, 3), in which the haldager sand and frederikshavn formations are estimated to offer two storage options within a narrow depth interval, the haldager sand formation providing the better reservoir (table 1). area 4 includes the gassum-1 well (figs 1, 3). the frederikshavn formation is more shallowly buried in this area (<1000 m; fig. 3d) and offers the most excellent storage properties in the study area (table 1). the haldager sand formation is not present in area 4 (fig. 3a). area 5 includes the kvols-1 well (figs 1, 3). this well indicates good reservoir properties of the haldager sand formation at a burial depth of 1940–1955 m, but also that the frederikshavn formation is a poor reservoir (table 1). assessment of injection rate and pore pressure indicative injection rates (shown as a well injection index) and pore pressures for the frederikshavn and haldager sand formations in the entire study area are presented in table 1. reservoir parameters are calculated as averages of all wells. the well injection index is assumed to correspond to the well production index; the pressure of the subsurface pore f luid in the formations is assumed to be hydrostatic. conclusions the frederikshavn and haldager sand formations constitute potential brine storage formations in the larger lille torup area and are sealed off by the chalk group and lower cretaceous unit. the haldager sand formation offers the best reservoir properties but at greater depth than the frederikshavn formation. the well injectivity index and pore pressure indicate favourable conditions for brine storage. five potential storage areas are suggested, compromising between burial depth and distance from the gas storage facility. references hjuler, m.l., andersen, m.s., nielsen, c.m., mathiesen, a., kristensen, l., skaarup, n. & nielsen, l.h. 2017: potential for establishing an injection well for brine storage near the gas storage facility at lille torup. danmarks og grønlands geologiske undersøgelse rapport 2017/20, 34 pp. mathiesen, a., kristensen, l., bidstrup, t. & nielsen, l.h. 2009: vurdering af det geotermiske potentiale i danmark. danmarks og grønlands geologiske undersøgelse rapport 2009/59, 85 pp. nielsen, l.h. 2003: late triassic – jurassic development of the danish basin and the fennoscandian border zone, southern scandinavia. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 459–526. vosgerau h., mathiesen a., andersen m.s., boldreel l.o., hjuler m.l., kamla e., kristensen l., pedersen c.b., pjetursson b. & nielsen l.h. 2016: a webgis portal for exploration of deep geothermal energ y based on geological and geophysical data. geological survey of denmark and greenland bulletin 35, 23–26. table 1. reservoir parameters of the haldager sand and frederikshavn formations in five areas suggested for brine storage reservoir parameters based on the vertical wells in the suggested areas (fig. 1). reservoir parameters of area 2 based on average values of the hyllebjerg-1, farsø-1, hobro-1 and kvols-1 wells. for detailed descriptions of parameters and uncertainties, see http://dybgeotermi.geus.dk/. area 1 farsø-1 haldager sand 1934 1952 18 16 11 18 138 2 hyllebjerg-1 haldager sand 1885 1894 9 9 9 22 344 3 average haldager sand 1909 1923 14 12 10 20 241 3 farsø-1 frederikshavn 1689 1839 150 25 9 17 106 1 hyllebjerg-1 frederikshavn 1664 1810 146 37 15 19 188 3 average frederikshavn 1676 1824 148 31 12 18 147 2 area 2 average haldager sand 1900 1920 20 16 12 20 255 3 average frederikshavn 1700 1756 56 33 8 15 133 1 area 3 hobro-1 haldager sand 1852 1891 39 24 18 19 175 3 hobro-1 frederikshavn 1741 1806 65 12 6 19 238 1 area 4 gassum-1 haldager sand 1176 1178 2 2 2 19 188 0.5 gassum-1 frederikshavn 1053 1154 101 66 65 30 1500 97 area 5 kvols-1 haldager sand 1940 1955 15 15 9 21 363 3 kvols-1 frederikshavn 1856 1912 56 56 0 5 0 0 well average haldager sand 1757 1774 17 13 10 20 242 2 9 well average frederikshavn 1601 1704 104 39 19 28 406 8 27 well formation thickness property to p be lo w m ea n se a le ve l ( m ) ba se b el ow m ea n se a le ve l ( m ) fo rm at io n th ic kn es s (m ) g ro ss s an d (m ) po te nt ia l r es er vo ir s an ds to ne (m ) a ve ra ge p or os ity (m d ) a ve ra ge r es er vo ir pe rm ea bi lit y (m d ) re se rv oi r tr an sm iss iv ity (m d ) w el l i nj ec tio n in de x (m 3 / ba r/ da y) authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen, denmark. e-mail: mlh@geus.dk. mailto:mlh@geus.dk geological survey of denmark and greenland bulletin 33, 2015, 17-20 17 thrust-fault architecture of glaciotectonic complexes in denmark stig a. schack pedersen and lars ole boldreel cross sections of glaciotectonic complexes are exposed in coastal cliff s in denmark, which allow structural studies of the architecture of thin-skinned thrust-fault deformation (pedersen 2014). however, the basal part of the thrust-fault complex is never exposed, because it is located 50 to 100 m below sea level. it is in the basal part the most important structure – the décollement zone – of the complex is found. th e décollement zone constitutes the more or less horizontal surface that separates undeformed bedrock from the displaced thrust-sheet units along the décollement level. one of the most famous exposures of glaciotectonic deformations in denmark is the møns klint glaciotectonic complex. th e structures above sea level are well documented, whereas the structures below sea level down to the décollement level are poorly known. modelling of deep structures was carried out by pedersen (2000) but still needs documentation. a glaciotectonic c omplex aff ecting comparable rock units, such as the chalk at møns klint, was recently recognised in seismic sections from jammerbugten in the north sea (fig. 1). th ese sections provide an excellent opportunity for comparable studies of the upper and lower structural levels in thin-skinned thrust-fault deformation, which is discussed in this paper with examples from three major glaciotectonic complexes. architecture of thrust-fault deformations in glaciotectonic complexes in contrast to fold-belt ranges, glaciotectonic complexes are relatively small and therefore easier to study. for these structural complexes, an architectural classifi cation was defi ned based on description and ordering of surfaces and their relations (pedersen 2014). it is emphasised that the creation of constructions comprising surfaces is the basic element of their architecture. in geology the use of architectural analysis is well known in investigations of sedimentary deposits. a concept for ordering of bounding surfaces in the architecture of aeolian dunes was suggested by brookfi eld (1977), and a similar concept was suggested by miall (1985) for facies analysis of fl uvial deposits. for the analysis of glacial architecture and construction of 3d geological models of glaciotectonic complexes the classifi cation of a hierarchy of bounding surfaces comprises four orders of surfaces (pedersen 2014). th e décollement surface is defi ned as a fi rst-order surface (fig. 2). th e décollement surface is the ‘base’ of the complex, and therefore the top of the complex also has to be defi ned as a fi rst-order surface. th is second fi rst-order surface is the topographic top of the tectonic complex, or alternatively, a truncating unconformity, above which post-deformational units occur. th e internal framework of a tectonic complex comprises thrust sheets. th ese are bounded by thrust faults, which are defi ned as second-order surfaces (fig. 2). th e thrust faults are diff erentiated into ramps and fl ats, where a ramp cross-cuts the bedding, whereas the fl at is more or less bedding-parallel. when two or more thrust sheets are bounded by ramps and fl ats they form duplexes. th ese generally form imbricate complexes or may be stacked so they form complex repetitions of the geological units (as exemplifi ed by pedersen 2005). th e folded beds comprise third-order surfaces. th ese are diff erentiated into anticlines, synclines, recumbent folds and monoclinal bends. folds may further be classifi ed from the © 2015 geus. geological survey of denmark and greenland bulletin 33, 17–20. open access: www.geus.dk/publications/bull weichselian maximum saalian maximum baltic sea north sea jb mk fk 300 km fig 1. extent of ice sheets during the two last glaciations and the location of the three glaciotectonic complexes mentioned in this paper. jb: the jammerbugt glaciotectonic complex was formed by an ice advance from central scandinavia during the saalian. fk: the fur knudeklint glaciotectonic complex was formed during an ice advance from norway during the late weichselian. mk: the møns klint glaciotectonic complex is exposed in a coastal cliff by the baltic sea, and it was formed during the latest part of the weichselian. 1818 orientation of their axial surface, the angle of their limbs and the inclination of their fold axes. fourth-order surfaces include all small-scale structures such as faults with small displacements; such faults are important for the understanding of the dynamic development. joints and anastomosing joints indicate early deformation impact, and the zone axis of conjugate faults indicates the direction of compaction. th e asymmetry of smalland mesoscale folds and the sense of displacement on faults as indicated by groove marks can be used to reconstruct the kinematics of deformation. for the macro-scale identifi cation of the head and tail of glaciotectonic complexes, a distal, a central and a proximal domain are defi ned. th e domain nearest to the foreland (the head end) is regarded as the distal part, which is commonly limited by the trace of the last thrust fault displaced towards the undeformed foreland (the tipline). th e central domain displays the bulk architecture of the complex. th e proximal domain comprises the deepest level of deformation with the most complicated structural relationships, potentially including superimposed deformation and mud diapirism. situated at the tail end, the proximal domain is delimited by the contact to the hinterland of the complex. for glaciotectonic complexes, the hinterland contact is the boundary between the hill and the hole in a ‘hill/hole pair’. at the time of dislocation, it formed the contact between the pushing ice and the dislocated geological units. the distal domain in the distal part of a glaciotectonic complex, the dip of the thrust fault ramps is gentle and the thrust fault fl ats are almost horizontal (fig. 3). th e thrust sheets are thinner than in the central domain, which is a consequence of the décollement surface that rises from the deepest level in the trailing end to the topographic surface in the foreland. one of the most surprising features of distal thrust sheets is their length. in the seismic section from the jammerbugt glaciotectonic complex the length of a thrust sheet exceeds 1 km, and the thrust sheets in the northern part of møns klint are more than 500 m long (fig. 3). such long thrust sheets are surprising when their thickness is taken into account. at møns klint the chalk sheets in the distal part of the glaciotectonic structure are only c. 25 m thick and one would expect that the forces pushing the thrust sheets would break them up into fragments. th e explanation for this missing fragmentation is that high porewater pressure along the thrust faults carries the unbroken thrust sheets. the central domain when a long and relatively thin thrust sheet is created in the distal part of a complex it is easy to understand that, when the thrusting propagates, the distal domain will move to the central domain during the formation of a new distal domain next to the foreland. two marked types of structures may form during this development: (1) the thrust sheets are broken into shorter segments creating imbricate fans along steeper-dipping thrust faults (pedersen 2005), or (2) super 3 1 3 2 1 1 1 2 3 3 2 2 2 1 sea level a b 50 m glacial deposits røsnæs clay formation stolleklint clay holmehus formation ash layers +1 to +13 ash layers –13 to +1 ash layers –33 to –13 fur formation north southc fig. 2. the fur knudeklint glaciotectonic complex with ash layers in the eocene diatomite of the fur formation that was deformed by the norwegian ice advance in the late weichselian. a: an anticline, a syncline and steeply dipping layers. b: imbricate duplexes. c: schematic section. 1: first order surfaces, the décollement surfaces at the base and the glaciotectonic unconformity at the top. 2: second-order surfaces, the thrust faults that divide the glaciotectonic complex into thrust-sheet segments. 3: thirdorder surfaces, the fold structures. to illustrate the typical third-order surfaces the hanging-wall anticlines have been extended above ground. fourth-order surfaces are too small to be illustrated, but are documented in pedersen (2014). the imbricate duplexes in the southern part of the complex are also seen in b. 19 posed thrust sheets are displaced together and passing over new, more deeply seated ramps. during this translation an antiformal stack is created, which is the explanation for the impressive structure at dronningestolen at møns klint (pedersen 2000, 2014; pedersen & gravesen 2009). a similar structure has been identifi ed in a seismic section from the central domain of the jammerbugt glaciotectonic complex. the proximal domain th e proximal part of a thin-skinned thrust-fault complex is characterised by an increasing number of thrust fault ramps and fl ats, imbricate thrust sheets and duplex segments (pedersen 2005). in fig. 4 this is illustrated by a section from the proximal part of the jammerbugt glaciotectonic complex and the southernmost imbricate thrust sheets at møns klint. th e thrust sheets at møns klint are c. 60 m thick, and the dips of the thrust faults are close to the maximum angle of fracturing (< 45º). th e thrusting probably includes superimposed tilting on deeper thrust faults below sea level. according to surlyk (1984) the stratigraphic level of the maastrichtian chalk is lower in the thrust sheets shown in fig. 4 than the chalk exposed in the distal domain in fig. 3. th us the thrusting and hence also the position of the décollement surface have shift ed to a deeper level in the proximal domain. th is relationship is also seen in the thrust-fault architecture of the seismic section from jammerbugten (fig. 4). in the distal and central domains the décollement surface is situated above the base of the chalk group (bc in fig. 4). in the proximal domain, the décollement surface drops down to the lower part of the marked refl ectors representing the base of the chalk group. th e marked bc refl ectors are present in the thrust sheets of the tailing part of the proximal domain. th e thrust sheets in the jammerbugt complex are about twice as thick as the thrust sheets at møns klint. th is refl ects that at møns klint only the frontal parts of the wedge-shaped thrust sheets are exposed, whereas in the seismic section the deeper, thicker parts of the thrust sheets can be recognised. conclusion th e architecture of thin-skinned thrust-fault deformation is described on the basis of three glaciotectonic complexes. th e thrust-fault architecture of thrust-fault belts and of glaciotectonic complexes is fairly similar even though the former are related to compressional regimes in plate-tectonic settings, the latter to compression caused by gravitational expansion of ice sheets. glaciotectonic thrust-fault complexes are divided into proximal (nearest to the source of force), 50 m b 500 m 200 m a bc fig. 3. thrust-fault architecture in the distal domains of two complexes. a: seismic section from the jammerbugt glaciotectonic complex. the strong ref lectors are interpreted as the base of the chalk group (bc) in the north sea. this implies that the main parts of the thrust sheets comprise upper cretaceous chalk. b: thin, gently dipping thrust sheets in the northern part of møns klint. the chalk at møns klint is of maastrichtian age. 2020 central and distal domains (farthest away from the source of force). th e distal domain includes the foreland boundary of the thrust-fault complex, and it is characterised by long and thin, gently dipping thrust sheets. th e central domain is characterised by sequentially superimposed folding of thrust sheets formed in the distal domain. imbricate thrustfault segments are formed when the sheets break. th e proximal domain is characterised by the shift of the décollement surface down to the deepest level, thicker thrust sheets and stacking of thrust-fault duplexes. references brookfi eld, m.e. 1977: th e origin of bounding surfaces in ancient aeolian sandstones. sedimentolog y 24, 303–332. miall, a.d. 1985: architectural-element analysis: a new method of facies analysis applied to fl uvial deposits. earth-science reviews 22, 261–308. pedersen, s.a.s. 2000: superimposed deformation in glaciotectonics. bulletin of the geological society of denmark 46, 125–144. pedersen, s.a.s. 2005: structural analysis of the rubjerg knude glaciotectonic complex, vendsyssel, northern denmark. geological survey of denmark and greenland bulletin 8, 192 pp. pedersen, s.a.s. 2014: architecture of glaciotectonic complexes. geosciences 4, 269–296. pedersen, s.a.s. & gravesen, p. 2009: structural development of maglevandsfald: a key to understanding the glaciotectonic architecture of møns klint, se denmark. geological survey of denmark and greenland bulletin 17, 29–32. surlyk, f. 1984: th e maastrichtian stage in nw europe, and its brachiopod zonation. bulletin of the geological society of denmark 33, 217–223. author’s addresses s.a.s.p., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: sasp@geus.dk l.o.b., department of geosciences and natural resource management, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. 500 m bc 200 m 50 m a b fig. 4. two examples showing thrust-fault architecture in the proximal parts of glaciotectonic complexes. a: seismic section from the jammerbugt glaciotectonic complex. the décollement surface is stepping down to the lower part of the marked ref lectors that represent the base of the chalk group (bc). b: the oldest chalk (surlyk 1984) at møns klint is found in the centre of the photograph, which shows the southernmost imbricate thrust sheets in the møns klint glaciotectonic complex. 1 geological survey of denmark and greenland bulletin 41 • 2018 review of survey activities 2017 edited by adam a. garde, ole bennike and w. stuart watt geological survey of denmark and greenland danish ministry of energy, utilities and climate 22 geological survey of denmark and greenland bulletin 41 key words geological survey of denmark and greenland, survey organisations, current research, denmark, greenland. cover photographs from left to right 1. hyperspectral analysis of inaccessible rock faces using landor sea-based platforms has potential to become a powerful geological mapping tool, as individual mineral species can be identified with this method. example from central west greenland. 2. 3d imaging by hand-held digital photogrammetry is used in both current geological mapping and assessment of landslide risks in greenland. photograph: jonas petersen. 3. potential storage sites for unwanted brine around the lille torup gas storage facility in jylland, and seismic lines used in the location of suitable sites. 4. studying intense glaciotectonic fracturing of cretaceous chalk at stevns klint. frontispiece: facing page the geus ice-sheet field camp photographed on 20 july, 2017 above the former camp century buried in the greenland ice sheet near thule air base. chief editor of this series: adam a. garde editorial board of this series: john a. korstgård, department of geoscience, aarhus university; minik rosing, geological museum, university of copenhagen; finn surlyk, department of geosciences and natural resource management, university of copenhagen scientific editors: adam a. garde, ole bennike and w. stuart watt editorial secretary: jane holst referees (numbers refer to first page of reviewed article): henrik friis & ida l. fabricius, dk (9); reinhard kirsch, de & michael engkilde, dk (13), theis i. sølling & jan audun, dk (17); jakob qvortrup christensen & lars kristiansen, dk (21); jakob qvortrup christensen & jette sørensen, dk (25); jørgen c. toft & arne thorshøj, dk (29); nicolaj krog larsen & anders bjørk, dk (33); andy whitham, uk & john korstgård, dk (39); steve piercey, ca & hartwig frimmel, de (43); christian rogass, de & asger k. pedersen, dk (47, 51); chris harrison & kate dickie, ca (57); asger k. pedersen, dk & ken mccaffrey, uk (63); louwrens hacquebord, nl & ole humlum, no (67); niels tvis knudsen, dk & kirsty langley, gl (71); james h. lever, us & jacob clement yde, no (75); xavier fettweis, be & horst machguth, ch (79); torben schmidt, dk & martin miles, no (83); gang lui & michael engkilde, dk (87); andreas møller & peter grønkjær, dk (91); robert tomas, ch (95); birgir v. óskarsson, is & max strunk, se (99). illustrations: stefan sølberg, adaam a. garde, ole bennike and susanne rømer layout and graphic production: jane holst and jacob lind bendtsen printer: rosendahls-schultz grafisk a/s, albertslund, denmark manuscripts received: 1 february – 28 may 2018 final versions approved: 20 february – 28 june 2018 printed: 15 august 2018 erratum: the repetition of fig. 3 in fig. 4’s position on page 73 has been corrected to show fig. 4 in the online version of this bulletin. issn (print) 1604-8156, isbn (print) 978-87-7871-500-5 issn (online) 1904-4666, isbn (online) 978-87-7871-501-2 citation of the name of this series it is recommended that the name of this series is cited in full, viz. geological survey of denmark and greenland bulletin. if abbreviation of this volume is necessary, the following form is suggested: geol. surv. den. green. bull. 41, 104 pp. available from geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark to buy bulletin in printed form please contact bogsalg@geus.dk and at www.geus.dk/bulletin41 (open access) © de nationale geologiske undersøgelser for danmark og grønland (geus), 2018 for the full text of the geus copyright clause, please refer to www.geus.dk/bulletin 3 44 39 update of the seamless 1:500 000 scale geological map of greenland based on recent field work in the wandel sea basin, eastern north greenland. k. svennevig 43 base-metal and ree anomalies in lower palaeozoic sedimentary rocks of amundsen land, central north greenland: implications for zn-pb potential d. rosa, j.f. slack and h. falck 47 mineral mapping by hyperspectral remote sensing in west greenland using airborne, ship-based and terrestrial platforms s. salehi and s.m. thaarup 51 hyperspectral analysis of lithologies in the arctic areas with abundant lichen cover s. salehi malaysia bangladesh vietnam greenlandcanada kenya ethiopia lebanon cameroon ghana senegal zambia malawi denmark norway china 7 review of survey activities 2017 f.g. christiansen 9 diagenetic impact on reservoir sandstones of the heno formation in the ravn-3 well, danish central graben s. pedersen, r. weibel, p.n. johannessen and n.h. schovsbo 13 potential for brine storage near the gas storage facility at lille torup, northern jylland, denmark .... m.l. hjuler, m.s. andersen, c.m. nielsen, a. mathiesen, l. kristensen, n. skaarup and l.h. nielsen 17 shale fabric and organic nanoporocity in lower palaeozoic shales, bornholm, denmark l.m. henningsen, c.h. jensen, n.h. schovsbo, a.t. nielsen and g.k. pedersen 21 chalk-glacitectonite, an important lithology in former glaciated terrains covering chalk and limestone bedrock s.a.s. pedersen, p. gravesen and k. hinsby 25 sedimentological and glaciotectonic interpretation of georadar data from the margin of the vig ice-push ridge, nw sjælland, denmark c.s. andersen & p.r. jakobsen 29 miocene oil-bearing diatom ooze from the north sea e. sheldon, e.s. rasmussen, k. dybkjær, t.e. eidvin, f. riis and r. weibel 33 initial observations of the shallow geology in tannis bugt, skagerrak, denmark m.j. owen, n.h. witt, z. al-hamdani, n. nørgaard-pedersen, k.j. andresen and j.o. leth 5 dark grey indicates non-european countries where geus has ongoing or recently completed projects. orange indicates countries with geus projects described in this volume. 57 new subsurface mapping offshore southern west greenland using geophysical and geological data u. gregersen, m.s. andersen, h. nøhr-hansen, e. sheldon, t.f. kokfelt, m. olivarius, c. knudsen, k.g. jakobsen and j.s. adolfssen 63 remote geological mapping using 3d photogrammetry: an example from karrat, west greenland e.v. sørensen and p. guarnieri 67 european trading, whaling and climate history of west greenland documented by historical records, drones and marine sediments n.e. mikkelsen, a. kuijpers, s. ribeiro, m. myrup, i. seiding and a.e. lennert 71 the greenland ice sheet – snowline elevations at the end of the melt seasons from 2000 to 2017 r.s. fausto and the promice team 75 initial field activities of the camp century climate monitoring programme in greenland w. colgan, a. pedersen, d. binder, h. machguth, j. abermann and m. jayred 79 circum-greenland, ice-thickness measurements collected during promice airborne surveys in 2007, 2011 and 2015 l.s. sørensen, s.b. simonsen, r. forsberg, l. stenseng, h. skourup, s.s. kristensen and w. colgan 83 observationally constrained reconstruction of 19th to mid-20th century sea-ice extent off eastern greenland d.a.m. hallé, n.b. karlsson, a.m. solgaard and c.s. andresen 87 examining the rare-earth elements (ree) supply– demand balance for future global wind power scenarios p. kalvig and e. machacek 91 analysis of cod otolith microchemistry by continuous line transects using la-icp-ms s.h. serre, k.e. nielsen, p. fink-jensen, t.b. thomsen and k. hüssy: tulstrup and m. pedersen 95 towards a common geological data infrastructure for europe j. tulstrup and m. pedersen 99 analytical procedures for 3d mapping at the photogeological laboratory of the geological survey of denmark and greenland e.v. sørensen and m. dueholm malaysia bangladesh vietnam greenlandcanada kenya ethiopia lebanon cameroon ghana senegal zambia malawi denmark norway china 66 7 review of survey activities 2017 flemming g. christiansen deputy director 2017 was a year where we all experienced how fatal geological forces can be for society. on june 17, a tragic natural disaster hit greenland. following a huge landslide into karrat fjord, major waves f looded the settlements of nuugaatsiaq and illorsuit. four persons were lost and many houses in nuugaatsiaq were destroyed. due to the continued high risk for more landslides, the inhabitants of the two settlements have not returned and the greenlandic authorities advise against visiting the risk area. such a natural disaster together with many extremes in weather and climate conditions around the world, also in denmark and greenland, directs our focus on the consequences of the changing climate. this requires regularly updated climate models and response with suggestions for adaptation to climate change and will have strong implications for geus’ continued research and monitoring in many years to come, including further studies and monitoring of geohazards. geus will have an important role in guiding society for better and safer living conditions in both denmark and greenland. it is necessary to work with such topics and provide society and authorities with transparent information. geus has presented a new website providing key information on many different research areas and with specific information and data from monitoring programmes like www. promice.dk, celebrating its 10 years anniversary in 2017 and www.campcenturyclimate.dk that was established in 2017. it is essential that such key information builds on results of a high scientific standard and that data are well documented in international publications, and in papers and maps in our own series. this issue of geus’ review of survey activities includes 22 papers covering many different activities in denmark, greenland and internationally. seven papers are on denmark, 11 on greenland and four on other themes. activities in denmark geus works with many different – and often closely related – topics in denmark such as the use of water, energy and mineral resources, protection of nature when exploiting resources, and the impact of climate change. the economic and political implications are very significant, and making up-to-date geological and geophysical data and information available for society, authorities and industry is of great value in this context. one paper is on the diagenetic impact of upper jurassic sandstones in the ravn-3 well in the danish central graben. understanding these processes is important for the production of oil from deeply buried oil fields. another paper is on the thickness, depth and properties of reservoir rocks within the sedimentary succession close to the lille torup gas storage facility in northern jylland. to increase the volume of caverns, saline brine from the salt structure must be stored elsewhere, and one of the options could be to re-inject the brine into the subsurface. a third paper deals with the controlling factors of porosity development in palaeozoic shales and the implications for shale-gas plays in denmark. an example from bornholm, demonstrates that this is controlled by both shale fabric and organic nanoporosity, in contrast to conventional sandstone reservoirs. understanding rocks formed by glacial processes is important in denmark, e.g. for f low modelling of ground water and for handling geotechnical problems when establishing new infrastructure. one paper describes the formation of chalk-glaciotectonite with examples from former glaciated terrains covering chalk and limestone bedrock from localities on møn, sjælland and jylland. a second paper presents sedimentological and glaciotectonic interpretation of georadar data from nw sjælland, where the interior structure of ridges has been characterised. for cost-reduction reasons, there is a growing interest for oil exploration in the youngest and shallowest part of the sedimentary succession in the north sea. a paper gives a detailed description of nanofossils, microfossils and palynomorphs in a miocene oil-bearing diatom ooze from the valhall field area in the norwegian sector. a final paper is on the shallow geology of tannis bugt in skagerak where habitat mapping has been carried out in a natura2000 area. the geological history here is very complex with deformed units and possibility of pre-quaternary bedrock being exposed on the sea bottom. © 2018 geus. geological survey of denmark and greenland bulletin 41, 7–8. open access: www.geus.dk/bulletin http://www.promice.dk http://www.promice.dk http://www.campcenturyclimate.dk http://www.geus.dk/bulletin 88 activities in greenland as in previous years, there was a high level of geological and glaciological activities in greenland in 2017: both traditional studies with focus on geological mapping, the mineral and petroleum potential and monitoring and research related to climate changes and their effects. one paper discusses the implications of a new 1:100 000 map from kilen in north greenland for the seamless 1:500 000 regional map of greenland. new procedures and documentation are necessary, as many geological maps from greenland are likely to be updated in digital versions in the coming years. a second paper on north greenland describes base-metal and rare-earth elements (ree) anomalies in lower palaeozoic sedimentary rocks and discusses the implications for the zinc and lead potential. hyperspectral remote sensing has a great potential for geological mapping and exploration in greenland. a paper from west greenland provides details on mineralogical mapping of basement rocks in the nagssugtoqidian orogen using airborne, ship-based and terrestrial platforms. another paper focuses on how the signal from lichens that often cover rocks in the arctic can be distinguished from the mineralogical signal, with examples of ultramafic rocks such as kimberlite. one paper presents results from subsurface mapping offshore southern west greenland using seismic interpretation also including various geological and geochemical analysis. this paper includes new and critical information from oil exploration wells drilled in 2010 and 2011 that penetrated the deeper part of the sedimentary succession and reached underlying basement and volcanic rocks. another paper uses 3d photogrammetry for lithological mapping and structural analysis, in this case from karrat fjord in west greenland. such understanding is also important for further evaluation of risk of landslides. climate-related research and monitoring at geus provide important data for global climate models and are often based on ground-truth data from the ice and fjords or offshore. one paper compares historical records of european trading and whaling in the disko bugt region with climate data from marine sediments and show interesting examples of the physical remains from the whaling period. another paper introduces an important climate indicator – the snowline elevation that is the maximum elevation during the melt season where snow remains from the previous accumulation season. based on satellite data and direct comparison with data from promice stations, a series of snowline maps covering all of greenland from 2011 to 2017 have been constructed. with new and updated climate models, there are concerns that remains from the former us camp century base buried under the ice in the thule area might get closer to the surface within the next century and that meltwater may interact with its waste long before. geus has started a new climate-monitoring programme and has mapped the extent and depth of the debris from the base with an ice-penetrating radar survey; results from the first field season are summarised in one contribution. a second paper describes results from airborne surveys in 2007, 2011 and 2015 where the elevation of the ice surface, top of bedrock, and the variation in thickness of the greenland ice sheet through time have been measured. another paper is on the sea-ice distribution along eastern greenland and iceland. original maps by lauge koch covering the 19th and 20th century have been digitised and analysed statistically. this can be very useful for future models of sea-ice variation in a changing climate. other themes as the national geological survey, geus has a strong obligation to participate in international assessments of resources, use state-of-the-art laboratory equipment, constantly develop new analytical techniques and make the ever-increasing volume of data available with systematic quality control and updated, user-friendly databases and distribution systems. one paper presents an examination of the supply-demand balance of ree, which is important for future global wind power scenarios; especially lack of neodymium and other elements for permanent magnets may be critical. another paper describes how analysis of the microchemistry of cod otoliths (ear stones) with the la-icp-ms technique can be applied to understand the age, growth history and migration of fish stock. a third paper gives an overview of the development and organisation of a common geological data infrastructure (egdi) for europe. egdi is important for the research collaboration and geological data sharing between the member states of the eurogeosurveys. finally, the last paper presents the procedures for 3d mapping at the photogeological laboratory at geus. this is a very strong tool for geological mapping, structural analysis and evaluation of the risk of natural geohazards such as landslides. geological survey of denmark and greenland bulletin 41, 2018, 25-28 25 glaciotectonic deformations often result in a high degree of variability, including glaciotectonic and sedimentary variability. redeposition of sediments during deformation increases the variability. ground-penetrating radar (gpr) has proven to be a good method to determine sedimentary structures in glaciof luvial deposits (olsen & andreasen 1994; van overmeeren 1998) as well as glaciotectonic structures (busby & merrit 1999; overgaard & jakobsen 2001). ref lection facies analysis (radar facies) is a useful tool in the characterisation and interpretation of deformed sediments (van overmeeren 1998; jakobsen & overgaard 2002; lerche et al. 2014). a gpr survey was carried out at jyderup skov in odsherred in north-west sjælland (fig. 1). the presence of parallel ridges in the area indicates glaciotectonic deformation. the aim of the gpr study was to map the interior of the ridge complex and to interpret the genesis of the ridges. geological setting the morphology of odsherred in the north-western part of sjælland is dominated by three large arc-shaped ice-push ridges (fig. 1a). the ice-push ridges (arcs) were formed in the late weichselian during the bælthav readvance and glaciof luvial deposits related to the ridge formation have been dated to be c. 17 000 years (houmark-nielsen 2008). the arcs cut each other and they were formed by three ice readvances of ice-lobes situated east of them. each arc is a polymorphological landscape built-up of several landscape types. data from boreholes show that the arcs contain dislocated paleocene clay and weichselian marine deposits indicating that the interior of the arcs is affected by glaciotectonic deformation. the investigated area is located in the western part of the vig arc (fig. 1b), which is situated in the centre of three arcs in odsherred with the reclaimed sidinge fjord to the east forming a central depression. on the stoss side towards sidinge fjord is a terrain of smooth ground moraine. the upper part of the vig arc is characterised by hummocky moraine and the western part consists of elongated ice-marginal moraines. larger f lat-topped kames occur within the hummocky moraine landscape and west of the ice-marginal moraine glaciof luvial deposits form an outwash plain. a number of elongated parallel ridges occur in the eastern part of the outwash plain (fig. 1c). a raw-material investigation shows that at least the upper 10 m consist of sand and gravel (region sjælland 2011), and borehole information shows the presence of sandy till. sedimentological and glaciotectonic interpretation of georadar data from the margin of the vig ice-push ridge, nw sjælland, denmark cecilie skovsø andersen and peter roll jakobsen 50 km sjælland odsherred jylland sweden germany c line05 1 km 43 m 1 m10 km c vig arc sidinge fjord 121 m –8 m ba b sejerø bugt fig. 1. a: map of denmark showing the location of odsherred. b: terrain model of odsherred, nw sjælland, with index map. c: terrain model of the investigated area showing the location of the georadar line line05 over the ice-margin ridges. © 2018 geus. geological survey of denmark and greenland bulletin 41, 25–28. open access: www.geus.dk/bulletin http://www.geus.dk/bulletin 2626 georadar survey and processing parameters five gpr lines were made perpendicular to the ridges and one was recorded parallel to the overall strike of the ridges. the occurrence of forest roads and paths in jyderup skov determined the location of the lines. the data were acquired in october 2015 using a 250 mhz sensors & software inc. georadar. due to the forest setting shielded antennae on a skid plate were used with a c. 40 cm offset. the traces were sampled with a step size of c. 5 cm and then stacked by a factor of 8. the line line05 provides the best image of the internal structure of the ridges (figs 1b, 2). processing of the raw line05 was carried out using pulseekko software by sensors & software inc. in the following steps: first, a dewow filter with an operational length of 1 pulse width was applied, followed by a stolt migration with an estimated velocity of 0.133 mns–1, which is typical value for dry sand. an automatic gain control with a pulse width of 1 and a maximum scaling factor of 700 was then applied, before the final topographic corrections were added. the vertical resolution is c. 20 cm. georadar facies description and interpretation the line05 profile is 850 m long and cross-cuts 10 ridges excluding the moraine and the two ridges behind the icemarginal moraine of the vig arc (fig. 2). four radar facies are distinguished in the profile. radar facies 1 (fig. 2) is interpreted as glaciof luvial sand and gravel based on the relatively strong parallel to subparallel ref lections with high contrast, which are moderately continuous to discontinuous. borehole data indicate that glaciof luvial sand and gravel are found to a depth of c. 20 m below the terrain surface. the ref lections are primarily planar to wavy shaped, but antiforms and synforms are also found (8.5 m wide on average; figs 2, 3a). the antiforms have a slightly asymmetric appearance with the western f lank being steeper 800 m 700 m 600 m 10 m 14 m 0 ns 50 ns ew radar facies 1 radar facies 2 radar facies 4radar facies 3 thrust fault 400 m 300 m 16 m 20 m 0 ns 50 ns fig. 3a fig. 3b 200 m 100 m 0 ns 50 ns 0 m 22 m 26 m inferred marker horizon 500 m fig. 2. interpretation of the ground-penetrating radar profile line05. the scale to the left shows metres above sealevel. the scale to the right shows twoway travel time in nanoseconds. the black line is an inferred marker horizon used for structural analysis. the vertical exaggeration is 1:4. the black boxes indicate details shown in fig. 3. 27 (typically c. 12°) than the eastern f lank (typically c. 6°). the antiform has an interlimb angle of typically c. 160°. the ref lectors show frequent displacements, which we interpret as thrust faults (figs 2, 3a). the offset is between 0.20 m and 4.80 m with an average of 1.36 m. the ref lections dip 4.0° to 13.6° dominantly to the east and are generally steepening upwards in a gentle concave to steep convex dipping pattern. the facies is truncated by facies 2, 3 and 4 in a concordant and erosional way (fig. 2). we describe the detailed characteristics of the thrusts in the next section. in radar facies 2 (figs 2, 3b) the ref lections are discontinuous and show a relatively low amplitude contrast. the ref lection pattern is chaotic at c. 280 m to subparallel at c. 325 m (fig. 3b) and c. 75 m, where the ref lections dip downwards at the ends of the facies. based on the facies characteristics, this facies is interpreted as a gravelly ablation till. facies 2 is found in patches and it drapes facies 1. radar facies 3 (figs 2, 3a) consists of steepening upward (on average 10°) moderately continuous to discontinuous and subparallel ref lections, this facies is mainly found on the western slope of the ridges. the ref lection pattern is similar to facies 1. based on the position of the facies and the ref lection pattern, facies 1 is likely to be the source of the sediments of facies 3 that were redeposited as solif luction sediments. this interpretation is in good agreement with the primary location of the facies on the western f lank of the ridges, where it is more inclined to slope failure. in radar facies 4 (fig. 2) the ref lection pattern can be described as continuous, parallel and diverging with a high density of downlaps and onlaps in the crests between ridges. the facies drapes the other three facies, and in some areas, it truncates facies 1 in an erosional way. facies 4 has a strong relative amplitude contrast. based on the ref lection pattern, facies 4 is interpreted as sand and gravel. the facies is typically thin and lacking on top of some of the ridges (figs 2, 3a). however, it is locally thick on the crests. the facies is interpreted as post-deformation deposits. structural geology the thrust-fault planes are commonly concave and convex rotating listric faults steepening upwards following and cross-cutting the bedding, with a dip of 2.5° to 21.9° (13.4° on average) mainly to the east. the westward dipping thrust faults are usually small and often back-thrusts from the more extensive eastward dipping thrusts. some of the thrusts are clustered in a complex splay pattern, where the main thrust jacks up with each splaying thrust. these thrust faults are interpreted as linked contractional, leading imbricate stacks, originating from the same root at a detachment. the displacement is greatest at the frontal thrust sheet. the leading imbricate stacks are primarily located beneath the ridges on the eastern f lank, but they also occur on the western f lanks in association with antiforms and synforms. fault-bend-folding style of thrusting with hanging-wall ramp-f lat-ramps and footwall f lat-ramp-f lats is evident from the concave–convex shape of the bedding along the fault plane. fault propagation folding is seen in the imbricate stacks where the tip line terminates in the bedding. by drawing an inferred marker horizon (fig. 2) on line05, the shortening of the line, caused by thrusting and folding, is calculated to be 12% of its initial length before deformation. formation of the ridges the formation of the ridges can be described tectono-stratigraphically in three steps: pre-tectonic deposits: radar facies 1 was deposited as glaciof luvial sand and gravel on a pro-glacial outwash plain. during a synand post-depositional event, radar facies 1 was folded and thrust into gentle antiand synforms. the thrusts are dense on the eastern f lank of the antiforms, and occur as thick, wide, complex imbricate fans. the slight asymmetry of the antiand synforms and the dip direction of the thrusts 20 m 26 m 20 m 26 m 0 ns 50 ns a 0 ns 50 ns b w e fig. 3. details from fig. 2 (same legend as fig. 2). a: ridge formed by thrusting, and subsequently smoothened by radar facies 3 and 4. b: relationship between radar facies 1, 2 and 4. 2828 and bedding indicate a direction of primary deformational stress from the east. tectonically penecontemporaneous deposits: radar facies 2 was deposited penecontemporanously as an ablation till. it occurs in patches and is only seen in one borehole (dgu no 190.196) c. 250 m south-west of line05, where the upper 2 m consist of sandy and gravelly till. radar facies 2 is recognised in three places along line05, at c. 75 m, c. 280 m and c. 325 m. at c. 325 m, the radar section cuts an elevated area, which does not have the distinct ridge morphology seen elsewhere. the f lattened morphology is in good agreement with deposition of ablation till, in contrast to the deformed elongated ridges elsewhere in the area. at c. 75 m the radar section is within an area of former stagnant ice, where ablation till should be expected. post-tectonic deposition: after the deformation came to an end, erosion of radar facies 1 occurred, and some thrust sheets are clearly truncated by solif luction sediments (radar facies 3) and post-deformation deposits (radar facies 4). the small parallel ridges west of the large vig arc may have been formed in a single deformational event creating a thinskinned thrust-fault complex in a gravity-spreading environment ( jakobsen & overgaard 2002; pedersen 2005) or as annual moraines formed at an oscillating ice-margin (krüger 1995; benediktsson et al. 2009). the presence of till deposits within the area with the small ridges indicates that the ice margin was situated in the area. the topographic relief of the ridges is pronounced and there is no indication of erosion of the top of the ridges. thus, the glacier has not moved past the individual ridges. we therefore suggest that the ridges were formed as ice-marginal push moraines created by seasonal advances and retreats of the ice margin. conclusions ground-penetrating radar was used to map the sedimentological and glaciotectonic structures of a series of parallel morine ridges of an area west of the vig arc in odsherred. the gpr profiles have a high resolution that allows detailed sedimentological and structural analyses. four radar facies are distinguished which represent different sedimentary environments and degrees of deformation and three tectonostratigraphic sequences are recognised: pre-tectonic, tectonically penecontemporaneous and post-tectonic deposits. the interior of the ridges is characterised by thrust faults and folds created by deformation from the east and the ridge morphology is clearly associated with the deformation structures. subsequently the ridge morphology has been smoothened by post-tectonic sedimentation. we suggest that ridges seen on the proximal part of the outwash plain, west of the vig arc, were formed as ice-push moraines by seasonal advances and retreats of the ice margin. references benediktsson, í.ö., ingólfsson, ó., schomacker, a. & kjær, k.h. 2009: formation of submarginal and proglacial end moraines: implications of ice-f low mechanism during the 1963-64 surge of brúarjökull, iceland. boreas 38, 440–457. busby, j.p. & merrit, j.w. 1999: quaternary deformation mapping with ground penetrating radar. journal of applied geophysiscs 41, 75–91. houmark-nielsen, m. 2008: testing osl failures against a regional weichselian glaciation chronolog y from southern scandinavia. boreas 37, 660–677. jakobsen, p.r. & overgaard, t. 2002: georadar facies and glaciotectonic structures in ice marginal deposits northwest zealand, denmark. quarternary science reviews 21, 917–927. krüger, j. 1995: origin, chronolog y and climatological significance of annual-moraine ridges at myrdaljökull, iceland. the holocene 5, 420–427. lerche, h., jakobsen, p.r. & pedersen, s.a.s. 2014: ribbed moraines formed during the retreat of the scandinavian ice sheet from eastern himmerland, ne jylland, denmark. geological survey of denmark and greenland bulletin 31, 39–42. pedersen, s.a.s. 2005: structural analysis of the rubjerg knude glaciotectonic complex, vendsyssel, northern denmark. geological survey of denmark and greenland bulletin 8, 192 pp. olsen, h. & andreasen, f. 1994: sedimentolog y and ground-penetrating radar characteristics of a pleistocene sandur deposit. sedimentary geolog y 99, 1–15. overgaard, t. & jakobsen, p.r. 2001: mapping of glaciotectonic deformation in an ice marginal environment with ground penetrating radar. journal of applied geophysics 47, 191–197. region sjælland 2011: råstof kortlægning. rapport 8, sand, grus, sten, jyderup, odsherred kommune, 38 pp. http://jupiter.geus.dk/rapportdb/ grundvandsrapport.seam?grundvandsrapportrapportid=90959 van overmeeren, r.a. 1998: radar facies of unconsolidated sediments in the netherlands: a radar stratigraphic interpretation method for hydrogeolog y. journal of applied geophysics 40, 1–18. authors’ addresses c.s.a., orbicon, linnés alle 2, 2630 taastrup, e-mail: cesa@orbicon.dk. p.r.j., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. http://jupiter.geus.dk/rapportdb/grundvandsrapport.seam?grundvandsrapportrapportid=90959 http://jupiter.geus.dk/rapportdb/grundvandsrapport.seam?grundvandsrapportrapportid=90959 mailto:cesa@orbicon.dk geological survey of denmark and greenland bulletin 38, 2017, 65-68 65 in 2009, the danish energy agency informed the geological survey of denmark and greenland (geus) that a new legal act (lov om fordring/forældelsesloven) would become effective in 2011. the new act introduced a limitation period of three years on the government’s right to request data from licensees’ oil and gas activities in denmark (www.retsinformation.dk 2007), and it became the catalyst for a major change in the standard procedure for licensees’ submission of seismic data related to exploration activities to geus. a consequence of the new legal act was that the danish authorities would have to request data from the licensee (following the consolidated act of the use of the subsoil) from the licensee no later than three years after their generation or publication; otherwise the authorities would have no legal right to the data. it was emphasised by the danish energy agency that geus would have to submit all requests for outstanding data to the licensees no later than 1 january 2011. during the 1980s and 1990s the standard procedure for data requests from geus did not include pre-stack seismic data, e.g. raw field data. a search in geus database showed that field data had been received from only a small percentage of existing 2d and 3d surveys (fig. 1). being the national data bank for geological data, geus had to respond to this risk of losing access to valuable data, and immediate action was needed. the national well data and subsurface archives geus and its danish predecessor the geological survey of denmark (dgu) have systematically collected and stored geological data from denmark for more than a 100 years. the idea of establishing a national data bank for geological data arose in the 1920s when danish law made it mandatory for everyone drilling in search for water to register certain geological information encountered during drilling and deliver it to dgu. the well data archive was established in 1926 to fulfil this purpose (troelstrup 1992). the search for oil in denmark began onshore in 1935. until the beginning of the 1980s data submitted to dgu from oil and gas activities were stored in the well data archive. for many years only few companies searched for oil in the danish sector. in 1962, the danish company a.p. møller a/s was granted exclusive rights to explore the danish subsoil according to the sole concession of 8 july 1962 (north the rescue of seismic field data from exploration activities in the danish north sea marianne m. hansen and nicolai rinds 5°e 3°e 6°e 55°n 56°n norway denmark 500 km 50 km fig. 1. 3d seismic field data status prior to the rescue project. green polygons: field data in geus’ archive. red polygons: field data not in geus’ archive. grey polygons: parts of seismic surveys outside the danish sector. 30 000 20 000 2d km 3d km2 10 000 0 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002 2006 2010 2014 fig. 2. annual seismic survey activities in denmark 1962–2014. © 2017 geus. geological survey of denmark and greenland bulletin 38, 65–68. open access: www.geus.dk/publications/bull 6666 sea fund 2012). this was renegotiated in 1981, and a large concession area was relinquished. in 1984 the first competitive licensing round resulted in an increased search for oil, and the submission of data to dgu increased (fig. 2, extracted from geus’ database). in the beginning of the 1980s, it was decided that a separate archive should be established – the subsurface archive – to store oiland gas-related data (kristoffersen 1995, 2017). the decision was made in order to fulfil increased requirements for a secure data environment and to control the strict confidentiality regulations applying to exploration and production data. data usage until 1980, dgu did not request digital seismic data from, the companies as part of its standard procedure. this was primarily due to the fact that only paper copies of seismic sections were used for in-house interpretation. furthermore, space for in-house storage was very limited, and the data owners themselves were obliged to store their digital field data for a period of time and to offer the data to dgu if they decided to discard them. at that time the data were stored on vast numbers of 9-track tapes. in general, the oil companies did not use digital data either, and if such data were requested it was often on a single line basis. by 1990, workstations had become a standard tool for interpretation and geophysical mapping in the oil industry, and access to the digital data became necessary. therefore digital processed seismic data were added to dgu’s standard data request, but their handling was a huge and timeconsuming task. licensees or companies were asked only to submit specific digital seismic data when they were needed for in-house interpretation, or if a specific request arrived from an external customer. as a consequence, dgu did not have a complete collection of digital processed seismic data at the time. until the 1990s, most of the seismic field data submitted to dgu came from relinquished or expired licences. in these cases, the data holders could decide to keep the seismic field data themselves or offer the data to dgu. although the authorities have always been able to request copies of the seismic field data this was not listed as a mandatory requirement until 2002 (danish energy agency 2002). data media and volumes the development of 3d data acquisition methods in the late 1980s resulted in an increasing amount of tapes being submitted to dgu. during the last 20 years, digital seismic data have regularly been submitted to the subsurface archive and maintenance of these data has been a constant challenge. the long-term use of the digital data can only be secured by keeping the data from degrading, by rewinding the 9-track tapes or transcribing the data to a new media on a regular basis. the oil industry has frequently changed their ‘standard tape media’, in order to secure the very expensive collected data and to reduce the storage space needed on board vessels and in archives. the most commonly used storage medium in the 1980s and 1990s was 9-track tapes. in the mid-1990s, more compact types appeared such as exabyte, dat and various versions of ibm tapes, which were smaller and could contain much more data per volume. this had a tremendous impact on the number of shelf metres needed for storage. for instance, one modern ibm3592-jd tape contains the same amount of data as 70 000 high-capacity 9-track tapes, which would require 1750 archive shelf metres (fig. 3). when transcribed storage space equals 6 lorries input: 70 000 9-track tapes of 145 mb (1750 shelf metres) output: 1 tape ibm3592-jd of 10 tb fig. 3. space reduction with the use of modern tapes media. source: ovationdata 2017. fig. 4. seismic data and tape drives at geus. 67 over time, geus has purchased various kinds of tape drives to be able to read the data and (on a small scale) make backup copies. in 2000, the subsurface archive contained data stored on up to 10 different tape media types, but mostly on c. 15 000 9-track tapes, including both seismic and well data, as well as data acquired in greenland waters. the archive also contained 3000 exabyte, dat and lto tapes and 5000 ibm tapes of various kinds. at geus tape copying is considered a specialist job since up-to-date equipment and specialised treatment of deteriorating 9-track tapes are required, and the task is very time consuming, expensive and never-ending. furthermore, vintage tape drives are difficult to maintain and acquisition of spare parts almost impossible. since 2002, geus has used an external company for all tape copying jobs. a few in-house tape drives are still being used and maintained for internal purposes (fig. 4). the data rescue project after geus was made aware of the new act and its consequences, it was decided in 2010 to start a project to rescue older seismic field data. the aim was to rescue i.e. locate, receive and store either the original or a copy of the seismic data from all oiland gas-related activities in denmark. the plan was within the first year to contact all companies which had been operators or had acquired data in the danish sector between 1980 and 1999. the plan for the following two years was to perform quality control of the submitted data, with completion of the project within three years. the following priorities were set up: field data were considered more important than processed data. 3d data were considered more valuable than 2d data. finally, onshore 2d data were considered more important than offshore 2d data, and data acquired from 1990 to 2000 were considered to be more valuable than older data. a search in geus’ database showed that almost no field data from before 1995 had been received, and that some field data had been received between 1995 and 2002. worst-case scenario a worst-case scenario in terms of expenditure and workload for geus was considered, assuming that all the companies chose to give up all their original field tapes and submit them to geus. it might be expected from the age distribution that most data might still be stored on the original 9-track tapes. if geus had to accept these directly, the subsurface archive would need large additional resources to cover the costs of external storage or for transcription to an in-house, modern storage medium. a rough calculation showed that if all the missing field data were submitted, geus could receive more than 190 000 tapes, out of which 170 000 were likely to be 9-track tapes. the cost of transcription was estimated to c. dkk 23 million (table 1). alternatively, if all the 170 000 9-track tapes were to be stored in-house the subsurface archive would need 4350 additional shelf metres. after making a list of 2d and 3d surveys from which the seismic field data had not been submitted, a priority list consisting of 48 3d surveys and 40 2d surveys was made. the next step was to contact the companies involved, but it proved difficult to locate some of the companies and relevant contact persons. in 2002, geus had sent requests for data to all licensees in the danish sector, typically to the company headquarters without a specific contact person. the outcome of this campaign was unfortunately almost 2d 3405 3405 140 476 700 3d 156 234 156 234 140 21 872 760 total cost 22 349 460 †assuming: all field data from 1995 and earlier are located. all data are stored on 9-track tapes. data are 60-fold. there is 1 km of data per tape. survey type total km in no. of tapes dkk per tape dkk total denmark table 1. estimated copying cost – worst-case scenario† 4°e3°e 5°e 6°e 55°n 56°n 50 km fig. 5. 3d field data status after the rescue project. for location and polygon colours, please see fig. 1. 6868 nill. the oil industry is a rapidly changing business, and some of the companies which had been active in the danish sector in the 1970s or 1980s no longer existed or had been taken over by or merged with other companies. keeping track of a company can be strenuous and time consuming, and the subsequent search for a relevant contact person was even more difficult. results and achievements as part of the data rescue project, 17 companies were contacted during 2010 and 2011. in general their responses to locate and deliver the missing data have been positive and cooperative. the project benefitted from the fact that two of the older oil companies are still operating in the danish sector, since both mærsk olie og gas a/s (mærsk) and dong energy e&p a/s (dong) have been in charge of, or involved in, data acquisition for many years. the most time-consuming part of this project turned out to be the quality control of the received data due to insufficient documentation, e.g. erroneous transmittals or missing acquisition and processing reports. the recovery process was initiated in 2010 by meetings with the two companies, whereby a large number of surveys from the priority list could be ticked off, and the focus then shifted towards contacting the owners of the remaining data. mærsk and dong decided to transcribe their original data themselves to modern media types. given the large quantities of data and tapes, this task was very time consuming. it took several years before the copying jobs were finalised and tapes could be submitted to geus, but it had the benefit that geus received all data on modern media types (ibm 3592 tapes or usb disks). initially, high-priority 3d field data from 34 of the 48 3d surveys on geus’ priority list were missing; to date geus has located 82% of the missing surveys and received data from 74% of them (fig. 5). geus has also received some missing processed data. because of the above-mentioned complications, the recovery project lasted six years instead of the anticipated three, with a time consumption of c. 1600 man hours at geus. over a six-year period geus has spent c. 1 million dkk on external copying. lessons learnt and conclusions in hindsight, the timing of the rescue project was optimal. between 2010 and 2014 the world experienced high oil prices (www.macrotrends.net 2017), which is likely to have encouraged the oil companies, especially mærsk and dong, to transcribe their original field tapes to modern media. the companies took the opportunity to recover their vintage data and thereby also save future storage costs. if the project was to be started today, the companies might have had other priorities and it might not have been possible for geus to keep the copying costs at a relatively low level compared to the worst-case scenario. to rescue seismic field data is both a cumbersome and potentially expensive task. however, seismic field data represent a valuable asset for evaluation of the hydrocarbon potential of a given area. new companies in the danish sector, especially smaller companies, commonly request field data from both 2d and 3d seismic surveys in order to reprocess existing data prior to committing themselves to acquisition of new seismic data. the access time to the field data is optimised, since the rescue project has provided geus with most of the field data requested by the companies. the data can also be used in future scientific studies. it is therefore an important task for a geological survey like geus to secure these data by making it a high priority to request and secure all data which are acquired from the danish subsurface. references danish energy agency 2002: danish executive order no. 56 of february 4, 2002 executive order on submission of samples and other information about the danish subsoil. danish executive order no. 56. [unofficial translation]. https://ens.dk/sites/ens.dk/files/oliegas/ submission_ samples_other_info_danish_ subsoil.pdf kristoffersen, f.n. 1995: dgu’s undergrundsarkiver [dgu’s subsurface archives]. in: binzer, k. (ed.): annual report 1994. copenhagen: geological survey of denmark, 102–105 [in danish]. kristoffersen, f.n. 2017: undergrundsarkiv fra kaos til moderne databank [the subsurface archive – from chaos to modern data bank]. hundested, 1 p. [unpublished report in danish]. north sea fund 2012: brief history of danish oil & gas exploration 1984 – 2011 – licensing rounds 1–6. renewed interest in hydrocarbon exploration in denmark. ahead of the 7th round in 2013, 14 pp. troelstrup, s. 1992: the national geological databank. in: binzer, k. (ed.): annual report 1991. copenhagen: geological survey of denmark, 45–47. www.macrotrends.net 2017: http://www.macrotrends.net/2516/wti-crudeoil-prices-10-year-daily-chart www. retsinformation.dk 2007: lov nr 522 af 06/06/2007 (forældelsesloven) – historisk. https://www.retsinformation.dk/forms/r0710. aspx?id=2655 [in danish – no translation available]. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: mmh@geus.dk. geological survey of denmark and greenland bulletin 33, 2015, 49-52 49 a quartz-wolframite-molybdenite vein and scheelite in amphibolite horizons from thrudvang peninsula, skjoldungen, se greenland diogo rosa and thomas ulrich during the south-east greenland mineral endowment task (segment) expedition in 2012, the possible mineral potential of the skjoldungen region was investigated. th e region is part of the archaean north atlantic craton, and includes the skjoldungen alkaline province (nielsen & rosing 1990; blichert-toft et al. 1995; kolb et al. 2013). a quartz-wolframite-molybdenite vein with phyllic alteration was identifi ed during the reconnaissance work in the northwestern part of the peninsula of th rudvang, close to the kangertikajik fj ord (ggu 446946; figs 1, 2). th e c. 30 cm wide, subvertical vein is hosted in mafi c granulite. however, the deformed nature of the vein and steep terrain did not allow us to establish its extent or general trend. two rusty amphibolite horizons, in the mafi c granulite hosting the vein, have anomalous concentrations of tungsten, but not of molybdenum (ggu 446934 and 446948; table 1). ultraviolet light examination conducted during the study revealed that tungsten is present as pale blue luminescing scheelite grains, rather than as wolframite, as in the vein. as such, these anomalous amphibolite samples are similar to scheelite-rich stratabound horizons documented in supracrustal sequences in the godthåbsfj ord region in southern west greenland, which were interpreted by appel & garde (1987) to be of exhalative origin. fluid inclusion study a sample from the quartz vein (ggu 446946) was investigated for fl uid inclusions in a thick section. th e quartz is very transparent and shows only very few fl uid inclusions which are generally aligned in secondary trails that are typically parallel and rarely crosscut each other (fig. 3a). th e inclusions vary in size from 5 to 20 mm and are euhedral in shape. only two inclusion trails showed irregular or deformed inclusion shapes. overall, only one type of inclusion was found, characterised by a dark single phase that fi lls the entire inclusion (fig. 3b). selected trails of 24 inclusions from three fl uid inclusion assemblages were used for microthermometry, to determine the phase transition during their cooling. th e dark phase in the inclusions contracted at around –95° to –110°c when a small vapour bubble appeared (fig. 3c). th e inclusions © 2015 geus. geological survey of denmark and greenland bulletin 33, 49–52 . open access: www.geus.dk/publications/bull greenland mafic granulite, minor paragneiss, meta-peridotite, amphibolite grey tonalitic to granodioritic gneiss (2781 ± 6 ma in skjoldungen area) tonalitic to granodioritic gneiss, locally agmatitic 1 km 63°30´n 41°w 446934 446946, 446948 t h r u d v a n g dragsfjord kangertikajik jættefjorden fig. 1. geological map of the peninsula of thrudvang and the surrounding areas (after kolb et al. 2013), showing the locations of the samples discussed in this paper. contour line spacing: 100 m. 5050 were then slowly heated at a rate of 3–5°c/min. th e vapour (liquid-gas) bubble homogenised between –59° and –50.4°c forming a single phase. th e range of the diff erent fl uid inclusion assemblages in individual trails is small (fig. 4). th ere was no melting of ice or clathrate observed. th e behaviour of the fl uid inclusions during the microthermometric experiments is typical for high-density liquid fig. 2. top: sampling the vein described in this paper. mid and bottom: field work in the kangertikajik fjord region, south-east greenland in 2012. photographs (mid and bottom): lars lund sørensen. 51 co2 inclusions that homogenise close to the co2 triple point at –56.6°c. th e density of the inclusions is calculated to c. 1.1 g/cm3. th e range of the homogenisation temperatures indicates that a small amount of other elements such as nitrogen is probably present in the fl uid. th e occurrence of one-phase liquid co2 inclusions in metamorphic rocks was interpreted by hollister (1990) and johnson & hollister (1995) to be related to grain boundary migration during re-crystallisation of quartz. th ey proposed that selective removal of h2o from h2o–co2 fl uid mixtures leads to enigmatic pure co2 inclusions. such processes cannot be excluded for ggu sample 446946, but are diffi cult to recognise. th erefore, it cannot conclusively be argued that the co2-rich fl uid is directly related to the w-mo mineralisation observed in these rocks, because it could well be that the fl uid inclusions were modifi ed during the metamorphic history of the sample. geochronology a molybdenite concentrate from the sampled vein was re– os dated and provided a neoarchaean age of 2749 ± 11 ma (table 2). th is age is similar to the laser ablation inductively coupled plasma mass spectrometry (la-icp-ms) date of c. 2740 ma for a porphyritic monzogranite and a laicp-ms date of 2753 ± 5 ma for the skirner bjerge syenite in the skjoldungen alkaline province, which are interpreted to have been emplaced during the fi rst (ds1) stage of regional transpression of the skjoldungen orogeny (kolb et al. 2013). th e vein documents a previously unknown tungstenmolybdenum mineralisation occurrence in greenland. previously known molybdenite occurrences in east greenland are related to palaeogene intrusions. furthermore, the age determination fi ts into the earliest of fi ve mo mineralising pulses, which, according to golden et al. (2013), correspond to supercontinent assembly events. in the case of the neoarchaean mo mineralising pulse, it can be linked to the assembly of kenorland during the neoarchaean, also known as superia (golden et al. 2013). mineral potential th e analysed molybdenite has a relatively low re concentration (table 2), which is typical of archaean molybdenite. th is low re concentration probably refl ects the limited mobility of re in the reducing environment that prevailed prior to oxidation of the atmosphere (golden et al. 2013). notwithstanding the reported secular variation of re concentrations 446934 rusty zone in 49.75 14.61 11.18 0.14 7.39 10.50 3.14 0.65 0.84 0.02 0.89 99.12 3 0.37 amphibolite 446946 w-mo quartz 94.95 1.57 1.10 0.01 0.11 0.36 0.44 0.11 0.05 0.02 0.49 99.2 263 1.60 vein 446948 rusty zone in 49.03 13.99 13.05 0.16 4.77 12.15 2.81 0.30 0.74 0.23 2.18 99.4 5 0.55 amphibolite table 1. whole rock geochemistry of w–mo mineralised samples from thrudvang, se greenland * ggu description sio 2 al 2 o 3 fe 2 o 3 mno mgo cao na 2 o k 2 o tio 2 p 2 o 5 loi total mo w no. % % % % % % % % % % % % ppm % * the samples were analysed at actlabs (canada), using fusion icp-oes (majors) and fusion icp-ms (mo and w). cb a 50 μm 50 μm 200 μm fig. 3. photomicrographs. a: parallel f luid inclusion trails. b: fluid inclusion trails with one-phase liquid co2 inclusions at room temperature. c: the same f luid inclusion trails at –120°c. 5252 in molybdenite, according to stein (2006), the re concentration can be used to establish the type of mineral occurrence and the economic potential. however, the re concentration in the analysed sample is intermediate between that of likely subeconomic molybdenite occurrences formed by local dehydration melting of biotite gneiss (with <20 ppm re or even sub-ppm re), and that of molybdenite of possible economic interest with a porphyry-style intrusion-related origin (with hundreds to thousands ppm re). th erefore, we cannot discriminate between the two mineralisation types and we cannot assess the economic potential of this occurrence, using this criterion. as such, the possibility that the studied vein may be linked to an intrusion and could be part of a wider mineralising system with economic potential remains. finally, bearing in mind the close spatial relations, it is considered that the mineralisation in the rusty amphibolite horizons is contemporaneous with the dated vein, and not of exhalative or syn-genetic origin. in this case, the scheelite in the amphibolite horizons was precipitated in the previously carbonatised mafi c to ultramafi c horizons in the host package, due to their enhanced reactivity to vein-derived mineralising fl uids. th is type of reaction can yield skarn-like occurrences, but they are probably not of economic interest – in contrast to the vein mineralisation, which could be of economic interest. acknowledgements th e work was carried out as part of the segment project, jointly fi nanced by the ministry of industry and mineral resources of the government of greenland and the geological survey of denmark and greenland. references appel, p.w.u. & garde, a.a. 1987: stratabound scheelite and stratiform tourmalinites in the archaean malene supracrustal rocks, southern west greenland. bulletin grønlands geologiske undersøgelse 156, 26 pp. blichert-toft , j., rosing, m.t., lesher, c.e. & chauvel, c. 1995: geochemical constraints on the origin of the late archean skjoldungen alkaline igneous province, se greenland. journal of petrolog y 36, 515–561. golden, j., mcmillan, m., downs, r.t., hystad, g., goldstein, i., stein, h.j., zimmerman, a., sverjensky, d.a., armstrong, j.t. & hazen, r.m. 2013: r henium variations in molybdenite (mos2): evidence for progressive subsurface oxidation. earth and planetary science letters 366, 1–5. hollister, l.s. 1990: enrichment of co2 in fl uid inclusions in quartz by removal of h2o during crystal-plastic deformation. journal of structural geolog y 12, 895–901. johnson, e.l. & hollister, l.s. 1995: syndeformational fl uid trapping in quartz; determining the pressure-temperature conditions of deformation from fl uid inclusions in the formation of pure co2 fl uid inclusions during grain-boundary migration. journal of metamorphic geolog y 13, 239–249. kolb, j., th rane, k. & bagas, l. 2013: field relationship of high-grade neoto mesoarchaean rocks of south-east greenland: tectonometamorphic and magmatic evolution. gondwana research 23, 471–492. nielsen, t.f.d. & rosing, m.t. 1990: th e archaean skjoldungen alkaline province, south-east greenland. rapport grønlands geologiske undersøgelse 148, 93–100. stein, h.j. 2006: low-rhenium molybdenite by metamorphism in northern sweden: recognition, genesis, and global implications. lithos 87, 300–327. authors’ addresses d.r., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: dro@geus.dk t.u., department of geoscience, aarhus university, høegh-guldbergs gade 2, dk-8000 aarhus c, denmark. 446946 54.02 0.14 33.95 0.09 1591 1 2749 11 table 2. re–os dating of a molybdenite occurrence at thrudvang, se greenland * ggu re 187re 187os model age ± 2σ no. ppm ± 2σ ppm ± 2σ ppb ± 2σ ma ma * carried out at als minerals (canada), using isotope dilution mass spectrometry with a carius-tube, solvent extraction, anion chromatography and negative thermal ionisation mass spectrometry techniques. 5 4 3 2 1 0 f re q u e n c y temperature (°c) –60 –58 –56 –54 –52 –50 fig. 4. histogram of f luid inclusion homogenisation temperatures for three-phase f luid inclusions. geological survey of denmark and greenland bulletin 33, 2015, 33-36 33© 2015 geus. geological survey of denmark and greenland bulletin 33, 33–36. open access: www.geus.dk/publications/bull relationship between groundwater chemistry and the precambrian basement rocks on eastern bornholm, denmark peter gravesen, rasmus jakobsen and bertel nilsson bornholm is situated south of sweden, in the sorgenfrei– tornquist zone (fig. 1). th e precambrian basement on northern and eastern bornholm consists of diff erent types of granitic and gneissic rocks with pegmatites, aplites and dolerite dykes (callisen 1934). th e age of the granite and gneiss is c. 1455 ma (waight et al. 2012). th is study deals with the østerlars–svaneke area north of paradisbakkerne and focuses on the geology and groundwater chemistry of the groundwater aquifers in the bornholm gneiss, paradisbakke migmatite and svaneke granite (fig. 2). th e geology and groundwater conditions in part of the study area were described by gravesen et al. (2011, 2013, 2014). miljøcenter roskilde (2009) described the groundwater conditions at the østerlars and østermarie waterworks. th e aim of this paper is to show the relations between rock composition, mineral alteration and groundwater chemistry in the low-permeability rocks using existing data from outcrops and boreholes. methods data on geology and groundwater chemistry were obtained from the jupiter database at the geological survey of denmark and greenland. information from more than 200 boreholes reaching basement rocks is included; in addition some data on the quaternary sediments were available. of the 200 boreholes, data on groundwater chemistry from 29 boreholes were available, in some boreholes as a series of analyses. data on fractures were collected from outcrops in the area during fi eld work in 2011. precambrian rock distribution and petrography th ree main rock types are found in the area. th e westernmost type is the medium-grained, foliated bornholm biotite gneiss which is usually dark grey, light grey or red grey; small areas with red grey granite or other colours also occur (callisen 1934; platou 1970). th e dark grey type consists of kfeldspar (35%), quartz (25%), plagioclase (25%), biotite (7%), hornblende (5%) and magnetite (3%) and minor amounts of apatite and traces of zircon, allanite, epidote and calcite (micheelsen 1961). light grey quartz gneiss and quartzitic types have a larger content of quartz and are oft en banded. large crystals of apatite and plagioclase occur. th e gneiss also contains skarn bodies with garnet and epidote or lenses with wollastonite, epidote and garnet. fineto medium-grained paradisbakke migmatite occurs in a restricted area between the bornholm gneiss and the svaneke granite (fig. 1) and consists of almost parallel, light grey granitic quartz-feldspar veins in a darker matrix. th e migmatite consists of k-feldspar (35%), quartz (23%), plagioclase (25%), hornblende (8%), biotite (7%), magnetite (1%) and titanite (1%), zircon and traces of allanite; calcite and epidote occur in the darker part but are rare in the lighter part (micheelsen 1961). th e svaneke granite consists of k-feldspar (36%), plagioclase (26%) and quartz (25%) with biotite (7%), hornblende (2%) and contains minor amounts of magnetite and titanite, palaeozoic sandstone dolerite dyke svaneke granite paradisbakke migmatite bornholm gneiss fault 2 k m s v a n e ke ø s t e r l a r s p a r a d i s b a k ke r n e 5 5 ° 6 ´ n 1 5 ° 2 ´ e l i s t e d n e x ø ø s t e r m a r i e å r s d a l e g r i s b y p r æ s t e b o q u a r r y s – t z o n e b o r n h o l m fig. 1. geological map of part of eastern bornholm, modified from varv (1977). inset: bornholm’s location in the sorgenfri–tornquist zone (s–t zone). 3434 as well as traces of apatite, zircon, epidote, allanite, calcite and fl ourite (micheelsen 1961). many small inclusions rich in mafi c minerals also occur and locally the content of apatite and fl ourite in the rock appears to be higher. th e granite is usually coarse-grained and greyish red but occasionally medium to coarse grained and yellow, yellow red or dark grey. th e svaneke granite can be divided into four types and a border facies bordering the gneiss and migmatite (platou 1968, 1970). th e border facies is commonly strongly lineated but also has non-lineated parts and a varying content of dark minerals. svaneke granite type i is light yellow and varies in grain size, and biotite is weakly altered to chlorite; this type occurs around svaneke and listed. svaneke granite type ii covers an area from the north coast and inland between the border facies and type i and types iii and iv. th e rock is medium to coarse grained and among the dark minerals hornblende, biotite and sphene are dominant. th e plagioclase and the dark minerals are weakly altered to unaltered. svaneke granite type iii covers a large area along the east coast from grisby to the palaeozoic sandstone north of nexø and is exposed at several places. th e rock is light yellow to light yellow red. th e svaneke granite type iv occurs as lenses in type iii; seen for example at årsdale. it is a dark red, coarse-grained rock and both the plagioclase and the dark minerals are strongly altered. in types iii and iv the hornblende, pyroxene and biotite may be altered to green chlorite, and magnetite is altered to hematite. especially in the coastal area around årsdale and southwards towards nexø the granite is strongly weathered and altered and contains 3–7% chlorite. th e rock readily disintegrates to form coarse gravel (årsdale gravel) and the fracture surfaces of the granite are covered by clayey material of green chlorite and yellow-brown limonite. fracture systems four fracture systems have been identifi ed in the area. th e fracture systems are seen in quarries in the paradisbakke migmatite along the northern rim of paradisbakkerne, in coastal exposures of the bornholm gneiss towards the north and in exposures of the svaneke granite towards the east and the north (von bubnoff 1942). two vertical fracture sets with orientations nne–ssw and ese–wnw and two horizontal fracture sets are found. th e 3d fracture network of crossing vertical, subvertical, horizontal and subhorizontal fractures forms the groundwater aquifers in the rocks. th e vertical fractures are mainly transport paths for infi ltrating water to the groundwater table, whereas the horizontal fractures form conduits for groundwater over long horizontal distances. horizontal fractures are present at least up to 90 m depth below the ground surface; two other shallower sets of horizontal fractures are also found (gravesen et al. 2014). information from boreholes shows that groundwaa b c d fig. 2. the different basement rock types. a: paradisbakke migmatite with pegmatite body, præstebo quarry. b: banded and folded bornholm gneiss, west of listed, c: svaneke granite, east coast of bornholm, d: weathered and fractured svaneke granite, east of listed. photographs: merete binderup. 35 ter is pumped up from both shallow and deep fractures, the deepest ones 144 m below ground surface. in the weathered rocks iron-bearing minerals are oxidised to yellow-brown clayey iron compounds and the dark minerals are altered to clayey green chlorite that is found on the fracture surfaces. clayey material found on fracture surfaces at depths up to 70 m probably have an impact on the chemistry of the groundwater. groundwater chemistry th e number of chemical analyses of groundwater from wells in the study area is unfortunately rather small and some parameters, especially from the svaneke granite, appear imprecise, e.g. ph values with only one digit. measurements of al concentrations are usually missing, which makes it impossible to assess the saturation state of al-silicates. however, measured concentrations of major cations and measured alkalinity (except for one outlier) appear reliable. speciation and calculations of mineral saturations using the soft ware phreeqc (parkhurst & appelo 2012) based on the parameters available, with reservations for the approximate ph values indicates that groundwater in all samples is slightly supersaturated with respect to calcite. a few analyses included measurements of sulphide and trace metal concentrations and the phreeqc calculations indicate that concentrations of trace metals such as pb and zn are likely controlled by sulphide phases. based on the major cations dissolved in the groundwater, it appears that weathering of the diff erent granite types leads to diff erent water chemistry. in a ternary plot (fig. 3) showing the relation between (charge equivalents) of ca, mg and na+k in the water, the bornholm gneiss is barely distinguishable from samples that come from aquifers in quaternary sand and gravel, whereas water samples from the paradisbakke migmatite and svaneke granite are enriched in mg and to some extent in na. na enrichment is most pronounced in samples collected close to the coast. high na concentrations are correlated with high cl concentrations, which indicates deposition of sea salts by dry and wet deposition. although also present in seawater, high mg concentrations do not show any correlation with cl concentrations, which indicates that mg comes from weathering reactions. th is is examined in more detail in fig. 4, where mg concentration versus alkalinity is plotted, which is a general indicator for the degree of weathering. as infi ltrating water rich in carbonic acid from the soil zone reacts with the rock, the carbonic acid is used and the alkalinity in the water increases. a sample from the svaneke granite with an unusually low alkalinity of 1.6 meq/l is considered an outlier and was removed from the dataset in fig. 4. it should be noted that the groundwater may have passed through several rock types before reaching the borehole where it was sampled, and there are no reliable groundwater ages so the relative weathering rates based on the water chemistry of the diff erent rocks implies that the bulk water samples from the boreholes represent comparable residence times of the water. th ere are only three paradisbakke migmatite samples; they indicate both low and high rates of weathering. two 14c datings have been made on water from the paradisbakke migmatite, the ages are rather uncertain, but the oldest of these dates is from the borehole with the highest mg concentration and alkalinity. based on the low alkalinity of the water, samples from the quaternary aquifers indicate the lowest rate of weathering, which could be expected. of fig. 4. plot of mg concentration versus alkalinity, which is considered an indicator for the degree of weathering. bornholm gneiss quaternary sand and gravel paradisbakke migmatite svaneke granite (near coast) svaneke granite mg% +k% na ca% 80 7070 80 9 0 7 0 7 0 7 0 7 0 8 0 8 0 9 0 bornholm gneiss quaternary sand and gravel paradisbakke migmatite svaneke granite type ii (near coast) svaneke granite types iii + iv (near coast) svaneke granite type ii svaneke granite types iii + iv m g ( m m o l/ l) alkalinity (meq/l) 1.2 1.0 0.8 0.6 0.4 0.2 0.0 4 5 6 7 8 9 10 fig. 3. ternary plot showing the relative distribution (on equivalent basis) of major cations (mg, ca and na+k) in water samples from wells in different granite types. part of the triangle was removed for clarity. 3636 the crystalline rocks, the bornholm gneiss appears to have the lowest weathering rate. two boreholes in the bornholm gneiss have been sampled using two pumps, giving water from diff erent depths (rasmussen et al. 2007). th ese samples show that the lowermost samples have much higher concentrations of fl uoride (1.1 and 1.9 mg/l compared to c. 0.6 and 0.4 mg/l for the mixed samples) and boron (34 and 47 μg/l compared to c. 20 μg/l for the mixed samples), presumably released from either amphiboles or biotite, perhaps apatite in the case of fl uoride. th e higher concentrations at depth indicate a longer residence time, but the phreeqc calculations indicate that the water is close to saturation for apatite so using fl uoride concentrations to quantify residence time could be diffi cult. th ere is no obvious relation between the diff erent types of svaneke granite and the apparent weathering rates based on mg and alkalinity concentrations in the groundwater. still, weathering rates appear to increase from the inland svaneke granite types iii andiv over the near coastal svaneke granite types iii and iv to the svaneke granite types i and ii that show the highest mg concentration and alkalinity, though types i and ii visually appear to be the least weathered. still the water chemistry indicates that the svaneke granites weather faster than the other granite type, this could be related to the many small, mafi c, mineral-rich inclusions found in the svaneke granite or could refl ect a general, primary, textural diff erence that leads to increased weathering rates. conclusions in spite of the small diff erences seen in terms of bulk mineralogy of the granitic and gnessic rocks and the subtypes there is a distinct diff erence in the observed groundwater chemistry. based on the major cations, especially mg, it appears that weathering of the diff erent basement rock types leads to diff erent water chemistry. references callisen, k. 1934: das grundgebirge von bornholm. danmarks geologiske undersøgelse ii. række 50, 266 pp. gravesen, p., binderup, m., nilsson, b. & pedersen, s.a.s. 2011: geological characterisation of potential disposal areas for radioactive waste from risø, denmark. geological survey of denmark and greenland bulletin 23, 21–24. gravesen, p., nilsson, b., binderup, m., larsen, t.b. & pedersen, s.a.s. 2013: geolog y, seismic activity and groundwater conditions at six potential disposal sites for radioactive waste from risø, denmark. geological survey of danmark and greenland bulletin 28, 13–16. gravesen, p., nilsson, b., rasmussen, p. & pedersen, s.a.s. 2014: borehole logs from the precambrian basement on bornholm, eastern denmark: geolog y and groundwater fl ow. geological survey of danmark and greenland bulletin 31, 15–18. hansen, m. & poulsen, v. (eds) 1977: geologi på bornholm, 96 pp. varv ekskursionsfører 1, københavn: tidsskrift et varv. micheelsen, h.i. 1961: bornholms grundfj æld. meddelelser fra dansk geologisk forening 14, 308–349. miljøcenter roskilde 2009: sårbarhedsvurdering af grundvandsressourcen på nordbornholm, 103 pp. roskilde: miljøcenter roskilde, miljøministeriet. parkhurst, d.l. & appelo, c.a.j. 2013: description of input and examples for phr eeqc version 3 – a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations. u.s. geological survey techniques and methods, book 6, chapter a43, 497 pp., available only at http://pubs.usgs.gov/tm/06/a43. platou, s.w. 1968: on the petrophysical properties of granitic rocks. geologiska föreningens i stockholm förhandlinger 90, 427–433. platou, s.w. 1970: th e svaneke granite complex and the gneisses on east bornholm. bulletin of the geological society of denmark 20, 93–133. rasmussen, p., klitten, k., nielsen, s. & jensen, p. 2007: bornholms regionskommune. logging og vandkemi i vandforsyningsboringer, 2006. danmarks og grønlands geologiske undersøgelse rapport 2007/36, 175 pp. von bubnoff , s. 1942: beiträge zur tektonik des skandinavischen südrandes. 2. die älteren granite bornholms im rahmen der svekofennidischen tektogenese. neues jahrbuch für mineralogie, geologie und paläontologie, beilagen-band 87, 277–396. waight, t., frei, d. & storey, m. 2012: geochronological constraints on granitic magmatism, deformation, cooling and uplift on bornholm, denmark. bulletin of the geological society of denmark 60, 23–46. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark; e-mail: pg@geus.dk geological survey of denmark and greenland bulletin 38, 2017, 17-20 17 the water framework directive (wfd) of the european union prescribes “good ecological status” of all waters. in terms of nitrate this means, among other things, to avoid eutrophication and achieve a good ecological balance in surface water systems for the benefit of the groundwater dependent flora and fauna (hinsby et al. 2012). in denmark, the nitrate load to estuaries has been nearly halved since the first national action plan was implemented in the mid-1980s, but further abatements are required in many areas to fulfil the wfd. new approaches to regulate nitrate use are needed with measures targeted to the areas where most effect is obtained, and this is recognised at political level. recent legislation allows farmers to increase nitrate application, but should at the same time introduce new mitigation measures and a more targeted approach to regulation. therefore the physical system, i.e. the geological framework and topography, of the catchment has to be understood (winter 1999). previous studies have shown that in hydrological catchments with high geological variability, sampling of groundwater in riparian zones, the stream water itself and water in the stream bed can help to identify near-stream areas with specific nitrate problems. detailed studies are, however, not feasible in all catchments, and development of representative typologies to guide an optimal location of mitigation measures in the catchment is thus needed. the present study is a detailed characterisation of nitrate transport and reduction in the groundwater–stream system in the river hagens møllebæk catchment for this purpose. study area and hydrogeological setting the hagens møllebæk catchment is located west of skive and discharges into skive fjord (fig. 1). the hydrological catchment covers 27.2 km2. the area is relatively flat with elevations between 1–52 m above sea level (a.s.l.) and slopes near the streams. quaternary clayey tills dominate in the west and south and glacial meltwater sand and gravel occur in the east. holocene sand, clay and organic deposits overlie the quaternary deposits in the stream-valley system and near the outlet of hagens møllebæk. in the southern part of the catchment, oligocene clay with very low permeability is found underneath a few metres of clayey till . the primary land use is agriculture, which covers more than 80% of the area. the soil types are clay (50%), sand (47%) and organic sediments (3%). nitrate transport pathways in riparian zones of the hagens møllebæk catchment, northern denmark bertel nilsson, anker lajer højberg and per jensen •••• •• • • • • • • • • • • 9 8 7 6 5 4 2 1 14 13 12 10 3 15 11• intensive • extensive stream hagens møllebæk catchment 52 m 1m 2 km monitoring station elevation skive fjord hagens m ølleb æ k hagens mølle jebjergdenmark sweden 50 km jylland skive ab fig. 1. a: topographical map of the hagens møllebæk catchment with locations of nitrate-measuring stations of riparian zones, drain pipe outlets, stream and stream bed. b: index map with position of study area. fig. 2. conceptual geological profile along hagens møllebæk with locations of numbered nitrate-measuring stations along the main stream channel. 1 24 8 12 13 1415 0 1 2 3 4 5 6 7 8 km -10 0 10 20 a lti tu de (m ) jebjerg hagens mølle holocene sand and clay late glacial sand clayey till meltwater sand and gravel oligocene clay © 2017 geus. geological survey of denmark and greenland bulletin 38, 17–20. open access: www.geus.dk/publications/bull 1818 conceptual geological model a conceptual geological model is presented in fig. 2 by a profile along the main stream of hagens møllebæk from jebjerg in the north (near station 15, fig. 1a) to hagens mølle (station 1) near the stream outlet into skive fjord. the model is based on existing geological data from the jupiter database and a quaternary soil map on a scale of 1:200  000 (both found at www.geus.dk). from the conceptual model, a general understanding of the contact and interaction between the stream and the underlying aquifers is established on catchment scale. between stations 4 and 5 the stream bed overlies poorly permeable clayey tills or oligocene clay with little or no expected water exchange. conversely, exchange of water and nitrate between the stream and the underlying aquifer is more likely where the stream bed is located directly on top of sandy aquifers. regional contact between aquifers and riparian zones the local geological and hydrogeological conditions in the riparian zone of the hagens møllebæk catchment were characterised at 12 localities by means of geological crosssections 10–100 m long, from the margin of the riparian zone adjacent to the cultivated field to the margin of the riparian zone on the opposite side of the stream channel (fig. 3). in each cross-section 8–10 boreholes were hand drilled to depths of 2–4 m and the sediment described at 15 cm intervals. from this geological profiling of the riparian zones, the hydrogeological contact between the stream system and the underlying aquifer was conceptualised according to the typology of groundwater – surface water interaction (gsi; dahl et al. 2007), see fig. 4a. the hydrogeological settings adjacent to the riparian area aquifer were classified at the twelve cross-sections (fig. 4b). combining the regional conceptual model (fig. 2) and the cross-sections, a preliminary delineation of local or regional sandy aquifers 0 20 40 60 80 100 m 4 5 6 7 ox red ox red ew 19 20 0 0 0 0 0 0.1 cultivated field riparian zoneriparian zone cultivated field stream altitude (m) organic-enriched topsoil postglacial freshwater clay postglacial freshwater sand meltwater sand and gravel flow path tile drain redox transition sampling point water table fig. 3. example of a cross section along hagens møllebæk (10 times vertical exaggeration). the profile represents a riparian hydrological type 6 of fig. 4a. nitrate concentrations in no3-n mg/l shown in groundwater, stream water and drain water. the water samples were collected in january 2017; the nitrate concentration in the submerged drain pipe outlet was about 15 mg/l, and 5–6 mg/l in the stream water. 3 1 3/5 5 6/7 6/7 3/5 5 3 1 1/2 3/6 6 • intensive• extensive stream hagens møllebæk catchment monitoring station 3 lateral local / 4 regional 7 unconfined local / 8 regional 5 bottom local / 6 regional 1 disconnected 2 confined riparian hydrogeological type 2 km holocene sand, clay and organic soils clayey till moraine sand and gravel meltwater sand and gravel holocene sand and clay beach dunes 3 a b •••• •• • • • • • • • • • fig. 4. riparian zones along hagens møllebæk and its tributaries, divided into riparian hydrogeological types. a: eight conceptual hydrogeological models of the riparian zone with different combinations of deposits with high (white-dotted) and low (grey) permeability (from dahl et al. 2007). b: classification of 12 cross-sections in the study area into types of riparian hydrogeological contacts (see also main text). 19 was obtained (fig. 5). further detailed field instigations are still needed at six of the locations to distinguish between local and regional aquifer characteristics. it is evident that stream reaches along the headwater of the stream system have contact to local shallow aquifers, and that the more central and down-gradient parts of the stream system have contact to a regional sand aquifer. observed exchange between stream water and groundwater stream discharges were measured on the same day in august 2016 at all stations using an ott acoustic digital current meter (ott hydromet gmbh). the groundwater flux to the stream system, quantified as the so-called specific baseflow, was calculated as the change in flow (q in l/sec) between an upstream and downstream location, divided by their distance along the stream. the specific baseflow for the summer day in august 2016 is shown in fig. 5b. the first-order streams provide the lowest inflow rates of groundwater to the stream (0–5 l/sec/km) because of limited or no interaction between the stream system and groundwater aquifers. higher-order (more down-gradient) stream reaches provide 5–25 l/sec/km. along a shorter reach between stations 4 and 5 the tributary loses water through the stream bed to the underlying shallow aquifer. at the twelve intensively monitored stations (fig. 1a), 8–10 piezometers were installed along the cross-sections using metal or polyethylene (peh) pipes with a screen length of 10 cm (metal) and 30 cm (peh). the metal piezometers were pushed into the subsurface with a pneumatic hammer. the peh pipes were manually pushed into the open boreholes for geological characterisation. all piezometers were levelled using the trimble® r8 gps system (vertical accuracy ±16 mm). vertical changes in the hydraulic heads between the water table in the stream (i.e. the water stage) and the intakes of the piezometers about 0.5 m below the stream beds were measured with an accuracy of ±1 cm. negative, vertical, hydraulic gradients indicate recharge to the groundwater aquifer, whereas positive gradients indicate discharge of groundwater into the stream. this made it possible to identify stream reaches where the exchange and direction between the stream and the aquifer can be assessed. the measurements carried out from august 2016 to january 2017 showed similar spatial distributions. this means that the vertical hydraulic gradients were positive along most stream reaches indicating groundwater discharge to the stream during the period august 2016 – january 2017. based on the detailed conceptual understanding of the local hydrogeological setting, the quantitative determination of baseflow and hydraulic gradients, the groundwater–stream interaction at the monitoring stations can be assessed. no or limited groundwater–stream interactions were found at stations 2–4, 6 and 15, while some or significant groundwater–stream interaction is expected to occur at stations 1 and 8–14 between the stream system and an •••••• • • • • • • • • • 2 km 2 km 0–5 10–25 < 0 5–10 hagens m øllebæ k •••••• • • • • • • • • • 9 8 7 6 5 4 2 1 14 13 12 10 3 15 11 •••••• • • • • • • • • • 9 8 7 6 5 4 2 1 14 13 12 10 3 15 11 2 km • intensive• extensive local regional 10–25 5–10 0–5 < 0 l/sec/km stream with monitoring station hagens møllebæk catchment monitoring station groundwater aquifers local and regional aquiferslocal and regional aquifers august 2016 october 2016 january 2017 25 mg/l 0 nitrate in stream water (mg/l)specific baseflow in august 2016specific baseflow in august 2016 nitrate in stream water (mg/l) a b c •13 fig. 5. aquifers and nitrate in the hagens møllebæk catchment. a: delineation of local and regional groundwater aquifers underneath the river system in contact with the river bed at the monitoring stations. b: estimated specific base f low for individual stream reaches in august 2016. c: nitrate concentrations in stream water sampled in august and october 2016 and in january 2017. 2020 underlying sandy aquifer of local or regional extent. further investigations of the hydraulic conditions are required at stations 5 and 7 before these can be classified. exchange of nitrate between groundwater, drains and stream water the nitrate transport pathways in riparian zones were assessed by collecting water samples from groundwater in the riparian zones, in drain-pipe outlets, in the stream bed and in stream water. groundwater samples were collected from the piezometers using 100 ml syringes. drain-pipe outlets to the stream were only observed near five of the crosssections (stations 4, 5, 8, 10 and 12). water from drains having outlets above the water stage in the stream was sampled by filling a bottle directly from the outlet. sampling of drain water from outlets below the water stage was more critical. here a 2–3 m long, 5 mm tube was pushed into the drain pipe and a sample collected with a 100 ml syringe. the stream water itself was sampled by filling a bottle of water flowing past the monitoring station. all water samples were analysed for nitrate (no3-n) few hours after collection using a portable photoflex std photometer (wtw gmbh, weilheim). in the cross-section of the riparian zone shown in fig. 3, groundwater samples with nearly 20 mg/l were collected in the oxic zone 25 m east of the stream, decreasing to 0 mg/l underneath the stream bed. normally, nitrate is not degraded in the oxic zone and the observed disappearance of nitrate in the riparian zone is likely due to the presence of microniches in the meltwater sand and gravel layer enriched with organic matter or pyrite, where nitrate degradation may occur. moreover, it is possible that simultaneous discharge of nitrate-free groundwater into the riparian zone and stream bed may dilute the nitrate concentration in the groundwater in the riparian zone. at present we do not possess field data on a sufficiently detailed scale to support this hypothesis. the stream water at the 15 measuring stations contained less than 5–6 mg/l of nitrate in the three sampling rounds in august 2016, october 2016 and january 2017, as expected with the highest values in january 2017 (fig. 5c). at all the stations we have monitored, the riparian zone seems to be efficient in removing nitrate from the groundwater. however, leaching of nitrate from the nearby agricultural areas through drainage pipes can bypass the riparian zone and enter the stream system. a river gauging station was established by the ministry of environment and food of denmark in december 2016 at the same position as station 1 in the present study. the gauging station measures the total river flow and nitrate runoff from the hagens møllebæk catchment to skive fjord. the preliminary results of this study indicate that it is useful to establish a dense monitoring system along streams to complement the new gauging monitoring station. we expect that this type of instrumentation can deliver the necessary insight to locate where nitrate-mitigation measures will be most effective. conclusions after the first six-months’ monitoring period (2016–2017), it seems likely that the nitrate loads to the streams in both summer and winter conditions almost entirely arise from nitrate transported by agricultural drains to hagens møllebæk. however, a longer monitoring period of two to three years is required to conclude this with more confidence. in the hagens møllebæk catchment, riparian zones along the stream reaches with widths from a few metres to 10 m seem to be very efficient in removing nitrate from groundwater before it discharges into the stream. however, drainage pipes allow nitrate-rich water to enter directly into the stream system bypassing the riparian zone. acknowledgements this work was funded by the innovation fund denmark through the project future cropping. the authors wish to thank bo v. iversen and peter k. engesgaard for constructive comments. references dahl, m., nilsson, b., langhoff, j. & refsgaard, j.c. 2007: review of classification systems and new multi-scale typology of groundwater – surface water interaction. journal of hydrology 344, 1–16. hinsby, k., markager, s., kronvang, b., windolf, j., sonnenborg, t.o. & thorling, l. 2012: threshold values and management options for nutrients in a catchment of a temperate estuary with poor ecological status. hydrology and earth system sciences 16, 2663–2683. winter, t.c. 1999: relation of streams, lakes, and wetlands to groundwater f low systems. hydrogeology journal 7, 28–45. authors’ address geological survey of denmark and greenland, øster voldgade 10, copenhagen, denmark. e-mail: bn@geus.dk. geological survey of denmark and greenland bulletin 41, 2018, 83-86 83 arctic sea ice has a significant impact on the global radiation budget, oceanic and atmospheric circulation and the stability of the greenland ice sheet (vaughan et al. 2013). prior to the era of aircraft and satellite, information on sea-ice extent relied on observations from ships and people living at the coast. this information is a valuable contribution to better understand the history of sea ice. however, the information exists in a range of formats, e.g., sea-ice extent before the late 1800s is typically reported in the literature as an annual index from a single geographical point or as hand-drawn maps. this makes it difficult to assess and compare data across time and space. the combination of digitised historical maps and single-point data makes the information more accessible and provides a record that can help understand the dynamics and processes of the climate and its interactions with the cryosphere (chapman & walsh 1993). in this study, maps of sea-ice extent by koch (1945) were digitised. we use these maps in combination with sea-ice charts from the danish meteorological institute (dmi) and koch’s sea-ice index from 1820 to 1939, to map estimated sea-ice extent between iceland and greenland going back to 1821. this information has not been included in even the most recent databases of arctic sea ice (walsh et al. 2015, 2017). furthermore, we extract time series of sea-ice extent at a number of locations and investigate the relationship between them. our observation area is along eastern greenland, between the southern tip of greenland at 59°46́ n northwards to 77°21́ n. digitising lauge koch’s maps koch’s (1945) monograph comprises over 400 small maps that show monthly sea-ice extent from 1877 to 1939. we digitised the maps for the months in those years that contained sea ice. the data used by koch were compiled by thoroddsen (1884) from annals that describe the sea-ice extent off iceland. the final result is 134 digital maps showing sea-ice extent from 1877 to 1939. these maps are available for download at http://dx.doi.org.pangaea.de/10.1594/pangaea.887453 reconstructing the extent of sea ice between greenland and iceland from koch’s index koch’s monograph contains a sea-ice index that categorises the width of the ice belt off iceland, based on observations from 1820 to 1939. the koch index has three main categories from a to c and subcategories from 1 to 3 for each letter (table 1). a represents a narrow ice belt year, b is a broad ice belt year and c depicts a very broad ice belt year. the number next to the letter indicates how far the sea ice spread off iceland. a subcategory value of 1 means the ice did not reach iceland, 2 means it had spread along the northern coast and 3 indicates it had spread down as far as the southern coast of iceland. koch described an a year as the least severe sea-ice observationally constrained reconstruction of 19th to mid-20th century sea-ice extent off eastern greenland danielle a.m. hallé, nanna b. karlsson, anne munck solgaard and camilla s. andresen ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! greenland iceland 0 500 1,000250 km %100-80 %79-60 ! ! %59-40 n o r t h a t l a n t i c o c e a n n probability of sea ice present based on the years 1893-1956 minimum and maximum extent for a1 years fig. 1. example of the final map, available for downloading, showing the probability of sea-ice extent based on historical maps from 1893 to 1956. © 2018 geus. geological survey of denmark and greenland bulletin 41, 83–86. open access: www.geus.dk/bulletin http://dx.doi.org.pangaea.de/10.1594/pangea.887453 http://dx.doi.org.pangaea.de/10.1594/pangea.887453 http://www.geus.dk/bulletin 8484 year, whereas c is the most severe sea-ice year, with b being of intermediate severity. for example, the year 1895 is classified as b3 because it had a wider area of sea ice that touched on northern iceland. table 1 gives a summary of the index for each year. the duration of sea ice is not taken into consideration in these indexes. the dataset we produced comes from three different sources of historical maps. the first is the digitised icelandic maps, the second source is the dmi sea-ice charts that we digitised for 1893 to 1900 for the months between march and september each year. we have only digitised sea-ice extent along the east coast to the southern tip of greenland from the dmi charts. these charts were based on ice conditions from variable sources such as land-based observations, scientific explorations and ship logs. the third source is shapefiles from dmi that are available online. these files contain digitised sea-ice data from 1901 to 1956 (underhill et al. 2014). we subsequently used these data to create the digitised maps. the dmi shapefiles were downloaded from the nsidc at: https://nsidc.org/data/ g10007/versions/1. the original maps used to create the shapefiles from 1893 to 1956 can be found on the nsidc website: https://nsidc.org/data/g02203/versions/1#. due to world war ii, there is a gap in the data from 1939 to 1946. digitisation of the maps was done using arcmap and exported as completed map files in jpeg format. next, and for ease of data manipulation, the images were processed to convert the values into binary arrays, so that sea ice has a value of 1 and no sea ice has a value of 0. this was done in order to better visualise and plot the data. for each category (a1, a2...c) of the index, where there are at least 10 years present (table 1) we created a map showing the probability that sea ice had a certain extent. the maps contain three lines of sea ice that depict 80–100%, 60–79% and 40–59% probability of sea-ice extent (fig. 1). the percentages are calculations of the average sea-ice extent. we used the average sea-ice extent for each year belonging to each category to calculate the frequency of the extent. for example, the dataset shows that in 80–100% of those years within a certain category the sea ice extended to the thick dashed line, 60–79% of the time the extent reached the solid black line and only 40–59% of the time did the sea ice extend to the thin dashed line. the result of this procedure is six maps (a1, a2, a3, b1, b2 and c) from 1893 to 1956. in some cases, we can go even further back in time; three maps showing iceland only (b2, b3 and c) have been constructed for the years 1877 to 1939. figure 2 shows an example of a c year. there are no probability maps for a years for the iceland-only maps, because of a lack of data. n iceland n o r t h a t l a n t i c o c e a n 100-80% 79-60% 59-40% 0 150 30075 km probability of sea ice extent based on the years 1877-1939 maximum and minimum extents for c years fig. 2. example of probability map of sea ice off iceland 1877 to 1939. index year 1884 1823 1853 1924 1830 1902 1862 1913 1836 1916 1821 1861 1914 1822 1868 1911 1922 1832 1867 1928 1831 1903 1876 1838 1917 1824 1870 1915 1828 1869 1918 1926 1839 1899 1930 1835 1923 1877 1850 1921 1825 1875 1919 1837 1878 1927 1841 1904 1933 1854 1925 1879 1880 1932 1827 1883 1938 1840 1881 1931 1843 1905 1937 1864 1929 1889 1885 1829 1886 1855 1882 1934 1844 1908 1871 1889 1890 1834 1895 1856 1887 1935 1845 1909 1872 1893 1897 1857 1896 1858 1888 1936 1846 1910 1873 1894 1898 1859 1906 1865 1891 1939 1848 1920 1901 1900 1912 1860 1907 1866 1892 total table 1. summary of how koch’s index was classified for each year from 1821 to 1939 a1 a2 a2 a2 a3 a3 b1 b1 b2 b2 b3 b3 b3 c c c 9 23 14 10 13 22 20 https://nsidc.org/data/g10007/versions/1. https://nsidc.org/data/g10007/versions/1. https://nsidc.org/data/g02203/versions/1 85 for further analyses of the sea-ice data, 12 points were selected (fig. 3) to pinpoint areas of interest in order to investigate if there is a relationship between the points. a conditional probability matrix (table 2) was created to analyse the relationship between the 12 selected points using the digitised datasets described above. we calculated the probability that if there is sea ice at a given point then there is sea ice at another point. for example, the value 0.177 in the last column indicates that if point 12 has sea ice then there is a 0.177 probability that point 11 also has sea ice. a strong probability is defined as a value of 0.850 to 1.000, a medium probability is defined as a value of 0.490 to 0.849 and a weak probability is less than 0.490. results in this section, we discuss the observed relationship between the east greenland sea ice and the sea ice off iceland using nine probability maps and the conditional probability matrix (table 2). koch describes an a1 year as a year when the ice between greenland and iceland would have been narrow and iceland free of ice throughout that year. during a1 years the probability maps show that sea ice would definitely have been present along the coast of greenland, down to the southern tip with f luctuations out from the coast but the ice would not have reached iceland. in a2 years, sea ice is approaching the north coast of iceland, but iceland itself would have been almost completely free of ice. it is further estimated that 80–100% of the time, sea ice would most likely have been at the northern part of the coast, and for only 60–79% of the time to be present at the southern part of iceland. in a3 years the sea-ice belt would have been wider at times extending into the northern fjords of iceland. in b years, the sea ice would have formed a broad belt north of iceland. koch describes in his report that the ice edge reached near 67°n and 15°w, which corroborates the digitised data. in b1 years, the probability maps ref lects a wider range of sea-ice extent along the coast of greenland. for example, at scoresby sund (point 7), the maps show that the fjord is not always covered by ice during those years. in b2 years, the probability map shows that the probability of 80 to 100% covers a larger area along greenland’s east coast, and has an extent of sea ice that reached further along the greenland 70°n 60°n 70°n 60°n 10°e 50°w 40°w 30°w 20°w 10°w 30°e60°w iceland faroe islands svalbard 1 5 6 10 9 12 7 8 114 3 2 fig. 3. map of the location of the twelve points used for the probability matrix. 1 2 3 4 5 6 7 8 9 10 11 12 1 1.000 0.916 0.896 0.942 0.789 0.625 0.889 0.898 0.880 0.969 0.828 0.169 2 0.924 1.000 0.948 0.942 0.842 0.500 0.937 0.933 0.930 0.984 0.841 0.171 3 0.896 0.940 1.000 0.919 0.789 0.625 0.913 0.918 0.907 0.977 0.832 0.168 4 0.976 0.976 0.960 1.000 0.842 0.500 0.980 0.988 0.981 0.977 0.845 0.165 5 0.060 0.064 0.060 0.062 1.000 0.750 0.063 0.063 0.062 0.094 0.082 0.316 6 0.020 0.016 0.020 0.015 0.316 1.000 0.016 0.016 0.016 0.031 0.026 0.375 7 0.900 0.940 0.924 0.950 0.842 0.500 1.000 0.961 0.946 0.961 0.823 0.163 8 0.920 0.948 0.940 0.969 0.842 0.500 0.972 1.000 0.965 0.984 0.845 0.169 9 0.912 0.956 0.940 0.973 0.842 0.500 0.968 0.976 1.000 0.984 0.828 0.167 10 0.498 0.502 0.502 0.481 0.632 0.500 0.488 0.494 0.488 1.000 0.509 0.305 11 0.771 0.777 0.775 0.754 1.000 0.750 0.758 0.769 0.744 0.922 1.000 0.177 12 0.977 1.000 0.977 1.000 0.140 0.070 0.953 1.000 1.000 0.907 0.953 1.000 table 2. a conditional probability matrix known point with sea ice the left hand column indicates the point with sea ice (in relation to fig. 2), while the rows show the probability of sea ice present relative to that point pr ob ab ili ty p oi nt h as s ea ic e 8686 icelandic northern coast. unlike that observed in b1 years, for b2 years scoresby sund was often filled with sea ice. finally, during c years, sea ice was present along the entire east greenland coast and for 40–59% of the years the ice would extend down the eastern coast of iceland. of the nine maps, the remaining three show sea-ice data off iceland from 1877 to 1939. these maps provide more details on sea-ice extent during a more severe ice period in the 1880s (kelly et al. 1987, based largely on koch’s index of icelandic sea-ice occurrence). in b2 years, there was a 40 to 59% probability of sea ice reaching all along the northern coast of iceland, but persisting mainly between iceland and greenland. the b3 years have a wider area between greenland and iceland and cover a further range along the northern icelandic coast. kelly et al. (1987) discuss three of the b3 years (1914, 1915 and 1938) as being years with extensive sea ice around iceland. during c years, the sea ice extended to the south coast of iceland. seven of these years (1881, 1882, 1887, 1888, 1892, 1911 and 1918) were severe sea-ice years for iceland (kelly et al. 1987). a statistical analysis was carried out to see if there is any correlation between sea ice being present at one point (table 2) to other points on the map. the strongest probabilities are the points along eastern greenland, points 1–4 and 7–9. this implies that if there is sea ice at one point along the coast then it is very likely that the rest of the eastern coast of greenland would have been filled with ice. point number 12 is located farther from the coast but has a perfect correlation with points 2, 4, 8 and 9 along the coast. the points farther from the coast 10–12 have a range of weak to strong probability with the other points. point 12 also shows a relatively higher probability value of 0.316 and 0.375 with points 5 and 6 than the other points closer to greenland, which all have weak values of less than 0.094. lauge koch’s index extends further back in time than the maps of the spatial extent. when using the probability maps, it is now possible to see how extensive the sea ice was likely to have been in the period from 1821 to 1893. the final application of the maps is to use them in combination with table 1 to be able to estimate sea-ice extent back to 1821. conclusion 134 maps showing sea-ice extent from 1877 to 1939 are available as jpeg files and shapefiles. detailed probability maps have been created from observed and estimated sea-ice conditions from observed data that date back to the early 1800s. these probability maps can be downloaded at https://dx.doi. org/10.1594/pangaea.887452 where the maps are available as jpeg files. the datasets can be used in further studies to help understand the characteristics of sea ice during the 19th and 20th centuries. previous studies have used koch’s sea-ice index to infer atmospheric circulation patterns (kelly et al. 1987). our new dataset can provide important input to studies of climatic variability in the (sub)arctic including the link between ice and atmospheric circulation modes such as the arctic and north atlantic oscillations (ao/nao) and thus helps predicting how the climate may respond to future sea-ice loss (screen et al. 2017). references chapman, w.l. & walsh, j.e. 1993: recent variations of sea ice and air temperature in high latitudes. bulletin of the american meteorological society 74, 33–47. kelly, p.m., goodess, c.m. & cherry, b.s.g. 1987: the interpretation of the icelandic sea ice record. journal of geophysical research: oceans 92(c10), 10835–10843. koch, l. 1945: the east greenland ice. meddelelser om grønland 130(3), 373 pp. screen, j.a. 2017: the missing northern european winter cooling response to arctic sea ice loss. nature communications 8, 14603. thoroddsen, t. 1884: den grönlandska drifisen vid island. ymer 1884, 145–160. underhill, v., fetterer, f. & petersen, c. 2014: arctic sea ice concentration and extent from danish meteorological institute sea ice charts, 1901–1956, version 1. boulder: nsidc (national snow and ice data center), https://dx.doi.org/10.7265/n5mp517m vaughan, d.g. et al. 2013: observations: cryosphere. in: stocker, t.f. et al. (eds): climate change 2013: the physical science basis. contribution of working group i to the fifth assessment report of the intergovernmental panel on climate change, 317–382. cambridge: cambridge university press. walsh, j.e., chapman, w.l. & fetterer, f. 2015, updated 2016: gridded monthly sea ice extent and concentration, 1850 onwards, version 1.1, boulder: national snow and ice data center. digital media, http:// dx.doi.org/10.7265/n5833pz5 walsh, j.e., fetterer, f., stewart, j.s. & chapman, w.l. 2017: a database for depicting arctic sea ice variations back to 1850. geographical review 107, 89–107, http://dx.doi.org/10.1111/j.1931-0846.2016.12195.x authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: dhalle23@gmail.com. https://doi.pangaea.de/10.1594/pangaea.887452 https://doi.org/10.7265/n5mp517m http://dx.doi.org/10.7265/n5833pz5 http://dx.doi.org/10.7265/n5833pz5 http://dx.doi.org/10.1111/j.1931-0846.2016.12195.x mailto:dhalle23@gmail.com geological survey of denmark and greenland bulletin 35, 2016, 1-8 1 geological survey of denmark and greenland bulletin 35 • 2016 review of survey activities 2015 edited by adam a. garde, ole bennike, kristine thrane and w. stuart watt geological survey of denmark and greenland ministry of energy, utilities and climate 22 geological survey of denmark and greenland bulletin 35 key words geological survey of denmark and greenland, survey organisations, current research, denmark, greenland. cover photographs from left to right 1 3d anthroprogenic model of urban infrastructure with buildings and pipes for combination with geological data. 2 elevated plain (c. 800 m a.s.l.) across precambrian basement cut by a deep valley, torngat mountains, labrador, canada. source: google earth. 3 th e geothermal energy potential in denmark is substantial and a webgis portal for exploration of deep geothermal energy based on geolocial and geophysical data has been launched. an interactive 3d tool in the portal gives an intuitive overview of the variations of subsurface topography. 4 aft er drilling two or more overlapping holes in the sea ice, a so-called kajak core with seabed sediments is retrieved for investigations of past climate. photo: jesper hoff mann. frontispiece: facing page field investigations at the sulugssut intrusive complex in the alpine terrain of east greenland. th e rocks formed during the initial stages of the opening of the north atlantic ocean at c. 55 ma. th e fi eld camp in the background was pitched on top of a glacier. photo: th omas f. kokfelt. chief editor of this series: adam a. garde editorial board of this series: john a. korstgård, department of geoscience, aarhus university; minik rosing, geological museum, university of copenhagen; finn surlyk, department of geosciences and natural resource management, university of copenhagen scientifi c editors: adam a. garde, ole bennike, kristine th rane and w. stuart watt editorial secretary: jane holst referees (numbers refer to fi rst page of reviewed article): katrine juhl andresen, dk (27); anonymous (59, 75); per bergmo, no (87); albertas bitinas, lt (47); lars ole boldreel, dk (35); c. kent brooks, uk (59); mikael calner, se (39); andy chadwick, uk (87); jacob q. christensen, dk (9, 47); stefan claesson, se (103); william colgan, ca (71); lynn dafoe, ca (83); christian deibjerg, dk (17); mikael erlström, se (23); ida fabricius, dk (43); wesley farnsworth, no (71); jens galsgaard, dk (31); christopher harrison, ca (63, 83); jens havskov, no (79); michael houmark-nielsen, dk (35); julie hollis, gl (95); jan jeppesen, dk (13); reinhard kirsch, de (23); margrethe kristensen, dk (9); mats larsbo, se (17); gert laursen, dk (13); jerry lloyd, uk (67); anders mattias lundmark, no (103); sebastian mernild, no (75); th orsten nagel, dk (99); allen nutman, au (55); asger ken pedersen, dk (63); toby rivers, ca (91); anders scherstén, se (55); denis schlatter, ch (99); vera schlindwein, de (79); iain sinclair, ca (91); jasna sinigoj, sl (95); jette sørensen, dk (27); svend stouge, dk (39); sander suicmez, dk (43); nicolas r. th ibault, dk (51); clemens ullmann, uk (51); tod waight, dk (31); jacob c. yde, no (71). illustrations: jette halskov, stefan sølberg, susanne rømer, adam a. garde and benny m. schark layout and graphic production: jane holst and annabeth andersen printer: rosendahls-schultz grafi sk a/s, albertslund, denmark manuscripts received: 8 january – 29 february 2016 final versions approved: 11 february – 1 may 2016 printed: 15 july 2016 issn (print) 1604-8156, isbn (print) 978-87-7871-438-1 issn (online) 1904-4666, isbn (online) 978-87-7871-439-8 citation of the name of this series it is recommended that the name of this series is cited in full, viz. geological survey of denmark and greenland bulletin. if abbreviation of this volume is necessary, the following form is suggested: geol. surv. den. green. bull. 35, 106 pp. available from geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350 copenhagen k, denmark phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: geus@geus.dk and at www.geus.dk/publications/bull © de nationale geologiske undersøgelser for danmark og grønland (geus), 2016 for the full text of the geus copyright clause, please refer to www.geus.dk/publications/bull 3 44 39 middle–upper ordovician and silurian stratigraphy and basin development in southernmost scandinavia n.h. schovsbo, a.t. nielsen and m. erlström 43 types of formation water and produced water in danish oiland gasfi elds: implications for enhanced oil recovery by injection of ‘smart’ water n.h. schovsbo, h.d. holmslykke, c. kjøller, k. hedegaard, l. kristensen, e. th omsen and k.h. esbensen 47 middle pleistocene interglacial deposits near herning, jylland, denmark b.v. odgaard, k.l. knudsen, o. bennike and h.j. granat 51 geochemistry of the maastrichtian rørdal member, jylland, denmark: ce anomaly as a palaeo-redox proxy c. knudsen and b.w. lauridsen greenland canada kenya ethiopia nigeria cameroon zambia ghana mozambique tanzania denmark norway iceland sweden finland 7 review of survey activities 2015 f.g. christiansen 9 miocene deposits at silkeborg, jylland, and their infl uence on hydrology p.r jakobsen, e.s. rasmussen, k. dybkjær and j. kidmose 13 3d hydrogeological modelling for urban subsurface management in odense, denmark s. mielby, t.m. pallesen and p.b.e. sandersen 17 monitoring of pesticide leaching from cultivated fi elds in denmark w. brüsch, a.e. rosenbom, n. badawi and p. olsen 23 a webgis portal for exploration of deep geothermal energy based on geological and geophysical data h. vosgerau, a. mathiesen, m.s. andersen, l.o. boldreel, m.l. hjuler, e. kamla, l. kristensen, c.b. pedersen, b. pjetursson and l.h. nielsen 27 towards a national 3d geological model of denmark p.b.e. sandersen, t. vangkilde-pedersen, f. jørgensen, r. th omsen, j. tulstrup and j. fredericia 31 pre-quaternary rocks and sediments with a high level of radioactivity in denmark p. gravesen and p.r. jakobsen 35 tectonic control on the formation of roskilde fjord, central sjælland, denmark s.a.s. pedersen and p. gravesen 5 grey indicates countries where geus has ongoing or recently completed projects. orange indicates countries with geus projects described in this volume. 55 new zircon u-pb and hf isotopic constraints on the crustal evolution of the skjoldungen region, southeast greenland t.f. kokfelt, t. næraa, k. th rane and l. bagas 59 in situ fractionation and inward migration of the solidifi cation front in the skaergaard intrusion, east greenland t.f.d. nielsen 63 palaeovalleys at the basal unconformity of the palaeoproterozoic karrat group, west greenland p. guarnieri, c.a. partin and d. rosa 67 investigations of past climate and sea-ice variability in the fj ord area by station nord, eastern north greenland n. nørgaard-pedersen, s. ribeiro, n. mikkelsen, a. limoges and m.-s. seidenkrantz 71 placing greenland ice sheet ablation measurements in a multi-decadal context d. van as, r.s. fausto, j. cappelen, r.s.w. van de wal, r.j. braithwaite, h. machguth and the promice project team 75 regional climate-model performance in greenland fi rn derived from in situ observations c. charalampidis, d. van as, p.l. langen, r.s. fausto, b. vandecrux and j.e. box 79 crustal structure over the nagssugtoqidian deformation front in west greenland: receiver function analysis t. dahl-jensen, p.h. voss and t.b. larsen 83 new geophysical and geological mapping of the eastern baffi n bay region, off shore west greenland u. gregersen, p.c. knutz and j.r. hopper 87 mapping of the co2 storage potential in the nordic region k.l. anthonsen, p. frykman and c.m. nielsen 91 burial and exhumation history of the labradornewfoundland margin: fi rst observations p. japsen, p.f. green, j.m. bonow, a.m. hinchey and d.h.c. wilton 95 th e greenland mineral resources portal – another step forward m. pedersen, m. hansen, b.h. heincke and l. th orning 99 afieldwork – an android app for offl ine recording of geological information and data display m. hansen, m.n. petersen, t.f. kokfelt and b.m. stensgaard jagedisplay: soft ware for evaluation of data distributions in u-th -pb geochronology t.b. th omsen, t. heijboer and p. guarnieri vietnam tajikistan 103 66 7 review of survey activities 2015 flemming g. christiansen deputy director 2015 was a tough year for many geologists around the world, and the years to come may be even tougher. low prices of oil, gas and other energy sources, and also of many mineral commodities have led to a significantly lower level of investments in exploration and production than seen in previous years. both society and industry suffer from much lower income, so cost reduction is the new buzzword; and many geologists have lost their jobs ‒ also in denmark and at geus. investments in data, projects and knowledge ‒ including many typical products from the geological survey of denmark and greenland (geus) ‒ are worryingly low and will eventually reduce the level of knowledge for decision makers in both the private and public sectors. commodity prices are, however, cyclic by nature, and it is very important for geus to continue to collect and compile new data, build up new knowledge and models based on research projects – and prepare for a future that will still rely on traditional resources but with a strong focus on a transition towards new green technologies that can reduce the consumption of fossil fuels and the emission of co 2 . this issue of geus’ review of survey activities has a broader content and a total of 24 four-page articles, more than seen for several years. it reflects that geus works on many different subjects and is preparing for a future where geology still plays an important part in the planning of important activities in denmark and greenland. eleven papers are on denmark, eight on greenland and five on international and general themes. activities in denmark geus’ danish activities and research cover a wide range of topics within our specific programme areas: data, water, energy, mineral resources and nature and climate, as well as many other basic research projects. the use of groundwater is very important for denmark, and geus carries out many studies on water resources, their protection and possible future challenges due to changes in climate and use. as a follow-up on previous studies of the miocene sedimentary succession in jylland, one paper focuses on deposits at silkeborg and their influence on hydrology. another paper describes 3d hydrogeological modelling important for the urban subsurface management in odense. a third paper is on the monitoring of pesticide leaching from cultivated fields in denmark, an activity that has been carried out for several decades. denmark has a large potential for subsurface geothermal energy. following several regional studies and many local case stories in preparation for drilling campaigns, geus has developed a webgis portal for exploration of deep geothermal energy based on geological and geophysical data. one paper describes this portal where the relevant geological and geophysical maps, data and key information from drilling are easily accessed. many of the applied studies emphasise the strong need for a comprehensive national 3d geological model of denmark. similar models are being developed in several other european countries in order to provide the best possible background for large resource and infrastructure projects. one paper describes the strategy behind the effort that geus is currently putting into developing such models and gives examples of how existing data and geological models can be applied. sediments and rocks in denmark generally have a low content of radioactive minerals and radon. some of the highest levels of radioactivity on mors and bornholm have been studied in detail to understand their geological control and distribution in space. this is described in one paper. another paper describes how the terrain in the roskilde area, and in particular the roskilde fjord, is controlled by deeper tectonic features that are clearly recorded in subsurface maps of the danian limestone and paleocene chalk, marl and clay. after several studies of the palaeozoic succession in denmark, it is now possible to make a complete middle‒upper ordovician and silurian stratigraphy and basin model for all of southern scandinavia. this is described in another paper using wireline logs as a correlation tool. several methods of enhanced oil recovery, e.g. injection of ‘smart’ water, have the potential to significantly increase oil production, and thereby income for danish society. to do this, a detailed understanding of different types of reservoirs is required, as shown in a paper describing the distribution and composition of primary formation water and produced water in the north sea oilfields. © 2016 geus. geological survey of denmark and greenland bulletin 35, 7–8. open access: www.geus.dk/publications/bull 88 interglacial marine deposits are fairly common in denmark but for the first time such deposits are described from kibæk in the herning area, where they occur several metres above present sea level. chalk is a very important rock for denmark. it is the reservoir for most of the oil and gas resources in the north sea, it is important as a groundwater reservoir in large areas onshore, and it is an important resource for cement production. one paper provides new details of geochemical stratigraphy as a tool to understand the depositional environments and their geographical correlation. activities in greenland once again there was a high level of activity in and about greenland in 2015. many large and small projects were carried out, studies that are important for evaluating and marketing the resource potential in greenland. the level of industrial activity in both oil and mineral exploration is very low at the moment, but it is important to prepare for a future when prices of the most important commodities will eventually rise again. for the last few years geus has focused on mapping and mineral evaluation activities in south-east greenland; this emphasis is now changing to west and north-west greenland. two papers give new information from southeast greenland. one paper describes new geochronological data using hf isotopes in zircon to unravel archaean crustal accretion processes in the skjoldungen region, and another provides entirely new insight into the fractionation processes of the world-famous skaergaard intrusion, which has been discussed for many decades. the last paper on greenland bedrock geology describes palaeoproterozoic palaeovalleys underlying the karrat group in the uummannaq region of west greenland, where new field activity has started. studies and monitoring of the greenland ice sheet and studies of marine sediments in the fjords around greenland result in important contributions from geus to global climate models. one paper investigates past climate and sea-ice variability in the remote eastern part of north greenland close to station nord. results from the important promice monitoring project with its focus on temperature sensitivity of ice sheet-ablation are presented in another paper. a third paper is on climate models based on in situ observations of greenland firn. passive, so-called receiver function analysis of seismological signals from natural earthquakes around the world can be used to information on the deep crustal structure, e.g. the depth to moho. one paper presents results from such a study across the nagssugtoqidian front in west greenland where a significant change in moho is recorded across an ancient plate boundary and subduction zone. systematic mapping of offshore sedimentary deposits and evaluation of the petroleum potential is crucial for planning and marketing of licensing rounds and for advice on subsequent exploration activities. after several successful licensing rounds and a relatively high level of activity, the seismic data coverage in baffin bay is now relatively high compared to many other regions around greenland. based on a systematic updated interpretation and mapping, one paper outlines some interesting possibilities for future exploration but also describes the main risks and uncertainties. international and broader technical themes geus also works overseas in many different countries with a variety of projects and is involved in broader thematic studies. over the years geus has been involved in several projects of carbon dioxide capture and storage (ccs), especially with european union and industrial funding. one paper summarises mapping of the storage capacity of sandstone aquifers in denmark and the nordic region, based on a large nordic collaboration project. another paper describes a preliminary study of the burial and exhumation history of the labrador-newfoundland margin using apatite fission track analysis and thermal maturity methods similar to previo us studies on the greenland side of the labrador sea. geus is constantly developing databases and facilities for easier access to and use of data, as well as new methodologies and technologies to make research easier, quicker and better for our geologists. one paper describes the greenland mineral resources portal; a new version of this was launched by geus and the ministry of mineral resources in greenland (mmr) in april 2015. the portal is based on decades of work and re-organisation of previous databases with an ambition of securing data and making them easily accessible through the internet. another paper is on a new app – afieldwork – that has been designed specifically for field work in greenland to make digital capture of data as easy and efficient as possible. the last paper presents the development of special software for evaluation of data distribution in u-th-pb geochronology – jagedisplay. geological survey of denmark and greenland bulletin 38, 2017, 33-36 33 denmark constitutes a low-enthalpy geothermal area. current geothermal production takes place from two sandstone-rich formations: the bunter sandstone and gassum formations. these formations form major potential geothermal reservoirs, but information about the permeability of the potential sandstone reservoirs is difficult to obtain. this may be explained by deposition in a variety of environments under different climatic conditions, and by variable diagenetic overprint (olivarius et al. 2015). thus, the sandstone characteristics and properties are diverse, and in areas where wells are scarce, the assessment of the extent and reservoir properties of sandstone layers is associated with much uncertainty. in order to reduce exploration risk it is therefore essential to develop a robust method for prediction of porosity and permeability prior to drilling. kristensen et al. (2016) presented a five-step method for predicting porosity and permeability averages of prospective geothermal formations in danish onshore areas with low data density. the method is based on the sandstone reservoir characteristics of the gassum formation from geological and petrophysical data acquired in deep wells. the main purpose was to reduce the uncertainties associated with prediction of reservoir properties. the study presented here investigates the efficiency of the five-step method when applied to the bunter sandstone formation. the study area extends from the west coast of denmark to the east coast of southernmost sweden, and from the danish border with germany to just north of the ringkøbing–fyn high (fig. 1). farther north, the bunter sandstone formation grades into the partly contemporary skagerrak formation. eighteen wells provided well-log and core-analysis data from the formation. the five-step method kristensen et al. (2016) developed the five-step method by integrating well log data from the gassum formation with porosity and permeability measurements obtained from conventional core analysis (ccal). the main concept behind the method is that the porosity is related primarily to depth, whereas the permeability depends on a range of parameters including porosity, mineralogy, grain size and sorting. thus, if the burial depth for a particular potential reservoir layer is known, a relatively reliable porosity estimate may be derived (step 1). a permeability estimate may then be obtained from a porosity–permeability relapre-drilling geothermal assessment of porosity and permeability of the bunter sandstone formation, onshore denmark morten leth hjuler and lars kristensen arnum-1 hønning-1 løgumkloster-1–2 varnæs-1 felsted-1 kegnæs-1 tønder-3–5 jelling-1 løve-1 søllested-1 ørslev-1 margretheholm-1 höllviksnäs-1 stenlille-19 rødby-1 50 km danish well swedish well major fault structural high n r i n g k ø b i n g – f y n h i g h n o r t h g e r m a n b a s i n d a n i s h b a s i n f a u l t z o n e 100 km fig. 1. the approximate extent of the bunter sandstone formation in southern denmark and adjacent areas (as delimited by the map frame), showing major structural elements and locations of investigated wells. maps showing e.g. the extent, thickness and data sources of the bunter sandstone formation are available from thewebgis portal at the geological survey of denmark and greenland (http://dybgeotermi.geus.dk/ ). © 2017 geus. geological survey of denmark and greenland bulletin 38, 33–36. open access: www.geus.dk/publications/bull 3434 tion (steps 2–4), and finally, the uncertainty can be assessed (step 5). therefore the depth of the sandstone layer is required. in areas with no wells, the depth can only be estimated from seismic data, which therefore indirectly control whether the five-step method can be applied. below, the main components of the five steps are defined and explained; for a detailed description of the concept, refer to kristensen et al. (2016). step 1: porosity–depth model. in order to predict the porosity of a formation, a regional porosity–depth relation is established. log-derived, effective porosity data subjected to cut-off by shale content (<30%) and porosity (>15%) are averaged for each well and plotted against estimated maximum burial depth. the resulting relation, the porosity– depth model, is expressed as ϕ log = a + b × d (equation 1), where ϕlog is the log-derived porosity, d is the burial depth and a and b are constants. step 2: initial permeability model. an initial, basin-wide porosity–permeability relation based on core-analysis data is established in order to predict permeability. subsequent to porosity cut-off (15%), this relation, i.e. the initial permeability model, is expressed as k ini = a × ϕcore b (equation 2), where kini is the core-gas permeability, ϕcore is the core porosity and a and b are constants. step 3: general permeability model. this model uses logderived, averaged permeabilities with the purpose of incorporating a dataset encompassing the entire formation and not only covering parts of the formation as is mostly the case with the core-based dataset used in step 2. equation 2 is used to calculate permeability estimates from the log-derived porosity. shale and porosity cut-offs of 30% and 15%, respectively, are applied. a cross-plot between log-derived and averaged porosity and permeability data points forms the basis for definition of a general permeability model expressed as k g = a × ϕlog b (equation 3), where kg is the log-derived permeability, ϕlog is the log-derived porosity and a and b are constants. step 4: local permeability model. the general permeability model is adapted to local conditions by multiplying equation 3 with a constant, c. thus, the general permeability model constitutes a template for the local permeability model, which may be expressed as k l = c × kg (equation 4), where kl is the local permeability. step 5: permeability-uncertainty range. a local area featuring several wells with a sufficient amount of appropriate log data is selected and a local permeability model is established. the extensive source data ensure a statistically well-restrained model and a consistent uncertainty range, which is assumed to be applicable to local models within the same formation in other parts of the danish area. below, the results of applying the five-step method to the bunter sandstone formation in denmark are described. application of the five-step method fourteen wells (fig. 1) provided data for the generation of a porosity–depth model for the bunter sandstone formation (fig. 2); data from the løgumkloster-1, 2 and 2a wells were excluded because of their location in a fault zone (fig. 1) where tectonic activity may have altered the sandstone properties. the porosity–depth model (step 1). unfortunately, the scattered data distribution prevented derivation of a mathematically defined trend line, and thus a reliable porosporosity % rødby-1 felsted-1 kegnæs-1 kværs-1 margretheholm-1 stenlille-19 varnæs-1 løve-1 ørslev-1 jelling-1 søllested-1 løgumkloster-2a løgumkloster-2 løgumkloster-1 tønder-3 tønder-4 tønder-5 margretheholm-1 stenlille-19 løgumkloster-1 tønder-4 tønder-5 average net porosity porosity–depth trend gluyas & cade (1997) 1500 2000 2500 3000 3500 0 10 20 30 es tim at ed   m ax im al   b ur ia l  d ep th  (m ) fig. 2. porosity–depth model (step 1) for the bunter sandstone formation. the shown model (black line) is an estimate by the authors; the løgumkloster wells were excluded from the model (see text) due to their location in a fault zone. a mechanical compaction curve (gluyas & cade 1997) is shown for comparison. modified from kristensen et al. (2016). 0 10 20 30 40 50 1 10 100 1000 10000 g as  p er m ea bi lit y  (m d ) porosity % initial permeability model: κini = 48084 × φcore3.4571 arnum-1 hønning-1 höllviksnäs-1 rødby-1 stenlille-19 tønder-3 tønder-4 tønder-5 porosity cut-off fig. 3. initial permeability model (step 2) for the bunter sandstone formation. 35 ity–depth model could not be generated. the shown trend line is the authors’ best estimate based on their general experience and knowledge of petrographic characteristics and diagenetic overprints. the generation of a permeability–depth model was attempted as an alternative to the porosity–depth model, but without success as the scattered data distribution prevented establishment of a well-defined trend line. the initial permeability model (step 2). eight of the wells shown in fig. 1 provided core-analysis data for the initial permeability model (fig. 3). in order to generate a reliable porosity–permeability relation based on comparable measurements, only permeabilities obtained from cleaned, unflawed plugs of productive lithologies, measured under similar testing conditions were used. data from uncleaned plugs and data points representing low permeabilities (<1 md) and unproductive lithologies (claystone/shale) were removed from the dataset. subsequently, shale and porosity cut-offs of 30% and 15%, respectively, were applied. the initial permeability model is based on 360 data points and is expressed by equation 5: k ini = 48084 × ϕcore 3.4571, where kini is in md and ϕcore is in per cent. the general permeability model (step 3). the log-derived permeability was calculated for 16 wells (fig. 1) using equation 5 with the log-derived porosity as input. løgumkloster-2a was discarded due to porosity cutoff. subsequently, the log-derived permeability was averaged and a cross-plot between averaged log-derived porosity and permeability was generated (fig. 4). the general permeability model is expressed by equation 6: k g = 0.0026 × ϕlog 3.7843 (fig. 4). the introduction of the general permeability model imposes a slightly higher specific permeability estimate than that calculated from the initial permeability model, i.e., k g > kini (fig. 4). the local permeability model (step 4). local permeability models were generated for the tønder and stenlille areas in order to demonstrate the variability of sandstone reservoirs within the bunter sandstone formation (fig. 5). for the tønder area, the local permeability model is expressed as k tønder = 1.7 × (0.0026 × ϕ 3.7843) (equation 7) and for the stenlille area as kstenlille = 0.8 × (0.0026 × ϕ 3.7843) (equation 8). permeability-uncertainty range (step 5). only the tønder area provides the data density needed for establishing an uncertainty range for a local permeability model. however, the number of data-supplying wells is limited to 3 (tønder-3–5), and the statistical basis from the available bunter sandstone formation data is insufficient to assess the uncertainty range. results and discussion porosities of the bunter sandstone formation are lower than derived from the mechanical compaction curve for uncemented sandstones (step 1, fig. 2), indicating that most of these sandstones contain clay and diagenetic cement (kristensen et al. 2016). at greater depths, the sandstones preserve relatively high porosity due to microporosity within detrital clays and diagenetic iron oxide/ hydroxide coatings that seemingly retard quartz cementation (olivarius et al. 2015). although a well-defined porosity–depth model (step 1) could not be created for the bunter sandstone formation, the range of log-derived average porosities from 17% to 25% within the 1500–3100 m depth interval indicates favourable porosity conditions irrespective of maximum burial depth (fig. 2). a corresponding averaged permeability range was calculated using the general permeability model (step 3, equation 6) with 17% and 25% as porosity inputs. within these bounds the permeability ranges from 132–557 md (fig. 6). from this observation, the geothermal prospectivity of the bunter sandstone formation is significant, provided sufficient reservoir thickness and temperature are present. 50 10 15 20 25 30 1 10 100 1000 10000 g as  p er m ea bi lit y  (m d ) porosity % log data: bunter sandstone fm general permeability model porosity cut-off initial permeability model: general permeability model:     κini = 48084 × φcore3.4571 κg = 0.0026 × φlog3.7843 core-analysis data: initial permeability data fig. 4. initial and general permeability models (steps 2, 3) for the bunter sandstone formation after averaging the log-derived permeability and porosity. 50 10 15 20 25 30 1 10 100 1000 10000 g as  p er m ea bi lit y  (m d ) core-analysis data: stenlille 19 (fm average) stenlille 19 tønder 3 (fm average) tønder 3 tønder 4 (fm average) tønder 4 tønder 5 (fm average) tønder 5 log data: general model  tønder model   stenlille model  porosity cut-off local permeability models: κtønder = 1.7 × 0.0026 × φ3.7843 κstenlille = 0.8 × 0.0026 × φ3.7843 porosity % fig. 5. local permeability models (step 4) for the bunter sandstone formation in the tønder and stenlille areas. 3636 the vast majority of data behind the initial permeability model (kini, step 2) belong to the tønder-3–5 wells. therefore, kini represents the tønder area rather than the entire study area. this data distribution issue was resolved by applying the averaging technique, whereby each well is represented by a single data point in the porosity–permeability plot. thus, by using averaged data, each well becomes equally influential in the general permeability model (k g, step 3), see fig. 4. further benefits of averaging the data are a dramatic reduction of the scatter of core-analysis measurements (fig. 3) and a significant narrowing of the uncertainty band associated with average permeability estimates. in step 4, the local permeability models generated for the tønder and stenlille areas, k tønder and kstenlille, demonstrate the importance of including local geological data when establishing local permeability models. at any porosity, k tønder is 1.7 times higher than kg and more than twice that of kstenlille. in contrast, kstenlille is 0.8 times lower than kg. these permeability variations may be explained by variations in deposition environment and maximum burial depth. at tønder, aeolian deposition favoured the generation of well-sorted, clay-free sandstones which, subsequent to maximum burial of c. 2000 m, resulted in high average porosities and permeabilities (c. 22% and 300 md, respectively); the presence of nitrogen gas may play a porositypreserving role. at stenlille, the sandstones were deposited in alluvial fan and braided river systems (olivarius & nielsen 2016) and maximum burial occurred at c. 3000 m, i.e. 1000 m deeper than at tønder (fig. 2), possibly causing the lower porosity (c. 19%) and permeability (c. 180 md) due to poorer sorting and a higher degree of mechanical compaction and diagenesis. it was not possible to establish a permeability uncertainty band for the bunter sandstone formation (step 5). however, assuming that the bunter sandstone and gassum formations respond similarly to the geological factors controlling permeability variations, it is suggested that the uncertainty range derived for the gassum formation by kristensen et al. (2016) is also applicable to the bunter sandstone formation. therefore, the uncertainty range may be expressed by multipliers of 2 and 0.5. conclusions it was not possible to generate a reliable porosity–depth model (step 1) for the bunter sandstone formation based on data and modelling from the gassum formation. however, using averaged porosities and permeabilities from all available wells (step 3), porosities from 17–25% and permeabilities from 132–557 md can be modelled in the depth range 1500–3100 m. local permeability models (step 4) for the bunter sandstone formation in the tønder and stenlille areas differ significantly from the general permeability model (step 3), which emphasises the importance of using local geological data for calibration of the general permeability model. a permeability uncertainty band (step 5) could not be established for the bunter sandstone formation due to insufficient data; however, the uncertainty range developed for the gassum formation in kristensen et al. (2016) may be applied. references gluyas, j. & cade, c.a. 1997: prediction of porosity in compacted sands. in: kupecz, j.a., gluyas j. & block, s. (eds): reservoir quality prediction in sandstones and carbonates. a apg memoir 69, 19–28. kristensen, l., hjuler, m.l, frykman, p., olivarius, m., weibel, r., nielsen, l.h. & mathiesen, a. 2016: pre-drilling assessments of average porosity and permeability in the geothermal reservoirs of the danish area. geothermal energy 4:6, 27 pp. olivarius, m. & nielsen, l.h. 2016: triassic paleogeography of the greater eastern norwegian-danish basin: constraints from provenance analysis of the skagerrak formation. marine and petroleum geology 69, 168–182. olivarius, m., weibel, r., hjuler, m.l., kristensen, l., mathiesen, a., nielsen, l.h. & kjøller, c. 2015: diagenetic effects on porosity– permeability relationships in red beds of the lower triassic bunter sandstone formation in the north german basin. sedimentary geology 321, 139–153. 50 10 15 20 25 30 1 10 100 1000 10000 g as  p er m ea bi lit y  (m d ) porosity % averaged log data: bunter sandstone fm general permeability model porosity cut-off 132 md 557 md   general permeability model:    κg = 0.0026 × φlog3.7843 fig. 6. porosity and permeability range for the bunter sandstone formation in the investigated wells in denmark. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: mlh@geus.dk geological survey of denmark and greenland bulletin 41, 2018, 91-94 91 fish otoliths, also called ear stones or statoliths, are calcified structures functioning as movement and equilibrium indicators in the inner ear of fish (fig. 1). from hatching to death these structures grow incrementally, with new material accreted daily (pannella 1971) in successive layers of protein (1–8%, degens et al. 1969) and calcium carbonate. the accretion rate of otoliths varies with fish growth, and in temperate species it is usually lowest during the winter season (hüssy et al. 2010). this results in concentric growth resembling the ringed structure in trees (fig. 1d), enabling the use of dendrochronological techniques to approximate the age and growth history of fish. during growth, certain elements are incorporated into the otolith structure, some associated with proteins and some with the calcium carbonate component (thomas et al. 2017), supplying a valuable record of different aspects in fish life history and serving as a potential environmental record. previous studies show that trace element and isotopic compositions of otoliths can be used as a proxy for reconstructing water chemistry, temperature and salinity (patterson et al. 1993; thorrold & shuttleworth 2000). other studies demonstrate that elemental histories can be used to investigate fish spawning and migration patterns (e.g. sturrock et al. 2012), and more recent studies use elements such as zn, cu and mg as indicators of seasonality (hüssy et al. 2016; limburg et al. 2018). combining this knowledge of elemental variation with the micro-beam capabilities of laser ablation inductively coupled plasma mass spectrometry (laicpms) turns otolith microchemistry into a powerful tool for studying important parameters fundamental for establishing modern, sustainable fisheries management policies (e.g. stock identification, migration, pollution indicators, spawning habitats, duration of larval and juvenile stages, and magnitude and timing of spawning). we present an analytical method developed by the geological survey of denmark and greenland (geus) in collaboration with the national institute of aquatic resources, technical university of denmark (dtu aqua), for element abundance analysis in otoliths. analyses of otoliths from baltic cod (gadus morhua; fig. 1) are used as an example for its application. analytical approach the microchemical analysis of otoliths focuses on mg, p, ca, mn, cu, zn, sr and ba, as these elements are typically incorporated into otoliths, and are either subject to environmental control (e.g. sr and ba correlate with water salinity) or physiological control (e.g. zn, cu and mg are useful to the interpretation of otolith growth history; hüssy et al. 2016 and references therein; limburg et al. 2018). the la-icpms facility at geus employs a nwr213 laser system coupled to an element 2 double-focusing, single-collector magnetic sector field icpms. operating conditions, data acquisition and processing parameters are listed in table 1. la-icpms is often the preferred technique for rapid, in-situ analyses of trace elements and isotopes obtained from natural samples, simon hansen serre, kristian ege nielsen, peter fink-jensen, tonny bernt thomsen and karin hüssy analysis of cod otolith microchemistry by continuous line transects using la-icp-ms 5 mm c d a 2 mm b fig. 1. a: cod specimen caught in the baltic sea. b: removal of otoliths, the cut is situated just above the eyes. c: otolith, with dotted line showing the direction of a cross-section. d: photograph (ref lected light) of a polished cross-section of an otolith. the red line shows the position of the laser scan. © 2018 geus. geological survey of denmark and greenland bulletin 41, 91–94. open access: www.geus.dk/bulletin http://www.geus.dk/bulletin 9292 as it requires little sample preparation and can produce high sample throughput, extracting elemental and isotopic information at a micrometre scale. most conventional la-icpms analysis is performed by spot analyses, following a bracketing analysis protocol using well-characterised standard materials. this is a powerful method when studying specific areas in solid materials. however, for compositional variations along millimetreto centimetre-scale transects, the spot approach becomes very time-consuming. for example, a 5 mm long transect requires about one hundred spots 40 µm in diameter, taking 3–4 hours to complete. spot analysis also introduces difficulties like downhole-element fractionation when the laser drills into the material. instead, research of fish otolith microchemistry favours faster sampling approaches such as line scans across the sample to acquire continuous timeresolved compositional profiles (a 5 mm long line takes c. 17 min, using a fixed scan speed of 5 μm s-1; e.g. søndergaard et al. 2015; hüssy et al. 2016). this approach is rapid, suppresses depth heterogeneity and avoids downhole elemental fractionation, as it ablates only to a depth of a few microns. the potential interfering effects of varying scan speeds, washout times and debris blanketing from the ablation are not yet studied, but this is intended in the near future. for ongoing otolith studies, we used a line-scan la-icpms approach to measure 325 cod otoliths (15–30 otoliths per day). the otoliths were embedded in epoxy resin and cut along the dorsoventral profile to expose the core and annuli. for streamlined, high-throughput analyses, custom-made epoxy mounts 7 × 0.8 × 0.8 cm large were cast, each holding 10 otoliths. a custom-made 10 cm2 sample holder with four mounts allows for analysis of 40 otoliths per day. for each otolith, a ref lected light optical photo depicting a line from core to edge (fig. 1d) was imported as an overlay image into the laser ablation software. the image was fitted to the otolith position in the live image, using reference points to facilitate the exact positioning of the line scans. the icpms analysis was optimised for dry plasma conditions through continuous linear ablation of the nist 612 standard. the signal-to-noise ratios were maximised for the isotopic mass range from mg to ba, while opting for low element-oxide production levels by minimising the 254uo 2 /238u ratio. instrumental drift was minimised by following a standard–sample–standard analysis protocol, bracketing every sample analysis by line analyses of the nist-612 and nist614 glass standards ( jochum et al. 2011), while the febs-1 otolith (sturgeon et al. 2005) and the macs-3 carbonate powder tablets ( jochum et al. 2012) provided quality control of the nist-612 standard measurements. the averaged 2σ accuracy and uncertainty of the standards were typically <5% for element abundances >1–3 ppm. data processing was done with software iolite v. 2.5 (hellstrom et al. 2008; paton et al. 2011) using the trace elements is data reduction routine. calculation of abundances were based on 43ca isotope as the internal standard, assuming 38.3 wt% ca in all otoliths, comparable to the certified ca concentration reported for the febs-1 otolith standard (sturgeon et al. 2005). application of the analytical approach on baltic cod the main purpose of the analyses is to answer research questions important to the fisheries management in denmark and greenland. the specific approach presented here and modified versions of this method are used in several projects addressing a range of management questions relating to stock structure, migrations and age determination. here, we highlight some preliminary results of the most advanced project. the project tagging baltic cod (tabacod) is a joint baltic collaboration aiming to develop a new age-estimation method based on seasonal variations in element concentrations along a gradient from the core (birth) to the edge (death) of otoliths. fish age is one of the key variables in stock table 1. instrument operating conditions, data acquisition and processing parameters instrumentation: thermo-fisher scientific element 2 double focusing sf-icp-ms forward power: 1470 w cones: ni plasma gas: 16 l min-1 auxiliary gas (he): 0.85 l min-1 nebuliser gas (ar): 0.95 l min-1 new wave research nwr 213 solid state nd:yag laser ablation system laser wavelength: 213 nm laser fluence: ~ 9.5 j cm-2 spot size: 40 µm repetition rate: 10 hz scan speed: 5 µm s-1 data acquisition and processing: analyte isotopes: 25mg, 31p, 43ca, 44ca, 55mn, 65cu, 66zn, 88sr, 137ba sampling time, ms: 10 10 10 10 10 10 10 10 10 samples per peak: 10 10 10 10 10 10 10 10 10 acquisition: time resolved (continuous analysis) along transects mass resolution: 300 (low) oxide production rate tuned to ≤0.3% uo2 (254uo2/238u) single analysis duration and setup: 30 s blank, 2–20 min ablation (sample dependent), 30 s washout software for data reduction: iolite version 2.5 (paton et al. 2011; hellstrom et al. 2008) standards: internal standard isotope: 43ca external standardisation: nist-612 glass secondary standards: nist-614 glass, febs-1 otolith powder and macs-3 carbonate powder pressed as tablets 93 assessment and has traditionally been obtained by visual examination of otolith cross-sections, where seasonal f luctuations in growth are visible as optically contrasting growth zones much like the rings in cross-sections of trees. in recent years, this traditional method has failed to provide reliable age information, thus posing severe management problems for the eastern baltic cod stock. initial results from the tabacod project on the seasonality in the otolith chemical composition are presented as an example of the application of the la-icpms approach. all analysed otoliths were acquired from cod that were subjected to a mark-recapture experiment. a total of c. 500 cod specimens were captured, externally marked, injected with srcl 2 and released again. when the cod were recaptured they were sent to dtu aqua for analysis. the srcl 2 is incorporated into the otolith as it grows and acts as an internal timestamp. the chemical signals from timestamp to edge corresponds to the time the fish spent at sea between capture and recapture. combining information on how many days the fish had been at sea, what time of year it was released/recaptured and how much it had grown since tagging allows us to validate our hypotheses on seasonally varying element concentrations. concentrations of elements like mg and zn vary with season (hüssy et al. 2016). figure 2 depicts core-to-edge compositional profiles of mg, p, mn, cu, zn and sr from the otolith shown in fig. 1d, corresponding to the entire life of the fish. the red line in fig. 2 marks where the sr concentration dramatically increases, representing the srcl 2 -tagging event. the mg, p and mn concentrations show clear and similar variations throughout the otolith structure on a scale of tens to hundreds of ppm. zn and cu concentrations vary around our analytical resolution threshold of c. 1–3 ppm and do not show significant systematic variations. the la-icpms data are currently undergoing statistical analysis to quantitatively identify seasonal variations. however, some analysed elements indicate clear patterns resembling seasonality. if a seasonality in element concentration occurs, superimposing individual transects (like the ones shown in fig. 2) of all cod in one plot will result in a generic signal. if element signals are random in relation to time, no such signal will be evident. figure 3 shows p concentrations from all analysed otoliths, standardised by dividing each measured value by the mean profile p concentration to remove the effect of differences in average p levels between individuals. all profiles were centred at the sr peak, since all cod were tagged during the same season (april to may of the same year). the time scale on the x-axis is estimated, assuming linear growth within years, similar growth in individuals across the year, and that all specimens were tagged and released on the same date of a given year. although there are individual differences between fish, fig. 3 indicates a general seasonal variation in distance to core μm 25mg 31p 55mn 65cu 66zn 88sr 20 40 60 ppm 250 500 750 1000 0 5 10 15 20 0.0 0.4 0.8 0 1 2 3 4 5000 10000 0 1000 2000 3000 4000 fig. 2. trace-element concentration profiles in ppm of the cod otolith shown in fig. 1d. the x-axis indicates the concentration along the profile from 0 µm, when the fish was born, to 4300 µm, when it died. the red line marks the position of the sr peak induced by srcl 2 injection. data from nielsen et al. (2018). as this cod was tagged in april, the sr timestamp corresponds to the coldest water temperatures experienced by the cod over a year, where mg and p concentrations are at a minimum. −400 0 400 800 −100 0 100 200 days around centered sr peak positions m ea n ce nt er ed 3 1 p p pm fr om a ll ot ol ith s fig. 3. variations of phosphorous concentration in all measured otoliths c. 200 days before and after the srcl 2 tagging and release experiment. on the x-axis, measurements are centred on the injection-induced sr peak. on the y-axis, measurements have been centred on the mean p concentration of each otolith transect. the red line is a generalised additive model smoothed curve. 9494 p concentrations. the total number of minima occurring in the profiles from birth to death thus corresponds to the number of winters the fish has experienced and hence its age. other ongoing projects migration patterns of the kattegat cod: this project seeks to map migration patterns of cod captured in the kattegat, which were genetically identified to belong to the north sea or western baltic stock. elemental profiles of 400 cod captured along a geographic gradient covering the entire kattegat will be compared with baseline samples from adjacent areas. comparing the results to information about the otoliths’ annual growth zones can reveal at what time in its life the cod has migrated to and from the kattegat. stock structure in capelin: with partners from greenland’s fishing industry this project investigates stock structure, migration and natal homing (the return to a birthplace to reproduce) of capelin (mallotus villosus) from 18 areas along the coasts of south and west greenland. the aim of this project is to provide counsel on sustainable management of a species that plays a vital role in the marine food chain. final remarks a la-icpms approach for quantitative, high-throughput transect measurements of otoliths was successfully set up at geus. data from 325 otoliths are being thoroughly examined, and only an ‘appetizer’ of the data is presented here. the la-icpms approach is adaptable for most solid carbonate (e.g. bivalves) and phosphate (e.g. teeth, horn) materials showing cross-surface compositional variations. analyte isotopes include most major, minor and trace elements and acquisition parameters are easily optimised for the specific sample type, thus providing a rapid and extremely versatile in-situ analytical approach for comparable natural materials. acknowledgements we thank balticsea2020 for financial support and mojagan alaei, geus, for laboratory assistance. references degens, e.t., deuser, w.g. & haedrich, r.l. 1969: molecular structure and composition of fish otoliths. marine biolog y 2, 105–113. hellstrom, j., paton, c., woodhead, j. & hergt, j. 2008: iolite: software for spatially resolved la-(quad and mc) icpms analysis. mineralogical association of canada short course series 40, 343–348. hüssy, k., hinrichsen, h.h., fey, d.p., walther, y. & velasco, a. 2010: the use of otolith microstructure to estimate age in adult atlantic cod gadus morhua. journal of fish biolog y 76, 1640–1654. hüssy, k., gröger, j., heidemann, f., hinrichsen, h.h. & marohn, l. 2016: slave to the rhythm: seasonal signals in otolith microchemistry reveal age of eastern baltic cod (gadus morhua). ices journal of marine science: journal du conseil 73, 1019–1032. jochum, k.p. et al. 2011: determination of reference values for nist sr m 610–617 glasses following iso guidelines. geostandards and geoanalytical research 35, 397–429. jochum, k.p., scholz, d., stoll, b., weis, u., wilson, s.a., yang, q., schwalb, a., börner, n., jacob, d.e. & andreae, m.o. 2012: accurate trace element analysis of speleothems and biogenic calcium carbonates by la-icp-ms. chemical geolog y 318–319, 31–44. limburg, k.e., wuenschel, m.j., hüssy, k., heimbrand, y. & samson, m. 2018: making the otolith magnesium chemical calendar-clock tick: plausible mechanism and empirical evidence. reviews in fisheries science & aquaculture 26, 1–15. nielsen, k., serre, s., thomsen, t. & hüssy, k. 2018: using la-icpms to investigate seasonality in cod otolith microchemistry. 33rd nordic geological winter meeting, dtu, kongens lyngby, denmark. abstract volume. pannella, g. 1971: fish otoliths: daily growth layers and periodical patterns. science 173, 1124–1127. paton, c., hellstrom, j., paul, b., woodhead, j. & hergt, j. 2011: iolite: freeware for the visualisation and processing of mass spectrometric data. journal of analytical atomic spectrometry 26, 2508–2518. patterson, w.p., smith, g.r. & lohmann, k.c. 1993: continental paleothermometry and seasonality using the isotopic composition of aragonitic otoliths of freshwater fishes. in: swart, p.k. et al. (eds): climate change in continental isotopic records. american geophysical union monograph (1993), 191–202. søndergaard, j., halden, n., bach, l., gustavson, k., sonne, c. & mosbech, a. 2015: otolith chemistry of common sculpins (myoxocephalus scorpius) in a mining polluted greenlandic fjord (black angel leadzinc mine, west greenland). water, air and soil pollution 226(10) 336, 12 pp. sturgeon, r.e., willie, s.n., yang, l., greenberg, r., spatz, r.o., chen, z., scriver, c., clancy, v., lam, j.w. & thorrold, s. 2005: certification of a fish otolith reference material in support of quality assurance for trace element analysis. journal of analytical atomic spectrometry 20, 1067–1071. sturrock, a.m., trueman, c.n., darnaude, a.m. & hunter, e. 2012: can otolith elemental chemistry retrospectively track migrations in fully marine fishes? journal of fish biolog y 81, 766–795. thomas, o.r.b., ganio, k., roberts, b.r. & swearer, s.e. 2017: trace element–protein interactions in endolymph from the inner ear of fish: implications for environmental reconstructions using fish otolith chemistry. metallomics 9, 239–249. thorrold, s.r. & shuttleworth, s. 2000: in situ analysis of trace elements and isotope ratios in fish otoliths using laser ablation sector field inductively coupled plasma mass spectrometry. canada journal of fisheries and aquatic sciences 57, 1232–1242. authors’ addresses s.h.s. & t.b.t., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k., denmark. e-mail: shs@geus.dk. k.e.n., p.f-j. & k.h., national institute of aquatic resources, technical university of denmark, kemitorvet, building 202, dk-2800 kgs. lyngby, denmark. mailto:shs@geus.dk geological survey of denmark and greenland bulletin 33, 2015, 81-84 81 composition of ilmenite and provenance of zircon in northern brazil christian knudsen, tonny b. thomsen, feiko kalsbeek, jeppe a. kristensen, helenice vital and roger k. mclimans th e mineral ilmenite (fetio3) is an important component of heavy-mineral placer deposits and constitutes the largest volume of valuable mineral in such deposits. th e minerals zircon (zrsio4) and rutile (tio2), which occur in lower concentrations than ilmenite in the deposits, have a greater value per ton – c. 1100 and 900 $/ton respectively – compared to ilmenite that ranges from 100 to 200 $/ton depending on its composition. other minerals such as staurolite, sillimanite, amphibole and garnet are generally also present in placer deposits, but are of minor or no commercial value and, e.g. amphibole needs to be separated from the valuable heavy minerals which adds to the production cost. ilmenite is more valuable as a raw material in titanium dioxide manufacture if the titanium content is enhanced by natural leaching of the iron component. when exploring for potentially economic heavy-mineral placer deposits, both the variation in composition and distribution of ilmenite are of interest. accordingly, it is also important to understand not only the concentration of heavy minerals in the ground but also the abundance and composition of the individual minerals. th e source (provenance), route and mechanism of transport from source to potential reservoir sandstones are of interest when attempting to understand petroleum systems in sedimentary basins. heavy minerals in reservoir sandstones contain a wealth of information about their formation that characterises their source. th us a database with the characteristics of possible sediment sources is a key tool to investigate the distribution, composition and other characteristics of the heavy minerals in a given area. both heavy-mineral exploration and locating off shore petroleum reservoir sand sources are relevant in northern brazil. in june 2011, the geological survey of denmark and greenland in cooperation with universidade federal do rio grande do norte, natal, rn, brazil set up a project to sample and analyse in situ cretaceous sandstones, sands in river beds and sands from the coastal sediments. th e results were entered into a database of heavy-mineral compositions and properties. th e variation in the distribution of the heavy minerals as well as their composition were determined for 34 samples from northern brazil using computer-controlled scanning electron microscopy (ccsem; keulen et al. 2012). u-pb ages of detrital zircons were determined by laser ablation inductively coupled plasma mass spectrometry (for analytical procedures see frei et al. 2006). four samples for the u-pb age determinations came from cretaceous sandstones, two from river beds and two from beaches. alteration of the heavy minerals when subjected to alteration in the sedimentary environment, heavy minerals react diff erently depending on the local physical and chemical conditions. in hot and humid conditions minerals such as olivine, pyroxene, amphibole © 2015 geus. geological survey of denmark and greenland bulletin 33, 81–84. open access: www.geus.dk/publications/bull ilmenite leucoxene rutile zircon staurolite silimanite-kyanite garnet epidote amphibole baía de marajó 45°w 3°s rio piranhas-açu amazon basin 200 km brazil são luís parnaíba acaraú !! ! !! ! ! !!! ! 40°w45°w 3°s 200 km 62–65 60–62 58–60 56–58 54–56 52–54 tio2 (%) quaternary neogene–quaternary tertiary–quaternary tertiary cretaceous jurassic triassic carboniferous–permian cambrian–devonian neoproterozoic–palaeozoic precambrian litho-chronology belem são luís fortaleza teresina tianguá são luís-grajaû basin parnaíba acaraú camelá sub-basin rio capim baía de marajó fig. 1. modal composition of the heavy-mineral fraction in sand samples from northern brazil. fig. 2. average composition of ilmenite and altered ilmenite in samples from beaches, from river beds and from outcrop of cretaceous sandstone. for location see fig. 1. 8282 and epidote are unstable and gradually disappear from the heavy-mineral assemblage (morton & hallsworth 1999). th e heavy-mineral assemblages in the fi ve easternmost beach sand samples from the northern brazilian coast (fig. 1) all contain abundant amphibole. th e source of those heavy minerals is the precambrian basement in the hinterland (pink, fig. 2). a similar, diverse, heavy-mineral assemblage is described by da silva & vital (2000) in samples from the rio piranhas-açu, north-eastern brazil. th e low degree of alteration of the heavy minerals is probably due to the climate which is arid in this part of brazil. th e heavy-mineral assemblages of the fi ve eastern samples change westwards with increasing contents of alumina-silicates such as staurolite, sillimanite and kyanite; minerals which must be abundant in the hinterland, and which can fi ngerprint the sediment source for the eastern samples. to the west of parnaíba (fig. 1), the heavy-mineral assemblages are dominated by ilmenite, leucoxene, rutile, staurolite and zircon, which are very stable minerals (morton & hallsworth 1999). th e precipitation, humidity and temperature increase towards the west and towards the amazon basin. th is may account for the mineralogical change indicative of intense alteration where even fairly stable heavy minerals like garnet have disappeared. th e cretaceous sandstone in the interior of northern brazil is altered by intense kaolinisation. mendes & truckenbrodt (2009) describe a mature heavy-mineral assemblage from albian sandstones (itapecuru group) in the são luísgrajaû basin and góes et al. (2007) described similar assemblages from the campanian–maastrichtian (ipixuna formation) in the camelá sub-basin to the west. only robust heavy minerals such as ilmenite, zircon, rutile and staurolite are present in the cretaceous samples inland south of são luís and baia de marajá (fig. 1) whereas less stable heavy minerals are lacking. th e higher degree of alteration found in the heavy-mineral assemblage in the coastal beach samples in the western section of the coast could accordingly also be an eff ect of re-deposition of cretaceous sandstones from the hinterland. ilmenite composition th e titanium content of ilmenite changes when it is subjected to chemical weathering; iron is leached and the relative content of titanium increases (fig. 3a). ultimately the mineral leucoxene, which mainly consists of tio2, is formed (bailey et al. 1956). a gradual increase of tio2 in ilmenite in beach sand is evidenced towards the west (fig. 2). as discussed above that may be an eff ect of increasing humidity, but it may also be caused by an infl ux of reworked sediment from altered cretaceous sandstones in the hinterland. th e tio2 content of ilmenite in the albian sandstones (itapetio 2 (%) 50 60 70 80 90 100 ilmenitetitanomagnetite leucoxene rutileb tio 2 (%) 50 60 70 80 90 100 50 40 30 20 10 0 f e 2 o 3 ( % ) ilmenite leucoxene rutile a a b c 50 µm fig. 3. ccsem analysis of titanium minerals from a cretaceous outcrop along rio capim (sample ggu 538118). a: the distribution of tio2 versus fe2o3 in the ilmenite, leucoxene and rutile show an inverse relationship between these two components, where fe2o3 decreases with increasing tio2 – and with the degree of weathering. b: histogram showing the content of tio2 in the titanium mineral grains. fig. 4. scanning electron microscope (sem) backscatter image of an ilmenite grain leached from the rim. in the light grey central part of the grain (a), the ilmenite is un-leached with preserved white hematite lamellae. surrounding the un-leached core there is a zone (b), where the hematite is leached away forming pores (black) and where the ilmenite shows partial leaching (dark grey patches). in the grey rim (c), the ilmenite is highly leached and almost all iron is removed leading to the formation of leucoxene. 83 curu group; eastern line of samples in fig. 2) is high and the tio2 content is even higher in the campanian–maastrichtian (ipixuna formation) located in the more humid climate to the west. th e heavy-mineral assemblage from a cretaceous outcrop along rio capim is dominated by ilmenite. figure 3b shows that the content of tio2 in the titanium minerals has a bimodal distribution with almost no unaltered ilmenite (50% tio2). th e bimodal distribution may indicate that the weathering is a two stage process. an example of chemical weathering of an ilmenite grain is shown in fig. 4. th e grain has a central core that is largely unaltered with hematite lamellae preserved, an intermediate zone where the hematite is leached away giving rise to porosity, and an outer margin that is completely transformed to leucoxene. zircon provenance th e crystalline basement complexes underlying the investigated sedimentary rocks in the eastern part of the area is the borborema province (de almeida et al. 1981) that is composed of a complex assemblage of palaeoproterozoic granitoid and metasedimentary gneisses, locally with outcrops of archaean rocks and with numerous plutons of neoproterozoic granite. neoproterozoic sedimentary successions are also present. palaeoproterozoic granitoid rocks are the most common, forming some 70% of the basement complex. th e são luís craton in the west is dominated by the trans amazonian orogeny with ages ranging from 2000 to 2200 ma (klein et al. 2005). th e u-pb age distribution patterns for eight samples from north-eastern brazil (fig. 5) show the ages of zircon sand grains. four of these are from cretaceous sandstone, two are riverbed sand, and two are coastal sand. th e age distributions (fig. 5) are complex. th e largest component in all samples is formed by palaeofig. 5. u/pb age distributions of detrital zircons from samples from northern brazil. the two green stars to the east represent sandstone samples from the albian itapecuru group and the two green stars to the west represent sandstone samples from the campanian–maastrichtian ipixuna formation. for location see fig. 1. beach sand river bed sand cretaceous sandstone 45°w 3°s 100 km ggu 538254, n = 76/114 ggu 538111, n = 94/140 ggu 538118, n = 86/119 age (ga) 210 3 50 40 30 20 10 0n u m b e r o f a n a ly se s ggu 538205, n = 103/125 age (ga) 210 3 50 40 30 20 10 0n u m b e r o f a n a ly se s ggu 538219, n = 96/119 age (ga) 210 3 50 40 30 20 10 0n u m b e r o f a n a ly se s ggu 538144, n = 75/117 210 3 50 40 30 20 10 0n u m b e r o f a n a ly se s ggu 538125, n = 62/105 age (ga)210 3 50 40 30 20 10 0n u m b e r o f a n a ly se s 30 20 10 0 n u m b e r o f a n a ly se s age (ga)210 3 40 30 20 10 0 age (ga)210 3 age (ga)210 3 50 30 20 10 0n u m b e r o f a n a ly se s 8484 authors’ addresses c.k., t.b.t. f.k. & j.a.k, geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark; e-mail: ckn@geus.dk h.v., universidade federal do rio grande do norte, natal, r n, brazil. r.k.mcl dupont titanium technologies, wilmington, de, usa. proterozoic zircons, 1800–2300 ma, comprising 50–70% of the zircon populations. archaean zircons (2500–3500 ma) constitute 10–25% of the population and neoproterozoic zircons (500–700 ma) constitute 10–20% of the population. only some 15% of the zircons have ages outside these age groups. th ere are no obvious diff erences in age for the zircon populations in the cretaceous sediments, the riverbed sands and the coastal sands. zircons with ages in the range 2000 to 2200 ma, equivalent to the trans-amazonian orogeny (green columns on fig. 5) are common in all samples, in good accordance with observations made by klein et al. (2005). th e content of zircons in the age range 1800–2000 varies considerably. neoproterozoic ages (blue columns on fig. 5) equivalent to braziliano or pan-african orogeny are less frequent in the analysed sands as compared to what is previously described from the borborema province (nascimento et al. 2007). discussion and conclusion th e heavy-mineral assemblages in the east are less mature than assemblages in the west. th at may refl ect a lower degree of alteration of the heavy minerals caused by a drier climate. in the hot and humid area to the west in the amazon basin, the heavy-mineral assemblages are very mature refl ecting the intense chemical attack and removal of heavy minerals such as pyroxene, amphibole and garnet. indications of more intense chemical alteration of the heavy minerals are also seen from the composition of ilmenite that shows decreasing iron content and accordingly increasing content of tio2 towards the west. cretaceous sandstones in the area are kaolinised and the heavy minerals are also strongly altered, most intensely in the hot and humid area in the amazon basin. th e high degree of alteration found in river and beach sediments in the western area could also be caused by reworking of previously altered cretaceous sandstones. apparently, nearly all zircons in the investigated sediments may originate from the underlying crystalline basement, suggesting mainly local source areas. th e zircon-age spectra are fairly uniform suggesting either that the geology in the source area is rather uniform or that the zircons were homogenised in the sedimentary environment and that the sand in the rivers and on the beach at least partly represent reworked cretaceous sandstones. acknowledgements dupont titanium technologies, wilmington, delaware, usa is thanked for fi nancial support. francisco canindé and miguel borges from universidade federal do rio grande do norte, natal, r n, brazil are thanked for help during the fi eldwork. references bailey, s.w., cameron, e.n., spedden, h.r. & weege, r.j. 1956: the alteration of ilmenite in beach sands. economic geolog y 51, 263–279. da silva, m.g. & vital, h. 2000: provenance of heavy-minerals in the piranhas-açu river, northeastern brazil. brazilian journal of geolog y 30, 453–456. de almeida, f.f.m., hasui, y., de brito neves, b.b. & fuck, r.a. 1981: brazilian structural provinces: an introduction. earth science reviews 17, 1–29. frei, d., hollis, j.a., gerdes, a., harlov, d., karlsson, c., vasquez, p., franz, c., johansson, l. & knudsen, c. 2006: advanced in situ geochronological and trace element microanalysis by laser ablation techniques. geological survey of denmark and greenland survey bulletin 10, 25–28. góes, a.m., rossetti, d.f. & mendes a.c. 2007: heavy mineral as a tool to refine the stratigraphy of kaolin deposits in the rio capim area, northern brazil. anais da academia brasileira de ciências 79, 457–471. keulen, n.t., frei, d., riisager, p. & knudsen, c. 2012: analysis of heavy minerals in sediments by computer-controlled scanning electron microscopy (ccsem): principles and applications. mineralogical association of canada short course 42, 167–184. klein, e.l., moura, c.a.v. & pinheiro, b.l.s. 2005: paleoproterozoic crustal evolution of the são luís craton, brazil: evidence from zircon geochronolog y and sm-nd isotopes. gondwana research 8, 177–186. mendes, a.c. & truckenbrodt, w. 2009: provenance of albian sandstones (itapecuru group), eastern border of são luís-grajaú basin, maranhão, using heavy mineral analysis and mineral chemistry. boletim do museu paraense emílio goeldi, ciências naturais 4, 57–74. morton, a.c. & hallsworth c.r. 1999: processes controlling the composition of heavy mineral assemblages in sandstones. sedimentary geolog y 124, 3–29. nascimento, m.d.s., góes, a.m. macambira, m.j.b. & brod, j.a. 2007: provenance of albian sandstones in the são luís–grajaú basin (northern brazil) from evidence of pb–pb zircon ages, mineral chemistry of tourmaline and and palaeocurrent data. sedimentary geolog y 201, 21–42. geological survey of denmark and greenland bulletin 33, 2015, 73-76 73© 2015 geus. geological survey of denmark and greenland bulletin 33, 73–76. open access: www.geus.dk/publications/bull digital models based on images taken with handheld cameras – examples on land, from the sea and on ice erik vest sørensen, morten bjerager and michele citterio geological outcrops can be comfortably modelled in three dimensions in the offi ce using images from a handheld digital camera. recent developments within the imaging techniques of structure from motion (lowe 2004; snavely et al. 2008; fonstad et al. 2013) and photogrammetry (hirschmüller 2005; james & robson 2012; favalli et al. 2012) have made it easier and cheaper to construct so-called digital outcrop models using stereoscopic images from standard digital cameras. th e digital outcrop model (bellian et al. 2005) is a 3d representation of the outcrop surface and is oft en displayed in the form of a polygon mesh or a point cloud. in this paper we present three examples of such point clouds from images obtained with a handheld digital camera. th e examples illustrate how outcrop topography or digital outcrop models can be constructed at diff erent scales, with diff erent accessibility and operational platforms. two examples illustrate outcrop scales of metres to kilometres, with images obtained by walking along excavated exposures in the faxe limestone quarry and from a boat sailing past the coastal cliff of stevns klint. th e third example illustrates detailed micro-topography of ice and snow surfaces where the images were obtained from a snowmobile on an ice cap in a.p. olsen land, north-east greenland. methods th e images were collected with a 36 megapixel nikon d800e camera equipped with a fi xed 35 mm f/1.4 zeiss lens. th e camera was locked at infi nity in the faxe quarry and stevns klint examples. in the third example from greenland, the camera was focused and locked so that objects at a distance of c. 2 m were in focus. th e images were recorded with ste55°15´20´´n 55°15´20´´n 12°7´30´´e 200 m 12°7´30´´e fig. 2a fig. 1. overview of the faxe limestone quarry. red dots: images obtained in 2013. green dots: images obtained in 2014. the inset map shows the location of the faxe quarry in denmark. orthophotograph from danish geodata agency. fig. 2. a: perspective view (towards the north-east) of the northern part of the faxe limestone quarry showing the constructed point cloud generated from oblique images obtained in 2014. the point cloud is coloured according to colour value of matched pixels and can be rotated freely in three-dimensions. for location see fig. 1. b: close-up of a bryozoan limestone mound with nodular f lint layers. b a fig. 2b 20 m 5 m 7474 reoscopic overlaps of up to 90%. in this way image acquisition for digital outcrop models diff ers from the traditional approach for 3d stereoscopic work (dueholm 1992), where a stereoscopic overlap of 60–80% is suffi cient to ensure good precision and continuous stereoscopic overlap. furthermore, images were acquired from much more varied image positions, for example in the faxe quarry study (fig. 1), compared with traditional 3d mapping, where images are typically collected along straight parallel lines. th e construction of the digital outcrop models from the images is based on automatic dense multi-view, stereomatching routines. th ese routines attempt to match each pixel across a range of images. because of the large overlap, the image baseline is quite small, which decreases the precision of matched pixels. th is is, however, compensated for by the redundancy of determining the same point in multiple images. in practice this approach yields a level of precision which is comparable to that typically obtained with stereoimages with 60% overlap, but with a much better automatic elimination of erroneously matched pixels. th is leads to the production of dense point clouds, which require little manual editing, making them well suited for visualisation. th e clouds can also be used in morphological analyses. a number of soft ware solutions can generate point clouds from images; in this study we used the professional version of agisoft photoscan and sure – photogrammetric surface reconstruction from imagery. walking along exposures – the faxe limestone quarry danian deep-water bryozoan and coral carbonate mounds are exposed in the faxe limestone quarry (fig. 1; 55°15́ 40˝n, 12°07´20˝e), which represents a perfect case study for 3d outcrop modelling. th e quarry was visited in 2013 and 2014, and a large collection of stereoscopic images documents the changing features of the active quarry. images of the quarry walls were collected using a handheld digital camera from a distance of 10–20 m, which translates into images with pixel sizes on the ground, also known as the ground sampling distance, in the millimetre range. we used a subset of the data from the northern part of the quarry that is being actively quarried. th e result of the reconstruction is a dense point cloud (fig. 2), which can be freely rotated in 3d and zoomed in on areas of interest. th is is a powerful way of visualising geological outcrop data. when combined with a periodic recording of digital images in the active quarry it can provide unique outcrop topographic data sets that make a reconstruction of the 3d mound topography possible in great detail. it also provides a data set that can be used to quantify volumes of specifi c characteristic rock types, such as the amount of black-grey nodular fl int in the greyish white bryozoan limestone mound systems. b a 10 m fig. 3. a: perspective view of the point cloud generated from a section with danien bryozoan limestone mounds in the coastal cliff of stevns klint. the point cloud is illustrated with rgb-values of matched pixels. b: perspective view of the filtered point cloud based on colour and surface roughness calculations. the inset map shows the location of stevns klint in denmark. fig. 4. perspective view of the reconstructed snow surface measuring 420 × 160 cm from the ice cap in a.p. olsen land, north-east greenland. footprint ruler 50 cm 75 sailing along exposures – stevns klint stevns klint (55°15́ 39˝n, 12°24́ 52˝e) was recently included in unesco’s world heritage list and is world famous for its excellent exposure of the cretaceous–palaeogene boundary. images were collected along 11 km of the coastal cliff from a boat in june 2014, adding new oblique images to the growing archive from previous studies (surlyk et al. 2006; pedersen & damholt 2012). th e images were collected from a distance of 10–300 m, which translates to pixel sizes in the millimetre to centimetre range. th is approach allows for high resolution mapping of the mound structures and megaand mesoscale bedding. images from a cliff section at stevnsfortet in the southern part of the cliff were selected to illustrate how simple manipulation of the generated point cloud data (fig. 3a) can be used to visualise the overall mound structures. characteristic black and grey fl int nodules follow the internal bedding of the bryozoan mounds and display a strong colour contrast to the light-coloured limestone that can be used to fi lter away light-coloured points. th e resulting point cloud can be analysed with calculations of outcrop parameters such as surface roughness and curvature or, with more sophisticated calculations, used in semi-automatic tracing of discontinuities such as joints, fractures or bedding, developed for terrestrial lidar data (garcia-sellés et al. 2011). th e result of the fi ltering is shown in fig. 3b, which illustrates the structure of the internal bedding in a diff erent way. with little eff ort this can be extended to include the entire 11 km surveyed part of the coastal cliff . standing on a snowmobile on an ice cap – north-east greenland th e third example is from an ice cap in a.p. olsen land (74°37´28˝n, 21°22´30˝w) in north-east greenland. th e small-scale topography of snow and ice infl uences the turbulent and radiative components of the surface energy balance, as it controls the aerodynamic roughness length and changes the surface albedo (munro 1989; warren et al. 1998; brock et al. 2006). surface roughness must also be accounted for in remote sensing of the cryosphere (könig et al. 2001). th e spatial scales relevant for such applications span several orders of magnitude, with required vertical accuracies in the order of millimetres (rees & arnold 2006). ground-based photogrammetry appears to be a viable technique to map snow and ice micro-topography in the fi eld down to a scale of centimetres (irvine-fynn et al. 2014). our aim is to demonstrate the feasibility of millimetre-scale accuracy over an outcrop scale of several square metres, under fi eld conditions. 50 cm a b c d 0.055 0.051 0.048 0.044 0.041 0.038 0.034 0.031 0.027 0.024 0.021 0.017 0.014 0.010 0.007 0.003 0 roughness elevation radius = 0.005 m radius = 0.05 m radius = 0.5 m 653.049 653.041 653.034 653.026 653.019 653.011 653.003 652.996 652.988 652.981 652.973 652.966 652.958 652.951 652.943 652.936 652.928 (m above sea level) fig. 5. point cloud of the surface shown in fig. 4, in plane view. a: coloured according to elevation height. b, c, d: coloured according to surface roughness. the surface roughness is calculated as the vertical deviation of each point from the best fitted plane defined by data within a sphere with a radius of 0.005 m (b), 0.05 m (c) and 0.5 m (d). 7676 for this experiment, a person standing on a snowmobile and pointing the camera obliquely downwards collected 29 images from diff erent positions. th e distance from the camera to the ground was c. 2 m. th is approach gives images with a ground sampling distance in the sub-millimetre range. th e generated data are a very dense point cloud (fig. 4). th e height of roughness elements per unit length is shown in fig. 5 over three diff erent spatial wavelengths of 0.005 m, 0.05 m and 0.5 m. th is case study shows that it is possible to obtain surface roughness data useful for glaciological and remote sensing applications by relatively simple means. summary th is study demonstrates that it is possible to generate highresolution topographic data at various scales with diff erent accessibility and operational platforms by using a standard digital camera and computer soft ware. th e method has a high potential for fi eld geologists, who wish to establish accurate outcrop topographic models that can be ‘brought to life’ and visualised in 3d surface models. th ese models can be freely rotated in three dimensions and are well suited for visualisation as well as quantitative purposes in geological mapping. th is is an important new addition to the way 3d mapping is undertaken in the photogrammetry laboratory at the geological survey of denmark and greenland. acknowledgements data from the faxe limestone quarry and stevns klint were obtained with support from geocenter denmark and the european science foundation cocar de-er n. references bellian, j.a., kerans, c. & jennette, d.c. 2005: digital outcrop models: applications of terrestrial scanning lidar technolog y in stratigraphic modeling. journal of sedimentary research 75, 166–176. brock, b.w., willis, i.c. & sharp, m.j. 2006: measurement and parameterization of aerodynamic roughness length variations at haut glacier d’arolla, switzerland. journal of glaciolog y 52, 281–297. dueholm, k.s. 1992: geologic photogrammetry using standard smallframe cameras. rapport grønlands geologiske undersøgelse 156, 7–17. favalli, m., fornaciai, a., isola, i., tarquini, s. & nannipieri, l. 2012: multiview 3d reconstruction in geosciences. computers & geosciences 44, 168–176. fonstad, m.a., dietrich, j.t., courville, b.c., jensen, j.l. & carbonneau, p.e. 2013: topographic structure from motion: a new development in photogrammetric measurement. earth surface processes and landforms 38, 421–430. garcía-sellés, d., falivene, o., arbués, p., gratacos, o., tavani, s. & muñoz, j.a. 2011: supervised identifi cation and reconstruction of nearplanar geological surfaces from terrestrial laser scanning. computers & geosciences 37, 1584–1594. hirschmüller, h. 2005: accurate and effi cient stereo processing by semiglobal matching and mutual information. in: schmid, c., soatto, s. & tomasi, c. (eds): proceedings of ieee conference on computer vision and pattern recognition (cvpr), san diego, ca, usa, 20–26 june 2005, 2, 807–814. irvine-fynn, t.d.l., sanz-ablanedo, e., rutter, n., smith, m.w. & chandler, j.h. 2014: instruments and methods. measuring glacier surface roughness using plot-scale, close-range digital photogrammetry. journal of glaciolog y 60, 957–969. james, m.r. & robson, s. 2012: straightforward reconstruction of 3d surfaces and topography with a camera: accuracy and geoscience application. journal of geophysical research 117(f3), f03017. könig, m., winther, j.g. & isaksson, e. 2001: measuring snow and glacier ice properties from satellite. reviews of geophysics 39, 1–27. lowe, d.g. 2004: distinctive image features from scale-invariant key points. international journal of computer vision 60, 91–110. munro, s. 1989: surface roughness and bulk heat transfer on a glacier: comparison with eddy correlation. journal of glaciolog y 35, 343–348. pedersen, s.a.s. & damholt, t. 2012: cliff collapse at stevns klint, south-east denmark. geological survey of denmark and greenland bulletin 26, 33–36. rees, w.g. & arnold, n.s. 2006: scale-dependent roughness of a glacier surface: implications for radar backscatter and aerodynamic roughness modelling. journal of glaciolog y 52, 214–222. snavely, n., seitz, s. & szeliski, r. 2008: modeling the world from internet photo collections. international journal of computer vision 80, 189–210. surlyk, f., damholt, t. & bjerager, m. 2006: stevns klint, denmark: uppermost maastrichtian chalk, cretaceous–tertiary boundary, and lower danian bryozoan mound complex. bulletin of the geological society of denmark 54, 1–48. warren, s.g., brandt, r.e. & hinton, o.p. 1998: eff ect of surface roughness on bidirectional refl ectance of antarctic snow. journal of geophysical research 103(e11), 25789–25805. authors address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail address: evs@geus.dk geological survey of denmark and greenland bulletin 33, 2015, 25-28 25 acoustic events on a small seismological network – shock waves from thunder and fireballs peter h. voss, trine dahl-jensen and tine b. larsen th e geological survey of denmark and greenland (geus) operates a network of seismic stations in denmark primarily to detect earthquakes. but from time to time other sources than earthquakes generate seismic signals that are detected at the stations. here we show that both meteoroids and thunder have generated seismic signals with high signal-to-noise ratios at some of geus’ seismic stations (fig. 1). th e purpose of the seismic stations is to provide data for the earthquake database of the kingdom of denmark, hosted and maintained by geus. in order to avoid that the earthquake database is contaminated by other events not related to tectonism, these events are given special markers when possible. meteoroids in their fall through the atmosphere two meteoroids generated sonic signals close to danish seismic stations with suffi cient energy to cause seismic signals (fig. 2). fireballs of the meteoroids were observed. th e sonic signal is interpreted as the sonic shock wave that is generated when the speed of the fi reball exceeds the speed of sound. th e fi rst observation was made on 17 january 2009 when a meteoroid entered the atmosphere from space above the baltic sea and landed fig. 1. map of denmark showing the location of seismic stations and towns mentioned in the text. the arrows show the paths of fireballs. 10°e 55° 57°n 50 km denmark sweden læsø aalborg kattegat germany stevns maribo frederikshavn klokkerholm baltic sea seismic station town or village fig. 2. a: seismograms from the two seismic sensors that recorded the passing shock wave of the 2009 fireball. data have been band-pass filtered from 5 to 10 hz. b: seismograms from three seismic sensors that recorded the shock wave of the 2014 fireball showing the first motion downward on three stations. data have not been filtered. c: the arrows mark the pulses of the n-wave of the 2014 fireball. data were band-pass filtered from 1 to 10 hz. b c station 2,z station 4,z station 5,z 1 2 s 1 2 s lld 2,z station 2,z station 4,z 1 2 3 4 5 6 7 8 9 s a lld 1,z © 2015 geus. geological survey of denmark and greenland bulletin 33, 25–28. open access: www.geus.dk/publications/bull 2626 near the town of maribo, lolland (fig. 1), where a meteorite with a weight of 25.8 g was found (haack 2012; haack et al. 2012). th e second meteoroid was recorded on 16 june 2014 on a small network of six seismic stations north of aalborg, jylland. th is meteoroid entered the atmosphere south of frederikshavn and possibly ended in the kattegat south of the island of læsø (fig. 1). no meteorite was found. th e seismograms of the shock waves from the 2009 fi reball are seen in fig. 2a. th ey were recorded on the geus seismic station located on stevns. th e station is equipped with two vertical sensors installed 208 metres apart, with sensor lld2 located 150° south-east by south of sensor lld1. th e acoustic signal arrived 0.33 s later at lld2 than at lld1 which suggests that the source of the signal was located to the south-east of the stations. th e duration of the signals diff ers by a factor of four, which might be an eff ect of the diff erent conditions at the sites where the sensors are installed. th e lld1 signal is from the original sensor, located in a small vault dug into the fi eld. th e lld2 signal is from an experimental installation of a similar sensor next to the wall of a large barn. th e longer duration of this signal was probably caused by the resonance of the shock wave by the barn. when seismic data from the 2014 fi reball were fi rst analysed, the lack of s-wave energy suggested that the source of the signals was a mine explosion in kattegat. but closer inspection of the signals showed that the fi rst motion of the detected p-wave was downward, consistent with dilatation at the source (fig 2b). th e expected fi rst motion of the p-wave from an explosion is upward in response to the compression exerted by the source on the surroundings. an analysis of the signals recorded on the six stations, seen in fig. 3, shows that the shock wave arrived at the stations from an almost easterly direction of approximately 96°, with an apparent surface velocity of 1255.8 m/s. assuming a sound speed of 342.2 m/s the incidence angle to the seismic stations is 15.9° from vertical. th ese results fi t well with the fi reball observations published at http://stjerneskud.info. th e observed fi reball trajectory derived by sørensen (2014) based on phonorth south east west fig. 3. seismic recordings from six seismic stations of the shock wave caused by the fireball on 16 june 2014. data are the up/down z component of the data. amplitudes are normalised and the data were band-pass filtered from 5 to 10 hz. the time is utc. fig. 4. photograph showing the meteoroid trajectory. the photograph was taken with a specially designed fireball camera on 16 june 2014 at 1:15 p.m. local time, in klokkerholm, jylland. the camera was turned upward and equipped with a fisheye objective. the meteor was visible for 3.9 s. the image was created by stacking all video frames showing the fireball. courtesy of kim lang, klokkerholm and anton sørensen, http:// stjerneskud.info. station 1,z station 2,z station 3,z station 4,z station 6,z station 5,z 23:19:00 23:19:1023:19:05 27 tographs taken at two locations in northern jylland (fig. 4) corresponds well with our calculation of the azimuth angle. th e crossing of the azimuth and the trajectory suggest that the source of the shock wave came from an altitude of 46 km in the upper part of the stratosphere over the island of læsø. but since sound in the atmosphere oft en follows nonlinear ray paths as seen by the low incidence angle, the derived altitude is very uncertain. th e changes in air pressure in the shock wave generate a seismic p-wave in the upper part of the earth. since the seismic p-wave travels faster than the shock wave, it can sometimes be detected just before the arrival of the shock wave as shown by, e.g. kanamori et al. (1991). but in the data from the two fi reballs that we have observed, we see no indication of p-wave signals arriving before the shock wave. as the sonic boom travels through the atmosphere, the change in pressure has an n-shaped pulse. at the conversion to seismic energy, the n-wave shows as two pulses on the seismogram (kanamori et al. 1991; cates & sturtevant 2002). th ree examples of n-waves recorded aft er the 2014 fi reball are shown in fig. 2c. th ese should not be confused with p-waves, which arrive through the ground. thunder th e six seismic stations north of aalborg, installed in a network with a radius of 5 km, have made it possible to detect signals that are normally regarded as noise, for instance thunder. th under couples to the ground like the sonic booms from, e.g. meteoroids, but since lightning oft en covers very large areas and occurs in sequences, the seismic signal consists of many peaks and is less impulsive (e.g. kappus & vernon 1991). an example of at least seven thunder signals within a short time window is seen in fig. 5. th e distance to a thunderstorm that will generate an observable signal depends on the power of the acoustic signal released by the thunder and the composition of the atmosphere at the time of the thunder, since changes in the atmosphere can dampen or amplify acoustic signals in diff erent directions. most of the thunder we have observed occurred close to our seismic stations, but we have also observed thunder up to 30 km from a seismic station. th e thunder signals diff er from earthquake signals and explosions by the absence of body waves and are characterised by an apparent surface velocity around the speed of sound. it is the apparent surface velocity of the thunder signals that discriminates the seismic signals from other noise signals, such as traffi c. since the distance between seismic stations is usually long (50 km), thunder will most oft en only be recorded by a single seismic station, whereas a minimum of three stations is needed to estimate the apparent surface velocity. it is therefore normally not possible to positively identify sonic waves. in order to identify thunder signals we verify the observations with the lightning measurements performed by the danish meteorological institute. maps of observed lightning in denmark are presented on the institute’s webpage (http://www.dmi.dk/vejr/maalinger/lyn/). discussion th e signals caused by sonic booms only constitute a small fraction of the observed seismic events in the geus earthquake database. but when they occur they must be identifi ed so that they do not contaminate the seismic data. th e sonic boom from the fi reball on 16 june 2014 was not reported by any persons. th e seismic recordings only contain signals u p to 50 hz which is close to the lower limit of the human hearing range (on average 31 hz). th e frequency spectra in fig. 6 show that the recorded seismic signal of the meteoroid shock wave on average contained less energy above 31 hz than for instance a thunder signal recorded on 1 november 2014. at around 15 hz the two signals have similar amplitudes, but again at lower frequencies the thunder signal is on average higher. with an energy content lower than a thunder signal, the sonic boom was probably not audible to humans. figure 6 also shows the spectra of the p-wave of a local magnitude 1.2 earthquake recorded on 4 august 2014, approximately 39 km from the seismic station. th e spectra of the p-wave are station 3,z station 5,z 11:25 11:26 11:27 11:28 station 1,z fig. 5. seismograms showing 4 minutes of data from the up/down sensor recorded at three stations as a thunderstorm passed by on 1 july, 2014. at least seven signals caused by thunder are seen. time is utc, data were band-pass filtered from 10 to 30 hz. www.dmi.dk/vejr/maalinger/lyn/ 2828 comparable to the thunder signal, at frequencies lower than 40 hz. hearing such a signal would require a coupling of the energy from the ground to the air, which would introduce an energy loss. when people send geus reports on earthquakes sounds, they are oft en related to movements in buildings. geus did not receive any reports from this earthquake being felt or heard. it is oft en the ground impact of meteors that is associated with danger, but the meteor that hit chelyabinsk, russia, on 15 february 2013 was a clear reminder that the shock wave may pose a signifi cant risk. more than 1600 people were hurt from falling debris and over 7300 buildings were damaged. seismic waves were observed at distances of more than 4000 km. th is corresponds to an earthquake magnitude of 3.6 (heimann et al. 2013). th e challenge of marking seismic events of non-tectonic nature in the earthquake database remains and we are still not able to identify and mark them all. although we have recorded explosions, glacial earthquakes, thunder and fi reballs we still have not detected any footquakes in denmark. footquakes are seismic signals from sport events like football, an example comes from the 2006 african cup. when cameroon scored goals during the games, people in cameroon who watched the games on tv jumped a lot and generated simultaneous signals on 20 seismic stations across the country (euler 2007). references cates, j.e. & sturtevant, b. 2002: seismic detection of sonic booms. journal of the acoustical society of america 111, 614–628. euler, g.g., wiens, d.a. & loft on, k.m. 2007: footquakes. iris newsletter 1, p. 13. haack, h. 2012: meteoritter – tidskapsler fra solsystemets oprindelse, 189 pp. copenhagen: gyldendal. haack, h. et al. 2012: maribo – a new cm fall from denmark. meteoritics and planetary science 47, 30–50. heimann, s., gonzález, á., wang, r., cesca, s. & dahm, t. 2013: seismic characterization of the chelyabinsk meteor’s terminal explosion. seismological research letters 84, 1021–1025. kanamori, h., mori, j., anderson, d.l. & heaton, t.h. 1991: seismic excitation by the space shuttle columbia. nature 349, 781–782. kappus, m.e. & vernon, f.l. 1991: acoustic signature of thunder from seismic records. journal of geophysical research-atmospheres 96, 10989–11006. sørensen, a.n. 2014: http://www.stjerneskud.info/fi reball/ event2014-06-16-01-15/ authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: pv@geus.dk 0 1 2 3 l o g a m p li tu d e 1 2 5 10 20 50 frequency (hz) meteroid thunder earthquake fig. 6. frequency spectra of meteoroid, thunder and earthquake waves. a time window of 2 s around the signal on the up/down z-sensor from station1 was used. the amplitude is uncorrected. the nyquist frequency is 50 hz. geological survey of denmark and greenland bulletin 31, 2014, 15-18 15 borehole logs from the precambrian basement on bornholm, eastern denmark: geology and groundwater flow peter gravesen, bertel nilsson, per rasmussen and stig a. schack pedersen bornholm is situated in the sorgenfrei–tornquist zone that separates the north-west european craton from the baltic shield and the east european platform (fig.1). the precambrian basement of northern and eastern bornholm consists of different granitic and gneissic mesoproterozoic rocks that are dated to c. 1455 ma (waight et al. 2012). it appears from the age data that granitic magmatism, deformation and metamorphism occurred over a relatively short time period. the rocks contain abundant pegmatite and aplite bodies. more than 250 mafic dykes occur. the dykes were intruded during three precambrian events at c. 1326 ma, 1220 ma, 950 ma and during a permian event at c. 300 ma (holm et al. 2010). the present study focuses on the østermarie–paradisbakke area north of paradisbakkerne and deals with the paradisbakke migmatite and part of the bornholm gneiss. the aim of the study was to map the distribution of fractures in the rocks and determine the groundwater flow in these low-permeability rocks using outcrop data and borehole logs. the survey was part of an investigation of potential areas for disposal of radioactive waste from the research centre risø area (gravesen et al. 2011a, b, 2012, 2013). rocks, fractures and groundwater the two types of crystalline basement rocks in the study area show similar mineralogy and are dominated by k-feldspar (35–38%), quartz (23–30%), plagioclase (22–25%) and hornblende (11–17%); biotite and other minerals also occur (micheelsen 1961). the bornholm gneiss is medium-grained and grey or reddish grey. the fineto medium-grained paradisbakke migmatite consists of almost parallel, light grey © 2014 geus. geological survey of denmark and greenland bulletin 31, 15–18. open access: www.geus.dk/publications/bull s k å n e b o r n h o l m b a l t i c s e a faults p a r a d i s b a k ke r n e ø s t e r m a r i e a b cretaceous clay, sand and limestone jurassic sand and clay silurian shale cambrian sandstone granite and gneiss with dykes 2 5 k m n b a l t i c s h i e l d e a s t e u ro p e a n p l a t f o r m n w e u ro p e a n c r a t o n s – t z o n e b o r n h o l m fig. 1. geological map of bornholm and skåne in southern scandinavia. the location of the two cross-sections shown in fig. 4 is indicated. inset: bornholm’s location in the sorgenfri–tornquist zone (s–t zone; from graversen 2009). fig. 2. paradisbakke migmatite in præstebo quarry at the northern rim of paradisbakkerne. horizontal and vertical fractures are common whereas oblique fractures are rare. the height of the outcrop is c. 12 m. 1616 granitic quartz-feldspar veins in a darker matrix. both rocks contain pegmatite bodies and are cut by thin nne–ssworiented dykes that were intruded c. 1220 ma ago. minor bodies of reddish grey granite are also present. the rocks are cut by four fracture systems, which can be observed in quarries with paradisbakke migmatite along the northern rim of paradisbakkerne (von bubnoff 1942; fig. 2). after deformation and cooling in the precambrian, large tectonic faults and fractures and minor vertical fractures were formed. the main fracture system in the area has an nne–ssw orientation, corresponding to the direction of the mafic dykes (micheelsen 1961). large linear, fault-controlled valleys are found in paradisbakkerne and in the western part of the precambrian basement on bornholm, but such valleys are absent in the study area. however, small vertical fractures with the same orientation are seen in outcrops. a second ese–wnw-oriented verical tectonic fracture system that shows the same orientation as palaeozoic faults was probably formed during a main phase of wrench faulting in the sorgenfrei–tornquist zone in the late palaeozoic or later (graversen 2009). zones of 4.5 m thickness contain thin fractures with centimetre-sized spacing, while single fractures can have up to 5 m spacing. small faults with slickensides are present and show that some horizontal movement has occurred. in addition to the vertical or subvertical fractures, rare occurrences of oblique fractures and conjugate fracture sets are also found. a third system of horizontal fractures (sheet jointing) at levels from 25 m to 100 m depth was probably formed by load release when an overburden of supposed younger deposits, probably of cambrian to quaternary age, was eroded and removed (spencer 1969). we assume that the spacing 10 20 30 40 50 0 100 10000 10050 inf low zo ne lit ho log y de pth (m ) flo w log (% ) major minor major major major precambrian gneiss and migmatitequaternary clayey till re lat ive in flo w 400 na tur al gam ma (a pi) 800 fo rm ati on re sis tiv ity (o hm -m ) so nic ve loc ity (k m/ s) 8040 co nd uc tiv ity (m s/m ) 84 fig. 3. litholog y and logs in borehole dgu no. 247.458. the f low-log data were acquired at a pumping rate of 1.3 m3 h–1. api: american petroleum institute units. 17 between the fractures increases downwards, because this is seen in quarries. a fourth fracture system consists of horizontal fractures near the ground surface with a spacing of 1–2 m, which also increases downwards. crushed rocks with blocky structures also occur. this system may have been formed by glaciers during the quaternary. the lower limit of the fractures is unknown but some horizontal fractures are found at 90 m below the ground surface. this means that water flow in vertical fractures that cross-cut the deep horizontal fractures can supply the deep fracture system with groundwater from above. the rocks in the area are slightly weathered and fe-containing minerals are oxidised to yellowbrown clayey, fe-rich deposits on some fracture surfaces. such deposits may prevent water flow in some of the fractures. most of the area is covered by a clayey till up to 6 m thick. the groundwater reservoir is characterised by a network of vertical to subvertical and horizontal to subhorizontal fractures. surface water is mainly transported to the groundwater zone in the vertical fractures and the groundwater can be transported over long distances in the horizontal fractures. it is difficult to map the subsurface fractures but data from borehole logs can contribute to our understanding of the network. normally the groundwater table is found a few metres below the ground surface but pumping will often lower the groundwater table because the storage capacity in the reservoir is small. the yield of boreholes in basement rocks on bornholm is commonly low, but boreholes supplying østermarie waterworks show high yields because of fracture systems in the rocks in this area. borehole logs eight private water boreholes in the study area were investigated by geophysical wireline logging. the water pump was removed in the morning and re-installed in the late afternoon after logging. the following geophysical parametres were measured: natural gamma radiation, formation resistivity, sonic velocity, conductivity and impeller flow. conductivity and flow log data were acquired during groundwater pumping from the borehole. natural gamma, resistivity and sonic velocity logs provide information on lithological variation in the borehole. the conductivity log gives information about groundwater chemistry and under certain conditions also provides information on groundwater inflow zones. the flow log measures the vertical flow velocity in the borehole. changes in flow velocity during pumping indicate groundwater inflow zones at specific depths or depth intervals in the borehole. results the results from the logging of borehole dgu no. 247.458 are shown in fig. 3 and two constructed geological sections through the study area are shown in fig. 4. in the c. 5 km long north–south section, the fracture inflow into four boreholes is shown (fig. 4a). the depths of water flow in the basement rocks indicate the location of fractures and the inflow is evaluated semi-quantitatively as ‘major’ or ‘minor’ in each borehole. ‘major’ indicates that the fracture inflow contributes a large part of the total inflow whereas ‘minor’ indicates only a minor contribution. ‘major’ inflows are interpreted from the flow log where an increase in the flow log (%) occurs, measured from the bottom towards the top of the borehole. ‘minor’ inflows are interpreted from the conductivity log where –25 –25 0 25 50 75 el ev at io n (m a .s. l.) 1 km south north groundwater level sea 247.3 69 247.4 03 247.5 67 247.5 41 247.4 32 a groundwater level 247.4 96 247.4 03 247.4 58 247.6 61 0 25 50 100 west east 1 kmb major inflowminor inflow fig. 4. two cross sections through the logged boreholes. for location see fig. 1. note different horizontal and vertical scales. 1818 changes in conductivity appear. the conductivity log can be more sensitive to minor influx zones than the flow log. it is relevant to compare the boreholes because they have the same low specific yield (0.05–0.22 m3/h–1). figure 4 shows fracture inflow at four different depth intervals. major inflow is registered near the bottom of the boreholes and minor fracture inflow is seen closer to the surface. the groundwater table is situated a few metres below the surface in all boreholes. it is not possible to directly determine the orientation of the fractures, but fractures that are found at the same level, at c. 10 to 12 m a.s.l., are likely to be horizontal or subhorizontal and hydraulically connected. in the c. 8 km long west–east section, fracture inflow is registered between c. 100 m a.s.l. and 25 m b.s.l. (fig. 4b). borehole dgu no. 247.496 at østermarie waterworks is included in this section (rasmussen et al. 2007). inflow is seen in all boreholes but the largest inflow is found at the bottom of borehole dgu no. 247.403. several important waterbearing fracture zones are found in the waterworks borehole. the fractures occur at shallower depths at at least four levels. the results from the logging survey appear to confirm the occurrence of important fracture systems at depth. fractures are located at different levels. horizontal fracture systems seen over a large area are found at 10–12 m a.s.l. and a similar system occurs at c. 20 m b.s.l. several smaller fracture systems without large water flow also occur. the most important and largest fracture system is found at 90 m below the surface, usually at the bottom of the boreholes. as mentioned above we cannot determine the orientation of the fractures from the borehole log survey, but the structural model indicates major elements of the fracture systems. the horizontal fracture spacing apparently increases with depth, but it is still posssible to find fracture systems with major water flow if they are connected to other vertical and horizontal fractures. conclusions the conclusions of the investigations are as follows: 1. the logging of the boreholes shows that fracture systems occur in all of them. 2. the fractures occur down to at least 90 m below the surface, and flow logging documents the occurrence of groundwater flow down to this depth. the downward transport of surface water to the horizontal fractures may be via vertical fractures to at least the same depth. 3. horizontal fractures are found at 10–12 m a.s.l. and at 20 m b.s.l. the fractures appear to be connected over kilometre-long distances. acknowledgements the danish parliament is thanked for financial support. we are grateful to local landowners that gave us permission to log their private boreholes. references graversen, o. 2009: structural analysis of superposed fault systems of the bornholm horst block, tornquist zone, denmark. bulletin of the geological society of denmark 57, 25–49. gravesen, p., nilsson, b., pedersen, s.a.s. & binderup, m. 2011a: low and intermediate level radioactive waste from risø, denmark. location studies for potential disposal areas. report no. 4. characterisation and description of areas bornholm. danmarks og grønlands geologiske undersøgelse rapport 2011/44, 85 pp. gravesen, p., binderup, m., nilsson, b. & pedersen, s.a.s. 2011b: geological characterisation of potential disposal areas for radioactive waste from risø, denmark. geological survey of denmark and greenland bulletin 23, 21–24. gravesen, p., nilsson, b., binderup, m. larsen, t. & pedersen, s.a.s. 2012: lavog mellem radioaktivt affald fra risø, danmark. omegnsstudier. rapport nr. 1. område østermarie-paradisbakkerne, bornholms regionskommune. danmarks og grønlands geologiske undersøgelse rapport 2012/123, 100 pp. gravesen, p., nilsson, b., binderup, m., larsen, t.b. & pedersen, s.a.s. 2013: geolog y, seismic activity and groundwater conditions at six potential disposal sites for radioactive waste from risø, denmark. geological survey of danmark and greenland bulletin 28, 13–16. holm, p.m., pedersen, l.e. & højsteen, b. 2010: geochemistry and petrolog y of mafic proterozoic and permian dykes on bornholm, denmark: four episodes of magmatism on the margin of the baltic shield. bulletin of the geological society of denmark 58, 35–65. micheelsen, h. 1961: bornholms grundfjæld. meddelelser fra dansk geologisk forening 14, 308–349. rasmussen, p., klitten, k., nielsen, s. & jensen, p. 2007: bornholms regionskommune. logging og vandkemi i vandforsyningsboringer, 2006. danmarks og grønlands geologiske undersøgelse rapport 2007/36, 91 pp. spencer, e.w. 1969: introduction to the structure of the earth, 597 pp. new york: mcgraw-hill. von bubnoff, s. 1942: beiträge zur tektonik des skandinavischen südrandes. 2. die älteren granite bornholms im rahmen der svekofennidischen tektogenese. neues jahrbuch für mineralogie, geologie und paläontologie, beilagen-band 87, 277–396. waight, t., frei, d. & storey, m. 2012: geochronological constraints on granitic magmatism, deformation, cooling and uplift on bornholm, denmark. bulletin of the geological society of denmark 60, 23–46. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: pg@geus.dk mailto:es@geus.dk geological survey of denmark and greenland bulletin 38, 2017, 73-76 73 where there scientific or political reasons behind denmark’s decision to establish its first seismological stations for earthquake monitoring? in a nation where earthquakes are few and of small magnitude, it is remarkable that since 1927 the geological survey of denmark and greenland (geus), and its predecessors back to the danish geodetic institute have recorded seismological events from permanent stations in denmark and greenland and shared data through international data centres. as early as 1907, on private initiative by e.g. harboe, a seismological station was established in godhavn, west greenland (harboe 1911). however, with time it became clear that the phase readings from the instruments lacked precision (fig. 1), and in 1912 monitoring was discontinued due to lack of funding (geodætisk institut 1978). having never officially joined the international seismological association, or suffered destructive earthquake within their territory, danish authorities did not at the time have any vested interest in operating expensive seismological stations. the origins of denmark’s seismological monitoring programme historians of science have argued that scientific knowledge of greenland equalled sovereignty (ries 2012; doel et al. 2016). inspired by their approach, i suggest that theformation of a network of danish and greenlandic seismological stations could be understood as an expression of national geopolitical strategy rather than a display of scientific vigour. by examining historical records from public institutions like the ministry of education, ministry of foreign affairs, ministry of war and the danish geodetic institute as well as letters from erik nørlund and inge lehmann, kept at the danish national archives and geus, it is possible to assess to what degree geopolitical considerations were a factor in establishing a seismological monitoring programme in denmark. in 1923, denmark became a full member of the international union of geodesy and geophysics (iugg), but it was not until october 1924 after the second iugg general assembly in madrid that (lack of ) seismological monitoring from its territory became an issue for denmark. before the assembly, a national committee for seismology had hastily been formed under the leadership of niels erik nørlund, professor of mathematics at copenhagen university and director of the danish geodetic service (den danske gradmaaling). after the assembly, nørlund reported to the ministry of education that there had been considerable pressure on denmark to record and share geophysical data from greenland. so substantial was the pressure that nørlund warned that unless denmark initiated a programme of general geodetic research, in particular seismological monitoring and international data sharing, other nations would question denmark’s authority in greenland (danish national archives (dna) 1). it was a potent threat, since the danish government rightfully feared that their claim to sovereignty over greenland could be contested by their neighbours. for example, a stipulation of the 1917-treaty between denmark and the usa regarding the sale of the west indies to the usa was, in addition to paying dkk 25 million, that the usa also acknowledged denmark’s sovereignty over greenland. norway on the other hand made counterclaims to parts of eastern greenland in 1924 and 1931 (kragh et al. 2008). over the next months, nørlund worked on securing support for his envisioned network of seismic stations. as arctic geopolitics and the beginning of earthquake monitoring in denmark and greenland a. lif lund jacobsen fig. 1. seismograms from the old station in godhavn kept at geus. these seismograms from 1907–1912 are among the oldest seismological records in existence. photo: danish national archives. © 2017 geus. geological survey of denmark and greenland bulletin 38, 73–76. open access: www.geus.dk/publications/bull 7474 director of the danish geodetic service, nørlund was appointed to reorganise national geodesy, including triangulation efforts which traditionally had been a key interest area of the army’s department of topography (generalstabens topografiske afdeling). using his position, he added seismology to the list of intended activities. in order to secure the necessary political backing and financial support from private funds, nørlund employed several different arguments. in addition to demonstrating sovereignty over greenland, he argued that denmark needed seismological stations because all cultural and refined nations in europe had a least one. also scientifically, seismological data constituted a valuable source of information for geodetic research. finally, he argued that international data sharing was a means to maintain international peace and collaboration. during the winter 1924/25, enough political and financial support was mustered that nørlund and the danish geodetic service could begin building the network. establishing seismological stations from 1925 to 1927 from early on, it was clear that while the danish government was willing to authorise the construction of seismological stations, much of the funds to build stations and buy scientific instruments had to come from private donations. in the spring of 1925, orders for a variety of different seismographs and other instruments were placed at international suppliers in england, germany, russia and the usa. not knowing which seismic frequencies they could expect and at a time where no standards for performance and accuracy exsisted, orders were for state-of-the-art seismograph models of different mechanical or electrical designs. the costly instruments were all paid for by the carlsberg foundation which also made significant contributions towards the construction costs of the stations. in addition, carlsberg also agreed to provide an annual grant to cover operating costs for two of the three stations, a practice that continued until the 1950s. without any practical knowledge about the working of seismological instruments or how they would react to the extreme climate of greenland, it was decided that a station in denmark should act as a testing and comparison site for the different instruments. at the same time negotiations began to secure space for stations both in copenhagen and greenland. historical records show that geopolitical and strategic considerations played a significant role in where to locate the three planned stations (e.g. dna 2). being relatively close to the city, the permanent station in copenhagen (cop) was the first to be completed. in the spring of 1925, the army handed over two caponieres located in the old fortifications of copenhagen (vestvolden) to be used as a seismological station. still being part of the military defense system, access to the station was restricted until well after the second world war. installations began in the autumn of 1926. by 17 february 1927 all instruments were in place and monitoring began, but due to occasional failure of the timing, the working of the station was not considered satisfactory before march. hereafter publication of the records began in a seismological bulletin. by then cop was equipped with the following seismographs: a wiechert 1000 kg horizontal (fig. 2), a wiechert 1300 kg vertical, three galitzin instruments (two horizontal and a vertical), a 2-component milne-shaw. later a 2-component wood-anderson seismograph was added. today historical bulletins and log book from all the stations can be found at http://seis.geus.net/seismic_service. html. as the largest of the three seismological stations in the network, cop had a fulltime caretaker to do daily maintenance and recording, paid by the carlsberg foundation and living in a nearby cottage. establishing and installing denmark’s first permanent seismological station was not an easy task for the untrained personnel hired by nørlund, and in recognition of their valuable contribution, inge lehmann and two students received a bonus worth nearly two months’ salary (dna 3). by all accounts, this was also the later so famous seismologist inge lehmann’s first encounter with seismological work, which principles she first began to study in earnest later that year. the station in ivittuut (ivi), south west greenland, was the second to be completed (fig. 3). with the help fig. 2. in cop’s caponiére xiii, the purely mechanical wiechert horizontal seismograph is still in its original location. photo: casper brogaard højer. 75 of the danish mining company kryolith mine og handelsselskabet, a seismological vault was blasted into the bedrock about 250 m from the mine’s main blasting sites (!) to determine the effect of blasting on the seismological instruments tests were made with a portable seismograph during the summer of 1926, but it was not before the summer of 1927 that the intended seismographs, a wiechert vertical and a wiechert horizontal seismograph, were installed (dna 4). operated, for an extra fee, by the local radio-telegraphist employed by the mining company, the station began recording on 24 august 1927 (bulletin ivigtut 1929). when the third and final station in the danish network was constructed, it became clear that that geopolitical arguments worked both ways between arctic nations. in september 1925, nørlund wrote to the danish ministry of foreign affairs that the danish geodetic service was considering a permanent seismological station on jan mayen because the island had an active volcano. it was a delicate subject since norway’s meteorological institute had annexed part of the island on behalf of norway. denmark had refused to officially state its position on the matter but maintained that some buildings within the norwegian-claimed area were owned by denmark. with the aid of the ministry of foreign affairs, an agreement was made with norway in march 1926 to the effect that the danish geodetic service could place a station on the norwegian part of jan mayen. however, shortly afterwards in july, norway announced that their meteorological institute would expand its activities to the whole island and claim it on behalf of norway (dna 5). in the summer of 1926, initial seismological tests were carried out on jan mayen by the danish geodetic service, but results were poor and it was decided to establish the station at the newly founded colony of scoresbysund (ittoqqortoormiit). founded in 1925, one of the colony’s purposes was to establish a danish presence in east greenland where norway also had made claims. construction of the station (sco) began in the summer of 1927, also here funded by the carlsberg foundation. by then the danish geodetic service had enough experience with construction and installation to proceed relatively quickly. a cellar was blasted into the bedrock, and on top of that a low building was constructed. to protect the instruments from variations in temperature the cellar was covered by 80 tons of rock and access restricted to a low corridor one could only crawl through. a second building housed the radio station and electronic recording instruments (geodætisk institut 1930). the installation of the seismological instruments went smoothly, as the station was equipped with two galitzin horizontal seismographs and a galitzin vertical seismograph transferred from cop (den danske gradmaaling 1928). fully funded by the carlsberg foundation the station began operation on 12 january 1928, with the local radio-telegraphists in charge of daily recordings (fig. 4). in the beginning the paper seismograms were sent annually to the geodetic institute by ship, but later it became practice that results from large events were radioed immediately to copenhagen. after 1928 in 1928 the danish geodetic service and the department of topography of the army general staff (generalstabens topografiske afdeling) merged to become the danish geodetic institute (danmarks geodætiske institut). inge lehmann, who had been the principal figure in setting up the copenhagen station and analysing data from all the fig. 3. the entrance to the seismological vault in ivittuut is next to the old tennis court. today (2014), the court is unkempt and ivittuut largely deserted. fig. 4. inge lehmann (second from the left) inspects sco presumably in the summer of 1928. photo: from inge lehmann’s private archive at the danish national archives. 7676 stations, was appointed chief of the geodetic institute’s new seismic section. the value of the greenlandic seismological stations as evidence of sovereignty was soon tested. in 1931, norway claimed parts of east greenland, denmark opposed the claim and the matter was put to the permanent court of international justice in the hague. in preparation for the trial, the ministry of foreign affairs asked the danish geodetic institute to prepare a series of reports about their scientific activities in greenland. in july 1932, inge lehmann forwarded a special report about the seismological station in scoresbysund to the ministry (dna 5) which was submitted as part of the evidence supporting the danish claim. in april 1933, the court decided against norway, recognising danish sovereignty over all parts of greenland. scientifically, the three stations also soon proved valuable by providing quality seismic records from remote, low-noise greenland, with efforts put into timing records and adjustment of instruments in the challenging environment. it was partly data from the seismological stations in ivittuut and ittoqqortoormiit that in 1936 enabled inge lehmann to deduce the existence of the earth’s inner core (lehmann 1936). today geus records seismological data from about 25 locations in denmark and greenland, including the original stations in copenhagen, ivittuut and ittoqqortoormiit, now equipped with modern digital instruments. conclusions historical documents from the danish national archives and geus clearly show that international geopolitics and strategic considerations played a significant role in the location of the seismological stations. especially denmark’s need to express its sovereignty over greenland played a pivotal role. it was by invoking arguments of power, culture, science and international peace the director of the danish geodetic service, erik nørlund, was able to gain the necessary political and financial support for establishing a network of seismological stations, and in 1928 establish a permanent danish seismological monitoring authority under the danish geodetic institute. as the danish government’s main interest was the strategic value of the seismological stations, it fell to private donations to unlock the scientific potential of the stations. it was therefore the logistic support of the kryolith mine og handelsselskabet and the long-term financial commitment of the carlsberg foundation that made it possible to equip and operate the stations at a high scientific standard. acknowledgements this study is part of a project on inge lehmann and the history of modern seismology 1925–1970, funded by the carlsberg foundation and danish national archives. the author wishes to thank trine dahljensen, tine b. larsen and peter voss for help and access to material kept at geus. references bulletin of the seismological station, ivigtut 1929. copenhagen: geodetic institute, http://seis.geus.net den danske gradmaaling 1928: aarsberetning 1. april 1927 – 31. marts 1928. seismisk arbejde, http://seis.geus.net danish national archives (1): niels erik nørlund (1885–1981): mat. vedr. union géodésique et géophysique int. (1924–1936). box 116. danish national archives (2): krigsministeriet 4. kontor, indkomne sager 1868–1950, 1895–1950. geodætisk institut 50.2. box a373. danish national archives (3): niels erik nørlund (1885–1981): regnskabet 1933/1934, regnskabsmateriale vedr. carlsbergfondet (1925– 1955). box 52. danish national archives (4): generalstabens topografisk afdeling (1842–1928). vedr. etablering og drift af seismisk station ivigtut, 1924–1953. sagsarkiv (1801–1978). box 50. danish national archives (5): geodætisk institut. journalsager (1925– 1988): 3 1 udenrigsministeriet 1925 – 3 1 udenrigsministeriet 1961. box 1. doel, r.e., harper, k.c. & heymann, m. 2016: exploring greenland’s secrets: science, technology. diplomacy, and cold war planning in global context, 1–22. in: doel, r.e., harper, k.c. & heymann, m. (eds): exploring greenland. palgrave studies in the history of science and technology, new york: palgrave macmillan. geodætisk institut 1930: the seismological stations københavn and scoresbysund copenhagen: geodetic institute. geodætisk institut. 1978: geodætisk institut 1928–1978. copenhagen: geodetic institute. harboe, e.g. 1911: das erdbebenobservatorium auf der disko-insel. leipzig: wilhelm engelmann, http://seis.geus.net kragh, h., kjærgaard p.c., nielsen n. & nielsen k.h. 2008: science in denmark, a thousand-year history. aarhus: aarhus university press. lehmann, i. 1936: p’. publications du bureau central seismologique international. serie a: travaux scientifique 14, 3–31. ries, c.j. 2012: armchairs, dogsleds, ships, and airplanes. field access, scientific credibility, and geological mapping in northern and north-eastern greenland 1900–1939. in: harbsmeier, m. et.al. (eds): scholars in the field. studies in the history of fieldwork and expeditions, 329–361. aarhus: aarhus university press. author’s addresses a.l.l.j., danish national archives, rigsdagsgården 9, dk-1218 copenhagen k, denmark and geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: llj@sa.dk. geological survey of denmark and greenland bulletin 33, 2015, 41-44 41 the continental shelf project of the kingdom of denmark – status and issues christian marcussen, finn mørk, thomas funck, willy lehmann weng and mikael pedersen th is paper summarises the status of the continental shelf project of the kingdom of denmark aft er the recent submission for an extended continental shelf in the area to the north of greenland. we discuss some of the similarities between the submission areas north of the faroe islands and north of greenland including the morphological continuation of ridges extending seaward of the geomorphical continental shelf. documentation of the sediment thickness in the adjoining basins and sediment continuity with the continental slope plays a vital role in the delineation of the outer limits of the extended continental shelf. here, we compare how these issues were addressed around the well-studied faroe islands and in the sparsely surveyed arctic ocean. th e kingdom of denmark ratifi ed the 1982 united nations convention on the law of the sea (unclos) in 2004. according to annex ii of unclos, the particulars of the outer limits of the extended continental shelf beyond 200 nautical miles shall be submitted to the commission on the limits of the continental shelf (clcs) within a period of ten years aft er ratifi cation. to acquire the necessary data for delineating the extended continental shelf, the continental shelf project of the kingdom of denmark was launched by the ministry of higher education and science in cooperation with the government of the faroe islands and the government of greenland (marcussen et al. 2004; marcussen & heinesen 2009). five partial submissions have been submitted by the kingdom of denmark regarding areas north of the faroe islands in 2009, south of the faroe islands in 2010, south of greenland in 2012, north-east of greenland in 2013 and north of greenland in 2014 (fig. 1). the area north of the faroe islands north of the faroe islands, the extinct ægir sea-fl oor spreading ridge is a prominent feature of the continental margin (figs 1, 2). th e initial opening of the north atlantic occurred along the ægir ridge with active sea-fl oor spreading in the eocene and oligocene. subsequent thermal subsidence of the oceanic crust resulted in the formation of the northern deep with a sediment accumulation of up to 3 km. th e clcs examined the partial submission regarding the area north of the faroe islands between 2012 and 2014 and gave special attention to: (1) the morphological continuation of the ægir ridge and (2) the continuity of sediments throughout the northern deep. in a strict morphological sense, the land mass of the faroe islands is connected to the faroe–iceland ridge (fig. 2). furthermore, the faroe–iceland ridge coalesces with and is morphologically linked to the ægir ridge. th is means that the ægir ridge is morphologically continuous with the rest of the continental margin © 2015 geus. geological survey of denmark and greenland bulletin 33, 41–44. open access: www.geus.dk/publications/bull nfm 150°e 1 000 km 30°w 50°n 30°e 50 °n 7 0 °n negm nfm sfm sgm sgm sgm ngm r u s s i a n f e d e r a t i o n n o r w a y n o r w a yc a n a d a g r e e n l a n d u sa f ar o e is la nd s fig. 1. the five partial submissions of the kingdom of denmark. red line: the 200 nautical mile limit of the five arctic coastal states in the arctic ocean. negm: north-east greenland margin. nfm: north faroes margin, ngm: north greenland margin. sfm: south faroes margin. sgm: south greenland margin. colour scale: see fig. 3. 4242 and lies within a common envelope of the foot of the continental slope. th us, in the sense of unclos, the ægir ridge is an integral part of the continental margin of the faroe islands, notwithstanding the tectonic and crustal differences between the two terrains (recommendations of the commission 2014). th e sediment thickness in the northern deep was documented primarily using modern seismic refl ection data. selected seismic lines were re-processed in order to improve the defi nition of the base of the sediments as well as the determination of the seismic velocities used for the depth conversion. th e clcs agreed with the procedure used to establish the sediment thickness, i.e. the methodology of depth conversion and the seismic interpretations. however, the clcs initially disagreed with the method by which the kingdom of denmark demonstrated sedimentary continuity throughout the northern deep. to satisfy the clcs, additional seismic lines, a sediment thickness map and gravity maps were provided and subsequently deemed suffi cient for this purpose. in march 2014, the clcs adopted the recommendations regarding the partial submission north of the faroe islands. th e commission agreed with the determination of the fi xed points establishing the outer limits of the continental shelf north of the faroe islands as originally listed in the submission. the area north of greenland th e lomonosov ridge is a sliver of continental crust that extends for a distance of almost 1800 km across the arctic ocean (fig. 3). th e ridge is 45 to 200 km wide, mostly fl at-topped to slightly rounded at its crest and rises from water depths of more than 4300 m in the adjacent basins to typically 1000 to 1300 m. th e shallowest part of the ridge is found towards greenland. th e lomonosov ridge was separated from the barents and kara shelves during the paleocene (55 to 60 ma), when sea-fl oor spreading started to open the eurasia basin. th is process continues today along the ultraslow-spreading gakkel ridge. th e geological development of the amerasia basin is not well understood, but most authors agree that the alpha and mendeleev ridges in that basin comprise a large igneous province of cretaceous age (e.g. jackson et al. 1986) and that sea-fl oor spreading has occurred in the canada basin (e.g. grantz et al. 1998). th e lomonosov ridge is morphologically continuous with the lincoln shelf north of greenland and furthermore shares geological characteristics with the land mass of greenland. th ese geological characteristics are based on evidence for continuous continental crust (jackson et al. 2010), similar lithologies and ages of rocks sampled from the fl anks of the ridge compared to rocks of the adjacent land masses, and a common tectonic history. in the sense of unclos, this means that the lomonosov ridge is a submarine elevation that is a natural component of the continental margin of greenland and therefore the extended continental shelf north of greenland extends across the arctic ocean to the 200 nautical mile line from russia (executive summary 2014). facing the amerasia basin, the lomonosov ridge is morphologically amalgamated with the alpha and mendeleev ridges and the chukchi borderland, which together are regarded as one complex but coherent morphological sea-fl oor high relative to the adjacent deep ocean fl oor within the eurasia and amerasia basins. th at is, all of this complex sea-fl oor high lies within a common envelope of the foot of the continental slope. however, the existing geological data for some of the individual sea-fl oor highs are insuffi cient to prove that they share geological characteristics with the greenland land mass. for this reason, and in accordance with unclos, the extended continental shelf, based on the alpha and mendeleev ridges and the chukchi borderland, is constrained to a distance of 350 nautical miles from the territorial sea baseline of greenland (executive summary 2014). 4°w 68°n 64°n 62°n 8°w8°w 0°8°w 100 kmf a r o e -s h e t l a n d c h a n n e l ja n m a y e n r id g e f a r o e i s l a n d s f a ro e -ic e lan d r idge v ø r i n g p l a t e a u æ g i r r i d g e n o r t h e r n d eep v ø r i n g p l a t e a u fig. 2. the northern continental shelf of the faroe islands showing the submission area. the continental shelf beyond 200 nautical miles in the area north of the faroe islands, as delineated in the submission, amounts to 87 792 km2 in area and is highlighted. green: agreed maritime boundaries within 200 nautical miles. red: faroese 200 nautical mile limit. yellow: iceland’s and norway’s 200 nautical mile limits. orange: outer limit of the continental shelf north of the faroe islands. colour scale: see fig. 3. 43 by analogy with the ægir ridge north of the faroe islands, bathymetric and morphological data show that the gakkel ridge coalesces with the continental slope north of greenland. th e oceanic, sea-fl oor-spreading characteristics of the gakkel ridge diff er geologically from the continental crust of greenland; hence the extended continental shelf based on the gakkel ridge cannot exceed 350 nautical miles from the territorial sea baseline of greenland (executive summary 2014). published seismic data from the amundsen basin north of greenland (weigelt & jokat 2001) indicate the presence of sediments of suffi cient thickness (i.e. at least 1200 m) for use in extending the continental shelf. for this reason, a purpose-built seismic acquisition system was developed (hopper et al. 2012) that could operate in the arctic sea ice and at sub-zero temperatures. to locate the most promising regions for seismic data acquisition, a sediment thickness map was derived from gravity inversion (døssing et al. 2014). th is study was based on the lomgr av airborne gravity data (døssing et al. 2013). th ree geus lomrog expeditions were carried out in 2007, 2009 and 2012 to acquire seismic data in the arctic ocean. however, ice conditions only allowed for a maximum streamer length of 300 m, which is too short to extract velocities from the seismic refl ection data. for this reason, sonobuoys were deployed along the profi les to record the seismic energy at larger off sets of up to 34 km. ray-tracing modelling was then used to obtain velocity models of sediments in the amundsen basin. th e velocities show little scatter (fig. 4). assuming normal compaction, the data points can be approximated by an exponential function of instantaneous slowness versus burial depth (al-chalabi 1997) using reduced major axis regression techniques. th e velocity–depth relationship obtained from this approach is shown in fig. 4 and can be used to convert the sediment thickness from time to depth. th e seismic refl ection lines surveyed were generally less than 50 km long and focused on regions that were more than 60 nautical miles away from the lomonosov ridge. as the clcs requires the documentation of sediment continuity, supplementary data had to be used. in ice-covered areas gravity data can supplement a sparse seismic database. for this reason, the results of the gravity inversion (døssing et x x x x x x x x x x x x x x x x x x x x x x x x x xx x x x x lena trough l a p t e v s h e l f m e n d e le e v r id ge a m e r a s i a b a s i n e u r a s i a b a s i n canada basin p o d v o d n i k o v b a s i n kara shelf e a s t s i b e r i a n s h e l f g a k k e l r id g e amundsen basin barents shelf a lp h a r id g e nansen basin r i d g e morris jesup rise makarov basin lincoln shelf l o m o n o s o v c a n a d i a n a r c t i c a r c h i p e l a g o s h e l f b e a u f o r t s h e l f c h u k c h i s h e l f c hukchi borderland greenland severnaya zemlya f ra nz j os ef la nd alaska svalbard ellesmere island s i b e r i a north pole 1 6 0 °w 8 0 °e 2 0 °e 1 0 0 °e 400 km 0 m 1 000 m 2 000 m 3 000 m 4 000 m bathymetry 8 0 °n 8 0 °n 140°e180° 100°w 0°80°w 20°w60°w 75°n70°n fig. 3. bathymetric map showing the main features of the arctic ocean. 4444 al. 2014) were used to document continuity of the sediments supported by additional subbottom profi ler and seismic refl ection data. concluding remarks th e continental shelf project of the kingdom of denmark mapped fi ve areas relevant to extended continental shelf beyond 200 nautical miles. th e project gathered bathymetric, geodetic, geological and geophysical data to compile the submission documents required by the clcs. despite diffi cult logistics, challenging climatic conditions and permanent ice cover in some of the fi ve areas, the project was completed within the initially allocated budget of 330 million dkk (44 million €) and the given time frame. large data sets have been acquired in the fi ve submission areas and key results have been or will be published in scientifi c journals. particularly valuable are the datasets in the arctic ocean as this remains a poorly studied frontier region. furthermore, the project was able to support other science projects by sharing logistics, in particular by providing access to icebreakers. th e results could not have been achieved without extensive international cooperation. due to the modus operandi of the clcs, recommendations for the latest submission north of greenland cannot be expected before the middle of the next decade. it represents a signifi cant challenge to keep both data and knowledge within the project updated and state of the art. references al-chalabi, m. 1997: instantaneous slowness versus depth functions. geophysics 62, 270–273. døssing, a., hopper, j.r., olesen, a.v., rasmussen, t.m. & halpenny, j. 2013: new aero-gravity results from the arctic: linking the latest cretaceous–early cenozoic plate kinematics of the north atlantic and arctic ocean. geochemistry, geophysics, geosystems 14, 4044–4065. døssing, a., hansen, t.m., olesen, a.v., hopper, j.r. & funck, t. 2014: gravity inversion predicts the nature of the amundsen basin and its continental borderlands near greenland. earth and planetary science letters 408, 132–145. executive summary 2014: partial submission of the government of the kingdom of denmark together with the government of greenland to the commission on the limits of the continental shelf – th e northern continental shelf of greenland. http://www.un.org/depts/los/clcs_ new/submissions_ fi les/dnk76_14/dnk2014_es.pdf gernigon, l., gaina, c., olesen, o., ball, p.j., péron-pinvidic, g. & yamasaki, t. 2012: th e norwegian basin revisited: from continental breakup to spreading ridge extinction. marine and petroleum geolog y 35, 1–19. grantz, a. et al. 1998: phanerozoic stratigraphy of northwind ridge, magnetic anomalies in the canada basin, and the geometry and timing of rift ing in the amerasia basin, arctic ocean. geological society of america bulletin 110, 801–820. hopper, j.r., trinhammer, p., marcussen, c. & funck, t. 2012: acquisition of seismic data in ice fi lled waters. american geophysical union, fall meeting 2012, abstract #c13e-0680. jackson, h.r., forsyth, d.a. & johnson, g.l. 1986: oceanic affi nities of the alpha ridge, arctic ocean. marine geolog y 73, 237–261. jackson, h.r., dahl-jensen, t. & the lorita working group 2010: sedimentary and crustal structure from the ellesmere island and greenland continental shelves onto the lomonosov ridge, arctic ocean. geophysical journal international 182, 11–35. marcussen, c. & heinesen, m. 2010: th e continental shelf project of the kingdom of denmark – status at the beginning of 2010. geological survey of denmark and greenland bulletin 20, 51–54. marcussen, c., christiansen, f.g., dahl-jensen, t., heinesen, m., lomholt, s., møller, j.j. & sørensen, k. 2004: exploring for extended continental shelf claims off greenland and the faroe islands – geological perspectives. geological survey of denmark and greenland bulletin 4, 61–64. recommendations of the commission on the limits of the continental shelf in regard to the partial submission made by the government of denmark together with the government of the faroes in respect of the continental shelf north of the faroe islands on 29 april 2009. adopted by the commission, with amendments, on 12 march 2014. http://www. un.org/depts/los/clcs_new/submissions_ fi les/dnk28_09/2014_03_14_ scdnk_ r ec_com_ 20140521.pdf weigelt, e. & jokat, w. 2001: peculiarities of roughness and thickness of oceanic crust in the eurasian basin, arctic ocean. geophysical journal international 145, 505–516. 0.0 0.5 1.0 1.5 2.0 d e p th b e lo w s e af lo o r (k m ) 1.5 2.0 2.5 3.0 3.5 4.0 velocity (km/s) fig. 4. sediment velocities in the amundsen basin obtained from ray-tracing of the sonobuoy recordings from the three geus lomrog expeditions. green circles show individual data points; the red line indicates an approximation obtained from reduced major axis regression techniques. authors' address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: cma@geus.dk geological survey of denmark and greenland bulletin 33, 2015, 9-12 9 the lower palaeozoic now fully cored and logged on bornholm, denmark niels h. schovsbo, arne t. nielsen and kurt klitten a 558 m long, complete section of the lower palaeozoic succession preserved onshore southern bornholm has been compiled from fi ve fully cored scientifi c wells, carried out between 2005 and 2012. th e scientifi c programme included coring and geophysical logging of the fi ve scientifi c wells that yielded a total of c. 750 m of partially overlapping cores as well as re-logging of water wells and acquisition of shallow seismic data. th e last well drilled, the sommerodde-1, cored the youngest preserved silurian strata on bornholm including strata not exposed in outcrops. th e well penetrated 168.1  m of silurian shales, 42.7 m of upper ordovician shales and 27.9 m of alum shale before it terminated at a depth of 250.3 m in the lower cambrian norretorp member of the læså formation. th e sommerodde-1 well documents that the lower silurian cyrtograptus shale is at least 91.7 m thick and that the rastrites shale is 76.4 m thick. th e complete lower cambrian succession has previously been covered by the 316.0 m deep borggård-1 well that terminated in basement rocks (nielsen et al. 2006). the lower palaeozoic in denmark th e lower palaeozoic is very thick in denmark, locally more than 4 km thick, and the deposition marks the transition from passive margin to a rapidly subsiding foreland basin developed in front of the caledonian orogen towards the south and west (lassen & th ybo 2012). th e palaeozoic strata onshore bornholm have been described in papers published over the last 150 years and constitute a classical topic in danish geology. however, previous studies have primarily focused on biostratigraphical aspects. contemporaneous strata throughout most of central and western denmark are deeply buried and hence, have only been reached by a few deep exploration wells (fig. 1), and thus the succession is rather poorly known. only in slagelse-1 and terne-1 in kattegat have the palaeozoic shales been fully penetrated whereas only the topmost parts of the silurian shales were reached by the rønde-1, nøvling-1, pernille-1 and stina-1 wells (fig.  1). a new shale gas exploration well, vendsyssel-1, is planned to be drilled in 2015 and is expected to penetrate the entire lower palaeozoic shale sequence in northern jylland (fig. 1). the sommerodde-1 well th e well was drilled as close as technically possible to the sommerodde beach locality described by bjerreskov & jørgensen (1983) where the youngest silurian strata onshore bornholm are exposed at low tide. prior to drilling, a seismic section was recorded in april 2012 and relevant water well sweden lower palaeozoic strata caledonian front borehole ringkøbing–fyn high pernille-1 kattegat terne-1 vendsyssel-1 rønde-1 nøvling-1 slagelse-1 stina-1 denmark norwegian–danish basin 50 km germany bornholm fig. 2 jylland fig. 2. geological map of southern bornholm showing the positions of scientific wells drilled 2005–2012. borggård-1 (dgu 247.627), skelbro-2 (dgu 246.817), billegrav-2 (dgu 248.61), hjulmagergård-1 (dgu 246.838) and sommerodde-1 (dgu 248.62) are shown as red dots, and the re-logged water wells sømarken-3 (dgu 248.39), sømarken-4 (dgu 247.312) and golf banen-1 (dgu 248.54) are shown as blue dots. areas where 2d seismic data were acquired are shown as black rectangles. the geological map is from a compilation by graversen (2009). nexø sommerodde-1 billegrav-2 golfbanen sømarken-4 sømarken-3 borggård-1 precambrian mesozoic palaeozoic fault 2 km 15°5´e 54°59.2´n hjulmagergård-1 skelbro-2 fig. 1. distribution of lower palaeozoic strata and deep wells reaching at least top silurian in denmark north of the caledonian front. the vendsyssel-1 well is planned to be drilled in 2015. © 2015 geus. geological survey of denmark and greenland bulletin 33, 9–12 . open access: www.geus.dk/publications/bull 1010 0 20 40 60 80 100 120 140 160 180 200 220 240 flow % fluid conductivity (ms/m) 0 40 80 120 160 3 4 510 100 1000 0 0 500 100 0 400 800 1200 r.m. a lu m s h al e d ic e ll o g r. l in d e g. log unit l.c. m .c . u p p e r o rd o v ic ia n l o w e r s il u ri an f u ro n . q r as tr it e s sh al e p-wave velocity (km/s)formation resistivity (ohm m)gamma ray (cps)optvlithologyperiod stratigraphy l.o. c y rt o gr ap tu s sh al e casing (scale change) d1 d2 d3 a b2 b3 b4 g1 g5 g4 g2 e3 e1 e2 f1 f5 f4 f3 f2 g3 n.m. depth (m) grey shale limestonesandstoneblack shale dark grey shale light grey shale fig. 3. selected logs measured in the sommerodde-1 well. the arrows indicate significant water inf low zones. the optic televiewer (optv) picture of the well is a 360° view of the borehole wall. flow %: water f low scaled to the total f low of 1.4 m3/h. q: quaternary. lo: lower ordovician. furon.: furongian. mc: middle cambrian. lc: lower cambrian. lindeg.: lindegård formation. dicellogr.: dicellograptus shales. k: komstad limestone. r m: rispebjerg member. nm: norretorp member of the læså formation. cps: counts per second. 11 reports were examined to locate potential faults in the area (fig. 2). th e well was drilled in november 2012, well logging was done by both the geological survey of denmark and greenland and rambøll and the hole was plugged and permanently abandoned in november 2013. a total of ten log runs were made including a full wave sonic log and an optic televiewer recording that provided a high resolution image of the borehole wall (fig. 3). th e sommerodde-1 well cored silurian shales between 6.5 and 174.6 m, ordovician shale above the alum shale formation between 174.6 and 217.3 m, a thin komstad limestone (middle ordovician) between 217.3 and 217.9 m, the cambro-ordovician alum shale formation between 217.9 and 245.8 m and lower cambrian sandand siltstone between 245.8 and 250.3 m (fig. 3). a total of 168.1 m silurian shales were thus cored. th e lower silurian rastrites shale was completely cored and is 76.4 m thick in the well. th e alum shale formation is 27.9 m thick and includes the middle cambrian andrarum and exsulans limestone beds. th e well was terminated at 250.3 m in the norretorp member of the læså formation aft er having penetrated the rispebjerg member (4.5 m thick). log stratigraphy in the sommerodde-1 well pedersen & klitten (1990) established a detailed log stratigraphical scheme (labelled units a–g on figs 3, 4) based on the gamma-ray variation in the lower palaeozoic shales on bornholm. th e log stratigraphy permitted correlation of un-cored water wells with fully cored scientifi c wells. th e log stratigraphy was later emended to also include the resistivity log, from which more detailed lithological information can be gained (schovsbo et al. 2011). in the sommerodde-1 all log-based units defi ned by pedersen & klitten (1990) were identifi ed and the previously un-divided g unit was divided into four new log units, labelled g1–g4 (fig. 3). th e units a–f were described by schovsbo et al. (2011) and, hence, only the new log units are briefl y described here. th e g unit is correlated here with the cyrtograptus shale as was originally done by pedersen & klitten (1990). th e base of the g unit has not previously been cored nor recognised in logs from water wells on bornholm. it is here placed at 98.2 m; above this level the resistivity and sonic velocity log readings increase (figs 3, 4). th e g1 subunit is 24 m thick and consists of light green to dark grey shales. th e unit is characterised by a steady increase in resistivity readings. subunit g2 is 18.5 m thick and consists of light grey to dark green shale. subunit g3 is 16 m thick and consists of light grey to dark green shale. th e top of the g3 subunit is defi ned where an increase occurs in the resistivity log, refl ecting a change to darker lithologies. numerous bentonite beds characterised by low resistivity and high gamma ray readings occur in g2 and g3. subunit g4 is a 10 m thick, dark-coloured interval. th e subunit is readily identifi ed in the core and on the optic televiewer log and by a slightly lower gamma-ray log response and distinctly higher resistivity readings compared to the subunits above and below. th e top of the g4 subunit is defi ned at a point of decrease in the resistivity log. subunit g5 is 23.5 m thick and comprises light grey to green shale characterised by low and stable gamma-ray values. th e subunit includes numerous silty to sandy beds similar to those exposed on the beach just south of the well location (bjerreskov & jørgensen 1983). gamma ray (cps) 40 80 120 160 log units gamma ray (cps)gamma ray (cps) sommerodde-1 resistivity (ohm m) 100 1000 resistivity (ohm m) 10 100 1000 billegrav-2billegrav-2 d ep th (m ) 0 20 40 60 80 100 120 140 160 180 0 40 80 120 160 50 100 150 200 20 40 60 d ep th (m ) d ep th (m ) 0 20 40 60 golfbanen-1 g2 g1 g5 g4 g3 f2 f1 f3 f4 f5 e3 fig. 4. correlation of the silurian sections in the sommerodde-1, billegrav-2 and golf banen-1 wells based on the gamma-ray (black line) and resistivity log (red line) responses. grey intervals show intervals where the log response was measured through the steel casing. 1212 correlation of silurian shales on southern bornholm th e g unit was originally defi ned based on the gammaray signature in the un-cored water well golf banen-1 that penetrated a section of the cyrtograptus shale (pedersen & klitten 1990). as part of the present study the golf banen-1 well was re-logged in order to expand the log signature and to enable correlation with the sommerodde-1 well (fig. 4). based on comparison with the sommerodde-1 well, the gamma ray and resistivity logs show that the golf banen-1 well penetrated a sequence from the g3 to the uppermost f5 unit. th e sommerodde-1 well is also correlated with the fully cored billegrav-2 well that penetrated the succession from the lower part of the f5 unit and downwards, thereby closing the correlation gap between the billegrav-1 well and the exposures in the øle å water course as presented by pedersen & klitten (1990). several of the rastrites shale log units are slightly thicker in the sommerodde-1 well than in the billegrav-2 well (fig. 4). in the latter several fault zones occur in this interval and it appears that parts of the section are missing due to faulting. in the sommerodde-1 well no fault zones are identifi ed and it is believed that the recorded thicknesses refl ect the true stratigraphical thicknesses. water-flow properties th e water infl ow in sommerodde-1 was evaluated from an impeller fl ow log during discharge of 1.4 m3/h supplemented by the fl uid conductivity log measured during the same discharge from the well. together the two logs show that most of the infl ow took place within the uppermost 75 m of the well (fig. 3). th e infl ow rates decrease rapidly with depth and the section below 80 m contributes with less than 20% of the total infl ow into the well. th e water conductivity is highest in the alum shale formation and in the lower part of the rastrites shale, 350–400 ms/m, but from a depth of 125 m and upwards several small infl ow sources with lower conductivity stepwise reduce the conductivity of the upwards fl owing water until it has a conductivity of 50 ms/m (fig. 3). in spite of the many infl ow points the specifi c yield is quite low, less than 0.1 m3/h/m, suggesting that only a few of the fractures in the shales are open and that these fractures occur within the uppermost 75 m. similar conditions are seen in many wells penetrating danian limestone and cretaceous chalk found near the surface, where fracture-based hydraulic conductivity is mainly found in the upper part, less than 70 m below the prequaternary surface. th is is probably because the fractures were formed due to pressure release in connection with the last deglaciation. in contrast, the deep, water-bearing open fractures on bornholm, as for instance observed in the nexø formation in the borggård-1 well at a depth of c. 300 m, were probably formed due to tectonic uplift . conclusions new knowledge on the palaeozoic geology of bornholm has been gained since 2005 from fi ve fully cored and geophysically logged scientifi c wells, re-logging of some water wells and acquisition of seismic data. a complete section of the lower palaeozoic has been pieced together by correlation of overlapping scientifi c well sections. th e research on bornholm has provided detailed insight into the palaeozoic stratigraphy and established a lithoand log-stratigraphical frame that is applicable in a regional context. combined with ongoing drilling activities in northern jylland this will provide a much better understanding of the evolution of the palaeozoic in denmark. acknowledgements we are thankful to landowner jette staberg, peter turner of faxe kalk a/s, kurt nielsen of rambøll and klaus bauer of gfz. th e greater part of the funding was received from geocenter denmark and total e&p denmark b.v. references bjerreskov, m. & jørgensen, k.å. 1983: late wenlock graptolite-bearing tuff aceous sandstone from bornholm, denmark. bulletin of the geological society of denmark 31, 129–149. graversen, o. 2009: structural analysis of superposed fault systems of the bornholm horst block, tornquist zone, denmark. bulletin of the geological society of denmark 57, 25–49. lassen, a. & th ybo, h. 2012: neoproterozoic and palaeozoic evolution of sw scandinavia based on integrated seismic interpretation. precambrian research 204–205, 75–104. nielsen, a.t., klitten, k. & hansen, h.p.b. 2006: borggård-1: en ny stratigrafi sk kerneboring på bornholm. geologisk nyt 6, 4–10. pedersen, g.k. & klitten, k. 1990: anvendelse af gamma-logs ved korrelation af marine skifre i vandforsyningsboringer på bornholm. dansk geologisk forening årsskrift 1987–89, 21–35. schovsbo, n.h., nielsen, a.t., klitten, k., mathiesen, a. & rasmussen, p. 2011: shale gas investigations in denmark: lower palaeozoic shales on bornholm. geological survey of denmark and greenland bulletin 23, 9–13. authors’ addresses n.h.s. & k.k., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: nsc@geus.dk a.t.n., natural history museum of denmark. øster voldgade 5-7, dk-1350 copenhagen k, denmark. geological survey of denmark and greenland bulletin 31, 2014, 1-8 1 geological survey of denmark and greenland bulletin 31 • 2014 review of survey activities 2013 edited by ole bennike, adam a. garde and w. stuart watt geological survey of denmark and greenland ministry of climate, energy and building 22 geological survey of denmark and greenland bulletin 31 key words geological survey of denmark and greenland, survey organisations, current research, denmark, greenland. cover photographs from left to right 1. a hercules aircraft from the us air force on the greenland ice sheet. photograph: dirk van as. 2. perhaps a future geologist searching for fossils in the faxe quarry. photograph: ole bennike. 3. in 2013 geus celebrated its 125th anniversary. photograph: jakob lautrup. 4. learning about geothermal energy by testing the temperature of the water. photograph: jakob lautrup frontispiece: facing page in 2012 and 2013 geus carried out field work in north greenland (see paper by bojesen-koefoed et al. in this issue). the overturned sedimentary rocks exposed along the margin of the glacier belong to a cretaceous succession in the harder fjord fault zone, wandel sea basin, northern peary land. photograph: jørgen a. bojesen-koefoed. chief editor of this series: adam a. garde editorial board of this series: john a. korstgård, department of geoscience, aarhus university; minik rosing, geological museum, university of copenhagen; finn surlyk, department of geosciences and natural resource management, university of copenhagen scientific editors: ole bennike, adam a. garde and w. stuart watt editorial secretary: jane holst referees (numbers refer to first page of reviewed article): meri-liisa airo, fi (63; morten ahlborn, no (23); jens asger andersen, dk (47); kresten anderskouv, dk (23); anonymous (83, 91); niels balling, dk (75), thue sylvester bording, dk (55); synnøve elvevold, no (95); ida fabricius, dk (27, 55); ola fredin, no (39); høgni kalsø hansen, dk (95); jens havskov, no (75); claus heilmann-clausen, dk (35); björn heincke, de (63); mads huuse, gb (43); christine hvidberg, dk (87); simon toft ingvertsen, dk (47); chris king, gb (31); john korstgård, dk (15, 67); cees laban, nl (43); michael larsen, dk (59); poul-henrik larsen, dk (59); sebastian h. mernild, cl (87); alex mitlehner, gb (35); steffen b. olsen, dk (51); veli-pekka salonen, fi (39); niels schrøder, dk (15); nigel smith, gb (19); inga sørensen, dk (51); leigh stearns, gb (79); lars stemmerik, dk (71); henrik stendal, gl (67); svend stouge, dk (19); vural sander suicmez, dk (27); david sutherland, usa (79); nicolas thibault, dk (31); thomas ulrich, dk (71); frans stephan van buchem, dk (23); jacob clement yde, no (83, 91). illustrations: benny m. schark, jette halskov, willy l. weng, frants v. platen-hallermund and christian brogaard pedersen layout and graphic production: kristian a. rasmussen printer: rosendahls-schultz grafisk a/s, albertslund, denmark manuscripts received: 17 january 2014 – 28 march 2014 final versions approved: 26 february 2014 – 9 may 2014 printed: 25 june 2014 issn 1603-9769 (review of survey activities) issn 1604-8156 (geological survey of denmark and greenland bulletin) isbn 978-87-7871-383-4 citation of the name of this series it is recommended that the name of this series is cited in full, viz. geological survey of denmark and greenland bulletin. if abbreviation of this volume is necessary, the following form is suggested: geol. surv. den. green. bull. 31, 98 pp. available from geological survey of denmark and greenland (geus) øster voldgade 10, dk-1350 copenhagen k, denmark phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: geus@geus.dk and at www.geus.dk/publications/bull © de nationale geologiske undersøgelser for danmark og grønland (geus), 2014 for the full text of the geus copyright clause, please refer to www.geus.dk/publications/bull mailto:geus@geus.dk 3 44 tanzania ethiopia mozambique zambia malawi indonesia singapore vietnam thailand india tajikistan korea greenland brazil denmark nigeria canada 7 review of survey activities 2013 f.g. christiansen 9 125 years of geological research for society j. fredericia and p. gravesen 15 borehole logs from the precambrian basement on bornholm, eastern denmark: geology and groundwater flow p. gravesen, b. nilsson, p. rasmussen and s.a.s. pedersen 19 the lower palaeozoic shale gas play in denmark n.h. schovsbo, a.t. nielsen and d.l. gautier 23 seismic stratigraphy and sedimentary architecture of the chalk group in south-west denmark c. larsen, j. ineson and l.o. boldreel 27 a novel technique for obtaining representative water samples during co2 core-flooding experiments on chalk at reservoir conditions c. kjøller and j. zuta 31 calcareous nannofossil and foraminifer biostratigraphy of the campanian–maastrichtian chalk of the femern bælt (denmark–germany) e. sheldon, c. morigi and s.d. møller 35 palynological and microfossil biostratigraphy and palaeoecology over the paleocene–eocene transition, femern bælt, northern germany p.a. richardt and e. sheldon 39 ribbed moraines formed during the retreat of the scandinavian ice sheet from eastern himmerland, ne jylland, denmark h. lerche, p.tr. jakobsen and s.a.s. pedersen 43 arctic plant remains of weichselian age from the danish north sea o. bennike, j.o. leth, j.b. jensen, n. nørgaard-pedersen and s. lomholt 47 stormwater management: methods for measuring near-surface infiltration capacity in clayey till b. bockhorn, m.b. jensen and k.e.s. klint 51 a multidisciplinary study of a geothermal reservoir below thisted, denmark m.l. hjuler, h. vosgerau, c.m. nielsen, p. frykman, l. kristensen, a. mathiesen, t. bidstrup and l.h. nielsen 5 tanzania ethiopia mozambique zambia malawi indonesia singapore vietnam thailand india tajikistan korea greenland brazil denmark nigeria canada geus working areas 2013 shown in grey. orange areas are covered in this volume. 55 estimating thermal conductivity from lithological descriptions – a new web-based tool for planning of ground-source heating and cooling c. ditlefsen, i. sørensen, m. slott and m. hansen 59 six years of petroleum geological activities in northeast greenland (2008–2013): projects and a view of the future j.a. bojesen-koefoed, p. alsen and f.g. christiansen 63 aeromagnetic survey in south-eastern greenland: project aeromag 2013 p. riisager and t.m. rasmussen 67 combining exploration and multivariate techniques to detect the bjørnesund west gold occurrence, southern west greenland d.m. schlatter and b. møller stensgaard 71 integrating 3d photogeology with aeromagnetic data as a tool for base-metal exploration in east greenland a. brethes, p. guarnieri and t.m. rasmussen 75 earthquake swarms in greenland t.b. larsen, p.h. voss, t. dahl-jensen and h.p. rasmussen 79 outlet glacier dynamics and bathymetry at upernavik isstrøm and upernavik isfjord, northwest greenland c.s. andresen, k.k. kjeldsen, b. harden, n. nørgaardpedersen and k.h. kjær 83 katabatic winds and piteraq storms: observations from the greenland ice sheet d. van as, r.s. fausto, k. steffen and the promice project team 87 mass loss from an ice-sheet drainage basin in west greenland m.l. andersen, s.b. andersen, l. stenseng, h. skourup, w. colgan, s.s. kristensen, j.p.m. boncori, a.p. ahlstrøm, x. fettweiss, r. forsberg, m. citterio, j.e. box, d. van as and r.s. fausto 91 surface albedo as a proxy for the mass balance of greenland’s terrestrial ice w. colgan, j.e. box, r.s. fausto, d. van as, v.r. barletta and r. forsberg 95 to what extent is denmark vulnerable to mineral supply shortage? p. kalvig, r.j. clausen, n. fold and k. hanghøj 66 7© 2014 geus. geological survey of denmark and greenland bulletin 31, 7–8. open access: www.geus.dk/publications/bull review of survey activities 2013 flemming g. christiansen deputy director 2013 was a very special year for the geological survey of denmark and greenland (geus), which acquired its present name in 1995 when the geological survey of denmark, established in 1888, and the younger geological survey of greenland were merged. on 4 april 2013 geus celebrated its 125th anniversary with a series of presentations by prominent guests and geus scientists followed by a reception and a gala evening. geus’ 125-year long history has provided an overwhelming body of results and experience, and today geus is broader, stronger and more international and collaborative than ever, covering all aspects of which a geological survey can be of use for society. the anniversary is also reflected in this issue of review of survey activities that contains a total of 22 four-page papers, 11 on denmark, nine on greenland and three on broader themes: co2 capture and storage, the recently established center for minerals and materials (mima) housed within the survey – and, of course, a paper dedicated to the 125th anniversary. this first paper highlights the anniversary and introduces the newly published book on the history of geus ‘we – the people down to earth’ (in danish: vi de jordbundne); a book that gives glimpses and highlights of the story of geus spiced with anecdotes on colourful characters, culture and politics. activities in denmark the activities and research in denmark by geus cover many topics within our main programme areas: data, water, energy, mineral resources as well as nature and climate. the island of bornholm has a different geological history from the rest of denmark; a dominance of outcropping basement rocks and palaeozoic sedimentary rocks gives special challenges and possibilities. one paper describes the use of geophysical wire-line borehole logs from the precambrian basement and the mapping of fracture patterns affecting groundwater flow. previous coring results from bornholm have provided important geological input for assessing the unconventional gas resources in the lower palaeozoic shales of denmark. based on several years of collaboration with geus, the u.s. geological survey presented their shale gas estimate in november 2013 suggesting that significant technically recoverable resources may be present in several prospective areas. chalk is a very important rock for denmark as it hosts more than 90% of the danish petroleum reserves in the north sea but it also has many other important uses. one paper is from a pilot project in south-west denmark where seismic stratigraphy and sedimentary architecture of the chalk group has been used in a geothermal evaluation. another paper describes a new technique for important co2 flooding experiments of chalk at reservoir conditions; if these experiments can be up-scaled, their results are potentially crucial to enhanced oil recovery. large infrastructure projects such as tunnels and bridges require detailed geotechnical knowledge of the subsurface, and based on material from new core holes, a more detailed understanding of understudied stratigraphic intervals may be reached. based on cores from the femern bælt, one paper describes a study of the calcareous microfossil and foraminiferal biostratigraphy of the campanian−maastricthian chalk, and another paper focuses on the palynological and microfossil biostratigraphy and palaeoecology of the paleocene− eocene transition. geus is involved in many studies of quaternary and recent geological processes. one paper describes ribbed moraines from eastern himmerland in jylland formed during the retreat of the scandinavian ice sheet. another paper focuses on plant remains from cores in the north sea, and demonstrates that parts of this area constituted an open, treeless, tundra-like environment in the weichselian. a third paper is on stormwater management, where a test site in høje taastrup has been used to evaluate the infiltration capacity of clayey till. based on field experiments, the paper discusses how different methods can be used to measure the infiltration capacity of the sediments. geothermal energy and ground-source heating may be of great importance in many areas in denmark in order to live up to the ambition that by 2050 energy and transport shall be 100% based on renewable energy. over many years, geus has been involved in an increasing number of projects covering different aspects of geothermal energy and groundsource heating. one paper describes a multidisciplinary approach to geothermal reservoir characterisation in thisted, 88 where denmark’s first plant was established already in 1984. the plant now needs to increase its capacity with a new borehole. another paper goes into detail about one of the critical key parameters – thermal conductivity of soils. activities in greenland once again there was a high level of field activities in greenland in 2013 with large field programmes in north greenland and in the gardar province in south greenland. many other field studies were also carried out. results from these large and small projects that are very important for evaluating and marketing the resource potential in greenland and for monitoring climate changes will be presented in the coming years. in this issue, results are presented from other completed and on-going projects. a first paper gives a review of six years of petroleum geological activities in north-east greenland with focus on completed projects, and takes a look at the future. the activities were carried out prior to the preparation of recently completed offshore licensing rounds, and the studies are very important for evaluating key geological risks such as occurrence and quality of petroleum source rocks, understanding critical reservoir intervals and the uplift history. they are therefore crucial for planning of future exploration activities by both the authorities and industry. several papers focus on mapping and evaluation of the mineral potential in greenland. one paper gives details of an aeromagnetic survey that was carried out in southern east greenland in 2013, a region where geus has been active over several years with large completed and planned field programmes. the paper outlines how data can be applied to map regional geological and tectonic features. the project aeromag 2013 has recently been released by the greenland authorities. another paper describes how exploration and multivariate techniques were used to detect a gold occurrence in southern west greenland. a third paper demonstrates how integration of 3d photogeology, aeromagnetic and other geophysical data can be used as a promising tool for base-metal exploration in the remote region of east greenland. earthquake swarms in greenland are a very interesting subject that can now be analysed in greater detail than previously thanks to an increased number of seismic stations. data from older detected swarms have been revisited and two new earthquake swarms have been identified on disko and off south-east greenland. shrinking of the ice sheet and local glaciers in greenland provide a significant contribution to global sea-level rise. understanding the dynamics and calculation of mass loss requires a detailed understanding of climate, glacier configuration and fjord bathymetry. one paper describes a case study from the upernavik isstrøm and upernavik isfjord in north-west greenland. the important monitoring programme of the greenland ice sheet (promice) that was initiated in 2007 continuously supplies crucial data that are used in a number of subsequent projects and in key publications. three papers in this issue use such data from promice. one is on katabatic winds and explanation of piteraq storms and is based on observations from the greenland ice sheet. a second is on mass loss on a basinal scale with its focus on a large area in west greenland. a third paper discusses the possibility of using surface albedo as a proxy for greenland ice mass balance. this is particularly important at the moment to help fill data gaps in gravimetric data from satellites. broader international activities internationally geus works in many different countries with a variety of projects and is also involved in broader thematic studies. the last paper addresses scarcity of mineral raw materials, a theme that has recently been placed high on the political agenda in the us, eu, including in denmark, as well as in asia. as a consequence of this, geus has established the center for minerals and materials (mima) in order to identify and study important raw material chains from source to use. one of the first tasks of mima is to enhance our knowledge of the risk of resource scarcity and the ensuing vulnerability of danish society. geological survey of denmark and greenland bulletin 35, 2016, 17-22 17© 2016 geus. geological survey of denmark and greenland bulletin 35, 17–22 . open access: www.geus.dk/publications/bull the danish pesticide leaching assessment programme (plap) was initiated in 1998 by the danish parliament in order to evaluate whether the use of approved pesticides will result in an unacceptable contamination of the groundwater, if applied under field conditions in accordance with current danish regulation. in this programme, water samples from variably saturated soil and groundwater collected at five cultivated fields are analysed for selected pesticides and their degradation products. the plap results are summarised and evaluated in yearly reports and used by the danish environmental protection agency in the regulation of pesticides in denmark (brüsch et al. 2015). in order to represent typical farming scenarios in denmark, the test fields are situated on meltwater and marine sands, and on tile-drained clayey soils in till areas. methods the five cultivated plap fields (1.2–2.4 ha), representing different soils and hydrogeological settings, spread across denmark (fig. 1) are located at silstrup, estrup and faardrup with tile-drained clayey soils, and at tylstrup and jyndevad with sandy soils (lindhardt et al. 2001). the groundwater table is shallow at all fields, which enables a rapid detection of any pesticide leaching to the groundwater (table 1). the plap fields are farmed according to conventional agricultural practice, and pesticides are applied in the maximum permissible doses and as specified in the regulations. water samples are collected weekly from drainage at the clayey till fields, and monthly from standard teflon suction cups in the unsaturated zone at the sandy fields, and from horizontal and vertical groundwater monitoring wells at all fields. the wells are installed in buffer zones surrounding the fields in order to avoid artificial transport pathways for pesticides and their degradation products from the surface to the groundwater. the vertical wells are located downstream from the field (fig. 2), except for one upstream vertical well, which is used to determine the upstream influx to the groundwater beneath the field. the horizontal wells are installed at the clayey till fields at depths of 2–3.5 m under the pesticide-treated areas, and at the sandy fields just beneath the fluctuating groundwater table. detection of pesticides or their degradation products can be directly related to the specific pesticide application to the plap fields by monitoring both the variably and fully saturated soil and accounting for potential upstream influx. in the drainage from the clayey till fields, the weighted average concentration of pesticides is based on flow-proportional sampling. in the two sandy soils, the weighted average pesticide concentration leached to the suction cups at 1 m depth is estimated from the detected concentrations and estimated percolation on a monthly basis (brüsch et al. 2015). the analytical programme includes relevant pesticides and their degradation products as well as inorganic compounds such as chloride, nitrate, phosphate and bromide, monitoring of pesticide leaching from cultivated fields in denmark walter brüsch, annette e. rosenbom, nora badawi and preben olsen silstrup estrup jyndevad fårdrup annual net precipitation < 150 mm 150–200 mm 200–250 mm 250–300 mm 300–350 mm 350–400 mm > 400 mm 100 km tylstrupsilstrup estrup jyndevad tylstrup faardrup estrup jyndevad faardrup clayey till field sandy field fig. 1. annual net-precipitation in denmark and the location of the five plap fields (http://www2.mst.dk/udgiv/publikationer/1992/87-503 -9581-5/pdf/87-503-9581-5.pdf; rosenbom et al. 2015). tylstrup and jyndevad are located in sandy areas with marine sand and glaciof luvial sand, respectively. silstrup, estrup and faardrup are situated in areas dominated by clayey till, and the three fields are drained. the sediments were deposited during and after the last glaciation. 1818 which is used as a tracer. the pesticides are generally analysed for two years following application, but the monitoring continues if significant leaching occurs. to evaluate the pesticide leaching, the water balance, including the percolation through the variably saturated soil, is assessed for all five plap fields using the numerical model macro (larsbo et al. 2005) based on long-term detailed monitoring of climate, crop-growth, soil water content, groundwater table, and if present, drainage flow (rosenbom et al. 2015). monitoring results according to the legislation of the european union, the maximum permissible concentration of any pesticide in groundwater is 0.1 μg/l (council of the european union 1994). this limit is not based on health investigations but was the analytical detection limit when the legislation was made in the 1980s, and was chosen to ensure that drinking water did not contain measurable amounts of pesticides. during the latest monitoring period from july 2012 to june 2014, a total of 7378 single analyses of different pesticides or their degradation products were carried out on water samples collected at the five sites. the leaching risk of 22 pesticides and 17 degradation products was evaluated after applying the specific pesticide on specific crops. of these 39 pesticides and their degradation products, 21 were not detected in any of the water samples. during the entire monitoring period from may 1999 to june 2014, 51 pesticides and 52 degradation products were analysed. these are listed in the appendix. the monitoring data showed leaching of 17 of the applied pesticides and their degradation products through the soil to tile drains or suction cups in average concentrations exceeding 0.1 μg/l. these are marked with asterisks in the appendix. the results of the monitoring also showed leaching of an additional 17 pesticides, but in low concentrations, marked by † in the appendix. although the concentrations exceeded 0.1 μg/l in several water samples collected from suction cups and tile drains at 1 m depth, the average leaching concentrations did not exceed 0.1 μg/l on an annual basis. in groundwater samples, twenty-one pesticides or their degradation products were only detected at concentrations table 1. characteristics of the five pesticide leaching assessment fields precipitation (mm/y)* 668 858 866 862 558 potential evapotranspiration (mm/y)* 552 555 564 543 585 area (ha) 1.1 2.4 1.7 1.3 2.3 tile drain no no yes yes yes depth to tile drain (m) 1.1 1.1 1.2 deposited by saltwater meltwater glacier glacier glacier sediment type fine sand coarse sand clay till clay till clay till topsoil classification loamy sand sand sandy clay loam sandy loam sandy loam tylstrup jyndevad silstrup estrup faardrup * based on the period 1961–1990, modified from lindhardt et al. (2001). 50 m vertical monitoring screen tile drain, inside field tile drain, outside field collector pipe groundwater flow sample point, horizontal screens horizontal monitoring screen, 3.5 m depth horizontal monitoring screen, 2 m depth 0 50 m10 m #1 outlet suction cup rain gauge buffer zone farmed area piezometer fig. 2. overview of the silstrup field and its technical installations. 19 below 0.1μg/l or not at all. these are marked by § in the appendix. at the three clayey till fields, several pesticides were detected in the drainage, whereas the frequency of detection in the groundwater monitoring screens beneath the tile drain system was lower and varied considerably between the three fields. in the two sandy fields, fewer pesticides and degradation products were generally detected, both in the variably saturated soil and in groundwater (table 2). the different leaching patterns in the sandy and clayey till fields can be attributed to specific hydrological, geological and geochemical conditions. the subsoil c horizon beneath the tile drains at the estrup field shows low permeability with few macropores (kjær et al. 2005; rosenbom et al. 2015) in contrast to the faardrup and silstrup fields, where the clayey till is characterised by fractures and heterogeneity. hence the fewer records of pesticides and degradation products in the groundwater at estrup than at faardrup and silstrup can be related to the low permeability at the former site. a comparison between the clayey till fields shows that the number of water samples containing pesticides and degradation products was higher at silstrup and estrup (35 and 40%, respectively) than at faardrup (15%). this can be attributed to different hydro-geochemical conditions and the low net precipitation at faardrup. the leaching pattern for non-pesticides shows that the average concentration of nitrate-n was much higher in both groundwater and drainage at faardrup than at the other two fields (table 2; ernstsen et al. 2015). however, the average chloride content in both drainage and groundwater at faardrup was higher than at silstrup (table 2), due to an up-concentration in the infiltration water caused by the low precipitation at faardrup. the occurrence of precipitation and subsequent percolation within the first month after application were generally higher at silstrup and estrup than at faardrup (table 1). at the clayey till fields, 59–78% of the different applied pesticides and their degradation products were detected in drainage water or groundwater (table 2), while only 28–33% of them were detected at the sandy fields. high pesticide concentrations dominated at the three clayey till fields, with 33–53% of the detections exceeding 0.1 μg/l, while only 11–16% of the detections at the two sandy fields exceeded the threshold limit. however, the limit of 0.1 μg/l is only relevant for groundwater and not for drainage water. the average nitrate concentrations were high in the groundwater of the sandy fields and lower at the clayey till fields (ernstsen et al. 2015). however, a high average nitrate concentration was recorded in both the drainage and groundwater from the faardrup field where the precipitation is low. this is probably because the uppermost part of the till is characterised by high permeability. it is therefore apparent that the pesticide and nitrate concentrations both reflect the geochemical conditions of groundwater and drainage water. further details regarding plap can be found in kjær et al. (2002, 2003, 2004, 2005, 2007, 2008, 2009, 2011), rosenbom et al. (2010), brüsch et al. (2013a, 2013b, 2015), ernstsen et al. (2015) and rosenbom et al. (2015). for further information please visit: http://pesticidvarsling.dk/monitor_uk/index.html. conclusions the results presented here provide an overall picture of the detections of pesticides and their degradation products in soil and groundwater in five monitored cultivated fields representing typical danish farming activities on clayey and sandy soils in the period from 1999 to 2014. the overall table 2. total number of pesticides analysed, detected, and detected below 0.1 μg/l in all sample types pesticides detections 16 19 39 45 38 and detections >0.1 μg/l 6 9 22 31 21 metabolites detections in % 28.1 32.8 59.1 77.6 66.7 >0.1 μg/l in % 10.5 15.5 33.3 53.4 36.8 groundwater avg nitrate-n 15.5 11.9 3.0 0.4 8.5 chloride 49.9 15.6 29.5 11.7 27.1 drainage avg nitrate-n ns ns 2.1 3.5 11.2 chloride ns ns 30.3 26.6 27.5 fine-grained sand coarse-grained sand clayey till tylstrup jyndevad silstrup estrup faardrup samples collected from suction cups, drainage and groundwater in the five plap fields between 01 january 2000 and july 2012. average nitrate and chloride concentrations from groundwater and drainage in the period january 2011 – july 2012. avg: average concentration in mg/l. ns: no samples. 2020 pesticide leaching detected in the monitoring programme is an outcome of the pesticide selection, hydraulic conditions, type of agriculture and the geochemical conditions such as the redox potential, aerobic conditions and hence the leaching of nitrate-n and potential persistence of individual pesticides. for instance, the leaching of pesticides is more pronounced in fractured clayey soils than in sandy soils due to fast transport in anaerobic fractures in the former soils, in contrast to slower matrix transport in the more aerated sandy soils. this is illustrated by the high number of recorded pesticides in drainage water and groundwater from clayey till soils due to bypassing of the topsoil by rapid leaching through well-connected macropores such as wormholes and fractures (rosenbom et al. 2015). the occurrence of pesticides in samples from the two sandy soils is probably specifically linked to the application of persistent pesticides such as metalaxyl-m applied to potatoes. references brüsch, w., kjær, j., rosenbom, a.e., juhler, r.k., gudmundsson, l., plauborg, f., nielsen, c.b. & olsen, p. 2013a: the danish pesticide leaching assessment programme: monitoring results may 1999 – june 2011, 108 pp. copenhagen, denmark: geological survey of denmark and greenland. brüsch, w., rosenbom, a.e., juhler, r.k., gudmundsson, l., plauborg, f., nielsen, c.b. & olsen, p. 2013b: the danish pesticide leaching assessment programme: monitoring results may 1999 – june 2012, 106 pp. copenhagen, denmark: geological survey of denmark and greenland. brüsch, w., rosenbom, a.e., badawi, n., v. platten-hallermund, f., gudmundsson, l., plauborg, f., nielsen, c.b., laier, t. & olsen, p. 2015: the danish pesticide leaching assessment programme: monitoring results may 1999 – june 2013, 110 pp. copenhagen, denmark: geological survey of denmark and greenland. council of the european union 1994: council directive 94/43/ec establishing annex vi to directive 91/414/eec concerning the placing of plant protection products on the market. official journal of the european union l227, 1.9.1994, 31–55. ernstsen, v., olsen, p. & rosenbom, a.e. 2015: long-term monitoring of nitrate transport to drainage from three agricultural clayey till fields. hydrology and earth system sciences 19, 3475–3488, http:// dx.doi.org/10.5194/hess-19-3475-2015. kjær, j. et al. 2002: the danish pesticide leaching assessment programme: monitoring results may 1999 – june 2001, 150 pp. copenhagen, denmark: geological survey of denmark and greenland. kjær, j., ullum, m., olsen, p., sjelborg, p., helweg, a., mogensen, b., plauborg, f., grant, r., fomsgaard, i. & brüsch, w. 2003: the danish pesticide leaching assessment programme: monitoring results may 1999 – june 2002, 158 pp. copenhagen, denmark: geological survey of denmark and greenland. kjær, j., olsen, p., barlebo, h.c., juhler, r.k., plauborg, f., grant, r., gudmundsson, l. & brüsch, w. 2004: the danish pesticide leaching assessment programme: monitoring results may 1999 – june 2003, 146 pp. copenhagen, denmark: geological survey of denmark and greenland. kjær, j., olsen, p., barlebo, h.c., juhler, r.k., henriksen, t., plauborg, f., grant, r., nyegaard p. & gudmundsson, l. 2005: the danish pesticide leaching assessment programme: monitoring results may 1999 – june 2004, 86 pp. copenhagen, denmark: geological survey of denmark and greenland. kjær, j., olsen, p., barlebo, h.c., henriksen t., plauborg, f., grant, r., nyegaard, p., gudmundsson, l. & rosenbom, a.e. 2007: the danish pesticide leaching assessment programme: monitoring results may 1999 – june 2006, 99 pp. copenhagen, denmark: geological survey of denmark and greenland. kjær, j., rosenbom, a., olsen, p., juhler, r.k., plauborg, f., grant, r., nyegaard, p., gudmundsson, l. & brüsch, w. 2008: the danish pesticide leaching assessment programme: monitoring results may 1999 – june 2007, 91 pp. copenhagen, denmark: geological survey of denmark and greenland. kjær, j., rosenbom, a., olsen, p., ernstsen, v., plauborg, f., grant, r., nyegaard, p, gudmundsson, l. & brüsch, w. 2009: the danish pesticide leaching assessment programme: monitoring results may 1999 – june 2008, 88 pp. copenhagen, denmark: geological survey of denmark and greenland. kjær, j., rosenbom, a.e., olsen, p., ernstsen, v., plauborg, f., grant, r., gudmundsson, l. & brüsch, w. 2011: the danish pesticide leaching assessment programme: monitoring results may 1999 – june 2010, 110 pp. copenhagen, denmark: geological survey of denmark and greenland. larsbo, m., roulier, s., stenemo, f., kasteel, r. & jarvis, n. 2005: an improved dual-permeability model of water f low and solute transport in the vadose zone. vadose zone journal 4, 398–406. lindhardt, b., abildtrup, c., vosgerau, h., olsen, p., torp, s., iversen, b.v., jørgensen, j.o., plauborg, f., rasmussen, p. & gravesen, p. 2001: the danish pesticide leaching assessment programme: site characterization and monitoring design, 73 pp. copenhagen, denmark: geological survey of denmark and greenland. rosenbom, a.e., brüsch, w., juhler, r.k., ernstsen, v., gudmundsson, l., plauborg, f., grant, r. & olsen, p. 2010: the danish pesticide leaching assessment programme: monitoring results may 1999 – june 2009, 102 pp. copenhagen, denmark: geological survey of denmark and greenland. rosenbom, a.e., olsen, p., plauborg, f., grant, r., juhler, r.k., brusch, w. & kjaer, j. 2015: pesticide leaching through sandy and loamy fields – long-term lessons learnt from the danish pesticide leaching assessment programme. environmental pollution 201, 75–90. authors’ addresses w.b.*, a.e.r. & n.b., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. p.o., department of agroecology, aarhus university, blichers allé 20, dk-8830 tjele, denmark. *present address: danmarks naturfredsningsforening, madsnedøgade 20, dk-2100 copenhagen ø, denmark. e-mail: wb@dn.dk 21 appendix. plap analyses from may 1999 to june 2014. part a aclonifen aclonifen † 111 § 298 amidosulfuron amidosulfuron 144 3 1 0.11 § 332 desmethyl-amidosulfuron 24 88 aminopyralid aminopyralid † 133 § 261 azoxystrobin azoxystrobin * 717 139 16 1.4 1798 3 0.04 cypm * 740 390 144 2.1 1910 69 5 0.19 bentazone bentazone * 1051 350 43 43 2603 81 8 0.6 2-amino-n-isopropyl-benzamide 561 4 0.06 1295 1 0.02 bifenox bifenox 303 17 3 0.38 751 7 1 0.1 bifenox acid * 278 55 47 8.6 702 29 23 3.1 nitrofen 303 11 4 0.34 751 boscalid boscalid † 56 § 111 bromoxynil bromoxynil 528 5 3 0.6 § 1122 chlormequat chlormequat † 95 2 0.017 § 190 clomazon clomazone 224 1 1 0.28 § 598 fmc 65317 216 1 1 0.3 577 clopyralid clopyralid 219 7 4 4.094 § 520 1 0.026 cyazofamid cyazofamid † 100 § 262 desmedipham desmedipham † 287 580 1 0.033 ehpc 199 383 diflufenican diflufenican 109 32 14 0.49 324 1 1 0.47 ae-b107137 * 121 19 1 0.13 333 1 0.016 ae-05422291 109 324 dimethoate dimethoate † 515 1 1 1.417 1253 1 0.085 epoxiconazole epoxiconazole 330 14 2 0.39 999 1 0.011 ethofumesate ethofumesate * 519 70 17 12 1095 36 7 1.4 fenpropimorph fenpropimorph † 657 2 0.038 1531 2 0.029 fenpropimorph acid 636 2 1 0.25 1435 flamprop-m flamprop-m-isopropyl 520 38 1 0.109 1204 1 0.024 flamprop 525 23 1 0.35 1212 florasulam florasulam † 146 351 florasulam-desmethyl 109 130 fluazifop-p-buthyl fluazifop-p-butyl 128 232 tfmp * 184 53 24 0.64 555 87 16 0.29 fluazifop-p 451 11 4 3.8 1109 7 1 0.17 fludioxonil cga 192155 † 11 § 48 cga 339833 11 48 fluroxypyr fluroxypyr * 521 4 3 1.4 1273 2 0.072 glyphosate glyphosate * 1091 429 136 31 2216 77 5 0.67 ampa * 1092 632 142 5.4 2217 37 0.08 iodosulfuron-methyl-natrium metsulfuron-methyl 332 1 0.054 842 iodosulfuron-methyl † 60 § 250 ioxynil ioxynil 527 24 7 0.25 1128 1 0.01 linuron linuron † 67 § 271 mancozeb etu 44 7 0.038 200 2 0.024 ebis 7 25 mcpa mcpa 354 14 3 3.894 916 1 0.019 2-methyl-4-chlorophenol 354 2 1 0.24 912 mesosulfuron-isopropyl mesosulfuron-methyl 153 13 0.059 § 411 mesosulfuron 119 119 mesotrione mesotrione † 50 § 156 amba 50 156 mnba 50 156 pesticide analyte tile drain and suction cup groundwater samples det. ≥0.1 max. samples det. ≥0.1 max. fifty-one pesticides and 52 degradation products analysed in the plap programme in the period may 1999 – june 2014. the columns show the number of water samples analysed, number of detections, and detections in concentrations ≥ 0.1μg/l in water samples from the variably-saturated zone (drainage and suction cups), and in groundwater (vertical and horizontal groundwater wells). det: number of detections. ≥0.1: number of detections ≥0.1μg/l. max: maximum concentration in μg/l. *: pesticides and their degradation products leached through soil to tile drains or suction cups in average concentrations above 0.1 μg/l. †: pesticides not detected or detected only in a few samples above their threshold concentrations at 1 m depth. §: pesticides and their degradation products not detected or only detected in a few samples in groundwater. 2222 appendix. plap analyses from may 1999 to june 2014. part b metalaxyl-m metalaxyl-m 207 15 0.037 592 79 23 1.3 cga 108906 * 215 175 69 4.8 593 468 128 2.7 cga 62826 * 216 100 25 1.2 593 147 8 0.68 metamitron metamitron * 515 103 31 26.369 1095 53 7 0.63 desamino-metamitron * 518 129 23 5.549 1094 78 16 1.3 metrafenone metrafenone 136 20 0.072 273 1 0.04 metribuzin metribuzin 97 2 0.024 414 1 0.014 diketo-metribuzin 340 256 63 0.69 552 479 336 1.372 desamino-diketo-metribuzin * 255 81 51 2.1 551 256 18 1.831 desamino-metribuzin * 91 392 pendimethalin pendimethalin 694 89 30 32 1811 1 0.052 phenmedipham phenmedipham 288 580 2 0.025 mhpc 288 2 1 0.19 580 1 0.053 3-aminophenol 109 245 picolinafen picolinafen 117 18 0.07 193 cl153815 * 117 31 11 0.5 193 pirimicarb pirimicarb 887 62 0.077 2120 6 0.035 pirimicarb-desmethyl-formamido * 707 29 13 0.379 1638 2 0.076 pirimicarb-desmethyl 780 8 0.053 1911 3 0.042 propiconazol propiconazole 899 32 3 0.862 2084 3 0.035 propyzamid propyzamide * 257 27 8 1.6 754 10 2 0.14 rh-24644 257 19 0.051 754 2 0.032 rh-24580 257 2 0.016 754 rh-24655 233 1 0.017 690 prosulfocarb prosulfocarb 199 6 1 0.18 516 5 0.032 pyridat pyridate 39 116 phcp 125 4 4 2.69 373 14 4 0.309 rimsulfuron rimsulfuron 117 367 ppu * 502 388 74 0.29 1519 432 13 0.23 ppu-desamino 502 186 6 0.18 1519 107 0.089 tebuconazole tebuconazole * 289 47 17 2 784 8 2 0.12 1.2.4-triazol * 16 7 1 0.17 terbuthylazine terbuthylazine * 513 213 56 11 1324 88 23 1.9 desethyl-terbuthylazine * 612 365 88 8.3 1664 261 33 0.94 desisopropylatrazine 414 156 2 0.44 996 92 0.047 hydroxy-terbuthylazine * 384 136 18 0.99 940 34 0.069 2-hydroxy-desethyl-terbuthylazine * 342 128 28 6.3 850 9 0.092 thiacloprid thiacloprid † 47 § 100 thiacloprid-amide 47 1 0.012 100 m34 55 100 thiacloprid sulfonic acid 56 100 thiamethoxam thiamethoxam † 132 § 359 cga 322704 132 359 triasulfuron triasulfuron † 82 § 301 triazinamin 393 1103 1 0.042 tribenuron-methyl triazinamin-methyl † 569 2 0.042 § 1523 triflusulfuron-methyl triflusulfuron-methyl † 95 288 in-e7710 95 5 0.014 288 in-m7222 95 288 1 0.052 in-d8526 95 288 pesticide analyte tile drain and suction cup groundwater fifty-one pesticides and 52 degradation products analysed in the plap programme in the period may 1999 – june 2014. the columns show the number of water samples analysed, number of detections, and detections in concentrations ≥ 0.1μg/l in water samples from the variably-saturated zone (drainage and suction cups), and in groundwater (vertical and horizontal groundwater wells). det: number of detections. ≥0.1: number of detections ≥0.1μg/l. max: maximum concentration in μg/l. *: pesticides and their degradation products leached through soil to tile drains or suction cups in average concentrations above 0.1 μg/l. †: pesticides not detected or detected only in a few samples above their threshold concentrations at 1 m depth. §: pesticides and their degradation products not detected or only detected in a few samples in groundwater. samples det. ≥0.1 max. samples det. ≥0.1 max. geological survey of denmark and greenland bulletin 33, 2015, 65-68 65© 2015 geus. geological survey of denmark and greenland bulletin 33, 65–68. open access: www.geus.dk/publications/bull observed melt-season snowpack evolution on the greenland ice sheet charalampos charalampidis and dirk van as due to recent warm and record-warm summers in greenland (nghiem et al. 2012), the melt of the ice-sheet surface and the subsequent runoff are increasing (shepherd et al. 2012). about 84% of the mass loss from the greenland ice sheet between 2009 and 2012 resulted from increased surface runoff (enderlin et al. 2014). th e largest melt occurs in the ablation zone, the low marginal area of the ice sheet (van as et al. 2014), where melt exceeds wintertime accumulation and bare ice is thus exposed during each melt season. in the higher regions of the ice sheet (i.e. the accumulation area), melt is limited and the snow cover persists throughout the year. it is in the vast latter area that models struggle to calculate certain mass fl uxes with accuracy. a better understanding of processes such as meltwater percolation and refreezing in snow and fi rn is crucial for more accurate greenland icesheet mass-budget estimates (van angelen et al. 2013). in may 2012, the fi eld campaign ‘snow processes in the lower accumulation zone’ was organised by the geological survey of denmark and greenland (geus) at the kan_u automatic weather station (67°0´0˝n, 47°1́ 1˝w; 1840 m above sea level), which delivers data to the programme for monitoring of the greenland ice sheet (promice; van as et al. 2013) and is one of the few weather stations located in the lower accumulation area of greenland (fig. 1, inset). during the expedition, we installed thermistor strings, fi rn compaction monitors and a snowpack analyser; we drilled fi rn cores, performed fi rn radar measurements, gathered meteorological data, dug snow pits and performed dye-tracing experiments. one important objective of the campaign was to understand the thermal variability in the snowpack during the melt season by monitoring with high-precision temperature probes (campbell scientifi c temperature probe, model 107; accuracy: better than ± 0.4°c over the range –24 to 48°c). six temperature probes were installed in the snowpack of the previous winter at depths of 0.05, 0.10, 0.20, 0.30, 0.40 and 0.70 m below the surface (fig. 1). th e data from the probes were stored at 30-minute intervals on data loggers, which also triggered additional measurements of radiation-shielded air temperature at 1.10 m, surface albedo and surface-height change due to accumulation and ablation. emitted longwave radiation was also recorded to be able to calculate the surface temperature assuming snow to be a black-body radiator. th e vertical position of the probes relative to the surface, which changes due to ablation and accumulation, was determined by the sonic ranger measurements. recorded temperatures aft er the probes surfaced were discarded. th e relatively shallow snowpack (0.70–0.80 m) was on top of fi rn of density ρ >500 kg m-3 which had accumulated in the previous years (fig. 1). in the upper fi rn we found ice lenses (ρ >800 kg m–3) several metres thick. within the snowpack, two thin ice layers were present, one at 0.30 m greenland fig. 1. after the installation of the temperature probes in may 2012 (thin black cables) at the location of k an_u on the greenland ice sheet. the thick grey cables are thermistor strings drilled into the firn. the inset map shows the location of the study area. 6666 and one at c. 0.50 m below the surface, both about 0.01 m thick. th e average density of the snow was determined to be roughly 360 kg m–3, yielding an accumulation of 0.25 ± 0.08 m water equivalent (w.e.) since the summer 2011 (charalampidis et al. 2015). below, we present observations from the period 02 may to 23 july and interpret the atmosphere–surface interaction and its impact on the subsurface snow layers, with the goal to quantify refreezing in the greenland accumulation area. atmosphere–snow interaction th e observations reveal a strong similarity between the nearsurface air temperature and the snow-surface temperature with changes of air temparature lagging on average 30–40 minutes behind. typically, the air remained warmer than the snow surface (fig. 2), implying a prevailing stable stratifi cation of the near-surface air. at night, the diff erence was larger (1.6–1.9°c) due to the reduced sunlight and subsequent cooling of the surface forced by longwave radiation. during the day, the temperature diff erence was smaller (0.6–1.2°c) primarily due to solar radiation heating the surface and reducing atmospheric stability. understandably, when air temperature exceeds 0°c, the temperature diff erence can be larger since the surface cannot exceed the melting point. on 6 may, overcast conditions and atmospheric stillness caused the increase of air temperature above +6°c (fig. 3a). th ese were the highest temperatures during the observational period and similar temperatures occurred also on two days in june (3 and 18). with the exception of 6 may, the air temperature remained negative until the last week of may. during this period, the temperature of the upper 0.20 m of snow followed a pronounced diurnal cycle, which at 0.20 m lagged about 10 hours behind the variations in surface temperature (fig. 3b), signifying the low thermal conductivity of snow. at 1840 m above sea level, the ice sheet generally experiences low melt rates. when melt occurs, it displays a diurnal cycle following air temperature. a diurnal cycle of positive air temperatures occurred fi rst on 27 may, marking the beginning of the melt season (fig. 3a). th e surface ablated in response to the warm conditions, while the snow temperatures revealed the distinct progression of a warming and thus wetting front moving vertically through the snowpack (fig. 3b). th e temperature at 0.70 m depth was aff ected by this 42 hours aft er surface melt initiated, i.e. an average warming front progression of only c. 17 mm h–1. th e entire snowpack became temperate aft er six days of ablation. th e slow progression of the warming front indicates a concurrent heterogeneous meltwater infi ltration to the fi rn below (humphrey et al. 2012). during the period 8–12 june, sub-freezing air temperatures occurred again (fig. 3a) and melting ceased. while the upper part of the snowpack remained close to 0°c, possibly containing liquid water, the deeper levels (0.4 m and below) cooled as heat was conducted downwards into the colder fi rn. melt resumed on 13 june, aff ecting snow temperatures at 0.7 m aft er 30 hours (fig. 3b), which is faster than in the previous melt period due to the reduced measurement depth, and changed snow properties. th ereaft er, the snow remained at the melting point until it ablated completely on 11 july. between 13 june and 11 july, there were fi ve occasions when the diurnal air/surface temperature cycle was interrupted by periods with warm night-time conditions resulting in enhanced ablation (fig. 3a). most notably, during the warm week of 8–14 july when the whole greenland icesheet surface area was reported to melt (nghiem et al. 2012), the air temperature at kan_u remained above +2°c for six days and melt was large. at the same time, the ‘watson river’, which drains this section of the ice sheet, experienced the highest discharge in 56 years, judging from the partial destruction of a 1956 bridge near the town of kangerlussuaq. snowpack evolution in may, the area received 0.12 m of fresh snow on top of the existing snowpack (fig. 4b) and the albedo remained at fresh snow values of 0.8–0.9 (fig. 4a). on 27 may, the surface began ablating and by the end of the day 0.05 m of the fresh snow had melted away. in the period until 8 june the average ablation rate was 0.02 m day–1, reducing albedo to c. 0.75, primarily due to snow metamorphosis. in principle, the energy needed to make temperate a uniform snowpack 0.7 m thick at –10°c is equivalent to the energy necessary for melting 0.04 m of snow at 0°c and a density of 360 kg m–3. th erefore, the generation of 15 mm of meltwater and its refreezing within the snowpack raises its temperature to 0°c. by the beginning of june when the entire snowpack had reached 0°c, the fi rst 0.15 m of snow (i.e. c. 50 mm of meltwater) had ablated. th is implies that approximately 70% of the meltwater either percolated deeper 1 3 5 7 9 11 13 15 17 19 21 23 time of the day (h utc) period: 2 may to 23 july 2012 (t a − t s ) av e ra ge ( °c ) −1 0 1 2 3 fig. 2. average temperature difference between air and surface during the day. the error bars show two standard deviations. solar zenith time is at 15:08 utc. 67 into the fi rn or was retained in liquid form in the snow by capillary forces. from the beginning of june onward, by lack of cold content, the snowpack was able to respond immediately to surface forcings (fig. 4b), and all percolating meltwater was routed toward the underlying fi rn. th e cold conditions and melt pause from 8 to 12 june were accompanied by snowfall resulting in 0.05 m of fresh snow accumulation (fig. 4b), thereby increasing the albedo above 0.8 (fig. 4a). melt resumed on 15 june with an average ablation rate of 0.03 m day–1 and with albedo dropping as low as 0.7, indicative of wet snow. small snowfall events also occurred in the beginning of july. during the warm days of 9 and 10 july the ablation rate exceeded 0.05 m day–1, removing the last of the 2011–2012 winter snowpack and revealing the underlying, water-saturated fi rn. consequently, the albedo dropped below 0.7, enhancing melt through the meltalbedo feedback (box et al. 2012). simulated refreezing rates a combination of temperature measurements and thermal conductivity simulations reveals the amount of refrozen water in the snow. a heat-conduction model was used to simulate the evolution of subsurface temperatures, using measured surface temperature and surface height change as input. th e model was run at temporal and spatial resolutions of 10 minutes and 0.10 m, respectively, and was re-initialised each day by measured temperature profi les at 00:00 utc. th e effective conductivity of the snow is a function of snow density (sturm et al. 1997) and the specifi c heat of snow depends on temperature (yen 1981). density profi les were initialised based on snow pit density measurements at the installation of the probes and were updated throughout the run taking refreezing into account. th e diff erence between the simulated and measured temperatures at the end of the day is a measure of the added latent heat during the day, and thus of the daily refreezing rates. th e simulation reveals that during the fi rst week of melt starting 27 may, refreezing occurred at all measurement depths within the snowpack (fig. 5a). th e peak refreezing occurred on 30 may and at depths below 0.50 m. during this period the total refreezing rate in the snowpack was comparable to the average melt rate of that fi rst period of melt (6 kg m–2 day–1; fig. 5b). th e subsequent cold content reduction and thinning snowpack resulted in low refreezing values below 0.4 kg m–2 day–1 at all depths. note that refreezing rates during the sub-freezing early period of our simulation are non-zero and large near the surface. it is possible that shortwave penetration in the snow plays a role or that our conduction model is fl awed in conditions of large temperature gradients in well-ventilated, low-density snow, which is valid for the start of the simulation period. however, in terms of total refreezing the early results add up to small values (fig. 5b). 0 4 2012 a 06 may 20 may 03 jun 17 jun 01 jul 15 jul −30 −25 −20 −15 −10 −5 0 t e m p e ra tu re ( °c ) b air (1.10 m) surface 0.05 m 0.10 m 0.20 m 0.30 m 0.40 m 0.70 m t e m p . ( °c ) fig. 3. observed temperatures of the near-surface atmosphere (a) and (sub)surface (b). 0.7 0.9 a lb e d o 2012 a in it ia l d e p th f ro m s u rf ac e ( m ) b 06 may 20 may 03 jun 17 jun 01 jul 0.7 0.4 0.3 0.2 0.1 0.0 −28 −24 −20 −16 −12 −8 −4 0 (°c) fig. 4. observed surface albedo (a) and thermal evolution (b) of the snowpack. the dark red contour signifies 0°c. fig. 5. calculated refreezing rates in the snow at 0.1 m spacial resolution (a) and combined (b). x 10−3 x 10−3 0.10 m 0.20 m 0.30 m 0.40 m 0.50 m 0.60 m 0.70 m 0 0.2 0.4 0.6 0.8 1 2012 a 06 may 20 may 03 jun 17 jun 01 jul 15 jul 0 2 4 6 r e fr . r at e b total r e fr e e zi n g ra te ( 1 0 3 k g m − 2 d ay − 1 ) 6868 th e non-zero values of roughly 0.1 kg m–2 day–1 at greater depth are considered the uncertainty for the entire simulation period. during the cold period in june, the refreezing rates increased again to 3 kg m–2 day–1 (fig. 5b), which is an indication that liquid water was available, primarily at depths 0.20–0.30 m, while the required cold content was being supplied by the surface. th is method of refreezing requires liquid water retention in the snow matrix while cold content becomes available, as opposed to the refreezing of meltwater percolating into layers at sub-freezing temperatures. th e heat between 0.60–0.70 m that was conducted to depths below the seasonal snow layer increased the available cold content, thus when melt occurred again, refreezing was prominent at those depths (15 june; fig. 5a). as the average melt rate aft er 13 june was c. 8 mm w.e. day–1, the refrozen water in the snowpack was less than 10% of this amount, implying liquid water retention or the routing of meltwater to the layers below. overall, the simulated density increase within the snowpack was between 70–80 kg m–3 for most levels. meltwater refreezing is a positive component in the mass budget (mass storage; harper et al. 2012), although in a warming climate with more frequent extreme melt conditions, the larger meltwater fl uxes in the snow and fi rn may result in rapid reduction of pore volume (van angelen et al. 2013). th e large melt of 2012 at the elevation of kan_u was a result of both high atmospheric temperatures (bennartz et al. 2013) and a relatively low albedo from the exposure of the water-saturated fi rn aft er the early removal of the relatively thin winter snowpack (charalampidis et al. 2015). th e high ice content of the fi rn as found during the measurement campaign is an indication of intense percolation during previous years. th ese snow processes are still quite poorly represented in modelling eff orts, also due to the dependency of horizontal meltwater runoff on the ice layers formed by refreezing. our results illustrate that especially the melt-albedo feedback in relation to pore-volume reduction makes the lower accumulation area of the greenland ice sheet highly responsive in a warming climate. acknowledgements th e data presented in this paper were gathered in close collaboration with the greenland analogue project. we are grateful to our snow processes in the lower accumulation zone project partners horst machguth, mike macferrin, andreas mikkelsen, rickard pettersson, katrin lindbäck, alun hubbard and sam doyle. th is is a publication in the framework of the programme for monitoring of the greenland ice sheet (promice) and contribution number 63 of the nordic centre of excellence svali, ‘stability and variations of arctic land ice’, funded by the nordic toplevel research initiative (tri). references bennartz, r., shupe, m.d., turner, d.d., walden, v.p., steff en, k., cox, c.j. kulie, m.s. miller, n.b. & pettersen, c. 2013: july 2012 greenland melt extent enhanced by low-level liquid clouds. nature 496, 83–86. box, j.e., fettweis, x., stroeve, j.c., tedesco, m., hall d.k. & steff en, k. 2012: greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers. th e cryosphere 6, 821–839. charalampidis, c. et al. 2015: changing surface-atmosphere energ y exchange and refreezing capacity of the lower accumulation area, west greenland. th e cryosphere discussions 9, 2867–2913. enderlin, e.m., howat, i.m., jeong, s., noh, m.-j., van angelen, j.h. & van den broeke, m.r. 2014: an improved mass budget for the greenland ice sheet. geophysical research letters 41, 866–872. harper, j., humphrey, n., pfeff er, w.t., brown, j. & fettweis, x. 2012: greenland ice-sheet contribution to sea-level rise buff ered by meltwater storage in firn. nature 491, 240–243. humphrey, n.f., harper, j.t. & pfeff er, w.t. 2012: th ermal tracking of meltwater retention in greenland’s accumulation area. journal of geophysical research: earth surface 117, f01010. nghiem, s.v., hall, d.k., mote, t.l., tedesco, m., albert, m.r., keegan, k., shuman, c.a., digirolamo, n.e. & neumann, g. 2012: th e extreme melt across the greenland ice sheet in 2012. geophysical research letters 39, l20502. shepherd, a. et al. 2012: a reconciled estimate of ice-sheet mass balance. science 338, 1183–1189. sturm, m., holmgren, j., könig, m. & morris, k. 1997: th e thermal conductivity of seasonal snow. journal of glaciolog y 43, 26–41. van angelen, j.h., lenaerts, j.t.m., van den broeke, m.r., fettweis, x. & meijgaard, e. 2013: rapid loss of fi rn pore space accelerates 21st century greenland mass loss. geophysical research letters 40, 2109–2113. van as, d., fausto, r.s., colgan, w.t., box, j.e. & the promice project team 2013: darkening of the greenland ice sheet due to the melt-albedo feedback observed at the promice weather stations. geological survey of denmark and greenland bulletin 28, 69–72. van as, d. et al. 2014: increasing meltwater discharge from the nuuk region of the greenland ice sheet and implications for mass balance (1960–2012). journal of glaciolog y 60, 314–322. yen, y.c. 1981: review of thermal properties of snow, ice and sea ice. crr el report 81–10, 27 pp. hanover, new hampshire: us army corps of engineerscold regions research and engineering laboratory. authors’ addresses c.c.* & d.v.a., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: cc@geus.dk *also at: department of earth sciences, uppsala university, villavägen 16, 752 36 uppsala, sweden. geological survey of denmark and greenland bulletin 1, 948 pp. geologic al survey of denmark and greenland bulletin 1 • 2003 the jurassic of denmark and greenland edited by jon r. ineson and finn surlyk geological survey of denmark and greenland ministry of the environment geological survey of denmark and greenland bulletin 1 keywords northwest europe, denmark, greenland, sweden, the netherlands, jurassic, chronostratigraphy, biostratigraphy, lithostratigraphy, sequence stratigraphy, structural history, basin evolution, sedimentology, palynostratigraphy, geochemistry, coal petrography/palynology cover palaeogeography of the mesozoic rift system in the north atlantic region in the middle jurassic (c. 160–180 ma), viewed towards the north. reconstruction by stefan sølberg, based on the palaeogeographic maps of ziegler (1990) and doré (1992). for references, see surlyk (2003, this volume). chief editor of this series: peter r. dawes scientific editors: jon r. ineson and finn surlyk copy editors: jon r. ineson and birgit eriksen editorial secretary: birgit eriksen critical readers: see list on page 6 illustrations (geus): stefan sølberg, gurli e. hansen bengaard, jette halskov, eva melskens, helle zetterwall photographic work (geus): jacob lautrup, benny m. schark, peter k. warna-moors lay-out and graphic production: carsten e. thuesen printers: schultz grafisk, albertslund, denmark manuscripts submission/acceptance dates: see individual articles printed: 28th october 2003 isbn 87-7871-116-9 geological survey of denmark and greenland bulletin the series geological survey of denmark and greenland bulletin replaces geology of denmark survey bulletin and geology of greenland survey bulletin. citation of the name of this series it is recommended that the name of this series is cited in full, viz. geological survey of denmark and greenland bulletin. if abbreviation of this volume is necessary the following form is suggested: geol. surv. den. green. bull. 1, 948 pp. available from geological survey of denmark and greenland (geus) øster voldgade 10, dk-1350 copenhagen k, denmark phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: geus@geus.dk or geografforlaget aps fruerhøjvej 43, dk-5464 brenderup, denmark phone: +45 63 44 16 83, fax: +45 63 44 16 97, e-mail: go@geografforlaget.dk  danmarks og grønlands geologiske undersøgelse (geus), 2003 5 6 7 9 23 61 75 115 147 217 233 247 265 301 349 367 403 contents dedication referees preface the jurassic of denmark and greenland: key elements in the reconstruction of the north atlantic jurassic rift system f. surlyk and j.r. ineson stratigraphy the lower jurassic of europe: its subdivision and correlation k.n. page the middle jurassic of western and northern europe: its subdivisions, geochronology and correlations j.h. callomon the upper jurassic of europe: its subdivision and correlation a. zeiss the jurassic dinoflagellate cyst zonation of subboreal northwest europe n.e. poulsen and j.b. riding denmark, southern sweden and the netherlands jurassic lithostratigraphy and stratigraphic development onshore and offshore denmark o. michelsen, l.h. nielsen, p.n. johannessen, j. andsbjerg and f. surlyk the jurassic of the netherlands g.f.w. herngreen, w.f.p. kouwe and th.e. wong danish central graben upper jurassic – lower cretaceous of the danish central graben: structural framework and nomenclature p. japsen, p. britze and c. andersen middle jurassic – early cretaceous rifting of the danish central graben j.j. møller and e.s. rasmussen sequence stratigraphy of the jurassic of the danish central graben j. andsbjerg and k. dybkjær sedimentology and sequence stratigraphy of the bryne and lulu formations, middle jurassic, northern danish central graben j. andsbjerg the use of spectral natural gamma-ray analysis in reservoir evaluation of siliciclastic sediments: a case study from the middle jurassic of the harald field, danish central graben i.l. fabricius, l. dahlerup fazladic, a. steinholm and u. korsbech sedimentology and sequence stratigraphy of paralic and shallow marine upper jurassic sandstones in the northern danish central graben p.n. johannessen volgian–ryazanian ‘hot shales’ of the bo member (farsund formation) in the danish central graben, north sea: stratigraphy, facies and geochemistry j.r. ineson, j.a. bojesen-koefoed, k. dybkjær and l.h. nielsen 3 439 459 527 543 555 585 611 631 659 723 777 813 865 893 931 danish basin and fennoscandian border zone triassic and jurassic transtension along part of the sorgenfrei–tornquist zone in the danish kattegat t.e. mogensen and j.a. korstgård late triassic – jurassic development of the danish basin and the fennoscandian border zone, southern scandinavia l.h. nielsen the jurassic of skåne, southern sweden a. ahlberg, u. sivhed and m. erlström an offshore transgressive–regressive mudstone-dominated succession from the sinemurian of skåne, sweden n. frandsen and f. surlyk lower jurassic (pliensbachian) ammonites from bornholm, baltic sea, denmark d.t. donovan and f. surlyk the lower–middle jurassic of the anholt borehole: implications for the geological evolution of the eastern margin of the danish basin o.b. nielsen, m.-s. seidenkrantz, n. abrahamsen, b.j. schmidt, e.b. koppelhus, h. ravn-sørensen, u. korsbech and k.g. nielsen burial depth and post-early cretaceous uplift of lower–middle jurassic strata in the fennoscandian border zone based on organic maturity h.i. petersen, l.h. nielsen, t. bidstrup and e. thomsen early and middle jurassic mires of bornholm and the fennoscandian border zone: a comparison of depositional environments and vegetation h.i. petersen, l.h. nielsen, e.b. koppelhus and h.s. sørensen east greenland the jurassic of east greenland: a sedimentary record of thermal subsidence, onset and culmination of rifting f. surlyk palynostratigraphy and palaeoenvironments of the rævekløft, gule horn and ostreaelv formations (lower–middle jurassic), neill klinter group, jameson land, east greenland e.b. koppelhus and g. dam palynostratigraphy and palaeoenvironment of the middle jurassic sortehat formation (neill klinter group), jameson land, east greenland e.b. koppelhus and c.f. hansen shallow marine syn-rift sedimentation: middle jurassic pelion formation, jameson land, east greenland m. engkilde and f. surlyk the jurassic of kuhn ø, north-east greenland p.c. alsgaard, v.l. felt, h. vosgerau and f. surlyk stratigraphy and sedimentology of a basement-onlapping shallow marine sandstone succession, the charcot bugt formation, middle–upper jurassic, east greenland m. larsen, s. piasecki and f. surlyk shelf-edge delta and slope deposition in the upper callovian – middle oxfordian olympen formation, east greenland m. larsen and f. surlyk 4 5 this book is dedicated to the memory of ole winther christensen (1951–1998), director of the geological survey of denmark (dgu) from 1990 to 1995 and the geological survey of denmark and greenland (geus) from 1995 to 1998. from its conception in the early 1990s, the ‘jurassic book’ has benefited from the progressive integration of danish geological institutions. this began in 1995 with the amalgamation of dgu with the geological survey of greenland (ggu) to form geus and culminated in 2002 with the opening of the geocenter copenhagen, a conglomeration of geus, the danish lithosphere centre (dlc), the geological museum and the geological and geographical institutes of the university of copenhagen. ole winther christensen played a key role in both these positive developments in danish geology. sadly, he was not to experience the full realisation of the geocenter copenhagen concept due to his untimely death in 1998. dedication 6 j. alexander, university of east anglia, uk j. andsbjerg, geological survey of denmark and greenland, denmark d.j. batten, university of wales, uk d.g. benson, texas, usa j.h. callomon, university college london, uk j. cartwright, cardiff university, uk b.m. cox, british geological survey, uk r.j. davey, simon petroleum technology ltd, uk r.j. davies, mobil north sea ltd, uk g. dietl, staatliches museum für naturkunde, germany d.t. donovan, university college london, uk t. dreyer, norsk hydro research centre, norway k. dybkjær, geological survey of denmark and greenland, denmark c.j. fielding, university of queensland, australia m.j. fisher, helensburgh, uk j. gjelberg, norsk hydro research centre, norway m.b. gowers, dong norge as, norway f. gramann, niedersächsisches landesamt für bodenforschung, germany d. guy-ohlsen, swedish museum of natural history, sweden a. hallam, birmingham university, uk s.d. harker, totalfinaelf exploration, uk g.f.w. herngreen, tno-nitg, the netherlands s.p. hesselbo, university of oxford, uk s. holloway, british geological survey, uk a. hurst, university of aberdeen, uk l.n. jensen, statoil norge as, norway j.a. korstgård, university of aarhus, denmark d.a. leckie, geological survey of canada, canada h.b. lindgreen, geological survey of denmark and greenland, denmark c. mangold, université claude bernard lyon i, france j.e.a. marshall, university of southampton, uk l.h. nielsen, geological survey of denmark and greenland, denmark a. nøttvedt, norsk hydro canada, canada s. olaussen, norsk agip as, norway t. olsen, statoil norge as, norway k.n. page, university of plymouth, uk n. parkinson, western atlas logging services, uk g.k. pedersen, university of copenhagen, denmark r.m. pegrum, statoil norge as, norway s. piasecki, geological survey of denmark and greenland, denmark k.t. pickering, university college london, uk d. pirrie, university of exeter, uk a.g. plint, university of western ontario, canada j.b. riding, british geological survey, uk a. ryseth, norsk hydro research centre, norway b.w. sellwood, reading university, uk r.j. steel, university of wyoming, usa g.m. sykes, helix rds ltd, uk n.h. trewin, university of aberdeen, uk r.v. tyson, university of newcastle, uk g. warrington, british geological survey, uk o.v. vejbæk, geological survey of denmark and greenland, denmark a.g. whitham, casp, uk a. wierzbowski, warsaw university, poland p.b. wignall, leeds university, uk referees the editors are indebted to the following referees, whose conscientious and incisive reviews have been invaluable in the production of this book – your efforts are greatly appreciated. the jurassic sedimentary successions of denmark and east greenland accumulated on opposite sides of a complex rifted seaway between present-day greenland and northwest europe. the mesozoic–cenozoic sedimentary basins created along this seaway are of major importance both scientifically, as they preserve a record of the early evolution of the north atlantic region, and economically as one of the rift arms contains the north sea petroleum province. the jurassic system, in particular, has been the focus of intensive study in northwest europe and greenland. not only has this system, since the days of william smith, been at the forefront of stratigraphic research but it also forms a critical component of the north sea hydrocarbon province, yielding both the most important source rocks and a wide range of sandstone reservoirs. although the stratigraphic development of the jurassic in denmark and east greenland can be compared at a number of levels, the nature of the occurrences in the two regions is very different. the jurassic of east greenland is one of the world’s best-exposed ancient rift basins and is widely regarded as a classic ‘field laboratory’. the jurassic strata are exposed in spectacular cliff sections that provide unique opportunities for detailed research into process sedimentology, genetic stratigraphy and 3d sedimentary architecture. the danish jurassic strata, in contrast, have limited outcrop but are well known from the subsurface, both on land and beneath the waters of the north sea. the papers collected in this volume reflect this contrast – the stratigraphic evolution of east greenland has been deciphered primarily on the basis of detailed outcrop geological studies whereas the corresponding stratigraphic analyses of the danish basin and the danish sector of the central graben are largely dependent on ‘remote’ subsurface data. jurassic stratigraphic research in denmark over the last two decades has benefited immensely from the interaction between these two contrasting yet complementary approaches. the origins of this book go back to the early 1990s when the idea was mooted for a book on the ‘jurassic of denmark and adjacent areas’, initially with a view to publication of the main results of ph.d. studies that were underway at the geological survey of denmark (dgu) at that time. in 1995, with the amalgamation of dgu with the geological survey of greenland (ggu) to form the geological survey of denmark and greenland (geus), the conceptual framework of the book expanded to include the jurassic of east greenland, a research area that was under sharp focus both at ggu and at the university of copenhagen. as the editing of the book entered the final phase, the geological survey relocated to the new geocenter copenhagen – a centralised amalgam of the survey (including the danish lithosphere centre) and the geological and geographical institutes and the geological museum of the university of copenhagen. from conception to publication, therefore, the book charts the changing structure of some of the central geological research bodies in denmark, and its completion coincided with the inception of a new integrated natural science research centre. the central aim of the book is to present the results of an intense period of research activity in denmark on the jurassic system over the last fifteen years – and, where relevant, to present these results at a comprehensive level that is almost impossible in modern scientific journals. although covering a range of subjects, the common thread that runs through the book is the detailed documentation of the history of the jurassic rift system as recorded in the sedimentary basins of greenland and denmark. particular areas of focus include: (1) the sedimentary and stratigraphic signatures of syn-rift successions, whether revealed by detailed outcrop study or on the basis of integrated reflection seismic, petrophysical and core data; and (2) testing and application of sequence stratigraphic models and concepts at a variety of scales and in different structural settings. although focussing on broad geoscientific topics of general relevance, the book also provides data of specific value to the hydrocarbon industry. the danish basin and, in particular, the danish central graben are prospective basins with exploration histories stretching back nearly fifty years. a number of jurassic fields are under development and production in the danish central graben, and exploration interest remains high. the structural, sedimentological and stratigraphic papers in this volume thus represent a direct source of essential data for the hydrocarbon industry. the onshore east greenland basins, in contrast, are not prospective per 7 preface se, yet the detailed sedimentological and stratigraphic analyses included here will be of particular interest to petroleum geologists both as direct stratigraphic analogues of the succession on the conjugate margin (midnorway shelf) and as reservoir analogues or case studies applicable particularly to the north sea region but also valid elsewhere. introductory chronostratigraphic reviews of the lower, middle and upper jurassic were planned from the outset, and contributions were solicited from three international authorities in this field, together with a paper on the jurassic of southern sweden. furthermore, a review of the jurassic of the netherlands was invited from the geological survey of the netherlands (rgd) for comparative purposes, building on previous close stratigraphic co-operation between dgu and rgd in the late 1980s. the aim has been to produce a book that is as balanced and consistent as possible, in terms of content, terminology and appearance. given the range of subjects covered, however, a certain degree of heterogeneity is inevitable and full consistency in terminology cannot be achieved. the gradstein et al. (1994) timescale is used in most cases but the haq et al. (1988) and harland et al. (1990) time-scales are employed by some authors; in all cases, the origin of the time-scale used is clearly indicated. several forms of chronostratigraphic terminology are in common use, all being inherently logical and fully acceptable; particularly prevalent are the ‘standard zone’ nomenclature (callomon & donovan 1974) and the ‘chronozone’ terminology, as laid down in the international stratigraphic guide (salvador 1994). editorial flexibility has been exercised here, although consistency within individual articles was required. to enhance uniformity, a common graphical style has been imposed wherever possible; detailed sedimentary logs are somewhat variable, however, being dictated by different individual styles and demands. in an enterprise of this type, undertaken over a number of years, there are clearly many people both in denmark and abroad who have helped us towards publication. the research projects that formed the initial stimulus behind the book were supported both by state funding – the danish energy agency (energy research program, efp), the danish natural science research council (snf), the danish research academy and the norwegian petroleum directorate (npd) – and by the private sector, including amerada hess, amoco, british petroleum, the carlsberg foundation, conoco, mærsk olie og gas, norsk hydro, saga petroleum and statoil. the long-term support of danish geological research by these funding bodies and companies is gratefully acknowledged. we are also indebted to a long list of international referees; their contribution is acknowledged elsewhere but their importance in upholding the international standard of the papers bears repetition. during the scientific and technical editing phase, we have leaned heavily on three key personnel: hanne b. sørensen, who converted editorial hieroglyphics into ordered manuscripts; birgit eriksen, who meticulously checked final manuscripts and proof copies; and stefan sølberg whose skilled graphical imprint is engraved on almost every illustration in the book. on editorial matters, we have also benefited greatly from close co-operation with peter r. dawes and esben w. glendal in the editorial office at geus. in the latter stages we have been increasingly reliant on the professional layout work by carsten e. thuesen. to all the above, we offer our heartfelt thanks. jon r. ineson finn surlyk on behalf of the ‘jurassic book’ convening group: jon r. ineson, finn surlyk, karen dybkjær, lars. h. nielsen, niels e. poulsen. references callomon, j.h. & donovan, d.t. 1974: a code of mesozoic stratigraphic nomenclature. in: colloque du jurassique à luxembourg 1967. mémoire du bureau de recherches géologiques et minières 75, 75–81. gradstein, f.m., agterberg, f.p., ogg, j.g., hardenbol, j., van veen, p., thierry, j. & huang, z. 1994: a mesozoic time scale. journal of geophysical research 99, 24051–24074. haq, b.u., hardenbol, j. & vail, p. 1988: mesozoic and cenozoic chronostratigraphy and cycles of sea-level change. in: wilgus, c.k. et al. (eds): sea-level changes – an integrated approach. society of economic paleontologists and mineralogists special publication 42, 71–108. harland, w.b., armstrong, r.l., cox, a.v., craig, l.e., smith, a.g. & smith, d.g. 1990: a geologic time scale 1989, 263 pp. cambridge: cambridge university press. salvador, a. (ed.) 1994: international stratigraphic guide. a guide to stratigraphic classification, terminology, and procedure, 2nd edition, 214 pp. boulder, colorado: international union of geological sciences and geological society of america, inc. 8 geological survey of denmark and greenland bulletin 38, 2017, 49-52 49 the onshore nuussuaq basin in west greenland is important for hydrocarbon exploration since many of the key petroleum systems components are well exposed and accessible for study. the basin has thus long served as an analogue for offshore exploration. the discovery of oil seeps on disko, nuussuaq, ubekendt ejland, and svartenhuk halvø (fig. 1) in the early 1990s resulted in exploration onshore as well. in several wells, oil stains were observed in both the siliciclastic sandstone and in the volcanic series. an important aspect of any petroleum system is a high quality reservoir rock. the aim of this paper is to review petrophysical aspects of the reservoir potential of key stratigraphic intervals within the nuussuaq and west greenland basalt groups. reservoir parameters and porosity–permeability trends for potential siliciclastic and volcanic reservoirs within the relevant formations of the nuussuaq basin are discussed below. geological setting the nuussuaq basin formed in the cretaceous–palaeogene as part of a complex system of linked rift basins that developed along west greenland during the opening of the labrador sea and baffin bay (oakey & chalmers 2012). as a result of neogene uplift, the sediments and overlying palaeogene volcanic rocks are exposed on disko, nuussuaq, upernivik ø and svartenhuk halvø (fig. 1, dam et al. 2009). the sedimentary succession is interpreted as deposited in fluvial, delta, shelf and deep marine environments, and is divided into ten formations forming the nuussuaq group (fig. 2). the overlying west greenland basalt group (wgbg) includes subaerial lava flows and hyaloclastite breccias (larsen et al. 2016). a companion paper to this contribution (sørensen et al. 2017, this volume) provides additional information regarding the structural development and potential source rock distribution of the nuussuaq basin. potential hydrocarbon reservoirs of albian–paleocene age in the nuussuaq basin, west greenland morten l. hjuler, niels h. schovsbo, gunver k. pedersen and john r. hopper halvø ubekendt ejland uummannaq d i s k o n u u s s u a q upe rniv ik ø ik kq it gro gw gt fp93 ma um fp94 ak gk ge pk an ki qi ikka rk uk ak pi well outcrop nuussuaq group quarternary units basement ice sheet fault oil shows west greenland basalt group formationoutcrop member ki ka atane kangilia kingittoq kangilia kingittoq annertuneq congl. pi ak ik ggu247801 ikorfat fault 566 m atane cores formation logswell faults atanepingu skansen ak fp93 it fp93-3-1 itilli fault zone 139 m atane kangiliaataata kuua qilakitsoq fp94 kq fp94-11-04 kuugannguaq-qunnilik fault 340 m itilli qi rk ge gane-1/1a 631 m agatdal+vaigat core logs atane atane qilakitsoq ravn kløft qilakitsoq ravn kløft+kingittoq gk gank-1 364 m kangilia+vaigat gro gro-3 itilli+kangilia+ well logs pk gt gant-1 891 m itilli+kangilia itillipingunnguup kuua anariartorfik an ik gw ganw-1 199 m vaigat agatdal+vaigat itilli atane anariartorfik ikorfat anariartorfik ravn kløft+kingittoq uk ma marraat-1 448 m vaigat well logs itilliukalersalik anariartorfik um umiivik-1 1200 m itilli+kangilia greenland 20 km20 km 54°w 71 ° 70 °3 0' 70 °n 71 °3 0' n svartenhuk 52°w eastern limit of n uussuaq basin eastern limit of n uussuaq basin fig. 1. geological map of the study area showing well and outcrop locations. abbreviations of outcrop, well and fault names are explained to the right, where lithostratigraphic units occurring at outcrops and wells are also listed. © 2017 geus. geological survey of denmark and greenland bulletin 38, 49–52 . open access: www.geus.dk/publications/bull 5050 lithology and distribution of relevant formations the atane formation is known from the eastern part of the nuussuaq basin east of the kuugannguaq–qunnilik fault, (kq fault, figs 1, 2). the formation is up to 800 m thick in individual outcrops and consists of delta deposits, which include laterally extensive sandstone sheets (dam et al. 2009). the mudstone-dominated, marine itilli formation (fig. 2) is known from northern and western nuussuaq (west of the ikorfat fault) and is more than 2.5 km thick (sønderholm & dam 1998). the umiivik member crops out in northern nuussuaq between the ikorfat and the itilli faults (fig. 1), whereas the anariartorfik member crops out west of the kq fault. the up to 438 m thick marine kangilia formation (fig. 2) crops out on northern nuussuaq between the ikorfat and itilli faults (fig. 1) and has been drilled in the gant-1 and gro-3 wells. it has also been measured in an outcrop on southern nuussuaq. mudstones dominate in the outcrops while sandstones dominate in the wells. the annertuneq conglomerate member mainly comprises conglomerates and sandstones (dam et al. 2009). the sub-marine to marine agatdal formation (fig. 2) is known from the agatdal area on central nuussuaq west of the ikorfat fault as well as from the gro-3 well west of the k–q fault (fig. 1). the formation is up to 148 m thick and consists of mudstones, sandstones and conglomerates (dam et al. 2009). the volcanic vaigat formation (fig. 2) is up to 1600 m thick in western nuussuaq and northern disko and increases to at least 5 km in thickness on ubekendt ejland (larsen et al. 2016). the lower part of the formation is dominated by hyaloclastic breccias that are overlain by lava flows. methods ten wells and eight sedimentary outcrop successions located in the nuussuaq basin and described by sønderholm & dam (1998) and dam et al. (2009) were analysed to quantify the sandstone component of the siliciclastic formations of the nuussuaq group. all sandstone intervals were defined as potential sandstone reservoirs and expressed as the cumulative sandstone thickness of a formation. potential reservoir content was defined as the cumulative sandstone thickness divided by formation thickness. the cumulative sandstone thickness in outcrops and wells was estimated from sedimentological logs and core descriptions. mudstones and heteroliths were classified as non-reservoir lithologies and included in the term ‘shale’. in the uncored gro-3 well, sandstone content was determined from wire-line logs and implies a shale content of 0–15%. five wells containing volcanic successions of the wgbg were analysed to identify potential reservoir sections within the hyaloclastite successions. these were quantified as the cumulative thickness of hyaloclastite breccias. lava flows were classified as non-reservoirs. porosity–permeability trends were established for the gane-1/1a, gant-1 and marraat-1 wells based on core analysis data. the porosity of the clastic formations in gro-3 was calculated from the density wire-line log. sandstones with porosities >10% are referred to as porous sandstones. a porosity log of the gane-1/1a well was generated from gamma-ray and density logs obtained from core scans. maligât u pe rn iv ik n æ s slibestensfjeldet kome atane itilli agatdal vaigat kangilia eqalulik atanikerluk wgbg quikavsak n uu ss ua q g ro up a lb ia n dan. pa le oc en e u pp er c re ta ce ou s lo w er c re ta ce ou s cen. tur. maas. se la nd ia n cam. san. con. w el l o ut cr opseries stage group formation member skansen ravn kløft kingittoq qilakitsoq aaffarsuaq anaanaa naujánguit ordlingassoq annertuneq conglomerate anariartorfik umiivik kussinerujuk fig. 2. lithostratigraphic scheme of the nuussuaq group and the lowermost part of the west greenland basalt group (wgbg). members studied here are indicated to the far right. modified from dam et al. (2009). 0 100 200 300 400 500 c um ul at iv e sa nd st on e th ic kn es s (m ) 0 500 1000 1500 2000 formation thickness (m) 10% sa ndston e 50 % sa nd sto ne 10 0% s an ds to ne 25% san dst one agatdal fm kangilia fm itilli fm atane fm fig. 3. formation thickness versus cumulative sandstone thickness, data from the analysed wells and outcrops in the nuussuaq basin. 51 reservoir properties of formations containing potential hydrocarbon reservoirs potential reservoirs were identified within sandstones of the atane, itilli, kangilia, and agatdal formations and hyaloclastite breccias of the vaigat formation (fig. 2). the main reservoir parameters including cumulative reservoir thickness (crt), potential reservoir content (prc) and porosity–permeability data are summarised below, with details in the electronic supplement (es). atane formation. crt is in the range 26–360 m corresponding to a prc of 45–80% (fig. 3 and es). the reservoir quality is well developed in central nuussuaq with sandstone porosities of 5‒25% (mean 17%) and air permeabilities of 0.5‒150 md (appel & joensen 2014). itilli formation. crt is in the range 21–458 m corresponding to a prc of 2–51% (fig. 3 and es). the relatively low content of potential sandstone reservoirs compared to the atane, kangilia and agatdal formations reflects significant variations within and between the members of the itilli formation. in the gro-3 well, the individual sandstone units are up to 100 m thick and average porosity is 4%. kangilia formation. crt is in the range 0–134 m corresponding to a prc of 0–72% indicating significant lateral variation in depositional environments (fig. 3 and es). in the mudstone-dominated successions, the annertuneq conglomerate member constitutes a potential reservoir. in the gro-3 well, porosities range between 5–17% (average 6%). agatdal formation. crt is in the range 71–148 m corresponding to a prc of 50–67% (fig. 3 and es). porosities of 6–21% and permeabilities up to 9 md were measured in the gane-1 well (fig. 4), and in the gro-3 well, an average formation porosity of 9% was assessed. vaigat formation. several oil shows have been encountered in the hyaloclastites and lava flows. only the hyaloclastites seem to possess the necessary permeability to constitute a reservoir despite indications of lower average porosities (6%) than the lava flows (8%). for identical porosity values, the permeability is 30 times higher for the hyaloclastites compared to the lava flows (fig. 4). the crt of the hyaloclastites is in the range 80–671 m corresponding to a prc of 84–100% (fig. 2 and es). porosity–permeability relations of potential reservoirs the regional distribution of porosity and permeability in the nuussuaq basin deposits is poorly known due to the scarcity of core measurements or studies concerned with the effects of diagenesis on reservoir quality (kierkegaard 1998). one relatively swift way of improving the porosity database is by using core scans to generate a porosity log (pedersen et al. 2013). this is shown for the agatdal formation in gane-1/1a in fig. 5. the core log-generated 0.01 0.1 1 10 100 a ir p er m ea bi lit y (m d ) 0 5 10 15 20 he porosity (%) trend a trend b marraat-1 wells formations gane-1/1a gant-1 agatdal fm vaigat fm (lava flows) kangilia fm vaigat fm (hyaloclastite) itilli fm oil shows gas fig. 4. helium porosity and air permeability for selected wells. oil shows are abundant along trend a (hyaloclastite reservoirs). both oil and gas shows occur in the lava f lows (trend b). the siliciclastic samples generally plot between the two trends. oil gas 600 650 700 depth (m) porosity (%) air permeability (md) core gamma ray (api) 0 5 10 10 0 200 400 600 80010.10.012015 sandstone shale intrusive rock core analysis core log-porosity core gamma ray gane-1/1a gane-1 gane-1a lithologyshowscore and log measurements, agatdal fm fig. 5. stratigraphical variation of lithology, porosity and permeability within the agatdal formation in the gane-1/1a well. 5252 porosity curve fits nicely with the core measurements and the core log-derived lithology corresponds well with the lithological log from dam et al. (2009). core analysis data from the marraat-1, gane-1/1a, and gant-1 wells were used to outline porosity–permeability trends within the siliciclastic and volcanic successions (fig. 4). in the siliciclastic reservoirs, the porosity and permeability data show a high degree of scatter and no consistent trend can be identified. the large range in porosity and permeability values probably reflects variations in grain size and diagenesis. a large part of the porosity in the gant-1 sandstones is secondary and related to dissolution of detrital feldspar grains (kierkegaard 1998). the hyaloclastite samples show a relatively high permeability–porosity ratio (trend a in fig. 4) compared to the lava flows (trend b in fig. 4). at 10% porosity, the expected permeability is 5 md for hyaloclastites, but only 0.8 md for lava flows, a tendency assumed to reflect textural control on permeability. in hyaloclastites, a network of connected pores ensures fluid or gas flow, whereas the isolated pore systems in lava flows strongly impede permeability, even at high porosity. conclusions the onshore nuussuaq basin in west greenland contains potential hydrocarbon reservoirs within the siliciclastic atane, itilli, kangilia and agatdal formations, and within the hyaloclastite intervals of the vaigat formation. the siliciclastic reservoirs occur in a wide range of geological environments from fluvial over deltaic to slope and marine settings. the potential reservoir sandstone content is generally more than 50% for the sections studied from the atane, kangilia and agatdal formations, but significantly lower in the itilli formation. the cumulative sandstone thickness is mostly >100 m for all formations, including the itilli formation. porosity and permeability data suggest that sandstone and hyaloclastite reservoirs may be of good quality with porosities up to 20%. permeabilities are mostly below 10 md. however, porosity and permeability data are restricted to the western part of nuussuaq and the diagenetic control on the reservoir quality is poorly understood regionally. acknowledgements this contribution is partly the result of a project funded by the ministry of mineral resources, greenland. references appel, a.u. & joensen, i.á. 2014: prograderende deltaaf lejringer fra øvre kridt, atane formationen, nuussuaqbassinet, centrale vestgrønland. unpublished bachelor thesis, department of geosciences and natural resource management, university of copenhagen, 49 pp. dam, g., pedersen, g.k., sønderholm, m., midtgaard, h., larsen, l.m., nøhr-hansen, h. & pedersen, a.k. 2009: lithostratigraphy of the cretaceous–paleocene nuussuaq group, nuussuaq basin, west greenland. geological survey of denmark and greenland bulletin 19, 171 pp. kierkegaard, t. 1998: diagenesis and reservoir properties of campanian – paleocene sandstones in the gant#1 well, western nuussuaq, central west greenland. geology of greenland survey bulletin 180, 31–34. larsen, l.m., pedersen, a.k., tegner, c., duncan, r.a., hald, n. & larsen, j.g. 2016: age of tertiary volcanic rocks on the west greenland continental margin: volcanic evolution and event correlation to other parts of the north atlantic igneous province. geological magazine 153(3), 487–511. oakey, g.n. & chalmers, j.a. 2012: a new model for the paleogene motion of greenland relative to north america: plate reconstruction of the davis strait and nares strait regions between canada and greenland. journal of geophysical research 117, 1–28. pedersen, g.k., schovsbo, n.h. & nøhr-hansen, h. 2013: calibration of spectral gamma-ray logs to deltaic sedimentary facies from the cretaceous atane formation, nuussuaq basin, west greenland. geological survey of denmark and greenland bulletin 28, 65–68. sønderholm, m. & dam, g. 1998: reservoir characterisation of western nuussuaq, central west greenland. danmarks og grønlands geologiske undersøgelse rapport 1998/6, 36 pp. sørensen, e.v., hopper, j.r., pedersen, g.k., nøhr-hansen, h., guarnieri, p., pedersen, a.k. & christiansen, f.g. 2016: inversion structures as potential petroleum exploration targets on nuussuaq and northern disko, onshore west greenland. geological survey of denmark and greenland bulletin 38, 45–48. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen, k, denmark. e-mail: mlh@geus.dk geological survey of denmark and greenland bulletin 41, 2018, 79-82 79 the greenland ice sheet has experienced an average mass loss of 142 ± 49 gt/yr from 1992 to 2011 (shepherd et al. 2012), making it a significant contributor to sea-level rise. part of the icesheet mass loss is the result of increased dynamic response of outlet glaciers (rignot et al. 2011). the ice discharge from outlet glaciers can be quantified by coincident measurements of ice velocity and ice thickness (thomas et al. 2000; van den broeke et al. 2016). as part of the programme for monitoring of the greenland ice sheet (promice; ahlstrøm et al. 2008), three airborne surveys were carried out in 2007, 2011 and 2015, with the aim of measuring the changes in greenland ice-sheet thicknesses. the purpose of the airborne surveys was to collect data to assess the dynamic mass loss of the greenland ice sheet (andersen et al. 2015). here, we present these datasets of observations from ice-penetrating radar and airborne laser scanning, which, in combination, make us able to determine the ice thickness precisely. surface-elevation changes between surveys are also presented, although we do not provide an in-depth scientific interpretation of these. instrumentation all three surveys were conducted using the same air greenland/norlandair de havilland dhc-6 twin otter aircraft, currently registered as tf-pof. this twin otter has been modified in such a way that part of the fuselage can be removed in the rear cargo hole providing an unobstructed view of the surface below the aircraft when airborne. the precise position of the aircraft (and instruments) is tracked by three geodetic dual-frequency gps receivers each connected to one of two gps antennas mounted on top of the aircraft. the orientation of the instruments is monitored by an inertial navigation system (ins). the primary ins is of the type honeywell h-764g. during the last two f lights, we also installed a back-up ins of the type oxts inertial+2. for measuring snowor ice-surface elevations, a near infrared, airborne laser scanner (als; forsberg et al. 2001) was mounted in the rear cargo hole, alongside the inss. the als f lown on the twin otter in 2007 was of the type riegl lms-q140i-60, which was upgraded to a riegl lms-q240i in 2011 and 2015. in 2007 and 2011, a 60 mhz coherent ice-penetrating radar, developed at the technical university of denmark (dtu), was also mounted to measure bedrock topography (christensen et al. 2000). survey design the survey f light path was designed as a polygon to encircle the entire greenland ice sheet where the surface of the ice circum-greenland, ice-thickness measurements collected during promice airborne surveys in 2007, 2011 and 2015 louise sandberg sørensen, sebastian b. simonsen, rené forsberg, lars stenseng, henriette skourup, steen savstrup kristensen and william colgan 2 km b 800 m ice surface bedrock transmit pulse 70.35 70.34 70.33 70.32 70.31 70.30 30.920 30.910 30.900 30.890 2400 2392 2384 2376 2368 2360 2352 2344 a la tit ud e (n or th ) longitude (west) el ev at io n (m ) fig. 1. a: example of full-resolution versus reduced-resolution (circles) airborne laser scanner (als) data. b: example of radargramme with a clear bedrock ref lector. © 2018 geus. geological survey of denmark and greenland bulletin 41, 79–82 . open access: www.geus.dk/bulletin http://www.geus.dk/bulletin 8080 is at an elevation of c. 1700 m above sea level, as well as to include survey lines over the centerline of several main outlet glaciers. the surveys have been carried out at four-year intervals (2007, 2011 and 2015). the planned f light path in 2007 left a data gap on the east coast (from c. 72n to c. 74n) which was bridged during the 2011 and 2015 surveys. all three surveys were planned to be carried out in august, as this timing represents the end of the melt season and ensures that the changes observed in surface elevations are not affected by individual accumulation events. due to bad weather conditions in august 2015, half of the survey (the part from constable pynt in east greenland clockwise to kangerlussuaq in west greenland) was carried out in october. the late acquisition of these data thus results in a potential bias of individual accumulation events due to snowfall in this dataset compared to the surveys in 2007 and 2011. as the f light path from 2011 was repeated in 2015, and since the bedrock elevation is not expected to change within this time frame, it was decided not to utilise the ice-penetrating radar on the last survey in 2015. surface-elevation data the als operates in the near-infrared wavelength band, which is ref lected from the snow or ice surface. this means that data can only be acquired during periods without clouds or fog below the aircraft. the sampling frequency of the als instrument is 10 khz, resulting in 40 across-track scan lines per second. each of these scan lines consists of 250 individual elevation measurements on-ground. the scan angle of 60° and the typical f light height of c. 300 m result in a swath width on ground of c. 300 m with c. 1 m resolution. the processing of the als data combines the raw als data with the positioning data from the gps and altitude data from the ins. post-processing of the data includes visual inspection to filter out laser ref lections from clouds. the positional uncertainty in both latitude and longitude is estimated to be ± 1 m, while the elevation uncertainty is estimated from track cross-over differences to be ± 0.05 to 0.1 m over f lat surfaces. to reduce the file size and to create a dataset which is more comparable to the resolution of the bedrock data, the full-resolution als data have been reduced to a spatial resolution of c. 100 m. this has been done through simple averag30°w50°w 60°n 65°n 70°n 75°n 80°n 80°n 30°w50°w 60°n 65°n 70°n 75°n 80°n 80°n n –500 –250 0 250 500 750 1000 1250 1500 bedrock elevation (m) 3000 2500 2000 1500 1000 500 surface elevation (m) 2011 500 km 2011 500 km fig. 2. a: surface elevations along the promice circum-greenland f lights in 2011. b: bedrock elevations along the promice circum-greenland f lights in 2011. 81 ing of available height measurements along and across track. an example of full-resolution versus reduced-resolution data is shown in fig. 1a. the data are compiled in one file per year (als_ yyyy.ave) and can be downloaded from http:// promice.dk/downloadairborne.html. as an example, the elevations from 2011 are shown in fig. 2a. bedrock-elevation data the ice-penetrating data acquisition consists of transmitting pulses at a pulse repetition frequency of 10 khz (i.e. sampling in the f light direction) and sampling the returned echo at 75 mhz, which results in 4096 samples per transmitted pulse. while internal scattering masks the desired echo, ref lection and absorption within the ice sheet reduce the strength of the returned echo. substantial processing is therefore carried out to produce a radargramme that enhances the detection of the echo from the bottom of the ice-sheet. a semi-automatic layer detection program is used to digitalise the surface and bedrock layers individually. in some areas, primarily near the ice margin in south greenland, the radar was not able to detect the bedrock due to heavily crevassed ice or water present within the ice. figure 1b shows a good example of a radargramme where a bottom echo was obtained. based on radar system setup, vertical uncertainty in radar-derived icesheet bed elevation is estimated to be ± 35 m, which is confirmed by the cross-over differences between the two surveys. the data are compiled in one file per year (ars_ yyyy. ave), which is also available for download from http://promice.dk/downloadairborne.html. as an example, the bedrock elevations from 2011 are shown in fig. 2b. surface-elevation changes having three surveys of surface elevations spanning eight years enables us to derive and analyse surface elevation changes along the f light lines. in fig. 3, we show the mean annual surface-elevation changes between august 2007 and august/october 2015. the map was generated by computing height differences between any points in the two (reduced resolution) datasets for the two years. height differences are computed only if the points are located not more than 200 m apart. by knowing the exact date of the survey, the rate of surface-elevation change can be computed. in the map in fig. 3, the part that was only f lown in 2007 is plotted with black, while the parts only surveyed in 2015 are shown in grey. there are some clearly visible gaps: one leg of the f light line is missing in north-eastern greenland from nioghalvfjerdsfjorden to hagen bræ and similarly and a part of the line is also absent south of jakobshavn isbræ. the gap in the north is caused by gaps in the 2015 dataset due to time and weather constraints. the gap south of jakobshavn isbræ is due to cloud cover in 2007. figure 3 shows that the mean annual elevation changes in the period 2007–2015 is clearly dominated by thinning with some main outlet glaciers such as jakobshavn isbræ and kangerlussuaq gletscher thinning rapidly. only a few places along the f light line are associated with thickening, e.g. at storstrømmen. the sections of the f light path in the southeastern parts that actually show modest thickening might be a result of accumulation since these parts of the 2015 survey were mapped in october after some snowfall in the area. elevation change data, such as presented here, are scientifically very valuable e.g. to validate satellite data and ice-sheet models. furthermore, the data presented here represens an important supplement to the heights and height differences 2 1 2.0 1.5 1.0 0.5 0.0 –0.5 –1.0 –1.5 –2.0 surface elevation change (m/yr) 30°w50°w 60°n 65°n 70°n 75°n 80°n 2007–2015 500 km 80°n 1 4 7 6 3 5 fig. 3. mean annual surface-elevation changes between 2007 and 2015 along the promice circum-greenland f light-paths. the part of the f light track for which only 2007 data are available is indicated in black, while 2015-only is indicated in grey. 1: nioghalvfjerdsfjorden. 2: storstrømmen. 3: constable pynt. 4: kangerlussuaq gletscher. 5: kangerlussuaq. 6: jakobshavn isbræ. 7: hagen bræ. http://promice.dk/downloadairborne.html http://promice.dk/downloadairborne.html http://promice.dk/downloadairborne.html http://promice.dk/downloadairborne.html 8282 available from the nasa operation icebridge field surveys (krabill et al. 2009; krabill 2014) as the f light lines cover different areas, and also our measurements are made at the end of the melt season while operation icebridge data are collected mainly in the spring. comparison to bedmachine v3 bedrock elevations the bedrock elevation dataset described above also represents a valuable legacy dataset that can be used by a wider scientific community. knowledge of bedrock elevations in greenland is essential in, e.g. ice-discharge studies and ice-sheet modelling. one widely used bedrock topography model is the one available in bedmachine v3 (morlighem et al. 2017) which is based on the conservation of mass and constrained by available measurements. the bedmachine v3 model is provided together with an error map, which shows how the error increases with increasing distance to measurement points. to evaluate whether the promice dataset can potentially contribute to an improvement of the bedmachine model in the future, we have extracted the bedmachine error values for all the 2007 and 2011 bedrock elevations in the promice datasets. the two corresponding histograms in fig. 4 show that in c. 50% of the data locations the error in the bedmachine v3 model is greater than 100 m, indicating that the promice dataset with an uncertainty of ± 35 m could indeed contribute positively to a future, improved version of the model. it may also be noted that only 25% of the bedmachine data are related with similar or lower errors than the promice dataset. acknowledgements this is a publication in the framework of the programme for monitoring of the greenland ice sheet (promice) – a danish government initiative funded through the danish cooperation for environment in the arctic (dancea). references ahlstrøm, a. & the promice team 2008: a new programme for monitoring the mass loss of the greenland ice sheet. geological survey of denmark and greenland bulletin 15, 61–64. andersen, m. et al. 2015: basin-scale partitioning of greenland ice sheet mass balance components (2007–2011). earth and planetary science letters 409, 89–95. christensen, e.l., reeh, n., forsberg, r., jørgensen, j.h., skou, n. & woelders, k. 2000: a low-cost glacier-mapping system. journal of glaciolog y 46, 531–537. forsberg, r., keller, k. & jacobsen, s.m. 2001: laser monitoring of ice elevations and sea-ice thickness in greenland. international archives of photogrammetry and remote sensing 34, 163–168. krabill, w.b. 2014: icebridge atm l2 icessn elevation, slope, and roughness. boulder, colorado, usa. http://nsidc.org/data/ilatm2. html (nasa distributed active archive center at the national snow and ice data center). krabill, w.b. et al. 2009: operation ice bridge =verview and results from aircraft laser altimetry. american geophysical union, fall meeting 14–18 december 2009. san francisco: abstract 3 pp. morlighem, m. et al. 2017: bedmachine v3: complete bed topography and ocean bathymetry mapping of greenland. from multibeam echo sounding combined with mass conservation. geophysical research letters 44, 11051–11061, http://dx.doi.org/10.1002/2017gl074954 rignot, e., velicogna, i., van den broeke, m.r., monaghan, a. & lenaerts, j.t. 2011: acceleration of the contribution of the greenland and antarctic ice sheets to sea level rise.  geophysical research letters  38, l05503. shepherd, a. et al. 2012: a reconciled estimate of ice-sheet mass balance. science 338, 1183–1189. thomas, r.r., akins, t., csatho, b., fahnestock, m., gogineni, p., kim, c. & sonntag, j. 2000: mass balance of the greenland ice sheet at high elevations. science 289, 426–428. van den broeke, m.r., enderlin, e.m., howat, i.m., kuipers munneke, p., noël, b.p.y., van de berg, w.j., van meijgaard, e. & wouters, b. 2016: on the recent contribution of the greenland ice sheet to sea level change. the cryosphere 10, 1933–1946. http://dx.doi.org/10.5194/tc10-1933-2016 c ou nt s 0 100 200 300 400 500 2011 2007 error (m) 25 000 20 000 15 000 10 000 5000 0 30–40 m 40–100 m >100 m <30 m 24.4 8.8 50.0 16.8 fig. 4. histograms showing the errors of the bedmachine bed topography grid in all the points where promice bedrock elevation data are available. the grey area shows the <35 m interval (uncertainty in the bedrock data). the pie chart shows to what extent the bedmachine model error is 0–30 m, 30–40 m, 40–100 m and more than 100 m. authors’s addresses l.s.s., s.b.s., r.f., l.s. & h.s., technical university of denmark, dtu space, geodynamics department, dk-2800 kongens lyngby, denmark. e-mail: slss@space.dtu.dk. s.s.k., technical university of denmark, dtu space, microwave & remote sensing department, dk-2800 kongens lyngby, denmark. w.c., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. http://nsidc.org/data/ilatm2.html http://nsidc.org/data/ilatm2.html http://dx.doi.org/10.1002/2017gl074954 http://dx.doi.org/10.5194/tc-10-1933-2016 http://dx.doi.org/10.5194/tc-10-1933-2016 mailto:slss@space.dtu.dk 71 the arctic region is warming more rapidly than the global average (amap 2017) and it is well established that this warming is at least partially responsible for the greenland ice sheet losing mass at an accelerating rate, raising concern worldwide (e.g. kahn et al. 2015; rahmstorf et al. 2015). it is essential to monitor the changes of the greenland ice sheet to be able to assess the potential environmental, social and economic implications around the globe, and to provide decision-makers with reliable data. the annual mass-budget deficit of the greenland ice sheet has grown over the past two decades due to increases in surface melting (van den broeke et al. 2017) and ice-f low acceleration (kahn et al. 2015). currently, and for the last two decades, the greenland ice sheet is the single largest arctic cryospheric contributor to global sea-level rise and the greenland ice-surface melt rates are projected to increase as the arctic continues to warm (amap 2017). the snowline is here defined as the maximum elevation during the melt season at which snow remains from the previous accumulation season (cogley et al. 2011). the snowline is a valuable climate indicator as its position integrates the competing effects of melt (increasing snowline elevation) and snow accumulation (decreasing snowline elevation). thus the snowline provides a key holistic variable indicating climate change. we have developed a methodology that determines snowline elevation utilising the moderate resolution imaging spectroradiometer (modis) sensor on the terra satellite. the modis sensor produces a global dataset on a daily basis, with a resolution varying between 250 m and 1 km, in 36 bands covering the visible to thermal wavelengths. using modis, we derived the maximum snowline altitude for the greenland ice sheet for the years 2000–2017. we are producing a freely available, consistent dataset that provides an important tool for the monitoring of the long-term impact of climate change on the greenland ice sheet. direct comparison with field observations from automatic weather stations (awss) from the programme for monitoring of the greenthe greenland ice sheet – snowline elevations at the end of the melt seasons from 2000 to 2017 robert s. fausto and the promice team* * signe b. andersen, andreas p. ahlstrøm, dirk van as, jason e. box, daniel binder, michele citterio, william colgan, konstanze haubner, karina hansen, nanna b. karlsson, kenneth d. mankoff, allan ø. pedersen, anne solgaard and baptiste vandecrux 500 km thu upe kpc tas kan nuk sco qas egp land 185.3 370.6 555.9 741.2 926.5 1112 1297 1482 1668 1853 2038 2224 2409 2594 2779 2965 3150 snowline 2016 promice gimp dem fig. 1. greenland map showing the location of promice automatic weather stations and the 2016 snowline as derived from terra satellite data using the moderate resolution imaging spectroradiometer (modis) sensor. the locations of the ground-control automatic weather stations (promice) are indicated. egp: east grip. k an: kangerlussuaq. kpc. kronprins christian land. nuk: nuuk. qas: qassimiut. sco: scoresby sund. tas: tasiilaq. thu: thule. upe: upernavik. dem: digital elevation model. gimp: greenland ice mapping project. © 2018 geus. geological survey of denmark and greenland bulletin 41, 71–74. open access: www.geus.dk/bulletin http://www.geus.dk/bulletin 7272 land ice sheet (promice) network validates the snowline dataset derived from modis. we use the services of the cryoclim internet portal, providing an operational and permanent service for long-term systematic climate monitoring of the cryosphere, to distribute our snowline product. more specifically, end-of-melt season, 1 km2 resolution raster grids illustrating snow and bare-ice surfaces, and snowline shape files can be downloaded via cryoclim. here, we describe the snowline classification algorithm, its validation and its interannual variations for 18 years spanning 2000–2017. snowline classification algorithm we processed all modis mod12km and mod03 scenes covering greenland from late july to the beginning of september 2000–2017. we used the surface-type detection algorithm of fausto et al. (2015) that distinguishes between bareice and snow surfaces. fausto et al. (2015) uses normalised thresholds (th) from calibrated radiances (mod021km) between the near-infrared band 5 (1230–1250 nm) and the visible band 10 (483–493 nm) with surface-type thresholds th dry snow ≤0.86, 0.86<th melting snow <0.94 and th glacier ice ≥0.94. the classification algorithm is updated by implementing a new surface-type threshold to address a ‘noisy’ snow classification over the northern part of the ice sheet identified by fausto et al. (2015). the algorithm is thus supplemented by th bare ice >265–2.1×lat, where lat is latitude. th bare ice is defined as: t h b a r e i c e = c 0 + c 1 × b 1+ c 2 × b 2 + c 3 × b 3 + c 5 × b 5 + c 7 × b 7 where c0=–0.0015, c1=0.160, c2=0.291, c3=0.243, c5= 0.112, c7=0.081 and b1 to b 7 designate band 1 to band 7. cloud-covered regions are removed using the mod35_l2 dataset. subsequently pixels are classified for every modis scene as either snow or bare ice for the whole greenland ice sheet. daily classification scenes are aggregated to yield a maximum extent of bare ice to define an end-of-melt-season snowline. snowlines from peripheral glaciers are generally excluded, and the snowline products are based on an algorithm success rate of over 95% classified pixels. validation to help validate the modis data we make use of the promice automatic weather station network that currently consists of two or three stations primarily in the ablation area in eight ice sheet regions. each automatic weather station records a suite of meteorological and glaciological measurements, supplemented by e.g. surface-height changes due to accumulation or ablation (fig. 1; van as et al. 2016). to validate the classified snowline elevation at the end of the melt season, we use the mass-budget values from the promice weather stations (fig. 2; e.g. fausto et al. 2012) at different elevations to calculate the vertical surface mass-balance gradient for all eight promice transects to determine the equilibrium line altitude (ela, zero mass budget), for direct comparison with modis estimated snowline elevation (fig. 1). aws balance profiles from the upernavik region, and those indicating an ela above 2000 m are excluded as we find them unrealistic. the location of the upper aws should be close to the actual ela to get the best balance profiles. in total, we exclude 25% or 17 out of 67 balance profiles. fig. 2. south greenland promice automatic weather station at the end of the 2013 melt season. from the stakes to the left of the weather station, the amount of melt (c. 4 m) is directly visible. the melt is also measured with a pressure transducer system drilled into the ice. 73 figure 3 illustrates the performance of the modis end-ofmelt-season snowline algorithm for all promice regions in greenland. the correlation (r=90%, p=0.0001, n=50) and the root-mean-square error (rmse=200 m) are reasonable as the ela and snowline elevation can be different due to superimposed ice formation (cogley 2011). the mean difference between snowline altitude and ela is −104 m. results and discussion figure 1 illustrates the location of remotely sensed snowline plotted on top of the digital elevation model (dem) from the greenland ice mapping project (gimp, howat et al. 2014). the snowline is easily visible in the southern, western, and northern parts of greenland due to the relatively even terrain, while the snowline shows a more complicated pattern in the mountainous terrain in east greenland (fig. 1). the snowline separates bare ice from snow areas and can therefore be used to document the change in bare-ice areas. we find the extent of bare-ice exposure to be increasing in the period 2000–2017 at an average rate of c. 500 km2 per year (fig. 4), which roughly corresponds to the size of the danish island of bornholm. this increase in the bare-ice area is insignificant, but it demonstrates a small average gain of melt over accumulation since 2000. the increasing trend in the bare-ice area is consistent with increasing greenland mass loss due to surface processes (van den broeke et al. 2017). both independent, in situ observations (machguth et al. 2016) and remotely sensed observations (hall et al. 2012; tedesco et al. 2017) show that the greenland melt area is expanding to higher elevations. further, the increase in bare ice enhances the positive feedback mechanism of a darkening ice sheet surface (ice is darker than snow), which affects the surface mass and energy balance of the greenland ice sheet (box et al. 2012). figure 4 also illustrates the inter-annual variability of the 2000–2017 snowlines, which is highly dependent on the complicated seasonal weather systems around greenland. for instance, the below average snowline of the snowy year of 2016/2017 is consistent with positive albedo anomalies that reduced melting in 2017 (tedesco et al. 2017). uncertainties associated with the different surface-type detection are assessed with the elas derived from the aws surface mass-budget observations. figure 3 shows a significant correlation between the modis snowline and elas derived independently from promice awss. a reason for the difference between the two can be that the modis data have a spatial resolution of 1 km2, pan-ice sheet coverage and quasi-daily temporal coverage, while the footprints of the in situ measurements are small (5–50 m2), and surface patchiness is clear in aerial photography (stroeve et al. 2006). fausto et al. (2015) discuss an august anomaly in their monthly surface-type data set during the 2010–2014 period, illustrated by a noisy melting-snow classification in the northern ice sheet, which was most likely due to false classification. however, with the updated bare-ice threshold, we improve the detection of snow and ice surfaces (fig. 1), visualised by a less noisy snow classification of snow in the northern part of the ice sheet, resulting in a more reliable climate indicator for greenland. conclusions remotely sensed modis data can yield daily, automated classification of the greenland ice sheet surface type (snow and ice). validation indicates a high correlation (0.9) between modis-derived snowline altitudes and elas estimated from in situ measurements. the end-of-melt-season 1000 1500 1700 1500 1300 1100 900 700 500 automatic weather station ela (m a.s.l.) kpc sco tas qas nuk kan upe thusn ow lin e el ev at io n (m a .s. l.) 500 2004 2009 2014 190 000 170 000 150 000 130 000 110 000 90 000 70 000 year a re a (k m ) 1999 2 bare-ice area y = 504x – 879029 fig. 3. the end-of-melt-season snowline elevation for 2000 to 2017 from modis vs. the promice aws-derived equiblibrium line altitude (ela). the blue line gives the 1:1 relation. the locations of the promice automatic weather stations are shown in fig. 1. fig. 4. end-of-melt-season bare-ice area for the greenland ice sheet for the years 2000–2017. 7474 snowline is useful as an ice-sheet climate indicator for the competing processes of surface accumulation and ablation, quantified by an average annual increase of c. 500 km2 of the bare-ice area for the 2000–2017 period. acknowledgements the programme for monitoring of the greenland ice sheet (promice) is funded by the geological survey of denmark and greenland (geus) and the danish ministry of energ y, utilities and climate under the danish cooperation for environment in the arctic (dancea), and is conducted in collaboration with dtu space, denmark’s national space institute, and asiaq (greenland survey). the nuk and k an stations were/are (co-)funded by the greenland climate research centre (gcrc) and the greenland analogue project (gap), respectively. this study was funded by dk esa-prodex under the cryoclim project. references amap 2017: snow, water, ice and permafrost in the arctic (swipa) 2017, 269 pp. oslo: arctic monitoring and assessment programme (amap). box, j.e., fettweis, x., stroeve, j.c., tedesco, m., hall, d.k. & steffen, k. 2012: greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers. the cryosphere 6, 821–839. cogley, j.g., hock, r., rasmussen, l.a., arendt, a.a., bauder, a., braithwaite, r.j., jansson, p., kaser, g., moller, m., nicholson, l. & zemp, m. 2011: glossary of glacier mass balance and related terms. ihp-vii technical documents in hydrolog y 86, iacs contribution 2. paris: unesco-ihp. fausto, r.s., van as, d. & promice project team 2012: ablation observations for 2008–2011 from the programme for monitoring of the greenland ice sheet (promice). geological survey of denmark and greenland bulletin 26, 25–28. fausto, r.s. et al. 2015: greenland ice sheet melt area from modis (2000–2014). geological survey of denmark and greenland bulletin 33, 97–100. hall, d.k., comiso, j.c., digirolamo, n.e., shuman, c.a., key, j.r. & koenig, l.s. 2012: a satellite-derived climate-quality data record of the clear-sky surface temperature of the greenland ice sheet. journal of climate 25, 4785–4798. howat, i.m., negrete, a. & smith, b.e. 2014: the greenland ice mapping project (gimp) land classification and surface elevation datasets. the cryosphere 8, 1509–1518. http://dx.doi.org/10.5194/tc-8-15092014 khan, s.a., aschwanden, a., bjørk, a.a., wahr, j., kjeldsen, k.k. & kjær, k.h. 2015: greenland ice sheet mass balance: a review. reports on progress in physics 78, 046801, 26 pp. http://dx.doi.org/10.1088/00344885/78/4/046801 machguth, h., macferrin, m., van as, d., box, j.e., charalampidis, c., colgan, w., fausto, r.s., meijer, h.a.j., mosley-thompson, e. & van de wal, r.s.w. 2016: greenland meltwater storage in firn limited by near-surface ice formation. nature climate change 6, 390–393. http:// dx.doi.org/10.1038/nclimate2899 rahmstorf, s., box, j., feulner, g., mann, m., robinson, a., rutherford, s. & schaffernicht, e. 2015: exceptional twentieth-century slowdown in atlantic ocean overturning circulation. nature climate change 5, 475–480. http://dx.doi.org/10.1038/nclimate2554 stroeve, j.c., box, j.e. & haran, t. 2006: evaluation of the modis (mod10a1) daily snow albedo product over the greenland ice sheet. remote sensing of environment 105, 155–171. http://dx.doi. org/10.1016/j.rse.2006.06.009 tedesco, m., box, j.e., cappelen, j., fausto, r.s., fettweis, x., hansen, k., mote, t., sasgen, i., smeets, c.j.p.p., van as, d., velicogna, i. & van de wal, r.s.w. 2017: greenland ice sheet: contribution to the arctic report card 2017. van as, d., fausto, r.s., cappelen, j., van de wal, r.s.w., braithwaite, r.j., machguth, h. & promice project team 2016: placing greenland ice sheet ablation measurements in a multi-decadal context. geological survey of denmark and greenland bulletin 35, 71–74. van den broeke, m.r., box, j.e., fettweis, x., hanna, e., noël, b., tedesco, m., van as, d., van de berg, w.j. & van kampenhout, l. 2017: greenland ice sheet surface mass loss: recent developments in observation and modelling. current climate change reports 3, 345–356. http://dx.doi.org/10.1007/s40641-017-0084-8 authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: rsf@geus.dk. http://dx.doi.org/10.5194/tc-8-1509-2014 http://dx.doi.org/10.5194/tc-8-1509-2014 http://dx.doi.org/10.1088/0034-4885/78/4/046801 http://dx.doi.org/10.1088/0034-4885/78/4/046801 http://dx.doi.org/10.1038/nclimate2899 http://dx.doi.org/10.1038/nclimate2899 http://dx.doi.org/10.1038/nclimate2554 http://dx.doi.org/10.1016/j.rse.2006.06.009 http://dx.doi.org/10.1016/j.rse.2006.06.009 http://dx.doi.org/10.1007/s40641-017-0084-8 mailto:rsf@geus.dk geological survey of denmark and greenland bulletin 41, 2018, 17-20 17 in organic-rich shales, pores form during oil and gas genesis within organic matter (om) domains. the porosity thus differs markedly from that of conventional reservoir lithologies. here we present the first description of shale fabric and pore types in the lower palaeozoic shales on bornholm, denmark. the pores have been studied using the focused ion beam scanning electron microscope (fib-sem) technique, which allows for high resolution sem images of ion polished surfaces. shale porosity is influenced by many factors including depositional fabric, mineralogical composition, diagenesis and oil and gas generation (schieber 2013). here we discuss some of these factors based on a study of lower palaeozoic shale samples from the billegrav-2 borehole on bornholm (fig. 1) undertaken by henningsen & jensen (2017). the shales are dry gas-mature (2.3% graptolite reflectance; petersen et al. 2013) and have been extensively used as analogies for the deeply buried palaeozoic shales elsewhere in denmark (schovsbo et al. 2011; gautier et al. 2014). the danish lower palaeozoic shale gas play was tested by the vendsyssel-1 well drilled in northern jylland in 2015. gas was discovered within a c. 70 m thick gas-mature, organicrich succession (ferrand et al. 2016). however, the licence was subsequently relinquished, due to a too low gas content. the present study confirms a close similarity of pore development between the shales on bornholm and in the vendsyssel-1 indicating a high porosity within this stratigraphic level throughout the subsurface of denmark. however, the rather different development of porosity in the different shale units presents a hitherto neglected aspect of the palaeozoic gas play in denmark. methods ten samples were selected for thin section and nanoscopic pore analyses based on a screening of 30 samples from the billegrav-2 borehole (fig. 2). total organic carbon (toc) was determined by measuring co 2 evolved from the shale fabric and organic nanoporosity in lower palaeozoic shales, bornholm, denmark lucy malou henningsen, christian høimann jensen, niels hemmingsen schovsbo, arne thorshøj nielsen and gunver krarup pedersen denmark 50 km bornholm skåne sweden germany kattegat norwegian–danish basinringkøbing–fyn high a billegrav-2 vendsyssel-1 lower palaeozoic strata caledonian fr well ont jylland fig. 1. distribution of lower palaeozoic strata and wells mentioned in the text. modified from schovsbo et al. (2011). fig. 2. stratigraphy of the billegrav-2 core and overview of samples and fabric types. modified from schovsbo et al. (2011). facies associations in the interval 35–125 m are adopted from the billegrav-1 well described by pedersen (1989); above this level the association is based on the present text. as fm: alum shale formation. dicel: dicellograptus shale. k: komstad limestone. lenticular: lenticular clast-rich mudstone. lin: lindegård mudstone. lithostratigr: lithostratigraphy. l: læså formation. mudsh: mudshale. fabric types: see text. sandstone limestone grey shale m ud st on e le nt ic ul ar bi om ot tle d si ltri ch black shale thin section; observed fabric toc / porosity sample pe ri od a ss oc ia tio n m ud sh . a s fm o rd ov ic ia n si lu ri an c am br ia n depth (m) fabric k l li th os tr at ig r. li n ra st ri te s sh al e d ic el si lts ha le m ud st on e 0 25 50 75 100 125 li th ol og y © 2018 geus. geological survey of denmark and greenland bulletin 41, 17–20. open access: www.geus.dk/bulletin http://www.geus.dk/bulletin 1818 combustion of acid pre-treated samples at 1300°c. porosity was measured in a double-chambered helium porosimeter at the geological survey of denmark and greenland. thin sections with a thickness of about 20 µm were prepared by pelcon material & testing aps. the sem imaging of nano to microscale porosity was performed on cross-sections that were milled and surface polished using a focused ion beam (fib) at the technical university of denmark. in order to minimise erosion of the ion-cut surface, the selected crosssection site was protected with a 3 µm thick layer of platinium. no coating of the imaged surfaces was applied. results each of the stratigraphical units shows a statistically significant correlation between toc and porosity (fig. 3). the rastrites shale at 30–62 m in the borehole is the most porous shale and is characterised by the highest ratio between toc and porosity, whereas the alum shale is the least porous shale, characterised by the lowest ratio between toc and porosity (fig. 3). the dicellograptus shale plots between these trends together with samples from the upper 30 m of the rastrites shale (fig. 3). four shale fabrics are distinguished: (1) a dark-coloured mudstone fabric with high concentrations of om and pyrite, (2) a lenticular clast-rich mudstone fabric, (3) a silt-rich mudstone fabric and (4) a bio-mottled mudstone fabric. the dark-coloured mudstone fabric was observed in five samples and it is the dominant fabric in the alum shale. the fabric comprises a clay-dominated mudstone with variable siltcontent that sometimes contains sand-sized authigenic barite (fig. 4a). the dark colour is due to high contents of dispersed om and pyrite. this fabric is attributed to a generally slow settling of particles in a low-energy depositional environment. the lenticular, clast-rich mudstone fabric is seen in four samples from the alum and rastrites shales (fig. 2). the content of om and pyrite is highest in the dark grey samples and lowest in the pale grey samples (fig. 4a). the typical lenticular clasts range in size from 500 µm to more than 2 mm and are composed of clay and silt-sized material. on a macroscopic scale, the lenticular clasts create a laminated appearance to the shale. the clasts are interpreted as deposited during episodic increases in energy in an otherwise low-energy environment. the silt-rich mudstone fabric (fig. 4b) shows varying concentrations of disseminated silt grains and is observed in four samples from the rastrites shale (fig. 2). more dense accumulations of silt grains in laminae and streaks are typically carbonate cemented. the fabric is assumed to be connected to episodic higher-energy currents in the otherwise low-energy depositional environment. the bio-mottled mudstone fabric (fig. 4c) occurs in three samples from the dicellograptus and rastrites shales. the fabric contains low amounts of om that also tends to be irregularly distributed, both across and along the bedding planes. the distribution ref lects the activities of depositfeeding organisms. the fabric is interpreted as deposited in a more oxic marine environment characterised by low om levels and presence of infaunal organisms. pores related to the om vary from simple isolated pores to large pore populations with internally complex structures. isolated pores are usually discrete and equant in shape and can occur both widely disseminated and in more dense populations (figs 4d, e). they also occur in om occupying the space between individual pyrite crystals in framboids (figs 4f, g). the pore-size is usually <100 nm. more dense populations of <50 nm-sized, foam-like pores are also observed. this pore type seems to populate entire om domains, but may also be surrounded by non-porous zones in presumably coherent om domains. a third pore type consists of highly irregular pores with complex internal sub-parts (fig. 4h). this type has a stalactite-like texture with irregular and serrated internal pore surfaces and may have internal fibrous textures resembling wood wool. pores related to the inorganic particles are mainly associated with irregularly shaped grains of quartz and pyrite (fig. 4i). these pores usually appear as discontinuous slits along parts of the grain surface or as curved embayments into the fig. 3. total organic carbon (toc) content versus porosity. arrows represent positive correlation trends (significant at a calculated probability of 0.1) within the stratigraphical units. points in brackets represent data omitted in the correlations. data from vendsyssel-1 are wire-line, log-derived average values (ferrand et al. 2016). po ro sit y (v ol . % ) 0 0 2 4 6 8 alum shale dicellograptus rastrites 3–30 m rastrites 30–62 m billegrav-2: rastrites shale lindegård fm dicellograptus shale alum shale fm vendsyssel-1 (average values): dicellograptus to lower rastrites shale? alum shale formation ( ) toc (wt.%) 12108642 y = 4.5 + 1.8x; r2 = 0.3 y = 4.1 + 0.48x; r2 = 0.7 y = 2.7 + 0.61x; r2 = 0.7 y = 1.7 + 0.26x; r2 = 0.3( ) 19 grain, and they are up to several 100 nm long. other pore types primarily related to inorganic particles are dissolution pores that occur where matrix minerals have become partly dissolved (fig. 4i). this pore type occurs only along the edges of carbonate minerals, and the pores tend to be elongated and irregularly shaped. discussion the variable correlation between the toc content and porosity for the alum, dicellograptus and rastrites shales indicates that pores in both organic and inorganic matter contribute to the total porosity. within each shale unit the toc content correlates with porosity suggesting that pores hosted in organic matter are dominant in all units but with additional contributions from inorganic porosity. a higher contribution of inorganic interparticle pores is seen in the dicellograptus and rastrites shales that add to the overall more porous nature of these shales (fig. 3). the dicellograptus and rastrites shales belong to the mudstone and siltstone associations of pedersen (1989) whereas the alum shale belongs to the mudshale association (fig. 2) and apparently the lithofacies was the main controlling factor of the porosity development. sem images show that the porosity predominantly occurs within amorphous om domains intermingled with the inorganic matrix minerals, rather than as inter-particle pores between the matrix minerals. however, not all om domains contain pores and those that do exhibit considerable variation in quantity, distribution and size of pores. the presence of om in the interparticle spaces cannot be explained entirely by the processes of admixing and subsequent compactional deformation of organic and inorganic fig. 4. micrographs of different mudstone fabrics and pores recognised in the palaeozoic shales. a: dark coloured mudstone fabric intercalated with laminae of lenticular clast-rich mudstone fabric, 119.78–119.80 m (alum shale formation). b: silt-rich mudstone fabric with normal grading, 41.15–41.17 m (rastrites shale). c: biomottled mudstone fabric, presumably chondrites, 86.68–86.70 m (dicellograptus shale). organic pores: d: rounded pores, 74.77–75.01 m (dicellograptus shale). e: sub-rounded pores, 24.78–24.80 m (rastrites shale). f: subrounded to rounded pores in pyrite, 115.63–115.65 m (alum shale formation). g: subrounded to rounded pores in pyrite, 115.63–115.65 m (alum shale formation). h: irregularly shaped and complex pores, 24.78–24.80 m (rastrites shale). inorganic pores. i: irregularly shaped pores surrounding silt to clay-sized grains, 115.63–115.65 m (alum shale formation).  1 mm 1 mm 1 µm a c d g e h f i b 1 mm 500 nm 500 nm 500 nm 500 nm 500 nm 2020 particles (cf. kennedy et al. 2002). instead, it appears that secondary om migrated into interparticle spaces during maturation. this interpretation is supported by observations of well-connected viscous-like om domains, which fill the spaces between matrix minerals. the dominant clay mineral in all the samples is illite (cf. pedersen 1989), which was either a detrital mineral or formed after diagenetic transformation of smectite during burial maturation. it may be assumed that an early migration of secondary om occurred during the temperature interval, which matches the diagenetic transformation of the clay minerals. this relationship between secondary om and diagenetically formed illite was also observed by schieber (2013) in gas-mature samples from the devonian marcellus shale in north america. loucks et al. (2012) suggested that most smectite is transformed to illite during early catagenesis, which supports the observation of presumed migrated om as interparticle fill. comparison with vendsyssel-1 one of the discouraging results of the vendsyssel-1 well was the low porosity and the unfavourable pore distribution in the shales (ferrand et al. 2016). the average toc content and porosity in the vendsyssel-1 well are within the same range as those measured in the billegrav-2 core (fig. 3). sem images of the alum shale from the vendsyssel-1 well show both non-porous om in the mudstone fabric and porous om of presumed secondary origin intermingled with clay minerals (ferrand et al. 2016) similar to the observations from the billegrav-2 core. the similarity suggests that the lower palaeozoic shales known from bornholm are valid analogues for the deeply buried palaeozoic shales in denmark. however, the rather different porosity development in the individual shale units presents a hitherto neglected aspect of the palaeozoic gas play in denmark. conclusions the study shows that the porosities of the lower palaeozoic shales are related to both organic and inorganic matter. the dominating porosity types in all stratigraphical units are those observed within organic matter. a clear relationship between shale fabric and organic nanoporosity has been observed in the lower palaeozoic shales and this indicates that shale composition, depositional environment, and diagenesis have all inf luenced the porosity development. the toc : porosity relationships in the vendsyssel-1 well are nearly identical to those observed in shales from bornholm indicating a high porosity. the alum shale is a low porous but toc-rich shale whereas the two other shale units studied are low in toc but relatively porous. this observation adds another variable factor to the danish shale gas play (cf. gautier et al. 2014). acknowledgements louise belmonte, formerly at the technical university of denmark, is thanked for providing access to the fib-sem. this paper is a contribution to the geocenter denmark projects 5–2015 and 3–2017. references ferrand, j., demars, c. & allache, f. 2016: denmark – l1/10 licence relinquishment recommendations report. total e&p, memo 1–9 available from: http://www.ft.dk/samling/20151/almdel/ef k/bilag/353/1651289.pdf. verified 17.01.2018. gautier, d.l., schovsbo, n.h. & nielsen, a.t. 2014: resource potential of the alum shale in denmark. unconventional resources technolog y conference (urtec), 25–27 august 2014, denver colorado. spe2014-1931754-ms. 10 pp. henningsen, l.m. & jensen, c.h. 2017: a petrographic analysis of pores and their distribution in palaeozoic organic-rich shale (the alum shale formation, the dicellograptus shale, and the rastrites shale) from the billegrav-2 core, bornholm, denmark,110 pp. unpublished master thesis, university of copenhagen. geus report files 34178 and 34179). kennedy, m.j., pevear, d.r. & hill, r.j. 2002: mineral surface control of organic carbon in black shale. science 295, 657–660. loucks, r.g., reed, r.m., ruppel, s.c. & hammes, u. 2012: spectrum of pore types and networks in mudrocks and a descriptive classification for matrix-related mudrock pores. aapg bulletin 96, 1071–1098. pedersen, g.k. 1989: the sedimentolog y of lower palaeozoic black shales from the shallow wells skelbro-1 and billegrav-1, bornholm, denmark. bulletin of the geological society of denmark 37, 151–173. petersen, h.i., schovsbo, n.h. & nielsen, a.t. 2013: ref lectance measurements of zooclasts and solid bitumen in lower palaeozoic shales, southern scandinavia: correlation to vitrinite ref lectance. international journal of coal petrolog y 114, 1–18. schieber, j. 2013: sem observations on ion-milled samples of devonian black shales from indiana and new york: the petrographic context of multiple pore types. aapg memoir 102, 153–171. schovsbo, n.h., nielsen, a.t., klitten, k., mathiesen, a. & rasmussen, p. 2011: shale gas investigations in denmark: lower palaeozoic shales on bornholm. geological survey of denmark and greenland bulletin 23, 9–12. authors’ addresses l.m.h., energinet, tonne kjærsvej 65, dk-7000 fredericia, denmark; email: lucymalou@gmail.com. c.h.j., region sjælland, alleen 15, dk-4180 sorø, denmark. n.h.s. & g.k.p., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. a.t.n., department of geosciences and natural resource management, university of copenhagen. øster voldgade 10, dk-1350 copenhagen k, denmark. http://www.ft.dk/samling/20151/almdel/efk/bilag/353/1651289.pdf http://www.ft.dk/samling/20151/almdel/efk/bilag/353/1651289.pdf mailto:lucymalou@gmail.com e2019430303-01 characterisation of incinerator bottom ash from a danish waste-to-energy plant: a step towards closing the material cycle rune j. clausen*1, per kalvig1 and jonas nedenskov2 geus bulletin is free to individuals and institutions in electronic form. the author(s) retain copyright over the article contents. r esearch article | open access geus bulletin vol 43 | e2019430303 | published online: 20 december 2019 https://doi.org/10.34194/geusb-201943-03-03 cineration process and these are typically composed of silicarich melts with recognisable remnants of glassware, ceramics and metal fragments. the extreme heterogeneity among iba fragments is ref lected not only in their chemical composition, but also in their variable density, shape and size from 2000 mm to less than 1 mm (fig. 1). iba characteristics, including their physical form and chemical composition, are the result of a wide range of dynamic parameters. first, the composition of the input to the incinerators – the municipal solid waste – is physically and chemically heterogeneous and complex. further, the temperature and fugacity conditions in the oven chamber vary locally due to the design of the chamber as well as irregular local f lux-effects, generated by variations in the solid-waste input. all in all, iba should be considered a multi-commodity deposit, for which detailed characterisation of the constituent materials is key to revealing its resource potential. methods four iba samples were collected in duplicate from amager bakke plant each day for 30 consecutive days in november 2017 (series a–d, fig. 2). series d was preserved as an archive sample, and a, b and c were analysed for their composition. each sample weighed c. 15 kg, and the total sampled material weighed c. 1800 kg. representative sampling and physical characterisation representative sampling of such heterogeneous material is a serious challenge. for example, the iba is moving on a shaking belt and is not distributed evenly, iba is hot (around 50–100°c) and fragments can be very large. we attempted to overcome the challenges by sampling a cross-section with a steel shovel taking care to avoid subconsciously ‘fishing’ for the un sustainable development goal 12, regarding responsible production and consumption of raw materials, guides ongoing international efforts to enhance sustainability in all parts of the mineral sector. of particular interest, is improving the recyclability of secondary waste streams and thereby increasing the efficiency of recycling end-oflife products. municipal solid waste – residual waste from household and industry – constitutes one of these secondary streams. it is typically incinerated in waste-to-energy plants producing two types of waste streams that carry a raw material resource potential: incinerator bottom ash (iba) and incinerator f ly ash (ifa). iba is of particular interest in the recycling industry, where it is commonly recycled to produce three main fractions: (i) ferrous material, (ii) non-ferrous material, and (iii) residual slag. in most cases the two metal fractions are separated further downstream in the value chain, prior to smelting. the residual, non-magnetic fraction (typically 0–45 mm) is used mainly as construction aggregate. improvements in the efficiency of existing separation technologies are still being made, but less effort is focussed on characterising the fundamental composition and mineral resource potential of iba. for this reason, the urban-x project was launched by the geological survey of denmark and greenland (geus) to characterise the composition and resource potential of various waste streams at amager bakke waste-to-energy plant in copenhagen, denmark. this paper discusses some of the main outcomes of the urban-x project with respect to iba, and a full analysis of all waste streams analysed at amager bakke is available in clausen et al. 2019. incinerator bottom ash iba material consists of all the non-combustible components of domestic and industrial waste. it can include components such as construction steel, household glass fragments, toys, electronic devices, cans, batteries, sofa springs, and boulder size aggregates. some of the aggregates form during the inhttps://doi.org/10.34194/geusb-201943-03-03 e2019430303-02 particular pieces. fragments of up to c.  200 mm were sampled, though due to the sampling bias associated with large fragments (relative to the size of the sampler) among other things, only fragment sizes less than or equal to 63 mm were considered representatively sampled. to create four sample series (a–d) carrying the same 30-day representation, four samples was extracted immediately one after the other. for physical characterisation, we combined one series into a composite sample, which represented the average iba material collected during the 30 days of sampling (c series, fig 2). first, all fragments larger than 63 mm were removed by hand and ruler in preparation for the splitter, where each sample was divided to retrieve a representative subsample. combining all 30 subsamples of series c produced a composite sample of 17 kg. the composite sample was then sieved into seven size fractions, which were further separated to isolate a number of characteristic components: ferro magnetic metal, nonmagnetic metal, glass, ceramics and building aggregates and melt. glass, ceramics and building aggregates were identified by manual-visual sorting. ferro magnetic metal was captured by a magnet and non-magnetic metal was identified with a metal-detector. the remaining material was classed as predominantly melt – fragments or conglomerations of fragments, which were partly or entirely melted, and did not belong to the other categories. the resulting fractions and material classes were weighed. all metal fragments underwent further analysis with x-ray f luorescence (xrf) to categorise them according to alloying elements; non-magnetics were subdivided into aluminium, alloyed aluminium, copper alloyed copper, and other metals. additional subdivisions were made according to the degree of degradation; glass for example was subdivided into four sub-classes. this part of the study is not reported in this article but can be found in clausen et al. 2019. chemical characterisation a classical mineral exploration approach would be to produce an iba ‘whole-rock’ chemical signature to identify potentially economic elements and minerals. but this is neither possible nor meaningful for iba material for the following reasons: 1. the technical challenge: homogenisation by means of crushing and milling of iba material is expensive, if not impossible, due to the content of ductile metal fragments. 2. the distributional challenge: the ‘whole rock’ chemical signature represents elements hosted by myriad chemically different fragments of materials and melts. however, it does not reveal the extent to which the element is available to mining/recycling, since it does not describe the size, shape and elemental composition of the particular fragments it is associated with. it follows that neither the ‘ore grade’ nor the ‘ore value’ of iba can be established only on the basis of bulk geochemical data. however, chemical data may point to elements occurring in elevated concentrations, on which further studies are required in order to assess their economic potential. this approach was applied in the urban-x project where a total of 62 1 cm b 1 cm c a fig. 1: example waste from amager bakke waste-to-energy plant. a: unprocessed incinerator bottom ash (reproduced from clausen et al. 2019). b: non-deformed glass fragments (sample number 567662 a; clausen et al. 2019). c: magnetic, non-deformed metal (sample number 567662 a; clausen et al. 2019). chemical elements were analysed by icp-ms and icp-oes on each of the 30 iba samples (the 0–63 mm size fraction from the b series after removing magnetic metal; fig 2). samples were prepared and analysed by actlabs, canada. a full description of sample preparation and analytical methods is supplied as supplementary information (file s1; https://doi. org/10.34194/geusb-201943-03-03). results and discussion five material classes dominated the coarse fraction of the iba-bulk sample: magnetic metal (29 wt%), non-magnetic metal (6 wt%), glass (14 wt%), ceramics and building aggregates (14 wt%) and melt (37 wt%; figs 1b, c). the composite iba-bulk sample consisted of 66 wt% coarse (2–63 mm) material and 34 wt% fine (< 2 mm) material. comparing the physical characterisation of each sieved fraction, it follows that each material class correlates to some extent with fragment size (fig 3). for example, building aggregates and magnetic metals are concentrated in the >32 mm fractions, while glass and non-magnetic metal are concentrated in the <32 mm fractions. distribution of the non-magnetic fraction is however less distinct across the various material classes (fig. 3). the annual resource potential of the five main classes in the 2–200 mm material fraction from the amager bakke plant are estimated and presented in table 1. the total mega tons per annum (mtpa) iba production in denmark and the eu-28 is 0.6 mtpa (miljøstyrelsen 2016) and 16 mtpa (iswa 2015), respectively. assuming the distribution of the five material groups measured for amager bakke iba is representative of iba in denmark and the eu, we can apply these class distributions to the national and eu-level data (table 1). for example, magneticand non-ferrous scrap could be as high as 230 000 tpa and 50 000 tpa, respectively, in denmark, and 4 200 000 tpa and 1 000 000 tpa, respectively, in the eu-28 (table 1). this eu-28 estimate must, physical characterisation >63 mm 31.5–63 mm 16–31.5 mm 8–16 mm 4–8 mm 2–4 mm >2 mm <2 mm sievingsplittercseries icp-ms archive archive archive d series b series grain size distribution chemical characterisation composite samples sieving a series archive fig. 2. sampling workf low and methods applied to each series (a–d) of sampled iba (modified from clausen et al. 2019). e2019430303-03 80 000 1 800 000 1 700 000 910 000 3 600 000 4 700 000 2 400 000 16 000 000e 30 000 68 000 63 000 34 000 137 000 177 000 91 000 600 000d 4000 9100 8400 4600 18 000 24 000 12 000 80 000 5b 11 10 6 23 29 15c 100 14 14 6 29 37 100 ceramics and aggregates glass non-ferrous metal magnetic metal (steel) slag melt total 0–2 mm fraction 2–63 mm >63 mm (mostly magnetic metal) estimated volume (tpa) all wte incinerators eu-28 estimated volume (tpa) all wte incinerators denmark estimated volume (tpa) adjusted (wt%)a measured (wt%) amager bakke a measured content adjusted to include estimates of the >63 mm and 0–2 mm fractions. b rough estimate of the >63 mm fragments in iba from amager bakke. c production from amager bakke, as estimated by amager resource center. d iba production in denmark based on multiple sources (miljøstyrelsen 2016; dansk affaldsforening et al. 2016). e iba production in the eu-28 estimated by iswa (2015). table 1. estimated annual resource volume produced by amager bakke waste-to-energy (wte) plant. potential volume in denmark and the eu-28 is extrapolated from the distribution among raw material groups observed at amager bakke https://doi.org/10.34194/geusb-201943-03-03 https://doi.org/10.34194/geusb-201943-03-03 however, be considered speculative and further studies are needed to quantify the resource potential in the eu. complete chemical analysis of the 0–63 mm iba fraction can be found in clausen et al. (2019). here we present only the nine elements that occurred in concentrations 10 times higher than the average crustal concentration and are thus considered candidates for resource extraction (table 2). when ranking these elements according to their level of enrichment compared to crustal concentration, sb, au and pb rank highest. since the various classes of potentially economic materials are unevenly distributed throughout the iba size fractions, it follows that the chemical composition also varies with grain size. therefore, a relevant question is, where in the iba are the nine elements in table 2 concentrated, i.e. elevated above the average (0–63 mm fraction) concentration? the 2–63 mm fraction of melt fragments were not measured in this study, but similar iba material (20–40 mm size fraction of melt fragments) was analysed at amager forbrænding in 2015 (kalvig et al. 2016; in service between 1970 and c. 2017, after which the new amager bakke plant operates in its place). the 20–40 mm melt fraction at amager forbrænding has a similar composition to the 0–63 mm fraction at amager bakke (table 2). in general, the 2–63 mm non-melt fragments (i.e. glass, building materials, magnetic metals and non-magnetic metal) originates from products used in household and industry, in which the elements in table 2 would not serve a functional purpose and are undesirable for economic, health and environmental reasons. measurements with xrf were carried out to see if any of the elements in table 2 could be detected among each category of non-melt fragments. none of the elements, except for zinc, registered above the limit of detection. zinc only registered in measurable quantities in a few non-ferrous metal fragments (data not shown). the xrf measurements thus support our general assumption, that the nine elements are mostly absent in the 2–63 mm non-melt fragments. we can thus assume that the 0–2 mm fraction is a source of elevated concentrations of the nine elements of interest. previous studies in holland support the notion that heavy metals are concentrated in the iba fines (muchova et al. 2009; muchová & rem 2006). summary and outlook iba f lows at the amager bakke plant likely carry a secondary raw material potential that is not yet fully realised. these include: (1) glass, (2) increased recycling efficiency on ferrous and non-ferrous metals, (3) higher value usage of melts and ceramics e.g. in concrete and asphalt and (4) potential extrac0 20 40 60 80 100 2–4 4–8 8–16 16–32 32–63 63–200 size fraction (mm) c om po sit io n of 5 m at er ia l cl as se s (% ) melt ceramics & building aggregate glass non-magnetic metals magnetic metals fig. 3. the distribution of main components according to fragment size. the characterized 2–63 mm fractions were considered representative of the total iba material. the 63–200 mm was not considered representative due to its size relative to the sampler, but a rough characterisation using a magnet was made nonetheless on the sampled material (modified from clausen et al. 2019). e2019430303-04 52 330 866 1.5 312 5.6 4.1 3355 118 210 154 98 72 66 41 31 39 12 42 480 980 1.8 150 3.2 4.7 3100 74 0.2 3.1 10 0.025 2.2 0.08 0.15 79 6.3 ppm ppb ppm ppm ppm ppm ppm ppm ppb sb au pb bi sn ag cd zn pd measured ave. conc.c earth crust enrichment factorb (no units) 0–63 mm (amager bakke) 20–40 mm (melt; amager forbrænding) earth crust ave. conc.a measured ave. conc. a obtained from periodictable.com. b earth crust enrichment factor is the element concentration relative to crustal concentration. table 2. content of selected elements in incinerator bottom ash produced by the amager bakke waste-to-energy plant c measured concentration of 10 fragments of melt materials from amager forbrænding, 2015 (kalvig et al. 2016). tion of metals such as antimony, gold, lead and zinc from the 0–2 mm fraction. future work should characterise these resource potentials in greater detail to enable their commercial exploitation. in addition, a comprehensive physical and chemical characterisation of the iba at similar plants would be a powerful tool to characterise the drivers of iba resource potential and to provide a foundation for closing some of the major gaps in the circular economy. to further enable commercial exploitation, efforts should be made to develop a preparatory recycling method of iba f lows. a preparatory method could for example involve a washing phase, as part of the existing water-cooling basin at amager bakke – a method whereby clean fragments larger than 2 mm are removed in one material stream, and fines undergo a density separation to separate a heavy density concentrate. this method could (1) enable recycling of clean, non-metal fragments due to the absence of heavy metals – and make the fragments available for visual sorting techniques, (2) increase performance of existing mechanical sorting techniques applied to metal fragments, (3) enable recovery of antimony, gold, lead and zinc from the heavy concentrate, (4) save storage space currently used to store iba for carbonation (whereby heavy elements are stabilised) – which in turn would minimise the oxidation of stored metals. references clausen r., kalvig, p. & nedenskov, j. 2019: karakterisering af slagge og f lyveaske fra affaldsforbrændingsanlægget amager bakke. overvejelser om råstofpotentialet. 2. udgave. mima rapport 2019/1, 231 pp. videncenter for mineralske råstoffer og materialer (mima) and geological survey of denmark and greenland (geus), denmark. accessed november 2019 at http://mima.geus.dk/wp-content/uploads/karakerisering-af-slagge-og-f ly veaske-fra-amager-bakke-overvejelser-omr%c3%a5stofpotentialet-2.-udgave-clausen-et-al-2019.pdf dansk affaldsforening et al. 2016: beate, benchmarking af affaldssektoren 2016 (data fra 2015), forbrænding, 29 pp. the danish energy agency, denmark. accessed november 2019 at https://ens.dk/sites/ens.dk/files/ affald/beate_afrapportering _forbraending _2016_29maj2017.pdf iswa 2015: bottom ash from wte plants – metal recovery and utilization. unpublished report, international solid waste association (iswa), austria. kalvig, p., clausen, r. & nedenskov, j. 2016: karakterisering af slagge og røggasaffald fra amager ressource center, 161 pp. unpublished report. videncenter for mineralske råstoffer og materialer, denmark. miljøstyrelsen 2018: affaldsstatistik 2016, 66 pp. the danish environmental protection agency, denmark. miljøprojekt no. 2020. https:// www2.mst.dk/udgiv/publikationer/2018/06/978-87-93710-39-9.pdf miljøstyrelsen 2016: kommissionens forslag til ændring af bilag iii i affaldsdirektivet (2008/98ef) med hensyn til fareegenskaber hp 14 (økotoksisk) (komitesag). notat til folketingets europaudvalg. ref. thfru. https://www.ft.dk/samling/20161/almdel/mof/bilag/35/1678142/index.htm muchová, l. & rem, p. c. 2006: metal content and recovery of mswi ash in amsterdam. in: v. popov, v. et al. waste management and the environment iii. wit transactions on ecolog y and the environment, 92. 211–216. https://doi.org/10.2495/wm060231 muchova, l., bakker, e. & rem, p. 2009: precious metals in municipal solid waste incineration bottom ash. water air soil pollution: focus 9, 107–116. https://doi.org/10.1007/s11267-008-9191-9 acknowledgements our thanks go to the reviewers tod waight and gang liu for their comments, and to marija blazanovic, tonny b. thomsen, nynke keulen, sebastian næsby malkki and frederik tevil for their help and guidance. the urban-x project was funded by amager bakke and videncenter for mineralske råstoffer og materialer (mima). how to cite clausen, r.j., kalvig, p. & nedenskov, j. 2019: characterisation of incinerator bottom ash from a danish waste-to-energ y plant: a step towards closing the material cycle. geological survey of denmark and greenland bulletin 43, e2019430303. https://doi.org/10.34194/ geusb-201943-03-03 *corresponding author: rune clausen | e-mail: rjc@geus.dk 1 geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350, copenhagen k, denmark. 2 amager ressource center, vindmøllevej 6, dk-2300, copenhagen s, denmark. e2019430303-05 http://mima.geus.dk/wp-content/uploads/karakerisering-af-slagge-og-flyveaske-fra-amager-bakke-overvejelser-om-r%c3%a5stofpotentialet-2.-udgave-clausen-et-al-2019.pdf http://mima.geus.dk/wp-content/uploads/karakerisering-af-slagge-og-flyveaske-fra-amager-bakke-overvejelser-om-r%c3%a5stofpotentialet-2.-udgave-clausen-et-al-2019.pdf http://mima.geus.dk/wp-content/uploads/karakerisering-af-slagge-og-flyveaske-fra-amager-bakke-overvejelser-om-r%c3%a5stofpotentialet-2.-udgave-clausen-et-al-2019.pdf https://ens.dk/sites/ens.dk/files/affald/beate_afrapportering_forbraending_2016_29maj2017.pdf https://ens.dk/sites/ens.dk/files/affald/beate_afrapportering_forbraending_2016_29maj2017.pdf https://www2.mst.dk/udgiv/publikationer/2018/06/978-87-93710-39-9.pdf https://www2.mst.dk/udgiv/publikationer/2018/06/978-87-93710-39-9.pdf https://www.ft.dk/samling/20161/almdel/mof/bilag/35/1678142/index.htm https://www.ft.dk/samling/20161/almdel/mof/bilag/35/1678142/index.htm https://doi.org/10.2495/wm060231 https://doi.org/10.1007/s11267-008-9191-9 https://doi.org/10.34194/geusb-201943-03-03 https://doi.org/10.34194/geusb-201943-03-03 mailto:rjc%40geus.dk?subject= _goback geological survey of denmark and greenland bulletin 38, 2017, 69-72 69 denmark has a long tradition for having central geological databases, including a systematic collection and storage of geological and hydrological information from all surficial boreholes which was initiated in 1926. since the mid-1970s such data have been stored digitally. a large variety of users access a central danish, geological database: the public, for information about their local drinking water quality, environmental employees in municipalities, regions and the state for using, entering and updating data as well as consultants and drilling companies working for public administration and local water works. the local danish administrative system previously consisted of 14 counties and 248 municipalities. the counties were responsible for groundwater mapping, drinking water management and activities concerning contaminated soil, as well as for harmonisation and transfer of data to the central database. with effect from 1 january 2007, this administrative system was replaced by five regions, seven environmental centres and 98 municipalities, which required major changes in the administrative handling of borehole data at the local and regional levels. for this, a public and shared central database was established and a countrywide harmonisation of data, transfer and storage was initiated and all geological, groundwater and drinking water data were transferred to this central database at geological survey of denmark and greenland (geus). in an updated database system, public authorities were set up to access the central database to store their relevant borehole data and almost all data were made publicly available. the database is maintained by geus. it is directly connected to other public databases at geus including the shallow geophysical database gerda, where e.g. borehole loggings are stored, and to the model database where simple geological models are stored (fig. 1). an integrated public information system for geology, groundwater and drinking water in denmark martin hansen and charlotte toftemann thomsen fig. 1. diagram showing a: the access to data in the jupiter database from different users and b: how data f low to and from the database. ws: web services. privileged users jupiter database pc jupiter xl read-only views jupiter tables unprivileged users users at geus geus databases drilling companies municipalities state agencies consultants borehole data groundwater data borehole data models reports borehole data geophysics models reports groundwater and drinking water data laboratories chemical analysis regions b. data flow a. access to jupiter data http – homepages, ws reading and download web forms updating using ws and https borehole, © 2017 geus. geological survey of denmark and greenland bulletin 38, 69–72 . open access: www.geus.dk/publications/bull 7070 this updated system is used by the municipalities to manage their water supply data (e.g. water supply structure, permits, groundwater and drinking water quality data), by state agencies to manage groundwater data from the groundwater mapping and by the regions to maintain their soil pollution data. the system has gradually been expanded since 2007 and now local authorities can store and maintain a wide range of their own data in the central database. the database system the database system currently consists of the following components: 1. a central database; 2. a public data model, agreed upon by a committee under the the danish natural environment portal; 3. a user-management system, managed by the the danish natural environment portal, providing direct access to the central database; 4. a suite of simple object access protocol (soap) web services – an interface that allows computer-to-computer communication. this enables local authorities to manage their own data in the central database through their own applications; 5. applications that can access the database utilising the components above. the central database the central database is based on geus’ jupiter database and run on an oracle database. it has been under development during the last 40 years. the extensions made since 2007 include full public online access to read data and write access for public authorities to almost all data types. the public part of the database is made available through a view layer exposing the public data model. the public data model the public data model can handle: • borehole data, including: localisation and administrative data, construction data, abandon data, geological description using common methodology, hydraulic head measurements, samples and analyses from soil, water and air; • surface soil and water sample data; • water supply data for water plants, agriculture and industry, including: extractions wells, well fields, water treatment plants, extraction permits, water quality data, water extraction, water use data, exchange of water between water works, ownership and contact persons; • soil pollution data: projects; soil, water and air chemistry data from boreholes, surface samples and remediation plants. the data model is being developed and maintained by geus, but all extensions and alterations have to be agreed upon by the groundwater group under the danish natural environment portal (dnep). this is a common public partnership between the ministry of environment and food of denmark (45%), the danish municipalities (45%) and the danish regions (10%), and it acts as an independent portal across boundaries of authority. its major goal is to ensure continued access to harmonised, updated, natural environmental data. the groundwater group itself consists of members appointed by the municipalities, name of user role privileges and use laboratory for entering and editing samples and chemical analyses. for laboratories to add data to the system. borehole write for entering and editing information about boreholes including location, geology/lithology and borehole construction. for consultants and local authorities to enter new boreholes. borehole read for reading publicly available data about bore holes, water, soil and air samples and analysis. drinking water for approving new drinking water samples with approval analyses. for users from the authorities to qua lity control new drinking water data and by approving the data, making them publicly available. groundwater for approving new groundwater samples with approval analysis. for users from the authorities to quality control the new groundwater data and by approving the data, making them publicly available. water level for entering and editing water-level measurements. for users from the authorities to enter and edit water-level measurements. sample approval for approving new water, soil and air samples with analyses from surface samples. for users from the authorities to quality control the new water, soil and air analyses from surface samples and by approving the data, making them publicly available. water resources for entering and updating information about water works. these data include water well fields, treatment plants, permits, annual volumes of extracted water, sampling sites and volumes of water shared between different water works. for the municipalities that survey the drinking water to create and update their drinking water structure. table 1. user roles and privileges 71 the danish environmental protection agency , the danish regions, dnep and geus. the public data model consists of more than 90 data tables. data responsibility agreement the data responsibility agreement determines which organisations are responsible for producing and maintaining which data, and for making the data available to the public. the various responsibilities are defined partly by legislation and partly through agreements signed by the participating partners and by voluntary reporting. at any time, any data set in the public database has one and only one responsible owner organisation. data ownership the ownership of data can be defined either by the user who enters the data or by the location of the data point. in this way, the municipality or region in question, a state agency and geus can own water-level measurements in the same well. each data owner is responsible for entering their own data and secure their quality. the analysing laboratory carrying out the quality control of drinking water is responsible for entering its data, and it owns the data until the data entry and quality control have been completed. after this step, the ownership is transferred to the municipality to which the water works belongs. the municipality has to release the data before it becomes publicly available. apart from quality control of the data sets, the new owner cannot alter the data. if errors are found during the quality control, the municipality must reject the water sample and all of its analyses, and the laboratory has to resubmit a corrected data set. user management the danish natural environment portal has a central user-management system which enables the user to use the same login credentials to access and update data in different systems. the users and their rights are managed locally by user administrators who define the user rights through a set of roles. each role defines to which part of the database the user shall have access. in this way it is the local administrator who decides who should be allowed to access the different public systems or obtain privileges to enter and edit data. the different roles in the jupiter system are presented in table 1. in addition to these roles, the system gives the users access to data according to their geographical location. for example, all users can access water works but only users from the municipality, where the water works is situated, can update the information (provided the user has the right role). data interface the data are available in several ways. most of the data are available through: jupiter’s homepage: this entry is read-only and mainly used by municipalities and members of the public to look up specific data (fig. 2). soap web services: these services give read-and-write access to different parts of the data model and have been under development since 2007. with this interface private companies can write applications for administrative units for their data management. these services constitute fig. 2. screen shot from the web map interfaces to jupiter showing boreholes and water plants from central sjælland. 7272 the main entry outside geus for update of data. see for example: http://webs.geus.dk/miljoeportal.groundwater.bboring.2.0.0/b-boring?wsdl for updating borehole data. wms/wfs: several of the data themes are exposed through web map services (wms) and web feature services (wfs). web map services deliver maps as bitmaps while web feature services can deliver the same data as geographical objects (point, lines and polygons) that can be used for spatial queries in a gis. these are used to support the map interface on the jupiter homepage, are available for end users, and can also be imported into local gis. these services are used mainly in systems made for the different administrating units. see for example the wms publishing borehole information http://data.geus.dk/geusmap/ows/25832.jsp?se rvice=wms&version=1.1.1&request=getcapabil ities&layers=jupiter_boringer_ws%2cjupiter_anlaeg_ws database download: advanced users can download data as database exports. in this way it is possible to export all available data to a local hard drive (excluding water quality control data not yet approved by the data owner and information about owners and contact persons). this function is meant for advanced users for e.g. geological modelling or complex calculations on groundwater chemistry. it is even possible to install a scheduled application that keeps the local database updated on a nightly basis with changes made in the central database. such local copies of the database are mainly used by consulting companies and large administrative units. discussion and conclusions nearly all data in the database must be publicly available. therefore, the access has been divided into two packages of services since the first version of the web services was developed up to january 2007. one set contains all the readonly functionality without any user management systems, while the other package contains functions for updating the data. however, due to very frequent use the read-only services will have to be revised in the near future. not all users comply with the rules set up for the use of the services, and since they are anonymous, it is difficult to identify those who break the rules. for example, users are not allowed to use the services in batch mode or create a local copy of the database. we can, however, see from the logs, that one or more read-only users behind a single ip-address make up to tens of thousands of calls on a daily basis and thus obviously do not comply with the rules set-up for the services. an increase from c. 200  000 to 12  000  000 calls per month in the last few years causes a heavy and increasing system load. if a login with user name and password was to be required to enter the read-only services, it would be possible to contact directly the users who use software that does not comply with the rules of use. the access would still be free of charge. a public, shared database like jupiter gives access to a very broad use, where the data can be combined with other public data or with private, non-public data. also the many different ways in which the data are available, such as web, web gis, different types of web services or download in database format, make the data highly usable. the user gets a coherent dataset containing geology, groundwater and drinking water data, where the water can be followed all the way from the borehole to the water plant. in recent years, the database has been used for analysis of public health in combination with drinking water quality. the free access to the publicly available data has greatly increased the value of the data. the authors do not know of any other publicly available, combined geology – groundwater – drinking water database systems like jupiter. as the system is based on a data model that has been agreed upon between different stakeholders from municipalities, regions, state agencies and the geological survey, the model can most probably be used as a good starting point for development of similar systems by other organisations and countries. references gerda database: http://data.geus.dk/geusmap/?lang=en&mapname=gerd a#layers=gerda_ projects%2cgerda_data jupiter database: http://data.geus.dk/geusmap/?mapname=jupiter&lang=en saml 2.0: https://en.wikipedia.org/wiki/saml_ 2.0 soap web services: https://en.wikipedia.org/wiki/soap the danish natural environment portal: http://www.miljoeportal.dk/ english/sider/default.aspx the model database: http://data.geus.dk/geusmap/?lang=en&mapname =modeldb authors’ address: geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: mh@geus.dk geological survey of denmark and greenland bulletin 35, 2016, 9-12 9© 2016 geus. geological survey of denmark and greenland bulletin 35, 9–12 . open access: www.geus.dk/publications/bull a motorway was constructed in 2010–2016 through the suburbs of the city of silkeborg (fig. 1). the danish road directorate wished to climate-proof the motorway against adverse future climate changes. the directorate collaborated with the geological survey of denmark and greenland (geus) to study the hydrological conditions. studies of historical and projected climate-change-driven variations in groundwater levels in relation to urbanised hydrological fluxes were conducted by kidmose et al. (2013, 2015). during the construction of the motorway, miocene and quaternary deposits were exposed in the slopes of the gudenå valley and late-glacial glaciofluvial deposits were found in the valley floor. this paper focuses on the miocene sediments and their influence on the local hydrological conditions. at silkeborg the gudenå valley is c. 35 m deep (fig. 1). the surrounding terrain is a till plain. in the slope of the valley, glaciofluvial sand is found below the till. miocene deposits are found below the glaciofluvial sand. the floor of the gudenå valley is covered by c. 15 m thick glaciofluvial deposits, which rest on miocene deposits. in borehole no. dgu 87.907 49 m of miocene deposits belonging to the vejle fjord formation are recorded, consisting primarily of marine clay with minor occurrences of sandy deposits. about 12 km south of silkeborg lower miocene deposits are seen in outcrops and boreholes (fig. 2). here the fluvial addit member of the billund formation (rasmussen at al. 2010) is separated from the underlying marine vejle fjord formation by a sharp erosional contact (rasmussen 2014). miocene deposits at silkeborg, jylland, and their influence on hydrology peter roll jakobsen, erik skovbjerg rasmussen, karen dybkjær and jacob kidmose 1 km silkeborg gudenå clayey till sandy till glaciofluvial sand outwash plain peat aeolian sand miocene deposits well no. 87.907 fig. 1. geological map of the silkeborg area. dashed line: motorway. 1 km 0 l e v e l (m ) 50 50 100 100 continental sand and gravel marine clay marine sand coal pre-miocene eastwest addit mb billund fm vejle fjord fm ? 8 7 .9 0 7 f ig . 3 quaternary deposits continental clay fig. 2. east–west profile about 12 km south of silkeborg (from rasmussen 2014). a composite log from silkeborg (fig. 3) and data from well no. dgu 87.907 are shown to the left. planar cross-bedding parallel bedding clay trace fossil sample for palynology hummocky cross-bedding sedimentary structures lithology fig. 4a fig. 4c fig. 4d fig. 4e fig. 4b a q u it an ia n a d d it m b , b il lu n d f m v e jl e f jo rd f o rm at io n 0 m 1 m 2 m 3 m 4 m 5 m 6 m 7 m 8 m 9 m sand gravel silt fine medium coarse fig. 3. composite sedimentological log of the temporarily exposed miocene deposits. 1010 sedimentology the section along the motorway comprised 9 m of miocene deposits (fig. 3). the lower part is characterised by cross-stratified medium-grained sand, dipping c. 30° towards the north (fig. 4a). a few trace fossils (skolithos?) are seen. the cross-stratified sand is sharply overlain by wave-formed, coarse-grained ripples. the crests of the ripples strike se–nw, and crest-to-crest spacing is in the range of 250 cm with amplitudes up to 35 cm (fig. 4b). the ripples show tangential cross-bedding towards the sw. in a nearby exposure, tidal bundles form the base of the section. the presence of clay layers varies systematically and is commonly characterised by double clay layers (fig. 4a). dips of cross-bedding are both sw and ne. the coarse-grained ripples are in turn overlain by a dark brown mud. the mud is succeeded by silt and fine-grained sand, c. 1.5 m thick. hummocky cross-stratifications (hcs) are common, especially in the upper part of the section. these are superimposed by 3 m of dark brown mud (fig. 4c) showing a slight increase in grain size upwards where hummocky cross-stratified sands are common (fig. 4d). a sharp boundary separates the mud from an overlying 2 m thick section of mediumto coarse-grained sand and gravel. this coarse-grained section is composed of tabular co-sets of cross-stratified beds dipping towards the south (fig. 4e). fig. 4. details of the miocene deposits. the stratigraphic positions of the photos are indicated on fig. 3. a: cross-stratified medium grained sand. double clay layers are indicated with small arrows. trace fossil is indicated with larger arrow. b: wave-formed, coarse grained ripples. c: thick dark mud succession. d: hummocky cross-stratification (hcs). e: tabular co-sets of cross-stratified beds. b c d e a 11 bioand chronostratigraphy and depositional environment in order to confirm the miocene age of the described succession and to achieve a more precise dating, two sediment samples were selected for palynological analysis. the stratigraphic positions of the samples are shown in fig. 3. one of the samples was almost barren, while the other contained a rich assemblage of organic particles dominated by bisaccate and non-saccate pollen. in addition, the sample contained a moderately rich and diverse dinoflagellate cyst (dinocyst) assemblage together with a few wood particles, cuticle, acritarchs and freshwater algae. this assemblage indicates a marine, inner neritic depositional environment with a high influx of freshwater (tyson 1995). the dinocyst assemblage is dominated by two species of the genus homotryblium: h.? additense (fig. 5a) and h. plectilum. among several other dinocyst taxa, a single specimen of the stratigraphically important species chiropteridium galea was found (fig. 5b). the dinocyst assemblage refers the sample to the chiropteridium galea zone (dybkjær & piasecki 2010). this dinocyst zone is dated to the early aquitanian (earliest miocene) and the age of the sample is 23.03–22.36 ma. palaeogeography the sand and gravel in the lower part of the section were deposited during an overall regression of the billund formation in the early miocene (rasmussen et al. 2010). the gravel was probably originally deposited in a fluvial environment during the most extended regression. the crossstratified sand in the lower part was formed in a marine bar that migrated landwards. the tidal bundles were formed by both ebb and flood currents, as indicated by the bipolar dips of cross-bedding, in an adjacent tidal inlet. the overlaying wave-formed, coarse-grained ripples were formed by marine reworking (leckie 1988) of the coarse-grained fluvial sediments laid down during maximum regression and now forms a transgressive lag (plint 1988). the depositional water depth of the coarse-grained ripples may lie in the range of 15 to 60 m (leckie 1988) – most likely in the lower end as the sea-level changes during this part of the miocene was c. 25 m (miller et al. 2005). the strike of the crests of the coarse-grained rippels, se–nw, indicates the trend of the palaeo-shoreline (leckie 1988). the succeeding mud and hcs-dominated silt and fine-grained sand were deposited in slightly deeper water, in the offshore transition zone. the mud-dominated part with few intercalations of hcs’s was deposited offshore near the storm wave base. the assemblage of organic particles indicates that the sediment was deposited in a marine depositional setting near the coast. the two homotryblium species further indicate that the palaeoenvironment was marine but probably with lowered salinity (dybkjær 2004). these interpretations support the sedimentological interpretations and palaeogeographic maps for the earliest miocene of jylland, indicating that large river and delta systems existed, which transported large amounts of freshwater and sediment from the north to the middle part of jylland (rasmussen et al. 2010). 20 μm20 μm a b fig. 5. a: homotryblium? additense. b: chiropteridium galea. fig. 6. palaeogeographical reconstructions of the silkeborg area. a: early aquitanian (earliest miocene, vejle fjord formation) tidal-dominated marine-barrier system. b: late aquitanian (addit member, billund formation) f luvial environment. grey line: motorway. a b1 km 1212 authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: prj@geus.dk the coarse-grained sand and gravel at the top of the studied succession, that sharply overlie the marine deposits, were deposited in a fluvial environment, the addit member of the billund formation (rasmussen et al. 2010; fig. 6). the dramatic change in the depositional environment was partly a result of an eustatic sea-level fall and partly a result of inversion of the norwegian–danish basin (rasmussen 2014). the latter resulted in marked incision in the middle and northern part of jylland during the late aquitanian. the miocene succession in silkeborg shows a strong resemblance to successions in boreholes and exposures about 12 km south of silkeborg (fig. 2). hydrology on the floor of the gudenå valley, wells with screens in the miocene deposits have artesian hydraulic heads, whereas the hydraulic head in the overlying glaciofluvial sediments is in hydraulic contact with the gudenå. this shows that the alternating miocene layers of the vejle fjord formation form a hydraulic barrier between deeper groundwater and the surficial glaciofluvial aquifer that is in contact with the motorway (fig. 7). in the higher terrain the measured hydraulic head in the quaternary glaciofluvial sand is very different from the hydraulic head measured in the underlying miocene deposits. this is because the 3 m thick miocene mud unit (fig. 4c) acts as a barrier. the addit member, however, is in hydraulic contact with the glaciofluvial sand (fig. 7). the hydraulic connection between the glaciofluvial sand found in the slopes of the valley and the glaciofluvial deposits in the valley floor is also affected by the miocene deposits as the 3 m thick mud unit separates them. the hydrogeological relations between the miocene deposits and the quaternary deposits illustrate the importance of applying detailed field-site geological evidence to get an impression of the local groundwater flow. acknowledgement the danish road directorate is thanked for access to the field site and funding. references dybkjær, k. 2004: morphological and abundance variations in homotryblium-cyst assemblages related to depositional environments; uppermost oligocene – lower miocene, jylland, denmark. palaeogeography, palaeoclimatology, palaeoecology 206, 41–58. dybkjær, k. & piasecki, s. 2010: neogene dinocyst zonation in the eastern north sea basin, denmark. review of palaeobotany and palynology 161, 1–29. kidmose, j., refsgaard, j.c., troldborg, l., seaby, l.p. & escrivà, m.m. 2013: climate change impact on groundwater levels: ensemble modelling of extreme values. hydrology and earth system sciences 17, 1619–1634. kidmose, j., troldborg, l., refsgaard j.c. & bischoff, n. 2015: coupling of a distributed hydrological model with an urban storm water model for impact analysis of forced infiltration. journal of hydrology 525, 506–520. leckie, d. 1988: wave-formed, coarse-grained ripples and their relationship to hummocky cross-stratification. journal of sedimentary research 58, 607–622. miller, k.g. et al. 2005: the phanerozoic record of sea-level changes. science 310, 1293–1298. plint, a.g. 1988: sharp-based shoreface sequences and “offshore bars” in the cardium formation of alberta; their relationship to relative changes in sea level: in: wilgus, c.k. et al. (eds): sea-level changes: an integrated approach: sepm, special publication 42, 357–371. rasmussen, e.s. 2014: development of an incised-valley fill under the influence of tectonism and glacio-eustatic sea-level change: valley morphology, fluvial style and lithology. journal of sedimentary research 84, 278–300. rasmussen, e.s., dybkjær, k. & piasecki, s. 2010: lithostratigraphy of the upper oligocene – miocene succession in denmark. geological survey of denmark and greenland bulletin 22, 92 pp. tyson, r. 1995: sedimentary organic matter: organic facies and palynofacies, 615 pp. london: chapman & hall. clayey till meltwater sand diamicton meltwater plain sand clay quaternary deposits miocene deposits w e ll n o . 8 7 .9 0 7 addit member vejle fjord formation sand sand/clay level (m) 60 50 40 30 20 10 0 –10 –20 fig. 7. conceptual geological model along the motorway alignment. geological survey of denmark and greenland bulletin 41, 2018, 9-12 9 oil and gas production from siliciclastic reservoirs has hitherto been in the danish central graben mostly from palaeogene and middle jurassic sandstone. the ravn field was the first upper jurassic field to start operation. the reservoir is composed of sandstone of the heno formation. production takes place at a depth of 4000 m, which makes ravn the deepest producing field in the danish north sea. the heno formation mainly consists of marine shoreface deposits, where foreshore, middle and lower shoreface sandstones constitute the primary reservoir. the results of this study of the diagenetic impact on the mineralogical composition, porosity and permeability are presented here. microcrystalline quartz has preserved porosity in the sandstone, whereas illite, quartz overgrowth and carbonate cement have reduced both porosity and permeability. geological background the ravn member of the heno formation is located on the heno plateau in the danish central graben (fig. 1; johannessen 2010). the ravn field was discovered in the ravn-1 well in 1986 and subsequently evaluated in the ravn-2 well in 1987. in 2010, the ravn-3 well was drilled to test the location of the oil–water contact and to evaluate the reservoir quality of the south-western flank of the field. oil was found at several intervals and the oil–water contact was located at a depth of 4572 m. the ravn member was deposited during an overall transgression of the heno plateau during the kimmeridgian. the member consists of up to 100 m thick marine shoreface deposits (johannessen 2010) where foreshore, middle and lower shoreface sandstones constitute the primary reservoirs (fig. 2). the sediments are strongly bioturbated and are dominated by very fineto fine-grained or muddy sandstones with occasional white, grey and light brown siltstones. methods sedimentological description of the ravn-3 core was made and 18 thin sections were prepared from samples from middle, lower and foreshore sandstones (fig. 2). petrographical investigations of the thin sections were undertaken with transmitted light microscopy. mineral abundances were quantified by point counting of minimum 500 grains. additional information was obtained from scanning electron microscopy (sem) of gold-coated rock chips and carbon-coated thin sections using a phillips xl 40 sem with a tungsten filament operating at 17 kv and 50–60 µa. porosity and permeability were measured on core plugs according to the api rp-40 standard (american petroleum institute 1998) at the geological survey of denmark and greenland. results the porosity and permeability of sandstone reservoirs ref lect, among other things, depositional environmental, mineralogical composition and post-depositional diagenetic changes. in order to understand what affected porosity and permeability, these factors were investigated. detrital components – quartz is the dominant component in all sandstones. the feldspar group consists of k-feldspar and minor albite. k-feldspar is typically partially dissolved and diagenetic impact on reservoir sandstones of the heno formation in the ravn-3 well, danish central graben simone pedersen, rikke weibel, peter n. johannessen and niels h. schovsbo ringkøbing–fyn high feda graben ål basin 25 km salt structure normal fault reverse fault well r-1r-3 r-2 a 56°n 4°e salt dome province gert ridge nl g uk central graben mid north sea high mandal high outer rough basin inge high heno plateau tail end graben national border n structural high dk b fig. 1. a: present structural framework of the danish sector of the central graben. r-1, r-2, r-3: ravn-1, -2 and -3 wells. b: overview of the north sea area. green: land. modified from johannessen (2010). © 2018 geus. geological survey of denmark and greenland bulletin 41, 9–12 . open access: www.geus.dk/bulletin http://www.geus.dk/bulletin 1010 minor mica, rock fragments and chlorite grains are present. accessory minerals are tourmaline, zircon and fe-ti oxides. detrital clay occurs as tangential coatings on detrital grains and as deformed clay clasts. diagenetic phases – sandstones are occasionally dominated by abundant sparry fe-dolomite and ankerite cement (fig. 3a; pedersen 2017). sporadic calcite inclusions occur enclosed in the fe-dolomite-ankerite cement. calcite from shell fragments was recognised in one sample. small amounts of fe-dolomiteankerite rhombs are present in samples where cement is not abundant. microcrystalline quartz coatings are common in several samples independent of depositional environment (fig. 3b). occasionally, excessive microcrystalline quartz also occurs in the intergranular pore space (fig. 3c). in a few sandstones, the detrital grain surfaces of quartz are only partly covered by microcrystalline quartz giving rise to growth of larger quartz overgrowths (fig. 3c). the amount of quartz overgrowths varies from 0.2 to 10.8 vol%. illite is present in all samples and depositional environments and occurs as fibrous and honeycomb-structured coatings (fig. 3d). authigenic illite occurs as protruding fibres growing from honeycomb-structured illiticsmectitic clay. illite fibres alternate with quartz overgrowths, and are at times enclosed in quartz overgrowth (fig. 3d). porosity versus permeability – the sandstones with highest porosity and permeability are dominated by microcrystalline quartz coatings and only little diagenetic illite is present together with a small amount of detrital clay (fig. 4; pedersen 2017). these sandstones are from the upper, middle and lower shoreface. two groups of sandstones are defined based on intermediate porosity and low to intermediate permeability. of these two groups, sandstones with quartz overgrowths and minor illite have slightly higher permeability than sandstones with microcrystalline quartz coatings and high illite and high detrital clay contents (fig. 4). these latter samples are from lower and middle shoreface. also the fe-carbonatecemented sandstones, which have the lowest porosity and permeability in the heno formation (fig. 4), represent lower and middle shoreface samples. comparison between the ravn-1, ravn-2 and ravn-3 wells – the ravn-3 well was correlated with the ravn-1 and ravn-2 wells based on available core and well log data (fig. 2). the various diagenetic phases in the ravn-3 well can be recognised in the other ravn wells. variations occur, such as quartz overgrowth and illitisation of detrital clay being more common in the ravn-1 well, compared to authigenic illite in the ravn-3 well, but the reservoir units can still be recognised. the variations seen in the ravn-1 cores are also present in the ravn-2 cores together with additional fractures filled with barite and ankerite. the porosity and permeability in the ravn-1 and ravn-2 wells lie within the same range as the sandstones in the ravn-3 well (fig. 4). cl si sand pbl lithology depositional environment sandstone clay or siltstone conglomerate lower shoreface middle shoreface foreshore structures disconnected wave ripples structureless due to bioturbation carbonate cemented sandstone thin section samples4619 m cl si sand pbl cl si sand pbl legend ravn-1 ravn-3 ravn-2 4280.77 m 4155 m 0 10 20 0.001 0.1 10 0 10 20 0 10 20 0.01 1 10 0.01 1 10 phi (%) kh (md) phi (%) kh (md) phi (%) kh (md) 0 20 40 60 80 100 120 h ei gh t ab ov e ze ro (m ) offshore low angle cross stratification fig. 2. correlation panel of the cored parts of the ravn-1, -2, and -3 wells. the ravn-1 and ravn-2 logs are modified from johannessen (2010), whereas the ravn-3 core was logged for this study. the depositional environment described in the ravn-3 well (panterra 2011) is based on ichnofacies. phi: heporosity. k h: horizontal permeability. cl: clay. si: silt. pbl: pebble. 11 discussion early carbonate cement – intergrown sparry fe-dolomite and ankerite cement (fig. 3a) is interpreted to be sourced from dissolved calcite from shell fragments. calcite inclusions still occur between fe-dolomite and ankerite. this is supported by quartz grains appearing to be ‘f loating’ in the carbonate cement, which indicates the previous presence of an early carbonate cement or fossils. fe-carbonates are considered more stable than calcite during late diagenesis and often replace earlier phases of carbonates (worden & burley 2003). early microcrystalline quartz – when early diagenetic microcrystalline quartz is present in the sandstones only minor quartz overgrowth has precipitated (fig. 3b). a biogenic opal ct phase, which has been dissolved without trace, may have resulted in supersaturated pore waters that sustained nucleation of microcrystalline quartz. grain-coating microcrystalline quartz has previously been proposed to preserve reservoir quality by impeding quartz overgrowth, which otherwise may occlude intergranular porosity and reduce permeability (aase et al. 1996; jahren & ramm 2000; weibel et al. 2010). the random growth of microcrystalline quartz may retard further development of both new microcrystalline quartz and quartz overgrowth ( jahren & ramm 2000; weibel et al. 2010). when microcrystalline quartz does not fully cover detrital quartz, it cannot inhibit precipitation of quartz overgrowth (aase et al. 1996; weibel et al. 2010). quartz overgrowths – late diagenetic quartz overgrowths formed where the quartz grains were only partly covered by microcrystalline quartz. the quartz overgrowths probably formed under low silica oversaturation, which favoured less nucleation and promoted the growth of larger crystals (fig. 3c; jahren & ramm 2000). more intensive quartz ceca fe-do + an mq il mq qo mq + il mq il il mq 5 µm 20 µm 20 µm 50 µm a b c d fig. 3. a: abundant fe-dolomite (fe-do) and ankerite (an) occluding porosity and permeability. remnants of the original early calcite (ca) cement are present. b: random and abundant microcrystalline quartz (mq ) coating detrital quartz grain, preventing quartz overgrowth (qo). note the fibrous illite (il). c: microcrystalline quartz on detrital quartz and in pore space together with authigenic illite. quartz overgrowth is partly enclosing microcrystalline quartz indicating that the quartz overgrowth precipitated later. d: abundant fibrous illite growing from honeycombstructured illite succeeding microcrystalline quartz and alternating with quartz overgrowth (qo). 10 1 0.1 0.01 0.001 0 5 10 15 2520 he porosity (%) g as p er m ea bi lit y (m d ) carbonate cemented microcrystalline quartz + illite + low detrital clay content microcrystalline quartz + illite + high detrital clay content thin section ravn-1 thin section ravn-2 thin section ravn-3 lower shoreface middle shoreface foreshore quartz overgrowth fig. 4. he porosity versus air permeability for all thin section samples from the ravn-3 well, together with data from the ravn-1 and ravn-2 wells. the thin section samples follow the trends from the ravn-3 well marked by the four ellipses, which depict the four characteristics of the diagenesis. the purple ellipse comprises samples dominated by microcrystalline quartz, illite and low detrital clay content. the green ellipse includes samples dominated by microcrystalline quartz, illite and high detrital clay content. the orange ellipse comprises samples dominated by quartz overgrowth and the blue ellipse by extensive sparry carbonate cement. 1212 mentation would have been expected in these quartz-rich sandstones (bjørlykke et al. 1989) as they have been buried to a depth of > 4 km and hence exposed to temperatures of 112–117°c as documented by vitrinite ref lectance. as no stylolites were observed and as quartz overgrowth precipitated before and alternating with illite growth, another source for silica must have been present prior to transformation of smectite to illite. the continued precipitation of quartz overgrowth was probably from a silica source from the transformation of smectite to illite and dissolution of kfeldspar (hower et al. 1976; boles & franks 1979). this is supported by the honeycomb-structured smectite-illite coatings and partially dissolved detrital k-feldspar. illite – illite occurring as honeycomb structured coatings (fig. 3d) is a strong indicator of a smectite precursor (e.g. pollastro 1985). during burial, the percentage of illite in mixed-layer illite/smectite compared to smectite increases since smectite becomes more unstable with increasing temperature and pressure (pollastro 1985), which may be the reason why only illite is present in the ravn-3 well. the honeycomb-structured illite commonly forms nucleation or growth points for fibrous illite. k-feldspar is typically dissolved concomitantly with smectite dissolution, and k-feldspar can be an additional source for k+ and al3+ for further illite precipitation (hower et al. 1976; boles & franks 1979). the additional k+ and al3+ from the dissolution of k-feldspar might have led to further precipitation of the fibrous illite on illite honeycomb structures and singular precipitation in pore space. fe-dolomite-ankerite rhombs are considered a by-product of the transition from smectite to illite, which may liberate ca2+ and fe2+. conclusions the porosity and permeability of the reservoir sandstones in the ravn-3 well are controlled by the diagenetic phases formed during early and late diagenesis. the reservoir sandstones with the highest porosity and permeability are dominated by low to moderate amounts of microcrystalline quartz, illite and detrital clay. however, the more distal lower shoreface sandstones with the same dominating diagenetic phases, but with higher detrital clay content, are considered a poor reservoir due to low porosity and permeability. sandstones with dominance of quartz overgrowth and low detrital clay content have moderate to high porosity and low permeability. carbonate-cemented sandstones are considered non-reservoir due to insignificant porosity and low permeability. references aase, n.e., bjørkum, p.a. & nadeau, p.h. 1996: the effect of grain-coating microquartz on preservation of reservoir porosity. aapg bulletin 80, 1654–1673. american petroleum institute 1998: api recommended practice 40. recommended practices for core analysis, 240 pp. second edition. washington dc: api publishing services. bjørlykke, k., ramm, m. & saigal, g.c. 1989: sandstone diagenesis and porosity modification during basin evolution. geologische rundschau 78, 243–268. boles, j.r. & franks, s.g. 1979: clay diagenesis in wilcox sandstones of southwest texas: implications of smectite diagenesis on sandstone cementation. journal of sedimentary research 49, 55–70. hower, j., eslinger, e.v., hower, m.e. & perry, e.a. 1976: mechanism of burial metamorphism of argillaceous sediment: 1. mineralogical and chemical evidence. geological society of america bulletin 87, 725–737. jahren, j. & ramm, m. 2000: the porosity-preserving effects of microcrystalline quartz coatings in arenitic sandstones: examples from the norwegian continental shelf. in: worden, r.h. & morad, s. (eds): quartz cementation in sandstones. international association of sedimentologists special publication 29, 271–280. johannessen, p.n., dybkjær, k., andersen, c., kristensen, l., hovikoski, j. & vosgerau, h. 2010: upper jurassic reservoir sandstones in the danish central graben: new insights on distribution and depositional environments, 12–34. in: vining, b.a. (ed.): petroleum geolog y: from mature basins to new frontiers. proceedings of the 7th petroleum geolog y conference. geological society, london. panterra geoconsultants 2011: sedimentolog y, petrography and reservoir quality of cores from the ravn-3 well, north sea, denmark. geus archive report file no 28698. pedersen, s.s. 2017: the diagenetic impact on reservoir sandstones of the heno formation in the ravn-3 well, danish central graben, denmark. unpublished master thesis, university of copenhagen. pollastro, r.m. 1985: mineralogical and morphological evidence for the formation of illite at the expense of illite/smectite. clays and clay minerals 33, 265–274. taylor, t.r., giles, m.r., hathon, l.a., diggs, t.n., braunsdorf, n.r., birbiglia, g.v., kittridge, m.g., macaulay, c.i. & espejo, i.s. 2010: sandstone diagenesis and reservoir quality prediction: models, myths, and reality. aapg bulletin 94, 1093–1132. weibel, r., friis, h., kazerouni, a.m., svendsen, j.b., stokkendal, j. & poulsen, m.l.k. 2010: development of early diagenetic silica and quartz morphologies – examples from the siri canyon, danish north sea. sedimentary geolog y 228, 151–170. worden, r. & burley, s. 2003: sandstone diagenesis: the evolution of sand to stone. in: burley, s.d. & worde, r.h. (eds): sandstone diagenesis: recent and ancient. international association of sedimentologists special publication 4, 3–44. authors’ addresses s.p., university of copenhagen, department of geosciences and natural resource management, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: simonepeder89@gmail.com. r.w., n.h.s. & p.j., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. mailto:simonepeder89@gmail.com geological survey of denmark and greenland bulletin 41, 2018, 43-46 43 during the 2013 field season, siliciclastic and carbonate rocks of the lower palaeozoic sedimentary succession of the franklinian basin in amundsen land, central north greenland, were collected for whole-rock geochemical analysis. these data are evaluated here in an attempt to identify possible hydrothermal signatures related to sediment-hosted zn-pb mineralisation, similar to that found in correlative strata at the large citronen fjord deposit located c. 100 km to the eastnorth-east. in this paper, we use the term sedex in a broad sense to describe stratiform, sediment-hosted deposits that formed either by syngenetic (exhalative) processes or by subsea-f loor replacement coeval with sedimentation (e.g. emsbo et al. 2016); the term mississippi valley-type (mvt) is used for non-stratiform zn-pb deposits that formed epigenetically during late diagenesis or tectonism (e.g. leach et al. 2010). regional setting the late precambrian to devonian franklinian basin extends c. 2000 km from the canadian arctic islands to eastern north greenland (higgins et al. 1991). in eastern north greenland, this basin fill overlies the proterozoic independence fjord group and the hagen fjord group, corresponding to the passive continental margin of laurentia. the franklinian basin is characterised by a transition from a deep-water trough, with mainly fine-grained siliciclastic strata, separated from shelf carbonates to the south (fig. 1; higgins et al. 1991). as summarised in kolb et al. (2016), zn-pb mineralisation in the franklinian basin resulted from two different events: early exhalative and/or sub-seaf loor replacement in deep-water siliciclastic rocks, and late epigenetic mvt mineralisation in shelf carbonates. the present study concerns the potential for zn-pb mineralisation in the lower ordovician to lower silurian amundsen land group, in amundsen land. in the study area, the amundsen land group comprises black bedded chert and laminated mudstone, commonly siliceous, with subordinate thin-bedded siliceous turbidites and greenish siltstone; locally, thick redeposited chert and limestone conglomerate interbedded with thick calcareous turbidites are present (friderichsen et al. 1982). the chert contains radiolarians (higgins et al. 1991), implying that biogenic silica is responsible for the quartz-rich nature of these rocks, and the siliceous mudstone. approximately 100 km east-north-east of the study area, in northern peary land, correlative siliciclastic rocks host the large undeveloped, sediment-hosted citronen fjord deposit (fig. 1; van der stijl et al. 1998), with reported total resources (measured + indicated + inferred), at a 2.0% zn cut off, of 132 mt with 4.0% zn and 0.4% pb (ironbark zinc base-metal and ree anomalies in lower palaeozoic sedimentary rocks of amundsen land, central north greenland: implications for zn-pb potential diogo rosa, john f. slack and hendrik falck greenland 20°w 82°n 30°w 100 km nava rana fjo rd esca rpme ntnava rana fjo rd esca rpme nt peary land johannes v. jensen land a b amundsen land silurian (sandy turbidite) cambro-ordovician (siltstone, mudstone) early cambrian (mudstone, sandstone, conglomerate) basement d ee pw at er de po sit s sh el f de po sit s silurian (carbonates) cambro-ordovician (carbonates, minor mudstone) early cambrian (sandstone, mudstone) franklinian basin proterozoic (sandstone, carbonates, dolerite, basalt) quaternary overburden kap washington volcanic rocks cretaceous–cenozoic (lava, pyroclastic rocks) wandel sea basin carboniferous–cenozoic (fluvial/marine sandstone, carbonates, shale) fig. 1. geology of central north greenland, showing locations of sampled section in amundsen land (a) and of citronen fjord zn-pb deposit (b); modified after escher & pulvertaft (1995). © 2018 geus. geological survey of denmark and greenland bulletin 41, 43–46. open access: www.geus.dk/bulletin http://www.geus.dk/bulletin 4444 2012). in the model of slack et al. (2015), this deposit formed predominantly by exhalative processes. younger epigenetic, carbonate-hosted, mvt zn-pb occurrences, found in the carbonate shelf in southern peary land, are related to the migration of basinal brines expelled by tectonism and/or hydraulic head caused by ellesmerian orogenic uplift during the middle to late devonian (rosa et al. 2016). in amundsen land, no carbonate shelf exists, so this mineralisation style is not expected to be present, although effects of the ellesmerian orogeny are well expressed by open to recumbent folds and local thrust faults. methods all samples were collected along one section across strata of the amundsen land group at wgs84 longitude 35°.3647 w and latitude 82°.9655 e (fig. 1). twenty-two samples of silty limestone, dolomitic mudstone and mudstone were analysed using a variety of methods. all data are from acme analytical laboratories ltd. in vancouver, british columbia (canada), except y and rare-earth elements (ree) that were determined at activation laboratories ltd. in ancaster, ontario (canada). detailed information on methods, standards, and uncertainties are given on the respective web sites (www.acmelab.com; www.actlabs.com). complete analyses of all 22 samples are available in appendix a (online excel file). results several samples have distinctive bulk compositions. for major-element oxides, one of three grey mudstones contains slightly high fe 2 o 3 t (7.83 wt%) relative to average shale (6.75 wt%; appendix iv in krauskopf & bird 1995); this sample also has elevated mno (0.14 wt%) in contrast to the other samples that contain <0.05 wt% mno. the three mudstones have uniformly low total s and organic c (<0.8 wt% and <0.7 wt%, respectively). for metals of economic and exploration interest, one mudstone sample is noteworthy for having slightly anomalous zn (174 ppm), pb (29.6 ppm), ni (75.0 ppm) and as (24.7 ppm) relative to average concentrations in shale (zn = 95 ppm; pb = 20 ppm; ni = 68 ppm; as = 13 ppm; krauskopf & bird 1995, appendix iv). one sample of silty limestone has the highest total s (1.27 wt%) and pb (63.0 ppm) among all 22 analysed samples, the latter concentration being highly anomalous relative to the average of 3.1 ppm pb for unaltered limestone (hartree & veizer 1982). abundances of ree vary greatly from 0.6–2.0 × average post-archaean australian shale (paas; fig. 2). most of the mudstone and all of the carbonate-rich samples (silty limestone, dolomitic limestone, calcareous shale) display relatively f lat paas-normalised patterns, which are typical of sedimentary rocks from throughout the geological record (e.g. mclennan 1989). however, one mudstone and both siliceous mudstone samples show slight depletion of light rareearth elements (lree). most of the silty limestone samples display slight enrichment of lree. calculated eu anomalies (eu/eu*), relative to paas, range from 0.90 to 1.51; 20 of 22 samples have positive anomalies, the three highest values (1.41–1.51) occurring in silty limestone. these eu anomalies are not an analytical artifact of ba interference on eu (e.g. slack et al. 2004), because no correlation exists between eu/ eu* and ba. also important is the fact that all samples display small negative ce anomalies (ce/ce*), which relative to paas vary from 0.81 to 0.95; most are true anomalies (i.e., unrelated to anomalous la enrichment), based on a discriminant plot of pr/pr* vs ce/ce* (fig. 3). field of shaley carbonates (n = 5) in hangingwall of citronen fjord deposit footwall of citronen fjord deposit 0.1 1 10 la ce pr nd sm eu gd tb dy ho er tm yb lu sa m pl e/ pa a s sa m pl e/ pa a s a 0.1 1 10 la ce pr nd sm eu gd tb dy ho er tm yb lu b mudstone siliceous mudstone silty limestone calcareous mudstone dolomitic mudstone fig. 2. plots of rare-earth element concentrations of representative samples of early palaeozoic sedimentary rocks from amundsen land group in amundsen land. a: mudstone and siliceous mudstone. b: calcareous mudstone, dolomitic mudstone, and silty limestone. field of samples hosting the citronen fjord deposit are included (slack et al. 2015), for comparison; note that small positive eu anomalies for these samples (1.16-1.29) are not evident due to overlapping patterns. normalisations are to average postarchean australian shale (paas); data from taylor & mclennan (1985). http://www.acmelab.com http://www.actlabs.com http://www.geus.dk/media/19170/nr41_p43-46-appendix-a-whole-rock-analyses.ods 45 discussion the presence in one mudstone sample of slightly high fe 2 o 3 t, zn, pb, ni and as is permissive evidence of a hydrothermal component being present in the basin. the small lree depletion in this sample and in the two siliceous mudstone samples (fig. 2a), likely ref lects the dissolution of detrital apatite, which in low-temperature sedimentary environments occurs by interaction with acidic f luids and not typical seawater-derived pore f luids (see slack et al. 2017). the geochemical data for this mudstone sample, namely elevated mno together with very low mo, record sedimentation and early diagenesis in oxic bottom waters (e.g. slack et al. 2017). oxic bottom waters are consistent with the presence of small negative ce anomalies in this sample, in both siliceous mudstone samples, and in most of the carbonate-rich rocks. these conditions, as well as the apparently low availability of h 2 s in pore f luids beneath the palaeo-sea f loor (total s <0.8 wt%), were also proposed by slack et al. (2015) for the host sedimentary rocks during initial formation of the citronen fjord deposit. however, according to their model for that deposit, only after emplacement of debris f lows that physically restricted the local basin and sealed off communication with the larger oxic ocean, did the venting of hydrothermal f luids turn the bottom waters anoxic and possibly locally very reducing (euxinic) and allow for sulphide preservation. if this model for the redox evolution of the citronen fjord deposit is correct, an analogous scenario for amundsen land (this study) hinges on verifying the local presence of anoxic to euxinic bottom waters, a requirement as yet unachieved, without supporting evidence from additional sampling and analyses. the presence of small positive eu anomalies in most samples is consistent with a hydrothermal component (e.g. lottermoser 1992). however, other non-hydrothermal processes can also create small positive eu anomalies in sedimentary rocks, both siliciclastic and carbonate. for example, in organic-rich black shales, small positive eu anomalies may form diagenetically in euxinic pore f luids (slack et al. 2017, and references therein), but no evidence of such f luids exists in the geochemically anomalous mudstone, based on its elevated mno (0.14 wt%) coupled with low organic c (0.37 wt%) and very low mo (1.75 ppm) contents, which together indicate oxic (not anoxic or euxinic) bottom waters and pore f luids (see slack et al. 2017). furthermore, toc values lack any correlation with metal concentrations. the relatively high fe 2 o 3 t content of this mudstone sample could be a hydrothermal signature, but might also ref lect a detrital component derived from a fe-rich source area. regarding the positive eu anomalies present in all of the carbonate samples, a possible non-hydrothermal origin for this anomaly may be related to a large clay component (tostevin et al. 2016), but this explanation is ruled out by the fact that the samples with the highest eu/eu* values (1.41–1.51) have uniformly low al 2 o 3 (0.49–0.62 wt%). given these observations, we conclude that the small positive eu anomalies ref lect a hydrothermal signature, involving the passage of reduced f luids that preferentially carried eu2+ (bau 1991). importantly, a hydrothermal origin has also been proposed by several workers for positive eu anomalies in the carbonate gangue and carbonate-rich wall rocks and country rocks of several stratiform sedex deposits (e.g. slack et al. 2004; frimmel 2009). the inferred hydrothermal component in the early palaeozoic siliciclastic and carbonate rocks of the studied section can be ascribed to either a distal or a proximal source, or both. in the case of a distal source, the likely prolonged (c. 105–106 y) venting of hydrothermal f luids into seawater to form the citronen fjord deposit could account for the eu incorporated into the distal mudstones and carbonates of amundsen land during sedimentation, by mixing of hydrothermally derived eu with seawater. in the latter case, involving a proximal source, the observed base-metal and ree anomalies – both eu and lree – in the samples analysed here could record a hydrothermal signature from a local system of either syngenetic or epigenetic origin. given the apparent lack of organic-rich black shales in the study area with anoxic or euxinic redox signatures, a syngenetic origin for this postulated zn-pb mineralisation is considered unlikely, either by purely exhalative or downward-penetrating brine processes (emsbo et al. 2016; sangster 2018). the occurrence of undiscovered mvt zn-pb deposits is also possible (rosa et al. 2016), but this type of mineralisation is characterised by negative, not 0.90 0.95 1.00 1.05 1.10 1.15 1.20 0.6 0.7 0.8 0.9 1.0 1.1 1.2 c e/ c e* pa a s pr/pr* paas true negative ce anomaly true positive ce anomaly fig. 3. plot of ce anomaly (ce/ce*) vs pr anomaly (pr/pr*) for analysed samples of early palaeozoic sedimentary rocks from the amundsen land group in amundsen land. data are normalised to paas. fields after bau & dulski (1996). symbols as in fig. 2. 4646 positive, eu anomalies in carbonate host rocks and gangue minerals (e.g. graf 1984; souissi et al. 2013). in summary, considering all available field and geochemical data, including the lack of evidence for anoxic or euxinic bottom waters during sedimentation, we suggest that the base-metal and ree anomalies highlighted in this study from the amundsen land group, in amundsen land, favour a potential for local sedex zn-pb mineralisation that formed mainly by the sub-sea-f loor replacement of carbonate-rich sediments. additional sampling and geochemical analysis are recommended for the study area, in order to better evaluate this mineral potential. acknowledgements this work was financially supported by geus and the ministry of mineral resources of greenland, through the nordzinc project. additional support was provided by the northwest territories geological survey, canada. per kalvig and erik vest sørensen of geus are acknowledged for collaboration during field work. we thank hartwig frimmel (university of würzburg) and steve piercey (memorial university of newfoundland) for helpful reviews. online appendix a: whole-rock analyses of early palaeozoic sedimentary rocks from the amundsen land group in amundsen land. references bau, m. 1991: rare-earth element mobility during hydrothermal and metamorphic f luid-rock interaction and the significance of the oxidation state of europium. chemical geolog y 93, 219–230. bau, m. & dulski, p. 1996: distribution of yttrium and rare-earth elements in the penge and kuruman iron-formations, transvaal supergroup, south africa. precambrian research 79, 37–55. emsbo, p., seal, r.r., breit, g.n., diehl, s.f. & shah, a.k. 2016: sedimentary exhalative (sedex) zinc-lead-silver deposit model. u.s. geological survey scientific investigations report 2010–5070–n, 57 pp. escher, j.c. & pulvertaft, t.c.r. 1995: geological map of greenland, 1:2 500 000. copenhagen: geological survey of greenland. friderichsen, j.d., higgins, a.k., hurst, j.m., pedersen, s.a.s., soper, n.j. & surlyk, f. 1982; 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the citronen fjord massive sulphide deposit, peary land, north greenland: discovery, stratigraphy, mineralization and structural setting. geolog y of greenland survey bulletin 179, 40 pp. authors’ addresses d.r., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k denmark. e-mail: dro@geus.dk. j.f.s., u.s. geological survey (emeritus), national center, ms 954, reston, va 20192 usa. h.f., northwest territories geoscience survey, p.o. box 1320, yellowknife, nwt x1a 2l9 canada. http://www.geus.dk/media/19170/nr41_p43-46-appendix-a-whole-rock-analyses.ods http://www.geus.dk/media/19170/nr41_p43-46-appendix-a-whole-rock-analyses.ods http://ironbark.gl/projects/greenland/citronen/ http://ironbark.gl/projects/greenland/citronen/ mailto:dro@geus.dk geological survey of denmark and greenland bulletin 41, 2018, 95-98 95 geology does not respect national borders. hence, in order to get geological overviews of europe, input from geological surveys in more than 35 countries is required. european policy makers have several times been forced to rely on the us geological survey to provide e.g. resource estimates from the european continent, but for obvious reasons there is a wish to base european decision making on european knowledge. consequently, the european commission and the european parliament have formulated a request for the establishment of a ‘geological service for europe’. in its strategy towards 2020, eurogeosurveys (egs) addresses the creation of such a service through three pillars. egs is an umbrella organisation through which national geological survey organisations of 36 european countries cooperate, referred to below as national surveys. the three pillars are designed to integrate input from all national surveys into a system that can swiftly act on urgent needs for knowledge-based decision support. the three pillars relate to joint research, data integration and sharing of facilities (fig. 1). whilst the third pillar has only recently been dealt with, the two first have already advanced through a number of recent initiatives. having been a key player in numerous eu projects for many years, the geological survey of denmark and greenland (geus) has attained a central role in the implementation of these two pillars of the strategy, both as coordinator of the european geological data infrastructure (egdi, www.europe-geology.eu) and as one of the biggest players in the so-called geoer a programme. geus participates in ten projects and is a partner in the secretariat and the coordinator of the geoer a information platform. the present paper outlines the main steps towards the current situation and provides a background for geus’ role in this. towards a eu geological knowledge base the european commission has contributed financially through several framework programmes to increase knowledge sharing, capacity building as well as cross-border and pan-european research within different geoscience domains. in most cases, data play a central role, and egs members have many years of experience in working together with the purpose of making geological data fair (findable, accessible, interoperable and reusable). in many cases, european projects have historically only had the participation of a limited number of national surveys, but in 2008 a f lagship project funded by the eu was launched with the participation of 20 national surveys as a logical follow-up of the global onegeology initiative (www.onegeology.org). onegeology aimed at assembling a geological map of the world on a scale of 1:1 000 000 by piecing together national contributions in whatever format they had, using distributed web services. the onegeologyeurope project went a step further. geus and the 19 other european national surveys worked together for two years to produce a distributed, web-based surface geological map of europe on a scale of c. 1:1  000  000 that was harmonised with a common data structure and agreed geological classifications. at that time, the project represented a leading edge activity, as it demonstrated the power of national organisations working together around a common data structure and nomenclature for geological units (geochronology and lithology). importantly, the project built on principles and rules from the inspire directive from 2007 and was thus not only a step on the way for the national surtowards a common geological data infrastructure for europe jørgen tulstrup and mikael pedersen the geological surveys of europe jo in t re se ar ch (g eo er a ) d at a in te gr ati on a nd h ar m on is ati on (e g d i) kn ow le dg e, c ap ac it y an d in fr as tr uc tu re s ha ri ng european geological service fig. 1. the three pillars of the egs strateg y for the establishment of a european geological service. © 2018 geus. geological survey of denmark and greenland bulletin 41, 95–98. open access: www.geus.dk/bulletin http://www.europe-geology.eu http://www.onegeology.org http://www.geus.dk/bulletin 9696 veys to fulfil their obligations towards the directive, but also served to demonstrate the feasibility of making geological data interoperable for europe and beyond. the results of the project were fed into the legal process to define the eu-wide inspire geological data specification, which since 2014 constitutes the implementing rules. upon the success of onegeologyeurope, a natural extension came with the increased attention on securing the supply of critical raw materials for european industry. this was partly based on the rare-earth element trade dispute that began in 2010 when china imposed strict export quotas for rare-earth elements. such elements are used in a number of high-technology industries, and since china accounts for 97% of the world production, the situation was considered critical (kalvig & machacek 2018, this volume). consequently, the european commission urgently needed an overview of raw materials resources in europe. this led to a number of eu projects. especially one of them had strategic importance for the egs, namely the minerals4eu project. geus cooperated with 27 other national surveys and other eu organisations to build the foundation for a european raw materials knowledge base, by extending the onegeologyeurope philosophy and by complying with and contributing to inspire. subsequently, other eu projects like eurare, prosum, mica and the recently launched or ama project have extended and/or improved this common knowledge base. at the same time geus also participates in the knowledge and innovation community (kic) for raw materials, through which a number of complementary projects are run in cooperation with universities and industrial partners. simultaneously with these raw materials projects, a number of other european data harmonisation projects were carried out within other egs research areas such as groundwater, energy, geohazards and soil. however, it became increasingly clear along the way that there was a need for coordination in order to increase the efficiency, reusability and sustainability – not only to meet european expectation, but also for the sake of geoscientists. this was addressed in the egs strategy that was published in 2014 and laid the foundation for the european geological data infrastructure. the european geological data infrastructure in 2012, egs’ members were granted a two-year eu project called egdi-scope, aiming to assess the possibilities of setting up a long-term sustainable european geological data infrastructure in line with the second pillar of the egs strategy. the initiative addressed the fact that almost all previous common european geoscience projects had succeeded in producing good european datasets and commonly also web-based dissemination platforms, but that such systems would typically disappear after a certain period because of lack of financial support for basic operation and maintenance. the egdi-scope project revealed that data from more than 80 past european projects, worth 400–700 million euro, could potentially be ‘saved’ and made available through a common data infrastructure which should also be the natural dissemination platform for future projects. geus was part of the egdi-scope core team and was in charge of stakeholder consultation, thereby analysing both end-user needs and interfaces to other large european earth science projects and initiatives. an important goal of egdi-scope was to pave the way for a larger eu project, whereby egdi could be implemented. fig. 2. the interactive map viewer of the european geological data infrastructure (egdi) portal through which hundreds of different data themes can be viewed in combination. the map shown here illustrates the concentration of lead in grazing land (coloured dots) on top of a geological map of europe. 97 unfortunately no appropriate horizon 2020 (eu’s framework programme) calls were launched, and two proposals targeting some generic electronic infrastructure calls were rejected. however, the concept of egdi was widely used in strategic communication, and eventually the situation became critical: everybody talked about egdi, but it did not exist. consequently, geus mobilised the so-called ‘spatial information expert group’ of the egs, and after a long process of argumentation and communication the egs general assembly accepted to provide in-kind resources from the national surveys to establish a first basic implementation of the egdi. egdi version 1 on 14 june 2016, the first version of egdi was launched at the premises of the egs secretariat in brussels. besides directors and other egs key persons, the audience comprised a number of distinguished eu commissioners representing different parts of the commission, including dg grow (raw materials), dg mare (maritime affairs), dg ener (geoenergy), dg rtd (research) and dg jrc (joint research and inspire). the participants were very happy with what they saw. even though it is not fully-f ledged, egdi v.1 contains most parts of the system that was identified under the egdi-scope project. a number of datasets from past european projects are included and made available through a common web portal (www.europe-geology.eu; fig. 2), which was to a large extent developed by geus. however, the portal is only a small part of egdi. the infrastructure itself consists of a complex of central databases, a metadata catalogue and distributed web services that all conform to the same standards. roles and responsibilities are agreed internally in egs, and work is in progress to establish a more permanent governance structure. egdi in the european landscape of electronic infrastructure egdi is not alone! there are many other related european initiatives (fig. 3) and a few will be mentioned here. the european plate observing system (epos) is a research infrastructure for solid-earth sciences in europe and is of strategic importance to the eu. it aims to facilitate research into natural disasters such as earthquakes and volcanic eruptions through the integration of geoscience data from a number of different research communities. geological data represent one of the domains that epos will integrate; the egs community is the main provider of such data. geus has a role in the implementation project epos-ip and actively uses this position together with other participating national surveys to ensure the complementarity between egdi and epos through various coordination activities. the european marine observation and data network (emodnet) is a large programme aiming at providing uniform access to marine data from europe’s coastal states. emodnet is divided into seven discipline-based themes, one of which deals with geological data. the emodnetgeology project has been running in several phases since it started in 2008. in the current third phase, geus has leading role in the work package dealing with data management and web portal development – again a strong position that geus uses to strengthen the coherence of the european e-infrastructure landscape through technical coordination with egdi, epos and other large initiatives. the role of egdi as a central data-bearing component in european geoscience research is continuously being strengthened through coordination with other european projects and programmes. one of these is geoer a. rmis, openecho... fig. 3. the central position of the egdi in the european e-infrastructure landscape. egdi serves geological data from a lot of different geological research areas and thereby contributes geological data to numerous european information systems through interoperable web services. 9898 geoera the first pillar of the egs strategy, the joint research pillar, is on its way to be implemented through an er a-net on ‘establishing the european geological surveys research area to deliver a geological service for europe (geoer a)’. the main objective of geoer a (http://geoera.eu) is to contribute to the optimal use and management of the subsurface. forty-eight national surveys from 33 european countries will participate in research projects under geoer a with the purpose of supporting a more integrated and efficient management as well as a more responsible and publicly acceptable exploitation and use of the subsurface. geoer a covers the three geoscientific themes of geo-energy, groundwater and raw materials; the projects will run for three years starting in july 2018. the three geoscientific themes share the objective of organising and disseminating a large amount of results in the form of digital maps and other data. furthermore, crossthematic integration of information is an important aspect of geoer a. it has therefore been decided to establish a common ‘information platform’ for the efficient integration of all it-related and technical issues (database and dissemination) from all geoer a projects. the platform will be capable of integrating up-to-date data, interpretations and models from different and distributed sources, both within and across the three main geoscientific themes of geoer a. the platform will be based on egdi which contains some of the functionality foreseen to be required by the geoer a projects. egdi will, however, have to be extended in order to handle and disseminate for instance 3d/4d geological models. in addition to organising the geoscientific projects, geoer a also carries out ‘foresight activities’ with the purpose of assessing how longer-term funding of the activities can be obtained and eventually lead to a ‘geological service for europe’. the safeguarding of the geoer a results through the information platform and the long-term operation and maintenance of the entire egdi should be seen in this context. the future one of the main challenges for all these european initiatives, including egdi, is to make them sustainable. all eu projects are run for a limited period after which the funding ends, and due to budget mechanisms, the european commission is not in a position to fund permanent maintenance of any system. egs has therefore continuously tried to find sustainable funding models to keep egdi alive in a technical and organisational sense. currently the egs members are able to finance the very basic operation of egdi. from 2018–2021 work within the geoer a projects will ensure that egdi will be significantly upgraded with much more data and functionality. with egdi becoming a continuously bigger and more integrated piece in the european puzzle, the chances of finding a long-term solution are on the increase, but a sustainable solution will probably have to be connected to the establishment of the ‘geological service for europe’ at least partly funded by eu. other challenges facing the generation of truly paneuropean harmonised geological datasets are that some of the most relevant data are considered confidential in some countries. this is for instance the case for some data about mineral occurrences in certain east european countries. in other countries the organisation and provision of data are the responsibility of regional authorities instead of national surveys, who are less committed to the european viewpoint on data than egs. finally, it has turned out that it is difficult to convert national geological databases and make them interoperable according to the requirements in the inspire implementing rules. many of these rules are very complicated, and many resources have been allocated to the database administrators at the national surveys in order to make their data compliant with the standards. references an effective raw materials strateg y for europe. european parliament resolution of 13 september 2011 on an effective raw materials strateg y for europe. https://eur-lex.europa.eu (2011/2056(ini)). communication from the commission to the european parliament, the council, the european economic and social committee and the committee of the regions. making raw materials available for europe’s future wellbeing. proposal for a european innovation partnership on raw materials. https://eur-lex.europa.eu (com(2012) 82). kalvig, p. & machacek, e. 2018: examining the rare-earth elements (r ee) supply-demand balance for future global wind power scenarios. geological survey of denmark and greenland bulletin 41, 87–90 (this volume). the eurogeosurveys vision towards a geological service for europe. htt p://www.eurogeosurveys .org/wp-content/uploads/2014/08/egsstrategy-document-2014-a4.pdf. authors’ address geological survey of denmark and greenland, øster voldgade 10, 1350 copenhagen k, denmark. e-mail: jtu@geus.dk. https://eur-lex.europa.eu https://eur-lex.europa.eu http://www.eurogeosurveys.org/wp-content/uploads/2014/08/egs-strategy-document-2014-a4.pdf http://www.eurogeosurveys.org/wp-content/uploads/2014/08/egs-strategy-document-2014-a4.pdf mailto:jtu@geus.dk geological survey of denmark and greenland bulletin 33, 2015, 1-7 1 geological survey of denmark and greenland bulletin 33 • 2015 review of survey activities 2014 edited by ole bennike, adam a. garde and w. stuart watt geological survey of denmark and greenland ministry of climate, energy and building 22 geological survey of denmark and greenland bulletin 33 key words geological survey of denmark and greenland, survey organisations, current research, denmark, greenland. cover photographs from left to right 1 fractured granite on the island of bornholm. photograph: merete binderup. 2 th e swedish ice-breaker oden in the arctic ocean. photograph: martin jakobssen. 3 a geologist enjoying the magnifi cent view over the landscape in south-east greenland. photograph: jakob lautrup. 4 a geologist crossing a local ice cap on nuussuaq peninsula in west greenland. photograph: jason briner. frontispiece: facing page ice conditions in the area north of greenland during the geus lomrog 2012 cruise with the swedish ice-breaker oden. see paper by c. marcussen et al. in this issue. photograph: th omas funck. chief editor of this series: adam a. garde editorial board of this series: john a. korstgård, department of geoscience, aarhus university; minik rosing, geological museum, university of copenhagen; finn surlyk, department of geosciences and natural resource management, university of copenhagen scientifi c editors: ole bennike, adam a. garde and w. stuart watt editorial secretary: jane holst referees (numbers refer to fi rst page of reviewed article): anonymous (17, 33); leon bagas, au (49); liz bagshaw, uk (69); niels balling, dk (21); sean brennan, usa (85); hilmar bungum, no (21); david burgess, ca (61); valeria caironi, it (53); mikael calner, se (9); jakob qvortrup christensen, dk (33); ida lykke fabricius, dk (13); xavier fettweis, be (65); peter gerling, de (85); henning haack, dk (25); maths halstensen, no (13); douglas r. hardy, usa (69); jens havskov, no (25); martin heinesen, fo (41); julie hollis, gl (53); niels tvis knudsen, dk (57); john korstgård, dk (17, 37); jeppe malmros, ch (57); ruth mottram, dk (65); asger ken pedersen, dk (45); minik rosing, dk (49); mark simoni, no (37); henrik stendal, gl (77, 81); svend stouge, dk (9); max strunck, se (73); phil symonds, au (41); leif th eilgaard, dk (29); henrik vedel, dk (29); tod e. waight, dk (45); jacob clement yde, no (61, 73). illustrations: benny m. schark, jette halskov, stefan sølberg, willy l. weng, susanne rømer and frants v. platen-hallermund layout and graphic production: kristian a. rasmussen printer: rosendahls-schultz grafi sk a/s, albertslund, denmark manuscripts received: 8 december 2014 – 12 may 2015 final versions approved: 27 january 2015 – 21 may 2015 printed: 7 july 2015 issn (print) 1604-8156 issn (online) 1904-4666 isbn (print) 978-87-7871404-6 isbn (online) 978-87-8771-405-3 citation of the name of this series it is recommended that the name of this series is cited in full, viz. geological survey of denmark and greenland bulletin. if abbreviation of this volume is necessary, the following form is suggested: geol. surv. den. green. bull. 33, 88 pp. available from geological survey of denmark and greenland (geus) øster voldgade 10, dk-1350 copenhagen k, denmark phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: geus@geus.dk and at www.geus.dk/publications/bull © de nationale geologiske undersøgelser for danmark og grønland (geus), 2015 for the full text of the geus copyright clause, please refer to www.geus.dk/publications/bull 3 33 relationship between groundwater chemistry and the precambrian basement rocks on eastern bornholm, denmark p. gravesen, r. jakobsen and b. nilsson 37 assessment of the mineral raw material potential in denmark – methods and major fi ndings j.k. keiding, p. kalvig, c. ditlefsen, s. lomholt and p.r. jakobsen 41 th e continental shelf project of the kingdom of denmark – status and issues c. marcussen, f. mørk, t. funck, w.l. weng and m. pedersen 45 magma mixing, mingling and hybridisation at diff erent crustal levels: snapshots from 1.9 billion years of magmatism in south-eastern greenland t.f. kokfelt, s.m. weatherley, j.k. keiding and t.b. árting 44 ghana greenland canada kenya burundi ethiopia nigeria cameroon malawi zambia bolivia bolivia denmark ghana brazil 7 review of survey activities 2014 flemming g. christiansen 9 th e lower palaeozoic now fully cored and logged on bornholm, denmark n.h. schovsbo, a.t. nielsen and k. klitten 13 down-hole permeability prediction – a chemometric wire-line log feasibility study from a north sea chalk well k.h. esbensen, n.h. schovsbo and l. kristensen 17 th rust-fault architecture of glaciotectonic complexes in denmark s.a.s. pedersen and l.o. boldreel 21 consistency of postglacial geodynamics for the kattegat region, southern scandinavia, based on seismological, geological and geodetic data s. gregersen and p.h. voss 25 acoustic events on a small seismological network – shock waves from thunder and fi reballs p.h. voss, t. dahl-jensen and t.b. larsen 29 a hydrological early warning system for denmark based on the national model h.j. henriksen, s. stisen, x. he and m.b. wiese grey indicates countries where geus had projects in 2014 orange indicates countries with geus projects decribed in this volume. 49 a quartz-wolframite-molybdenite vein and scheelite in amphibolite horizons from th rudvang peninsula, skjoldungen, se greenland d. rosa and t. ulrich 53 follow-up on ujarassiorit mineral hunt fi nds and outreach activities, south-east greenland m.d. poulsen, h. paulick, d. rosa, v.j. van hinsberg, j. petersen and l.l. th omsen 57 greenland ice sheet melt area from modis (2000– 2014) r.s. fausto, d. van as, j.a. antoft , j.e. box, w. colgan and the promice project team 61 unique applied glaciology challenges of proglacial mining w. colgan, h.h. th omsen and m. citterio 65 observed melt-season snowpack evolution on the greenland ice sheet c. charalampidis and d. van as 69 automatic weather stations for basic and applied glaciological research m. citterio, d.v. as, a.p. ahlstrøm, m.l. langer, s.b. andersen, j. e. box, c. charalampidis, w.t. colgan, r.s. fausto, s. nielsen and m. veicherts 73 digital models based on images taken with handheld cameras – examples on land, from the sea and on ice e.v. sørensen, m. bjerager and m. citterio 77 investigations of detrital zircon, rutile and titanite from present-day labrador drainage basins: fi ngerprinting the grenvillean front t.b. th omsen, c. knudsen and a.m. hinchey 81 composition of ilmenite and provenance of zircon in northern brazil c. knudsen, t.b. th omsen, f. kalsbeek, j.a. kristensen, h. vital and r.k. mclimans 85 reserves and resources for co2 storage in europe: the co2stop project n. poulsen, a. bocin-dumitriu, s. holloway, k. kirk, f. neele and n. smith 5 thailand vietnam phillippines indonesia singapore india tajikistan 7© 2015 geus. geological survey of denmark and greenland bulletin 33, 7–8. open access: www.geus.dk/publications/bull review of survey activities 2014 flemming g. christiansen deputy director over the past decades the geological survey of denmark and greenland (geus) has gradually changed from an organisation that focussed on basic mapping and research to one that provides knowledge for discussions and decisions within society and the political system in denmark and greenland. knowing the importance – and in some cases controversy – of many of these decisions, it is of the utmost importance that such input is based on high-quality and well-documented research that is objective, transparent and easily accessible. such input to important public and political discussion is also refl ected in this issue of the review of survey activities that contains a total of 20 four-page papers, eight on denmark, eighth on greenland and four on broader themes. in addition to many classical research summary papers, there are also examples of activities giving input to important political decisions on energy such as shale gas and carbon capture and storage technology, use of and exploration for mineral resources in denmark and greenland, climate (monitoring of the greenland ice sheet) and foreign policy (international boundaries). activities in denmark th e activities and research in denmark of geus cover a wide range of topics within our main programme areas: data, water, energy, mineral resources as well as nature and climate. th e island of bornholm has a diff erent geological history from the rest of denmark; a dominance of outcropping basement rocks and palaeozoic sedimentary rocks gives special research possibilities. one paper summarises information on the lower palaeozoic from scientifi c wells. th is succession is now fully cored and logged, thereby providing important data for correlation to other regions for assessing resources in denmark and scandinavia and for local use of water supplies. chalk is a very important rock type for denmark as it hosts more than 90% of the danish petroleum reserves in the north sea. one paper discusses one of the main challenges, namely prediction of permeability, which is a very critical parameter for production performance. geus is involved in many studies of quaternary and recent geological processes. one paper describes thrust-fault architecture of glacio-tectonic complexes using 3d geological models based on integrated photo-data from cliff sections with high resolution seismic data. geus records seismological events at many locations in denmark and greenland, data that are useful for many different purposes. one paper applies seismological, geological and geodetic data to discuss the consistency of postglacial geodynamics (especially uplift ) in the kattegat region. another paper provides examples of shock waves from thunder and fi reballs that have been detected on seismograms. th e use of groundwater is very important for the danish society, and geus carries out many studies on water resources and possible future scenarios due to changes in climate and use. one paper uses the comprehensive and constantly updated dk-model in the process of developing a hydrological early-warning system for denmark that can be important for water plans for emergency managers. another paper describes the relationship between groundwater chemistry and the weathering of precambrian basement rocks on eastern bornholm. th e center for minerals and materials (mima) at geus was established to identify and study important raw material chains from source to use, with the goal of enhancing our knowledge of the risk of resource scarcity and the ensuing vulnerability of the danish society. one paper gives an assessment of the mineral resource potential of the onand off shore areas in denmark with focus on methods and the main results. denmark has a high potential for aggregates, various clays, chalk and lime, salt and granite – but there are also many confl icting interests on the use of land and seabed where detailed planning and regulations are required. activities in greenland once again there was a high level of activity in and concerning greenland in 2014. many large and small projects were carried out, studies that are important for evaluating and marketing the resource potential in greenland. th e level of activity in both oil and mineral exploration is rather low at present, but it is very important to prepare for a future when 88 prices of the most important commodities will rise again. monitoring of ice and predicting climate changes are also important geus activities. th e work on the continental shelf project reached a new culmination point, when the 5th submission concerning a very large area north of greenland, with great international media coverage, was sent jointly to the commission on the limits of the continental shelf by the government of the kingdom of denmark and the government of greenland in december 2014. one paper gives a status for the recent work on the project and mentions some of the issues for the coming years where data and results will be presented and used in negotiations, maintainance and hopefully supplemented by additional scientifi c data. several papers focus on mapping and evaluation of the mineral potential in greenland. one paper gives snapshots of the magmatic history in south-eastern greenland with examples of magma mixing, mingling and hybridisation at diff erent crustal levels. a second paper gives details of mineralisation in the skjoldungen area, south-east greenland, where tungstenand molybdenum-bearing minerals have been discovered within veins in amphibolites. a third paper follows up on the annual ujarassiorit public mineral hunt in south-east greenland where a number of interesting samples have been found by local stone collectors (e.g. corundum, precious and base metals), and where considerable time during fi eld work was used for outreach activities in several small settlements. studies and monitoring of the greenland ice sheet and local glaciers provide a signifi cant contribution to models for global sea-level rise. th e important monitoring programme of the greenland ice sheet (promice) that was initiated in 2007 continuously supplies crucial data that are used in a number of subsequent projects and in key publications. th ree papers in this issue use such data from promice. one discusses the ice-sheet melt area, where data from modis (nasa’s moderate-resolution imaging spectroradiometer) are validated against promice data. a second is on the observed melt-season snowpack evolution of the greenland ice sheet. a third paper gives a technical description of the automatic weather stations that have been developed for basic and applied research. a fourth paper addresses applied glaciological challenges of proglacial mining, which may be important in greenland where several potential mining sites are located very close to the margin of the ice sheet. broader thematic activities internationally geus also works in many diff erent countries with a variety of projects and is involved in broader thematic studies. th e fi rst of these thematic papers describes how digital outcrop models can be made based on images from a handheld camera, with examples from land, sea and ice. a second paper gives details of a so-called provenance study in labrador, canada, using detailed analytical data on zircon, rutile and titanite that can be applied to map out boundaries between major orogenic terrains. another provenance study of heavy minerals from northern brazil is also presented, in this case with focus on titanium placer deposits. th e challenge of climate change demands reduction in global co2 emissions. one of the most promising technical solutions is to use carbon dioxide capture and storage (ccs). th e fi nal paper is a summary of the co2stop project, which has designed a database on storage capacity in 27 european countries and identifi ed important gaps in our knowledge. geological survey of denmark and greenland bulletin 33, 2015, 85-88 85© 2015 geus. geological survey of denmark and greenland bulletin 33, 85–88. open access: www.geus.dk/publications/bull reserves and resources for co2 storage in europe: the co2stop project niels poulsen, andrei bocin-dumitriu, sam holloway, karen kirk, filip neele and nichola smith th e challenge of climate change demands reduction in global co2 emissions. in order to fi ght global warming many countries are looking at technological solutions to keep the release of co2 into the atmosphere under control. one of the most promising techniques is carbon dioxide capture and storage (ccs), also known as co2 geological storage. ccs can reduce the world’s total co2 release by about one quarter by 2050 (iea 2008, 2013; metz et al. 2005). ccs usually involves a series of steps: (1) separation of the co2 from the gases produced by large power plants or other point sources, (2) compression of the co2 into supercritical fl uid, (3) transportation to a storage location and (4) injecting it into deep underground geological formations. co2stop is an acronym for the co2 storage potential in europe project. th e co2stop project which started in january 2012 and ended in october 2014 included data from 27 countries (fig. 1). th e data necessary to assess potential locations of co2 storage resources are found in a database set up in the project. a data analysis system was developed to analyse the complex data in the database, as well as a geographical information system (gis) that can display the location of potential geological storage formations, individual units of assessment within the formations and any further subdivisions (daughter units, such as hydrocarbon reservoirs or potential structural traps in saline aquifers). finally, formulae have been developed to calculate the storage resources. th e database is housed at the joint research centre, the european commission in petten, the netherlands. background and methods co2 storage resource assessment a resource can be defi ned as anything potentially available and useful to man. th e pore space in deeply buried reservoir rocks that can trap co2 is a resource that can be used for co2 storage. it is of utmost importance to be aware that the mere presence of a resource does not indicate that any part of it can be economically exploited, now or in the future. a reserve can be defi ned as that part of a resource that is available to be economically exploited now using currently available technology. th us, in order to move from a resource estimate to a reserve estimate, a whole series of technical, economic, legal and socio-economic criteria must be applied. th ese criteria will then identify the fraction of the resource that can actually be economically exploited in a particular jurisdiction area, using available technology. consequently, a very high level of technical assessment is required to demonstrate the existence of a co2 storage reserve, and in most cases these kinds of resources are only available within a demonstration or commercial storage project. for these reasons, it was impossible to defi ne any co2 storage reserves in the present project. 16°w 16°e 32°e 48°e 56°e 64°e 50°n 42°n 0 16°e0° 58°n 50°n 500 km 42°n 66°n co 2 stop project covered by geological surveys universities national institutes geol. survey/university not in co 2 stop latvia covered by the estonian-latvian transboundary project 8°e fig. 1. twenty-seven countries participated in the co2stop project. latvia was covered by the estonian–latvian border project. the following member states of the european union participated: austria, belgium, bulgaria, croatia, czech republic, denmark, estonia, france, germany, greece, hungary, ireland, italy, latvia, lithuania, the netherlands, poland, portugal, romania, slovakia, slovenia, spain and uk and the following non-member states: macedonia, norway, serbia and switzerland. 8686 storage mechanisms co2 can be retained in reservoir rocks by a number of mechanisms: (1) structural and stratigraphic trapping, in which co2 is retained by impermeable barriers, (2) residual trapping, in which free phase co2 is trapped by capillary forces in pore spaces, (3) dissolution of co2 into pore fl uids, (4) precipitation of co2 into minerals and (5) adsorption onto shale or coal layers. only the fi rst two of these mechanisms are signifi cant within a co2 storage project’s time frame of 10 to 50 years; the other mechanisms take much longer (van der meer & van wees 2006). th erefore, most previous studies of co2 storage resources (e.g. usgs assessment; doe storage atlases; norwegian assessment; iea best practices document) focussed on determining the amount of co2 that can be retained in conventional reservoir rocks as a dense fl uid in the fl uid-fi lled pore spaces between the grains that make up the matrix of the rock and in fl uid-fi lled fractures. moreover, the vast majority of the co2 will be trapped either in structural and stratigraphic traps or by capillary forces as a residual saturation (bachu et al. 2007). constraints on co2 storage capacity each jurisdiction area contains a given amount of pore space within its subsurface. th e total resource of pore space that is potentially available for co2 storage is that part which can be fi lled with, and will retain, injected co2. geology and physics dictate that this will be far less than the available total pore space. th ese limitations mean that only a small fraction of the total resource of pore space can be fi lled with co2. it is possible to defi ne a common method that can be used to estimate the fraction of the total pore space resource that can be used for storage (brennan 2014). if appropriate co2 densities at reservoir conditions are applied to this volume, this allows estimation of the theoretical co2 storage resource. in practice, only a fraction of the theoretical co2 storage resource in any given jurisdiction area can actually be utilised – for a variety of technical, economic, legal and social reasons. in the co2stop project, the pore space in a jurisdiction area is subdivided into reservoir formations. th ese are mappable bodies of rock which display mainly suffi cient porosity and permeability. each reservoir formation contains one or more storage units. a storage unit is defi ned as a part of a reservoir formation that is found at depths greater than 800 m and which is covered by an eff ective cap rock. th ese units are potential co2 storage units and they form the basis for the co2 storage assessments made in the co2stop project. each storage unit may contain one or more daughter units. daughter units are defi ned as structural or stratigraphic traps which have the potential to immobilise co2 within them, e.g. structural domes or proven oil and gas fi elds. th e storage potential of daughter units can be estimated separately in co2stop. the co2stop method th e co2stop project has established a database, a geographical information system (gis; esri’s arcgis 10) and a calculation engine that can provide probabilistic estimates of co2 storage capacities. th e data analysis & interrogation tool is a combination of microsoft access (data interrogation tool), and excel (storefit tool) with external code (linked to excel) to perform injection rate calculations. calculations carried out with the database analysis & interrogation tool include: storage capacity, injection rates and stochastic analyses of the storage capacity and injection rates (fig. 2). th e work to establish internationally recognised standards for capacity assessments was initiated by the carbon sequestration leadership forum (cslf) about a year before the start of the european union geocapacity project, and a cslf task force has been active since. th e paper ‘estimation of co2 storage capacity in geological media – phase 2’ by bachu et al. (2007) published by the cslf presents comprehensive defi nitions, concepts and methods to be used in estimating co2 storage capacity. as in the eu geocapacity, the co2stop method complies with the cslf recommendations. th e methods and calculations for determining the fractions of the resource, used in the co2stop project, also align with the recent international energy agency proposals for harmonising co2 storage capacity estimation methods (heidug 2013). th e co2stop method estimates the tasr (see below) and the storage resource in structural and stratigraphic traps, which have later been divided into two subsets: hydrocarbon fi elds and aquifer daughter units. the technically accessible co2 storage resource (tasr) th e co2stop calculation engine can produce a resource estimate that is similar to the technically accessible co2 storage resource (tasr) estimated by the us geological survey (brennan et al. 2010; blondes et al. 2013; u.s. geological survey geologic carbon dioxide storage resources assessment team 2013). th is is the fraction of the theoretical storage resource that can be accessed using all currently available technologies regardless of cost. th e international energy agency recommended that the fi rst step in all co2 storage resource estimates should be to assess the tasr (heidug 2013). 87 th e co2stop estimate diff ers in one main respect from the tasr estimated by the u.s. geological survey method, namely that co2stop adds the storage capacity of hydrocarbon fi elds to that of the saline aquifers. th is has to be done because the pore volume of the hydrocarbon fi elds is not provided in the project’s database, so it cannot be subtracted from the pore volume of the storage units before their storage capacity is estimated. th ere are other minor diff erences in the constraints and assumptions; nevertheless, the two methods produce results that are suffi ciently similar to allow them to be compared. results th e assessment of the various fractions of the co2 geological storage resource performed in the co2stop project is currently only at a provisional level. unfortunately, large diff erences exist between the types and quality of data available for each country, and the extent to which the data can be made public also varies widely. some countries only have data available from traps for buoyant fl uids, where the tasr will be low not taking into account any potential for storage outside such traps by residual saturation. some countries have included aquifer formation data; here the tasr calculation will be more meaningful. in the great majority of countries, uncertainties related to lack of reservoir parameter data also remain. th e acquisition of such data will potentially require a sustained campaign of geological mapping and characterisation of storage capacity, or at least signifi cantly more time and fi nancial resources to assemble and enter all available data. th ese factors limit the results obtained from the co2stop project and it is recommended that further resources are made available for improving the results. in a european context, the technically accessible co2 storage resource (tasr) or theoretical storage resource should only be used for extra-european international resource comparisons because it is clear that the tasr is several times greater than the practical co2 storage capacity. consequently quoting the tasr can be misleading, giving false impressions of capacity if a critical distinction between resource and reserve estimates is not made. co2stop gis data analysis tool co2stop data interrogation system co2 injection capacity data entry system view, filter and export data import results dsf: deep saline formation dgf: depleted gas field fill data calculations & data choices primary input output data storefit areas studied for the co2stop gis s to ra ge i d c ap ac it y d at ab as e (m t) f ie ld e x e n t (k m 2 ) t h ic k n e ss (m ) s t o r a g e u n it t r a p t r a p n a m e c a s e n a m e c a s e n o messages input file output file countries studied countries not participating in co 2 stop project aquifer daughter units hydrocarbon daughter units storage units formations length name 62 89 fig. 2. schematic representation of the database analysis & interrogation tool, showing the gis and the storefit monte carlo analysis tool. arrows indicate data exchange between the separate elements of the tool. the map shows the reported resources in the co2stop project. 8888 conclusions th e calculations of co2 storage locations throughout europe made by the co2stop project database paint a broad picture, but also identify the gaps in our knowledge. th ese gaps must be fi lled with further data entry and, potentially, new geological studies, seismic surveys and drilling must be undertaken to make more precise data available. a common european legislation allowing equal access to proprietary subsurface information would be benefi cial for this purpose. it is critically important to understand the assumptions that lie behind the storage capacity estimates. th ese are especially relevant for saline formations, the capacities of which were derived without taking regulatory or economic limitations into account. th e co2stop method has made signifi cant progress towards establishing probabilistic estimates of the co2 storage resource in europe in a way that will allow comparisons with other regions of the world, and which will also be useful to policy makers. however, the partial data entry into the project database means that the current project only marks the beginning of the process of resource estimation and certainly not the end. acknowledgements th e co2stop project was funded by the european commission (project no ener/c1/154-2011-si2.611598). we express our sincere thanks to andrei bocin-dumitriu (ec joint research centre) and to kai tullius, øivind vessia, rakel hunstad and ilinca balan from the european commission, directorate general for energ y for their help and support with this project and to this report and the other deliverables. we also thank the co2stop project partners for their contributions of country specifi c information. legal notice th is publication is based on a project for the european commission; however it refl ects the views only of the authors, and the commission cannot be held responsible for any use which may be made of the information contained therein. references bachu, s., bonijoly, d., bradshaw, j., burruss, r., christensen, n.p. holloway, s. & mathiassen, o.m. 2007: estimation of co2 storage capacity in geological media – phase 2. work under the auspices of the carbon sequestration leadership forum (www.cslforum.org). final report from the task force for review and identifi cation of standards for co2 storage capacity estimation, 43 pp. washington: carbon sequestration leadership forum. blondes, m.s. et al. 2013: national assessment of geologic carbon dioxide storage resources –methodolog y implementation. u.s. geological survey open-file report 2013–1055, 26 pp., http://pubs.usgs.gov/ of/2013/1055/ brennan, s.t. 2014: th e u.s. geological survey carbon dioxide storage effi ciency value methodolog y: results and observations. energ y procedia 63, 5123–5129. brennan, s.t., burruss, r.c., merrill, m.d., freeman, p.a. & ruppert, l.f. 2010: a probabilistic assessment methodolog y for the evaluation of geologic carbon dioxide storage. u.s. geological survey open-file report 2010/1127, 31 pp. heidug, w. (ed.) 2013: methods to assess geologic co2 storage capacity: status and best practice, workshop report, 44 pp. paris: international energ y agency. iea 2008: energ y technolog y perspectives: scenarios and strategies to 2050, 650 pp. paris: international energ y agency. iea 2013: technolog y roadmap. carbon capture and storage, 63 pp. paris: international energ y agency. metz, b. et al. (eds) 2005: carbon dioxide capture and storage. ipcc 2005, 431 pp. cambridge university press. u.s. geological survey geologic carbon dioxide storage resources assessment team 2013: national assessment of geologic carbon dioxide storage resources – results (ver. 1.1, september 2013). u.s. geological survey circular 1386, 41 pp. van der meer, l.g.h. & van wees, j.d. 2006: eff ects of co2 solubility on the long-term fate of co2 sequestered in a saline aquifer. th e leading edge 25, 1276–1280. authors’ addresses n.p., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: nep@geus.dk a.b.-d., european commission, dg jrc, institute for energy and transport, energy technology policy outlook unit, westerduinweg 3, 1755 le petten, the netherlands. s.h. & k.k., british geological survey (bgs), kingsley dunham centre, keyworth, nottingham, ng12 5gg, uk. f.n., tno, earth environment and life sciences, postal address: p.o. box 80015, 3508 ta utrecht, the netherlands. n.s., british geological survey, murchison house, west mains road, edinburgh, eh9 3la, uk. geological survey of denmark and greenland bulletin 31, 2014, 19-22 19 the lower palaeozoic shale gas play in denmark niels h. schovsbo, arne t. nielsen and donald l. gautier the unconventional gas resources in the lower palaeozoic shale of denmark were recently assessed by the united states geological survey (usgs; gautier et al. 2013). assuming unrestricted application of best practice current technology, recoverable gas resources of 0 to 130 × 109 nm3 gas were estimated onshore (mean = 67 × 109 nm3 gas) and 0 to 228 × 109 nm3 gas were estimated offshore (mean = 119 × 109 nm3 gas), i.e. a total estimated mean of 186 × 109 nm3 gas (nm3: normal cubic metre, unit used for natural gas at 0°c and 101.325 kpa). nearly all of this potential resource is assumed to be contained in the cambro-ordovician alum shale. the wide range of estimates reflects the sparse data and the geological uncertainty inherent in the still untested play. the estimated mean quantity of gas resource is comparable to the total volume of gas produced from the danish part of the north sea during 1972–2011 and twice the amount of the estimated remaining reserves of conventional gas in the danish part of the north sea. the assessment is the result of collaboration between the geological survey of denmark and greenland (geus) and usgs. geus and the university of copenhagen contributed with the geological input data and models and usgs provided assessment methodology and north american resource analogues. in this paper the geological model that underlies the assessment is presented along with some additional considerations on the nature of the play. details and methodology of the assessment itself were summarised by gautier et al. (2013). the danish shale gas play shale gas is an unconventional energy resource in which gas is produced directly from a shale source rock. highly productive formations in north america are regionally extensive, tens of metres thick, highly organic-rich, and have been buried sufficiently to reach the temperatures necessary for thermal gas generation. the technique of using horizontal drilling and hydraulic fracturing to extract gas from shale was developed in north america, where it has had a significant impact on gas markets. application of this technology has not yet led to shale gas production in europe. the first shale gas exploration borehole in denmark, the vendsyssel-1, is due to be drilled in northern jylland in 2015 by the company total e&p (fig. 1). since 2009, geus has conducted a wide range of shale gas evaluation programmes including screening of onshore denmark for potential shale gas units. the evaluation is partly based on extensive shallow coring on bornholm where the shale is accessible immediately beneath a thin quaternary cover (schovsbo et al. 2011). the main target for exploration in denmark is the alum shale formation, which is up to 180 m thick and unusually rich in organic matter, typically with 5–10% total organic carbon (toc; schovsbo et al. 2011). organic-rich shales also occur in younger ordovician– silurian successions. these black shales are thinner and less toc-rich than the alum shale, but may still be interesting for shale gas exploration. thermal modelling the terne-1 borehole, drilled in kattegat in 1985 (fig. 1), penetrated a 180 m thick alum shale formation and is a © 2014 geus. geological survey of denmark and greenland bulletin 31, 19–22 . open access: www.geus.dk/publications/bull fig. 1. map showing simplified distribution of lower palaeozoic strata in denmark and the location of scientific and exploration boreholes used for the geological assessment. the position of the planned vendsyssel-1 borehole is also shown. in all boreholes made so far in denmark and skåne, the alum shale is mature to gas rank and positioned beneath a palaeozoic sequence less than 1 km thick; at these sites the shale did not contain significant amounts of gas. the distribution of lower palaeozoic strata is from nielsen & schovsbo (2011). 100 km bornholm skåne sweden germany kattegat c4 a3 b2 terne-1norwegian–danish basinringkøbing–fyn high jylland lower palaeozoic strata caledonian front borehole sæby-1 vendsyssel-1 slagelse-1 2020 key borehole for shale gas exploration in denmark. thermal modelling of terne-1 was carried out to calibrate the burial history and maturation profiles. the alum shale contains a marine type ii kerogen that yields lighter hydrocarbons on maturation than typical type ii kerogen. maturity gradients were constructed by converting the reflectance values of vitrinite-like particles to vitrinite-equivalent values following petersen et al. (2013) since vitrinite-like particles in the alum shale mature at lower temperatures than true vitrinite. the modelling showed that the lower palaeozoic shales were buried within a caledonian foreland basin and that large volumes of oil were probably generated during the silurian (gautier et al. 2013). in most areas, kerogen subsequently attained a maturation rank of dry gas, cracking the previously formed oil. in the carboniferous and early permian, the palaeozoic succession was faulted, tilted and subjected to intensive erosion (fig. 2). local permo-carbonifereous igneous intrusive rocks occur in the terne-1 borehole and elsewhere. however, these did not affect the regional maturity related to burial. in the area of the terne-1 borehole, subsidence resumed in the permo-triassic and maximum reburial probably occurred in cretaceous to early palaeogene time as is the general scenario in denmark (fig. 2). modelling suggests that the thermal rank reached during the palaeozoic was not exceeded during the reburial of the terne-1 area. nevertheless, because of sparse data and modelling uncertainty, we cannot exclude that some shale could have retained hydrocarbongeneration potential throughout the palaeozoic, and additional hydrocarbons may have formed during the mesozoic and cenozoic in some areas. the geological model for the assessment in denmark only two boreholes outside the skåne–bornholm area penetrate the alum shale (slagelse-1 and terne-1; fig. 1), hence the prospective area of the alum shale was delimited largely without borehole data. the analysis was based on maps of (1) the depth to the base of the palaeozoic (lassen & thybo 2012), (2) the distribution of palaeozoic strata (vejbæk & britze 1994) and (3) the regional thickness of the alum shale formation and its subdivisions (updated and somewhat modified from buchardt et al. 1997). these maps were used to identify areas where the alum shale is thicker than 20 m, gas mature and within a current depth interval of 1.5–7 km, which are relevant parameters for gas exploration. the prospective areas (fig. 3a) largely follow the margins of the norwegian–danish basin. alum shale is most likely also present in the central part of the basin, but the shale is here buried too deeply for exploration. the alum shale thins out or is missing on the ringkøbing–fyn high and southwards towards the caledonian front (fig. 1). sweet-spot mapping within the prospective area exploration undertaken by shell in skåne, southern sweden (boreholes a3, b2 and c3 in fig. 1), indicates that the alum shale formation, which is now located at 700–800 m depth, does not contain gas in economically producible quantities and that gas leakage from the shale has increased the risk for a viable gas play (pool et al. 2012). reservoir pressure reduction caused by uplift and loss of reservoir integrity due to faulting and fracturing are the likely mechanisms of gas loss. in skåne the gas may have leaked out through millions of years of uplift and progressive erosion since it formed more than 400 million years ago. in denmark, in contrast to skåne, the palaeozoic shale was reburied in the mesozoic and thus may retain gas to a greater degree. two types of areas with different risks of gas leakage were defined in the geological model, based on the thickness of palaeozoic strata mapped by lassen & thybo (2012). preserved thickness is taken as the best indicator for the magnitude of uplift and thus for the risk of reservoir depressurisafig. 2. timing of main events affecting the gas potential in the alum shale in southern scandinavia. palaeogene 2.6 quarternary neogene periodma era eon cretaceous jurassic triassic permian carboniferous devonian silurian ordovician cambrian precambrian pa la eo zo ic ph an er oz oi cm es oz oi c c en oz oi c 23 66 145 201 252 299 359 419 444 485 541 uplift uplift and possible loss of gas volcanic intrusions renewed burial burial and generation of gas deposition of the alum shale 21 tion in late palaeozoic time (fig. 3b). accordingly, within the prospective area, ‘sweet spots’ were defined as fault blocks that contain alum shale overlain by more than 1 km of palaeozoic strata (e.g. below the blue line in fig. 4), indicating less intensive late palaeozoic uplift and erosion and, hence, greater probability of gas retention (fig. 4). where the alum shale is overlain by less than 1 km of lower palaeozoic strata, the formation is inferred to have been uplifted to less than 1 km during the late palaeozoic, and those areas are therefore classified as non-sweet spot areas in the assessment. all the boreholes drilled so far in the alum shale in denmark and skåne play have been in non-sweet spots as defined here, with the highest reported gas saturation of 20% (pool et al. 2012). hence the quality of sweet spots remains to be tested. the difference in uplift history, and thus potentially in the gas content, is accounted for in the assessment model of gautier et al. (2013) by adopting different estimated ultimate recovery (eur) and success ratios for boreholes drilled in sweet spots (average eur 13.1 × 106 nm3 gas) versus nonsweet spots (average eur 6.7 × 106 nm3). development strategies the usgs assessment methodology assumes unrestricted application of best practice current technology, which in the present case is expected to be horizontal drilling with multistage hydrofracturing. in denmark the ordovician–silurian shale overlying the alum shale may constitute a rather thick (c. 300 m) additional interval in which other development strategies may be relevant. this inference is based on fig. 3. a: prospective areas in denmark for gas in the alum shale. b: distribution of sweet spots versus non-sweet spots within the prospective area of denmark (the term sweet spot is defined in the text). alum shale is likely also present in the deeper parts of the norwegian–danish basin, but here it is buried more than 7 km, i.e. too deeply for shale gas exploration with the current costs of drilling. alum shale non-sweet spot alum shale sweet spot alum shale buried 5.0–7.0 km alum shale buried 1.5–5.0 km 50 km a b norwegian–danish basin norwegian–danish basin 2222 the terne-1 borehole where a 250 m thick shale interval with toc values of 1–3% overlies the alum shale. these stratigraphic intervals are the targets for exploration in poland, lithuania and other countries in the eastern sector of the basin and may constitute an important additional reservoir in denmark. in addition, a tight gas play in upper silurian or lower permian sections may also be present in the subsurface of denmark and might add to the unconventional resource estimate. conclusions the estimated technically recoverable shale gas resource is comparable to the total volume of gas produced from the danish part of the north sea in the period 1972–2011 and twice the amount of remaining reserves of conventional gas in the danish sector of the north sea. however, in contrast to the resource estimates for the north sea, the estimated shale gas resource does not take economic viability into account. shale gas exploration in denmark is in its early stages. this is reflected in the large range of the estimate. it is thus crucial to obtain information from new boreholes, notably from sweet-spot areas, in order to calibrate and constrain the resource estimation model. the impact on the resource estimate from other development strategies or from additional play intervals and plays is not taken into consideration in the gas resource estimate by gautier et al. (2013). whether this is relevant awaits the evaluation of the first danish exploration borehole to be drilled in the lower palaeozoic in northern jylland. references buchardt, b., nielsen, a.t. & schovsbo, n.h. 1997: alun skiferen i skandinavien. geologisk tidsskrift 1997(3), 1–30. gautier, d.l., charpentier r.r., gaswirth, s.b., klett, t.r., pitman, j.k., schenk, c.j., tennyson, m.e. & whidden, k.j. 2013: undiscovered gas resources in the alum shale, denmark. u.s. geological survey fact sheet 2013–3103, 4 pp. lassen, a. & thybo, h. 2012: neoproterozoic and palaeozoic evolution of sw scandinavia based on integrated seismic interpretation. precambrian research 204–205, 75–104. mogensen, t.e. & korstgård, j.a. 2003: triassic and jurassic transtension along part of the sorgenfrei–tornquist zone, in the danish kattegat. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 439–458. nielsen, a.t. & schovsbo, n.h. 2011: the lower cambrian of scandinavia: depositional environment, sequence stratigraphy and palaeogeography. earth science reviews 107, 207–310. petersen, h.i., schovsbo, n.h. & nielsen, a.t. 2013: reflectance measurements of zooclasts and solid bitumen in lower palaeozoic shales, southern scandinavia: correlation to vitrinite reflectance. international journal of coal petrolog y 114, 1–18. pool, w., geluk, m., abels, j. & tiley, g. 2012: assessment of an unusual european shale gas play: the cambro-ordovician alum shale, southern sweden. proceedings of the society of petroleum engineers/european association of geoscientists and engineers unconventional resources conference, 20–22 march, 2012, vienna, 152339. schovsbo, n.h., nielsen, a.t., klitten, k., mathiesen, a. & rasmussen, p. 2011: shale gas investigations in denmark: lower palaeozoic shales on bornholm. geological survey of denmark and greenland bulletin 23, 9–12. vejbæk, o.v. & britze, p. (compilers) 1994: geological map of denmark 1:750 000. top pre-zechstein (two-way traveltime and depth). danmarks geologiske undersøgelse kortserie 45, 8 pp., 3 maps. authors’ addresses n.h.s, geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: nsc@geus.dk a.t.n., natural history museum of denmark, øster voldgade 5–7, dk-1350 copenhagen k, denmark. d.l.g., consulting geologist, 3954 nelson court, palo alto, california 94306, usa. fig. 4. conceptual cross section showing the subsurface geolog y in northern jylland. the alum shale is present in tilted fault blocks below the caledonian unconformity. sweet spots are the areas with lowest risk of gas leakage during late palaeozoic uplift and are defined as regions where the alum shale is overlain by more than 1 km of lower palaeozoic strata. modified and generalised from mogensen & korstgård (2003). sæby-1 0 4 2 6 ns d ep th (k m ) alum shale silurian shale ordovician– clay and sandstone unconformity 1 km depth in palaeozoic fault sweet spot basement 5 km palaeozoic post-palaeozoic clay and siltstone chalk sandstone geological survey of denmark and greenland bulletin 38, 2017, 29-32 29 geothermal resources in the deep subsurface in many parts of denmark have the potential to form a central component in the future danish energy supply for district heating. geothermal energy is sustainable and environmentally friendly and independent of climatic and seasonal variations, in contrast to solar and wind energy. furthermore, geothermal plants may be integrated with other green energy supplies. the sandstone reservoirs from which the warm geothermal water is extracted may also act as temporary storage for excess heat e.g. from industrial production processes or from solar-heated water in summer periods when the demand for heating is low. therefore, there are many good reasons to include geothermal energy in denmark’s energy mix. despite this, only three geothermal plants exist at present at thisted, copenhagen and sønderborg (fig. 1). several district heating companies have, however, shown interest in geothermal energy and have taken the first step towards estimating if suitable geological conditions are present within their respective district heating areas. this has been done by analysing geological and geophysical data gathered from the nearest deep wells and seismic surveys, in some cases supplemented with new seismic data. although these analyses generally show promising geothermal potential, hesitation prevails when it comes to drilling the actual geothermal wells. deep drilling is complicated and expensive, but necessary in order to deduce if productive reservoir sandstones are present that can produce the required volumes of geothermal water. in order to mitigate the geological risks and facilitate utilisation of geothermal energy, publicly supported initiatives financed by research grants have been undertaken for the last 40 years. thereby our knowledge of the danish subsurface and the reservoir properties of deep geothermal sandstones has considerably increased, and fundamental uncertainties regarding subsurface structures and resources have been reduced. the many promising results are publicly available via the newly established geothermal webgis portal at the geological survey of denmark and greenland (vosgerau et al. 2016). furthermore, the industry is now taking more interest in geothermal exploration and sees it as a promising business case into which it is willing to invest and share the risks associated with expensive wells. the public sector facilitates this development by supporting research projects via grants from the energy technology development and demonstration programme of the danish energy agency (eudp) and the innovation fund denmark. these projects involve research institutes, district heating companies, private companies and other stakeholders. the present paper deals with the outcome of one of these projects called the geothermal pilot hole, financially supported by the eudp. the project elucidates e.g. how drilling can be made less expensive by focusing on geothermal sandstone reservoirs at depths shallower than c. 2200 m, thereby allowing the use of small rigs suitable towards a geothermal exploration well in the gassum formation in copenhagen henrik vosgerau, ulrik gregersen, lars kristensen, sofie lindström, anders mathiesen, carsten m. nielsen, mette olivarius and lars henrik nielsen 100 km denmarkdenmark t s sweden petrophysical log data no data or poor quality reasonable or good seismic data coverage and quality very poor poor resonable good very good 12°e 56°n lavø-1 karlebo-1/1a slagelse-1 stenlille-1 stenlille-19 sjælland amager fig. 2 20 km• • • •• • • • margretheholm-1/1a /-2 margretheholm-1/1a /-2 fig. 1. coverage and quality of seismic and petrophysical log data from deep wells in sjælland. the quality indeces ref lect to which degree the data can be used to extract information about major geothermal sandstone reservoirs in the deep subsurface. the margretheholm wells are part of the existing geothermal plant in copenhagen. stars mark the approximate positions of the two areas of interest. on the inset map the locations of the thisted (t) and sønderborg (s) plants are shown. © 2017 geus. geological survey of denmark and greenland bulletin 38, 29–32 . open access: www.geus.dk/publications/bull 3030 for operation in urban areas. for comparison, the existing geothermal plant in copenhagen utilises water from the lower triassic bunter sandstone formation at a depth of c. 2.6 km. another important part of the project is to provide a well-constrained prognosis of relevant reservoir parameters (depth, thickness, transmissivity, production capacity, temperature, etc.) of geothermal sandstone reservoirs of the upper triassic – lower jurassic gassum formation within two prospect areas of special interest in northern copenhagen (fig. 1). this activity will provide the necessary background to select the location of an exploration well in a future phase of the project yet to be granted. previous studies have shown that the subsurface of copenhagen contains large quantities of geothermal energy which may form a substantial contribution to domestic heating for hundreds of years to come, and the two areas in northern copenhagen (stars, fig. 1) have already been selected as relevant, based on suitable geological conditions and infrastructure. copenhagen is a major city with a substantial demand for heating and like other danish cities it has a well-established district heating network, and for these reasons it is an obvious site for geothermal energy. the gassum formation constitutes the most well-known sandstone reservoir in denmark and is exploited for geothermal energy in thisted and sønderborg and for gas storage at stenlille. it is dominated by fine to medium-grained sandstones alternating with darker-coloured claystones, siltstones and thin coal seams. the sand was deposited in the danish basin mainly as marine shoreface sand in relatively continuous and widely distributed bodies, as well as deposits in river channels, estuaries and lagoons. in the copenhagen area, the gassum formation occurs in depths of around 2000 m and has a temperature of c. 60°c (balling et al. 2016), sufficiently high to make a district heating plant economically profitable. furthermore, the depth is shallow enough to prevent serious diagenetic alteration under high pressure and temperature conditions which might reduce the porosity and permeability of the reservoir sandstones (kristensen et al. 2016). the results of the project phases conducted so far illustrates e.g. that the subsurface geological conditions may vary considerably within a city area, thus influencing the geothermal potential. geological database the critical subsurface geological information from deep wells and seismic lines in central and north-eastern sjælland (fig. 1) controls the reservoir prognosis for the two prospect areas in northern copenhagen. the seismic coverage is reasonable around these two areas, especially because an e–w-trending seismic line of very good quality occurs immediately north of them. detailed analysis of this and other nearby lines has been used to identify and estimate the depth and thickness of the gassum formation in the two prospect areas. the two areas are separated by the nnw–sse-striking amager fault which forms part of a major regional fault zone, along which the easternmost part of sjælland has been down-faulted (fig. 2). the seismic mapping reveals that the gassum formation is thicker and occurs at a deeper level in the eastern area than in the western area. deep wells in north-eastern sjælland are limited to margretheholm-1/1a and -2, karlebo-1/1a and lavø-1 from which no cores of the gassum formation exist, and n e a m ager fault zone base gassum fm base gassum fm base c halk western prognosis area w m ar gr et he ho lm -1 m ar gr et he ho lm -2 a m ager fault zone gassum fm base chalk twt (ms) -1100 -1400 -1300 -1200 eastern prognosis area 2 km seismic line hgs001 seismic line hgs1e11 seismic line hgs8n13 sea level øresund sweden fjerrit slev fm fjerritslev fm gassum fm fjerritslev fm base chalk gassum fm view position and direction 5 km n a m ager fault zone fig. 2. seismic lines in 3d view seen towards northern copenhagen and margretheholm in northern amager. the view position and direction are shown on the inserted location map, as is the overall trend of the amager fault zone. the coloured surface ref lects the depth and morphology of the base of the gassum formation, clearly illustrating the different, fault-controlled positions of the two prospect areas west and east of the fault. the thickness of the gassum formation, marked on the seismic profiles, increases considerably from west to east across the amager fault zone. depths are shown as seismic two-way travel time, twt. 31 the petrophysical log data from lavø-1 are of poor quality. however, a large amount of good quality petrophysical log and core data exist from the stenlille area in the central part of sjælland, c. 60 km west of the two areas of interest (fig. 1), although not all of the well data are equally relevant for setting up a reservoir prognosis for the gassum formation in the prospect areas. representative well data have been chosen based on e.g. sequence stratigraphic and biostratigraphic analysis and on similarities to the prospect areas in terms of structural setting, depositional environment, inferred distance from the palaeoshoreline, sediment sources, petrography, burial depth, diagenetic alternation, etc. in general, the data from the margretheholm and karlebo-1/1a wells are considered the most relevant for the eastern prospect area, as also these wells are located on the eastern, down-faulted side of the amager fault (fig. 2). the locations of the lavø-1 and the stenlille wells west of the amager fault justify a higher weighting of data from these wells in the prognosticating of the western area. estimated reservoir values based on the seismic data, the gassum formation is estimated to be around 200 m thick with its top at c. 2000 m below sea level in the eastern of the project areas in copenhagen, and around 150 m thick with its top at c. 1750 m below sea level in the western area (table 1). core and petrophysical well log data form the basis for estimating the reservoir properties of the sandstones including local porosity–permeability models (fig. 3). the porosity and permeability values are estimated to be slightly lower in the eastern than in the western area, most likely related to its deeper burial depth and corresponding higher pressure–temperature conditions (table 1). the reservoir transmissivity, given by multiplying the estimated thickness of potential reservoir sand with the estimated reservoir permeability, is an important parameter as it expresses the overall performance of the reservoir. as a rule of thumb, the transmissivity of a sandstone interval in the danish subsurface should be greater than 10 darcy-m in order to constitute a potential geothermal reservoir. both areas fulfil this criterion as the estimated reservoir transmissivity for the gassum formation is 25 and 28 darcy-m, respectively, for the two areas. although the estimated porosity, permeability and transmissivity values are slightly higher in the western area, this does not necessary qualify this as better for geothermal exploitation. this is because the geothermal water of the gassum formation in the eastern area benefits from being hotter than in the western area (65°c versus 57°c, table 1) as a consequence of its greater depth. reservoir model simulations reservoir simulations in both of the prospect areas have shed further light on the suitability of the gassum formation for geothermal exploitation. the reservoir data and interpreted regional seismic surfaces have thus been used to simulate flow rates and the time span before cooled water from injection wells will reach the production wells. in each of the simulations, separate production and injection wells supplemented with a vertical spud well were used. simulation runs with different well spacings show that the distance between the production and injection wells at depth can be kept as low as 900 m without cold-water breakthrough at the production well within the simulation period of 25 years. given that the injection and production wells would typically originate from the same surface table 1. estimated reservoir values for the gassum formation in two potential areas§ prospect areas in copenhagen western eastern macro reservoir parameters depth to top of formation (m below sea level) 1750 2000 thickness (m) 150 200 thickness, potential reservoir sand (m) 75 80 water-conducting properties (reservoir sand) porosity (%) 25 21 gas permeability (md) 300 250 reservoir permeability (md) 375 313 reservoir transmissivity (kh) (dm) 28 25 temperature (°c), middle of formation 57 65 §see kristensen et al. (2016) for details. mah-2 (swc) stenlille-1 to -6 (ccal) copenhagen model stenlille model copenhagen: y = 0.000377x4.3622 stenlille: y = 0.000222x4.3622 10 20 30 10 100 1000 10000 pe rm ea bi lit y (m d ) porosity % 0 1 fig. 3. porosity–permeability models based on gas measurements on core material at laboratory conditions. the ‘copenhagen model’ represents the eastern prospect area and is based on measurements on sidewall cores from the margretheholm-2 well, whereas the ‘stenlille model’ represents the western prognosis area and is based on conventional core analysis data from several stenlille wells. the methodology for establishing local porosity–permeability models is described in kristensen et al. (2016). 3232 position, short distances between the injection and production wells at the reservoir level are preferred in order to minimise the inclination of the well trajectory. this will lower the drilling risks, as drilling generally becomes more complicated with increasing inclination. overall, the simulations showed suitable production capacities for both locations but that the eastern location is more favourable because of higher production and injection rates for the same pressure applied to the wells, a more favourable production temperature profile, as well as thicker reservoir intervals which will delay breakthrough of cold water from the injection to the production well because the cold-water front is spread over a thicker reservoir interval. concluding remarks and perspectives the various geological and geophysical analyses presented here indicate that the gassum formation is suitable for geothermal exploitation in both of the prospect areas. the production may be further enhanced if geothermal energy is produced simultaneously from the gassum formation and from sandstones in the lower part of the overlying fjerritslev formation. this formation largely consists of tight mudstones, but in eastern sjælland its basal part contains several sandstones which may contribute to a geothermal production. although the simulations point out the eastern area as being more favourable for a geothermal production, other factors must also be considered in a final selection of a borehole location, such as drilling costs related to different drilling depths and non-geological parameters such as the position of the well in relation to the district heating and other surface infrastructure. well data from eastern sjælland are scarce and of varying quality. especially the lack of cores from penetrated sandstones is a shortcoming, as such material is very valuable in estimating reservoir properties as shown by the extrapolation of core data from the stenlille wells for the prospect areas in copenhagen. several packages of sandstones and intervening mudstones in the gassum formation have thus been correlated between the wells at stenlille and eastern sjælland and are therefore also expected to be present in the two prospect areas themselves. regional seismic mapping, palynological analysis and comparison of petrophysical log data patterns furthermore indicate that the paleogeographic setting and depositional environments during the deposition of the gassum formation were broadly similar in stenlille and in the prospect areas. in addition, u-pb radiometric dating of detrital zircon grains from the gassum formation indicates that all of these deposits were sourced mainly from reworking of the lower triassic bunter sandstone formation on the ringkøbing–fyn high, a regional basement ridge forming the southern margin of the danish basin. extrapolation of the stenlille data as far as to eastern sjælland inevitably implies some uncertainties. a new well in copenhagen from which cores, petrophysical log data and hydraulic test data can be collected and analysed will considerably increase the accuracy of predictions of reservoir properties of the gassum formation in greater copenhagen as well as in the hillerød and farum areas in northeastern sjælland, where initial investigations have also been performed. hence, the geological and economic risks associated with the establishment of a geothermal plant will be reduced, not only in copenhagen but in eastern sjælland as a whole. furthermore, a new well will make it possible to compare existing core data (including direct porosity and permeability measurements) with petrophysical log data and hydraulic test data from intervals of penetrated reservoir sandstone, and will thus provide a unique possibility to verify to what extent traditional petrophysical log data can be used to estimate the reservoir properties of geothermal sandstones. this knowledge is important for evaluation of the geothermal potential in a specific area based on data from existing wells, and for selecting suitable log tools for estimation of the porosity, permeability and injectivity of potential reservoir sandstones in general. acknowledgements the eudp is thanked for financial support. references balling, n., fuchs, s., poulsen, s.e., bording, t.s., nielsen, s.b., mathiesen, a. & nielsen, l.h. 2016: development of a numerical 3d geothermal model for denmark. proceedings, european geothermal congress, strasbourg, france. kristensen, l., hjuler, m.l., frykman, p., olivarius, m., weibel, r., nielsen, l.h. & mathiesen, a. 2016: pre-drilling assessments of average porosity and permeability in the geothermal reservoirs of the danish area. geothermal energy 4(6), 2–27, http://dx.doi.org/10.1186/ s40517-016-0048-6 vosgerau, h., mathiesen, a., andersen, m.s., boldreel, l.o., hjuler, m.l., kamla, e., kristensen, l., pedersen, c.b., pjetursson, b. & nielsen, l.h. 2016: a webgis portal for exploration of deep geothermal energy based on geological and geophysical data. geological survey of denmark and greenland bulletin 35, 23–26. authors’ address: geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: hv@geus.dk geological survey of denmark and greenland bulletin 38, 2017, 37-40 37 the lower palaeozoic succession in scandinavia includes several excellent marine source rocks notably the alum shale, the dicellograptus shale and the rastrites shale that have been targets for shale gas exploration since 2008. we here report on samples of these source rocks from cored shallow scientific wells in southern sweden. the samples contain both free and sorbed hydrocarbon gases with concentrations significantly above the background gas level. the gases consist of a mixture of thermogenic and bacterially derived gas. the latter likely derives from both carbonate reduction and methyl fermentation processes. the presence of both thermogenic and biogenic gas in the lower palaeozoic shales is in agreement with results from past and present exploration activities; thermogenic gas is a target in deeply buried, gas-mature shales in southernmost sweden, denmark and northern poland, whereas biogenic gas is a target in shallow, immature-marginally mature shales in south central sweden. we here document that biogenic gas signatures are present also in gas-mature shallow buried shales in skåne in southernmost sweden. in south central sweden (västergötland, östergötland, närke and öland, fig. 1), shallow (present burial <150 m) immature to marginally mature bituminous shale has been known for decades to contain gas and is currently under exploration (see summary in schultz et al. 2015). since 2009, many deep (>800 m) exploration drillings in northern poland (including the lebork s-1 well, lehr & keeley 2016), the vendsyssel-1 well in denmark (ferrand et al. 2016) and the a3-1, b2-1, c4-1 wells in skåne in southernmost sweden (pool et al. 2012), have demonstrated that the lower palaeozoic shale succession contains gas also in these areas (fig. 1). in denmark and skåne, the average gas content is 30 ft3 gas per ton of rock in the organicrich alum shale formation (pool et al. 2012; ferrand et al. 2016). the equivalent shale formation in northern poland contains up to 268 ft3 gas per ton of rock in the lebork s-1 well (lehr & keeley 2016), which is comparable to the content within the core area of north american shale gasproducing formations (e.g. jarvie 2012). in this study, we present empirical data on the composition and isotope signatures of gas measured in shallow (<158 m) core samples from five scientific core drillings in southern sweden, viz. albjära-1, lönstorp-1, gislövshammar-2, hällekis-1 and djupvik-1 (fig. 1, table 1). sampling and analyses were performed in 1991–1992 as part of the energy research project efp-1313/88-2 and the pre-westphalian source-rocks in northwest europe (prewsor) project (schovsbo & laier 2012). this paper aims at further characterising the gas composition. samples and analyses the molecular composition and isotope signatures of the occurring gases were measured in 27 core samples (table 1). the samples were selected during drilling and consist of 4–8 cm long core intervals with a diameter of 5.5 cm. the samples from albjära-1 and lönstorp-1 were sealed in metal containers and stored at –18°c until they reached the laboratory for analysis. the free gas was subsequently anageneration and origin of natural gas in lower palaeozoic shales from southern sweden niels hemmingsen schovsbo and arne thorshøj nielsen djupvik-1 albjära-1 a3-1 c4-1 gislövshammar-2 lebork s-1 hällekis-1 b2-1 vendsyssel-1 lönstorp-1 figur 1. one collumn wide öland baltic sea bornholm sweden denmark skåne västergötland östergötland närke poland lower palaeozoic strata caledonian front exploration well scientific borehole 200 km fig. 1: location of wells mentioned and occurrence of lower palaeozoic strata in southern scandinavia. modified from nielsen & schovsbo (2015). © 2017 geus. geological survey of denmark and greenland bulletin 38, 37–40. open access: www.geus.dk/publications/bull 3838 lysed by the geological survey of denmark and greenland (geus) by puncturing the containers through a septum before opening. samples from gislövshammar-2, hällekis-1 and djupvik-1 were analysed by the federal institute for geosciences and natural resources (bgr), germany. these samples were stored at –18°c at the drill site and subsequently transferred to a container filled with liquid nitrogen at –196°c. the free gas was measured by allowing the deep-frozen sample to equilibrate to room temperature in a sealed container. for all samples the sorbed gas in the rock matrix was liberated by treating the sample with phosphoric acid following the procedure outlined by faber & stahl (1983). gas composition the sorbed methane concentrations range from 118 to 23867 ppb (micrograms per kg of rock) and the free gas contents from 3 to 13420 ppm (fig. 2). the concentrations thus far exceed the level of background gas of 20–50 ppb for methane as defined by whiticar (1994). the gas content is strongly related to thermal rank of the sampled shales. the gas-mature samples from gislövshammar-2, albjära-1 and lönstorp-1 have c. ten times higher yields than the thermally immature samples from the hällekis-1 and djupvik-1 wells (fig. 2). the gas content appears not to be related to the total organic content in the mature samples. this is exemplified by the fact that the highest yields of sorbed gas are found in the rastrites shale (toc average <1%) and the lowest yields in the alum shale, which on average contains 9% toc in skåne and on bornholm (fig. 2). isotope composition and carbon isotope signatures the gas molecule and isotopic compositions of the analysed samples plot within the bacterial to thermogenic fields in a bernard diagram (fig. 3a ). the microbial gas is characterised by much higher negative isotope values than seen in the thermogenic-sourced methane. this signature is most clearly expressed in the free gas samples from mature shales that also have 10 to 100 times higher c 1/(c2+c3) molecular ratios than the sorbed gas, which is also typical for biogenic gas (fig. 3a). one column wide alme. ra st rit es linde. 480 e. c . m a m .c am br ia n500 510 470 460 450 440 430 490 si lu ri an fu ro ng ia n ea rl y o rd ov ic ia n m .o rd ov ic ia n la te o rd ov ic ia n grey shalelimestone siltstone black shale -80 -60 -40 δ13cmethane ‰ pdbtoc wt% 0 5 1510 figure 2. ba a lu m s ha le g dicello. tø ye n sh al e k b gas: sorbed free mature immature 6 000 ppb 2 000 ppm 13 000 ppm 25 000 ppb fig. 2. stratigraphy of the lower palaeozoic shales. a: total organic carbon (toc) content in shales from the skåne–bornholm area (modified from schovsbo 2003). b: methane isotope composition of sorbed and free gas from samples of thermally mature shale in the albjära-1, gislövshammar-2, and lönstorp-1 wells and from samples of thermally immature shale in the hällekis-1 and djupvik-1 wells. e.c.: early cambrian. g: gislöv fm. b: bjørkåsholmen fm. k: komstad limestone. alme.: almelund shale. dicello.: dicellograptus shale. linde.: lindegård formation. green area in b outlines the variation field defined by samples from the djupvik-1 and hällekis-1 wells. table 1. wells and analysed samples§ well formation n depth range (m) gislövshammar-2 tøyen s. 1 19.8 gislövshammar-2 alum s. 4 31.8–88.3 djupvik-1 alum s: 1 2.0 hällekis-1 tøyen s. 2 9.9–17.3 hällekis-1 alum s, 4 23.4–39.8 albjära-1 almelund 1 99.6 albjära-1 tøyen s. 3 114.8–134.5 albjära-1 alum s. 5 139.6–157.0 §full analytical results are available on request from the first author. 39 the propane versus ethane isotope gas signature is suggested to reflect the maturity of the source and this relationship can be used for a gas-to-source-rock correlation (whiticar 1994). the analysed gas signatures follow this prediction, as immature alum shale samples from the hällekis-1 well plot with relatively depleted isotope signatures of propane and ethane compared to the thermally mature alum shale samples (fig. 3b). isotope data from lithuanian and polish oil and gas reservoirs in middle cambrian sandstone, sourced by alum shale (kotarba & lewan 2013), plot with intermediate signatures (fig. 3b). the thermally mature samples (gislövshammar-2 well), however, exhibit a considerable variation in propane isotope composition from –22 to –39‰ pdb, suggesting a mixture of differently derived gases. this may be caused by addition of bacterially derived ethane and/or biodegradation of a propane component (cf. whiticar 1994). the thermally immature alum shale samples from the djupvik-1 well (marked with 0.32 %gr in fig. 3b) and samples from tøyen shale from the hällekis-1 well (marked as tøyen 0.53%gr in fig. 3b) plot within an apparent gas maturity of 0.8–1.2% ro according to the values indicated in fig. 3b (whiticar trend line), i.e. with much higher maturities than measured, suggesting that gas migration has occurred. in the hällekis-1 well the migrated gas may have formed in response to intrusion of permo-carboniferous dikes that locally matured the shales in south central sweden (cf. schultz et al. 2015). in the vicinity of the djupvik-1 drill site-mature shale and igneous activity are unknown and the relatively high maturity remains puzzling. deuterium isotopes measurements of deuterium and carbon isotopes in methane offer additional information on the source of the natural gases and on the processes that may have modified their composition (whiticar 1994). figure 3c shows the deuterium versus carbon isotope composition of methane in the analysed samples. the gas composition exhibits a % ro 0.1 1 10 100 1000 thermogenic bacterial ke ro ge n ty pe ii t yp e i ii microbial oxidation c 1 / ( c 2 + c 3) δ13cmethane (‰ pdb) -80 a -70 -60 -50 -40 -30 3.0 2.0 % ro 1.5 0.7 0.5 alum 0.53 % gr tøyen 0.53 % gr 1.7 % gr poland–lithuania 0.6–1.4 % gr 0.32 % gr 1.1 -20-30-40-50 -40 -36 -32 -28 -24 -20 δ1 3 c pr op an e (‰ p d b) δ13cethane (‰ pdb) b bacterial carbonate reduction geothermal early mature thermogenic mix and transitionbacterial methyl-type fermentation δ1 3 c m et ha ne (‰ p d b) δdmethane (‰ smow) -350 -300 -250 -200 -150 -1 0 0 -8 0 -6 0 -4 0 -2 0 c whiticar (1994) general trend line mature offshore poland–lithuania sourced by alum shale (kotorba & lewan 2013) immature fig. 3. compostion and isotope signatures of organic carbon. a: ‘bernard diagram’ showing the ratio c1/(c2+c3) versus δ 13cmethane for all samples. this type of diagram is used to determine the origin of the gases and is modified from whiticar (1994). for legend, see fig. 2. b: relationship between δ13cethane and δ 13cpropane. tøyen and alum 0.53% gr denote stratigraphy and maturity of samples from the hällekis-1 well. the graptolite ref lectance (% gr) is from pedersen et al. (2013); grönvik locality is used for djupvik-1; estimate for offshore poland. c: δd and δ13c for methane. for legend, see fig. 2. the isotope signatures of the various sources are from whiticar (1994). 4040 large degree of scatter, but free gas from thermally mature samples plots in the bacterial carbonate reduction field, whereas free gas from immature samples plots towards the bacterial methyl-type fermentation fields, suggesting that different processes generated the depleted methane isotope compositions (fig. 3c). the sorbed gas compositions in general plot away from bacterial sources, indicating that a thermogenic signature is preserved (fig. 3c). implications for shale-gas prospectivity the gas-isotope composition suggests that significant postgeneration modification occurred although the timing is unknown. the biogenic isotope signature of the gases in skåne resembles similar signatures seen in östergötland (schultz et al. 2015). here schultz et al. inferred that methyl-fermenting processes contributed to the methane content. however, the gas-isotope signature was not as depleted as seen in this study, possibly owing to the mixed shale oil – biogenic nature of the östergötland alum shale play. according to schultz et al. (2015) the biogenic gas was generated after the pleistocene glaciation, as modern meteoric water was able to infiltrate the shale and create the right conditions for bacterial activities. we envisage that similar conditions may have affected the shallowly buried shales in skåne. krüger et al. (2014), however, show that highly mature kerogen has a much smaller microbial generative gas potential than immature to marginally mature kerogen, since thermal maturity limits the amount of easily biodegradable organic matter that can be transformed to methane. conclusions lower palaeozoic shales in south central sweden and southernmost sweden contain natural gas that exceeds the level of background gas. the gas content is strongly related to the thermal rank of the sampled shales, and mature samples have approximately ten times higher yields than the immature samples. the gas is generated by both thermogenic and bacterial processes. the microbial gas signature is most clearly expressed in the free gas samples from mature shales that also have 10 to 100 times higher molecule c 1/(c2+c3) ratios than the sorbed gas. migration may have occurred related to gas formation in response to intrusion of permo-carboniferous dikes that locally matured the shales in south central sweden. acknowledgements we thank troels laier (geus) for comments and suggestions to an earlier version of the manuscript. the authors wish to thank mikael erlström and maciej kotarba for constructive comments that improved the paper. references faber, e. & stahl, w. 1983: analytic procedure and results of an isotope geochemical surface survey in an area of the british north sea. geological society special publications (london) 12, 51–63. ferrand, j., demars, c. & allache, f. 2016: denmark – l1/10 licence relinquishment recommendations report. total e&p, memo 1-9. available from: http://www.ft.dk/samling/20151/almdel/efk/bilag/353/1651289.pdf. verified 7.4.2017. jarvie, d.m. 2012: shale resource systems for oil and gas: part 1 – shalegas resource systems. a apg memoir 97, 69–87. kotarba, m.j. & lewan, m.d. 2013: sources of natural gases in middle cambrian reservoirs in polish and lithuanian baltic basin as determined by stable isotopes and hydrous pyrolysis of lower palaeozoic source rocks. chemical geology 345, 62–76. krüger, m., van berk, w., arning, e.t., jiménez, n., schovsbo, n.h., straaten, n. & schulz, h.-m. 2014: the biogenic methane potential of european gas shale analogues: results from incubation experiments and thermodynamic modelling. international journal of coal geology 136, 59–74. lehr, j.h. & keeley, j. 2016: alternative energy and shale gas encyclopedia. 912 pp. john wiley & sons. nielsen, a.t. & schovsbo, n.h. 2015: the regressive early – mid cambrian ‘hawke bay event’ in baltoscandia: epeirogenic uplift in concert with eustasy. earth science reviews 151, 288–350. petersen, h.i., schovsbo, n.h. & nielsen, a.t. 2013: ref lectance measurements of zooclasts and solid bitumen in lower palaeozoic shales, southern scandinavia: correlation to vitrinite ref lectance. international journal of coal petrology 114, 1–18. pool, w., geluk, m., abels, j. & tiley, g. 2012: assessment of an unusual european shale gas play – the cambro–ordovician alum shale, southern sweden: proceedings of the society of petroleum engineers/european association of geoscientists and engineers unconventional resources conference, vienna, austria, 20–22 march, 2012, 152339. schovsbo, n.h. 2003: the geochemistry of lower palaeozoic sediments deposited on the margins of baltica. bulletin of the geological society of denmark 50, 11–27. schovsbo, n.h. & laier, t. 2012: composition and gas isotope signature of shale samples from 5 scientific wells in sweden. geological survey of denmark and greenland report 2012/17, 1–25. schulz, h.-m., biermann, s., van berk, w., krüger, m., straaten, n., bechtel, a., wirth, r., lüders, v., schovsbo, n.h. & crabtree, s. 2015: from shale oil to biogenic shale gas: retracing organic-inorganic interactions in the alum shale (furongian-lower ordovician) in southern sweden. a apg bulletin 99, 927–956. whiticar, m.j. 1994: correlation of natural gases with their sources. a apg memoir 60, 261–283. authors’ addresses n.h.s., geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350 copenhagen k, denmark; e-mail: nsc@geus.dk a.t.n., department of geosciences and natural resource management, university of copenhagen. øster voldgade 10, dk-1350 copenhagen k, dk. geological survey of denmark and greenland bulletin 41, 2018, 87-90 87 rare-earth elements (ree) are considered critical raw materials (crm; ec 2018; us department of the interior 2018) and essential in the technological transformation of the energy sector into carbon-free technologies such as wind turbines, electrified transport and led-lights. the new technologies have led to swiftly expanding markets for ree products, in which china has achieved a monopolistic role in all segments of the ree value chains. political strategies aimed to establish ree supplies outside china are currently being implemented within the eu and in other western countries in order to ensure an adequate future ree supply. however, new ree value chains outside china have not yet materialised. the aim of this paper is to assess whether the global ree supply from present and potential mines can keep pace with the ree demand for the expanding offshore wind energy sector (fig. 1). a successful development of this sector outside china relies on an adequate supply of particularly neodymium (nd) and to some extent praseodymium (pr), terbium (tb) and dysprosium (dy), used in permanent magnets for windmill generators. in 2015, about 82% of the global nd-oxide production was used in the permanent magnets examining the rare-earth elements (ree) supply– demand balance for future global wind power scenarios per kalvig and erika machacek 37 38 mine deposit type pea started/ completed mine development fs started/ completed abandoned/ on hold resource estimate 36 39 8 12 11 9 7 10 22 21 2943 42 40+41 35 34 4527 28 49 26 46 33 32 30 31 25 13 48 17 16 15 14 20 18+19 24 44 4723 34 51 2 6 carbonatite iron-oxide-apatite hydrothermal alkaline igneous placer bauxite ion-adsorption clays 1 browns range 2 charley creek 3 dubbo zirconia 4 mount weld 5 nolans 6 yangibana 7 ashram main 8 eco ridge 9 foxtrot 10 kipawa/zeus 11 montviel 12 strange lake 13 bayan obo 14 china minmetals 15 china minmetals 16 china minmetals 17 chinalco 18 ganzhow mining group 19 guangdong rising nf 20 xiamen tungsten 21 kringlerne 22 kvanefjeld 23 chavara 24 manavalakurichi 25 kutessay ii 26 ngualla 27 kangankunde 28 songwe hill 29 lofdal 30 khibiny 31 lovozero 32 norra kärr 33 aksu diamas 34 ngualla, tanz. 35 wigu hill 36 bear lodge 37 bokan 38 mountain pass 39 round top 40 glenover (rsa) 41 steenkampskraal 42 zandkopsdrift 43 buena norte 44 lahat 45 tantalus 46 gakara 47 dong pao 48 tomtorskoye 49 nkombwa hill geus/mima april 2018 fig. 1. global rare-earth element mines and advanced exploration projects. fs: feasibility study. pea: pre-economic assessment. © 2018 geus. geological survey of denmark and greenland bulletin 41, 87–90. open access: www.geus.dk/bulletin http://www.geus.dk/bulletin 8888 production (adamas 2016). here we evaluate the future supply and demand situations for nd, pr, tb and dy in the global wind energy sector in the form of three scenarios, one for 2020 and two for 2030 based on high and low demand. the balance is discussed. our assessment ref lects the challenge caused by limited insight into the ree supply chains inside china, and the figures presented in this paper are therefore only indicative. scenarios for future global ree demand of the wind energy sector in 2016, the global wind energy council reported a total global wind power capacity of 487 gw (gwec 2016), of which the offshore capacity amounted to 3% according to the global status report 2017 for renewables. due to the otherwise very high maintenance costs of the offshore wind energy, it depends in part on direct-drive and hybrid wind turbine technologies that use ree-based permanent magnet (pm) or high-temperature superconducting (hts) generators (barteková 2016). this is why the offshore wind energy sector is the focus of this study. our scenarios solely deal with technologies using permanent magnets in which nd is vital. barteková (2016) specifies the consumption of total rare-earth element oxides (treo) for the individual types of magnets used in wind turbines and indicates the individual ree used. the reo content per magnet varies by generator design between c. 23–35%, highest in the permanent magnet of a direct-drive synchronous generator (pmsg-dd), and lowest in hybrid single and multistage synchronous generators (pmsg-sg and pmsgmg). the relative magnet weight proportions of the four reos are about 95% nd, 4% pr, 0.99% tb and 0.01% dy (barteková 2016). in order to estimate the future reo-demand of the sector, the following assumptions about the wind energy technology are made based on barteková (2016, p. 158), who reported that in 2014 the ree-based permanent magnet technology accounted for 4% of the offshore wind technology, equally divided between direct-drive and hybrid generator designs. for our 2016 baseline scenario, we (i) increased this share to 5%, (ii) maintained the equal split between direct-drive and hybrid generator technologies, and (iii) subdivided the hybrid generator designs equally into single and multistage gearbox designs. further, we assume that in 2016, china held 8% and the rest of the world (row) 92% of the global offshore wind capacity. from the 2016 baseline scenario, we developed three scenarios: (1) the reo use in the total global offshore wind energy capacity in 2020, and (2, 3) low and high forecasts of the same in 2030. we set the regional offshore shares to 85% for row and 15% for china. see details in table 1. pr nd tb dy pr nd tb dy pr nd tb dy pr nd tb dy 2016 2020 2030-low 2030-high     row 104 2.5 26 0.26 267 6.3 66 1 589 13.9 146 1 986 23.4 244 2 9 ton ton tonkton ton ton tonkton ton ton tonkton ton ton tonkton 215 2 0.02 23 551 6 0 104 2.5 26 0 174 4.1 43 0china 0 5000 0 10 000 15 000 20 000 25 000 ton a     china 0 200 400 600 800 1000 1200 ton pr 4 0 90 8 1 0 0 0 10 1 230 20 2 0 0 0 0 0 45 8 0 0 11 2 1060 187 27 5 631 111 7 1 row nd tb dy pr nd tb dy pr nd tb dy pr nd tb dy 2016 2020 2030-low 2030-high b fig. 2. rare-earth metal demand by wind energ y deployment in china and the row in 2016, and forecasts for 2020 and 2030. a: assuming that all offshore wind technolog y is centred on r ee-based permanent magnets. b: assuming that only a small share of offshore wind technolog y uses r eebased permanent magnets, and differentiating between varying r ee uses per pm generator technolog y. note: both figures show cumulated (forecasted) individual r ee use by examined wind energ y technolog y in the respective year. row: the rest of the world. table 1. forecast scenarios for installed global offshore wind energy capacity in 2020 and 2030 forecast 2020 739 gw 5% = 37 gw 5% = 1.85 gw forecast 2030 low 1260 gw 7% = 88 gw 10% = 8.80 gw forecast 2030 high 2110 gw 7% = 148 gw 10% = 14.80 gw ree permanent magnets installed capacity offshore capacity %assumptions, this survey from gwec (2016a) global totalwind energy capacity scenarios global offshore 89 our scenarios are based on the estimates by gwec (2016) for 2020, 2030-low, and 2030-high global wind energy capacity. it is important to note the large variability in the underlying assumptions. the most significant parameter is the share of ree-based permanent magnets deployed in offshore installations. for instance, if all offshore technology capacity would employ ree-based permanent magnet technology and 75% of this was installed with the highest ree-using direct-drive design, this would result in the consumption 16 400–27 500 tons nd-oxide in 2030 ( fig. 2a). in contrast, the wind-turbine sector will demand only about 740–1250 tons nd-oxide (fig. 2b) for the alternative technology split-up outlined in table 1. scenarios for the future global ree supply in 2016, the primary global production of total rare-earth oxides (treo) amounted to 129 000 tons, of which china produced 83%, australia 11%, russia 2%, brazil 1%, india 1% and malaysia, thailand, and vietnam still less (usgs 2017). although the treo supply figures for 2016 reported by different sources are rather similar (usgs 2018: 23 680 tons; adamas 2016: 24  377 tons), there are major discrepancies at national level. this partly stems from the assumed contributions of the non-reported market which may account for 25–30% (roskill 2016) and from uncertainties pertaining to production and smelting quota (adamas, personal communications 2018). this study applies the figures for for 2016 from usgs (2018), and contribution from nonreported production is not considered. the 2016 supplies of pr, nd, dy and tb from china and seven row countries are shown in figs 3a, b. the official chinese production quota for 2016 was set to 105 000 tons treo (machacek & kalvig 2017); our estimate of the regional reo production is based on kingsnorth (2016) and shown in fig. 3a. given that no scheduled production quotas for 2020 and 2030 are available, our china 2020 and 2030 supply scenarios are arbitrarily set to an increase of 5% p.a., ref lecting the anticipated growth in demand (dutta et al. 2016), the potential for higher capacity on existing plants, as well as continued efforts to transform the informal sector into to a formal one. the row supply in the 2020 and 2030 scenarios is developed as follows: of the recorded 320 ree exploration projects outside china, 99 are reported to be active (s&pdatabase 2017). our search revealed that 31 of these projects, located in 12 countries, have reached an advanced stage (fig. 1). these 31 projects are divided into four classes of development, which are in turn translated into expected production start-ups in 2020, 2025, 2030 and 2035. the estimates of relative reo grades and targeted production of pr, nd, tb and dy are based on tmr (2015) and company data. where relative grade data are not available, our estimate is based on the actual ree mineralogy. according to these data, new reo productions in australia, usa, and vietnam are expected in 2020. in 2030, reo will also 5000 10 000 15 000 20 000 25 000 30 000 35 000 pr a nd tb dy pr nd tb dy pr nd tb dy 2016 2020 (5% growth p.a.) 2030 (5% growth p.a.) yunnan hunan fujian guangdong guangxi jiangxi shandong sichuan inner monglia to n 46 69 17 4 23 28 4 88 6 56 75 21 1 78 34 5 56 2 17 54 10 77 9 24 4 34 4 96 1000 0 2000 3000 4000 brazil vietnam thailand malaysia india russia australia b pr nd tb dy pr nd tb dy pr nd tb dy 2016 2020 2030 to n 10 49 32 74 62 33 1 10 49 37 24 62 33 1 10 49 37 24 62 33 1 5000 0 10 000 15 000 20 000 25 000 vietnam usa turkey tanzania sweden south africa namibia malawi greenland canada burundi australia c 2016 2020 2030 pr nd tb dy pr nd tb dy pr nd tb dy 0 0 0 0 23 2 76 0 32 20 5 72 04 24 9 49 37 7 21 59 to n fig. 3. current and future r ee production scenarios. a: current and forecasted chinese production of praseodymium, neodymium, terbium and dysprosium in seven regions. forecast assumes a general 5% annual increase. b: current and forecasted production of praseodymium, neodymium, terbium and dysprosium in row. forecast assumes a static production. c: forecasted production of praseodymium, neodymium, terbium and dysprosium from 31 advanced r ee projects outside china. 9090 be supplied by canada, greenland, malawi, namibia, south africa, sweden, tanzania and turkey (figs 1, 3c). the scenarios indicate row-treo productions of 6920 tons in 2020 and 154 075 tons in 2030 (fig. 3c). discussion and summary we demonstrate here that the level of detail applied to estimates of the future use of different types of generators and their relative shares allow for great variance in the current and forecast ree demand by the wind energy sector. against this background, our row scenario for 2020 points to a nd demand by the wind energy sector within a wide range of 230–6300 tons (fig. 2), while our row supply forecast for nd-oxide from both current and new mines is around 4500 tons. a top-down approach indicates that the ree-based permanent magnets for the wind sector absorb 10%, equivalent to about 4000 tons treo (lucas et al. 2015). adamas (2016) estimates that nd-oxide accounts for c. 73% of the treo in the permanent magnets for the wind sector. in effect this means that in 2020, the total nd-oxide supply for the wind energy sector would be roughly 3000 tons nd-oxide, i.e. in the middle range of the forecasted global demand for this purpose. for the 2030 low scenario and with ree technology applied in some but not all offshore technology, the global nd-oxide demand by the wind sector is forecasted to c. 740 tons and for the 2030 high scenario close to 1250 tons. if it is assumed that all offshore technology will draw on ree use, these figures increase to 16 400 and 27 500 tons, respectively. our global supply forecast of nd-oxide in 2030 from current operations is about 35 000 tons from china and 3700 tons from row, to which advanced row ree projects could contribute an additional c. 25 000 tons if all projects go into production. if the 10% share of the ree-based permanent magnet sector as well as a stable demand for ree-based permanent magnets from the wind sector are maintained, about 450 tons nd-oxide could be made available by row suppliers in 2020, and 2900 tons in 2030. however, in the scenarios based on generator technologies that consume a higher percentage of ree-based magnets, the estimated row supply is inadequate and an additional nd-oxide supply will be required, e.g. from chinese ree operators. this study shows that there are currently significant uncertainties in trying to determine both the current ree demand and supply in the wind sector and in building scenarios for 2020 and 2030. given that nd-dy permanent magnets represent a fast-growing sector, there is a need to establish a comprehensive, research-based and harmonised framework for precise estimates of the future supply and demand scenarios for ree-based permanent magnets. references adamas 2016: rare earth market outlook: supply, demand, and pricing from 2016 through 2025 report, 822 pp. adamas intelligence. barteková, e. 2016: the role of rare earth supply risk in low-carbon technolog y innovation. in: borges de lima, i. & leal filho, w. (eds): rare earths industry: technological, economic, and environmental implications. amsterdam: elsevier, 437 pp. dutta, t., kim, k-h, uchimiya, m., kwon, e.e., jeon, b-h, deep, a. & yun, s-t. 2016: global demand for rare earth resources and strategies for green mining. environmental research 150, 182–190. ec 2018: report on critical raw materials and the circular economy, 69 pp. commission staff working document. swd(2018) 36 final. gwec 2016: global wind energ y outlook 2016. fried, l. et al. (eds), 44 pp. gwec and institute for sustainable futures, university of technolog y sydney. kingsnorth, d.j. 2016: curtin university publication on the rare earth industry in 2016. lucas, j., lucas, p., le mercier, t., rollat, a. & davenport, w. 2015: rareearth-based permanent magnets preparation and uses, 231–249. in: rare earths. amsterdam: elsevier. machacek, e. & kalvig, p. (eds) 2017: road map for r ee material supply autonomy in europe. eur ar e, european r ee market survey (component d1.2). 141 pp + appendix. roskill informations services ltd. 2016: rare earths: global industry, markets and outlook to 2026, 396 pp. roskill reports on metals and minerals, 16th revised edition. s&p-database 2017: s&p global market intelligence metals & mining database 2017. technolog y metals research (tmr) 2015: advanced rare-earth projects: http://www.techmetalsresearch.com/metrics-indices/tmr-advancedrare-earth-projects-index/ (accessed 9 february, 2018). us department of the interior 2018: draft list of critical minerals. feb 16, notices. federal register 83(33), 7065–7068. usgs 2018: mineral commodity summaries. us geological survey. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: pka@geus.dk. http://www.techmetalsresearch.com/metrics-indices/tmr-advanced-rare-earth-projects-index/ http://www.techmetalsresearch.com/metrics-indices/tmr-advanced-rare-earth-projects-index/ mailto:pka@geus.dk geological survey of denmark and greenland bulletin 33, 2015, 37-40 37© 2015 geus. geological survey of denmark and greenland bulletin 33, 37–40. open access: www.geus.dk/publications/bull assessment of the mineral raw material potential in denmark – methods and major findings jakob kløve keiding, per kalvig, claus ditlefsen, steen lomholt and peter roll jakobsen aggregates and other mineral raw materials are important prerequisites for the continual development of the infrastructure and economic growth of a country. th e production of these raw materials in denmark amounted to c. 4.5 m3 per capita in 2012, which was 57% higher than the average in eu and efta countries (uepg 2014). in this perspective, it is essential to locate and assess the danish mineral resources in order to plan future exploitation, especially in densely populated regions where both spatial competition for landuse and demands for raw materials are high. here we present the methods used in a recent resource evaluation that for the fi rst time includes danish resources both on land and at sea and summarises some of the main fi ndings of this analysis. th e importance of availability of mineral raw materials such as sand, gravel, clay and limestone for a society cannot be overestimated: they are prerequisites for the development of the infrastructure and a wide range of products for the industrial sector. th e supply of these raw materials is the result of complex value chains, which in turn are based on indicated (see below) and exploited mineral resources from which the raw materials can be processed and turned into commercial materials and products. globally, sand and gravel account for the largest volume of solid material extracted, with c. 15–25 billion m3 excavated annually, and demand increasing rapidly (geas 2014). th e danish mineral industry includes exploitation of loose aggregate, limestone and chalk, diff erent types of clay, salt and granite, and amounted to c. 35 million m3 in 2012 of which aggregate alone accounted for c. 90% (statistics denmark 2012a, b). according to a recent forecast, the demand for sand and gravel in 2036 will be c. 40 million m3 (regionernes videncenter for miljø og ressourcer 2014). th e greater part of the sand and gravel excavated in denmark is used as aggregate and fi ller for concrete and other construction purposes. limestone is mainly used for cement production as industrial fi ller and as soil conditioner. th e clay industry is fairly diversifi ed and uses clay for bricks, insulation stones, membranes and special products such as absorbents and ion-exchange media. salt is mainly used for de-icing of roads and in the food and chemical industries. about 35 000 persons were employed in the primary and secondary sectors of this part of the danish industry in 2013 with a turnover of about 3500 million dkk (statistics denmark 2012a, b). exploitation of mineral resources in denmark takes place at designated sites and the administration is controlled by the danish nature agency for the marine resources and the danish regions for the resources on land. th ere are about 630 onshore sites for excavation of sand, gravel, clay, limestone and granite, and about 100 off shore dredging sites for sand and gravel. are there suffi cient mineral resources in denmark to cover the future demand? sometimes it is postulated that denmark is endowed with abundant sand and gravel deposits, and aggregates are thus oft en considered an essentially unlimited resource that will be available for exploitation in the foreseeable future. th is is an oversimplifi ed assumption because (1) aggregates cover a diverse group of commodities and not all qualities and types are equally abundant, (2) the distribution of mineral raw materials refl ects the local geology and aggregates are geographically unevenly distributed and oft en have to be transported over considerable distances from the excavation site to the end-use location, and (3) there are many diff erent and oft en competing landuse interests particularly in a densely populated country like denmark; exploitation of raw materials does not necessarily have the highest priority. an assessment of the aggregate resources in terms of their size, type and location – in conjunction with an evaluation of possible areas of confl ict with other interests – is crucial for both future resource and landuse planning. on this background the center for minerals and materials (mima) conducted the fi rst comprehensive danish raw material resource assessment comprising both onshore and off shore areas. additional work on mapping the value chains related to the danish raw material sector is in progress. methods th is assessment covers the following resources: aggregates (sand, gravel and pebble); limestone and chalk; clay (clay for bricks and tiles; bentonitic clay; diatomite); salt and granite. aggregates cover a large and diverse group of materials that can be divided into diff erent quality classes according 3838 to their composition. traditionally, quality classes applied to marine and terrestrial resources are diff erent. in order to compare the marine and terrestrial inventories this assessment uses the classifi cation used for exploitation of marine deposits. it discriminates between six commercial classes (fig. 1): sand 0, sand 1, gravel 2, pebble 3, filler sand 4 and sand x (unspecifi ed quality). it is beyond the scope of this short paper to describe the defi nition of the various classes and qualities in detail but they refl ect diff erence in grain size, grain size distribution, as well as an assessment of the petrographic composition (i.e. the content of reactive, unstable and porous mineral grains). for further details see ditlefsen et al. (2015). th is survey is based on data available to the geological survey of denmark and greenland (geus) as per october 2014. th e evaluation of land-based resources is based on previous investigations, including mapping of raw materials reported to or conducted by geus, as well as new resource assessments conducted by regional authorities within the present extraction areas. borehole data and geological maps were also used. for the fi rst time we also incorporated data from geophysical surveys conducted for hydrogeological mapping. th is allowed us to screen large parts of the terrestrial area for potential undiscovered raw material resources. th e resources addressed in this paper are classifi ed by reliability of the resource data and are divided into three classes, namely measured, indicated and inferred. th e criteria for assigning the resources to the diff erent categories were described by larsen (1994) and ditlefsen et al. (2015). in essence, the measured resources encompass raw materials that are mapped in detail and have well-known quality parameters. th eir characterisation thus has a high degree of certainty (± 20%). indicated resources are oft en based on shallow geophysical surveys and a small number of boreholes and have a lower reliability. inferred resources are based on geophysical data only, or on relatively sparse geological data, regional-scale mapping, etc. to compile the nation-wide assessment, data from the communes (98 in total) and from 41 marine study areas were amalgamated. fig. 1. map of denmark showing the location and areal extent of the different quality classes of aggregate mineral resources used in this assessment. the map illustrates the combined resources of measured and indicated resources. 5 0 k m 10°e 55°n 57°n 55°n 57°n sweden germany s a n d 0 s a n d 1 g r ave l 2 pe b b l e 3 f i l l e r s a n d 4 s a n d x , u n s p e c i f i e d q u a l i t y german waters swedish waters norwegian waters bornholm jylland copenhagen 15°e 55°n based on an assessment of the profitable excavation depth, the compilation assesses the volume of raw materials that is available within the top 25 m below surface, except for salt, which is exploited from deeper-seated salt diapirs and therefore considered to a depth of 500 m below terrain surface. based on the same reasoning, we excluded areas with more than 5 m thick layers of soil or other material (overburden) covering the soughtaft er resource. when evaluating areas with limestone and chalk, only deposits with less than 10  m of over39 burden were considered. data for aggregates were compiled for both marine and terrestrial areas, whereas the remaining raw material groups were only considered on land since at sea they occur under a thick sedimentary cover and are therefore of no interest for exploitation. all areas with resources were screened with respect to commonly occurring confl icting interests (here referred to as ‘no-go’ fi lters). th is assessment thus specifi es both gross volumes, comprising the total volume of the resources and net volumes, taking into account the eff ect of ‘no-go’ fi lters. th e latter are calculated by subtracting volumes underlying areas that are claimed for other landuse from the total mineral resource fi gures. th e ‘no-go’ fi lter areas include nature protection areas (natura 2000 areas, historical monuments, state-protected areas, etc.), major built-up and paved areas, and marine waters less than 6 m deep where exploitation is prohibited according to present-day jurisdiction, but areas less than 0.01 km2 in size are excluded. since this is not a full list of areal restrictions, the available area for mineral extraction as well as the extractable net volumes will be smaller due to other local pre-existing priorities. results and conclusions th e mineral assessment presented here covers about 40% of the danish marine and terrestrial areas. possible resource occurrences have been indicated in about 10% of the surveyed areas. th e calculated gross and net mineral resources are summarised in table 1, and fig. 1 shows the geographical distribution of the various resource types and qualities of aggregates, the largest commodity group apart from salt. salt is the dominant resource in terms of volume for all three classes and comprises 89% of the measured net resource volumes (table 1). salt, however, is a special raw material that table 1. summary (in million cubic metres) of calculated gross and net mineral resources in denmark aggregates granite clay chalk and limestone salt total gross resources measured 4603 38 46 293 34 669 39 649 indicated 10 747 0 68 89 809 230 820 134 inferred 80 064 3175 1190 9192 489 671 583 292 net resources measured 4073 38 46 293 34 669 39 119 indicated 9621 0 66 89 809 230 819 006 inferred 68 888 2020 1029 7048 489 671 568 656 sum 95 414 3213 1304 9574 1 333 570 1 443 075 sum 82 582 2058 1141 7430 1 333 570 1 426 781 table 2. calculated net volumes (million cubic metres) of aggregate resources in denmark * unspecified quality. sand 0 sand 1 gravel 2 pebble 3 filler sand 4 sand x total marine resources measured 184 2273 207 77 111 2852 indicated 1214 6334 739 135 94 8516 inferred 497 1183 106 13 418 2217 terrestrial resources measured 191 656 18 191 165 1221 indicated 259 554 10 178 104 1105 inferred 43 96 0 13 66 519 66 671 * total assessment measured 184 2466 863 95 302 165 4073 indicated 1214 6593 1293 145 272 104 9621 inferred 497 1226 202 13 431 66 519 68 888 total sum 1895 10 283 2358 253 1005 66 788 82 582 sum (marine) 1895 9790 1052 225 623 13 585 sum (land) 493 1306 28 382 66 788 68 997 4040 diff ers from the other mineral resources in several ways: (1) a fundamentally diff erent extraction method is used, (2) it is only found at great depths and (3) and it is regulated by the danish subsoil act (undergrundsloven) in contrast to the other resources assessed here that are regulated by the raw materials act (råstofl oven). on a national scale, the measured resources of aggregates account for c. 10% of the registered mineral resources, followed by chalk and limestone (c. 1%; whereas the volumes of clay and granite account for less than 1%). for all the fi ve types of raw material considered, the volume of the inferred resource class is enormous (table 1). however, only minor fractions of these volumes will be available for exploitation due to confl icting landuse interests. aggregates mainly come from either glaciofl uvial deposits or from lateand postglacial marine deposits. marine deposits are more mature than glaciofl uvial deposits and usually contain smaller amounts of reactive grains that are harmful to constructions. in addition, older deltaic and fl uvial deposits of pure quartz sand are found in central jylland and on and around the island of bornholm. granites in denmark are confi ned to bornholm where they are part of the precambrian basement that is exposed or just covered by thin quaternary deposits on the northern two thirds of the island. clay is mainly of glaciolacustrine or marine origin, while limestone and chalk are marine formations of cretaceous and early cenozoic age. th e salt resources in denmark are permian in age and related to evaporates from the zechstein basin. most salt deposits are found at more than 3 km depth, and are of no economic interest. locally, however, the salt has been mobilised and is found in shallower diapirs at depths of 200–300 m. sand x (unspecifi ed quality) is the largest class in the aggregate group and comprises c. 81% of the total volume of all aggregates (table 2). th e resources in this class are currently based only on geophysical screening and require a more thorough characterisation with respect to grain size, grain-size distribution, petrographic composition as well as better constraints on the spatial distribution. however, this class off ers unique possibilities to focus future exploration for aggregates in relevant areas. sand 1, gravel 2, pebble 3 and filler sand 4 are the present commercial classes. th ese qualities are not equally distributed, hence about 95% of the sand 1 resources are located off shore, and about 88% of the pebble 3 resources are found onshore (measured resources, table 2). within the onshore areas, the sand and gravel resources are unevenly distributed, for example, very limited proven gravel resources are indicated close to the city of copenhagen. th ese observations are important for long-term planning of how to exploit the known resources. th ere is an up to 19% diff erence between distribution of gross and net deposits for the various raw material qualities when looking at measured and indicated resource classes. th e largest changes are seen for pebble 3 (19%), filler sand 4 (18%), sand 1 (10%) and sand 0 (7%). th e eff ect of the ‘no-go’ fi lters is generally rather limited for most of the commodities and raw material classes due to a few very large deposits. th is is in particular the case when including the inferred resources, which overshadows localscale restrictions, and thus in places the fi lters have a major impact on the resulting resource fi gures. also, a number of other constraints may be considered prior to designation of a resource resulting in substantial lower net resource fi gures. th is survey shows that denmark is endowed with enormous mineral resources of aggregates, clay and special clay, chalk and limestone, and salt and granite. however, to what extent these resources will be available as raw materials for the mineral industry is uncertain since it depends on local landuse and restrictions. finally, this assessment shows that both off and onshore aggregate deposits will have to be considered in order to secure the supply of all quality classes. references ditlefsen, c.b., lomholt, s., skar, s., jakobsen, p.r., kallesøe, a.j., keiding, j.k. & kalvig, p. 2015: danske mineralske råstofressourcer. kvantitativ analyse baseret på geologiske og geofysiske data. mima report 2015/1, 61 pp. copenhagen: geological survey of denmark and greenland. geas (global environmental alert service) 2014: sand, rarer than one thinks. www.unep.org/pdf/unep_geas_march_2014.pdf larsen, b. 1994: material sammensætningen i submarine råstoff orekomster – et metodestudium. dgu kunderapport 91, 51 pp. københavn: danmarks geologiske undersøgelse. regionernes videncenter for miljø og ressourcer 2014: fremskrivning af råstoff orbruget for 2013–2036. region syddanmark. råstoff er 4, 27 pp. statistics denmark 2012a: statistikbank – råstoff er indvundet fra havet. http://w w w.statisti kban ken.d k/statban k5a/selectvarva l/define. asp?maintable=rst3&planguage=0 statistics denmark 2012b: statistikbank – råstoff er indvundet på land. http://w w w.statisti kban ken.d k/statban k5a/selectvarva l/define. asp?maintable=rst01&planguage=0 uepg (union européenne des producteurs de granulats) 2014: european aggregates association. a sustainable industry for a sustainable europe. annual review 2013-2014. http://www.uepg.eu/uploads/ modules/publications/uepg-ar2013-2014_v28.pdf authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark; e-mail: jkk@geus.dk www.unep.org/pdf/unep_geas_march_2014.pdf http://www.statistikbanken.dk/statbank5a/selectvarval/define.asp?maintable=rst3&planguage=0 http://www.statistikbanken.dk/statbank5a/selectvarval/define.asp?maintable=rst01&planguage=0 http://www.uepg.eu/uploads/modules/publications/uepg-ar2013-2014_v28.pdf << /ascii85encodepages false /allowtransparency false /autopositionepsfiles true /autorotatepages /pagebypage /binding /left /calgrayprofile (dot gain 15%) /calrgbprofile (srgb iec61966-2.1) /calcmykprofile (coated fogra27 \050iso 12647-2:2004\051) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.7 /compressobjects /off /compresspages true 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/pdfxoutputintentprofileselector /usename /pagemarksfile /romandefault /preserveediting true /untaggedcmykhandling /leaveuntagged /untaggedrgbhandling /leaveuntagged /usedocumentbleed false >> ] /syntheticboldness 1.000000 >> setdistillerparams << /hwresolution [2400 2400] /pagesize [595.276 841.890] >> setpagedevice geological survey of denmark and greenland bulletin 33, 2015, 13-16 13 down-hole permeability prediction – a chemometric wire-line log feasibility study from a north sea chalk well kim h. esbensen, niels h. schovsbo and lars kristensen permeability in chalk depends primarily on porosity but also on other factors such as clay and quartz content, and can theoretically be described by the kozeny equation using empirically determined constants (mortensen et al. 1998; røgen & fabricius 2002). recent attempts to predict permeability from wire-line logs have shown that compressional velocity within operative chalk units, defi ned by specifi c surface and hydraulic properties established from stratigraphy and core plugs, can provide excellent well permeability predictions (alam et al. 2011). high-quality predictions depend on a solid knowledge of a multitude of parameters of the relevant ‘operative rock types’. th e more detailed this a priori knowledge is, the better predictions can be achieved. but this approach may, or may not, be fast enough for wellsite operations or when core data are lacking. in this study, we illustrate a situation for direct permeability prediction if only well-site, wire-line logs are available. th is pilot study is based on multivariate descriptor relationships, specifi cally aimed at direct permeability prediction, using all immediately available wire-line characteristics and/or core (plug) information in a top-down mode with sequential exclusion of non-correlated, irrelevant variables. we show prediction-model results based on [log] data only and on [log + plug] data. other relevant descriptors could be included in an augmented x-matrix, such as quantitative core and facies descriptions while still retaining the fast wellsite perspective. however, such data were not included in this feasibility study. material and methods core and log data are from the m-1x well in the danish part of the north sea; core data were collected in the mid1990s during a multi-disciplinary reservoir study (dons et al. 1995). th e m-1x well intersects the danian ekofi sk formation and the maastrichtian tor formation (kristensen et al. 1995). core analysis included determinations of conventional he-porosity and air permeability, whole-rock ca, mg, fe, mn and sr concentrations, δ13c and δ18o isotope ratios, per cent carbonate and per cent non-carbonate. before data analysis all concentrations were corrected to represent weight pr. volume. m-1x was drilled in 1971 on the dan field structure (fig. 1), and encountered a c. 200 m thick hydrocarbon-bearing zone in the chalk. petrophysical evaluation shows the top reservoir is at 1800 m; a gas cap was encountered down to 1880 m and the oil–water contact was found at 2036 m. a 192 m long core was collected from the hydrocarbon-bearing zone with a core recovery of c. 75%. wire-line logs included gamma ray (gr), sonic, formation density, spontaneous potential (sp), calliper, induction log (deep resistivity), lateral log (deep resistivity), micro-lateral log (shallow resistivity; mll) and short normal resistivity (medium resistivity). core data depth and well-log readings were adjusted and aligned applying an estimated common depth shift of 3 m. log readings were sampled for each plug depth to ensure a common plug-log training data set. two chemometric techniques were used, principal component analysis (pca) and partial least squares (pls) regression. pca transforms a matrix of measured data (n samples, p variables), x, into sets of projection sub-spaces delineated by principal components (each a linear combination of all p variables), which display variance-maximised interre© 2015 geus. geological survey of denmark and greenland bulletin 33, 13–16. open access: www.geus.dk/publications/bull 4°e gas field in chalk oil field in chalk inversion zone fault zone studied well 55°30´n dan field m-1x 10 km uk germany norway denmark the netherlands 500 km fig. 1. location of well m-1x in the dan field in the danish part of the north sea. 1414 lationships between samples and variables respectively (martens & næs 1989; höskuldsson 1996; esbensen 2010). pca score plots display groupings, or clusters, between samples based on compositional similarities, as described by the variable correlations (shown in accompanying loading plots), and also quantify the proportion (%) of total data-set variance that can be modelled by each component, see fig. 2. all data analyses in this work are based on auto-scaled data [x-x(avr)/std]. pls regression replaces the classical multiple linear regression and allows direct correlations to be modelled between y and the multivariate x data, among other compensating for debilitating co-linearity between xvariables, (martens & næs 1989; höskuldsson 1996; esbensen 2010). pls regression models are used extensively in science, technology and industry for prediction purposes where the critical success factor is proper validation (esbensen & geladi 2010). both pca and pls result in informative score plots, loading plots (pls: loadingweights) and prediction validation plots, which are the prime vehicles for detailed interpretation of complex data relationships. pls components are based on [x,y] covariance optimisation, but the scientifi c interpretation of the derived scores and loading-weights plots follows procedures which are identical to the pca. validation was based on a test set prepared before modelling: as the m-1x data set is limited, it was sorted with respect to the rhob mg nonc fe dt sp gr mn mll sr il por perm sn ll ca carb ekofisk fm tor fm hod fm δ18o δ13c pca 1 (38%) –8 –4–6 –2 0 2 4 pc a 2 (3 1% ) 6 4 2 0 –2 –4 –6 –8 pca 1 (38%) –0.4 –0.2 0.0 0.2 0.4 0.4 0.2 0.0 –0.2 –0.4 pc a 2 (3 1% ) a b fig. 2. principal component analysis. a: loading and b: score relations for the full training data set (ekofisk, tor and hod formations). the plot models 69% of the total data variance, the proportions are shown along each component axis (38 + 31%). a: abbreviations see fig. 3. –6 –4 –2 0 2 4 6 8 p l s 2 (3 5 % , 2 % ) reference air permeability (md) 0 2 4 6 8 p re d ic te d a ir p e rm e ab il it y ( m d ) pls 1 pls 2 pls 4 pls 6 % e x p la in e d y -v ar ia n c e pls1 (39%, 86%) pls 5 pls 7pls 3 dt gr il ll mll rhob sn sp carb nonc ca mg fe mn sr por perm pls1 (30%, 86%) –0.4 –0.2 0.0 0.2 0.4 0.6 p l s 2 ( 3 5 % , 2 % ) δ18o δ13c y = 0.44 + 0.88x r2 = 0.83 c d ba 4 2 0 –2 –4 –6 –8 0.6 0.4 0.2 0.0 –0.2 –0.4 –0.6 100 80 60 40 20 0 8 6 4 2 0 fig. 3. pls regression model [log + plug] variable set; full training set with ekofisk, tor and hod formations. a: pls x-space score plot (t1-t2). b: corresponding loading-weights plot (w1-w2). c: modelled y-variance. d: prediction versus reference plot. two outliers were deleted from the original data set. proportions of total data variance modelled shown along each pls component [x%, y%]. gr: gamma ray. dt: compressive wave interval travel time. r hob: formation density. il: induction log. ll: lateral log. mll: micro lateral log. sn: short normal resistivity. sp: spontaneous potential. por: he-porosity. perm: air permeability. ca: calcium. mg: magnesium. fe: iron. mn: manganese. sr: strontium. carb: carbonate volume content [calculated]. nonc: non-carbonate [calculated as 100% – carbonate volume %]. for data analysis, concentrations were transformed to weight per volume rock values. legend see fig. 2 15 full permeability range before being randomly split into two independent data sets, i.e. the training versus the test set, securing a realistic prediction performance validation (esbensen 2010; esbensen & geladi 2010). results th ere is a marked and fundamental diff erence in rock properties between the ekofi sk formation and the tor and hod formations (fig. 2). th e ekofi sk formation shows a high concentration of non-carbonate, fe and mn and high gr and mll levels. th ese characteristics are well-known from the north sea region, which forces a cautious approach to data set defi nition. th e developed permeability model may, or may not, apply to both the tor and the hod formations and the ekofi sk formation. th is will depend on whether the relationships between the x data from the three formations are similar with respect to correlation to permeability. a two-component pls model on the full (log + plug) variable set predicts permeability with satisfactory validation results as seen in the prediction versus reference plot in fig. 3 (slope 0.88; r2 = 0.83), suggesting that the pls model leads to better permeability estimates than normally achieved from conventional poro-perm plots. conventional statistics pertaining to a fi tted linear regression model between predicted (y) versus reference (x) values are used to express the degree of prediction strength: slope and regression coeffi cient, r2. for both these modelling indices the criterion is to be as close to 1.00 as possible. such validation statistics must be based on proper validation (esbensen & geladi 2010). th e permeability model is primarily carried by positively correlated por, ll, il, sn and negatively correlated rhob and gr, but several other log and composition variables also have minor, but signifi cant infl uence. from the loading-weights plot it is diffi cult to resolve any fully irrelevant variables; pls models benefi t from using a full x-variable complement; variable selection is not needed in this case. variable relationships are interpreted in the more appropriate pls loading-weight plots; a technical detail not to be elaborated on here, as interpretation follows the same principles (martens & næs 1989; esbensen 2010). figure 4 shows permeability prediction only based on log data (ekofi sk formation excluded), simulating a situation in which there are only well-site, wire-line logs available for the fastest possible permeability prediction. th e validation results for this model (slope 0.77; r2 = 0.75) are lower, but still acceptable for direct on-site permeability screening based on fig. 4. pls regression model (logs only). a: pls x-space loading weights plot (t1-t2). b: prediction versus reference plot. proportions of total data variance modelled shown along each pls component [x%, y%]. legend see fig. 2, abbreviations see fig. 3. –0.6 –0.4 –0.2 0.0 0.2 0.4 0.6 pls 1 (71%, 84%) il 0.4 0.2 0.0 –0.2 –0.4 –0.6 –0.8 6 4 2 0 p re d ic te d a ir p e rm e ab il it y ( m d ) p l s 2 ( 1 3 % , 4 % ) 0 2 4 6 8 reference air permeability (md) y = 0.61 + 0.77x a b rhob dt sp mll ll perm sn gr r2 = 0.75 fig. 5. reservoir properties versus depth. a: wire-line density log and core porosity measurements. b: predicted air permeability based on the model presented in fig. 4, compared with reference permeability (core measurements). the reservoir is gas filled from 1800 to 1880 m and oil filled down to a depth of 2036 m. the permeability model does not apply to the ekofisk formation (red rectangle). 1800 1850 1900 1950 2000 2050 tor hod ekofisk a b 2.4 2.0 0 5 10 4020 d ep th (m ), m d core porosity (%) permeability predictor (x=logs, tor and hod), md density (g/cm3) core measurement 1616 contemporaneous log data alone. th e results in figs 3 and 4 indicate that the tor formation can be modelled equally well with, or without, the hod formation. figure 5 shows stratigraphic permeability results for the all-logs prediction model (fig. 4), plotted together with measured core porosity (%) and density. an all-logs prediction model is fully able to characterise the hod and tor formations, but not the ekofi sk formation. for the latter, additional core information is necessary (fig. 3). discussion th e compositional diff erence between the ekofi sk formation and the tor formation has also previously been studied by multivariate data analysis (kunzendorf & sørensen 1989), pointing to a relationship between reservoir quality and geochemistry. røgen & fabricius (2002) showed that these compositional and textural relations are also refl ected in specifi c surface area diff erences between the formations, and thus in permeability and porosity diff erences. our analysis shows that high permeability is closely related to high porosity, and to high resistivity (fig. 3; ll, il, sn), whereas low permeability is related to high density and high gr, high non-carbonate content and thus to impure chalk with high concentrations of mn, fe and mg. røgen & fabricius (2002) also showed that quantitative mineral data can help to explain permeability values better. our analysis also shows that permeability predictions from wire-line logs alone strongly depend on the sonic and resistivity logs (fig. 4; dt, il, ll, sn and sp). th ese fi ndings complement those of alam et al. (2011) in which permeability was also predicted but based on the sonic log alone (dt). our analysis further shows that it is pos sible to model permeability more comprehensively by including the full set of readily available wire-line logs. conclusions th e present study confi rms that multiple parameters control permeability levels. both log data and core data can be used advantageously in direct pls prediction; there are real benefi ts in including the full set of available well-site parameters. prediction of permeability from models based on log information alone is useful for screening purposes, whereas permeability prediction from models based on both log data and core data are, not surprisingly, signifi cantly better. which approach to use depends on the context in which permeability prediction is used, especially on the time available for securing the additional core information from the laboratory. th is study shows that direct well-site permeability prediction is feasible. improvements can be made by adding standard he-porosity data and other easily measured conventional laboratory core parameters. th e feasibility study was based on a 192 m long chalk interval in a single well only. th e database can be extended to include more of the comprehensive core data available from the danish north sea. based on an augmented data set, it is in principle an easy task to refi ne this pilot study to investigate the more general limits of the feasibility demonstrated. a parallel study based on a similar approach using log data and logs + core data also proved successful for prediction of ‘functional rock types’ for other lithologies than chalk, i.e. alum shale (schovsbo et al. 2015). functional rock types may correlate with rock strength and can here be used for optimisation of the completion design. references alam, m.m., fabricius, i.l. & prasad, m. 2011: permeability prediction in chalks. a apg bulletin 95, 1991–2014. dons, t., jacobsen, f. & stentoft , n. 1995: chalk diagenesis and reservoir properties – dan fi eld case study. dgu service report 15, 2 vols, 251 pp., 259 pp. københavn: danmarks geologiske undersøgelse. esbensen, k.h. 2010: multivariate data analysis, in practise. an introduction to multivariate data analysis and experimental design, 5th edition, 598 pp. oslo: camo. esbensen, k.h. & geladi, p. 2010: principles of proper validation: use and abuse of re-sampling for validation. journal of chemometrics 24, 168–187. höskuldsson, a. 1996: prediction methods in science and technolog y 1, basic theory, 405 pp. holte: th or publishing. kristensen, l., dons, t., maver, k.g. & schiøler, p. 1995: a multidisciplinary approach to reservoir subdivision of the maastrichtian chalk in the dan fi eld, danish north sea. aapg bulletin 79, 1650–1660. kunzendorf, h. & sørensen, p. 1989: geochemical criteria for reservoir quality variations in chalk from the north sea, 99 pp. roskilde: risø national laboratory. martens, h. & næs, t. 1989: multivariate calibration, 419 pp. chichester: wiley. mortensen, j., engström, f. & lind, i. 1998: th e relationship among porosity, permeability, and specifi c surface of chalk from the gorm field, danish north sea. spe reservoir evaluation & engineering 13, 245–251. røgen, b. & fabricius, i.l. 2002: infl uence of clay and silica on permeability and capillary entry pressure of chalk reservoirs in the north sea. petroleum geoscience 8, 287–293. schovsbo, n.h., esbensen, k.h., nielsen, a.t., derbez, e., gaucher, e.c., poirier-coutansais, x., riou, a., tallone, p. & milton-taylor, d. 2015: rock types in the scandinavian alum shale resource play: defi nitions and predictions. 77th eage conference & exhibition, madrid, 1–4 june, 2015. abstract. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: ke@geus.dk geological survey of denmark and greenland bulletin 33, 2015, 29-32 440 40 25 20 200 precipitation in fil tra tio n 740 s ur fac e f l o w sea stream flow atmosphere evapotranspiration over sea unsaturated zone 15 abstraction 15 evapotranspiration groundwater wind groundwater flow 29 th e rapidly increasing impacts of climate change are likely to require changes in relevant institutions (ipcc 2012). an example is the growing need for immediate information on the entire water cycle (fig. 1), with quantitative assessments of critical hydrological variables and fl ow interactions between diff erent domains, e.g. atmosphere, plant-soil, surface water, groundwater and the sea, as they take place. potential measures include early warning systems, risk communication between decision makers and local citizens, sustainable land management, including land use planning as well as ecosystem management and restoration (ipcc 2012). early warning systems (kundzewicz 2013) that provide information and monitoring of past and present hydrological conditions as well as forecasting of hydrological conditions (e.g. water content, fl ow and water levels) are fi rst steps in developing fl ooding indicators for operational use. fig. 1. water balance in mm/year for a typical danish area. with climate change the freshwater cycle is no longer in a steady state. early warning and monitoring keeps us continuously updated and gives us an overview. this is important for our ability to combat the impact of climate change and manage the water resources proactively. it is possible that a nationwide system can be linked to local early warning systems and can make use of national overviews based on national hydrological models. flooding and drought events are complex phenomena with several key mechanisms including intense and long lasting precipitation or lack of precipitation in the case of drought and interaction with water uses. water consumers use groundwater for drinking water, food production, households and livestock, energy production and recreational activities. at the same time, water authorities have to manage surface and groundwater to sustain ecological systems, and support vital ecological conditions for plants and animals in rivers and wetlands. it is obvious that it is vital for society to have water in the right amount in the right place at the right time. th erefore, we must understand the water cycle, i.e. how overland drainage and surface runoff are generated, how water fl ows in the upper soil layers and in the deeper subsurface, how it is discharged in water courses and lakes and how freshwater interacts with the sea. one or two decades ago, water management was developed and operated under the assumption of static conditions, a paradigm which now is dead according to milly et al. (2008). it is stated by milly et al. (2008, p. 573) that “stationarity – the idea that natural systems fl uctuate within an unchanging envelope of variability – is a foundational concept that permeates a hydrological early warning system for denmark based on the national model hans jørgen henriksen, simon stisen, xin he and marianne b. wiese © 2015 geus. geological survey of denmark and greenland bulletin 33, 29–32 . open access: www.geus.dk/publications/bull 3030 training and practice in water-resource engineering . . . . stationarity is dead because substantial anthropogenic change of the earth’s climate is altering the means and extremes of precipitation, evapotranspiration, and rates of discharge of rivers”. in the new paradigm, in the non-stationary world, real-time modelling and a continuity of monitoring systems are critical for dealing with the increasing impact of extremes. globally natural disaster costs have more than quadrupled since 1985 (georgieva 2014). early warning and monitoring systems that can transfer operational hydrological knowledge to community-based climate change adaptation planning and emergency management, are assumed to be fundamental for building societal resilience, both in the phases of pre-disaster, disaster response and post-disaster, and in general for extending monitoring techniques with network-based public participation. th e geological survey of denmark and greenland (geus) fi nanced a two year project (2012–2014), in order to determine the requirements for a hydrological system capable of providing real-time and forecast simulations based on a national hydrological model (the dk-model; www. vandmodel.dk; henriksen et al. 2003; stisen et al. 2012; højberg et al. 2013), and how the system can be linked with local early warning systems. th is paper describes four scenarios discussed at a participatory workshop in october 2014 and the workshop’s outcome. th e workshop provided geus with valuable insight and feedback relevant for the future development of a nation-wide, real-time modelling and water cycle monitoring system for denmark, including the possible input to an early warning system and real-time forecasting to operate at local level. structuring the needs – four scenarios for an early warning system design th e four scenarios, used in the workshop, for the design of a hydrological, real-time forecasting system linked to local level, community-based, emergency management are shown in fig. 2. scenario 1: an updated national model can provide an estimate of the actual status of water resources in denmark based on the calibrated national model (the dk-model) with updated climatic data, and available on-line with absolute values, indices or anomalies (below, same as, or above normal). scenario 2: a national model that can forecast the state of the water resources on a short timescale or as a seasonal prognosis, based on forward modelling simulations using weather forecast data. th is could be used as an early warning system and as a starting point for local, community-based emergency management. scenario 3: decision support is a scenario where local communities use a decision support tool for integrated assessment and management (kelly et al. 2013), for incorporating local knowledge and experience, and where simulation results from the national model in forecasting mode are included. th is scenario builds on a combination of monitored data and model output. th e output from this model might be with physical variables, thematic maps, indices or anomalies. scenario 4: a complex local model where a local detailed model (such as mike 11 or mike urban) uses simulated results from the national model in forecasting mode as input or boundary conditions. th is can be combined with monitoring data in a data assimilation framework. th e national model data in this scenario are physical variables delivered as pointor gridded data. a representative catchment area (skjern å; fig. 3) was selected for the workshop to test and demonstrate a prototype of a web-based, hydrological warning system for professional users. th e system provides hydrological simulations from groundwater levels, stream fl ow and water content in the root zone. webpages can be tailor-made to meet the requirements of end-users and continuously adapt to changing user demands. numerical results from simulations on a national fig. 2. the four real-time forecasting scenarios discussed in the text. scenario 1: updated dkmodel, scenario 2: dk-model forecast, scenario 3: local decision support and scenario 4: complex local model. 31 scale could also be provided. hourly values of climatic and discharge data at ahlergaarde station 250082 were used for the prototype demonstration. setting up the workshop a participatory workshop (hare & krykow 2005) was held in copenhagen for the purpose of eliciting stakeholder ideas and opinions and get feedback from prospective users. participants were planners and emergency managers from local authorities, water supply companies, ministries and consulting agencies. th e workshop had invited speakers from the holstebro, aarhus and fredensborg municipalities and local authorities that had already implemented local, real-time forecasting and early warning systems. th e danish hydraulic institute (dhi) and the danish meteorological institute (dmi), geus’ two partners in the project, also presented their experiences. both of these institutions have more than 20 years of experience developing and implementing modelbased early warning systems in denmark and abroad. prior to the workshop, an invitation was sent to those employed with climate change adaptation and emergency management at local and national levels. a questionnaire was attached to the invitation which explained why geus had initiated the project, introduced the four scenarios and briefly described the hydrological components that the national model can simulate. th e prototype of the web interface was described. th e goal of the workshop was an in-depth discussion of user requirements as a supplement to the web questionnaire which had 27 respondents. a total of 34 participants signed up for the workshop; eight came from geus, one from dmi, one from dhi, nine from local authorities, four from national ministries, ten from consulting companies and one from a large water-supply company. th e workshop was a one day event. th e fi rst block contained three presentations by geus participants: introduction to the real-time project, technical challenges in real-time modelling and web presentation of real-time data for the river skjern å catchment area. th is was followed by two invited presentations by dmi (better prediction of heavy rain) and the dhi (early warning systems in relation to hydrology and the freshwater cycle). th ree invited speakers from local authorities talked about fl ooding from the river storå in holstebro, the usserød å project in fredensborg and an early warning model with emphasis on fl ooding and groundwater monitoring in the urban area of aarhus. finally, there was a group session with three groups each addressing the same four questions. (1) what are the requirements for realtime forecasting? do you miss an overview of the hydrological state of an area in your daily work or in situations with fl ooding or drought? (2) what information would be benefi cial during such a situation, absolute or relative values; and which components of the hydrological cycle are the most important? (3) what is the time perspective in such an extreme event: days, hours or other? what would be the most appropriate frequency for updating the forecasts? (4) would a national overview make any diff erence in forecasting hydrological events, and how can or should the prototype be developed further? how can the present dk-model be part of such a system? outcome of the workshop th e results of the discussions were presented by groups. group 1 recommended linking national and local systems and presented a variety of requirements from diff erent local authorities posing potential challenges to the entire concept. th ey noted that problems with fl ooding, drought and emergency management are highly site specifi c. data assimilation is an important component in the early warning systems and there are many diff erent sources of observational data, e.g. from local authorities and the danish road directorate. a merged dataset is preferred. group 2 noted that real-time data for shallow groundwater levels are lacking but it may be possible to use observations from geotechnical boreholes. an investigation of geotechnical boreholes is necessary in order to establish a new operational groundwater level monitoring network. more emphasis should be given to a real-time early warning system instead of the present forecasting system with a short time horizon of only days. th e quality of early warnings should be quantifi ed in order to demonstrate how reliable the model can describe 5 km9°e 56°10´n discharge station hydraulic head observation stream ahlergaarde catchment station 250082 fig. 3. pilot case study for river skjern å, ahlergaarde catchment area. green: low elevation areas. dark yellow: high elevation areas. 3232 extremes. it is important to simulate water levels including storm surges. data and forecasts should be available online. group 3 noted that in many cases local authorities have their own local data which could provide input to the national model. local authorities may not have a groundwater model so co-operation between geus and local authorities are encouraged. local authorities experience an increased demand for warning and action capabilities. at the same time, local authorities are reluctant to issue warnings because they do not wish to be overcautious or risk subsequent claims. absolute values of physical variables are requested and data of levels of surface water and shallow groundwater are the most urgent. it was also suggested that continuous monitoring of water levels and early warning of changes in these levels are the most interesting for short-term forecasts, especially when local authorities do not have early warning systems, which is consistent with what was proposed by group 2. from a temporal perspective, precipitation events are highly diverse and it may not always be the short-term cloudbursts that are the most infl uential. long periods of rainfall (e.g. from a few days in succession to prolonged periods of rain) can signifi cantly increase groundwater levels in western and central jylland and snowmelting events can also cause extreme fl ooding. for the moment the national model has a limited applicability with its focus on water fl ow simulations. it is necessary to simulate water levels with local models. discussion and conclusion a participatory workshop discussion real-time forecasting was held to get feedback and get into dialogue with water planners and emergency managers from local authorities, water companies and national authorities. at the workshop, a prototype website illustrating four scenarios of national and local early warning systems was presented for the skjern å, ahlergaarde catchment area with selected events. th e workshop recommended that geus should focus on realtime modelling with the dk-model (scenario 1). th e fi rst step is to update the national coverage of climatic data input from dmi; real-time discharge fl ow and groundwater level monitoring are required; and the necessity of data assimilation and other types of uncertainty analyses have to be further evaluated. if a forecast model is included (scenario 2), complex data assimilation is required, however, this can compromise the water and mass balance of the model. th e water balance and simulation of the whole water cycle should be addressed by the early warning systems (most participants found that soil moisture, discharge in rivers and groundwater levels should be represented in such a system). eventually, an improved system for collecting observations of precipitation (or use of high-resolution radar measurements adjusted with rain-gauge data from a coarse network) is needed because the current network of rain-gauge stations has a poor national coverage. th e early warning system should be able to deliver results for discharge stations and boundary conditions for subsequent use in local models (scenarios 3 and 4). acknowledgements th e study was conducted as part of the geus-funded project: ‘realtidsvarsling’. th e paper is a nor dr ess (nordress.hi.is) contribution. we are grateful for the input and feedback of the participants at the workshop. references georgieva, k. 2014: post-haiyan – a way forward. speech/14/441 by eu commissioner for international cooperation, humanitarian aid and crisis response. asem conference on disaster risk reduction and management. manila, 5 june 2014. hare, m. & krykow, j. 2005: participatory processes for the design of water storage areas – theme group iii inception report of the trust project. seecon report 1/2005, 68 pp. osnabrück: hoogheemraadschap van schielanden en der krimpenerwaard. henriksen, h.j., troldborg, l., nyegaard, p., sonnenborg, t.o., refsgaard, j.c. & madsen, b. 2003: methodolog y for construction, calibration and validation of a national hydrological model for denmark. journal of hydrolog y 280, 52–71. højberg, a.l., troldborg, l., stisen, s., christensen, b.s.b. & henriksen, h.j. 2012: stakeholder driven update and improvement of a national water resources model. environmental modelling and soft ware 40, 202–213. ipcc 2012: managing the risks of extreme events and disasters to advance climate change adaptation, a special report of working groups i and ii of the intergovernmental panel on climate change, 582 pp. cambridge: cambridge university press. kelly, r.a. et al. 2013: selecting among fi ve common modelling approaches for integrated environmental assessment and management. environmental modelling & soft ware 47, 159–181. kundzewicz, z.w. 2013: floods: lessons about early warning systems. in: gee, d. et al. (eds): late lessons from early warnings: science, precaution, innovation, 347–368. eea report no. 1/2013. copenhagen: european environment agency. milly, p.c.d., betancourt, j., falkenmark, m., hirsch, r.m., kundzewicz, z.w., lettenmaier, d.p. & stouff er, r.j. 2008: stationarity is dead: whither water management? science 319, 573–574. stisen, s., højbjerg, a.l., troldborg, l., refsgaard, j.c., christensen, b.s.b., olsen, m. & henriksen, h.j. 2012: on the importance of appropriate precipitation gauge catch correction for hydrological modelling at mid to high latitudes. hydrolog y and earth system sciences 16, 4157–4176. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: hjh@geus.dk geological survey of denmark and greenland bulletin 33, 2015, 21-24 21 consistency of postglacial geodynamics for the kattegat region, southern scandinavia, based on seismological, geological and geodetic data søren gregersen and peter h. voss th e earthquake map of denmark is constantly being improved. together with data from western sweden and southern norway it shows more and more convincingly a gradual, scattered earthquake activity across the kattegat region from low activity in the precambrian basement of scandinavia to lack of earthquakes in south-western denmark and northern germany. th e activity is only partly connected with mapped geological features. th e three most recently felt earthquakes in denmark augment and support this pattern with two or three activity concentrations in the seas around denmark (fig. 1). th e smoothness and irregularities of this picture must in some way be related to the geological structure as well as to the geodynamic pattern of postglacial uplift mapped from geology and geodesy. since the dominant stress fi eld, from the lithospheric plate motion is smooth (gregersen & voss 2010), a natural question is whether the picture © 2015 geus. geological survey of denmark and greenland bulletin 33, 21–24. open access: www.geus.dk/publications/bull 8°e 12°e 16°e 20°e 56°n zone ringkøbing – fyn high tornquist sweden germany denmark norway kattegat magnitude 100 km important geological line noticeable historical earthquake latest felt earthquakes 5 4 3 2 magnitude fig. 1. the latest three felt earthquakes in denmark shown on the best available earthquake map of the kattegat and the surrounding regions (gregersen & voss 2014). little earthquake activity is seen north-east of the gradual margin of the fennoscandian shield between the tornquist zone and the ringkøbing–fyn high. in contrast, no activity is seen in south-western denmark and north-western germany. only a few small earthquakes have been recorded in the south-eastern part of the area shown on the map; this is because only few seismographs are located in that region. 2222 of postglacial uplift , seen from the geological and geodetic perspective shows local irregularities? th e broad-scale uplift pattern in denmark since the last ice age has been known since the review published by mertz (1924). all later papers have referred to this general pattern of uplift towards the north-east and subsidence towards the south-west with reference to the present sea level. th e present paper relates the regional seismological pattern to the smooth and consistent patterns in postglacial geology and geodesy, as well as to the existing local investigations on geodynamics. interpretations of the measured uplift of shorelines on læsø, in the middle of the kattegat (fig. 2), have given rise to opposing views on regularity versus irregularity between the present authors and hansen et al. (2012). th e measurements show that the elevation of the oldest postglacial shorelines on læsø fi t in the regional pattern with regard to elevation, but not with regard to time. in this paper we propose that the time diff erence is only apparent. uplift patterns recent overviews of the geological evolution of the region of denmark, including the uplift since the time of fl ooding, termed the littorina sea transgression, have been presented by christensen (2001) and noe-nygaard et al. (2006). th e former provided ages for the oldest shorelines, from radiocarbon dating, pollen and human settlement evidence. it is seen that the uplift increases gradually from the south-west towards the north-east (fig. 2). th e general pattern with increasing ages towards the north-east has been convincingly argued for by christensen (2001). th e ages in fig. 2 are the oldest for each location for the littorina sea period that lasted several thousands of years. during this long time period the postglacial uplift of the lithosphere approximately followed the rising water level, within about one metre. both were infl uenced by the melting ice sheets aft er the last ice age. th e situation, with repeated small transgressions and regressions, was illustrated by christensen (2001), noe-nygaard et al. (2006) and clemmensen et al. (2012). th e latter paper shows that this period of several thousand years ends rather abruptly with a large regression lasting until present time. th e start of the regression can be dated by optically stimulated luminescence (osl), when no later transgressions disturb the dark, covered parts of the beach sediments used for dating. th e elevation of raised beaches and ages determined for anholt (fig.  2) by clemmensen et al. (2012) are interpreted as a period of ‘simultaneous’ land uplift and sea-level rise for several thousands of years followed by a period of continuing land uplift and slower sea-level changes. th is is suggested generalised for the kattegat region in fig. 3 with times that are diff erent for diff erent locations. in fig. 3 two kinds of arrows are seen. th e thick arrow points to the oldest shoreline that has not been disturbed by a transgression. sediments from this shoreline can be dated by the osl method. on anholt it has been dated to 2300 years bc (clemmensen et al. 2012). th e thin arrows point to archaeological time periods which can be dated by pollen hobrohobro 7.57.5 4500 bc4500 bc aalborgaalborg hobrohobrohobrohobro aalborg denmarkdenmark jyllandjylland denmark 50 km10°e 10°e 56° 56°n hobro copenhagen 23 6300 bc 20 6000 bc 15 12 5200 bc 9 4600 bc 8 7.5 4500 bc 4.8 4200 bc 1 3600 bc 0 3600/2500 bc 0 2 2 6 8 10 12 4 4 2 3 frederikshavn læsø anholt rügen jylland skåne skagerrak kattegat aalborg sweden fig. 2. general picture of the elevation patterns of postglacial shorelines in metres above present sea level, according to christensen (2001). shaded circles and zones refer to locations mentioned in the text, where irregularities have been claimed. ages of highest shorelines of the littorina sea, i.e. after the last ice age, are from christensen (2001). this figure is a corrected version of a figure presented by gregersen & voss (2012) and by gregersen (2014), where the ages were incorrectly quoted. 23 analysis, radiocarbon dating or human settlement indicators for places close to the beach where plants or human remains have survived close to the shoreline or just above it. in fig. 2 the anholt age from christensen (2001) is 4500 years bc, i.e. 2200 years before the osl age mentioned above. only in special cases will an older shoreline from within the littorina sea time, protected from transgression, show up by osl dating as in anholt (clemmensen et al. 2012). on læsø all ages were determined by osl and all are young compared to regions with similar elevations of the highest shorelines (fig. 2; hansen et al. 2012; j.m. hansen, personal communication, 2013–2014). th ose authors also suggest that older shorelines are not observed on læsø because they were eroded by waves. we suggest that this shows that only the right part of fig. 3 is relevant for læsø. in contrast, data from both the left and right parts are available from anholt. many other regions such as northern jylland and western sweden are well described by the left part of fig. 3 (christensen 2001, fi g. 2; christensen & nielsen 2008). th is point was discussed by gregersen & voss (2010, 2012, 2014) and gregersen (2014) who suggested that the age determinations ought to be redone using the same methods for points of comparable uplift in northern jylland, on læsø and in western sweden (see fig. 2). a smooth picture with only small irregularities is also shown by a recent geodetic picture of uplift velocities based on all available data from levelling, global positioning system (gps) and sea-level gauges (fig. 4). both the geological picture illustrated by fig. 2 and the geodetic picture in fig. 4 show the main, general features. geological and physically small irregularities are generalised into the broad-scale regional picture. in addition, the geodetic picture is based on measurements carried out over only approximately 100 years. updating with greater detail will be appreciated in the future. figures 2 and 4 indicate regularity so far. discussion of irregularities from the literature in addition to the irregularity proposed for læsø, several more irregularities have been proposed for diff erent regions in denmark (figs 2, 4). some of them show irregularities in the sedimentary succession which may be connected to larger-scale postglacial faulting, e.g. the carlsberg fault in the copenhagen area described by rosenkrantz (1937) and ovesen et al. (2002) or faulting reported from mid-jylland by jakobsen & pedersen (2009). other irregularities could be directly related to the postglacial uplift pattern, as described by lykke-andersen & borre (2000) and gregersen & schmidt (2001) for the region from hobro via aalborg to frederikshavn or by hansen et al. (2012) for harbours in time of littorina sea h e ig h t o f b e a c h p re se n t ti m e c . 1 m e tr e increasing age 2.0 1.8 1.6 1.4 1.2 1.2 1.0 0.8 0.6 0 .6 0 .4 2.2 25 km denmark sweden læsø 0 .8 s o u t h e r n d e n m a r k hallandsåsen copenhagen fig. 3. conceptual model showing the elevation of shorelines in kattegat as a function of age. the model shows the generalised concept of uplift with minor oscillations in the grey band of the order of one metre from several sources mentioned in the text. the arrows point to age data, thin arrows to archaeological data, thick arrow to osl data. only for anholt older osl data supplement the archaeological dates. fig. 4. generalised uplift velocities (mm/year) from knudsen et al. (2012) based on levelling, gps and sea-level gauges. the velocities have been corrected from an earlier version by gregersen & voss (2014). the shaded circles and zones show locations where irregularities have been claimed, and which are discussed in the text. 2424 southern denmark, based on 100 years of water-level measurements. th e irregularity locations in the middle of skåne in southern sweden and on rügen in northern germany are based on geodetic measurements. th e case in southern sweden (pan et al. 1999) has been rejected by swedish geodesists because of inaccuracy (h.-g. scherneck, personal communication 2015). th e case in northern germany is based on a personal communication by r. dietrich in 2008. it was claimed that geodetic levelling indicates similar changes in uplift rates as those seen in northern jylland by lykke-andersen & borre (2000), but it awaits further confi rmation by geodesists. th e claims by mörner (2003) on postglacial earthquakes near hallandsåsen, based on geological irregularities were taken up on a fi eld excursion in the summer of 2013 by 12 international seismologists on the initiative of the fi rst author of this article. th e outcome was “possible but not probable”. conclusion th e discussion as to whether the evidence for lack of major irregularities in the geology and geodesy fi elds is suffi ciently strong to be signifi cant is heated (hansen et al. 2012; gregersen & voss 2012). recent papers by gregersen & voss (2012, 2014) and by gregersen (2014) claim that the irregularities are so small compared to the uncertainties in the measurements that they are insignifi cant, and thereby not disturbances of the regularity. th ey are only possibilities. th ey need supporting evidence in the form of irregularities in the generalised geodynamics. our view is that such supporting evidence is lacking. th e consequence of the consistency of the regional geophysical fi elds is that the short term, thousand-years evidence from seismology adequately describes the geodynamics and its irregularities. we suggest that the use of diff erent methods for dating of the shorelines results in that diff erent phases of the uplift are dated. th e osl dates refl ect the last infl uence of the waves on the loose sediments of the shore, whereas the archaeological dates refl ect the several thousand-year long littorina sea time when land plants left remains in the dry ground near the shoreline. th e age determinations are diff erent because diff erent phenomena were measured. references christensen, c. 2001: kystbosættelse og havniveauændringer i stenalderen. in: jensen, o.l., sørensen, s.a. & hansen, k.m. (eds): danmarks jægerstenalder – status og perspektiver, 183–193. hørsholm: hørsholm egns museum. christensen, c. & nielsen, a.b. 2008: dating the littorina sea shore levels in denmark on the basis of data from a mesolithic coastal settlement on skagens odde, northern jutland. polish geological institute special papers 23, 27–38. clemmensen, l., nielsen, l. & konnerup-madsen, j. 2012: anholt. geoviden 2012/1, 20 pp. gregersen, s. 2014: jordskælvsrisiko i danmark? – forslag til fremtidens studier. kvant 2014/2, 30–34. gregersen, s. & schmidt, k. 2001: tektonik i danmark. sorgenfrei–tornquist zonen. geologisk nyt 2001/1, 16–17. gregersen, s. & voss, p. 2010: irregularities in scandinavian postglacial uplift /subsidence in time scales tens, hundreds, thousands of years. journal of geodynamics 50, 27–31. gregersen, s. & voss, p.h. 2012: eff orts to include geological and geodetic observations in the assessment of earthquake activity in denmark. geological survey of denmark and greenland bulletin 26, 41–44. gregersen, s. & voss, p.h. 2014: review of some signifi cant claimed irregularities in scandinavian postglacial uplift on timescales of tens to thousands of years – earthquakes in denmark? solid earth 5, 109–119. hansen , j.m., aagaard, t. & binderup, m. 2012: absolute sea levels and isostatic changes of the eastern north sea to central baltic region during the last 900 years. boreas 41, 180–208. jakobsen, p.r. & pedersen, s.a.s. 2009: fracture valleys in central jylland – a neotectonic feature. geological survey of denmark and greenland bulletin 17, 33–36. knudsen, p., engsager, k. & khan, s.a. 2012: dokumentation for beregning af ny uplift -model 2011, 19 pp. unpublished report. lyngby: dtu space. lykke-andersen, h. & borre, k. 2000: aktiv tektonik i danmark – der er liv i sorgenfrei–tornquist zonen. geologisk nyt 2000/6, 12–13. mertz, e.l. 1924: oversigt over de senog postglaciale niveauforandringer i danmark. danmarks geologiske undersøgelse ii. række 41, 49 pp. mörner, n.-a. 2003: paleoseismicity of sweden – a novel paradigm, 320 pp. stockholm: university of stockholm. noe-nygaard, n., knudsen, k.l., & houmark-nielsen, m. 2006: fra istid til og med jægerstenalder. in: sand-jensen, k. & larsen, g. (eds): naturen i danmark, geologien, 303–331. copenhagen: gyldendal. ovesen, n.k., blem, h., gregersen, s., møller, h.m.f. & frederiksen, j.k. 2002: recente terrænbevægelser i københavn. dansk geoteknisk forenings bulletin 19, 183–192. pan, m., sjöberg, l.e., talbot, c. & asenjo, e. 1999: gps measurements of crustal deformation in skåne, sweden between 1989 and 1996. gff 121, 67–72. rosenkrantz, a. 1937: bemærkninger om det østsjællandske daniens stratigrafi og tektonik. meddelelser fra dansk geologisk forening 9, 199–212. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: sg@geus.dk geological survey of denmark and greenland bulletin 33, 2015, 45-48 45 magma mixing, mingling and hybridisation at different crustal levels: snapshots from 1.9 billion years of magmatism in south-eastern greenland thomas f. kokfelt, samuel m. weatherley, jakob k. keiding and trygvi b. árting during fi eld work in 2014, we investigated a suite of igneous intrusions in south-eastern greenland between 65° and 67°n. many of the intrusions show widespread evidence for juxtaposition of diff erent magmas in the liquid state and subsequent mixing, mingling and hybridisation. here we present fi eld evidence for these processes from three areas that diff er in age and geological setting. we discuss the signifi cance of mingling, mixing and hybridisation features in the fi eld area, motivated by their abundance in the area, the morphological variation between intrusions that were emplaced at diff erent crustal levels, the implications for magma genesis in collisional and rift settings, and the implications for the interior dynamics of igneous bodies. magmatism in south-eastern greenland th e magmatic history of south-eastern greenland broadly falls into two episodes: (1) the proterozoic nagssugtoqidian orogeny and preceding subduction, and (2) the palaeogene opening of the north atlantic. th e nagssugtoqidian orogen formed by a ne–sw collision between the rae and the north atlantic cratons that started at c. 1880 ma and ended with a post-orogenic collapse at c. 1740–1690 ma (see kolb 2014 and references therein). several intrusions and intrusive complexes are associated with the orogeny (fig. 1). th ese include the c. 1885 ma ammassalik intrusive complex, interpreted as originating in an island arc, several post-tectonic granites, and the intermediate to felsic ikaasartivaq intrusive complex with an uncertain intrusion age of 1680 ma (kalsbeek et al. 1993). th ree separate intrusions of diorite and tonalite are found north of ikaasartivaq strait. th e ages of these palaeoproterozoic intrusions, their geotectonic setting and relationship to the other intrusive bodies are poorly constrained. intrusive complexes from the palaeogene extend from 66° to 75°n. th ey were emplaced between c. 55 and 25 ma (larsen et al. 2014 and references therein) and encompass mafi c to felsic compositions of alkaline to tholeiitic affi nity in addition to carbonate-related lithologies (nielsen 2002). th e intrusive complexes and associated coeval lavas and coastparallel dyke swarms are all part of the palaeogene north atlantic igneous province (naip) that formed as a result of oceanic rift ing under the infl uence of the ancestral icelandic mantle plume (brooks 2011). in this contribution, we present evidence for magma mingling, mixing and hybridisation in south-eastern greenland, focusing in particular on the ammassalik intrusive complex, the ikaasartivaq intrusive complex and the kialineq intrusive centre. magma mixing, mingling and hybridisation magma mixing is a recognised process operating in most magmatic systems worldwide and may be a trigger for generating volcanic eruptions (sparks & sigurdsson 1977). th e term ‘mixing’ refers to a process where two magmas blend to form a new magma of intermediate composition. th e extent to which the magmas blend or mix critically depends on diff erences in the rheological properties and the relative proportions of the juxtaposed magmas (sparks & marshall 1986). important parameters that determine the rheology of a given magma include temperature, composition and crystal load. for large property contrasts, the mixing process will © 2015 geus. geological survey of denmark and greenland bulletin 33, 45–48. open access: www.geus.dk/publications/bull kialineq intrusive centre tasiilaq intrusion ikaasartivaq intrusive complex ammasalik intrusive complex tasiilaq 67°n 34°w laube gletscher laube gletscher syenite intrusion ikaasartivaq strait palaeogene basalt 50 km greenland pre-cretaceous rocks cretaceous/palaeogene sedimentary rocks intrusion desribed here other intrusions fig. 1. geological map of south-eastern greenland showing some of the prominent intrusions and intrusive centres in the region. the intrusions described here are the c. 1885 ma tasiilaq intrusion of the ammassalik intrusive complex, the c. 1680 ma ikaasartivaq intrusive complex and the c. 35 ma kialineq intrusive centre. +10 –8 4646 typically be incomplete and the original magmas remain as identifi able units; the result is a mingled magma. hybridisation refers to the general mixing process that may produce a range of variably heterogeneous intermediate magmas. classical examples of magma mixing and mingling include eroded plutonic systems within the naip including iceland (brooks 2011). a common feature in many of these exhumed magma reservoirs is the occurrence of ‘net-veined’ complexes consisting of felsic, mafi c and hybrid (intermediate) rocks. tasiilaq intrusion of the ammassalik intrusive complex – th e tasiilaq intrusion, dated to 1886 ± 2 ma (hansen & kalsbeek 1989), is the central part of the palaeoproterozoic ammassalik intrusive complex that forms a c. 85 × 20 km wnw–ese-trending array of three large mafi c intrusions (fig. 1). th e intrusion mainly comprises leuconorite that cross-cuts melagabbro, and late anorthosite and hypersthene veins that cross-cut the leuconorite and melagabbro. th e wall rock is quartzofeldspathic garnet-rich gneiss, which has granulite facies assemblages close to the contact, and has been mobilised and mixed with the intrusive rock forming a marginal zone of hybrid rocks. based on thermobarymetry and fl uid inclusion data, andersen et al. (1989) concluded that the intrusion crystallised at c. 1000–1100°c and 6–8 kbar (c. 18–24 km depth), i.e. in the middle to deep crust. in the fi eld, melagabbro oft en forms 20–100 m wide trains within larger domains of leuconorite, defi ning the same general wnw–ese-orientation as the overall structures of the ammassalik intrusive complex. in some cases leuconorite has intruded melagabbro forming sharp angular contacts (fig. 2a); in other outcrops, the two lithologies form lenticular intermingled bodies with smeared out, wavy contacts and with no chilled margins (fig. 2b). ikaasartivaq intrusive complex – th e ikaasartivaq intrusive complex is composed of mafi c and felsic intrusions, which straddles the ikaasartivaq fj ord c. 25 km north of tasiilaq (fig. 1). th e complex measures c. 32 × 25 km and comprises rocks of granitic, dioritic and gabbroic composition. it was fi rst mapped by wright et al. (1973), who described it as a lateor post-orogenic calc-alkaline suite related to the uplift of the area. th ese authors proposed that the complex was emplaced into relatively shallow crustal levels based on observations of sharp contacts between intrusive units and negligible evidence for contact or retrogressive metamorphism. mixing and hybridisation features within the intrusive complex are ubiquitous and show a range of styles and morphologies. in the main body of the complex, mingling features between diorite and granite are observed at millimetreto metre-scales in the form of blobs and globules and occasionally as angular net-veined areas. although mingling features are quite pervasively developed throughout the complex, they tend to be more prominent and abundant in the western part of the intrusion. here they oft en occur as rather extensive pilfig. 2. examples of composite magmatic systems intruded at different crustal levels. a, b: the tasiilaq intrusion representing deep to middle crustal levels. a: leuconorite intruding melagabbro in a semi-molten state. b: mingling structures with lensoidal wavy contacts between leuconorite (no) and melagabbro (gb). c, d: the ikaasartivaq intrusive complex intruded at intermediate to upper crustal levels. c: a c. 5 m wide composite mafic-felsic dyke intruded into gneiss basement. d: contact of dyke with gneiss (gn) wall rock, marginal zone of hybridised magma (hyb), and interior part of dark, distorded diorite pillows (di) in pale granite (gr) matrix; note crenulated, chilled margins in diorite. e, f: the kialineq intrusive centre that represents a shallow intrusion (<5 km). e: a 4–5 m wide composite sheet of syenite with up to metre-sized mafic pillows in diorite. f: composite dyke in the syenite body (sy) at laube gletscher showing evidence of mingling and hybridisation on a small scale. di di a b c d e f gb no hyb gr gn sy hyb 47 low complexes that texturally resemble the mafi c-felsic mixed rocks in the kialineq intrusive centre (see below). th e complex also hosts a range of composite dykes and sills, some of which are texturally similar to the classical net-veined complexes in iceland. mingling and mixing features within these smaller bodies include caulifl ower textures, irregular margins between mafi c globules and felsic host melt (fig. 2c, d), and decimetreto several metre-scale mafi c pillows within felsic material. th e margins of intrusive features and edges of individual mafi c globules commonly show signs of hybridisation as indicated by intermediate coloured rocks (fig. 2d). kialineq intrusive centre – th e kialineq intrusive centre is located c. 200 km north of tasiilaq (fig. 1) in an extremely rugged terrain. it is dominated by gabbro-diorite-syenitegranite plutons and is cut by numerous coast-parallel mafi c dykes. many of the plutons are closely associated with extensive mafi c-felsic mixed magma complexes (brooks 2011 and references therein). only a few radiometric ages are available, but they appear to show a bimodal distribution with mafi c magmatism at 56–49 ma, represented by the mafi c imilik intrusion, followed by a hiatus and subsequent activity at 37– 35 ma of plutons with more evolved compositions (larsen et al. 2014). although the chronology is poorly constrained, it agrees with the fi eld observations and suggests a general sequence of emplacement of gabbro, mafi c dykes, mafi c-felsic complexes, syenite and granite. mafi c-felsic complexes, oft en referred to as net-veined complexes, are widespread and ubiquitous in the kialineq district, and have also been reported elsewhere from the naip (nielsen 2002). th e vertical extent of the mafi c-felsic complexes is rarely well exposed in the kialineq intrusive centre, but fi eld evidence suggests that these complexes can be at least 400 m thick. although the fi eld relationships are complex and vary substantially with locality, they show that the mafi cfelsic complexes are dominated by dioritic pillows surrounded by comagmatic syenites (fig. 2e). th e pillows range in size from c. 0.1 to 2 m in diameter and consist of fi neto mediumgrained diorite, typically coarsening from rim to centre with some pillows having chilled rims against the syenites. th is implies a signifi cant thermal gradient existed between the two liquids. more typical sensu stricto net-veined textures of angular mafi c blocks separated by rather homogeneous syenite matrix also occur. such breccia-type textures testify that the basic material in some cases was partly solidifi ed when the syenite was emplaced. in contrast, the pillow complexes suggest synmagmatic interaction and mingling that demonstrate the co-existence of mafi c and felsic liquids. hybridisation was observed at the laube gletscher (fig. 2f), but is generally rare in the area. interestingly, vesicles and centimetre-sized miarolitic cavities are common features in kialineq intrusive rocks, showing that exsolution of gaseous phases occurred. th ese exsolution features, along with the occurrences of ring dykes and bell-jar plutons, indicate a shallow emplacement depth in a subvolcanic (cauldron) environment. discussion, summary and outlook we have described three examples of mafi c-felsic complexes in south-eastern greenland that show distinct mingling features irrespective of diverse geological settings, level of emplacement in the crust and compositional range. here we briefl y discuss the main diff erences between the three areas in order to constrain the key responsible processes that generated the observed features. th e tasiilaq intrusion represents a deep crustal end-member of the study area. compared to the other two examples, the mingled lithologies of the tasiilaq intrusion (leuconorite and melagabbro) contrast less strongly in composition, and so large diff erences in solidus temperatures are unlikely. further support for this hypothesis is off ered by the lack of chilled margins at lithological contacts, although this could in part also refl ect the slow cooling of the intrusion. th e textural relationships between the two main lithologies are consistent with leuconorite being intruded into melagabbro at a point where the latter was partly solidifi ed. th e mingling-like features are oft en smeared out defi ning a general wnw–ese orientation, suggesting a syn-magmatic infl uence from the regional stress fi eld of the orogen. overall, the tasiilaq intrusion seems to record a markedly diff erent and more tectonised image of mingling relations between magmas of minor compositional contrast than shown by the other two examples. th e mingling features found in the ikaasartivaq intrusive complex and the kialineq intrusive centre show many overall similarities, but also some notable diff erences. both areas represent fairly high crustal levels as opposed to the tasiilaq intrusion and contain an apparent bimodality of magma compositions (oft en referred to as the ‘daly gap’), including diorite and syenite/granite as end-members. th e common observation in both systems are chilled mafi c pillows or blobs in contact with felsic melts, indicating that a considerable temperature contrast existed between the respective mingling liquids. th is excludes a model in which the mingling components are formed by silicate liquid immiscibility processes that otherwise are believed to be important in many magmatic systems. only limited evidence for hybridisation is seen in the kialineq intrusive centre as compared to the common occurrence in the ikaasartivaq intrusive complex (fig. 2c vs. fig. 2e). th is could refl ect diff erences in a range of parameters, 4848 especially in the crustal level. since temperature gradients between magma and host rock are greater at shallow crustal levels, the time window for mixing and hybridisation in the kialineq system is expected to be shorter. th is may account for better preservation of end-member compositions in the kialineq intrusive centre than the other two examples studied. in all three areas studied, the scales at which mafi c and felsic components mingle to form blobs of diff erent sizes probably refl ect multiple factors, such as contrasts in viscosity, temperature and density of the mingling magmas, the relative abundance of mafi c to felsic magmas. it is beyond the scope of this paper to discuss these parameters in detail, but we suggest that blob development indicates an environment where diff erences in magma temperatures are small. unsurprisingly, these features are found in the largest intrusions. caulifl ower textures with grain size reduction indicate environments with stronger thermal gradients and these are typically found in the shallower environments or in smaller, sill or sheet-like bodies. in summary, igneous rocks in south-eastern greenland provide abundant evidence for bimodal magmatism, and magma mingling, mixing and hybridisation in diff erent tectonic settings and crustal levels. key diff erences between the three areas relate partly to various extents of mingling vs. hybridisation and partly to textural and structural characteristics of the interface between mafi c and felsic components (e.g. blob vs. pillow size, extent of grain-size reduction, degree of surface crenulation). th e governing factors are several, including (1) depth of emplacement which determines thermal conditions and cooling rates, (2) diff erences in magma-intensive parameters for the sets of dual end-members (temperature, density, viscosity, chemical composition, crystal contents), (3) the relative proportions of the mafi c and silicic end-members, and (4) size and geometry of the intrusive bodies (small dykes or sheets vs. large magma chamber systems). future work aims to qualify the reasons for the diff erences in more detail, to assess how the region fi ts into a broader understanding of magmatism and petrogenesis in diff erent tectonic settings and to investigate the coupled chemical and physical dynamics of juxtaposed magmas. one aspect will be to understand how the mingling features relate to the geological setting and intrusion shape, and investigate how these rocks compare to net-veined complexes in rift settings and andesites in arc and collisional settings. another aspect regards the origin of the apparent bimodality and understanding the role of magma mixing as a process masking the compositional gap. detailed petrological, geochemical and isotopic studies will be carried out to characterise endmember components in order to address the petrogenetic link between the mafi c and felsic components. th is will help to distinguish between models of fractional crystallisation versus partial melting of the archaean crust and to explain the apparent bimodality. acknowledgements th e work is part of the segment project that aims to evaluate the economic potential of the larger tasiilaq area and to gather geological information in general and is fi nanced by the ministry of industry and mineral resources in greenland and the geological survey of denmark and greenland. special thanks to christian tegner, chip lesher and th omas ulrich for collaborative fi eldwork in the kialineq area. references andersen, t., austrheim, h. & bridg water, d. 1989: p–t and fl uid evolution of the angmagssalik “charnockite” complex, se greenland. in: bridg water, d. (ed.): fluid movements – element transport and the composition of the deep crust, 71–94. dordrecht: kluwer academic publishers. brooks, c.k. 2011: th e east greenland rift ed volcanic margin. geological survey of denmark and greenland bulletin 24, 96 pp. hansen, b. & kalsbeek, f. 1989: precise age for the ammassalik intrusive complex. rapport grønlands geologiske undersøgelser 146, 46–47. kalsbeek, f., austrheim, h., bridg water, d., hansen, b.t., pedersen, s. & taylor, p.n. 1993: geochronolog y of archaean and proterozoic events in the ammassalik area, south-east greenland, and comparisons with the lewisian of scotland and the nagssugtoqidian of west greenland. precambrian research 62, 239–270. kolb, j. 2014: structure of the palaeoproterozoic nagssugtoqidian orogen, south-east greenland: model for the tectonic evolution. precambrian research 255, 809–822. larsen, l.m., pedersen, a.k., tegner, c. & duncan, r.a. 2014: eocene to miocene igneous activity in ne greenland: northward younging of magmatism along the east greenland margin. journal of the geological society 171, 539–553. nielsen, t.f.d. 2002: palaeogene intrusions and magmatic complexes in east greenland, 66 to 75° n. danmarks og grønlands geologiske undersøgelse rapport 2002/113, 249 pp. sparks, s.r.j., sigurdsson, h. & wilson, l. 1977: magma mixing: a mechanism for triggering acid explosive eruptions. nature 267, 315–318. sparks, r.s.j. & marshall, l.a. 1986: th ermal and mechanical constraints on mixing between mafi c and silicic magmas. journal of volcanolog y and geothermal research, 29, 99–124. wright, a.w., tarney, j., palmer, k.f., moorlock, b.s.p. & skinner, a.c. 1973: th e geolog y of the angmassalik area, east greenland and possible relationships with the lewisian of scotland. in: park r.g. & tarney, j. (eds): th e early precambrian of scotland and related rocks of greenland, 157–177. keele: university of keele. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: tf k@geus.dk geological survey of denmark and greenland bulletin 33, 2015, 57-60 57 greenland ice sheet melt area from modis (2000–2014) robert s. fausto, dirk van as, jens a. antoft, jason e. box, william colgan and the promice project team* th e greenland ice sheet is an excellent observatory for global climate change. meltwater from the 1.8 million km2 large ice sheet infl uences oceanic temperature and salinity, nutrient fl uxes and global sea level (ipcc 2013). surface refl ectivity is a key driver of surface melt rates (box et al. 2012). mapping of diff erent ice-sheet surface types provides a clear indicator of where changes in ice-sheet surface refl ectivity are most prominent. here, we present an updated version of a surface classifi cation algorithm that utilises nasa’s moderateresolution imaging spectroradiometer (modis) sensor on the terra satellite to systematically monitor ice-sheet surface melt (fausto et al. 2007). our aim is to determine the areal extent of three surface types over the 2000–2014 period: glacier ice, melting snow (including percolation areas) and dry snow (cuff ey & paterson 2010). monthly 1 km2 resolution surface-type grids can be downloaded via the cryoclim internet portal (www.cryoclim.net). in this report, we briefl y describe the updated classifi cation algorithm, validation of surface types and inter-annual variability in surface types. classification algorithm th e algorithm uses normalised thresholds (th ) from calibrated radiances (mod021km) between the near-infrared band 5 (1230–1250 nm) and the visible band 10 (483– 493  nm). th is updated classifi cation improves on fausto et al. (2007) by implementing new surface type thresholds: th dry snow≤0.86, 0.86<th melting snow<0.94 and th glacier ice≥0.94. data gaps can be caused by cloud cover, which is identifi ed from the mod35_l2. th e ratio between band 1 (620–670 nm, red visual) and band 7 (2105–2155 nm, shortwave infrared) as well as the magnitude of band 1 are used to identify non-glacierised terrain (fausto et al. 2007). daily classifi cation scenes are aggregated to yield a monthly greenland surface type (gst) product. for the gst product, pixels are classifi ed according to their most frequently occurring (cloud-free) colour during a month. th e maximum melt extent (gstmax) is defi ned by a given pixel classifi ed as melting or bare ice. th e pixel class must occur at least one day per month. th e gstmax product thus contains information about brief melt events. conversely, a minimum melt extent (gstmin) is calculated from pixels classifi ed as dry snow at least once per month. pixels from areas not cov* signe b. andersen, andreas p. ahlstrøm, morten l. andersen, michele citterio, charalampos charalampidis, karen edelvang, konstanze haubner, signe h. larsen, martin veicherts and anker weidick 22 50 250 km 225 0 3000 2750 2500 100 0 150 0 175 0 20 00 2 5 0 0 2 2 5 0 1 7 5 0 1 5 0 0 1 2 5 0 200 0 qas nuk kan thu upe kpc sco tas fig. 1. greenland map showing the locations of promice automatic weather stations. each dot represents two or three stations. elevation contours in metres. © 2015 geus. geological survey of denmark and greenland bulletin 33, 57–60. open access: www.geus.dk/publications/bull 5858 ered by ice are excluded from greenland melt area calculations employing the melting snow and glacier ice types in the gst, gstmax, and gstmin products (fausto et al. 2007). validation th e promice automatic weather station (aws) network currently consists of eight regions each with two or three stations at a variety of low elevations on the greenland ice sheet (fig. 1; ahlstrøm et al. 2008; citterio et al. 2015). most stations are located in the ablation area, and are thus transitioning from snow-covered to bare ice surfaces through the melt season. each station records a suite of meteorological and glaciological measurements, including ice temperature to 10 m depth and surface height changes due to accumulation or ablation (citterio et al. 2015). to validate the three surface types we classify, we use daily mean surface albedo (α), the ratio between incoming and outgoing solar radiation and surface temperature (t) data for the 2008–2014 period from the aws. based on α and t, we defi ne three classifi cations for aws sites: dry snow (α > 0.7 or t < –7°c), melting snow (0.7 > α > 0.55), and glacier ice (α < 0.55; cuff ey & paterson 2010). employing the t criterion acknowledges the infl uence of diurnal cycles at the beginning of the melt season. as a validation example, the in situ albedo and nearest-pixel classifi cation at kan_l in 2009 are presented in figs 2 and 3, including a visual comparison with the passive microwave melt area product (pmp) by mote (2007). th e kan_l station, located c. 10 km from the ice sheet margin at 680 m elevation, transitions through all three surface types during the melt season, from dry snow to melting snow to glacier ice. relative to the 2000–2014 period, the 2009 surface melt was normal in west greenland, with maximum melt areal extent in august. at kan_l, the surface melted from may to august, with a daily mean albedo generally between 0.5 and 0.6 (fig. 2). th e algorithm accuracy for the kan_l site may be assessed by an error matrix (table 1). th e diagonal represents successful classifi cations, the total number represents all classifi cations and the ratio between the sum of the diagonal and total is the accuracy. th e algorithm yields 79% successful classifi cations at kan_l, with an overall accuracy of 71%. th e classifi cation algorithm performs best in the south and worst in the north, with accuracies of 87% (nuk_l) and 61% (kpc_u), respectively. figure 2 illustrates changes in surface type during summer 2009, between 15 may and 14 september, according to the aws data; all but two classifi cations were successful. results and discussion th e melt area from this algorithm and the pmp of mote (2007), illustrated in fig. 3 for 12 july 2012, are consistent with the reported melt area by nghiem et al. (2012), who documented that 98.6% of the ice-sheet surface had melting. th e gst also demonstrates close visual correspondence with pmp for the 2000–2014 modis period (fig. 4). in fig. 4 we have plotted the yearly maximum values of the gst, gstmax and gstmin products, as well as the pmp maximum extent of greenland melt area. th e increasing trends of gstmax and gstmin indicate a rising frequency of melt events and increasing summer melt, which is corroborated by the pmp which is comparable with gstmax. th e trend for pmp between 1979 and 2000 and 2000 and 2012 are almost identical making the pmp and gstmax trends comparable. overall, an expansion of the melt area to higher elevations is apparent (fig. 4). fausto et al. (2007) suggested that a sub-monthly gst product is non-optimal, because missing data due to cloud cover is the primary problem in determining the melt area. when trying to characterise all of greenland, hall et al. (2012) also found clear-sky, day-count problems, and also suggested that a sub-monthly product would have signifi cant uncertainty. however, uncertainties associated with the difa lb ed o c la ss ifi ca ti o n 3 2 1 1 0.8 0.6 0.4 0.2 0 91 111 131 151 171 191 211 231 251 271 91 111 131 151 171 191 211 231 251 271 day of year day of year fig. 2. daily gst classification for 2009 of the k an_l pixel and albedo measured at the k an_l automatic weather station. 1: glacier ice. 2: melting snow. 3: dry snow. table 1. error matrix for the assessment of kan_l gst\aws* glacier ice melting snow dry snow total glacier ice 32 14 0 46 melting snow 3 33 1 37 dry snow 0 5 21 26 * gst: greenland surface type aws: automatic weather station 59 ferent surface types are assessed with the number of observations and standard deviation for each cloud-free pixel of the gst product (fausto et al. 2007). th e modis data have the advantages of high spatial resolution (1 km2), pan-ice sheet coverage and quasi-daily temporal coverage, while the footprints of the in situ measurements are small. th e aws surface type classifi cations are therefore not an ideal ground truth for the surface classifi cation. furthermore, whereas both gst and pmp melt area products can give daily results, the pmp surface microwave emittance originates not only from the surface but the top metre of the snow or fi rn, and is infl uenced by the water content in the snow during the previous days (mote 2007). modis classifi cation is sensitive to cloud cover, but the spatial resolution of pmp is 625 times coarser than gst. during the melt period, exposed glacier ice in the ablation zone can have sub-zero temperatures. such areas are included in the melting area, because the algorithm only makes use of the visual and near-infrared spectrum. hence the melt area that we map might be more representative of the cumulative melt area during the melt period. however, if exposed, glacier ice in the ablation zone is covered by snow it will be mapped as non-melting areas. an august anomaly in monthly gst is evident during the 2010–2014 period. all august images indicate a noisy melting snow classifi cation in the northern ice sheet (not shown), which is most likely due to false classifi cation. however, anomalous, high concentrations of dust or reddish material have been observed on the ice sheet during recent late summers (dumont et al. 2014). increasing dust concentrations are problematic for the fi xed threshold algorithm we employ, because of enhanced absorption in near infrared wavelengths. despite this possible biased source, an increasing trend in the melt area for the modis and pmp periods (fig. 4) is consistent with increasing greenland mass loss due to surface processes (tedesco et al. 2013). both independent, remotely sensed observations (hall et al. 2012) and in situ observations (mcgrath et al. 2013) show that the greenland melt area is expanding to higher elevations. fig. 4. yearly maximum melt area values and trends according to greenland surface type (gst), maximum melt extent (gstmax), minimum melt extent (gstmin) and passive microwave melt area product (pmp). 60°w 30°w 60°n 75°n a b no data/clouds melting snow dry snow glacier ice surface melting non-melting areas fig. 3. melt area on the greenland ice sheet for 12 july 2012 a: passive microwave melt area product (pmp). b: greenland surface type classification. m e lt a re a ( k m 2 ) 1800 1600 1400 1200 1000 800 600 400 200 0 1979 1986 1993 2000 2007 2014 time (year) gst gstmax gstmin pmp y = 9.0x − 17533 y = 35.3x − 69982 y = 3.3x − 6459 y = 22.1x − 43255 6060 conclusions th e modis data can yield daily, automated classifi cations of the greenland ice sheet into bare ice, melting and dry snow areas. validation indicates that the surface classes are useful as ice-sheet climate indicators. th e surface-type products are complementary to existing ice-surface temperature (hall et al. 2012) and melt-area (mote 2007) products. acknowledgements th e programme for monitoring of the greenland ice sheet (promice) is funded by the geological survey of denmark and greenland (geus) and the danish ministry of climate, energ y and building under danish cooperation for environment in the arctic (dancea), and is conducted in collaboration with the national space institute (dtu space) and asiaq (greenland survey). th e nuk and k an stations were/are (co-)funded by the greenland climate research centre (gcrc) and the greenland analogue project (gap), respectively. th anks to t. mote for making the passive microwave product (pmp) available. th is study was funded by dk esa-prodex under the cryoclim project. references ahlstrøm, a.p. et al. 2008: a new programme for monitoring the mass loss of the greenland ice sheet. geological survey of denmark and greenland bulletin 15, 61–64. box, j.e., fettweis, x., stroeve, j.c., tedesco, m., hall, d.k., steff en, k. 2012: greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers. th e cryosphere 6, 821–839. citterio, m., robert s. fausto, r.s., ahlstrøm, a.p., andersen, s.b., van as, d., charalampidis, c. & veicherts, m. 2015: automatic weather stations for basic and applied glaciolog y. geological survey of denmark and greenland bulletin 33, 69–72. cuff ey, k.m. & paterson, w.s.b. 2010: th e physics of glaciers, 693 pp. burlington: butterworth-heinemann/elsevier. dumont, m. et al. 2014: contribution of light-absorbing impurities in snow to greenland’s darkening since 2009. nature geoscience 7, 509– 512. fausto, r.s., mayer, c. & ahlstrøm, a.p. 2007: satellite-derived surface type and melt area of the greenland ice sheet using modis data from 2000 to 2005. annals of glaciolog y 46, 35–42. hall, d.k., comiso, j.c., digirolamo, n.e., shuman, c.a., key, j.r. & koenig, l.s. 2012: a satellite-derived climate-quality data record of the clear-sky surface temperature of the greenland ice sheet. journal of climate 25, 4785–4798. ipcc 2013: climate change 2013: th e physical science basis. working group i contribution to the fift h assessment report of the intergovernmental panel on climate change, 1535 pp. cambridge university press. mcgrath, d., colgan, w., bayou, n., muto, a. & steff en, k. 2013: recent warming at summit, greenland: global context and implications. geophysical research letters 40, 2091–2096. mote, t.l. 2007: greenland surface melt trends 1973–2007: evidence of a large increase in 2007. geophysical research letters 34, l22507. nghiem, s.v., hall, d.k., mote, t.l., tedesco, m., albert, m.r., keegan, k., shuman, c.a., digirolamo, n.e. & neumann, g. 2012: th e extreme melt across the greenland ice sheet in 2012. geophysical research letters 39, l20502. tedesco, m., fettweis, x., mote, t., wahr, j., alexander, p., box, j.e. & wouters, b. 2013: evidence and analysis of 2012 greenland records from spaceborne observations, a regional climate model and reanalysis data. th e cryosphere 7, 615–630. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: rsf@geus.dk geological survey of denmark and greenland bulletin 33, 2015, 77-80 77 investigations of detrital zircon, rutile and titanite from present-day labrador drainage basins: fingerprinting the grenvillean front tonny b. thomsen, christian knudsen and alana m. hinchey a multidisciplinary provenance study was conducted on stream sediment samples from major rivers in the eastern part of labrador, canada (fig. 1). th e purpose was to fi ngerprint the sources that deliver material to the stream sediments and to the reservoir sand units deposited off shore in the sedimentary basins in the labrador sea. we used a multimineral u-pb geochronological approach employing rutile and titanite in addition to zircon to obtain unbiased age data. th e purpose of this was to characterise the diff erent igneous and metamorphic episodes that occurred in labrador, which is an area with highly variable geology characterised by the palaeoproterozoic south-eastern churchill province in the north-west, the archaean nain plutonic suite in the north-east, the palaeoproterozoic makkovik province in the east and the mesoproterozoic grenville province to the south. th e fi eld work was carried out in 2012 and 2013 and the study is a collaborative project between the geological survey of denmark and greenland and the geological survey of newfoundland and labrador. in this paper we focus on three samples from the southern part of the study area where two parts of the grenville orogeny are found (fig. 1). the use of zircon, rutile and titanite in sedimentary provenance investigations methods for obtaining geochronological information from various detrital minerals for quantitative sedimentary provenance purposes have developed rapidly over recent years. th is is mostly due to advances in high-throughput microanalytical techniques such as laser ablation inductively coupled plasma mass spectrometry (la-icpms). th e emphasis on u-pb geochronology has primarily been on detrital zircon, as it typically provides precise age information of the source rocks. zircon, however, is not usually the mineral of choice for dating the history of rocks with a complex tectonothermal evolution, as it typically survives most processes occurring in the rock cycle from sedimentation to high grade metamorphism and oft en even magmatic processes. th is means that zircon typically refl ects several orogenic cycles (e.g. okay et al. 2011) and is less suited for recording information about processes related to the metamorphic or hydrothermal reaction history of a rock. th e ti minerals, rutile and titanite, occur in a variety of magmatic, hydrothermal, metamorphic and sedimentary rock types, oft en together with zircon (e.g. force 1991; frost et al. 2001; zack et al. 2004). although detrital rutile is less abundant than zircon, the widespread occurrence of rutile in a wide range of mediumto high-grade, and also high-pressure (blueschist and eclogite facies), metamorphic rocks as well as in sediments and sedimentary rocks (force 1980, 1991), combined with its high mechanical and chemical stability during weathering, transport and diagenesis (e.g. morton & hallsworth 1999), makes it a prime candidate in provenance studies (zack et al. 2011). rutile forms under amphibolite and higher metamorphic facies conditions and is typically unstable at lower grade conditions (force 1980, © 2015 geus. geological survey of denmark and greenland bulletin 33, 77–80. open access: www.geus.dk/publications/bull ggu 539754 ggu 539828 ggu 539845 proterozoic nain plutonic suite grenville province exterior thrust belt interior magmatic belt makkovik and se churchill provinces archaean superior province nain province sample drainage area 100 km 54°n 52°n 54°n 60°n 66°w 62°w 56°w 62°w66°w fig. 1. simplified geological map of labrador. 7878 1991; triebold et al. 2007, 2011), where it usually breaks down to form other ti minerals such as titanite or ilmenite at greenschist facies conditions. rutile, therefore, typically yields chronological and petrogenetic information refl ecting the timing and conditions of the last medium to high-grade or high-pressure metamorphic event (zack et al. 2011; okay et al. 2011). titanite is widespread in a variety of rock types typically of more calcic compositions, and is usually rare in rocks with low cao/al2o3 ratios such as peralkaline granitoids and peraluminous granites (frost et al. 2001). titanite occurs in very lowto high-grade metamorphic rocks and survives under ultra-high pressure conditions (force 1991; frost et al. 2001), although it is typically scarce or absent in most granulite-facies metamorphic rocks (krogh & keppie 1990). even though titanite is a widespread mineral and occurs as detrital and authigenic grains in sedimentary rocks, it has rarely been used to date deposition, diagenesis or low-grade metamorphism. detrital titanite was fi rst used as a sedimentary provenance tool by mcateer et al. (2010). th e reason that titanite is not routinely used for provenance investigations is probably that it is more susceptible to abrasion during sedimentary transport than zircon and rutile, resulting in reduced occurrence or absence as a detrital component in sediments and sedimentary rocks. titanite, however, is more reactive than zircon or rutile during metamorphism and forms at temperatures below 700°c. th is provides the mineral with a large potential to record ages for a wide range of low to moderate temperature geological crustal processes (frost et al. 2001; mcateer et al. 2010; muhling et al. 2012). th us, if present in sedimentary rocks, titanite is an ideal candidate for dating regional or local metamorphism. in addition, because most metamorphic events are associated with deformation, titanite can date potential deformation stages in metamorphic terranes (frost et al. 2001). th erefore, it is possible to recognise sediment sources from detrital titanite and rutile data that are not represented in zircon data and thus gain additional chronological and petrogenetic insight into the tectonothermal history of the source regions (mcateer et al. 2010, 2014). furthermore, rutile and titanite generally contain 5–10 times less u than zircon, thus metamictisation of these minerals is relatively rare. consequently, in rocks with u-rich zircon and titanite or rutile, the zircon might show metamictisation, and therefore would be more prone to degradation during transport and weathering, and is thus likely to be excluded from a detrital study (fedo et al. 2003). titanite and rutile, on the other hand, have the potential to retain the magmatic record of the u-rich zircon source as well as the metamorphic episodes that may have occurred prior to deposition. u-pb analysis and data processing in this study, u-pb dating was carried out on mineral grains embedded in epoxy mounts at the la-icpms facility at the geological survey of denmark and greenland using a nwr213 nd:yag laser system coupled to an element 2 double-focusing, single-collector, magnetic sector-fi eld icpms. mineral grains were separated by routine separation methods including a wilfrey water-shaking table, frantz electromagnetic separation and heavy liquids. zircon, rutile and titanite grains were picked by hand under a binocular microscope from the resulting heavy mineral fractions and mineral compositions were qualitatively controlled by semeds. for rutile and titanite, laser beam pre-ablation using a spot size slightly larger (40 μm) than the analysis spot size (25 μm) was performed prior to the la-icpms analysis to avoid surface contamination. data processing was performed off -line using the soft ware iolite (paton et al. 2010, 2011) and the vizualage data reduction scheme vers. 2.5 by petrus & kamber (2012). th e data were corrected for background signal, time-dependent fractionation, instrumental drift and down-hole isotopic fractionation. in order to validate our results, the measurements were bracketed throughout the entire analysis sequences by analyses of natural mineral standards. th ese include the gj-1 and plesovice zircons, the rutiles r10, r13, r19 (provided by courtesy of t. zack, university of gothenburg) and sugluk-4 (l. bracciali, british geological survey), and the titanite a1772 (y. lahaye, geological survey of finland) and seiland ( j. kosler, university of bergen). in contrast to zircon, common pb in titanite and rutile is generally lattice bound and can occur in signifi cant proportions. th us, common pb correction typically needs to be applied for these minerals. however, common pb usually has negligible eff ects for titanites or rutiles with 206pb/204pb ratios >300 (frost et al. 2001), whereas the initial common pb isotopic composition typically has greater eff ects on analyses with 206pb/204pb ratios <300 and therefore the results must be treated more cautiously. only the titanite grains in this study typically have large proportions of common pb, whereas most zircon and rutile only contain a small or negliable amount of common pb. titanite ages reported herein are corrected for common pb. some of the titanite grains contained a signifi cant amount of common pb and some of the titanite ages are potentially of a slightly lower accuracy compared to ages obtained for rutile and zircon that were not common pb corrected. th e correction for common pb was performed using the present-day terrestrial common pb estimate of stacey & kramers (1975) and the measured mass 204 (204pb + 204hg) corrected for 204hg calculated from measured 202hg and the natural 204hg /202hg ratio. 79 results of the provenance study u-pb age distributions of zircon, rutile and titanite from three representative river samples are shown in the probability–density diagrams in fig. 2. th e three samples were collected in areas within the grenvillean orogenic belt that are characterised by ages around 1000 ma. sample ggu 539754 comes from the northern part of the orogenic belt (the exterior thrust belt), sample ggu 539828 from the central part and sample ggu 539845 from the southern part (the interior magmatic belt). th e samples all contain zircon grains older than the grenville orogeny, refl ecting the ability of zircon to maintain older magmatic formation signatures through the younger grenvillean orogenesis. th e three areas show distinct diff erences in detrital zircon ages. th e frequency of c. 1000 ma old grenvillean zircon ages is much lower in the northern exterior thrust belt than in the central part and especially in the southern interior magmatic belt, where crust was formed during the grenville orogeny. in the southern area (ggu 539845) both palaeoand mesoproterozoic zircon ages are common, with the highest abundance at c. 1500 ma, whereas the samples from the central area (ggu 539828) and the northern exterior thrust belt (ggu 539754) are dominated by palaeoproterozoic zircons with a peak at c. 1650 ma. however, there is a second distinct mesoproterozoic peak at c. 1360 ma in the northern area and a signifi cantly reduced abundance of mesoproterozoic zircon ages in the central area. as expected, the detrital rutile ages peak just below 1000 ma for all three samples, refl ecting rutile formation or complete u-pb system resetting of older rutile grains during mediumto high-grade metamorphic stages of the grenville orogeny. titanite shows grenvillean ages for all three samples. in the sample from the southern interior magmatic belt all titanite ages are c. 1000 ma old, corresponding to the rutile age distribution, whereas a more complex age pattern, with palaeoand mesoproterozoic titanites, is seen in the samples from the central and northern areas. th is indicates that many more titanite grains from the latter areas survived the grenvillean metamorphism than (1) rutile from the same areas and, (2) titanite and rutile from the southern interior magmatic belt. th e occurrence of pre-grenvillean titanite and absence of pre-grenvillean rutile in the central and northern areas could be due to the diff erence in the u-pb isotopic system closure temperatures of the two minerals; rutile has a lower closure temperature at c. 400–500°c than titanite with a closure temperature at c. 500–700°c. hence the age pattern depends on the metamorphic grade to which minerals were exposed during the grenville orogeny. th e occurrence of titanite ages and lack of rutile ages indicate mediumto high-grade metamorphic conditions, probably upper amphibolite facies. during the grenville orogeny, the metamorphic grade of the new crust was probably higher in the southern interior magmatic belt than in the central and northern areas. we suggest that the closure temperature of n = 10/16 n = 5/11 n = 32/32 n = 4/4 n = 140/140 n = 129/130 n = 8/9 n = 26/26 n = 136/137 0 0.00108 0.00217 0.00325 0.00434 0.00542 0 0.00245 0.00491 0.00736 0.00982 0.01227 p ro b ab il it y 0 0.00214 0.00428 0.00642 0.00857 0.01071 0 0.00266 0.00533 0.00799 0.01066 0.01332 p ro b ab il it y 0 0.00119 0.00238 0.00357 0.00477 0.00596 0.00076 0.00152 0.00228 0.00304 0.0038 p ro b ab il it y 12 10 8 6 4 2 0 12 10 8 6 4 2 0 12 10 8 6 4 2 0 2 1 0 2 1 0 2 1 0 f re q u e n c y 0.00149 0 0.00299 0.00448 0.00598 0.00747 f re q u e n c y 0 0.0023 0.0046 0.00689 0.00919 0.01149 0 0.00118 0.00236 0.00354 0.00472 0.0059 f re q u e n c y 0 500 1000 1500 2000 t it an it e r u ti le z ir c o n age (ma) 0 500 1000 1500 2000 age (ma) 0 500 1000 1500 2000 age (ma) ggu 539754 the nortern exterior thrust belt ggu 539828 the central part ggu 539845 the southern interior magmatic belt 30 25 20 15 10 5 0 30 25 20 15 10 5 0 30 25 20 15 10 5 0 0 fig. 2. probability–density diagrams showing u–pb age distributions for three samples collected in labrador. n = x/y (in red) denotes the total number of analysed zircon grains ( y) of which x are ‘concordant’ (i.e. <10% discordant from concordia). light grey: ages that are >10 % discordant (relative to wetherill concordia), dark grey: ‘concordant’ ages within <10% discordance (i.e. <10%). blue line at 1000 ma: late stage of the grenville orogeny. 8080 both ti minerals was overstepped, resulting in isotopic age resetting of any pre-grenvillean titanite and rutile grains and formation of new grenvillean age titanite and rutile. concluding remarks th e wide range in the detrital zircon u-pb ages within the grenvillean orogenic belt refl ects formation age diff erences of the rocks that were brought into the orogenic process. accordingly, for the best characterisation of the sediment source, it is not suffi cient to know the age of the orogeny that aff ected the area; it is also nessesary to know the lateral distribution of the rock units in the area as well as the ages of the zircons (and other minerals) from these units. moreover, diff erent units contain diff erent amounts of e.g. zircon. an effi cient way to map the lateral age variation is to analyse detrital minerals collected from present-day drainage systems. references fedo, c.m., sircombe, k.n. & rainbird, r.h. 2003: detrital zircon analysis of the sedimentary record. in: hanchar, j.m. & hoskin, p.o. (eds): zircon: experiments, isotopes and trace element investigations. mineralogical society of america, reviews in mineralog y 53, 277–303. force, e.r. 1980: th e provenance of rutile. journal of sedimentary petrolog y 50, 485–488. force, e.r. 1991: geolog y of titanium-mineral deposits. geological society of america, special papers 259, 112 pp. frost, b.r., chamberlain, k.r. & schumacher, j.c. 2001: sphene (titanite): phase relations and role as a geochronometer. chemical geolog y 172, 131–148. krogh, t.e. & keppie, j.d. 1990: age of detrital zircon and titanite in the meguma group, southern nova scotia, canada: clues to the origin of the meguma terrane. tectonophysics 177, 307–323. mcateer, c.a., daly, j.s., flowerdew, m.j., connelly, j.n., housh, t.b. & whitehouse, m.j. 2010: detrital zircon, detrital titanite and igneous clast u–pb geochronolog y and basement–cover relationships of the colonsay group, sw scotland: laurentian provenance and correlation with the neoproterozoic 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contributions to mineralog y and petrolog y 161, 581–596. zack, t., von eynatten, h. & kronz, a. 2004: rutile geochemistry and its potential use in quantitative provenance studies. sedimentary geolog y 171, 37–58. zack, t., stockli, d.f., luvizotto, g.l., barth, m.g., belousova, e., wolfe, m.r. & hinton, r.w. 2011: in situ u-pb rutile dating by la– icp–ms: 208pb correction and prospects for geological applications. contributions to mineralog y and petrolog y 162, 515–530. authors’ adresses t.b.t. & c.k., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: tbt@geus.dk a.m.h., geological survey of newfoundland and labrador, 50 elizabeth avenue, st. john’s, nl, canada. geological survey of denmark and greenland bulletin 42, 2018, 115-126 115 provenance of basinal sandstones in the upper jurassic hareelv formation, jameson land basin, east greenland mette olivarius, morten bjerager, nynke keulen, christian knudsen and thomas f. kokfelt zircon u–pb geochronolog y and heavy mineral ccsem analysis were used to interpret the provenance of oxfordian–volgian sandstones of the hareelv formation in east greenland. six samples were collected from the blokelv-1 core drilled in southern jameson land, and the zircon age distributions and heavy-mineral assemblages are quite uniform. the samples contain a wide spectrum of archaean to palaeozoic zircon ages with peak ages at 2.71, 2.49, 1.95, 1.65, 1.49, 1.37, 1.10 and 0.43 ga when combining all data. the heavy-mineral compositions show derivation from felsic source rocks, some of which were metamorphic. the results reveal that the sediment was derived from the caledonides, and it is plausible that some or all of the material has experienced several cycles of sedimentation. devonian and carboniferous sediments preserved north of the area have zircon age distributions that correspond to those from the hareelv formation, and such rocks may have been reworked into the jameson land basin. the provenance signature describes both the gravity-flow sandstones of the hareelv formation and the delta-edge sands that are inferred to have fed them. lithological and provenance contrasts between the sandstones of the sjællandselv member and those of the katedralen member indicate a shorter transport distance, source to sink, suggestive of proximal topographic rejuvenation in the volgian. keywords: east greenland, hareelv formation, upper jurassic, sediment provenance, zircon geochronolog y, heavymineral analysis ___________________________________________________________________________ geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350 copenhagen, denmark. e-mail: mol@geus.dk the fully cored borehole blokelv-1 was drilled in 2008 to a depth of 233.8 m in southern jameson land, east greenland (fig. 1) to provide reservoir and source-rock information on the mudstone-dominated upper jurassic hareelv formation that also includes numerous gravityflow sandstones (bjerager et al. 2018a, this volume). the east greenland caledonides, which form the basement for the mesozoic succession, comprise a complex series of archaean to palaeozoic lithologies (higgins & leslie 2008), and therefore the post-caledonian sedimentary successions preserved along the east and north-east greenland coast (fig. 1) are expected to contain a wide range of zircon age populations. detrital zircon ages from jurassic sediments in east greenland have previously only been reported from the lower jurassic succession in the jameson land basin where the elevated liverpool land high was the primary source area (slama et al. 2011). significantly different zircon age distributions are to be expected in the upper jurassic sediments in the jameson land basin since the liverpool land high was gradually onlapped and drowned during the middle jurassic (surlyk 2003). the present study employs zircon geochronolog y and heavy-mineral analysis to characterise the upper jurassic sandstones of the hareelv formation in the blokelv-1 core and to identify the source areas of these sandstones. © geus, 2018. geological survey of denmark and greenland bulletin 42 , 115–126. available at: www.geus.dk/bulletin42 mailto:mol@geus.dk http://www.geus.dk/bulletin42 116116 geological setting the caledonian orogen in east greenland formed during the palaeozoic closure of the iapetus ocean and continental collision between baltica and laurentia (mckerrow et al. 2000). the caledonian foreland of laurentia (greenland) consists mainly of crystalline rocks that are presently exposed in tectonic windows along the rim of the greenland ice sheet (fig. 1; henriksen et al. 2008). the caledonian orogen is composed of several westward displaced thrust sheets that consist of archaean to silurian crystalline and sedimentary rocks (higgins et al. 2004). the crystalline complexes in the orogen were formed during archaean and palaeoproterozoic times (thrane 2002). the sediments of the krummedal supracrustal sequence were deposited in the late mesoproterozoic to early neoproterozoic and underwent high-grade metamorphism, migmatisation and partial melting in the early neoproterozoic (kalsbeek et al. 2000, 2008a; watt et al. 2000). a thick sedimentary succession was subsequently deposited in the eastern part of the area which consists of the neoproterozoic eleonore bay supergroup overlain by the upper neoproterozoic tillite group and the lower palaeozoic kong oscar fjord group (higgins et al. 2004). this succession and the underlying basement units were partially affected by caledonian metamorphism. marine sedimentation was terminated during the uplift caused by the caledonian crustal thickening, and lateto post-caledonian continental sediments were deposited during the devonian after the extensional collapse of the caledonian orogen (larsen et al. 2008). the caledonian orogeny caused renewed granite intrusion and migmatisation during the ordovician–silurian (kalsbeek et al. 2001). fig. 1. geological map of the caledonian belt in east and north-east greenland based on stemmerik et al. (1997), henriksen et al. (2008) and kalsbeek et al. (2008b). the sampled blokelv-1 borehole is located in southern jameson land. note that the sediments and metamorphic rocks are categorised by their depositional ages. palaeogene volcanic rocks devonian continental neoproterozoic and caledonian granite cambrian–silurian neoproterozoic (mainly eleonore bay supergroup) meso–neoproterozoic metamorphic rocks (including krummedal supracrustal sequence) archaean–palaeoproterozoic crystalline complex tectonic windows with crystalline rocks thrust fault/shear zone cretaceous jurassic triassic permian carboniferous hareelv & raukelv formations 70°n 74°n jameson land i n l a n d i c e caledonides kong oscar fjord 100 km25°w liverpool land sc o r e s b y s u n d h g f h h e g d c b b–h f localities for zircon age data from literature (see fig. 7) blokelv-1 borehole mol prov 1 117 the post-caledonian sedimentary succession of carboniferous to palaeogene age is exposed along the coast of east and north-east greenland from 70° to 76°n (fig. 1; e.g. stemmerik et al. 1992) except where it is overlain by extensive palaeogene plateau basalts that were extruded in association with the north atlantic continental breakup (brooks 2011). thermal subsidence in the sedimentary basins was succeeded by rifting in the middle jurassic and a thick succession was deposited in the jameson land basin until the rifting in the region waned in the earliest cretaceous (surlyk 2003). the oxfordian olympen formation with its marine basinal mudstones and deltaic sandstones is the only part of the upper jurassic succession that is preserved in northern jameson land (fig. 2), where it is exposed on the highest mountain peaks (larsen & surlyk 2003). the orientation of planar cross-bedding in the delta-top deposits in the upper part of the formation (zeus member) shows that the delta prograded towards the south. in southern jameson land, a near-complete upper jurassic succession is exposed and consists of basinal mudstones interbedded with gravity-flow sandstones of the oxfordian–kimmeridgian katedralen member of the hareelv formation (surlyk 2003). these sandstones were formed by collapse of the drowned shelf-edge delta deposits of the olympen formation situated at the northern margin of the jameson land basin (figs 2, 3) (bjerager et al. 2018b, this volume). some of the gravity-flow sandstones of the katedralen member were remobilised and intraformationally injected after burial (surlyk et al. 2007). the coarser-grained gravity-flow sandstones of the volgian sjællandselv member of the hareelv formation c re ta ce ou s lo w er u pp er ju ra ss ic o xf or di an l l l l m u u u u sy st em se ri es te th ys (s ta nd ar d) bo re al su bs ta ge m k im m er id gi an be rr ia sia n ti th on ia n ry az an ia n vo lg ia n age (ma) 140 150 160 145 155 stage s njameson land hareelv fm? hareelv fm hades mb olympen fm zeus mbzeus mb sa katedralen mb sjællandselv mb shallow marine sandstone shelf transition silty–sandy mudstones and heterolith deep marine sandstone deep shelf (basin) mudstone mass-flow sandstone remobilised/injected sandstone raukelv fmraukelv fm id 6 id 5 id 4 id 3 id 2 id 1 samples (id 1–6) source rockprograding unit mol prov 2 bl ok el v1 fig. 2. stratigraphic scheme of the upper jurassic succession in jameson land based on bjerager et al. (2018b, this volume). 118118 were subsequently deposited in the jameson land basin (fig. 3) in response to a regional sea-level fall; southwards progradation of the shelf-edge clinothems of the raukelv formation into the basin led to repeated shelf-edge collapse and the initiation of the gravity flows (surlyk 2003; surlyk & noe-nygaard 2005). the provenance of the jurassic sedimentary basins in east greenland based on sedimentological data has been interpreted as the basement rocks of the greenland craton, in addition to some reworking of clastic sediments (surlyk 2003). the devonian–carboniferous sediments exposed north of jameson land during the early jurassic were onlapped during the middle jurassic and thus became less important sediment sources, but this situation may have changed during the late jurassic due to increased rifting and consequent exhumation and erosion of uplifted fault-block crests. samples and methods provenance analysis was performed on sandstones from six intervals in the blokelv-1 core (fig. 2). five of the samples are from the katedralen member (sample id 2–6) and one is from the sjællandselv member (sample id 1) of the hareelv formation. the sampled sandstones are structureless, grey, fineto medium-grained, moderately to well-sorted and the grains are angular to sub-rounded (bjerager et al. 2018a, this volume). some of the sampled sandstones comprise high-density turbidites (sample id 1, 4) whereas others are injectites (sample id 2, 3, 5, 6). zircon u–pb geochronology samples were crushed in order to liberate the individual grains and then sieved to retrieve the fraction <500 µm. heavy-mineral concentrates were produced on a watershaking wilfley table. zircon grains were hand-picked n deep-water marine sandstone bodies drowned (relict) sandy shelf (olympen fm, zeus mb)shallow marine sandstone hareelv fm, katedralen mb raukelv fm hareelv fm, sjællandselv mb offshore marine mudstone inferred coastline transition zone marine sandstone/mudstone heterolith 50 kma b mol prov 3 j a m e s o n l a n d traill ø milne land fig. 3. palaeogeographic reconstructions of jameson land and surrounding areas based on surlyk (2003) and bjerager et al. (2018b, this volume). the facies distribution is tentative in most areas since the distribution in the present-day offshore area is inferred and the succession has been removed by erosion in some of the present-day onshore areas. 119 in a random fashion to ensure that all grain sizes, shapes and colours were represented. the grains were cast into epoxy and polished to expose a central cross-section of each grain. the mount was cleaned in an ultrasonic bath with propanol, and then loaded into the sample cell of the laser ablation system for age dating. approximately 160 grains were analysed per sample ensuring that even small age populations are detected (vermeesch 2004). all data were acquired with a single spot analysis on individual zircon grains using a beam diameter of 30 µm and a crater depth of c. 15–20 µm. the amount of ablated material approximates 200–300 ng for the ablation time of 30 sec. the ablated material was analysed on an element2 (thermo finnigan, bremen) single-collector, double focusing, magnetic sector-field, inductively coupled plasma mass spectrometer (icp-ms) with a fastfield regulator for increased scanning speed. the total acquisition time for each analysis was 60 sec., with the first 30 sec. used to measure the gas blank. the instrument was tuned to give large, stable signals for the 206pb and 238u peaks, low background count rates (typically around 150 counts per second for 207pb) and low oxide production rates (238u16o/238u generally below 2.5%). 202hg, 204(pb+hg ), 206pb, 207pb, 208pb, 232th and 238u intensities were determined through peak jumping using electrostatic scanning in low-resolution mode and with the magnet resting at 202hg. mass 202hg was measured to monitor the 204hg interference on 204pb where the 202hg/204hg ≡ 4.36, which can be used to correct significant common pb contributions using the model of stacey & kramers (1975). the elemental fractionation induced by the laser ablation and the instrumental mass bias on measured isotopic ratios were corrected through standard-sample bracketing using the gj-1 zircon ( jackson et al. 2004). long-term external reproducibility was monitored by repeated analyses of the plešovice zircon standard (slama et al. 2008). the analytical data are reported in an online supplementary data file. the reported ages are based on 207pb/206pb derived ages for the >0.8 ga (billion years) analyses, and 206pb/238u ages for the <0.8 ga analyses, as the latter is more precise for the younger age range. the propagation of the analytical errors follows the principles of sambridge & lambert (1997). age measurements lacking a stable 207pb/206pb plateau or with a u/pb or pb/ pb error >10% were discarded. a correction for common pb was applied on up to 7% of the concordant analyses from each sample. the data are plotted using kernel density estimation (vermeesch 2012) employing analyses that are <10% discordant. heavy-mineral analysis the grain-size interval 45–710 µm was collected by sieving of crushed samples. heavy-liquid separation utilised bromoform with a specific density of 2.82 g/cm3, and the total heavy-mineral weight percentage (wt%) of the chosen grain-size interval was measured. the heavy-mineral concentrates were embedded in epoxy and polished. heavy-mineral chemistry was determined by computercontrolled scanning electron microscopy (ccsem) at geus on a philips xl40 sem equipped with two energ y dispersive x-ray (edx) detectors: a thermo nanotrace and a pioneer voyager detector (keulen et al. 2008, 2012). approximately 1200 grains were analysed in each sample, of which between 22 and 327 grains were used in the mineral statistics. this is because the heavymineral samples contain mica minerals and authigenic heavy minerals, which were excluded from the heavymineral suite results due to their dependency on depositional environment and diagenesis. as there is a large compositional overlap between the minerals amphibole, pyroxene and tourmaline in standard-less edx analyses, these have been combined into one group in this study, labelled mafic minerals. the group of other heavy minerals includes ilmenite, corundum, monazite and xenotime, each of which is present in amounts <5%. results the zircon u–pb age data can be found in the online supplementary material. the age data are displayed using kernel-density estimation (fig. 4) and cumulative age distribution (fig. 5). the zircon ages cover a broad archaean to palaeozoic age span, but with the dominant zircon u–pb ages occurring between 2.0 and 1.0 ga (fig. 4). eight peak ages are present when combining all data: 2.71, 2.49, 1.95, 1.65, 1.49, 1.37, 1.10 and 0.43 ga. the relative proportion between the ages in each sample is illustrated by dividing the data into six age intervals (table 1). the grains older than 2.2 ga comprise 12– 23% of each sample, whereas grains with ages of 2.2–1.8 ga constitute 6–23%. pronounced peak ages are present within each of the 1.8–1.6, 1.6–1.3 and 1.3–0.8 ga age intervals, which cover 17–25, 14–22 and 18–34% of the measured ages, respectively (table 1). the youngest age interval of 0.6–0.3 ga is present in small proportions of 0–3% in the samples. the shallowest sample (sample id 1) is the only sample that does not have an age peak at 1.66–1.64 ga, which is pronounced in the other samples (fig. 4). the 120120 cumulative age distributions show that no significant difference exists between the six measured age distributions since the distance between the curves is small (fig. 5). kolmogorov-smirnov (k-s) tests (guynn & gehrels 2010) were performed on the zircon age data to determine if the samples were derived from different sources by comparing the distance between the cumulative agedistribution curves (fig. 5). two samples are regarded as significantly dissimilar if they have a p-value <0.05 and they will then probably have different provenance. the results show that all p-values are >0.05 (table 2). it is therefore unlikely that the samples came from different parent populations at a 95% confidence level. the samples id 2–4 resemble each other well according to the high p-values of 0.99. the sample id 5 shows good resemblance to the samples id 1 and id 6 (p-values of 0.97 and 0.91, respectively). pr ob ab ili ty 0 30 20 10 0 6 4 2 0 6 4 2 pr ob ab ili ty pr ob ab ili ty pr ob ab ili ty pr ob ab ili ty pr ob ab ili ty pr ob ab ili ty 0 6 4 2 0 6 4 2 8 0 6 4 2 0 6 4 2 age (ga) 0.0 1.0 2.0 3.0 4.00.5 1.5 2.5 3.5 neoproterozoic mesoproterozoic palaeoproterozoic archaeanphanerozoic id 1 id 2 id 3 id 4 id 5 id 6 7.41 m 43.16 m 69.78 m 139.27 m 181.53 m 221.18 m n/n = 115/158 n/n = 113/156 n/n = 100/155 n/n = 118/158 n/n = 100/156 n/n = 114/162 id 1–6 all data n/n = 660/945 1.65 0.43 2.49 2.71 1.95 1.10 1.37 1.49 1.14 1.36 1.65 2.71 2.70 0.45 1.65 1.76 1.47 1.13 1.92 0.97 2.46 1.37 2.83 0.43 1.10 1.43 1.64 1.87 2.67 1.97 2.52 2.83 0.42 1.09 1.49 1.66 1.96 2.79 1.32 2.42 1.11 1.43 1.64 1.96 2.770.44 2.54 1.35 2.96 1.10 1.50 1.73 2.740.43 2.46 1.93 2.27 2.99 n um be r of g ra in s mol prov 4 fig. 4. zircon u–pb ages of the hareelv formation. the ages are plotted with a black line and annotated peak ages using kernel density estimation (vermeesch 2012) and histograms with a 25 myr bin interval. only zircon ages with <10% discordance are plotted, which is signified by “n/n” (the number of concordant analyses out of the total number of analyses). the lowermost panel shows the distribution of all zircon ages from the six samples, and this dotted line is shown on all samples for comparison. 0.3 0.8 1.3 1.6 1.8 2.2 0.6 1.3 1.6 1.8 2.2 3.8 7.41 m id 1 2 27 20 17 12 23 43.16 m id 2 3 27 22 19 12 17 69.78 m id 3 0 34 17 24 6 19 139.27 m id 4 3 31 18 20 16 12 181.53 m id 5 id 6 3 24 14 18 23 18 18221.18 m 2 18 17 25 20 age interval (ga) min. age max. age number of zircon grains (%) table 1. distribution in six age intervals of the analysed zircon grains with concordant ages mol prov table 1 121 the heavy-mineral assemblage consists, in decreasing order of abundance, of rutile, mafic minerals, zircon, leucoxene, garnet, apatite, epidote, olivine and small amounts of other minerals (fig. 6). the garnets are classified as almandine and generally contain more mg than ca. when including mica minerals in the heavy-mineral assemblage, they constitute 60–91% of the mineral grains. muscovite comprises 72–98% of the mica minerals. the heavy-mineral content is largest in the uppermost sample (table 3). discussion the age distribution of all analysed zircon grains from the hareelv formation is shown in fig. 7a, and selected published zircon age data from older rocks in the area are shown in figs 7b–h for comparison. basement and metasediment signal the dominant zircon age populations present in the crystalline basement complexes of east greenland (fig. 1) have age ranges of about 2.8–2.5 and 2.0–1.8 ga (fig. 7h; thrane 2002). these archaean and palaeoproterozoic rocks are primarily orthogneisses of granitic to tonalitic composition, and their heavy-mineral assemblages are therefore dominated by mafic minerals and mica minerals. the metasedimentary rocks of the krummedal supracrustal sequence (fig. 1) mainly have zircon ages of 1.8–1.0 ga (fig. 7g; watt et al. 2000; leslie & nutman 2003). they consist primarily of pelitic and psammitic metasediments that underwent intermediate to highgrade metamorphism, resulting in a heavy-mineral assemblage dominated by mica minerals and garnet with localised sillimanite (watt & thrane 2001; leslie & nutman 2003). the zircon ages of the archaean and palaeoproterozoic basement complexes in east greenland correspond largely to two of the oldest age populations recorded in the hareelv formation with peak ages of 2.71 and 1.95 ga (fig. 7). however, the latest archaean to earliest palaeoproterozoic ages in the hareelv formation with a peak age of 2.49 ga are not comparable to ages reported by thrane (2002) from the basement complexes west of kong oscar fjord (fig. 1); such ages may therefore be present in other areas of the complexes. the ages of the krummedal supracrustal sequence concur with the late palaeoproterozoic and the mesoproterozoic age populations in the hareelv formation with peak ages of 1.65, 1.49 and 1.10 ga (fig. 7). the mesoproterozoic age population with peak age of 1.37 ga in the hareelv formation is only pronounced in some of the samples (fig. 4), and the population is not evident in the krummedal supracrustal sequence (fig. 7). the late palaeoproterozoic and late mesoproterozoic age populations are dominant both in the hareelv formation and in the krummedal supracrustal sequence. however, id 1 id 2 id 3 id 4 id 5 id 6 7.41 m id 1 0.447 0.382 0.477 0.966 0.476 43.16 m id 2 0.447 0.993 0.992 0.477 0.093 69.78 m id 3 0.382 0.993 0.880 0.194 0.080 139.27 m id 4 0.477 0.992 0.880 0.301 0.122 181.53 m id 5 0.966 0.477 0.194 0.301 0.909 221.18 m id 6 0.476 0.093 0.080 0.122 0.909 table 2. p-values of the k-s test of the zircon age data mol prov table 2 < 45 µm 45–710 µm > 710 µm 45–710 µm total 7.41 m id 1 5.3 23.3 71.4 4.74 1.10 43.16 m id 2 18.5 81.0 0.5 0.94 0.76 69.78 m id 3 10.8 89.2 0.0 0.87 0.77 139.27 m id 4 6.9 table 3. grain size and heavy-mineral content of the analysed sandstones 50.6 42.4 0.47 0.24 181.53 m id 5 5.4 37.5 57.1 1.21 0.45 221.18 m id 6 6.2 30.9 62.9 1.50 0.46 grain size of sandstones (wt%) heavy-mineral content (wt%) mol prov table 3 0.0 1.0 2.0 3.0 4.0 age (ga) 0.5 1.5 2.5 3.5 100 0 80 60 40 20 c um ul at iv e % id 1 id 2 id 3 id 4 id 5 id 6 7.41 m 43.16 m 69.78 m 139.27 m 181.53 m 221.18 m mol prov 5 fig. 5. cumulative age distributions of zircons from the hareelv formation. 122122 the metamorphic rocks of the east greenland caledonides comprise a complex series of lithologies and the krummedal supracrustal sequence is not representative for them all. the ages of the caledonian granites that formed between 466 and 423 ma in east greenland (leslie & nutman 2003; kalsbeek et al. 2008a; rehnström 2010) are in agreement with the minor age population with a peak age of 0.43 ga present in five of the samples from the hareelv formation (fig. 4). the high contents of fe and mg in the garnets in the hareelv formation suggest an origin from a felsic al-rich rock type that has been subjected to intermediate to high metamorphic conditions. the presence of zircon, rutile, leucoxene and apatite (fig. 6) is also consistent with derivation from felsic source rocks such as granites and granitic gneisses. the proportion of mafic minerals relative to the remaining heavy minerals is smaller in the hareelv formation than in the probable crystalline and metasedimentary source rocks in the east greenland caledonides. this may be indicative of several cycles of sedimentation prior to deposition in the jameson land basin since mafic minerals break down easily during weathering and transport (morton & hallsworth 1999). furthermore, amphibole and sillimanite largely dissolve during the first 3 km of burial (andò et al. 2012) and the studied hareelv formation was buried to about 2.8 km prior to cenozoic uplift (green & japsen 2018, this volume). hence, the proportions of the mechanically and chemically stable heavy minerals, such as zircon and rutile, are high compared to the other heavy minerals in the hareelv formation (fig. 6). the negligible amount of ilmenite in the heavy-mineral suite of the sandstones probably indicates that leucoxene formed at the expense of ilmenite (weibel 2003). the interpretation of the non-mica heavy-mineral assemblage reported in fig. 6 is based on rather few grains because of the high content of mica minerals and authigenic heavy minerals (ankerite and pyrite) in the samples, so the variations in the relative proportions between the heavy minerals are not significant. it should be noted, however, that a similar suite of heavy minerals is present in all the samples (fig. 6). the provenance signal of the two finest-grained samples (id 2, 3; table 3) shows no significant deviation from the remaining samples (tables 1, 2, figs 4–6) so it is not influenced by grain size. the number of grains >710 µm in size is overestimated (table 3) since it was not possible to disintegrate all individual grains during crushing of the samples. reworking of older sediments zircon age data from the neoproterozoic eleonore bay supergroup, including the nathorst land group and the lyell land group, have peak ages of 1.75 and 1.05 ga, respectively (fig. 7; dhuime et al. 2007; slama et al. 2011). these ages are not prominent in the hareelv formation, so only a minor amount of sediment can have been reworked from this part of the eleonore bay supergroup into the jameson land basin during the late jurassic. however, it should be noted that the seven samples from the eleonore bay supergroup are not considered representative of the entire 14 km thick succession. devonian and carboniferous sediments in the kong oscar fjord area (fig. 1) have a wide range of age populations (slama et al. 2011) that resemble those in the hareelv formation (fig. 7). the relative dominance of the various age peaks, however, is not similar for the different sediments (this study and slama et al. 2011): the devonian sediments contain fewer archaean ages and more early neoproterozoic and palaeozoic ages than the hareelv formation, whereas the carboniferous sediments contain fewer middle palaeoproterozoic ages and more palaeozoic ages than the studied sandstones. however, some degree of modification of the provenance signal id 1 7.41 m n = 22 id 2 43.16 m n = 327 id 3 69.78 m n = 148 id 4 139.27 m n = 114 id 5 181.53 m n = 40 id 6 221.18 m n = 60 mafic mineral other olivineleucoxene rutile zircon epidote apatite garnet mol prov 6fig. 6. heavy-mineral contents of the hareelv formation excluding mica minerals and authigenic heavy minerals. the number of employed analyses (out of the total number of analyses of c. 1200 per sample) is indicated by ‘n’. 123 is likely to have occurred during erosion and transport. furthermore, the paucity of the database that provides the comparison should be taken into account; the 8 km thick devonian succession is covered by only three samples and the 2 km thick carboniferous succession is represented by two samples. thus, the hareelv formation may have been sourced by reworking of devonian and/or carboniferous sediments into the jameson land basin. ultimately, all the sediments originate from the same areas in the caledonides, which must comprise a combination of the archaean–palaeoproterozoic crystalline complexes (with their late archaean to middle palaeoproterozoic zircon age spectrum), the meso-neoproterozoic metasediments (with their late palaeoproterozoic to late mesoproterozoic zircon age spectrum) and the intruded caledonian granites (fig. 7). these units are closely interrelated in the present-day exposed part of the east greenland caledonides (fig. 1), where a thick section of the krummedal supracrustal sequence must have been eroded to ex0 4 2 0 40 20 60 pr ob ab ili ty pr ob ab ili ty pr ob ab ili ty pr ob ab ili ty pr ob ab ili tyn um be r of g ra in s 0 8 4 12 0 8 4 12 0 30 20 10 0 6 4 2 0 4 2 pr ob ab ili ty pr ob ab ili ty a b c d e f g h age (ga) 0.0 1.0 2.0 3.0 4.00.5 1.5 2.5 3.5 neoproterozoic mesoproterozoic palaeoproterozoic archaeanphanerozoic 1.11 1.63 2.73 0.44 1.11 1.65 2.68 0.43 1.87 1.48 1.38 0.97 1.05 1.50 2.67 1.95 1.84 0.44 1.08 1.62 1.07 1.751.64 2.73 1.11 1.51 1.67 0.42 archaean–palaeoproterozoic rocks crystalline basement complexes meso–neoproterozoic metasediments krummedal supracrustal sequence neoproterozoic sediments eleonore bay supergroup nathorst land group neoproterozoic sediments eleonore bay supergroup lyell land group middle devonian sediments kap kolthoff group upper carboniferous sediments traill ø group lower jurassic sediments neill klinter group upper jurassic sediments hall bredning group hareelv formation 6 samples, n = 660 id 1–6, this study 5 samples, n = 510 slama et al. 2011 2 samples, n = 192 slama et al. 2011 3 samples, n = 314 slama et al. 2011 3 samples, n = 339 slama et al. 2011 4 samples, n = 59 dhuime et al. 2007 3 samples, n = 62 watt et al. 2000, leslie & nutman 2003 11 samples, n = 53 thrane 2002 pr ob ab ili ty 0 30 20 10 1.65 0.43 2.49 2.71 1.95 1.10 1.37 1.49 mol prov 7 fig. 7. zircon u–pb ages of the analysed upper jurassic sandstones (a) compared to older sediments and basement complexes (b–h; watt et al. 2000; thrane 2002; leslie & nutman 2003; dhuime et al. 2007; slama et al. 2011). ages with <10% discordance are employed and they are plotted using kernel density estimation (vermeesch 2012). the locations of the samples are shown in fig. 1. 124124 pose the underlying crystalline basement (higgins et al. 2004). the liverpool land high was uplifted during the early jurassic and supplied sediment to the jameson land basin (surlyk 2003). the dominant age populations with peak ages of 1.62 and 0.44 ga found in lower jurassic sediments in the eastern jameson land basin (fig. 7; slama et al. 2011) correspond to ages present in liverpool land in the eclogite terrane and in caledonian granitoid rocks, respectively (augland et al. 2011, 2012). this distinctive age signature is not present in the hareelv formation, so the latter cannot have received material from liverpool land or its derived sediments. this is in accordance with the gradual jurassic onlap onto liverpool land (surlyk 2003) indicating that it was no longer a source area in late jurassic times. sediment transport it is plausible that the sediments in the hareelv formation and the associated shelf-edge systems were derived partly or fully from reworking of palaeozoic sediments, as described above. in that case, a contribution may have come from immediately north-west of the basin, where carboniferous sediments are exposed today (fig. 1), and/ or from farther south where these strata were probably outcropping in jurassic times. the paleozoic sediments were onlapped during the middle jurassic, but increased faulting associated with the rifting that began in the middle jurassic is known to have led to local erosion of fault crests during the late jurassic (surlyk 2003). such faulting may also have occurred inland (west) of the jameson land basin, thereby resulting in reworking of palaeozoic sediments. small differences exist between the zircon age distributions of the hareelv formation (table 1; fig. 5), but none of the analysed samples was found to be statistically dissimilar according to the performed k-s tests (table 2). this suggests a consistent and persistent transport path for the sands deposited in this part of the jameson land basin in the late jurassic. the results of the provenance analysis of the hareelv formation may also be used to characterise the shelfedge sediments that collapsed and subsequently were redeposited by gravity flows (fig. 3). the feeding shelfedge sands are represented by the proximal facies of the olympen formation (or younger equivalents) during deposition of the katedralen member and subsequently by the raukelv formation during deposition of the sjællandselv member (surlyk 2003; surlyk et al. 2007; bjerager et al. 2018b, this volume). the olympen formation (zeus member) and the raukelv formation (fig. 2) are both interpreted to have been deposited during relative lowstands in the region, but the source terranes that supplied sediment to the northern shelf edge of the jameson land basin may not have been entirely the same during these two time intervals since there are some distinctive differences between the samples from the katedralen and sjællandselv members. the sandstone from the sjællandselv member (id 1) has a higher heavy-mineral content (table 3) and a higher proportion of archaean zircon grains (table 1) than the sandstones from the katedralen member (id 2–6). the sjællandselv member sample has a peak age at 1.73 ga, but lacks the pronounced peak age at 1.66–1.64 ga in the remaining samples (fig. 4), and sandstones from the sjællandselv member are coarsergrained than the katedralen member sandstones (surlyk 2003; bjerager et al. 2018a, this volume). furthermore, the sjællandselv member sample contains 4% rock fragments compared to only 0–1% in the samples from the katedralen member (olivarius et al. 2018, this volume). this could indicate rejuvenation of the topography during the volgian such that the raukelv formation received some of its sediment from more proximal sources in comparison to the previous shelf-edge sands. this is in accordance with the late jurassic rifting that caused block faulting and thereby created local sediment sources through erosion of tilted footwall crests (surlyk 2003). conclusions the large range of zircon u–pb ages in the upper jurassic hareelv formation resembles the zircon age spectrum in the caledonides of east and north-east greenland. the heavy-mineral suite and garnet composition in the sandstones indicate derivation from felsic rocks. archaean–palaeoproterozoic crystalline complexes, meso– neoproterozoic metamorphic rocks and caledonian migmatites and granites are considered to represent the original source of the material. some or all of the material may, however, have undergone several sediment cycles before deposition in the jameson land basin in the late jurassic. sediment supply to the hareelv formation from reworking of devonian and carboniferous sediments is plausible since the preserved parts of these successions contain corresponding age populations. however, it should be emphasised that the database for comparison is limited. 125 the provenance signature is a reflection of the area exposed to lowstand erosion during the accumulation of the southwards prograding shelf-edge deltas that subsequently fed the gravity flows of the hareelv formation. the provenance signature is rather uniform in the oxfordian–kimmeridgian katedralen member, but there are a number of indications of a shorter sediment transport distance for the sands of the early volgian sjællandselv member, potentially reflecting rejuvenation of the topography during rifting. supplementary data to this article can be found online at: www.geus.dk/bulletin42 acknowledgements john boserup, anders pilgaard, fiorella f. aguilera, mojagan alaei, jørgen kystol and ingerlise nørgaard are thanked for sampling and analysis. dirk frei, niels henriksen, kristine thrane and peter appel provided valuable advice and jette halskov kindly did the artwork. the referees, jiri slama and martin sønderholm, are thanked for insightful comments that significantly improved the manuscript. references andò, s., garzanti, e., padoan, m. & limonta, m. 2012: corrosion of heavy minerals during weathering and diagenesis: a catalog for optical analysis. sedimentary geolog y 280, 165–178. augland, l.e., andresen, a. & corfu, f. 2011: terrane 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(eds): petroleum geolog y of the upper jurassic – lower cretaceous of east and north-east greenland: blokelv-1 borehole, jameson land basin. geological survey of denmark and greenland bulletin 42, 65–84 (this volume). rehnström, e.f. 2010: prolonged paleozoic magmatism in the east greenland caledonides: some constraints from u-pb ages and hf isotopes. the journal of geolog y 118, 447–465. sambridge, m. & lambert, d.d. 1997: propagating errors in decay equations: examples from the re-os isotopic system. geochimica et cosmochimica acta 61, 3019–3024. slama, j. et al. 2008: plešovice zircon – a new natural reference material for u–pb and hf isotopic microanalysis. chemical geolog y 249, 1–35. slama, j., walderhaug, o., fonneland, h., kosler, j. & pedersen, r.b. 2011: provenance of neoproterozoic to upper cretaceous sedimentary rocks, eastern greenland: implications for recognizing the sources of sediments in the norwegian sea. sedimentary geolog y 238, 254–267. stacey, j.s. & kramers, j.d. 1975: approximation of terrestrial lead isotope evolution by a two-stage model. earth and planetary science letters 26, 207–221. stemmerik, l., christensen, f.g., piasecki, s., jordt, b., marcussen, c. & nøhr-hansen, h. 1992: depositional history and petroleum geolog y of the carboniferous to cretaceous sediments in the northern part of east greenland. norwegian petroleum federation, special publication 2, 67–87. stemmerik, l., clausen, o.r., korstgård, j., larsen, m., piasecki, s., seidler, l., surlyk, f. & therkelsen, j. 1997: petroleum geological investigations in east greenland: project ‘resources of the sedimentary basins of north and east greenland’. geolog y of greenland survey bulletin 176, 29–38. surlyk, f. 2003: the jurassic of east greenland: a sedimentary record of thermal subsidence, onset and culmination of rifting. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 659– 722. surlyk, f. & noe-nygaard, n. 2005: a forced regressive shelf-margin wedge formed by transition-slope progradation: lowermost cretaceous rauk plateau member, jameson land, east greenland. bulletin of the geological society of denmark 52, 227–243. surlyk, f., gjelberg, j. & noe-nygaard, n. 2007: the upper jurassic hareelv formation of east greenland: a giant sedimentary injection complex. in: hurst, a. & cartwright, j. (eds): sand injectites: implications for hydrocarbon exploration and production. aapg memoir 87, 141–149. thrane, k. 2002: relationships between archaean and palaeoproterozoic crystalline basement complexes in the southern part of the east greenland caledonides: an ion microprobe study. precambrian research 113, 19–42. vermeesch, p. 2004: how many grains are needed for a provenance study? earth and planetary science letters 224, 441–451. vermeesch, p. 2012: on the visualisation of detrital age distributions. chemical geolog y 312–313, 190–194. watt, g.r., kinny, p.d & friderichsen, j.d. 2000: u–pb geochronolog y of neoproterozoic and caledonian tectonothermal events in the east greenland caledonides. journal of the geological society (london) 157, 1031–1048. watt, g.r. & thrane, k. 2001: early neoproterozoic events in east greenland. precambrian research 110, 165–184. weibel, r. 2003: alteration of detrital fe-ti oxides in miocene fluvial deposits, central jutland, denmark. bulletin of the geological society of denmark 50, 171–183. _________________________________________________________________________________ manuscript received 18 december 2015; revision accepted 29 august 2017 geological survey of denmark and greenland bulletin 35, 2016, 23-26 23 the danish subsurface contains deep geothermal resources which may contribute for hundreds of years to the mixed danish energy supply (mathiesen et al. 2009). at present only a limited fraction of these resources are utilised in three existing geothermal power plants in thisted, margretheholm and sønderborg (fig. 1) where warm formation water is pumped to the surface from a production well and, after heat extraction, returned to the subsurface in injection wells (fig. 2). deep geothermal energy has the advantage of being a sustainable and environmentally friendly energy source which is furthermore independent of climate and seasonal variations, in contrast to wind and solar energy. the implementation of deep geothermal energy for district heating replacing conventional energy sources, especially coal and oil, may thus lead to a considerable reduction in the emission of greenhouse gases. there are therefore good reasons to include geothermal energy as a central component in denmark’s future supply of energy for district heating. furthermore, heat-demanding industries may consider the possibility to integrate geothermal energy and energy storage in their production process. in order to facilitate the use of geothermal energy, a broad majority in the danish parliament has granted financial support for initiatives within the geothermal field (energy policy agreement of march 22, 2012). the present paper deals with one of the outcomes of this agreement, namely a webgis portal with an overview of existing and a webgis portal for exploration of deep geothermal energy based on geological and geophysical data henrik vosgerau, anders mathiesen, morten sparre andersen, lars ole boldreel, morten leth hjuler, elina kamla, lars kristensen, christian brogaard pedersen, bjarni pjetursson and lars henrik nielsen margretheholm sønderborg thisted margretheholm sønderborg thisted geothermal potential no potential one reservoir two or more reservoirs structurally complex area and limited seismic data fig. 1. distribution of lithostratigraphic units with reservoir properties suitable for geothermal exploration in the geothermal depth zone (800–3000 m), see the main text. the red line indicates the transect covered by the geosection shown in fig. 5. positions of the operating geothermal plants are shown. fig. 2. principle sketch of a geothermal power plant with production and injection wells to a deep-seated geothermal sandstone reservoir. © 2016 geus. geological survey of denmark and greenland bulletin 35, 23–26. open access: www.geus.dk/publications/bull t e m p e ra tu re g ra d ie n t 2 5 – 3 0 °c /k m sasasasasasasasasaasasasas ndndndndndndndndndndnd aaaaaaaaandndndndndndndndndddnnd gggggggggggggrararararararrararararavevevevevevevevveveveev llllllll clclclclclclclccclayayayayayayayayaya tttttttttttttilililililililili llllllllllll chchchchchchchchchchchchchchchhhalalalalalalalalaalallalla kkkkkkkkkkkkkkkk clclclclclclclclclclclccclclclcllclayayayayayayayayaayaaayayayyaystststststststststststttsttttononononononononononononononooo eeeeeeeeeeeeeee sasasasasasasasasasaasandndndndndndndndndddndn stststststststststttononononononononnonnneeeeeeeeee gegegegegegeggegegegeeeototototototototooo hehehehehehehheeheer mrmrmrmrmrmmrmrmmmr alalalalalalalal rererererereerrerrrrr seseseseseseeseseeseservrvrvrvrvrvrvrvrvrvoioioioioioiooioiooo rrrrrrrrrr ~1,5 k m 2,5 km ~75°c p ro d u ct io n w e ll in je c ti o n w e ll 2424 interpreted geological and geophysical data. this will be relevant for all stakeholders in the exploration of deep geothermal resources in the danish subsurface. the portal focuses on geothermal reservoirs within the 800–3000 m depth interval and provides an overview of the amount and quality of existing geodata, the geological composition of the subsurface, and interpreted thematic products such as geological maps of potential geothermal reservoirs. a comprehensive map from the portal showing onshore and nearoffshore locations where the geological conditions are potentially suitable for extraction of deep geothermal energy in denmark is shown in fig. 1. many of the thematic maps are outcomes of the project the geothermal energy potential in denmark – reservoir properties, temperature distribution and models for utilization under the programme sustainable energy and environment funded by the danish agency for science, technology and innovation. geological requirements for geothermal exploitation in denmark, successful geothermal exploitation in the deep subsurface requires the presence of thick and laterally coherent sandstone reservoirs with high porosity and permeability, which can ensure effective extraction and re-injection of formation water. a thick and coherent reservoir which is not hydraulically compartmentalised by faults, lateral lithological changes (e.g. grain size) and/or diagenetic features such as compaction and mineralisation implies that a large volume of warm water may be accessible, and that production and injection wells can be placed at appropriate distances from each other while remaining hydraulically connected. a certain distance, e.g. 1,5 km, is needed between the filter screens at reservoir level in order to delay the arrival time of the cool, re-injected water to the vicinity of the production well (fig. 2). as a rule of thumb this delay should be more than 30 years. on its way to the production well, the cooled water is reheated to some extent by the reservoir matrix and by heat transfer from poorly or non-permeable boundary strata (usually claystone) above and below the reservoir sandstones. another important requirement is to find areas where the product of temperature and extractable water volume is large enough to ensure an economically viable geothermal plant. the temperature–depth gradient of 25–30°c/km in the danish subsurface implies that at depths shallower seismic data coverage and quality very poor poor resonable good very good petrophysical log data quality no data or poor uncertain good or resonable seismic data coverage and quality very poor poor reasonable good very good petrophysical log data and quality data absent or poor uncertain reasonable or good fig. 3. coverage and quality of seismic and petrophysical log data from deep wells. the quality indexes ref lect to which degree the data can be used to extract information about geothermal relevant lithostratigraphic units in the deep subsurface. 25 than 800 m the temperature is generally too low, whereas at depths greater than 3000 m, diagenetic alterations related to high pressure–temperature conditions reduce the porosity and permeability of the reservoir sandstones (poulsen et al. 2015; kristensen et al. 2016). hence, the focus of the portal is the 800–3000 m depth interval. the geological database the geological data that provide information about denmark’s deep subsurface mainly consist of information from deep wells and seismic surveys collected over a number of years during oil and gas exploration, and to a lesser extent during studies of potential gas storage and geothermal exploration. the geographical coverage and quality of the data vary considerably as outlined in fig. 3. generally, it is possible to obtain detailed information about the penetrated sedimentary successions from the well data including the depth, thickness and reservoir properties of sandstone reservoirs, e.g. based on core data and petrophysical evaluation of well log data (fig. 4). the seismic data have been used for largescale mapping of the depth, thickness and lateral extent of lithostratigraphic units known to contain geothermal reservoir sandstones, as well as for identification and mapping of major faults (fig. 5). this work involved compilation and integration of the many seismic surveys of different age and quality into a coherent seismic network. then the network was interpreted in its entirety and used to generate nationwide depth maps to important subsurface horizons, with conversions from seismic-wave travel time to depths below sea level. g as su m f o rm at io n -1580 -1480 -1600 -1500 -1520 -1540 -1560 -1460 1580 1600 1500 1620 1520 1640 1540 1660 1560 gr api0 250 6 160 ms/ft dt 60 inches cali 16 10000 md perm_log 1 prs nphi 0.6 v/v dec.0 rhob 1.7 3g/cm 2.7 phie 0 % 40 metres m (tvdss) coresdepth (m md) raw logs permeability porosity sandstone shale coal potential reservoir sand fig. 4. petrophysical log evaluation of the gassum formation in the stenlille-1 well including interpretations of lithology, porosity and permeability. gr: gamma-ray log. api: gamma ray radioactivity expressed in accordance with the american petroleum institute. cali: caliper log. dt: sonic log. prs: potential reservoir sand. nphi: total porosity log. rhob: density log. perm_log: permeability log. phie: effective porosity log. md: measured depth. tvdss: vertical depth below sea level. danian limestone and chalk group haldager sand fm frederikshavn fm fjerritslev fm gassum fm incl. lower jurassic unit fault top pre-zechstein skagerrak fm (skagerrak–kattegat platform) bunter sandstone fm and skagerrak fm (time equivalent subinterval to bunter sandstone fm) zechstein group skagerrak– kattegat platform sorgenfrei–tornquist zonedanish basinringkøbing–fyn high 0 -1 -2 -3 -4 t w t ( s) nesw nøvling-1 nøvling-1 flyvbjerg-1 flyvbjerg-1 frederikshavn-1 frederikshavn-1 haldager-1 haldager-1 sæby-1 sæby-1 25 km fig. 5. a regional sw–ne geosection through central and northern jylland as outlined in fig. 1. the profile is constructed on the basis of composite seismic profiles shown in the background. mapped lithostratigraphic units with individual treatment in the portal are highlighted. these include those units which may contain geothermal sandstone reservoirs. in several places the units are truncated by faults, and vertical salt movement from the zechstein group has in places uplifted or penetrated the overlying succession. major structural elements are indicated. depth is given in seismic two-way travel time (s). 2626 the depth maps were subsequently used as a base for a new set of maps where constrained reservoir properties such as porosity and temperature were added in relation to depth. in general, the amount of data is too limited for traditional statistical uncertainty analysis. however, based on quality and spatial density analysis and geus’ general experience, rough uncertainty intervals for the estimated reservoir values are presented for each well in the portal. the webgis portal – content, functionality and perspectives the first map in the webgis portal shows those areas where lithostratigraphic units, containing sandstones with sufficient reservoir properties are considered to be present within the depth interval of 800–3000 m (fig. 1). the lithostratigraphic units are also treated separately and linked with several relevant theme maps showing e.g. depth, thickness, major faults, reservoir transmissivity and temperature. additional data, available in the portal, can be added to each of these maps, such as the distribution and quality of seismic data and petrophysical log data from deep wells. the depth maps can also be visualised through an interactive 3d viewer providing an intuitive overview of the subsurface topography of a selection of important horizons (fig. 6). these maps are to be considered as indicative and are only meant for regional use. this is because the geological data in many areas only provide a rough picture of the subsurface, especially where data are sparse and/or of poor quality. in addition, some of the maps are based on several stages of approximations and generalisations, for instance where largely depth-depending reservoir parameters are paired with depth maps derived from seismic surveys, as briefly described above. the maps are not final. new well and seismic data can be added and new interpretation tools such as seismic interpolation tools can be included. refined geological models may also lead to modifications. however, the present maps give a good indication of where in denmark deep geothermal exploration is relevant, as seen from the geological prerequisites. the use of the maps may thus ensure that new geothermal exploration is directed towards those areas that appear to be most promising based on current knowledge. the various geological map themes also form an important basis for an initial analysis of the geothermal potential at a specific site where the construction of a geothermal plant is considered. in this first step, the maps give an overview of the potential geothermal reservoir intervals (lithostratigraphic units) that may be relevant at the site, and information regarding the type, amount and quality of existing geological data. a more comprehensive estimate of the geothermal potential in a specific area must be based on detailed analysis of the local data and incorporation into local geological models. this work model has been used in an assessment of 28 potential geothermal sites in denmark in the so-called screening project; another outcome of the above-mentioned policy agreement. the results of this work are also accessible free of charge from the webgis portal at http://dybgeotermi.geus.dk. references kristensen, l., hjuler, m.l., frykman, p., olivarius, m., weibel, r., nielsen, l.h. & mathiesen, a. 2016: pre-drilling assessments of average porosity and permeability in the geothermal reservoirs of the danish area. geotherm energy 4:6, 2–27, http://dx.doi.org/ 10.1186/ s40517-016-0048-6 mathiesen, a., kristensen, l., bidstrup, t. & nielsen, l.h. 2009: vurdering af det geotermiske potentiale i danmark. danmarks og grønlands geologiske undersøgelse rapport 2009/59, 30 pp. poulsen, s.e., balling, n. & nielsen, s.b. 2015: a parametric study of the thermal recharge of low enthalpy geothermal reservoirs. geothermics 53, 464–478. fig. 6. interactive 3d tool, available in the webgis portal, visualising the variation of subsurface topography of mapped seismic horizons in a given 10 × 10 km area around a selected point. authors’ address geological survey of denmark and greenland, øster voldgade 20, dk-1350 copenhagen k, denmark,. e-mail: hv@geus.dk the jurassic of denmark and greenland 265 the jurassic deposits in the danish central graben are of particular interest in relation to hydrocarbon exploration, as they include units of reservoir sandstones as well as oiland gas-producing source rocks (fig. 1). hydrocarbon discoveries have been made in both middle and upper jurassic sandstones, and the middle jurassic harald field is under production. the distribution of both reservoirs and source rocks reflects the complex sequence stratigraphy of the jurassic of the danish central graben jan andsbjerg and karen dybkjær a sequence stratigraphic framework is established for the jurassic of the danish central graben based primarily on petrophysical log data, core sedimentology and biostratigraphic data from about 50 wells. regional seismic lines are used to assist in the correlation of some wells and in the construction of isochore maps. in the lower jurassic (hettangian–pliensbachian) succession, five sequences have been identified. the middle jurassic is subdivided into four sequences that together span the uppermost aalenian/lowermost bajocian to the callovian. in the upper jurassic, better well coverage permits greater stratigraphic resolution, and 11 sequences are identified and mapped. on the basis of the sequence stratigraphic correlation and the construction of isochore maps for individual sequences, the jurassic basin history of the danish central graben can be subdivided into seven discrete phases: (1) shallow marine and offshore sediments deposited in a prerift basin extending from the north sea to the fennoscandian border zone (hettangian–pliensbachian). (2) uplift and erosion in association with a toarcian–aalenian north sea doming event. a major hiatus represents this phase in the study area. (3) terrestrial and marginal marine sedimentation during initial rifting (latest aalenian/earliest bajocian – late callovian). (4) early oxfordian – early kimmeridgian transgression during and after a rift pulse. the sedimentary environment changed from coastal plain and marginal marine to fully marine. (5) regression associated with a cessation or slowing of subsidence during a structural rearrangement that took place in the late kimmeridgian during a break in the main rift climax. shallow to marginal marine sandstones were deposited above an erosion surface of regional extent. (6) deep-water mudstones deposited in a composite graben with high subsidence rates related to rift pulses (latest late kimmeridgian – middle middle volgian). (7) deposition of organic-rich mudstones and turbidite sandstones during the late middle volgian – early ryazanian. the main basin shallowed, became more symmetrical and experienced a decreasing rate of subsidence, recording the onset of the post-rift stage. a relative sea-level curve is constructed for the middle–late jurassic. it shows close similarity to published eustatic (global) and relative (north atlantic area) sea-level curves in the latest bathonian – late early kimmeridgian, but differs in the late kimmeridgian – middle volgian interval, probably due to the high rate of subsidence in the study area. keywords: danish central graben, jurassic, sequence stratigraphy, palaeogeography, basin evolution, sea-level changes geological survey of denmark and greenland, geocenter copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: ja@geus.dk geological survey of denmark and greenland bulletin 1, 265–300 (2003) © geus, 2003 tectonic evolution of the area and a depositional history strongly influenced by relative sea-level changes. data from a large number of wells in the study area have been released in recent years, contributing important new information to this study. the aim of this paper is to present a sequence stratigraphic model for the jurassic deposits of the danish central graben. 266 ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■ ■ ▲ ▲ ▲ ■■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■■ ■■■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■■ ■ ■ emma-1 cleo-1 22 1 karl-1 tordenskjold-1 gulnare-1 i-1 elin-1 deep adda-1 v-1 ugle-1 m-8 u-1 deep gorm-1 anna-3 o-1 2/12-12/11-7 baron-2 amalie-1 ravn-2 ravn-1 w-1 eg-1 liva-1 b-1 falk-1 elly-1 elly-2 elly-3 edna-1 jens-1 n. jens-1 bo-1 e-1 adda-1 alma-1 se. igor-1 g-1 kim-1 lone-1 diamant-1 gwen-2 q-1 jeppe-1 mona-1 nora-1 iris-1 3/7-4 lulu-1 2/12-2 gert-31 4 w. lulu-3 john flank-1 s ø g n e b asin piggvar terrace g ert ridge feda graben inge h igh heno plateau m ads h igh tail end g raben a rne–e lin g raben poul plateau r o sa b asin gertrud plateau/graben m andal h igh ål basin o uter rough basin c offee soil fault salt dome province mid north sea high ringkøbing–fyn high (east north sea block) reverse fault triangles showing dip of fault plane normal fault boxes showing dip of fault plane salt structure well ▲ ■■ 20 km n 4°e 5°e 24 56°30' 56°n 500 km uk central graben moray firth basin viking graben norway denmark germany the netherlands fig. 1. maps showing the location of the study area (dark blue) within the jurassic north sea rift system, the jurassic structural elements in the danish central graben and the position of the wells incorporated in the study; note that all wells forming the database for the isochore and palaeogeographic maps are indicated, although some are not specifically mentioned in the text or illustrated. the middle jurassic harald field is delimited by the location of the west lulu-1, -2 and -3 wells; note that the structural feature denoted the gertrud plateau/graben is so indicated to reflect the structural evolution of this region in the late jurassic, from a positive plateau in the early late jurassic to an actively subsiding graben from the early volgian. regional geology the central graben forms the southern part of the north sea rift system. active rifting took place in this area both in the triassic and in the late middle jurassic – late jurassic (roberts et al. 1990; ziegler 1990). the 500 km long central graben, approximately 150 km of which are situated in the danish north sea sector, consists of a nnw–sse-trending complex of half-grabens, and a subordinate n–s-trending segment to the south extending into the german and dutch sectors. the main bounding fault in the danish sector is the coffee soil fault, which forms the eastern margin of the danish central graben (fig. 1). the early jurassic was characterised by a slow relative sea-level rise and deposition of marine muds of the fjerritslev formation, probably over most of the danish area (fig. 2; larsen 1966; michelsen 1978, 1989; pedersen 1986; michelsen et al. 1987). in latest early jurassic – earliest middle jurassic times, the whole area was uplifted and most of the lower jurassic section was removed by erosion (hallam & sellwood 1976; ziegler 1982, 1990; underhill & partington 1993). the uplift may have occurred in response to the development of a rift dome extending 700 km in a north–south direction and 1000 km east–west across the central north sea (whiteman et al. 1975; eynon 1981; ziegler 1990; underhill & partington 1993). domal uplift appears to have been accompanied by the development of a volcanic complex at the triple junction between the viking graben, the central graben and the moray firth basin (ziegler 1990). sedimentation resumed in the danish part of the central graben during the middle jurassic, with deposition of the sandstone-dominated bryne and lulu formations and the mudstonedominated middle graben formation (michelsen et al. 2003, this volume). these sediments are restricted to the søgne basin, the tail end graben and the salt dome province (vollset & doré 1984; jensen et al. 1986). the first marine transgression in the danish central graben occurred during the callovian–oxfordian, probably reflecting the onset of domal collapse combined with eustatic sea-level rise (ziegler 1990; underhill & partington 1993). 267 u pp er volgian kimmeridgian oxfordian callovian bathonian bajocian aalenian toarcian pliensbachian sinemurian hettangian sand-dominated formations m id dl e lo w er s n nw se poul fm lola fm fjerritslev fm farsund fm ju ra ss ic middle graben fm marine mud-dominated formations paralic mud-dominated formationorganic-rich mudstones missing section farsund fm heno fm lulu fm bryne fm heno fm bo mbbo mb ryazanian chronostratigraphy l. cret. fjerritslev fm lola fm middle graben fm bryne fm fig. 2. jurassic lithostratigraphy of the danish central graben, based on jensen et al. (1986) and michelsen et al. (2003, this volume). l. cret., lower cretaceous. during late jurassic time, the feda graben, the heno plateau and the gertrud graben became actively subsiding depositional basins, and the depositional area was later extended to the outer rough and ål basins (fig. 1). deep-water conditions were established in the danish central graben during the oxfordian–kimmeridgian, when the marine mudstones of the lola formation were deposited. during the late kimmeridgian, shallow marine sandstones of the heno formation were deposited on plateau areas. the transgression culminated during the volgian with deposition of the deep marine mudstones of the farsund formation (vollset & doré 1984; jensen et al. 1986). the early cretaceous saw a change to more passive thermal subsidence (roberts et al. 1990). in addition to rift tectonics, basin development in the central graben was also strongly influenced by the presence of mobile zechstein salt. salt movements had a profound influence on the development of depocentres in the søgne basin, the tail end graben and the salt dome province (korstgaard et al. 1993; sundsbø & megson 1993). stratigraphic methods the stratigraphic analysis is based on data from about 50 wells that penetrate jurassic deposits in the danish central graben, and a few wells from the norwegian north sea sector located near the boundary (fig. 1). well logs, including gamma-ray, sonic, neutron/density and resistivity logs, sedimentological core logs, lithology logs, and biostratigraphic data were used in the study. furthermore, a number of interpreted regional seismic lines were included to support the generation of isochore maps. biostratigraphy the biostratigraphic data used in this study are confined to palynomorphs because information from other groups of microfossils is too scarce in most wells to be useful for detailed correlation. the biostratigraphic correlations are based on events rather than recognition of biozones. the events used in our study are mainly last occurrence datums (i.e. first downhole appearance) of dinoflagellate cyst species (fig. 3). the biostratigraphic information utilised in the study includes published data (birkelund et al. 1983; hoelstad 1986; poulsen 1986, 1991; heilmann-clausen 1987; johannessen et al. 1996), unpublished reports of the geological survey of denmark and greenland and of industrial service companies, and the results of new analyses made specifically for this study. due to poor core coverage, being generally restricted to sandy successions of relatively few wells, most data were derived from cuttings samples. although sample quality in the lower jurassic succession was variable, it was possible to establish a palynostratigraphic framework based on a small number of events and stratigraphically diagnostic palyno-assemblages (fig. 3a). a detailed palynostratigraphical subdivision of the middle jurassic succession is precluded by the sparse occurrence of age-diagnostic palynomorphs (fig. 3b); although scanty, the available records made it possible to give an approximate age for the sequences and major events in the middle jurassic. in the upper jurassic, the large sediment thicknesses, the somewhat better data quality, the favourable environment, and the higher diversity of dinoflagellate cyst species probably all contribute to a higher biostratigraphic resolution (fig. 3c). sequence stratigraphy the sequence stratigraphic terminology applied is that introduced by the exxon group (posamentier et al. 1988; posamentier & vail 1988; van wagoner et al. 1988, 1990). sequences are subdivided into lowstand, transgressive and highstand systems tracts. a four-fold subdivision with the addition of the forced regressive systems tract (hunt & tucker 1992, 1995) is not attempted due to the scale of the study and the nature of the data. construction of the sequence stratigraphic framework is based on correlation of well log patterns, combined with biostratigraphic datings. the most conspicuous log patterns, supported by the most important biostratigraphic events, were used to produce a coarse grid, within which more detailed correlations were made. most commonly the gamma-ray logs were used for high-resolution correlations but resistivity logs formed the primary tool in some organic-rich mudstone units. distinct sonic log markers were occasionally used for correlation. maximum flooding surfaces (mfs) are considered the most reliable correlation surfaces in successions dominated by marine mudstones, whereas sequence boundaries (sb), and occasionally flooding surfaces (fs), are of primary importance in silty and sandy units. both sb and mfs key surfaces can normally be traced through most of the basin. in sections dominated by marine mudstones and siltstones, the sb is usually picked at the turnaround point between a coars268 269 age dapcodinium priscum cerebropollenites macroverrocosus2) liasidium variabile liasidium variabile dapocodinium priscum5) boreal standard zones bioevents (palynology) first appearance datums last occurrence datums time in ma ep o ch ea rl y ju ra ss ic 190 195 185 200 205 la te t ri as si c (gradstein et al. 1994) la te la te l la te la te ea rl y ea rl y m id dl e ea rl y ea rl y e m id dl e dispansum pseudoradiosa aalensis thouarsense variabilis bifrons falciferum tenuicostatum spinatum margaritatus davoei ibex jamesoni raricostatum oxynotum obtusum turneri semicostatum bucklandi angulata liasicus planorbis marshi reticulatus rhaetian hettangian sinemurian pliensbachian toarcian first appearance last occurrence tie to boreal standard zones uncertain a fig. 3. bioevents used for dating the sequences in the lower jurassic (a), middle jurassic (b) and upper jurassic – lowermost cretaceous (c) of the danish central graben. the tie to boreal standard zones are according to riding & thomas (1992), unless otherwise indicated: 1, fenton & riding (1987); 2, dybkjær (1991); 3, poulsen (1991); 4, costa & davey (1992); 5, poulsen (1992); 6, poulsen & riding (2003, this volume). note in fig. 3c: (1) the species indicated with an asterisk (muderongia simplex) was previously referred to muderongia sp. a davey 1979; see further discussion in poulsen (1996). (2) although the lod is indicated at the base of the kerberus zone, the species senoniasphaera jurassica (double asterisk) may occur sporadically up to the anguiformis zone. e, early; l, late. ening-upwards unit and a fining-upwards unit, or at the sharp base of a relatively coarse-grained bed occupying the position of the turnaround point. well logs form the primary tool for the identification of lithologies, sedimentary facies and sedimentary successions, and thus for the identification of key surfaces and systems tracts. the cored sections have been the subject of more detailed sedimentological facies analysis and palynofacies investigations (hoelstad 1986; johannessen & andsbjerg 1993; johannessen et al. 1996; andsbjerg 2003, this volume; ineson et al. 2003, this volume; johannessen 2003, this volume); these results have been used to support the sequence stratigraphic subdivision. the lower jurassic succession shows laterally consistent log patterns and, where a unit has not been removed by erosion, correlation of key surfaces is possible over wide areas. in the middle jurassic section, only two or three key surfaces can be correlated from one subbasin to another. a more detailed, four-fold sequence subdivision of the middle jurassic deposits within the søgne basin is presented by andsbjerg (2003, this volume). the laterally uniform log patterns of most of the upper jurassic succession allow detailed well correlations. in addition to the gamma-ray log, the resistivity logs proved to be a robust tool for high-resolution correlations in the lower volgian succession of the 270 lamberti athleta coronatum jason calloviense herveyi koenigi discus orbis hodsoni morrisi subcontractus progracilis tenuiplicatus zigzag parkinsoni garantiana subfurcatum humphriesianum sauzei laeviuscula discites concavum murchisonae opalinum callovian bathonian bajocian aalenian impletosphaeridium varispinosum adnatosphaeridium caulleryi impletosphaeridium varispinosum kekryphalospora distincta1) 180 170 165 175 160 la te la te la te l ea rl y ea rl y ea rl y e m id . m id dl e m id dl e age boreal standard zones bioevents (palynology) first appearance datums last occurrence datums time in ma (gradstein et al. 1994) m id dl e ju ra ss ic ep o ch first appearance last occurrence tie to boreal standard zones uncertain b southern feda graben and the northernmost heno plateau. most key surfaces in the upper jurassic succession are picked in marine mudstones and siltstones. of these key surfaces, only one sequence boundary (the base kimm-2 sb) shows any sign of significant erosion. unusually high organic contents in the upper volgian – ryazanian mudstones of the bo member (michelsen et al. 2003, this volume) probably influence log responses and impede sequence stratigraphic interpretation (ineson et al. 2003, this volume). in the uppermost sequence of this study, ryaz-1, a maximum flooding surface is not identified. it might have been picked at the highest gamma-ray peak in accordance with conventional sequence stratigraphic concepts, but in this case all of 271 age boreal standard zones bioevents (palynology) first appearance datums last occurrence datums time in ma ep o ch (gradstein et al. 1994) 150 155 140 145 albidum stenomphalus icenii kochi runctoni lamplughi preplicomphalus primitivus oppressus anguiformis kerberus okusensis glaucolithus albani fittoni rotunda pallasioides pectinatus hudlestoni wheatleyensis scitulus elegans autissiodorensis eudoxus mutabilis cymodoce baylei rosenkrantzi regulare serratum glosense tenuiserratum densiplicatum cordatum mariae la te ju ra ss ic ea rl y c re ta ce o us ea rl y ea rl y ea rl y ea rl y la te la te la te la te m id dl e m id dl e dingodinium spinosum4) dichadogonyaulax culmula4) rotosphaeropsis thula4) egmontodinium expiratum4) egmontodinium polyplacophorum dichadogonyaulax pannea glossodinium dimorphum muderongia simplex* gochteodinia mutabilis senoniasphaera jurassica6)** scriniodinium inritibile occisucysta balia perisseiasphaeridium pannosum oligosphaeridium patulum cribroperidinium longicorne subtilisphaera? paeminosa endoscrinium luridum stephanelytron scarburghense endoscrinium galeritum scriniodinium crystallinum nannoceratopsis pellusida compositosphaeridium polonicum rigaudella aemula wanaea spp. ctenidodinium continuum subtilisphaera? paeminosa3) s.? inaffecta3) oxfordian ryazanian volgian kimmeridgian first appearance last occurrence tie to boreal standard zones uncertain paratolliavalanginian c the bo member may form part of the transgressive systems tract as suggested for this type of deposits by posamentier & james (1993). this level marks the top of the studied succession. in those wells where the uppermost part of the farsund formation is preserved, it is dated as late ryazanian. sequence stratigraphic subdivision and basin history the jurassic succession in the danish central graben is subdivided into 20 sequences, referred to according to their age (i.e. hettangian sequences: hett-1, hett-2). the main characteristics of each sequence – log expression of sequence boundaries, lithology, thickness, age – are summarised and illustrated below. the lower boundary is described for each sequence, the upper boundary being described under the succeeding sequence. lithologies in the sequence descriptions have been interpreted primarily on the basis of gamma-ray logs, supported by other log types and by core data when available. in the sandstone-dominated intervals, increasing gamma-ray values are interpreted to reflect finingupwards grain-size trends, and decreasing values to reflect coarsening-upwards trends. in the mudstone successions, changing gamma-ray values are interpreted to reflect changes in clay content; increasing gammaray values are thus interpreted to record increasing clay content and decreasing gamma-ray values to record decreasing clay content. thin carbonate beds are represented by low-value gamma-ray spikes. mudstone intervals with exceptionally high gamma-ray values are interpreted as being particularly rich in organic matter. based on these inferred relationships between gammaray values and lithologies, increasing-upwards gammaray patterns are generally interpreted to be characteristic of the transgressive systems tract (tst) and decreasingupwards gamma-ray patterns of the highstand systems tract (hst). the maximum flooding surface (mfs) is picked at the turnaround point where gamma-ray values are at a maximum between the increasing gammaray values of the tst below and decreasing gamma-ray values of the hst unit above. the identified sequences are of approximately the same order of thickness. due to variations in subsidence rate, the duration of the sequences recognised in the lower and middle jurassic is somewhat longer than for the upper jurassic sequences. all sequences, however, probably correspond to 3rd order sequences as defined by vail et al. (1977) and van wagoner et al. (1990). the evolution of the danish central graben can be considered in terms of seven depositional phases on the basis of the subdivision of the jurassic deposits into sequences and systems tracts. the significant influence of tectonics on depositional patterns in rift settings has been demonstrated by a number of studies (surlyk & clemmensen 1983; rosendahl 1987; gabrielsen et al. 1990; prosser 1993; nøttvedt et al. 1995). however, we have attempted to relate the development of the depositional phases to the effects of both tectonics and eustasy. the nomenclature and subdivision of rifting phases introduced by prosser (1993) and adapted by nøttvedt et al. (1995) are used in an attempt to relate the depositional phases of the present study to rifting stages. the proto-rift stage is characterised by flexural subsidence and interrupted by domal uplift. the subsequent rift stage is subdivided into rift initiation and rift climax: rift initiation is associated with fault block compartmentalisation and weak tilting whereas the rift climax is characterised by the maximum rate of fault displacement and strong tilting. the early post-rift stage is marked by the cessation of significant activity at the main faults and a declining rate of regional subsidence. it should be appreciated, however, that the three stage model of nøttvedt et al. (1995) refers to the evolution of rift basins in general. in the present study, the model has been applied to minor basins in a large rift structure and the evolution of these basins may not be representative of the rift structure as a whole. this is emphasised by the diachronous onset of subsidence in neighbouring basins, as described below. in the present study, several pulses of active faulting are inferred to have taken place between the initiation of the middle jurassic rift stage and the early cretaceous early post-rift stage. we have followed surlyk (1978, 1989) and blair & bilodeau (1988) in correlating overall fining-upwards successions in rift basins with periods of active tectonic subsidence, and large-scale coarsening-upwards successions with periods of relative tectonic quiescence. phase 1. pre-rift shallow marine deposition (hettangian–pliensbachian) sequence definitions hett-1 sequence the hett-1 sequence is present only in the deep gorm-1, m-8 and u-1 wells; it consists of marine mudstones. the lower sequence 272 boundary is located at the change from the low gamma-ray values of the underlying triassic deposits to the high gamma-ray values, characteristic of the mudstones of the hett-1 sequence (figs 4, 5). the boundary may be abrupt or gradational. the thickness of the sequence attains a maximum of 23 m in m-8. stratigraphically useful bioevents have not been recorded from this unit. the sequence is thought to be of hettangian age due to its stratigraphic position in the lowermost part of the fjerritslev formation, unconformably overlying upper triassic deposits. hett-2 sequence the marine mudstones of the hett-2 sequence have only been found in six wells but are considered to extend throughout the salt dome province. the boundary between the hett-1 and hett-2 sequences is located at a shift to mudstones characterised by somewhat lower clay contents (figs 4, 5). in wells where the hett-2 sequence directly overlies pre-jurassic sediments (e.g. edna-1; fig. 5), the lower sequence boundary is marked by an abrupt lithological shift. the thickness of the sequence shows very little variation, attaining a maximum of 64 m in edna-1. the abundance of bisaccate pollen of pinuspollenites minimus within this sequence in the edna-1, john flank-1 and o-1 wells indicates the presence of the pinuspollenites–trachysporites zone of lund (1977). this zone is known from the danish basin, skåne and northern germany and is referred to the hettangian (lund 1977; dybkjær 1991). a hettangian age is further supported by the occurrence of the dinocyst species dapcodinium priscum in the wells mentioned above and the absence of the pollen species cerebropollenites macroverrucosus (fig. 3a). sin-1 sequence the marine mudstones of this sequence probably extend throughout the salt dome province. the lower sequence boundary is typically located at a marked shift to mudstones with higher clay contents (figs 4, 5). the thickness of the sequence attains a maximum of 63 m in deep gorm-1. the last occurrence datum (lod) of dapcodinium priscum in the lower part of the sequence in the o-1 well, and the first appearance datum (fad) of cerebropollenites macroverrucosus in core samples from the middle part of the sequence in the deep gorm-1 well, indicate a latest hettangian – early sinemurian age for the lower part of the sequence. in combination with the lod of liasidium variabile close to the upper boundary of this sequence in o-1, this indicates a latest hettangian – sinemurian age for the sequence (fig. 3a). pliens-1 sequence this sequence is only present in the deep gorm-1 and edna-1 wells situated in the north-western part of the salt dome province. in both wells, it is represented by marine mudstones. the lower sequence boundary is located at the top of the well-defined coarsening-upwards hst of the sin-1 sequence (figs 4, 5). the thickness of the sequence attains a maximum of 63 m in edna-1. the common occurrence (in sidewall cores) of pollen referred to the genus chasmasporites indicates the presence of the chasmasporites zone (koppelhus & nielsen 1994), defined in the korsodde section, bornholm, denmark. the chasmasporites zone is referred to the pliensbachian, an age assignment supported by the stratigraphic position of this sequence immediately above the lod of liasidium variabile. the acme of the small, spherical pollen referred to the genus spheripollenites, characteristic of the uppermost pliensbachian – lower toarcian deposits in the danish basin and known from many other locations in northwest europe (dybkjær 1991), has not been reported from the danish central graben. this may indicate that deposits of latest pliensbachian – toarcian age are absent in the study area. pliens-2 sequence the marine mudstones of this sequence have only been recognised in the deep gorm-1 and edna-1 wells (fig. 4). the sequence boundary is positioned where the lithology changes abruptly from silty mudstones of the pliens-1 hst to more clay-rich mudstones (fig. 5). in the deep gorm-1 well, the sequence is represented by less than 10 m of clay-rich mudstone; in edna-1, the sequence attains a thickness of 62 m. the common occurrence (in sidewall cores) of chasmasporites sp. pollen in edna-1 and the absence of a spheripollenites sp. acme and of other toarcian bioevents (such as the fad of the spore genera leptolepidites, ischyosporites, manumia or staplinisporites), indicate a pliensbachian age for this sequence. basin evolution the early jurassic was a tectonically quiescent period between phases of active rifting in the triassic and in the middle–late jurassic (cartwright 1991; nøttvedt et al. 1995). a eustatic rise in sea level during the early jurassic was proposed by hallam (1981) and haq et al. (1988), compatible with observations from the danish basin (michelsen 1978, 1989; pedersen 1986; dybkjær 1988, 1991). uniform lithologies, dominated by shelf mudstones, indicate that marine conditions existed across a major north sea basin and extended into the danish basin (michelsen 1978, 1982, 1989; michelsen et al. 1987; pedersen 1985; nielsen 2003, this volume). the lower jurassic marine mudstones within the study area have only been found in the salt dome province. they were probably deposited over a wider area, but were removed by erosion during the regional uplift phase (phase 2) at the early–middle jurassic transition (andersen et al. 1982; gowers & sæbøe 1985; underhill & partington 1993). the extent of lower 273 274 k im m -1 o x2 * * m id dl e ju ra ss ic , u nd iff er en ti at ed pl ie ns -2 pl ie ns -1 si n1 h et t2 h et t2 h et t1 c al -1 o x1 si n1 b aj -1 – b at -1 c al -1 – ?k im m -1 g r so ni c 41 64 m r es g r so ni c 39 35 m r es g r so ni c 34 30 m r es g r so ni c 23 14 m r es g r so ni c 31 55 m ed na -1 d ee p g o rm -1 u -1 jo hn f la nk -1 o -1 r es 20 k m o -1 jo hn f la nk -1d ee p g o rm -1 u -1 ed na -1 m ar in e m ud st o ne m ar in e si lt st o ne m ar in e an d pa ra lic sa nd st o ne fl uv ia l s an ds to ne fl o o dp la in m ud st o ne an d si lt st o ne 10 0 mm ax im um f lo o di ng s ur fa ce se qu en ce b o un da ry jurassic deposits in the deepest parts of the tail end graben and the søgne basin is unknown due to the lack of wells penetrating the base of the middle jurassic in these areas. five transgressive–regressive cycles, corresponding to the hett-1 – pliens-2 sequences are identified in the lower jurassic succession (e.g. deep gorm-1, edna-1; fig. 4). individual sequences show a remarkable lateral consistency in thickness (fig. 4), indicating a uniform subsidence history in the study area during most of the early jurassic. phase 2. uplift and erosion in the proto-rift phase (latest pliensbachian – latest aalenian) basin evolution a major unconformity separates lower jurassic deposits from the overlying middle and upper jurassic deposits over much of the north sea area. it has been suggested that this unconformity was caused by domal uplift in the toarcian to aalenian, centred at the triple junction between the viking graben, the moray firth basin and the central graben (whiteman et al. 1975; hallam & sellwood 1976; eynon 1981; ziegler 1982; underhill & partington 1993). the unconformity may therefore be an example of a proto-rift unconformity, described by nøttvedt et al. (1995) as being typical of rift systems with thermally-induced domal uplift before or at the onset of active stretching. as a result of the regional uplift, most of the lower jurassic deposits were removed. in the southern part of the danish central graben, where lower jurassic deposits are preserved, differential erosion of the upper part of the succession may be due to local salt tectonics. regional erosion caused a larger part of the succession to be removed over the top of the salt structures. the full lower jurassic succession shows thickness variations from about 60 m in u-1 to about 260 m in edna-1 (fig. 4). reworked lower jurassic palynomorphs recorded from the upper kimmeridgian sandstones of the heno 275 facing page: fig. 4. sequence stratigraphic correlation of the lower, middle and lowermost upper jurassic in the salt dome province. the lower jurassic succession is truncated by an unconformity at the base of the middle jurassic. the depth given beneath each well in this and subsequent correlation panels indicates the depth of the lowermost tieline (typically base-jurassic section) below well reference level; for those few wells that did not penetrate the jurassic section, the depth indicates the base of the logged section (i.e. well total depth). the log suite utilised in the study and illustrated in this and subsequent figures includes gamma-ray (gr), sonic velocity (sonic) and resistivity (res) logs. 50 m gr sonic res pliens-2 pliens-1 sin-1 hett-2 3864 m b. msl. fj er ri ts le v fm d ud ge o n sa lif er o us f m lo w er j ur as si c t ri as si c h et ta ngi an si ne m ur . pl ie ns ba ch ia n m. jur. sequences lithostratigraphy chronostratigraphy lithostratigraphy chronostratigraphy edna-1 gr sonic res cal-1 pliens-1 sin-1 hett-2 3698 m b. msl. fj er ri ts le v fm lo w er j ur as si c h et ta ng ia n si ne m ur . pl ie ns ba ch ia n sequences deep gorm-1 hett-1 m . ju r. c al lo vi an m . g ra be n fm bryne fm pliens-2 maximum flooding surface sequence boundary fig. 5. lower jurassic sequences (hett-1 – pliens-1) in the deep gorm-1 and edna-1 wells. for reference purposes, the depth (in metres below mean sea level) is indicated for a selected sequence boundary, typically in the upper levels of the illustrated section (see also figs 6, 10, 12, 19, 22). jur., jurassic; m., middle; sinemur., sinemurian. formation in the northern part of the danish central graben (gwen-2; johannessen et al. 1996) supports the assumption that lower jurassic deposits were significantly more extensive prior to mid-jurassic erosion. phase 3. terrestrial and marginal marine deposition during the rift initiation stage (latest aalenian/earliest bajocian – late callovian) sequence definitions aalen-1 sequence this sequence is encountered in most wells drilled in the søgne basin and in the nora-1 well in the tail end graben (figs 6, 7). it lies unconformably on either pre-jurassic or lower jurassic deposits. the tst dominates the sequence and consists of a number of minor, backstepping, fining-upwards sandstone intervals, interpreted as stacked fluvial channels, with subordinate floodplain or lacustrine mudstones. the mfs is a distinct gamma-ray high, situated close to the strongly erosional upper sequence boundary. the thickness of the sequence attains a maximum of 69 m in west lulu-1 (fig. 6). no stratigraphically useful bioevents were recorded from this sequence, but the lack of toarcian bioevents (as discussed above with respect to the pliens-1 and pliens-2 sequences) and the lod of kekryphalospora distincta in the sequence above, may be seen as indirect evidence of an aalenian or earliest bajocian age. baj-1 sequence the baj-1 sequence extends throughout the søgne basin and the tail end graben (nora-1), and further south to the northern and eastern parts of the salt dome province (e.g. alma-1, o-1). it may also be present in structurally deep locations elsewhere in the salt dome province. the lower sequence boundary is a pronounced erosional surface (figs 4, 6, 7). the lower part of the sequence typically consists of two laterally extensive channel sandstones separated by a fining-upwards/coarsening-upwards fine-grained interval (e.g. amalie-1; fig. 6). the channel sandstone interval may be interpreted as a lowstand systems tract (lst). overlying this interval is a fining-upwards tst (amalie-1, west lulu-1; fig. 7). the hst consists of floodplain sandstones and mudstones. the thickness of the sequence attains a maximum of 99 m in amalie-1. the lod of kekryphalospora distincta in the upper part of this sequence in the alma-1 well indicates an aalenian or earliest bajocian age for the sequence (fig. 3b). bat-1 sequence this sequence is present in all wells that encountered middle jurassic deposits in the søgne basin, the tail end graben, the salt dome province and the southernmost heno plateau (figs 6, 7). in most wells, the lower sequence boundary is located at the base of a finingupwards channel sandstone (e.g. west lulu-1; fig. 6). the mfs is located in a mudstone interval, several metres thick. the hst is rarely present due to erosion; where present (e.g. west lulu-1; fig. 6), it consists of a coarsening-upwards interval of interbedded mudstones and sandstones. the thickness of the sequence attains a maximum of 64 m in west lulu-1. the occurrence (in a core sample) of adnatosphaeridium caulleryi in the lower part of this sequence in west lulu-1 indicates an age no older than bathonian (fig. 3b). in combination with the occurrence of impletosphaeridium varispinosum immediately above the upper boundary of the sequence in west lulu-3, this indicates a possible age range for this sequence of latest bajocian – earliest callovian. cal-1 sequence this sequence is present in areas where the bat-1 sequence is also found (fig. 8a). in most wells, the lower sequence boundary is a very distinct erosional surface (see amalie-1; fig. 6), which locally shows truncation of at least 10–20 m (e.g. west lulu-3; fig. 7). the sequence boundary is overlain by a section of fluvial to estuarine channel sandstones up to 30 m thick (e.g. amalie-1), which is interpreted as the fill of an incised valley. this interval probably represents the lst and the lowermost part of the tst. in the søgne basin and the tail end graben, the remainder of the tst consists of a succession of sandstone-dominated, paralic to shallow marine deposits, overlain by fully marine mudstones (fig. 7). the paralic deposits include a number of coal beds, up to 3 m thick. the hst consists of a rather indistinct coarsening-upwards interval of marine mudstones. the sequence has a depocentre in the northern part of the tail end graben (fig. 8a). in the nora-1 well, where the sequence includes a section that contains tuffaceous sediments (4986–4932 m), it attains a thickness of 288 m. in other wells, the sequence does not exceed 100 m in thickness. the lod of impletospaeridium varispinosum in the lower part of this sequence in west lulu-3 combined with the lod of ctenidodinium continuum in the sequence above (ox-1) in u-1 and west lulu-1 indicate an early callovian to earliest oxfordian age for this sequence. the occurrence of wanaea acollaris and w. thysanota in the middle part of the sequence in the john flank-1 and west lulu-1 wells supports this age assignment (fig. 3a). basin evolution deposition resumed in the danish central graben with the accumulation of uppermost aalenian or lowermost bajocian terrestrial sediments after the regional uplift and possible incipient collapse of the domal structure. subsequent middle jurassic deposits rest unconformably on pre-jurassic and lower jurassic sediments (fig. 4). 276 the initiation of syn-rift subsidence is demonstrated by an asymmetric distribution of the sediment package in the søgne basin as shown by seismic evidence (møller 1986, fig. 5; cartwright 1987; korstgaard et al. 1993, figs 39, 40) and well log data (andsbjerg 2003, this volume). salt tectonics also influenced sediment distribution and the location of local depocentres in the søgne basin, the tail end graben and the salt dome province (mogensen et al. 1992; korstgaard et al. 1993). middle jurassic deposits are preserved in the søgne basin, the tail end graben and the salt dome province with a depocentre located to the east near the coffee soil fault (figs 4, 7). sandstones and mudstones of sequences aalen-1 – bat-1 were deposited in a fluvially dominated environment during the early part of the middle jurassic (latest aalenian/earliest bajocian – late bathonian; fig. 9a). deeper parts of the basins were periodically inundated by lakes. lacustrine conditions in the central parts of the basins were coeval with wet floodplain conditions in marginal locations. the occurrence locally of rare marine palynomorphs and tidal indicators such as flaser bedding and double mud-drapes suggest that deposition took place in a coastal plain setting. however, during this period, fully marine conditions are only reported from the dutch part of the central graben (van adrichem boogaert & kouwe 1993). a coastline must therefore have been located in the southern part of the danish sector or in the german sector of the central graben. the regional transport direction in the danish central graben was probably towards the coastline in the south, parallel to the basin axis. within the middle jurassic succession, several levels of well-developed, erosionally-based channels, prograding deltas and splays, and lacustrine and floodplain mudstone units form correlatable units over a wide area, comprising the søgne basin and the tail end graben. this suggests a common, external control on base level, such as rift tectonics, eustatic sea-level change, climate change or a combination of these factors. in the søgne basin, the northern tail end graben and possibly in the salt dome province, the deposits of the aalen-1 – bat-1 sequences are cut by a significant erosion surface, the basal sequence boundary of cal-1 (fig. 7). the development of this surface was caused by a major fall in relative sea level. at the time of formation of this surface, the regional slope had changed from a southwards to a northwards dip (andsbjerg 2003, this volume). the erosional surface, which is commonly developed at the base of extensive fluvial or estuarine channel sandstones, is suggested to be the bounding 277 sequences lithostratigraphy chronostratigraphy lithostratigraphy chronostratigraphy sequencesgr sonic res kimm-2 kimm-1 baj-1 aalen-1 4874 m b. msl. lo la f o rm at io n b ry ne f o rm at io n lu lu fm m id dl e ju ra ss ic amalie-1 cal-1 u pp er j ur as si c up pe rm o st a al en ia n b aj o ci an b at ho ni an c al lo vi an u pp er k im m er id gi an o xf . – l. k im m . gr sonic res cal-1 bat-1 baj-1 3488 m b. msl. lo la fm lu lu fm m id dl e ju ra ss ic up pe rm o st a al en ia n b aj o ci an west lulu-1 aalen-1 u . ju r. t ri as si c u . k im m . b at h. c al lo vi an – l. k im m . b ry ne f o rm at io n b ac to n g p bat-1 oxf-1 ox-1 – kimm-1 50 m maximum flooding surface flooding surface sequence boundary fig. 6. middle–late jurassic sequences in the amalie-1 and west lulu-1 wells illustrating, in particular, the characteristics of the middle jurassic (aalen-1 – cal-1) sequences. bath., bathonian; jur., jurassic; kimm., kimmeridgian; l., lower; oxf., oxfordian; u., upper. 278 k im m -1 o x2 o x1 c al -1 b at -1 b aj -1 a al en -1 c al -1 – k im m -1 b aj -1 a al en -1 20 k m a m al ie -1 w .l ul u3 lu lu -1 1 n o ra -1 m ar in e m ud st o ne m ar in e si lt st o ne m ar in e an d pa ra lic sa nd st o ne fl uv ia l s an ds to ne fl o o dp la in m ud st o ne an d si lt st o ne m ax im um f lo o di ng s ur fa ce se qu en ce b o un da ry g r so ni c 38 31 m r es w . l ul u3 g r so ni c 38 41 m r es w . l ul u1 g r so ni c 36 99 m r es lu lu -1 g r so ni c 53 43 m r es a m al ie -1 g r so ni c 53 38 m r es n o ra -1 10 0 m f ig . 7 . se q u e n ce s tr at ig ra p h ic c o rr e la ti o n o f th e m id d le an d l o w e rm o st u p p e r ju ra ss ic i n t h e s ø g n e b as in a n d t h e n o rt h e rn t ai l e n d g ra b e n . a n u n co n fo rm it y a t th e b as e o f th e c al -1 s e q u e n ce t ru n ca te s u n d e rl y in g s e q u e n ce s. surface of an incised valley (andsbjerg 2003, this volume). the valley-fill is dated to the latest late bathonian – early callovian. in the søgne basin, the channel sands were initially deposited in straight or sinuous rivers, which show an increase in tidal influence with time. in the salt dome province, channel sandstones are either stacked or isolated and may show fining-upwards trends typical of sinuous channel fills or blocky gamma-ray motifs, indicating deposition in a straight or braided river (e.g. john flank-1, u-1; fig. 4; koch 1983). the incised valley-fill of the søgne basin is capped by a coal bed up to 3 m thick. later in the callovian, a low-energy coastal plain or delta plain characterised by small distributary channels, lagoons and coal swamps, was established in the southern part of the study area (koch 1983). contemporaneously, a barrier coast separated tidal lagoons at the margins of the søgne basin and the northern tail end graben from a wave-dominated marine bay in the central and eastern parts of these basins (fig. 9b). 279 ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■300–400 m 200–300 m 100–200 m 50–100 m 0–50 m sequence absent fault well ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■■ a cal-1 ox-1 c ox-2 b 20 km 20 km 20 km fig. 8. isochore maps of the cal-1 (a), ox-1 (b) and ox-2 (c) sequences. the distribution of the cal-1 and ox-1 sequences illustrates a pronounced depocentre in the northern tail end graben, continuing south into the rosa basin. a second depocentre is present in the southern tail end graben – eastern salt dome province. the three maps chart a progressive transgression in the area of the ravn and elly wells (fig. 1), in the south-eastern part of the heno plateau. phase 4. rift pulse related transgression (early oxfordian – early kimmeridgian) sequence definitions ox-1 sequence this sequence is restricted to the tail end graben, the deeper parts of the søgne basin, the salt dome province and the flanks of the heno plateau (fig. 8b). the lower boundary of the sequence is located at the top of a well-developed coarsening-upwards interval (e.g. deep gorm-1; nora-1; fig. 10). at the western margin of the basin, a sandy lst up to 12 m thick may be present, erosionally overlying pre-jurassic deposits (e.g. elly-2; fig. 10). in most wells, the sequence consists of marine mudstones; only in elly-2 are sandstones a major component of the sequence. the thickness of the sequence attains a maximum of 189 m in nora-1. a significant depocentre occurs in the northern part of the tail end graben (fig. 8b). the lod of ctenidodinium continuum in the middle part of the sequence in u-1 indicates an early oxfordian age for at least the lower part of the sequence. combined with the lod of rigeaudella aemula close to the upper boundary in the falk-1 well, this indicates an early–middle oxfordian age for the sequence (fig. 3c). 280 5 6 ° 3 0 ’ 4° 00’ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■■ 5 6 ° 0 0 ’ 4° 00’ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■■ shelf shoreface/shore lagoon and barrier bayhead delta floodplain with river lake no deposition/no preservation fault well ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■■ a aalenian – bathonian/ earliest callovian early–middle callovian b c late callovian – earliest oxfordian 20 km 20 km 20 km fig. 9. palaeogeographic maps for the middle – earliest late jurassic. the maps illustrate the gradual transition from a terrestrially-dominated environment (a) through a tidallyinfluenced coastal plain (b), to a fully marine environment (c). deposits of the lowermost part of the middle jurassic succession may have been present in the western part of the danish central graben, and removed by erosion during hanging-wall uplift in association with early half-graben subsidence. due to lack of data, the distribution of middle jurassic deposits in the feda graben is uncertain. ox-2 sequence the distribution of this sequence corresponds to that of ox-1 (fig. 8c). the lower sequence boundary is normally located at the top of a coarsening-upwards interval (e.g. nora-1; fig. 10). in a few wells situated at the western margin of the basin, the lower sequence boundary may be located at the sharp base of an up to 10 m thick sandstone unit referred to the lst (e.g. elly-2). with the exception of these sandstones at the basin margin, the sequence consists of marine mudstones. the thickness of the sequence attains a maximum of 117 m in nora-1. a depocentre for this sequence extends from the northern tail end graben to the rosa basin (fig. 8c). the lod of rigeaudella aemula immediately below the lower sequence boundary in falk-1 combined with the lod of compositosphaeridium polonicum close to the upper boundary of this sequence in u-1 indicates an earliest late oxfordian age for this sequence (fig. 3c). kimm-1 sequence the sequence is missing from the north-western part of the study area (fig. 11a). the lower boundary of the sequence is normally located at the top of a coarsening-upwards interval (e.g. nora-1; fig. 10). in the heno plateau area, the mfs is normally situated immediately above a marked gamma/sonic spike (e.g. elly-2, ravn-1; figs 10, 12). 281 3373 m b. msl. cal-1 pliens-2 ox -1 ox-2 kimm-1 kimm-2 4226 m b. msl. kimm-2 ox-2 ox-1 kimm-1 cal-1 u pp er ju ra ss ic t ri as si c * * middle oxfordian bryne fm * * middle oxfordian deep gorm-1 elly-2 gr ressequences lithostratigraphy chronostratigraphy gr sonic ressequences lithostratigraphy chronostratigraphy gr sonic ressequences lithostratigraphy chronostratigraphy ox-1 3825 m b. msl. kimm-1 ox-2 kimm-2 lo la f o rm at io n m . g ra b. fm fa rs un d fm fj er ri ts le v fm c al lo vi an l. o xf . u pp er o xf o rd ia n u . o xf o rd . – l. k im m . u pp er k im m . pl ie ns ba ch ia n u pp er ju ra ss ic m id dl e ju ra ss ic lo w er ju ra ss ic lo la f m h en o fm lo w er o xf . u . o xf .– l. k im . u pp er o xf . u pp er k im m . fa rs un d fm u pp er ju ra ss ic u pp er o xf o rd ia n – lo w er k im m er id gi an lo w er o xf o rd ia n lo la f o rm at io n c al lo vi an m id dl e ju ra ss ic m . g ra be n fm u pp er o xf o rd ia n u pp er k im m er id gi an m id dl e o xf o rd ia n nora-1 sonic maximum flooding surface flooding surface sequence boundary 50 m fig. 10. sequence stratigraphic breakdown of the lower upper jurassic in the deep gorm-1, elly-1 and nora-1 wells illustrating the features of the sequences ox-1 – kimm-1. kim./kimm., kimmeridgian; l., lower; m. grab., middle graben; oxf./oxford., oxfordian; u., upper. the sequence consists of marine mudstone. the maximum measured thickness is 250 m (nora-1). the sequence has a well-defined depocentre in the central part of the tail end graben (fig. 11a). the lod of compositumsphaeridium polonicum immediately below the lower boundary of this sequence in u-1 and the lod of scriniodinium crystallinum and of nannoceratopsis pellucida close to the upper boundary in a number of wells (e.g. amalie-1, anne-3, emma-1, john flank-1, m-8, u-1, west lulu-2) indicate a late oxfordian – early kimmeridgian age for this sequence (fig. 3c). basin evolution in the tail end graben, subsidence along the coffee soil fault accelerated in the early oxfordian resulting in a highly asymmetric distribution of the oxfordian – lower kimmeridgian sediment package and in very large thicknesses of sediments in the central and eastern parts of the tail end graben (figs 8a, 13; fig. 13 faces page 294). this suggests that the tail end graben had entered the rift climax stage. during this phase, fault-controlled sub282 a kimm-1 kimm-2 c kimm-3 b ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■300–400 m 200–300 m 100–200 m 50–100 m 0–50 m sequence absent fault well ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ 20 km 20 km 20 km fig. 11. isochore maps of the kimm-1 (a), kimm-2 (b) and kimm-3 (c) sequences. comparison of a and b illustrates the progressive transgression of the northern heno plateau, the gertrud plateau and the feda graben area from the late oxfordian – earliest late kimmeridgian. subsidence of the southern feda graben began during the latest early – earliest late kimmeridgian. note the relatively uniform distribution of sediments within the northern part of the tail end graben. during deposition of sequence kimm-3 (late kimmeridgian), a central depocentre developed throughout the length of the tail end graben and the salt dome province, striking roughly nw–se. sidence in the danish central graben mainly occurred along n–s-trending faults (møller & rasmussen 2003, this volume). the lower oxfordian – lower kimmeridgian succession is characterised by an overall transgressive development during which the depositional environment shifted from paralic to fully marine. the marked transgression reflects the interaction of the increased subsidence rate (see above) and a eustatic rise in sea level that has been documented from the north sea rift system and elsewhere (hallam 1978, 1988; haq et al. 1988; surlyk 1990). fully marine conditions were established in the søgne basin in latest callovian – earliest oxfordian times (cal-1, tst) with the introduction of the shelf mudstones of the lola formation. a coastal plain environment probably still dominated parts of the salt dome province to the south, indicating that the callovian–oxfordian transgression entered the danish central graben from the north (figs 9b, c). during the early oxfordian, the tail end graben, the south-eastern marginal parts of the heno plateau, 283 4029 m b. msl. fa rs un d fo rm at io n kimm-2 u pp er j ur as si c u pp er k im m er id gi an kimm-1 ox-2 u pp er o xf o rd ia n – lo w er k im m er id gi an kimm-3 lo la f o rm at io n u pp er o xf o rd ia n 5389 m b. msl. u pp er j ur as si c fa rs un d fo rm at io n kimm-3 kimm-2 u pp er k im m er id gi an h en o fm pe rm ia n z ec hs te in g ro up h en o fm ox-2 4026 m b. msl. u pp er j ur as si c u pp er o xf . kimm-2 kimm-1 u . o xf . – l. k im m . u pp er k im m er id gi an h en o fm lo la fm fa rs un d fm kimm-3 kimm-4 lo la f m kimm-4 kimm-4 nora-1 gr sonic ressequences lithostratigraphy chronostratigraphy gert-4 gr sonic ressequences lithostratigraphy chronostratigraphy ravn-1 gr sonic ressequences lithostratigraphy chronostratigraphy 50 m maximum flooding surface flooding surface sequence boundary fig. 12. upper jurassic stratigraphy of the gert-4, nora-1 and ravn-1 wells illustrating, in particular, the characteristics of the kimm-2 and kimm-3 sequences. kimm., kimmeridgian; l., lower; oxf., oxfordian; u., upper. the salt dome province, and the rosa basin were also transgressed (ox-1, ox-2; figs 8b, c, 9c, 13). the remainder of the heno plateau and possibly areas further west were slowly submerged during the late oxfordian – early kimmeridgian (kimm-1; figs 11a, 14; fig. 14 follows page 294). marginal marine sandstones were deposited locally on the southern part of the heno plateau during this transgression (e.g. elly-2; fig. 14) but marine mudstones of the lola formation were deposited over most of the basin. a number of minor transgressive–regressive cycles can be discerned within the overall transgressive succession of marine mudstones (e.g. nora-1; fig. 13). the main basinal part of the study area was thus characterised by an offshore environment during this period. an inner shelf to shoreface environment developed, however, on the gertrud plateau and the northern part of the heno plateau at the end of this depositional phase (fig. 15b). 284 ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■shelf shoreface barrier and strandplain lagoon no deposition/preservation fault well ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■■ a late oxfordian – early kimmeridgian latest early – earliest late kimmeridgian c late kimmeridgian b 20 km 20 km 20 km fig. 15. palaeogeographic maps for the late oxfordian – late kimmeridgian (late jurassic). during the late oxfordian – early kimmeridgian (a), transgression continued across the northern heno plateau, the gertrud plateau and the feda graben areas (see also fig. 9c). after a major regression (base kimm-2 sb), marginal and shallow marine conditions dominated the plateau areas (b). subsequently, renewed transgression resulted in a westwards shift of the coastline and extension to the west of paralic and marginal marine conditions (c). phase 5. shallow marine deposits and changing structural patterns (late kimmeridgian) sequence definitions kimm-2 sequence this sequence is found throughout the study area east of the mads and inge highs (fig. 11b). the lower boundary has been placed at a conspicuous surface that, even in the deeper parts of the basin, shows an abrupt shift from high to low gamma-ray values, probably indicating an erosion surface (figs 10, 12). in parts of the study area, such as the feda graben, the northern part of the gertrud plateau and the northern part of the heno plateau, this surface coincides with the unconformity that separates the prejurassic and the upper jurassic deposits (e.g. gert-4; fig. 12). on the heno plateau, the lst is thought to be represented by a unit of conglomerates and coarse-grained sandstones less than 5 m thick (e.g. ravn-1; fig. 12) although it should be noted that johannessen (2003, this volume) refers this interval to the lowermost tst. in more distal settings, the lst is represented by a 10–15 m thick sandstone or sandy siltstone unit (e.g. elly-2; fig. 10). in the proximal settings of the heno and gertrud plateaus and the southern feda graben, the tst consists of paralic and shallow marine sandstones and mudstones. in basinal settings (e.g. nora-1), the tst is represented by a well-defined fining-upwards interval (fig. 12). this interval consists of silty claystone, siltstone or silty sandstone, becoming coarser grained towards the heno plateau. in the central part of the heno plateau (e.g. ravn-1), most of the hst was removed by erosion during the subsequent lowstand. on the northern heno plateau, the gertrud plateau and in the southern feda graben, the hst consists of a section that coarsens upwards from sandy siltstones to gravelly sandstones of shoreface origin (johannessen et al. 1996; johannessen 2003, this volume). in basinal settings, the hst consists of a coarsening-upwards interval of marine mudstones, siltstones and sandstones. the thickness of the sequence attains a maximum of 319 m in cleo-1. major depocentres for this sequence are located in the southern tail end graben – eastern salt dome province, in the northern tail end graben – søgne basin and in the feda graben (fig. 11b). a latest early kimmeridgian to earliest late kimmeridgian age is indicated by the lod of endoscrinium galeritum in the lower part of the sequence in edna-1 and west lulu-1 and the fad of subtilisphaera? paeminosa and s.? inaffecta in the lower part of the sequence in gert-1 combined with the lod in the sequence above of stephanelytron scarburghense in the gert-2, jeppe-1 and lulu-1 wells (fig. 3c). kimm-3 sequence the distribution of this sequence corresponds to that of the kimm-2 sequence (fig. 11c). in the central part of the heno plateau (e.g. ravn-1; fig. 12), the lower sequence boundary is represented by an erosion surface overlain by shallow marine conglomerates or gravelly sandstones. further north, on the heno plateau and in the gertrud plateau – feda graben area, the sequence boundary is marked by a thin conglomerate in several wells (johannessen 2003, this volume). in more basinal areas, south and east of the heno plateau, the lower sequence boundary is located at the top of a well-defined coarsening-upwards interval (e.g. nora-1; fig. 12). in the heno plateau – northernmost salt dome province area (e.g. ravn-1), the tst is developed as a backstepping set of parasequences that consist of marine silty sandstones, siltstones and claystones. in the feda graben – gertrud plateau area, the tst consists of shallow marine sandstones and siltstones that grade upwards to marine mudstones (e.g. gert-4; fig. 12). in some wells (e.g. jeppe-1; fig. 14), an abrupt change from marine sandstones to mudstones, interpreted as a flooding surface, replaces part of the coarsening-upwards section. in the tail end graben (e.g. nora-1), the tst is represented by a thin fining-upwards interval of marine mudstones. the hst typically consists of marine mudstones. in the feda graben – gertrud plateau area and in the søgne basin, the hst terminates in a distinct coarsening-upwards interval, which includes siltand sandstones (e.g. gert-4; fig. 12). the thickness of the sequence attains a maximum of 387 m in cleo-1. major depocentres are located in the søgne basin, the feda graben and the southern tail end graben – salt dome province (fig. 11c). the lod of stephanelytron scarburghense in the lower to middle part of this sequence in gert-2 and jeppe-1 and the lod of endoscrinium luridum in the succeeding sequence (kimm-4) indicate a late kimmeridgian age for this sequence (fig. 3c). basin evolution the basin configuration changed significantly during the late early kimmeridgian – late kimmeridgian. fault activity and fault-related subsidence waned and at the end of the period a new pattern of dominantly nnw– sse-trending faults was established (møller & rasmussen 2003, this volume). this development marked a pause between two rift pulses. at this time, the tail end graben, including the søgne basin and most of the heno plateau, formed one major half-graben with an eastwards-dipping hanging-wall slope. accommodation space had been created in the feda graben prior to this phase. the feda graben was separated from the tail end graben by a transfer zone (fig. 11b). the lack of rift-related subsidence, probably combined with a regional fall in sea level in the beginning of this phase, caused a significant relative sea-level fall. this sea-level fall caused the development of a distinctive 285 erosional sequence boundary traceable over most of the danish central graben (figs 13,14); it can be seen on seismic sections as an onlap surface (erik s. rasmussen, personal communication 1997). the succeeding transgression, caused by eustatic or regional relative sea-level rise, gave rise to a gradual flooding of the heno plateau, the southern part of the feda graben and the gertrud plateau area. two higherorder sea-level cycles can be recognised during this overall transgression; the kimm-2 sequence records the first cycle, the kimm-3 sequence the second. while marginal areas were characterised by deposition of sand in shallow marine to paralic environments, low-energy marine conditions prevailed in the deeper parts of the basin during the kimm-2 cycle (fig. 15b). sand was deposited in a high-energy shoreface environment on the southern part of the heno plateau and in a back-barrier environment on the northern part of the heno plateau and in the area of the gert ridge (johannessen et al. 1996; johannessen 2003, this volume). the flooding of the heno plateau area forced the coastline back from its position near the eastern margin of the plateau at the beginning of the transgression to the western margin of the heno plateau or possibly further west at the time of maximum flooding. subsequently, the shallow areas in the western part of the basin were separated from the marine basin to the east by a zone of sand-dominated prograding shoreface. the coastline was re-established in a position at the eastern edge of the heno plateau at the end of this cycle (fig. 15c). in latest early kimmeridgian time (lower kimm-2 sequence), the relatively limited accommodation space in the central parts of the heno plateau was rapidly filled with deposits of the lst and tst, before maximum flooding was attained (e.g. ravn-1, falk-1; fig. 14). a relatively thick tst was deposited in the feda graben due to a rapidly subsiding basin floor. after the time of maximum flooding, most remaining available accommodation space occurred in the tail end graben and the deeper parts of the feda graben where a thick hst was deposited (e.g. g-1, gert-4; fig. 14). by the end of the first sealevel cycle (kimm-2), an area consisting of the southern feda graben and the heno and gertrud plateaus was exposed or dominated by shallow-water conditions. deep-water conditions only prevailed in the central parts of the tail end graben and the søgne basin. the kimm-3 sequence is characterised by a major depocentre in the feda graben where thick marine deposits are related to the early onset of the next phase of subsidence. a central depocentre developed throughout the length of the tail end graben and the salt dome province, striking roughly nw–se (fig. 11c). coarse-grained conglomeratic shoreface deposits were deposited immediately above the sequence boundary (the base kimm-3 sb) on the heno plateau (johannessen 2003, this volume). these deposits were overlain by backstepping parasequences of shallow marine sand and silt (e.g. falk-1, ravn-1; figs 12, 13). the beginning of the next phase of subsidence caused a gradual change from coarseto fine-grained shallow marine deposits in basinal settings of the feda graben. an abrupt shift from shallow marine sandstone to offshore mudstone can be seen in marginal areas of the feda graben and on the gertrud plateau (e.g. gert-2, gwen-2, jeppe-1; fig. 14). when fully marine conditions were established in the feda graben, a very high rate of subsidence in this area impeded the re-establishment of paralic conditions during the highstand part of the cycle. in the tail end graben and søgne basin, the kimm-3 sequence consists of a thin unit of marine mudstones. at the beginning of kimm-3 time, accommodation space on the heno and gertrud plateaus was limited by an initial sea-level fall and a low rate of subsidence. the limited accommodation space available was mainly filled by deposits of the tst (fig. 14). in the remainder of the study area, there was sufficient accommodation space for the development of the hst (e.g. cleo-1, g-1; figs 16, 17, following page 294). on the southern part of the gertrud plateau and adjoining parts of the heno plateau, the remaining accommodation space was filled with shallow marine hst deposits followed by exposure and bypass (e.g. gwen-2; fig. 14). phase 6. deep-water mudstones in a composite graben: rift pulses and passive subsidence (latest late kimmeridgian – middle middle volgian) sequence definitions kimm-4 sequence this sequence has the same areal distribution as the kimm-2 and kimm-3 sequences (fig. 18a). on the heno plateau, the lower sequence boundary is typically placed where the lithology changes abruptly from the sandstones and siltstones of the underlying sequences to fully marine mudstones (e.g. ravn-1; fig. 12). in basinal areas, the lower sequence boundary is located at the top of a coarseningupwards interval, which in the feda graben (e.g. gert-4) and in the søgne basin (e.g. lulu-1; fig. 17) may be distinct. in the feda graben 286 – gertrud plateau area, the tst is well-developed (e.g. gert-2, gwen-2; fig. 19), whereas over much of the heno plateau, the salt dome province and in the tail end graben, it often occurs in a condensed form (e.g. nora-1; fig. 12). in general, the hst is much thicker than the tst (e.g. gert-2, nora-1; figs 12, 19); both the tst and hst consist of marine mudstones. the thickness of the sequence attains a maximum of 318 m in gert-4. the sequence has an elongated depocentre in the eastern part of the tail end graben and a secondary depocentre in the feda graben (fig. 18a). a late kimmeridgian age is indicated for the sequence based on the lod of stephanelytron scarburghense in the sequence below combined with the lod of endoscrinium luridum close to the upper sequence boundary in amalie-1 and cleo-1 (fig. 3c). volg-1 sequence this sequence has the same areal distribution as the previous sequences (fig. 18b). in the feda graben – gertrud plateau area and on the heno plateau, the lower sequence boundary is located at the top of a thin but conspicuous coarsening-upwards interval (fig. 19). in the more basinal settings of the tail end graben, the søgne basin, and the salt dome province, the boundary is situated at the turnaround point between rather indistinct coarsening-upwards and fining287 ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ n■■500–600 m 400–500 m 300–400 m 200–300 m 100–200 m 50–100 m 0–50 m sequence absent fault well ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■■■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■ ■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■■ ■■ a kimm-4 volg-1b c volg-2 20 km 20 km 20 km ■■ ■ ■ fig. 18. isochore maps of the kimm-4 (a), volg-1 (b), and volg-2 (c) sequences. during the latest kimmeridgian and earliest volgian (a, b), an asymmetric basin geometry was reestablished with an elongate depocentre near the coffee soil fault; a secondary depocentre developed in the eastern søgne basin during the earliest early volgian. the outer rough and ål basins were transgressed in the early volgian (c). upwards units (e.g. g-1, nora-1; fig. 16). in several wells in the salt dome province, the tst is missing and the mfs amalgamates with the underlying sequence boundary (e.g. deep gorm-1; fig. 14). the mfs is marked by a conspicuous peak on the gamma-ray, sonic and resistivity logs. both the tst and hst consist of marine mudstones. the thickness of the sequence attains a maximum of 210 m in gert-4. the main depocentre of the sequence is in the eastern part of the tail end graben and in the eastern søgne basin. a secondary depocentre is present in the feda graben (fig. 18b). the sequence is referred to the earliest early volgian (fig. 3c) based on the lod of endoscrinium luridum in the sequence below combined with the lod of subtilisphaera? paeminosa in the upper part of the sequence in a number of wells (e.g. amalie-1, deep gorm-1, gert-2, -4, gwen-2, ravn-2, u-1). 288 volg-4 kimm-4 4048 m b. msl. c ro m er k no ll g p c ro m er k no ll g p r ya z. r ya z. u pp er k im m . f ar su nd f o rm at io n volg-2 volg-1 volg-3 lo w er v o lg ia n m .– u . v o lg . h en o fm volg-4 4018 m b. msl. * upper volgian m id dl e v o lg ia n fa rs un d fo rm at io n volg-3 volg-2 volg-1 kimm-4 lo w er v o lg ia n u pp er k im m er id gi an * 3930 m b. msl. fa rs un d fo rm at io n volg-3 u pp er j ur as si c u pp er k im m . m id dl e v o lg ia n volg-2 volg-1 lo w er v o lg ia n elin-1 gr sonic ressequences lithostratigraphy chronostratigraphy gert-2 gr sonic ressequences lithostratigraphy chronostratigraphy gwen-2 gr sonic ressequences lithostratigraphy chronostratigraphy u pp er j ur as si c l. c re t. l. c re t. u pp er j ur as si c 50 m maximum flooding surface sequence boundary fig. 19. upper kimmeridgian – volgian sequence stratigraphy of the elin-1, gert-2 and gwen-2 wells, highlighting the features of the kimm-4 – volg-3 sequences. kimm., kimmeridgian; l. cret., lower cretaceous; m.–u. volg., middle–upper volgian; ryaz., ryazanian. volg-2 sequence although partly or completely eroded in most wells in the salt dome province, this sequence is recognised throughout the remainder of the danish central graben, including the outer rough and ål basins (fig. 18c). the lower sequence boundary of this sequence is rather indistinct in most wells, being located at the top of a weak coarsening-upwards trend within the hst of the volg-1 sequence below (fig. 19). in basinal settings, where the sequence is relatively thick, the tst is four to five times thicker than the hst; in settings where the sequence is relatively thin, the tst and hst are of comparable thickness. the sequence consists of marine mudstones. the maximum thickness of the sequence measured in wells is 344 m (e-1) although seismic data indicate thicknesses in excess of 400 m in the prominent tail end graben depocentre. a secondary depocentre is present in the feda graben (fig. 18c). the lod of subtilisphaera? paeminosa in the sequence below (volg-1) and of oligospaeridium patulum in the sequence above (volg-3) indicate an early volgian age for this sequence. this is further supported by the lod of cribroperidinium? longicorne in the lower part of the sequence in the eg-1 and emma-1 wells (fig. 3c). volg-3 sequence the sequence is present over much of the study area but is missing locally in the south-western part of the salt dome province and in the area around the mandal high, probably due to erosion (fig. 20a). the lower sequence boundary is positioned at the top of a coarsening-upwards interval (e.g. elin-1, gert-2; fig.19). in a number of wells where the section is relatively thin, the sequence boundary is placed at the base of a somewhat coarser bed (e.g. gwen-2; fig. 19). the volg-3 sequence consists of marine mudstones. the thickness of the sequence attains a maximum of 259 m in e-1. the primary depocentre in the tail end graben branches into the arne–elin graben. secondary depocentres are present in the gertrud and feda grabens and in the outer rough basin (fig. 20a). the lod of oligosphaeridium patulum in the lower part of this sequence in a number of wells (e.g. deep gorm-1, elly-2, falk-1, gert-2, gert-4, i-1, m-8, u-1, v-1) combined with the lod of occisucysta balia in the middle to upper part of the sequence in the bo-1, gert-2, gwen-2 and ravn-2 wells indicate a latest early volgian – middle middle volgian age for this sequence. this is supported by the lod of perisseiasphaeridium pannosum in the upper part of the sequence in gert-1 and gert-2 (fig. 3c). basin evolution in this depositional phase, the occurrence of rift pulses is reflected by syn-rift successions with fining-upwards log patterns separated by successions with overall coarsening-upwards patterns, as described from the mesozoic of east greenland by surlyk (1978). a rift pulse in late kimmeridgian time is indicated by the asymmetric sed289 ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■■■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■ ■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■■■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■ ■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■■200–300 m 100–200 m 50–100 m 0–50 m sequence absent fault well a volg-3 volg-4b 20 km 20 km fig. 20. isochore maps of the volg-3 (a) and volg-4 (b) sequences. in the latest early – middle middle volgian (a), subordinate depocentres developed in the arne–elin graben and in the outer rough basin. the asymmetric half-graben geometry of the tail end graben became less pronounced during the middle–late volgian (b). iment distribution of the kimm-4 deposits in the tail end graben (fig. 18a). another pulse in the earliest early volgian is reflected by fining-upwards log patterns in the lower part of the volg-1 sequence (e.g. g-1, gert-4; fig. 14) and by seismic data from the tail end graben (møller & rasmussen 2003, this volume). a further rift pulse in the early volgian is interpreted from the abrupt change from low to high gamma-ray values immediately below the volg-2 mfs (e.g. gert-4, nora-1; figs 14, 16). the latter two rift pulses are recorded on seismic data from the tail end graben where they resulted in a rotational tilt package (møller & rasmussen 2003, this volume, fig. 7). the tail end graben and the heno plateau acted initially as one major asymmetric basin, with an elongate, nw–se-oriented depocentre located in the tail end graben. during the early volgian, this depocentre expanded into the eastern part of the søgne basin, where subsidence increased significantly (fig. 18a, b). the feda graben continued as an important depocentre. the gertrud graben and the outer rough and ål basins became actively subsiding elements at the time 290 ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■■shoreface sands offshore/basinal muds basin floor sands submarine fan no deposition/no preservation fault well ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■■■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■ ■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ a late kimmeridgian earliest early – late volgian b c late volgian – late ryazanian 20 km 20 km 20 km fig. 21. palaeogeographic maps for the late kimmeridgian – late ryazanian. in the early volgian, the outer rough and ål basins were transgressed (compare a and b). fan and basin floor sandstones were deposited in deep parts of the basin during the late volgian – ryazanian (c). of deposition of the volg-2 sequence (figs 17, 18c). later during this phase, increased fault activity resulted in the generation of several minor sub-basins, for example the arne–elin graben which became a distinct depocentre in the early middle volgian during deposition of the volg-3 sequence (figs 18c, 20a). plateau areas draped by heno formation sandstones were drowned and a coarsening-upwards succession of marine siltstones and mudstones of the farsund formation was deposited above the kimm-4 mfs (e.g. ravn-1; fig. 14). thin stormor gravity-derived sand layers were occasionally deposited in the søgne basin (figs 17, 21a). during the early volgian, the outer rough and ål basins were also transgressed, and fully marine conditions were established (figs 17, 21b). shoreface sands were deposited at the western margin of the outer rough basin, as documented by data from the uk sector of the central graben (mackertich 1996; spathopoulos et al. 2000). phase 7. organic-rich mudstones and basin axis turbidites (late middle volgian – early ryazanian) sequence definitions volg-4 sequence this sequence has not been found in the søgne basin and mandal high area; it is also missing from parts of the outer rough basin and the salt dome province. the sequence is present in all other parts of the study area (fig. 20b). the lower boundary of the volg-4 sequence is positioned at the top of the well-defined coarseningupwards hst of the volg-3 sequence below (e.g. elin-1; fig. 22). in a number of wells, the sequence boundary is further marked by the abrupt base of a slightly more silty or sandy unit (e.g. jeppe-1). in many wells (e.g. iris-1, jeppe-1), the lower part of the tst typically shows a fining-upwards/coarsening-upwards pattern; in v-1, this unit is developed as a 30 m thick sandstone unit (fig. 23). in these wells, the remainder of the tst consists of a short, distinct fining-upwards mudstone section. in other wells, the tst is represented by a simple fining-upwards interval of marine mudstones (e.g. bo-1, elin-1; fig. 22). the upper boundary of this sequence is commonly an erosion surface and the upper part of the hst is thus missing in many wells (e.g. gwen-2, jeppe-1; figs 19, 22). where a major part of the hst is preserved, it typically shows consistently high gammaray values (e.g. bo-1, elin-1). due to the increasingly organic-rich nature of the sediments (see below), the gamma-ray log is not considered a fully reliable grain-size indicator. despite the high gammaray readings, descriptions of the cuttings indicate the presence of sandand siltstone in this interval. it is therefore assumed that the high gamma-ray readings are caused by the presence of organic-rich ‘hot shales’ and not necessarily by a lack of sandand silt-sized material. the sequence consists of marine, organic-rich mudstone with siltand sandstone interbeds. the thickness of the sequence attains a maximum of 189 m in elin-1. the sequence shows a more even distribution than the previous sequences, but depocentres are still recognisable in the tail end graben, the arne–elin graben, the feda graben and the outer rough basin (fig. 20b). the lod of scriniodinium inritibile in the lower part of the sequence in bo-1 and of senoniasphaera jurassica in the lower to middle part of the sequence in a number of wells (e.g. bo-1, deep gorm-1, elin-1, gwen-2, i-1, jeppe-1, ravn-2, w-1) indicate a middle middle volgian age for the lower part of the sequence. in combination with the lod of egmontodinium polyplacophorum in the middle to upper part of the sequence in the bo-1, deep adda-1, e-1, i-1, lone-1 and v-1 wells, this indicates a middle middle volgian to late volgian age for the sequence. this age assumption is supported by the lod of one or more of the dinocyst species dichadogonyaulax pannea, glossodinium dimorphum, muderongia simplex (the form previously referred as muderongia sp. a; poulsen & riding 2003, this volume) and gochteodinia mutabilis within the sequence in a number of wells (e.g. bo-1, deep gorm-1, e-1, elin-1, gwen-2, i-1, iris-1, v-1; fig. 3c). ryaz-1 sequence the distribution of the ryaz-1 sequence corresponds to the distribution of the volg-4 sequence (see above). the development of the ‘hot shales’ of the bo member within this sequence and the transition to more calcareous sediments at the top of the farsund formation makes sequence stratigraphic analysis problematic. neither a mfs nor an upper boundary of the sequence have been picked. the sequence is not necessarily limited to the marine mudstones of the farsund formation but may straddle the boundary to the overlying cromer knoll group. the lower sequence boundary is normally distinct and often erosional (e.g. bo-1, elin-1, jeppe-1; fig. 22). turbidite sandstones occur above the boundary in several wells (e.g. iris-1, jeppe-1; fig. 23). in certain wells that lack such turbidite sandstones (e.g. e-1, gert-2), the bioevents of the turbidite-bearing section are absent; this hiatus is interpreted to have resulted from erosion or sediment bypass, updip from areas in which turbidite sands accumulated (ineson et al. 2003, this volume). the turbidite interval may represent lowstand and possibly early transgressive deposits. in areas without active turbidite transport or deposition, this interval is characterised by a gradual upwards increase in gamma-ray values, probably representing the background sedimentation of the basin (e.g. bo-1). this increase in the strength of the gammaray signal culminates in the highest gamma-ray values in the entire jurassic studied section. this interval corresponds to the ‘hot unit’ of jensen et al. (1986), formalised as the bo member (farsund formation) by michelsen et al. (2003, this volume). the dominant lithology is 291 organic-rich marine mudstone; the mudstones are locally interbedded with turbidite sandstones (ineson et al. 2003, this volume).the thickness of this interval, from the basal sequence boundary to the top of the farsund formation, attains a maximum of 326 m in iris-1. the lod of egmontodinium expiratum in the lower part of this sequence in a number of wells (e.g. bo-1, edna-1, gert-2) and of rotosphaerotopsis thula immediately above the ‘hottest’ part of the bo member (e.g. in anne-3, bo-1, e-1, edna-1, gert-2, jeppe-1) indicate a late volgian – early ryazanian age for this part of the sequence. the uppermost part of the farsund formation is of late ryazanian age. this is indicated by the lod of dingodinium spinosum which coincides broadly with the upper boundary of the farsund formation in a number of wells (e.g. deep gorm-1, e-1, edna-1, jens-1, jeppe-1, kim-1, lone-1, v-1; ineson et al. 2003, this volume) and by the lod of dichadogonyaulax culmula at the same stratigraphic level in the e-1, edna-1 and gert-2 wells (fig. 3c). basin evolution the rate of subsidence decreased in the tail end graben and the salt dome province during this phase; in combination with decreased sediment supply, this resulted in stratigraphic condensation. according to the time-scale of gradstein et al. (1994), the succession deposited during phase 7 represents a period of c. 5.5 million years, 292 4392 m b. msl. jeppe-1 * volg-2 volg-3 volg-4 ryaz-1r ya za ni an volg-3 2577 m b. msl. u pp er j ur as si c bo-1 ryaz-1 volg-4 m . v o lg ia n fa rs un d fo rm at io n * * upper volgian * upper volgian gr sonic res 3741 m b. msl. c ro m er k no ll g p c ro m er k no ll g p c ro m er k no ll g p sequences lithostratigraphy chronostratigraphy gr sonic ressequences lithostratigraphy chronostratigraphy gr sonic ressequences lithostratigraphy chronostratigraphy elin-1 u pp er j ur as si c u . v o lg . volg-4 volg-3 m id dl e v o lg ia n ryaz-1 fa rs un d fo rm at io n r ya za ni an lo w er c re ta ce o us lo w er c re ta ce o us 50 mmaximum flooding surface sequence boundary r ya za ni an lo w er c re ta ce o us u pp er j ur as si c m id dl e v o lg ia n fa rs un d fo rm at io n fig. 22. uppermost jurassic to lowermost cretaceous stratigraphy of the bo-1, elin-1 and jeppe-1 wells illustrating the characteristic features of the volg-4 – ryaz-1 sequences. m., middle; u. volg., upper volgian. 293 r ya z1 v o lg -4 v o lg -3 v o lg -3 v o lg -4 r ya z1 20 k m je pp e1 m o na -1 ir is -1 el in -1 v -1 d ee p a dd a1 e1 m ar in e m ud st o ne m ar in e si lt st o ne m ar in e an d pa ra lic sa nd st o ne m ax im um f lo o di ng s ur fa ce se qu en ce b o un da ry g r so ni c r es je pp e1 g r so ni c r es m o na -1 g r so ni c r es ir is -1 g r so ni c r es el in -1 g r so ni c r es e1 g r so ni c r es d ee p a dd a1 g r so ni c r es v1 10 0 m46 45 m 42 02 m 45 50 m 41 30 m 33 48 m 29 79 m 31 03 m f ig . 2 3 . se q u e n ce s tr at ig ra p h ic c o rr e la ti o n o f th e u p p e rm o st u p p e r ju ra ss ic a n d l o w e rm o st c re ta ce o u s in t h e t ai l e n d g ra b e n an d t h e g e rt ru d g ra b e n . f an a n d b as in f lo o r sa n d st o n e s ar e co m m o n i n t h e u p p e r v o lg ia n – r y az an ia n s u cc e ss io n . approximately equal to the time represented by the 2–10 times thicker succession of phase 6. fault activity ceased along large segments of the main boundary fault (møller & rasmussen 2003, this volume), and this caused the geometry of the tail end graben to change from an asymmetric rift to a more symmetrical saucer-like basin with a relatively uniform sediment distribution (fig. 20b). these changes are the first indications in the tail end graben of the beginning of an early post-rift stage. minor depocentres continued to exist in the northern part of the tail end graben and in the arne–elin graben. subsidence continued in the feda graben and in the outer rough basin. the deposits of phase 7 consist of marine mudstones of the farsund formation. they generally show a gradual increase in gamma-ray and toc values culminating in the ‘hot shales’ of the bo member in the uppermost part (figs 17, 23; jensen et al. 1986; ineson et al. 2003, this volume). below the bo member, a well-developed sequence boundary separates the volg-4 and ryaz-1 sequences. this sequence boundary is strongly erosional in most wells on the northern part of the heno plateau and along the southern margin of the feda and gertrud grabens (e.g. jeppe-1; fig. 17). above the sequence boundary, sandstones are present in a number of wells along the basin axes of the tail end graben and the gertrud graben (figs 21c, 23). the sandstones were deposited from turbidity currents (iris-1) and debris flows (jeppe-1) and may have originated from a number of sources, such as the east north sea block of the ringkøbing–fyn high, the mandal high and the gert ridge (nielsen 1985; ineson et al. 2003, this volume). their occurrence may be related to changed drainage patterns in the hinterland after subsidence had ceased along major segments of the main boundary fault, and to erosion of inverted structures or crests of rotated fault blocks. relative sea-level changes on the basis of the sequence stratigraphic framework presented here (fig. 24), a relative sea-level curve can be constructed for the middle–late jurassic time interval and compared with eustatic curves proposed by haq et al. (1988) and hallam (1988) based on north sea and global data and with the relative sea-level curve of surlyk (1990) for east greenland (fig. 25). the lower jurassic has only been penetrated by wells in a small part of the study area, and no attempt has been made to construct a sea-level curve for this part of the succession. data are lacking from the toarcian and most of the aalenian due to the regional uppermost aalenian or lowermost bajocian unconformity. good biostratigraphic datings become available from the uppermost bathonian–callovian and upwards; the sea-level curve thus has its starting point at this level. wells from the basin centre and intermediate positions were preferred in selecting data for the construction of the curve. the relative sea-level changes have been interpreted mainly from lithological changes (e.g. changes in mud content in marine sediments) reflecting bathymetrically related changes in energy level. lithological changes were interpreted from well log patterns and cores. sedimentary facies, palynofacies and the extent of marine flooding surfaces have also been used. high uranium contents in some marine mudstones, related to organic matter content rather than clay proportion, can cause large deflections on the well logs, thus hampering lithological interpretation. for that reason, sea-level interpretations were not attempted in the ‘hot shales’ of the bo member. the coastal plain deposits of latest bathonian – earliest callovian age were transgressed during the callovian – earliest oxfordian in most of the danish central graben. a relative sea-level rise caused a rapid, step-wise transgression that expanded the basin laterally and drowned previous sediment sources. the sea-level rise and transgression continued throughout the oxfordian and culminated in the early kimmeridgian. this development, from the latest bathonian to the late early kimmeridgian, is almost identical to the sea-level curves of haq et al. (1988) and hallam (1978, 1981, 1988), based on north sea and global data, and the curve of surlyk (1990) for east greenland. the gradual collapse of the north sea dome (hallam & sellwood 1976; ziegler 1982; underhill & partington 1993) and the initiation of rifting in the danish central graben may have influenced transgressive trends in the region during this period. however, the resemblance between the relative sea-level curve of this study and the curves of haq et al. (1988), hallam (1988) and surlyk (1990) may indicate that a common causal factor of super-regional or global extent also influenced sea-level changes during this interval. the uppermost lower kimmeridgian – upper kimmeridgian of the danish central graben is characterised by a double lowstand peak. the other sea-level curves are close to their maximum at this level. the lowstand in the danish central graben probably evolved as a result of a sea-level fall during a pause in rift-induced subsidence (phase 5). 294 after the lowstand event, the late kimmeridgian – late middle volgian interval shows an overall rise in relative sea level, interrupted by a number of minor falls. this overall trend differs from the fall seen in most of the other sea-level curves, probably due to the continued high subsidence rate in the danish central graben, which neutralised the effect of the global sea-level fall indicated by the other curves. the minor relative sealevel falls in the interval may reflect pauses between periods of active subsidence. lithology prediction an important reason for undertaking a sequence stratigraphic study of a hydrocarbon-producing basin is to improve lithology and reservoir prediction. the predictive potential in syn-rift units is much less than in post-rift units. this is due to the problems for orderly sediment dispersal caused by the creation of tilted fault blocks and sub-basins, by the continuous presence of accommodation space on the lower hanging-wall slopes of tilted fault blocks, and by the local supply of sand 295 fluvial and estuarine sandstones estuarine/lagoonal sandstones, heteroliths, mudstones and coal beds shoreface sandstones/siltstones offshore mudstones; locally sandy or silty deep marine sandstones organic-rich offshore mudstones floodplain/lacustrine mudstones hiatus sequence boundary chronostratigraphy se qu en ce st ra ti gr ap hy ringkøbing– fyn high nesw danish central graben oxfordian kimmeridgian volgian ryazanian callovian bathonian bajocian l l l l l l u u u u u u m m m m aalenian a al en -1 – b aj -1 pl ie ns -1 , pl ie ns -2 b at -1 c al -1 1 2 r ya z1 k im m o xvo lg 1 1 2 2 3 3 4 4 toarcian pliensbachian 80 km fjerritslev fm bryne fm lulu fm heno fm lola fm farsund fm bo mb fig. 24. generalised sequence stratigraphic diagram of the middle jurassic – lowermost cretaceous succession. relative duration of stages after gradstein et al. (1994). l, lower; m, middle; u, upper. from erosion of uplifted footwall shoulders. however, in the middle to upper jurassic syn-rift deposits of the danish central graben, the sandstone units seem to show a systematic distribution, which may be related to the combination of sea-level changes and periods of little tectonic subsidence. the bathonian–callovian sandstones, that are widely distributed in the søgne basin, the tail end graben and the salt dome province, resulted from a generous supply of sand from the active denudation of the north sea dome area and a relatively low and only slowly increasing accommodation space in the rift initiation stage. the best reservoir sandstones occur in the lowstand and transgressive systems tracts of the baj-1, bat-1 and cal-1 sequences (figs 4, 7), in the form of laterally extensive fluvial channel sandstones and tidal and shoreface sandstones in the uppermost part of the sandstone unit, deposited prior to the final transgression. the desirable combination of large fluvial and tidal channels and extensive wave-reworked sandstones occurs in the deeper parts of the søgne basin and the tail end graben. in these areas, subsidence was sufficiently fast to create accommodation space for successions of wave-influenced sediments up to 30 m thick during the final middle jurassic transgression (andsbjerg 2003, this volume). an overall transgressive development is interpreted for the late jurassic. the largest concentration of reservoir sandstones in this succession (the heno formation) was deposited during a pause in the otherwise rapid subsidence. the sand is concentrated on the heno plateau, the gertrud plateau and along the southern margin of the feda graben. the heno plateau constituted an upper hanging-wall slope of a major half-graben, the tail end graben, and the gertrud plateau probably 296 valanginian age sea-level curveslow high ryazanian volgian kimmeridgian oxfordian callovian bathonian bajocian aalenian toarcian pliensbachian sinemurian hettangian short term long term dating uncertain dating uncertain danish central graben (this study) wollaston forland embayment jameson land embayment hallam (1988) surlyk (1990) haq et al. (1988) fig. 25. comparison of the relative sealevel curve of this study with the sealevel curves presented by haq et al. (1988), hallam (1988) and surlyk (1990). figure modified after surlyk (1990), according to the gradstein et al. (1994) time-scale. comprised a transfer zone between the tail end and feda grabens (figs 11, 13, 14). possible source areas for the sandstones were to the north-east, where the ula formation and bryne formation sandstones were located, and to the west, on the mid north sea high (figs 15b, c). fluvial systems and/or marine current and wave activity may have facilitated sediment transport to the gertrud and heno plateaus. a similar scenario was envisaged by howell et al. (1996) for the southern uk central graben. the turbidite and debris flow sandstones of the upper volgian – ryazanian constitute potential reservoirs (fig. 23). most of the sands were deposited during depositional phase 7, when subsidence had decreased, and parts of the danish central graben had broken up into fault-bounded sub-basins. inactivity of some coffee soil fault segments (møller & rasmussen 2003, this volume) may have increased the drainage area in the marginal hinterland and opened new sediment transport routes, causing an increased sand supply. sediment dispersal in the receiving basin was still hampered by a topography dominated by tilted fault blocks and many small subbasins. the most extensive sandstones are present immediately above the ryaz-1 basal sequence boundary. sandstones have not been encountered in the few released wells drilled in the danish part of the outer rough and ål basins. however, the presence of volgian reservoir sandstones of a type similar to the heno formation is reported from wells nearby in the uk sector (mackertich 1996; spathopoulos et al. 2000). conclusions the depositional history of the danish central graben in the jurassic shows a relationship to contemporaneous rift stages and to relative and eustatic sea-level changes. the basin development in the jurassic is subdivided into seven depositional phases that reflect this interplay: phase 1 (hettangian–pliensbachian). during phase 1, pre-rift marine mudstones were deposited in a stable epicontinental sea, that stretched across a major part of the north sea region. the deposits were removed from large parts of the central north sea region by subsequent erosion (phase 2). phase 2 (latest pliensbachian – latest aalenian/earliest bajocian). this corresponds to the tectonic protorift stage, being characterised by domal uplift and regionally extensive erosion. phase 3 (latest aalenian/earliest bajocian – late callovian). the middle jurassic sandstones owe their presence to erosion of the north sea dome, and to slow generation of accommodation space during initial rifting (initiation of the tectonic rift stage). subsidence rates increased in the callovian and oxfordian, heralding the onset of the climax of the tectonic rift stage. this resulted in marine flooding and cessation of sand deposition. phase 4 (early oxfordian – early kimmeridgian). in the oxfordian – early kimmeridgian, the tail end graben entered the rift climax resulting in the development of a half-graben. marine mudstones were deposited during this phase. phase 5 (late kimmeridgian). extensive sand deposition took place in the early late kimmeridgian during a halt in subsidence between two rift pulses. sand was deposited over a large area with low accommodation space, which was created on the hangingwall plateau. exposed highs and land areas outside the graben supplied the sand. due to the decrease in subsidence in the tail end graben, input of finegrained sediment could catch up with accommodation space generation, probably resulting in a flat topography at the end of this phase. phase 6 (latest late kimmeridgian – middle middle volgian). during this phase, renewed rifting caused rapid subsidence in the study area. several rift pulses occurred during this interval. due to the high overall rate of subsidence, sand deposition associated with relative sea-level falls did not occur. the danish central graben began to break up into minor subbasins during this phase. phase 7 (late middle volgian – ryazanian). subsidence decreased over large areas of the basin, which had probably entered an early post-rift stage. major segments of the coffee soil fault became inactive, resulting in a shallower, more symmetrical basin. active subsidence continued in a number of subbasins. highly organic-rich mudstones are prominent in the deposits of this phase. the mudstones are interbedded with turbidite and debris flow sand deposits locally, in particular along the tail end graben – gertrud graben basin axis and along the eastern margin of the tail end graben. 297 comparison of the sea-level curve constructed for the danish central graben with published sea-level curves indicates that deposition in the periodically very rapidly subsiding rift basin was strongly influenced by tectonics. in the latest bathonian – late early kimmeridgian, the overall deepening trend resulted from both eustatic sea-level rise and rift-related subsidence. during the rest of the late jurassic, the deepening trend was primarily related to the high subsidence rate associated with rifting. most sediments were deposited between rift pulses in accomodation space that was generated during the rift pulses or by passive subsidence; only a relatively minor proportion of the sediments was deposited during the rift pulses. acknowledgements we had fruitful discussions with colleagues jon r. ineson, peter n. johannessen, jens j. møller and erik s. rasmussen. we gratefully acknowledge the comments of jon r. ineson and erik s. rasmussen on an early manuscript and those of the two referees, m.j. fisher and d.n. parkinson. the work formed part of a ph.d. study at copenhagen university for the first author, who extends his gratitude to supervisor finn surlyk for his thorough and critical comments. eva b. koppelhus and niels e. poulsen kindly supplied us with palynological datings. the work was supported by the danish energy agency (efp-92, 1313/920002), mærsk oil and gas a/s and norsk hydro udforskning a.s./amerada hess a/s. references andersen, c., olsen, j.c., michelsen, o. & nygaard, e. 1982: structural outline and development. in: michelsen, o. 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(eds): sea-level changes – an integrated approach. society of economic paleontologists and mineralogists special publication 42, 39–45. van wagoner, j.c., mitchum, r.m., campion, k.m. & rahmanian, v.d. 1990: siliciclastic sequence stratigraphy in well logs, cores and outcrops: concepts for high-resolution correlation of time and facies. american association of petroleum geologists methods in exploration series 7, 55 pp. vollset, j. & doré, a.g. (eds) 1984: a revised triassic and jurassic lithostratigraphic nomenclature for the norwegian north sea. norwegian petroleum directorate bulletin 3, 53 pp. whiteman, a.j., rees, g., naylor, d. & pegrum, r.m. 1975: north sea troughs and plate tectonics. norges geologiske undersøkelse 316, 137–161. ziegler, p.a. 1982: geological atlas of western and central europe, 130 pp. the hague: elsevier for shell internationale petroleum maatschappij. ziegler, p.a. 1990: tectonic and palaeogeographic development of the north sea rift system. in: blundell, d.j. & gibbs, a.d. (eds): tectonic evolution of the north sea rifts, 1–36. oxford: clarendon press. manuscript received 30 may 1997; revision accepted 9 february 2000. ryaz-1 volg-4 volg-3 volg-2 volg-1 ryaz-1 volg-4 volg-3 volg-2 volg-1 kimm-4 kimm-2 kimm-3 kimm-1 ox-2 ox-1 cal-1 bat-1 baj-1 aalen-1 20 km elin-1 falk-1 ravn-1 ravn-2 nora-1baron-2 marine mudstone marine siltstone marine and paralic sandstone fluvial sandstone floodplain mudstone and siltstone maximum flooding surface sequence boundary gr sonic 4401 m res ravn-2 gr sonic 4307 m res ravn-1 gr sonic 4174 m res falk-1 gr sonic 5233 m res baron-2 gr sonic 4719 m res elin-1 gr sonic 5338 m res nora-1 100 m fig. 13. sequence stratigraphic correlation of the middle and upper jurassic on the heno plateau and in the tail end graben; the profile represents a dip section from the heno plateau to the tail end graben. ryaz-1 volg-4 volg-3 volg-2 volg-1 kimm-4 kimm-3 kimm-2 kimm-1 volg-2 volg-1 kimm-4 kimm-3 kimm-2 100 m 20 km gert-4 gert-2 jeppe-1 ravn-1 falk-1 g-1 deep gorm-1 elly-2 gwen-2 marine mudstone marine siltstone marine and paralic sandstone fluvial sandstone floodplain mudstone and siltstone maximum flooding surface flooding surface sequence boundary gr sonic 5352 m res gert-4 gr sonic 4876 m res gert-2 gr sonic 5041 m res jeppe-1 gr sonic 4355 m res gwen-2 gr sonic 4307 m res ravn-1 gr sonic 4174 m res falk-1 gr sonic 4080 m res elly-2 gr sonic 3935 m res deep gorm-1 gr sonic 3816 m res g-1 fig. 14. sequence stratigraphic correlation of the upper jurassic succession from the feda graben across the heno plateau to the southern tail end graben. onlap of the base jurassic unconformity can be seen on the southern part of the heno plateau (i.e. from deep gorm-1 to ravn-2). the base kimm-2 sequence boundary exhibits a distinct log break, interpreted as an erosional surface that cuts into underlying marine mudstones in the southern part of the study area. the upper part of the kimm-3 sequence and possibly the lowermost part of the kimm-4 sequence onlaps the kimm-3 flooding surface in the feda graben and on the southern heno plateau. cleo-1 amalie-1 nora-1 e-1 g-1 volg-1 kimm-4 kimm-3 kimm-2 cal-1 – kimm-1 ryaz-1 volg-4 volg-3 volg-2 volg-1 kimm-4 kimm-3 kimm-2 kimm-1 volg-2 gr sonic 4622 m res gr sonic 5122 m res gr sonic 4805 m res gr sonic 4719 m res gr sonic 4087 m res gr sonic 3816 m res elin-1 20 km amalie-1 cleo-1 elin-1 nora-1 g-1 e-1 marine mudstone marine siltstone marine and paralic sandstone fluvial sandstone floodplain mudstone and siltstone maximum flooding surface sequence boundary 100 m fig. 16. sequence stratigraphic correlation of the upper jurassic succession in the tail end graben; the profile is parallel to the basin axis. volg-2 volg-1 kimm-4 kimm-3 kimm-2 cal-1 – kimm-1 bat-1 baj-1 volg-2 volg-3 volg-4 ryaz-1 20 km cleo-1 lulu-1 w. lulu-2 karl-1 jeppe-1 lone-1 kim-1 tordenskjold-1 marine mudstone marine siltstone marine and paralic sandstone fluvial sandstone floodplain mudstone and siltstone maximum flooding surface flooding surface sequence boundary gr sonic 3532 m res tordenskjold-1 gr sonic 4602 m res kim-1 gr sonic 3797 m res lone-1 gr sonic 5041 m res jeppe-1 gr sonic 4819 m res karl-1 gr sonic 3944 m res w. lulu-2 gr sonic 3699 m res lulu-1 gr sonic 4709 m res cleo-1 100 m fig. 17. sequence stratigraphic correlation of the upper jurassic in the northern part of the danish central graben. the profile is perpendicular to the main structural elements from the outer rough basin in the west to the søgne basin in the east. the sub-basins were transgressed in a stepwise manner from east to west from the middle jurassic to the earliest early volgian. geological survey of denmark and greenland bulletin 31, 2014, 23-26 23© 2014 geus. geological survey of denmark and greenland bulletin 31, 23–26. open access: www.geus.dk/publications/bull seismic stratigraphy and sedimentary architecture of the chalk group in south-west denmark connie larsen, jon ineson and lars ole boldreel the chalk group is ubiquitous in the subsurface of the danish basin and its upper levels are exposed locally onshore, most notably in eastern denmark. although many subsurface studies have been made of the group in the danish basin, most of these have been in the eastern part of denmark (e.g. esmerode et al. 2007; surlyk & lykke-andersen 2007) whereas the stratigraphy and character of the chalk group in the western onshore region is less well-known. the work described here was undertaken as a bsc project at the department of geosciences and natural resource mangement at the university of copenhagen by the first author as part of regional seismic mapping work contributing to an evaluation of the geothermal energy potential in denmark. the aim of this paper is to present a summary of the key results of the study. we have subdivided and mapped the distribution of the chalk group in the northern north german basin and the south-western danish basin based on digital reflection seismic profiles. we also highlight seismic architectural features that testify to periods of active bottom currents. geological setting following rifting in late carboniferous – early permian times, the mesozoic history of the danish basin was dominated by thermal subsidence, albeit with an important midjurassic uplift event and phases of localised inversion in the late cretaceous – palaeogene (liboriussen et al. 1987). the combination of high sea-levels, a peneplaned hinterland and aridity in northern europe in the late cretaceous led to a reduced influx of siliciclastic sediment to the sea and favoured the accumulation of pure pelagic chalk composed primarily of skeletal fragments from coccolithophorid algae. the pelagic chalk deposits were subject to redistribution by various processes including downslope mass-flow movements from 50 km ringkøbing – danish basin tornquist zone fyn high a b jylland north sea 55°n 57°n sorgenfrei– 10°e <500 m 500–1000 m 1000–1500 m 1500–2000 m >2000 m fault salt dome late cretaceous inversion basement high 50 km 10°e seismic line (conventional) seismic line (high resolution) kegnæs-1 boreholedcj-7 (fig. 3) north german basin fig. 1. structural map of the danish basin (a) showing the thickness of the upper cretaceous – danian chalk group (modified after rasmussen & surlyk 2012); note that the study area (shown in detail in b) straddles a major structural high, the ringkøbing–fyn high. the enlarged map (b) displays the seismic lines and deep boreholes used in this study; highlighted in red are the kegnæs-1 borehole (see fig. 2) and the seismic line illustrated in fig. 3. 2424 slope instability caused by syndepositional tectonics as well as along-slope bottom currents that sculpted the sea floor into valleys, channels, drifts, ridges and mounds (e.g. surlyk & lykke-andersen 2007). results the subdivision of the chalk group is based on seismic facies analysis and seismic structural analysis, and the resultant seismic units are correlated to wireline-logs and stratigraphic units from seven deep boreholes (fig. 1). the study used 2d digital and scanned seismic profiles from nine surveys on and offshore; the digital high-resolution and conventional offshore data are of high quality whereas onshore the digital data are of good quality and the few older scanned data are of low quality. the interval between the base and top of the chalk group on the seismic profiles is divided into seismic units based on the recognition and mapping of relatively strong, bounding reflectors. the brief descriptions of the units given below are based on the interpretation of all the seismic profiles in the study area. in the northern part of the study area, the chalk group is subdivided into 10 seismic units but the uppermost unit is absent south of the ringkøbing–fyn high, i.e. only nine units are recognised in this area (figs 1, 2). the inferred ages of these units are based on correlation to dated borehole sections. seismic units 1–3 show parallel, continuous or discontinuous reflector patterns with low amplitude. boundaries of unit 1 are clearly defined on gamma-ray logs (fig. 2) whereas the boundaries of unit 3 are typically marked by minor log fluctuations. units 1–3 are recognised throughout the study area and are broadly of cenomanian, turonian and coniacian ages respectively. seismic units 4–6 display discontinuous, semi-parallel internal reflector patterns which are locally chaotic. boundaries can be correlated with minor gamma-ray log fluctuations in most boreholes; the base of unit 6 is marked by a prominent sonic peak log in the kegnæs-1 borehole (fig. 2). units 4–6 are recognised throughout the study area and are of probable santonian, early campanian and late campanian ages respectively. seismic units 7 and 8 show discontinuous, semi-parallel internal reflector patterns that become chaotic locally. correlation to log data in boreholes can be difficult but a clear response is observed on the gamma-ray logs in some of the boreholes; the unit is recognised throughout the study area and probably of early to mid-maastrichtian age. stratigraphy danian pa le oc en e u pp er c re ta ce ou s up pe r lo w er lo w er c re t. maastrichtian campanian santonian coniacian turonian cenomanian albian seismic unit age ma 9 65.6 70.6 83.5 85.8 89.3 93.5 99.6 8 7 200 300 400 tw ow ay t ra ve l t im e (m se c) 500 600 700 6 5 4 3 2 1 500 m kegnæs-1 sonic gamma fig. 2. seismic profile (in two-way travel-time, twt) intersecting the kegnæs-1 borehole, illustrated by the sonic log (blue) and gamma-ray log (red), and showing the correlation between the seismic units and the chronostratigraphy, based on data from gearhart (1986). 25 seismic unit 9 commonly shows localised disturbance of the internal reflector pattern but elsewhere exhibits a parallel, continuous to discontinuous pattern. the unit boundaries are readily correlated to gamma-ray logs and are recognised throughout the study area. unit 9 is of probable late maastrichtian age. seismic unit 10 is only present in the western part of the study area, north of the ringkøbing–fyn high, and wedges out to the south near the ringkøbing–fyn high. it shows a parallel, continuous or discontinuous internal reflector pattern with high amplitude. it is recognisable on some of the gamma-ray logs and is probably of early danian age. based on seismic facies analysis, seismic units 1–3 and 9 (cenomanian, turonian, coniacian and upper maastrichtian ages respectively) typically display parallel and low-angle, mounded internal geometries, whereas seismic units 4–8 (santonian, campanian, lower maastrichtian) show lowangle, mounded, sigmoidal, oblique and hummocky forms (fig. 3). evidence of seismic truncation, linked in some cases to log or biostratigraphic data, indicates the presence of three unconformities in the upper chalk group at ‘mid-campanian’ (base unit 6), ‘base maastrichtian’ (base unit 7) and ‘top maastrichtian’ (top unit 9, base unit 10 where present); these surfaces seem to be associated with complex systems of major drift, minor mounded drift and channel-like features (fig. 3). discussion mapping the distribution and thickness of the chalk group seismic units in the study area illustrates both regional trends, related to active inversion of the sorgenfrei–tornquist zone during deposition of the chalk group, and local trends related to the influence of the ringkøbing–fyn high. the structural control exerted by late cretaceous inversion along the sorgenfrei–tornquist zone is reflected by the over400 600 800 2000 m a b c d e seismic unit 5, probably early campanian in age seismic unit 7, probably early–mid-maastrichtian in age su 5 su 7 su 8 su 9 seismic unit 8, probably early–mid-maastrichtian in age seismic unit 9, probably late maastrichtian in age nw sse dcj-07 nw sse 1000 m nw sse 1000 m nw sse 1000 m 1000 m a a a b d e b c c d e b tw ow ay t ra ve l t im e (m se c) fig. 3. internal architecture of selected seismic units in the seismic profile dcj-07 (for location, see fig. 1): unit 5 (green), unit 7 (pink), unit 8 (blue) and unit 9 (purple). the accompanying sketches illustrate the internal architecture of these units; the bounding surfaces indicated in colour are defined on fig. 2 . 2626 all geometry of the chalk group and the gentle northward tilt of the base of the chalk group (see also lykke-andersen & surlyk 2004). the influence of the ringkøbing–fyn high, at least episodically, is indicated by both the distribution of the danian strata and by the evidence of active bottom current activity. the danian chalk succession (seismic unit 10) is limited to the area north of the ringkøbing–fyn high and locally these deposits are preserved in trough-like, channel features. this distribution is consistent with the work of thomsen (1995) who reported that the danian succession wedges out in the south-western part of jylland, crossing the ringkøbing–fyn high. major drifts, minor mounded drifts and channel-like features are identified north of the ringkøbing–fyn high and represent a complex depositional system that is mainly recognised in the campanian–maastrichtian interval; such features were not identified south of the ringkøbing–fyn high. most of the structures are recognised on nw–se and nnw–sse-oriented seismic lines indicating, together with internal architecture, drift migration towards the nw or nnw. a comparable, complex system has been described in the øresund area (esmerode et al. 2007; surlyk & lykkeandersen 2007) where it is seen in middle santonian – campanian and upper maastrichtian intervals, and is considered to be analogous to modern deep-water contourite systems; i.e. that the deposits were moulded by bottom currents that flowed parallel to bathymetric contours. such processes do not seem to have influenced the santonian succession in the study area of south-west denmark, possibly because there was no significant bathymetric relief in this part of the basin at that time. in addition to the upper surface of the chalk group south of the ringkøbing–fyn high, two intra-chalk unconformities are recognised seismically over the entire study area, the inferred mid-campanian hiatus and the ‘base maastrichtian’ surface; note that the former is correlated to a pronounced cemented layer (hardground?) and a biostratigraphically defined middle campanian hiatus in the kegnæs-1 borehole (gearhart 1986). according to abramovitz et al. (2010), two major unconformities are recognised within the chalk group in the southern part of the danish central graben: one within the turonian–campanian hod formation and one at the base of the overlying maastrichtian tor formation boundary. although it is possible that the ‘intra-hod’ unconformity may correspond in part to the mid-campanian hiatus in jylland, this event in the danish central graben has typically been attributed a santonian age (e.g. abramovitz et al. 2010). it is noteworthy, however that a mid-campanian inversion event is well-known from the central graben in the netherlands sector (van der molen et al. 2005). the ‘base-tor’ unconformity of the danish central graben may correspond to the base maastrichtian unconformity recognised in this study. future work will focus on tying the jylland data set with that of the betterstudied chalk group of eastern denmark. acknowledgements the regional investigations to assess the geothermal energy potential in denmark are supported by the danish agency for science, technology and innovation, and interreg4a (european regional development fund). references abramovitz, t., andersen, c., jacobsen, f.c., kristensen, l. & sheldon, e. 2010: 3d seismic mapping and porosity variation of intra-chalk units in the southern danish north sea. in: vining, b.a. & pickering, s.c. (eds): petroleum geolog y: from mature basins to new frontiers 1, 537– 548. london: geological society. esmerode, e.v., lykke-andersen, h. & surlyk, f. 2007: ridge and valley systems in the upper cretaceous chalk of the danish basin: contourites in an epeiric sea. in: viana, a.r. & rebesco, m. (eds): economic and palaeoceanographic significance of contourite deposits. geological society special publication (london) 276, 265–282. gearhart 1986: biostratigraphy report. texaco 5410/5-1 danish well [kegnæs-1], 33 pp. unpublished report, gearhart geo consultants ltd. (in archives of geus – file 9689). liboriussen, j., ashton, p. & tygesen, t. 1987: the tectonic evolution of the fennoscandian border zone in denmark. tectonophysics 137, 21–29. lykke-andersen, h., & surlyk, f. 2004: the cretaceous–palaeogene boundary at stevns klint, denmark: inversion tectonics or sea-floor topography? journal of the geological society (london) 161, 343–352. rasmussen, s.l. & surlyk, f. 2012: facies and ichnolog y of an upper cretaceous chalk contourite drift complex, eastern denmark, and the validity of contourite facies models. journal of the geological society (london) 169, 435–447. surlyk, f. & lykke-andersen, h. 2007: contourite drifts, moats and channels in the upper cretaceous chalk of the danish basin. sedimentolog y 54, 405–422. thomsen, e. 1995: kalk og kridt i den danske undergrund. in: nielsen, o.b. (ed.): danmarks geologi fra kridt til i dag, 31–67. århus: geologisk institut, aarhus universitet. van der molen, a.s., dudok van heel, h.w. & wong, t.e. 2005: the influence of tectonic regime on chalk deposition: examples of the sedimentary development and 3d-seismic stratigraphy of the chalk group in the netherlands offshore. basin research 17, 63–81. authors’ addresses c.l. & l.o.b., department of geosciences and natural resource mangement, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: gnk171@alumni.ku.dk j.i., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. geological survey of denmark and greenland bulletin 38, 2017, 61-64 61 the sedimentary record of the glaciated margins of the north atlantic holds evidence of past ice-sheet activity, and reflects spatial and temporal variations in the ice– ocean–climate interaction as well as the influence of tectonic processes. furthermore, the record of cross-shelf ice sheets provides a direct link between the continental ice cover and the deep ocean, a relevant issue in the context of climate research. with a four-year funding period, a marie curie initial training network on the glaciated north atlantic margins (glanam) was started in the spring 2013. the network involved international partners from both academia and industry and enrolled 15 young scientists working in different areas of the north atlantic margins. the geological survey of denmark and greenland was partner in the network, leading the greenland margin research and hosting three fellows. one of the main topics of the glanam project was to investigate the impact of the ice sheets on the large-scale evolution of the east greenland margin. the present work summarises some new insights into the glacial history of the central east greenland margin gained through a study within this project (fig. 1). the glaciated east greenland margin the dynamic evolution of the greenland ice sheet is related to the glacial history of the northern hemisphere (e.g. thiede et al. 2010). despite evidence of glaciated hinterland and tidewater glaciers in greenland during the eocene and miocene (e.g. thiede et al. 2010), the onset of large-scale glaciations in the northern hemisphere, where ice expanded onto the continental shelf, has been suggested to date between 5 and 2.5 ma based on a marked decrease in global benthic δ18o values and the presence of ice-rafted debris deposits (e.g. bailey et al. 2013). since the midpliocene the oscillation of the ice sheets of the northern hemisphere, and thus of the east greenland margin, is considered to have followed the glacial–interglacial cycles (e.g. sarnthein et al. 2009). major tectonic events related to the miocene–pliocene uplift of the east greenland margin have been pointed to as instigators of the eastwards glacial advance across the shelf (døssing et al. 2016). furthermore, the build-up of the north atlantic ice sheets has also been influenced by the oceanographic circulation which, along east greenland, is mainly controlled by the east greenland current (egc; fig. 1; sarnthein et al. 2009). the egc is a southward-flowing current formed by a complex system of branches and different water masses (våge et al. 2013). asynchronous ice-sheet development along the central east greenland margin: a glanam project contribution lara f. pérez and tove nielsen 15°w denmark strait kong oscar fjord kejser franz joseph fjord kangerlussuaq scoresby sund ce nt ra l e as t g re en la nd m ar gi n geikie plateau bl os se vil le ky st iceland 25°w30°w 20°w 67° n 68°n 73°n egc egc jameson land geikie ll fig. 1. bathymetric map of the study area based on the international bathymetric chart of the arctic ocean (ibcao; jacobsson et al. 2012). contour interval: 500 m. orange lines: ref lection seismic profiles. red lines: sub-bottom and multibeam data. red dot: odp site 987. black arrows: general circulation of the east greenland current (egc). ll: liverpool land. note the outwards bulging of the shelf edge off the major fjords. © 2017 geus. geological survey of denmark and greenland bulletin 38, 61–64. open access: www.geus.dk/publications/bull 6262 it is an important component of the atlantic meridional overturning circulation (amoc) and therefore has implications for the global climate system (de schepper et al. 2015). the contribution of the egc to the amoc has been partly controlled by tectonic pulses of the denmark strait (parnell-turner et al. 2015), a 600 m deep threshold located around 67°n (fig. 1). the denmark strait is part of the greenland–scotland ridge and constitutes a natural boundary that divides the east greenland margin into a northern and southern part, which have experienced different ice-sheet dynamics. our study focuses on the glacial history of the margin section that lies just north of the denmark strait, i.e. the central east greenland margin (fig. 1). database and interpretation procedure based on a large database of 2d seismic reflection profiles (fig. 1), we have divided the sedimentary record into major seismic sequences, which show evidence of various sedimentary processes (pérez et al. unpublished data). a local dataset of high-resolution reflection seismic, sub-bottom profiles and swath bathymetry allowed for a detailed breakdown of the recent stratigraphic and morphological features (pérez et al. unpublished data). the ages of the major seismic sequences have been assessed by a direct tie to site 987 of the ocean drilling program off scoresby sund (fig. 1; pérez et al. unpublished data ). seismic-stratigraphic analyses of these datasets made a large-scale reconstruction of key stratigraphic events possible, revealing several stages of the greenland ice sheet dynamics along the central east greenland margin from late miocene to present. evidence for cross-shelf ice sheets and ice streams central east greenland is characterised by large fjords, many of which are connected with cross-shelf troughs that are up to 300 m deep and 35 km wide (fig. 1). these troughs were formed by erosion of ice streams that passed from the fjords across the shelf, delivering a concentrated accumulation of sediments to the shelf edge (e.g. batchelor & dowdeswell 2014). from there the sediments were transported down the slope as glacigenic debris flows that build up to form large prograding wedges called troughmouth fans. the presence of a trough-mouth fan is often revealed in the seabed morphology as an outwards bulging of the shelf edge (fig. 1), and the youngest debris flows are often observed on the present-day seabed. ice streams are recognised as one of the most important controls on ice-sheet configuration and stability (e.g. stokes et al. 2016). therefore the study of palaeo-ice stream behaviour and dynamics by mapping buried cross-shelf troughs and trough-mouth fans is a useful tool in reconstructing former ice-extent and palaeoclimate variability (e.g. batchelor & dowdeswell 2014). in addition, submarine glacial forms outside the cross-shelf troughs hold clues of the existence of more steady, grounded ice. notable features are grounding-zone wedges up to 160 m high identified along the central east greenland shelf. these ridge-like sedimentary features mark a temporary position of the ice margin on the shelf (dowdeswell & fugelli 2012). discussion prograding deposits off blosseville kyst dating back to the late miocene constitute the first evidence of cross-shelf glaciations on the central east greenland margin (fig. 2). the oceanward glacial advance continued during the early pliocene, where cross-shelf troughs and trough-mouth fans off blosseville kyst and scoresby sund denote ice-sheet growth with ice streams occasionally reaching the palaeo shelf edge (fig. 2). this glacial intensification coincided with the first large-scale glaciation reaching to the palaeoshelf edge along the south-western greenland margin (nielsen & kuijpers 2013). during the middle pliocene (3.65–2.90 ma), the seismic-stratigraphic analysis denotes a period of glacial retreat along the central east greenland margin. as the ice retreated, the oceanic current took over the control of the depositional environment, indicated by a predominance of current-generated wavy facies. the observed glacial retreat is coeval with the global mid-pliocene warmth (3.3–3.0 ma; e.g. robinson 2009) and a supposed enhancement of the egc along the east greenland margin (e.g. raymo et al. 1996). thick trough-mouth fan deposits led to a major oceanward advance of the shelf edge off scoresby sund, providing evidence of multiple cross-shelf glaciations during the quaternary (fig. 2). the ice-sheet extension was largest during latest pliocene – earliest pleistocene (2.90–2.33 ma), revealing a slightly older age for the onset of margin progradation off central east greenland than observed farther north off north-east greenland (c. 76°n), where the first margin progradation began c. 2.5 ma (berger & jokat 2009). the large progradation of the central east greenland margin coincided with the proposed onset of major northern hemisphere cooling at 2.7 ma (e.g. bailey et al. 2013) and the suggested full-scale glaciation of greenland at 2.9 ma (sarnthein et al. 2009). 63 in addition to the cross-shelf troughs off blosseville kyst and scoresby sund, grounding-zone wedges are identified on the shelf off liverpool land within the quaternary sequences, providing evidence of steady, grounded ice. thus, repeated glacial advances over the shelf, occasionally reaching the shelf edge, are inferred along the entire central east greenland margin during the quaternary (fig. 2). however, the study of glacigenic debris-flow deposits observed on the high-resolution dataset of the liverpool land margin (fig. 1) indicates that the quaternary glacial advances to the shelf edge were not synchronous along the margin. the glacigenic debris-flow deposits identified within the early pleistocene sequences in the southern part of the liverpool land dataset suggest a distal downslope input from the scoresby sund ice stream, in agreement with higher sediment supply to the north of the scoresby sund trough-mouth fan between 1.77 and 0.78 ma (laberg et al. 2013). an upward increase of glacigenic debris-flow deposits within the upper seismic section indicates an intensification of glacial control on the sedimentation during the middle pleistocene. this scenario matches the increase in global ice volume that accompanied the mid-pleistocene transition c. 0.9–0.8 ma (head & gibbard 2005) and gave rise to the growth of larger ice sheets in the northern hemisphere (e.g. dowdeswell et al. 1997; stokes et al. 2016). the internal distribution of the middle pleistocene glacigenic debris-flow deposits points to a changing sediment source through time. whereas the oldest glacigenic debris-flow deposits are most abundant in the southern part of the liverpool land area, pointing to an ice-stream source in scoresby sund, the youngest glacigenic debrisflow deposits are more abundant in the northern part of the study area and thus are likely feed by an ice stream from kong oscar fjord (fig. 2). this northern-sourced pattern continued during the latest pleistocene and holocene, in agreement with the presence of ice-rafted debris trapped inside scoresby sund during the last 10 ka (stein et al. 1993) and the southward-pointing, cross-shelf trough off this fjord observed in the present-day seafloor (dowdeswell et al. 1997). farther north, moraines related to the maximum extent of the greenland ice sheet during the last glacial maximum have been identified off kejser franz joseph fjord (evans et al. 2002). shelf slope bloss eville kyst live rpo ol l shelf slope bloss eville kyst live rpo ol l eg c eg c tmf gdf t tmf gdf t ss ss ka ka quaternary late miocene – early pliocene ko ko basin plain basin plain glacial erosion fig. 2. 3d sketch of the central east greenland margin development during the late miocene – early pliocene and the quaternary showing the main morphological features and key depositional processes. within the same age range, darker colours represent older processes or deposits. t: trough. tmf: trough-mouth fan. gdf: glacigenic debris-f low deposit. blue lines on shelf: predominantly glacial erosion. orange lines on slope: predominantly progradation. blue arrows: egc: east greenland current. ka: kangerlussuaq. ss: scoresby sund. ko: kong oscar fjord. 6464 concluding remarks our data indicate an early cross-shelf glaciation off blosseville kyst during the late miocene and early pliocene followed by major cross-shelf glaciations off scoresby sund during the early quaternary and off liverpool land in the late quaternary. higher resolution of the quaternary data off liverpool land indicates that the activity of the scoresby sund ice-stream system was gradually taken over by the kong oscar fjord ice-stream system during the pleistocene. overall, our study reveals an asynchronous growth of the ice sheet across the shelf, with a marked northward progradation of ice-stream activity from the late miocene to the present along the central east greenland margin. acknowledgements the research leading to these results received funding from the people programme (marie curie actions) of the eu fp7 programme fp7/2007-2013/ under rea grant agreement no. 317217. the research forms part of the glanam (glaciated north atlantic margins) initial training network. for further information on the glanam project visit www.glanam.org. references bailey, i., hole, g.m., foster, g.l., wilson, p.a., storey, c.d., trueman, c.n. & raymo, m.e. 2013: an alternative suggestion for the pliocene onset of major northern hemisphere glaciation based on the geochemical provenance of north atlantic ocean ice-rafted debris. quaternary science reviews 75, 181–194. batchelor, c.l. & dowdeswell, j.a. 2014: the physiography of high arctic cross-shelf troughs. quaternary science reviews 92, 68–96. berger, d. & jokat, w. 2009: sediment deposition in the northern basins of the north atlantic and characteristic variations in shelf sedimentation along the east greenland margin. marine and petroleum geology 26, 1321–1337. de schepper, s., schreck, m., beck, k.m., matthiessen, j., fahl, k. & mangerud, g. 2015: early pliocene onset of modern nordic seas circulation related to ocean gateway changes. nature communications 6, 8659, http://dx.doi.org/10.1038/ncomms9659 døssing, a., japsen, p., watts, a.b., nielsen, t., jokat, w., thybo, h. & dahl–jensen, t. 2016: miocene uplift of the ne greenland margin linked to plate tectonics: seismic evidence from the greenland fracture zone, ne atlantic. tectonics 35, 257–282. dowdeswell, j.a. & fugelli, e.m.g. 2012: the seismic architecture and geometry of grounding-zone wedges formed at the marine margins of past ice sheets. geological society of america bulletin 124, 1750–1761. dowdeswell, j.a., kenyon, n.h. & laberg, j.s. 1997: the glacierinf luenced scoresby sund fan, east greenland continental margin: evidence from gloria and 3.5 khz records. marine geology 143, 207–221. evans, j., dowdeswell, j.a., grobe, h., niessen, f., stein, r., hubberten, h.w. & whittington, r.j. 2002: late quaternary sedimentation in kejser franz joseph fjord and the continental margin of east greenland. geological society special publications (london) 203, 149–179. head, m.j. & gibbard, p.l. 2005: early-middle pleistocene transitions: an overview and recommendation for the defining boundary. geological society special publications (london) 247, 1–18. jakobsson, m. et al. 2012: the international bathymetric chart of the arctic ocean (ibcao) version 3.0. geophysical research letters 39, l12609. laberg, j.s., forwick, m., husum, k. & nielsen, t. 2013: a re-evaluation of the pleistocene behavior of the scoresby sund sector of the greenland ice sheet. geology 41, 1231–1234. nielsen, t. & kuijpers, a. 2013: only 5 southern greenland shelf edge glaciations since the early pliocene. scientific reports 3, 1875. parnell-turner, r., white, n.j., mccave, i.n., henstock, t.j., murton, b. & jones, s.m. 2015: architecture of north atlantic contourite drifts modified by transient circulation of the icelandic mantle plume. geochemistry, geophysics, geosystems 16, 3414–3435. raymo, m.e., grant, b., horowitz, m. & rau, g.h. 1996: mid-pliocene warmth: stronger greenhouse and stronger conveyor. marine micropaleontology 27, 313–326. robinson, m.m. 2009: new quantitative evidence of extreme warmth in the pliocene arctic. stratigraphy 6, 265–276. sarnthein, m., bartoli, g., prange, m., schmittner, a., schneider, b., weinelt, m., andersen, n. & garbe-schönberg, d. 2009: mid-pliocene shifts in ocean overturning circulation and the onset of quaternary-style climates. climate of the past discussions 5, 269–283. stein, r., grobe, h., hubberten, h., marienfeld, p. & nam, s. 1993: latest pleistocene to holocene changes in glaciomarine sedimentation in scoresby sund and along the adjacent east greenland continental margin: preliminary results. geo-marine letters 13, 9–16. stokes, c.r., margold, m., clark, c.d. & tarasov, l. 2016: ice stream activity scaled to ice sheet volume during laurentide ice sheet deglaciation. nature 530, 322–326. thiede, j., jessen, c., knutz, p., kuijpers, a., mikkelsen, n., nørgaardpedersen, n. & spielhagen, r.f. 2010: millions of years of greenland ice sheet history recorded in ocean sediments. polarforschung 80, 141–159. våge, k., pickart, r.s., spall, m.a., moore, g.w.k., valdimarsson, h., torres, d.j., erofeeva, s.y. & nilsen, j.e.ø. 2013: revised circulation scheme north of the denmark strait. deep sea research part i. oceanographic research papers 79, 20–39. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark; e-mail: lfp@geus.dk geological survey of denmark and greenland bulletin 31, 2014, 27-30 27 a novel technique for obtaining representative water samples during co2 core-flooding experiments on chalk at reservoir conditions claus kjøller and john zuta there is a huge potential for using co2 gas to recover additional oil after water flooding in reservoir chalk. however, the injection of co2 into chalk reservoirs will disturb the chemical equilibrium between formation water, injection water and chalk. a proper understanding of these co2induced interactions and the resulting changes in the physical properties at representative reservoir conditions is required. unfortunately, reliable chemical data are rare because data cannot be acquired directly at reservoir conditions with present-day techniques. in published experiments, water samples are in many cases obtained at atmospheric conditions with the aid of a back-pressure regulator. thus, water samples are not representative of in situ reservoir conditions and if proper care is not taken, the collected data cannot be used to judge the magnitude of the chemical reactions taking place at reservoir conditions. however, in some cases water obtained at laboratory conditions can give information on in situ reservoir conditions by using geochemical speciation models to account for dissolved gases that are lost from the effluents during sampling (bachu & adams 2003). the objective of this study was to develop and test a new technique for obtaining water samples during co2-brine– rock interactions in reservoir chalk under representative reservoir conditions and gain a better understanding of the chemical interactions which occur during the injection of co2. the experiments were performed by injecting co2-saturated seawater at supercritical co2 conditions, at a pressure of 17.24 mpa (2500 psig; pounds per square inch of gauge pressure) and a temperature of 75°c. these values are typical of a region in a chalk field where the rock is exposed to long term reactions with flow of co2-bearing water. in addition, the numerical code phreeqc-3 (parkhurst & appelo 2013) was used to reproduce the experiments by assuming equilibrium between calcite and injected fluids. in this way, we can validate the sampling procedure and investigate how the measured parameters (ph, co2 pressure, calcium (ca) and bicarbonate (hco3–) concentrations) compared with the calculated parameters. reservoir chalk samples chalk plugs for the experiment were sampled from the maastrichtian tor formation in the central north sea and were first cleaned of salt and oil with methanol and toluene. following initial determination of porosity and permeability, the samples were saturated with synthetic formation water (fw). all plugs had a diameter of 3.81 cm and a length of approximately 7.5 cm; plugs with similar petrophysical properties (table 1) were used to check the reproducibility of the studied sampling procedure. the compositions of synthetic formation water, synthetic seawater and co2 synthetic saturated seawater are listed in table 2. experimental setup the setup/rig for the experiments is shown in fig. 1. it includes three cylinders with pistons placed in an oven to maintain constant temperature. two of the cylinders were used © 2014 geus. geological survey of denmark and greenland bulletin 31, 27–30. open access: www.geus.dk/publications/bull waste co2-saturated waterlimit of oven seawater flooding plug eq ui l. p lu g primary sample loop (13 ml) separation point secondary sample cylinder (125 ml) pressure transducer pressure transducer ph-meter pressure transducer st1 st2 pt1pt2 primary sample loop (13 ml) fig. 1. experimental setup/rig within the oven. the rig has two primary sample loops. 2828 for the delivery of co2-saturated seawater and seawater. the third cylinder was used as a waste tank and for maintaining fluid pressure. all the fluids were injected at a constant rate of 6.5 ml/h with the plug in a horizontal position. the injection of co2-saturated seawater was preceded by injecting close to 3.5 pore volume (pv) of seawater to mimic the present-day water flooding. at the end of the injection of co2-saturated seawater, seawater was again injected through the plug. at this point, equilibrium with calcium carbonate was obtained in the injection fluid by first passing the seawater through the equilibrium plug (fig. 1). this was done in order to avoid any further dissolution of chalk in the plug under study. the final seawater flooding was performed to displace any residual co2 gas and bring the concentrations back to initial levels. water sampling technique the system for obtaining water samples was located at the downstream end of the rig (fig. 1). it consists of two primary sample loops each with a volume of c. 13 ml. this enabled continuous collection of water samples for every 13 ml (c. 0.5 pore volume) of plug flooded. the sampling was done by alternating the flow process between the two primary loops with the aid of computer-controlled valves (cv-210 valves) without disrupting the injection process. the primary sample loops were connected to a secondary sample cylinder with a volume of 125 ml by a separation point. water samples were transferred from the primary sample loop to the secondary sample cylinder by a de-pressurisation step. this made it possible to collect water samples for a set of chemical parameters (ca and hco3– concentrations) at predefined sampling intervals. the ph and co2 pressures of the de-pressurised effluents were measured on-line in the secondary sample cylinder after the de-pressurisation step. the sampling from the secondary sample cylinder was subsequently done as fast as possible, in less than 5 min., thereby providing a consistent chemical dataset for the conditions prevailing in the secondary sample cylinder. in this way it was possible to validate the subsequent numerical calculations used to estimate the in situ chemical conditions. a detailed description of the sampling procedure as well as documentation for the consistency of the collected dataset was published by kjøller & zuta (2012). batch modelling with phreeqc-3 the modelling was performed at the same conditions – pressure and temperature of 17.24 mpa (2500 psig) and 75°c as the experiments, in order to estimate the true in situ reservoir condition chemistry. three equilibrium steps in a closed system were investigated: (1) equilibrium between co2 and seawater corresponding to the injected solution, (2) equilibrium between co2-saturated seawater and calcite, representing reservoir conditions, and (3) composition of the solution after de-pressurisation in the secondary sample cylinder. a good fit between experimental and numerical data after step table 1. petrophyscial properties of plugs prior to the injection of co2-saturated water at 17.24 mpa (2500 psig) and 75°c 17a 32.60 26.94 1.36 19a 30.60 25.59 1.49 porosity pore volume permeability plug id (%) (ml) (md) table 2. composition (in mg/l) of synthetic formation water (fw), seawater (sw), and co2-saturated seawater (csw) na 22866 11090 11090 k 175 408 408 mg 226 1370 1370 ca 1244 434 434 sr 142 6.8 6.8 cl– 38383 20173 20173 hco3 – 22 30 70 so4 2– – 2780 2780 ions (fw) (sw) (csw) 0 0.033 0.067 0.100 0.133 0.167 0.200 0.233 4 4.5 5 5.5 6 6.5 7 7.5 0 5 10 15 20 25 c o 2 p re ss ur e (m pa ) ph pore volume ph plug 17a ph plug 19a co2 pressure plug 17a co2 pressure plug 19a fig. 2. measured ph and co2 pressure for plug 17a and parallel plug 19a versus cumulative, injected pore volume. ph 3.2 4.8 6.3 ca (mg/l) 438 1970 1970 alkalinity, hco3 – (mg/l) 82 3274 3308 saturation index (calcite) –3.78 0 1.43 chemical parameter step 1 step 2 step 3 table 3. composition of resulting solutions at the two different equilibrium steps followed by the de-pressurisation step based on calculations with phreeqc.dat database in phreeqc-3 29 3 is considered as a validation of the numerical estimate of reservoir conditions in step 2 (kjøller & zuta 2012). results figures 2–4 show ph, co2 pressure, ca, and hco3– concentrations measured as a function of injected cumulative pore volumes. the compositions of the resulting solutions calculated at the three steps with phreeqc-3 are shown in table 3. equilibrium of co2 and seawater results in an initial co2-saturated seawater solution with a ph of 3.2 and a saturation index of calcite of –3.78 (table 3, step 1), an indication of a strong dissolution potential for chalk. thus, co2 is dissolved and reacts with water to form carbonic acid (h2co3). it is part of this acidity that is removed as the dissolution process advances into the plugs. the dissolution of calcium carbonate in the plugs takes place according to the overall chemical reaction: during the injection of seawater within the first 3.5 pore volume, the ph increases to between 7.5 and 7.7 and subsequently decreases to an average of 6.1 during the injection of co2-saturated seawater (fig. 2). at the final stage of the experiment, the ph increases again to the initial seawater ph level, an indication that all the residual co2 was removed from the plugs during the injection of seawater in equilibrium with chalk. the calculated decrease in ph at reservoir conditions (table 3, step 2) corresponds with the measured decrease in ph after 3.5 pore volume, where breakthrough of the co2-saturated seawater is observed. however, the calculated reservoir condition ph of 4.8 is much lower than the average measured ph during the injection of co2-saturated seawater. this was expected since the ph was measured after the de-pressurisation step where co2 gas had already degassed from the solution. thus, taking the ph (6.3) of the degassed solution into account in the numerical simulation provides an excellent fit to the average measured ph of 6.1 (table 3, step 3). the co2 pressure in the secondary sample cylinder varied between 0.17 mpa (25 psig) and 0.24 mpa (35 psig) at the de-pressurisation stage during the injection of co2-saturated seawater (fig. 2). this matches with the calculated co2 pressure of 0.20 mpa (28.9 psig) in the gas phase of the secondary sample cylinder (table 4), and further validates the numerical calculations. according to the equation, degassing of co2 from the water samples, caused by the transfer of water samples from the primary sample loop to the secondary sample cylinder, was expected to result in precipitation of caco3. comparison of ca and hco3– concentrations measured in both filtered and unfiltered water samples showed no evidence of mobilisation or precipitation of fine particles during the de-pressurisation stage, neither in plug 17a nor in plug 19a (fig. 3a, b). the ca concentration decreases during the first 3.5 pore volume to the ca-concentration level in seawater h co caco ca 2hco2 3 3 2 3+ +" + table 4. properties of the gas phase generated after the de-pressurisation stage in the 125 ml secondary sample cylinder with the phreeqc.dat database in phreeqc-3 total pressure 2.00 mpa (28.9 psig) gas volume 1.25e-001 litres molar volume 1.38e+001 litres/mole p×vm/rt 0.99228 (compressibility factor z) 0 500 1000 1500 2000 2500 3000 3500 0 500 1000 1500 2000 2500 0 5 10 15 20 25 h c o 3– c on ce nt ra tio n (m g/ l) c a co nc en tr at io n (m g/ l) pore volume ca filt ca ca sw ca fw hco3 – filt hco3 – a fig. 3. measured ca and hco3– concentrations for filtered and unfiltered water samples in plugs 17a (a) and 19a (b) versus cumulative, injected pore volume. filt: filtered. sw: synthetic seawater. fw: synthetic formation water. 0 500 1000 1500 2000 2500 3000 3500 0 500 1000 1500 2000 2500 0 5 10 15 20 25 c a co nc en tr at io n (m g/ l) ca filt ca ca sw ca fw hco3 – filt hco3 – h c o 3– c on ce nt ra tio n (m g/ l) pore volume b 3030 of c. 450 mg/l. subsequently, the measured ca concentration increases to an average of 1200–1300 mg/l during the injection of co2-saturated seawater, which is due to dissolution of calcium carbonate in the plugs. at the final steps of the experiment, the ca concentration again decreases to the seawater level during injection of seawater to remove residual co2 from the plugs. in the geochemical model, the calculated ca concentration of 1970 mg/l at reservoir conditions (table 3, step 2) is simulated by dissolution of calcite at reservoir conditions, and does not take into account the possible precipitation of calcium carbonate during sampling. therefore, the calculated reservoir-condition ca concentration is higher than the concentrations measured in the experiments during the period with co2-saturated seawater flooding. since no mobilisation or deposition of suspended fine particles in the water samples were observed, the difference in ca concentration must be attributed to deposition of fine calcium carbonate particles on the inner surface walls of the secondary sample cylinder during the pressure-reduction stages. in line with this, the simulated saturation index (si) with respect to calcite of 1.43 after de-pressurisation (table 3, step 3) is higher than the saturation indices between 0.6 and 1.2 that can be calculated based on the measured water chemistry. if the saturation index with respect to calcite is constrained to be between 0.6 and 1.2 in the numerical calculations in step 3, the calculated ca concentration at the sampling conditions varies between c.1150–1650 mg/l, which is in much better agreement with the actually measured ca concentrations (fig. 3). similar considerations and conclusions can be made for the hco3– -concentration trend during the experiment. thus, the measured hco3– concentration averages 2350–2550 mg/l during the injection of co2 saturated seawater, while the calculated hco3– concentration after de-pressurisation is 3308 mg/l when no constraints on the saturation index with respect to calcite are applied (table 3, step 3). however, accounting for some calcium carbonate precipitation during de-pressurisation will diminish the difference between calculated and measured concentrations, and overall it is suggested that the calculated reservoir condition concentrations shown in table 3, step 2 represent the true in situ reservoir conditions prevailing in the plugs during experiments. the general decrease in measured ca and hco3– concentrations during the injection of co2-saturated seawater from 3.5 to 15 pore volume (fig. 3), suggests that, with time, there is an increasing amount of calcium carbonate precipitating in the secondary sample cylinder during sampling. for future studies, this gradual change in calcium carbonate precipitation should be avoided in order to minimise the uncertainty in the measured data, and thereby also the uncertainty of the numerical estimate of the reservoir condition chemistry (table 3, step 2). conclusions • a new sampling technique was developed and used to study co2-brine–rock interactions in reservoir chalk at reservoir conditions. • the similar results obtained in the parallel plugs validate the sampling procedure and show a high degree of reproducibility. • the results from the experiment and the modeling show increased levels of calcium and alkalinity (hco3–) with decreasing ph during the injection of co2-saturated water at reservoir conditions. there were, however, differences between the measured and calculated calcium concentration and hco3– concentration which is probably due to accumulation of fine calcium carbonate particles on the inner walls of the secondary sample cylinder during the de-pressurisation stage. • further refinement of the method may include modification of the secondary sample cylinder, in order to minimise the accumulation of fine calcium carbonate particles on its inner surface walls. acknowledgements we are grateful to dansk undergrunds consortium (duc) – a co-operation between a.p. møller maersk, shell, chevron and nordsøfonden (the danish north sea fund) – for sponsoring the work. references bachu, s. & adams, j.j. 2003: sequestration of co2 in geological media in response to climate change: capacity of deep saline aquifers to sequester co2 in solution. energ y conversion and management 44, 3151–3175. kjøller, c. & zuta, j. 2012: co2-brine–rock interactions in reservoir chalk rock – a coupled experimental and numerical approach for obtaining hydrochemical results at reservoir conditions. paper sca201204 presented at international symposium of the society of core analysts, aberdeen, scotland, uk, 27–30 august, 2012, 12 pp. parkhurst, d.l. & appelo, c.a.j. 2013: description of input and examples for phr eeqc version 3 – a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations. u.s. geological survey techniques and methods, http:// pubs.usgs.gov/tm/06/a43/. authors’ address: geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: clkj@geus.dk geological survey of denmark and greenland bulletin 33, 2015, 69-72 69 automatic weather stations for basic and applied glaciological research michele citterio, dirk van as, andreas p. ahlstrøm, morten l. andersen, signe b. andersen, jason e. box, charalampos charalampidis, william t. colgan, robert s. fausto, søren nielsen and martin veicherts since the early 1980s, the geological survey of denmark and greenland (geus) glaciology group has developed automatic weather stations (awss) and operated them on the greenland ice sheet and on local glaciers to support glaciological research and monitoring projects (e.g. olesen & braithwaite 1989; ahlstrøm et al. 2008). geus has also operated awss in connection with consultancy services in relation to mining and hydropower pre-feasibility studies (colgan et al. 2015). over the years, the design of the aws has evolved, partly due to technological advances and partly due to lessons learned in the fi eld. at the same time, we have kept the initial goal in focus: long-term, year-round accurate recording of ice ablation, snow depth and the physical parameters that determine the energy budget of glacierised surfaces. geus has an extensive record operating awss in the harsh arctic environment of the diverse ablation areas of the greenland ice sheet, glaciers and ice caps (fig. 1). th e current geus-type aws (fig. 2) records meteorological, surface and sub-surface variables, including accumulation and ablation, as well as for example ice velocity. a large part of the data is transmitted by satellite near real-time to support ongoing applications, fi eld activities and the planning of maintenance visits. th e data have been essential for assessing the impact of climate change on land ice. th e data are also crucial for calibration and validation of satellite-based observations and climate models (van as et al. 2014). th e current version of the geus aws was developed in 2007 (sensors and tripod) and in 2008 (data logger, satellite data telemetry and power management) coinciding with the establishment of the programme for the monitoring of the greenland ice sheet (promice; ahlstrøm et al. 2008) and the glaciobasis programme monitoring an ice cap in a.p. olsen land in north-east greenland (apo; fig. 1). in con© 2015 geus. geological survey of denmark and greenland bulletin 33, 69–72 . open access: www.geus.dk/publications/bull 22 50 stations on the ice sheet stations on local glaciers discontinued stations 250 km 225 0 3000 2750 2500 100 0 150 0 175 0 20 00 2 5 0 0 2 2 5 0 1 7 5 0 1 5 0 0 1 2 5 0 200 0 apo qas nuk kan mal thu upe kpc sco mit tas har nhf nas ime ami paq ste jdl fig. 1. sites monitored by the geological survey of denmark and greenland with automatic weather stations. the currently active sites on the greenland ice sheet (red dots) consist of transects with two or three stations at different elevations. qas: qassimiut (2000–). nuk: qamanaarsuup sermia, nuuk (1979–1989, 2008–). k an: kangerlussuaq (2008–). upe: upernavik (2008–). thu: tuto ramp, thule (2008–). kpc: kronprins christian land (1993–1994, 2008–). sco: violin gletscher near scoresby sund (2008–). tas: tasiilaq (2004–). currently active sites on local glaciers (blue dots), with one to three aws per site are apo: ice cap in a.p. olsen land (2008–). mal: malmbjerg (2008–). mit: mittivakkat glacier (1995–). sites where geus had automatic weather stations in the past (black dots), some of which in cooperation with the former greenland technical organisation: jdl: nordbogletscher, johan dahl land (1977–1983). ami amitsuloq ice cap (1981–1990). paq: pakitsoq (1984–1987). nas: narsap sermia (2003–2006). iso: isortuarsuup tasia (1984–1987). nhf: nioghalvfjerdsfjorden (1996–1997). har: hare gletscher (1994–1995). ste: steenstrup gletscher (2004–2008). ime: imersuaq (1999–2002). sts: storstrømmen (1989–1994). 7070 nection with consulting work, the fi rst aws with the new design (mal; fig. 1) was installed in 2008 for quadra mining ltd., vancouver, canada (now kghm international ltd., lubin, poland) near the malmbjerg molybdenum occurrence in stauning alper, central east greenland (citterio et al. 2009), followed in 2008 and 2009 by three more stations on the ice sheet in the kangerlussuaq region (kan, fig. 1). th ese stations are part of the greenland analogue project (gap; van as et al. 2012) for skb, the swedish nuclear fuel and waste management company (stockholm, sweden) and posiva oy (olkiluoto, eurajoki, finland). th e geus aws model in use now is a reliable tool that is adapted to the environmental and logistical conditions of polar regions. it has a proven record of more than 150 stationyears of deployment in greenland since its introduction in 2007–2008, and a success rate of c. 90% defi ned as the fraction of months with more than 80% valid air-temperature measurements over the total deployment time of the 25 stations in the fi eld. th e rest of this paper focuses on the technical aspects of the geus aws, and provides an overview of its design and capabilities. station requirements th e geus aws is the fundamental component of a monitoring network which can include numerous stations, a satellite data link, and a receiving database where telemetry data are decoded and validated before further analysis and dissemination. th e cost-eff ective aws delivers timely researchquality data year-round from glacier ablation areas in remote locations. th e aws must therefore require little maintenance, with a target of maximum one visit per year. power generation and battery capacity must be suffi cient to operate through the polar night. data quality must be assured by accurate measurement techniques including aspiration of radiation shields and tilt correction of (shortwave) radiometer measurements. th e mechanical construction of the station must keep the sensors at a constant height above the ice surface, which can ablate more than 9 m of ice per year in south greenland (van as et al. 2011), and the station must be able to survive burial in snow in the winter months. timeliness of data availability and the assessment of station health demand satellite data telemetry both in summer and winter. to our knowledge, no other commercially available aws satisfi es all these requirements. sensors, data logger and telemetry th e geus aws can be fi tted with any sensor, but the standard aws measures air temperature and humidity, wind speed and direction, atmospheric pressure, downward and refl ected solar shortwave radiation, downward and upward longwave radiation, subsurface (ice) temperatures, snow depth, ice ablation, gps position, as well as diagnostic parameters such as battery voltage and ventilator power consumption, and 2-axes station tilt necessary for correcting shortwave radiation measurements. table 1 lists sensor types, their measurement heights and uncertainty as specifi ed by the manufacturers. th e geus aws is designed to minimise measurement errors where possible, for instance by actively aspirating the radiation shield inside which air-temperature and humidity sensors are located. successful error detection and management increases with user experience and specialist knowledge. two of the sensors listed in table 1 are designed and manufactured in-house at geus for use on ice: the 8-levels thermistor string and the pressure transducer assembly (pta) that measure ice ablation (fausto et al. 2012). th e pta works by relating decrease of bottom hydraulic pressure (corrected for atmospheric pressure), measured inside an antifreeze-mixture fi lled hose drilled into the ice, to surface a cb d 10 9 8 7 11 25 6 14 3 12 fig. 2. standard sensor suite of the automatic weather station on arcturus gletscher at the malmbjerg molybdenum prospect. a: the main instrument boom. b: the tripod and the sites of the thermistor string and pressure-transducer assembly drilled into the ice. c: the sonic rangerstake frame drilled into the ice. d: the inside of the data logger enclosure. the numbers refer to the list in table 1. 71 lowering due to ice ablation. both the pta and the thermistor string can easily be interfaced to most data loggers. all analog and digital sensors are connected to a campbell cr1000 data logger housed in a watertight enclosure together with a campbell am16/32a analog multiplexer and supporting circuitry. th e logger is programmed to record in 10-minute cycles throughout the year. th e only exception is the gps, which is not needed at such a high rate and is activated less frequently in order to economise power. th e campbell cr1000 data logger is an established platform that is widely used in polar climates both in the arctic and in antarctica (lazzara et al. 2012). th e multiplexer is confi gured to support half-bridge measurement of thermistors from up to four 8-level thermistor strings (only one is normally used), in addition to 32 single-ended or 16 diff erential analog measurements (only six of each type are normally used), providing large fl exibility for customised sensor suites. th e main local data storage is a removable fl ashcard rated for operation over extended temperature ranges. for reference, a 256 mb card will log in excess of 7 years of 10-minute records. to provide redundancy of data storage, the internal logger memory is confi gured to store 1-hour average records and can hold in excess of one year of data as a backup for the fl ashcard. data can be retrieved during on-site maintenance by swapping the fl ashcard or downloading its content to a laptop. th e robustness of the system is illustrated in fig. 3 by an uninterrupted 2008–2015 time series from the apo_m station in north-east greenland, the fi rst aws built entirely according to the current geus design. aft er seven years in the fi eld, this station still employs the original electronics, telemetry, battery and tripod hardware although sensors have been periodically replaced according to a scheduled recalibration plan. satellite data telemetry can transmit up to 340 bytes per message through the iridium short burst of data (sbd) service. th e program running on the cr1000 data logger implements a full soft ware handshake with the transmitter to ensure that a satellite is in view and that data are correctly transferred from the logger to the transmitter and the iridium satellite. if no acknowledgement of successful transmission is received from the satellite, the data logger will retry the transmission once, or queue the unsent message for delivery at a later time, depending on iridium service availability. th is mode of operation ensures a low rate of message loss and relatively low power consumption by avoiding unnecessary transmission attempts. th e stations binary-encode data before transmission, reducing data transmission costs by about 2/3. further transmission costs can be saved by transmitting the less transient variables at longer intervals. power th e long polar night and low temperatures exert a strong infl uence on the aws design. th e aws operates on solar power and rechargeable sealed lead-acid batteries for a nomi fig. 3. an example of 10-minute observations of air temperatures from 2008 to 2015 from the apo_m station on an ice cap in a.p. olsen land in north-east greenland. table 1. current sensors used on a standard geus automatic weather station parameter and sensor height manufacturer, type and sensor accuracy the numbers refer to fig. 2 where the positions of the sensors on an automatic weather station are shown.the heights of the sensors above the surface are indicative. the accurate heights are measured before and after every maintenance visit. 1. air temperature and relative rotronic mp102h with pt100 and hc2-s3 probe (±0.1 k, ± 0.8% rh, at humidity, 2.7 m 23°c ± 5 k), housed in a rs12t aspirated shield 2. radiation (downward and reflected solar shortwave, kipp & zonen cnr1 (uncertainty in daily totals < 10%) or cnr4 downward and upward longwave; 2.9 m) (uncertainty in daily totals < 5% shortwave, < 10% longwave) 3. wind speed and direction, 3.1 m r.m. young 05103-5 (± 0.3 ms–1 or 1%, ± 3°, non-riming conditions) 4. snow depth campbell scientific sr50 or sr50a (± 1 cm or 0.4%) 5. 2-axes radiometer tilt hl planar ns-25/e2 in geus assembly (± 0.2°) 6. iridium satellite antenna iridium at1621-142 quad-helix 7. iridium sbd modem u-blox neo module 7. iridium sbd modem nal research sbd-9601 or sbd-9602 8. atmospheric pressure setra model 278 (± 2.5 hpa, at −40 to 60°c) 9. ice ablation and snow depth campbell scientific sr50 or sr50a (± 1 cm or 0.4%) 10. subsurface temperature profile geus thermistor string with 8 rs components thermistors 151-243 (± 0.2°c, at 0°c) 11. ice ablation geus pta with ørum & jensen elektronik nt1400 or nt1700 (± 2.5 cm) 12. gps antenna trimble p/n 56237-40 active ceramic patch 29 july 2010 29 july 2012 29 july 2014 10 0 −10 −20 −30t e m p e ra u re ( °c ) 29 july 2008 7272 nal total of 112 ah at 12 v. th e power system is composed of the main unregulated 12 v power rail permanently supplying the data logger directly from the batteries, two 12 v unregulated rails controlled by soft ware through two external solid-state switches, and one switched 5 v regulated rail under direct data logger control. th is arrangement allows independent powering up of the radiation shield aspirator fan, the gps and satellite transmitter, the 5 v loads of the sonic rangers, temperature and humidity sensors, tilt meter and multiplexer. a single 10 w solar panel is wired to the main 12 v rail through a power schottky diode to prevent that the solar panel drains the battery during the winter months, and to eliminate the need for a charge regulator, which occasionally failed in previous aws designs. a soft ware-controlled low-power mode is activated when battery voltage under load falls below a confi gurable threshold (set to 11.5 v), which is never reached in normal circumstances. in low-power mode, operation continues almost as normal, but the most power-demanding functions (aspiration fan, satellite telemetry and gps) are deactivated. th e low-power mode is exited once solar charging brings the battery suffi ciently above the voltage threshold. th e soft ware can be confi gured for polar day and night operation, for instance to reduce data transmission rates during winter. th e typical monthly power requirements of a geus aws as confi gured for promice is 17 ah in summer, 11 ah in winter and 1.3 ah in low-power mode. tripod and sonic ranger frame th e tripod is constructed from 1˝ and 1.5˝ aluminium tubes with steel wires connecting legs and mast in a tetrahedral structure for a stable free-fl oating tripod. most of the sensors are fi xed to a horizontal boom at c. 2.9 m above surface. th e battery box, which weighs c. 50 kg, is suspended under the mast to improve station stability by increasing the aws mass and lowering the centre of gravity. th e tripod can be folded and transported in a small helicopter. during maintenance visits, which normally take 3–4 hours and include replacements of sensors due for recalibration, re-drilling of sensors and occasional repairs, the tripod can be easily tilted so that it does not have to be disassembled. th e sonic ranger frame is also built from 1˝ aluminium tubes, and its three vertical legs are drilled into the ice a few metres away from the aws tripod. concluding remarks th e geus aws has been developed, produced and deployed operationally by geus, and supplied to partners within denmark and abroad. it is a proven solution for a wide range of basic and applied glaciological research in arctic and alpine settings and is available through research collaborations or commercial sale. th e standard design can accommodate signifi cant expansion of the sensor suite. th e geus aws is readily available and supported as a stand-alone or as a component of wider services including fi eld deployment, maintenance, training and data management and analysis. acknowledgements we thank ole b. olesen, carl e. bøggild, wim boot, peer jørgensen, and other people who were instrumental in the technical development of the geus aws over the years. the promice and glaciobasis monitoring programmes are funded by the danish energ y agency (ens). references ahlstrøm, a.p. and the promice project team 2008: a new programme for monitoring the mass loss of the greenland ice sheet. geological survey of denmark and greenland bulletin 15, 61–64. citterio, m., mottram, r., larsen, s.h. & ahlstrøm, a.p. 2009: glaciological investigations at the malmbjerg mining prospect, central east greenland. geological survey of denmark and greenland bulletin 17, 73–76. colgan, w., thomsen, h.h. & citterio, m. 2015: unique applied glaciolog y challenges of proglacial mining. geological survey of denmark and greenland bulletin 33, 61–64. fausto, r.s., van as, d., ahlstrøm, a.p. & citterio, m. 2012: assessing the accuracy of greenland ice sheet ice ablation measurements by pressure transducers. journal of glaciolog y 58, 1144–1150. lazzara, m.a., weidner, g.a., keller, l.m., thom, j.e. & cassano, j.j. 2012: antarctic automatic weather station program: 30 years of polar observation. bulletin of the american meteorological society 93, 1519–1537. olesen, o.b. & braithwaite, r.j. 1989: field stations for glacier-climate research, west greenland. in: oerlemans, j. (ed.): glacier f luctuations and climatic change, 207–218. dordrecht: kluwer academic publishers. van as, d., fausto, r.s. & the promice project team 2011: programme for monitoring of the greenland ice sheet (promice): first temperature and ablation records. geological survey of denmark and greenland bulletin 23, 73–76. van as, d., hubbard, a.l., hasholt, b., mikkelsen, a.b., van den broeke, m.r. & fausto, r.s. 2012: large surface meltwater discharge from the kangerlussuaq sector of the greenland ice sheet during the recordwarm year 2010 explained by detailed energ y balance observations. the cryosphere 6, 199–209. van as, d. et al. 2014: increasing meltwater discharge from the nuuk region of the greenland ice sheet and implications for mass balance (1960–2012). journal of glaciolog y 60, 314–322 authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: mcit@geus.dk geological survey of denmark and greenland bulletin 42, 2018, 133-147 133 burial and exhumation history of the jameson land basin, east greenland, estimated from thermo chronological data from the blokelv-1 core paul f. green and peter japsen apatite fission-track analysis (afta) data in two upper jurassic core samples from the 231 m deep blokelv-1 borehole, jameson land, east greenland, combined with vitrinite reflectance data and regional afta data, define three palaeo-thermal episodes. we interpret localised early eocene (55– 50 ma) palaeotemperatures as representing localised early eocene heating related to intrusive activity whereas we interpret late eocene (40–35 ma) and late miocene (c. 10 ma) palaeotemperatures as representing deeper burial followed by successive episodes of exhumation. for a palaeogeothermal gradient of 30°c/km and likely palaeo-surface temperatures, the late eocene palaeotemperatures require that the upper jurassic marine section in the borehole was buried below a 2750 m thick cover of upper jurassic – eocene rocks prior to the onset of late eocene exhumation. as these sediments are now near outcrop at c. 200 m above sea level, they have been uplifted by at least 3 km since maximum burial during post-rift thermal subsidence. the results are consistent with estimates of rock uplift on milne land since the late eocene and with interpretation of ocean drilling program (odp) data off south-east greenland suggesting that mid-cenozoic uplift of the margin triggered the marked influx of coarse clastic turbidites during the late oligocene above a middle eocene to upper oligocene hiatus. keywords: east greenland, jameson land, upper jurassic, apatite fission-track analysis, burial, exhumation ___________________________________________________________________________ p.f.g., geotrack international, 37 melville road, brunswick west, victoria 3055, australia. e-mail: mail@geotrack.com.au p.j., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark with sedimentary basins offshore east greenland yet to be drilled, the onshore jameson land basin (surlyk 2003) provides a window into the nature of potential jurassic source-rock sequences in offshore basins. understanding the thermal history and maturity development in the onshore sequences can therefore provide unique insights into the prospectivity of the offshore basins. the jameson land basin has itself been the focus of hydrocarbon exploration by a group of concessionaries with atlantic richfield (arco) as operator, but in 1990 the group decided not to continue exploration (christiansen et al. 1992; mathiesen et al. 2000). one of the main geological risks that arco critically assessed was the thermal maturity of their main target, the upper permian carbonates, since earlier studies had concluded that tertiary exhumation had removed up to 3 km of cretaceous sediments and paleocene–eocene volcanic rocks across the basin (christiansen et al. 1992). currently, greenland gas and oil a/s and nunaoil a/s hold a hydrocarbon exploration and exploitation licence across much of the jameson land basin (www.govmin.gl). presented here is a thermal history study of samples obtained from the core from the blokelv-1 borehole, drilled by geus in 2008 to provide detailed information about the upper jurassic stratigraphy and petroleum system of the jameson land basin (fig. 1). geus suc© geus, 2018. geological survey of denmark and greenland bulletin 42 , 133–147. available at: www.geus.dk/bulletin42 mailto:mail@geotrack.com.au http://www.govmin.gl http://www.geus.dk/bulletin42 134134 cessfully drilled and cored the blokelv-1 borehole in the central part of the basin (ground level 200 m above sea level; a.s.l.), targeting the upper jurassic prolific sourcerock interval of the hareelv formation (bjerager et al. 2018a, this volume). the 231 m thick, marine succession cored in the blokelv-1 borehole covers the middle oxfordian to lower volgian interval. the core has 100% recovery, and it consists of interlayered organic-rich, laminated mudstones, massive sandstones and heterolithic sandstone–mudstone intervals of the katedralen member and massive sandstones of the sjællandselv member of the hareelv formation. the recovered core is of very high quality and has been subject to an extensive sampling and analytical programme designed to investigate aspects of the petroleum geolog y of the jameson land basin and published in nine papers (ineson & bojesenkoefoed (eds) 2018, this volume). the dataset provides an excellent reference for kimmeridge clay formationequivalent deposits in the north atlantic area. at first glance, the relatively low-lying landscape of the jameson land basin is in sharp contrast to the high terrains of the volcanic province along blosseville kyst to the south of scoresby sund, where elevations reach 3.7 km a.s.l. this might initially suggest that jameson fig. 1. a: simplified geology of the jameson land basin and adjacent areas showing the location of the blokelv-1 borehole (modified after surlyk 2003); inset shows the location of the study area in east greenland. bk: blosseville kyst. k: kangerlussuaq. b: stratigraphic column of the blokelv-1 borehole showing the stratigraphic level of the two samples used in this study (1, gc1052-1; 2, gc1052-2). log modified from bjerager et al. 2018a, this volume). litho: lithostratigraphic subdivision. chrono: chronostratigraphic subdivision. sj. mb: sjællandselv member. td: total depth. b c c' 74°n 76°n milne land profile in f ig. 6 s c o r e s b y s u n d 25 km22°w24°w26°w 20°wliverpool land a b permian carboniferous pre-carboniferous fault sandstone mudstone igneous intrusion gc1052 sample blokelv-1 71°n 72°n palaeogene volcanics triassic cretaceous jurassicice k bk j a m e s o n l a n d chrono.litho. volgian o xf or di an m id dl e up pe r lo w er up pe r k im m er id gi an u pp er ju ra ss ic h ar ee lv f or m at io n k at ed ra le n m em be r sj. mb depth (m) 50 1 2 100 150 200 233.8 td pj 1 135 land has undergone a less complex post-jurassic history of uplift and erosion compared to regions to the south. however, thermochronological data from the jurassic sediments of the jameson land basin presented here (see also mathiesen et al. 2000; hansen et al. 2001) provide evidence of post-jurassic burial and exhumation that is surprisingly similar to the region around kangerlussuaq, to the south (larsen & saunders 1998; brooks 2011; bonow et al. 2014; japsen et al. 2014). thermal history interpretation afta data two sandstone core samples from the lower and upper levels of the blokelv-1 borehole (fig. 1b) were processed for apatite fission-track analysis (afta), and both samples gave excellent apatite yields. apatite fission track ages of 50.4 ± 6.2 ma and 38.5 ± 4.0 ma in the two samples are much less than the depositional age of the sampled units; at depths of less than 250 m (and present-day temperatures less than 20°c), this degree of age reduction immediately shows that the sampled units have been much hotter in the past. mean track lengths of 12.25 ± 0.22 µm and 11.71 ± 0.23 µm also demonstrate that these samples have been hotter in the past, prior to cooling to present-day temperatures. full details of the afta data are provided in appendix 1. quantitative thermal history constraints have been extracted from the data using principles outlined by green & duddy (2012) and green et al. (2013), with results summarised in table 1. afta data from both samples provided highly reliable thermal history constraints. thermal history interpretation of afta data the afta data in sample gc1052-1 can be explained in terms of two palaeo-thermal episodes, as detailed in table 1. in contrast, the afta data in sample gc10522 require three palaeo-thermal episodes to explain all aspects of the data, although the precise timing of the earliest episode cannot be defined with confidence. this is because the palaeotemperature of 100–110°c in the second episode produced almost total annealing of all tracks formed up to that time, largely masking the previous history. on the basis of evidence discussed below, we table 1. palaeotemperature analysis summary: afta and vr data from the blokelv-1 borehole sample mean present stratigraphic vr** maximum onset maximum onset number depth temperature* age (%) palaeotemp.+ of cooling+ palaeotemp.+ of cooling+ gc1052(m below kb) (°c) (ma) (°c) (ma) (°c) (ma) 1 6 5 159–146 100–105 58–28 70–80 17–5 23.59 159–146 0.52 86 32.78 159–146 0.54 90 68.77 159–146 0.50 83 80.77 159–146 0.55 91 92.74 159–146 0.56 93 104.79 159–146 116.82 159–146 0.56 96 152.75 159–146 0.61 100 164.82 159–146 0.68 113 176.77 159–146 0.62 102 188.77 159–146 0.65 108 200.76 159–146 0.66 109 212.77 159–146 0.78 125 2 219 12 159–146 >110 55–50? 100–110 50–28 80–85 13–3 224.74 159–146 0.74 121 combined timing (ma): 55–50 13–5 50–28 * present temperature estimates based on an assumed surface temperature of 4°c, and an assumed thermal gradient of 30°c/km. ** from bojesen-koefoed et al. (2018). + thermal history interpretation of afta data is based on an assumed heating rate of 1°c/myr and a cooling rate of 10°c/myr. quoted ranges for palaeotemperature and onset of cooling correspond to ±95% confidence limits. conditions shown in italics represent events that cannot be rigorously defined from the afta data. pj table 1 136136 infer that the earlier event in which this sample cooled below 110°c was related to igneous activity in the region (larsen 2018, this volume), in the interval 55 to 50 ma. timing constraints derived from afta data in each sample are listed in table 1, and in table 2 these constraints are compared with the timing of three cenozoic cooling episodes defined from afta data in two previous studies of the east greenland margin: (a) a study of the region north of the jameson land basin (thomson et al. 1999) and (b) a study in the kangerlussuaq region to the south of jameson land ( japsen et al. 2014). the similarity in timing of the late eocene and the late miocene cooling episodes defined in this study and in the previous studies suggests that each represents a regional, synchronous cooling episode across the entire region, and by combining all constraints we arrive at our preferred timing of the onset of cooling in these events, between 40 and 35 ma and ~10 ma (table 2). in addition to the episodes shown in fig. 2, japsen et al. (2014) also defined late oligocene and early miocene palaeo-thermal episodes in the region around kangerlussuaq, but these are restricted to that region and do not extend to the jameson land basin, so are not considered here. we interpret the three events illustrated in fig. 2 (from table 2) in the following way: 55–50 ma event. the timing of the early eocene (55–50 ma) event overlaps with that of intensive palaeogene intrusive activity and correlates with the age of c. 53 ma for dykes and sills in the jameson land basin (hald & tegner 2000; larsen 2018, this volume). palaeotemperatures associated with this event are 100°c or above and are identified sporadically around the region ( japsen et al. 2014). on this basis, the palaeotemperatures characterising this episode are interpreted to be due either to contact or hydrothermal effects associated with igneous activity. no convincing evidence for any regional paleocene to mid-eocene cooling (related to exhumation) has been identified for samples in the area around jameson land (thomson et al. 1999; japsen et al. 2014), and the geological history recorded south of jameson land indicates that subsidence and burial dominated at the palaeocene–eocene transition (brooks 2011; bonow et al. 2014). 40–35 ma event. late eocene cooling beginning between 40 and 35 ma was interpreted largely in terms of regional uplift resulting in kilometre-scale exhumation by both japsen et al. (2014) in the kangerlussuaq region and thomson et al. (1999) in the region to the north of jameson land. japsen et al. (2014) interpreted the endresult of this phase of exhumation to have been a regional peneplain, the upper planation surface (ups) of bonow et al. (2014). the presence of late eocene intrusive bodies around traill ø (price et al. 1997) suggests the possibility locally of a significantly elevated basal heat flow in this region at this time. 10 ma event. late miocene cooling beginning at c. 10 ma was again detected by both japsen et al. (2014) in afta data 55–50 50–28 13–5 blokelv samples gc1052-1, -2 afta data (study a) 40–30 10–5 afta data (study b) * 40–35 ~10 age of intrusion (study c) ~53** (55–51) preferred regional timing 55–50 40–35 ~10 (early eocene) (late eocene) (late miocene) dominant mechanism of cooling cooling after intrusive heating exhumation exhumation table 2. intervals defining the beginning of episodes of cooling from afta data onset of cooling (ma) study a. 11 outcrop samples from northern east greenland, north of the jameson land basin, 72–74°n (thomson et al. 1999). study b. 90 samples from outcrops and drillholes in a regional study of southern east greenland focussed between 68 and 70°n (japsen et al. 2014). study c. analysis of the igneous intrusions in the blokelv cored borehole (larsen 2018, this volume). *japsen et al. (2014) related an event of cooling with overlapping timing (55–50 ma) in southern east greenland to the emplacement of the kangerlussuaq intrusion. **the blokelv sills are tholeiitic basalts considered to belong to the main group of dykes and sills in the jameson land basin which has been dated at ~53 ma. the intrusions form part of a 55–51 ma group of tholeiitic basalt intrusions that were emplaced within the sedimentary basins in east greenland (larsen 2018, this volume). pj table 2 137 the kangerlussuaq region and thomson et al. (1999) to the north of jameson land. in both cases cooling was interpreted in terms of regional uplift resulting in kilometre-scale exhumation. outcrop samples at low elevations around kangerlussuaq cooled from peak palaeotemperatures around 60–70°c at this time. japsen et al. (2014) interpreted these values to represent burial below the ups that defines the present-day surface of elevated summits along the blosseville kyst. table 2 illustrates a high degree of consistency between the timing of cooling identified in this study and the dominant regional episodes identified by thomson et al. (1999) and japsen et al. (2014). on this basis, the results from sample gc1052-1 are interpreted as representing the two most recent episodes (i.e. late eocene and late miocene), while these two episodes as well as the early eocene episode are recognised in sample gc1052-2. thermal history interpretation of vitrinite reflectance data results of vitrinite reflectance (vr) analyses are plotted against depth below surface in fig. 3, together with equivalent vr (vr eq ) values derived from rock-eval t max values (bojesen-koefoed et al. 2018, this volume). also shown are the ranges of equivalent vr values (vr eq ) derived from afta data in samples gc1052-1 and -2 (defined by the maximum paleotemperature in each sample), together with the vr profile predicted on the basis 0 0255075100125 time (ma) 150175200225250 50 100 150 200 250 d ep th (m ) q gc1052-1 stratigraphic age regional cooling episodes: regional constraints on the onset of cooling palaeothermal constraints from afta sample triassic jurassic cretaceous cenozoic gc1052-2 55–50 ma 40–35 ma ~10 ma pj 2 fig. 2. timing constraints on cooling episodes derived from afta data in two samples from the blokelv-1 borehole (horizontal bars) plotted against depth. the regional constraints on the onset of cooling in three palaeo-thermal episodes (vertical bars) are based on afta data in the blokelv samples and in regional studies (table 2). q: quaternary. fig. 3. maturity indicators in samples from the blokelv-1 borehole plotted against depth; vr values (table 1) together with equivalent vr values (vreq) derived from rock-eval tmax data and equivalent ranges of vr defined from the afta data. note that the orange arrow for the deeper sample indicates that the constraints on maturity from the afta data only provide a lower limit. the solid sub-vertical line shows the profile predicted from the “default thermal history”, i.e., the history calculated from the assumption that all units throughout the well are currently at their maximum temperatures since deposition. the horizontal lines indicate the position of thin basaltic sills intruded into the hareelv formation (note the maturity effects close to these intrusions). 0 20 40 60 80 120 140 160 180 200 220 240 100 0.2 0.3 0.4 0.5 0.7 1.0 2.0 gc1052-2 gc1052-1 d ep th (m ) default history maturity (%ro) u pp er ju ra ss ic sill sill sill measured vr values (bojesen-koefoed et al. 2018, this volume) equivalent vr from afta equivalent vr from tmax afta sample horizon pj 3 138138 of the default thermal history (i.e. the history expected if the section has never been any hotter than it is today). both vr and vr eq data plot well above the profile predicted by the default thermal history, confirming the evidence from afta that the sampled units have been hotter than their present-day temperatures at some time since deposition. mean vr values tend to be slightly lower than the vr eq values derived from the t max data throughout the section. in general, t max values tend to be sensitive to a range of factors and are not used quantitatively to provide estimates of maximum palaeotemperature in the way that vr data are. note that the t max data define local contact effects due to the three recognised intrusions, which the vr values do not show. maximum palaeotemperatures derived from the vr values (based on burnham & sweeney 1989) are listed in table 2, and show a progressive downhole increase from 86°c to 125°c through the section intersected in the borehole. this apparent increase of c. 40°c over a depth interval of c. 200 m is equivalent to a thermal gradient of 200°c/km, which is well outside the range of typical sedimentary basin thermal gradients (allen & allen 2013). integration of results from afta with the vr data resolves this apparent anomaly, as explained below. integration of afta and vr data, palaeotemperature profiles and mechanisms of heating and cooling palaeotemperature constraints from afta and the measured vr values are plotted against depth in fig. 4. maximum palaeotemperatures derived from vr values at depths between 20 m and 120 m are c. 10–20°c lower than the late eocene palaeotemperature range of 100–105°c indicated by afta data in sample gc10521 at similar depths. in contrast, maximum palaeotemperatures of c. 125°c derived from the two deepest vr values at depths of 210–225 m are higher than the late eocene palaeotemperatures derived from afta in sample gc1052-2 at a similar depth. they are, however, consistent with the early eocene palaeotemperature defined from afta data in this sample. furthermore, as illustrated in fig. 4, maximum palaeotemperatures derived from vr values between 150 m and 200 m are consistent with the trend of the late eocene palaeotemperatures derived from afta in samples gc1052-1 and -2. we interpret the mismatch at shallow depths between vr values and the late eocene palaeotemperature range from afta in sample gc1052-1 as due to suppression of reflectance levels at these depths. suppression is commonly observed in upper jurassic organic-rich mudstones of the north atlantic region (wilkins et al. 1992; newman 1997). bjerager et al. (2018b, this volume) and bojesen-koefoed et al. (2018, this volume) provided detailed discussions of the differences between the organic material above and below c. 100 m in the cored interval. they showed that at shallow depths, amorphous marine 0 20 40 60 80 100 120 140 160 180 200 220 240 260 temperature (°c) 0 50 100 150 200 250 d ep th (m ) afta sample horizon (with sample number) maximum palaeotemperature from vr estimates of maximum post-depositional palaeotemperatures from afta sill sill sill u pp er ju ra ss ic gc1052-2 gc1052-1 local heating? 30°c/km30°c/km low due to suppression of vr? thermal gradient (°c/km) 100 80 60 40 20 pj 4 fig. 4. interpreted palaeotemperature profiles describing the palaeotemperatures in two episodes derived from afta and vr data in the blokelv-1 borehole. based on evidence from regional studies of east greenland (table 2), we interpret the early eocene (55–50 ma) maximum palaeotemperature (green arrow) revealed by afta data in sample gc1052-2 to represent localised heating due to intrusive activity. the late eocene (40–35 ma) and late miocene (c. 10 ma) palaeotemperatures (red and blue horizontal bars, respectively) revealed by afta are interpreted to represent the effects of burial, with late eocene cooling representing the onset of regional, post-jurassic exhumation, and late miocene cooling representing the final phase of exhumation. it is thus inferred that the vr values recorded above 120 m in the borehole (yellow datapoints) are anomalously low due to suppression of ref lectance in the sourcerock facies (organic-rich mudstones) (wilkins et al. 1992; newman 1997). we regard the vr values below 120 m (red datapoints) as reliable indications of the degree of post-depositional heating. linear profiles (red and blue lines) represent our preferred interpretation (based on regional data) involving palaeogeothermal gradients of ~30°c for the late eocene and miocene episodes. 139 organic material dominate whereas an increased content of terrigenous organic material occurs at depth. as illustrated in fig. 4, maximum palaeotemperatures from vr data at depths between c. 150 m and 200 m, together with late eocene palaeotemperatures derived from afta in samples gc1052-1 and -2 define a linear profile characterised by a palaeogeothermal gradient around 30°c/km. late miocene palaeotemperatures defined from afta in the two samples are also consistent with a similar palaeogeothermal gradient. this gradient contrasts markedly with the apparent gradient of c. 200°c/ km defined by the vr data (see above), and is more typical of heating related to deeper burial. accepting this interpretation, units throughout the borehole underwent a major phase of cooling in the late eocene (beginning between 40 and 35 ma), followed by a later phase of cooling in the late miocene (c. 10 ma). most units cooled from maximum post-depositional palaeotemperatures in the late eocene event but locally some horizons reached higher palaeotemperatures in the early eocene, presumably reflecting the effects of intrusive bodies. this interpretation is consistent with the results reported from the kangerlussuaq region to the south by japsen et al. (2014), who regarded the late miocene and late eocene cooling episodes as representing successive episodes of exhumation, while early eocene events were interpreted as local effects associated with igneous intrusions. thermal history synthesis on the basis of the discussion presented above, we interpret the palaeotemperature constraints derived from afta and vr data in the blokelv-1 borehole as representing the combined effects of deeper burial followed by successive episodes of exhumation in the late eocene and miocene, as well as localised early eocene heating due either to contact heating or hydrothermal effects associated with intrusive activity. the results provided here are highly consistent with regional data and the interpretation presented here is regarded as reliable. thermal history reconstruction here we present reconstructed thermal and burial-uplift histories for the upper jurassic section intersected in the blokelv-1 borehole (fig. 5) based on the results presented above. it should be emphasised that while the preferred reconstruction illustrated here provides a satisfactory explanation of the afta and vr data from this well, the reconstruction is not unique. therefore, it is important to appreciate those aspects of the histories that are constrained by the data, and those that are not. factors that can be confidently defined in this study (within the limits of analytical uncertainty) include: (a) magnitude of heating at the palaeothermal maximum and the subsequent palaeo thermal peaks and (b) timing of the onset of cooling in each episode. factors that can be defined when samples are available over a sufficiently large range of depths or elevations, but cannot be constrained in this study include: (a) palaeogeothermal gradients during each episode and (b) additional burial during each episode for a specified value of palaeogeothermal gradient. aspects which cannot be uniquely defined in any situation include: (a) thermal history prior to the palaeo-thermal maximum and/or the subsequent palaeo-thermal peak, (b) amounts of re-burial between multiple episodes within a single unconformity and (c) detailed style of cooling history from each episode. figure 5a illustrates a possible thermal history reconstruction for the sedimentary units intersected in the blokelv-1 borehole, based on the synthesis developed above. key aspects of this reconstruction are: • surface temperature of 20°c at 30 ma and earlier, decreasing to 10°c at 10 ma and to a present-day value of 4°c over the last 12 myr. • palaeogeothermal gradient of 30°c/km, constant to the present day. • localised heating within the vicinity of sample gc1052-2 to a palaeotemperature around 120°c, shown at c. 53 ma but any time between 56 and 45 ma is allowed by the regional timing constraints on this episode. • an additional 2750 m of section deposited above the upper jurassic section intersected in the borehole, between 146 and 35 ma (resulting in heating of sample gc1052-1 to c. 100°c prior to late eocene cooling and exhumation). • subsequent removal of 1150 m (arbitrary) of section between 35 and 30 ma, followed by deposition of a further 600 m (arbitrary) of section between 30 and 10 ma. • removal of the remaining 2200 m of additional section between 10 ma and the present day. note that the amount of re-burial between the two episodes of exhumation cannot be controlled by the data, 140140 and therefore also the amount of section removed in the initial episode beginning at 35 ma is also not constrained. this reconstruction is considered to provide a reliable depiction of the post-depositional history of the upper jurassic section intersected in the blokelv-1 borehole. note that in this reconstruction, for the purposes of illustration, the localised heating around sample gc1052-2 at c. 53 ma is shown as taking place over a duration of 2 myr, as is the subsequent cooling. however, in reality heating and cooling would have been much more rapid, and for that reason the true maximum palaeotemperatures would have been much higher. comparison with previous studies magnitude of exhumation christiansen et al. (1992) presented the results of a first study of the exhumation of the jameson land basin. they based their estimate on a range of observations including thermal maturity parameters, apatite fissiontrack parameters, porosity and seismic velocities; in particular they reported vr values up to 0.6% for organicrich permian and jurassic formations at outcrop. they interpreted their data to indicate that between 1.5 and 3 km of overburden had been removed across the basin, 0 20 40 60 80 100 160 140 120 100 80 time (ma) 60 40 20 0 120 te m pe ra tu re (º c ) possible reconstruction j k pa pe o m gc1052-1 gc1052-2 ? possible reconstruction j k pa pe o m 0 2000 1500 1000 500 2500 3000 bu ri al d ep th (m ) 160 140 120 100 80 time (ma) 60 40 20 0 regional constraints on the onset of cooling palaeothermal constraints from afta in sample gc1052-1 palaeothermal constraints from afta in sample gc1052-2 thermal histories for the two sample horizons approximate burial depths during late eocene and late miocene palaeothermal peaks ? a b pj 5 fig. 5. schematic illustration of the preferred thermal (a) and burial (b) history reconstruction for the section intersected in the blokelv-1 borehole based on the afta and vr data. j: jurassic. k: cretaceous. pa: palaeocene. e: eocene. o: oligocene. m: miocene. p: pliocene. a: comparison of palaeothermal constraints from afta in two samples (red and blue boxes) with thermal histories of the corresponding sample horizons (red and blue curves). the vertical columns show the preferred timing of three dominant palaeothermal episodes identified in the region (fig. 2; table 2). black line at the top of the diagram defines the assumed palaeosurface temperature. b: burial and exhumation history corresponding to a; the blue boxes show the approximate depth of burial during the late eocene and late miocene palaeothermal peaks. note that no convincing evidence for regional paleocene to mid-eocene exhumation has been identified for samples in the area around jameson land (thomson et al. 1999; japsen et al. 2014). 141 and that the lost cover likely consisted of more than 1 km of cretaceous sediments as well as 1–2 km of palaeogene basalts (primarily across the southern part of the basin). mathiesen et al. (2000) investigated the denudation history of the jameson land basin using basin modelling constrained by apatite fission-track data. they concluded that the upper jurassic sediments that are exposed at the present day across jameson land were buried below a 2–3 km thick rock column: (1) a cretaceous succession that varied from 1.3 km in the south to 0.3 km in the north; (2) a wedge of palaeogene volcanics with a thickness of >2 km in the south thinning to <0.1 km in the north. according to their calculations, the erosion happened in response to tectonic uplift of c. 1 km. the magnitude of the section removed at the location of the blokelv-1 borehole defined in this study (c. 2.8 km) thus agrees well with that estimated by mathiesen et al. (2000) (removal of 2 –3 km of section across jameson land). hansen et al. (2001) studied the late mesozoic – cenozoic thermal history of the jameson land basin constrained by apatite and zircon fission-track data of permian to jurassic sedimentary rocks at outcrop. these authors interpreted their results in terms of regional thermal evolution related to burial leading to temperatures close to and in excess of the maximum temperatures of the apatite annealing interval (c. 125°c) followed by cooling mainly due to cenozoic uplift and erosion. furthermore, basaltic dyke and sill intrusions were found locally to cause resetting of apatite fission-track ages. these results are thus broadly in agreement with the conclusions presented here. our estimate of the magnitude of the section removed above the blokelv-1 borehole (c. 2.8 km) agrees well with the results of bonow et al. (2014) and japsen et al. (2014) in their studies of the area between milne land and kangerlussuaq (68–71°n) based on integration of evidence from stratigraphic landscape analysis, thermochronolog y and the stratigraphic record (fig. 6). these authors argued that the present-day high elevation in east greenland is the result of three tectonic phases of uplift and erosion during the cenozoic that followed the eruption of voluminous flood basalts onto a largely horizontal lava plain near sea level at the paleocene– eocene transition (larsen & saunders 1998; brooks 2011; bonow et al. 2014), viz: 1. the late eocene (c. 35 ma) phase of uplift and erosion led to formation of an oligo–miocene erosion surface (peneplain) near sea level, the upper planation surface (ups). 2. uplift of this surface in the late miocene (c. 10 ma) led to formation of a lower surface (the lower planation surface, lps) by incision below the uplifted ups. 3. an early pliocene uplift phase (c. 5 ma) led to incision of valleys and fjords below the lps, resulting in mountain peaks reaching 3.7 km a.s.l. today, remnants of the ups are preserved west of jameson land near the summits of milne land at c. 2 km a.s.l. bonow et al. (2014) estimated the magnitude of rock uplift at milne land to be c. 2.7 km based on larsen et al.’s (1989) investigation of zeolite isograds (levels of equal thermal alteration; see also neuhoff et al. 1997), and on their argument that the absence of the shallow and less altered zeolite zones may be explained by the removal of these zones by erosion. for milne land, they concluded that a section of about 900 m had been removed above the basalt flows that cover the summits there (assuming a palaeogeothermal gradient of 40°c at the time of zeolite formation). bonow et al. (2014) then assumed that the palaeo-surface during the formation of the zeolites was near sea level (shortly after the eruption of the volcanics 3 milne land land surface prior to onset of late eocene denudation relative to present-day sea level removed section present-day land area w e jameson land ? liverpool land 25 km blokelv borehole 2 el ev at io n (k m a .s. l.) 1 0 pj 6 fig. 6. present-day elevation profile with indication of the section removed since late eocene maximum burial. based on bonow et al. (2014) and japsen et al. (2014). for location of profile, see fig. 1. 142142 at the paleocene–eocene transition at a time of regional subsidence; brooks 2011). consequently, the basalts, now at c. 1800 m a.s.l., have been uplifted 2700 m (i.e. 1800 + 900 m) since the formation of the zeolites in the eocene. japsen et al. (2014) found that the ups that defines the summits of milne land at c. 2 km a.s.l. represents the remnants of the oligo-miocene peneplain that was formed by erosion to sea level after late eocene uplift and erosion, and that this peneplain was uplifted to its present elevation during uplift that began in the late miocene. assuming that the lost cover of 900 m (estimated from zeolite isograds) had been removed after late eocene maximum burial, the magnitude of rock uplift was about 2.9 km since the late eocene. these estimates of the magnitude of rock uplift thus match those presented here because the upper jurassic marine sediments at outcrop (now at c. 200 m a.s.l.) at the blokelv-1 location have been uplifted by a minimum of 3.0 km since their maximum burial below a (now lost) cover of c. 2.8 km in the late eocene. timing of burial and exhumation with no way of determining the timing of the onset of exhumation, christiansen et al. (1992) and mathiesen et al. (2000) assumed that the exhumation of the jameson land basin accelerated after the palaeogene volcanic eruptions. the present study, however, clearly shows that the onset of exhumation was in the late eocene (c. 35 ma) and documents that the exhumation process took place in at least two stages. these results thus imply that the section of rocks removed across jameson land not only included volcanic rocks extruded at the paleocene– eocene transition (as assumed by mathiesen et al. 2000) but also a sedimentary cover deposited during the 20 myr that followed the volcanic eruptions till the onset of exhumation in the late eocene. the geological record from the area south of jameson land confirms the timing of the cenozoic events of burial and exhumation presented here. the area between scoresby sund and kangerlussuaq subsided after continental breakup at 56 ma. this is documented by the igtertivâ formation which immediately overlies the main basalts of larsen et al. (1989, 2013) and includes volcanic flows interdigitated with marine sediments. the volcanic pile of the main basalts is up to 6 km thick and was erupted in less than 1 myr (pedersen et al. 1997). subsidence continued during deposition of the fluvial to shallow-marine kap dalton group (early to mid lutetian), which interfingers with and overlies the igtertivâ formation in a downfaulted block at kap dalton (larsen et al. 1989, 2005, 2013). results from odp site 918, off se greenland (leg 152, c. 63°n) show that major uplift of the margin occurred long after continental break-up. larsen et al. (1994) reported that the marine, lower eocene sediments drilled there indicated low sedimentation rates with limited terrigenous influx before a middle eocene to upper oligocene hiatus. larsen et al. (1994) thus argued that mid-cenozoic uplift of the inner margin triggered the sudden, voluminous influx of coarse clastic turbidites at this odp site during the late oligocene. uplift phases in the late miocene and in the pliocene are consistent with the late miocene, early pliocene and middle pliocene ages of seismic sequence boundaries within the late neogene and quaternary deep-sea sedimentary succession off se greenland (clausen 1998). conclusions three palaeo-thermal episodes affected the upper jurassic sediments penetrated by the blokelv-1 borehole based on afta and vr data combined with regional afta data. these episodes are interpreted to be due to the following mechanisms: • early eocene (55–50 ma) palaeotemperatures represent localised early eocene heating related to intrusive activity. • late eocene (40–35 ma) palaeotemperatures represent deeper burial followed by exhumation. • late miocene (c. 10 ma) palaeotemperatures represent deeper burial followed by exhumation. the presence of two elevated planation surfaces in the region that were formed and uplifted after the volcanic eruptions supports the interpretation of the palaeothermal data in terms of episodic rather than monotonic cooling (bonow et al. 2014; japsen et al. 2014). the late eocene palaeotemperatures require that c. 2800 m of upper jurassic – eocene rocks covered the upper jurassic section in the borehole prior to the onset of late eocene exhumation, assuming a palaeogeothermal gradient of 30°c/km and likely palaeo-surface temperatures. this implies that maximum burial in the jameson land basin was achieved long after the rift climax in central east greenland at the jurassic–cretaceous tran143 sition (surlyk 2003) and after the volcanic eruptions that accompanied break-up in the north-east atlantic at the paleocene–eocene transition (pedersen et al. 1997). as the upper jurassic sediments at the location of the blokelv-1 borehole now crop out at c. 200 m a.s.l., they have been uplifted by at least 3 km since maximum burial during post-rift thermal subsidence. such a magnitude of rock uplift is comparable with estimates from milne land where a regional peneplain (the upper planation surface, ups) defines the summits at c. 2 km a.s.l. this surface was formed by erosion to sea level (after removal of a rock column of c. 900 m) following late eocene uplift and subsequently uplifted to its present elevation during uplift that began in the late miocene. consequently, the rock uplift on milne land was c. 2.9 km since the late eocene. rock uplift in the order of 3 km since the late eocene has thus affected a wide area, far beyond the boundaries of the jameson land basin. that strong uplift of the east greenland margin began at the eocene–oligocene transition is supported by interpretation of odp data off south-east greenland which suggest that uplift of the margin at this time triggered the marked influx of coarse clastic turbidites during the late oligocene above a middle eocene to upper oligocene hiatus. acknowledgements we acknowledge the pertinent and constructive comments of the referees, andrew carter and andrew g. whitham. jette halskov and stefan sølberg are thanked for graphical support. reference list allen, p.a. & allen, j.r. 2013: basin analysis: principles and application to petroleum play assessment, 632 pp. indianapolis: john wiley & sons. bjerager, m., bojesen-koefoed, j. & piasecki, s. 2018a: the upper jurassic blokelv-1 cored borehole in jameson land, east greenland – an introduction. in: ineson, j. & bojesen-koefoed, j.a. 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(eds): petroleum geolog y of the upper jurassic – lower cretaceous of east and north-east greenland: blokelv-1 borehole, jameson land basin. geological survey of denmark and greenland 42, 127–132 (this volume). larsen, l.m., pedersen, a.k., sørensen, e.v., watt, w.s. & duncan, r.a. 2013: stratigraphy and age of the eocene igtertivâ formation basalts, alkaline pebbles and sediments of the kap dalton group in the graben at kap dalton, east greenland. geological society of denmark bulletin 61, 1–18. larsen, l.m., watt, w.s. & watt, m. 1989: geolog y and petrolog y of the lower tertiary plateau basalts of the scoresby sund region, east greenland. grønlands geologiske undersøgelse bulletin 169. 164 pp. larsen, m., heilmann-clausen, c., piasecki, s. & stemmerik, l. 2005: at the edge of a new ocean: post-volcanic evolution of the palaeogene kap dalton group, east greenland. in: doré, a.g. & vining, b. 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(eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 659–722. thomson, k., green, p.f., whitham, a.g., price, s.p. & underhill, j.r. 1999: new constraints on the thermal history of north-east greenland from apatite fission-track analysis. geological society of america bulletin 111, 1054–1068. wilkins, r.w.t., wilmshurt, j.r., russel, n.j., hladky, g., ellacott, m.w. & buckingham, c. 1992: fluorescence alteration and the suppression of vitrinite reflectance. organic geochemistry 18, 629–640. _________________________________________________________________________________________ manuscript received 16 december 2015; revision accepted 8 february 2018 145 slide current ns ni na ρs ρi ratio u cl ft age ref grain no (ppm) (wt%) (ma) g1124-9 3 1 23 36 4.414e+04 1.015e+06 0.043 8.1 0.04 12.2 ± 12.4 g1124-9 6 14 51 24 9.270e+05 3.377e+06 0.275 27.0 0.03 76.4 ± 23.1 g1124-9 7 0 13 49 0.000e+00 4.216e+05 0.000 3.4 0.14 0.0 ± 36.1 g1124-9 10 29 129 30 1.536e+06 6.833e+06 0.225 54.7 0.01 62.6 ± 13.0 g1124-9 11 18 48 24 1.192e+06 3.178e+06 0.375 25.4 0.06 104.1 ± 28.9 g1124-9 12 6 35 60 1.589e+05 9.270e+05 0.171 7.4 0.05 47.8 ± 21.2 g1124-9 13 27 96 60 7.151e+05 2.543e+06 0.281 20.3 0.02 78.2 ± 17.2 g1124-9 14 6 53 42 2.270e+05 2.005e+06 0.113 16.0 0.03 31.6 ± 13.6 g1124-9 15 54 339 20 4.290e+06 2.693e+07 0.159 215.6 0.11 44.4 ± 6.6 g1124-9 16 4 33 35 1.816e+05 1.498e+06 0.121 12.0 0.00 33.8 ± 17.9 g1124-9 17 1 13 60 2.648e+04 3.443e+05 0.077 2.8 0.08 21.5 ± 22.3 g1124-9 18 9 110 42 3.405e+05 4.162e+06 0.082 33.3 0.03 22.9 ± 8.0 g1124-9 19 5 18 30 2.648e+05 9.534e+05 0.278 7.6 0.02 77.3 ± 39.1 g1124-9 20 19 49 80 3.774e+05 9.733e+05 0.388 7.8 0.02 107.6 ± 29.2 g1124-9 21 4 32 70 9.080e+04 7.264e+05 0.125 5.8 0.02 34.9 ± 18.5 g1124-9 22 31 234 80 6.158e+05 4.648e+06 0.132 37.2 0.03 37.0 ± 7.1 g1124-9 23 11 113 50 3.496e+05 3.591e+06 0.097 28.7 0.03 27.2 ± 8.6 g1124-9 25 4 27 50 1.271e+05 8.581e+05 0.148 6.9 0.02 41.3 ± 22.2 g1124-9 28 1 6 100 1.589e+04 9.534e+04 0.167 0.8 0.07 46.5 ± 50.2 g1124-9 32 25 93 50 7.945e+05 2.956e+06 0.269 23.7 0.21 74.8 ± 17.0 269 1515 4.309e+05 2.427e+06 19.4 for abbreviations, see page 147 area of basic unit = 6.293e+07 cm2 χ2 = 47.992 with 19 degrees of freedom p(χ2) = 0.0% age calculated using a zeta of 392.9 ± 7.4 for cn5 glass ρd = 1.424e+06 cm 2 nd = 2241 ρd interpolated between top of can; ρd = 1.388e+06 cm 2 nd = 1092 ρd interpolated between bottom of can; ρd = 1.461e+06 cm 2 nd = 1149 age dispersion = 38.770% ns / ni = 0.178 ± 0.012 mean ratio = 0.176 ± 0.024 pooled age = 49.5 ± 3.6 ma central age = 50.4 ± 6.2 ma 0 50 100 150 0.0 0.1 0.2 0 -2 +2 76 0 43 21 1.00 0.75 0.50 0.25 0.00 0.0 0.5 1.0 1.5 2.0 wt% cl wt% cl 30 20 10 0 0 5 10 15 20 track length (µm) n fr ac tio n fi ss io ntr ac k ag e (m a) ml: 12.25 µm std dev: 2.28 ft age: 50.4 ma stratigraphic age 107 200 0.25 radial plot of single grain ages* distribution of chlorine (cl) contents in apatite grains single grain age vs. weight % cl for individual apatite grains distribution of confined track lengths pj appendix sample 1 * see appendix b in geotrack report gc1052 (available online) for details of radial plot construction. colour datapoints indicate wt% cl: dark blue: <0.1%. green: 0.1-0.2%. pale blue: 0.2-0.3%. appendix 1: analytical details of the afta data sample gc1052-1: apatite this appendix documents the raw fission-track count data together with radial/compositional graphical plots. the location of the two samples (gc1052-1, gc1052-2) in the blokelv-1 core is indicated in fig. 1. 146146 slide current ns ni na ρs ρi ratio u cl ft age ref grain no (ppm) (wt%) (ma) g1124-10 3 15 84 50 4.767e+05 2.670e+06 0.179 21.3 0.23 49.9 ± 14.1 g1124-10 4 5 31 70 1.135e+05 7.037e+05 0.161 5.6 0.20 45.1 ± 21.8 g1124-10 10 7 56 50 2.225e+05 1.780e+06 0.125 14.2 0.01 35.0 ± 14.1 g1124-10 11 9 126 30 4.767e+05 6.674e+06 0.071 53.2 0.01 20.0 ± 6.9 g1124-10 12 3 63 28 1.703e+05 3.575e+06 0.048 28.5 0.02 13.4 ± 7.9 g1124-10 14 41 198 35 1.861e+06 8.990e+06 0.207 71.7 0.08 57.9 ± 10.1 g1124-10 15 14 94 36 6.180e+05 4.149e+06 0.149 33.1 0.01 41.7 ± 12.0 g1124-10 16 1 12 28 5.675e+04 6.810e+05 0.083 5.4 0.02 23.4 ± 24.3 g1124-10 17 9 48 48 2.980e+05 1.589e+06 0.188 12.7 0.10 52.4 ± 19.1 g1124-10 19 5 54 30 2.648e+05 2.860e+06 0.093 22.8 0.03 25.9 ± 12.1 g1124-10 21 16 152 40 6.356e+05 6.038e+06 0.105 48.2 0.04 29.5 ± 7.8 g1124-10 22 7 35 40 2.781e+05 1.390e+06 0.200 11.1 0.02 55.9 ± 23.2 g1124-10 23 5 54 40 1.986e+05 2.145e+06 0.093 17.1 0.14 25.9 ± 12.1 g1124-10 24 15 86 35 6.810e+05 3.905e+06 0.174 31.1 0.00 48.8 ± 13.7 g1124-10 25 10 57 42 3.783e+05 2.157e+06 0.175 17.2 0.00 49.1 ± 16.9 g1124-10 26 8 93 36 3.531e+05 4.105e+06 0.086 32.7 0.02 24.1 ± 8.9 g1124-10 29 7 101 70 1.589e+05 2.293e+06 0.069 18.3 0.00 19.4 ± 7.6 g1124-10 30 21 84 40 8.343e+05 3.337e+06 0.250 26.6 0.01 69.8 ± 17.1 g1124-10 33 0 7 40 0.000e+00 2.781e+05 0.000 2.2 0.02 0.0 ± 74.1 g1124-10 34 17 95 40 6.754e+05 3.774e+06 0.179 30.1 0.04 50.0 ± 13.3 215 1530 4.126e+05 2.936e+06 23.4 for abbreviations, see page 147 area of basic unit = 6.293e-07 cm2 χ2 = 32.061 with 19 degrees of freedom p(χ2) = 3.1% age calculated using a zeta of 392.9 ± 7.4 for cn5 glass ρd = 1.429e+06 cm 2 nd = 2241 ρd interpolated between top of can; ρd = 1.388e+06 cm 2 nd = 1092 ρd interpolated between bottom of can; ρd = 1.461e+06 cm 2 nd = 1149 age dispersion = 27.489% ns / ni = 0.141 ± 0.010 mean ratio = 0.132 ± 0.014 pooled age = 39.3 ± 3.1 ma central age = 38.5 ± 4.0 m sample gc1052-2: apatite 0 -2 +2 69 0 49 2713 1.00 0.75 0.50 0.25 0.00 0.0 0.5 1.0 1.5 2.0 wt% cl 40 30 20 10 0 0 5 10 15 20 track length (µm) pj appendix sample 2 n fr ac tio n ml: 11.71 µm std dev: 2.36 ft age: 38.5 ma 0.0 0.1 0.2 0.25 wt% cl fi ss io ntr ac k ag e (m a) radial plot of single grain ages* distribution of chlorine (cl) contents in apatite grains single grain age vs. weight % cl for individual apatite grains distribution of confined track lengths * see appendix b in geotrack report gc1052 (available online) for details of radial plot construction. colour datapoints indicate wt% cl: dark blue: <0.1%. green: 0.1-0.2%. pale blue: 0.2-0.3%. purple: >0.3%. stratigraphic age 0 50 100 150 200 147 table abbreviations na = number of grid squares counted in each grain ns = number of spontaneous tracks in na grid squares ni = number of induced tracks in na grid squares ratio = ns/ni u (ppm) = uranium content of each grain (= u content of standard glass × ρ i /ρ d ) cl (wt%) = weight percent chlorine content of each grain ρ s = spontaneous track density (ρs) = ns/ (na × area of basic unit) ρ i = induced track density (ρi) = ni/(na × area of basic unit) ft age = fission-track age, calculated using equation b.1 area of basic unit = area of one grid square chi squared = χ2 parameter, used to assess variation of single grain ages within the sample p(chi squared) = probability of obtaining observed χ 2 value for the relevant number of degrees of freedom, if all grains belong to a single population age dispersion = % variation in single grain ages ns/ni = pooled ratio, total spontaneous tracks divided by total induced tracks for all grains mean ratio = mean of (ns/ni) for individual grains zeta = calibration constant, determined empirically for each observer ρ d = track density (ρ d ) from uranium standard glass (interpolated from values at each end of stack) n d = total number of tracks counted for determining ρ d pooled age = fission track age calculated from pooled ratio n s /n i . valid only when p(χ2) >5% central age = alternative to pooled age when p(χ2) <5% geological survey of denmark and greenland bulletin 4, 2003, pp 25-28 25 in denmark the supply of drinking water is based almost solely on groundwater. during the past few decades danish groundwater monitoring has encountered numerous instances of pollution with pesticides and their metabolites (geus 2003a). as a result, some hundreds of abstraction wells out of about 8000 in general water supply have been closed. with this background, there is a particular concern for reducing the leaching of pesticides into the groundwater. in the present study an approach for identification of areas potentially prone to pesticide leaching is described. the potential risk of leaching of pesticides from agricultural areas into groundwater is minimised through a procedure of approval; however, some leaching still occurs (geus 2003b). the danish counties are therefore obliged to identify areas where there is a particular risk of pesticide leaching, and where restrictions in use of pesticides may be introduced to reduce the risk (miljøstyrelsen 2000). the geological survey of denmark and greenland (geus) and the danish institute of agricultural sciences (djf) have carried out a project, focusing on sandy agricultural areas, that attempts to establish the necessary background knowledge for identifying areas particularly prone to pesticide leaching. the project aims to distinguish vulnerable and less vulnerable areas, both locally and nationwide, in a cost-effective way. aim and approach the conditions under which pesticides leach from the ground surface into aquifers have been intensively investigated (e.g. flury 1996; worral et al. 2002). a general knowledge as to the circumstances and parameters that determine the fate of pesticides is thus already available. the objective of the project has been to establish a consistent set of data for danish conditions, which will allow spatial comparison of pesticide leaching vulnerability on the basis of parameters that are known, or suspected to, influence leaching. since mapping is the key to the identification of vulnerable areas, emphasis has been placed on generating a set of data based on soil parameters that can be easily and relatively inexpensively obtained. for this purpose field sites have been chosen within eight areas of western denmark (jutland) with different geological settings (fig. 1). for each site, measuring of geological and pedological profiles have been carried out and samples collected for analysis. to determine which areas are the most vulnerable to leaching, simulations have been carried out using the macro4.3 model (jarvis 2002). the relationships between soil hydraulic properties, pesticide sorption (sensu e.g. dubus et al. 2001) and disappearance (beulke & brown 2001), and the more readily obtainable soil parameters (here termed ‘inherent soil parameters’), have been investigated on the basis of data obtained from the field sites, pre-existing databases and the published literature. studies have aimed at determining the extent to which pesticides as a whole, or in characteristic groups, will leach under similar boundary conditions and reflect different combinations of inherent soil parameters. pesticide leaching in danish groundwater: identification of vulnerable areas erik nygaard, vibeke ernstsen, carsten s. jacobsen, ole h. jacobsen, rené k. juhler, peter van der keur, svend e. olesen, jim rasmussen, per rosenberg and henrik vosgerau fig. 1. location of the studied field sites in jutland, denmark. the soil types of the eight selected areas are also shown. geological survey of denmark and greenland bulletin 4, 25–28 (2004) © geus, 2004 26 simulations the study of vulnerability to leaching is focused on criteria that are robust with respect to climatic variation and land use. all the field sites chosen were on pig farms, with normal crop rotation, farm manure application, and the relevant pesticides were applied to the maximum permitted. the pesticides mcpa, metribuzin and glyphosat, and methyltriazinamin, a transformation product of tribenuronmethyl, have been studied in most detail. for glyphosat, sorption values and disappearance rates are so high that leaching could not be simulated. repeated model simulations (montecarlo type) for metribuzin indicated that leaching will occur at significant levels, while no leaching could be simulated for mcpa and methyltriazinamin (fig. 2). to illustrate the possible relationships, e.g. the hydraulic properties of the soil and the degree of leaching, eight different combinations of sorption and degradation properties of the topsoil and the lower soil were designed (fig. 3). these combinations represent a wide range in properties for which the occurrence of leaching can be simulated. such designed compounds are therefore suitable for further analysis. keeping the sorption and disappearance parameters constant, the influence of hydraulic properties on leaching can also be studied (see below). these simulations were undertaken for the sandy soil profiles stored in a djf nationwide database (fig. 2). the results indicate that maintaining the disappearance rate constant, the sorption properties of the topsoil will generally dictate the level of leaching (fig. 3). cross-plots of the simulation results for the designed compounds further indicate, by their good correlation, that irrespective of the combination of designed parameters, leaching will dominantly occur in the same soil profiles (fig. 4). fig. 2. normalised concentration of metribuzin at a depth of 1 m in all sandy soil profiles stored in a national database held at djf (one profile for every 50 km2). fig. 3. number of investigated profiles ranked according to potential for leaching of eight designed combinations of pesticides. the ranking array of profiles is different for the eight curves; see also fig. 4. correlation the input parameters for simulation (sorption, disappearance and hydraulic properties) are expensive to establish and therefore not viable for extensive or general mapping. consequently, using a correlation analysis, an attempt has been carried out in order to substitute these parameters by more readily available soil parameters. the key inherent soil parameters evaluated are soil grain size distribution, soil bulk density, organic carbon content, cation exchange capacity, ph, the content of oxalate and dithionit extractable iron and aluminium. indicators of biological activity have also been evaluated (arylsulphatase activity and substrate induced respiration). two methods of correlation analysis have been applied to study the possible correlation between inherent soil properties, hydraulic properties and pesticide specific parameters: neural network computing and multivariate data analysis. based on neural networking computing, soil water release curves have been estimated from hydraulic properties, and a satisfactory prediction of the soil-water release characteristics obtained (fig. 5). measured values of sorption and disappearance rate have been correlated with the key inherent soil parameters by multivariate data analysis (esbensen 2002). the sorption and disappearance values were predicted at the 85% level of variance for the investigated pesticides (fig. 6). the number of soil parameters required to obtain this correlation vary according to pesticide type. the content of organic carbon in the topsoil is generally the most important soil parameter, but other soil parameters such as ph and clay content were also important in some examples. grouping of pesticides extensive analyses have been carried out for a large group of pesticides at a few localities, in order to clarify whether the results with respect to the four intensely studied compounds can be applied to a broader group of pesticides. this has been investigated by correlation analysis between inherent soil properties and sorption for all the compounds. these investigations suggest that pesticides may be arbitrarily grouped in one or a few major groups, which have similar relationships to inherent soil parameters. the two compounds that do not correspond with the explanation (glyphosat and the metabolite 4 isopropyl aniline from isoproturon) are relatively strongly sorbing and degrading in sandy soils. 27 fig. 4. cross-plots of leaching of pairs of hypothetical pesticides in fig. 3. the plots illustrate the extent to which the hypothetical pesticides leak through the same profiles. a: low correspondence between profiles with the least leaking pesticides with high sorption in the topsoil and less in the lower soil. b: high correspondence between profiles with intermediate leaking pesticides with high sorption in the topsoil and none in the lower soil. c: high correspondence between profiles with the most leaking pesticides with low sorption in the topsoil and none in the lower soil. d: two families of relatively high correspondence, where one profile has high sorption and low disappearance in the topsoil, and the other has low sorption and high disappearance in the topsoil. fig. 5. measured versus neural-network predicted retention curves for three of the investigated soil types. 28 delineation in practice based on correlations of soil parameters and leaching, and grouping of pesticides, the values of soil and other parameters that may be useful for identifying soils where leaching may occur, have been investigated. knowing the rank of importance of the soil parameters, and possibly their critical values, criteria have been established for a two-phase approach in mapping. it is suggested that, initially, areas with little risk of leaching may be identified and delineated based on the few most descriptive soil parameters. these parameters can to some extent be obtained from existing geographical data, and the cost of establishing new data is relatively low. the remaining areas particularly prone to leaching can be mapped on the basis of soil parameters necessary for simulating and predicting the leaching of the pesticides. references beulke, s. & brown, c.d. 2001: evaluation of methods to derive pesticide degradation parameters for regulatory modelling. biology and fertility of soils 33(6), 558–564. dubus, i.g., barriuso, e. & calvet, r. 2001: sorption of weak organic acids in soils: clofencet, 2,4-d and salicylic acid. chemosphere 45,767–774. esbensen, k.h. 2002: multivariate data analysis in practice, 598 pp. oslo, norway: camo process as. flury, m. 1996: experimental evidence of transport of pesticides through field soils: a review. journal of environmental quality 25, 25–45. geus 2003a: grundvandsovervågning 2003, 110 pp. københavn, danmark: danmarks og grønlands geologiske undersøgelse. geus 2003b: the danish pesticide leaching assessment programme, monitoring results, may 1999 to june 2002. third report, 123 pp. copenhagen, denmark: geological survey of denmark and greenland, danish institute of agricultural sciences, national environmental research institute. jarvis, n.j. 2002: the macro model (version 4.3). technical description. available at: http://www.mv.slu.se/bgf/ miljøstyrelsen 2000: zonering. vejledning 3, 156 pp. københavn, danmark: miljøstyrelsen. worral, f., besien, t. & koplin, d.w. 2002: groundwater vulnerability: interactions of chemicals and site properties. the science of the total environment 299, 131–143. fig. 6. measured versus model-predicted sorption (kf) for mcpa using multivariate data analysis. authors’ addresses e.n., v.e., c.s.j., r.k.j., p.v.d.k., j.r., p.r. & h.v., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: en@geus.dk o.h.j. & s.e.o., danish institute of agricultural sciences, blichers allé, postbox 50, 8830 tjele, denmark. << /ascii85encodepages false /allowtransparency false /autopositionepsfiles true /autorotatepages /all /binding /left /calgrayprofile (dot gain 20%) /calrgbprofile (srgb iec61966-2.1) /calcmykprofile (u.s. web coated \050swop\051 v2) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.4 /compressobjects /tags /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjdffile false /createjobticket false /defaultrenderingintent /default /detectblends true /colorconversionstrategy /leavecolorunchanged /dothumbnails 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<feff4f7f752890194e9b8a2d5b9a5efa7acb76840020005000440046002065874ef65305542b8f039ad876845f7150cf89e367905ea6ff0c4fbf65bc63d066075217537054c18cea3002005000440046002065874ef653ef4ee54f7f75280020004100630072006f0062006100740020548c002000520065006100640065007200200035002e0030002053ca66f465b07248672c4f86958b555f3002> >> >> setdistillerparams << /hwresolution [2400 2400] /pagesize [595.000 842.000] >> setpagedevice geological survey of denmark and greenland bulletin 28, 2013, 13-16 13 geology, seismic activity and groundwater conditions at six potential disposal sites for radioactive waste from risø, denmark peter gravesen, bertel nilsson, merete binderup, tine b. larsen and stig a. schack pedersen in 2003 it was decided by the danish parliament that low and intermediate-level radioactive waste from the danish nuclear research facility, risø, is to be stored at a permanent disposal site (ministeriet for sundhed og forebyggelse 2008; gravesen et al. 2012a). both the issue of storage and the selection of potential sites have caused considerable public debate. in this paper we report on the most recent geological investigations intended to further improve the data base for the selection and decision process, although no conclusions have been drawn at this stage. the waste might be deposited on the land surface, partly below surface or totally below surface, and pre-quaternary rocks and deposits are the main general targets. in 2011 six potential areas were selected for further studyd and evaluation of their suitability for disposal of radioactive waste. the study evaluated local groundwater conditions and earthquake hazards, infrastructure, wildlife, environment, water supply (especially drinking water) and heritage monuments (gravesen et al. 2011, 2012b). the new studies of the six potential sites and their surroundings were performed by the geological survey of denmark and greenland aided by the danish nature agency (naturstyrelsen), and included drilling of several new boreholes. geological setting the areas that were chosen for further study were selected from 22 initial targets (gravesen et al. 2011) based on compliance with specific criteria (see below) that had previously been established from geological models (gravesen et al. 2012a). the six selected areas (fig. 1) are located in different geological settings. the østermarie-paradisbakkerne area on bornholm consists of precambrian paradisbakke migmatite and bornholm gneiss. in the rødbyhavn area on lolland, palaeocene clay rests on maastrichtian chalk, while the kertinge mark area on fyn comprises thick palaeocene clay deposits overlying danian limestone. in the hvidbjerg area of north-west jylland, palaeocene and eocene clay forfig. 1. map of denmark showing the locations of the six areas selected for detailed studies of their suitability as disposal sites for radioactive waste from risø. © 2013 geus. geological survey of denmark and greenland bulletin 28, 13–16. open access: www.geus.dk/publications/bull kerkertinge mark rødbyhavn skive vest hvidbjerg tthise l o l l a n d f a l s t e r m ø n østermarieparadisbakkerne north sea skagerrak kattegat baltic sea fig. 2 b o r n h o l m s j æ l l a n d f y n j y l l a n d d e n m a r k g e r m a n y s w e d e n 50 km 55°n 10°e 57°n 14°e 1414 mations rest on danian limestone and are covered by oligocene and miocene clay formations. farther to the east and south-east, at thise and skive vest (west), oligocene and miocene clay, respectively, are present. quaternary clayey till overlies the pre-quaternary rocks and sediments at all sites. collection of seismic, borehole and groundwater data part of the new study consisted of an evaluation of earthquake potential. the seismic activity in denmark has been recorded instrumentally since 1929, and in later years by an interconnected network of seismic stations in denmark and surrounding countries. older earthquakes were examined from descriptions in the literature. for the three potential sites on bornholm, lolland and fyn available seismic data within a radius of 50 km were evaluated. for the three areas in north-west jylland a radius of 75 km was used. in the new study additional boreholes were drilled in each of the six selected areas. sediment samples were collected from each metre and analysed, and several types of continuous geophysical logs were performed in most boreholes. such logs are particularly useful for extrapolations between the samples. on bornholm, eight existing water abstraction wells for domestic use were logged for idenfication of fractures in the bedrock. evaluation of groundwater, drinking water and water supplies was based on new information and existing literature, as well as local knowledge of potential groundwater problems. the latter was obtained by interviewing local specialists and acquisition of written accounts and other information collected by the local authorities. survey results data from the borehole samples and from the geophysical logs have provided important new information on the geological models of the investigated areas, which comprise data on lithology and stratigraphy as well as tectonic and sedimentological structures. all the relevant information has been compiled into six technical reports by the geological survey of denmark and greenland, which are available at geus’ website, http://www.geus.dk/program-areas/natureenvironment/denmark/radioaktivt_ af fald/index-dk.htm. the main topics are: boreholes and logging, seismic activity and earthquakes, groundwater and drinking water, climate and climate changes and local planning (infrastucture, wildlife, environment, cultural heritage, raw materials, agriculture and water supply structure). all this information will be used in the ongoing evaluation of the areas and identification of the two most suitable areas. in this paper only selected results are presented, including geological traverses through the six areas. geological data the precambrian crystalline rocks on bornholm are thick and extensive and contain a network of fractures. knowledge of the fracture systems in the østermarie-paradisbakkerne area is important for evaluation of groundwater f low and storage, and for evaluation of the stability of the host rocks. horizontal and vertical fractures to a depth of 12 m can be observed in quarries. the number of horizontal fractures appears to decrease downwards, while their spacing increases. this is a normal observation in the uppermost crust. the geophysical borehole logs comprise natural gamma-ray, resistivity, sound velocity, f luid temperature, f luid conductivity and f low logs, which can be used to document fractures at various levels from 20 m below the surface down to a depth fig. 2. geological cross section through palaeogene–neogene deposits of the skive vest area, extending from rettrup in the west to skive in the east. the positions of the boreholes with dgu numbers are indicated along the top of the figure. west (rettrup) d ep th (m ) vejle fjord formation skive claybrej ning fo rmatio n 1 km +40 –30 0 –20 –10 +10 +20 +30 east (skive) 55.1068 .1072 .383 .311 .418 .657 .1228 .1069 .1022 .1229 .533 .503 .532 .152 .85 .180.114 .148a .1120 .507 .1119 palaeogene–neogene deposits clayey till meltwater sand http://www.geus.dk/program-areas/nature-environment/denmark/radioaktivt_affald/index-dk.htm http://www.geus.dk/program-areas/nature-environment/denmark/radioaktivt_affald/index-dk.htm 15 of 90 m. extrapolations of the borehole data suggest that some fractures are horizontal or subhorizontal and connected over larger distances. quaternary clayey and sandy tills on bornholm are mostly only a few metres thick. the pre-quaternary rocks and deposits throughout the remaining parts of denmark are fine-grained, have low permeability, and are covered by quaternary clayey tills. the clay deposits are generally relatively thick and appear to be of wide horizontal distribution within the selected areas, ref lecting the fact that the deposits represent marine depositional environments. furthermore, the deposits are characterised by low degrees of glaciotectonic disturbance and pre-quaternary tectonic movements. these characteristics meet the criteria described by gravesen et al. (2011, 2012a) based on the guidelines of the international atomic energy agency (iaea 1994). at rødbyhavn, palaeocene fine-grained deposits and plastic clay from the æbelø and holmehus formations resting on maastrichtian chalk have been documented from geophysical surveys and boreholes drilled for bentonite exploration and geotechnical purposes related to the femern bælt fixed link. the characteristics of the c. 80 m thick clay sequence and the overlying up to 40 m thick hard quaternary clayey till demonstrate that the deposits are in situ, although tectonic disturbances are known to exist outside the area. within and just outside the kertinge mark area, up to 75  m thick palaeocene kerteminde marl and æbelø formation overlying danian limestone have been documented. the new boreholes demonstrate that non-calcareous black clay of the æbelø formation occurs above calcareous grey clay of the kerteminde marl in the northern part of the kertinge mark peninsula, forming the natural stratigraphical sequence. quaternary clayey till up to 40 m thick is found above these formations. some layers are very sandy and gravelly as shown by samples from the boreholes and from geophysical logs. in the hvidbjerg area, palaeocene and eocene grey clay of the kerteminde marl and diatomite from the fur formation rest on danian limestone on the northern f lank of the uglev salt diapir. the formations are covered by oligocene and miocene black-brown mica clay deposits from the brejning and vejle fjord formations, with a total of up to 100 m thickness. thick quaternary clayey till comprises the top 20 m. the new borehole demonstrates a more complex buildup of the succession with unconformities caused by tectonic episodes and erosion. in the thise area, more than 100 m thick layers of oligocene mica clay from the brejning formation and green-grey, fine-grained clay from the branden clay unit are covered by up to 18 m thick quaternary clayey till. the new borehole penetrated 22 m of brejning formation below 19 m of quaternary clayey till. the oligocene deposits form an erosional inlier bordered by buried valleys filled with quaternary till and meltwater deposits. in the skive vest area, up to 100 m of oligocene and miocene deposits of fine-grained grey skive clay unit (to the east) and black-brown mica clay from the brejning and vejle fjord formations (to the west) are present; the layers dip slightly to the west (fig. 2). two new boreholes penetrated the two youngest formations down to 50 m below the surfig. 3. earthquake epicentres in the north-west jylland region. the magnitude on the richter scale is shown by the size of the dots (from gravesen et al. 2012b). other earthquake epicentres in the danish region are not shown on this map. magnitude 1 magnitude 2 magnitude 3 magnitude 4 no magnitude aalborg aarhus horsens d e n m a r k kristiansand 58˚n 57˚n 57˚n 56˚n 11˚e9˚e8˚e7˚e6˚e 9˚e 10˚e 11˚e north sea skagerrak kattegat 10˚e 1616 face, possibly indicating that the two formations are found in situ as also indicated by other borehole data in the area. a thin cover of quaternary clayey till is present. seismic activity and earthquakes the seismic activity in most of denmark is low, but a little higher in north-west jylland than in other parts of the country. the most seismically active region relevant for the current investigation is located in skagerrak and the north sea, while epicentres on land are rare (fig. 3). the earthquake magnitudes are low, with values mainly below 3 on the richter scale. no epicentres are found on bornholm, although some occur in the nearshore areas of the baltic sea. bornholm has not been seismically active in recent historical time, although an earthquake in 1875 possibly had its epicentre on west bornholm. small earthquakes in the baltic sea and southern sweden can sometimes be registered on bornholm. according to instrumental and historical sources, lolland does not seem to be seismically active, and the seismicity on fyn is very low. some minor earthquakes have been measured on fyn, but the historical literature does not suggest any earthquake activity. a slightly higher seismicity is found in north-west jylland around hvidbjerg, thise and skive vest, since many small earthquakes located in the north sea and skagerrak are registered on land. historical literature also suggests many small earthquakes around these three areas, and some damage to buildings has occurred. an earthquake in 1841 is probably the largest earthquake registered in denmark. groundwater conditions and drinking water all six areas are situated outside areas of special drinking water interests (osd), which are the most important danish supply areas for drinking water. major regional groundwater reservoirs are also absent, although some small reservoirs are important for local supplies. on bornholm the basement rocks form a fractured groundwater reservoir with restricted groundwater f low at various levels. the reservoir has a limited yield but is used locally in an area where connection to public water utilities is difficult and costly. the rødbyhavn area is almost totally devoid of groundwater reservoirs, although some surface water is extracted for drinking purposes. the kertinge mark area also lacks groundwater reservoirs, but local aquifers close to the surface are used for water supply. just south-east of this area, groundwater reservoirs in an osd area supply the town of kerteminde with drinking water. the reservoir is small and vulnerable because of its restricted size and thickness, and no alternative sources exist in the neighbourhood. in the hvidbjerg area, almost no goundwater is pumped because groundwater reservoirs are lacking. the thise area has some local abstraction from thin meltwater sand reservoirs. an area which is particularly vulnerable to nitrate contamination (nfi) occurs east of thise waterworks. just east and north of the area, osd areas with sand reservoirs are found in buried valleys. throughout the skive vest area, local water supplies use sand and gravel reservoirs; no public or private water utilities are found. final remarks the present investigations of the geology, earthquake risks, groundwater and drinking water conditions are crucial for the selection of two areas for further examination before a final disposal site can be chosen. before the selection of the two areas an environmental impact assessment (eia) has to be performed. also the possibilities of export of the waste to a foreign country have to be investigated. finally the design and establishment of a temporary disposal for the waste have to be described and evaluated. acknowledgement financial support was provided by the parliament of denmark. references gravesen, p., nilsson, b., pedersen, s.a.s. & binderup, m. 2011: lowand intermediate level radioactive waste from risø, denmark. location studies for potential disposal areas. report no. 11. områdebeskrivelser – description of areas. geological survey of denmark and greenland report 2011/51, 64 pp. gravesen, p., binderup, m., nilsson, b. & pedersen, s.a.s. 2012a: geological characterisation of potential disposal areas for radioactive waste from risø, denmark. geological survey of denmark and greenland bulletin 23, 21–24. gravesen, p., nilsson, b., binderup, m. larsen, t. & pedersen, s.a.s. 2012b: lavog mellem radioaktivt affald fra risø, danmark. omegnsstudier. rapport nr. 5. område thise, skive kommune. geological survey of denmark and greenland report 2012/127, 81 pp. iaea 1994: siting of near surface disposal facilities. safety guides. safety series 111-g-3.1, 37 pp. ministeriet for sundhed og forebyggelse 2008: beslutningsgrundlag for et dansk slutdepot for lavog mellemaktivt affald, 47 pp. københavn: ministeriet for sundhed og forebyggelse. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: pg@geus.dk mailto:es@geus.dk geological survey of denmark and greenland bulletin 28, 2013, 1-8 1 geological survey of denmark and greenland bulletin 28 • 2013 review of survey activities 2012 edited by ole bennike, adam a. garde and w. stuart watt geological survey of denmark and greenland ministry of climate, energy and building 22 geological survey of denmark and greenland bulletin 28 key words geological survey of denmark and greenland, survey organisations, current research, denmark, greenland. cover photographs from left to right 1. the 1097 m high finnefjeld is located in the central part of the maniitsoq impact structure, west greenland. photograph: adam a. garde. 2. investigation of a coastal cliff section at a potential disposal site for radioactive waste. photograph: merete binderup. 3. setting up an automatic camera to monitor frontal variations of a glacier in west greenland. photograph: robert fausto. 4. collecting samples in cameroon, using a hand auger. photograph: christian knudsen. frontispiece: facing page in 2012 geus published a geological map of the island of mors in north-west jylland. the map sheet comprises the coastal cliff section hanklit on northern mors, with exposures of light layers of moler and dark layers of volcanic ash, overlain by glaciof luvial deposits from the last ice age. the moler has been folded and up-thrusted by ice advancing from the north. photograph: stig a. schack pedersen. chief editor of this series: adam a. garde editorial board of this series: john a. korstgård, department of geoscience, aarhus university; minik rosing, geological museum, university of copenhagen; finn surlyk, department of geosciences and natural resource management, university of copenhagen scientific editors: ole bennike, adam a. garde and w. stuart watt editorial secretaries: jane holst and esben w. glendal referees (numbers refer to first page of reviewed article): holger lykke andersen (21); anonymous (37); luke b. bateson, uk (25); stefan bernstein, dk (45); albertas bitinas, lt (21); kristian bitsch, dk (33); dave burgess, ca (69); jakob qvortrup christensen, dk (13); gregers dam, dk (61); ole gravesen, dk (65); christoph a. hauzenberger, g (53); jens havskov, no (41); jens asger jensen, dk (33); maths halstensen, no (37); larry hulbert, ca (45); joakim stiel korshøj, dk (25); john korstgård, dk (65, 73); peter langen, dk (69); nicolaj krog larsen, dk (29); poul-henrik larsen, dk (61); björn lund, se (41); mogens marker, no (57); claudio milisenda, g (53); matthias moros, g (17); ole bjørslev nielsen, dk (9); asger ken pedersen, dk (49); anette petersen, dk (29); alar rosentau, ee (17); martin sønderholm, dk (9); inga sørensen, dk (13); henrik stendal, gl (49, 73); jeroen van gool, dk (57); thomas zack, se (73). illustrations: benny m. schark, jette halskov, stefan sølberg, kristian a. rasmussen, willy l. weng, frants v. platen-hallermund layout and graphic production: kristian a. rasmussen printers: rosendahls-schultz grafisk a/s, albertslund, denmark manuscripts received: 22 january 2013 – 14 march 2013 final versions approved: 15 february 2013 – 21 may 2013 printed: 10 july 2013 issn 1604-8156 isbn 978-87-7871-357-5 citation of the name of this series it is recommended that the name of this series is cited in full, viz. geological survey of denmark and greenland bulletin. if abbreviation of this volume is necessary, the following form is suggested: geol. surv. den. green. bull. 28, 76 pp. available from geological survey of denmark and greenland (geus) øster voldgade 10, dk-1350 copenhagen k, denmark phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: geus@geus.dk and at www.geus.dk/publications/bull © de nationale geologiske undersøgelser for danmark og grønland (geus), 2013 for the full text of the geus copyright clause, please refer to www.geus.dk/publications/bull 3 44 tanzania mozambique zambia indonesia vietnam china korea greenland philippines brazil denmark ghana nigeria cameroon 7 review of survey activities 2012 f.g. christiansen 9 drowning of the miocene billund delta, jylland: land–sea fluctuations during a global warming event e.s. rasmussen, t. utescher and k. dybkjær 13 geology, seismic activity and groundwater conditions at six potential disposal sites for radioactive waste from risø, denmark p. gravesen, b. nilsson, m. binderup, t.b. larsen and s.a.s. pedersen 17 a baltic ice lake lowstand of latest allerød age in the arkona basin, southern baltic sea o. bennike and j.b. jensen 21 late glacial to early holocene development of southern kattegat c. bendixen, j.b. jensen, o. bennike and l.o. boldreel 25 terrain subsidence detected by satellite radar scanning of the copenhagen area, denmark, and its relation to the tectonic framework p. r. jakobsen, u. wegmuller, r. capes and s.a.s. pedersen 29 geological map of denmark 1:50 000 – map sheet mors, nw denmark s.a.s. pedersen, p.r. jakobsen, l.tougaard and p. gravesen 33 assessing urban groundwater table response to climate change and increased stormwater infiltration m.t. randall, l. troldborg, j.c. refsgaard and j.b. kidmose 37 evaluation of total groundwater abstraction from public waterworks in denmark using principal component analysis b.l. sørensen and r.r. møller 41 seismic activity in denmark: detection level and recent felt earthquakes t. dahl-jensen, p.h. voss, t.b. larsen and s. gregersen 5 tanzania mozambique zambia indonesia vietnam china korea greenland philippines brazil denmark ghana nigeria cameroon geus working areas 2012. orange areas are covered in this volume. 45 the norite belt in the mesoarchaean maniitsoq structure, southern west greenland: conduit-type ni-cu mineralisation in impact-triggered, mantlederived intrusions? a.a. garde, j. pattison, t.f. kokfelt, i. mcdonald and k. secher 49 geochemistry and petrology of gold-bearing hydrothermal alteration zones on qilanngaarsuit, southern west greenland m. koppelberg, a. dziggel, d.m. schlatter, j. kolb and f.m. meyer 53 fingerprinting of corundum (ruby) from fiskenæsset, west greenland n. keulen and p. kalvig 57 lineament mapping and geological history of the kangerlussuaq region, southern west greenland k.e.s. klint, j. engström, a. parmenter, t. ruskeeniemi, l.c. liljedahl and a. lehtinen 61 calibration of spectral gamma-ray logs to deltaic sedimentary facies from the cretaceous atane formation, nuussuaq basin, west greenland g.k. pedersen, n.h. schovsbo and h. nøhr-hansen 65 a new seamless digital 1:500 000 scale geological map of greenland m. pedersen, w.l. weng, n. keulen and t.f. kokfelt 69 darkening of the greenland ice sheet due to the melt-albedo feedback observed at promice weather stations d. van as, r.s. fausto, w.t. colgan, j.e. box and the promice project team 73 titanium minerals in cameroon c. knudsen, j. penaye, m. mehlsen, r.k. mclimans and f. kalsbeek 66 7 review of survey activities 2012 flemming g. christiansen deputy director 2012 was a good and stable year for the geological survey of denmark and greenland (geus). in recent years geus has been through a long – and very constructive – process of establishing a new strategy that ref lects the changes in society and new demands from many different stakeholders. with a new strategy in place there has been greater focus on geus’ activities and research projects. 2012 was a very active year with many projects, field work and offshore data acquisition, which promises well for maintaining a high level of research in the coming years. with the establishment of the new series geological survey of denmark and greenland bulletin in 2003 it was decided to make a yearly review of survey activities. this issue is the tenth and, together with previous issues, provides a good overview of the survey’s wide range of research and advisory activities. this issue contains a total of 17 four-page papers, nine on denmark, seven on greenland and one on a project in cameroon. activities in denmark the activities and research in denmark by geus cover many different topics within our main programme areas: data, water, energy, mineral resources as well as nature and climate. as a follow-up on many previous studies of the miocene succession and its groundwater resources, one paper gives a detailed discussion of the drowning of the billund delta in jylland during a period of previous global warming. geus has been involved in the technical work that is required before a permanent disposal site can be selected for lowand intermediate-level radioactive waste. one paper describes the geological data and knowledge and key parameters such as lithology, groundwater, seismic activity, effect of climate change and local infrastructure that have been applied to narrow down the initial number of 22 areas to six potential sites. geus is involved in many studies of quaternary and recent geological processes. one paper describes deposits from the baltic ice lake in the arkona basin in the southern baltic sea. another paper presents results on the late glacial to early holocene development of southern kattegat. a third paper describes terrain subsidence interpreted from satellite radar scanning with special focus on copenhagen and its tectonic framework. systematic geological mapping on a scale of 1:25 000 and publication of 1:50  000 scale systematic sheets continues. in some places it is appropriate to make regional maps of, for example islands, on a single sheet. an example of this is described in a paper on the map sheet mors. geologically, mors is an interesting island with beautifully exposed glaciotectonic structures in cliff sections, and the characteristic eocene clayey diatomite with volcanic ash layers, a unit known as ‘moler’. the use of groundwater is very important for danish society and geus carries out many studies on water resources and possible future changes due to climate and use. one paper discusses models for urban groundwater table response to climate change and increased stormwater infiltration using the town of silkeborg and a proposed course of a new motorway around silkeborg as a case study. another paper evaluates groundwater abstraction from public waterworks in denmark by using advanced statistical methods to correct data. geus records seismological events at six locations in denmark. one paper describes the developments in detection level and completeness from 2000 to 2012 with examples of recent felt earthquakes (north sea on 19 february 2010 and kattegat on 6 august 2012) and explosions. activities in greenland there was a high level of field activities in greenland in 2012 with a major mapping and geochemical programme in south-east greenland, a large field and shallow-core drilling programme in north greenland, and the lomrog iii cruise in the arctic ocean. the latter was the last data acquisition of the danish continental shelf project. many other field studies were also carried out. results from these large and small projects will be presented in the coming years. in this issue results are presented from other completed and ongoing projects. one paper discusses the possibility that nickel and copper occurrences in the norite belt in the maniitsoq area could be impact-induced as they are found in a recently described giant and deeply eroded, very old (3 ga) impact structure © 2013 geus. geological survey of denmark and greenland bulletin 28, 7–8. open access: www.geus.dk/publications/bull 88 in this area. gold occurrences have been reported during geus expeditions to west greenland some years ago, and another paper provides more constraints on ore formation and f luid-rock interaction. corundum in gem quality (ruby) has been known since the 1960s near fiskenæsset in southern west greenland and it is possible that mining will start within a few years. one paper gives a detailed description of the geochemistry that can be used to fingerprint the greenlandic rubies. since 2008, the greenland analogue project (gap) has carried out a wide range of studies in an area near kangerlussuaq in west greenland to understand the many different processes that might take place if a deep geological repository for spent nuclear fuel is affected by glaciation. one paper focuses on structural investigations in this area, especially the mapping of lineaments and other late features. as a followup on several decades of studies in the nuussuaq basin in west greenland, a spectral gamma-ray characterisation has been made on the cretaceous atane formation to set up a better model for interpretation of lithology and grain-size variation in wells without cores. systematic geological overview mapping of greenland has been the backbone of the survey’s work in greenland over the past 65 years ago. in the period 1971–2004, 14 maps were published on a scale of 1:500 000. with the development of the internet, geological maps worldwide are rapidly changing from traditional paper sheets to digital publications. geus has produced a new seamless digital 1:500 000 scale map covering the whole of greenland. one paper describes the background, the digitisation and the geological harmonization involved. it is expected that such maps will be widely used in the future. the new map is an important geus contribution to the global onegeology portal. the important monitoring programme of the greenland ice sheet (promice) continuously supplies new crucial data and one paper discusses the darkening of the greenland ice sheet and the increase in surface melting. international activities internationally geus works in many different countries with a variety of projects. the last paper in this issue is about titanium minerals in cameroon and it focuses on understanding the primary formation, weathering and re-deposition of rutile in the area. geological survey of denmark and greenland bulletin 4, 2003, pp 93-96 93 between october 2001 and the end of 2003 there was a close co-operation between the geological survey of denmark and greenland (geus) and the geological survey department of ghana (gsd), as part of a project to enhance gsd’s institutional capabilities and effectiveness, mainly in the fields of management, geological mapping, map production and data handling. during this period a team of geologists, gis (geographic information system) and database experts as well as administrative staff from geus have visited gsd, and gsd officers have visited geus in copenhagen. the main obstacles to gsd becoming an effective organisation are its status as a department under the ghana ministry of mines, insufficient funding by the government, and poor remuneration of its professional staff. to overcome these obstacles, attempts are being made to change the status of gsd from a ‘civil servant organisation’ into a semiautonomous institution, which will permit the survey to generate funding for its core activities by providing services to outside organisations, and pay better salaries to its personnel. despite many problems, geological mapping has been resumed and three new geological maps have been produced by gsd during the project and stored in gis format. a mapping manual has been prepared, and the structure and ‘mission and vision statements’ for the survey have been revised. geology and mineral resources ghana lies in west africa, at between 5° and 11° north of the equator (fig. 1). it has a surface area of c. 240 000 km2 and c. 20 million inhabitants. its main export commodities are gold, cocoa and timber. apart from gold, ghana hosts major occurrences of manganese, bauxite, diamonds and other raw materials. most of western and northern ghana is underlain by palaeoproterozoic, isoclinally folded, metabasaltic and metasedimentary rocks of the ‘birimian supergroup’ (age ~ 2.2 ga; taylor et al. 1992; hirdes & davis 1998). the metabasalts (fig. 2) form a number of ne–sw-trending volcanic belts, separated by metasedimentary basins (fig. 1; kesse 1985; leube et al. 1990). a slightly younger, unconformable unit of sandstones and conglomerates, the ‘tark-waian group’, overlies the birimian volcanic rocks (fig. 1). rocks of the birimian supergroup are cut by numerous granitoid intrusions (fig. 3), which have yielded ages of 2.2–2.1 ga (hirdes et al. 1992). most of ghana’s mineral deposits are associated with birimian supracrustal rocks; gold also occurs within tarkwaian conglomerates. the central part of the country is occupied by a thick succession of undeformed neoproterozoic to early palaeozoic sedimentary rocks, mainly sandstones (the ‘voltaian basin’), geological survey of denmark and greenland bulletin 4, 93–96 (2004) © geus, 2004 co-operation with the geological survey department of ghana feiko kalsbeek, bjørn hermansen, christian knudsen, leif thorning and marianne thorsen fig. 1. simplified geological map of ghana, modified from kesse (1985). granitoid rocks are subdivided into c. 2.2 ga ‘belt-type granites’ and c. 2.1 ga ‘basin-type granites’, which are mineralogically and chemically distinct (hirdes et al. 1992). which have not been studied in detail. the eastern part of the country consists of a number of thrust sheets composed of sedimentary and crystalline rocks, the ages of which are not well known. they were emplaced during the pan-african orogenic cycle ~ 600 ma ago (hirdes & davis 2002). along the coast and offshore a succession of palaeozoic and mesozoic sedimentary rocks occurs, and there is a limited offshore production of hydrocarbons. the geological survey department of ghana and geus’ involvement the geological survey department of ghana was established in 1913 as the ‘gold coast geological survey’. through the years it has made major contributions to the understanding of the geology of the country, forming the basis for exploration and exploitation of the mineral resources. geological mapping before the second world war was restricted mainly to regional studies, and the first geological map at 1:1 000 000 was published in 1955. after gaining independence in 1957, the new ghana government invested much energy in the survey in order to boost the mineral industry, and during the 1960s and 1970s large parts of the country were geologically mapped in more detail. in the beginning the survey was supported by a number of geologists from the former soviet union, but this co-operation was brought to an end for political reasons. since the early 1980s gsd has been supported in several projects by the german bundesanstalt für geowissenschaften und rohstoffe (bgr). nevertheless, mainly as the result of economic starvation, the activities of the survey during the last few decades have gradually diminished. equipment could not be maintained, qualified staff left, and ultimately the survey was no longer able to perform many of its natural duties. during the late 1990s the ghana government decided that gsd should be gradually reconstructed and upgraded in order to improve its effectiveness. this process has been supported by the world bank, through a loan from the nordic development fund. geus was selected to help with the reconstruction of gsd under a contract with the minerals commission of ghana (ndf credit 156-14). the project ran from 1 october 2001 to 31 december 2003, and the contract sum was c. € 350 000. aims of the project the main topics to be addressed during the project were: 1. formulation of new ‘mission and vision statements’. 2. development of a new organisational structure. 3. reorganisation of the survey’s division for geological mapping, including the preparation of a gsd mapping manual. 4. upgrading the survey’s capability to handle digital data and provide information in digital form. 5. supporting the survey’s programme of human resources development. several of these topics had been initiated by gsd before the beginning of its co-operation with geus. 94 fig. 2. pillow lava at butre, a coastal village west of takoradi. hammer for scale. approach the original plan for the project was that a consultant should provide the survey with a single adviser. in geus’ bid for the project, however, it was suggested that, instead of providing one adviser, a team should be formed to support the survey, consisting of a team leader, who would spend about half of the time in ghana, and a number of short-time specialists would make periodic visits. in this way it was thought that geus would be able to provide support in a number of subjects which could not be covered by one single person. permission was later obtained for gsd officers to visit geus in copenhagen for shorter periods, instead of geus officers visiting ghana. an inception report was prepared jointly by geus and gsd in december 2001 to outline further plans for the project. progress reports were prepared for each of the four following half-year periods, including mission reports on each visit made. in december 2003 a draft final report was submitted. gsd’s formal status gsd is at present a department under the ghana ministry of mines. this has a number of consequences that impede the development of the survey as an effective organisation: 1. governmental funding is insufficient. 2. salaries are very low, as the staff are employed as public servants. young geologists have difficulties in supporting their families and will leave for better paid jobs as soon as possible. as a result of low salaries, poor funding and lack of other incentives, the level of job satisfaction is low. 3. as a ministerial department the survey has to follow strict rules for promotion of its personnel. seniority plays a far greater role in this process than qualifications and performance. 4. dismissal of redundant personnel is virtually impossible under the present situation. the survey has some 300 employees, far more than can be kept usefully occupied with the available funding. the problems for gsd imposed by its status as a ministerial department have been recognised by the government and, with legal advice from geus, a new ‘geological survey act’ has been prepared and submitted to the ministry of mines for further consideration. this act, if and when accepted by the ghana parliament, will transform the survey into a semiautonomous organisation, which will be able to generate funding for its core activities by providing services to outside organisations. moreover, the survey will have the possibility of adjusting the number of staff employed to its actual needs. in a close co-operation between gsd and geus, ‘mission and vision statements’ for this new organisation were formulated, and an organisational structure suggested. main achievements during the project lack of sufficient funding for field work etc. has severely limited the success of the project. nevertheless, with geus support, gsd has made significant progress, especially in the fields of geological mapping, gis applications, database issues and human resources development. geological mapping at the beginning of the present project, geological mapping had been started in five areas in ghana. four of these map95 fig. 3. strongly deformed granitoid gneisses at abuesi, a coastal village west of takoradi. the gneiss has been dated at c. 2180 ma (zircon upb); a granitic vein has yielded zircon and monazite u-pb ages of c. 2100 ma (d.w. davis in loh & hirdes 1999). 96 ping projects were completed by june 2002, and new geological maps were produced. mapping in one area could not be concluded; this is an area in eastern ghana consisting of supracrustal rocks that require experience in stratigraphy and sedimentology, at that time not available at gsd. all mapping teams were visited in the field. most of the geologists responsible for the mapping do an excellent job. however, most of the junior (assistant) geologists need more training before they will be able to carry out independent mapping projects. compilation of the new geological maps (1:100 000) was carried out in accra. thin sections and chemical analyses prepared by geus were used for the correct identification of the various rock types. the final maps were prepared by the staff of gsd’s gis laboratory with support from geus. this was the first time that new gis geological maps have been produced at the survey. digitising old geological maps and reports in order to save old geological maps in gsd’s archives from deterioration, digitising of existing maps has had a high priority during the project. a database was made with information on all existing maps. geus helped train gsd staff in the application of gis in map production. fourteen old maps were digitised during the project period, and a cdrom with these maps has been prepared. this has been one of the most successful parts of the project. databases since there is an urgent need for gsd to be able to present its data to the public in the form of databases, a major effort has been made to upgrade the survey’s experience in this field. geus has analysed which databases would be most needed and, in order to improve the understanding of database issues at gsd, a minerals occurrence database has been established. human resources development continuous training of its staff as well as recruitment of skilled young geologists will be necessary for gsd to become a strong and professional geological survey. in this context major parts of geus’ efforts under the project have been directed to practical on-the-job training of gsd personnel. apart from training related to geological mapping, gis and databases described above, geus has provided a collection of thin sections with descriptions of typical greenland rocks, given courses in the microscopic study and classification of rocks, provided training in geological mapping for two gsd geologists as participants in geus’ 2002 mapping project in greenland, sponsored an excursion for a group of gsd geologists in the western and central regions of ghana, and conducted a training course for gsd’s management on internal co-operation and related issues. sustainability there is no doubt that co-operation with geus has improved the ability of gsd to carry out several of its main functions. however, for these improvements to be sustainable in the future, it is imperative that the survey is changed into a semi-autonomous organisation. only then will the survey have the possibility to generate income to cover parts of its running expenses. moreover, it would be able to adapt the number of staff to its actual needs and provide better wages for its remaining personnel, thereby improving job satisfaction and limiting the number of well-qualified staff that leave the organisation. references hirdes, w. & davis, d.w. 1998: first u-pb zircon age of extrusive volcanism in the birimian supergroup of ghana/west africa. journal of african earth sciences 27, 291–294. hirdes, w. & davis, d.w. 2002: u-pb zircon and rutile metamorphic ages of dahomeyan garnet-hornblende gneisses in southeastern ghana, west africa. journal of african earth sciences 35, 445–449. hirdes, w., davis, d.w. & eisenlohr, b.n. 1992: reassessment of proterozoic granitoid ages in ghana on the basis of u/pb zircon and monazite dating. precambrian research 56, 89–96. kesse, g.o. 1985: the mineral and rock resources of ghana. xiv + 610 pp. rotterdam: balkema. leube, a., hirdes, w., mauer, r. & kesse, g.o. 1990: the early proterozoic birimian supergroup of ghana and some aspects of its associated gold mineralization. precambrian research 46, 139–165. loh, g. & hirdes, w. 1999: explanatory notes for the geological map of southwest ghana 1:100,000 sekondi (0402a) and axim (0403b) sheets. with contributions from c. anani, d.w. davis and u.k. vetter. geologisches jahrbuch reihe b. heft 93, 149 pp. + 2 maps. taylor, p.n., moorbath, s., leube, a. & hirdes, w. 1992: early proterozoic crustal evolution in the birimian of ghana: constraints from geochronology and isotope geology. precambrian research 56, 97–111. authors’ address geological survey of denmark and greenland, 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<feff4f7f752890194e9b8a2d5b9a5efa7acb76840020005000440046002065874ef65305542b8f039ad876845f7150cf89e367905ea6ff0c4fbf65bc63d066075217537054c18cea3002005000440046002065874ef653ef4ee54f7f75280020004100630072006f0062006100740020548c002000520065006100640065007200200035002e0030002053ca66f465b07248672c4f86958b555f3002> >> >> setdistillerparams << /hwresolution [2400 2400] /pagesize [595.000 842.000] >> setpagedevice geological survey of denmark and greenland bulletin 4, 2003, pp 29-32 29 groundwater is the major source of drinking water in many european countries, and in denmark alone it accounts for more than 99% of the drinking water supply. within the past decade pesticide residues have frequently been detected in groundwater, in many cases at levels exceeding the 0.1 µg/l limit set by the european community. as a consequence, drinking water abstraction wells have had to be closed in many places in denmark and other european countries, and a vast amount of money is expended to monitor groundwater pesticide levels. a degradation product of the herbicide dichlobenil, 2,6-dichlorobenzamide (bam), is the most common cause of drinking water well closure in denmark. triazines and their metabolites also contaminate groundwater in many countries, and pose a similar risk to the drinking water supply. analysis of most pesticides and their degradation products is usually carried out by concentrating the samples by solvent extraction, and identifying the contaminants using gas chromatography (gc) or high-pressure liquid chromatography (hplc) combined with mass spectrometry (ms). these methods, although robust and well established, are very time-consuming and require specialised instrumentation. the large quantity of solvents used is another drawback to these methods, as the solvents themselves may be carcinogenic and are also well known contaminants of groundwater. the development of cheap, more sensitive and more rapid pesticide assays is therefore urgent. due to their very high sensitivity, immunological methods have long been used in biological science for analysing a large variety of organic structures, but have only recently been introduced to environmental analysis. the benefit of such assays is primarily their high sensitivity, which allows the analysis to be undertaken without the need to concentrate the samples, but also the facility of dealing with large numbers of samples. compared to conventional analyses, immunological methods face two major drawbacks – one related to specificity and the other to the fact that only very few chemicals can currently be analysed simultaneously. the crux of the specificity problem is that although antibodies react very specifically with particular chemical structures, these same structures may be present in analogous compounds. thus antibodies developed to recognise, for example the herbicide atrazine might also recognise other triazines (bruun et al. 2001). an important scientific challenge is therefore the development of highly specific assays recognisimmunological analysis of pesticides: a new tool in groundwater testing jens aamand, leif bruun and claus bo vöge christensen fig. 1. development of monoclonal pesticide antibodies is initiated by covalent conjugation of the pesticide to a carrier protein. this pesticide-carrier complex is injected into mice and after approximately two months the mice have produced antibodies against the pesticide. selected mice are sacrificed and the spleen is removed to isolate the antibody-producing cells. these cells are difficult to cultivate in vitro, and they are therefore fused with myeloma cells to ensure the viability of the antibody-producing cells. the fused hybridoma cells are cultivated, tested and isolated to achieve monoclonal cultures, which produce one type of antibody only with special characteristics such as binding efficiency and specificity. slightly modified from aamand et al. (2003). geological survey of denmark and greenland bulletin 4, 29–32 (2004) © geus, 2004 ing each individual compound, as well as assays recognising groups of related chemicals. with respect to the simultaneous analysis of numerous chemicals, this can be resolved by implementing the new biochip technology, which incorporates the parallellity of sample screening. on a pesticide biochip many specific immunological assays are carried out in isolated small spots on a glass or polymer surface. each spot has a size of approximately 150 micrometers and forms a specific analysis. such a miniaturised platform will be usable for monitoring programmes where water samples have to be screened for a range of chemical contaminants. the overall objectives of this study have been (1) to develop immunoassays for high-sensitivity analysis of specific pesticides and chemically related groups of pesticides, and (2) to transfer the developed assays to a miniaturised biochip platform in a manner allowing analysis of several pesticides simultaneously. immunological analysis of pesticides the basis for the development of new immunological analyses is the antibody that reacts with complementary molecules, the so-called antigens. antibodies are part of the immunological defence system in animals and humans for protection against pathogenic vira and bacteria. following an infection, the organism produces antibodies that recognise and bind to specific molecular structures on the surface of the penetrating bacteria or virus (the antigens). upon the binding of antibodies, other effector functions of the immune system identify and destroy the bacteria. the chemical structures of the pesticides themselves are too small to induce an immunological response. however, by linking the pesticides to larger carrier molecules it is possible to deceive the immune system into starting the production of antibodies against the pesticide (fig. 1). to initiate antibody production the pesticide-carrier complex is injected into an animal, e.g. a rabbit or a mouse, thus inducing an immunological response resulting in the production of antibodies against the pesticide-carrier complex. antibodies are produced by so-called b-cells each producing a single antibody species, which recognise a specific structure on the pesticide. as the animal contains many b-cells which all produce antibodies, a range of antibodies reacting with different structures on the pesticide and with different affinity will be generated. by purification of the antibodies from the blood serum, a polyclonal antibody serum is obtained, containing antibodies from different b-cells. however, it is often more appropriate to produce monoclonal antibodies (mab), i.e. specific antibodies all arising from the same b-cell clone. production of monoclonal antibodies when it has been established by serological screening that the immunised animal produces antibodies with the correct specificity, the spleen, which contains many antibody-producing cells, is removed and grown in culture. clones producing antibodies with the desired properties are then selected. it is possible to select antibodies that react with chemical structures specific for a single pesticide molecule, or alternatively a structure shared by a group of pesticides such as the triazines. in addition to their high specificity monoclonal antibodies also have the advantage of consistency. it is always possible to reculture the hybridomas and produce further antibodies with exactly the same characteristics. development of immunological assays the next step following the selection of suited antibodies is the development of an immunochemical pesticide assay. the analysis is often carried out as a so-called competitive immunoassay in microtitre plates, which are preformed plastic plates with 96 wells (fig. 1). a known amount of pesticide is immobilised on the bottom of the wells. the samples to be analysed are added to the wells (typically 100 µl), followed by 30 fig. 2. example of a competitive assay. in cases with high concentrations of pesticides in the sample, fewer antibodies will bind to the pesticide immobilised to the surface (e.g. the bottom of the microtitre plate) and a low signal will be measured. if the samples do not contain the pesticide, maximal amounts of antibody will bind to the surface resulting in a high signal. slightly modified from aamand et al. (2003). the addition of the antibodies. at this point the antibodies can react with either the pesticide immobilised in the microtitre plates or the pesticide in the sample itself. if the concentration of the pesticide in the sample is low, more antibodies will react with the immobilised pesticides and vice versa. when the reaction is completed the microtitre plate wells are washed, leaving only the immobilised pesticideantibody complex (fig. 2). the antibodies can be directly monitored if coupled with an enzyme, catalysing an enzymesubstrate reaction that yields a coloured end product. the accumulation of the end product is then monitored by absorbance measurements and compared spectrophotometrically to the absorbance of known standards (fig. 3). new immunological assays have been developed for several triazines including their degradation products (bruun et al. 2000a, b, 2001) and for bam (bruun et al. 2000c). all assays have a very low detection limit in the range of 0.01–0.02 µg/l, making them ideal for monitoring specific pesticide residues in groundand drinking water. analyses are typically carried out in four replicates, and each microtitre plate also contains a number of pesticide standards. a total of 13 samples can be analysed at each microtitre plate within a period of 3–4 hours. from microtitre plate to pesticide biochip one of the drawbacks of the microtitre format is that it is only possible to analyse for one pesticide in each routine. however, changing the analysis format from microtitre plates to biochips allows for the analysis of several compounds simultaneously. the term ‘biochips’ describes an analysis where the chemical reactions are not separated by wells, but are carried out on a planar surface such as a glass slide. the principle of the analysis is the same as for the microtitre plates, but the reagents are added as microspots (in the nanoliter range) on the glass surface. using a robot equipped with printing pins, about 2000 samples/cm2 can be added as separate spots on the surface. all chemical reactions are then carried out within the individual spots. for the pesticide biochip fluorescence-conjugated monoclonal antibodies were used, which enables the detection of separate signals from each spot on the surface by use of a laser scanner (fig. 4). as a result of the small dimensions, the individual reactions equilibrate faster and the complete analysis of a biochip can be carried out within 90 minutes. the analyses on the biochips are also more sensitive than on microtitre plates. we have developed a pesticide biochip for bam and atrazine with a sensitivity of about 1 ng/l (fig. 5), which is 100 times less than the limit value for drinking water set by the eu (belleville et al. 2003, 2004). possibilities and limitations the benefits of the immunochemical analyses compared to chromatographic techniques are that: (1) less sample volume is needed, which means an easier transport of samples to the laboratory; (2) no solvents or other chemicals are necessary which potentially could pollute the environment; and (3) the immunochemical analyses are much cheaper to carry out. at present, the immunochemical techniques only enable the analysis of a few compounds simultaneously. in contrast, chromatographic methods (e.g. hplc or gc/ms) provide the concentration of a range of compounds within the same routine. however, use of the pesticide biochips opens the possibility of analysis of more compounds simultaneously. at present the biochip includes bam and atrazine only, but in theory it is possible to include additional pesticides as soon as usable antibodies become available. another problem to be faced is related to the specificity of the antibodies. many antibodies may react not only with the targeted pesticide, but also with chemically related compounds. this is the case for the atrazine antibodies that may also react with other triazine herbicides (bruun et al. 2001). the specificity, however, is not a problem with bam, because the reactivity of the antibody with other compounds is negligible (bruun et al. 2000c). the new pesticide biochip enables the analysis of pesticides in a single drop of water in concentrations as low as 1 ng/l. in principle the pesticide biochip allows the analysis of a range of pesticides, but for the development of such multicomponent analysis further antibodies are needed with high specificities to the individual pesticides. 31 fig. 3. example of a standard curve. note the inverse relationship between pesticide concentration and signal. slightly modified from aamand et al. (2003). 32 acknowledgement the present work is supported by the immunalyse project (grant no. 9901188) financed by the danish research agency. references aamand, j., bruun, l. & christensen, c.b.v. 2003: mus hjælper til med pesticidanalyser. dansk kemi 84, 29–31. belleville, e., dufva, m., aamand, j., bruun, l. & christensen, c.b.v. 2003: quantitative assessment of factors affecting the sensitivity of a competitive immunomicroarray for pesticide detection. biotechniques 35, 1044–1051. belleville, e., dufva, m., aamand, j., bruun, l., clausen, l. & christensen, c.b.v. 2004: quantitative microarray pesticide analysis. journal of immunological methods 286, 219–229. bruun, l., koch, c., jakobsen, m.h. & aamand, j. 2000a: a new monoclonal antibody for the sensitive detection of cyanazine and other striazines in water by elisa. food and agricultural immunology 12(4), 253–262. bruun, l., koch, c., jakobsen, m.h. & aamand, j. 2000b: new monoclonal antibody for the sensitive detection of hydroxy-s-triazines in water by enzyme-linked immunosorbent assay. analytica chimica acta 423, 205–213. bruun, l., koch, c., pedersen, b., jakobsen, m.h. & aamand, j. 2000c: a quantitative enzyme-linked immunoassay for the detection of 2,6dichlorobenzamide (bam): a degradation product of the herbicide dichlobenil. journal of immunological methods 240, 133–142. bruun, l., koch, c., jakobsen, m.h., pedersen, b., christiansen, m. & aamand, j. 2001: characterisation of monoclonal antibodies raised against different structures belonging to the s-triazine-group of herbicides. analytica chimica acta 436, 87–101. fig. 4. laserscan of a pesticide biochip designed to analyse for bam and atrazine. each spot represents a single analysis of a standard with a known concentration. within each concentration the six spots to the left are bam and the six spots to the right are atrazine. slightly modified from aamand et al. (2003). authors’ addresses j.aa., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: jeaa@geus.dk l.b., statens serum institut, artillerivej 5, dk2300 copenhagen s, denmark. c.b.v.c., technical university of denmark, department of microand nanotechnology, ørsted plads 345, dk-2800 kongens lyngby, denmark. << /ascii85encodepages false /allowtransparency false /autopositionepsfiles true /autorotatepages /all /binding /left /calgrayprofile (dot gain 20%) /calrgbprofile (srgb iec61966-2.1) /calcmykprofile (u.s. web coated \050swop\051 v2) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.4 /compressobjects /tags /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjdffile false /createjobticket false /defaultrenderingintent /default /detectblends true /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedjoboptions true 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hydrochloric acid in horizontal wells in north sea chalk reservoirs. photo: peter frykman. 2. as part of the greenice project, sea-ice thickness in the arctic ocean was measured using airborne helicopter-based electromagnetic profiling in 2004. the project is funded by the eu and carried out in co-operation between the geological survey of denmark and greenland (geus) and the alfred-wegener-institute for marine and polar research (awi) as well as other research institutes. photo: sibylle goebell, awi. 3. investigations related to geological storage of co2 from fossil fuels are becoming an increasingly important field of work for geus. photo: peter k. warna-moors. 4. geophysical investigations of the fault-related gold occurrences on the island of storø, not far from nuuk, the capital of greenland (see article on page 65). photo: peter w.u. appel. frontispiece: facing page the goldmine at nalunaq, south greenland. the mine opened in 2004 after more than ten years of intensive geological and technical investigations. photo: sven monrad jensen. chief editor of this series: adam a. garde scientific editors: martin sønderholm and a.k. higgins editorial secretaries: esben w. glendal and birgit eriksen illustrations: jette halskov lay-out and graphic production: annabeth andersen printers: schultz grafisk, albertslund, denmark manuscripts submitted: 7 december 2004 – 25 february 2005 final versions approved: 1 april 2005 printed: 29 july 2005 issn 1604-8156 issn 1603-9769 isbn 87-7871-164-9 geological survey of denmark and greenland bulletin the series geological survey of denmark and greenland bulletin replaces geology of denmark survey bulletin and geology of greenland survey bulletin. citation of the name of this series it is recommended that the name of this series is cited in full, viz. geological survey of denmark and greenland bulletin. if abbreviation of this volume is necessary, the following form is suggested: geol. surv. den. green. bull. 7, 80 pp. available from geological survey of denmark and greenland (geus) øster voldgade 10, dk-1350 copenhagen k, denmark phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: geus@geus.dk or geografforlaget aps rugårdsvej 55, dk-5000 odense c, denmark phone: +45 63 44 16 83, fax: +45 63 44 16 97, e-mail: go@geografforlaget.dk © danmarks og grønlands geologiske undersøgelse (geus), 2005 4 review of survey activities 2004 k. sørensen 7 oil generation from coal source rocks: the influence of depositional conditions and stratigraphic age h.i. petersen 9 identification of hydrocarbons in chalk reservoirs from surface seismic data: south arne field, north sea p. japsen, a. bruun, i.l. fabricius and g. mavko 13 forward modelling of seismic response from north sea chalk o.v. vejbæk and r. rasmussen 17 a revised lithostratigraphy for the paleogene – lower neogene of the danish north sea p. schiøler, j. andsbjerg, o.r. clausen, g. dam, k. dybkjær, l. hamberg, c. heilmann-clausen, l.e. kristensen, i. prince and j.a. rasmussen 21 seismology: neotectonics and structure of the baltic shield s. gregersen, m. glendrup, t.b. larsen, p. voss and h.p. rasmussen 25 new methods in provenance studies based on heavy minerals: an example from miocene sands in jylland, denmark c. knudsen, d. frei, t. rasmussen, e.s. rasmussen and r. mclimans 29 groundwater quality monitoring in denmark j. stockmarr 33 contents geus working areas 2004. orange areas are covered in this volume. 5 steam treatment of contaminated groundwater aquifers – development of pathogenic micro-organisms in soil c.s. jacobsen, s. elmholt, c.b. jensen, p.b. jakobsen and m. bender 37 field experimental design for pesticide leaching – a modified large-scale lysimeter b. nilsson, j. aamand, o.s. jacobsen and r.k. juhler 41 the storebælt gateway to the baltic j.b. jensen, o. bennike, w. lemke and a. kuijpers 45 quantifying the relationship between pollen sedimentation in lakes and land cover using historical maps a.b. nielsen 49 climatic warming: a trigger for glacial iceberg surges (‘heinrich events’) in the north atlantic? a. kuijpers, h. heinrich and m. moros 53 on-line presentation of mineral occurrences in greenland l. thorning, l.aa. christensen, b.m. nielsen, f. schjøth and h. stendal 57 precambrian mineralising events in central west greenland (66°–70°15´n) h. stendal and a.a. garde 61 greenstone belts in the central godthåbsfjord region, southern west greenland j.a. hollis, j.a.m. van gool, a. steenfelt and a.a. garde 65 detection of kimberlitic rocks in west greenland using airborne hyperspectral data: the hypergreen 2002 project t. tukiainen and l. thorning 69 prospecting for dimension stones in greenland t.v. rasmussen and h.k. olsen 73 small-scale mining – hazards and opportunities in kyrgyzstan and mongolia p.w.u. appel 77 7 in this second issue of review of survey activities the main themes of the survey’s work in denmark, greenland and elsewhere are presented for a professional, but not specialist readership. out of 18 articles, five report on greenland activities, and this reflects the obligation of the survey to spend approximately 30% of its finance law grant on greenlandrelated activities. the first four articles deal with petroleum-related matters and illustrate some of the pertinent questions concerning the prospective part of the north sea. although most oil generated in the north sea has its origin in marine shales of late jurassic age, oil and condensate have also been generated from paralic, coal-bearing sediments of middle jurassic age. most hydrocarbons in the danish north sea are found in chalk reservoirs, but paleocene reservoirs also contribute to danish oil production; both scenarios are covered by articles in this volume. as a result of the restructuring of governmental research organisations initiated by the present danish government, the seismological research – which until 2004 was part of the danish national survey and cadastre – has been moved to the geological survey of denmark and greenland (geus). the seismology group signals this move with a contribution to this year’s review concerning the baltic shield, of which eastern denmark forms a marginal part. geus has responsibility for monitoring groundwater quality throughout denmark. this responsibility carries with it an obligation for research into the processes affecting groundwater quality. this is an important field of research in a country with widespread and intensive agricultural activities, and that relies almost exclusively on groundwater for its water supply. a group of three reports in this volume witness to the range of important activities carried out by the departments of the survey working with ground water. quaternary research at the survey is presented in three articles that cover vegetation history, the evolution of the baltic following the last deglaciation and climate research in the north atlantic. the articles describing marine geology activities build on a long-standing co-operation between geus and the baltic sea research institute in warnemünde, germany. the survey’s activities in greenland in 2004 were concentrated in west greenland. three papers focus on investigations related to the mineral potential of the precambrian basement terranes, while one covers the possibility of exploiting dimension stones suitable for the international market. such studies cannot be carried out without a thorough regional knowledge of the geology of greenland. in 2004 geus reached a milestone in regional geological mapping of greenland when the last of 14 bedrock geology maps at 1:500 000, which together cover all of greenland’s ice free land areas, was published. the survey’s activities in denmark and greenland have now reached a similar stage, in the sense that in both countries resources spent on systematic mapping projects have now become subordinate to more focused activities. although the systematic regional mapping of greenland has reached its primary goal, this is not recorded by a separate article, and there are other activities in geus’ broad portfolio of tasks that, for one reason or another, are not covered by articles in this volume; to mention a few: greenland petroleum geology both onand offshore; surveys adjacent to the faroe islands and greenland directed towards the continental shelf project; ongoing mapping in greenland and denmark; projects relating to nationwide modelling of groundwater flow; work on geothermal resources and co2 sequestration. furthermore, the important activities dealing with data handling and the creation of new data in geus laboratories are not described as such. how these activities ultimately come together to the benefit of the general public and industry is, however, illustrated by the paper on on-line presentation of mineral occurrences in greenland. during 2004, geus carried out work in more than 20 countries outside denmark, greenland and the faroe islands (see map in table of contents in this issue). one such project related to small-scale mining in mongolia and kyrgyzstan is described. information on the survey’s activities not dealt with in this volume can be found on the geus website. review of survey activities 2004 kai sørensen director e2019430001-01 every four years the geological survey of denmark and greenland (geus) develops and implements new strategies to ensure that we are able to help meet the ever-changing challenges that face society. in 2018 these discussions were shaped by important issues like climate change and climate adaptation, and their consequences for our use of energy, minerals and water resources. as part of this strategic focus, geus introduced a new publication strategy in 2018 that seeks to increase our publication rate of high impact science, and to gain more visibility within the international scientific community and the media. many different tools will be applied to make such a long-term cultural change possible, including modernisation of geus’ own publication series. it is therefore very promising to see this issue of review of survey activities (rosa) published in a modernised bulletin. the geus bulletin is an international open-access publication with peer-reviewed papers. for the first time rosa is published online only and all papers can be downloaded shortly after completion. papers are easily identified and cross-referenced with dois (digital object identifiers), and keywords and publication history are provided. in addition, there are better possibilities for provision of online supplementary data to document large datasets. this new format will hopefully allow for a much quicker and more efficient distribution and thereby attract higher interest from the media and society. this issue of review of survey activities includes 16 papers covering many different activities in denmark, greenland and beyond. six papers are on denmark, eight on greenland, and two on other themes. due to the new format, several of the papers are slightly longer than in previous years, where the four-page limit sometimes made it difficult to fully document and discuss key results. activities in denmark geus activities and research in denmark cover a wide range of topics within our specific programme areas: data, water, energy, mineral resources, nature and climate. our strong focus on climate change and climate adaptation is ref lected in several papers. one very interesting paper on sea-level rise in denmark combines the representative concentration pathway 4.5 scenario (“paris agreement” climate pathway) with local reconstructions of glacio-isostatic rebound curves to calculate future differences in sea level between skagen, copenhagen and esbjerg. another paper presents a statistical discussion on how models of precipitation and temperature projections can be downscaled from coarse meteorological grids to the much more detailed grids that geus is using in our danish national water resources model. understanding properties of reservoir sandstones and their f luids is very import for predicting production models of petroleum and geothermal energy, or for carbon capture and storage (ccs). one paper provides an analysis of porosity-preserving microquartz coatings in deeply buried jurassic sandstones in the danish central graben and the implications for production parameters. another paper gives a first classification of different brine types in mesozoic reservoirs in areas with a geothermal potential onshore denmark. this is very important for evaluating the scaling risk prior to new drilling. after many years of unsuccessful onshore petroleum exploration in denmark and the expectation of only limited potential in this area, the danish government finally decided in february 2018 to halt all further petroleum exploration onand nearshore. one paper describes the exploration history in the region since the last major study was completed in 1987, and reviews the various exploration play types. much of the data and results from this decades-long period of onshore exploration are very important for developing a more detailed understanding of the potential for geothermal energy and ccs in many parts of denmark. the last danish paper provides new information on the deeply incised and partly sediment-filled channels in storebælt using radiocarbon ages, and thereby suggests new models for the history of water connections between kattegat and the baltic sea. review of survey activities 2018 flemming g. christiansen*1 deputy director, geological survey of denmark and greenland (geus) geus bulletin is free to individuals and institutions in electronic form. the author(s) retain copyright over the article contents. pr eface | open access geus bulletin vol 43 | e2019430001 | published online: 07 august 2019 https://doi.org/10.34194/geusb-201943-00-01 https://doi.org/10.34194/geusb-201943https://doi.org/10.34194/geusb-201943-01-01 https://doi.org/10.34194/geusb-201943-01-02 https://doi.org/10.34194/geusb-201943-01-03 https://doi.org/10.34194/geusb-201943-01-04 https://doi.org/10.34194/geusb-201943-01-05 https://doi.org/10.34194/geusb-201943-01-06 https://doi.org/10.34194/geusb-201943-00-01 e2019430001-02 activities in greenland once again, there was a high level of activity in greenland in 2018. geus continues to focus on climate projects related to the promice monitoring programme. furthermore, there are many traditional studies on petroleum and mineral resources, and some new initiatives on geohazards. two papers are on promice services. the first provides a complete mass balance for the greenland ice sheet between 1995 and 2015. data were obtained by repeated measurements of altitude and ice thickness circumscribing the ice sheet at 1708 m altitude – a 5415 km long perimeter survey. the second paper provides an update of the annual calving front lines for 47 marine outlet glaciers distributed throughout greenland. the net area change of these glaciers is significant over the period 1999–2018 and these data will be important for mass balance calculations. mineral exploration by industry has remained relatively low in recent years, and most petroleum activities have stopped since all supermajors and majors have left greenland. it is, however, important to prepare for a future when prices of the most important commodities eventually rise again. one paper provides interesting results on u-pb dating of titanite in paleogene sandstones in a volcanic terrane in east greenland. this can be very important for constraining sources of sedimentary rocks and can help to date the precipitated titanite. another paper is on the liverpool land basement high (llbh), which could offer a large and interesting analogue for fractured basement reservoirs that have recently attracted interest in petroleum exploration in several places in the north atlantic. llbh is well exposed and provides good possibilities for developing 3d models of faults, fractures and veins and their connectivity. sampling may provide information on their origin, e.g. timing and f luid conditions. spaceborne remote sensing data can be a fast and costeffective tool in early mineral exploration. a case study from wollaston forland, north-east greenland is presented. they compare data from aster and sentinel-2 to discriminate between various lithological units. aster seems to give the best results for this mapping purpose. glacial rock f lour has recently been suggested as a natural fertiliser that could be used especially in tropical areas with poor soil quality. one paper describes mapping and sampling of such deposits in lake tasersuaq, west greenland. on 17 june 2017 a large landslide in karrat fjord triggered a devastating tsunami. in the weeks that followed, geus was deeply involved in coordinating information and knowledge from many dedicated scientists in order to advise the greenland authorities. it soon became evident that there was a strong need for a better understanding of the risk of landslide-generated tsunamis across greenland. it is particularly important to understand how an apparent increase in the number of events relates to climate change, and how geology, terrain and local climate control the distribution of risk area. in 2018, geus completed a screening study of the risk of major landslides. one paper gives an overview of historical records and applied mapping and satellite techniques that have been used to map the occurrence of more than 500 landslides in greenland. another paper documents a multidisciplinary case study of a landslide in 2018 in the karrat fjord, using seismological data, geological data, optical satellite images and radar satellite data to describe activity before and during the event. other activities internationally, geus collaborates with a number of research institutes on a wide variety of projects, including broader thematic studies and the development of new techniques and databases. based on our own high-quality analytical techniques, geus has worked with provenance studies for several decades and we have compiled large amounts of zircon ages and other types of provenance data in greenland, the north atlantic and the north sea. these data are useful for researchers and industry, and so geus and the norwegian petroleum directorate (npd) have collaboratively launched an online database, the so-called north atlantic provenance database, to collate these regional data. one of the papers in this issue provides an introduction to a number of the visualisation and statistical tools available in the database, which will be developed further in the coming years. the last paper is on the use of drones equipped with multisensors for geological mapping and mineral exploration. the development of light weight magnetic and hyperspectral tools together with a high quality positioning system made in collaboration with several european partners is described, together with a presentation of preliminary results from two mining areas in finland. how to cite christiansen, f.g. 2019: review of survey activities 2018: preface. geological survey of denmark and greenland bulletin 43, e2019430001. https://doi.org/10.34194/geusb-201943-00-01 *corresponding author: flemming g chrisitansen | e-mail: fgc@geus.dk 1 geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350, copenhagen k, denmark. https://doi.org/10.34194/geusb-201943-02-01 https://doi.org/10.34194/geusb-201943-02-02 https://doi.org/10.34194/geusb-201943-02-03 https://doi.org/10.34194/geusb-201943-02-04 https://doi.org/10.34194/geusb-201943-02-05 https://doi.org/10.34194/geusb-201943-02-06 https://doi.org/10.34194/geusb-201943-02-07 https://doi.org/10.34194/geusb-201943-02-08 https://doi.org/10.34194/geusb-201943-03-01 https://doi.org/10.34194/geusb-201943-03-02 https://doi.org/10.34194/geusb-201943-00-01 mailto:bhm%40geus.dk?subject= geological survey of denmark and greenland bulletin 3, 151-171 151 total for climatic regions ...l: 1 (1.4%) the holocene skagen: 71 (28.7%) from the skagen boring, 71 holocene species have been recorded. the boreo-lusitanian group dominates with 54 species (76.1%) of the holocene mollusc species from the skagen well. one purely lusitanian species, vitreolina collensi, has been found, while all the other species occur in the boreal and to some extent the arctic. in this way the skagen well material resembles that of other regions like the vendsyssel, limfjord and north sea during the holocene. the skagen well material has all been recorded to certain stratigraphical levels, as seen in appendix 6, so the climatic indications through time appear, but the number of molluscan species is very low. in the preboreal/boreal, only three species have been recorded. this has been explained as a result of a deeper water where the echinoids dominate. higher up in the sequence, the number of molluscs increases – 23 species in the subboreal and 68 species in the subatlantic. through the chronostratigraphical levels, the climatic regions of the boreo-lusitanian from the dominating one, and the purely lusitanian vitreolina collensi as mentioned above occurs in the subboreal and subatlantic. however, as already stated, the development of the facies in the skagen well during the holocene does change the environment from the deeper-water facies with few molluscs through the bottom community with turritella communis into the prolific shallow-water community. in this way the youngest part covering the subboreal–subatlantic is also by far the part with the highest species diversity. the environmental changes within the seven regions through the late quaternary evaluated by the molluscan communities met with in the seven stages the seven chronological stages which have been described according to their climatic affinities are seen in fig. 102 and fig. 103 covering the eemian, the early/ middle weichselian, the late weichselian, the preboreal/ boreal, the atlantic, the subboreal, and the subatlantic. in this way the climatic cycle during the late quaternary is demonstrated on the basis of marine mollusc species which indicate that the eemian has by far the highest amount of the more temperate species, while the holocene reached its maximum during the atlantic, although only slightly more than the other stages within the holocene, as already commented upon in the previous chapter. it is generally accepted that the eemian summer temperatures were higher – about 2°c above the present. with glaciers smaller than the present day, this means that the sea level was 4–6 m higher than today (andersen & borns 1994, pp. 44–49). and as pointed out by donner (1995, p. 39): “the submergence was clearly greater after the saalian glaciation than after the weichselian and possibly after the older glaciations”. donner sees this in northern europe as “a result of a comparatively great downwarping of the earth’s crust during the extensive saalian glaciation”. the rebound since the last glaciation has come to an end within the danish area (petersen 1985c, 1991b). this means that the eemian deposits, when found in denmark in nonglacio-dislocated state, can be regarded as being in the original position related to sea level, although there might be some movements in relation to neo-tectonic activities, as mentioned earlier. in the light of the observations mentioned above, the seven regions will be discussed according to the environmental characteristics such as the climatic affinities for the molluscs recorded in appendix 6 for each region, as appearing in fig. 103. however, for the holocene still as many as 130 species including the recent ones (95) not found as subfossil have not been dated to give their first appearance, see fig. 102: unknown arrival in holocene. at the end of each of the seven stages the molluscan communities sensu c.g.j. petersen will be presented in tables 3–9. geus bulletin no 3.pmd 09-07-2004, 09:10151 152 eemian stage 130 000 – 115 000 b.p. the bælt sea, region 1 appendix 6 and fig. 103 already forchhammer (1842, p. 64) designated cyprina (arctica) islandica to be the characteristic bivalve of the bælt sea eemian, as known to the present-day geologists. furthermore, forchhammer points out that the characteristic bivalve, cyprina islandica, occurs every where in large quantities, but always in crust specimens. however, all the shell fragments occurring together show that the specimen has been broken after deposition in the clay, most probably by the cataclysms which have given the beds their tilt. johnstrup (1882a, p. 55) points to the indications of the molluscs as being a deposition of a shallow-water sea and also mentioned the mytilus beds. johnstrup points out (1882a, p. 56) that the dislocated floes – as already noticed by forchhammer – have the original succession within each floe, saying that the cyprina clay and the mytilus beds have not been disconnected during the dislocations. later investigations by nordmann (harder 1900; nordmann 1908, 1913) demonstrated that the venus aurea as observed by johnstrup (1882a, p. 66) could be regarded in parts as the no longer living tapes aureus gm. var eemiensis nordmann or tapes senescens doederlein; in this book paphia aurea senescens. the tapes species do represent shallow-water environments (see the chapter on the molluscan species), and therefore the whole of the bælt sea region can be characterised by the three bivalves mentioned above, from the eulittoral to the infralittoral shallow-water zones: mytilus, tapes and cyprina. among the three species mentioned, the tapes species (paphia aurea senescens) also remains as the only subfossil bivalve from denmark which can be regarded as an index fossil from the marine eemian. the stratigraphical position of the marine eemian is according to jessen & milthers (1928, p. 179) contemporaneous with the mixed oak forest zone and the carpinus zone in the interglacial bogs; furthermore, jessen & milthers conclude (1928, p. 341) that the climate of jylland and nw germany in that part of the interglacial period which answers to zone f [culmination of the curves for mixed oak forest] was no less atlantic in character than (100%) (100%) (100%) (100%) (100%) (100%) (100%) 3 11 48 48 16 53 3 290 14 140 36 41 27 93 77 72 486 1 2 6 5 10 19 14 1 1 2 1 11 7 11 2 6 5 6 3 2 4 2 3 2 15 1 5 3 14 7 8 1 1 1 90 21 70 56 53 10 3 1 (3%) (5%) (17%) (12%) (7%) (53%) (34%) (4%) (1%) (3%) (1%) (8%) (19%) (27%) (7%) (6%) (6%) (8%) (2%) (6%) (10%) (2%) (4%) (3%) (11%) (3%) (12%) (11%) (15%) (9%) (11%) (1%) (1%) (1%) (64%) (78%) (75%) (73%) (74%) (7%) (4%) (1%) frequency: number of molluscs column per cent, % climatic affinity eemian early/middle late weichselianweichselian preboreal/ boreal atlantic subboreal subatlantic total number of species unknown arrival in holocene arctic arctic, subarctic arctic, subartic, boreal, lusitanian arctic, subarctic, boreal subarctic, boreal subarctic, boreal, lusitanian boreal boreal, lusitanian lusitanian total number of species column per cent, % 3 5 s ub fo ss il sp ec ie s 9 5 r ec en t sp ec ie s pleistocene holocene time: the seven stages fig. 102. the seven stages from the eemian through the weichselian – comprising the early/middle weichselian and late weichselian – to the end of the holocene. preboreal–boreal, atlantic, subboreal, and subatlantic are here shown according to their climatic affinities based on the molluscan record. geus bulletin no 3.pmd 09-07-2004, 09:10152 153 (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (2%) (3%) (10%) (73%) (12%) (2%) (10%) (7%) (9%) (28%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (100%) (5%) (5%) (5%) (21%) (63%) (2%) (2%) (5%) (5%) (3%) (3%) (9%) (72%) (16%) (2%) (4%) (5%) (20%) (1%) (5%) (1%) (11%) (73%) (9%) (2%) (8%) (5%) (12%) (14%) (32%) (16%) (13%) (2%) (11%) (2%) (56%) (16%) (11%) (5%) (7%) (33%) (7%) (7%) (29%) (14%) (43%) (7%) (2%) (6%) (2%) (1%) (4%) (14%) (14%) (29%) (43%) (17%) (8%) (4%) (5%) (3%) (17%) (53%) (19%) (6%) (3%) (17%) (50%) (33%) (11%) (10%) (1%) (25%) (75%) (17%) (5%) (6%) (11%) (37%) (23%) (9%) (14%) (33%) (33%) (23%) (13%) (15%) (6%) (17%) (8%) (5%) (5%) (5%) (4%) (8%) (12%) (77%) (2%) (3%) (4%) (4%) (33%) (67%) (1%) (0%) (6%) (3%) (16%) (74%) (3%) (5%) (6%) (5%) (13%) (87%) (2%) (3%) (22%) (78%) (6%) (4%) (1%) (8%) (3%) (17%) (71%) (2%) (9%) (10%) (15%) (12%) (7%) (7%) (85%) (3%) (2%) (5%) (50%) (50%) (5%) (0%) (100%) (2%) (50%) (50%) (1%) (0%) (6%) (6%) (6%) (78%) (6%) (4%) (3%) (2%) (6%) (8%) (16%) (11%) (5%) (5%) (63%) (5%) (10%) (1%) (33%) (3%) (33%) (67%) (1%) (0%) (4%) (4%) (9%) (78%) (4%) (2%) (5%) (2%) (4%) (4%) (100%) (0%) (13%) (25%) (63%) (2%) (2%) (1%) (1%) (7%) (3%) (10%) (1%) (75%) (1%) (2%) (8%) (10%) (8%) (33%) (11%) (4%) (11%) (11%) (33%) (33%) (11%) 59 19 32 91 55 14 7 36 4 35 9 26 3 31 15 23 77 27 2 8 2 36 19 3 23 1 8 68 7336 12 57 64 20 84 3 462 25 1 1 2 18 1 1 1 2 5 1 5 2 7 1 51 1 8 1 1 2 2 2 28 2 3 2 1 1 12 1 2 1 2 2 1 5 23 2 13 5 18 1 6 2 13 55 2 2 23 1 1 1 1 2 3 1 6 19 7 2 1 1 3 2 4 13 8 3 5 1 1 3 3 1 1 2 3 20 1 2 6 43 7 1 1 1 4 12 1 3 23 5 1 5 1 10 66 8 9 7 1 6 1 31 1 4 2 6 1 age ep o ch p le is to ce ne h o lo ce ne region 1. bælt sea 2. baltic sea 3. kattegat 5. north sea 6. vendsyssel 7. skagen 3. kattegat 6. vendsyssel 7. skagen 6. vendsyssel 7. skagen 5. north sea 7. skagen 1. bælt sea 2. baltic sea 3. kattegat 4. limfjorden 5. north sea 6. vendsyssel 7. skagen 3. kattegat 4. limfjorden 5. north sea 6. vendsyssel 7. skagen 4. limfjorden 5. north sea 7. skagen eemian early/middle weichselian late weichselian preboreal/ boreal atlantic subboreal subatlantic total of species in number row per cent, % column per cent, % total of species: in number row per cent, % column per cent, % arctic a, s boreal b, l lusita-nian a, s, b a: arctic, s: subarctic, b: boreal, l: lusitanian a, s, b, l s, b s, b, l climatic affinity fig. 103. climatic characterisation (affinity) of mollusc assemblages for each region over the seven stages (ages) since the eemian. geus bulletin no 3.pmd 09-07-2004, 09:10153 154 the climate of the litorina period in postglacial time. also s.t. andersen (1965, pp. 499–500) points to the eemian as having an oceanic and warm climate. in his diagram from hollerup, zone 5 represents the climax forest. jessen & milthers (1928, p. 179) bring forth the view of nordmann saying that the lusitanian mollusc fauna was moving into the baltic basin by way of the sounds that cut diagonally through the southern portion of the cimbrian peninsula. however, this idea is, as discussed earlier, not accepted by the present author, where a connection to the west is advocated to be over the kattegat–vendsyssel–skagen regions. an eastern open connection to the white sea over finland and russia will be discussed in connection with the baltic region. the baltic, region 2 appendix 6 and fig. 103 in the baltic sea part of denmark the number of recorded marine molluscs from the eemian has fallen to 19 species compared to the bælt sea region, and no purely lusitanian species occur. however, as pointed out earlier, this change in the climatic situation regarding the baltic fauna can be seen as a consequence of the fact that here only the deeper-water assemblage characterised by turritella communis occurs, although one of the species known from the characteristic part of the bælt sea fauna is recorded, i.e. arctica islandica. however, the tapes species are not met with in this region. the deeper-water environment is therefore well characterised by the turritella community. although the decline in number of species very much resembles the present-day situation between the bælt sea and the baltic as mentioned earlier, five species in the eemian fauna, including turritella communis, show a salinity above the present conditions in the baltic. from the study of diatoms at ollala in eastern fennoscandia, forsström et al. (1988, p. 322) write: “this mixture of warm and cold indicators probably means that the eemian sea in the baltic basin had a connection both to the north sea in the west and to the arctic ocean via the white sea basin in the northeast”. only a few works from eastern fennoscandia have been based on molluscan studies. however, among the papers by zans (1936), sokolova et al. (1972), and gross (1967), gross mentions the following molluscs: portlandia arctica, clinocardium ciliatum, heteranomia squamula, macoma calcarea, littorina littorea, and cerastoderma edule. here the three last mentioned species occur in the eemian from the danish baltic and clinocardium ciliatum from the vendsyssel region, although here in the upper turritella terebra zone correlated to the early weichselian, as discussed later. portlandia arctica has not been recorded from the danish eemian, although it occurs in the beds below the eemian in the anholt boring (the kattegat region), where seidenkrantz (1993, p. 284) also has demonstrated foraminiferal zones a–d with arctic species. gross (1967, p. 118) regards the arctic and arctic– boreal molluscs in the eemian clay as: “relikte aus der portlandia-transgression des dnepr ii-spätglazials, die nach dem pollen-profil und -diagramm der eem-transgression voranging”. the older correlation of the so-called weissmeer transgression by zans (1936, table 1) contains further details on the molluscs upon which the correlation has been based, and it also includes the danish area, mentioning ‘dänische inseln’ after ødum (1933) and ‘skaerumhede’ after jessen et al. (1910). however, the occurrence of the high-arctic portlandia arctica should be placed in the late saalian, as seen in the kattegat region mentioned above, while the arctic–boreal species clinocardium ciliatum could be taken as a relict in the skærumhede sequence from the late saalian environment within the danish area or introduced by the cooling in the early weichselian. the faunal development has been worked out in more detail between the eastern fennoscandia and the danish area (funder et al. 2002). the connection to the arctic over the white sea during the eemian seems to be well established, but only for a shorter time, 1000–2000 years of the more than 10 000 years that the eemian sea existed in the baltic region (funder 2000, p. 68). the kattegat, region 3 appendix 6 and fig. 103 from the kattegat region, 32 species have been recorded, with a high amount of boreo-lusitanian species (72%). five species are lusitanian, among which are found the characteristic eemian species of the shallow-water environment, including the tapes species. however, also the deeper-water environment is represented by the turritella community in this region. geus bulletin no 3.pmd 09-07-2004, 09:10154 155 on anholt, the turritella community occurs at a depth of around 70 m b.s.l., and the tapes fauna in the isefjord area at ejby at a depth of around 10 m a.s.l. the latter is considered to be in situ (madsen 1968). it is tempting to regard the two localities as being at about their original elevation in relation to an eemian sea level some what higher than the recent one, since the glacio-isostatic rebound had expired (petersen 1991b). on the basis of the scattered eemian localities of which some are floes in the weichselian glacial deposits, the maximum extent of the eemian sea cannot be given. however, both the shallow-water environment characterised by the tapes species and the deeper water by the turritella species have been demonstrated. in this way both of the characteristic marine environments from the bælt sea and the baltic respectively are represented in the kattegat region. the north sea, region 5 appendix 6 and fig. 103 the largest amount of mollusc species within the eemian have been recorded from the north sea region, or to be more precise from the coastal region of the north sea. in the danish part of the north sea, many studies on microfossils from the oil and gas fields have demonstrated eemian deposits in the central north sea, but their macrofossils have not been studied (knudsen 1985a, 1986). however, the large amount (91) of molluscs from the coastal region fall into different facies, as seen in the previous regions when a much lower number was looked at. gripp (1964) uses the ‘senescens sand’ and ‘turritella ton’ to give his idea of the marine order of the strata. however, in this context, working with regions and not with localities, it should be emphasised that the development of different facies most probably happened in parallel. gripp (1964, p 223) expresses this himself in saying: “tapes-sand und turritellen-ton sind die beiden facies, die während des ansteigs des meeresspiegels entstanden”. as seen from the species found in the danish north sea coastal region, we do find the turritella species and tapes species, but also the occurrences of donax vittatus should be mentioned as a facies indicator, characterising the high-energy coastal environment from this area facing the eemian north sea. from recent studies on foraminifera in northern germany at the kiel canal, knudsen (1986) shows that the marine transgression took place in the warm part of the eemian, and hinsch (1985) in his mollusc study from the same area revealed three mollusc communities characterising the shallow-water environment, with such genera as mytilus-cerastoderma, acanthocardiavenerupis and bittium-varicorbula. however, the old material from many localities in the danish north sea region cannot be worked out to such detail, although all the marine mollusc species mentioned by hinsch (1985) have been recorded from the danish eemian north sea region. when the molluscan fauna in the danish eemian north sea region is compared with the eemian on the west coast of norway as described by mangerud et al. (1981), 20 molluscan species out of the 35 species recorded from the fjøsangerian are known from the north sea region and 7 species from other eemian regions in denmark. here macoma calcarea and nuculana pernula belonging to the arctic–boreal group occur in the vendsyssel and skagen regions, and in the baltic region macoma calcarea representing deeper water during the eemian, while chlamys islandicus, which does not occur in the danish eemian deposits, is found in the weichselian recorded from the vendsyssel region. this means that the fjøsangerian can be regarded as slightly cooler than the danish north sea eemian deposits. another marine eemian deposit in norway described by andersen et al. (1983) at bø on karmøy (sw norway) revealed 25 molluscan species from the avaldsnes interglacial described in detail by sejrup (1987). here as many as 20 species are in common with those in the danish north sea region, and one, hinia incrassata, has been recorded from the eemian in the vendsyssel region. four species have not been found in the danish eemian. these are the arctic–lusitanian and arctic– boreal species puncturella noachina and boreotrophon clathratus respectively, the latter occurring in the late weichselian deposits in the vendsyssel region. this is much in line with the observations from the fjøsangerian deposits. the four non-occurrences in the danish eemian among the boreo-lusitanian species pecten maximum and lucinoma borealis, the latter being common at both norwegian localities, are difficult to explain. among the 8 purely lusitanian species recorded from the north sea region, only plagiocardium papillosum occurs in the norwegian eemian at fjøsanger, which again points to a slightly cooler position for the norwegian localities. geus bulletin no 3.pmd 09-07-2004, 09:10155 156 the vendsyssel region, region 6 appendix 6 and fig. 103 the eemian mollusc fauna from vendsyssel comprises 55 species with no purely lusitanian climatic affinity, while quite a few (nine species ~ 16%) are found in the arctic and the boreal zones. the stratigraphical position has been well elucidated through foraminiferal investigations (knudsen & lykke-andersen 1982; knudsen 1984, 1985b, 1992; lykke-andersen 1987). the study by lykke-andersen (1987, fig. 5) also involves the molluscs, and references are made to the zones established on the basis of macrofossils. according to the foraminiferal studies, the transition to the early weichselian takes place around 120 m b.s.l. in the skærumhede i sequence (jessen et al. 1910), which is about 140 m b.s. this means that the upper part of the turritella terebra zone falls within the early weichselian. the two arctic to high boreal species serripes groenlandicus and clinocardium ciliatum at depths of 132 m and 127 m b.s. respectively are discussed by nordmann (jessen et al. 1910, pp. 124–128), and the climatic indications from turritella communis mean that the assemblage existed at the transition between the high and middle boreal. in the paper by knudsen (1992), it is said that an abrupt faunal change at the eemian–weichselian boundary reflects a drop in water depth of at least 50 m and a subsequent drop in temperature of several degrees. the drop in temperature might well be reflected in the mollusc fauna by the occurrences of the two bivalves mentioned above, and for the drop in sea level it is tempting to recall the observed occurrence of the eulittoral mytilus edulis at a depth of 135 m b.s.l. in the skærumhede i boring and up to the abra nitida zone, which forms the transition to the arctic turritella erosa community as mentioned earlier. therefore, within the vendsyssel area the eemian (isotopic stage 5e) is represented by a turritella community that continues into the beds representing the isotopic stages 5d–a (knudsen 1992, fig. 4). the hordalandian stage in western norway contains serripes groenlandicus and clinocardium ciliatum species and is referred to the early weichselian (mangerud et al. 1981). arctic conditions first occurred in the macrofossil zones turritella erosa, balanus crenatus and macoma calcarea (bahnson et al. 1974), which cover the portlandia arctica zone sensu nordmann (jessen et al. 1910, fig. 8). the skagen region, region 7 appendix 6 and fig. 103 the 14 eemian molluscs found in the skagen boring are the lowest number recorded within the eemian sites. however, the finds are a clear omen of the deeperwater environment not encountered earlier in denmark on the basis of molluscs. the recorded molluscs point to an environment like the deeper part of the skagerrak today, with a community such as the amphilepis norvegica/pecten vitreus, where the latter (delectopecten vitreus) occurs in the skagen well, as mentioned earlier. the boundary to the overlying arctic deposits characterised by the occurrences of portlandia arctica is sharp and coincides with a sedimentological change to a diamicton with dropstones in the arctic part, as found in the skærumhede sequence within the turritella erosa zone (bahnson et al. 1974). therefore, in the skagen well no transition zone from substage 5e to 5d–a can be demonstrated in the molluscan faunas. the recorded eemian communities and/or characteristic molluscan species for six regions with eemian marine deposits are given in table 3. 1. bælt sea mytilus edulis littoral tapes spp. shallow arctica islandica deeper 2. baltic littoral shallow turritella t. communis deeper 3. kattegat mytilus edulis littoral tapes spp. shallow turritella t. communis deeper 5. north sea donax vittatus littoral tapes spp. shallow turritella t. communis deeper 6. vendsyssel littoral shallow turritella t. communis ~ 100 m 7. skagen littoral shallow amphilopsis/pecten delectopecten vitreus > 100 m region community species depth table 3. eemian communities and/or characteristic molluscan species geus bulletin no 3.pmd 09-07-2004, 09:10156 157 early/middle weichselian stage 115 000 – 25 000 b.p. the kattegat, region 3 appendix 6 and fig. 103 although the number of mollusc species recorded from the kattegat region during the early/middle weichselian is low – seven species – the climatic indications for the arctic environment are clear, considering that all species can be found in the high arctic, and that one species, portlandia arctica, is high arctic par excellence, and macoma calcarea indicates shallow water. the stratigraphical position of the arctic macoma community found in the kattegat region – holmstrup on sjælland – has been determined by foraminiferal correlation and aminostratigraphical investigations, as mentioned earlier (petersen & buch 1974; miller & mangerud 1985). recently, the foraminiferal studies of the quaternary sequence in the anholt boring have demonstrated a middle weichselian deposit at a depth of about 50 m b.s.l. (seidenkrantz 1993). considering the information given by knudsen (1992) on a drop of sea level of around 50 m during the transition from the eemian to the weichselian, the middle weichselian beds in the cored section on anholt may represent rather shallow-water deposits. this is in accordance with the occurrence of the arctic macoma community. the vendsyssel region, region 6 appendix 6 and fig. 103 foraminiferal studies by lykke-andersen (1987) indicate that the early weichselian beds are represented by the upper turritella terebra zone, and that the deeper-water temperate turritella community continued into the first part of the weichselian with the following abra nitida zone as a transition to the arctic deeper-water turritella community (turritella erosa). together with the arctic and arctic–subarctic species (seven in number, forming nearly 20% of the mollusc species), the sedimentological data show the occurrences of ice-rafted material recorded both from the skærumhede i and the skærumhede ii borings (jessen et al. 1910, p. 76; bahnson et al. 1974, figs 3, 4, 7) reflecting arctic conditions. it has been argued by nordmann (jessen et al. 1910) that species within the genera mytilus, cyprina, zirphaea, nassa, and bittium must be regarded as allochthonous and older elements. however, they could also be regarded as stray finds from contemporary shallow-water to littoral deposits occurring within times of higher temperatures in the near-shore areas, similar to the near-shore fauna of middle weichselian age – the bø interstadial (40–64 ka) with gibbula cineraria and mytilus edulis, the latter occurring frequently (sejrup 1987). during the younger part of the marine middle weichselian – around 32 000 b.p. – when the shallow-water arctic macoma community was established, no mytilus edulis or bittium reticulatum have been recorded. the development of the bottom communities within the older weichselian sequence is therefore given by the transition from the turritella communities in deeper water to the arctic macoma community in shallow water. the skagen region, region 7 appendix 6 and fig. 103 very few molluscs have been found in the skagen boring of older weichselian age. the four species are all arctic, and the occurrence of portlandia arctica shows that high arctic conditions have prevailed and ice-rafted material occurs. there is no indication of near-shore fauna as recorded from the vendsyssel region. from this, it might be concluded that the deposition of these beds took place in the first part of the middle weichselian, contemporaneous with the deposition of the turritella erosa beds of the skærumhede sequence, but at a water depth of more than 100 m, as demonstrated earlier. from the few finds, it is not safe to point to a certain community on the basis of molluscs. however, the community in deeper arctic waters is described by other animals than molluscs, i.e. the ascidia–spongia epifauna, and at depths exceeding 200 m by gorgonocephalus species. from the estimate on water depth taken in comparison with the early part of the arctic sequence in the vendsyssel region, the palaeodepth must have been well above 100 m. the recorded early/middle weichselian communities and/or characteristic molluscan species are given in table 4. geus bulletin no 3.pmd 09-07-2004, 09:10157 158 late weichselian stage 25 000 – 10 000 b.p. the vendsyssel region, region 6 appendix 6 and fig. 103 the 35 mollusc species found in the vendsyssel region are in number very close to the number of species encountered in the vendsyssel region during the early/ middle weichselian (36 species). however, as seen in fig. 103, the percent of molluscs with a wide range and only connected to the subarctic and southwards is higher in the late weichselian (46%) compared to the early/middle weichselian (28%). this can be explained by the way the development in the two seas before and after the main glaciation, the older and younger yoldia sea respectively took place. the deposits from the older yoldia sea reflect the transition from deeper arctic to shallow-water arctic communities, the turritella and macoma communities respectively. the late weichselian beds within the shallow-water environment show a development from the arctic macoma community to the boreo-arctic mytilus-zirphaea community after 13 000 b.p., with a deeper-water community characterised by the portlandia arctica species, as outlined by petersen (1984), which could be part of the deeper macoma community – the so-called ophiocten zone. these observations form the background for the earlier given explanation of the occurrences of boreal shallow-water species such as mytilus edulis in the deeper-water arctic community in the older weichselian deposits from the vendsyssel region. the occurrences of the mytilus edulis species in the late weichselian deposits in large quantities are described by jessen (1899). the dates of the earliest occurrences of zirphaea and mytilus go back to 12 770 and 12 520 b.p. 14c years respectively. all the 30 14c dates forming the base for the evaluation of the late weichselian sea levels and occurrences of fauna communities as figured in petersen (1984, fig. 1) have been listed by petersen & rasmussen (1995a, table 1). it appears that the dates older than 13 000 b.p. 14c years all come from hiatella arctica and macoma calcarea (only one date) going as far back as 14 650 ± 190 b.p. 14c age. considering the mollusc species inhabiting the waters “of the swedish west coast shortly after deglaciation” (fredén 1986, p. 55), one finds also chlamys islandica and mytilus edulis shortly after 13 000. the latter within the time span of its first dated occurrence in the younger yoldia sea deposits in denmark. as to the deeper-water deposits also around 13 000, one can take the sample from the dybvad clay pit (fig. 1) dated to 13 010 ± 190 b.p. 14c which contained the following molluscs: hiatella arctica, mya truncata, macoma torelli, portlandia arctica, buccinum groenlandicum and cylichna occulta (petersen 1984). it is seen that still after the immigration of boreo-arctic fauna to the shallow-water environment, showing an amelioration in climate, the arctic community persisted in the deeper water as shown by the dating from the bindslev clay pit giving 12 650 ± 180 14c age b.p., with species such as macoma calcarea and portlandia arctica. the same situation can be estimated from the investigation of the pleistocene/holocene boundary in south-western sweden (the moltemyr core) where “zone z comprising the samples from 560 cm to 650 cm, is characterised by portlandia arctica and nucula tenuis (nuculoma tenuis, here taken as a species with a wide climatic range), and by the absence of many of the species of the overlaying zone (such as mytilus edulis) … the water depth during deposition of zone z was greater than during any of the other zones (above) probably more than 20 m” (feyling-hanssen 1982, p. 128). regarding the climatic indication of portlandia arctica, feyling-hanssen (1982, p. 131) quotes andersen (1975, p. 54) saying: “evidently, portlandia arctica lived near the ice fronts [in southern norway] also during older, glacial phases, but it seems to have disappeared from our coasts shortly after the ra event, probably due to a warming of the sea”. 3. kattegat littoral arctic macoma m. calcarea shallow deeper 6.vendsyssel littoral arctic macoma m. calcarea shallow arctic turritella t. erosa ~ 90 m turritella t. communis ~ 90 m 7. skagen littoral shallow ascidia–spongia 100–200 m region community species depth table 4. early/middle weichselian communities and/or characteristic molluscan species geus bulletin no 3.pmd 09-07-2004, 09:10158 159 according to sørensen (1979), the disappearance of portlandia arctica from the oslo fjord area occurred somewhat before 10 000 b.p. the younger dryas marine deposits have not been demonstrated in the vendsyssel region but are recorded from the skagen region, which will be discussed next. the skagen region, region 7 appendix 6 and fig. 103 the nine species recorded from the skagen well indicate an arctic deeper-water community very much like the arca-astarte crenata community (ockelmann 1958). there are no finds of species which could be referred to the more shallow-water environment as seen in the case of the vendsyssel region to the south both during the early/middle weichselian and the late weichselian. through most of the history of the cored section of pleistocene age, the skagen well has revealed mollusc assemblages from a deeper-water environment. also the transition to the holocene takes place in deeper water. the purely arctic species portlandia arctica together with bathyarca glacialis is found right up to the strata dated to around 10 000 b.p. forming the pleistocene– holocene boundary in the skagen well. however, in the description of the shell fauna of the marine clays in the oslo fjord region, brögger (1900, p. 685) states: “portlandia arctica is never found in the arca clay”. later datings of the ‘middle arca clay’ and the ‘younger arca clay’ given by b.g. andersen (1965, p. 118) yielded early preboreal ages. in the younger arca clay from norway, species such as mytilus edulis, zirfaea crispata, and macoma balthica (b.g. andersen 1965, table 2) are also found, which characterise the shallowwater deposits in vendsyssel after 13 000 b.p. 14c age. the recorded recent occurrence of bathyarca glacialis from southern iceland implicates extension into the high-boreal region, although the main extension is in the arctic. the norwegian records of bathyarca glacialis come from a more shallow-water environment, as seen from the occurrences of the three shallowwater species mentioned above. the recorded late weichselian communities and/or characteristic molluscan species are given in table 5. the preboreal–boreal stage 10 000 – 8000 14c years b.p. the north sea, region 5 appendix 6 and fig. 103 mollusc faunas from the late weichselian have here been recorded only from the vendsyssel and skagen regions. as seen in fig. 103, the early part of the holocene, the preboreal and boreal, have a record of 26 species, with as many as 77% (20 species) boreo-lusitanian. this is in contrast to the records from the late weichselian, when the arctic–boreal elements dominated, with 54% in the vendsyssel region and 55% in the skagen well, the latter with only a few species and representing a deeper-water environment. the preboreal–boreal north sea faunas contain eulittoral as well as shallow-water species. mytilus edulis, littorina littorea and cerastoderma edule characterise the littoral zone and macoma balthica the shallow-water zone. using the characteristic species from the c.g.j. petersen community concept, the oldest recorded faunal communities from the north sea might be the mytilus epifauna community with littorina littorea, and the macoma infauna community with cerastoderma edule. also the abra community on mixed bottoms with phaxas pellucidus, corbula gibba and mya truncata might be reflected in the recorded species. the skagen region, region 7 appendix 6 and fig. 103 as discussed earlier, the environment of the earliest holocene, the preboreal and boreal, can be referred to the maldane-ophiura sarsi community. this deep6. vendsyssel mytilus/zirphaea z. crispata littoral arctic macoma m. calcarea shallow ophiocten zone portlandia arctica deeper 7. skagen littoral shallow arca-astarte bathyarca glacialis deeper region community species depth table 5. late weichselian communities and/or characteristic molluscan species geus bulletin no 3.pmd 09-07-2004, 09:10159 160 water community observed in the skagen region compared to the shallow-water communities recorded from the north sea coastal region once more demonstrates the unique position of the deeper-water communities observed in the skagen well material compared to the other regions in denmark through the late quaternary. the recorded preboreal–boreal communities and/or characteristic molluscan species are given in table 6. the atlantic stage 8000–5000 14c years b.p. the bælt sea, region 1 appendix 6 and fig. 103 out of the 47 species known from the bælt sea region, 31 have been recorded from the atlantic (fig. 103). the littoral zone with mytilus edulis, littorina littorea, littorina saxatilis, cerastoderma edule, and macoma balthica from the shallow-water zone, is recorded; furthermore, the abra alba community together with corbula gibba. these faunal elements reveal the mytilus epifauna community with ostrea edulis, which no longer occurs in this area. in the infralittoral zone is the macoma infauna community where such species as paphia aurea, tapes decussatus, and venerupis pullastra have been found, and finally the abra community with corbula gibba. also the epifauna on the vegetation is reflected in rissoa albella, r. membranacea, and r. inconspicua and other gastropods. also the bivalve parvicardium exiguum is associated with the vegetation. the communities mentioned are still to be found in the bælt sea region, whereas paphia, tapes, venerupis and ostrea are no longer found in this region. the baltic, region 2 appendix 6 and fig. 103 fifteen mollusc species out of the 19 recorded from the baltic region during the holocene can be referred to the atlantic (fig. 103). the occurrences of mytilus edulis and littorina littorea are referred to the mytilus epifauna community in the littoral zone, while species, as macoma balthica, cerastoderma edule, and scrobicularia plana represent the macoma infauna community in shallow water. the occurrences of both littorina littorea and scrobicularia plana are characteristic for the atlantic in the baltic and are now absent. spärck (1950) points to the wider extent of scrobicularia plana in the stone age as a consequence of warmer water in those days; however, in the present work the higher salinity is preferred as an explanation, as mentioned earlier. this is supported by the occurrences of gastropods like bittium reticulatum, rissoa albella, and aporrhais pespelicani, species recorded from other regions today with higher salinity. it should be noticed that scrobicularia plana and littorina species have been demonstrated as far north in the baltic as estonia (kessel & raukas 1979, fig. 9), although only with a low percentage but persisting into the subboreal. the unexpected find of ostrea edulis from estonia has later been re-evaluated as transported there by some seamen and thrown then overboard (in a letter from prof. a. raukas, may 1995). according to nordmann (1903b, 1906), madsen (1944), and spärck (1942, fig. 21), the southernmost finds of subfossil oysters are the bælt sea and øresund off landskrona. the kattegat, region 3 appendix 6 and fig. 103 from the kattegat region, only half of the recorded species have been dated so as to give a first appearance date. this amounts to 23 species from the atlantic (fig. 103). all of the dated species come from geologically mapped areas and not from the kattegat proper. therefore the observed species all come from shallow-water environments, excluding the deeper-water environment recorded from foraminifera (christiansen et al. 1993; seidenkrantz & knudsen 1993). 5. north sea mytilus m. edulis littoral macoma m. balthica shallow abra a. alba deeper 7. skagen littoral shallow maldana/ophiura > 150 m region community species depth table 6. preboreal–boreal communities and/or characteristic molluscan species geus bulletin no 3.pmd 09-07-2004, 09:10160 161 from the listed species dated to the atlantic the mytilus epifauna community with littorina littorea and the macoma infauna community with cerastoderma edule and tapes decussatus can be pointed out. furthermore, the abra community with corbula gibba, which is common in present-day inner danish waters (thorson 1950), is present. the limfjord, region 4 appendix 6 and fig. 103 this region has the highest number of recorded mollusc species from the holocene, viz. 147 species, and 77 have been dated to the atlantic (fig. 103). petersen (1918, pp. 22–36) described the communities in the limfjord region covering the macoma balthica, the venus and the abra communities. also an area with mya truncata is mentioned, forming a transition zone between the macoma and the abra communities. in patches the epifauna elements such as mytilus edulis and modiola modiolus are found. from the zostera vegetation, the rissoa and bittium species are mentioned. all of the characterising species from these communities have been recorded from the atlantic. paphia aurea, tapes decussatus, venerupis rhomboides and venerupis pullastra were represented during the atlantic, where as only venerupis pullastra is present in the limfjord today. ostrea edulis was well established during the atlantic, as seen from the species composition of the ‘køkkenmødding’ (kitchen midden) (petersen 1986a, figs 3, 4). the above-mentioned species and cerastoderma edule occurred in the infralittoral zone in large quantities most probably in the tidal zone which was the best collecting grounds for the stone age people. in a multi-lobed body of water such as the limfjord, many habitats have existed during the atlantic. however, also the development through time has been considered, as seen in the case of the marine stages in tastum sø – once the southernmost part of skive fjord (rasmussen & petersen 1980). in the northern part of the former limfjord during the atlantic, the deeper-water fauna with abra alba and corbula gibba can be demonstrated at the vust locality (petersen 1981, p. 502). the recorded atlantic communities have very much in common with the recent communities. the north sea, region 5 appendix 6 and fig. 103 twenty-seven species immigrated during the atlantic in the north sea coastal region (fig. 103), and chamelea striatula and spisula subtruncata characterise the venus community and are very common in the recent north sea region. also paphia aurea and tapes decussatus make their appearance in the north sea region during the atlantic. according to hessland (1943), tapes decussatus should immigrate to the west coast of sweden already in the boreal, while paphia aurea, venerupis rhomboides and venerupis pullastra followed in the atlantic. this is a close parallel to the recorded immigration to the limfjord region, although here following the transgression and not superjacent to older marine deposits as in the north sea. the vendsyssel region, region 6 appendix 6 and fig. 103 the dates from the vendsyssel region during the holocene are made on only a few species. however, the faunal assemblages sensu nordmann (jessen 1905) can be commented upon in the light of immigration dates observed in the neighbouring limfjord region. nordmann (jessen 1905, p. 145) operates with five assemblages (from a to e) with the following headings: a) beach deposits b) oyster banks c) deposits in coves and sounds d) deposits in fjords and sounds with muddy bottoms and no current e) lagoonal deposits a) beach deposits the first type – the beach deposits – cannot be considered in any relation to the community concept sensu c.g.j. petersen, since the dominating part of the shell material has been redeposited. however, as a geological unit, it points to a former sea level stand, albeit difficult to date, because of the allochthonous character of these deposits. among the 90 species listed from this region (southgeus bulletin no 3.pmd 09-07-2004, 09:10161 162 ern part of vendsyssel), nordmann (jessen 1905, table a) points to spisula subtruncata and fabulina fabula as being conspicuous, but other species may dominate at some localities, as seen from the table. both species pointed out by nordmann are recorded from the limfjord during the atlantic. b) oyster banks as pointed out by petersen (1918, p. 52), the so-called oyster banks in the recent limfjord have 1 or 2 specimens per m2. however, the places recorded by nordmann are located on former narrow channels where the oysters occurred in large quantities together with chlamys varia, hiatella arctica, retusa truncatula, mysella bidentata, parvicardium exiguum, paphia aurea, venerupis pullastra, bittium reticulatum, rissoa inconspicua, rissoa parva, buccinum undatum, nucula nitidosa, triphora adversa, cerastoderma edule, and hydrobia ulvae, all of which are recorded from the limfjord during the atlantic. only two species mentioned by nordmann (jessen 1905, p. 147) as being characteristic from some of the oyster banks, caecum glabrum and acmaea virginea, have their earliest record from the limfjord in the subboreal. therefore the oyster banks sensu nordmann seem to be well established in the vendsyssel region already during the atlantic, considering the dates obtained from the limfjord region. the oyster banks from the atlantic appear to be characteristic features with their high diversity of species and huge quantities of ostrea edulis not met with in present-day danish waters. this could be seen as a parallel to the fluctuation in the population of oysters observed during the last hundred years in danish waters, but should rather be connected with changes in the tidal currents which changed to a minimum during the following stage – the subboreal (petersen 1993), and put an end to the large oyster banks. c) deposits in coves and sounds from these deposits nordmann points to species such as spisula subtruncata, modiolus modiolus, thracia phaseolina, and corbula gibba as being characteristic of coves and sounds. they have all been recorded from the limfjord during the atlantic, and they represent species known from the deeper-water deposits both as epifaunal elements (modiolus modiolus) and infaunal elements as found in the c.g.j. petersen communities, the modiola and abra communities respectively. this is further demonstrated by the following species mentioned by nordmann (jessen 1905, p. 148): cerastoderma edule, parvicardium scabrum, nucula nitidosa, hiatella arctica, chamelea striatula, timoclea ovata, venerupis pullastra, fabulina fabula, tellimya ferruginosa, lunatia alderi, and retusa truncatulus. also these species have been dated back to the atlantic in the limfjord region. ostrea edulis occurs, but as stray finds among the infauna elements dominating in the above-mentioned assemblage that includes abra alba, which occurs in most of the samples, although not frequently (jessen 1905, table c). d) deposits in fjords and sounds with muddy bottoms and no current from such deposits nordmann mentioned the finds of zostera, which was a well established vegetational element in the recent limfjord, according to petersen & jensen (1911, map 1). the dominating species in this assemblage, which resembles the present-day fauna in such environments, are hydrobia ulvae, littorina littorea, littorina obtusata, rissoa membranacea, cerastoderma edule, mytilus edulis, scrobicularia plana, paphia aurea, bittium reticulatum, hinia reticulata, onoba semicostata, parvicardium exiguum, macoma balthica, and ostrea edulis, the last two species only with a few specimens. all the above-mentioned species occurred in the limfjord region during the atlantic. the littorina, rissoa, and parvicardium species might often be found on the zostera vegetation. among the dominating species also mentioned by nordmann, some have not been dated back to the atlantic (in the limfjord region) but occur in the subboreal, viz. littorina tenebrosa, akera bullata, and retusa obtusa. however, already the species recorded from the atlantic point to the so-called echinocyamus community (spärck & lieberkind 1921), although the echinoids have not been recorded by nordmann (jessen 1905). e) lagoonal deposits these deposits represent two assemblages, according to nordmann (jessen 1905, p. 150), viz. an older more open-water environment with species such as mactra stultorum, tellimya ferruginosa, chamelea striatula, fabulina fabula, ensis ensis, lunatia catena, lunatia alderi, and aporrhais pespelicani, which are mixed with faunal elements from the lagoon itself, such as hydrobia ulvae, scrobicularia plana, and mytilus edulis. in connection with a zostera vegetation, rissoa membranacea and lacuna vincta may occur in huge quantities. geus bulletin no 3.pmd 09-07-2004, 09:10162 163 such a deposit cannot be compared to any of the petersen communities, although they play an important role in the geological setting, as was the case also with the beach deposits. in the northern and eastern part of vendsyssel, further comments will be added to the shallow-water and beach deposits with the finds of the dosinia and mya arenaria species. they have been dated to the subboreal and subatlantic respectively and are therefore commented upon later. the skagen region, region 7 appendix 6 and fig. 103 nearly all of the eight recovered species from the atlantic (fig. 103) show a deep-water fauna, which on the basis of the dominating role of the echinoids is tentatively referred to the amphiura community known from the present-day skagerrak. the final large eustatic rise took place during the late boreal – early atlantic, and the difference in isostatic rebound from 8000 b.p. between the skagen and limfjord regions is around 31 m, with the highest amount in the north (skagen). it appears that the water depth in the skagen region must have been up to 100 m during the atlantic (petersen 1981, 1991b). therefore, the occurrence of a single spisula subtruncata shell must be taken as far outside its habitat, considering that the modern depth range of this species is 0–36 m (petersen 1986c, table 2). the recorded atlantic communities and/or characteristic molluscan species are given in table 7. the subboreal stage 5000–2500 14c years b.p. the bælt sea, region 1 appendix 6 and fig. 103 there are no dated mollusc finds from the subboreal in the bælt sea region. as stated for the atlantic in this region, the bottom communities known from the present day were already established, but they included some species such as tapes and ostrea which are no longer extant in this area. however, as paphia aurea and ostrea edulis still occurred in the iron age sites – from the subatlantic – it is most probable that these species persisted there, while tapes decussatus and venerupis pullastra expired during the subboreal in the bælt sea region (petersen 1985c, fig. 5). the baltic, region 2 appendix 6 and fig. 103 there is no dated record of molluscs from the subboreal in the danish part of the baltic. therefore the change in the atlantic littorina fauna, into the lymnaea sea fauna, which occurred during the subboreal around 4000 b.p. (fredén 1980, p. 70), must be taken from observations outside denmark. the mollusc fauna from estonia shows that littorina littorea, rissoa membranacea, and scrobicularia plana persisted there until about the end of the subboreal (kessel & raukas 1979, fig. 9). the implications of this should be that these species must have been present in the danish area throughout the subboreal. in the central part of the baltic, around gotland, lymnaea peregra f. baltica re-immigrates after the 1. bælt sea mytilus m. edulis/ostrea edulis littoral macoma m. balthica/tapes spp. shallow abra a. alba deeper 2. baltic mytilus m. edulis/littorina littorea littoral macoma m. balthica shallow deeper 3. kattegat mytilus m. edulis littoral macoma m. balthica/tapes spp. shallow abra a. alba deeper 4. limfjord mytilus/modiola m. edulis/tapes spp. littoral macoma m. balthica shallow abra/venus a. alba deeper 5. north sea littoral shallow venus chamelea striatula deeper 6. vendsyssel littoral modiola m. modiolus shallow abra a. alba deeper 7. skagen littoral shallow amphiura parvicardium minimum ~ 100 m region community species depth table 7. atlantic communities and/or characteristic molluscan species geus bulletin no 3.pmd 09-07-2004, 09:10163 164 maximum of the littorina transgression (munthe 1940, p. 124). this gastropod was also present in the early, more brackish part of the littorina sea deposits in fakse bugt. in estonia (kessel & raukas 1979, fig. 9), the reappearance of lymnaea took place around 4000 b.p., implying that the salt-demanding species (littorina, rissoa, and scrobicularia) occurred together with the brackish lymnaea species throughout the later part of the subboreal! the kattegat, region 3 appendix 6 and fig. 103 the mollusc faunas recorded from the kattegat region represent only part of the total faunal complex within this large region, and have been dated only on djursland. however, this demonstrates the expiring tidal amplitude in the early part of the subboreal. the only dated immigrants to the fauna from the central part of djursland during the subboreal are onoba semicostata and littorina tenebrosa. both extended into the baltic today and tolerate brackish water. in this way they are typical for the environmental changes recorded in the marine faunas from djursland. the fauna during the atlantic was characterised by ostrea edulis, tapes decussatus, macoma balthica, and corbula gibba. bittium reticulatum was present in large quantities, but disappeared in the subboreal. also the decline in numbers of hydrobia ulvae and its replacement in equal numbers by hydrobia ventrosa speak in favour of a more brackish-water influence. the implications of the study of mollusc species on a quantitative basis in connection with 14c dates and pollen analyses confirm that the fauna during the tapes sea period was more prolific than nowadays. however, it also demonstrates as a new point of view that this applies only for the atlantic. in petersen (1993, p. 368) it is argued that the change in sedimentation rate from the atlantic to the subboreal, which has been calculated for the korup sø area on djursland, points to a lowering of the tidal range in danish waters since the atlantic. this is explained in that way that sedimentation will stay low as far as the tidal current reaches and allows halophilous species to live far up in the fjords according to the observations on the faunal record. furthermore, an older record from the mapping of the area of flaser bedding seen as a tidal bedding supports such an explanation. it was tempting to see the change from the littorina sea to the lymnaea sea in the baltic on the background of such a lowering of the tidal impact in the inner danish waters. however, as shown in the preceding section on the baltic, the change occurred around 4000 b.p. recalling the statement by c.g.j. petersen that the deposition of the tapes layers has happened in a period when the danish waters from a hydrographical point of view have been more like the north sea or the open sea than now, it is clear that a tidal impact could make the difference and explain the large oyster banks far into the roskilde fjord in north-eastern sjælland and other former fjord regions facing the kattegat region. the well-dated ertebølle coastal sites (‘køkkenmøddinger’ – kitchen middens) from all over denmark also present a large amount of ostrea edulis from the atlantic and demonstrate that the molluscan diet later in the subboreal was based on the cardium species (andersen 1991, 1995). this situation has lasted into the iron age, as seen in the shell middens from the bælt sea area (petersen 1985c, fig. 5). however, this change mostly affected the fjord complex. consequently the kattegat region still has the communities listed for the atlantic. the limfjord, region 4 appendix 6 and fig. 103 the 36 species which immigrated into the limfjord during the subboreal (appendix 6) can be considered according to their way of life, presented from the list below. age: subboreal climatic regions: asb. class gastropoda subclass prosobranchia order archaeogastropoda margarites helicinus (phipps 1774) subclass opisthobranchia order anaspidea retusa obtusa (montagu 1803) total for climatic regions asb. : 2 (5.6%) climatic regions: asbl class gastropoda geus bulletin no 3.pmd 09-07-2004, 09:10164 165 subclass prosobranchia order archaeogastropoda acmaea tessulata (müller 1776) order neotaenioglossa lacuna pallidula (da costa 1778) total for climatic regions asbl: 2 (5.6%) climatic regions: .sbl class gastropoda subclass prosobranchia order archaeogastropoda acmaea virginea (müller 1776) class bivalvia subclass pteriomorpha order pterioida delectopecten vitreus (gmelin 1791) total for climatic regions .sbl: 2 (5.6%) climatic regions: ..bl class gastropoda subclass prosobranchia order archaeogastropoda helcion pellucidum (linnaeus 1758) gibbula tumida (montagu 1803) skenea basistriata (jeffreys 1877) order neotaenioglossa littorina tenebrosa (montagu 1803) lacuna parva (montagu 1803) cingula semistriata (montagu 1808) rissoa violacea desmarest 1814 caecum glabrum (montagu 1803) aporrhais pespelicani (linnaeus 1758) order heterogastropoda epitonium turtonis (turton 1819) vitreolina philippii (rayneval & ponzi 1854) order neogastropoda hinia incrassata (ström 1768) raphitoma purpurea (montagu 1803) raphitoma linearis (montagu 1803) subclass heterobranchia order heterostropha chrysallida decussata (montagu 1803) chrysallida indistincta (montagu 1808) ebala nitidissima (montagu 1803) eulimella laevis (brown 1827) ondina divisa (j. adams 1797) ondina diaphana (jeffreys 1848) subclass opisthobranchia order anaspidea akera bullata müller 1776 class bivalvia subclass palaeotaxodonta order nuculoida nucula nucleus (linnaeus 1767) subclass pteriomorpha order pterioida palliolum striatum (müller 1776) palliolum tigerinum (müller 1776) subclass heterodonta order veneroida mactra stultorum (linnaeus 1758) lutraria lutraria (linnaeus 1758) ensis ensis (linnaeus 1758) order myoida pholas dactylus linnaeus 1758 total for climatic regions ..bl: 28 (77.8%) climatic regions: ...l class gastropoda subclass prosobranchia order neotaenioglossa alvania lactea (michaud 1830) onoba proxima (forbes & hanley 1850) total for climatic regions ...l: 2 (5.6%) total for age subboreal: 36 (14.6%) the archaeogastropoda are all (six) epifauna on seaweeds or on hard substrates. the neotaenioglossa have seven epifaunal elements mostly on seaweeds and two infauna species, of which aporrhais pespelicani is a shallow infauna animal. the heterogastropoda with epitonium turtonis and vitreolina philippii are associated with other animals, the former feeding on anemone or preying on other species and the latter being an intermittent parasite of echinoderms (fretter & graham 1982, p. 387). the heterostropha with six species are predators or external parasites. the anaspida with two species, akera bullata and retusa obtusa, are epifauna and infauna species respectively, the former on zostera in shallow water and the latter in mud or fine sand connected with the macoma community. the only nuculoida found, nucula nucleus, belongs to the shallow infauna. the pterioida with three species are referred to the epifauna, since the delectopecten vitreus is found attached with its byssus on hard substrates. the veneroida have three species which are all referred to the infauna. lutraria lutraria and ensis ensis are deep-borrowing. geus bulletin no 3.pmd 09-07-2004, 09:10165 166 the myoida with pholas dactylus bores in different substrates. when taking the above-mentioned groups of species associated with other animals, carnivores, predators, and boring species as a whole, we have three categories: the epifauna with 47.2%, the infauna with 19.4%, and other elements with 33.4% of the species immigrated during the subboreal. when the same procedure is followed for the 77 species which have been dated to the atlantic in the limfjord region, we find that the percentages for the epifauna, the infauna and other elements are 31%, 46.8% and 22% respectively, which shows that the epifauna element becomes the dominating one in the subboreal among the newcomers. this might tentatively be connected with a denser vegetation in the subboreal of sea-weed. the north sea, region 5 appendix 6 and fig. 103 nineteen species make their first appearance in the danish north sea during the subboreal. when considering their way of living and their grouping into epifauna, infauna and other elements, it appears that the groups are of equal size, i.e. five, six and eight species respectively. however, the number is too low to be used for any comparison with other regions. in the north sea region the dates of first appearance go back to the preboreal–boreal stage, showing that the initial stages were dominated by the infauna species; the preboreal–boreal: seven epifauna, 16 infauna, and four other elements; the atlantic: six epifauna, 17 infauna, and four other elements. the development of the bottom communities in the north sea region seems in this way to corroborate the changes observed in the limfjord region from the atlantic to the subboreal. these changes are in facies rather than climatic. a slightly more temperate fauna was met with during the atlantic, as mentioned earlier, and it has consequently no bearing on the observed changes. but the expiring tidal influence in the danish waters taking place in the early subboreal might have been of some importance for the environmental changes reflected through the bottom communities. the vendsyssel region, region 6 appendix 6 and fig. 103 the vendsyssel region does not give much information on the immigration of species during the holocene. however, the dosinia beds were described from this area and have been dated quite recently in the type area around strandby north of frederikshavn (nordmann 1904; petersen 1991b). the oldest date for the dosinia exoleta, which is the characteristic species for the dosinia beds, is 4240 ± 85 b.p. in 14c years (k5318). this earliest dated occurrence of dosinia exoleta corresponds to a hydrographical change in the kattegat region described by nordberg & bergsten (1988) and nordberg (1989). the demonstrated lowering of the tidal influence in the inner danish waters took place also in the early part of the subboreal. petersen (1976) pointed out that seven mollusc species hitherto known only from the dosinia beds also occur in the raised marine deposits from the western part of the limfjord, i.e. lucinoma borealis, hinia incrassata, venerupis rhomboides, abra prismatica, lutraria lutraria, pholas dactylus, and helcion pellucidum. furthermore, not only ten species from the dosinia beds are also in the deposits from the limfjord but five of them occurred already during the atlantic: gari fervensis, turritella communis, lucinoma borealis, abra prismatica, and venerupis rhomboides. these species, representing an infauna assemblage very much like the dosinia species, were also characteristic of the early holocene dominating infauna mollusc assemblage. mörner (1969, pp. 384–386, and table 1) points out that some species in the dosinia fauna occur in older layers along the swedish west coast, referring to the works by hessland (1943) and antevs (1917). however, this is not the case with the characterising dosinia species, in as much as dosinia exoleta has not been demonstrated in the studies by hessland and antevs and dosinia lincta occurs only in the younger deposits referred to the subboreal. among the 15 species listed, eight have been recorded from the limfjord, out of which epitonium turtonis, oenopota turricola, acteon tornatilis, and cylichna cylindracea have their first appearance in the atlantic, and lutraria lutraria, pholas dactylus, and alvania lactea appeared in the subboreal, whereas the occurrence of modiolus adriaticus in the limfjord has not been dated. in this way, we are left with only six species which have not been found in other regeus bulletin no 3.pmd 09-07-2004, 09:10166 167 gions outside vendsyssel older than the subboreal: pecten maximus, dosinia exoleta, dosinia lincta, gari depressa, alvania cimicoides, and trivia monacha. only the characterising species dosinia exoleta has been dated as mentioned above, and recently donax vittatus from vr. holmen in the northern part of vendsyssel, west of strandby, with the oldest date of this bivalve hitherto obtained in the danish deposits, 4240 ± 75 14c age b.p. (aar-1481). this date shows that donax characterising the highenergy shore deposits occurred in danish waters since the subboreal. the further revision of the dosinia fauna shows that only very few species are limited to the vendsyssel region both in time and space. therefore, it cannot be sustained for the danish material as mentioned by mörner (1969, p. 384) that: “the dosinia layers contains a great number of new boreo-lusitanic immigrants” of the molluscs entirely belonging to the dosinia layers according to nordmann (1904), only three species, out of the 26 species mentioned, do not occur in danish waters today, according to jensen & knudsen (1995), viz. trivia monacha, gari depressa, and alvania cimicoides. only trivia monacha seems to be purely lusitanian, since a recent distribution to the north sea is questioned by fretter & graham (1981, p. 329), and there is no record from scandinavia. the other two species have a boreo-lusitanian distribution. the skagen region, region 7 appendix 6 and fig. 103 the 23 species, out of which only vitreolina collensi is purely lusitanian, can be evaluated according to their way of life. vitreolina collensi belongs together with aclis minor and melanella alba to the eulimacea, which are probably associated with echinoderms (fretter & graham 1982, p. 397). the eulimacea, together with the epitoniacea, usually prey on anthozoans. the heterostropha, including the family pyramidellidae which lives ectoparasitically on other marine organisms (jensen & knudsen 1995), are here represented by eulimella scillae. finally within the veneroidae, mysella bidentata and tellimya ferruginosa are commensals on echinoids, but can also be found free-living. for the rest of the 23 species found during the subboreal in the skagen well, it applies that 16 species belong to the infauna, including onoba vitrea which tends “to live in muddy places, often so muddy that one wonders how the animals keep the mantle cavity clear” (fretter & graham 1978b, p. 170). it appears from the above-mentioned dates based on type of bottom-dwelling animals that the fauna belongs to the deep-level sea bottoms which goes well together with the turritella-venus communities. the recorded subboreal communities and/or characteristic molluscan species are given in table 8. the subatlantic stage 2500– 14c years b.p. the configuration of land and sea in the danish realm was very close to that of today. the isostatic movements during this time span have been so small that they did not affect the general outline (petersen 1991b). however, the coastal development, in the formation of simplified coastline and spits especially in the west towards the north sea and in the north facing the skagerrak and the kattegat respectively, still affected the contour of the land. 1. bælt sea mytilus m. edulis littoral macoma m. balthica/ostrea/paphia shallow abra a. alba deeper 2. baltic mytilus m. edulis littoral macoma m. balthica shallow deeper 3. kattegat mytilus m. edulis littoral macoma m. balthica shallow abra a. alba deeper 4. limfjord mytilus/modiola m. edulis littoral macoma m. balthica shallow venus/abra a. alba deeper 5. north sea littoral shallow venus chamelea striatula deeper 6. vendsyssel donax d. vittatus littoral dosinia d. exoleta shallow deeper 7. skagen littoral shallow venus/turritella t. communis deeper table 8. subboreal communities and/or characteristic molluscan species region community species depth geus bulletin no 3.pmd 09-07-2004, 09:10167 168 for the main part of the danish waters, the recent marine bottom communities were established, some of them already since the atlantic, although the few characterising tapes and ostrea species are no longer extant in great numbers or have totally vanished from the danish seas. therefore, the actual map of the petersen (1914, 1918) bottom communities as seen today will be commented upon in relation to the few, but important changes observed during the subatlantic, region by region. the bælt sea, region 1 appendix 6 and fig. 103 the bottom communities mapped from the bælt sea region comprise the macoma balthica community in the shallow-water area and the abra alba community in deeper water (petersen 1918), the latter community with tridonta borealis and macoma calcarea. the former has been recorded from the subfossil finds but not dated, while the latter has a dated occurrence back in the atlantic and is considered part of the abra alba community as a deep infauna element. considering the present distribution of the astarte species, it is most probable that tridonta borealis invaded the bælt sea and the baltic already in the early holocene along with the transgression in the early atlantic. the gregarious occurrences of ostrea edulis recorded from the atlantic in the bælt sea region vanished in the iron age (petersen 1985c). this species is no longer found in the bælt sea region, nor is paphia aurea, which also occurred at the iron age sites too (petersen 1985c, fig. 5). the steady occurrence of ostrea edulis since the atlantic, although in reduced numbers, might have led to an experiment in cultivating oysters south of lolland in the fehmern bælt (winther 1876, p. 114), although an unsuccessful one. the distribution of oysters within the danish waters seems to have changed very much right up to the present day, with many records from the 19th century of oyster banks from places where no records are found today (kröyer 1837; seaman & ruth 1997). the baltic, region 2 appendix 6 and fig. 103 the macoma balthica community covers the whole area of the baltic, implying that in this area the otherwise shallow-water bivalve extends into greater depths – more than 50 m (petersen 1918). also in this area, tridonta borealis and tridonta elliptica have been found in great quantities east of bornholm but not dated. however, according to johansen (1916, fig. 5), tridonta borealis and tridonta elliptica are recorded only from areas with a salinity of more than 10‰, but zenkevitch (1963, p. 338, fig. 167) points to many finds further to the north in the baltic, where the salinity is lower. as stated earlier, the change from the littorina sea stage to the lymnaea sea stage took place during the subboreal. the present situation with a mya sea stage – a term established by munthe (1894) – took place at a very late date. munthe (1894, p. 14) said: “since mya arenaria is an easily identified and characteristic species in the present baltic it seems suitable to call the present time the ‘mya-time’ or ‘mya arenaria-time’ in opposition to ‘littorina-time’ etc.” the kattegat, region 3 appendix 6 and fig. 103 among the subfossil species both, dated and undated, no records of chlamys striatula and turritella communis are found. these characterising species for the venus and deeper venus communities respectively have a wide extension on the map by petersen (1918) in the kattegat region. also the deeper-water epifaunal elements – characterised by modiolus modiolus – are missing in our subfossil record. only the macoma balthica and abra alba communities are recognised in the subfossil material. however, the development in the skagen well sequence to the north in the kattegat region of mollusc species reveals the venus-turritella communities and can be taken as part of the development in the central kattegat region not sampled at the time of this study on molluscs. in the present day northern kattegat, stray specimens of ostrea edulis have been recorded (jensen & knudsen 1995, p. 40). otherwise among the more spectacular tapes sea species, tapes decussatus, dated from the atlantic, and paphia aurea, not dated but occurgeus bulletin no 3.pmd 09-07-2004, 09:10168 169 ring in the subfossil fauna, have disappeared from the danish waters. the limfjord, region 4 appendix 6 and fig. 103 this region has been studied in more detail, regarding the recent fauna, than the other regions, and references can be made also to jensen (1919). the abra community is here divided into three associations, i.e. nucula-corbula, abra-solen, and abrasolen-mya associations. in more shallow water the abra community is replaced by the macoma balthica community. all of these communities are recorded by their mollusc species in the subfossil fauna, here including the mya arenaria in the subfossil assemblage. however, the only dated subfossil immigrating species from the subatlantic is donax vittatus, which appeared around 2000 years b.p. in the northernmost part of the limfjord region in the beach ridges, around 1000 years before the closing of the western and northern entrance to the limfjord. the closing of the entrances from the north sea and skagerrak changed the limfjord region into a freshwater basin between a.d. 1200 and 1825, however, with periods of saltwater influence (kristensen et al. 1995). a comparison between the subfossil fauna before the freshwater stage and the recent one after the north sea broke through in the western part of the limfjord in 1825 shows that the subfossil fauna had only a slightly higher affinity to more temperate water than the recent one. also in this place the tapes, venerupis and paphia species make the difference, in the way that only venerupis pullastra finds its way back to the region after 1825. paphia aurea, however, has a dated occurrence from the same deposits as donax vittatus to 1910 ± 100 14c years b.p. (petersen 1976). it is seen that paphia aurea in this region, as in the bælt sea, has a record up into the iron age before it became extinct in the danish waters. ostrea edulis repopulated the limfjord region after 1825 and reached a wide extension in this region already in the second half of the 19th century (collin 1871). however, the population has suffered from strong fluctuations not only in the limfjord but also in other danish waters, as shown on the map by kröyer (1837). spärck in several papers on the biology of oysters (ostrea edulis), published in reports of the danish biological station, also discussed the fluctuations in the nw european population of oysters (spärck 1950, pp. 43–45). spärck reached the conclusion that the summer temperature of the water was crucial, both being too low and too high, which affected the oyster in its reproduction and in food supply respectively. furthermore, severe winters might affect the population, although less than the summer temperatures. however, these changes did not mean a total disappearance of the oyster, but only a reduction to such a level that the industrial exploitation had to stop. when taking into account the many studies on the population of oysters, one could use the results in a general conclusion on the variations found in the whole population of molluscan species, especially for the group having their northern limit within the boreal region: even small variations in the climate may influence the size of the population. also the environmental changes as shown within the danish area during the holocene, such as the lowering of the tidal amplitude in the early part of the subboreal, had a severe influence on the populations in the inner danish waters. here again, oysters can be taken as an example by the termination of the huge oyster banks known from the atlantic. spärck (1950, p. 44) draws attention to the oyster banks in holland and the british isles, where the density of the population is far greater because of the tidal movements. however, not only the hydrographical changes through time, in the tide, but also the coastal evolution, such as the formation of simplified coastline and spits, play an important role in the distribution and new finds of molluscan species. the north sea, region 5 appendix 6 and fig. 103 only eight species have been recorded as immigrants during the subatlantic. however, two of them, donax vittatus and dosinia lincta, deserve special attention. only parvicardium ovale and dosinia lincta have their first dated appearance. the other species, except donax vittatus with occurrence in the subboreal, have been recorded from the atlantic at various places listed in appendix 6. in referring to the c.g.j. petersen bottom community map covering also the north sea, the macoma geus bulletin no 3.pmd 09-07-2004, 09:10169 170 balthica and the venus communities are found in the danish north sea coastal region, the former in bays and off the southern part of the west coast (petersen 1914), the latter around the westernmost part of the limfjord and the jydske rev wnw of the bovbjerg coastal cliff (petersen 1994a). a landscape like the limfjord of today was found 75 km towards wnw in the area of the jydske rev. following the transgression in the early part of the holocene, the glacial landscape in an area of the present jydske rev was eroded and the high-energy coast approached the appearance of the present one. in the northern part forming an erosion coast and in the southern part at blåvands huk an aggradation coast, both characterised by the presence of donax vittatus. in the southern part the aggradation started around 800 bc some 2000 m east of the present coastline (petersen 1994a, p. 24) as seen from the dating of donax vittatus to 2620 ± 75 b.p. 14c years (aar-1480) off the inland cliff at grærup (fig. 1). at bovbjerg, the strata with donax vittatus in the agger spit are dated to 410 ± 65 b.p. (petersen 1985a). the formation of the spits closing the former bays on the jylland west coast is a consequence of the formation of a simplified coast. further to the north, donax vittatus from kovad bro in the northernmost part of the limfjord, 6 km inland, gave a date of 1910 ± 100 b.p. (petersen 1976), showing that the beach progressed 6 km during approximately 2000 years (petersen & andreasen 1989, fig. 1). it is tempting to introduce the idea that the enormous change in the land–sea configuration in the eastern part of the north sea affected the tidal currents in the inner danish waters. this could possibly have occurred when most of the jydske rev formation was eroded to such a level that the tidal current from the south was no longer braked and consequently the present-day interference with the tidal current came into existence. it is the interference between the two tidal currents in the skagerrak today that makes the tidal amplitude small in the inner danish waters (nielsen 1939; kuenen 1950). dosinia lincta has been dated (870 ± 110 b.p. 14c years) in the jydske revsand formation in the vibrocore 562001 around 75 km off the coast of jylland at a depth of 32 m (petersen 1994a, p. 18, fig. 3). the assemblage from these strata comprises spisula subtruncata, phaxas pellucidus, fabulina fabula, chamelea striatula, dosinia exoleta, corbula gibba, cochlodesma praetenue and thracia phaseolina, most of them characterising the jydske revsand formation. the vendsyssel region, region 6 appendix 6 and fig. 103 the coastal development in the eastern part of the region facing the kattegat takes place in the form of migrating bars (schou 1949, fig. 17b), the so-called rimmer and doppe system sensu jessen (1905). the venus and the macoma balthica communities are found in the coastal zone, the former dominating in the northern part, whereas the latter forms a small area between shore and the venus community to the south towards the entrance to the limfjord at hals (petersen 1918). in the north at strandby, locus typicus of the dosinia beds, the layers with dosinia exoleta are superposed by a layer characterised by spisula subtruncata. these beds with spisula in great quantities were dated to 2640 ± 75 (petersen 1991b), the end of the subboreal, and at a level of 4.2 m a.s.l. this corresponds to a stage in the development of the skagen spit up to 4 km south of højen, where the beach ridges have an elevation of 5 m a.s.l. in the southern part of the vendsyssel region around hals another of the faunal elements of the dosinia beds – lutraria lutraria – has for long been regarded as extinct (petersen 1992). however, “from 1990 onwards live specimens have been collected regularly near frederikshavn and on the skagerrak-coast” (jensen & knudsen 1995, p. 43). also many shells of lutraria lutraria were found along the shore south of jerup halfway between frederikshavn and aalbæk. the immigration of mya arenaria cannot be taken as an indication of changes in climate, as this species mainly belongs to the boreal region and has been transferred by man from north america. what made the find so important has a more historical than geological bearing, namely that the dates obtained from the sampling at jerup demonstrated that the american softshell clam (mya arenaria) predated columbus’ voyage in 1492, having an age of a.d. 1245–1295 at ± 1 s.d. this led to the conclusion that the vikings were better candidates than columbus to be the first to find north america (petersen et al. 1992b). the significance of changes in facies is clearly demonstrated in the next and final section describing the subatlantic faunal development in the skagen region. geus bulletin no 3.pmd 09-07-2004, 09:10170 171 the skagen region, region 7 appendix 6 and fig. 103 the subatlantic molluscan fauna from the skagen well comprises 68 species with 75% belonging to the boreolusitanian region and only one lusitanian species, vitreolina collensi. however, the more interesting fact from the younger part of the skagen sequence is the total lack of macoma balthica. in this way it presents the finest resemblance with the recent bottom community map (petersen 1918), and shows that the macoma balthica community disappears in the northern part of the east coast of jylland. this means that during the last stage of the spit formation at the site of the present skagen animals, from the venus community dominated along shore. this is also documented by the high amount of infauna elements, with 35 out of the 68 species recorded. furthermore, some of the 11 epifauna gregarious species usually connected with the vegetation can be excluded, since they occur only as stray finds, viz. lacuna pallidula, rissoa violacea, and bittium reticulatum, as discussed earlier. the rest of the molluscs (22 species) are carnivores, predators, external parasites, and commensals. turning these figures into percentages, the epifauna species amount to 16.2% and the infauna to 51.5%. comparing this with the limfjord region where an equal number of species have been found during the atlantic and the subboreal, it appears that the number of infauna species from the atlantic to the subboreal falls from 46.8% to 19.4% and the epifauna elements rise from 31.2% to 47.2% in the limfjord. counting the limfjord region as an inner danish water today, it is worth noticing that during the atlantic the situation was much more like the ‘open’ waters as seen in the skagen figures. considering that the tidal amplitude really was lowered in the early part of the subboreal, this would to some extent explain the observed changes in the limfjord from the atlantic to the subboreal. the recorded subatlantic communities according to the maps by petersen (1914,1918) with characteristic molluscan species are shown in table 9. table 9. subatlantic communities according to the bottom community maps* with characteristic molluscan species 1. bælt sea mytilus m. edulis littoral macoma m. balthica/÷ostrea/paphia shallow abra a. alba deeper 2. baltic mytilus m. edulis littoral macoma m. balthica/+mya arenaria shallow macoma m. balthica deeper 3. kattegat mytilus m. edulis littoral macoma m. balthica shallow abra/venus a. alba deeper 4. limfjord mytilus/modiola m. edulis littoral macoma m. balthica/÷paphia aurea shallow abra a. alba deeper 5. north sea donax d. vittatus littoral macoma m. balthica shallow venus chamelea striatula deeper 6. vendsyssel littoral macoma m. balthica shallow venus chamelea striatula deeper 7. skagen donax d. vittatus littoral spisula s. subtruncata shallow venus chamelea striatula deeper * petersen (1914, 1918). region community species depth geus bulletin no 3.pmd 09-07-2004, 09:10171 geological survey of denmark and greenland bulletin 23, 2011, 33-36 33 in the summer of 2010, the geological survey of denmark and greenland (geus) mapped the potential raw materials and substrate types, over large parts of the danish economic sector of the north sea, in cooperation with orbicon a/s. the mapping was carried out for the danish nature agency; it is part of the general mapping of raw material resources within the territories of the danish state and forms part of the input for the implementation of the european union’s marine strategy framework directive. the purpose was (1) to provide an overview of the distribution, volume and composition of available raw materials and (2) to identify, describe and map the distribution of the dominant marine bottom types. methods during the first part of the field work a single beam echo sounder for bathymetrical data, a side scan sonar for mapping the seabed surface as well as a chirp (1–10 khz) and a sparker (1 khz) were used to map the layers below the seabed with up to 50 m penetration. after preliminary interpretation, the acoustic data acquisition was followed by sediment sampling using a vibrocorer with up to 6 m penetration and a grab sampler in order to investigate the characteristics of the sediments. in addition, the seabed was filmed using a video camera mounted on a remotely operated vehicle (rov) to document the seabed sediment substrate and benthic fauna. the field work was divided into three phases (fig. 1, table 1): phase 1: mapping of both raw materials and bottom types, phase 2: mapping of bottom types alone and phase 3: geological mapping. bathymetry and geological model the data from the phase 1 area made it possible to map the bathymetry and develop a geological model for the area. the bathymetric data show a nw–se-trending ridge 25–30 m below present sea level interpreted as the offshore continuation of the main stationary line (msl) that formed during the last glacial maximum (fig. 2a; houmark-nielsen & kjær 2003). the high area comprises the core areas of jyske rev and lille fisker banke. north of the msl a series of ridges trending nne–ssw that are 20–40 km long and 5–10 km broad dominate the bathymetry. the crests of the ridges are 18–24 m b.s.l. and the troughs around 40 m b.s.l. these large ridges are interpreted as early holocene giant tidal sand ridges. backstripping shows the pre-holocene transgression surface and accentuates the msl (fig. 2b). south of the msl the bathymetry shows a gentle south-western slope, which we interpret as drowned sandur deposits that formed in front of the melting scandinavian ice sheet. mapping of raw materials and habitats in the danish sector of the north sea jørn bo jensen, sara borre, jørgen o. leth, zyad al-hamdani and laura g. addington 50 km 4°e 6°e 56°n 57°n 8°e jylland border of the exclusive economic zone vibrocore video grab sample and video phase 1 seismic grid phase 2 seismic grid phase 3 seismic grid a b c main stationary line (msl) fig. 1. map of the economic sector of the danish north sea showing the seismic grids and sampling positions in the combined raw material and marine bottom-type mapping carried out in 2010. a: phase 1 area. b: phase 2 area. c: phase 3 area. © geus, 2011. geological survey of denmark and greenland bulletin 23, 33–36. open access: www.geus.dk/publications/bull 3434 the pre-quaternary surface is close to the seabed in the phase 1 area (figs 3, 4; nielsen et al. 2008) where it is overlain by a few tens of metres of quaternary sediments. thicker quaternary deposits are found in local depressions connected with salt domes and in n–s-trending buried tunnel valleys that are incised into the pre-quaternary deposits (huuse & lykke-andersen 2000). the quaternary sediments overlie miocene sand and clay, danian limestone and locally cretaceous chalk. the quaternary stratigraphy in the north sea is poorly known, but south of the msl elsterian and saalian till deposits have been identified on the seismic sections and in sediment cores in a situation similar to that found in the onshore hill islands in western jylland. to some extent the deeply incised valleys are filled with pre-weichselian sand and eemian marine silt and sand (figs 3, 4). to a large extent the weichselian deposits are related to the msl. they are partly seen as glaciotectonic deformations in the sparker data, and partly as till deposited below and at the margin of the ice sheet. glaciof luvial sand and gravel are located in depressions in the weichselian landscape and proximal to distal sandur sediments overlying glacial deposits south of the msl (figs 3, 4). late glacial marine deposits overlie the glacial deposits at present water depths greater than 40 m, which ref lects the relative sea level around 17 000 years bp (leth 1996), shortly after the last deglaciation (fig. 3). from c. 17  000 years bp the relative sea level dropped to reach a minimum of about 50 m b.s.l. at c. 11 000 years bp. at that time only the northernmost part of the phase 1 area was below sea level (fig. 2b) and a widespread hiatus is seen that lasted until submergence in connection with the holocene transgression. the relative sea level rose continuously from c. 11 000 to c. 6000 years bp to reach a maximum level at 1–3 m above the present sea level. over the past 6000 years the relative sea level fell to its present level. the holocene deposits can be divided into four units: 50–52 48–50 46–48 44–46 42–44 40–42 38–40 36–38 34–36 32–34 30–32 28–30 26–28 24–26 22–24 20–22 18–20 depth (m) 20 km 7°e 7°e 57°n 56°30´n 7°e 7°e a b jyskejyske revrev lille fiskerlille fisker bankebanke jyske rev lille fisker banke msl msl phase survey grid (km) acoustic profiles (km) vibrocores grab samples video data 1 2 × 5 c. 3000 60 24 85 2 7 × 7* / 7 × 15 c. 3000 – 31 67 3 7 × 7 c. 2500 – – – * eastern area, western area. table 1. details of phases 1–3 # # fig. 2. bathymetry and palaeo-morpholog y of the phase 1 area (fig. 1), off north-west jylland. a: bathymetry. b: palaeo-morpholog y in metres below present sea level of the pre-holocene transgression surface. the weichselian main stationary line (msl) is located in the lille fisker banke – jyske rev area, between the stippled lines. 35 early holocene giant tidal sand ridge deposits. the giant tidal sand ridges are connected to the msl which trends nne–ssw and attains heights up to 20 m (figs 2–4). the architecture implies that the ridges were formerly connected to the shore and formed by tidal currents during the holocene sea-level rise, mostly by trapping of sediment within tidal eddies generated by headlands or f low convergence. similar giant sand ridges related to holocene sea-level rise have been reported from the english channel (reynaud et al. 2003). early holocene fine-grained marine and fjord sediments. incised valleys formed in the easternmost part of the phase 1 area during the lowstand period and during the initial part of the holocene transgression (fig. 3). fine-grained marine sediments were deposited in such valleys in protected areas east of jyske rev, and brackish fine-grained sedimentation took place in palaeo-fjords similar to the present limfjorden (agger clay; leth 1996). holocene beach ridge and spit deposits. these accumulations formed during the progressive transgression when the glacial deposits were isolated as islands in the open sea. erosion, transport and deposition led to the formation of beach deposits on the lee side of jyske rev. sub-recent to recent mobile sand. around 8000–7000 years ago the shallow parts (18–20 m b.s.l.) of the phase 1 area were transgressed by the sea. the present wave system and the jutland current developed (gyllencreutz et al. 2006), which resulted in the formation of mobile sand waves and major sand banks in the jyske rev and lille fisker banke region. the mobile sand deposits reached several metres in thickness and the bedforms can have wavelengths of over 100 m. potential for raw material we have identified a number of stratigraphical units that could be of interest to the sand and gravel industry. preweichselian sand in buried tunnel valleys is of potential interest in areas where no or little cover sediment is found. pre-quaternary deposits pre-weichselian till pre-weichselian valley fill (sand?) eemian marine silt and sand weichselian till weichselian glaciofluvial sand and gravel weichselian sandur silt and sand late glacial marine silt and sand early holocene valley fill border of deep valley holocene marine sand and gravel 7°e 57°n 56°30´n 20 km 2000600010 00014 000 d e p th ( m ) age (years bp) -40 -20 0 fig. 3. seabed surface sediments in the phase 1 area (fig. 1). the location of the geological profile (fig. 4) is shown with a red stippled line. the inset diagram is a model of relative sea-level changes after the last deglaciation in the study area. nnw se d e p th ( m b e lo w s e a le v e l) 30 40 60 50 5 km sse nw fig. 4. nw–se geological profile through the phase 1 area (fig. 1) covered in the first phase. for legend and location of profile see fig. 3. 3636 this is seen in the south-eastern part of the phase 1 area, but little is known about the volume and quality of the material accumulated in the tunnel valleys. weichselian glaciof luvial sand and gravel deposits along the msl are of great interest as a resource for concrete production. however, this resource occurs only sporadically and is often covered by several metres of holocene sediments. giant holocene sand ridges in the north-western part of the phase 1 area are the most noteworthy sand resource in the region because of their enormous volume of around 8 × 109 m3. the resource is easily accessible and consists of mediumgrained sand that is well suited for land reclamation, beach nourishment and concrete production. drowned coastal deposits are the traditional dredged resource in the jyske rev area. this resource consists of high quality sand and gravel for concrete production as the high energy level during erosion and transport of the sediments has removed the light particles. recent mobile sand is often deposited in sand waves and the sediment consists of well-sorted, medium-grained sand that is excellent for beach nourishment. however, before this resource is removed it is crucial to ensure that the sand waves are not part of the present sand budget of the coast. geological seabed units as bottom types and possible sand-eel fishery areas bottom-type mapping was part of the seabed mapping task for the danish nature agency. since the seabed sediments form the habitat for marine benthic organisms and are of vital importance to the distribution of marine life, the seabed sediments have been used for mapping the dominant bottom types. a number of additional parameters such as light penetration, salinity and temperature inf luence the distribution of faunal types, but a close link between till deposits on jyske rev and the natura 2000 code 1170 stone reef type (boedeker et al. 2006) is obvious. a close link is also seen between giant sand ridges and the natura 2000 code 1110 sand bank type. the mapping of the geological unit giant sand ridges as sand banks was compared with the distribution of sand-eel fishing grounds in the jyske rev and lille fisker banke areas ( jensen et al. 2011) and a nearly perfect match was found. concluding remarks we have developed a geological model that can form the basis of combined mapping of raw material and marine bottom types in the lille fisker banke and jyske rev areas. weichselian glaciof luvial deposits, early holocene giant, tidal sand ridges, middle holocene drowned, coastal sand and gravel deposits and sub-recent to recent mobile sand waves and banks form potential or substantiated raw material geological units. examples of dominant bottom types are the jyske rev till deposits that are classified as a stone reef of the seabed type, and the early holocene giant tidal sand ridges that represent a sand bank type. sand-eel fishing grounds have been used as an example of the close linkage between geology, bottom types and fish habitats. acknowledgement the danish nature agency is thanked for permission to publish the paper. references boedeker, d., krause, j.c. & von nordheim, h. 2006: interpretation, identification and ecological assessment of the natur a 2000 habitats ‘sandbank’ and ‘reef ’. in: von nordheim, h., boedeker, d. & krause, j.c. (eds): progress in marine conservation in europe, natur a 2000 sites in german offshore waters, 47–64. berlin: springer. gyllencreutz, r., backman, j., jakobsson, m., kissel, c. & arnold, e. 2006: postglacial paleoceanography in the skagerrak. the holocene 16, 975–985. houmark-nielsen, m. & kjær, k.h. 2003: southwest scandinavia 40–15 kyr bp: palaeogeography and environmental change. journal of quaternary science 18, 769–786. huuse, m. & lykke-andersen, h. 2000: overdeepened quaternary valleys in the eastern danish north sea: morpholog y and origin. quaternary science reviews 19, 1233–1253. jensen, h., rindorf, a., wright, p.j. & mosegaard, h. 2011: inferring the location and scale of mixing between habitat areas of lesser sandeel through information from the fishery. ices journal of marine science 68, 43–51. leth, j.o. 1996: late quaternary geological development of the jutland bank and the initiation of the jutland current, ne north sea. geological survey of norway bulletin 430, 25–34. nielsen, t., mathiesen, a. & bryde-auken, m. 2008: base quaternary in the danish parts of the north sea and skagerrak. geolological survey of denmark and greenland bulletin 15, 37–40. reynaud, j.-y., tessier, b., auffret, j.-p., berné, s., de batist, m., marsset, t. & walker, p. 2003: the offshore quaternary sediment bodies of the english channel and its western approaches. journal of quaternary science 18, 361–371. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: jbj@geus.dk geological survey of denmark and greenland bulletin 7, 2004, p 25-28 25 recent danish seismological projects involving neotectonic investigations and structural studies have determined the edge of the baltic shield underlying denmark. the most active earthquake zones in denmark are located in northwestern jylland and adjoining offshore areas, and in the region around kattegat, øresund and north-east sjælland (fig. 1). this pattern was originally recognised by lehmann (1956) and has been confirmed by several later studies, e.g. gregersen et al. (1998). recent, more detailed investigations have documented that changes in the pattern of earthquake activity have occurred within a short time span. the most pronounced example of change – possibly related to exploitation of hydrocarbons – is an activity recorded in the central graben area of the north sea that was first documented by gregersen et al. (1998). the south-western margin of the precambrian baltic shield separates areas of different earthquake activity (fig. 1; gregersen et al. 1991). although lithospheric stresses are more or less uniform in northern europe, there are pronounced differences in the behaviour of the lithosphere across denmark. the north-eastern area underlain by the baltic shield experiences brittle failure as recorded by common earthquakes, whereas earthquakes are virtually absent in the region southwest of the shield (fig. 1). the margin of the baltic shield as defined by earthquake activity is not identical with that distinguished structurally in sedimentary studies (eugeno-s working group 1988; vejbæk & britze 1994), in crustal studies (abramovitz & thybo 2000), or by recent studies of the structure of the subcrustal lithosphere (gregersen et al. 2002; shomali et al. 2002). the physical edge of the baltic shield cannot be uniquely determined on the basis of seismological studies. the earthquakes recorded, although of low magnitude, do give information about the released stresses. the earthquakes seem to be a response to a dominant nw–se compression, also apparent elsewhere in scandinavia and northern europe geological survey of denmark and greenland bulletin 7, 25–28 (2005) © geus, 2005 seismology: neotectonics and structure of the baltic shield søren gregersen, martin glendrup,tine b. larsen, peter voss and hans peter rasmussen 5°e 54°n 58°n 100 km denmark s j ø kattegat 5 stz rfh rfh cg rfh el north sea 10°e 15°e fig. 1. computed locations of earthquakes around denmark during the last 75 years, supplemented by locations provided by the university of bergen based on arrival time readings from at least five seismograph stations. at shallow depths the south-western boundary of the baltic shield coincides with the sorgenfrei–tornquist zone (stz). cg, central graben; el, elbe line; j, jylland; rfh, ringkøbing –fyn high; s, sjælland; ø, øresund. (slunga et al. 1984; slunga 1989; gregersen 1992; müller et al. 1992). these stresses are part of the large-scale stress systems associated with continued plate motion pattern (gregersen & basham 1989; zoback et al. 1989). in contrast to present low-magnitude earthquakes, postglacial sediments in northern scandinavia have preserved features interpreted as caused by earthquakes of magnitudes around 7; these major, c. 9000 years old earthquakes are believed to be related to the post-glacial uplift of scandinavia (e.g. arvidsson et al. 1991; gregersen 2002). earthquakes are always related to fault activity, but attempts to link recent earthquakes occurring in and around denmark to geologically known faults have only been partly successful (gregersen et al. 1996). the most significant fault zone in denmark, the sorgenfrei–tornquist zone, is only locally active. recent geodetic and seismic investigations demonstrate that the two sides of the sorgenfrei–tornquist zone are characterised by different patterns of deformation, but the zone itself is not defined by a present-day seismicity trend crossing the central parts of denmark (fig. 1). seismological monitoring in denmark seismological monitoring in denmark has until recently been carried out by a staff of four full-time workers and one temporary employee at the danish national survey and cadastre (kms). this function was transferred to the geological survey of denmark and greenland (geus) in 2004. the monitoring is carried out with four permanent seismographs located in denmark, and four permanent and ten temporary stations located in greenland. currently a technical transfer from analogue to digital data handling is almost complete. this involves changes of the data processing for local earthquake signals and substitution of the earthquake location program by an improved version described below. the earthquake list covering the danish area has recently been updated to include all recognised small earthquakes (see www.geus.dk). supplementary data on earthquakes, which other agencies have located in the danish area, can be found on the web pages of the university of bergen in norway (www.ifjf.uib.no/seismologi) and the university of helsinki in finland (www.seismo.helsinki.fi). recomputation of earthquake locations the computer program hitherto used in denmark for computing earthquake locations (hypolg) is a modified version of the globally distributed location program (hypo71) from the united states geological survey (lee & lahr 1972; gregersen 1979). the current location program (hypocenter) now used at geus is that of lienert et al. (1986) and forms part of the analysis program for digital seismograph data (seisan) from the university of bergen (havskov & ottemöller 1999). the consistency of new and old procedures has been tested by analysis and comparison of all the seismogram records of danish earthquakes for the period 1995–2002 (fig. 2). the input to the two programs is the same. the hypolg program has an option for disregarding those readings that are not in agreement with the rest, i.e. have arrival time anomalies larger than three standard errors, while such anomalous readings are preserved and included in the computations in the seisan version of hypocenter. this difference has been taken into consideration in the comparison of the two programs, such that the same readings were included in both. the distance between any two computed locations of the same earthquake is typically 2 to 3 km. the largest differences of 7 to 13 km determined for four earthquakes are due either to few station readings (4–5) or poor azimuth coverage (overweight of readings from a small azimuth interval). the error in location determination for the same earthquake decreases with increased input of more arrival times. 26 denmark 57°n 55°n 100 km 4°e 8°e 12°e 16°e fig. 2. comparison of computed earthquake locations for the period 1995–2002, using the hypolg software (yellow dots) and the new seisan software (red dots). the results are very satisfactory and the shift to the earthquake location program hypocenter included in seisan (lienert et al. 1986; lienert & havskov 1995) is made for 2003 and the following years. the errors in the locations measured through the root mean square of the travel time anomalies with seisan are no higher than 3.1 sec. with an average of 1.76 sec. hypolg has a root mean square average of 1.88 sec. for the location of the 76 earthquakes. tor project a major international teleseismic project implemented in 1996 had the objective of delineating the lithospheric differences and the shape of the edge of the baltic shield across the sorgenfrei–tornquist zone. the tor project (teleseismic tomography across the tornquist zone) represents a collaboration between geophysical and geological institutes in sweden, germany, poland, france, the czech republic, switzerland, the netherlands and the usa with danish leadership (gregersen et al. 2002). field work and interpretation studies carried out by most partner institutions were completed in the years 1996–2002, except for a danish ph.d. study that is still active. the tor seismograph array (fig. 3) covered areas where extensive seismic crustal studies (i.e. in the depth range 0–60 km) over the last two decades have identified a terrane boundary between the ancient plates of baltica and avalonia. the tor project extends below this level into the subcrustal parts of the lithosphere (i.e. depth range 50–300 km). methods of investigation have included studies of pand s-wave travel time tomography, surface wave dispersion, receiver function, sks splitting and scattering analyses (shomali et al. 2002). in the tomographic cross-section (fig. 4) the local deviations from a homogeneously layered reference model are shown. sharp and steep boundaries between ‘fast’ and ‘slow’ 27 58°n 4°e 12°e 20°e 54°n 50°n 200 km denmark norway fig.4 sweden poland germany the netherlands czech republic fig. 3. the locations of seismometers during the field work for the tor project 1996–1997. red dots, short period seismographs; blue dots, broad-band seismographs; green line, deep crustal to mantle crosssection shown in fig. 4. 0 3 2 1 0 –1 –2 –3 100 200 300 51 52 53 54 55 56 57 58 °n el rfh stz avalonia crust baltica crust a b c d p -v e lo c it y p e rt u rb at io n ( % ) d e p th ( k m ) fig. 4. deviations in p-wave velocities in a deep crustal to mantle cross-section acquired to a depth of 350 km during the tor project (from shomali et al. 2002). for location of line see fig. 3. the colouring indicates velocities lower (red) or higher (blue) than the average at any level. the edge of the baltic shield as defined by sedimentary basin studies is located by the sorgenfrei–tornquist zone (stz). however, crustal transition occurs gradually within frame a between the ringkøbing–fyn high (rfh) and the elbe line (el). a subcrustal transition occurs within frame b, and another pronounced and steep transition occurs in frame c, roughly coinciding with the stz. a third, deep and less pronounced lithospheric transition occurs beneath the baltic shield in frame d. 28 lithosphere are seen as changes from red to blue in frames b and c, and the change from light blue to dark blue (frame d). together these boundaries represent a major change in the lithosphere between the precambrian shield in scandinavia and areas dominated by phanerozoic deposits in central europe. although temperatures and pressures are large at the investigated depths, it should be noted that the changes are stepwise and not gra-dual, as might be expected. the disparity in the position of the edge of the shield as defined at shallow crustal levels in the flanking sedimentary basins by the sorgenfrei–tornquist zone, and that at deep crustal and subcrustal levels is significant. recent crustal studies have indicated that the transition occurs somewhere between the elbe line and the ringkøbing–fyn high (fig. 4, frame a; abramovitz & thybo 2000). the subcrustal lithosphere edges revealed by the tor investigations (in frames b, c and d of fig. 4) appear to be related to the shallow crustal transitions. however, the actual relationships between the changes observed at shallow and deep crustal levels are not well understood, and further geophysical studies are desirable. references abramovitz, t. & thybo, h. 2000: seismic images of caledonian lithosphere-scale collision structures in the southeastern north sea along mona lisa profile 2. tectonophysics 317, 27–54. arvidsson, r., gregersen, s., kulhanek, o. & wahlström, r. 1991: recent kattegat earthquakes – evidence of active intraplate tectonics in southern scandinavia. physics of the earth and planetary interiors 67, 275–287. eugeno-s working group 1988: crustal structure and tectonic evolution of the transition between the baltic shield and the north german caledonides (the eugeno-s project). tectonophysics 150, 253–348. gregersen, s. 1979: earthquakes in the skagerrak recorded at small distances. bulletin of the geological society of denmark 28, 5–9. gregersen, s. 1992: crustal stress regime in fennoscandia from focal mechanisms. journal of geophysical research 97, 11821–11827. gregersen, s. 2002: earthquakes and change of stress since the ice age in scandinavia. bulletin of the geological society of denmark 49, 73–78. gregersen, s. & basham, p.w. (eds) 1989: earthquakes at north-atlantic passive margins: neotectonics and postglacial rebound, 716 pp. dordrecht: kluwer academic press. gregersen, s., korhonen, h. & husebye, e.s. 1991: fennoscandian dynamics: presentday earthquake activity. tectonophysics 189, 333–334. gregersen, s., leth, j., lind, g. & lykke-andersen, h. 1996: earthquake activity and its relationship with geologically recent motion in denmark. tectonophysics 257, 265–273. gregersen, s., hjelme, j. & hjortenberg, e. 1998: earthquakes in denmark. bulletin of the geological society of denmark 44, 115–127. gregersen, s., voss, p., shomali, z.h. & tor working group 2002: summary of project tor: delineation of a stepwise, sharp, deep lithosphere transition across germany–denmark–sweden. tectonophysics 360, 61–73. havskov, j. & ottemöller, l. 1999: seisan earthquake analysis software. seismological research letters 70, 532–534. lee, w.h.k. & lahr, j.c. 1972: hypo71: a computer program for determining hypocenter, magnitude, and first motion pattern of local earthquakes. u.s. geological survey open file report 72-224, 100 pp. lehmann, i. 1956: earthquakes in denmark. bulletin of the geological society of denmark 13, 88–103 (in danish with abstract in english). lienert, b.r. & havskov, j. 1995: a computer program for locating earthquakes both locally and globally. seismological research letters 66(5), 26–36. lienert, b.r., berg, e. & frazer, l.n. 1986: hypocenter: an earthquake location method using centered, scaled, and adaptively damped least squares. bulletin of the seismological society of america 76, 771–783. müller, b., zoback, m.l., fuchs, k., mastin, l., gregersen, s., pavoni, n., stephansson, o. & ljunggren, c. 1992: regional patterns of tectonic stress in europe. journal of geophysical research 97, 11783–11803. shomali, z.h., roberts, r.g. & tor working group 2002: non-linear body wave teleseismic tomography along the tor array. geophysical journal international 148, 562–574. slunga, r.s. 1989: focal mechanisms and crustal stresses in the baltic shield. in: gregersen, s. & basham, p.w. (eds): earthquakes at northatlantic passive margins: neotectonics and postglacial rebound, 261 –276. dordrecht: kluwer academic press. slunga, r., norrman, p. & glans, a.-c. 1984: seismicity of southern sweden, 106 pp. stockholm: forsvarets forskningsanstalt. vejbæk, o.v. & britze, p. (compilers) 1994: geological map of denmark, 1:750 000. top pre-zechstein (two-way travel time and depth). danmarks geologiske undersøgelse kortserie 45, 8 pp. zoback, m.l. et al. 1989: global patterns of tectonic stress. nature 341, 291–298. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: sg@geus.dk geological survey of denmark and greenland bulletin 7, 2004, p 13-16 13 seismic data are mainly used to map out structures in the subsurface, but are also increasingly used to detect differences in porosity and in the fluids that occupy the pore space in sedimentary rocks. hydrocarbons are generally lighter than brine, and the bulk density and sonic velocity (speed of pressure waves or p-wave velocity) of hydrocarbon-bearing sedimentary rocks are therefore reduced compared to non-reservoir rocks. however, sound is transmitted in different wave forms through the rock, and the shear velocity (speed of shear waves or s-wave velocity) is hardly affected by the density of the pore fluid. in order to detect the presence of hydrocarbons from seismic data, it is thus necessary to investigate how porosity and pore fluids affect the acoustic properties of a sedimentary rock. much previous research has focused on describing such effects in sandstone (see mavko et al. 1998), and only in recent years have corresponding studies on the rock physics of chalk appeared (e.g. walls et al. 1998; røgen 2002; fabricius 2003; gommesen 2003; japsen et al. 2004). in the north sea, chalk of the danian ekofisk formation and the maastrichtian tor formation are important reservoir rocks. more information could no doubt be extracted from seismic data if the fundamental physical properties of chalk were better understood. the presence of gas in chalk is known to cause a phase reversal in the seismic signal (megson 1992), but the presence of oil in chalk has only recently been demonstrated to have an effect on surface seismic data (japsen et al. 2004). the need for a better link between chalk reservoir parameters and geophysical observations has, however, strongly increased since the discovery of the halfdan field proved major reserves outside four-way dip closures (jacobsen et al. 1999; vejbæk & kristensen 2000). a link between reservoir porosity and sonic velocity in the south arne chalk acoustic properties of the chalk of the danish south arne field have been investigated at three scales by analysing core data, log readings and surface seismic data (japsen et al. 2004). the south arne field is located in the central north sea and chalk porosities of up to 45% are found in the reservoir at almost 3 km depth (fig. 1). the velocity–porosity trend for pure chalk samples from the south arne field matches a modified upper hashin-shtrikman (muhs) curve fitted to ekofisk field chalk (walls et al. 1998). the curve was smoothly extended to 45% porosity using core data from the high-porosity south arne chalk. based on this curve, the acoustic properties of chalk may be calculated as a function of water saturation. this is done by applying gassmann’s equations, which relate the elastic properties of a rock saturated with one fluid to those of the same rock saturated with a different fluid (cf. mavko et al. 1998). the results indicate a pronounced change in the relationship between pand svelocities for chalk saturated with light oil for porosities above c. 30% (fig. 2). this relationship is described by the poisson ratio, and this can provide information about lithology and fluid content of hydrocarbon-bearing reservoirs. for a rock of a given porosity, high pore fluid density results in high p-wave velocity and high poisson ratio, whereas hydrocarbons with low fluid density result in low p-wave velocity and almost unchanged s-wave velocity and a low poisson ratio. these results from the model of the acoustic properties of the chalk indicate that light oil in the high-porous chalk of the south arne field may be detected through amplitude identification of hydrocarbons in chalk reservoirs from surface seismic data: south arne field, north sea peter japsen, anders bruun, ida l. fabricius and gary mavko geological survey of denmark and greenland bulletin 7, 13–16 (2005) © geus, 2005 2820 2900 2900 3000 3000 ekofisk north sea south arne halfdan denmark rigs-1 rigs-2 sa-1 1 km i-1x 56°03´n 4°15´e fig. 1. the south arne field; top chalk structure with location of selected wells. versus offset (avo) inversion of surface seismic data. this is because the variation in seismic reflection amplitude with change in distance between shotpoint and receiver may indicate differences in rock properties above and below the reflector. changes in avo can be directly related to changes in the poisson ratio and thus to differences in pore fluid properties. the uppermost part of the chalk of the south arne field is rich in clay (the ekofisk formation). core data indicate that clayrich chalk has significantly smaller pand s-velocities and a higher poisson ratio than observed for pure chalk (see japsen et al. 2004, fig. 2). the relatively small velocities for a given porosity are probably an artefact due to a reduction in porosity because clay fills up the pore space without affecting the acoustic properties of the chalk matrix. however, the amount of silicates (typically quartz and clay) cannot always be predicted from the gamma log, because the chalk may be rich in very fine-grained silicates which are not all radioactive. in water-wet chalk the amount of very fine-grained material may be estimated from the water saturation (cf. fabricius et al. 2002). the muhs model of the acoustic properties of the chalk is therefore scaled according to silicate content estimated from the water saturation. comparison of well log data and core data the link between the surface seismic data and the reservoir properties in the south arne field is complicated by difficulties in interpreting the sonic log, because mud filtrate has invaded the reservoir near the well bore where the sonic log is registered (fig. 3). the water saturation can be estimated at intermediate and long distances from the bore hole based on resistivity logs, but not adjacent to the well bore. however, the sonic waves travel close to the well bore and it is thus difficult to perform ‘fluid substitution’ of the data, i.e. to transform the acoustic data from the pore fluid environment where they are measured to the fully hydrocarbon-saturated environment of the reservoir (the virgin zone; cf. gommesen 2003). comparison of p-wave velocity and porosity from log and core data clearly shows that the logging data record conditions close to the well bore, where mud filtrate has almost completely flushed the reservoir (fig. 4). core porosities match log porosities estimated from the density log assuming full invasion of mud filtrate (fig. 4a) and p-wave velocities of brine saturated cores generally correspond to readings of pwave velocity in the borehole (fig. 4b). estimation of invasion effects is usually difficult because of the lack of different types of data, and this study underlines the importance of having access to core data. 14 fig. 3. illustration of the effects of invasion of mud filtrate (blue) into a reservoir saturated with hydrocarbons (red). lower left diagram shows how water saturation (sw) increases towards the bore hole. lower right diagram shows how the p-velocity also increases towards the borehole due to the higher density of the mud filtrate compared to the hydrocarbons. the seismic data are influenced by water saturation in the virgin zone (sw, registered by the deep resistivity log), and the acoustic log by the properties close to the well bore, whereas the shallow resistivity log registers the water saturation at some distance from the well bore (sxo). water saturation and sonic velocity are thus not known at the same di-stance from the bore hole, and therefore the acoustic properties of the virgin zone cannot be easily estimated. a b 0.1 0.2 0.3 0.4 0 10 20 30 40 10 20 30 40 50 10 20 30 40 50 1.0 0.8 0.6 0.4 0.2 0.0 m o d u li ( g p a) porosity (%) porosity (%) p o is so n r at io ( -) k g sw fig. 2. acoustic properties of chalk as a function of porosity and water saturation (sw). a: bulk (k) and shear modulus (g); b: poisson ratio. note the pronounced difference in the poisson ratio between brine and oil for porosities above c. 30%. muhs prediction based on fine-scale mixing and fluid properties for the south arne field. modified from japsen et al. (2004). w at e r sa tu ra ti o n distance from drill hole distance from drill hole acoustic log acoustic log seismic data seismic data vp ? sxo ? sw v e lo c it y comparison of well log data and seismic data two approaches may be followed to estimate the acoustic properties of the virgin zone in order to compare well data with seismic data (both are based on gassmann’s equations): 1. transformation of the sonic data to reservoir conditions based on an estimation of the water saturation near the well bore. this can be done using land’s (1968) equation that gives a smooth estimate of the water saturation some distance from the well bore (corresponding to the more scattered registrations by the shallow resistivity log). 2. estimation of the acoustic properties of the reservoir from the muhs model with porosity and water saturation as input (based on the deep resistivity log). estimation of the poisson ratio versus depth in the reservoir depends very much on the approach taken (fig. 4). in the first approach, moderate invasion is assumed and a featureless variation of the poisson ratio results (fig. 4c, dashed black curve). in the second approach, forced displacement of the hydrocarbons near the well bore is assumed and forward modelling results in a characteristic pattern with pronounced peaks at top ekofisk formation and top tor formation, and low values in the highly porous tor reservoir (full red curve). the latter pattern is in good agreement with the inverted seismic data (fig. 5b, blue avo curve). the avo attributes were calculated from the angle-dependent impedance inversions combined with information on the absolute level of chalk velocity which is not contained in the seismic data (bach et al. 2003). acoustic impedance, shear impedance and the poisson ratio were extracted at the location of the rigs-2 well. the avo results show a good match with the well log data. a low poisson ratio in the tor formation near the rigs2 well is in agreement with the presence of light oil in the highly porous chalk of the south arne field. the first approach based on land’s (1968) equation results in a mismatch between log and seismic estimates of the poisson ratio in the virgin zone (fig. 4c, dashed red curve versus fig. 5b, blue avo curve). land’s equation (and the shallow resistivity log) thus apparently underestimates the mud-invasion close to the well bore in the highly porous parts of the reservoir and probably reflects the conditions at some distance from where the sonic log p-wave propagates. this suggestion is further supported by the coincidence of log estimates of density and p-wave velocity with results from core samples saturated with brine. the content of hydrocarbons thus appears to drop to a very low value close to the well bore where the p-wave velocity reaches its maximum value restricting the propagation of p-waves to a very narrow zone, whereas the propagation of s-waves is less affected by the pore fluid content (fig. 3). the second approach based on the muhs model results in a good match between log and seismic estimates of the poisson ratio in the virgin zone (fig. 4c, full red curve versus fig. 5b, blue avo curve). the best way to estimate the acoustic properties of the virgin zone is therefore to use the extended modified upper hashin-shtrikman velocity–porosity relation for chalk. avo inversion of the seismic data based on such synthetic sonic logs reveals a zone of very low 15 muhs sonic log muhs landís eq. a b c m e as u re d d e p th ( m ) 2780 2800 2850 1 2 3 4 0.1 0.2 0.3 0.40 25 50 75 100 sw, porosity (%) velocity (km/s) poisson ratio (-) e k o fi sk f m e k o fi sk f m vs vp core vp core vs core vp core vs core porosity t o r f m t o r f m fig. 4. log data and predictions from the corrected muhs model based on porosity and water saturation for the chalk section in the rigs-2 well. a: porosity (estimated from the density log) and water saturation (sw). b: pand s-wave velocity (vp, vs). data (blue curves) and predictions from the corrected muhs model (red curves). c: poisson ratio in the virgin zone; prediction of the corrected muhs model (full red curve), prediction based on land’s (1968) equation (black dashed curve). in the high-porosity oil zone of the tor formation, the oil is predicted to be almost completely flushed. this is indicated by the closeness of the measured vp log (blue curve) and measured vp for the brine saturated cores (green circles), whereas the predicted vp for the virgin zone is low (red curve based on the muhs model and sw). modified from japsen et al. 2004. poisson ratio that correlates with the oil reservoir in the tor formation. in this way avo inversion provides direct evidence for the presence of oil in highly porous chalk of the south arne field. references bach, t., espersen, t.b., pedersen, j.m., rasmussen, k.b., hinkley, r. & pillet, r.p. 2003: seismic inversion of avo data. in: hansen, p.c., jacobsen, b.h. & mosegaard, k. (eds): methods and applications of inversion, 31–42. berlin: springer verlag. fabricius, i.l. 2003: how burial diagenesis of chalk sediments controls sonic velocity and porosity. american association of petroleum geologist bulletin 87, 1755–1778. fabricius, i.l., mavko, g., mogensen, c. & japsen, p. 2002: elastic moduli of chalk as a reflection of porosity, sorting and irreducible water saturation. society of exploration geophysicists technical programme and expanded abstracts 21, 1903–1906. gommesen, l. 2003: prediction of porosity and fluid in chalk from acoustic measurements, 94 pp. ph.d. thesis. lyngby: technical university of denmark. jacobsen, n.l., engstrøm, f., uldall, a. & petersen, n.w. 1999: delineation of hydrodynamic/geodynamic trapped oil in low permeability chalk. society of petroleum engineers paper 56514, 10 pp. japsen, p., bruun, a., fabricius, i.l., rasmussen, r., vejbæk, o.v., pedersen, j.m., mavko, g., mogensen, c. & høier, c. 2004: influence of porosity and pore fluid on acoustic properties of chalk: avoresponse from oil, south arne field, north sea. petroleum geoscience 10, 319–330. land, c.s. 1968: calculation of imbibition relative permeability for twoand three-phase flow from rock properties. society of petroleum engineers journal 1968, 149–156. mavko, g., mukerji, t. & dvorkin, j. 1998: the rock physics handbook, 329 pp. cambridge: cambridge university press. megson, j.b. 1992: the north sea chalk play; examples from the danish central graben. in: hardman, r.f.p. (ed.): exploration britain: geological insights for the next decade. geological society special publication (london) 67, 247–282. røgen, b. 2002: north sea chalk – textural, petrophysical and acoustic properties, 106 pp. ph.d. thesis. lyngby: technical university of denmark. vejbæk, o.v. & kristensen, l. 2000: downflank hydrocarbon potential identified using seismic inversion and geostatistics: upper maastrichtian reservoir unit, dan field, danish central graben. petroleum geoscience 6, 1–13. walls, j.d., dvorkin, j. & smith, b.a. 1998: modeling seismic velocity in ekofisk chalk. society of exploration geophysicists technical programme and expanded abstracts 17, 1016–1019. b t w o w ay t im e ( s) t w o w ay t im e ( s) poisson ratio (-) poisson ratio (-) acoustic impedance (106 kg/m2s) top ekofisk top tor base chalk well log avo result base chalk top ekofisk top tor acoustic impedance (106 kg/m2s) a 2.7 2.8 0.15 0.30 0.45 0.15 0.45 2.7 2.8 5 ne 7 rigs-2 6 8 9 10 sw 134 fig. 5. two-way time section with avo inversion of seismic data and inserted log response for the rigs-2 well computed from forward modelling of the corrected muhs model (fig. 4). a: acoustic impedance (density × vp). b: poisson ratio. very good agreement is observed between avo and log estimates for the acoustic impedance. note the peaks in the tight zones near top ekofisk formation (top chalk) and top tor formation. there is also good agreement between the log and avo estimates of the poisson ratio, e.g. the peak at top tor formation and the low values within the tor formation. this pattern cannot be resolved by the log if the acoustic properties are estimated from the sonic log because the water saturation near the well bore is unknown. seismic quality is severely reduced south-west of the well location due to an overlying gas cap. modified from japsen et al. (2004). 16 authors’ addresses p.j., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: pj@geus.dk a.b., ødegaard & danneskiold-samsøe a/s, titangade 10, dk-2200 copenhagen n, denmark. i.l.f., technical university of denmark, building 115, anker engelundsvej 1, dk-2800 lyngby, denmark. g.m., stanford university, stanford, california 94305-2215, usa. geological survey of denmark and greenland bulletin 7, 2004, p 57-60 57 the geological survey of denmark and greenland (geus) and the bureau of minerals and petroleum (bmp, under the government of greenland) have co-operated on the international promotion of the mineral resources of greenland for more than ten years. the government of greenland follows a strategy aimed at the development of a mining and petroleum sector in greenland capable of yielding a significant proportion of the national income. to reach this goal it is necessary to attract international investment. in respect of mineral exploration, many parts of greenland can still be considered virgin territory and it is therefore vital that all data relevant for the identification of possible exploration targets are available to the international mining industry. geus has produced many compilations of geoscience data for that purpose in traditional reports, on cd-roms and in scientific journals. in 2004, a new source of geoscience information was developed based on an interactive gis facility on the internet, and mineral exploration data and information from a region in central west greenland are now accessible at the greenland mineral occurrence map (gmom) website at geus (fig. 1; www.geus.dk/gmom). technically, this new facility will be maintained and developed in accordance with general principles for internet services adopted by geus (e.g. tulstrup 2004). new information from other regions of greenland will gradually be added. compilation of available information in databases and company reports for the specific purpose of producing a completely up-todate mineral occurrence map in electronic form on the internet, existing data and information in the databases and archives of geus have been assessed, and the relevant extracts and syntheses are included in a new database develon-line presentation of mineral occurrences in greenland leif thorning, lisbeth aa. christensen, bo møller nielsen, frands schjøth and henrik stendal geological survey of denmark and greenland bulletin 7, 57–60 (2005) © geus, 2005 fig. 1. the greenland mineral occurrence map (gmom) is a new on-line service to the international mining industry introduced in january 2005. the figure shows the gmom website with an index map of greenland and various explanatory notes. the first region to be included in the map is part of west greenland. oped as part of the gimmex system (thorning et al. 2004). for each locality the database contains a compiled summary of relevant data, including geus’ assessment of the site and its relevance for a general understanding of the economic potential of a region. the database is used for the compilation and assessment process in geus in preparation for the production of the map. a selection of attributes, i.e. properties related to each locality, is used for the construction of the maps in the esri arcgis environment. the selected attributes are available as tables in the gis environment, giving the user of the gmom website access to data and information required for further study of the mineralised locality. among the attributes are geus’ suggestions for a likely standard model for the mineralisation according to eckstrand et al. (1996). the importance of the locality is indicated by a first, rough classification as to whether the locality is an indication, a showing, a prospect or a deposit, and a code signifying its classification according to unece (1997). the database also contains standardised descriptions of the localities, including photographs, detailed maps and references when available. some localities of similar nature have been grouped, and one locality has been chosen as type locality for the group. the content of the gmom database will increase as additional localities from other regions of greenland are included. new data will originate from geus’ own investigations and from company exploration activities as these become public. once in the database they will be available for inclusion in the gmom, which thus becomes a dynamic map display of exploration data and information. gis interface to on-line greenland mineral occurrence map the gmom database is the source of information for the on-line greenland mineral occurrence map. this on-line facility has been created using the esri arcims environment and users only need their internet browser to gain access to the greenland mineral occurrence map. apart from the map itself, the gmom website contains an introduction to the map, and provides a brief background together with explanations and definitions, references and other relevant information. from the index map at the gmom website, the user can choose the area of interest among pre-set options. the map server controls the session in a new window and places a fully operational gis system at the user’s disposal (fig. 2). the information from the gmom database is the primary data to be displayed. however, a number of optional gis layers are available for inclusion on the map according to the user’s choice. based on data from other gimmex geoscience databases at geus, different backdrop maps for the display of mineralised sites are available, such as a topographic map, on which features such as rivers and lakes can be shown or omitted (fig. 2), a digital elevation model (fig. 3) and coloured anomaly maps of airborne geophysical data or geochemical data (fig. 4). the mineralised localities are shown as coloured symbols, which correspond to different commodity groups, such as precious metals, base metals, industrial minerals, etc., while the number is the locality identification in the gmom database. 58 fig. 2. opening view of gmom, showing the main part of the first region in greenland to be presented. various backdrop maps can be used. data from the mineralised localities can be inspected using the i-button or the hyperlink-button (the flash). the arcims standard gis tools available allow zooming, selection of layers, searches in the table of the active layer, measuring distances on the map and displaying or omitting features. selections of sites can be made according to name, location, commodity or any of the other attributes stored in the gmom database. the properties of individual localities can be obtained through selection of a location symbol on the map. clicking on the symbol with the mineral occurrence layer selected as active will bring up a table of information in the frame below the map with all the attributes as defined on the gmom website. this includes a hyperlink to a file in pdf format with a description of the mineralisation and its surroundings. the description can be called to the screen by using the hyperlink in the table, or by using the gis hyperlink button (the flash) before clicking on the symbol for the locality on the map. the user can select different backdrops for the map from the choices available and customise the map to his purpose. since this is all done in an arcims environ59 fig. 3. example from gmom showing the use of a digital elevation model as backdrop for the localities, which are coloured according to the type of commodity. the table displayed in the lower frame shows information for locality number 150. fig. 4. inspection of the summary information sheet of locality number 94 in the gmom database, a probable copper showing. the backdrop map shows a total intensity magnetic field anomaly map (shaded relief). the description of the site can also be downloaded as a pdf file (separate window). 60 ment, map and attribute data can be downloaded to the user’s own environment in a number of ways and incorporated with the user’s own data as required. at the launch date (january 2005) the on-line segment of the gmom covers systematically arranged data and information for a region of west greenland between latitudes 66° and 70°15´n, relying mostly on the recently completed mineral resource assessment programme for central west greenland (stendal et al. 2004). this includes much new data from 160 numbered localities within the area. however, there may be more interesting localities than those presently compiled since some of the areas within the region are still only explored at reconnaissance level. this illustrates the advantage of presenting the greenland mineral occurrence map in a dynamic form on the internet, rather than printed on paper. new information will be entered into the database as it becomes available from released company data or from further geus activities, and up-todate versions of the maps will therefore be available to users in the future. more data to come in 2005 more regional data from mainly south greenland and north-east greenland will be included in the greenland mineral occurrence map. furthermore, thematic maps for the entire country will be built into the system, and other accessory information will be made available for professional users interested in the mineral exploration potential of greenland. references eckstrand, o.r., sinclair, w.d. & thorpe, r.i. (eds) 1996: geology of canadian mineral deposit types. geology of canada 8, 640 pp. ottawa: geological survey of canada. stendal, h., nielsen, b.m., secher, k. & steenfelt, a. 2004: mineral resources of the precambrian shield of central west greenland (66° to 70°15´n). part 2. mineral occurrences. danmarks og grønlands geologiske undersøgelse rapport 2004/20, 212 pp. thorning, l., christensen, l. schjøth, f. & stendal, h. 2004: greenland mineral occurrence map. danmarks og grønlands geologiske undersøgelse rapport 2004/28, 52 pp. tulstrup, j. 2004: environmental data and the internet: openness and digital data management. geological survey of denmark and greenland bulletin 4, 45–48. unece, 1997: united nations international framework classification for reserves/resources. solid fuels and mineral commodities. united nations economic commission for europe energy/wp.1/r.77, 174 pp. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: lth@geus.dk geological survey of denmark and greenland bulletin 7, 2004, p 45-48 45 the present-day storebælt (great belt), the waterway between the islands of fyn and sjælland (fig. 1), contains deeply incised valleys, locally more than 50 m deep, and is of crucial importance to the water exchange between the fully marine kattegat and the brackish baltic sea. the role of this important gateway changed significantly during the late and post-glacial period (since 15 000 b.p.), when the baltic basin experienced alternating freshwater, brackish and marine conditions as a result of changes in relative sea level (figs 2, 3). the importance of the storebælt in understanding the dynamics of the baltic basin is reflected in the large number of studies carried out (see bennike et al. 2004). the first detailed sedimentological and stratigraphic studies in the storebælt area that demonstrated the presence of early holocene freshwater deposits below the seabed were those of krog (1960, 1965, 1971), who also presented the first shore-displacement curve for the area (krog 1979). the balkat project the late and post-glacial evolution of the south-western baltic sea has been studied in detail during the past 15 years as part of the multi-disciplinary balkat project, a co-operation between the geological survey of denmark and greenland (geus), the baltic sea research institute in warnemünde, and other partners (jensen et al. 2002). acquisition and interpretation of shallow seismic data and sampling of vibrocores form the basis for sequence stratigraphic and sedimentological studies, which together with microand macropalaeontological studies have resulted in detailed interpretations of depositional environments. the chronology has been established by numerous radiocarbon dates. initial studies focused on the fakse bugt and gedser rev region and the history of the baltic ice lake (jensen & stecker 1992; lemke & kuijpers 1995; jensen et al. 1997) and were followed by detailed studies of the ancylus lake stage (jensen et al. 1999). further studies of relative shorelevel changes in the region (bennike & jensen 1998) and the femer bælt threshold (lemke et al. 2001) showed that local ice lakes developed in front of the retreating fennoscandian ice sheet. two major transgressions of the baltic ice lake are recorded, with maximum highstand levels of approximately 30 m and 20 m below present sea level (figs 2, 3; björck 1995). the ancylus lake transgression reached just above the southern threshold of the storebælt, and was followed by a regression that presumably exposed large parts of the former lake bottom (figs 2, 3). the identification of these lake stages in the femer bælt area show a much wider distribution than previously expected, with possible connections to the kattegat (yoldia sea, littorina sea) via the storebælt (fig. 3). studies in southern kattegat and the northern storebælt region have revealed that a late pleistocene relative sea-level the storebælt gateway to the baltic jørn bo jensen, ole bennike,wolfram lemke and antoon kuijpers geological survey of denmark and greenland bulletin 7, 45–48 (2005) © geus, 2005 falster langelandsbêlt germany sweden poland fakse bugt ø resu n d 12°e 14°e 54°n 55°n 10°e 56°n 20 m 20 m 40 m 20 m lille bælt g edser rev femer bælt baltic sea kattegat 50 km s toreb æ lt jylland fyn sjælland denmark fig. 1. present-day general bathymetry of the south-western baltic sea. location of fig. 5 (red frame) and the northern and southern thresholds in storebælt (red circles) are shown. highstand was followed by a lowstand during the latest pleistocene (12 000 – 11 500 b.p.; fig. 2). this was in turn succeeded by the littorina sea transgression, which resulted in a series of back-stepping coastal deposits (jensen et al. 2002). recent studies under the balkat project have been concentrated in the central storebælt area and the northern and southern threshold areas in order to obtain a more detailed understanding of the interaction between the kattegat and the baltic basin. the storebælt gateway the central storebælt area, between the fully marine kattegat and the brackish baltic basin, has been influenced by drainage from lakes in the baltic area and marine transgressions from the kattegat. both depend on the relative levels of the southern and northern thresholds. in this area the incised valley fills provide a unique opportunity to study the initial effects of drainage and transgression, as well as the timing of these events, that – with some delay – had a great influence on the baltic area. during the later stages of the balkat project, shallow seismic data and vibrocores have been collected for the area extending from the northern entrance to the southernmost part of the storebælt. the relative sea level changes in the southernmost kattegat region (fig. 2) are clearly recognised at the entrance to the storebælt, where late glacial marine highstand sediments are cut by the younger dryas lowstand erosional unconformity and followed by an early holocene succession of channel fill, estuary river mouth sediments and backstepping shoreface deposits (fig. 4a, b; bennike et al. 2000; jensen et al. 2002). the northern storebælt threshold is located in a less than 1 km wide incised valley (figs 1, 5). profiles north and south of the threshold (fig. 4c, d) show that marine transgressive deposits are found in the incised valley north of the threshold, whereas a transitional brackish unit exists below the littorina sea deposits south of the threshold. radiocarbon datings of the brackish sediments using terrestrial plant macrofossils indicate that the initial transgression of the littorina sea took place at about 9400 b.p. the central storebælt incised valley (figs 1, 4e) was formed by meltwater during the deglaciation about 17 000 b.p. (bennike et al. 2004), and the initial fill is represented by late glacial lake sediments. the youngest late glacial unit is restricted to the channels, and is believed to be the baltic ice lake extension into the storebælt area. the late glacial sediments are truncated by an erosional unconformity overlain by lower holocene freshwater sediments that include river and lakeshore deposits, and followed by extensive lake deposits formed in the time interval between 10 900 and 8800 b.p. (bennike et al. 2004). deposition of the early river deposits is coeval with the maximum level of the ancylus lake. the initial sign of the marine transgression in the central storebælt area is dated to 8100 b.p. by marine shells. 46 northern threshold ancylus lake baltic ice lake southern threshold littorina transgression 10 30 50 –10 –30 –50 s h o re -l e ve l (m ) years b.p. 16 000 12 000 8000 4000 0 central kattegat northern storebælt femer bælt fig. 2. shore level changes relative to present-day sea level in central kattegat, northern storebælt and femer bælt. the levels of the thresholds in the storebælt are indicated. 10 500 b.p.15 000 b.p. yoldia sea littorina sea 100 km 100 km baltic ice lake ancylus lake ice fig. 3. palaeogeographical maps showing the distribution of land and sea/lake at 15 000 years and 10 500 years b.p. the threshold in the southernmost part of the storebælt is found in a few hundred metres wide channel at about 25 m below present sea level (figs 1, 4f, 5). however, fine-grained freshwater sediments dated to the time of maximum ancylus lake transgression at 10 300 b.p. brings the pre-ancylus lake threshold down to about 30 m below present sea level. there is no evidence of a rapid ancylus lake drainage (dana river) as earlier proposed by björck (1995). initial marine transgression of the storebælt based on the recently collected data it is possible to reconstruct a palaeogeographical scenario for the initial holocene marine transgression (10 000 – 9500 b.p.) of the storebælt area (fig. 5). at about 10 000 b.p. the ancylus lake was mainly drained by a river system located in the storebælt area with an outlet in the southern kattegat area (bennike et al. 2000). in general, the drainage pathway through the storebælt was restricted to channels less than 1 km wide. a transitional brackish estuary was restricted to the area immediately north-east of the northern threshold. the transgression of the littorina sea resulted in flooding of the northern storebælt threshold at about 9500 b.p. and a brackish environment extended to about 20 km south of the threshold. at the same time, a large local lake developed in the central and southern part of the storebælt area due to a ground-water level rise, related to the relative sea level rise north of the northern storebælt threshold, and brackish and marine conditions were gradually established in these areas around 9400–9100 b.p. (winn et al. 1998; bennike et al. 2004). future perspectives during the 15 years of balkat co-operation a unique database covering the late and postglacial sediments in the southwestern baltic region has been generated. the main key areas have now been studied, but further biostratigraphical investigations and datings are required for lillebælt, øresund and parts of kattegat. when this work is completed, a detailed model of the postglacial evolution of the western baltic region can be developed including data on palaeogeography, fauna and flora evolution, and climatic changes. this model will be of great importance for future scientific co-operation involving marine geological, archaeological, ecological and palaeo-climatic studies in the rest of the baltic region. furthermore a detailed knowledge on the palaeogeographic evolution is important in locating potential sand and gravel resources. large offshore construction works may also 47 sw ne –20 m –40 m –40 m –50 m –20 m –30 m –20 m –40 m –20 m –20 m –30 m –40 m 5 kmb ew sw ne lg w e lg lg gas w e ew 1km northern threshold southern threshold a c d e f gas 1km 1km 1km 1km till local ice lake baltic ice lake freshwater brackish marine highstand marine transgression littorina sea p le is to c e n e h o lo c e n e fig. 4. profiles illustrating the influence of the northern and southern thresholds in the zone between the fully marine kattegat and the brackish to lacustrine central and southern parts of the storebælt. for location of profiles, see fig. 5. benefit from the studies. for example, the planned femer bælt link bridge requires seabed information for geotechnical, raw material and hydrographic evaluations, as well as for monitoring possible impacts on the environment. acknowledgement our friend and colleague, wolfram lemke, unexpectedly passed away on 21 april 2005. we wish to acknowledge his enthusiastic participation in our joint projects and his inspiring contributions to our long-standing co-operation. his premature death is a great loss to the scientific community. references bennike, o. & jensen, j.b. 1998: lateand postglacial shore level changes in the southwestern baltic sea. bulletin of the geological society of denmark 45, 27–38. bennike, o., jensen, j.b., konradi, p.b., lemke, w. & heinemeier, j. 2000: early holocene drowned lagoonal deposits from the kattegat, southern scandinavia. boreas 29, 272–286. bennike, o., jensen, j.b., lemke, w., kuijpers, a. & lomholt, s.j. 2004: lateand postglacial history of the great belt, denmark. boreas 33, 18–33. björck, s. 1995: a review of the history of the baltic sea, 13.0–8.0 ka bp. quaternary international 27, 19–40. jensen, j.b. & stecher, o. 1992: paraglacial barrier–lagoon development in the late pleistocene baltic ice lake, southwestern baltic. marine geology 107, 81–101. jensen, j.b., bennike, o., witkowski, a. & kuijpers, a. 1997: the baltic ice lake in the south-western baltic: sequence-, chronoand biostratigraphy. boreas 26, 217–236. jensen, j.b., bennike, o., witkowski, a., lemke, w. & kuijpers, a. 1999: early holocene history of the southwestern baltic sea: the ancylus lake stage. boreas 28, 437–453. jensen, j.b., petersen, k.s., konradi, p., kuijpers, a., bennike, o., lemke, w. & endler, r. 2002: neotectonics, sea-level changes and biological evolution in the fennoscandian border zone of the southern kattegat sea. boreas 31, 133–150. krog, h. 1960: post-glacial submergence of the great belt dated by pollen-analysis and radiocarbon. report of the international geological congress, xxi session, part iv, 127–133. krog, h. 1965: on the post-glacial development of the great belt. baltica 2, 47–60. krog, h. 1971: the early post-glacial development of the storebælt as reflected in a former fresh water basin. quaternaria 14, 85–92. krog, h. 1979: the quaternary history of the baltic, denmark. in: gudelis, v. & königsson, l.-k. (eds): the quaternary history of the baltic, 207–217. uppsala: uppsala university. lemke, w. & kuijpers, a. 1995: late pleistocene and early holocene palaeogeography of the darss sill area, southwestern baltic. quaternary international 27, 73–81. lemke, w., jensen, j.b., bennike, o., endler, r., witkowski, a. & kuijpers, a. 2001: hydrographic thresholds in the western baltic sea: late quaternary geology and the dana river concept. marine geology 176, 191–201. winn, k., erlenkeuser, h., nordberg, k. & gustafsson, m. 1998: paleohydrography of the great belt, denmark, during the littorina transgression: the isotope signal. meyniana 50, 237–251. 48 authors’ addresses j.b.j, o.b & a.k., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: jbj@geus.dk w.l., baltic sea research institute, seestrasse 15, d-18119 rostock-warnemünde, germany. 10 000 b.p. f e d c a northern threshold southern threshold b 56°n 55°n 9 500 b.p. f e d c a northern threshold southern threshold b 56°n 55°n 11°e 11°e 25 km 25 km a b fig. 5. palaeogeographical maps of the storebælt area during initial holocene transgression. a: at c. 10 000 years b.p., before the transgression of the northern threshold, the ancylus lake was connected to kattegat via a river system ending in a narrow, brackish estuary. b: after the threshold was transgressed at c. 9000 years b.p., a much more extensive brackish water estuarine complex developed at the mouth of the river, and a major lake was formed in the central part of the storebælt area. for legend and sections a–f see fig. 4. geological survey of denmark and greenland bulletin 7, 2004, p 33-36 as the drinking water supply in denmark is totally based on groundwater, monitoring of the groundwater quality is extremely important to the danish community. with more than 62% of the total land area under agricultural use the danish government has determined that the entire area is vulnerable to nitrate polution, and therefore the groundwater monitoring programme should cover the entire country. the danish groundwater monitoring programme comprises water supply well monitoring, the groundwater monitoring network and agricultural watershed monitoring (figs 1, 2) and is described on www.groundwater.dk. the programme is part of the national action programme for the water environment and nature, novana (svendsen & norup 2004; svendsen et al. 2005). groundwater quality monitoring is carried out on the basis of data from approximately 6200 public water supply wells. furthermore, a detailed analytical programme is carried out on 1415 well screens from the monitoring network comprising 70 catchment areas, and on 100 shallow screens from the five agricultural watersheds (svendsen et al. 2005). the detailed quality monitoring includes analyses for 97 chemical elements, comprising 26 main elements, 14 heavy metals, 23 organic micro-pollutants and 34 pesticides and metabolites. nitrate the water supply wells generally have long screens and are intended to provide representative information on the distribution of the nitrate content in primary groundwater reservoirs. data from water extraction wells are, however, biased since the wells are intended to ensure production of drinking water with nitrate concentrations below the maximum admissible concentration (mac) of 50 mg nitrate per litre. the groundwater monitoring wells give a more accurate picture of the general nitrate pollution in the danish groundwater. in 1998–2004, mean nitrate concentrations were above the mac limit for drinking water in 16.9% of the wells, whereas about 60% had no nitrate (< 1 mg nitrate per litre). the spatial distribution of nitrate in the groundwater aquifers varies. west of the weichselian glaciation borderline (fig. 1), the outwash plains are dominated by upper, unconfined aquifers overlying deeper, confined quaternary and miocene sands. east of the glaciation borderline the sandy meltwater deposits and the pre-quaternary limestone aquifers are generally covered by clayey till which reduces or prevents nitrate pollution (fig. 3). over the past half century the use of fertilisers in farming has intensified dramatically (fig. 4). groundwater from the monitoring screens has been dated using the cfc (chlorofluorocarbon) content (geus 2004), and demonstrates that the highest nitrate values reflect the increase in the use of fertilisers (fig. 4). continued monitoring will show whether the decrease in the use of fertilisers during the last decade will result in a decrease in the nitrate content, or whether the increasing use of manure will maintain high nitrate levels. preliminary data suggest, however, that since 1979 farmers have adapted their spreading practice for fertilisers and manure such that nitrate pollution is now following a declining trend. 33 groundwater quality monitoring in denmark jens stockmarr geological survey of denmark and greenland bulletin 7, 33–36 (2005) © geus, 2005 < 35 000 35 000 – 350 000 350 000 – 3500 000 water extraction in m3 > 3500 000 50 km10°e 12°e8°e 55°n 57°n fig. 1. extraction of water for domestic consumption from approximately 3000 danish public waterworks in 2001. all waterworks (except one) are based on groundwater extraction. red dashed line indicates the position of the weichselian glaciation borderline. the island of bornholm is shown in the inset map. modified from fraters et al. (2005). nickel, arsenic and other inorganic trace elements the most widespread impact from inorganic trace elements is due to nickel derived from oxidation of pyrite, bravoite and other heavy metal bearing sulphides (fig. 5). massive dissolution of sulphides occurs in areas where large-scale extraction of groundwater has caused lowering of the groundwater table, followed by an influx of oxic groundwater. during dissolution, some of the nickel is adsorbed by contemporaneously precipitated manganese oxide. the trapped nickel is, however, released when the groundwater table rises again, since this leads to reducing conditions and dissolution of the manganese oxides. implementation in 2001 of the eu drinking water directive in danish legislation has led to increased concern with respect to arsenic, for which the mac value was decreased from 50 to 5 µg/l. nine per cent of the monitoring well screens in the groundwater monitoring programme currently exceed 5 µg/l in all samples, while 14% exceed 5 µg/l in at least one sample (fig. 6). the distribution of arsenic is to a large degree controlled by redox conditions, as the solubility of arsenic is about ten times higher in reducing environments compared to oxidising conditions. high arsenic concentrations are mainly found in aquifers underlying clayey sediments. as a result of seven years of groundwater monitoring, the background levels of the 23 inorganic trace elements analysed are well known and are illustrated by the cumulative curves in fig. 7. most curves show a regular distribution, e.g. strontium (sr) and mercury (hg), indicating little or no pollution, whereas the skewed curves for aluminium (al) and nickel (ni) reflect pollution. pesticides and metabolites analytical results from the water supply wells, the groundwater monitoring areas and the agricultural watersheds differ markedly (fig. 8). only agricultural pesticides were detected in water samples collected from young groundwater in the agricultural watersheds, whereas in water samples collected in the groundwater monitoring network other pesticides, such as those used in consolidated areas like urban areas, roads or farmyards have also been found. pesticides and their metabolites are found in more than 25% of all wells (table 1; geus 2004). the most frequently found pesticide group consists of triazines and their metabolites. these compounds are commonly found in both farming and urban areas. in the agricultural watersheds the triazines and their metabolites make up about half of all recorded pesticides and metabolites. in water supply wells the analytical data indicate a very high frequency of 2,6-dichlorobenzamide (bam) findings. twenty-five per cent of the wells contain bam, and 10% have concentrations above the mac value of 0.1 mg/l. bam is a metabolite from dichlobenil and chlorothiamide that were commonly used prior to 1997 as a total herbicide in urban areas, along roads and in farmyards. 34 fig. 2. network of danish national groundwater monitoring areas (catchments) and selected agricultural watersheds covered by the extended monitoring programme. from stockmarr & nyegaard (2004). 12°e10°e8°e 55°n 56°n 57°n 50 km groundwater monitoring areas agricultural watersheds 0 20 40 60 80 100% 0–10 10–20 20–30 30–40 40–50 50–60 60–70 70–80 80–90 ≤ 1 mg/l no3 1–50 mg/l no3 > 50 mg/l no3 d e p th ( m ) n = 894 n = 1 500 n = 1 746 n = 1 413 n = 1 050 n = 711 n = 456 n = 282 n = 149 fig. 3. distribution of nitrate versus depth to well screen in groundwater monitoring and water supply wells. the data cover the period 1998– 2003 and are grouped into three classes according to mean nitrate. from geus (2004). pesticides and metabolites 1998–2003 number % number % number of analysed screens screens with findings findings ≥ 0.1µg/l (mac) monitoring network 1020 437 42.8 153 15.0 agricultural watersheds 75 52 69.3 19 25.3 water supply wells 5515 1443 26.2 355 6.4 table 1. pesticides and metabolites in danish groundwater mac: maximum admissible concentration. from geus (2004). the monitoring network demonstrates high detection rates for pesticides in the upper 40–50 m of wells tested, and a lower number of findings with increasing depth (fig. 8). pollution in shallow groundwater drinking water from 628 dug wells and shallow drilled wells used for single private supply and minor partnership supplies (less than nine families) was investigated in a research project focusing on the youngest groundwater (brüsch et al. 2004). in 35% of the investigated wells, pesticides and their metabolites were recorded with values above the mac value for drinking water (0.1 mg per litre), whereas 11% of wells had more than ten times the mac value. the research project showed that nitrate pollution in 22% of the wells was above 50 mg per litre. the mac level for bacteria was exceeded in 48% of the wells whereas 31% contained coliforme bacteria. in total, 68% of the private supply and minor partnership supply wells delivered undrinkable water. fig. 5. occurrence of nickel in danish water supply wells, 1998–2003. slightly modified from geus (2004). fig. 6. occurrence of arsenic in danish water supply wells, 1998–2003. slightly modified from geus (2004). 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 0 20 40 60 80 100 120 140 nitrate in groundwater (mg/l) fertiliser (kg n/ha) mean nitrate concentration use of fertilisers per year 0 50 100 150 200 250 300 350 400 oxic zone (o 2 > 1 mg/l) anoxic zone (no 3 > 1 mg/l) fig. 4. nitrate content versus cfc age of groundwater. the annual use of nitrogen fertilisers is shown for comparison. groundwater data from the anoxic zone are corrected on the basis of sulphate content. slightly modified from geus (2004). 12°e10°e8°e 55°n 56°n 57°n 50 km > 20 µg/l ≤ 20 µg/l nickel 12°e10°e8°e 55°n 56°n 57°n 50 km > 5 µg/l ≤ 5 µg/l arsenic 35 36 conclusions during the last two decades many water supply wells have been closed due to pollution; initially this was a result of nitrate pollution, and subsequently also to pesticide pollution. nickel contamination has also closed some wells, and it is feared that arsenic will cause closure of more wells. in some cases the water supply companies have extended their production wells to greater depth instead of closing them, but often this is not a viable solution. due to government policy that drinking-water production should be based on pure groundwater requiring only simple treatment (aeration and iron removal), only few water supply companies have had permission to install advanced water treatment for removal of pesticides or nickel. however, more and more water supplies are expected to need advanced water treatment in the future. nitrate pollution is still the most serious problem because intensive agricultural practices cause leakage of nitrate into groundwater and surface water. while a series of action plans have been introduced to reduce nitrate pollution, much of the young groundwater and most of the surface water in denmark are seriously polluted by nitrate. references brüsch, w., stockmarr, j., kelstrup, n., von platen-hallermund, f. & rosenberg, p. 2004: pesticidforurenet vand i små vandforsyningsanlæg. danmarks og grønlands geologiske undersøgelse rapport 2004/9, 85 pp. fraters, b., kovar, k., willems, w.j., stockmarr, j. & grant, r. (eds) 2005: monitoring effectiveness of the eu nitrates directive action programmes. results of the international monno3 workshop, the hague, the netherlands, 11–12 june, 2003. rivm report 680100002/2005, 290 pp. geus 2004: grundvandsovervågning 1998–2003, 48 pp. københavn: danmarks og grønlands geologiske undersøgelse. stockmarr, j. & nyegaard, p. 2004: nitrate in danish groundwater. in: razowska-jaworek, l. & sadurski, a. (eds): nitrates in groundwater. international association of hydrogeologists, hydrogeology, selected papers 5, 187–199. stockmarr, j., nyegaard, p., larsen, c.l., felding, g. & brüsch, w. 2002: groundwater quality monitoring in denmark. third international conference on water resources and environment research (icwrer), dresden, germany 22–26 july, 2002, proceedings, 165–169. svendsen, l. & norup, b. (eds) 2004: novana. det nationale program for overvågning af vandmiljøet og naturen. programbeskrivelse – del 1. danmarks miljøundersøgelser, faglig rapport fra dmu 495, 45 pp. svendsen, l.m., van der bijl, l., boutrup, s. & norup, b. (eds) 2005: novana. det nationale program for overvågning af vandmiljøet og naturen. programbeskrivelse – del 2. danmarks miljøundersøgelser, faglig rapport fra dmu 508, 128 pp. author’s address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: sto@geus.dk 0.0001 0.001 0.01 0.1 1.0 10 100 1000 10 000 g/l asas crcr cucu ii lili ni hghg cdcd b ba brbr srsrpbpb as cr cu i limo va znhg cd b ba br srpb % 0 20 40 60 80 100 alalal fig. 7. inorganic trace elements found in danish monitoring wells from 1993 to 1999. the skewness of the distribution pattern in the curves for nickel (ni) and aluminium (al) reflects pollution. regular distributions, as e.g. for hg and sr, indicate little or no pollution. slightly modified from stockmarr et al. (2002). fig. 8. occurrence of pesticides and metabolites in water supply and groundwater monitoring wells versus depth to top of well screen, 1998– 2003 as percentage of number of screens investigated. slightly modified from geus (2004). d e p th ( m ) findings above maximum admissible concentrationfindings 0 10 20 30 40 50 60%0 10 20 30 40 50% groundwater monitoring wellswater supply wells 0–10 10–20 20–30 30–40 40–50 50–60 60–70 70–80 80–90 90–100 geological survey of denmark and greenland bulletin 23, 2011, 37-40 37 the brackish baltic sea and the more saline kattegat are connected by three straits, lillebælt, storebælt and øresund (fig. 1). of the three straits, lillebælt is the narrowest, with 700 m at its narrowest point, widening out towards the south to around 25 km (fig. 2). in the narrow parts of lillebælt, water depths around 30–50 m are common. in the northern part of lillebælt the depth is 16–18 m and in the southern part the depth is around 35 m. storebælt and øresund have played important roles as outlets during the history of the baltic sea, and their histories have been much discussed (björck 1995; bennike et al. 2004). in contrast, lillebælt has received little attention. in this paper we present 11 new radiocarbon accelerator mass spectrometry (ams) ages and propose a curve for holocene relative shore-level changes in lillebælt. we use the term shore-level changes rather than sea-level changes because we have constructed both lake-level and sea-level changes. during the last deglaciation of the lillebælt region, large channels were eroded by northward-f lowing subglacial meltwater. these channels are now found at the bottom of the strait, and most of them are kept free of sediments by strong bottom currents. however, late and postglacial sediments are found in some parts of the channels. several submerged settlements have been reported from the lillebælt region (andersen 1985). they are dated to the mid-holocene from artefacts and by radiocarbon dating. methods combined high-resolution, sub-bottom profiling and sediment coring were carried out from r/v alexander von humboldt. the seismo-acoustic equipment included a sediment echosounder (fig. 3), and the profiles obtained were used for the selection of the core sites (fig. 4). a 6 m long vibrocorer was used for coring. we also had access to vibrocores and seismic profiles from a survey conducted in connection with a planned gas pipeline. this material was handed over to the geological survey of denmark and greenland (geus) from dansk olie og naturgas a/s. selected cores with the most complete stratigraphy were sub-sampled for studies of macrofossils. the samples were wet sieved and analysed using a dissecting microscope. repostglacial, relative shore-level changes in lillebælt, denmark ole bennike and jørn bo jensen 10°e 14°e 56°n 57°n sweden denmark germany kattegat storemecklenburg bælt femern bælt baltic sea bucht kieler lillebælt øresund fig. 2 bucht 50 km jylland fyn fig. 1. map of denmark and surrounding area showing the location of lillebælt and the other straits connecting the baltic sea to kattegat, as well as place names mentioned in the text. fig. 2. bathymetry of lillebælt with the location of the vibrocores indicated. © geus, 2011. geological survey of denmark and greenland bulletin 23, 37–40. open access: www.geus.dk/publications/bull 55°30´n 10°e 10°e mr009a la010 281900 la006b 281910 la003 fyn jylland als fig. 3 55°30´n 55°n 0–10 10–20 20–30 >30 water depth (m) 10 km 3838 mains of plants and marine molluscs were submitted for ams radiocarbon dating (table 1). several published dates were also used for the reconstruction of shore-level changes (table 2; k-samples are conventional ages, and the lus-sample is an ams age). we have used a reservoir age of 400 years for the marine samples, however, the reservoir age may have varied somewhat during the holocene (olsen et al. 2009). sediments, palaeoecology and chronology the oldest sediments consist of till that shows an internal, chaotic ref lection pattern and a sharp upper boundary. a few cores also penetrated meltwater sand. till and meltwater sand accumulated during the last glaciation and deglaciation of the region. the glacial deposits are locally overlain by late glacial sediments, which are found in the channels. the late glacial sediments show conformable internal ref lectors, and consist of clay, silt and fine-grained sand. one sample has been dated to 11 400–11 900 cal. years bp, corresponding to a late younger dryas age (table 1, poz-8924). we suggest that the late glacial sediments were partly deposited in a branch of the baltic ice lake. in the deeper parts of lillebælt, black, organic-rich sediments are widespread. the sediments are commonly laminated and may contain abundant fragments of small roots and fruits of telmatic plants. some of this sediment is swamp peat, but most of it is coarse detritus g yttja. the organic-rich sediments are usually overlain by laminated calcareous g yttja clay. however, in core la006b lake sediments are found below peat. this succession is interpreted as overgrowing of a basin. samples from the lake deposits gave ages of c. 11 000–8800 cal. years bp (early holocene, table 1, poz-5754, poz-5755, poz-5753, poz-8859, poz8860). 27 22 17 d e p th ( m b .s .l .) marine deposits early holocene freshwater deposits late glacial deposits glacial deposits la003 la003 281910 281910 281900 281900 la006b la006b 1 km a b fig. 3. a: original seismic profile, obtained by a sediment echosounder. b: interpretation below. for location see fig. 2. cores labelled 2819xx were collected from r/v alexander von humboldt, and cores labelled la were collected for dansk olie og naturgas a/s. 11 000 7100 11 600 10 600 281900 c la y s il t s an d c la y s il t s an d c la y s il t s an d c la y s il t s an d h ii h i gl h i lg ? ? 7600 281910 ss ss ss ss 11 000 la003 core 10 800 la006b l it h o lo g y s tr u c tu re s d e p th ( m b e lo w s e a le ve l) 25 26 27 28 29 24 ss radiocarbon age lamination structureless irregular lamination bioturbation silt/clay/gyttja/marl sand pebbles peat heterolithic fig. 4. sedimentological logs from vibrocores from the lillebælt. radiocarbon ages are in calibrated calendar years bp. gl: glacial. lg: late glacial. h i: early holocene freshwater. h ii: brackish and marine holocene deposits. 39 marine sediments from protected areas consist of laminated or bioturbated, fine-grained, organic-rich mud. sandy and silty sediments are found in shallow water areas and in areas with strong bottom currents (fig. 3). shells and shell fragments of marine molluscs are common. on the acoustic records, the marine deposits are mostly transparent or show continuous ref lectors parallel to the lower boundary. in three cores we dated the lowermost shell of marine molluscs we could find. the oldest age determination is c. 7700 cal. years bp (table 1, poz-5790). in core la010 bioturbated sand is present in the upper part of the core. the fauna implies brackish conditions. a sample from the bottom of the sand unit was dated to c. 8500 cal. years bp (table 1, poz-5767). we suggest that the sand marks the first marine inf luence in the area. shore-level changes on the basis of the available radiocarbon ages, we have reconstructed relative shore-level changes in the region (fig. 5). the relative shore level was low during the early part of the holocene and probably rose slowly throughout the early holocene, and at the same time a large lake existed in the area. as the shore level rose this lake increased in size and at around 8500 cal. years bp it was transformed into a brackish water body. two dates from core mr009a provide an important fix point for the shore-level evolution (table 1). the dates show that a peat now found 9 m below sea level was transgressed by the sea between c. 8200 and c. 7700 cal. years bp, and around 8000 cal. years bp marine conditions were established. later sea-level changes are constrained by six published radiocarbon dates (table 2). they comprise two dates of wood from marine gyttja, two dates from ostrea edulis shells, an age from a bone found in a grave at a water depth of 2.7 m and a bone of harp seal from a submarine settlement. the two latter dates come from sites that were situated above the contemporary sea level. discussion in lillebælt, late glacial sediments are found in incised channels. the younger dryas sequence that consists of finegrained laminated clay and silt is followed by a hiatus which was probably formed during the final drainage of the baltic ice lake, when shore level dropped around 25 m over a few years (björck 1995). the maximum shore level of the baltic ice lake in the south-western baltic sea was around 20 m b.s.l., and this lake may have extended as far west as southwestern kieler bucht ( jensen et al. 2002). the baltic ice lake may also have extended into southern lillebælt. core laboratory species* sediment depth age ( c calibrated no. no. b.s.l. (m) years bp) age (years bp) § la003 poz-5754 m. trifoliata, c. mariscus detritus gyttja 28.10–28.20 9670 ± 50 10 789–11 210 p. australis la006b poz-5755 m. trifoliata, c. mariscus lake marl 26.02–26.03 9460 ± 50 10 567–11 068 la010 poz-5767 b. albae, c. mariscus brackish sand 16.60–16.70 7700 ± 70 8384–8599 la010 poz-5753 m. trifoliata, c. mariscus lake gyttja 16.72–16.78 7880 ± 50 8556–8976 mr009a poz-5790 mytilus edulis marine mud 9.70 7280 ± 40 7842–7649 mr009a poz-5805 b. albae peat 9.80–9.90 7420 ± 50 8074–8372 281900 poz-8820 arctica islandica marine sand 25.00–25.05 6590 ± 40 6994–7225 281900 poz-8859 p. tremula, b. nana lake clay 26.50–26.60 9350 ± 50 10 419–10 702 281900 poz-8860 p. tremula, b. albae detritus gyttja 26.80–26.88 9670 ± 50 10 789–11 210 281900 poz-8924 salix sp. clay 26.98–27.08 10 110 ± 60 11 401–11 910 281910 poz-8821 m. edulis, m. balthica marine sand 25.25–25.26 7140 ± 40 7528–7692 * full names are: menyanthes trifoliata, cladium mariscus, phragmites australis, betula sect. albae, betula nana, populus tremula, mytilus edulis, maco ma balthica. § calibration is according to the intcal09 dataset (terrestrial samples) and the marine09 dataset (marine samples). table 1. new radiocarbon ams age determinations from lillebælt 14 terrestrial peat lake deposit brackish sediment marine fossils marine gyttja bone from grave seal bone from settlement d e p th ( m b e lo w s e a le ve l) 12 10 8 6 4 2 0 mr009a age (cal. ka bp) mr009a 281900281910 la006b la003 m m sg b b m g s 0 10 20 30 la010 281900 fig. 5. curve showing relative shore-level changes in southern lillebælt during the holocene. green: lake phase. red: brackish water phase. blue: marine phase. ka: 1000 years. 4040 during the earliest holocene, large parts of lillebælt were dry land, but local bogs and lakes must have existed in the deeper parts. as the shore level began to rise, local lakes and bogs became widespread. during continued shore-level rise, bogs were transformed into lakes, and a large lake developed in the southern part of lillebælt. it was connected to another large lake to the south in kieler bucht, and to other large lakes in femer bælt, mecklenburg bucht and storebælt. later, the ongoing eustatic sea-level rise led to brackish and then to marine conditions in lillebælt. the first marine inf luence was via storebælt when southern lillebælt was a fjord. however, the fjord was transformed into the lillebælt strait during continued rapid sea-level rise. the oldest dated marine shell from lillebælt is from 7700 cal. years bp, but brackish water conditions are suggested at 8600–8384 cal. years bp. the youngest lake deposits (around 17 m below sea level) are dated to 8976–8556 cal. years bp. in storebælt, the oldest dated marine shell gave an age of 8100 cal. years bp (bennike et al. 2004), and in the mecklenburg bucht, the oldest shell date is c. 8000 cal. years bp (rößler et al. 2011). the early holocene deposits in lillebælt show no indication of a lowering of the shore level before being inundated by marine waters. conclusions glacial till and holocene marine deposits are widespread in lillebælt. in the deeply incised channels late glacial and early holocene non-marine deposits are found, these units are separated by an erosional boundary. the late glacial deposits were probably deposited during pre-allerød and allerød times, as well as during the younger dryas. the early holocene non-marine deposits have yielded ages between 11 000 and 8800 cal. years bp. the late glacial unit consists of lake deposits, and we suggest that the baltic ice lake extended into southern lillebælt. during the early holocene, a large lake existed in southern lillebælt; this lake expanded in size during shorelevel rise. the oldest shell of a marine mollusc from lillebælt is dated to 7700 cal. years bp, but brackish conditions were probably established at around 8500 cal. years bp. acknowledgement the captain and crew of r/v alexander von humboldt, and in particular the cruise leader, the late wolfram lemke are thanked for their help during the marine cruise. references andersen, s.h. 1985: tybrind vig, a preliminary report on a submerged ertebølle settlement on the west coast of fyn. journal of danish archaeolog y 4, 52–69. bennike, o., jensen, j.b., lemke, w., kuijpers, a. & lomholt, s. 2004: lateand postglacial history of the great belt, denmark. boreas 33, 18–33. bennike, o., rasmussen, p. & aaris-sørensen, k. 2008: the harp seal (phoca groenlandica erxleben) in denmark, southern scandinavia, during the holocene. boreas 37, 263–272. björck, s. 1995: a review of the history of the baltic sea, 13.0–8.0 ka bp. quaternary international 27, 19–40. jensen, j.b., kuijpers, a., bennike, o., laier, t. & werner, f. 2002: new geological aspects for freshwater seepage and formation in eckernförde bay, western baltic. continental shelf research 22, 2159–2173. olsen, j., rasmussen, p. & heinemeier, j. 2009: holocene temporal and spatial variation in the radiocarbon reservoir age of three danish fjords. boreas 38, 458–470. petersen, k.s. & rasmussen, k.l. 1996: the impact of radiocarbon datings on natural historical sciences in denmark: especially paleozoological and shore-line datings. pact 49, 117–130. rößler, d., moros, m. & lemke, w. 2011: the littorina transgression in the southwestern baltic sea: new insights based on proxy methods and radiocarbon dating of sediment cores. boreas 40, 231–241. doi: 10.1111/j.1502-3885.2010.00180.x. laboratory material depth age ( c calibrated reference no. b.s.l. (m) years bp) age (years bp)* k-3558 human bone 2.7 6740 ± 80 7459–7727 andersen (1985) k-4150 alnus wood 4.7 6380 ± 100 7153–7480 andersen (1985) k-4149 tilia wood 2.8 5370 ± 100 5922–6317 andersen (1985) k-5680 ostrea edulis shells 5.0 5940 ± 70 6645–6995 petersen & rasmussen (1995) k-5681 ostrea edulis shells 4.0 5780 ± 70 6445–6797 petersen & rasmussen (1995) lus-6136 phoca groenlandica bone 2.0 5595 ± 50 5885–6144 bennike et al. (2008) *calibration is according to the intcal09 dataset (terrestrial samples) and the marine09 dataset (marine samples). table 2. published radiocarbon age determinations from lillebælt 14 authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: obe@geus.dk geological survey of denmark and greenland bulletin 6, 89-97 89geological survey of denmark and greenland bulletin 5, 89–97 © geus, 2004 jurassic dinoflagellate cysts from hochstetter forland, north-east greenland stefan piasecki and lars stemmerik three sections in hochstetter forland, north-east greenland, referred to the jurassic payer dal and bernbjerg formations, have been analysed for dinoflagellate cysts. the dinoflagellate cysts, new finds of ammonites and previously recorded marine faunas form the basis for improved dating of the succession. the basal strata of the payer dal formation at kulhus is here dated as late callovian, peltoceras athleta chronozone, based on the presence of relatively abundant limbicysta bjaerkei, mendicodinium groenlandicum, rhychoniopsis cladophora and tubotuberella dangeardii in an otherwise poor upper callovian dinoflagellate assemblage. ammonites have not been recorded from these strata. the upper payer dal formation at agnetesøelven is dated as late oxfordian, amoeboceras glosense – amoeboceras serratum chronozones, based on the presence of sciniodinium crystallinum, together with cribroperidinium granuligera and stephanelytron sp. the age is in accordance with ammonites present in the uppermost part of the formation at søndre muslingebjerg. new ammonites in the bernbjerg formation at agnetesøelven together with dinoflagellate cysts indicate an earliest kimmeridgian age, rasenia cymodoce and aulacostephanoides mutabilis chronozones. the upper callovian dinoflagellate cysts from hochstetter forland belong to a local brackish to marginal marine assemblage, which only allows a fairly broad correlation to coeval assemblages in central east greenland. in contrast, the oxfordian and kimmeridgian assemblages are fully marine and can be correlated from milne land in central east greenland via hochstetter forland to peary land in eastern north greenland. keywords: ammonites, boreal, dinoflagellate cysts, hochstetter forland, jurassic, north-east greenland geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: sp@geus.dk the northernmost onshore jurassic outcrops in east greenland occur in hochstetter forland and, some 60– 80 km farther north, on store koldeway (fig. 1); the stratigraphy of the latter area is described in an accompanying paper (piasecki et al. 2004a, this volume). the hochstetter forland peninsula is dominated by flat lowlands dissected by small streams; outcrops of pre-quaternary sediments are restricted to stream cuts and low coastal cliffs scattered throughout the region (fig. 1). however, at søndre muslingebjerg to the south, caledonian basement and middle–upper jurassic sandstones and coals are faulted and reach up to approximately 400 m above sea level. caledonian basement and jurassic sediments also crop out in northern hochstetter forland, east of agnetesø, and the meanders of agnetesøelven (the river from agnetesø to the coast) erode into marine jurassic sediments deposited on basement rocks (fig. 1). the jurassic stratigraphy of the hochstetter forland area is based on records of marine faunas including ammonites from several isolated exposures (ravn 1911; surlyk 1978). the lowermost deposits consist of the non-marine to marginal marine muslingebjerg formation, which is undated owing to the absence of marine fossils. the overlying sands of the payer dal formation contain upper oxfordian ammonites in the upper geus bulletin no 5.pmd 29-10-2004, 11:1489 90 part, and are followed by mudstones of the bernbjerg formation that yield upper oxfordian – lower kimmeridgian ammonites (surlyk 1978). the outcrops at kulhus and agnetesøelven expose the main part of the jurassic succession in hochstetter forland. these localities were visited during fieldwork in 1987 in order to collect material for palynological analysis with the aim of refining the stratigraphy. the present paper describes for the first time the dinoflagellate cyst floras from these northern outcrops close to the transition to the boreal dinoflagellate cyst province, for example in peary land (håkansson et al. 1981) and on svalbard (århus 1988). material at kulhus (fig. 1; locality 1), on the south coast of hochstetter forland west of søndre muslingebjerg, sand and coal seams were sampled during a ground stop on helicopter reconnaissance in 1987. only one sample (ggu 351570) contains dinoflagellate cysts. two closely situated localities at agnetesøelven were spotted from the air and visited during a short ground stop. the westernmost sandstone outcrop (locality 2) was measured and two fine-grained samples with at least some potential for palynology were collected from two horizons (fig. 2). eastwards and down-river, the sandstone-dominated succession was seen to be faulted against a succession of laminated mudstones (locality 3), and this was closely sampled for palynology (fig. 3). only a few, well-preserved dinoflagellate cysts were recovered from the sand succession at locality 2. by 20ºw 20 km 76º30'n undifferentiated, mostly glacial deposits cretaceous locality fault caledonian crystalline basement søndre muslingebjerg kulhus nanok n hochstetter forland 1: milne land 2: jameson land 3: wollaston forland 4: hochstetter forland 5: store koldewey 6: germania land jurassic 7: peary land greenland 500 km agnetesø 2 3 7 1 2 3 4 56 1 1 agnetesøelven fig. 1. simplified sketch map of hochstetter forland illustrating the jurassic outcrops and the sampled localities. the map is modified from surlyk (1978, fig. 1). geus bulletin no 5.pmd 29-10-2004, 11:1490 91 contrast dinoflagellate cysts are abundant but poorly preserved in the mudstones at locality 3. ammonites are abundant in the lower, pyritic, part of the mudstone succession and in loose concretionary beds at the base of the cliff. these ammonites provide independent stratigraphical control of the dinoflagellate cyst assemblages. all of the samples from the three localities on hochstetter forland were prepared by traditional palynological methods and analysed for their content of dinoflagellate cysts. geology the jurassic succession on hochstetter forland is divided into the muslingebjerg, payer dal and bernbjerg formations of the vardekløft group. the marine sandstones of the payer dal formation were previously included in the pelion member of the vardekløft formation (sensu surlyk 1978); the pelion member is now raised to formation status (surlyk 2003, fig. 5). kulhus (locality 1) the low coastal cliff at kulhus, south-west hochstetter forland (fig. 1, locality 1), comprises 3–4 main coal belemnite bivalve oyster pecten spp. planolites ispp. wood bioturbation fine-grained sand planar lamination/bedding ggu sample fossils, etc. planar cross-lamination lenticular lamination trough cross-bedding scour and fill shell bed structures lithology hard bed mud sand 0 5 15 25 30 35 10 20 m 351538 351537 351537 mud pyrite ammonite fig. 2. sedimentological log of the upper payer dal formation at agnetesøelven (locality 2) showing the positions of analysed samples. geus bulletin no 5.pmd 29-10-2004, 11:1491 92 seams interbedded with black carbonaceous shales and light-coloured sandstones of the muslingebjerg formation (clemmensen & surlyk 1976). no marine fossils have been recorded from the formation but the high sulphur content of the coals and shales suggests a marine depositional environment (petersen et al. 1998). the jurassic succession at kulhus extends up the western flank of søndre muslingebjerg where the stratigraphically highest strata contain upper oxfordian ammonites referable to the amoeboceras glosense and/ or a. serratum zones (ravn 1911; sykes & surlyk 1976). coals and shales of the muslingebjerg formation have been prepared palynologically without finding any microscopic marine fossils. at kulhus, the first dinoflagellate cysts appear in the basal mudstone bed of the overlying payer dal formation, immediately above the highest coal seam, at the same level as the earliest marine faunas. restricted assemblages of sporomorphs from the underlying coals indicate an overall jurassic age. agnetesøelven (localities 2 and 3) fine-grained sandstone, with abundant marine fossils, is exposed at locality 2 and referred to the payer dal formation (figs 1, 2). shell beds of pecten spp., oysters, other bivalves and serpulids occur throughout the succession and are commonly concentrated in scour fills. belemnites are present, but no ammonites were recovered during the short visit. woody material and small logs are also common. the sandstone is intensely bioturbated and many sedimentary structures are obliterated although cross-bedding or lamination is recognisable in most beds. planolites ispp. is common at certain horizons. the shale succession exposed at locality 3 is referred to the bernbjerg formation. it consists of laminated, dark mudstones alternating with lenticular-bedded, fine-grained, grey sandstones (fig. 3). ammonites and bivalves are abundant in a concretionary bed low in the section and belemnites and bivalves occur scattered higher in the succession. the concretionary beds are washed out from the lowermost succession and lie at the foot of the cliff. they contain accretions of ammonites in several stacked laminae together with abundant buchia sp. abundant male and female individuals occur together in the ammonite assemblages (j.h. 351546 351547 351548 351545 351544 351543 351542 351541 351540 351539 mud sand 0 5 10 15 20 25 m fig. 3. sedimentological log of the bernbjerg formation at agnetesøelven (locality 3) showing the positions of analysed samples. for legend, see fig. 2. geus bulletin no 5.pmd 29-10-2004, 11:1492 93 callomon, personal communication 1999). the assemblage is equivalent to ammonite fauna 15 from milne land in the lower rasenia cymodoce zone, lower kimmeridgian (fig. 4; birkelund & callomon 1985; j.h. callomon, personal communication 1999). lower kimmeridgian ammonites have been reported previously from sandstones at the locality of nanok in southern hochstetter forland (frebold 1932). ammonites of the lowermost kimmeridgian rasenia cymodoce and aulacostephanoides mutabilis zones, have been collected from mudstones of the bernbjerg formation in hochstetter forland (frebold 1932; surlyk 1978). stratigraphy basal payer dal formation (locality 1) dinoflagellate cysts. an unusual and relatively poor assemblage of dinoflagellate cysts was recorded immediately above the lithological transition from the barren muslingeelv formation to the fossiliferous payer dal formation (fig. 5). limbicysta bjaerkei, pilosidinium fensomei and pareodinia halosa dominate the assemblage, in association with gonyaulacysta jurassica, nannoceratopsis sp., occisucysta sp., pareodinia sp., solisphaeridium sp., tubotuberella cf. dangeardii and tubotuberella cf. egemenii. single specimens of atopodinium haromense, mendicodinium groenlandicum and rhynchodiniopsis cladophora were recorded. age. stratigraphically diagnostic species are few in this assemblage. in east greenland, limbicysta bjaerkei has not been recorded stratigraphically higher than the basal boreal middle jurassic in the cranocephalites borealis chronozone in jameson land (milner & piasecki 1996). however, a stratigraphical range of middle callovian and possibly into lowermost upper callovian has been reported from both the subboreal and arctic regions (smelror 1987, 1993). in jameson land, m. groenlandicum appears no lower than the kosmoceras jason chronozone (mid-callovian) and distinct rhynchodiniopsis cladophora and tubotuberella dangeardii appear in the basal upper callovian in the peltoceras athleta chronozone (milner & piasecki 1996). in conclusion, the sparse data indicate an age equivalent to the earliest late callovian, p. athleta chronozone (fig. 4). an early callovian age previously indicated for this unit (petersen et al. 1998) was based on a sample that was subsequently found to be from another section and locality. depositional environment. the dinoflagellate cyst assemblage is dominated by three species (fig. 5). limbicysta bjaerkei is possibly an acritarch because no clear archaeopyle has been documented. the assemblage differs markedly from normal marine assemblages described from time equivalent strata in milne land (piasecki 1996). bailey & hogg (1995) reported abundant l. bjaerkei in otherwise non-marine assemblages. this may indicate that the associated, frequent species, pilosidinium fensomei and pareodinia halosa, may have had similar environmental preferences. the abundance of l. bjaerkei – together with the restricted lithostratigraphy biostratigraphy formation ammonite zone age based on dinoflagellate cysts chronozones bernbjerg a. mutabilis r. cymodoce a. mutabilis r. cymodoce early kimmeridgian payer dal a. glosense – a. serratum a. glosense – a. serratumlate oxfordian late callovian p. athleta muslingebjerg no marine fossils (callovian?) pre-p. athleta chronostratigraphy fig. 4. summary of the jurassic stratigraphy of hochstetter forland. geus bulletin no 5.pmd 29-10-2004, 11:1493 94 assemblage – is taken as evidence for estuarine, brackish depositional environments during the initial transgression of hochstetter forland. upper payer dal formation (locality 2) dinoflagellate cysts. dinoflagellate cysts are relatively sparse in these sediments. however, the diversity is moderately good and the preservation is fine. ambonosphaera calloviense is the only dinoflagellate species represented by more than one or two specimens in the assemblage (fig. 5). ambonosphaera calloviense, sirmiodinium grossii and sentusidinium sp. are the only species common to both samples. age. despite the paucity of dinoflagellate cysts, the co-occurrence of sciniodinium crystallinum, cribroperidinium granuligera and stephanelytron sp. indicates a late oxfordian age i.e. amoeboceras glosense to amoeboceras serratum chronozones, by comparison to hold with hope and milne land further to the south (piasecki 1996; piasecki et al. 2004a, b, this volume; figs 1, 4). none of the other dinoflagellate cysts are inconsistent with this age, which is also in accordance with the age indicated by ammonites from the uppermost payer dal formation at søndre muslingebjerg (ravn 1911; sykes & surlyk 1976). however, the dinoflagellate cyst assemblage is too restricted to allow a more precise correlation. depositional environment. the low abundance combined with the moderate diversity of dinoflagellate cysts indicates near-shore marine deposition in a high-energy environment. the sandy sediments with a rich benthic fauna, partly in situ and partly reworked into shell beds, support this interpretation. bernbjerg formation (locality 3) dinoflagellate cysts. dinoflagellate cysts are abundant and relatively diverse, but their preservation is poor. the composition of the assemblages varies significantly through the relatively short section (fig. 5). extremely abundant sirmiodinium grossii characterises the lower part of the section and is gradually replaced by abundant gonyaulacysta jurassica sensu lato in the upper part. five other species appear in succession with distinct and characteristic maxima through the succession (fig. 5). abundant nummus sp. occurs together with the maximum numbers of escharisphaeridium pocockii in the lower part of the succession. this is followed closely by a maximum abundance of cribroperidinium granuligera, then by a maximum of perisseiasphaeridium pannosum (together with gonyaulacysta jurassica sensu lato) and finally by maximum abundance of occisucysta cf. monoheuriskos in the uppermost sample. a comparable succession of dinoflagellate cyst assemblages has been recorded across the boundary of the payer dal and bernbjerg formations at kløft ii on store koldewey (piasecki et al. 2004a, this volume). at this locality, a maximum of g. jurassica sensu lato is followed by abundant p. pannosum and occisucysta cf. monoheuriskos, similar to that recorded from the upper part of the section at agnetesøelven (locality 3). assemblages dominated by nummus sp., e. pocockii and c. granuligera were not recorded at store koldewey, but these species are present. in contrast, the stratigraphically significant paragonyaulacysta capillosa is abundant at store koldewey, whereas it is rare in the succession at agnetesøelven. age. the succession cannot be older than early kimmeridgian based on the ammonite fauna in the basal strata, which is indicative of the lower rasenia cymodoce zone. this is in accordance with the dinoflagellate cyst assemblage of abundant sirmiodinium grossii and frequent gonyaulacysta jurassica, adnatosphaeridium sp. and paragonyaulacysta capillosa. to the south, on milne land, p. capillosa first appears in the r. cymodoce chronozone and is followed by perisseiasphaeridium pannosum in the succeeding aulacostephanoides mutabilis chronozone (piasecki 1996). at agnetesøelven, the appearance of p. pannosum higher in the succession accordingly indicates an age equivalent to the a. mutabilis chronozone for this part of the succession (fig. 4). dinoflagellate cysts indicative of younger jurassic strata were not recorded. lower kimmeridgian ammonites have previously been recorded from the bernbjerg formation on hochstetter forland. an ammonite fauna referable to the a. mutabilis zone has been recovered from the nanok and agnetesøelven regions (frebold 1932; surlyk 1978). depositional environment. the dinoflagellate cysts are strongly degraded. they are physically broken, and angular imprints of crystals and deep circular imprints of spherical pyrite framboids obscure the sculpture and structure of their walls. together with the undisturbed lamination of the sediments, this indicates deposition geus bulletin no 5.pmd 29-10-2004, 11:1494 95 50250 66.00 61.00 56.00 53.00 50.00 47.00 45.00 40.00 25.00 20.00 1.00 351548 351547 351545 351544 351543 351542 351541 351539 351538 351537 351570 jurassic oxfordian–kimmeridgiancallovian bernbjergpayer dal 1 veryhachium spp. 2 tubotuberella dangeardii 3 atopodinium haromense 4 sentusidinium rioultii 5 mendicodinium groenlandicum 6 dissiliodinium spp. 7 botryococcus spp. 8 limbicysta bjaerkei 9 pilosidinium fensomei 10 solisphaeridium spp. 11 tubotuberella cf. egemenii 12 occisucysta spp. 13 nannoceratopsis spp. 14 pareodinia cf. stegasta 15 valensiella spp. 16 rhynchodiniopsis cladophora 17 pareodinia spp. 18 gonyaulacysta jurassica 19 pareodinia halosa 20 stephanelytron spp. 21 tenua spp. 22 ambonosphaera calloviense 23 sentusidinium spp. 24 sirmiodinium grossii 25 scriniodinium crystallinium 26 cribroperidinium granuligera 27 pareodinia cf. pachyceras 28 scriniodinium spp. 29 tubotuberella apatela 30 avellodinium cf. falsificum 31 rhynchodiniopsis cf. cladophora 32 scriniodinium cf. crystallinium 33 leptodinium spp. 34 leptodinium subtile 35 cribroperidinium sp. 36 paragonyaulacysta cf. capillosa 37 escharisphaeridia pocockii 38 nummus spp. 39 atopodinium spp. 40 occisucysta cf. monoheuriskos 41 adnatosphaeridium spp. 42 pareodinia stegasta 43 epiplosphaera spp. 44 sentusidinium pelionense 45 barbatacysta spp. 46 perisseiasphaeridium pannosum 47 paragonyaulacysta capillosa 48 paragonyaulacysta spp. 49 prolixosphaeridium granulosum 50 tubotuberella rhombiformis a lph a b et ic a l spec ies list 41 a dnatosphaeridium spp. 22 a m bonosphaera calloviense 3 a topodinium harom ense 39 a topodinium spp. 30 avellodinium cf. falsificum 45 barbatacysta spp. 7 botryococcus spp. 19 pareodinia halosa 26 c ribroperidinium granuligera 35 c ribroperidinium sp. 6 d issiliodinium spp. 43 epiplosphaera spp. 37 escharisphaeridia pocockii 18 g onyaulacysta jurassica 33 leptodinium spp. 34 leptodinium subtile 5 m endicodinium groenlandicum 13 n annoceratopsis spp. 38 n um m us spp. 12 o ccisucysta spp. 40 o ccisucysta cf. m onoheuriskos 48 paragonyaulacysta spp. 47 paragonyaulacysta capillosa 36 paragonyaulacysta cf. capillosa 27 pareodinia cf. pachyceras 14 pareodinia cf. stegasta 17 pareodinia spp. 42 pareodinia stegasta 8 lim bicysta bjaerkei 46 perisseiasphaeridium pannosum 9 pilosidinium fensom ei 49 prolixosphaeridium granulosum 31 r hynchodiniopsis cf. cladophora 16 r hynchodiniopsis cladophora 32 scriniodinium cf. crystallinium 25 scriniodinium crystallinium 28 scriniodinium spp. 44 sentusidinium pelionense 4 sentusidinium rioultii 23 sentusidinium spp. 24 sirm iodinium grossii 10 solisphaeridium spp. 20 stephanelytron spp. 21 tenua spp. 29 tubotuberella apatela 11 tubotuberella cf. egem enii 2 tubotuberella dangeardii 50 tubotuberella rhom biform is 15 valensiella spp. 1 veryhachium spp. sample height metre ggu sample no. system stage formation h o chstetter fo rland k ulhus and a gnetesø elven > 50 specim ens 20 – 50 specim ens 5–19 specim ens 1– 4 specim ens fig. 5. stratigraphical distribution chart of dinoflagellate cysts in samples from all three localities. the sample heights indicated are largely arbitrary, although the three localities are arranged in stratigraphic order. sample at 1 m is from locality 1, samples at 20 m and 25 m are from locality 2 (arbitrary spacing, see fig. 2 for correct locations) and samples at 40–66 m are from locality 3 (spacings approximately to scale, see fig. 3 for precise locations). the recorded species are arranged by their first stratigraphical appearance. geus bulletin no 5.pmd 29-10-2004, 11:1495 96 below wave base in a low-oxygenated environment. lenticular laminae with small-scale ripples, however, show that the bottom water was not completely stagnant and that the sea floor was periodically swept by weak bottom currents. correlation studies of the jurassic ammonite and dinoflagellate cyst stratigraphy in east greenland, combined with sedimentological studies and sequence stratigraphical interpretations, contribute towards an integrated model in which units can be identified by their content of dinoflagellate cysts. the present study of the dinoflagellate cyst assemblages on hochstetter forland contributes basic data to this complex study. the assemblage dominated by limbicysta bjaerkei in the basal payer dal formation at kulhus has not been recorded anywhere else in east greenland. this assemblage comprises the first marine fossils to have been deposited above the coal-bearing floodplain environment of the muslingebjerg formation. the dinoflagellate cyst assemblage records deposition in a marginal marine to brackish environment. the overlying sandstones are interpreted as tidal facies followed by shoreface facies (petersen et al. 1998), reflecting a rise in relative sea level. this assemblage thus characterises marginal marine environments at the feather-edge of the jurassic depositional basin during a major drowning event (alsgaard et al. 2003). the poor dinoflagellate cyst assemblage in the upper payer dal formation is not representative of this stratigraphic interval, compared to the assemblages recorded from other localities in east greenland. however, it is associated with a stratigraphic unit equivalent to the a. glosense and a. serratum chronozones that previously has been identified throughout east greenland, i.e. in milne land, jameson land and hold with hope (engkilde 1994; piasecki 1996; vosgerau et al. 2004, this volume). the dinoflagellate cyst assemblage from the bernbjerg formation at agnetesøelven is known from milne land in the south to store koldewey in the north, and a similar assemblage occurs in the ladegårdsåen formation in peary land, north greenland (fig. 1; piasecki 1966; piasecki et al. 2004a, this volume). the dinoflagellate cyst assemblage correlates with the r. cymodoce and a. mutabilis chronozones. it is associated with a major kimmeridgian flooding event which allowed more permanent shelf anoxia to spread to shallow shelf areas of east greenland (milne land, wollaston forland, hold with hope, store koldewey) and north greenland (peary land). maximum flooding occurred in the a. mutabilis to a. eudoxus chrons. conclusions new ammonite data confirm and refine earlier age determinations of the jurassic succession on hochstetter forland. the age of the upper payer dal formation in hochstetter forland is confirmed as late oxfordian, and the age of the bernbjerg formation is confirmed as earliest kimmeridgian. the dinoflagellate cyst stratigraphy from the three localities is fragmentary. the assemblage from the lower payer dal formation at kulhus has not been reported from any other section in east greenland; it is important because it represents marginal marine conditions associated with a major flooding event of earliest late callovian age, p. athleta chronozone (fig. 4). this limits the age of the muslingeelv formation upwards. the assemblage in the upper payer dal formation is restricted, but supports the previously recorded late oxfordian age, corresponding to the a. glosense and/ or a. serratum chronozones. the third assemblage is well known from east greenland and dates the bernbjerg formation at agnetesøelven to the earliest kimmeridgian, r. cymodoce and a. mutabilis chronozones (fig. 4). this assemblage is associated with a major transgressive event characterised by extensive shelf anoxia in east greenland. acknowledgements the work was initiated as part of the project ‘resources of the sedimentary basins of north and east greenland’ supported by the danish research councils and completed by support from the carlsberg foundation ans. 980089/0-262. john h. callomon is thanked for the identification of the ammonites. the referees, d.j. batten and 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(eds): the jurassic of north-east greenland. geological survey of denmark and greenland bulletin 5, 73–88 (this volume). ravn, j.p.j. 1911: on jurassic and cretaceous fossils from northeast greenland. meddelelser om grønland 45(10), 437–500. smelror, m. 1987: bathonian and callovian (middle jurassic) dinoflagellate cysts and acritarchs from franz josef land, arctic soviet. polar research 5, 221–238. smelror, m. 1993: biogeography of bathonian to oxfordian (jurassic) dinoflagellates: arctic, nw europe and circum-mediterranean regions. palaeogeography, palaeoclimatology, palaeoecology 102, 121–160. surlyk, f. 1978: mesozoic geology and palaeogeography of hochstetter forland, east greenland. bulletin of the geological society of denmark 27, 73–87. surlyk, f. 2003: the jurassic of east greenland: a sedimentary record of thermal subsidence, onset and culmination of rifting. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 659–722. sykes, r.m. & surlyk, f. 1976: a revised ammonite zonation of the boreal oxfordian and its application in north-east greenland. lethaia 9, 421–436. vosgerau, h., larsen, m., piasecki, s. & therkelsen, j. 2004: a new middle–upper jurassic succession on hold with hope, north-east greenland. in: stemmerik, l. & stouge, s. (eds): the jurassic of north-east greenland. geological survey of denmark and greenland bulletin 5, 51–71 (this volume). geus bulletin no 5.pmd 29-10-2004, 11:1497 geological survey of denmark and greenland bulletin 6, 19-29 19 the fluviatile bristol elv formation, a new middle jurassic lithostratigraphic unit from traill ø, north-east greenland jens therkelsen and finn surlyk a new lithostratigraphic unit, the bristol elv formation, is erected in this paper. it is only known from traill ø, east greenland, where it unconformably overlies triassic redbeds of the fleming fjord formation and is overlain by lithologically similar shallow marine upper bajocian sandstones of the pelion formation. the age of the formation is not well constrained but is probably early bajocian. the bristol elv formation is at least 155 m thick and consists of conglomerates, coarse-grained pebbly sandstones and subordinate mudstones, deposited in braided rivers. a finer-grained lacustrine/floodplain unit, c. 37 m thick, is interbedded with the fluvial sandstones at one locality. deposition of the fluvio-lacustrine bristol elv formation marks a major change in basin configuration and drainage patterns, reflecting the onset of the important, protracted middle–late jurassic rift event in east greenland. keywords: fluvial, lacustrine, middle jurassic sediments, new formation, north-east greenland j.t., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. present address: skude & jacobsen, næstvedvej 1, dk-4760 vordingborg, denmark. e-mail: jth@sjas.dk f.s., geological institute, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. geological survey of denmark and greenland bulletin 5, 19–29 © geus, 2004 the first detailed description of the jurassic sandstones on the islands of traill ø and geographical society ø (fig. 1) was presented by donovan (1953, 1955, 1957) who grouped the deposits in the yellow series of maync (1947). donovan’s work was focused on the sediments exposed in the bjørnedal area in south-eastern traill ø while the sandstones exposed at mols bjerge and svinhufvud bjerge received less attention. donovan (1953, p. 64) suggested that black shales interbedded with sandstones and occasional conglomerates, which he termed the plant beds, were deposited in a marine embayment, or possibly on the subaerial part of a debris fan. higher in the sandstone unit, he found evidence for periodic marine incursions as indicated by occasional ammonite-bearing levels. a lithostratigraphic scheme covering the jurassic of jameson land in east greenland was erected by surlyk et al. (1973) and was extended to the areas north of kong oscar fjord by surlyk (1977). the middle jurassic sandstones of traill ø and geographical society ø were placed in the pelion member of the vardekløft formation. this scheme has recently been revised in the light of much new work in the region resulting in rank changes and establishment of new formations and members (see surlyk 2003, fig. 5). fieldwork in the traill ø area has revealed that sandstones formerly referred exclusively to the shallow marine pelion formation (pelion member in: surlyk 1977) actually consist of a lower fluvial unit overlain by marine sandstones (price & whitham 1997; stemmerik et al. 1997). the fluviatile deposits are placed in a new lithostratigraphic unit, the bristol elv formation, which is erected here as the basal unit of the middle jurassic vardekløft group on traill ø (fig. 2). the new formation consists dominantly of conglomerates, coarse-grained pebbly sandstones and subordinate mudstones and was deposited in a braided river environment, probably in middle jurassic, early bajogeus bulletin no 5.pmd 29-10-2004, 11:1419 20 72 ■ ■ ■ ■ ■ ■ geographical society ø traill ø 24ºw 23ºw 22ºw 73º00'n 72º45'n 72º30'n 72º15'n 72 00′ n svinhufvud bjerge 10 km mols bjerge vælddal jameson land ■ ■ ■ ■ ■ ■ månedal ■ ★ ★ ★ ★ kong oscar fjord n=16 n=22 n=31 n=23 2 1 4 3 ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ g re en la nd localities faults palaeocurrent direction (n=22: number of measurements) distribution of the bristol elv formation ★1 ■ cian time. in one section, fine-grained sandstones, mudstones, mediumto coarse-grained sandstone beds and thin coal seams occur intercalated with the fluvial sandstones, and are interpreted as lacustrine or floodplain deposits. bristol elv formation new formation history. the strata assigned here to the new bristol elv formation were included in the yellow series (maync 1947) by donovan (1953) and were referred to the pelion member of the vardekløft formation by surlyk (1977). the fluvial nature of the lower part of the succession was recognised independently by price & whitham (1997) and stemmerik et al. (1997), and labelled pm1 by the former authors. fig. 1. map showing the distribution of the bristol elv formation in the traill ø area, the position of localities and palaeocurrent directions. the map is modified from stemmerik et al. (1997). geus bulletin no 5.pmd 29-10-2004, 11:1420 21 name. after the river bristol elv in the southern part of mols bjerge, traill ø (fig. 1). type section. southern part of svinhufvud bjerge (fig. 1, locality 1) on the south coast of traill ø (figs 1, 3). reference sections. north-eastern svinhufvud bjerge (fig. 1, locality 2), northern and southern mols bjerge (locations 3, 4) and vælddal, all on traill ø (figs 1, 4). thickness. the formation is at least 155 m thick in the southern part of svinhufvud bjerge, whereas thicknesses in excess of 80 m are recorded in northern mols bjerge and at bristol elv in the southern part of mols bjerge. thicknesses of 280 m and 520 m in the southern and northern svinhufvud bjerge areas, respectively, and 310 m in northern mols bjerge were stated by price & whitham (1997), but these large values have not been corroborated by our study (surlyk & noenygaard 2001). lithology. the bristol elv formation consists mainly of conglomerates, pebbly sandstones and sandstones in the mols bjerge area, whereas more fine-grained deposits are intercalated in the svinhufvud bjerge area. the bulk of the formation consists of yellowish to whitish, poorly sorted, coarse-grained sandstones, pebbly sandstones and fine pebble conglomerates with subrounded to well-rounded quartzite pebbles and mudstone intraclasts. black to dark grey mudstones with centimetre-thick autochthonous coal beds occur intercalated with the sandstones and conglomerates at several levels. the coarse-grained deposits show largescale trough cross-bedding, but the structures are mostly poorly defined. the cross-bedded sets are 0.15–2.0 m thick, and form cosets up to 7 m thick. also observed are large-scale scour-and-fill structures (fig. 5), planar cross-bedding, planar lamination, rare water escape structures and imprints of tree trunks, which may be found in accumulations. the sediments commonly form fining-upwards units, up to 16 m thick. on the south coast of traill ø, a sandstone unit, c. 19 m thick, shows evidence of gently dipping bedforms (fig. 6, corresponding to the 134–153 m interval in fig. 3). at svinhufvud bjerge, the coarse-grained units are separated by mudstone units up to 6 m thick, while the coarsegrained units at mols bjerge are amalgamated without any fine-grained interbeds. the mudstones in the svinhufvud bjerge area are very uniform in grain size and overlie the sandstones with a sharp boundary. they show a well-developed to faint lamination, which is commonly disturbed by rooting. a few centimetre-thick layers of mediumgrained sandstone occur in the upper part of the mudstone units at the same level as the rootlets. the orientation of cross-bed trough axes and foreset azimuths of planar cross-beds in the sandstones at mols bjerge generally indicates westerly palaeocurrent directions, whereas the directions in the svinhufvud bjerge area are generally towards the south-east. stylolites are common in the coarse-grained sandstones and fine-grained conglomerates at mols bjerge but have not been observed at svinhufvud bjerge. a succession of mainly black to dark grey mudstones and fine-grained sandstones, c. 37 m thick, with intercalated coal beds and coarse-grained sandstones occurs in the type section at svinhufvud bjerge (fig. 3, 170–207 m in log). the sandstones are trough crossbedded, structureless, cross-laminated or lenticular fleming fjordscoresby land bristol elv pelion hiatus fossilbjerget vardekløft parnas mb olympen bernbjerg formation hall bredning kimmeridgian oxfordian callovian bathonianm id dl e u pp er ju ra ss ic tr ia ss ic bajocian groupstagesystem u u m l m l u u m l l fig. 2. lithostratigraphic scheme of the jurassic succession in the traill ø area. the age of the bristol elv formation is poorly constrained, but an early bajocian age is the most likely. based on clemmensen (1980) and d. strogen (personal communication 2000); see also surlyk (2003). geus bulletin no 5.pmd 29-10-2004, 11:1421 22 30 20 10 0 320 310 300 290 280 270 260 250 240 220 210 200 190 180 170 160 150 140 130 120 110 mud sand pebble c. 19 m poorly exposed c. 40 m poorly exposed c. 30 m basaltic sill m b ri st o l el v f o rm at io n ? tr ia ss ic pe lio n f o rm at io n fl em in g fj o rd f o rm at io n mud sand pebble m mudstone sandstone pebbly sandstone conglomerate coal lithology palaeocurrent direction degree of bioturbation belemnite rootlets stems/logs plant fragments stylolites coalified logs diplocraterion habichi ophiomorpha nodosa coarsening-upwards fining-upwards sub-vertical burrows structureless sand structureless conglomerate parallel lamination wavy bedding cross-lamination structures tabular cross-bedding trough cross-bedding lenticular bedding concretion mudstone clasts slump hummocky and swaley cross-stratification geus bulletin no 5.pmd 29-10-2004, 11:1422 23 facing page: fig. 3. type section (locality 1) of the bristol elv formation. south svinhufvud bjerge, traill ø. position shown in fig. 1. bedded, and display both sheet-like and lenticular geometries. some of the sandstones show poorly developed wavy surfaces, are weakly bioturbated and contain rare mudstone flasers. the mudstones are mainly laminated or weakly laminated and contain conspicuous root horizons, in situ tree stumps, fern leaves and early diagenetic sideritic concretions. sandstone beds up to 10 cm thick with wave ripple crossstratification, similar to micro-hummocky cross-stratification, occur in the mudstones. the ripples have wavelengths up to 30 cm and heights up to 5 cm. immediately above one of these sandstone beds, rounded pebbles up to 4 cm in diameter are present. a sandstone bed, c. 1 m thick, showing swaley cross-stratification occurs intercalated in the mudstones (fig. 3, 172–173 m in log, fig. 7b). the wave-rippled and swaley cross-stratified beds form part of two small coarsening-upwards units, 7 m and 5 m thick, in the lowest part of the succession (fig. 3, 170–182 m in log, fig. 7a). the lower part of the units consists of laminated and faintly laminated mudstones, which in the lowest unit are intercalated with wave-rippled and swaley cross-stratified sandstone beds. the units grade upwards into very fine-grained sandstones, showing poorly developed wavy surfaces, cross-lamination, lenticular bedding and rare mudstone flasers. unidentified trace fossils occur in both units and the top beds in the upper coarsening-upwards unit are penetrated by rootlets. above these two units, coal beds up to 0.45 m thick and thin mudstone beds occur together with 0.2–2.5 m thick beds of trough cross-bedded, medium-grained sandstone to fine pebble conglomerate with sharp basal surfaces, showing palaeocurrents towards the east-south-east (fig. 3, 182– 207 m in log). locally, these beds are overlain by fineto very fine-grained sandstones, forming poorly defined fining-upwards successions. pyrite is not present in the coals, but occasionally replaces organic detritus in the sandstones. the coals consist almost entirely of non-detrital vitrinite, which together with the presence of root horizons beneath the coal beds show that they are autochthonous. boundaries. the formation unconformably overlies the upper triassic fleming fjord formation at svinhufvud bjerge and mols bjerge as well as in vælddal (clemmensen 1980; d. strogen, personal communication 2000). the upper boundary is placed at an erosional surface draped by a pebble lag overlain by marine sandstones of the pelion formation, which is dominated by mediumto coarse-grained, planar cross-bedded and structureless sandstones with ammonites, belemnites, bivalves and marine trace fossils. distribution. the formation is known only from svinhufvud bjerge, mols bjerge and vælddal in eastern traill ø (fig. 1). the lacustrine/backswamp unit described from the type section is probably correlative to the plant beds of donovan (1953, 1957), which occur in vælddal (henrik vosgerau, personal communication 1998). geological age. no macrofaunas were found within the bristol elv formation. a few relatively well preserved but as yet unidentified fern leaves were retrieved from a single bed in the lacustrine/floodplain unit in the southern part of svinhufvud bjerge. harris (1946) reported a stem identified as equisetites sp. a. of inferred early jurassic age from kap palander in the northernmost mols bjerge. harris (1946) pointed out, however, that this specimen also resembles species of late triassic or middle jurassic ages, and that it does not give any precise age indication. preliminary palynological analysis of samples from the lacustrine/backswamp deposits suggests a broad late toarcian – bathonian age (karen dybkjær, personal communication 1998). age diagnostic palynomorphs include callialasporites dampieri (late early toarcian or younger), callialasporites turbatus (late toarcian or younger), callialasporites segmentatus (late early toarcian or younger) and foraminisporis jurassicus (middle rhaetian – bajocian) (batten & koppelhus 1996). the upper bajocian cranocephalites borealis zone is represented in the immediately overlying pelion formation sandstones (donovan 1953, 1957; callomon 1993; alsen 1998). this is the lowest middle jurassic ammonite zone recognised in east greenland. in jameson land, the pelion formation contains a relatively thick marine sandstone unit without ammonites below the lowest occurrence of cranocephalites borealis. this unit overlies dark mudstones of the sortehat formation the top of which is of early bajocian age (underhill & partington 1993; koppelhus & hansen 2003). the unit is thought to be a distal marine correlative of the bristol elv formation. this is supported by the stratigraphic position of both units, underlying marine pelion sandstones of the c. borealis chronozone geus bulletin no 5.pmd 29-10-2004, 11:1423 24 0 10 20 30 40 50 60 70 m pebbl.sand pebbl.sandpebbl.sand 0 10 20 30 40 50 60 70 m locality 2 north-eastern svinhufvud bjerge locality 3 northern mols bjerge locality 4 southern mols bjerge 30ð40 m 0 5 10 15 20 25 m geus bulletin no 5.pmd 29-10-2004, 11:1424 25 and by the marked lithological similarity of the pelion and bristol elv formations. lower jurassic rocks have never been documented outside jameson land and all available data thus point towards an early bajocian age for the bristol elv formation. depositional environment the coarse-grain size, the presence of fining-upwards units and trough cross-bedding, the unidirectional palaeocurrents towards the west (in mols bjerge) and south-east (in svinhufvud bjerge) and the abundance of mudstone intraclasts, the absence of dinoflagellate cysts and marine body and trace fossils indicate that the main part of the bristol elv formation was deposited in a high-energy fluvial environment. studied samples all show very low total sulphur (ts) contents (max. 0.43%) and high c/s values (> 10). these data support the interpretation of a terrestrial environment of deposition (berner & raiswell 1984). in the svinhufvud bjerge area, one sandstone unit, approximately 20 m thick, shows macroforms interpreted as downstream or lateral accretion structures such as epsilon cross-bedding (allen 1963; fig. 6). the lower c. 13 m of this unit displays a fining-upwards trend, possibly representing lateral channel migration (allen 1964, 1965). the depth of the channel corresponds to at least the thickness of the macroform (leeder 1973). if the interpretation of the macroforms is correct, the channel depths were in the 10–13 m range. fluvial styles and models were categorised in terms of channel sinuosity/braiding, sediment type and characteristic architectural elements by miall (1985, 1996). the depositional features of the bristol elv formation, especially concerning the within-channel element and the relatively large channel depths suggest deposition in the ‘perennial deep braided river’ type of miall (1996). reliable interpretation of a fluvial system cannot, however, be based on vertical sections alone (miall 1996). analysis of bounding surfaces, and extent, shape and facies relations of the architectural elements has, however, not been possible in the present case due to the nature of the outcrop. the interbedded mudstones may, due to the sharp boundary to the underlying coarse sandstones and conglomerates, represent relatively abrupt channel abandonment and subsequent passive in-filling of channels and thus cover a confined area, or they may be more extensive bodies covering the entire floodplain area. the studied exposures do not allow conclusions on the lateral extent of the mudstone units. the finegrained homogeneous nature of the mudstones, however, suggests that the distance to the nearest active fluvial channel must have been relatively large leading to deposition of only the finest grain sizes. the sudden change from very coarse sandstone to homogeneous mudstone also indicates a very abrupt abandonn s fig. 5. coarse-grained sandstone and fine-grained conglomerate with large-scale scour-and-fill structures (indicated by dashed lines below encircled person). bristol elv formation; north-eastern svinhufvud bjerge. facing page: fig. 4. composite detailed reference section from northeastern svinhufvud bjerge (locality 2) and reference sections from northern and southern mols bjerge (localities 3, 4). positions shown in fig. 1. for legend, see fig. 3. geus bulletin no 5.pmd 29-10-2004, 11:1425 26 ment of the active channels, which in a relatively short time shifted to a position farther away. floodplains in braided river systems are not commonly described in the literature, but studies by reinfelds & nanson (1993) of the waimakariri river, new zealand, show that braided rivers, contrary to the common conception, may include large areas of finegrained floodplains. during avulsion events, extensive wetland areas were established and contributed greatly to trapping and deposition of large volumes of finegrained material (e.g. smith et al. 1989). a similar situation may have occurred at least twice during the lifetime of the bristol elv formation river system, as shown by the occurrence of 3–6 m thick floodplain mudrocks in the section on the south coast of traill ø (figs 1, 6). the presence of root horizons and thin coal beds shows that the floodplain was densely vegetated and developed into peat swamps, before the river channel migrated back over the area and peat formation ceased. fine-grained sediment present in the middle part of the type section in svinhufvud bjerge is interpreted to have been deposited in a lacustrine/backswamp environment. fine-grained sandstones intercalated with black and dark grey mudstone in the lower part of this lacustrine/backswamp unit show swaley cross-stratification and wave ripple cross-lamination associated with a pebble lag (figs 3, 7). swaley cross-stratification is interpreted as the result of storm-wave deposition above fairweather wave base and has been described from very shallow depths in the large lake superior (greenwood & sherman 1986; sherman & greenwood 1989). the wave ripple cross-lamination shows that some vigorous agitation must have occurred, probably during storm events (e.g. allen 1982). the structures and the associated pebble lag are probably the result of shoreface erosion during storms, and subsequent transport into deeper waters by storm-induced currents (cf. dam & surlyk 1992, 1993). in the uppermost part of the lacustrine succession, the occurrence of a unit that shows coarsening-upwards from mudstone to very finew e 20 m fig. 6. fluvial, floodplain and lacustrine deposits on the south coast of traill ø (locality 1). note the 20 m thick sandstone body in the centre (see fig. 3, 134–153 m in log) showing down-stream or lateral accretion structures (dashed lines) with bedforms dipping gently to the right (east). the sandstone body overlies dark floodplain mudstones. type section of the bristol elv formation. geus bulletin no 5.pmd 29-10-2004, 11:1426 27 grained sandstone (fig. 3, 177–182 m) possibly records in-filling of the lake, resulting in lake shoreline progradation and gradual shallowing. the presence of rootlets shows that the lake was sufficiently shallow to allow colonisation of vegetation. higher in the succession (fig. 3, 182–207 m), abundant conspicuous root horizons show that vegetation spread across the shores of the lake, which eventually turned into a backswamp environment. the repeated development of autochthonous coal beds in the middle and upper part of the unit suggests that the backswamps were densely vegetated. the 0.2–2.5 m thick trough cross-bedded sandstone beds associated with the coal beds, probably represent splays into the backswamp from active channels, which were possibly situated north-west of the area. the lack of pyrite in the coal is a good indication of deposition in a freshwater environment (cohen et al. 1984; brown & cohen 1995; phillips & bustin 1996). the plant beds of donovan (1953, 1957) in vælddal are interbedded with coarse-grained sandstones and conglomerates dominated by large-scale trough crossbedding, while hummocky and/or swaley cross-stratification, small-scale cross-lamination, root horizons and fossilised leaves occur in the finer grained sediments (henrik vosgerau, personal communication 1998). if the plant beds of donovan (1953, 1957) are correlatives of the mudstone-dominated part of the bristol elv formation type section in svinhufvud bjerge, a system with a b fig. 7. lacustrine deposits from the bristol elv formation, south coast of traill ø (locality 1). length of knife is 21 cm. a: thin micro-hummocky cross-stratified / wave ripple cross-laminated sandstone intercalated with laminated mudstone. b: sandstone bed showing swaley crossstratification. geus bulletin no 5.pmd 29-10-2004, 11:1427 28 scattered lakes may have existed in the area. the lateral extent of this system must have been at least 20 km. gradual in-filling of the lake resulted in development of a wetland area with peat swamps, which was periodically covered by sheet-sands and cut by confined channels where sand was deposited. thin coarsening-upwards units, which probably represent crevasse splays or deltas, show that active fluvial channels were present in the adjacent area, and the lake system was eventually replaced by a fluvial braided channel system, represented by trough cross-bedded coarse-grained pebbly sandstones. this environment persisted until the area was transgressed by the sea and the shallow marine sandstones of the pelion formation were deposited. acknowledgements this study was undertaken under the auspices of the project ‘resources of the sedimentary basins of north and east greenland’, supported by the danish research council. we thank karen dybkjær and stefan piasecki for palynological contributions, jan andsbjerg, gregers dam, and jon r. ineson for critical reading of an early manuscript version and reviewers d. strogen and michael larsen for constructive reviews. references allen, j.r.l. 1963: the classification of cross-stratified units, with notes on their origin. sedimentology 2, 93–114. allen, j.r.l. 1964: studies in fluviatile sedimentation: six cyclothems from the lower old red sandstone, anglo-welsh basin. sedimentology 3, 163–198. allen, j.r.l. 1965: a review of the origin and characteristics of recent alluvial sediments. sedimentology 5, 89–191. allen, j.r.l. 1982: sedimentary structures; 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(eds): sequence stratigraphy and facies associations. international association of sedimentologists special publication 18, 419–448. donovan, d.t. 1953: the jurassic and cretaceous stratigraphy and palaeontology of traill ø, east greenland. meddelelser om grønland 111(4), 150 pp. donovan, d.t. 1955: the stratigraphy of the jurassic and cretaceous rocks of geographical society ø, east greenland. meddelelser om grønland 103(9), 60 pp. donovan, d.t. 1957: the jurassic and cretaceous systems in east greenland. meddelelser om grønland 155(4), 214 pp. greenwood, b. & sherman, d.j. 1986: hummocky cross-stratification in the surf zone: flow parameters and bedding genesis. sedimentology 33, 33–46. harris, t.m. 1946: liassic and rhaetic plants collected in 1936– 38 from east greenland. meddelelser om grønland 114(9), 39 pp. koppelhus, e.b. & hansen, c.f. 2003: palynostratigraphy and palaeoenvironment of the middle jurassic sortehat formation (neill klinter group), jameson land, east greenland. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 777–811. leeder, m.r. 1973: fluviatile fining-upwards cycles and the magnitude of palaeochannels. geological magazine 110(3), 265–276. maync, w. 1947: stratigraphie der jurabildungen ostgrönlands zwischen hochstetterbugten (75°n) und dem kejser franz joseph fjord (73°n). meddelelser om grønland 132(2), 223 pp. miall, a.d. 1985: architectural-element analysis: a new method of facies analysis applied to fluvial deposits. earth-science reviews 22(4), 261–308. miall, a.d. 1996: the geology of fluvial deposits: sedimentary facies, basin analysis and petroleum geology, 582 pp. berlin: springer-verlag. phillips, s. & bustin, r.m. 1996: sulfur in the changuinola peat deposit, panama, as an indicator of the environments of geus bulletin no 5.pmd 29-10-2004, 11:1428 29 deposition of peat and coal. journal of sedimentary research 66(1), 184–196. price, s.p. & whitham, a.g. 1997: exhumed hydrocarbon traps in east greenland: analogs for the lower–middle jurassic play of northwest europe. american association of petroleum geologists bulletin 81(2), 196–221. reinfelds, i. & nanson, g. 1993: formation of braided river floodplains, waimakariri river, new zealand. sedimentology 40, 1113–1127. sherman, d.j. & greenwood, b. 1989: hummocky cross-stratification and post-vortex ripples: length scales and hydraulic analysis. sedimentology 36, 981–986. smith, n.d., cross, t.a., dufficy, j.p. & clough, s.r. 1989: anatomy of an avulsion. sedimentology 36, 1–24. stemmerik, l., clausen, o.r., korstgård, j., larsen, m., piasecki, s., seidler, l., surlyk, f. & therkelsen, j. 1997: petroleum geological investigations in east greenland: project ‘resources of the sedimentary basins of north and east greenland’. geology of greenland survey bulletin 176, 29–38. surlyk, f. 1977: stratigraphy, tectonics and palaeogeography of the jurassic sediments of the areas north of kong oscars fjord, east greenland. bulletin grønlands geologiske undersøgelse 123, 56 pp. surlyk, f. 2003: the jurassic of east greenland: a sedimentary record of thermal subsidence, onset and culmination of rifting. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 659–722. surlyk, f. & noe-nygaard, n. 2001: cretaceous faulting and associated coarse-grained marine gravity flow sedimentation, traill ø, east greenland. in: martinsen, o.j. & dreyer, t. (eds): sedimentary environments offshore norway – palaeozoic to recent. norwegian petroleum society (npf) special publication 10, 293–319. surlyk, f., callomon, j.h., bromley, r.g. & birkelund, t. 1973: stratigraphy of the jurassic – lower cretaceous sediments of jameson land and scoresby land, east greenland. bulletin grønlands geologiske undersøgelse 105, 76 pp. underhill, j. & partington, m.a. 1993: use of genetic sequence stratigraphy in defining and determining a regional tectonic control on the ‘mid-cimmerian unconformity’ – implications for north sea basin development and the global sea-level chart. in: weimer, p. & posamentier, h.w. (eds): siliciclastic sequence stratigraphy: recent developments and applications. american association of petroleum geologists memoir 58, 449–484. geus bulletin no 5.pmd 29-10-2004, 11:1429 geological survey of denmark and greenland bulletin 6, 1-4 1 geological survey of denmark and greenland bulletin 6 · 2004 east greenland caledonides: stratigraphy, structure and geochronology edited by a.k. higgins and feiko kalsbeek geological survey of denmark and greenland ministry of the environment geus bulletin 6.pmd 10-02-2005, 09:531 2 geological survey of denmark and greenland bulletin 6 keywords caledonides, east greenland, geochronology, stratigraphy, structure. cover west-dipping white and rusty brown quartzites of the lower cambrian slottet formation, at slottet in the eleonore sø foreland window, resting unconformably on dark clastic sediments of the palaeoproterozoic eleonore sø complex. the summit of slottet (1933 m high) is 600 m above the glacier surface. chief editor of this series: adam a. garde scientific editors of this volume: a.k. higgins and feiko kalsbeek editorial secretaries: esben w. glendal and birgit eriksen critical readers: arild andresen (norway), brian chadwick (uk), lars clemmensen (denmark), clark r.l. friend (uk), david g. gee (sweden), john s. peel (sweden), john e. repetski (usa), minik rosing (denmark), rob strachan (uk) and martin whitehouse (sweden) illustrations: helle zetterwall digital photographic work: benny m. schark and jakob lautrup graphic production: knud gr@phic consult, odense, denmark printers: schultz grafisk, albertslund, denmark manuscripts submitted: 10 november 2003 final versions approved: 9 june – 14 september 2004 printed: 30 december 2004 isbn 87-7871-148-7 geological survey of denmark and greenland bulletin the series geological survey of denmark and greenland bulletin replaces geology of denmark survey bulletin and geology of greenland survey bulletin. citation of the name of this series it is recommended that the name of this series is cited in full, viz. geological survey of denmark and greenland bulletin. if abbreviation of this volume is necessary, the following form is suggested: geol. surv. den. green. bull. 6, 93 pp. available from geological survey of denmark and greenland (geus) øster voldgade 10, dk-1350 copenhagen k, denmark phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: geus@geus.dk or geografforlaget aps rugårdsvej 55, dk-5000 odense c, denmark phone: +45 63 44 16 83, fax: +45 63 44 16 97, e-mail: go@geografforlaget.dk © danmarks og grønlands geologiske undersøgelse (geus), 2004 geus bulletin 6.pmd 10-02-2005, 09:532 3 contents preface a.k. higgins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 lower palaeozoic stratigraphy of the east greenland caledonides m.p. smith, j.a. rasmussen, s. robertson, a.k. higgins and a.g. leslie . . . . . . . . . . . . . . . . . . . . . . . . . 5 the neoproterozoic rivieradal group of kronprins christian land, eastern north greenland m.p. smith, a.k. higgins, n.j. soper and m. sønderholm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 the caledonian thin-skinned thrust belt of kronprins christian land, eastern north greenland a.k. higgins, n.j. soper, m.p. smith and j.a. rasmussen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 palaeoproterozoic age of a basement gneiss complex in the charcot land tectonic window, east greenland caledonides k. thrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 reconnaissance pb-pb dating of single mineral phases by the step-leaching method: results from the caledonides of east greenland k. thrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 the eleonore sø and målebjerg foreland windows, east greenland caledonides, and the demise of the ‘stockwerke’ concept a.k. higgins and a.g. leslie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 geus bulletin 6.pmd 10-02-2005, 09:533 4 preface the east greenland caledonides extend from 70° to 81°30′n, and have been the subject of a series of regional mapping programmes between 1968 and 1998. the entire orogen is now covered by five published 1:500 000 geological map sheets. the six papers in this bulletin concern a variety of topics relating mainly to kronprins christian land (79°–81°30′n) and the kong oscar fjord region (72°–75°n). the paper by smith et al. on lower palaeozoic stratigraphy proposes amendments to several stratigraphical units that occur in kronprins christian land and nearby lambert land. in the kong oscar fjord region, two new formations are defined for quartzite and limestone/dolostone units that crop out in foreland windows, and the lower palaeozoic succession of the fjord region of east greenland is formally placed in the kong oscar fjord group. the second paper by smith et al. describes and formally defines the neoproterozoic rivieradal group of kronprins christian land. the paper by higgins et al. analyses the thinskinned fold-and-thrust belt that marks the transition between foreland and orogen in kronprins christian land, and presents a balanced cross-section restoration. the two geochronological papers by thrane report the results of ion microprobe zircon analyses from orthogneisses in the charcot land window (72°n), and results of reconnaissance pb-pb dating by the stepleaching method. the final paper by higgins & leslie reviews the history of geological research in the eleonore sø and målebjerg areas of the kong oscar fjord region (72°– 75°n). recognition that the two areas are part of the caledonian foreland implies that the two thrust sheets structurally overlying the eleonore sø and målebjerg windows have large displacements (~ 100 km each), and that the ‘stockwerke’ concept of the orogen that focused on in situ vertical movements can finally be laid to rest. a.k. higgins geus bulletin 6.pmd 10-02-2005, 09:534 geological survey of denmark and greenland bulletin 1, 61-73 61 middle jurassic sediments occur in almost all parts of what is conventionally drawn as the present-day continent of europe – from portugal to the caucasus, sicily to svalbard, the hebrides to the petshora – but in the context of the present book, we shall confine ourselves essentially to western and northern europe, broadly from the alps to the arctic (fig. 1). the shelf-seas of the barents shelf and svalbard, also still part of europe today, are not included, but the eastern shores of greenland are. the palaeolatitudes in the middle jurassic were about 15º lower than they are today, so that europe straddled the temperate zones from the sub-tropical to the sub-arctic. this is fully reflected both in the lithoand biofacies of the sediments, ranging from the predominantly warm-water carbonates in the south, with their immensely diverse fossil biotas, to the siliciclastics with their impoverished fossil assemblages in the north. historically, western europe, as the cradle of geological science together with its superbly developed jurassic successions, has given us a longstanding knowlthe middle jurassic of western and northern europe: its subdivisions, geochronology and correlations john h. callomon the palaeogeographic settings of denmark and east greenland during the middle jurassic are outlined. they lay in the widespread epicontinental seas that covered much of europe in the post-triassic transgression. it was a period of continuing eustatic sea-level rise, with only distant connections to world oceans: to the pacific, via the narrow viking straits between greenland and norway and hence the arctic boreal sea to the north; and to the subtropical tethys, via some 1200 km of shelf-seas to the south. the sedimentary history of the region was strongly influenced by two factors: tectonism and climate. two modes of tectonic movement governed basinal evolution: crustal extension leading to subsidence through rifting, such as in the viking and central grabens of the north sea; and subcrustal thermal upwelling, leading to domal uplift and the partition of marine basins through emergent physical barriers, as exemplified by the central north sea dome with its associated volcanics. the climatic gradient across the 30º of temperate latitude spanned by the european seas governed biotic diversity and biogeography, finding expression in rock-forming biogenic carbonates that dominate sediments in the south and give way to largely siliciclastic sediments in the north. geochronology of unrivalled finesse is provided by standard chronostratigraphy based on the biostratigraphy of ammonites. the middle jurassic saw the onset of considerable bioprovincial endemisms in these guide-fossils, making it necessary to construct parallel standard zonations for boreal, subboreal or nw european and submediterranean provinces, of which the nw european zonation provides the primary international standard. the current versions of these zonations are presented and reviewed. keywords: northwest europe, north sea, east greenland, middle jurassic, palaeogeography, geochronology, ammonite biostratigraphy, standard chronostratigraphy university college london, 20 gordon street, london wc1h 0aj, uk. e-mail: johncallomon@lineone.net geological survey of denmark and greenland bulletin 1, 61–73 (2003) © geus, 2003 62 t tt t t t tt t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t tt t t t andøya 500 km vi ki ng s tr ai ts m ar in e bo re al b at ho ni an te th ys marine marine sm ar de lta ic hrl ? ? ? ? nb lu aq ? vo he vi hp ? hi tr 211/21-1 ndb sp vg lbl co pb bo fr sw mc cnsd mo cg ca llo via n bbaajjoocciiaann -bbaatthhoonn iiaann b ajocian–bathonian car bon ates jameson land east greenland ttt land paralic/deltaic siliciclastics volcanics coastline probable coastline speculative facies boundary tethyan shelf edge extent of the central north sea dome well 50° 40° 30° 0° 10°10° mnsh rfh skåne 9/10b-1 edge of that system unrivalled in detail. this is particularly the case in the middle jurassic. it provides the primary standard for comparisons with the rest of the world. to this denmark has contributed little, for its jurassic lies almost wholly in the subsurface. more recently, the post-war quest for petroleum has opened up what had largely been an immense geological terra incognita, the circum-global arctic. it quickly became apparent that the middle jurassic of the arctic could not be simply correlated with that of western europe because of non-overlapping endemisms in the distributions of the critical geochronometers, here the ammonites as guide-fossils. but at the same time, danish geological expeditions to east greenland revealed the key to correlations through the presence there of a residual sedimentary and biostratigraphical record so good that it has in turn become the chronostratigraphical standard for the whole of the arctic. this gives the jurassic of east greenland an importance out of all proportion to the modest extent of its outcrops. the middle jurassic makes also an important contribution to another area of more recent geological exploration. it is that of the former shelf-seas whose sediments now lie under the north sea and along the margins of the southern north atlantic, and whose interplay of tectonics and patterns of sedimentation form the major topics in other papers of the present volume. here, denmark does play a significant role by virtue of its position between the centres of active rifting in the north sea and the passive littoral margins of the baltic craton. the role of east greenland is twofold. firstly, it offers unique opportunities for direct study of fine examples, now splendidly exhumed onshore, of the kind of structures and basin-fills widespread in the subsurface of the north sea, important in the search for petroleum but necessarily mapped largely by indirect geophysical methods. secondly, the biostratigraphy of its ammonites provides the most precise available timecontrol on the genetic sedimentology and basin analysis, at a level of time-resolution that can significantly steer the interpretations. this chronostratigraphy is outlined here in some detail. palaeogeography, sedimentary basins and tectonics the middle jurassic experienced a continuing first-order worldwide (eustatic) rise in average sea level, reflected in the transgressive sediments still preserved on almost all of the surviving palaeocratonic, peri-oceanic margins of the former supercontinent pangea. taking the most optimistic estimate (see, for example, discussion by hallam 1988) of, say, + 200 m for the jurassic as a whole, this would suggest a mean value in the region of 50–100 m for thicknesses of epicontinental marine middle jurassic sediments that could be ascribed to eustatically-created accommodation space. one of the most plausible direct estimates to date (sahagian et al. 1996), based on the truly cratonic russian platform, gives about 30 m for the bajocian–callovian inclusive. whatever the meaning of such a figure might be generally, it does provide a yardstick when trying to estimate, or derive, the relative importance of the shorter-period, higher-order processes that modulate almost all sedimentary successions more locally. this includes the relative importance of higher-order eustatic fluctuations and regional tectonics in particular. palaeogeographically, the region around denmark during the jurassic lay still firmly inland on the laurentian craton (fig. 1). the landscape was one of gently undulating post-caledonian and post-hercynian topography whose highs had been eroded during the carboniferous and permian and whose lows had accumulated shallow marine evaporites and lacustrine or fluviatile continental sediments during the triassic, a period of historically low worldwide sea level. the marine transgressions marking the onset of a new major cycle of eustatic sea-level rise at the beginning of the jurassic then flooded a vast peneplain and inaugurated the regime of very extensive, shallow epicontinental seas so characteristic of the jurassic and cretaceous, far distant from the oceans and having few, if any, close current analogues. to the east lay the eurasian continent, almost as large as it is today. to the north lay fen63 facing page: fig. 1. the palaeogeography of western europe in the middle jurassic in early–mid bathonian times. the dot-dashed lines south of ar–lbl represent the approximate northerly limits of dominantly carbonate lithologies. the channel shown between greenland and the hatton–rockall landmass (the east greenland rift of ziegler 1982) is highly conjectural. aq, aquitaine basin; ar, armorica; bo, bohemia; cnsd, central north sea dome; co, cornubia; fr, franconia; he, helvetic highs (aar, gothard, mt. blanc massifs); hi, hurry inlet; hp, hebridean platform; hrl, hatton–rockall landmass; lbl, london– brabant landmass; lu, lusitanian basins; mc, massif central; mnsh, mid north sea high; mo, moray firth basin; nb, newfoundland banks; pb, paris basin; rfh, ringkøbing–fyn high; sm, spanish meseta; sp, shetland platform; sw, swabia; tr, trondheim fjord; vg, viking graben; vi, vindelicia; vo, vocontian trough. noscandia, firmly emergent during the whole of the jurassic. to the west lay the shallow seas covering the north sea, the british isles and what are now the continental shelves of the north atlantic, with the north american continent as far as idaho and british columbia beyond. to the south lay the shallow basins of the european platform, such the anglo-parisian, aquitanian, keltiberian, rhodano-helvetic, franco-swabian, lower saxonian and polish basins. the nearest ocean was the tethys, 1200 km to the south. access to it was not unrestricted but open through several broad channels. the only other access to the world’s oceans was northwards, through the viking straits, another broad seaway lying between fennoscandian norway and laurentian greenland (not the viking graben, a tectonic entity), connecting the central european seas with those of the arctic and thence the pacific. a number of residual hercynian rumps persisted as basin highs or even islands during the middle jurassic. they include the anglo-brabant landmass (‘london– ardennes island’), the scottish highlands, cornubia, armorica, the massif central, the harz (hercynia), bohemia and silesia. none of these were large or high enough to be major passive sources of primary coarse siliciclastic sediment, and although transgressive middle jurassic shoreline deposits may be observed at various places on them, the extent of their proximal facies is usually rather local. the largest source of both coarse and fine siliciclastics must have been the scandinavian crystalline massifs to the north and east and, in the viking straits, also greenland. the coarser sediments now occupy much of the shelves of the north atlantic and a broad belt extending from the northern north sea over denmark into the baltic. the finer sediments were very widely dispersed and the predominant facies of the european middle jurassic – the brown jura – north of the carbonate belts are clays, silts and fine-grained sands. supply in most cases kept up with demand and even in troughs created by local subsidence (see below), water depths stayed more or less constant. the epicontinental european seas were shallow, perhaps in the range 0–100 m, and quite small oscillations of relative sea level could produce transgressions and regressions over great distances. the positions of former shorelines are therefore often more than usually elusive. this general first-order picture was however widely disrupted by tectonic movements. the break-up of pangea had commenced and by the middle jurassic, gondwana had parted from laurasia. the north atlantic remained closed, but the central atlantic had opened and west africa was now separated from appalachian america by 1000 km of ocean. the effects of these major continental movements were clearly not localised in the tethys but felt also further north. one widespread expression was in the form of rifting into horst and graben or halfgraben structures. thus, the vocontian trough in southern france contains up to 750 m of middle jurassic sediments (terres noires); the lusitanian basin off western portugal up to 700 m; the central graben of the north sea, up to 1000 m; the viking graben of the northern north sea, up to 250 m; and the basins of the viking straits whose fill is now preserved onshore in east greenland, up to 700 m. these were correlated major perturbations extending over 2000 km on a single plate. extensional rifting was complemented by other perturbations of a different character: a transient regional uplift centred in the central north sea (ziegler 1982), driven by thermal upwelling of a subcrustal plume and followed by its dissipation and subsidence. the history of this event has been recently described in considerable detail by underhill & partington (1993, 1994). the rise of the dome began in the late early jurassic (toarcian). it broke marine surface in the aalenian with the onset of erosion, providing a new source of sediment for its surrounding basins. it culminated with the effusion at its centre of a thick lava pile up to 1500 m thick, probably during the bathonian–callovian. formerly termed the rattray formation (deegan & scull 1977), these middle jurassic volcanics have been redefined as the rattray volcanics member and the ron volcanics member, both of the pentland formation (richards et al. 1993). deflationary subsidence with erosional peneplanation was substantially complete in the late oxfordian and was followed by marine transgression. the differential uplift of the central dome is estimated to have been (at least) 400–500 m. the whole cycle of topographic uplift and subsidence had a period of 40 ma, but its highest point lay in the middle jurassic. its palaeogeographic effects extended over an area more than 1200 km across, from the east shetland platform in the north to the scottish highlands and yorkshire in the west, to the london–brabant massif in the south and the ringkøbing–fyn high in the east and taking in the mid north sea high – covering in fact almost the whole of the north sea. movements were more likely to have been pulsed than steady, both of doming and of rifting. their sedimentary expressions could therefore well have been at least partly time-correlated across the region and given rise to widely recognisable successions of sequences and systems tracts. but with such a strong tectonic overprint, both of doming and of rifting, claims to be able successfully to identify an 64 underlying higher-order eustatic cyclicity in the middle jurassic of the north sea seem somewhat improbable. palaeolatitude, climatology and bioprovincialism the shelf-seas of the european middle jurassic ranged in latitudes from about palaeolatitude 28°n (henceforth abbreviated to p-48°) in the south, at the northern margins of the tethys, to about p-48°n at, say, central east greenland (smith et al. 1981). the climatic gradient is clearly evident in sedimentary facies. in the south, carbonates dominate, such as lime mudstones and skeletal grainstones, including coarse echinoderm ‘breccias’. there are widely developed carbonate platforms and ramps. in the north, carbonates are rare or absent and never rock-forming. the pattern between these extremes is complex. it was evidently determined by an interplay of current patterns and topography, which strongly influenced the distribution of both benthic and nektoplanktonic biotas. thus, for instance, the eastern paris basin, the jura and what are now the helvetic alps (p-32°n) saw the build-up of a range of thick bioclastic carbonate platforms in the bajocian–bathonian. these shielded the swabo-franconian basin lying behind them from tethyan influence on its western side, its southern and eastern sides being bounded by the vindelician and bohemian massifs. the contrast between the paris and swabo-franconian basins, lying at similar palaeolatitudes, could therefore hardly be greater, the former abounding in a rich and highly diverse warmwater fossil biota; the latter, a sediment-starved basin with a highly impoverished fauna and almost no carbonates. further north-west, the warm-water carbonates and their rich biotas, with corals, reached the cotswolds of england (p-37°n), whereas the middle jurassic of northern germany at the same latitude was almost as impoverished as that of franconia. the furthest north that tethyan warm-water influences are detected is scoresby sund, east greenland (p-48°n), where bathonian hermatypic corals have been found very close to the transgressive western shoreline of the viking straits (håkansson et al. 1971; callomon & birkelund 1980). of immediate concern is the influence of the factors outlined above on the distribution of one group of organisms, the ammonites, for these are the leading guide-fossils whose biostratigraphy provides the primary standard chronostratigraphy over the whole region. the middle jurassic saw a strong segregation of the ammonites into three faunal provinces. these occupy successive, broadly latitudinal belts. the most southerly belt lies along the northern margins of the tethys, including iberia (but not the betic and subbetic basins of andalucia), aquitaine, the southern paris basin, the southern jura, peri-carpathian poland and much of the balkans. it is usually referred to as the submediterranean province of the tethyan realm. its ammonite faunas are rich, diverse and characteristic of warm-water, shallow neritic shelf-seas. they differ from those of the tethyan province proper mainly in compositions, which are reflections of different bioecological habitats. the true tethyan faunas are made up predominantly of pelagic groups such as phylloceras and lytoceras and are found in the pelagic carbonates of former seamounts and carbonate platforms still preserved, for example, in andalucia, sicily, the apennines, the venetian and austrian alps and the southern balkans. their places of entombment were not necessarily in deep water – some of them accumulated cross-bedded oolites – although their living habitats almost certainly were. they do occasionally mingle with the faunas of the shelf-seas, but then invariably as rare stragglers. the next belt constitutes the subboreal province of the boreal realm. it extended from the scottish highlands in the north (p-42°n) across northern europe (southern england, normandy, boulonnais, germany and the northern jura, northern and central poland) into the moscow–volga–donets basins on the russian platform, across the northern caucasus into trans-caspian turkmenistan and the basins of the amudarya, north of afghanistan, before now being lost under the himalayan ranges of the pamirs. in the aalenian, bajocian and bathonian, the distinction between submediterranean and subboreal faunas lies almost wholly in their diversities rather than in their mutually exclusive distributions. the provinces are therefore rarely explicitly differentiated in these stages and their faunas usually referred to simply as ‘european’. the diversity-differentiation is however already clearly discernible in the aalenian, during which typically submediterranean families reached dorset in abundance (callomon & chandler 1994) while being virtually unknown in swabia and franconia. the subboreal province became clearly differentiated from the submediterranean province only in the later middle jurassic, the callovian. it was characterised mainly by two families, the cardioceratidae and kosmoceratidae, whose distributions were complementary to those of the submediterranean reineckeiidae and oppeliidae. the boundaries could be sharp, as in going from southern normandy into touraine and poitou, or very diffuse, with much overlap, as in germany. 65 the third, most northerly, belt constitutes the boreal province of the boreal realm. it existed sporadically already in the toarcian and aalenian, but became clearly and strongly differentiated in the late early and early late bajocian. it then persisted into the cretaceous. it occupied the shelf-seas of the arctic (there being no positive evidence of the existence at that time of a truly oceanic arctic ocean), from the alaskan north slope through the yukon over the canadian arctic archipelago into svalbard and the whole of the barents sea including franz josef land, novaya zemlya and the petshora basin, the laptyev sea and kheta and lena basins in north-central siberia, and thence into north-eastern siberia and back to the bering straits. during the middle jurassic this sea, forming a rough triangle of sides 5000 km, was largely land-locked on two sides, by laurentia and eurasia (see map in callomon 1985, text-fig. 6a). communication in the early middle jurassic with the rest of the world’s oceans was possible in only two areas. the first was through a series of gateways into the northern pacific, between kolyma in far-eastern siberia and eastern alaska (although an anywhere near precise knowledge of where these gateways lay must await a satisfactory plate-tectonic reconstruction of this whole region). the second was the relatively narrow channel of the viking straits leading southwards to the epicontinental seas of europe and thence to the tethys. a third route opened in the late middle jurassic, in the callovian, when marine transgression from the petshora across the russian platform finally inundated the moscow–volga basins and thence completed the connections with the european epeiric seas from the east. the connecting route of particular interest here is the one between laurentia and fennoscandia along the viking straits. the largely landlocked middle jurassic seas of the arctic developed their own endemic faunas of ammonites, which lived and evolved there in almost total isolation from those further south. they did however venture down the viking straits as far as the shetland islands. here the seas divided into two channels (fig. 1). the westerly one passed southwards to the west of ireland, along the faroe–rockall troughs and perhaps others even further west, and gave connections with the western tethys presumably via the lusitanian seas west of iberia. little detail is so far known about the middle jurassic history of these channels. the easterly channel passed to the east of the shetlands in the general direction of the north sea and its sediments are preserved and well-documented in the viking graben, particularly in the brent field (deegan & scull 1977; underhill & partington 1993). the most southerly point from which fully marine boreal bathonian sediments with ammonites have so far been described appears to be at total’s well 9/10b-1 (bruce field, 59°40´n, p44°n; callomon 1979), 170 km ese of lerwick in the shetlands. progress further southwards into the north sea was then blocked by the emergent central north sea dome. its western non-marine flanking sediments have long been recognised in the various ‘estuarine series’ found in the aalenian–bathonian middle jurassic of britain, from scotland to the eastern midlands. marine connections between the northern north sea and the normal marine seas of wessex, and the north german and polish basins were completely cut by a physical barrier. no middle jurassic ammonites have been recorded from denmark, although typical european faunas are again well-represented in the southern baltic (stoll 1934). the ammonite faunas of the boreal and european provinces were wholly segregated: no region of overlap is known. both faunas evolved independently and provide the biochronologies on which the standard chronozonations are based. this means, however, that these chronozonations have had to be worked out independently, one standard scale for each province (see below), and correlations between these provincial scales continue to range from problematic to impossible. of particular interest here is the fact that the most detailed biochronology of the boreal bajocian–bathonian ammonites anywhere in the arctic has been that recorded in central east greenland, through an unusually favourable combination of circumstances (callomon 1993). it provides currently the chronostratigraphic standard of reference for the whole of the arctic. what of the channels to the west of ireland? no boreal middle jurassic ammonites have so far been found anywhere along their former courses, although this may be due wholly to lack of outcrop or sampling in boreholes. certainly no ammonites penetrated as far south as the lusitanian basins (p-30°n). yet that there must have been a fully marine connection is attested by those hermatypic corals found in milne land, east greenland: they could have got there by no other route. the failure of the ammonites to migrate southwards therefore probably reflects an ecological barrier: a case perhaps of inability to migrate against a northerly-flowing warm-water current carrying an inimical food-chain. direct marine connections between the arctic and europe were restored in the early callovian. a second boreal family of ammonites, the kosmoceratidae, also with a long pre-callovian history in the arctic, suddenly appeared in europe. but whether the connection was via the viking straits or via the russian platform 66 was until recently not clear: new discoveries now make the latter the more probable (gulyaev & kiselev 1999a, b; mitta 2000; mitta & starodubtseva 2000). the earliest, a kepplerites, has been found in the upper bathonian of franconia (dietl & callomon 1988). it resembles a form from the lower calyx zone of east greenland (see below), also of late bathonian age. the first horizon with abundant kepplerites keppleri (oppel) has been traced from southern england (upper cornbrash) via northern and southern germany to the northern jura and probably as far as the caucasus. it marks the base of the callovian stage and also has close relatives in east greenland. it is closely followed by the earliest horizon with abundant cadoceras of the cardioceratidae, also traceable from dorset via germany to the northern jura, with now closely related forms all over the russian platform (cadoceras elatmae (nikitin)). yet the earliest known ammonites from marine sediments directly overlying non-marine deltaic facies in scotland came from considerably higher levels, in the early koenigi zone on the east coast (moray firth) and in the late koenigi zone on the west coast (skye). furthermore, no callovian ammonites have been recorded from anywhere in the central north sea. indisputably direct marine connections between the arctic seas and those of europe via the viking straits were however fully reestablished in the late callovian (athleta zone). the same standard zonation can be applied to sediments from the top of the lower callovian upwards in both the viking straits as preserved in east greenland and throughout northern europe (see below). standard zonal chronostratigraphy the middle jurassic is made up chronostratigraphically of four standard stages: aalenian (lowermost, aalen, south-west germany), bajocian (bayeux, normandy), bathonian (bath, england) and callovian (uppermost, kellaways, wiltshire, england) (fig. 2). the chronometric ages of its boundaries are not directly very closely determined, but recent reviews (harland et al. 1990; odin 1994; gradstein et al. 1994) are in tolerable agreement in assigning to the middle jurassic a duration of 21 ma, i.e. close to a third of the 62–68 ma of the jurassic as a whole. published chronometric ages for individual stage boundaries are largely based on non-chronometric estimates of their relative durations, such as the number of standard chronostratigraphic zones or subzones they (now) contain, and should be treated with corresponding caution (see pálfy 1995; pálfy et al. 2000). the standard zones and subzones used here are chronozones defined by their bounding time-planes and are at the lowest two levels (vi and vii) of a hierarchy of successively finer subdivisions of the geological column, of the jurassic system (iii), its series (iv) and stages (v) (callomon 1994, 1995). the observational basis is the biostratigraphy of the most sensitively timediagnostic guide-fossils available, here the ammonites, which serve to characterise the zones in terms of their contents and to correlate successions. in most cases even finer time-resolutions are possible within a subzone, based on the recognition in it of more than one distinguishable – in an evolutionary sense – biohorizon, whose number can increase with the growth of knowledge of a highly incomplete geological record (callomon 1995). figure 3 shows standard zonations for the three ammonite biogeographic provinces represented in western europe. such zonations grow with time and knowledge. the oldest, going back substantially to oppel (1856–58) is that covering the northwest european or subboreal province, in which lie most of the outcrops studied during the classical age of geology (column a). it is the best known and most complete and hence provides the primary standard. the zonation used today in the submediterranean province is shown alongside it at the left (column b). its bathonian part became established in the 1940–50s, its callovian part a little later. the boreal zonation shown in the column at the right (c) was wholly unknown before 1959. the purpose of diagrams such as these is to represent what are effectively relative time-scales. but as there are no independent ways of estimating the relative durations of the time-periods represented by zones 67 oxfordian stagesseries callovian bathonian bajocian aalenian toarcian middle jurassic (dogger) fig. 2. the primary standard stages of the middle jurassic. 68 u pp er m id dl e lo w er u pp er m id dl e lo w er u pp er b at ho ni an c al lo vi an morrisi 37 36 35 33 32 31 34 30 29 28 24 23 22 21 20 19 18 17 14 13 11 10 9 8 3 2 1 ? ? zones zones & horizonszones lamberti athleta coronatum jason orbis zigzag parkinsoni garantiana subfurcatum zones calloviense koenigi herveyi discus nordenskjoeldi apertum calyx variabile cranocephaloide ishmae greenlandicus arcticus pompeckji indistinctus borealis lamberti (alligatus) athleta coronatum anceps gracilis herveyi (bullatum) discus retrocostatum zigzag bremeri subcontractus progracilis tenuiplicatus (as subboreal) (a) banksi polygyralis baculata dichotoma tetragona acris truellei bomfordi convergens macrescens yeovilensis tenuiplicatus progracilis subcontractus morrisi hodsoni blanazense hannoveranus hollandi discus keppleri terebratus kamptus gowerianus curtilobus galilaeii calloviense enodatum medea jason obductum grossouvrei phaeinum proniae spinosum henrici lamberti subzones & horizons subzones & horizons boreal province nw european / subboreal province submediterranean province b a c xx• xix• xviii• xvii• xvi• xv• xiv• xiiib• xiiia• xii• xi• xb• xa• ix• viii• viib• viia• vi• v• iv• iii• ii• i• 14• 13• 12• 11• 10• 9• b aj o ci an lo w er a al en ia n lo w er u pp er (submediterranean province not differentiated) concavum bradfordensis murchisonae discites ovalis sauzei humphriesianum laeviuscula formosum concavum gigantea bradfordensis murchisonae obtusum haugi sayni trigonalis laeviuscula cycloides humphriesianum blagdeni scissum opalinum fig. 3. the standard zonal chronostratigraphy of the middle jurassic in the three ammonite faunal biogeographic provinces represented in europe. the primary standard is the northwest european or subboreal, shown in the centre (column a). the secondary standard in the submediterranean province is on the left (b), that in the boreal province on the right (c). for annotations, see text. the submediterranean zonation for the aalenian and lower bajocian is the same as the northwest european/subboreal and is not separately indicated. no ammonite faunas of these ages are known from the boreal province itself. in the toarcian (lower jurassic) below, a separate zonation is again introduced for the mediterranean/tethyan province. or subzones, there is no unique or permanent way of drawing the diagrams. the scheme adopted here is to assume that the time-intervals between adjacent distinguishable ammonite biohorizons in the primary standard (a) are equal. as they are the smallest time-intervals at present resolvable by means of ammonites, the errors in this assumption are likely to have the least effect on the implied relative durations of the coarser units, the zones and subzones. the known number of such resolvable biohorizons is of course not final either. but as the european standard has been worked on intensively over a long time, it is safe to say that in the middle jurassic at least, we are now close to what is achievable in timeresolution by means of ammonites. taking the estimates of duration of the middle jurassic quoted at the beginning, of 21 (± 4?) ma, the average time-interval between faunal horizons (115) is 180 (± 36) ka; the average duration of a standard zone (28) is 750 (± 150) ka. correlation between european subboreal and submediterranean scales (a–b) is sufficiently close to draw them on the same scale. correlation between the european and boreal scales (a–c) even at zonal level is so imprecisely known that they have to be drawn quite independently. it is however probable that the lowest, borealis zone correlates with levels at around the lower–upper bajocian boundary. such a correlation had been previously postulated on the basis of a chain of correlations via the north american cordillera (callomon 1985, p. 64). it has now been confirmed through measurements of the stable isotopic ratio of strontium (87sr/86sr) in belemnites (j.h. callomon, unpublished data; m. engkilde, personal communication 1997). scale c is therefore also drawn on a faunal-horizon equal-interval assumption, based on the best available ammonite biochronology of east greenland. the boreal intervals have, however, been stretched somewhat relative to those of the european standard, to take the borealis zone down to the early upper bajocian. a: european subboreal primary standard the names of both zones and subzones as currently in use have been written out. to complete their definitions, the bounding time-planes of these standard chronostratigraphic units have to be fixed in boundary stratotype sections. while such definitions have been proposed for many of the zones and subzones, none have so far been formally ratified by the international commission on stratigraphy, whose aspirations do not currently descend below the level of standard stages (cowie et al. 1986). the lack of such formal definitions appears to have remarkably little consequence in practical day-to-day affairs. the reason has been pointed out repeatedly (callomon 1995) and is important. it is that rocks are correlated by means of the contents of zones – what lies between the bounding time-planes – rather than by correlation of the time-planes themselves. the wide variations in the relative time-values and numbers of subzones in zones as shown in the column are almost entirely of historical origin, reflecting a compromise between the growth of knowledge (faunal horizons) and a desire to retain some stability in zonal nomenclature. (in the times of oppel (1856–58) and of waagen (1867), the number of zones in what is today’s middle jurassic was 13; in arkell’s review of 1956 it was 21; here it has grown to 28). aalenian–bajocian based on recent revisions (callomon & chandler 1990; callomon 1995; callomon & cope 1995). bathonian the chronostratigraphy of this stage was one of the last to be worked out in europe because of exceptionally difficult ammonite biostratigraphy – scattered part-sections with only sparse ammonites. the first comprehensive modern syntheses by gabilly (1965) and mangold (1970) were based on the successions in western and eastern france, respectively. a review by westermann & callomon (1988) of its faunal successions was given in terms of 16 faunal horizons, some of which (9–14) are numbered here. some subsequent refinements in the upper bathonian of swabia were reported by dietl & callomon (1988), and a discrepancy between the middle and upper bathonian boundaries as drawn in the northwest european and submediterranean classifications was resolved by mangold (1988). the most recent reviews, by callomon & cope (1995, p.73) and mangold & rioult (1997), differ in some details of nomenclature but retain essentially the same biostratigraphic basis of faunal horizons. thus horizon 11, of procerites quercinus, is elevated into a quercinus subzone of the northwest european hodsoni zone, thereby raising the base of the orbis zone by one horizon; and the convergens and yeovilensis subzones of the zigzag zone are given separate names in the submediterranean province. the historically-conditioned difference between 69 the numbers of faunal horizons in the lower–middle and upper bathonian respectively is here particularly marked. callovian much new information in recent years has greatly amplified our knowledge of the lower and upper parts of the stage. the former was revised by callomon et al. (1988) and page (1989), the latter by dietl (1994 and unpublished data, based on excavations in swabia) and callomon & cope (1995). the herveyi zone is the former macrocephalus zone renamed, after it was discovered that the type-horizon of the index macrocephalites macrocephalus (schlotheim) did not in fact lie in its eponymous zone (callomon et al. 1992). a similar change of index will have to be made for the spinosum subzone of the athleta zone, because the type-horizon of kosmoceras spinosum (j. de c. sowerby) is now known to lie in the lamberti zone. only the coronatum zone remains in need of a modern revision. the middle–upper callovian boundary as reproduced here was defined in terms of the phyletic transients of the lineage of kosmoceras in england (callomon 1964, 1968) and not on the first appearance of peltoceras, which came in a little later. the upper boundary of the callovian stage, and hence the middle–upper jurassic boundary, has always been taken biostratigraphically to lie between the highest known faunal horizon of the lamberti zone, that of quenstedtoceras paucicostatum lange, and the lowest horizon of the oxfordian mariae zone, that of q. woodhamense arkell. it was usually easy to recognise because over large parts of northwest europe it is marked by a non-sequence. the discovery of expanded sequences across the boundary, e.g. in dorset and southern france, has made the final choice of stratotype section a matter of current debate. b: submediterranean secondary standard aalenian–bajocian the northwest european zonation is applicable and no separate scheme has been introduced. bathonian also reviewed by westerman & callomon (1988) and mangold & rioult (1997). the northwest european zonation is used for the lower and all but the topmost middle bathonian. differentiation became marked only in the upper bathonian. the submediterranean succession was worked out mainly in france, particularly in poitou (gabilly 1965), the southern paris basin and the southern jura (mangold 1970). there its uppermost part appears to be marked also by a widespread faunal or stratigraphical non-sequence, so that the bathonian– callovian boundary was until recently not clearly characterised (see below). callovian based predominantly on the faunal succession in western france worked out by cariou (1980, 1984). his labelling of faunal horizons (i–xx) has been included here, although the names of the subzones, many of which contain only a single faunal horizon, have been omitted. both bottom and top of the succession are marked by regionally widespread gaps. since figure 3 was drawn, however, a newly discovered section at buffevent, near niort in poitou, shows an expanded succession that spans the bathonian–callovian boundary (b. balusseau, p. branger and e. cariou, personal communications 2000). most particularly, one of its beds has yielded kepplerites keppleri, characteristic of the basal faunal horizon of the callovian stage by definition (callomon & dietl 2000). the bases of the callovian stages in both primary nw european (a) and secondary submediterranean (b) classifications can therefore be taken to coincide exactly. there remain some nomenclatural inconsistencies to be resolved, in that while some of the zones, e.g. gracilis and anceps, are named after distinct submediterranean indices, others, such as coronatum and athleta, share their names with their counterparts in the primary standard (a). yet these zones are independently defined and are of slightly different extents. the submediterranean athleta zone, for instance, has been chosen to begin at the first appearance of peltoceras in the hecticoceras trezeense horizon, xv, which lies at a level near the top of the phaeinum subzone of the primary athleta zone. the lowest callovian zone had for a long time been given a separate name and identity, the bullatum zone, as neither its base nor its top could be closely correlated with the primary standard. precise correlation of its base has now been achieved (see above) and so the main obstacle overcome. it has therefore been entered in figure 3 also under the name of the primary index as herveyi zone (olim macro70 cephalus). as its top, the base of the overlying gracilis zone, continues to be independently defined, it may be more appropriate, however, to continue to follow french usage (thierry et al. 1997) and to retain the bullatum zone in the submediterranean classification. an analogous alternative for the name of the top callovian zone in the submediterranean province, instead of lamberti, would be [perisphinctes] alligatus zone. c: boreal secondary standard this was recently reviewed by callomon (1993), based on the ammonite succession in east greenland. almost no ammonite faunas of aalenian – early bajocian ages have been recorded anywhere in the european arctic, and in much of the region the record of this period is marked either by stratigraphical gaps, or unfossiliferous or non-marine deposits (smelror 1994). in east greenland, the youngest ammonite faunas known from below the borealis zone are of early toarcian age (pseudolioceras lythense, bifrons zone). in svalbard and the barents shelf, the same is probably true, for claims to have recognized earliest aalenian ammonites, associated with toarcian forms, in a remanié conglomerate, the brentskardhaugen bed (wierzbowski et al. 1981), are based almost certainly on misidentifications as close aalenian homoeomorphs of the older toarcian species. the borealis zone is clearly recognisable throughout the whole of the arctic and is now known to correlate with the lower upper bajocian of europe or levels even a little older (see general discussion above). thereafter, the faunal horizons are numbered 1–35 up to the top of the lower callovian, as in callomon (1993), with a few subsequent additions based on recent unpublished field observations. they form the basis of the boreal zonation. zones have so far not been subdivided, and their different relative durations also reflect the historical evolution of knowledge. in the middle and upper callovian of east greenland, ammonites are so sparse (although the succession is thick) that they contribute nothing further to standard chronostratigraphy. elsewhere, for example in arctic russia and siberia, the upper callovian is divided into a lower zone of longaeviceras keyserlingi and an upper zone of eboraciceras subordinarium (meledina 1977), but the ammonite biostratigraphy is so fragmentary that they have not been included here. conclusion the middle jurassic of those parts of europe under discussion in this volume encompasses a highly diverse range of tectonic, sedimentary and palaeobiotic developments. to unravel their evolution successfully calls for the closest possible time-control of the rocks: of time-correlations over distances and of time-resolution more locally. fortunately, such time-control is provided by an abundance of good guide-fossils, the ammonites, whose biostratigraphy has given us a chronostratigraphic calendar of unrivalled finesse and hence, conversely, the clocks for dating individual rocks with great precision. the construction of the calendar has taken much effort over many years in many countries and the calendar that has emerged may seem complicated. but the rewards justify the effort needed to master these complexities. acknowledgement this review was written during the tenure of a leverhulme emeritus fellowship, which is gratefully acknowledged. references arkell, w.j. 1956: jurassic geology of the world, 806 pp. edinburgh, london: oliver & boyd. callomon, j.h. 1964: notes on the callovian and oxfordian stages. in: maubeuge, p.l. (ed.): colloque du jurassique à luxembourg 1962, 269–291. luxembourg: publication de l’institut grandducal. callomon, j.h. 1968: the kellaways beds and the oxford clay. in: sylvester-bradley, p.c. & ford, t.d. (eds): the geology of the east midlands, 264–290. leicester, uk: leicester university press. callomon, j.h. 1979: marine boreal bathonian fossils from the northern north sea and their palaeogeographical significance. proceedings of the geologists’ association (london) 90, 163–169. callomon, j.h. 1985: the evolution of the jurassic ammonite family cardioceratidae. in: cope, j.c.w. & skelton, p.w. (eds): evolutionary case histories from the fossil record. special papers in palaeontology 33, 49–90. london: palaeontological association. callomon, j.h. 1993: the ammonite succession in the middle jurassic of east greenland. bulletin of the geological society of denmark 40, 83–113. callomon, j.h. 1994: jurassic ammonite biochronology of greenland and the arctic. bulletin of the geological society of denmark 41, 128–137. 71 72 callomon, j.h. 1995: time from fossils: s.s. buckman and jurassic high-resolution geochronology. in: le bas, m. (ed.): milestones in geology. geological society memoir (london) 16, 127–150. callomon, j.h. & birkelund, t. 1980: the jurassic transgression and the mid–late jurassic succession in milne land, central east greenland. geological magazine 117, 211–226. callomon, j.h. & chandler, r.b. 1990: a review of the ammonite horizons of the aalenian – lower bajocian stages in the middle jurassic of southern england. in: cresta, s. & pavia, g. 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(eds): 2nd international symposium on jurassic stratigraphy (lisbon 1987) 1, 359–376. lisbon: universidade nova de lisboa. callomon, j.h., dietl, g. & niederhöfer, h.-j. 1992: on the true stratigraphic position of macrocephalites macrocephalus (schlotheim 1813) and the nomenclature of the standard middle jurassic ‘macrocephalus zone’. stuttgarter beiträge zur naturkunde b 185, 65 pp. cariou, e. 1980: l’étage callovien dans le centre-ouest de la france. première partie: stratigraphie et paléogéographie. thèse, docteur ès sciences naturelles, université de poitiers, u.e.r. sciences fondamentales et appliquées 325, 110 pp. cariou, e. 1984: biostratigraphic subdivision of the callovian stage in the subtethyan province of ammonites, correlations with the subboreal zonal scheme. in: michelsen, o. & zeiss, a. (eds): international symposium on jurassic stratigraphy (erlangen 1984) 2, 315–326. copenhagen: geological survey of denmark. cowie, j.w., ziegler, w., boucot, a.j., bassett, m.g. & remane, j. 1986: guidelines and statutes of the international commission on stratigraphy (ics). courier forschungsinstitut senckenberg 83, 14 pp. deegan, c.e. & scull, b.j. 1977: a standard lithostratigraphic nomenclature for the central and northern north sea. institute of geological sciences report 77/25, 36 pp. london: her majesty’s stationery office. dietl, g. 1994: der punctulatum-horizont – ein neuer ammoniten faunen-horizont aus dem schwäbischen ornaten-ton (obercallovium, mittlerer jura). geologische blätter von no-bayern 43, 15–32. dietl, g. & callomon, j.h. 1988: der orbis-oolith (oberbathonium, mittl. jura) von sengenthal/opf., fränk. alb, und seine bedeutung für die korrelation und gliederung der orbiszone. stuttgarter beiträge zur naturkunde b 142, 31 pp. gabilly, j. 1965: le jurassique inférieur et moyen sur le littoral vendéen. travaux de l’institut de géologie et anthropologie préhistorique de la faculté des sciences de poitiers 5, 67–107. gradstein, f.m., agterberg, f.p., ogg, j.g., hardenbol, j., van veen, p., thierry, j. & huang, z. 1994: a mesozoic time scale. journal of geophysical research 99, 24051–24074. gulyaev, d.b. & kiselev, d.n. 1999a: on marine boreal upper bathonian on the central russian platform. doklady akademii nauk 367, 95–98 (in russian). gulyaev, d.b. & kiselev, d.n. 1999b: boreal marine upper bathonian in middle povolzhia [middle volga] (ammonites and stratigraphy). stratigrafiya, geologicheskiya korrelatsiya 7, 79–94 (in russian). håkansson, e., birkelund, t., heinberg, c. & willumsen, p. 1971: preliminary results of mapping the upper jurassic and lower cretaceous sediments of milne land. rapport grønlands geologiske undersøgelse 37, 32–41. hallam, a. 1988: a reevaluation of jurassic eustasy in the light of new data and the revised exxon curve. in: wilgus, c.k. et al. (eds): sea-level changes – an integrated approach. society of economic paleontologists and mineralogists special publication 42, 261–273. harland, w.b., armstrong, r.l., cox, a.v., craig, l.e., smith, a.g. & smith, d.g. 1990: a geologic time scale 1989, 263 pp. cambridge: cambridge university press. mangold, c. 1970: stratigraphie des étages bathonien et callovien du jura méridional. documents du laboratoire de géologie de la faculté des sciences, lyon 41(1), 376 pp. mangold, c. 1988: reports of the working groups: bajocian/ bathonian boundary and bathonian. in: rocha, r.b. & soares, a.f. (eds): 2nd international symposium on jurassic stratigraphy (lisbon 1987) 1, 17–18. lisbon: universidade nova de lisboa. mangold, c. & rioult, m. 1997: 7. bathonien. in: cariou, e. & hantzpergue, p. (eds): biostratigraphie du jurassique ouesteuropéen et méditerranéen. bulletin du centre de recherches elf exploration production mémoire 17, 55–62. meledina, s.v. 1977: ammonites and stratigraphic zoning of the callovian in siberia. trudy instituta geologii i geofiziki (novosibirsk) 356, 290 pp. (in russian). mitta, v.v. 2000: ammonites and biostratigraphy of the lower callovian of the russian platform. byulletin kollektsionnogo fonda vnigni, moskva 3, 144 pp. (in russian with german abstract). mitta, v.v. & starodubtseva, i.a. 2000: w.a. stchirowsky and the study of the mesozoic in the alatyr–kurmysh area (basin of the middle volga). vernadsky museum novitates, moscow 5, 20 pp. (in russian with english abstract). odin, g.s. 1994: geological time scale (1994). comptes rendus de l’académie des sciences (paris) série 2 318, 59–71. oppel, a. 1856–58: die juraformation englands, frankreichs und des südwestlichen deutschlands, nach ihren einzelnen gliedern eingeteilt und verglichen, 857 pp. stuttgart: ebner & seubert. page, k.n. 1989: a stratigraphical revision for the english lower callovian. proceedings of the geologists’ association (london) 100, 363–382. pálfy, j. 1995: development of the jurassic geochronologic scale. hantkeniana, budapest 1, 13–25. pálfy, j., smith, p.l. & mortensen, j.k. 2000: a u-pb and 40ar/39ar time scale for the jurassic. canadian journal of earth sciences 37, 923–944. richards, p.c., lott, g.k., johnson, h., knox, r.w.o’b. & riding, j.b. 1993: jurassic of the central and northern north sea. in: knox, r.w.o’b. & cordey, w.g. (eds): lithostratigraphic nomenclature of the uk north sea 3, 219 pp. nottingham: british geological survey. sahagian, d., pinous, o., olferiev, a. & zakharov, v. 1996: eustatic curve for the middle jurassic – cretaceous based on russian platform and siberian stratigraphy: zonal resolution. american association of petroleum geologists bulletin 80, 1433–1458. smelror, m. 1994: jurassic stratigraphy of the western barents sea region: a review. in: cariou, e. & hantzpergue, p. (eds): 3ème symposium international de stratigraphie du jurassique (poitiers 1991). geobios mémoire spécial 17, 441–452. smith, a.g., hurley, a.m. & briden, j.c. 1981: phanerozoic paleocontinental world maps, 102 pp. cambridge: cambridge university press. stoll, e. 1934: die brachiopoden und mollusken der pommerschen doggergeschiebe. abhandlungen aus dem geologisch-palaeontologischen institut der universität greifswald 13, 62 pp. thierry, j., cariou, e., elmi, s., mangold, c., marchand, d. & rioult, m. 1997: 8. callovien. in: cariou, e. & hantzpergue, p. (eds): biostratigraphie du jurassique ouest-européen et méditerranéen: zonations parallèles et distribution des invertébrés et microfossiles. bulletin du centre de recherches elf exploration production mémoire 17, 63–78. underhill, j.r. & partington, m.a. 1993: jurassic thermal doming and deflation in the north sea: implications of the sequence stratigraphic evidence. in: parker, j.r. (ed.): petroleum geology of northwest europe: proceedings of the 4th conference, 337–345. london: geological society. underhill, j.r. & partington, m.a. 1994: use of genetic sequence stratigraphy in defining and determining a regional tectonic control on the “mid-cimmerian unconformity” – implications for north sea basin development and the global sea-level chart. in: weimer, p. & posamentier, h.w. (eds): siliciclastic sequence stratigraphy: recent developments and applications. american association of petroleum geologists memoir 58, 449–484. waagen, w. 1867: über die zone des ammonites sowerbyi. benecke’s geognostisch-paläontologische beiträge 1, 507–668. westermann, g.e.g. & callomon, j.h. 1988: the macrocephalitinae and associated bathonian and early callovian (jurassic) ammonoids of the sula islands and new guinea. palaeontographica a 203, 1–90. wierzbowski, a., kulicki, c. & pugaczewska, h. 1981: fauna and stratigraphy of the uppermost triassic and the toarcian and aalenian deposits in the sassenfjorden, spitsbergen. acta palaeontologica polonica 26, 195–241. ziegler, p.a. 1982: geological atlas of western and central europe, 130 pp. the hague: elsevier for shell internationale petroleum maatschappij. 73 manuscript received 19 april 1996; revision accepted 13 november 1998. geological survey of denmark and greenland bulletin 4, 2003, pp 21-24 the search for new, deep-seated drinking water resources in denmark has increased significantly during the past five years as a result of the discovery of excessive amounts of nitrate, pesticides and other pollutants in shallow groundwater boreholes (e.g. nygaard et al. 2004, this volume). to find and map these aquifers, a multidisciplinary sequence stratigraphic approach has successfully been applied to the miocene deposits of southern jutland, where especially the odderup and ribe formations are known as a main aquifer for drinking water from several test wells (rasmussen et al. 2002). recently, a more systematic study of the miocene succession in central and western jutland has been initiated by the geological survey of denmark and greenland (geus) under contract with local authorities. it includes detailed sedimentological descriptions of outcrops, sedimentological and log-interpretations of new stratigraphic boreholes and interpretation of new high-resolution seismic data (fig. 1). a number of outcrops and wells have been studied palynologically, resulting in a detailed dinoflagellate cyst stratigraphy and in palynofacies interpretations. the results of these studies have been integrated in the regional geological and stratigraphic model (fig. 2). two new aquifers have been discovered: the bastrup sand and the billund sand. the bastrup sand has already been exploited as a main aquifer in central and southern jutland, and has been referred to either the ribe or odderup formations. however, new stratigraphic results reveal that the bastrup sand is a separate unit in the miocene succession. the billund sand is a deep-seated aquifer located more than 100 m and often more than 150 m deep, and is therefore not penetrated by standard water supply wells which rarely reach c. 100 m. the billund sand was first revealed by multichannel seismic data deriving from former oil-exploration carried out in 21 the billund delta: a possible new giant aquifer in central and western jutland erik s. rasmussen, karen dybkjær and stefan piasecki fig. 1. map of southern jutland showing palaeoenvironments of the billund delta, the location of boreholes and the seismic section mentioned in the text. fig. 2. lithostratigraphy of the miocene succession in jutland compiled from larsen & dinesen (1959), rasmussen (1995), dybkjær & rasmussen (2000) and rasmussen et al. (2002). bs, billund sand; gs, gram silt/sand; hs, hvidbjerg sand; vfs, vejle fjord sand member. geological survey of denmark and greenland bulletin 4, 21–24 (2004) © geus, 2004 the billund area (fig. 3a). the resolution of these seismic data is very poor, but one interpretation of the dipping reflectors (clinoforms) seen in fig. 3a was of a delta complex. this agrees with outcrop studies along the fjords of eastern jutland which suggest that a spit complex was deposited in this area during the early miocene. the billund sand was tested by the vandel mark well in 2001, which penetrated c. 40 m of sand at a depth of 200 m. the presence of a regional major sand body was later confirmed by new high-resolution seismic data and by the billund and løvlund wells in 2002. the billund well penetrated 50 m of mediumto coarse-grained sand, and chemical tests of the water quality were good. however, a water supply well at fjand in western jutland has had problems with so-called ‘brown water’ – water enriched in organic matter (humus). saline water may also be expected close to older deep-seated faults. this paper summarises the results of a mapping programme of the billund sand initiated in the summer of 2003. 22 fig. 3. two seismic sections from the billund area. a: the old multichannel seismic line dcj-05. b: the new shallow seismic line gi01 (courtesy of cowi a/s). the red framed area in fig. 3a corresponds to the section shown in fig. 3b. the clinoformal reflection pattern is indicated in yellow. fig. 4. correlation panel of four boreholes, with gamma-ray log signature, trending n–s in the billund area. the seismic section adjacent to the store vorslunde well shows the correlation of a clinoformal reflection pattern with sand. note that the billund delta pinches out between the vandel mark and the almstok wells. seismic data courtesy of cowi a/s. the billund delta the billund sand represents a major early miocene delta prograding southwards from norway into the danish area. the study of the billund delta includes interpretation of seismic data, lithological descriptions and interpretation of logs from new boreholes, sedimentological descriptions and interpretation of outcrops, dating and correlation of the succession by biostratigraphy (mainly dinoflagellates) and finally interpretation of the depositional environment based on palynofacies. integration of these disciplines has resulted in a robust geological model for the delta that provides a basis for the prediction and location of good reservoir rocks suitable as aquifers for drinking water. seismic mapping in order to map the extent and thickness of the delta, seismic data from both the north sea and jutland have been used. based upon the study of the seismic data an isochore map of the delta has been constructed. the delta extends from 50 km west of the present-day west coast of jutland trending nw–se across jutland, from ringkøbing in the west to billund in central jutland. east of billund the main delta bends northwards, and the eastern limit follows a line from the town of give northwards. the estimated size of the delta is in the order of 10 000 km2 whereas its thickness varies from 300 m in the north sea to less than 100 m in central jutland. associated spit complexes that outcrop in eastern jutland are rarely thicker than 30 m. in some areas the seismic data are characterised by strongly southwards-dipping reflectors (clinoforms; fig. 3b). correlation of seismic data with borehole information reveals that where the clinoforms are distinct, they represent massive sands (fig. 4); north of billund, the massive sands may be up to 75 m thick. the billund delta complex is characterised by a pinchout distance of c. 2 km which in recent delta systems is a characteristic feature of wave-dominated deltas (cf. løseth & helland-hansen 2001). study of boreholes a number of recent, deep boreholes have penetrated the billund delta (fig. 4). these show that the delta comprises a coarsening-upwards succession of mediumto coarse-grained sand with gravel and thin clay layers locally present. a very coarse-grained layer succeeded by a thinning-upwards succession in the store vorslunde borehole indicates that some of the sand was deposited in channels. the thickness of the delta sand varies from 40 m in store vorslunde to 50 m in the billund borehole. however, the eg-3 well (fig. 1), an old deep exploration well, indicates that up to 100 m of sand may be present. study of outcrops a spit system corresponding to the down-drift part of the billund delta outcrops along the fjords in eastern jutland (fig. 5; friis et al. 1998). these deposits are known as the vejle fjord formation (fig. 2). during the last five years these outcrops have been relatively well exposed, and new sequence stratigraphic, biostratigraphic and sedimentological studies have been carried out indicating that a major nw–se-trending spit was located near the southern part of vejle fjord. north of the spit, organic-rich, fine-grained sediments were laid down in a lagoon. sand-rich lagoonal sediments were deposited near inlets, e.g. at dykær. south of the 23 fig. 5. block diagram showing the depositional model of the billund delta. in the upper block diagram the seismic panel shows a prograding delta and the pinchout between the billund and almstok wells. the lower diagram illustrates data from outcrops and wells indicating the presence of a spit complex. note that the spit complex correlates with the delta front at store vorslunde. seismic data courtesy of cowi a/s. 24 spit, ebb-dominated tidal deltas were deposited; examples of these are exposed in a sandpit at pjedsted (fig. 6). at lillebælt, upper and lower shoreface sediments were deposited, and are excellently exposed in coastal cliffs at the old lillebælt bridge (lillebæltsbro) on funen and at børup (fig. 1). the sedimentological study of the vejle fjord formation indicates that the sediments were laid down in a wave-dominated depositional environment with some tidal influence (rasmussen et al. 2002). future perspectives the billund delta may be one of the most important future aquifers for drinking water in western and central jutland. furthermore, the excellent seismic data and the good outcrops in eastern jutland make it possible to use the billund delta as a good analogue for jurassic reservoir rocks in the central and viking grabens of the north sea. references dybkjær, k. & rasmussen, e.s. 2000: palynological dating of the oligocene–miocene successions in the lille bælt area, denmark. bulletin of the geological society of denmark 47, 87–103. friis, h., mikkelsen, j. & sandersen, p. 1998: depositional environment of the vejle fjord formation of the upper oligocene – lower miocene of denmark: a back island/barrier-protected depositional complex. sedimentary geology 17, 221–244. larsen, g. & dinesen, a. 1959: vejle fjord formation ved brejning: sedimenterne og foraminiferfaunaen (oligocæn–miocæn). danmarks geologiske undersøgelse ii. række 82, 114 pp. løseth, t.m. & helland-hansen, w. 2001: predicting the pinchout distance of shoreline tongues. terra nova 13, 241–248. nygaard, e., ernstsen, v., jacobsen, c.s., jacobsen, o.h., juhler, r.k., van der keur, p., olesen, s.e., rasmussen, j., rosenberg, p. & vosgerau, h. 2004: pesticide leaching in danish groundwater: identification of vulnerable areas. geological survey of denmark and greenland bulletin 4, 25–28 (this volume). rasmussen, e.s. 1995: vejle fjord formation: clay mineralogy and geochemistry. bulletin of the geological society of denmark 42, 57–67. rasmussen, e.s., dybkjær, k. & piasecki, s. 2002: miocene depositional systems of the eastern north sea basin, denmark. development of sedimentological and stratigraphical principles in modern sedimentology. danmarks og grønlands geologiske undersøgelse rapport 2002/89, 131 pp. fig. 6. tidal sandstone deposits from an ebb-dominated delta succession associated with a spit complex, deposited down-drift from the main billund delta. pjedsted sandpit, for location see fig. 1. width of track approx. 50 cm. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: esr@geus.dk << /ascii85encodepages false /allowtransparency false /autopositionepsfiles true /autorotatepages /all /binding /left /calgrayprofile (dot gain 20%) /calrgbprofile (srgb iec61966-2.1) /calcmykprofile (u.s. web coated \050swop\051 v2) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.4 /compressobjects /tags /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjdffile false /createjobticket false /defaultrenderingintent /default /detectblends true /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedjoboptions true /dscreportinglevel 0 /syntheticboldness 1.00 /emitdscwarnings false /endpage -1 /imagememory 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<feff4f7f752890194e9b8a2d5b9a5efa7acb76840020005000440046002065874ef65305542b8f039ad876845f7150cf89e367905ea6ff0c4fbf65bc63d066075217537054c18cea3002005000440046002065874ef653ef4ee54f7f75280020004100630072006f0062006100740020548c002000520065006100640065007200200035002e0030002053ca66f465b07248672c4f86958b555f3002> >> >> setdistillerparams << /hwresolution [2400 2400] /pagesize [595.000 842.000] >> setpagedevice geological survey of denmark and greenland bulletin 23, 2011, 1–8 1 geological survey of denmark and greenland bulletin 23 • 2011 review of survey activities 2010 edited by ole bennike, adam a. garde and w. stuart watt geological survey of denmark and greenland ministry of climate and energy 22 geological survey of denmark and greenland bulletin 23 key words geological survey of denmark and greenland, survey organisations, current research, denmark, greenland. cover photographs from left to right 1. small-scale miner with gold concentrate. photograph: peter w.u. appel. 2. work at the microscope. photograph: peter k. warna-moors. 3. many survey employees are engaged in laboratory work. photograph: peter k. warna-moors. 4. development of geological models is becoming increasingly important. photograph: peter k. warna-moors. frontispiece: facing page in 2010 the survey carried out extensive mapping projects in the north sea. the crane is carrying a tow-fish with (1) a side-scan sonar for mapping the seabed and (2) a chirp sonar for mapping the layers below the seabed. photograph: ole bennike. chief editor of this series: adam a. garde editorial board of this series: john a. korstgård, department of earth sciences, university of aarhus; minik rosing, geological museum, university of copenhagen; finn surlyk, department of geography and geology, university of copenhagen scientific editors: ole bennike, adam a. garde and w. stuart watt editorial secretaries: jane holst and esben w. glendal referees: (dk = denmark etc.; numbers refer to first page of reviewed article): anonymous (21, 37, 41, 53, 73), niels balling, dk (49); jason box, usa (73); michele crosetto, e (41); gregers dam, dk (61); david lundbek egholm, dk (69); synnøve elvevold, n (57); ida fabricius, dk (13); rasmus fensholt, dk (81); tom frisch, cnd (69); svend funder, dk (29); rikke harlou, dk (57); jens havskov, n (49); claus heilmann-clausen, dk (61); rasmus jakobsen, dk (45); john a. korstgård, dk (53, 77); gunnar larsen, dk (45); nicolaj krog larsen, s (33); kaj lax, s (77); ole bjørslev nielsen, dk (17); bent odgaard, dk (29); odleiv olesen, n (81); asger ken pedersen, dk (65); gunver krarup pedersen, dk (17); sandra piazolo, s (65); peter sandersen, dk (25); ulf sivhed, s (9); inga sørensen, dk (21); jette sørensen, dk (25); svend stouge, dk (9); szymon uścinowicz, pl (37); ole v. vejbæk, dk (13); jacob clement yde, n (33). illustrations: stefan sølberg, with contributions from jette halskov, eva melskens and benny m. schark layout and graphic production: annabeth andersen printers: rosendahls . schultz grafisk a/s, albertslund, denmark manuscripts received: 21 december 2010 – 6 may 2011 final versions approved: january–may 2011 printed: 15 july 2011 issn 1603-9769 (review of survey activities) issn 1604-8156 (geological survey of denmark and greenland bulletin) isbn 978-87-7871-313-1 citation of the name of this series it is recommended that the name of this series is cited in full, viz. geological survey of denmark and greenland bulletin. if abbreviation of this volume is necessary, the following form is suggested: geol. surv. den. green. bull. 23, 84 pp. available from geological survey of denmark and greenland (geus) øster voldgade 10, dk-1350 copenhagen k, denmark phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: geus@geus.dk and at www.geus.dk/publications/bull © de nationale geologiske undersøgelser for danmark og grønland (geus), 2011 for the full text of the geus copyright clause, please refer to www.geus.dk/publications/bull 3 44 ghana uganda tanzania mozambique greenland united kingdom norway faroe islands kenya spain sweden denmark bahrain belgium angola democratic republic of the congo cameroun ethiopia nigeria bolivia brazil togo mauritius malawi namibia botswana lesotho south africa zimbabwe zambia yemen swaziland seychelles germany the netherlands 7 review of survey activities 2010 f.g. christiansen 9 shale gas investigations in denmark: lower palaozoic shales on bornholm n.h. schovsbo, a.t. nielsen, k. klitten, a. mathiesen and p. rasmussen 13 mapping porosity anomalies in deep jurassic sandstones – an example from the svane-1a area, danish central graben t. abramovitz 17 differentiation of palaeogene sand by glauconitic and geochemical fingerprinting, siri canyon, danish north sea m. olivarius, c. knudsen and j.b. svendsen 21 geological characterisation of potential disposal areas for radioactive waste from risø, denmark p. gravesen, m. binderup, b. nilsson and s.a.s. pedersen 25 a digital, spatial, geological model of the miocene in jylland, denmark m. kristensen, t. vangkilde-pedersen and e.s. rasmussen 29 a new middle pleistocene interglacial sequence from måløv, sjælland, denmark o. bennike, e. lindgård, h.j. granat, r.c. preece and f. viehberg 33 mapping of raw materials and habitats in the danish sector of the north sea j.b. jensen, s. borre, j.o. leth, z. al-hamdani and l.g. addington 37 postglacial, relative shore-level changes in lillebælt, denmark o. bennike and j.b. jensen 41 detection of terrain changes in southern denmark using persistent scatterer interferometry s.a.s. pedersen, g. cooksley, m. gaset and p.r. jakobsen 45 does road salt affect groundwater in denmark? s.m. kristiansen, f.d. christensen and b. hansen 5 vietnam phillipines india 49 comprehensive nuclear-test-ban treaty – a peace-keeping initiative with scientific impact t.b. larsen, p.h. voss, t. dahl-jensen and s. gregersen 53 free, online danish shallow geological data m. hansen and b. pjetursson 57 remnants of mesoarchaean oceanic crust in the tartoq group, south-west greenland k. szilas, v.j. van hinsberg, a.f.m. kisters, t.f. kokfelt, a. scherstén and b.f. windley 61 palaeogene deposits in north-east greenland h. nøhr-hansen, l.h. nielsen, e. sheldon, j. hovikoski and p. alsen 65 analysis of palaeogene strike-slip tectonics along the southern east greenland margin (sødalen area) p. guarnieri 69 kennedy channel and its geophysical lineaments: new evidence that the wegener fault is a myth t.m. rasmussen and p.r. dawes 73 programme for monitoring of the greenland ice sheet (promice): first temperature and ablation records d. van as, r.s. fausto and the promice project team 77 dodex – geoscience documents and data for exploration in greenland p. riisager, m. pedersen, m.s. jørgensen, f. schjøth and l. thorning 81 quality control of airborne geophysical data from the eu mining sector support programme, ghana t.m. rasmussen, l. thorning, a.v. olesen and f. schjøth geus working areas 2010. orange areas are covered in this volume. for further information on other working areas please refer to our website: www.geus.dk/international 66 7 2010 was a good and stable year for the geological survey of denmark and greenland (geus) with focus on research, often in international collaboration. despite the continued effects of the international financial crisis, which has had serious implications for many of our national and international partners, geus has had a period with many new projects and successful completion of many projects. this is also ref lected in the present eighth annual issue of review of survey activities which describes selected projects that geus and its partners carry out in denmark, greenland and internationally. together with the previous seven published issues, it provides a good overview of the survey’s range of research and advisory activities. it contains a total of 19 four-page papers: 12 on denmark, six on greenland, and one project in ghana. energy policy is again high on the political agenda in denmark. the government presented a new energy 2050 strategy with strong emphasis on the reduction of co 2 emission. the strategy depends on a stable supply of and income from oil and gas in the north sea during a long transition period before most of denmark’s energy supply becomes co 2 neutral, competitive and stable. geus’ research lies within a variety of different aspects of energy as well as of climate development, climate monitoring and adaptation to climate changes. three papers concentrate on various aspects of petroleum geology in denmark. one of them provides an overview of a core-drilling project in lower palaeozoic shales on bornholm as an unconventional shale gas resource analogue. another paper describes mapping of very deep jurassic targets in the svane-1 area in the north sea, and a third paper gives a geochemical fingerprinting of palaeogene reservoir sands from the siri canyon in the north sea and discusses the implications from being able to distinguish between in situ and mobilised sand. geus works on many other aspects of the geology of denmark, such as groundwater, climate and the environment including issues where geology is important to society. seven papers ranging from applied geology to more basic research are found in this volume. decisions on disposal of danish lowand intermediate-level radioactive waste have to be taken in the coming years, and a number of key geological parameters are used for the final selection of a permanent depository. the work has resulted in the selection of 22 areas, of which six are preferred. the miocene succession in jylland contains several large groundwater bodies, and a 3d model is important for future planning; this is described in another paper. with a continued need for raw materials to large infrastructure projects, systematic mapping and understanding of available marine resources are important. the results from a project in the north sea carried out for the danish nature agency are presented in one paper. two papers describe basic research on a new pleistocene interglacial sequence from sjælland and on postglacial relative shore-level changes in lillebælt. another paper presents results of the detection of terrain changes using satellite data with south-western jylland as a case. one paper discusses how sensitive the groundwater quality in denmark is to the use of road salt in winter. the danish contribution to the nuclear-test-ban treaty is also described, demonstrating how useful the data from the monitoring systems are for understanding earthquakes. in 2010, there was a high level of field activities in greenland. in addition to major projects in southern west greenland, south-east greenland and north-east greenland there were many smaller activities in other areas. the work in southern west greenland continued, and results are described in a paper on the tartoq group, a possible very old slab of oceanic crust. field work and shallow core drilling in north-east greenland continued in 2010. in this issue results on previously almost unknown palaeogene sand are presented, including new critical information on age and depositional environment. structural data from the sødalen area in southern east greenland are presented in a paper that concentrates on unravelling the strike-slip tectonics in palaeogene time. one paper adds additional evidence from magnetic data contrareview of survey activities 2010 flemming g. christiansen deputy director © geus, 2010. geological survey of denmark and greenland bulletin 23, 7–8. open access: www.geus.dk/publications/bull 88 dicting the existence of a major structural feature (the wegener fault) in the kennedy channel between north greenland and ellesmere island in canada. studies of the ice sheet and glaciers in greenland have attracted international interest over many years due to the possible implications of a rising sea level. geus is involved in many glaciological and meteorological projects and monitoring programmes. one paper gives a presentation on the large-scale programme for monitoring of the greenland ice sheet (promice) with description of the weather station network and preliminary temperature data. easy access to comprehensive and updated information and data is a very important part of the work geus carries out in denmark and greenland. this is the topic of two papers, one on free, online danish geological data where the jupiter database currently includes information from more than 260 000 shallow wells. the other paper gives a description of dodex (geoscience documents and data for exploration in greenland), which is an interactive web application, which gives the public and mining companies easy access to all non-confidential reports relevant to mineral exploration. internationally geus works in many different countries with many project types. the last paper in this issue is about work in ghana where geus has been active for many years with capacity building and geological and geophysical projects. the paper gives an overview of quality control of airborne geophysical data. geological survey of denmark and greenland bulletin 28, 2013, 9-12 9 drowning of the miocene billund delta, jylland: land–sea fluctuations during a global warming event erik skovbjerg rasmussen, torsten utescher and karen dybkjær lower miocene strata from boreholes and, in particular, at outcrops in the lillebælt and limfjorden areas of jylland provide a natural laboratory for studying the drowning of a major delta system during a period of global warming. detailed studies of sedimentary structures, fossil algae, spores and pollen give information about depositional environments, local temperatures and precipitation. by comparing with the global climatic record from the same period, a detailed reconstruction of the flooding of a low-relief delta system can be made, with emphasis on the global warming after the glacial event mi1a. the local temperature increase following the mi1a event is estimated to be c. 5°c. the billund delta during the early miocene, a delta system prograded into the eastern part of the north sea (fig. 1), with a sediment source in present-day norway and central sweden. for more than 100 million years, the eastern north sea was a relatively deep basin, but due to tectonism associated with the alpine orogeny and the opening of the north atlantic both the hinterland and the marginal areas of the basin were uplifted during the latest oligocene – early miocene (e.g. knox et al. 2010). inversion tectonism in the norwegian–danish basin resulted in shallower water depths of c. 100 m in the eastern north sea. contemporaneous uplift of the norwegian mountains provided a high sediment supply sourcing a major delta system prograding southwards into the north sea region. the delta front was shaped by wave action, similar to the present-day nile and danube deltas (bhattacharya & giosan 2003), with a size comparable to the latter. spit and barrier systems formed east of the main delta lobes (fig. 1) due to the prevailing westerly winds in the north sea area at that time. from the geological record, it is seen that the delta system prograded as far south as present-day southern jylland (fig. 1a). drowning of the land the depositional environments of the billund delta system are reconstructed from sedimentological studies (figs 1, 2). during the maximum extent of the delta, most of present-day jylfig. 1. palaeogeographic reconstruction of the early miocene in the eastern part of the north sea basin. a: billund formation during maximum regression. b: klintinghoved formation during initial transgression (kolding fjord member). c: klintinghoved formation during maximum transgression. modifided from rasmussen et al. 2010. © 2013 geus. geological survey of denmark and greenland bulletin 28, 9–12 . open access: www.geus.dk/publications/bull 100 km 100 km vonsild rønshoved hagenør hostrup gyldendal vester thorsted b c 100 km a jyllandjylland north seanorth sea lillebæltlillebælt 1010 land was covered by braided f luvial channels and f lood-plain environments (fig. 1a). in the late stage of delta progradation, the delta plain was irregular due to topographic elements formed associated with falling sea level, i.e. down-stepping delta platforms and incisions, and due to minor inversion of the basin (e.g. rasmussen et al. 2010). during later f looding, most of the deposits were redistributed by the action of waves. mud and fine-grained sand were winnowed away and transported into the deeper sea, whereas coarse-grained sand and gravel were reworked and redeposited locally. therefore, a widespread lag of gravel caps the shoreface sand of the underlying billund formation (fig. 3a, c). intense wave action on the main delta system shed sand towards the east, resulting in the formation of spit and barrier systems in eastern jylland (fig. 1b); lagoons and tidal f lats developed north of these systems. both shoreface and lagoonal deposits accumulated in a depositional setting dominated by waves. the shoreface sand is dominated by hummocky and swaley, cross-stratified sand, and the lagoonal mud is commonly intercalated with washover fans (fig. 3b). from the sedimentary record, it is seen that the initial drowning of the billund delta system was characterised by f looding and re-establishment of land in two phases (fig. 2), which only inf luenced the distal part (tens of kilometres) of the delta plain. transgressive deposits up to 15 m thick are found at localities around lillebælt, rønshoved and hagenør (fig. 2). at hagenør, two stacked lagoonal mud units separated by shoreface sand show that relatively stable barrier systems were established twice during the transgression (figs 2, 3b). during the main f looding, the low-relief delta plain (similar present-day delta systems have gradients of c. 1/20  000) was f looded relatively quickly, and only up to c. 1 m of transgressive sediments were deposited, e.g. at hostrup (figs 2, 3c). at this locality, the relatively rapid changes in depositional environment during the main transgression are seen from the coexistence of the marine trace fossil ophiomorpha and rootlets (schaubcylendrichnus; fig. 3c). from studies of global sea-level changes in the early miocene, it appears that sea-level variations in the order of 25 m occurred during the mi1a event (miller et al. 2005). this change in sea level resulted in rapid progradation during the sea-level fall. the succeeding f looding can be followed for c. 75 km towards the north-east in the danish area (fig. 1c). maximum f looding has not been documented at any outcrop in denmark, but the sedimentary succession at hostrup indicates that the shoreline was located not far from this locality at any time because the marine mud of the klintinghoved formation is strongly inf luenced by terrestrial matter throughout the section. most of the 25 m of sea-level change must be explained by the 15 m transgressive deposits found at rønshoved and hagenør (compaction can be ignored in sorted shoreface sand) in the southern part of the delta system where some relief was created during the sea-level fall and lowstand. additional 5 m of relief of the main delta calculated from 75 km of f looding gives a total of 20 m of transgressive deposits. as the sea-level changes were in the order of 25 m (miller et al. 2005), the remaining 5 m can be ascribed to more or less stable conditions for a period (aggradation of the system) or waning of the inversion tectonism. in the upper part of the hostrup and gyldendal sections, the fig. 2. correlation panel of the lillebælt area and limfjorden. depositional environments mud sand gravel lithology in borehole datum top billund offshore sand shoreface sand barrier island sand marine mud klintinghoved fm kolding fjord mb billund fmbillund fm washover flat sand and mud lagoonal clay 0 gyldendal 5 m hostrup 0 5 m 0 5 m hagenør 0 5 10 m rønshoved (east) psa nd c l si vonsild 100 90 80 m b.s.l.m b.s.l. gamma ray log vester thorsted gamma ray log psa nd c l si psa nd c l si psa nd c l si 170 160 150 140 sse nnw 11 increased intercalation of hummocky, cross-stratified sand layers indicates resumed progradation of the shoreline. climate and vegetation change changes in continental climate and vegetation in the study area around the mi1a glacial event and the subsequent drowning of the billund delta system were reconstructed from pollen and spores (fig. 4). although terrestrial signals are commonly diluted in marine strata due to transport and reworking, our data show close correlation with the evolution recorded in the marine part. climate reconstruction using the ‘coexistence approach’ of mosbrugger & utescher (1997) shows distinct cooling during the formation of the billund delta and the sealevel lowstand that culminated at c. 164 m in the vester thorsted well (fig. 4). this is followed by warming that coincides with sea-level rise and drowning of the delta system. the cooling event is characterised by declining winter temperatures, with a fall of c. 5°c mean temperature in the coldest month. summer temperatures were stable to begin with, but later increased during progressive transgression (hagenør sample). the palynomorph record points to humid conditions with over 1000 mm annual rainfall over the time span analysed. the precipitation was not equally distributed throughout the year but showed distinct seasonality (cf. monthly precipitation records, fig. 4). the monthly means indicate that cooling was accompanied by declining precipitation during the wettest season and hence to a lesser degree of seasonal rainfall. fig. 3. photographs of lithologies of the outcrops of the billund and klintinghoved formations. a: shoreface deposits from rønshoved. note the gravel layer, the base of which forms the lower part of the klintinghoved formation. b: lagoonal deposits from hagenør. note that sand-rich washover fans dominate the upper part. c: transgressive sand and marine mud of the klintinghoved formation at hostrup. the lag of gravel at the base of the klintinghoved formation is seen in the lower part of the photograph. both rootlets and marine trace fossils are found in the sand-rich deposits. o: ophiomorpha, sch: schaubcylindrichnus (rootlets). fig. 4. climate records and synthesised pollen diagram for depth range 149–173 m of vester thorsted borehole. results obtained from lagoonal silts deposited in the trangressive phase of sequence c are shown on top. the lagoonal silts were sampled in the nearby hagenør outcrop. cmt: cold month mean, mat: mean annual temperature, wmt: warm month mean, mpdry, mpwarm, mpwet: mean precipitation of the driest, warmest and wettest month. a b ca o b c lag gravel rootletslagoon shoreface lagoon washover flat lag gravel billund fm billund fmbillund f rootletslagoon shoreface lagoon washover flat rootletslagoon shoreface lagoon washover flat o o sch sch 25 cm25 cm o o billund fm billund fm lag gravellag gravel 150 155 160 165 170 175 -5 0 5 10 15 20 25 30 temperature (°c) d ep th (m ) 1: pinus 2: far distance/alt. elements 3: lacustrine 4: swamp forest 5: coastal shrub 6: alluvial wetland vegetation 7: deciduous forest 8: evergreen forest/shrub 9: conifer forest 10: zonal herbs 11: ferns 0 25 50 75 100 palynomorph associations (%) 3000 50 100 150 200 250 precipitation (mm) vester thorsted hagenør cmt mat wmt mpdry mpwarm mpwet 1212 in the warmer climate reconstructed higher up in the transgressive systems track (sample hagenør), the region received more precipitation in the warm season. the palynomorph record also allows us to follow the evolution of continental ecosystems triggered by climate and sea-level change. the synthesised pollen diagram (fig. 4) shows frequency variations of groups ref lecting regional to local biomes. pollen groups 1 and 2 comprise the pine family that includes many prolific pollen producers. association 1 mainly comprises pine, but in the hagenør sample small percentages of cedar and cathaya are also seen. the latter, monotypic genus occurs today as an endemic relict in central china. other members of pinaceae such as abies, picea and larix (group 2), frequently referred to vegetation of higher altitudes, are not important in the spectra (<3.5%). pine pollen can be dispersed over long distances and are relatively enriched in open marine palynomorph spectra (e.g. larsson et al. 2011). the overall declining trend of pine pollen recorded in the vester thorsted samples (from 45% at the base to 25% at 160 m) traces the falling sea-level and increased terrigenous input during the formation of the delta. the high pine pollen value for hagenør (>50%) coincides with the rising sea-level of the transgressive phase. lacustrine group 3, comprising lacustrine plankton, pteridophyte and angiosperm limnophytes, reaches its highest values (c. 5%) during the cooling event (at 164 m) and probably marks the most proximal conditions, together with fern group 11 that is frequent at the levels immediately above. these components originate from the local vegetation found on unstable, alluvial deposits on the delta plain. two groups of palynomorphs (4 + 5) that probably represent the vegetation of coastal swamps attain very high proportions during delta formation and show a distinct increase from c. 40 to over 55% which allows us to trace the ongoing regression. low values at hagenør (c. 10%) indicate that coastal swamps drowned as sea level rose. the arboreal vegetation on the coastal swamps comprises taxodioids (taxodium, sciadopitys and other cupressaceae), with ericaceae and myricaceae representing the shrub layer. pollen from alluvial wetland vegetation (6) play a minor role in the spectra and indicate a lack of widespread riverine forests, whereas palynomorphs usually assigned to zonal vegetation (groups 7–10) are present with 10 to 15% as permanent background. the zonal vegetation was a diverse, mixed conifer / broadleaved forest with evergreen and deciduous oak, magnolia, chestnut, sweetgum, members of juglandaceae, hemlock, coast redwood and palms. it is noteworthy that climate changes recorded in the section affected its generic composition. during the cool phase, between 156 and 164 m, the forest almost completely lost its broadleaved evergreen species, and thus had a more temperate aspect. concluding remarks during a global warming in the early miocene when the local temperature increased by 5°c, the billund delta system was f looded. the displacement of the shoreline was in the order of 75 km and affected the coastal vegetation. up to 15 m of alternating lagoonal and shoreface deposits were formed in the distal portion of the delta evidencing some stability in the early phase due to antecedent relief and high sediment supply. the main low-relief delta plain was, however, f looded quickly and only left c. 1 m of transgressive deposits. yearly precipitation rates were in the order of 1000 mm; the warming was accompanied by changes in seasonal patterns of rainfall so that during warmer periods there is a tendency to more summer rain. acknowledgements the nature agency centres in ribe, ringkøbing and aarhus are thanked for financial support. t.u. thanks the german science foundation (dfg) for finacial support. references bhattacharya, j.p. & giosan, l. 2003: wave-inf luenced deltas: geomorphological implications for facies reconstruction. sedimentolog y 50, 187–210. knox, r. et al. 2010: cenozoic.  in: doornenbal, j.c. & stevenson, a.g. (eds): petroleum geological atlas of the southern permian basin area, 210–223. houten, the netherlands: european association of geoscientists & engineers (eage) publications. larsson, l.m., dybkjær, k., rasmussen, e.s., piasecki, s., utescher, t. & vajda, v. 2011: miocene climate evolution of northern europe: a palynological investigation from denmark. palaeogeography, palaeoclimatolog y, palaeoecolog y 309, 161–175. miller, kg., kominz, m.a., browing, j.v., wright, j.d., mountain, g.s., katz, m.e., sugarman, p.j., cramer, b.s., christie-blick, n. & pekar, s.f. 2005: the phanerozoic record of global sea-level changes. science 310, 1293–1298. mosbrugger, v. & utescher, t. 1997: the coexistence approach: a method for quantitative reconstructions of tertiary terrestrial palaeoclimate data using plant fossils. palaeogeography, palaeoclimatolog y, palaeoecolog y 134, 61–86. rasmussen, e.s., dybkjær, k. & piasecki, s. 2010: lithostratigraphy of the upper oligocene – miocene succession in denmark. geological survey of denmark and greenland bulletin 22, 93 pp. authors’ addresses e.s.r. & k.d., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: esr@geus.dk t.u., steinmann institute, university of bonn, nußallee 8, 53115 bonn; senckenberg research institute / bik f, senckenberganlage 25, 60325 frankfurt/ main, germany. mailto:hl@geus.dk geological survey of denmark and greenland bulletin 6, 67-76 67geological survey of denmark and greenland bulletin 6, 67–76 © geus, 2004 reconnaissance pb-pb dating of single mineral phases by the step-leaching method: results from the caledonides of east greenland kristine thrane reconnaissance pb-pb step-leaching analyses have been carried out on garnet and kyanite from the krummedal supracrustal sequence in east greenland, yielding respectively neoproterozoic and caledonian ages. these data support previous analyses suggesting that the krummedal supracrustal sequence, widespread in southern parts of the east greenland caledonides, was affected by both an early neoproterozoic and a caledonian thermal event. titanite and apatite fractions from the underlying crystalline basement rocks were analysed in order to obtain metamorphic ages, as a contrast and supplement to the numerous existing protolith ages on orthogneisses. the titanite yielded a date of 486 ± 15 ma which, if interpreted as a true age, is older than the usual range of caledonian ages in east greenland. the significance of this date is uncertain, but one possibility is that it reflects extension and subsidence taking place prior to caledonian collision. the apatite, in contrast, yielded a very young caledonian date of 392 ± 24 ma that may reflect the cooling of the basement gneisses to < 500°c subsequent to collision. keywords: caledonian, east greenland, geochronology, neoproterozoic, step-leaching geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. present address: geological institute, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. email: kthrane@geol.ku.dk the pb-pb step-leaching (pbsl) method of frei & kamber (1995) makes it possible to date a range of rock-forming minerals that are normally difficult to date due to the low parent to daughter isotope ratios. stepwise leaching of the mineral phases increases the data spread in uranogenic (207pb/204pb – 206pb/204pb) and thorogenic vs. uranogenic (208pb/204pb – 206pb/ 204pb) diagrams, and as a consequence the precision of pb/pb isochrons is improved (frei et al. 1997). another advantage of the method is that the corresponding uranogenic and thorogenic pb ratios of the different leach solutions can be observed, and a signature of pb-containing microscopic mineral inclusions revealed. leach solutions that do not follow a linear pattern in the 208pb/204pb vs. 206pb/204pb diagram reveal sources with different th/u ratio from that of the host mineral. if all the analyses fall on a linear trend in the uranogenic diagram then the mineral inclusions are in isotopic equilibrium with the host mineral. investigations by the pbsl method were undertaken on selected samples collected during the 1997 and 1998 geological survey of denmark and greenland expeditions to the kong oscar fjord region (72°–75°n) of the east greenland caledonides (henriksen 1998, 1999). the study area (fig. 1) is made up of major caledonian thrust sheets displaced westwards across foreland windows (see also higgins & leslie 2004, this volume; thrane 2004, this volume). the thrust sheets incorporate archaean and palaeoproterozoic orthogneiss complexes overlain by a thick late mesoproterozoic – early neoproterozoic metasedimentary succession known as the krummedal supracrustal sequence; the latter is structurally overlain by the neoproterozoic eleonore bay supergroup and tillite geus bulletin 6.pmd 10-02-2005, 09:5467 68 group, and lower palaeozoic rocks. these rock units have been variably reworked during the caledonian orogeny. samples in this study, pbsl analyses were carried out on garnet and kyanite from samples 426050 and 422766 of the late mesoproterozoic – early neoproterozoic krummedal supracrustal sequence (kalsbeek et al. 2000), with the objective of constraining the age of metamorphism which produced these minerals. in addition, pbsl analyses were undertaken on titanite from a garnet amphibolite (426037) and a gabbroic gneiss (426018), and on an apatite fraction from a tonalitic basement gneiss (426008). the latter three samples all derive from the crystalline basement complex underlying the krummedal supracrustal sequence (fig. 1), and the aim was to determine metamorphic ages for the mineral phases in the samples. whole-rock pb analyses were also carried out on samples 426008, 426018 and 426050. zircon grains from the crystalline basement complex in the study area analysed by ion microprobe have hitherto only yielded archaean and palaeoproterozoic magmatic ages. although the rocks form parts of caledonian thrust sheets and have undergone extensive caledonian deformation and metamorphism, so far not a single caledonian age has been obtained from zircon (thrane 2002). while caledonian k-ar mineral ages have previously been recorded from all rock types in the study area (e.g. rex & higgins 1985), the spread in ages and uncertainties inherent in the method is indicative only of a metamorphic overprint of approximately caledonian age. 27 27º nathorst landcharcot land gletscherland suess land andrée land c a le d o n ia n f o ld b el t archaean mainly gneiss complexes palaeoproterozoic mainly gneiss complexes neoproterozoic (eleonore bay supergroup) to ordovician caledonian granites post-caledonian mesoproterozoic krummedal supracrustal sequence 72º 426008 426018 426050 422766 50 km extensional fault archaean–palaeoproterozoic boundary thrust detachment 456037 ff fig. 1. simplified geological map of the study area in the east greenland caledonides, with sample localities discussed in the text. supracrustal rocks of palaeoproterozoic age in charcot land are included with the palaeoproterozoic gneiss complexes. ff, forsblad fjord. geus bulletin 6.pmd 10-02-2005, 09:5468 69 methods for the samples analysed in the present study, a 200 mm sieve fraction of each mineral separate was purified by hand-picking. the samples were digested in a series of steps using procedures documented in table 1; the method used was modified after that of berger & braun (1997) and frei et al. (1997). the purified pb was loaded on re filaments with silica gel and h 3 po 4, and the isotopic ratios analysed on the vg sector 54it instrument at the university of copenhagen. most analyses were performed using the faraday multi-collector; a few steps that contained very little pb were analysed with the single collector (ion counting daly detector). fractionation of pb was monitored by repeated analyses of the nbs 981 standard (values of todt et al. 1993) and amounted to 0.103 ± 0.016 %/ amu. the calculations of regression lines follow the method of ludwig (1999). errors quoted are 2 f. five to seven acid-leach steps were undertaken on each mineral separate. whole-rock pb and pbsl isotope data are listed in table 2 and plotted in figs 2–5. pbsl results krummedal supracrustal sequence the late mesoproterozoic – early neoproterozoic krummedal supracrustal sequence is widely distributed in the southern part of the east greenland caledonides between 70° and 74°n (fig. 1; higgins 1988). sample 426050 was collected from the krummedal supracrustal sequence south of innermost forsblad fjord, close to the faulted contact with the crystalline basement complexes (fig. 1). the general metamorphic grade of the krummedal supracrustal sequence is amphibolite facies, and the sample consists of quartz + plagioclase + k-feldspar + garnet + biotite + kyanite + sillimanite + amphibole + muscovite + titanite. the garnet and biotite represent early phases, while kyanite is a later phase that overgrows the deformation fabric of the biotite. kyanite and k-feldspar crystallised at the same time, demonstrating that the rock has been exposed to high p–t conditions; during cooling, sillimanite, titanite and secondary biotite crystallised, and part of the kyanite was consumed during formation of muscovite. garnet and kyanite were analysed by pbsl (fig. 2). seven steps were performed on the garnet; all the steps, together with the whole-rock analysis, fall on a linear array in the 207pb/204pb vs. 206pb/204pb diagram table 1. sample data stepwise dissolution procedures mix = 1.5n hbr – 2n hcl 12:1 mixture. all steps except number 1 were left on the hotplate during the dissolution time. 236 mix 10 4.4n hbr 45 8.8n hbr 3 8.8n hbr 24 conc. hf 48 conc. hf 260 8.8n hbr 290 97 mix 10 4.4n hbr 45 8.8n hbr 3 8.8n hbr 24 conc. hf 48 conc. hf 260 719 mix 30 1.0n hbr 60 4.0n hbr 3 8.8n hbr 6 8.8n hbr 12 conc. hf 24 conc. hf 340 195 mix 10 4.4n hbr 45 8.8n hbr 3 8.8n hbr 24 conc. hf 48 conc. hf 260 71 mix 10 4.4n hbr 90 8.8n hbr 3 8.8n hbr 24 conc. hf 50 conc. hf 340 139 10 60 1.0n hbr 3 1.5n hbr 3 8.8n hbr 3 7n hno 3 9 sample weight step 1 time step 2 time step 3 time step 4 time step 5 time step 6 time step 7 time mg min. min. hrs hrs hrs hrs hrs 426050 garnet 426050 kyanite 422766 kyanite 426018 titanite 426037 titanite 426008 50% mix + 50% mix + apatite 50% h 2 o 50% h 2 o geus bulletin 6.pmd 10-02-2005, 09:5469 70 table 2. pb-pb step leaching (pbsl) data sample phase step 206pb/204pb ± 2 σ* 207pb/204pb ± 2 σ* 208pb/204pb ± 2 σ* r1 r2 426050 wr 19.39 0.01 15.65 0.01 38.91 0.03 0.96 0.93 426008 wr 14.32 0.01 14.61 0.01 38.51 0.03 0.93 0.92 426018 wr 17.10 0.04 15.13 0.04 37.76 0.09 0.99 0.98 426050 grt 1 23.34 0.64 16.01 0.44 39.09 1.08 1.00 1.00 426050 grt 2 29.02 0.75 16.34 0.43 43.66 1.14 0.97 0.98 426050 grt 3 69.99 1.99 18.74 0.53 116.25 3.30 1.00 1.00 426050 grt 4 272.79 6.53 32.93 0.79 436.00 10.43 1.00 1.00 426050 grt 5 99.56 1.31 20.49 0.27 44.90 0.59 1.00 1.00 426050 grt 6 139.41 0.74 23.99 0.13 57.17 0.31 1.00 1.00 426050 grt 7 152.05 4.39 24.48 0.71 87.67 2.53 1.00 1.00 426050 ky 1 19.53 0.06 15.66 0.05 38.17 0.11 0.99 0.98 426050 ky 2 20.45 0.14 15.70 0.11 38.52 0.27 0.99 1.00 426050 ky 3 24.26 0.23 15.82 0.15 47.05 0.44 0.99 0.99 426050 ky 4 34.83 0.16 16.42 0.08 65.68 0.31 0.99 0.99 426050 ky 5 20.00 0.02 15.70 0.02 38.09 0.05 0.95 0.94 426050 ky 6 33.13 0.19 16.49 0.10 38.81 0.22 0.99 0.99 422766 ky 1 18.23 0.05 15.49 0.04 37.96 0.10 0.99 0.98 422766 ky 2 19.92 0.16 15.64 0.12 40.81 0.32 0.99 1.00 422766 ky 3 42.22 0.52 16.75 0.21 82.30 1.03 0.97 0.98 422766 ky 4 171.43 19.09 24.12 2.69 326.96 36.41 1.00 1.00 422766 ky 5 137.46 5.87 22.08 0.95 258.40 11.04 1.00 1.00 422766 ky 6 20.59 0.04 15.70 0.03 38.60 0.07 0.98 0.97 422766 ky 7 27.19 1.02 16.16 0.61 39.21 1.48 1.00 1.00 426018 tit 1 16.50 0.02 15.09 0.02 37.40 0.04 0.95 0.95 426018 tit 2 19.47 0.05 15.27 0.04 38.22 0.11 0.99 0.99 426018 tit 3 104.74 1.13 20.29 0.22 56.20 0.61 1.00 1.00 426018 tit 4 152.44 0.53 22.89 0.08 65.29 0.23 0.99 0.99 426018 tit 5 120.05 0.35 20.97 0.06 56.99 0.17 0.99 0.99 426018 tit 6 122.84 0.92 21.14 0.16 57.72 0.43 1.00 1.00 426037 tit 1 16.53 0.22 15.11 0.20 37.11 0.50 1.00 1.00 426037 tit 2 20.87 0.09 15.30 0.07 40.03 0.18 0.99 0.99 426037 tit 3 76.66 1.92 18.21 0.46 46.56 1.17 1.00 1.00 426037 tit 4 69.70 1.09 17.90 0.28 48.30 0.76 1.00 1.00 426037 tit 5 36.53 0.18 16.15 0.08 41.79 0.21 0.99 0.99 426037 tit 6 36.78 0.27 16.18 0.12 41.76 0.31 1.00 1.00 426008 apa 1 27.93 0.06 15.36 0.04 40.96 0.09 0.99 0.99 426008 apa 2 37.36 0.04 15.95 0.02 39.13 0.05 0.97 0.96 426008 apa 3 38.28 0.03 15.91 0.01 38.70 0.04 0.93 0.85 426008 apa 4 38.68 0.08 16.08 0.03 38.73 0.08 0.99 0.98 426008 apa 5 64.84 0.94 21.41 0.31 35.92 0.52 1.00 1.00 wr = whole-rock, grt = garnet, ky = kyanite, tit = titanite, apa = apatite. r1 = 206pb/204pb vs.207pb/204pb error correlation (ludwig 1988). r2 = 206pb/204pb vs.208pb/204pb error correlation (ludwig 1988). * errors are two standard deviations absolute (ludwig 1988). geus bulletin 6.pmd 10-02-2005, 09:5470 71 (3) (2) wr (6) (7) (1) (1) 426050 garnet 426050 garnet 426050 kyanite 426050 kyanite a 826 + 96 ma (mswd = 0.14) 20 7 p b / 20 4 p b (5) 0 100 200 300 c 20 7 p b / 20 4 p b 20 8 p b / 20 4 p b (3) 2010 24 28 32 36 40 70 60 50 40 30 500 400 300 200 100 0 20 8 p b / 20 4 p b all datapoints: 876 + 93 ma (mswd = 11.2) (3) (3) (4) 426050 monazite 426050 monazite e 20 7 p b / 20 4 p b 206pb / 204pb 206pb / 204pb 0 100 200 300 500 400 300 200 100 0 20 8 p b / 20 4 p b 34 38 26 30 22 14 18 10 17.0 16.2 16.6 15.8 15.4 15.0 36 28 32 24 16 20 12 (3) (5) (7) (6) (2) (1) b 0 100 200 300 (4) (2) (5) (6) (1) d (3) (4) (4) (5) (6) ▲ ▲ ▲ ▲ ▲ ▲ ▲ (2) ▲ ▲ ▲▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ wr mo na zit e t ren d garnet trend zircon trend (3) (4) (3) f 0 100 200 300 (4) wr ▲wr garnet kyanite (4) (4) 2010 24 28 32 36 40 901 + 42 ma (mswd = 1.86) fig. 2. uranogenic (207pb/204pb – 206pb /204pb) and thorogenic vs. uranogenic (208pb/204pb – 206pb /204pb) pb isotope diagrams with pbsl data from step-leaching experiments on garnet (a, b) and kyanite (c, d), from mica schist sample 426050 (krummedal supracrustal sequence). e and f are steps representing monazite inclusions within the garnet and kyanite. geus bulletin 6.pmd 10-02-2005, 09:5471 72 (fig. 2a) yielding a 207pb/206pb date of 876 ± 93 ma (mswd = 11.2). the 208pb/204pb vs. 206pb/204pb diagram (fig. 2b) reveals the presence of mineral inclusions in the garnet. the different th/u ratios of the host mineral and the inclusions may explain the large mswd value of the errorchron. steps 3 and 4 have very high th/u ratios, interpreted as representing monazite inclusions (th/u > 3; dewolf et al. 1996). all the monazite is leached out in step 4, causing the observed drop in the th/u ratio. the very low th/u ratio in steps 5 and 6 is characteristic of zircon leach steps (th/u < 1; dewolf et al. 1996). all the zircon is dissolved in step 6. step 7 was undertaken because of the red colour of the residue after step 6, showing that garnet was still present. the only leach steps dominated by garnet are the two first, where all the most primitive pb is extracted, and step 7. these three steps together with the wholerock analysis yield an isochron date of 826 ± 96 ma (mswd = 0.14). the large error of the date is due to the low precision of step 7. the same procedure was carried out on kyanite, and again there is evidence for the presence of both monazite and zircon inclusions (fig. 2d). steps 3 and 4 are dominated by monazite, and step 6 by zircon. three steps (1, 2 and 5) are interpreted as representing kyanite, but while the individual analyses are very precise they do not form a sufficiently wide spread in the pb ratios to yield a precise date. the pb wholerock analysis and the kyanite-dominated steps define a slope which yields an isochron date of 1219 ± 790 ma (mswd = 0.24). given the large uncertainty, this date does not yield any useful chronological information. the monazite-dominated steps from the garnet (3 and 4) and the kyanite (3 and 4) plot on a linear trend in both the 207pb/204pb vs. 206pb/204pb and 208pb/ 204pb vs. 206pb/204pb diagrams (fig. 2e, f). the four monazite steps yield an isochron date of 901 ± 42 ma (mswd = 1.86). the monazite and garnet dates are in general accordance with the ion microprobe analyses of metamorphic zircon rims from the krummedal supracrustal sequence that have yielded neoproterozoic ages around 940 ma (thrane et al. 1999a, b; kalsbeek et al. 2000). the cores of detrital zircons from the same study yielded ages ranging from c. 1100 to 1900 ma, and it therefore serves no practical purpose to calculate an age from the zircon steps, as these will represent a mixture of ages. sample 422766, also derived from the krummedal supracrustal sequence, was collected by j.c. escher and k.a. jones in the southern part of andrée land, very close to the contact with the structurally underlying crystalline basement (fig. 1). the sample contains garnet and kyanite crystals up to 5 cm in diameter. the kyanite was analysed by pbsl, while the garnet was considered too altered to justify analysis. seven steps were undertaken on the kyanite, and the analyses represent an almost perfect leaching pattern (fig. 3); all fall on a linear array in both the 207pb/204pb vs. 206pb/204pb and 208pb/204pb vs. 206pb/204pb diagrams, except for step 7 which has a lower 208pb/204pb ratio that probably indicates the presence of zircon inclusions. a 207pb/206pb date of 437 ± 62 ma (mswd = 2.6) is obtained using all the steps, while if step 7 is excluded a date of 445 ± 58 ma (mswd = 3.2) is obtained. the large error is due to the analytical error of steps 4 and 5. (3) (7) (2) (6) (1) (3) (7) (2) (6)(1) 422766 kyanite 28 24 20 16 12 a 445 + 58 ma (mswd = 3.2) 20 7 p b / 20 4 p b (5) (4) 0 40 80 120 160 200 240 422766 kyanite 400 300 200 100 0 b 20 8 p b / 20 4 p b (5) (4) 0 40 80 120 160 200 240 206pb / 204pb fig. 3. uranogenic (207pb/204pb – 206pb /204pb) and thorogenic vs. uranogenic (208pb/204pb – 206pb /204pb) pb isotope diagrams with pbsl data from step-leaching experiments on kyanite, from mica schist sample 422766 (krummedal supracrustal sequence). geus bulletin 6.pmd 10-02-2005, 09:5472 73 crystalline basement the east greenland caledonian orogen is dominated by major thrust sheets of reworked orthogneiss complexes. the crystalline basement is divided into an archaean terrain to the south of 72°50′n and a palaeoproterozoic terrain to the north (fig.1; thrane 2002). pbsl analyses on titanite from a metagabbroic gneiss (426018) in the archaean crystalline basement complex west of innermost forsblad fjord (fig. 1) were undertaken. this gabbroic gneiss has yielded a smnd model age (t dm ) of 3.25 ga (thrane 2002). the whole-rock analysis has the same pb ratios as step 1, indicating that the whole-rock and titanite are in equilibrium. the six leach steps together with the wholerock analysis yield an isochron date of 504 ± 48 ma (mswd = 1.81). however, the 208pb/204pb vs. 206pb/ 204pb diagram (fig. 4b) suggests that the titanite contains small amounts of monazite inclusions, which result in slightly elevated th/u ratios for steps 3 and 4 compared with the titanite trend. if steps 3 and 4 are excluded, an isochron date of 486 ± 15 ma (mswd = 0.16) is obtained (fig. 4a). titanite from a sheared garnet amphibolite (426037) cutting the basement gneisses of nathorst land (fig. 1) was also analysed. all six data points define an isochron date of 335 ± 140 ma (mswd = 0.11; fig. 4c); the large error of the date is due to the limited spread in the data points, as well as the large analytical errors of steps 3 and 4. in the 208pb/204pb vs. 206pb/ 204pb diagram (fig. 4d) the analyses show an unusual (3) (2) (wr) (6) (1) (1) 426018 titanite 426037 titanite a 486 + 15 ma (mswd = 0.16) all steps: 335 + 140 ma (mswd = 0.11) 20 7 p b / 20 4 p b (5) 0 40 80 120 160 200 c 20 7 p b / 20 4 p b 206pb / 204pb 206pb / 204pb 20 8 p b / 20 4 p b (3) 4010 50 70 90 50 46 42 33 34 70 60 50 40 30 20 8 p b / 20 4 p b (4)23 25 19 21 17 15 13 19 20 17 18 16 15 14 0 20 40 60 80 100 (3) (2) wr (6) (1) b (5) 0 40 80 120 160 200 (4) 426018 titanite (3) (2) (6) (1) d (5) (4) 426037 titanite (4) (5) (6) ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ (2) ▲ ▲ ▲ ▲ fig. 4. uranogenic (207pb/204pb – 206pb /204pb) and thorogenic vs. uranogenic (208pb/204pb – 206pb /204pb) pb isotope diagrams with pbsl data from step-leaching experiments on titanite from a gabbroic gneiss in the basement (a, b; sample 426018) and a garnet amphibolite (c, d; sample 426037). geus bulletin 6.pmd 10-02-2005, 09:5473 74 pattern: step 2 has an elevated th/u ratio compared to the general trend while step 3 has a lower th/u ratio. these features cannot be explained by the presence of monazite and zircon inclusions. if steps 2 and 3 are excluded from the isochron an even less precise date of 309 ± 230 ma (mswd = 0.03) is obtained. apatite from a tonalitic basement gneiss (426008) collected west of innermost forsblad fjord (fig. 1) was also analysed. zircon crystals from this sample have yielded u-pb ages of c. 2800 ma (thrane 2002). apatite dissolves much more easily than silicate phases, so a weaker acid and shorter leaching times were used in this experiment. the analyses form a complex pattern (fig. 5). step 1 is too thorogenic to derive from apatite, and it is interpreted instead as influenced by allanite since this is very easily dissolved and has a higher th/u ratio than apatite. step 2 is less thorogenic than step 1, but more so than step 3, and is therefore interpreted as a mixture between allanite and apatite. step 3 is the only step dominated by apatite. the only possible way to obtain a date is thus by combining the whole-rock analysis and step 3, which yields a date of 392 ± 24 ma (fig. 5a). step 1 falls on the isochron, while step 2 falls slightly above, demonstrating that the two mineral phases were almost in equilibrium, with the presumed allanite being slightly older corresponding to its higher closure temperature. in the 208pb/204pb vs. 206pb/204pb diagram it seems that both steps 3 and 4 are apatite steps, but in the 207pb/ 204pb vs. 206pb/204pb diagram it is clear that step 4 is older and must be influenced by zircon inclusions which were leached out in the strong acid of step 5. the whole-rock analysis and step 5 yield a date of 2159 ± 46 ma. summary and discussion the analyses reported in this paper are the first pbsl analyses reported on rocks from the caledonian orogen of east greenland. all the samples have been analysed only once. several of the dates obtained are not consistent with existing ages from the area, and some of the new dates are also somewhat controversial; replicate analyses should therefore be made for all the samples, to confirm that the dates are consistent, before any definite interpretations can be made. thus different interpretations are presented in the discussion that follows. the reliability of the pbsl method is still an open question. the main concern is the importance of the micro-inclusions contained in the mineral being analysed, and whether it is possible to be certain which combination of minerals is dissolved and affect the individual steps. this important point has not yet been resolved, and must be kept in mind when evaluating the new dates. supracrustal rocks the pbsl study demonstrates that neoproterozoic monazite and garnet are present in the krummedal supracrustal sequence; evidence of caledonian monazite has previously been reported (kalsbeek et al. 2000). zoned garnets have often been recorded (elvevold & gilotti 1999; thrane et al. 1999b), of which 23 23 19 17 15 13 a 426008 apatite 392 + 24 ma 20 7 p b / 20 4 p b 42 40 38 36 34 b 426008 apatite 20 8 p b / 20 4 p b 206pb / 204pb (wr) (wr) (1) (2) (5) (4) (3) (1) (2) (3) (4) (5) 0 20 40 60 70 0 20 40 60 70 fig. 5. uranogenic (207pb/204pb – 206pb /204pb) and thorogenic vs. uranogenic (208pb/204pb – 206pb /204pb) pb isotope diagrams with pbsl data from step-leaching experiments on apatite from a tonalitic basement gneiss (sample 426008). geus bulletin 6.pmd 10-02-2005, 09:5474 75 the outer rims are interpreted to be caledonian whereas there has previously been doubt as to whether the cores were neoproterozoic or early caledonian. in contrast, the presence of neoproterozoic kyanite has not been demonstrated in this study. petrographically it is often difficult to determine to which mineral paragenesis the kyanite belongs, and thus it cannot be ruled out that some of the kyanite in parts of the krummedal supracrustal sequence may be neoproterozoic (elvevold & spears 2000). evidence of early caledonian metamorphism in the crystalline basement? the closure temperature for titanite is estimated by dahl (1997, and references therein) to be in the range of 620–680°c, and by cherniak (1993) in the range of 575–707°c, depending on the grain size. the titanite date of 486 ± 15 ma for sample 426018, together with the date of the monazite inclusions, suggest that the crystalline basement did experience caledonian medium to high-grade metamorphism. no other ages of c. 486 ma have yet been obtained in east greenland. the age of the caledonian collision in east greenland is usually referred to the interval 430–425 ma, on the basis of zircon ages from granite intrusions and the time of migmatite formation in the krummedal supracrustal sequence (watt et al. 2000; kalsbeek et al. 2000, 2001). no comparable zircon ages have been recorded in the crystalline basement rocks in the study area, where evidence of the caledonian overprint is restricted to imprecise lower concordia intercept ages ranging from 467 ± 18 ma to 443 ± 25 (thrane et al. 1999a). it is not possible to determine whether these lower intercept ages correspond to the ‘traditional’ east greenland caledonian range of events, or to a potential earlier event. in north-east greenland caledonian zircons have been recorded in some palaeoproterozoic gneisses (kalsbeek et al. 1993), which is in line with the assumption that the crystalline basement complexes of this northern region were more strongly reworked during the caledonian orogeny. it might be speculated that the titanite date of 486 ± 15 ma is a cooling age, while the slightly older monazite micro-inclusions in the titanites could represent the peak of a collision event – comparable to the early caledonian event in scandinavia (mørk et al. 1988; andréasson 1994, 2000). however, this is not possible in east greenland, since ordovician carbonates were still being deposited in the iapetus-margin basin that lay east of the laurentian crystalline basement at this time; there is no associated clastic input that would be expected if a collision had taken place nearby. the exceptionally thick ordovician carbonate succession in east greenland (smith 1991) is indicative of a significant increase in the rate of subsidence, and it is possible that the c. 500 and 486 ma dates are instead related to extension. the c. 430 ma ages are thus still the best indication of the main caledonian collision phase in east greenland. apatite, yielding the youngest caledonian date of 392 ± 24, could be interpreted to represent the time where the basement gneisses cooled to < 500°c (dahl 1997). acknowledgements the isotope data described in this paper were acquired at the geological institute, university of copenhagen. robert frei is thanked for introducing and guiding me in the pb-pb step-leaching method. jan c. escher and kevin a. jones kindly provided sample 422766. critical comments on the manuscript by adam a. garde, a.k. higgins and feiko kalsbeek are greatly appreciated. this project was based on funding from the danish natural science research council. minik rosing and martin whitehouse are thanked for reviewing the manuscript. references andréasson, p.g. 1994: the baltoscandian margin in neoproterozoic – early palaeozoic times. some constraints on terrane derivation and accretion in the arctic scandinavian caledonides. tectonophysics 231, 1–32. andréasson, p.g. 2000: finnmarkian deep-seated imbrication of a margin of baltica: evidence from high-grade deformation zones in the kebnekaise mts., swedish caledonides. 24. nordiske geologiske vintermøte, trondheim, norway, 6–9 january, 2000. abstract volume. geonytt 1, 32 only. berger, m. & braun, i. 1997: pb-pb dating of apatite by a stepwise dissolution technique. chemical geology 142, 23–40. cherniak, d.j. 1993: lead diffusion in titanite and preliminary results on the effects of radiation damage on pb transport. chemical geology 110, 177–194. dahl, p.s. 1997: a crystal-chemical basis for pb retention and fission-track annealing systematics in u-bearing minerals, with implications for geochronology. earth and planetary science letters 150, 277–290. dewolf, c.p., zeissler, c.j., halliday, a.n., mezger, k. & essene, e.j. 1996: the role of inclusions in u-pb and sm-nd garnet geus bulletin 6.pmd 10-02-2005, 09:5475 76 geochronology: step-wise dissolution experiments and trace uranium mapping by fission track analysis. geochimica et cosmochimica acta 60, 121–134. elvevold, s. & gilotti, j.a. 1999: reaction history of metapelitic rocks from goodenough land, east greenland. in: frederiksen, k.s. & thrane, k. (eds): second symposium on east greenland geology, mainly caledonian. abstract volume. danmarks og grønlands geologiske undersøgelse rapport 1999/21, 31 only. elvevold, s. & spears, f.s. 2000: garnet zoning and reaction history of anatectic pelites in the east greenland caledonides. 24. nordiske geologiske vintermøte, trondheim, norway, 6– 9 january, 2000. abstract volume. geonytt 1, 62 only. frei, r. & kamber, b.s. 1995: single mineral pb-pb dating. earth and planetary science letters 129, 261–268. frei, r., villa, i.m., nagler, t.f., kramers, j.d., przybylowicz, w.j., prozesky, v.m., hofmann, b.a. & kamber, b.s. 1997: single mineral dating by the pb-pb step-leaching method: assessing the mechanisms. geochimica et cosmochimica acta 61, 393– 414. henriksen, n. 1998: north-east greenland 1997–1998: a new 1:500 000 mapping project in the caledonian fold belt (72°–75°n). geology of greenland survey bulletin 180, 119–127. henriksen, n. 1999: conclusion of the 1:500 000 mapping project in the caledonian fold belt in north-east greenland. geology of greenland survey bulletin 183, 10–22. higgins, a.k. 1988: the krummedal supracrustal sequence in east greenland. in: winchester, j.a. (ed.): later proterozoic stratigraphy of the northern atlantic regions, 86–96. glasgow and london: blackie and son ltd. higgins, a.k. & leslie, a.g. 2004: the eleonore sø and målebjerg foreland windows, east greenland caledonides, and the demise of the ‘stockwerke’ concept. in: higgins, a.k. & kalsbeek, f. (eds): east greenland caledonides: stratigraphy, structure and geochronology. geological survey of denmark and greenland bulletin 6, 77–93 (this volume). kalsbeek, f., nutman, a.p. & taylor, p.n. 1993: paleoproterozoic basement province in the caledonian fold belt of north-east greenland. precambrian research 63, 163–178. kalsbeek, f., thrane, k., nutman, a.p. & jepsen, h.f. 2000: late mesoproterozoic to early neoproterozoic history of the east greenland caledonides fold belt: evidence for grenvillian orogenesis? journal of the geological society (london) 157, 1215–1225. kalsbeek, f., jepsen, h.f. & nutman, a.p. 2001: from source migmatites to plutons: tracking the origin of ca. 435 ma s-type granites in the east greenland caledonide orogen. lithos 57, 1–21. ludwig, k.r. 1988: a computer program to convert raw u-th-pb isotope ratios to blank-corrected isotope ratios and concentrations with associated error-correlations. united states geological survey, open file report of-82-820. ludwig, k.r. 1999: isoplot/ex version 2.00: a geochronological toolkit for microsoft excel. berkeley geochronology center, special publication 2. mørk, m.b., kullerud, k. & stabel, a. 1988: sm-nd dating of seve eclogites, norrbotten, sweden – evidence for early caledonian (505 ma) subduction. contributions to mineralogy and petrology 99, 344–351. rex, d.c. & higgins, a.k. 1985: potassium–argon mineral ages from the east greenland caledonides between 72° and 74°n. in: gee, d.g. & sturt, b.a. (eds): the caledonide orogen: scandinavia and related areas, 1115–1124. chichester: john wiley & sons. smith, m.p. 1991: early ordovician conodonts of east and north greenland. meddelelser om grønland geoscience 26, 81 pp. thrane, k. 2002: relationships between archaean and palaeoproterozoic basement complexes in the southern part of the east greenland caledonides: an ion microprobe study. precambrian research 113, 19–42. thrane, k. 2004: palaeoproterozoic age of the basement gneiss complex in the charcot land tectonic window, east greenland caledonides. in: higgins, a.k. & kalsbeek, f. (eds): east greenland caledonides: stratigraphy, structure and geochronology. geological survey of denmark and greenland bulletin 6, 57–66 (this volume). thrane, k., kalsbeek, f. & watt, g.r. 1999a: evidence for a grenville event in the east greenland caledonian fold belt. in: frederiksen, k.s. & thrane, k. (eds): second symposium on east greenland geology, mainly caledonian. abstract volume. danmarks og grønlands geologiske undersøgelse rapport 1999/21, 37 only. thrane, k., watt, g.r., kinny, p.d., jones, k.a. & escher, j.c. 1999b: early neoproterozoic breakup of rodinia: sims u-pb ages from the east greenland caledonides. eug 10, terra abstracts 4, 119 only. todt, w., cliff, r.a., hanser, a. & hofmann, a.w. 1993: recalibration of nbs lead standards using a 202pb + 205pb double spike. terra abstracts 5 (supplement 1), 396 only. watt, g.r., kinny, p.d. & friderichsen, j.d. 2000: u-pb geochronology of neoproterozoic and caledonian tectonothermal events in the east greenland caledonides. journal of the geological society (london) 157, 1031–1048. geus bulletin 6.pmd 10-02-2005, 09:5476 geological survey of denmark and greenland bulletin 4, 2003, pp 97-100 97 the vietnam petroleum institute (vpi) and the geological survey of denmark and greenland (geus) have carried out a programme of geoscientific research and institutional capacity building since 1995. it has included geoscientific projects focused on assessment of the hydrocarbon potential of selected sedimentary basins, technology transfer and inhouse training at vpi in hanoi and at geus in copenhagen. co-operation is continuing within the framework of a new, long-term project that aims to strengthen research capacity in vietnam within the fields of basin analysis and modelling. history of co-operation in 1993 ccop-representatives (co-ordinating committee for geoscience programmes in east and southeast asia) visited geus to investigate the possibility of co-operation within research capacity development in the ccop-countries. the danish energy authority (dea) subsequently approved a project proposal, and the first joint project between vpi and geus was initiated in 1995. the commencement of geoscientific studies showed an urgent need for interpretation tools at vpi, and modern geological and geophysical interpretation facilities were installed at vpi in 1996 with support from the danish international development assistance (danida). following the successful completion of the first geoscientific project, dea approved funding for a second phase. the projects were accompanied by a series of ccop workshops held at vpi, and ‘on-thejob-training’ (ojt) programmes at geus for vpi geoscientists (nielsen et al. 2003). the two first geoscientific projects were aimed at an analysis of the hydrocarbon potential of the song hong basin (fig. 1). seismic interpretation, field work, stratigraphic evaluation, and assessment of results from the few exploration wells drilled in the basin were carried out (dien et al. 1997, 1998, 1999; andersen et al. 1998, 1999; nielsen et al. 1999). seismic facies analyses together with investigations of thermally immature potential source rocks at localities in the song hong basin where inversion structures expose oil-prone oligocene lacustrine mudstones and thin coals, led to the identification of areas for future hydrocarbon exploration (petersen et al. 2001, in press). the implementation of these initial projects revealed a fundamental need for enhancement of the research skills of vpi geoscientists as part of an institutional development programme. an application for a long-term geoscientific research capacity building project was submitted to danida’s enreca project in the year 2000. basin analysis and assessment of hydrocarbon potential the enreca project was approved in august 2001. the main aims were to undertake an integrated analysis and modelling of sedimentary basins in vietnam, to assess their hydrocarbon potential and to establish a geoscientific background geological survey of denmark and greenland bulletin 4, 97–100 (2004) © geus, 2004 petroleum potential of sedimentary basins in vietnam: long-term geoscientific co-operation with the vietnam petroleum institute lars henrik nielsen and ioannis abatzis fig. 1. regional map showing the prospective vietnamese cenozoic offshore basins. on which decisions concerning exploration and exploitation of hydrocarbons could be based. the studies are carried out by geoscientists from vpi and geus, with support from scientists at the hanoi university of mining and geology, vietnam and the university of copenhagen, denmark. the first phase of the project, focusing on the cenozoic phu khanh basin offshore central vietnam (fig. 1), will last for three years; long-term co-operation can be extended in up to four phases. one of the principal short-term objectives is to provide a research-driven assessment of the hydrocarbon potential of the basin. activities initiated during the first phase of the project include seismic interpretation, field work, drilling of a 500 m deep core-well, geochemical and petrographic analyses, the initiation of five vietnamese and four danish m.sc. studies, and several training courses. seismic interpretation the phu khanh basin is almost unexplored; it is covered only by an open seismic grid and no wells have yet been drilled. the cenozoic basin-fill overlies strongly faulted older sedimentary rocks and granitic basement that crop out along the present-day coastline. the basement is cut by deep, listric, eastward-dipping faults formed during rifting, which probably began during the palaeogene. the basin-fill consists of a syn-rift succession separated from the overlying post-rift succession by an unconformity that may be related to the opening of the south china sea. on seismic profiles the syn-rift wedges are characterised by continuous reflectors interpreted to represent lacustrine sediments, i.e. potential source rocks, whereas transparent zones are interpreted to represent fluvial sands (fig. 2). the middle miocene to recent post-rift succession can be divided into eight seismic sequences forming an eastwardthickening succession. the lower three sequences are thin, and their limited distribution is in part determined by structural uplift, whereas the more widely distributed overlying five sequences show distinct basinward prograding shelf-edge clinoforms. analyses of the seismic facies and geometry of the sequences suggest a variety of sandy depositional environment, such as fluvial channels, shorefaces and basin floor fans that may all form potential reservoirs for hydrocarbons generated from syn-rift lacustrine source rocks. high amplitude reflectors over structural highs are interpreted as miocene carbonate build-ups that can also form potential reservoirs. oil seeps oil seeps occurring at the basin margin have long been known from onshore coastal outcrops, but their nature has remained controversial. however, geochemical analyses of petroleum impregnation in cracks and fractures in weathered cretaceous granites, tar mats on the beach, oil on vegetation, and mud with oil from shrimp-farm basins, have shown the presence of biodegraded petroleum, with biological markers pointing to a marly source rock with some terrestrial input (bojesen-koefoed et al. 2003, 2004). the oil contains 30norhopanes characteristic of carbonate-derived petroleum, as well as oleanane, a marker of contributions from angiosperm higher land plants. the presence of petroleum in narrow fissures in freshly cleaved granite testifies to the indigenous 98 fig. 2. seismic profile of the phu khan basin. the coastal oil seeps are located immediately west of the profile and indicate an updip migration path of hydrocarbons generated from a possible kitchen in the phu khanh basin. for location, see fig. 1. nature of the oil, and an origin from oil spills is therefore unlikely. samples from shrimp basins show the presence of similar oil, although more altered by biodegradation. one sample collected from a tar mat on the beach shows characteristics similar to those of cenozoic lacustrine oils found elsewhere in vietnam, for instance in the song hong basin. the close similarity of these oils suggests that pods of prolific lacustrine petroleum source rocks may be regionally distributed. rift-lake successions and source rocks in order to investigate the formation and hydrocarbon potential of rift-lake systems associated with transtensional faulting, outcrop studies were carried out in the song ba trough supplemented by studies of a continuous core from the 500 m deep enreca-1 well. the song ba trough was formed by transtensional faulting in the onshore continuation of the tuy hoa shear zone that marks the southern boundary of the phu khanh basin (fig. 1). the outcrops expose coarsegrained sandstones and conglomerates interbedded with lacustrine mudstones and scattered coal beds. the core-well encountered 480 m of sediments, beginning with thin fluvial sandstones overlying granite. the sandstones are overlain by lacustrine mudstones interbedded with thin sandstones, whereas fluvial sandstones dominate the upper part of the core. the lacustrine mudstones contain organic matter, commonly exceeding 5 wt%, and many samples have a hydrogen index (hi) of more than 300 mg hc/g toc (total organic carbon), occasionally exceeding 700 mg hc/g toc (fig. 3). the organic matter is mainly composed of fluorescent amorphous organic matter, alginite and liptodetrinite, corresponding to type i kerogen, and may be an excellent source for oil. the results suggest that oil-prone mudstones were primarily formed in periods when the sedimentation rate was outpaced by formation of new accommodation space. significance for future exploration activities and research interpretation of the seismic profiles suggests the presence of possible reservoirs and deep-seated kitchens in the phu khanh basin. one possible kitchen is situated down-dip along a likely migration route to the oil seeps (fig. 2). thus, there is evidence that the common petroleum system found in south-east asian basins, which rely on syn-rift lacustrine mudstones and coals, is also active in the phu khanh basin. the investigated rift-lake succession in the onshore song ba trough may thus be a valid analogue for older and deeply buried syn-rift sequences in the phu khanh basin. 99 fig. 3. core log of a selected interval of the enreca-1 core-well, which penetrated a 500 m thick rift-succession of lacustrine mudstones. a significant amount of preserved organic matter indicates an excellent source rock for oil generation. the core-well is located in the song ba trough, see fig. 1. hc, hydrocarbon; hi, hydrogen index; toc, total organic carbon. 100 acknowledgements the energy research programme of dea, the royal danish embassies in hanoi and bangkok, danida’s fellowship center and danida are thanked for their financial support. vpi and petrovietnam are acknowledged for their institutional support and permission to publish the results. references andersen, c., tiem, p.v., mathiesen, a. & nielsen, l.h. 1998: some new thermal maturity modelling results using the yükler 1 d software and seismic facies mapping in the northern part of the song hong basin. in: toan, t.n., quy, n.h. & ngoc, n.v. (eds): proceedings of con ference on vietnam petroleum institute 20 years development and prospects. hanoi, vietnam, may 1998, 273–284. andersen, c., mathiesen, a., nielsen, l.h., tiem, p.v. & dien, p.t. 1999: petroleum systems in the northern part of the song hong basin, gulf of tonkin – vietnam. proceedings from international conference on tectonics, stratigraphy and petroleum and mineral systems of palawan, borneo and surrounding areas, palawan island, philippines, 29 november – 3 december 1999 (cd-rom). bojesen-koefoed, j.a., nytoft, h.p., dau, n.t., ha, n.t.b., hien, l.v., quy, n.h., nielsen, l.h. & petersen, h.i. 2003: geochemical characteristics of seep oils from dam thi nai (qui nhon), central vietnam – implications for exploration in the offshore phu khanh basin. 21st international meeting on organic geochemistry, krakov, poland, 8–12 september, 2002. abstracts 2, 193–194. bojesen-koefoed, j.a., nytoft, h.p., dau, n.t., ha, n.t.b., hien, l.v., quy, n.h., nielsen, l.h. & petersen, h.i. 2004: seep oils from dam thi nai (qui nhon), central vietnam; the enreca-project reports promising implications for the future exploration in the offshore phu khanh basin. in: jarupongsakul, t. & saito, y. (eds): 5th international conference on asian marine geology. igcp475 deltamap/ apn megadelta, bangkok, thailand, 13–18 january. abstracts p. 25 only. dien, p.t., nielsen, l.h., andersen, c. & nhuan, d.v. 1997: late mesozoic to cenozoic basin development along the north-west margin of the east vietnam sea. petrovietnam review 4, 5–10. dien, p.t., nielsen, l.h., andersen, a., tiem, p.v. & nhuan, d.v. 1998: late mesozoic – cenozoic events along the north-west margin of the east vietnam sea. in: toan, t.n., quy, n.h. & ngoc, n.v. (eds): proceedings of conference on vietnam petroleum institute 20 years development and prospects. hanoi, vietnam, may 1998, 125–131. dien, p.t., quy, n.h., tiem, p.v., tai, p.s., andersen, c. & nielsen l.h. 1999: basin analysis and petroleum system of the song hong basin. in: hiep, n. et al. (eds): geology and petroleum in vietnam, 44–67. hanoi, vietnam: youth publishing. nielsen, l.h., mathiesen, a., bidstrup, t., vejbæk, o.v., dien p.t. & tiem, p.v. 1999: modelling of hydrocarbon generation in the cenozoic song hong basin, vietnam; a highly prospective basin. journal of asian earth sciences 17, 269–294. nielsen, l.h., abatzis, i., petersen, h.i., bojesen-koefoed, j. & nytoft, h.p. 2003: geo-scientific co-operation between vietnam petroleum institute and geological survey of denmark and greenland, 1995–2002. results, lessons learned, and views for the future. petrovietnam review 2, 32–48. petersen, h.i., andersen, c., anh, p.h., bojesen-koefoed, j.a., nielsen, l.h, nytoft, h.p., rosenberg, p. & thanh, l. 2001: petroleum potential of oligocene lacustrine mudstones and coals at dong ho, vietnam – an outcrop analogue to terrestrial source rocks in the greater song hong basin. journal of asian earth sciences 19, 135–154. petersen, h.i., nytoft, h.p. & nielsen, l.h. in press: characterisation of oil and potential source rocks in the northeastern song hong basin, vietnam: indications of a lacustrine-coal sourced petroleum system. organic geochemistry. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: lhn@geus.dk << /ascii85encodepages false /allowtransparency false /autopositionepsfiles true /autorotatepages /all /binding /left /calgrayprofile (dot gain 20%) /calrgbprofile (srgb iec61966-2.1) /calcmykprofile (u.s. web coated \050swop\051 v2) /srgbprofile (srgb iec61966-2.1) /cannotembedfontpolicy /warning /compatibilitylevel 1.4 /compressobjects /tags /compresspages true /convertimagestoindexed true /passthroughjpegimages true /createjdffile false /createjobticket false /defaultrenderingintent /default /detectblends true /colorconversionstrategy /leavecolorunchanged /dothumbnails false /embedallfonts true /embedjoboptions true /dscreportinglevel 0 /syntheticboldness 1.00 /emitdscwarnings 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<feff4f7f752890194e9b8a2d5b9a5efa7acb76840020005000440046002065874ef65305542b8f039ad876845f7150cf89e367905ea6ff0c4fbf65bc63d066075217537054c18cea3002005000440046002065874ef653ef4ee54f7f75280020004100630072006f0062006100740020548c002000520065006100640065007200200035002e0030002053ca66f465b07248672c4f86958b555f3002> >> >> setdistillerparams << /hwresolution [2400 2400] /pagesize [595.000 842.000] >> setpagedevice geological survey of denmark and greenland bulletin 1, 527-541 527 jurassic sedimentary rocks in sweden are restricted to skåne (scania), and adjacent offshore areas. they were deposited in areas separated by tectonic structural elements, each area reflecting different depositional and tectonic settings. the major areas are the ängelholm trough, the helsingborg area, the landskrona–kävlinge area, south-west skåne, central skåne, the vomb trough and the fyledalen fault zone (fig. 1). skåne is situated at the transition between the danish basin to the south-west and landmasses including the baltic shield to the north-east. therefore, small relative sea-level changes played a significant role in controlling the lateral facies distribution. the jurassic successions in skåne comprise sediments that accumulated in coastal plain to shallow shelf environments. the present distribution of jurassic deposits in skåne represents remnants of a once more extensive cover (norling et al. 1993). cretaceous–cenozoic inversion resulted in significant erosion of the deposits once deposited within the sorgenfrei–tornquist zone (norling & bergström 1987; erlström et al. 1997). lower jurassic deposits are by far the most widely preserved. they occur in troughs such as the ängelholm trough, the landskrona–kävlinge area, south-west skåne includthe jurassic of skåne, southern sweden anders ahlberg, ulf sivhed and mikael erlström in sweden, jurassic strata are restricted to skåne and adjacent offshore areas. jurassic sedimentary rocks predominantly comprise sandy to muddy siliciclastics, with subordinate coal beds and few carbonate-rich beds. during mesozoic times, block-faulting took place in the sorgenfrei– tornquist zone, a tectonic zone which transects skåne in a nw–se direction. the jurassic depositional environments in skåne were thus strongly influenced by uplift and downfaulting, and to some extent by volcanism. consequently, the sedimentary record reveals evidence of numerous transgressions, regressions and breaks in sedimentation. relative sea-level changes played a significant role in controlling the facies distribution, as deposition mainly took place in coastal plain to shallow shelf environments. the alluvial deposits in skåne include floodplain palaeosols, autochthonous coals, overbank sandstones, and stream channel pebbly sandstones. restricted marine strata comprise intertidal heteroliths with mixed freshwater and marine trace fossil assemblages, and intertidal delta distributary channel sandstones. shallow marine sediments encompass subtidal and shoreface sandstones with herringbone structures, and bioturbated mudstones with tempestite sandstones. offshore deposits typically comprise extensively bioturbated muddy sandstones. floral remains, palaeopedology, clay mineralogy and arenite maturity indicate a warm and humid climate in skåne throughout the jurassic, possibly with slightly increasing aridity towards the end of the period. most jurassic strata in skåne have been subjected to mild burial diagenesis, and the petroleum generative window has rarely been reached. keywords: skåne, southern sweden, fennoscandian border zone, danish basin, jurassic, lithostratigraphy, depositional environments, diagenesis a.a., department of geology, lund university, sölvegatan 13, s-223 62 lund, sweden. e-mail: anders.ahlberg@geol.lu.se u.s. & m.e., geological survey of sweden, kiliansgatan 10, s-223 50 lund, sweden. geological survey of denmark and greenland bulletin 1, 527–541 (2003) © geus, 2003 528 ing the höllviken graben, the hanö bay basin, the vomb trough and the fyledalen fault zone, and as erosional remnants on precambrian basement in central skåne. the rhaetian – lower jurassic succession is up to 250 m in thickness (sivhed 1984), whereas the middle and upper jurassic sediments are 75–300 m thick (norling 1972; norling et al. 1993). in skåne, most information on jurassic strata comes from the helsingborg area (norling 1972; sivhed & wikman 1986; norling & wikman 1990) and in the fyledalen fault zone, where relatively well-exposed sections occur (norling et al. 1993). in other areas, the development of the jurassic is incompletely known. results presented by vossmerbäumer (1969, 1970), rolle et al. (1979), ahlberg (1990, 1994), erlström et al. (1991, 1994), pieńkowski (1991a, b) and arndorff (1994) have added to the understanding of the depositional conditions and the relationship between the different areas of deposition. the aim of the present paper is to give an overview of the work hitherto done on the stratigraphy and sedimentology of the onshore jurassic strata in skåne, including previously unpublished discoveries and ideas. structural framework throughout the jurassic, block faulting played a significant role in skåne. the faulting was strongly influenced by major plate tectonic events, i.e., the break-up of pangea, the closing of tethys and the opening of the north atlantic (ziegler 1990). the early alpine tectonic phases in northwest europe resulted in the activation of the tornquist zone along lineaments established during the palaeozoic (norling & bergström 1987; erlström et al. 1997). the tornquist zone (fig. 1) is subdivided into the sorgenfrei–tornquist and teisseyere– tornquist zones (see discussions in liboriussen et al. 1987; norling & bergström 1987; eugeno-s working group 1988; berthelsen 1992; michelsen & nielsen 1993; thomas et al. 1993; thybo et al. 1994; erlström et al. 1997; vejbæk 1997). the sorgenfrei–tornquist zone links with the rønne graben and continues north-westwards through skåne to the northwestern part of jylland. the teisseyere–tornquist zone extends south-east from the rønne graben into poland. in general, tectonism actively controlled deposition and erosion in skåne throughout the jurassic, leaving bornholm skurup platform rø nn e g ra be n höllviken graben hanö baydenmark skåne rom ele block rom eleåsen fault zone fyledalen fault zone kullen–ringsjön–andrarum fault zone colonus shale trough sweden 25 km sv ed al a fa ul t z o ne ä h v c s f k l 14°e 56°n 55°n norway sweden denmark fig. 1. major tectonic elements of skåne, after erlström et al. (1997). stippled area índicates the sorgenfrei–tornquist zone, at the transition from the baltic shield in the north-east to the danish basin in the south-west. ä, ängelholm trough; c, central skåne; f, fyledalen fault zone; h, helsingborg area; k, kävlinge area; l, landskrona area; s, sw skåne; v, vomb trough. for additional outcrop and core locations, see sivhed (1984) and norling et al. (1993). different patterns of deposition and lacunas in individual tectonic blocks. major structural elements include the romele block, the höllviken graben, the colonus shale trough and the ängelholm trough. major faults include the kullen–ringsjön–andrarum fault zone, the fyledalen fault zone, the romeleåsen fault zone and the svedala fault zone (fig. 1; thomas et al. 1993; erlström et al. 1997). parts of the romele block, including the vomb trough (formed in the late cretaceous), were subjected to erosion and non-deposition during the late middle jurassic, while others persisted as depocentres. within the fyledalen fault zone, jurassic deposits are tilted or overturned due to uplift of the colonus shale trough (norling & bergström 1987; erlström et al. 1997). in the colonus shale trough, most triassic and jurassic deposits were removed by erosion associated with the late cretaceous – neogene inversion tectonics of the sorgenfrei–tornquist zone. a similar development has been observed in the rønne graben, which indicates the existence of a linked graben structure superimposed on the tornquist zone during much of the jurassic (vejbæk 1985; thomas & deeks 1994; vejbæk et al. 1994; erlström et al. 1997). depositional development in skåne, upper triassic (norian) fining-upwards cycles of coarse-grained, alluvial fan deposits grade upwards and basinwards into smectite-rich siltstones and mudstones, in which caliche nodules and halite pseudomorphs have been found (arndorff 1994). at the onset of the rhaetian, mineralogically mature, coal-bearing, kaolinite-rich siliciclastics were deposited, reflecting a regional change from warm semi-arid to warm and humid conditions, and an accompanying reduction in relief. the humidity was enhanced by the opening of interior seaways by rifting (manspeizer 1994). these climatic conditions dominated in skåne in the jurassic (hallam 1994). the lower jurassic deposits in skåne accumulated during a relatively quiet tectonic period, with a regional downwarp towards the depocentres of the danish basin (norling & bergström 1987). the succession in northwestern skåne is characterised by rhaetian–hettangian coastal plain to deltaic sediments succeeded by shallow marine deposits of sinemurian–aalenian age. in central skåne, rhaetian–hettangian sediments unconformably overlie deeply weathered precambrian gneiss. volcanic necks and associated pyroclastic deposits occur in central skåne (norin 1933); these have been dated to the early jurassic – middle jurassic transition (tralau 1968, 1973; bylund & halvorsen 1993). as a result of middle jurassic rifting in the north sea (ziegler 1990), tectonic unrest was transferred to skåne, which was subjected to uplift (norling & bergström 1987). marine influence ceased, and most of skåne was subjected to erosion which probably removed much of the lower jurassic succession. however, in certain areas (e.g. ängelholm trough and the fyledalen fault zone), deposition continued in coastal plain to shallow marine environments. during the late jurassic, new marine transgressions affected skåne (norling & bergström 1987). coastal and shallow marine sediments of oxfordian age were deposited, after a period of rapid facies changes in the late middle jurassic (norling 1981; norling & bergström 1987; erlström et al. 1997). after a period of relative quiescence, tectonic activity in skåne increased again at the jurassic–cretaceous transition, which led to reactivation (inversion) of pre-existing fault systems (erlström et al. 1997). in general, a warm and humid climate prevailed in skåne and adjacent areas during much of the jurassic (hallam 1994; manspeizer 1994), and vegetation largely covered coastal plains, which resulted in the formation of autochthonous coal beds. these conditions also favoured low-ph chemical weathering in the hinterlands, along sediment transport paths and during pedogenesis. therefore, jurassic strata in skåne include mineralogically mature sandstones, and clay mineral suites with a considerable content of kaolinite. in the late jurassic, the region was subjected to increasing aridity which caused very limited evaporite mineral formation in skåne (caliche nodules). lithostratigraphy the lithostratigraphic scheme of the jurassic succession in skåne (fig. 2) was established by norling (1972, 1981), sivhed (1984) and norling et al. (1993). the jurassic successions are subdivided into the höganäs, rya and annero formations and the informal mariedal formation (fig. 2; norling et al. 1993). exceptions to this do occur. in central skåne, the rhaetian–hettangian is referred to the höör sandstone, which in places is overlain by lithostratigraphically unspecified sediments. in the ängelholm trough, the middle jurassic is referred to the vilhelmsfält formation; in the fyledalen fault zone, the lower jurassic is referred to the informal 529 530 röddinge formation. in the subsurface of south-west skåne, an incomplete succession of jurassic strata ranging from the aalenian to the tithonian has been recorded. this resembles exposed penecontemporaneous strata fairly well, and it is thought likely that parts of the höganäs, rya and annero formations are represented, at least in part, in south-west skåne (norling 1981; d. guy-ohlson, personal communication 1994). höganäs formation stratigraphy and distribution the höganäs formation constitutes a transitional unit between the continental kågeröd formation and the shallow marine rya formation. the formation is wellknown and well-defined in the helsingborg area (sivhed 1984; figs 1, 2). it can be traced in deep wells in southwest skåne (brotzen 1950; larsson et al. 1994) and it is also represented on the skurup platform (thomas et al. 1993). the plant-bearing sediments at rödalsberg and munka tågarp in the fyledalen fault zone (möller & halle 1913) are here tentatively referred to the höganäs formation. it is possible that the members of the höör sandstone in central skåne can be correlated to similar strata of the höganäs formation (troedsson 1951). the höganäs formation is up to 250 m thick in the helsingborg area (sivhed & wikman 1986), 150 m in the ängelholm area (bölau 1959), 40 m in the svedala area (larsson et al. 1994) and probably more than 150 m in the höllviken area. palynomorph dating of the höganäs formation indicates a rhaetian–hettangian age (lund 1977; guy-ohlson 1981). in the ängelholm trough and in the helsingborg area, the höganäs formation is subdivided into the vallåkra and bjuv members (rhaetian) and the helsingborg member (hettangian). landskrona (l) – kävlinge (k)ängelholm trough (ä) helsingborg area (h) sw skåne (s) central skåne (c) vomb trough & fyledalen fault zone (v & f) tithonian kimmeridgian oxfordian callovian bathonian bajocian aalenian toarcian pliensbachian sinemurian hettangian rhaetian norian m id dl e la te ea rl y ju ra ss ic c re t. t ri as si c annero fm annero fm annero fm vilhelmsfält fm mariedal fm mariedal fm rya fm pyroclastic sediments höör sandstone höganäs fm kågeröd fm ? ? ?in co m pl et e su cc es si o n, n o t de fin ed röddinge fm berriasian fig. 2. lithostratigraphic scheme of the jurassic of skåne, modified from norling et al. (1993). the localities are indicated on fig. 1. 531 sedimentology and petrography the vallåkra member has been reported to comprise poorly stratified kaolinitic and smectitic mudstones and sandstones with sphaerosiderite concretions; the upper parts of the vallåkra member have yielded a restricted marine fauna (troedsson 1948, 1951). the bjuv member is bounded below and above by extensive autochthonous coals. coals, kaolinitic mudstones, heteroliths (flaser and lenticular bedded sandstones and mudstones) and mineralogically mature arenites are common in this member (ahlberg 1994; arndorff 1994). the bjuv member is dominated by floodplain deposits, including mature palaeosols (stacked underclays and autochthonous coals), interbedded with isolated fluvial channel and crevasse splay sandstones (ahlberg 1994; arndorff 1994). in these sediments, numerous dinosaur footprints have been observed (bölau 1952; gierlinski & ahlberg 1993). in addition, sparse evidence of marine influence on the floodplains has been observed, indicating a coastal plain setting. the marine signatures include heteroliths with rhizocorallium isp. and diplocraterion isp. burrows (ahlberg 1994) and dinoflagellates (s. lindström, personal communication 1996). the höganäs formation has traditionally been referred to as deltaic, including 12 deltaic cycles. nine of these are found in the uppermost member, the helsingborg member (troedsson 1950, 1951). this stratigraphic unit includes floodplain strata similar to those of the bjuv member. here, however, the floodplains were subjected to several restricted marine incursions (vossmerbäumer 1969, 1970; ahlberg 1990, 1994; pieńkowski 1991a, b). these are testified by the presence of molluscs, foraminifera (very rare), a well-developed partly marine trace fossil assemblage (fig. 3a), and indications of tidal activity. the tidal signatures include abundant bioturbated muddy heteroliths, which locally show bimodal fig. 3. features of the höganäs (a), rya (b, c) and mariedal (d) formations. a: two diplocraterion isp. burrows associated with rootlets in a muddy heterolith (helsingborg member, helsingborg railway tunnel), representing mixed marine and non-marine bioturbation in a mudflat. b: herringbone structures in marine sandstone (döshult member, laröd road section). c: backscatter electron image of berthierine ooids in thin section (rydebäck member, drill core rydebäck–fortuna 4, at a depth of 67.20 m). d: overturned autochthonous coal bed with pyrite concretions, overlying pedogenically altered sand with rootlets. the parent material (i.e. the light sand without pedogenic overprint to the right) includes diplocraterion isp. burrows. the section probably records infilling of an interdistributary bay and subsequent stabilisation by peat. photo from the top of the fuglunda member, eriksdal sand quarry. a b c d 532 ripple orientation and scoured sand-filled channels. in addition, cosets of cross-bedded sandstones with rhythmically spaced mud drapes and reactivation surfaces have been observed, which indicate uniform westwards (basinwards) sediment transport, possibly in tidallyinfluenced delta distributary channels (fig. 4). the overall facies architecture of the höganäs formation in north-west skåne is dominated by floodplain or muddy bay deposits, which encase laterally restricted sandstone bodies (troedsson 1951; ahlberg 1994). this is suggestive of a high and constant rate of subsidence and vertical sediment accretion (and availability of accommodation space). tabular basinwide sandstone bodies have been described at two levels within the helsingborg member (troedsson 1951). one of these occurs at the base of the hettangian succession, where rhaetian overbank sediments are abruptly followed by hettangian gravel and sand deposited in braided rivers. this change may have been caused by hinterland uplift (troedsson 1951), but could also reflect the upstream effects of a relative sea-level fall in the danish basin. a maximum flooding surface has been recognised in the upper rhaetian of the danish basin, overlain by a sequence boundary and a lower hettangian lowstand systems tract. this low sea-level stand induced basinwards progradation of lowstand shoreface sand, from the margins towards the depocentres of the danish basin (nielsen 1994; nielsen 2003, this volume). such a lowering in stratigraphic base level may have increased the alluvial slope, and triggered the early hettangian onset of braided stream deposition recorded in north-west skåne (ahlberg 1994; see posamentier et al. 1992; shanley & mccabe 1994). in addition, an abrupt increase in surface runoff could have caused a similar depositional pattern (ahlberg 1994). höör sandstone stratigraphy and distribution the höör sandstone crops out in the central part of skåne (fig. 1), where it forms erosional remnants directly overlying weathered precambrian crystalline basement. the 50 m thick formation is of rhaetian–hettangian age, according to its macroand microflora (antevs 1919; troedsson 1940; lund 1977). the threefold division includes a lower unnamed unit, up to 15 m thick, overlain by the stanstorp member (up to 15 m thick; local term: ‘kvarnstenen’ = millstone). the uppermost member, the vittseröd member (up to 25 m thick; local term: ‘byggnadsstenen’ = building stone), is exposed in several abandoned quarries south-east of höör (norling et al. 1993; wikman & sivhed 1993). sedimentology and petrography the höör sandstone outcrops are only a few m2 in size, thus precluding detailed interpretation of depositional setting. the basal unit is presently not exposed, but has been reported to comprise fine-grained sandstones, mudstones and clays (wikman & sivhed 1993). fig. 4. muddy heteroliths and sandy foreset beds with rhythmically spaced mud drapes (arrow) in the helsingborg member. these deposits probably represent bedforms that migrated into an intertidal interdistributary bay. pauses in foreset migration and subsequent mud draping occurred during tidal slackwater (sellwood 1972; terwindt 1981; tyge 1990). section exposed temporarily in 1928 in the centre of helsingborg; photo from the collection of g. troedsson. the middle unit, the stanstorp member, is composed of arkoses, subarkoses and quartz arenites. polymict conglomerates, mudstones and thin coal laminae occur in the unit, and impressions of fossil wood are abundant (troedsson 1940). sedimentary structures include large-scale cross-bedding, cut and fill structures, and a thin, graded event layer with an erosional basal conglomerate and superimposed current ripples, indicating waning energy conditions. a tentative interpretation of the sediments of the stanstorp member is that they were deposited in a continental environment subjected to floods (g. pieńkowski, personal communication 1988). the uppermost unit, the vittseröd member, consists of fine-grained, quartz-cemented quartz arenites and subarkoses. texturally, the sandstones are fairly mature and they have probably been thoroughly reworked by waves and currents. sedimentary structures include trough cross-bedding, which in places form herringbone structures, and rip-up mud clasts on bedding surfaces. plant fragments are not as common as in the stanstorp member, and beds rich in bivalve impressions have been reported (troedsson 1940). the member probably consists of nearshore marine sediments, surrounding islands of weathered precambrian gneiss, forming an archipelago (norling et al. 1993). rya formation stratigraphy and distribution the marine rya formation (fig. 2) is subdivided, from base to top, into the döshult, pankarp, katslösa and rydebäck members. the formation is recognised in the ängelholm, helsingborg, landskrona and kävlinge areas. in south-west skåne, the rya formation is missing or only poorly developed (norling & skoglund 1977; norling 1981, 1982; larsson et al. 1994). based on foraminifers, ammonites and ostracodes, the döshult member is dated to the early sinemurian, the pankarp member to the late sinemurian, the katslösa member to the late sinemurian – early pliensbachian and the rydebäck member to the late pliensbachian – late aalenian (reyment 1969; norling 1972; sivhed 1980, 1984). sedimentology and petrography the döshult member is characterised by coarse-grained sandstones and siltstones in the lower part, and is dominated by clays and marls rich in marine fossils in the upper part. the member is up to 80 m thick in the ängelholm, helsingborg and landskrona areas (bergström et al. 1982). at present, the basal part of this member is exposed at three localities in the helsingborg area (for locations, see norling et al. 1993). these contain mineralogically and texturally mature, trough crossbedded sandstones, commonly with herringbone structures showing north and south oriented palaeocurrent directions (fig. 3b). the occurrence of herringbone structures in well-sorted sand (tidal or not) suggests high energy foreshore to subtidal marine depositional conditions for the lower part of the member. in an abandoned quarry in north-west skåne (gantofta brickpit in the helsingborg area, outcrop very limited at present) the upper part of the döshult member commences with bioturbated marine nearshore sands, including diplocraterion isp., rhizocorallium isp., chondrites isp. and planolites isp. burrows, as well as abundant marine invertebrate body fossils (frandsen & surlyk 2003, this volume). this is followed by a bioturbated shelf mudstone with storm-deposited sand and silt intercalations (tempestites). a massive red mudstone with scarce marine body fossils and burrows follows, which is interpreted as having been deposited rapidly, in a low energy but oxidising environment. the youngest part of the succession comprises siltstones and mudstones, with carbonate-rich beds, deposited in a shallow marine setting (rolle et al. 1979). the pankarp member has an estimated thickness of up to 70 m in the subsurface of the ängelholm, helsingborg and landskrona areas. in the kävlinge area, the thickness is about 20 m (sivhed 1980; norling 1981; norling et al. 1993). in westernmost skåne, the pankarp member has been observed in small diameter drill cores. there, the member is subdivided into a lower unit of variegated clays and shales, a middle, poorly sorted silty to sandy unit including a coal bed, and an upper monotonous mudstone unit which is silty and organicrich at the base, and reddish–greenish at the top (sivhed 1980; norling et al. 1993). in the uppermost part of one core, the pankarp member comprises lenticular bedded heteroliths with planolites isp. burrows. the katslösa member is mainly known from the subsurface in westernmost skåne, and it has a thickness of 30–40 m in the ängelholm, helsingborg and landskrona areas. in the kävlinge area, the thickness is about 75 m (sivhed 1980; norling 1981; norling et al. 1993). the most complete section, at katslösa in the helsingborg area, was described and sampled by troedsson (1951), as he followed a temporary trench dug perpendicular to the strike of the tilted strata. sedimento533 logical interpretations given here are mainly based on the results of recent petrographical studies of museum collections, combined with published lithological descriptions (troedsson 1951; norling 1972). the katslösa member yields a rich marine microfauna and macrofauna, and it is dominated by homogeneous mudstone deposited in a marine low-energy environment. thin beds of matrix-rich quartz wackes are common. they are typically mineralogically mature but texturally highly immature with abundant angular sand grains. the matrix comprises organic matter, micrite, mica and clay minerals. in thin section, the sandstones show evidence of intense burrowing, which has obliterated depositional structures. scattered berthierine ooids, as well as authigenic siderite crystals have been observed. the rydebäck member is up to 70 m thick in the ängelholm, helsingborg and landskrona areas. it is only known from subsurface material in westernmost skåne, and sedimentological conclusions herein are entirely based on observations from two wells (drill cores rydebäck–fortuna-1 and -4). the member comprises a uniform succession of muddy arenites with a rich marine microfauna (mostly foraminifera), and represents deposition in an offshore low-energy environment (norling 1972). the sediments are strongly burrowed, which has caused an effective mixing of sand and mud, resulting in the forming of quartz wackes. the sand is quartz-rich, and grains are typically well rounded. berthierine ooids are common constituents of the sediment (fig. 3c). in conclusion, deposition of the rya formation began with nearshore coarse clastics, and continued with offshore mudstones with tempestites (the döshult member), followed by offshore muddy sediments with a brief nonmarine interval (the pankarp member), and ended with deposition of open marine low-energy deposits (the katslösa member and the rydebäck member). hence, the marine rya formation shows an overall fining-upwards trend, and an up-section bathymetric deepening of the depositional environment. it is notable that the stormdominated, hummocky cross-stratified hasle formation on bornholm is contemporaneous with the muddy katslösa member of the rya formation (surlyk & noenygaard 1986; koppelhus 1995). the depositional environment in western skåne was either physically protected from the storm energy due to basin topography, or deposition in skåne took place below storm wavebase. berthierine ooids occur scattered in the katslösa member and are increasingly abundant up-section in the rydebäck member. there is an intriguing possibility that iron ooid formation was promoted by precipitation of iron and silica from volcanic exhalative fluids rising up through the substrate, as has been reported from modern marine sediments offshore indonesia (heikoop et al. 1996). this hypothesis has emerged with the recent publication of new age data for the volcanic rocks in skåne, which now appear to be comparable in age to the prominent iron ooid-bearing deposits, i.e. the rydebäck member and the röddinge formation (see below). röddinge formation stratigraphy and distribution due to the limited degree of exposure and the weathered state of the surficial strata, the informal stratigraphic unit ‘röddinge formation’ was introduced for the iron-rich deposits in the fyledalen fault zone, primarily at kurremölla (norling et al. 1993). the röddinge formation is largely known from museum collections, and it has been dated by ammonite biostratigraphy to be of sinemurian–pliensbachian age (moberg 1888; reyment 1959). based on unpublished museum data (sample locations, etc.), it is calculated that the röddinge formation has a thickness of several hundreds of metres. petrography the röddinge formation is dominated by fineto medium-grained quartz arenites, with subordinate thin conglomerates. the sediments are moderately consolidated by berthierine or siderite cement, and berthierine oolites are common in the succession. the ooids are generally around 0.3 mm in diameter and ellipsoidal in shape. the core commonly consists of detrital quartz or heavy minerals, surrounded by concentric microlaminae of berthierine. the deposits are strongly affected by modern weathering and are characterised by a red, brown or yellow stain (iron hydroxides). unweathered deposits, known from boreholes, are greyish dark green due to the content of berthierine and siderite. the iron content is 8–10% in the weathered sandstones, up to 20% in the oolites, and at kurremölla a 1.7 m thick oolite bed has an iron content of up to 35%. this ore bed was mined during the 1930s (hadding 1933). due to the poor, weathered exposure, the röddinge formation has not been subjected to detailed facies 534 analysis. in general, the mineralogical and textural maturity of the sands imply prolonged reworking. marine influence is clearly indicated by finds of ammonites and crinoids (hadding 1933). the shape of the iron ooids indicate diagenetic precipitation, prior to and during sediment compaction. as discussed above with respect to the berthierine ooids in the rydebäck and katslösa members, volcanic activity may have stimulated the process. lateritisation has been suggested as another possible source for the iron enrichment in the sediments (nilsson 1992). vilhelmsfält formation and mariedal formation stratigraphy and distribution middle jurassic sediments are found in parts of western skåne, in the fyledalen fault zone and in the ängelholm trough. the deposits are divided into two formations, the vilhelmsfält formation and the mariedal formation (norling et al. 1993). the vilhelmsfält formation is restricted to the ängelholm trough. it has been dated as bajocian–bathonian on palynological grounds (guy-ohlson 1971, 1986, 1989). similarities between the vilhelmsfält formation and the fuglunda member of the mariedal formation were noted by bölau (1959), but such a correlation cannot be confirmed at present. use of the informal name ‘mariedal formation’ was recommended by norling et al. (1993), until the identity of the formation is resolved. the mariedal formation crops out in the fyledalen fault zone, and is also found in the landskrona and helsingborg areas (fig. 1). it has been divided into the fuglunda member and the overlying glass sand member, which are dated to the bajocian and the bathonian, respectively, on palynological and palaeobotanical grounds (tralau 1966, 1968). the fuglunda member is up to 75 m thick, whereas the glass sand member has a thickness of up to 100 m (norling et al. 1993). lithology of the vilhelmsfält formation the vilhelmsfält formation consists mainly of sandy, micaceous mudstones with plant remains and sandy intercalations. a thin coal bed has been observed in a sandy layer in the lower part of the formation. the formation is more than 75 m thick (bölau 1959). lithology and sedimentology of the mariedal formation in a quartz sand quarry at eriksdal in the fyledalen fault zone, the fuglunda member comprises thirteen deltaic cycles of coals, heteroliths and sandstones (koch 1979; rolle et al. 1979). the coals are commonly associated with rootlet horizons and immature palaeosols (fig. 3d). hence, they were formed autochthonously, primarily by in-situ accumulation of wood in peat swamps. indeed, between each coal bed, several soil formation ‘attempts’ (i.e. immature palaeosols) may be distinguished. the palaeosols differ clearly from their parent material in terms of colour, texture and degree of stratification. typically, the lower boundaries are gradational, and the upper boundaries are sharp. rooting and eluviation of clay minerals and organic matter are additional pedogenic characteristics (allen & wright 1989). the heteroliths include the full spectrum from almost pure mudstone (rich in clay-sized coal detritus) with slightly lenticular silt laminae, through lenticular, wavy and flaser bedded heteroliths. a partly marine trace fossil assemblage is characteristic of the heteroliths, including diplocraterion isp. and monocraterion isp. the bioturbated muddy heteroliths interfinger with sandy heteroliths, autochthonous coals and palaeosols. they were probably deposited in intertidal low energy environments, i.e. interdistributary bays (rolle et al. 1979). abundant large (< 10 cm) pyrite concretions occur in the coals and the organic-rich heteroliths, implying a marine influence on the eodiagenesis (curtis & coleman 1986). flaser bedded, sandy heteroliths commonly show trough cross-bedding, mud drapes, climbing ripples and channel scour. this facies probably represents deposition in tidal channels. in the eriksdal quarry, a coarse-grained, pebbly sandstone showing scour-andfill structures, forms a lenticular body encased in the coals and heteroliths of the fuglunda member. this facies probably represents a delta distributary channel fill. in conclusion, the fuglunda member at eriksdal shows typical features of a delta plain environment. the glass sand member (up to 100 m thick) succeeds the fuglunda member in the eriksdal quartz sand quarry. the sediments consist predominantly of coarseand fine-grained sandstone (or sand), with minor intercalations of heteroliths and mudstone with diplocraterion isp. burrows (rolle et al. 1979). differing interpretations have been offered for the depositional setting of these sediments. the member was described by rolle et al. (1979) as being of foreshore and lagoonal origin. 535 536 clay silt sand clay silt sand clay silt sand clay silt sand 1 m c b a c d d d fig. 5. log from the glass sand member at eriksdal (j. johansson and l. adrielsson, personal communication 1998). a, shallow stream or unconfined flow (sheet flood) deposits from crevasse splays close to an active channel; b, distal crevasse splay deposits in extremely shallow interdistributary bay (or floodplain) area; c, turbiditic deposition in standing water, probably by subaqueous overbank floods; d, distributary channel deposits showing two-dimensional dunes with superimposed ripples, three-dimensional dunes and cross-channel bars implying unidirectional flow; e, channel erosion and lateral migration with slump sediments (massive sand and large peat (coal) balls, i.e. reworked floodplain swamp deposits) from river bank collapse; f, channel fill deposits dominated by ripple-laminated sand, fining-upwards; g, channel fill concluded and establishment of flora. f. surlyk (personal communication 1998) considers the glass sand member to represent high-energy tidallydominated environments ranging from tidal inlets and open estaurine conditions with large tidal sand bars, flats and channels to marine foreshore; the upper boundary of the member is interpreted to record a major relative sea-level fall. in contrast, j. johansson and l. adrielsson (personal communication 1998) investigated a section through the glass sand member and concluded that fluvial deposits prevail throughout, with few signs (e.g. trace fossils) indicating proximity to the marine realm (fig. 5). these workers thus proposed that the succession probably represents the fluvial-dominated part of a delta plain. 537 clay silt sand clay silt sand clay silt sand massive bedding, sandstone horizontal lamination normal grading planar cross-stratification trough cross-stratification scour-and-fill structures ripple cross-lamination, trough ripple cross-lamination, tabular mudstone reworked peat ball slumping trace fossils (diplocraterion) roots d f e e d f g annero formation stratigraphy and distribution from below, the annero formation (fig. 2) is subdivided into the fortuna marl, the fyledalen clay, the nytorp sand, and the vitabäck clay. based on biostratigraphy (foraminifera, ostracodes and palynomorphs), the fortuna marl is referred to the bathonian–oxfordian, the fyledalen clay to the oxfordian–kimmeridgian, the nytorp sand to the kimmeridgian–tithonian, and the vitabäck clays to the tithonian–berriasian (christensen 1968; norling 1972, 1981; erlström et al. 1991). sediments referred to the annero formation are found in western skåne including the ängelholm trough, in the fyledalen fault zone and in the vomb trough, and have been described by norling (1972, 1981) and erlström et al. (1991). the fortuna marl is restricted to the landskrona– kävlinge area, where it has a thickness of up to 10 m (guy-ohlson & norling 1988). the fyledal clay is about 30 m thick in the helsingborg–landskrona area and in the ängelholm trough, and more than 55 m thick (estimated to 140 m) in the fyledalen section, and 24 m thick in the vomb trough. the nytorp sand is 20–25 m thick in the helsingborg–landskrona area, 20 m thick in the fyledalen section and 5 m thick in the assmåsa borehole. the vitabäck clay is 20–25 m thick in the ängelholm and vomb troughs, more than 5 m thick in the landskrona–helsingborg area, and more than 34 m thick in the fyledalen section (norling 1981). lithology and petrography the thin fortuna marl has only been observed in a few drill cores of limited quality, and sedimentological information is therefore minimal. the strata comprise sandstone, carbonate-rich siltstones and mudstones, with a marine microfauna (guy-ohlson & norling 1988). the fyledal clay is characterised by a uniform succession of greenish and organic-rich clays, interrupted by thin silt and sand beds (guy-ohlson & norling 1988; erlström et al. 1991). the sediment displays, on the one hand, continental and freshwater indicators such as rootlet beds, oligohaline–mesohaline ostracodes and caliche nodules. on the other hand, marine indicators are also recorded, such as calcareous foraminifera. erlström et al. (1991) thus suggested that deposition mainly took place on a muddy coastal plain, with stagnant ponds (lagoons). fining-upwards sandstone wedges (< 1 m thick) with erosional bases have been observed in the fyledal clay at the eriksdal quartz sand quarry. these include gravel with rip-up mud clasts and mollusc shells at the base, as well as reworked glauconite in their higher parts. the sand wedges have been interpreted as washover fan deposits (erlström et al. 1991). the occurrence of upper jurassic evaporites and euryhaline biota are very few, but may be of particular significance. whereas the caliche nodules are well preserved, it is unclear if the gypsum is of primary origin. in any case, these represent the only signs of aridity in the jurassic successions of skåne. hence, skåne may have been only marginally influenced by the late jurassic north-eastwards migration of the arid climate zone of western and central pangea (hallam 1994). the nytorp sand is not accessible for facies analysis. however, due to its stratigraphic position between the fyledal clay and the similar vitabäck clay, erlström et al. (1991) inferred deposition in a back-barrier environment. the vitabäck clay, which straddles the jurassic– cretaceous boundary, is primarily known from lithological and palaeontological investigations of samples, as continuous sections are not available. the mud-dominated formation shows similarities to the fyledal clay, only with a slightly higher content of sandy beds. palynomorphs, ostracodes and molluscs indicate nonmarine conditions with brackish marine influence, and deposition probably took place on a muddy coastal plain (ekström 1985; erlström et al. 1991). jurassic volcanism and pyroclastic deposits in central skåne, numerous mesozoic basaltic necks occur (norin 1933). the basalts are typically vitrophyric with columnar structures, and undersaturated with respect to silica (see wikman & sivhed 1993 and wikman et al. 1993 for reviews). k-ar datings of the basalts indicate bathonian and aptian ages (printzlau & larsen 1972; klingspor 1976). recent palaeomagnetic datings, however, have yielded older, toarcian–aalenian ages (bylund & halvorsen 1993). despite the abundant volcanic necks in skåne, the distribution of pyroclastic deposits appears surprisingly limited. this, and the abundance of lithified magma spray droplets, may indicate a hawaiian or strombolian type of eruptive activity, i.e. rather passive eruptions of low-viscosity basaltic magma (scarth 1994). only locally, around the volcanic necks of central skåne, up to 50 m thick volcanic tuffites occur, which presently are exposed 538 in two sections (norling et al. 1993). no correlative pyroclastic beds have yet been identified in sedimentary basins surrounding central skåne. the tuffites are dominated by lapilli, which in thin section show clusters of tiny spherical condensed glass particles which are now diagenetically transformed to clay minerals and other relatively stable minerals. other constituents comprise rare volcanic bombs (typically 5–10 cm in cross-section), angular and rounded gneiss boulders (typically 5–15 cm in cross-section), probably from the sidewall, scattered detrital quartz grains, and pieces of fossil wood, including large logs. palynological dating of the tuffites has yielded an age at the early–middle jurassic boundary (tralau 1973). in central skåne, the volcanic intrusions have probably had a profound effect on the diagenesis of the lower jurassic arenites (see below). diagenesis, thermal history and petroleum potential in the jurassic strata of skåne, most diagenetic properties were obtained rather soon after deposition, i.e. eodiagenetically. hence, the sediments were influenced by surficial features such as climate, groundwater and pedogenic processes. due to only moderate burial temperatures, burial diagenetic features are less pronounced (ahlberg 1996). a low thermal impact has been confirmed by guy-ohlson (1989; personal communication 1994) who observed low thermal alteration index (tai) values of palynomorphs (around 3) throughout the jurassic of skåne. the rhaetian–hettangian höör sandstone in central skåne is an exception to this. as revealed by cathodoluminescence microscopy and fluid inclusion analysis, the höör sandstone was subjected to flushing of hot hypersaline brines, which probably were released in association with the early–middle jurassic volcanic events (ahlberg 1994). the organic content of the jurassic strata in skåne is typically dominated by gas prone kerogen (type iii), which is below, or at the onset of, thermal maturity (ahlberg 1996). as the burial heat was insufficient, hydrocarbon maturity can only have been achieved locally, possibly in association with faulting and volcanic activity. the faults, however, were also potential escape routes for migrating hydrocarbons (ahlberg 1996; ahlberg & olsson 2001). references ahlberg, a. 1990: provenance, stratigraphy, palaeoenvironments and diagenesis of the lower jurassic strata in the helsingborg railway tunnel, southern sweden, 2, 54 pp. unpublished licentiate thesis, lund university, sweden. ahlberg, a. 1994: deposition and diagenesis of the rhaetian– hettangian succession (triassic–jurrassic) in southern sweden: a synthesis. lund publications in geology 123, 16 pp. ahlberg, a. 1996: petroleum in the mesozoic of sweden – why not? 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geologiske undersøgelse serie a 34, 23 pp. vossmerbäumer, h. 1969: paläoökologische ausdeutung fossiler wurzelböden. geologiska föreningens i stockholm förhandlingar 91, 112–126. vossmerbäumer, h. 1970: untersuchungen zur bildungsgeschichte des unteren lias in schonen (schweden). geologica et palaeontologica 4, 167–193. wikman, h. & sivhed, u. 1993: beskrivning till berggrundskartan kristianstad sv. sveriges geologiska undersökning serie af 155, 106 pp. wikman, h., bergström, j. & sivhed, u. 1993: beskrivning till berggrundskartan helsingborg so. sveriges geologiska undersökning serie af 180, 114 pp. ziegler, p.a. 1990: geological atlas of western and central europe, 2nd edition, 239 pp. amsterdam: elsevier for shell internationale petroleum maatschappij. manuscript received 2 september 1994; revision accepted 31 may 2000. geological survey of denmark and greenland bulletin 23, 2011, 61–64 61 scattered occurrences of palaeogene sediments are found in north-east greenland, where they overlie unconformably cretaceous sediments and are capped by palaeogene basalts. these sediments have received little attention (watt 1994), except for relatively recent studies (nøhr-hansen & piasecki 2002; jolley & whitham 2004; larsen et al. 2005; heilmann-clausen et al. 2008). as part of an ongoing petroleum geological study that focuses on the jurassic–cretaceous succession, the palaeogene sediments were included to better constrain their age, depositional environment and relation to the basalts. several localities were investigated on wollaston forland, sabine ø and hold with hope, a few of which are described here (fig. 1). eastern wollaston forland and sabine ø discontinuous outcrops of mostly loose and un-cemented palaeogene sediments occur in haredal, eastern wollaston forland. a n–s-striking normal fault with 100–125 m of downthrow to the east separates the main outcrop in the southern slope into two blocks. the best exposed succession is situated in the western footwall block, where the succession dips 20° to the sw (fig. 2). it overlies marine mudstones of late albian age (wigginsiella grandstandica subzone (v1) of nøhr-hansen 1993) in the footwall block and of early to middle campanian age (indicated by the dinocysts alterbidinium ioannidesii and cerodinium diebelii) in the hanging wall block; however, the contact to the cretaceous is not exposed. a poorly exposed palaeogene succession in the northern slope is probably from the hanging wall block; the base of the succession and underlying strata are not exposed. haredal, southern slope. approximately 200 m of palaeogene sediments are partly exposed in the footwall block, forming two upward-coarsening units overlain by basalts (fig. 2). the lower unit consists of more than 70 m of dark grey mud overlain by 54 m of fineto medium-grained sand beds alternating with thinner heteroliths topped by more than 2 m of coarse-grained sand. the succession is of earliest ypresian age based on the presence of the dinocyst apectodinium augustum (fig. 3) and the nannofossil discoaster lenticularis. the palynological assemblage is dominated by reworked material from upper jurassic (e.g. gonyaulacysta jurassica), mid to upper cretaceous (e.g. hapsocysta benteae, chatangiella spp. and wodehouseia spinata) and lower paleocene (e.g. alisocysta margarita). the presence of a. augustum may correlate with the a. augustum (p6b) subzone described from the central north sea (mudge & bujak 1996) and correlated palaeogene deposits in north-east greenland henrik nøhr-hansen, lars henrik nielsen, emma sheldon, jussi hovikoski and peter alsen fig. 1. geological map of the wollaston forland – hold with hope study area in north-east greenland. the location of the studied sections corresponds to the distribution of palaeogene sediments. © geus, 2011. geological survey of denmark and greenland bulletin 23, 61–64. open access: www.geus.dk/publications/bull young sund g a e l h a m k e b u g t lille pendulum kap broer ruys sabine ø wollaston forland hold with hope palnatoke bjerg ice quaternary intrusive complexes (48–28 ma) basaltic sills and dykes basaltic plateau lavas (58–54 ma) palaeogene cretaceous jurassic triassic palaeozoic daneborg to b i a s d a l 20°w 74°n jackson ø harefjeld haredal fosdalen langsiden dronning augusta dal 25 km home forland faults studied section greenland 6262 e le v at io n 400 m 380 360 340 320 300 280 260 240 220 200 e . p al ae o ge n e p e ri o d /e p o c h s ta ge palyno zones palyno zones c h ro n o st ra ti gr ap h y c h ro n o st ra ti gr ap h y p 6 a . a u g u st u m z o n e p 6 b a . a u g u st u m s u b zo n e s am p le s p a la e o p e ri d in iu m p yr o p h o ru m a p e ct o d in iu m a u gu st u m a re o lig e ra s p p . c e ro d in iu m s tr ia tu m d e fl a n d re a o e b is fe ld e n si s p a la e o cy st o d in iu m b u lli fo rm e t h a la ss ip h o ra d e lic a ta a p e ct o d in iu m p a n ic u la tu m g la p h yr o cy st a r e ti in te xt a a lis o cy st a m a rg a ri ta c e ro d in iu m d ie b e lii p a la e o cy st o d in iu m a u st ra lin u m c e ro d in iu m s p e ci o su m p h th a n o p e ri d in iu m s p p . ? ? ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? dinoflagellate cysts haredal southern slope, eastern wollaston forland haredal southern slope haredal northern sloped is co a st e r le n ti cu la ri s d is co a st e r ge m m e u s? h e lic o sp h a e ra s e m in u lu m t ri b ra ch ia tu s o rt h o st yl u s na n p z o n e s z o n e e le v at io n 220 a. augustum top a. augustum base a. augustum base a. margarita base t. evittii top m 200 180 160 140 120 100 80 60 e . p al ae o ge n e p e ri o d /e p o c h s ta ge p 6 a . a u gu st u m z o n e s u b zo n e s am p le s a re o lig e ra s p p . c e ro d in iu m d ie b e lii g la p h yr o cy st a c f. r e ti in te xt a p a la e o p e ri d in iu m p yr o p h o ru m s p o n go d in iu m d e lit ie n se t ri th yr o d in iu m e vi tt ii s e n o n ia sp h a e ra i n o rn a ta a lis o cy st a m a rg a ri ta c o rd o sp h a e ri d iu m i n o d e s d in o c y st s p 4 h n h 2 0 0 2 m u ra to d in iu m f im b ri a tu m p a la e o cy st o d in iu m b u lli fo rm e s e n e ga lin iu m i te rl a a e n se c e ro d in iu m s tr ia tu m a p e ct o d in iu m a u gu st u m a p e ct o d in iu m p a n ic u la tu m d e fl a n d re a o e b is fe ld e n si s t h a la ss ip h o ra d e lic a ta a p e ct o d in iu m h o m o m o rp h u m ? ? ? ? ? ? ? ? dinoflagellate cysts e c re t. l a lb . (v) (v1) p 6 b a . a u g u st u m n p 9 n p 1 0 n p 1 1 u . n p 1 0 n p 1 1 ? n p 1 2 clay silt sand ? ? ? ? pebbl.clay silt gnl. sand cross bedding cross lamination wavy and flaser bedding erosive contact clay and coal clast sandstone mudstone muddy sandstone basalt conglomerate lithology planar lamination sedimentary structures ? 220 ? ? ? g ?? l .. t h an e ti an ? e . y p re si an l . t h an e ti an ? e . y p re si an ? ? 1 2 3 4 a. augustum top e . d an ia n ? e . s e la n d ia n a b fault west east with the paleocene–eocene thermal maximum (petm) which occurred at about 56 ma and lasted for c. 170 kyr (harding et al. 2011). the upper, coarser-grained part only yielded two dinocyst species cerodinium sp. and areoligera sp. and no nannofossils. the upper unit consists of more than 20 m of dark grey silty and sandy mud overlain by slightly heterolithic, finegrained sand (22 m), fine-grained sand (10 m), conglomerate and pebbly sandstone (8 m) topped by a few metres of sand, mud and carbonaceous mud or coal. the palynologifig. 2. a: southern slope and fault at haredal. the highest mountain is c. 700 m high. b: sedimentological logs and range charts of selected in situ dinocysts and calcareous nannofossils. numerals in the zones of the northern slope are: 1: alisocysta margarita zone, 2: senegalinium iterlaaense zone or palaeocystodinium bulliforme zone, 3: trithyrodinium evittii zone and 4: spongodinium delitiense subzone (nøhr-hansen et al. 2002). na: nannofossils, np: palaeogene nannoplankton zone. v, v1: subtilisphaera kalaalliti zone and wigginsiella grandstandica subzone (nøhr-hansen 1993). 63 cal assemblages below the conglomerate are dominated by reworked material of mid – late cretaceous age and a few specimens of paleocene age. the succession is of early ypresian (early eocene) age based on poorly preserved specimens of the dinocysts apectodinum augustum, apectodinium paniculatum, def landrea oebisfeldensis and the nannofossil tribrachiatus orthostylus (fig. 3). samples above the conglomerate yielded a few reworked upper cretaceous and paleocene dinocysts together with a few indeterminate algae and the nannofossil helicosphaera seminulum (fig. 3). the latter indicates an age not younger than mid ypresian for the youngest dated sediments in haredal; this is compatable with a mid ypresian radiometric 39ar/40ar age of 55.02 ± 0.49 ma for the oldest lava analysed from wollaston forland (l.m. larsen personal communication 2008). haredal northern slope. approximately 180 m of sediments were studied on the northern slope of haredal (fig 1). the lower 40 m consist of dark grey mud with a palynological assemblage dominated by reworked material from mid – upper cretaceous strata (e.g. hapsocysta benteae, chatangiella spp. and aquilapollenites spp.). the presence of trithyrodinium evittii, spongodinium delitiense and a few specimens of senoniasphaera inornata in the two lowermost samples indicates an early paleocene age and may correlate with the lower danian trithyrodinium evittii zone (fig. 2) established from west greenland (nøhr-hansen et al. 2002). the presence of common senegalinium iterlaaense and palaeocystodinium bulliforme in the two overlying samples indicates a mid to late danian age correlating with the senegalinium iterlaaense and palaeocystodinium bulliforme zones (2 and 3 in fig. 2), whereas the next sample contains a few specimens of the dinocysts alisocysta margarita and cerodinium striatum indicating a late danian/?early selandian age correlating with the alisocysta margarita zone (nøhr-hansen et al. 2002; 1 in fig. 2). the upper 130 m of sand and mud contain very few in situ palynomorphs, however the presence of apectodinium augustum indicates correlation with the apectodinium augustum (p6b) subzone, indicating an ?early selandian – thanetian hiatus. outer haredal, dronning augusta dal and sabine ø. palaeogene sediments from the southern slope of the easternmost part of haredal, on the eastern slope of dronning augusta dal, and on the north-eastern slope of harebjerg, sabine ø were also studied and sampled (fig. 1).the successions all contain the petm dinocyst marker apectodinium augustum. north-eastern hold with hope langsiden. interbedded in dark grey mud at langsiden (fig. 1) occurs an 8 m thick unit with sharp-based, upwardfining successions of conglomerate and pebbly sand, up to a few metres thick containing large reworked mudstone clasts. the palynological assemblage from the underlying mud is dominated by a reworked f lora of late maastrichtian age indicated by the presence of triblastula wilsonii and wodehouseia octospina. the presence of in situ trithyrodinium evittii, spongodinium delitiense and a few specimens of senoniasphaera inornata indicates correlation with the lower danian trithyrodinium evittii zone (nøhr-hansen et al. 2002). the mudstone clasts yielded a mid cretaceous f lora. the palynomorph assemblage of two samples from the overlying mud is likewise dominated by a reworked upper cretaceous f lora; however, the lower sample also contains a few specimens of the dinocysts alisocysta margarita and cerodinium striatum, indicating correlation with the upper danian/?lower selandian alisocysta margarita zone (nøhrhansen et al. 2002). the presence of thalassiphora delicata in the upper sample indicates a latest danian/early selandian age (nøhr-hansen & piasecki 2002). east of fosdalen. approximately 6 m of loose, white-grey, fineto medium-grained sand with scattered small clay clasts 1 42a 2b 3 65 987 10 20 μm 20 μm 20 μm 20 μm 20 μm 20 μm 20 μm 2 μm2 μm2 μm20 μm fig. 3. images of selected dinocysts (1–7) and nannofossils (8–10). 1: trithyrodinium evittii. 2a, b: alisocysta margarita. 3: thalassiphora delicata. 4: gen et sp. indet. of piasecki et al. (1992). 5: apectodinium augustum. 6: apectodinium paniculatum. 7: def landrea oebisfeldensis. 8: discoaster gemmeus? 9: helicosphaera seminulum. 10: tribrachiatus orthostylus. 6464 overlain by a less than 2 m thick bed of dark grey mud covered by volcanic rocks overlies mid cretaceous sandy mudstone east of fosdalen (fig. 1). the palynological assemblage of the mud bed is dominated by spores and pollen and some reworked dinocysts of mid to late cretaceous age. in situ specimens of the dinocyst gen. et sp. indet. of piasecki et al. (1992; fig. 3) also occur, suggesting fresh to brackish water. the species is common in wells offshore eastern canada just above the apectodinium augustum p6b subzone (h. nøhrhansen, unpublished data). the occurrence of the species immediately below the basalts may indicate an earliest ypresian age. discussion the new biostratigraphic dating shows that the palaeogene sediments on wollaston forland, hold with hope and sabine ø comprise paleocene and earliest eocene strata with a hiatus that probably spans the major part of the selandian and thanetian. the age of the underlying cretaceous deposits east of the fault in haredal is early–middle campanian, much younger than the middle albian previously described from wollaston forland (nøhr-hansen 1993). the stratigraphic gap between the cretaceous and palaeogene sediments thus decreases towards the basin to the east. the large amount of reworked cretaceous marine palynomorphs including a late maastrichtian f lora documents uplift of cretaceous marine sediments and major erosion during the early palaeogene. the ages of the youngest palaeogene sediments and the oldest f lood basalts appear to be almost identical; however, the nature of the contact between the sediments and basalts needs to be further investigated to determine whether the contact is angular, as is suggested in places by a relatively steep dip of the sediments. discontinuous conglomerate beds with rounded quartzite pebbles and boulders up to 20 cm, as well as cross-bedded sandstones, terminate the upper unit in haredal and are interpreted as f luvial channel deposits. the absence of basaltic clasts indicates that deposition occurred prior to the volcanic events. the thin overlying succession with a coaly bed is interpreted as an aggrading coastal plain subject to marine inundations. however, the principal part of the palaeogene sediments accumulated in a marine environment as indicated by marine dinocysts and the presence of scattered marine trace fossils. thin, fine-grained sandstone beds with f lute casts and a massive lower part overlain by beds with parallel lamination and cross-lamination in outer haredal indicate deposition from turbidite currents. the sharp-based, finingupward conglomerate beds and pebbly sand from langsiden embedded in mud are interpreted as channelised gravity f low deposits. the two upward-coarsening units in haredal suggest that the palaeogene sediments mainly accumulated during two major depositional phases. potential by-pass surfaces are identified at the cretaceous–palaeogene boundary, at the top of the lower unit, at the base of the f luvial conglomerates and possibly at the sediment–basalt boundary. coarsegrained sediments may have been transported toward the basin area to the east along these surfaces. references harding, i.c. et al. 2011: sea-level and salinity f luctuations during the paleocene–eocene thermal maximum in arctic spitsbergen. earth and planetary science letters 303, 97–107. heilmann-clausen, c., abrahamsen, n., larsen, m., piasecki, s. & stemmerik, l. 2008: age of the youngest paleogene f lood basalts in east greenland. newsletters on stratigraphy 43, 55–63. jolley, d.w. & whitham, a.g. 2004: a stratigraphical and palaeoenvironmental analysis of the sub-basaltic palaeogene sediments of east greenland. petroleum geoscience 10, 53–60. larsen, m., heilmann-clausen, c., piasecki, s. & stemmerik, l. 2005: at the edge of a new ocean: post-volcanic evolution of the palaeogene kap dalton group, east greenland. in: doré, a.g. & vining, b. (eds): petroleum geolog y: north-west europe and global perspectives. proceedings of the 6th petroleum conference london 2, 923–932. london: geological society. mudge, d.c. & bujak, j.p. 1996: paleocene biostratigraphy and sequence stratigraphy of the uk central north sea. marine and petroleum geolog y 13, 295–312. nøhr-hansen, h. 1993: dinof lagellate cyst stratigraphy of the barremian to albian, lower cretaceous, north-east greenland. grønlands geologiske undersøgelse bulletin 166, 171 pp. nøhr-hansen, h, & piasecki, s. 2002: palaeocene age of sub-basaltic sediments at savoia halvø, east greenland. geolog y of greenland survey bulletin 191, 111–116. nøhr-hansen, h., sheldon, e. & dam, g. 2002: a new biostratigraphic scheme for the paleocene onshore west greenland and its implications for the timing of the pre-volcanic evolution. in: jolley, d.w. & bell, b.r. (eds): the north atlantic igneous province: stratigraphy, tectonic, volcanic and magmatic processes. geological society, special publications (london) 197, 111–156. piasecki, s., larsen, l.m., pedersen, a.k. & pedersen, g.k. 1992: palynostratigraphy of the lower tertiary volcanics and marine clastic sediments in the southern part of the west greenland basin: implications for the timing and duration of the volcanism. rapport grønlands geologiske undersøgelse 154, 13–31. watt, w.s. 1994: stratigraphy and correlation of the tertiary plateau basalts in north-east greenland. rapport grønlands geologiske undersøgelse 162, 185–194. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: hnh@geus.dk geological survey of denmark and greenland bulletin 7, 2004, p 29-32 29 new techniques using computer controlled scanning electron microscopy (ccsem) and laser ablation – inductively coupled plasma – mass spectroscopy (la-icp-ms) have recently been developed at the geological survey of denmark and greenland (geus) to determine source, compositional variation and sedimentary pathways of sandstones. these new timeand cost-efficient methods are highly applicable in petroleum and mineral exploration. this paper illustrates how the provenance and variability of miocene titanium-rich sands in western and central jylland have been investigated, but the methods are presently also used offshore the faroe islands and in east and west greenland. ccsem and la-icp-ms utilise simple sample preparation methods, are relatively rapid and less expensive than conventional methods and yield more information. heavy mineral (titanium) exploration techniques exploration for economic concentrations of valuable heavy minerals, particularly ti-bearing minerals, necessitates knowledge of their compositional variation and the sand transport processes into the sedimentary basin where they are found (morton & hallsworth 1999; morton et al. 2004). conventional provenance studies employ methods such as sensitive high resolution ion microprobe (shrimp) and electron microprobe analysis (empa) that require time-consuming and often tedious sample preparation, are thus expensive, and are therefore not suitable as a standard exploration technique. as part of a provenance study of ilmenite-rich sands occurring in the miocene of western denmark carried out at geus, it was the aim to develop a more cost-efficient standard analytical tool that could integrate bulk rock chemostratigraphic data, mineral compositional data and age information. this study describes the use of ccsem and la-icp-ms as alternative techniques, capable of providing detailed information relevant to sand provenance more rapidly and less expensively than conventional methods. general geological setting the coastline of the proto-north sea had a nw–se trend across central jylland during the miocene (fig. 1). the coastal regions were sourced by large rivers draining the western part of the scandinavian shield during the early miocene. a distinct change to a more westerly transport direction occurnew methods in provenance studies based on heavy minerals: an example from miocene sands in jylland, denmark christian knudsen, dirk frei,thomas rasmussen, erik s. rasmussen and roger mclimans geological survey of denmark and greenland bulletin 7, 29–32 (2005) © geus, 2005 250 km 350–420 ma 900–1150 ma 1200–1500 ma 1500–1770 ma 1650–1855 ma 1800–1900 ma archaean denmark baltic sea north sea sedimentary cover rocks jylland deltaic and continental deposits beach deposits lagoonal deposits marine deposits stauning 50 km 1 2 3 4 1 sønder omme2 isenvad4 store vorslunde3 8°e 16°e 24°e 32°e 40°e 58°n 66°n fig. 1. left: palaeogeographic map showing distribution of environments in jylland during deposition of the odderup formation (middle miocene; from rasmussen 2004). above: map showing basement ages found in scandinavia and the baltic area (modified from gaál & gorbatschev 1987). red during the mid-miocene (rasmussen 2004). the climate was warm temperate to subtropic. heavy mineral enrichment has been found in beach sands of what were barrier islands (odderup formation and bastrup sand) and in offshore storm sand deposits (stauning sand, figs 1, 2; knudsen 1998; fisher 2003). major and trace element geochemistry during exploration for heavy mineral accumulations, a large number of drill holes were completed in western and central jylland. ilmenite-bearing sand samples (bulk rock) from the drill holes were analysed by x-ray fluorescence (xrf). in the vorslunde area, the analytical results show that the finegrained micaceous sand belonging to the stauning sand (rasmussen 2004) has a distinct geochemical signal compared to the overlying medium-grained quartz sand of the odderup formation (fig. 3). the fe/ti ratio (fig. 3a) is higher in the stauning sand compared to the odderup formation as iron is leached out of the ilmenite during alteration of the sediment (weibel 2003). the higher fe/ti ratio in the stauning sand indicates that it has suffered less leaching than the odderup formation. the v/ti ratio (fig. 3b) is higher in the stauning sand than the odderup formation, indicating a higher vanadium content in the ilmenite of the stauning sand. as vanadium is less likely to be leached out of the ilmenite than iron, this may reflect a difference in the composition of ilmenite in the source areas for the sands in the two units. the y/ti ratio (fig. 3c) is higher in the stauning sand than the odderup formation indicating that the stauning sand has a different heavy mineral assemblage; presumably a higher content of primary monazite and xenotime which are the main carriers of yttrium. this may indicate a different ratio between monazite and xenotime in the source regions of the two units. computer controlled scanning electron microscopy the ccsem method, developed and applied in provenance analyses at geus (frei et al. 2005), provides the following: 1. modal abundances of the heavy minerals. 2. major element composition of the individual grains. 3. grain-size and grain-shape data for the grains. 4. maturity of the ti-minerals. for ccsem analysis, the bulk sample and 500 to 1500 grains of the heavy mineral fraction obtained by heavy liquid separation are embedded in epoxy such that no grains touch each other. 30 odderup fm arnum fm gram fm bastrup sand stauning isenvad vorslunde stauning sand sdr. omme sw ne lithostratigraphy marine silt and clay fluvial and marine sand brackish water silt and clay coal hodde fm fig. 2. simplified miocene lithostratigraphy of the study area with position of sample localities indicated (modified from rasmussen et al. 2004). 0 1 2 3 4 5 a b c 0 2 4 6 8 10 % tio 2 0 2 4 6 8 10 0 20 40 60 80 0 20 40 60 0 2 4 6 8 10 stauning sand odderup formation stauning sand odderup formation stauning sand odderup formation % tio 2 % tio 2 % f e 2 o 3 p p m v p p m y fig. 3. xrf analyses of sand from the vorslunde area. for location, see fig. 1. modal abundances of the heavy mineral suite the chemical composition of the grains is detected as well as such physical parameters as aspect ratio, circularity, perimeter, length and number of grains counted. this information is used to calculate the modal abundances and grain-size distributions of the detected minerals. in fig. 4, the modal abundance of heavy minerals in the odderup formation is compared to the underlying stauning sand. the odderup formation is dominated by stable heavy minerals such as ilmenite, rutile and zircon, whereas the stauning sand contains a large proportion of mafic silicates vulnerable to dissolution during alteration (weibel 2003), indicating a higher maturity of the odderup formation sands. titanium content of the titanium minerals the tio2-distribution in the ti-mineral fraction (i.e. ilmenite, rutile and leucoxene) of a sediment is a very sensitive indicator of its maturity. the continuous alteration of primary ilmenite (with an average stoichiometric tio2-content around 50 wt%) to leucoxene by leaching of iron, leads to a significant increase in the tio2-grade of the ti-mineral fraction in a mature sediment (e.g. weibel 2003). since the ccsem analysis yields the average chemical compositions of all minerals present in a given sample, the tio2-distribution of the ti-mineral fraction can easily be calculated without the need for time-consuming mineral separation. the average tio2-content of around 68 wt% observed in the odderup formation (fig. 5) is indicative of a mature sediment. in contrast, the majority of the data for the stauning sand scatters around the normal tio2-content of 50 wt% (fig. 5), characteristic of primary, unleached ilmenite, indicating a less mature sediment. this supports the interpretation of fig. 3a mentioned above. garnet composition the compositional variability of the detrital garnet fraction in sediments is also a very useful provenance indicator (e.g. morton 1985; morton & hallsworth 1994). garnet compositions are normally determined by point-counting a representative number of grains using electron microprobe analysis. using ccsem, information on the chemical variability of the garnet fraction in a sample is acquired concomitantly with the titanium mineral data during routine operation, i.e. no further sample preparation or analytical steps are required. laser ablation – inductively coupled plasma – mass spectrometry for la-icp-ms age determinations, zircons are separated from the bulk samples using conventional heavy liquid and magnetic separation methods. the final separation step is 31 odderup fm (sønder omme) odderup fm (vorslunde) stauning sand (stauning) stauning sand (vorslunde) ti-magnetite ilmenite leucoxene rutile zircon garnet kyanite-sillimanite -staurolite mafic silicates fig. 4. modal abundances in the heavy mineral fraction of odderup formation sand and stauning sand determined by ccsem. for location, see fig. 1. 30 38 46 54 62 70 78 86 94 0 10 20 30 m in e ra l w t% 0 10 20 30 m in e ra l w t% odderup formation stauning sand tio 2 (wt%) 30 38 46 54 62 70 78 86 94 tio 2 (wt%) fig. 5. distribution of tio2-content of the ti-mineral fraction in the odderup formation and the stauning sand at vorslunde, determined by ccsem. the higher tio2-content in the quartz sand reflects its higher maturity. for location, see fig. 1. made by hand-picking individual zircon grains using an optical microscope. for analysis, the individual detrital zircon grains are mounted on adhesive tape. the la-icp-ms dating is based on measuring the 207pb-206pb ratios in the zircon, and the data are in good agreement with data from shrimp analyses (frei et al. 2005). the different provenance of the various miocene sandy units is also reflected by their detrital zircon age distribution data (fig. 6) . the bastrup sand and the odderup formation are characterised by a bimodal distribution of the ages, with peaks around 1100 and 1600 ma, whereas the stauning sand has a broad distribution with a single peak around 1500 ma and a scattering of ages between 2500 ma and 3000 ma. when compared to the map showing the distribution of ages in the scandinavian shield and the baltic area (fig. 1), a north and north-easterly provenance for the bastrup sand and the odderup formation is likely, whereas the stauning sand probably has a more easterly source, where older rocks are more common. however, the bastrup sand and the odderup formation are coarser grained, and were not deposited in the same environment. there is a possibility that the differences are due to sveco-norwegian zircons being larger and thus being less frequent in the fine-grained sediments of the stauning sand. acknowledgement the results presented here are a part of a study carried out with financial support from dupont titanium technologies. references fisher, t. 2003: georadar investigations and sedimentology of miocene heavy mineral deposits, central jylland, 178 pp. unpublished m.sc. thesis, university of copenhagen, denmark. frei, d., rasmussen, t., knudsen, c., larsen, m., whitham, a. & morton, a. 2005: linking the faroese area and greenland: new methods and techniques used in an innovative, integrated provenance study. annales societatis scientiarum færoensis supplementum 43, 1–7. gaál, g. & gorbatschev, r. 1987: an outline of the precambrian evolution of the baltic shield. precambrian research 35, 15–52. knudsen, c. 1998: heavy mineral exploration in miocene sediments, jylland. danmarks og grønlands geologiske undersøgelse rapport 1998/45, 44 pp. morton, a.c. 1985: a new approach to provenance studies: electron microprobe analysis of detrital garnets for middle jurassic sandstones of the northern north sea. sedimentology 32, 553–566. morton, a.c. & hallsworth, c.r. 1994: identifying provenance-specific features of detrital heavy mineral assemblages in sandstones. sedimentary geology 90, 241–256. morton, a.c. & hallsworth, c.r. 1999: processes controlling the composition of heavy mineral assemblages in sandstones. sedimentary geology 124, 3–29. morton, a.c., hallsworth, c. & chalton, b. 2004: garnet compositions in scottish and norwegian basement terrains: a framework for interpretation of north sea sandstone provenance. marine and petroleum geology 21, 393–410. rasmussen, e.s. 2004: stratigraphy and depositional evolution of the uppermost oligocene–miocene succession in western denmark. bulletin of the geological society of denmark 51, 89–109. rasmussen, e.s., dybkjær, k. & piasecki, s. 2004: the billund delta: a possible new giant aquifer in central jutland. geological survey of denmark and greenland bulletin 4, 21–24. weibel, r. 2003: alteration of detrital fe-ti oxides in miocene fluvial deposits, central jutland, denmark. bulletin of the geological society of denmark 50, 171–183. authors’ addresses c.k., d.f., t.r. & e.s.r., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: ckn@geus.dk r.mcl., dupont titanium technologies, experimental station, e352/217, route 141 and henry clay, wilmington, de 19808, usa. 32 n u m b e rs o f zi rc o n s n u m b e rs o f zi rc o n s 0 5 10 15 20 0 0 5 10 15 20 1000 2000 3000 million years 0 1000 2000 3000 million years 0 1000 2000 3000 million years 0 1000 2000 3000 million years odderup formation, vorslunde, quartz sand 123 zircon grains stauning sand, sønder omme, mica sand 181 zircon grains bastrup sand, isenvad, quartz sand 118 zircon grains stauning sand, stauning, mica sand 128 zircon grains 0 5 10 15 20 0 5 10 15 20 fig. 6. age distribution among detrital zircons from miocene sands in jylland. note the bimodal distribution of zircon ages in the odderup formation and the bastrup sand in contrast to the unimodal and generally older ages in the stauning sand (see text for discussion). geological survey of denmark and greenland bulletin 1, 349-366 349 the use of spectral natural gamma-ray analysis in reservoir evaluation of siliciclastic sediments: a case study from the middle jurassic of the harald field, danish central graben ida l. fabricius, louise dahlerup fazladic, armgard steinholm and uffe korsbech a cored sandstone interval from the middle jurassic harald field of the danish north sea was chosen for an investigation of the mineralogical sources for the gamma-ray activity, and with the purpose of determining how the spectral natural gamma (sng) log could be used as an indicator of reservoir quality. core intervals of quartz arenites and quartz wackes were selected. although no linear relationship was found between clay content and potassium (k), thorium (th), or uranium (u), the k content characterises three discrete lithofacies. lithofacies i has a grain-supported texture, with a predominance of quartz grains; only minor fine-grained matrix is present. sandstones of lithofacies i have a low k content and most of the k is hosted in feldspar. porosity varies between 23% and 28% and permeability is in the range 200–2000 md. lithofacies ii sandstones have a grain-supported texture, with a predominance of quartz grains; fine-grained matrix fills the intergranular volume. sandstones of lithofacies ii have an intermediate k content, with k-feldspar, mica, and illite as the main sources. porosity varies between 11% and 17% and permeability is in the range 0.4–25 md. lithofacies iii has a matrix-supported texture with quartz grains floating in a clay-rich matrix. samples from lithofacies iii have the highest k signal. illite and illitised kaolinite are roughly equal in importance as sources of k. porosity is up to 11% and permeability up to 0.5 md. the th and u content of all lithofacies is governed primarily by the presence of heavy minerals; no apparent general relationship between u and total organic carbon (toc) was found. comparisons between the core measurements of k, th, and u, and the sng log disclosed a discrepancy between the calibrations of laboratory and borehole measurements. for u the discrepancy contains an erratic element, whereas the difference for k and th can be eliminated by correction factors. thus, the conclusions based on laboratory measurements appear to be applicable to the log data, and, using corrected k values, the facies subdivision can be extended throughout the reservoir section based on the sng log. keywords: danish central graben, north sea, middle jurassic, sandstone reservoir, gamma-ray spectometry, mineralogy, geochemistry i.l.f., l.d.f.*, a.s.‡ & u.k., technical university of denmark (dtu), dk-2800 lyngby, denmark. *present address: internationalt patent-bureau, dk-2630 tåstrup, denmark. ‡present address: jar›frø›isavni›, brekkutún 1, fo-110 tórshavn, faroe islands. e-mail: ilf@er.dtu.dk geological survey of denmark and greenland bulletin 1, 349–366 (2003) © geus, 2003 350 natural gamma-ray wireline logging is commonly used for lithological, or more precisely mineral, identification in boreholes. in sandstone reservoir sections, its main purpose is to obtain an indication of the clay content and thus, reservoir quality. schlumberger (1982) has described two types of gamma-ray logs: the conventional gamma ray log records the total natural gamma radiation in the borehole independent of the energy of the gamma rays, whereas the spectral natural gamma-ray (sng) probe measures the gamma-ray spectrum, i.e. the energy distribution of the gamma rays. the gamma rays originate from the decay of radiogenic potassium (40k), thorium (232th) and uranium (238u), each of which exhibit a characteristic energy spectrum. the measured energy spectrum is transformed into concentrations of k, th and u (schlumberger 1982). in the west lulu-3 appraisal well of the middle jurassic harald field, sng logging was performed in order to differentiate micaceous sand from shale. this distinction should in theory be possible from the th/k ratio, but the picture is complicated because several radioactive minerals are present in the micaceous sandstones that give a more shale-like response. the purpose of this study was to identify the radioactive minerals in the sandstones and to estimate their contribution to the gamma-ray spectrum. furthermore, the aim was to identify the gamma-spectral characteristics of intervals with different reservoir quality. with these objectives, we sampled the cores of west lulu-3 and defined three lithofacies based on petrographical and mineralogical data. the three lithofacies chosen are expected to have characteristic reservoir qualities as reflected by porosity and permeability. gamma-spectral data were obtained in the laboratory for each of the three lithofacies, and the laboratory data were compared with the log data. the harald field the harald field is situated in the danish portion of the søgne basin in the north-eastern part of the danish central graben (fig. 1). the hydrocarbon reservoir is located in sandstones of the middle jurassic bryne and lulu formations (johannessen & andsbjerg 1993; andsbjerg 2003, this volume; michelsen et al. 2003, this volume). according to johannessen & andsbjerg (1993) and andsbjerg (2003, this volume), this succession represents a range of paralic and coastal plain environments (fig. 2), and is overlain by the marine shales of the lola formation. the sng log over the cored section of west lulu-3 is represented in figure 3. geochemistry of potassium, thorium and uranium hassan et al. (1976) examined the mineralogy and chemical composition of 500 samples of varying lithology from different environments of deposition. of particular relevance to this work, their data included k, th and u measurements. the following conclusions concerning the occurrence of these three elements are based on hassan et al. (1976) as well as schlumberger (1982), and nielsen et al. (1987). potassium potassium is a major element in many rock-forming minerals. the radioactive isotope 40k constitutes 0.0118% of the total potassium in a mineral, and the gamma signal from the radioactive decay is an important indicator of mineralogical composition. the most common k-bearing minerals in sedimentary rocks are k-feldspar, mica and illite. k-feldspar and mica are more common in sandstones, illite in shales. k-feldspar and mica have a greater k content than illite, and thus the gamma-ray flux is only a measure of clay content in the absence of significant k-feldspar (cowan & myers 1988). glauconite can also be a significant source of k in sedimentary rocks. typical potassium contents of k-bearing minerals are: illite, 4.5%; muscovite, 7.9–9.8%; plagioclase, 0.54%; k-feldspar, 10.9–14.0% (nielsen et al. 1987). engstrøm (1981) measured k, th and u in danish cenozoic strata (clay, silt and sand) and found results in accordance with the distributions and concentrations mentioned above. kaolinite is sometimes reported to contain minor amounts of k and th, but ideal kaolinite contains neither elements (see below). straightforward relationships between k and clay content should not be expected. in miocene–pliocene shales from the north sea, berstad & dypvik (1982) found a positive correlation between k and the clay content. this was inferred to be mainly controlled by the illite of the clay fraction. on the contrary, in paleocene and eocene strata, radioactivity and clay content are negatively correlated. this is probably because the clay fraction is rich in a kpoor smectite, derived from basaltic volcanic material. thorium thorium is a common trace element in most geological environments. in weathering environments it is prac351 ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■ ■ ▲ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■ ■ ■■ ■■ ■■ ■ ■ ■ ■ ■■ ■■■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■■ ■ ■ w. lulu-4 w. lulu-3 feda graben inge highmid north sea high heno plateau tail end g raben a rne–elin g raben ringkøbing–fyn high gertrud graben/ plateau o uter rough basin c offee soil fault east n orth sea block søgne basin 56°30´n reverse fault triangles showing dip of fault plane normal fault boxes showing dip of fault plane salt structure well harald field fault plane ▲ ■■ 20 km 4°e 500 km uk norway denmark germany the netherlands fig. 1. the location of the west lulu-3 well within the harald field in the danish sector of the north sea central graben. inset map shows the central graben (blue) straddling the national boundaries and branching northwards into the outer moray firth and viking graben systems; the area of the enlarged map of the northern danish central graben is indicated in red. w. lulu-4 w. lulu-3 coal sequence boundary studied core section paralic and shallow marine (sand-dominated) fluvial and estuarine in incised valley alluvial plain and lacustrine shallow marine (mud-dominated) 50 m base jurassic 3784 m b. msl base jurassic 3793 m b. msl lola fm lulu fm bryne fm triassic gr sonicgr sonic ssw nne fig. 2. log correlation of the middle jurassic in the harald field area showing the stratigraphic position of the west lulu-3 cored section under study in this paper; for location of wells, see fig. 1. modified from andsbjerg (2003, this volume). 352 ii ii ii iii iii i i i iii iii iii iii iii iii iii ii ii i ii i i i iii shallow marine (lower shoreface) back barrier and shallow marine c o as ta l p la in lo la f m lu lu f m b ry ne f m estuarine and fluvial channels, peat mires alluvial plain li th o st ra ti gr ap hy d ep th ( m b . m sl ) se di m en ta ry en vi ro nm en t li th o fa ci es sa m pl e a b c d1 d2 e f g h i j k1 k2 l1 l2 m n o p q1 q2 r s 3560 3580 3600 3620 3640 3660 3680 3700 3720 u (ppm) th (ppm) k (%) th/k (10-4) lithofacies from k-log -10 20 0 0 10 i ii iii10 0 5 tically insoluble and is thus commonly concentrated in residual deposits such as bauxite and clay. important quantities of thorium are found in the heavy minerals monazite, rutile and zircon. zircon normally contains 100–2500 ppm th (nielsen et al. 1987), while monazite may contain substantially more. pure clay samples typically contain 5–30 ppm th (adams & weaver 1958). theoretical considerations indicate that th4+, with an ionic radius of 0.97 nm, cannot be accommodated in the layer structure of clay minerals, so that th in these minerals could be assumed to be fixed by adsorption (adams & weaver 1958). hurst & milodowski (1994) stated, however, that the origin of th in clay minerals is unclear, and proposed that it is caused by inclusions of clay-sized heavy minerals. in the samples of hassan et al. (1976), the th content correlated with the content of clay minerals, but it was not proven that the clays were responsible for the th enrichment. uranium under neutral ph conditions, the uranyl ion ((uo)2+) forms ionic complexes with carbonates, which control its dispersion and mobility in nature. the uranyl ion also forms numerous complexes with organic compounds (e.g. humic acids), which facilitate its fixation by organic and mineral matter. hassan et al. (1976) found that u shows a strong correlation with organic carbon, probably because uo2 precipitates under reducing conditions. factors other than the content of organic matter (such as the availability of u) may be important for the occurrence of u in sediments as exemplified by the data of berstad & dypvik (1982). in shales from the cenozoic of the north sea, these workers found no correlation between u and total organic carbon (toc). uranium also occurs as a trace element in accessory minerals (zircon contains 300–3000 ppm u; nielsen et al. 1987) and in colloidal fe-oxide/hydroxide coatings on mineral grains. uranium species may also be adsorbed onto clay minerals. methods borehole gamma-ray measurement the sng tool used for logging of the west lulu-3 borehole uses five continuous energy windows covering the entire energy range from 0.1–3.0 mev (fig. 4). the heart of the tool is a sodium iodide (nai) crystal that detects the gamma rays in the borehole. a gamma-ray detector based on a nai crystal is able to produce accurate data on the radioactivity in the surroundings. to interpret the spectrum correctly, however, it is necessary to take into account the influence of the drilling mud, variations in the borehole diameter and the standoff of the probe. the (net) uranium count rate in window w4 is usually low (fig. 4), and the uranium measurements therefore become dependent on the count rates of the low-energy windows w1 and w2, which are influenced the most by the borehole parameters. this results in an unreliable u log curve. by using the whole spectrum, high count rates are attained, i.e. the statistical accuracy of the counting is high, but borehole correction factors must be included. laboratory gamma-ray measurement similar techniques can be used for laboratory measurements of gamma radiation from k, th and u in rock samples. laboratory measurements were obtained with nai crystals using three energy windows centred around the three most prominent gamma energy k, th and u peaks of the spectrum (fig. 4). these measurements are in the high-energy part of the spectrum and thus less dependent on geometry, density and matrix influence. however, by using only counts from a fraction of the spectrum, longer counting times are needed. for the present study, 19 core-sections (each c. 80 cm long) of the west lulu-3 cores were selected on the basis of core inspection and the k, th and u signals of 353 facing page: fig. 3. the natural spectral gamma-ray log over the cored interval of west lulu-3. samples investigated in the present study are indicated by the letters a–s. for the construction of the lithofacies log, the k value from the spectral gamma borehole log was multiplied by 0.8 (as recommended in the text). intervals in which the k content is < 0.7% are referred to lithofacies i, those with 0.7–2% k are referred to lithofacies ii and the sediments with > 2% k are assigned to lithofacies iii. the corresponding lithofacies of the core samples, as determined by laboratory measurements, are indicated by roman numerals. the sedimentary environment interpretations are by j. andsbjerg (personal communication 1995; see also andsbjerg 2003, this volume). 354 the sng log. ten of the sections are from the bryne formation, six are from the lulu formation and the upper three sections are from the lower levels of the lola formation (figs 2, 3). the sections were chosen to cover the range of different k, th and u concentrations and ratios in the interval 11 800–12 300 ft below kelly bushing , corresponding to c. 3560–3720 m below mean sea level. each section was measured in the laboratory by a spectral natural gamma-ray scanner with a nai crystal, and on the basis of these results, typical core intervals, 5–7 cm long, were selected from each core section for more detailed analysis. a total of 23 samples were collected. for each of these samples, the k, th and u contents were determined by a ge(li) gamma spectrometer. most samples were selected from intervals with stable k, th and u readings. mineralogy and chemistry after removal of a reference slab, samples were taken for the preparation of thin sections and polished specimens. the thin sections were described by optical microscopy, and the polished specimens were used for back-scatter electron microscopy (bsem) and energydispersive microprobe analysis (eds). for each selected interval, a sample of c. 125 g was cut out, crushed and homogenised. measurement of toc, inorganic carbon and sulphur was undertaken on 0.5 g size sub-samples after ignition in a leco cs 225 furnace. the k, th and u content of the crushed samples was measured by placing the samples inside a laboratory nai crystal gamma spectrometer. by this method, low levels of radioactivity can be measured. approximately 120 g of each sample were subsequently separated into grain-size fractions by wet and dry sieving. the mineral content of the clay size (< 2 µm), fine silt size (2–20 µm), coarse silt – very fine sand (20–125 µm), and coarser sand fractions (125–250 µm, 250–600 µm and > 600 µm) was determined by x-ray diffractometry (xrd) using ni-filtered cu-kα radiation at apparatus settings of 40 kv and 40 ma with the step scanning variant slit. the effectiveness of the grain-size separation and the mineralogy of the fractions was checked by microscopy. on the basis of these data, the separated fractions for each sample were remixed into three portions: clay (< 2 µm), silt and very fine sand (2–125 µm) and coarser sand (> 125 µm). these three portions were chosen because within each portion, only minor differences in mineralogy were observed. for each of the three portions, the k, th and u concentrations were determined by gamma-ray spectrometry. separation of the samples into fractions of individual minerals was not attempted, but the mineralogical composition of the samples was estimated, and the contribution from each mineral to the total k was inferred in the following way. the amount of organic matter in each sample was assumed to be equal to the toc. the amount of carbonate was calculated from inorganic carbon with reference to xrd data. all sulphur was assumed to be associated with pyrite unless barite was detected, in which case optical microscope and xrd data formed the basis for partitioning the sulphur between barite and pyrite. the amounts of k-feldspar, w1 w2 w3 w4 w5 1 mev0 10 0 00 c o un ts p er c ha nn el ( 10 00 s ec ) 20 0 00 2 mev energy k window u window th window fig. 4. natural gamma-ray spectrum measured in the laboratory with a nai crystal. energy windows used for concentration determinations are centred around the three most prominent highenergy k, th and u peaks. natural gamma-ray spectra measured in boreholes contain the same peaks, but the spectra are blurred compared to a laboratory-measured spectrum, and the peaks are less distinct. the tool for the natural gamma ray spectrometry log in the west lulu-3 well uses five continuous windows, w1–w5, covering the energy range from 0.1 to 3.0 mev. at lower energies, the spectrum shape is significantly influenced by the borehole geometry and mud density. 355 clay minerals and mica were calculated from the gamma spectrometry and eds potassium measurements, guided by the semi-quantitative xrd and microscope data on mineral abundance. on the basis of these data and eds analysis of the k content in the observed minerals, the contribution from each mineral to the total k was calculated. the presence and identity of heavy minerals were determined by microscopy and eds analysis. results facies analysis on the basis of thin-section microscopy, the samples were classified into lithofacies i, ii and iii; a similar classification was developed by vernik & nur (1992; table 1). lithofacies i (five samples) comprises well-sorted quartz arenites with a maximum clay content of 2–3%. the samples are from sedimentary rocks that are primarily interpreted to represent channel-fill sediments within paralic and coastal plain/floodplain environments (fig. 3; johannessen & andsbjerg 1993; andsbjerg 2003, this volume). porosity is in the range 23–28%, and permeability is in the range 200–2000 md. lithofacies ii (eight samples) consists of grain-supported quartz arenites with up to 18% clay. the samples are from sedimentary rocks interpreted to represent coastal plain/floodplain and lower shoreface environments of deposition (fig. 3; johannessen & andsbjerg 1993; andsbjerg 2003, this volume). porosity is in the range 11–17% and permeability is in the range 0.4–25 md. lithofacies iii (ten samples) comprises wackes and sandy shales (matrix-supported, with occasional grainto-grain contacts) containing more than 18% clay. the 93 1 1 1 1 3 87 1 1 5 1 1 3 1 89 1 1 5 1 3 93 3 1 1 1 1 81 1 1 13 3 1 88 2 1 7 1 1 88 2 1 7 1 1 88 2 1 3 3 3 73 3 2 2 5 11 1 1 2 77 2 3 9 9 68 6 24 2 59 2 1 15 15 8 60 3 4 9 18 2 2 2 60 3 4 9 18 1 2 2 1 38 1 16 33 2 10 41 1 10 45 3 43 4 15 30 8 32 1 6 56 5 44 1 2 25 25 3 25 1 1 31 16 2 23 1 28 14 56 1 1 36 1 7 35 18 2 1 27 1 2 45 23 1 1 h 3619.4 i 0.09 0.26 0.4 e 3588.5 i 0.14 2.47 0.1 g 3610.4 i 0.03 0.64 0.1 m 3665.2 i 0.13 0.13 0.3 j 3635.6 ii 0.04 3.18 0.0 l1 3660.7 i 0.08 0.25 0.2 l2 3661.0 i 0.13 0.19 0.1 s 3720.1 i 0.38 0.08 0.0 a 3561.2 ii 1.40 0.67 0.5 q2 3698.7 ii 0.03 0.19 0.0 k2 3654.2 iii 0.04 1.88 0.1 r 3700.0 ii 0.05 8.23 0.2 b 3566.3 ii 0.01 2.18 1.0 c 3573.9 ii 0.10 2.20 0.9 d2 3585.9 iii 0.31 10.25 0.1 f 3591.6 iii 0.03 2.84 0.1 d1 3585.5 iii 0.05 8.28 0.2 i 3627.0 iii 0.00 5.00 0.1 q1 3698.0 iii 0.32 0.12 0.0 p 3689.7 iii 2.70 0.93 0.0 k1 3653.8 iii 0.10 1.10 0.1 n 3671.0 iii 0.30 0.80 0.0 o 3680.7 iii 0.02 0.51 0.0 0.03 0.0 0.1 0.15 0.15 0.07 0.0 0.15 0.15 0.07 0.0 0.15 0.03 0.0 0.07 0.4 0.4 0.07 0.0 0.15 0.2 0.0 0.1 0.3 0.2 0.0 0.1 0.3 0.03 0.15 0.1 0.3 0.01 0.14 0.2 0.44 0.07 0.09 0.5 0.3 0.3 0.7 0.4 0.0 0.0 0.15 0.8 0.1 0.3 0.04 0.7 0.4 0.44 0.07 0.04 0.7 0.4 0.44 0.018 1.0 1.1 0.1 0.0 1.4 0.7 0.0 0.15 0.9 1.1 0.4 0.0 1.7 0.4 0.1 0.0 0.3 1.3 0.2 0.15 0.16 2.2 0.1 0.15 1.7 1.0 0.0 0.0 0.18 2.5 0.7 0.15 0.3 3.2 0.2 0.15 in o rg an ic c ar bo n ( ca rb o na te ) o rg an ic c ar bo n (t o c ) su lp hu r qu ar tz ( + a lb it e) k -f el ds pa r m us co vi te ill it e ka o lin it e do lo m it e si de ri te py ri te co al ba ri te he av y m in er al s gl au co ni te ka o lin it e ill it e m us co vi te fe ld sp ar gl au co ni tesample* geochemical data (wt%) interpreted mineral content (%; based on xrd, bsem and petrography) interpreted contribution to k content (%) depth metre b. msl lithofacies * samples listed in order of increasing k content (bulk sample), see table 3. table 1. geochemical data, mineralogy and interpreted mineral contribution to k content sampled facies are interpreted, in the main, to represent a coastal plain/floodplain environment of deposition (fig. 3; johannessen & andsbjerg 1993; andsbjerg 2003, this volume). porosity is less than or equal to 11%, and permeability below 0.5 md. characteristic bsem images of each lithofacies are presented on figure 5. crushing and grain size separation were successful for samples of lithofacies i, and some of lithofacies ii, but not for samples of lithofacies iii and several lithofacies ii samples, where the coarser fractions contain mineral aggregates. although the fine fractions may include pieces broken from the coarser grains during sample crushing, no such pieces were observed. the sieve data are presented in table 2. mineralogy quartz is present in all samples as sandand silt-sized grains. samples of lithofacies i contain sand-size quartz grains with diameters greater than 130 µm, samples of lithofacies ii have quartz grains of very fine sand and coarse silt size (50–130 µm), and samples of lithofacies iii, as a rule, contain only silt-size particles. one sample of lithofacies iii though, contains quartz grains as 356 0,1 mm 0,1 mm 0,1 mm 1 2 3 fig. 5. back-scatter electron microscope images. a: lithofacies i, core sample e. porous, grain-supported quartz arenite with isolated heavy mineral grains, such as zircon (1). b: lithofacies ii, core sample c. grain-supported quartz wacke, with no visible porosity. grains include: 2, pyrite; 3, glauconite. c: lithofacies iii, core sample k2. matrix-supported quartz wacke. sample‡ lithofacies (> 125µm) (2–125µm) (< 2µm) total (%) (%) (%) (%) h i 77.99 17.63 3.18 98.8 e i 49.08 46.41 3.04 98.53 g i 69.02 24.44 2.84 96.3 m i 58.2 37.64 2.71 98.55 j ii 45.19 46.52 6.76 98.47 l1 i 64.07 31.08 3.94 99.09 l2 i 62.11 32.39 6.47 100.97 s i 74.05 21.57 3.85 99.47 a ii 0.6 89.67 6.78 97.05 q2* ii 25.97 13.95 k2* iii 9.8 70.37 18.54 98.71 r* ii 7.51 81.96 7.3 96.77 b* ii 3.07 83.48 8.61 95.16 c* ii 4.24 82.82 10.49 97.54 d2* iii 24.22 63.8 7.45 95.47 f* iii 23.79 58.95 15.72 98.46 d1* iii 23.69 66.38 6.8 96.87 i* iii 21.68 62.86 11.32 95.86 q1* iii 10 73.92 17.4 101.32 p* iii 31.28 54.7 10.05 96.03 k1* iii 28.89 52.31 13.71 94.91 n* iii 14.12 67.84 9.6 91.56 o* iii 16.62 65.62 17.26 99.5 *the silt and sand fractions contain lumps of non-disaggregated material. ‡ samples listed in order of increasing k content (bulk sample), see table 3. table 2. grain-size fractions of crushed samplesa b c large as 80 µm. some diagenetic quartz overgrowths are seen in samples of lithofacies i and ii. feldspar. k-feldspar grains have been detected in 18 of the 23 samples from a combination of xrd, thin-section study and eds. in 16 of the samples, grains of plagioclase and k-feldspar have been found, and in four samples only plagioclase was found. the only type of plagioclase detected by eds is albite. the content of plagioclase barely exceeds a few percent by volume in any sample, and no quantification was attempted. the estimated quartz content (table 1) therefore probably includes a minor component of plagioclase. both degraded and fresh feldspars are observed in lithofacies iii samples, whereas feldspar grains in lithofacies i and ii samples are generally degraded. no indications of preferential degradation of either plagioclase or k-feldspar was noted. muscovite was found in most samples (table 1). the textural relationships indicate that the muscovite is of detrital origin. it is generally fresh and unaltered. eds analysis indicated a k content close to the ideal (10%). illite is present in the clay fraction of most samples, with the exception of some from lithofacies i (table 1). eds analysis indicated that the illites of samples a–p contain around 7% k and the illites of samples q–s contain 5% k. illite was found in clay of apparently detrital origin (fig. 6a). 357 0,1 mm 0,1 mm 0,1 mm 0,1 mm fig. 6. back-scatter electron microscope images. a: allochthonous clay (illite and kaolinite) between sand grains in sandstone of lithofacies ii; core sample j. b: authigenic kaolinite platelets in sandstone of lithofacies i. the bright grain in the upper part of the picture is rutile; core sample m. c: particles of barite (white) caught in the pore space of a lithofacies i sandstone, due to drilling mud invasion; core sample h. d: the fabric observed in c, at higher magnification, showing the characteristic textural habit of barite. a c d b 358 kaolinite was detected in all samples, being the dominant mineral in several samples of lithofacies iii. authigenic kaolinite as well as detrital kaolinite were observed (fig. 6). no attempt was made to differentiate between different polytypes. the measured k content of the kaolinites (by eds) in the present samples have the following general pattern: samples a–c, around 0.1% k; samples d–m, approximately 3% k; samples n–s, approximately 1% k. heavy minerals. grains of zircon, rutile and chromite were identified by optical microscopy and eds. they occur in significant amounts in sample e and g of lithofacies i, and in sample j of lithofacies ii. pyrite is present in most of the samples where it is commonly associated with organic matter (fig. 5). carbonate. dolomitic cement was found in several samples (table 1). in sample a, fe-rich dolomite was identified with a mg/fe (atomic) ratio of 1.4 (based on eds). in sample p (lithofacies iii), many siderite concretions, as well as dolomite, are present. the illite-rich sample p is from an interval that is interpreted to record an alluvial plain setting (fig. 3; andsbjerg 2003, this volume). this concurs with the common observation of siderite in anoxic freshwater deposits (postma 1983). barite is present in minor amounts, as indicated by the xrd pattern of four samples of lithofacies i (table 1). barite was only found in the clay and silt fractions. bsem imaging reveals the textural habit of the barite, showing that the barite content is the result of infiltration of fine-grained particles from the drilling mud into permeable lithofacies i sandstones (fig. 6c, d). glauconite was found in the three samples (a–c) from the lola formation. this is thought to concur with the interpreted environment of deposition (lower shoreface). a potassium content of 2–4 wt% was measured by eds. gamma-spectral analysis the results of the gamma-spectral analysis of the crushed samples are listed in table 3. the results from gammaspectral analysis of the clay fractions are given in table 4. gamma-spectral analysis of clay fraction sample* lithofacies k (%) th (ppm) u (ppm) h i 1.65 ± 0.10 7 ± 3 2.4 ± 0.6 e i 1.80 ± 0.14 18 ± 4 1.7 ± 0.8 g i 2.28 ± 0.13 9 ± 3 1.9 ± 0.8 m i 2.81 ± 0.15 15 ± 4 3.5 ± 0.9 j ii 2.36 ± 0.07 8.7 ± 1.5 2.7 ± 0.3 l1 i 2.50 ± 0.10 15 ± 3 2.1 ± 0.6 l2 i 2.02 ± 0.07 10.9 ± 1.7 1.5 ± 0.4 s i 2.98 ± 0.12 12 ± 3 1.6 ± 0.7 a ii 3.50 ± 0.11 18 ± 2 1.6 ± 0.5 q2 ii 2.88 ± 0.05 10.1 ± 1.1 2.1 ± 0.3 k2 iii 1.63 ± 0.05 12.3 ± 1.1 3.6 ± 0.2 r ii 4.05 ± 0.07 19.0 ± 1.4 5.9 ± 0.3 b ii 2.98 ± 0.08 13.8 ± 1.7 3.5 ± 0.4 c ii 3.54 ± 0.05 15.2 ± 1.0 4.1 ± 0.2 d2 iii 2.14 ± 0.06 10.9 ± 1.4 2.4 ± 0.3 f iii 2.41 ± 0.05 14.2 ± 1.0 3.8 ± 0.2 d1 iii 2.64 ± 0.06 12.0 ± 1.4 4.7 ± 0.3 i iii 2.42 ± 0.05 13.1 ± 1.0 3.0 ± 0.2 q1 iii 3.41 ± 0.05 12.0 ± 0.1 2.1 ± 0.2 p iii 4.17 ± 0.08 18.5 ± 1.6 3.1 ± 0.4 k1 iii 3.36 ± 0.07 15.7 ± 1.3 3.9 ± 0.3 n iii 4.35 ± 0.06 16.5 ± 1.2 2.4 ± 0.3 o iii 4.29 ± 0.05 16.2 ± 0.9 2.7 ± 0.2 uncertainties are one standard deviation. *samples listed in order of increasing k content (bulk sample), see table 3. table 3. gamma-spectral analysis of bulk sample sample* lithofacies k (%) th (ppm) u (ppm) h i 0.25 ± 0.01 1.0 ± 0.4 0.4 ± 0.1 e i 0.42 ± 0.02 8.2 ± 0.5 3.2 ± 0.1 g i 0.47 ± 0.02 3.8 ± 0.4 1.5 ± 0.1 m i 0.57 ± 0.01 2.7 ± 0.4 1.1 ± 0.1 j ii 0.59 ± 0.01 1.8 ± 0.4 0.3 ± 0.1 l1 i 0.60 ± 0.02 2.6 ± 0.6 0.5 ± 0.1 l2 i 0.60 ± 0.02 5.5 ± 0.4 0.9 ± 0.1 s i 0.67 ± 0.02 1.0 ± 0.4 0.1 ± 0.1 a ii 0.87 ± 0.02 3.9 ± 0.5 1.2 ± 0.1 q2 ii 1.18 ± 0.02 5.7 ± 0.5 1.2 ± 0.1 k2 iii 1.21 ± 0.03 10.7 ± 0.6 3.9 ± 0.1 r ii 1.92 ± 0.03 8.0 ± 0.6 2.6 ± 0.1 b ii 1.99 ± 0.03 8.0 ± 0.6 2.8 ± 0.1 c ii 2.00 ± 0.03 11.6 ± 0.6 3.2 ± 0.1 d2 iii 2.05 ± 0.04 13.3 ± 0.7 4.0 ± 0.2 f iii 2.15 ± 0.03 13.2 ± 0.6 4.0 ± 0.1 d1 iii 2.17 ± 0.02 10.2 ± 0.5 3.4 ± 0.1 i iii 2.17 ± 0.03 11.1 ± 0.7 3.3 ± 0.1 q1 iii 2.37 ± 0.03 10.3 ± 0.6 2.5 ± 0.1 p iii 2.42 ± 0.03 7.3 ± 0.5 2.7 ± 0.1 k1 iii 2.89 ± 0.03 12.3 ± 0.6 2.7 ± 0.1 n iii 3.30 ± 0.03 16.2 ± 0.6 3.6 ± 0.1 o iii 3.51 ± 0.03 16.9 ± 0.6 3.2 ± 0.1 sample size: 18 cm3. uncertainties are one standard deviation. *samples listed in order of increasing k content (bulk sample). table 4. the data for the coarser fractions are not listed. these fractions do not represent the values for the ‘true’ grain size interval because of the incomplete disaggregation of the original sample. the interpreted total mineralogy of the samples, and the interpreted contribution from each mineral to the total k content of each sample, are listed in table 1. potassium concentrations are low in lithofacies i samples (< 0.7%), higher in lithofacies ii samples (0.6–2%), and highest in lithofacies iii (generally > 2% although 359 4 3 2 1 0 20 15 10 5 0 5 4 3 2 1 0 25 20 15 10 5 0 5 4 3 2 1 0 8 6 4 2 0 3550 3575 3600 3625 3650 depth (m b. msl) depth (m b. msl) depth (m b. msl) depth (m b. msl) depth (m b. msl) depth (m b. msl) 3675 3700 3725 3550 3575 3600 3625 3650 3675 3700 3725 3550 3575 3600 3625 3650 3675 3700 3725 3550 3575 3600 3625 3650 3675 3700 3725 3550 3575 3600 3625 3650 3675 3700 3725 3550 3575 3600 3625 3650 3675 3700 3725 k in t o ta l s am pl e (% ) t h in t o ta l s am pl e (p pm ) u in t o ta l s am pl e (p pm ) k in c la y fr ac ti o n (% ) t h in c la y fr ac ti o n (p pm ) u in c la y fr ac ti o n (p pm ) lithofacies i lithofacies ii lithofacies iii fig. 7. content of k, th and u in total crushed samples and in clay fractions versus sample depth. samples of lithofacies i contain less than 0.7% k, whereas the th and u values are variable, dependent on a varying content of heavy minerals. samples of lithofacies ii have 0.6–2% k, and variable contents of th and u. samples of lithofacies iii generally have more than 2% k, more than 7 ppm th and more than 2.5 ppm u. the clay fraction data indicate a stratigraphic variation in k content, decreasing slightly with depth down to 3650 m followed by a broad increase between 3650 and 3725 m. the th content tends to follow the same pattern as k. similar variations are not apparent for u. 360 one sample contains 1.2% k; figs 7, 8). this differentiation of lithofacies in terms of k content was not observed for the clay fraction. considering all the data, the k content of the clay component shows a weak decrease with increasing depth to around 3650 m; at greater depths, the data show considerable scatter but appear to broadly increase between 3650 and 3725 m (fig. 7). the th and u concentrations of the total samples are variable in lithofacies i and ii, but uniformly high in lithofacies iii (fig. 7). the th content in the clay fraction follows roughly the same pattern as the k content (see above), while no pattern is apparent for the u content of the clay fraction (fig. 7). for lithofacies ii and iii samples, roughly constant th/k ratios of 3 x 10-4 – 10 x 10-4 were obtained, whereas lithofacies i samples show significant variation in this ratio (2 x 10-4 – 22 x 10-4; fig. 9). this is a consequence of lithofacies i samples being low in k but having variable th and u contents; it is assumed that this variability is governed by the heterogenereous distribution of heavy minerals within the facies. total organic carbon (toc) fragments of organic matter are found in most samples of lithofacies ii and iii and in a single sample of lithofacies i. a general negative relationship between car250 200 150 100 50 0 0 1 2 k (%) 3 4 q ua rt z gr ai n si ze ( µm ) lithofacies i lithofacies ii lithofacies iii fig. 8. median size of quartz grains, estimated from thin sections, vs. k content. samples of lithofacies i contain less than 0.7% k and comprises quartz grains in the range 130–220 µm. samples of lithofacies ii contain 0.6–2% k and consist of quartz grains in the range 50–130 µm. samples of lithofacies iii generally contain more than 2% k and are made up of quartz grains less than 80 µm in size. fig. 9. th/k ratio vs. k content. the th/k ratio does not effectively separate the lithofacies i, ii and iii, although lithofacies i samples rich in heavy minerals can be differentiated by their high th/k ratio. 0.0025 0.0020 0.0015 0.0010 0.0005 0 0 1 2 3 4 t h/ k r at io k (%) lithofacies i lithofacies ii lithofacies iii fig. 10. u concentrations in the total samples and in the clay fractions vs. toc. no general relationship between u and toc is apparent from the two figures. total samples of lithofacies i are low in toc and show a large variation in u, samples of lithofacies ii show a scattered pattern, while samples of lithofacies iii give constant high u values and a large variation in toc. 5 4 3 2 1 0 0 2 4 6 8 10 12 u in t o ta l s am pl e (p pm ) 8 6 4 2 0 0 2 4 6 8 10 12 u in c la y fr ac ti o n (p pm ) toc (wt%) toc (wt%) lithofacies i lithofacies ii lithofacies iii bonate and toc can be noticed (table 1). samples of lithofacies i give low toc values but show a large variation in u content (fig. 10). samples of lithofacies ii display a large variation in both toc and u, while lithofacies iii samples have a high content of u and a large toc variation. uranium concentration and toc are apparently independent. location of potassium the data suggest that feldspar is the main source of k in the k-poor lithofacies i sandstones, while mica and kaolinite are a minor source (fig. 11). the intermediate k content of lithofacies ii sandstones is probably primarily due to feldspar, mica and illite, while kaolinite contributes less. in the k-rich lithofacies iii samples, feldspar is of only minor importance, whereas illite and kaolinite are inferred to have roughly equal importance as a source of k. in figure 11, inferred contributions to the total k from the minerals in each sample are presented in order of depth. the low k values measured by eds in kaolinites from below 3660 m (i.e. samples l1–s) are responsible for the low contribution to the total k attributed to kaolinite below this depth. 361 a b c d1 d2 e f g h i j k1 sample k/kmax k2 l1 l2 m n o p q1 q2 r s 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 i ii iii a b 4 3 2 1 0 k in m in er al s (% ) 4 3 2 1 0 k in m in er al s (% ) glauconite feldspar muscovite illite kaolinite fig. 11. the cumulative contributions of the k-bearing minerals to the total k concentration, both for individual samples (a) and ranked in progressive k content (b). glauconite is only present in the samples from the lola formation (above 3575 m, i.e. samples a–c), while illite gains drastically in importance relative to kaolinite below 3665 m (samples n–s). in samples of lithofacies i, k-feldspar is the dominant source of potassium; in samples of lithofacies ii, k-feldspar, muscovite and illite dominate; in samples of lithofacies iii, illite and partly illitised kaolinite are the major sources of potassium. 362 laboratory gamma spectrometry of cores vs. log data comparison between the sng log data and the results from the measurements of the gamma radiation in the laboratory reveals significant differences (fig. 12). on average, the laboratory data indicate 20% lower k concentrations than the log data. for th, the laboratory results are on average 5% lower than the log values. interpretation of the u data is complicated; the log shows negative concentrations in some intervals, and no correlation was found between log data and laboratory measurements. this concurs with the findings of hurst (1990) who also observed that u values from the sng log in north sea boreholes were unreliable. discussion diagenetic factors the coexistence of kaolinite and feldspar in sandstones has been the subject of much discussion in the literature (lindgreen 1985; bjørkum & gjelsvik 1988; aja et al. 1991; bjørkum et al. 1993). at temperatures higher than 50–80°c (or according to bjørlykke & egeberg (1993), above 90–100°c), kaolinite and k-feldspar may react to form authigenic illite and quartz cement. the extensive illitisation of sandstones of the garn formation, offshore norway, is interpreted to have arisen because the sandstone reached either a temperature of 140°c or a time-temperature index (tti) of 100 (ehrenberg 1990; see waples 1980 for an introduction to the tti maturity index). a temperature near the critical value of 140°c was recorded during logging of the studied reservoir interval of west lulu-3. quartz cement is frequently observed, and some detrital kaolinite contains up to 3% k, while no k was detected in the authigenic kaolinite. an explanation for the varying degree of illitisation of kaolinite can be a difference in polytype between the detrital and authigenic kaolinite. ehrenberg et al. (1993) described replacement of kaolinite by dickite in three sandstone formations on the norwegian continental shelf. apparently, the transformation from kaolinite to dickite takes place at temperatures above 120–130°c via dissolution/re-precipitation. ehrenberg et al. (1993) found more extensive illitisation of kaolinite than of dickite, possibly because this process is kinetically favoured over illitisation of dickite. the presence of carbonate and kaolinite cements is thought to reflect the release of acid pore waters from shales. milliken & land (1991) related the acid pore waters to illitisation of smectite, whereas curtis (1983) and hansley & nuccio (1992) attributed the acid pore water to the maturation of kerogen. the acid pore water destabilises carbonate and aluminosilicates in the shales, co2 and metal ions go into solution, and sediment compaction forces some of these modified pore waters into sandstones. if the sandstones contain reactive feldspar (i.e. detrital metamorphic or magmatic feldspars), acids 3654 3656 3658 3660 depth (m b. msl) 3662 3664 3666 3668 4 2 0 20 10 0 4 2 0 k ( % ) li th o fa ci es t h (p pm ) u ( pp m ) k1k2 l1l2 m samples iii ii i ii lab. data log data fig. 12. comparison between the log data and the results from the measurements in the laboratory for core sections k, l and m. the k and th data compare reasonably well, whereas the u readings are unrelated. the lithofacies derived from the log values are marked by roman numerals. from the shales are effectively buffered, thus allowing precipitation of carbonate and/or kaolinite. curtis (1983) concluded that once the supply of reactive detrital feldspar is exhausted through dissolution and albitisation, shale-derived hydrogen ions remobilise carbonate in sandstones, generating secondary porosity and fluids with high pco2. no secondary porosity was recognized in thin sections of the west lulu-3 samples, and in line with the interpretation of curtis (1983), feldspar is present in practically all samples. lithofacies identification based on gamma spectrometry as demonstrated by figures 7 and 8, the samples from the three lithofacies are most effectively separated on the basis of the k content. thus grain-supported porous (clay-poor) quartz arenites (lithofacies i) contain < 0.7% k, grain-supported, clay-rich quartz arenites (lithofacies ii) contain 0.6–2% k whereas the matrix-supported wackes of lithofacies iii contain > 2% k. in figure 3, the distribution of these three lithofacies is presented, calculated on the basis of (corrected) log data. lithofacies ii occurs throughout the section but particularly dominates the uppermost interval where it is interpreted to represent a lower shoreface sedimentary environment (j. andsbjerg, personal communication 1995). lithofacies i, showing good reservoir properties, is common in the upper part of the bryne formation and in the lulu formation where it typically occurs within channel-fill sections of paralic (estuarine) origin (j. andsbjerg, personal communication 1995; andsbjerg 2003, this volume). the clay-dominated lithofacies iii is mainly found in the lower part of the studied section which is interpreted to represent an alluvial plain sedimentary environment (j. andsbjerg, personal communication 1995; andsbjerg 2003, this volume). schlumberger (1982) reported how the nsg tool can differentiate between different types of sandstone. feldspathic sandstones or arkoses will typically have th/k ratios less than 1 x 10-4, because of their low th and their high k contents whereas micaceous sandstones have a th/k ratio close to 2.5 x 10-4 because of the presence of th-bearing heavy minerals. the th/k ratios in claybearing sandstones are still higher. this is consistent with the present clay-bearing samples (lithofacies ii and iii) which have th/k ratios of 3 x 10-4 – 10 x 10-4. by contrast, this ratio varies widely in the lithofacies i samples (th/k: 2 x 10-4 – 22 x 10-4), depending on the feldspar and heavy mineral content. thus, high th/k ratios can be found in mineralogically mature lithofacies i sandstones. the lithofacies as defined in this study are expected to reflect the reservoir quality of the rock, but they cannot be predicted from the th/k ratio. hurst (1990) also found th/k cross-plots to be poorly suited to identifying and quantifying the clay mineralogy of sandstones. potassium content of minerals as noted above, feldspar is inferred to be the main source of k in lithofacies i and ii samples, whereas illite and kaolinite are the dominant sources of k in lithofacies iii samples. the k-feldspars of lithofacies i and ii samples commonly appear degraded, but a k content of c. 14% is typical. the illite has a highly variable k content, whereas the larger mica grains (muscovite) have a k content close to the ideal (10%). some kaolinite grains (mainly diagenetic) are free of k, while others (probably detrital) have a k content of about 3%. in the samples from the shallow marine lola formation, glauconite contributes to the k content. the k content of the glauconite was measured to be 2–4% by eds. the k content of the clay fraction of the samples shows no apparent relationship with lithofacies, but shows broad variation with depth, as described earlier. this could be explained by a change in clay mineralogy due to diagenesis (see above), as some indications of transformation of kaolinite into illite were noted. this explanation, however, is contradicted by two observations: (1) the pattern does not show a uniform depthrelated trend and (2) several of the deepest samples are rich in kaolinite relative to illite. the best explanation for the broad variations with depth is probably stratigraphic variations in the provenance of the clastic material. sources of uranium and thorium hassan et al. (1976) and schlumberger (1982) have reported that uranium commonly shows a strong correlation with organic carbon. in common with the data of berstad & dypvik (1982), this study has demonstrated no such correlation. imam & trewin (1991) stated that in the sandstones of the claymore sandstone member of the kimmeridge clay formation, the contribution to radioactivity from organic matter is minor, while the high gamma-ray radiation is considered to be due to high k-feldspar concentrations and radioactive heavy minerals, particularly zircon and monazite. our data support their conclusions. 363 comparison of log and laboratory data the observed discrepancy between log and laboratory measurements could be due to calibration problems, differences in measuring geometry or due to the influence of the drilling mud. calibration one may assume that both borehole tool and laboratory equipment are in this case calibrated correctly. the laboratory equipment for measurements of samples is regularly checked using reference material from the international atomic energy agency in vienna (iaea 1987). the core scanner is checked using secondary reference material. according to standard practice, the sng tool is calibrated regularly. measuring geometry the individual samples investigated in the laboratory are much smaller than the volume contributing to the measurements of the borehole logging tool in the borehole. however, systematic variations such as those observed for k and th cannot be explained in this way. moreover, most samples were selected from intervals with stable concentrations of th, u and k, so that this source of error is considered to be of minor importance. the crushed samples were measured in a fixed geometry (in a laboratory nai crystal detector), and the core slices of different thickness were measured using reference material with similar geometries. the accuracy of the core scanner is dependent on core geometry (regular or fractured cores). for the cores investigated, such influence is minor and, in any event, for irregular cores the concentrations of k, th and u should be influenced to almost the same extent. the accuracy of borehole measurements is dependent on borehole geometry (variations in diameter). however, the associated caliper log indicates a fairly constant borehole diameter. borehole mud borehole measurements are influenced by the density and chemistry of the drilling mud. no major potassium-, thorium-, or uranium-bearing additives (e.g. kcl) were present in the mud. major amounts of barite were added in order to achieve a mud density of 1.9 g/cm3. barite attenuates gamma-rays entering the borehole from the formation, especially in the lower part of the energy spectrum. if this influence is not properly taken into account, low or even negative u concentrations may result from the calculations. from data reported by ellis (1982), calculated th concentrations may be expected to be higher than the real concentrations under conditions of high barite content. normally, a correction for high density borehole mud is included in the calculations by the logging company, but that apparently was not the case for the west lulu-3 log. the problem is not trivial because it is impossible to perform recalculations without detailed information on the correction program. by multiplying the log concentrations of th and k by 0.95 and 0.80 respectively, values approximately similar to those measured in the laboratory can be obtained. unfortunately the log concentrations of u cannot be transformed to comply with the laboratory values by any simple procedure. conclusions 1. from optical microscopy, x-ray diffraction and eds microprobe data, we infer that the main sources of potassium are feldspar, muscovite, illite and illitised kaolinite. k-feldspar is the main source in samples with a limited amount of clay, while illite and illitised kaolinite are most important in the clay-rich intervals. 2. neither gamma-spectral k nor th was found to be a measure of clay content, but the k concentration provides a method of recognising the three broad lithofacies adopted here. porous quartz arenites have k concentrations below 0.7%, grain-supported quartz arenities with pore-filling clay have k concentrations between 0.6 and 2%, while matrix-supported wackes normally have k concentrations above 2%. it is possible, therefore, to define the lithofacies on the basis of the k signal of the spectral natural gamma log. 3. the k content of the clay fraction varies as a function of depth, independent of sandstone texture. this is probably the result of changes in clay provenance. 4. the th/k ratio does not give an indication of the lithofacies in this study. clay-bearing samples (those of lithofacies ii and iii) have th/k ratios of 3 x 10-4 – 10 x 10-4, whereas in the lithofacies i samples this 364 ratio varies widely (th/k: 2 x 10-4 – 22 x 10-4) depending on the content of feldspar and heavy minerals. 5. thorium and uranium signals are primarily indicative of the presence of heavy minerals in the sediments. no correlation was found between the u content and the total organic carbon content. 6. the volume of individual samples investigated in the laboratory is much smaller than the volume ‘seen’ by the sng logging tool in the borehole. however, most samples were selected from intervals with stable concentrations of th, u and k, so that the samples are inferred to be representative for the depth intervals from which they were taken. therefore, the geochemical results obtained in the laboratory can in general be compared directly to log data. only few of the samples were taken from depth intervals with strongly varying concentrations of th, u and k. 7. a major discrepancy was observed between log data and laboratory gamma spectrometry data. before interpreting the borehole log from west lulu-3, the k concentrations should be multiplied by 0.8, and the th concentrations by 0.95. the u concentrations cannot be corrected. acknowledgements k. carlsen, m. christensen, v. knudsen, h. møller, s. nguyen, a. steffensen and i. søndergaard are thanked for technical assistance. f. larsen (geological survey of denmark and greenland), f. engstrøm (mærsk olie og gas as) and s. talman (technical university of denmark) are thanked for critically reading the manuscript. special thanks are extended to the referees a. hurst (university of aberdeen) and j. andsbjerg (geological survey of denmark and greenland) for valuable advice. references adams, j.a.s. & weaver, c.e. 1958: thorium-to-uranium ratios as indicators of sedimentary processes: example of concept of geochemical facies. american association of petroleum geologists bulletin 42, 387–430. aja, s.u., rosenberg, p.e. & kittrick, j.a. 1991: illite equilibria in solutions: i. phase relationships in the system k2o–al2o3–sio2–h2o. geochimica et cosmochimica acta 55, 1353–1364. andsbjerg, j. 2003: sedimentology and sequence stratigraphy of the bryne and lulu formations, middle jurassic, northern danish central graben. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 301–347 (this volume). berstad, s. & dypvik, h. 1982: sedimentological evolution and natural radioactivity of tertiary sediments from the central north sea. journal of petroleum geology 5, 77–88. bjørkum, p.a. & gjelsvik, n. 1988: an isochemical model for formation of authigenic kaolinite, k-feldspar and illite in sediments. journal of sedimentary petrology 58, 506–511. bjørkum, p.a., walderhaug, o. & aase, n.e. 1993: a model for the effect of illitization on porosity and quartz cementation of sandstones. journal of sedimentary petrology 63, 1089–1091. bjørlykke, k. & egeberg, p.k. 1993: quartz cementation in sedimentary basins. american association of petroleum geologists bulletin 77, 1538–1548. cowan, d.r. & myers, k.j. 1988: surface gamma ray logs: a correlation tool for frontier areas: discussion. american association of petroleum geologists bulletin 72, 634–636. curtis, c.d. 1983: link between aluminium mobility and destruction of secondary porosity. american association of petroleum geologists bulletin 67, 380–393. ehrenberg, s.n. 1990: relationship between diagenesis and reservoir quality in sandstones of the garn formation, haltenbanken, mid-norwegian continental shelf. american association of petroleum geologists bulletin 74, 1538–1558. ehrenberg, s.n., aagaard, p., wilson, m.j., fraser, a.r. & duthie, d.m.l. 1993: depth-dependent transformation of kaolinite to dickite in sandstones of the norwegian continental shelf. clay minerals 28, 325–352. ellis, d.v. 1982: correction of ngt logs for the presence of kcl and barite muds. society of professional well log analysts 23rd annual logging symposium, july 6–9, 1982. transactions, paper o, 12 pp. engstrøm, f. 1981: fortolkningsgrundlag for sng-log, 469 pp. unpublished ph.d. thesis, danmarks tekniske universitet, lyngby, danmark. hansley, p.l. & nuccio, v.f. 1992: upper cretaceous shannon sandstone reservoirs, powder river basin, wyoming: evidence for organic acid diagenesis. american association of petroleum geologists bulletin 76, 781–791. hassan, m., hossin, a. & combaz, a. 1976: fundamentals of the differential gamma ray log – interpretation technique. society of professional well log analysts 17th annual logging symposium, june 9–12, 1976. transactions, paper h, 18 pp. hurst, a. 1990: natural gamma-ray spectroscopy in hydrocarbonbearing sandstones from the norwegian continental shelf. in: hurst, a., lovell, m.a., & morton, a.c. (eds): geological applications of wireline logs. geological society special publication (london) 48, 211–222. hurst, a. & milodowski, a. 1994: characterisation of clays in sandstones: thorium content and spectral log data. society of professional well log analysts 16th european formation evaluation symposium, october 11–13, 1994. transactions, paper s, 18 pp. iaea 1987: preparation and certification of iaea gamma-ray spectrometry reference materials. report file number iaea/rl/148. vienna: iaea (international atomic energy agency). 365 366 imam, m.b. & trewin, n.h. 1991: factors contributing to high gamma-ray levels in upper jurassic sandstone reservoirs of the claymore oilfield, north sea. marine and petroleum geology 8, 452–460. johannessen, p.n. & andsbjerg, j. 1993: middle to late jurassic basin evolution and sandstone reservoir distribution in the danish central trough. in: parker, j.r. (ed.): petroleum geology of northwest europe: proceedings of the 4th conference, 271–283. london: geological society. lindgreen, h. 1985: diagenesis and primary migration in upper jurassic claystone source rocks in north sea. american association of petroleum geologists bulletin 69, 525–536. michelsen, o., nielsen, l.h., johannessen, p.n., andsbjerg, j. & surlyk, f. 2003: jurassic lithostratigraphy and stratigraphic development onshore and offshore denmark. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 147–216 (this volume). milliken, k.l. & land, l.s. 1991: reverse weathering, the carbonate–feldspar system, and porosity evolution during burial of sandstones. american association of petroleum geologists bulletin 75, 636 only (abstract). nielsen, b.l., løvborg, l., sørensen, p. & mose, e. 1987: gammaray analysis for u, th and k on bulk cutting samples from deep wells in the danish subbasin and the north german basin, 82 pp. unpublished report, risø national laboratory, denmark. postma, d. 1983: pyrite and siderite in brackish and freshwater swamp sediments. american journal of science 282, 1151–1183. schlumberger 1982: natural gamma-ray spectrometry. essentials of n.g.s. interpretation, 69 pp. houston, texas: schlumberger educational services. vernik, l. & nur, a. 1992: petrophysical classification of siliciclastics for lithology and porosity prediction from seismic velocities. american association of petroleum geologists bulletin 76, 1295–1309. waples, d.g. 1980: time and temperature in petroleum formation: application of lopatin’s method to petroleum exploration. american association of petroleum geologists bulletin 64, 916–926. manuscript received 26 august 1994; revision accepted 16 october 1997. geological survey of denmark and greenland bulletin 7, 2004, p 9-12 9 although it was for many years believed that coals could not act as source rocks for commercial oil accumulations, it is today generally accepted that coals can indeed generate and expel commercial quantities of oil. while hydrocarbon generation from coals is less well understood than for marine and lacustrine source rocks, liquid hydrocarbon generation from coals and coaly source rocks is now known from many parts of the world, especially in the australasian region (macgregor 1994; todd et al. 1997). most of the known large oil accumulations derived from coaly source rocks have been generated from cenozoic coals, such as in the gippsland basin (australia), the taranaki basin (new zealand), and the kutei basin (indonesia). permian and jurassic coal-sourced oils are known from, respectively, the cooper basin (australia) and the danish north sea, but in general only minor quantities of oil appear to be related to coals of permian and jurassic age. in contrast, carboniferous coals are only associated with gas, as demonstrated for example by the large gas deposits in the southern north sea and the netherlands. overall, the oil generation capacity of coals seems to increase from the carboniferous to the cenozoic. this suggests a relationship to the evolution of more complex higher land plants through time, such that the highly diversified cenozoic plant communities in particular have the potential to produce oil-prone coals. in addition to this overall vegetational factor, the depositional conditions of the precursor mires influenced the generation potential. the various aspects of oil generation from coals have been the focus of research at the geological survey of denmark and greenland (geus) for several years, and recently a worldwide database consisting of more than 500 coals has been the subject of a detailed study that aims to describe the oil window and the generation potential of coals as a function of coal composition and age. depositional conditions hydrocarbons are derived from the aliphatic chains in the organic matrix. the dominant organic matter in conventional marine source rocks (type ii kerogen), and also lacustrine source rocks (type i kerogen), is formed from algae. this type of organic matter is geochemically quite uniform and contains an abundance of long-chain n-alkanes, a prerequisite for oil formation. coals are composed of transformed higher land plant material (mainly vitrinite or type iii kerogen) and are compositionally much more heterogeneous and complex. compared to algae-derived organic matter, the organic matter is richer in oxygen and contains fewer longchain n-alkanes. therefore coals inherently have lower oil generation potential. however, paralic coals that have been influenced by seawater during deposition may be enriched in hydrogen (higher h/c ratios; figs 1, 2; petersen & rosenberg 1998; sykes 2001), and incorporation of the hydrogen into aliphatic chains may increase the generation capacity. hydrogen enrichment is related to the activity of sulphate -reducing bacteria, and is commonly associated with increased contents of sulphur (fig. 1). in the søgne basin (north sea), for example, a clear facies-related change in generation potential is recorded for middle jurassic coal source rocks. the coals were formed on marine-influenced coastal geological survey of denmark and greenland bulletin 7, 9–12 (2005) © geus, 2005 oil generation from coal source rocks: the influence of depositional conditions and stratigraphic age henrik i. petersen c e n o zo ic ju ra ss ic p e rm ia n c ar b o n if e ro u s > 1% sulphur (d.a.f.) 0.5–1% sulphur (d.a.f.) < 0.5% sulphur (d.a.f.) 0 0.1 0 0.4 0.2 0.8 0.6 1.4 type i type ii type iii 1.2 1 h /c ( at o m ic r at io ) o/c (atomic ratio) 0.2 0.3 fig. 1. the h/c ratio of coals from the major coal-forming geological periods displayed on the so-called ‘van krevelen diagram’. note that coals with a low sulphur content have a tendency to plot towards the lower part of the ‘type iii’-band and coals with a higher sulphur content towards the upper limit of the band. this feature is not related to coal age; d.a.f., dry ash-free. plains, and the thickest, most landward parts of the coals generated gas and condensate (harald field and trym discovery), whereas the coals that formed close to the palaeo-coastline generated oil (lulita field; e.g. petersen et al. 2000; petersen & brekke 2001). the influence of depositional conditions on the generation potential is independent of coal age (fig. 2; petersen in press). the depositional conditions of peat-forming mires may thus help to predict the source rock quality of the coals. generation potential the evolution of the generation potential (hydrogen index = hi) with increasing maturity is shown in fig. 2. the majority of the coal samples fall within a band that narrows with increasing maturity due the gradual homogenisation of the organic matter. the generation potential is exhausted around a vitrinite reflectance of 2.0% ro, but the coals may still possess a considerable potential (hi up to 190 mg hc/g toc) at the end of the conventional oil window at about 1.3% ro. a prominent feature of the hi-band is the initial increase in hi up to a maximum hi-value (e.g. huc et al. 1986; sykes 2001; petersen 2002, in press), defined by the himax line between 0.6% ro and 1.0% ro. the increase in hi is caused by the formation of an additional generation potential due to structural reorganisation of the coal matrix, possibly including incorporation of water-derived hydrogen (lewan 1997; schenk & horsfield 1998). this means that the ‘true’ generation potential of coals is equivalent to the himax, which is derived by translating the coals along their maturation pathway to the maximum value (fig. 2; sykes & snowdon 2002). coals with an himax < 150 mg hc/g toc are considered to be mainly gas-prone (fig. 2). compared to carboniferous, permian and jurassic coals, cenozoic coals attain the highest himax values (himax = 250–370 mg hc/g toc; petersen in press). however, the himax value may not necessarily be an expression of the ability to generate oil. the type of generated petroleum is dependent on the chain length of the n-alkanes in the coal structure. the hi is a measure of the hydrogen in the coal, but this may not be present as long-chain n-alkanes, but rather as shorter chains with a potential to form only gas or condensate. this may particularly be the case for carboniferous coals. coals with approximately similar hi values should theoretically contain the same proportion of hydrogen and thus have potentially the same petroleum generation capacity. information about the type of generated petroleum can be obtained by investigating the chain length of the n-alkanes in the solid coal structure by fourier transform infrared spectrometry (ftir) and by ruthenium tetroxide catalysed oxidation. the peak at 2850 cm–1 in the ftir spectrum is used to estimate the relative proportion of ch2 (dry, ash-free basis), which is taken as a measure of the proportion of oliphatic chains in the coal (fig. 3). in general, carboniferous coals contain a lower proportion of ch2 compared to cenozoic and jurassic coals with similar hi values. similarly, the proportion of aliphatic hydrogen is lower for carboniferous coals (fig. 3). cenozoic coals also have significant gas potential (estimated from the ch3 peak at 2955 cm –1), which is in good agreement with the coal-sourced south-east asian oil fields, that commonly also contain significant proportions of gas (e.g. the kutei basin, indonesia). ruthenium tetroxide catalysed oxidation of the coal structure essentially ‘chops’ off the aliphatic chains in the coal matrix, which after appropriate chemical treatment can be analysed by gas chromatography mass spectrometry (gc-ms). by adding an internal standard the obtained chromatograms can be directly compared. in general, carboniferous coals contain low proportions of n-alkanes with a carbon number > c19, whereas cenozoic coals in particular are much richer in long-chain aliphatics. the difference in the chemical structure between, for exam10 fig. 2. evolution in the hydrogen index (hi) with increasing maturity shown by 507 coal samples (petersen in press). coals with an hi < 150 mg hc/g toc are considered mainly gas-prone (shaded area). coals with increased sulphur contents have a tendency for higher hi values due to hydrogen-enrichment in the coal-structure. during initial thermal maturation the hi increases to a maximum value (himax), which is a better estimate of the true generation potential of a coal. the himax can be estimated by translating the hi value for a coal along its maturation pathway to the himax line (sykes & snowdon 2002); for example the coal with an hi of 185 (blue star) shows a correction of hi by 50 mg hc/g toc (himax = 230 mg hc/g toc); d.a.f., dry ash-free. 0 0.5 1.51 2 2.5 3 c e n o zo ic ju ra ss ic p e rm ia n c ar b o n if e ro u s > 1% sulphur (d.a.f.) 0.5–1% sulphur (d.a.f.) < 0.5% sulphur (d.a.f.) 500 400 300 200 100 185 235 0 ga sp ro n e o il -p ro n e h y d ro ge n i n d e x ( m g h c /g t o c ) vitrinite reflectance (%ro) ~0.60%ro ~1.0%ro line of himax h h ple, carboniferous and cenozoic coals, can be related to the original coal-forming vegetation, and may explain why carboniferous coals are principally gasor condensate-prone, whereas cenozoic coals can be highly oil-prone. in contrast to the carboniferous woody, gymnospermous mire vegetations, the cenozoic coals were formed from an advanced and diverse vegetation, which may have produced a more aliphatic-rich vitrinitic organic matter upon deposition. the effective oil window (oil expulsion window) the complex, heterogeneous composition of coals results in a three-phase oil generation model (fig. 4; petersen in press): (1) onset of hydrocarbon generation, (2) hydrocarbon buildup in the coal to the expulsion threshold, and (3) oil expulsion in the so-called effective oil window. figure 4 shows the free hydrocarbons in the coals with increasing maturity. from 0.6–0.7% ro to 0.85–1.0% ro, the amount of oil increases in the coals up to a maximum value, after which it decreases. this decrease indicates the onset of efficient oil expulsion, and the maximum bi-value thus corresponds to the start of the effective oil window (oil expulsion window). the maturity at which oil expulsion starts and the range of the effective oil window is dependent on the initial generation potential of the coals (fig. 4). it should, however, be noted that the effective oil window for coals extends to higher maturities than the conventional oil window. coals generating < 12 mg hc/g 11 fig. 4. evolution in bitumen index (bi = s1 / toc) with increasing maturity. initially, hydrocarbons build up in the coal to a maximum value, which indicates the start of the effective oil window. coals with < 12 mg hc/g toc (shaded area) are considered to have a limited expulsion efficiency (gas-prone). in general, cenozoic coals generate the highest amounts of hydrocarbons, and they also reach the expulsion threshold at the lowest maturities as shown by the extension of the expulsion line down to 0.65% ro. (a) carb. (b) m. jurassic (a) carb. (b) m. jurassic3000 2950 28502900 2800 2750 cm-1 carboniferous coal, ruhr, germany m. jurassic coal, danish north sea ch2 ch3 hal/h (wt.%, d.a.f.) hal/mg coal (d.a.f.) 2850 cm-1: symmetric ch2 2955 cm-1: asymmetric ch3 h/c = 0.76 hi = 182 0.83%ro h/c = 0.79 hi = 205 0.82%ro a b c 60 40 20 0 b it u m e n i n d e x ( m g h c /g t o c ) ~0.65%ro ~0.85%ro ~1.0%ro ~1.05%ro gas-prone 0 0.5 1.51 2 2.5 3 vitrinite reflectance (%ro) start of the effective oil window (oil expulsion window) unknown age cenozoic jurassic permian carboniferous fig. 3. a: ftir spectra (aliphatic stretching region) of carboniferous and middle jurassic coals with similar h/c ratios, hi values, and vitrinite reflectances. the middle jurassic coal shows a much higher relative response at 2850 cm–1, which is an indication of a higher proportion of aliphatic chains in the coal structure. b: calculated relative proportions of aliphatic chains (ch2) and ch3. c: calculated relative proportions of aliphatic hydrogen. the low values for the carboniferous coal suggest a primary gas generation potential; d.a.f., dry ash-free. 12 toc are considered to possess a limited oil expulsion efficiency. cenozoic coals generate the largest amounts of hydrocarbons and they tend to reach the expulsion threshold at the lowest maturities (from 0.65% ro; fig. 4). the broadest effective oil window is thus related to cenozoic coals, and may extend from approximately 0.65–2.0% ro. jurassic, permian and carboniferous coals reach the start of the effective oil window at higher maturities (0.85–0.9% ro). the jurassic coals show some ability to generate and expel hydrocarbons, whereas several of the carboniferous and permian coals seem to have a limited expulsion efficiency; these coals are principally gas-prone. as described above, the organic matter in carboniferous coals possesses an inherently low ability to generate oil. hence, the effective oil window for the carboniferous coals is in reality an effective gas/condensate window. conclusion coals can act as source rocks for oil accumulations. the generation potential is related to the depositional conditions of the coal-forming mires, with marine influence having a positive effect by increasing the hydrogen content in the vitrinitic organic matter. in addition, an overall vegetational control seems to be exerted on the source rock potential. carboniferous coals contain lower proportions of long-chain n-alkanes and aliphatic hydrogen in the coal matrix than younger coals. cenozoic coals generally contain high proportions of long-chain n-alkanes and possess a high oil generation potential in addition to a high gas potential. during maturation, coals form an additional generation potential, and hydrocarbon generation can be described as a three-phase process, including a hydrocarbon build-up phase in the coals before onset of efficient expulsion. the effective oil window starts at higher maturities than the conventional oil window, and in addition extends to higher maturities. cenozoic coals display the broadest effective oil window, whereas the effective oil window for carboniferous coals is, in reality, an effective gas/condensate window. this enhanced understanding of oil generation from coal source rocks is being directly employed by geus in petroleum geological projects that are being carried out, for example, in vietnam (cf. nielsen & abatzis 2004). acknowledgement the carlsberg research foundation (ans-1293 & ans-1293/20) is thanked for financial support. references huc, a.y., durand, b., roucachet, j., vandenbrouke, m. & pittion, j.l. 1986: comparison of three series of organic matter of continental origin. organic geochemistry 19, 191–204. lewan, m.d. 1997: experiments on the role of water in petroleum formation. geochimica et cosmochimica acta 61, 3691–3723. macgregor, d.s. 1994: coal-bearing strata as source rocks – a global review. in: scott, a.c. & fleet, a.j. (eds): coal and coal-bearing strata as oil-prone source rocks? geological society special publication (london) 77, 107–116. nielsen, l.h & abatzis, i. 2004: petroleum potential of sedimentary basins in vietnam: long-term geoscientific co-operation with the vietnam petroleum institute. geological survey of denmark and greenland bulletin 4, 97–100. petersen, h.i. 2002: a re-consideration of the ‘oil window’ for humic coal and kerogen type iii source rocks. journal of petroleum geology 25, 407–432. petersen, h.i. in press: the petroleum generation potential and effective oil window of humic coals related to coal composition and age. international journal of coal geology. petersen, h.i. & brekke, t. 2001: source rock analysis and petroleum geochemistry of the trym discovery, norwegian north sea: a middle jurassic coal-sourced petroleum system. marine and petroleum geology 18, 889–908. petersen, h.i. & rosenberg, p. 1998: reflectance retardation (suppression) and source rock properties related to hydrogen-enriched vitrinite in middle jurassic coals, danish north sea. journal of petroleum geology 21, 247–263. petersen, h.i., andsbjerg, j., bojesen-koefoed, j.a. & nytoft, h.p. 2000: coal-generated oil: source rock evaluation and petroleum geochemistry of the lulita oilfield, danish north sea. journal of petroleum geology 23, 55–90. schenk, h.j. & horsfield, b. 1998: using natural maturation series to evaluate the utility of parallel reaction kinetics models: an investigation of toarcian shales and carboniferous coals, germany. organic geochemistry 29, 137–154. sykes, r. 2001: depositional and rank controls on the petroleum potential of coaly source rocks. in: hill, k.c. & bernecker, t. (eds): eastern australasian basins symposium, a refocused energy perspective for the future. petroleum exploration society of australia special publication, 591–601. sykes, r. & snowdon, l.r. 2002: guidelines for assessing the petroleum potential of coaly source rocks using rock-eval pyrolysis. organic geochemistry 33, 1441–1455. todd, s.p., dunn, m.e. & barwise, a.j.g. 1997: characterizing petroleum charge systems in the tertiary of se asia. in: fraser, a.j., matthews, s.j. & murphy, r.w. (eds): petroleum geology of southeast asia. geological society special publication (london) 126, 25–47. author’s address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: hip@geus.dk geological survey of denmark and greenland bulletin 4, , pp. 33-36 33 the first dna-based methods for direct quantification of soil protozoa, and a dna-based quantification method to describe the spread of phenanthrene-degrading bacteria in soil and freshwater aquifers, have recently been developed at the biopro research centre at the geological survey of denmark and greenland (geus). well-known genes for phenoxyalcanoic acid degradation have been used to monitor the in situ degradation of phenoxyalcanoic acid pesticides. studies have been initiated on the short-lived mrna molecules that are expected to provide a shortcut to the understanding of low, yet important, microbial activity in geological samples. this article reviews recent developments in techniques based on analysis of nucleic acids from soils and aquifers. analytical work has been carried out mainly on soil samples from a former asphalt production plant at ringe (fig. 1). the ringe plant constitutes one of the most polluted industrial sites in denmark, and is a priority site of studies by the biopro research centre. although rich in carbon, the ringe subsoil is an oligotrophic environment due to the high content of polycyclic aromatic hydrocarbons (pah). this is an environment where the supply of nutrients to microorganisms is low, leading to slow growth, low total numbers of microorganisms and small cells. to study microbial communities of oligotrophic environments, analytical methods with low detection limits are needed. until recently, microorganisms of natural environments were mainly studied by cultivation-dependent methods. however, microorganisms that can be cultured on agar plates are now known to represent only a small fraction of the total microbial community. modern methods, therefore, need to be based on the detection of biomolecules in the microorganisms rather than being dependent on growth of the microorganisms. the best available techniques are based on dna and rna molecules (fig. 2), which due to their high level of resolution allow closely related organisms or functional genes to be distinguished. in the following review, examples are given of applications of these nucleic acid based methods. direct analysis of microbial populations in soil and freshwater aquifers using nucleic acid based techniques carsten s. jacobsen, julia r. de lipthay, mikkel bender, line fredslund, anders r. johnsen and kaare johnsen fig. 1. location of the former asphalt plant at ringe, one of the most polluted industrial sites in denmark. the biopro research centre at geus monitored in situ degradation of phenoxyalcanoic acid pesticides. the pits, sampling sites and wells were used to determine the distribution of contamination of tar (pale red) and kerosene (green) in the subsoil. a field injection experiment, using a mixture of six different herbicides was carried out at a shallow sandy aquifer at vejen. modified from rosenbom et al. (2000). geological survey of denmark and greenland bulletin 4, 33–36 (2004) © geus, 2004 dna analysis is not limited to living organisms unlike other microbial analysis tools, dna analyses may be carried out on both living and dead material, as long as the dna has not been degraded. for analysis of dna in soils, a major problem is the presence of humic substances, that even at low concentrations interfere with the enzymes used in the dna amplification process. all research groups working with soil nucleic acids experience problems with amplification of dna when soils contain much humic material. one way to solve this problem is to use selective purification methods in which single-stranded dna is selectively purified from the soil using a molecular ‘fishing rod’ equipped with the complementary dna strand. after extracting the gene of interest, it is possible to multiply its numbers using the ‘polymerase chain reaction’ (pcr; saiki et al. 1985). pcr is an exponential reaction in which a single dna strand can, in principle, produce four million identical copies by 25 cycles of multiplication. in pcr, two small dna sequences, corresponding to two regions on the gene, are selected as priming sites for two segments of complementary dna. these small dna pieces are designated ‘primers’. the primers serve as the target of the pcr, and lead to the formation of a large number of dna molecules identical to the original gene. the primers are constructed by consulting dna sequence databases on the internet. since these databases are very comprehensive, it is possible to construct primer sets that are specific for the desired taxonomic or functional groups. this technique has, for example, enabled forensic experts to produce enough dna molecules to determine whether the genomic fingerprint of a person matches that of a bloodstain at the scene of a crime. we have used this technique widely for the analysis of microorganisms in the environment, and the detection limit is less than 40 cells in a sample (jacobsen 1995). the challenge is now not only to detect, but also to quantify the dna from very few cells in soil and freshwater aquifers. quantitative dna techniques for the enumeration of soil flagellates and bacteria as a consequence of the exponential nature of pcr, it is an excellent technique for the detection of specific dna sequences. on the other hand, it is not quantitative, and small differences in the efficiency of the reaction affect the final number of dna copies. several methods have been proposed to resolve this problem. one possibility is using the principle of ‘most probable number’ (mpn) estimates, where the dna template is serially diluted in several replicate reactions. by looking at which dilutions of template dna that give a product from the pcr, and in how many of the replicate reactions, an estimate of the original number of genes in the sample can be made. this approach has been used to develop the first successful molecular detection and quantification of protozoa in soil (fredslund et al. 2001). this new technique represents a breakthrough in reliable enumeration of soil protozoa, since these often small and amoeboid organisms are difficult to enumerate using microscopy techniques. traditionally, the enumeration was based on growth-dependent techniques, where the cultivable fraction of the total protozoan populations was not known. in our study, a part of the 18s rdna of the common soil flagellate heteromita globosa was sequenced and pcr primers for this gene were developed. in a sterilised soil at the ringe asphalt production plant, the population dynamics of this flagellate and the phenanthrene-degrading bacterium pseudomonas putida ous82 were quantified using both growth-dependent techniques and the mpn-pcr assay (fredslund et al. 2001). alternative methods for quantification of dna are the real-time pcr and the competitive pcr methods. in realtime pcr, the dna multiplication is monitored on-line using a combination of fluorescent dna stains and fibre optics coupled to a computer. geus has recently received funding from the danish natural science research council to implement this technique. competitive pcr makes use of an internal standard in the form of a similar, but shorter dna molecule, which is recognised and hence amplified by the same primer set as the template dna (the dna that needs to be quantified). the 34 fig. 2. all information regarding cell function and structure is contained as a genetic code in the cell dna. each gene encodes a specific function by dictating the synthesis of a specific protein. before proteins are synthesised, the genes are copied (transcribed) into messenger rna (mrna). after transcription, the mrna is translated into protein by protein-synthesising machinery called ribosomes. the sequence of bases in the mrna, copied after the base sequence in the gene, determines the structure and function of the protein. internal standard is added to the reaction mixtures in decreasing amounts and competes with the template dna for amplification. thus, the amount of product from the internal standard is inversely related to the initial amount of the template dna. competitive pcr exploits the highly sensitive nature of the pcr process, while using an internal standard to bypass the quantification problems inherent in the amplification reaction (johnsen et al. 1999). microbial changes in aquifers contaminated with phenoxyalcanoic acid herbicides this section focuses on specific genes of interest rather than on organisms. phenoxyalcanoic acid herbicides are extensively used in agriculture, and include compounds such as mecoprop (mcpp), 2,4-dichlorophenoxyacetic acid (2,4-d) and dichlorprop. a common pathway for 2,4-d degradation has been determined for the bacterial strain ralstonia eutropha jmp134, and the catabolic genes (tfd) encoding the specific enzymes have been identified (fig. 3; don et al. 1985). the in situ adaptation processes of the indigenous microorganisms when exposed to these herbicides have been investigated by studying the impact on a microbial community in a freshwater aquifer. a field injection experiment was carried out at a shallow sandy aquifer at vejen, denmark (fig. 1). during a seven-month period, a mixture of six different herbicides, including mcpp and dichlorprop, was continuously injected into the aquifer creating a contaminant plume (broholm et al. 2000). sediment and groundwater samples from herbicideexposed (1 and 2) and non-exposed (nx) sites (fig. 4a) were collected, and the impact on microbial community structure and function was studied (de lipthay et al. 2000). laboratory incubations demonstrated that sediment samples collected inside the contaminant plume had acquired a significantly increased capacity for herbicide mineralisation compared to samples from non-exposed sites (fig. 4a). thus, the in situ exposure to herbicides resulted in microbial communities that were better adapted to the degradation of phenoxyalcanoic acids. this was further demonstrated by greatly increased populations of pesticide degraders inside the pesticide plume, both when enumerated by cultivation, and when quantified by the number of pesticide genes (tfdabc) detected by pcr methods (fig. 4b, treatment 1 and 2). pesticide degraders and their tfd genes were undetectable outside the plume (fig. 4b, treatment nx). the most likely 35 fig. 3. pathway for degradation of 2,4-d as elucidated in the bacterial strain ralstonia eutropha jmp134. the tfda gene encodes a 2,4-d dioxygenase, tfdb encodes a 2,4-dichlorophenol hydroxylase, and tfdc encodes a chlorocatechol 1,2-dioxygenase. the 2,4-dichloromuconic acid generated by the activity of the tfdc gene product is further transformed to intermediates of the tricarboxylic acid cycle by the activity of other tfd gene products. fig. 4. a: mineralisation of the phenoxyalcanoic acid herbicides 2,4-d (red) and mcpp (blue) in laboratory incubations of sediment samples from herbicide exposed (1, 2) and non-exposed (nx) sites of the vejen aquifer. b: effect of in situ herbicide exposure in two exposed (1, 2) sites on microbial biomass of 2,4-d and mcpp degraders, and on the presence of tfda, tfdb and tfdc genes. data show that indigenous microbial communities carry the tfd genes and are capable of degrading phenoxyalcanoic acids. explanation is that microorganisms carrying the tfd genes had a selective advantage in that they could make use of the pesticides as sources of carbon and energy. the data suggest that natural attenuation is a likely procedure for clean up of this group of herbicide compounds when originating from pointsource contaminations. analysis of microbial activity applying mrna techniques the presence or absence of specific microorganisms may be determined by use of cultivation or dna-based techniques, although these methods give no information as to whether the organisms are actually active in the environment. microbial activity may be measured in several ways. the first sign of activity in microbial cells is the synthesis of messenger-rna (mrna; fig. 2). these molecules have half-lives of only a few minutes, and the detection of mrna thus ensures that the genes of interest are actually expressed at the time of sampling. another approach is to detect the activity of the gene products – the enzymes. however, the longevity of enzyme activities is variable. a third approach is to measure the target molecules of the enzymes, i.e. the pollutant molecules. by use of analytical chemical methods such as gas and liquid chromatography, the concentration of target molecules may be measured, and the dissipation of pollutants indicates microbial activity. a major topic of future studies in microbial ecology will be the assessment of microbial activity by the application of mrna techniques to answer which microorganisms are active, and under which conditions their genes are expressed. the two most commonly used techniques for detection of mrna (fig. 2) are reverse transcription polymerase chain reaction (rt-pcr) and rna-rna hybridisation. in rt-pcr, the first step is a reverse transcription process the conversion of mrna into copy dna (cdna). reverse transcription requires a small dna primer to bind to the mrna in order to initiate synthesis of cdna. thus, specific mrnas can be amplified by using sequence-specific primers in the rt-pcr reaction. following synthesis of cdna, a normal pcr is carried out to multiply the cdna, and the resulting pcr products are detected by usual dna detection techniques. direct rna-rna hybridisation analyses exploit a completely different principle; this is directly quantitative but lacks the sensitivity of rt-pcr. first, the total content of mrna is extracted. then the mrna of interest is identified by binding of a specific rna probe with a sequence complementary to the mrna gene of interest (hybridisation). by using a ‘radiolabelled’ probe, the final quantification of the mrna of interest is easily done by determining the amount of ‘radiolabelled’ bound to the mrna. a study using freshwater samples artificially contaminated with the herbicide 2,4-d, revealed a significant increase in the amount of tfda mrna, as measured by hybridisation of rna extracts using a tfda specific probe. this demonstrates that the 2,4-d degraders in the freshwater samples were actively degrading the 2,4-d (fig. 5). transcription of tfda was, however, transient and the degradation of 2,4-d continued although mrna levels dropped. these observations illustrate that the herbicide-degrading enzymes encoded by the mrna last longer in the cells than the mrna ‘signal’ itself. references broholm, m.m., rügge, k., tuxen, n., mosbæk, h., & bjerg, p.l. 2000: migration and degradation of pesticides in an aerobic groundwater aquifer: field injection experiments. in: bjerg, p.l., engesgaard, p. & krom, t.d. (eds): proceedings of the international conference on groundwater research, copenhagen, 169–170. rotterdam: balkema. de lipthay, j.r., johnsen, k., aamand, j., tuxen, n., albrechtsen, h.-j. & bjerg, p.l. 2000: continuous exposure of pesticides in an aquifer changes microbial biomass, diversity and degradation potential. in: bjerg, p.l., engesgaard, p. & krom, t.d. (eds): proceedings of the international conference on groundwater research, copenhagen, 157–158. rotterdam: balkema. don, r.h., weightman, a.j., knackmuss, h.-j. & timmis, k.n. 1985: transposon mutagenesis and cloning analysis of the pathway for degradation of 2,4-dichlorophenoxyacetic acid and 3-chlorobenzoate in alcaligenes eutrophus jmp134(pjp4). journal of bacteriology 161(1), 85–90. fredslund, l., ekelund, f., jacobsen, c.s. & johnsen, k. 2001: development and application of a most probable number-pcr assay to quantify flagellate populations in soil samples. applied and environmental microbiology 67(4), 1613–1618. jacobsen, c.s. 1995: rapid microscale detection of specific bacterial dna in soil using magnetic capture-hybridization and polymerase chain reaction amplification assay (mch-pcr). applied and environmental microbiology 61(9), 3347–3352. johnsen, k., enger, ø., jacobsen, c.s., thirup, l. & torsvik, v. 1999: quantitative selective pcr of 16s ribosomal dna correlates well with selective agar plating in describing population dynamics of indigenous pseudomonas spp. in soil hot spots. applied and environmental microbiology 65(5), 1786–1789. rosenbom, a.e., klint, k.e.s., fredericia, j., springer, n. & andersen, g. 2000: pore-to-core scale-up studies of the transport properties of organic pollutants with natural attenuation. danmarks og grønlands geologiske undersøgelse rapport 2000/79, 39 pp. saiki, r.k., scharf, s., faloona, f., mullis, k.b., horn, g.t., erlich, h.a. & arnheim, n. 1985: enzymatic amplification of ß-globin genomic sequences and restriction site analysis for diagnosis of sickle cell anemia. science 230, 1350–1354. 36 authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: csj@geus.dk << /ascii85encodepages false /allowtransparency false /autopositionepsfiles true /autorotatepages /all /binding /left /calgrayprofile (dot gain 20%) /calrgbprofile (srgb iec61966-2.1) 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<feff4f7f752890194e9b8a2d5b9a5efa7acb76840020005000440046002065874ef65305542b8f039ad876845f7150cf89e367905ea6ff0c4fbf65bc63d066075217537054c18cea3002005000440046002065874ef653ef4ee54f7f75280020004100630072006f0062006100740020548c002000520065006100640065007200200035002e0030002053ca66f465b07248672c4f86958b555f3002> >> >> setdistillerparams << /hwresolution [2400 2400] /pagesize [595.000 842.000] >> setpagedevice geological survey of denmark and greenland bulletin 7, 2004, p 21-24 intense drilling activity following the discovery of the siri field in 1995 has resulted in an improved understanding of the siliciclastic palaeogene succession in the danish north sea sector (fig. 1). many of the new wells were drilled in the search for oil reservoirs in sand bodies of paleocene–eocene age. the existing lithostratigraphy was based on data from a generation of wells that were drilled with deeper stratigraphic targets, with little or no interest in the overlying palaeogene sediments, and thus did not adequately consider the significance of the palaeogene sandstone units in the danish sector. in order to improve the understanding of the distribution, morphology and age of the palaeogene sediments, in particular the economically important sandstone bodies, a detailed study of this succession in the danish north sea has recently been undertaken. an important aim of the project was to update the lithostratigraphic framework on the basis of the new data. the project was carried out at the geological survey of denmark and greenland (geus) with participants from the university of aarhus, dong e&p and statoil norway, and was supported by the danish energy agency. most scientific results cannot be released until september 2006, but a revised lithostratigraphic scheme may be published prior to that date. formal definition of new units and revision of the lithostratigraphy are in preparation. all of the widespread palaeogene mudstone units in the north sea have previously been formally established in norwegian or british wells, and no reference sections exist in the danish sector. as the lithology of a stratigraphic unit may vary slightly from one area to another, danish reference wells have been identified during the present project, and the lithological descriptions of the formations have been expanded to include the appearance of the units in the danish sector. 21 a revised lithostratigraphy for the palaeogene – lower neogene of the danish north sea poul schiøler, jan andsbjerg, ole r. clausen, gregers dam, karen dybkjær, lars hamberg, claus heilmann-clausen, lars e. kristensen, iain prince and jan a. rasmussen geological survey of denmark and greenland bulletin 7, 21–24 (2005) © geus, 2005 5°e 4°e 57°n 56°n c o ffe e so il fault 50 km 20 40 60 80 100 thickness (m) siri-3 siri canyon f-1x inez-1 siri-1 siri-2 c entral g raben north sea denmark fig. 1. map showing the study well data base superposed on an isochore map of the lista formation. the lista formation thickens towards the northern part of the mapped area; this thickening is mainly due to the presence of sandstone bodies within the siri canyon. many of the sandstone bodies recently discovered in the danish sector have a limited spatial distribution and were sourced from other areas than their contemporaneous counterparts in the norwegian and british sectors. these sandstone bodies are therefore defined as new lithostratigraphic units in the danish sector, and are assigned danish type and reference sections. there is a high degree of lithological similarity between the palaeogene–neogene mudstone succession from danish offshore boreholes and that from onshore exposures and boreholes, and some of the mudstone units indeed seem identical. however, in order to acknowledge the traditional distinction between offshore and onshore stratigraphic nomenclature, the two sets of nomenclature are kept separate herein. in recent years oil companies operating in the north sea have developed various in-house lithostratigraphic charts for the paleocene–eocene sand and mudstone successions in the danish and norwegian sectors. a number of informal lithostratigraphic units have been adopted and widely used. in the present project, these units have been formally defined and described, maintaining their original names whenever feasible, with the aim of providing an unequivocal nomenclature for the palaeogene – lower neogene succession in the danish sector. it has not been the intention to establish a sequence stratigraphic model for this succession in the north sea; the reader is referred to the comprehensive works of michelsen (1993), neal et al. (1994), mudge & bujak (1994, 1996a, b), michelsen et al. (1995, 1998), danielsen et al. (1997) and rasmussen (2004). methodology the multidisciplinary project integrates biostratigraphic results from palynology and micropalaeontology with results from sedimentological studies, petrophysical log interpretation and conventional seismic interpretation, in an attempt to identify, describe and correlate lithological units. the lithostratigraphy proposed is based on analysis of petrophysical logs from more than 80 wells (fig. 1) and studies of cuttings samples and core sections. lithostratigraphic well correlation is supported by results from biostratigraphic analysis of 29 wells encompassing both palynological and micropalaeontological data. this analysis has established a detailed succession of first downhole occurrences of biostratigraphical events which are of crucial importance for well correlation and age determination in the region. resulting well correlations have been matched with results from interpretation of key seismic sections. a revised lithostratigraphy an important outcome of the project is a revised lithostratigraphic chart for the siliciclastic palaeogene – lower neogene succession of the danish north sea (fig. 2). the chart is based on the subdivision proposed by deegan & scull (1977), but incorporates subsequent improvements by hardt et al. (1989) and knox & holloway (1992). the revised lithostratigraphy presented in fig. 2 has its genetic base at the top of the chalk group (ekofisk for22 fig. 2. diagram showing the correlation between key lithostratigraphic schemes for the central graben and eastern north sea. white: mudstone units. yellow: sandstone units. names in bold indicate units of formation or group rank. nordland group hordaland group balder sele lista unnamed unit ekofisk cen5 cen4 cen3 cen2 cen1 north sea marl ekofisk nordland group hordaland group balder sele lista våle ekofisk nordland group lark horda balder tay m o u sa h e fr in g d u fa f re ja k o lg a f u r r in d id u n t y r b o r sele lista l is ta f o rt ie s c ro m ar ty m e y v a d e f o r ti e s a n d re w f is k e b a n k f is k e b a n k f r ig g maureen m a u re e n ekofisk ekofisk nordland group lark horda balder sele bue ve vile våle deegan & scull (1977) kristoffersen & bang (1982) hardt et al. (1989) knox & holloway (1992) this study r o g a la n d g ro u p mation). the top is at the mid-miocene unconformity, a basinwide erosion surface that separates the oligocene to middle miocene hordaland group from the overlying middle miocene to recent nordland group. the succession is subdivided into seven formations containing eleven new members. the våle, lista, sele, fur, balder, horda and lark formations of previous lithostratigraphic schemes are adequate for subdividing the danish sector at formation level and are retained herein with expanded lithological descriptions. the five first-mentioned formations constitute the rogaland group of early selandian (late paleocene) to earliest eocene (pre-classical ypresian) age, and the horda and lark formations constitute the hordaland group of ypresian (early eocene) to early serravallian (middle miocene) age. rogaland group the våle formation (hardt et al. 1989) consists of light grey to greenish grey marlstones and is retained largely unchanged from its original description. the lista formation (deegan & scull 1977) is subdivided into three new mudstone members (vile, ve and bue). the predominantly light to dark grey mudstones of the vile and bue members are separated by the greenish, bluish to red coloured mudstones of the ve member. the sele formation (deegan & scull 1977) overlies the lista formation; the boundary is placed where laminated dark grey to black mudstones overlie the light to dark grey, smectitic, non-laminated mudstones of the bue member. this boundary definition differs from that used by knox & holloway (1992), who placed the lista–sele boundary at the base of the bue member as recognised here (fig. 2). incidentally, the lista–sele boundary as originally defined coincides with the paleocene–eocene boundary recently approved by the international commission of stratigraphy, at the conspicuous 13c isotope excursion in chron c24r. the balder formation is retained largely unchanged from its original description by deegan & scull (1977). the fur formation (pedersen & surlyk 1983) is characterised by interbedded diatomite and tuffs and has been recognised in one norwegian and three danish offshore wells by thomsen & danielsen (1995) at a similar stratigraphic level to that of the sele and balder formations. it is therefore included in the north sea lithostratigraphic chart (fig. 2). hordaland group the horda and lark formations of knox & holloway (1992) are introduced in the danish sector for the basinal mudstones that overlie the balder formation. the horda formation consists of greenish-grey to greyish-green fissile mudstone, whereas the lark formation comprises greenishgrey to dark brown non-fissile mudstones. the transition from the horda to the lark formation is characterised by a significant increase in gamma ray response. sandstone members eight discrete sandstone members have been recognised in the palaeogene – lower neogene mudstone succession (fig. 2). the lower five of these occur exclusively in the siri canyon, a 20 km wide and up to 200 m deep erosional depression that truncates reflectors in the chalk group (fig. 1; hamberg et al. 2005). the bor member is a sandstone unit in the våle formation. three sandstone members occur in the lista formation and are named tyr, idun and rind. the sele and horda formations each contain sandstone units for which the names kolga and hefring members are proposed, respectively. the hefring member occurs in an area south of the siri canyon. two sandstone members (dufa and freja) are present in the lark formation. the dufa member occurs in the north-eastern part of the danish sector, around the wells f-1x and inez-1 (fig. 1); the freja member occurs above the siri canyon, south of the siri-1 well (fig. 1). rogaland group sandstones: reservoir facies the economically important paleocene–eocene oil reservoir sandstones of the rogaland group are situated at the mouth of, and within, the siri canyon (fig. 1). the sandstones occur as in situ sediment bodies deposited by gravity flows and as remobilised, injected sandstones (hamberg et al. 2005). although the sandstone bodies occur at different stratigraphic levels within the rogaland group, they are strikingly uniform. the sandstones are quartzose and very fineto finegrained, well sorted and rich in glaucony with a greenish grey colour. the sandstone bodies appear massive and structureless with primary sedimentary structures preserved only in their basal part. individual sandstones may be up to 100 m thick but are usually much thinner. identification and correlation of individual sandstone members are feasible by means of 3d seismic data, with support from borehole logs and high-resolution biostratigraphy. an example of results from such an integrated correlation in the lower part of the siri canyon is shown in fig. 3. 23 acknowledgements this work was made possible through grants from the danish energy authority, under the energy research programme 2000. dong e&p is thanked for access to lithostratigraphic data from siri canyon wells. references danielsen, m., michelsen, o. & clausen, o.r. 1997: oligocene sequence stratigraphy and basin development in the danish north sea sector based on log interpretations. marine and petroleum geology 14, 931–950. deegan, c.e. & scull, b.j. (compilers) 1977: a standard lithostratigraphic nomenclature for the central and northern north sea. institute of geological sciences report 77/25; norwegian petroleum directorate bulletin 1, 36 pp. hamberg, l., dam, g., wilhelmson, c. & ottesen, t.g. 2005: paleocene deep-marine sandstone plays in the siri canyon, offshore denmark – southern norway. in: doré, a.g. & vining, b.a. (eds): petroleum geology: north west europe and global perspectives. proceedings of the 6th petroleum geology conference, 1185–1198. london: geological society. hardt, t., holtar, e., isaksen, d., kyllingstad, g., lervik, k.s., lycke, a.s. & tonstad, k. 1989: revised tertiary lithostratigraphic nomenclature for the norwegian north sea. in: isaksen, d. & tonstad, k. (eds): a revised cretaceous and tertiary lithostratigraphic nomenclature for the norwegian north sea. norwegian petroleum directorate bulletin 5, 35–55. knox, r.w.o’b. & holloway, s. 1992: paleogene of the central and northern north sea. in: knox, r.w.o’b. & cordey, w.g. (eds): lithostratigraphic nomenclature of the uk north sea, 133 pp. nottingham: british geological survey. kristoffersen, f.n. & bang, i. 1982: cenozoic excl. danian limestone. in: michelsen, o. (ed.): geology of the danish central graben. danmarks geologiske undersøgelse serie b 8, 62–71. michelsen, o. 1993: stratigraphic correlation of the danish onshore and offshore tertiary successions based on sequence stratigraphy. bulletin of the geological society of denmark 41, 145–161. michelsen, o., danielsen, m., heilmann-clausen, c., jordt, h., laursen, g. & thomsen, e. 1995: occurrence of major sequence stratigraphic boundaries in relation to basin development in cenozoic deposits of the southeastern north sea. in: steel, r.j. et al. (eds): sequence stratigraphy on the northwest european margin. norsk petroleum forening special publication 5, 415–427. michelsen, o., thomsen, e., danielsen, m., heilmann-clausen, c., jordt, h. & laursen, g. 1998: cenozoic sequence stratigraphy in the eastern north sea. in: de graciansky, p.-c. et al. (eds): mesozoic and cenozoic sequence stratigraphy of european basins. society of economic paleontologists and mineralogists special publication 60, 91–118. mudge, d.c. & bujak, j.p. 1994: eocene stratigraphy of the north sea basin. marine and petroleum geology 11, 166–181. mudge, d.c. & bujak, j.p. 1996a: paleocene biostratigraphy and sequence stratigraphy of the uk central north sea. marine and petroleum geology 13, 295–312. mudge, d.c. & bujak, j.p. 1996b: an integrated stratigraphy for the paleocene and eocene of the north sea. in: knox, r.w.o’b., corfield, r.m. & dunay, r.e. (eds): correlation of the early paleogene in northwest europe. geological society special publication (london) 101, 91–113. neal, j.e., stein, j.a. & gamber, j.h. 1994: graphic correlation and sequence stratigraphy in the palaeogene of nw europe. journal of micropalaeontology 13, 55–80. pedersen, g.k. & surlyk, f. 1983: the fur formation, a late paleocene ash-bearing diatomite from northern denmark. bulletin of the geological society of denmark 32, 43–65. rasmussen, e.s. 2004: the interplay between true eustatic sea-level changes, tectonics, and climate changes: what is the dominating factor in sequence formation of the upper oligocene – miocene succession in the eastern north sea basin, denmark? global and planetary change 41, 15–30. thomsen, e. & danielsen, m. 1995: transitional paleocene/eocene ashbearing diatomite in the eastern north sea. tertiary research 15, 111–120. siri-2 siri-1 siri-3 rind mb idun mb kolga mb tyr mb tyr mb horda fm sli dbf fan aau ama ppy balder fm sele fm lista fm våle fm 50 m ipf gda fig. 3. correlation diagram of the rogaland group in the lower part of the siri canyon (well locations shown in fig. 1). horizontal distance not to scale. in this section the tyr member consists of three sandstone beds separated by mudstone layers. the idun member cuts deeply into the underlying lista formation. key biostratigraphic downhole events are shown to the left. sli, subbotina linaperta; dbf, decrease in benthic foraminifera; fan, influx of fenestrella antiqua; aau, apectodinium augustum; ama, alisocysta margarita; ppy, common palaeoperidinium pyrophorum; ipf, increase in planktonic foraminifera; gda, globoconusa daubjergensis. authors’ addresses p.s., j.a., k.d., l.e.k. & j.a.r., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: pos@geus.dk o.r.c. & c.h.-c., department of earth sciences, university of aarhus, dk-8000 århus c, denmark. g.d. & l.h., dong, agern allé 24–26, dk-2970 hørsholm, denmark. i.p., statoil norway, forusbeen 50, n-4035 stavanger, norway. 24 geological survey of denmark and greenland bulletin 7, 2004, p 49-52 49 pollen records from lake sediments have a great potential for providing information on the quantitative composition of past vegetation and land cover in the surrounding landscape. this can contribute to a better understanding of the development of the cultural landscape and interactions between human impact on the landscape and natural conditions like soil and climate. a good understanding of the history of cultural landscapes is necessary for choosing appropriate management strategies for areas dependent on cultural impact, such as heaths, meadows and dry pastures. it is also important for archaeological research concerning utilisation of the landscape in earlier periods. furthermore, quantitative reconstructions are relevant for climate research. here they can be used to test climate models, since model predictions of past climate can be translated into past vegetation, which can then be compared to pollen-based reconstructions. past vegetation cover is also a necessary input to climate models, as it influences albedo, evapotranspiration and carbon storage and cycling. quantifying vegetation from fossil pollen samples requires a detailed understanding of the way vegetation is reflected in pollen assemblages, including the approximate size of the area of vegetation represented. the relationship between pollen and vegetation is complicated by the fact that different plant species produce different amounts of pollen, and that pollen types are dispersed differently in the atmosphere, depending on their size, shape and weight. these pressing challenges in pollen analysis have attracted much attention in recent years. models have been developed to describe and simulate species specific pollen dispersal, to quantitatively relate pollen proportions to plant abundance, as well as estimate pollen productivity and to quantify the pollen source area of different types of basins (parsons & prentice 1981; prentice & parsons 1983; prentice 1985; sugita 1993, 1994; sugita et al. 1997, 1999; broström 2002; bunting et al. 2004). the geological survey of denmark and greenland (geus) has in recent years contributed to the development and validation of such models through the project agrar 2000 (odgaard 1999; nielsen 2003), where quantitative estimates of past land cover in different regions of denmark were one of the main objectives, and through participation in the international research network pollandcal (pollen landscape calibration), funded by nordforsk (nordic research board), which focuses on further model development, validation and application. the historical analogues approach modern analogues of past landscapes are very rare in denmark due to extensive changes to the cultural landscape during the past two centuries. these include intensification of agricultural practices, such as drainage, fertilisation and use of pesticides, plantations of introduced tree species and reductions in areas of pasture, wetland and heathland. the resulting changes in species composition, vegetation structure and growing conditions have affected the relationship between vegetation and pollen sedimentation through changes in pollen productivity and dispersal (nielsen & odgaard 2004). quantifying the relationship between pollen sedimentation in lakes and land cover using historical maps anne birgitte nielsen geological survey of denmark and greenland bulletin 7, 49–52 (2005) © geus, 2005 fig. 1. map showing the location of the 30 danish calibration sites and nine test sites used to assess the use of historical land cover and pollen assemblage data and the erv model for vegetation reconstruction. modified from nielsen & odgaard (2005). 50 km 12°e10°e8°e 56°n 55°n 57°n denmark swedentest sites calibration sites navnsø store økssø skånsø kragsø dallerup sø gudme sø avnsø store gribsø gundsømagle sø modern pollen datasets are thus not suitable as a standard for reconstructing cultural landscapes from fossil pollen samples. these problems may be overcome by using historical data (odgaard & rasmussen 2000; nielsen & odgaard 2004), although this approach involves several sources of error and potential bias, including a lack of spatial precision and detail, problems in interpretation of land cover signatures, biased species selection, changes in nomenclature and potential dating problems. in spite of these problems, most of which arise because the historical data were usually not created with the purpose of describing the plant species distribution in detail, this and other studies have shown that historical analogues can provide new insights and assist the interpretation of palaeoecological data. the historical calibration dataset collected for this study consists of pollen samples from around a.d. 1800 (identified by 210pb dating) from 30 small (3–30 ha) danish lakes (fig. 1), and land cover data from historical maps around the lakes (nielsen 2003). the historical maps used were the so-called ‘parish maps’, which show areas of different land cover, such as arable fields, forest, meadow and heath around a.d. 1800 at scale 1:20 000. spatial plant distribution was estimated from the land cover using historical data (b. fritzbøger and j.r. rømer, personal communication 2000) and comparison to modern analogues of old cultural landscape types in southern sweden (broström 2002), where areas of traditional land use are more common than in denmark. the nine study sites of the agrar 2000 project (nielsen & odgaard 2005) were not included in the calibration dataset, so these could be used as independent test sites (fig. 1) for the vegetation reconstructions. distance weighting vegetation data plants growing near a depositional basin contribute more to the pollen assemblages in the basin than plants farther away. vegetation data should therefore be distance weighted to reflect the ‘pollen sample’s view’ of the landscape, before pollen/vegetation calibration is applied (prentice 1985). the vegetation data from the historical maps were distance weighted according to the prentice/sugita model of pollen dispersal and deposition (prentice 1985; sugita 1993) using computer programs developed by s. sugita (1994, unpublished data 2002). in this model, pollen dispersal is assumed to follow sutton’s (1953) equation for the dispersal of small particles in the atmosphere, and depends on the weight and size of pollen grains, which are species specific, and on wind speed and atmospheric conditions. only windborne pollen is considered by the model, so only lakes with small or no inlet streams were used as calibration sites. the model's predictions of pollen assemblages deposited in different basins have been validated for forested landscapes in north america (calcote 1995; sugita et al. 1997; davis 2000) and for cultural landscapes in sweden and denmark (broström 2002; nielsen 2004; nielsen & sugita in press). the extended r-value model the quantitative relationship between the pollen assemblages from the lakes and the distance weighted plant abundance estimated from the historical maps was analysed using the extended r-value (erv) model (parsons & prentice 1981; prentice & parsons 1983; sugita 1994). this model was developed to achieve quantitative vegetation reconstructions from pollen proportions. the basic assumption is that the pollen loading of species k at site i (ρik) is linearly related to the distance weighted plant abundance of species k in the relevant source area of site i (xik): ρik = αixik + yio (1) where αi is the pollen productivity of species i, and yio is the amount of pollen of species i originating outside the relevant source area. both are assumed to be constant among sites in a region. if yio is furthermore assumed to form a constant proportion (zi) of the total plant abundance at the site (erv submodel 2), it is possible to relate pollen percentage to vegetation percentage, and estimate αi and zi from a dataset of pollen counts and distance weighted plant abundance, using a maximum likelihood method (prentice & parsons 1983). once these parameters are estimated, the inverse form of the erv model can be used to reconstruct plant proportions from pollen proportions. pollen productivity (αi) and the background component (zi) for four groups of plants (trees, poaceae, cerealia and calluna) were estimated from the a.d. 1800 vegetation and pollen data (table 1; nielsen & odgaard 2005). the estimated values of αi are relative, as one taxon (here poaceae) is chosen as reference taxon. the relative pollen productivity estimates of cerealia and calluna are lower than those for southern sweden (broström et al. 2004), whereas the estimate for trees in denmark is higher than that for sweden (sugita et al. 1999). the differences may be explained by the swedish estimates being based on analyses of moss polsters, while the danish estimates derive from lake sediments. tree pollen may be more easily dispersed to lakes than herb pollen, because it is released at a greater height. a difference in species composition within the plant groups between denmark in a.d. 1800 and sweden today may also contribute to the observed differences (nielsen 2004). 50 estimating pollen source area the spatial scale reflected by pollen samples is vital for quantitative reconstructions of past vegetation and landscape inferred from fossil pollen data, and a rigorous definition of the pollen source area is needed. sugita (1994) proposed the concept of the ‘relevant source area of pollen’ (rsap), defined as the area beyond which the correlation between pollen deposition at each site and the surrounding vegetation does not improve. the pollen loading (in terms of amount and composition) coming from beyond rsap is constant between sites within a region, corresponding to yio in equation (1). the radius of rsap can be estimated simultaneously with erv model parameters from the dataset of pollen counts and distance weighted plant abundance, and the distance where the likelihood function score of the erv calculations no longer decreases, because fit of the model no longer improves (sugita 1994). by analysing the data from the calibration sites, the radius of rsap for the danish lakes is estimated to c. 1800 m from the centre of lakes for all sites (nielsen & sugita in press). a difference in rsap radius of 400–500 m between eastern and western denmark was observed. this can be explained by a difference in the average patch size of the vegetation between regions (33 ha around eastern sites, 79 ha around western sites). both simulations (sugita 1994; broström 2002; bunting et al. 2004; nielsen & sugita in press) and empirical data (calcote 1995; nielsen & sugita in press) suggest that rsap is affected primarily by the spatial distribution of vegetation, especially patch size. rsap has been shown to be largely independent of fall speed or relative pollen productivity of the taxa present in the landscape, so the species involved have little effect on rsap (bunting et al. 2004; nielsen & sugita in press). the size of rsap is important for the interpretation of fossil pollen assemblages, as it is only vegetation within this area that potentially can be reconstructed. reconstructing land cover the estimates of αi and zi from the calibration sites were used to reconstruct vegetation composition around the nine test sites, applying the inverse form of the erv model (prentice & parsons 1983). the reconstructions are compared to distance weighted vegetation composition in rsap of the test sites from historical maps (fig. 2). the reconstructions based on the erv model reflect actual differences in vegetation among the test sites much more clearly than the pollen pro51 αi (sd) zi (sd) α, southern sweden poaceae 1.0 (0.0) 0.94 (0.022) 1.0 cerealia 0.95 (0.20) 0.11 (0.025) 3.2 calluna 2.06 (0.042) 0.10 (0.005) 4.7 trees 9.41 (0.48) 1.33 (0.002) 5.95 pollen productivity (αi) and background component (zi) estimated from the calibration sites, using erv submodel 2. for comparison, pollen productivity estimated from moss samples from southern sweden (sugita et al. 1999; broström et al. 2004) are also listed. table 1. erv parameter estimates fig. 2. a: pollen proportions in the a.d. 1800 sediment of the nine test sites. b: distance weighted vegetation proportions reconstructed from the pollen counts using the reverse erv model, and the parameters estimated from the calibration sites (table 1). c: the distance weighted vegetation proportions within 1800 m of the centre of the test sites, calculated from the a.d. 1800 land cover maps. cerealia calluna poaceae trees 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% a vn sø st or e g ri bs ø g ud m e sø g un ds øm ag le s ø d al le ru p sø st or e ø ks sø sk ån sø n av ns ø k ra gs ø a: pollen proportions c: vegetation from maps b: reconstructed vegetation portions of the samples. for example, the samples from all test sites contain more than 25% tree pollen, although the surroundings of many sites contain very little woodland, a fact which is reflected by the reconstructions. the amount of calluna tends to be higher in the reconstructions than estimated from the maps, which could indicate that the estimated αi for this species is too low, or that the a.d. 1800 heathlands were richer in calluna than was assumed based on present-day heathlands in southern sweden. however, the reconstructions clearly distinguish the sites where heathland was common (store økssø, skånsø, navnsø and kragsø; fig. 1). the reconstructed amounts of cerealia reflect very well the differences in the amount of arable land between the test sites. conclusions the use of historical maps has proved very useful for quantifying the relationship between pollen sedimentation and vegetation. it has provided an empirical validation of the prentice/sugita model of pollen dispersal for open cultural landscapes (nielsen 2004), made it possible to estimate the relevant source area of pollen, and provided insights into the factors affecting rsap (nielsen & sugita in press). finally, it has provided a set of erv model parameters and shown that erv-based reconstructions reflect the actual patterns of vegetation composition around the lakes (nielsen & odgaard 2005). the next step is to apply these findings to fossil pollen diagrams and reconstruct the cultural landscape of earlier periods, from which no maps are available. this research will continue at geus in the coming years, thanks to a grant from the carlsberg foundation. acknowledgements bent odgaard (university of aarhus, denmark) and peter rasmussen (geus) are thanked for providing pollen data from test sites, and shinya sugita (university of minnesota, usa) for access to unpublished computer programs. this is publication no. 10 in the project agrar 2000, funded by the danish research councils. it is also a contribution to the nordforsk network pollandcal, co-ordinated by m.-j. gaillard (university of kalmar, sweden). references broström, a. 2002: estimating source area of pollen and pollen productivity in the cultural landscapes of southern sweden – developing a palynological tool for quantifying past plant cover. lundqua thesis 46, 101–115. lund: university of lund. broström, a., sugita, s. & gaillard, m.-j. 2004: pollen productivity estimates for the reconstruction of past vegetation cover in the cultural landscape of southern sweden. the holocene 14, 368–381. bunting, m.j., gaillard, m.-j., sugita, s., middleton, r. & broström, a. 2004: vegetation structure and pollen source area. the holocene 14, 651–660. calcote, r. 1995: pollen source area and pollen productivity: evidence from forest hollows. journal of ecology 83, 591–602. davis, m.b. 2000: palynology after y2k – understanding the source area of pollen in sediments. annual review of earth and planetary sciences 28, 1–18. nielsen, a.b. 2003: pollen based quantitative estimation of land cover – relationships between pollen sedimentation in lakes and land cover as seen on historical maps in denmark a.d. 1800. danmarks og grønlands geologiske undersøgelse rapport 2003/57, 135 pp. nielsen, a.b. 2004: modelling pollen sedimentation in danish lakes around a.d. 1800 – an attempt to validate the pollscape model. journal of biogeography 31, 1693–1709. nielsen, a.b. & odgaard, b. 2004: the use of historical analogues for interpreting fossil pollen records. vegetation history and archaeobotany 13, 33–43. nielsen, a.b. & odgaard, b. 2005: reconstructing land cover from pollen assemblages from small lakes in denmark. review of palaeobotany and palynology 133, 1–21. nielsen, a.b. & sugita, s. in press: estimating relevant source area of pollen for small danish lakes around a.d. 1800. the holocene. odgaard, b. 1999: landbrugslandskabet gennem 2000 år. geologi – nyt fra geus 1, 4–6. odgaard, b.v. & rasmussen, p. 2000: origin and temporal development of macro-scale vegetation patterns in the cultural landscape of denmark. journal of ecology 88, 733–748. parsons, r.w. & prentice, i.c. 1981: statistical approaches to r-values and pollen-vegetation relationship. review of palaeobotany and palynology 32, 127–152. prentice, i.c. 1985: pollen representation, source area, and basin size: toward a unified theory of pollen analysis. quaternary research 23, 76–86. prentice, i.c. & parsons, r.w. 1983: maximum likelihood linear calibration of pollen spectra in terms of forest composition. biometrics 39, 1051–1057. sugita, s. 1993: a model of pollen source area for an entire lake surface. quaternary research 39, 239–244. sugita, s. 1994: pollen representation of vegetation in quaternary sediments: theory and method in patchy vegetation. journal of ecology 82, 881–897. sugita, s., macdonald, g.m. & larsen, c.p.s. 1997: reconstruction of fire disturbance and forest succession from fossil pollen in lake sediments: potential and limitations. in: clark, j.s. et al. (eds): sediment records of biomass burning and global change, 387–412. berlin: springerverlag. sugita, s., gaillard, m.-j. & broström, a. 1999: landscape openness and pollen records: a simulation approach. the holocene 9, 409–421. sutton, o.g. 1953: micrometeorology, 333 pp. new york: mcgraw-hill. 52 author’s address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: abn@geus.dk geological survey of denmark and greenland bulletin 7, 2004, p 37-40 37 steam treatment of contaminated soil and aquifer sediment is a promising method of cleaning soil. the treatment is based on steam injection into a water saturated porous aquifer (gudbjerg et al. 2004), by which the heat transfers the contaminants into the vapour phase, allowing entrapment in an active carbon filter connected to a large vacuum suction device. the treatment is effective against several important groundwater contaminants, including pentachlorophenole and perchloroethylene, typically found in association with industrial processes or dry cleaning facilities. furthermore, as an example of removal of non-aqueous phase liquids (napls) large amounts of creosote have been recovered after steam injection in a deep aquifer (kuhlmann 2002; tse & lo 2002). steam treatment is dependent on the complete heating of the soil volume under treatment. the steam has a strongly adverse impact on trees and other plants with deep root systems within the soil, but no other visible effects have been reported. the aim of the activities undertaken during collaborative projects carried out by the geological survey of denmark and greenland (geus) and the danish institute of agricultural sciences (djf) for the danish environmental protection agency and the local authorities in copenhagen (københavns amt) was to establish to what extent the microbial community was affected by the steam treatment of the soil. a few results from the literature indicate that the microbial activity increases in steam treated soil (richardson et al. 2002), probably due to microbial degradation of the soil contaminants in combination with microbial utilisation of heatkilled organisms. it is, however, not known whether this increased microbial activity is associated with the development of pathogenic micro-organisms; these are typically able to grow at higher temperatures than the general microbial community in soil. geological survey of denmark and greenland bulletin 7, 37–40 (2005) © geus, 2005 steam treatment of contaminated groundwater aquifers – development of pathogenic micro-organisms in soil carsten suhr jacobsen, susanne elmholt, carsten bagge jensen, pia bach jakobsen and mikkel bender denmark hedehusene copenhagen 100 km steam steam ground surface ground water level gases and polluted water removed and cleaned up steam steam collection well contaminated soil fig. 1. sketch of steam treatment facility at a strongly contaminated industrial site at hedehusene, west of copenhagen. inset map shows location. 38 the steam treatment in hedehusene hedehusene is situated approximately 25 km to the west of copenhagen, and the contaminated soil and groundwater aquifer here results from various industrial activities primarily carried out between 1920 and 1970. these activities include a dry cleaning facility and several small workshops. from both types of industry, trichloroethylene and tetrachloroethylene are often found as groundwater contaminants. the groundwater aquifer in hedehusene was known to be contaminated with high concentrations of trichloroethylene, which has been a constant hazard to an important drinking water production well downstream from the site. pumping, treating and recycling water at the site over many years had controlled the distribution of the contamination, but the main contamination was still present at very high levels and has become a long-term threat to continued groundwater extraction. the steam treatment in hedehusene was carried out during the winter 2001–2002. wells delivering steam were buried nine metres below the land surface, allowing the transfer of steam below the contamination plume (fig. 1). the steam was pumped continuously for a period of five months, until the temperature reached 90°c. heating of the soil allowed the transfer of the contaminant to the vapour phase which was then trapped in an active carbon filter. heat-tolerant micro-organisms found at the hedehusene site the site was monitored by sampling surface soil and soil from approximately 50 cm depth on 11 september 2001 (before the steam treatment), and resampling during and after the steam treatment. sampling was undertaken six times with the latest sampling on 26 october 2004. in general, it was found that the number of heat-tolerant micro-organisms increased after the heat treatment, and that some of the heat-tolerant micro-organisms could still be found three years after the 2001–2002 steam treatment. heat-tolerant bacteria are defined as able to continue growing at temperatures of 42°c, and heat-tolerant fungi as those able to continue growing at 37°c. such high temperatures do not occur naturally at the site, and soil micro-organisms originating from this site are not expected to be able to grow at such high temperatures. heat tolerance is one of the main characteristics that distinguish normal soil microorganisms from pathogenic micro-organisms found in human patients. general microbial community adaptation to growth at high temperature the effect on the general microbial community was investigated by assessing its growth rate on 24 different microbial food sources. a small amount of soil was added to 24 different microbial growth media and incubated at either 20°c or 42°c. this technique revealed that the microbial community in the control plot was very constant in its ability to utilise the different food sources during the sampling period. furthermore, the microbial community in the control plot showed little ability to utilise food sources at the elevated temperature (an area approximately 30 m away from the heating zone). in contrast, the heated soil showed a massive and long-lasting a b c d 5 cm fig. 2. changes of microbial metabolic fingerprints using comparisons of the ability of micro-organisms to grow on different carbon substrates. the appearance of coloration in each section indicates growth of microorganisms. a high number of positive sections at 42°c indicate a high number of organisms able to grow at temperatures associated with pathogenic micro-organisms. a: steam-treated soil with growth at 20°c. b: control soil with growth at 20°c. c: steam-treated soil with growth at 42°c. d: control soil with growth at 42°c. 39 increase in the ability of the microbial community to utilise the food sources at 42°c (fig. 2). it is well known that micro-organisms differ in their ability to survive in soil. some are able to form spores that can stay inactive in the soil for years while others die out due to predation and competition with micro-organisms having a very low level of metabolic activity. we have chosen two different representatives of heat-tolerant micro-organisms: a bacterium without the ability to form spores, and a fungus which forms conidia. although these conidia are able to germinate and grow in the laboratory, they need not be active in the soil. both species showed a clear response to soil heating as described below. aspergillus fumigatus – an unusual pathogenic and allergenic micro-organism aspergillus fumigatus is a remarkable and unusual pathogen because in addition to causing life-threatening invasive disease of immuno-compromised human patients, it can also cause allergic reactions in persons with fully functional immune systems (latgé 1999; denning et al. 2002). a. fumigatus is easily identified and is distinguished by rapidly growing colonies in characteristic turquoise to dark green colours, by the phialides curving to be roughly parallel to each other and to the axis of the stipe, and the presence of small conidia in columns (fig. 3; klich & pitt 1988). a. fumigatus is regularly reported as a dominant species in various types of compost, but never as a dominant species in soil (domsch et al. 1993). a. fumigatus was only found in very low numbers in the untreated control plot, but in the heat-treated soil this fungal species was abundant. a. fumigatus was still present in elevated numbers at the last sampling in october 2004 in the heat-treated soil, but the numbers were slowly declining. it seems, however, likely that the elevated numbers of a. fumigatus will continue for some time due to the ability of the fungus to form conidia. pseudomonas aeruginosa – an opportunistic pathogen pseudomonas aeruginosa is an opportunistic pathogen, meaning that it exploits any defects in the human host defences to initiate an infection. it causes urinary tract infections, respiratory system infections and also bone and joint infections. furthermore, it is associated with gastrointestinal infections and a variety of systemic infections, particularly in patients with severe burns and in immuno-compromised cancer and aids patients. p. aeruginosa infections are a serious problem for patients hospitalised with cancer, cystic fibrosis and burns. the case fatality rate for these patients is 50%. p. aeruginosa increased from non-detectable (less than 100 cells per gram of soil) in the non-treated soils to 105 cells per gram of soil in the heat-treated soil (fig. 4). p. aeruginosa is a 1 cm fig. 3. colony of aspergillus fumigatus isolated from steam-treated soil. fig. 4. pseudomonas aeruginosa isolated from steam-treated soil. the photograph was taken in ultraviolet light to show the characteristic fluorescence of this bacteria genus. diameter of view is 9 cm. representative of fast growing soil bacteria that are unable to form spores. in contrast to a. fumigatus, the population of p. aeruginosa decreased rapidly after the heat treatment, and after one year the numbers were again below the detection level. this reduction was probably due to predation and lack of competing abilities when the temperature decreased. need for monitoring of microbial sideeffects in relation to steam treatment micro-organisms differ in their ability to develop resting forms. a. fumigatus develops conidia that can remain in soil for many years. these resting conidia may not be active in the soil, even if they can be detected on agar plates when analysed in the laboratory. in contrast, p. aeruginosa does not form resting spores, and detection on agar plates in the laboratory is connected to activity of the bacterium in the soil. the present project highlights the need for microbial risk assessments in connection with new steam treatment projects. the high level of potentially pathogenic micro-organisms expected after heat treatment of a soil points to the need for monitoring these organisms in connection with new steam treatment projects. references denning, d.w., anderson, m.j., turner, g., latgé, j.-p. & bennett, j.w. 2002: sequencing the aspergillus fumigatus genome. the lancet infectious diseases 2, 251–253. domsch, k.h., gams, w. & anderson, t.-h. 1993: compendium of soil fungi 1, 2, 2nd edition, 860 pp., 406 pp. eching: ihw-verlag. gudbjerg, j., trotschler, o., farber, a., sonnenborg, t.o. & jensen, k.h. 2004: on spurious water flow during numerical simulation of steam injection into water-saturated soil. journal of contaminant hydrology 75, 297–318. klich, m.a. & pitt, j.i. 1988: a laboratory guide to the common aspergillus species and their teleomorphs, 116 pp. north ryde, australia: csiro division of food processing. kuhlman, m.i. 2002: analysis of the steam injection at the visalia superfund project with fully compositional nonisothermal finite difference simulations. journal of hazardous materials 92, 1–19. latgé, j.-p. 1999: aspergillus fumigatus and aspergillosis. clinical microbiology reviews 12, 310–350. richardson, r.e., james, c.a., bhupathiraju, v.k. & alvarerez-cohen, l. 2002: microbial activity in soils following steam treatment. biodegradation 13, 285–295. tse, k.k.c. & lo, s.-l. 2002: desorption of pcp-contaminated soil: effect of temperature. water research 36, 284–290. authors’ addresses c.s.j., p.j. & m.b., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: csj@geus.dk s.e., danish institute of agricultural sciences, blichers allé 20, dk8830 tjele, denmark. c.b.j., copenhagen county, soil and groundwater department, stationsparken 27, dk-2600 glostrup, denmark. 40 geological survey of denmark and greenland. bulletin 10, 9-12 upper maastrichtian chalks form important hydrocarbon reservoirs in the danish sector of the north sea and have been intensively studied, yet their lithological uniformity can frustrate attempts to develop a high-resolution stratigraphic subdivision and a genetic understanding of the factors controlling production and sedimentation of the pelagic carbonate ooze. recent research into these topics, supported by the danish energy authority, was carried out by the geological survey of denmark and greenland (geus) in collaboration with the geological institute, university of copenhagen by means of a multidisciplinary study involving quantitative/semiquantitative palynology, micropalaeontology (nannofossils, foraminifers) and isotope geochemistry, integrated with detailed sedimentology. two key wells were selected, the m-10x well from the dan field and the e-5x well from the tyra se field (fig. 1), based on the extensive core coverage in these wells and on their position in the southern part of the danish central graben where evidence of large-scale resedimentation (and consequent stratigraphic complexity) is uncommon within the maastrichtian section. in focusing on such a pelagic carbonate system, the ultimate aim is a holistic understanding of the marine system including temperature variation, nutrient supply and distribution, salinity, watermass layering, circulation and oxygen distribution. all these factors influence organic productivity and thus the accumulation of biogenic sediment. this study concentrated on a number of palaeoceanographic signals that can be derived from the sedimentary record, summarised in fig. 2. planktonic organisms, both phytoplankton (e.g. coccolithophores, some dinoflagellates) and zooplankton (e.g. foraminifers) provide a record of conditions in the upper watermasses, largely within the photic zone, while bottom conditions are indicated by epifaunal/infaunal organisms (e.g. benthic foraminifers) and bioturbation, and by the sedimentological evidence of depositional processes at the sea floor. on a larger scale, the input of terrestrial organic material relative to the marine component can provide an indirect measure of shoreline migration and thus relative sea-level change, a factor that is also reflected in the δ13c isotopic composition of the seawater, as recorded by the biogenic carbonate ooze. © geus, 2006. geological survey of denmark and greenland bulletin 10, 9–12. available at: www.geus.dk/publications/bull stratigraphy and palaeoceanography of upper maastrichtian chalks, southern danish central graben jon r. ineson, bjørn buchardt, susanne lassen, jan a. rasmussen, poul schiøler, niels h. schovsbo, emma sheldon and finn surlyk 4°00' 5°00' 5°00' 55°30' 56°00' 56°30' east north sea block tyra-igor ridge salt dome province c o ffee so il fault tyra se field denmark dan field e-5x m-10x 25 km fault zone inversion zone oil field in chalk gas field in chalk studied wells uk norway denmark germany the netherlands 500 km fig. 1. map showing the location of the two key wells, m-10x (dan field) and e-5x (tyra se field), and the dominant late cretaceous structural elements in the danish central graben. 9 photic zone phytoplankton zooplankton benthic epi/infauna soft-bodied infauna seawater chemistry (13c, 18o) terrestrial organic matter sediment fabri c/st ruc tur e fig. 2. cartoon (scale arbitrary) showing the source of the palaeoceanographic signals utilised in the project; see text for explanation. stratigraphy a prerequisite for this palaeoceanographic study was a wellconstrained stratigraphic breakdown of the succession to permit confident intrabasinal correlation and comparison with regional/global events described in the literature. although awaiting formal assignment, the upper maastrichtian and danian chalks of the danish central graben are herein referred to the tor and ekofisk formations, respectively, as defined from the norwegian sector of the north sea. despite the numerous biostratigraphic studies undertaken on this stratigraphic interval in the danish sector, much of the information is in the form of company reports, and published data are few. a high-resolution biostratigraphic study was thus undertaken to identify internationally recognised biozones related to the dinoflagellate cyst, nannofossil and microfossil floras and faunas. detailed stable isotope investigations were incorporated to examine the potential role of chemostratigraphy. this resulted in a consistent framework for the uppermost maastrichtian of the two key wells in the southern danish central graben, exemplified by the subdivision of the m-10x cored section shown in fig. 3. as a supplement to the zonal biostratigraphy, semi-quantitative data provide a second tier of stratigraphic constraints; these include dinoflagellate (palaeocystodinium denticulatum, palynodinium grallator), foraminifer (praebulimina laevis, pseudotextularia elegans) and nannofossil (watznaueria barnesiae) acme events. the maastrichtian–danian boundary in the m-10x and e-5x cored sections is marked by a distinctive hardground developed in the uppermost c. 1 m of the tor formation. the association of complex cross-cutting thalassinoides networks, the cemented and bored upper layer and the irregular, pitted, glauconite-impregnated upper surface are indicative of a mature, evolved hardground surface, recording a protracted period of non-sedimentation at the sea floor. the occurrence of mixed late maastrichtian and early danian faunal and floral assemblages within the uppermost metre beneath the hardground surface suggests that the burrow systems remained open into danian time, thus accumulating complex multi-generational fills. the lowermost danian biozones are absent above the hardground indicating that this surface remained exposed at the sea floor for at least several hundred thousand years. palaeoceanography analysis of palaeoceanographic trends and evolution in the late maastrichtian in the study area has required integration of a wide range of detailed data, only a fraction of which can be reviewed in this summary. in the following, selected aspects of the full dataset (see ineson et al. 2004a) are presented to provide the essential framework of the palaeoceanographic model. sedimentology the upper maastrichtian chalk succession in the southern danish central graben is lithologically uniform, comprising pure coccolith-rich chalks with rare skeletal grains larger than silt grade, and a dominant ‘lime mudstone’ texture. in the dan field area, the cored upper maastrichtian section is divisible into a lower cyclic succession, characterised by metre-scale laminated/bioturbated cycles, and an upper succession that is thoroughly bioturbated and overtly non-cyclic (fig. 3). it has been proposed that the laminated facies in the 10 6618 6617 6616 6615 6614 6613 l it h o lo g y d e p th ( fe e t) d e p o si ti o n al / b io ge n ic st ru c tu re s f ra c tu re s, st y lo li te s cycle 2 cycle 3 cycle 1 6450 feet 6500 6550 6600 6650 b io tu rb at e d c h al k l am in at e d – b io tu rb at e d c y c li c c h al k biostrat. l it h o st ra t. m ic ro . p al y n o . n an n o . c h ro n o st ra t. dan. ic o p d e h b o p gr f c s 2 3 a f c s 2 3 b u c 2 0 b u c 2 0 c u c 2 0 d p 1 a eko. fm t m a t o r f o rm at io n t p e b ar re n n n t p 2 e * * u p p e r m aa st ri c h ti an chalk mudstone enhanced lam/bio cyclicity chalk wackestone marly chalk hardground fig. 3. stratigraphic framework of the cored upper maastrichtian section in the m-10x well showing the broad subdivision into lower cyclic and upper non-cyclic, bioturbated chalks; the expanded section shows two laminated–bioturbated cycles, characteristic of the lower cyclic chalks. dan., danian; eko., ekofisk. palynological zones/subzones: ico, isabelidinium cooksoniae; pde, palaeocystodinium denticulatum; hbo, hystrichostrogylon borisii; pgr, palynodinium grallator; tma, tanyosphaeridium magdalium; tpe, thalassiphora pelagica. asterisk indicates mixed floral and faunal assemblages of late maastrichtian and danian aspect associated with the top tor formation hardground. lower chalks represents an alternation of thin (millimetrescale) chalk turbidites and hemipelagites; preservation of this primary sedimentary layering is thought to relate to low levels of oxygen on the sea floor (damholt & surlyk 2004). the alternation of laminated and bioturbated chalks thus records rhythmic shifts in bottom-water oxygenation; subtle shifts in the floral and faunal assemblages across these cycles suggest that such changes may have been controlled by variation in the degree of watermass stratification (ineson et al. 2004b). in addition to the lack of overt cyclicity and the ubiquitous bioturbation, the upper chalks are also lithologically more variable, including rare incipient hardground surfaces, skeletal-rich chalks (wackestones) and an isolated marly chalk bed (fig. 3). a subtle environmental change is thus indicated from a rhythmically stratified watermass to a more homogeneous watermass under which the sea floor was well ventilated and locally/periodically influenced by weak bottom currents. palynofacies and stable isotopes a number of palynological parameters can be utilised to provide a sea-level record, such as the relative proportions of marine and non-marine palynomorphs and the relative abundance of the genus impagidinium (an indicator of open ocean conditions) within the dinoflagellate assemblages. these parameters provide a consistent sea-level signal in the two central graben wells (ineson et al. 2004a). the lower, cyclic chalks record an overall gradual sea-level fall culminating in a ‘peak lowstand’ near the base of the p. grallator dinoflagellate zone (fig. 4, c. 6500 ft) coinciding with the level of the incipient hardground surfaces. palynofacies data from the succeeding bioturbated chalks record a subsequent sea-level rise and a variable signal up to the barren interval at the top of the maastrichtian section. it has been observed widely that the carbon isotope (δ13c) record broadly tracks the eustatic sea-level curve (e.g. jarvis et al. 2002). the δ13c values for the lower, cyclic chalks decrease gradually up-section, paralleling the palynofacies trend and adding support to the sea-level interpretation. in both wells, the lowest δ13c values in the upper maastrichtian section occur just beneath the base of the p. grallator zone. nannoflora and foraminifers the nannofloral assemblages are diverse (average species richness of 22) and show only minor compositional fluctuations with time, reflecting overall a stable, cool water (boreal), oligotrophic (low nutrient) setting. subtle shifts in the relative proportions of certain taxa, however, are thought to reflect changes in the nature of the upper watermasses, and although the precise control (i.e. temperature, nutrient level, salinity) can be difficult to isolate, interpretation can be facilitated by comparison with other datasets. two examples are shown in fig. 4. lucianorhabdus cayeuxii has been demonstrated to occur preferentially in relatively inshore shelf sediments (pospichal & wise 1990); the general increase in the relative abundance of this species in the upper half of the studied sec11 1.00 1.25 1.50 1.75 2.00 δ13c ‰ v-pdb log (marine/nonmarine ratio) -0.5 0.5 10-1 planktic/benthic ratio 0 % %0 50 0 50 20 40 60 80 100% 6450 feet 6500 6550 6600 6650 ic o p d e h b o p gr t m a t p e b ar re n d in o fl ag . z o n e c h ro n o st ra t. d an . u p p e r m aa st ri c h ti an lucianorhabdus cayeuxii high productivity indicators isotopic variation palynofacies nannoflora foraminiferal fauna fig. 4. selected data from the m-10x well, illustrating the palaeoceanographic evolution in the late maastrichtian, as discussed in the text. for stratigraphic terms and key, see fig. 3; the horizontal dashed line indicates the boundary between the lower cyclic and upper non-cyclic chalks. the nannofossil genera grouped together to provide an indication of changing fertility levels are biscutum, discorhabdus, chiastozygus and zeugrhabdotus. tion is thus compatible with the overall shallowing trend indicated by the sedimentological and palynological data. certain nannofossil species are considered to be indicative of increased nutrient levels (e.g. watkins 1989); the combined signal exhibited by these species clearly mirrors the subdivision of the succession into cyclic and non-cyclic chalks (fig. 4), possibly reflecting a change in nutrient partitioning in the water column under different palaeoceanographic states. the foraminifer assemblages are dominated by planktonic forms, particularly the ecologically tolerant heterohelix globulosa, and plankton/benthos (p/b) ratios are typically over 70% (fig. 4). the benthic fauna is of outer shelf aspect overall, with rare agglutinated forms. a feature of particular note in the m-10x foraminifer dataset is the anomalously low p/b values at 6490–6500 ft, associated with an increase in the relative abundance of a mid-shelf benthic foraminifer, p. laevis. this shallowing signal from the foraminifer data coincides with the sedimentological and palynofacies data indicating the ‘peak lowstand’ in the late maastrichtian chalk sea. acme of the planktonic foraminifer p. elegans and the nannofossil w. barnesiae in the upper, non-cyclic chalks are indicative of warmer surface waters in the region at this time and are symptomatic of a global warming event in the latest maastrichtian (huber & watkins 1992; olsen et al. 2001). late maastrichtian palaeoceanographic evolution palaeoecological data, from semi-quantitative analysis of foraminifer, coccolith and dinoflagellate faunas and floras, integrated with isotopic, palynofacies and sedimentological data has led to a model for the palaeoceanographic evolution of the danish central graben in the late maastrichtian involving two contrasting oceanographic systems. the lower half of the cored section records a cool-water, oligotrophic, deep shelf that was prone to stratification. breakdown of this rhythmically stratified system accompanied a long-term gradual fall in sea level, perhaps reflecting a depth-related threshold beyond which stratification was no longer favoured. the upper half of the cored section records an increasingly dynamic and varied mid-shelf to deep shelf setting with a complex blend of environmental signals – sea-level change, watermass warming and evidence of low but variable productivity. following turnover of the stratified system, the combined datasets record a progressive shallowing to a peak lowstand located just above the base of the p. grallator dinoflagellate zone boundary; this sea-level event can be correlated with a key sequence boundary in the type maastrichtian of the netherlands (schiøler et al. 1997). acknowledgement the danish energy authority (grant no.1313/01-0001) is thanked for financial support. references damholt, t. & surlyk, f. 2004: laminated–bioturbated cycles in maastrichtian chalk of the north sea: oxygenation fluctuations within the milankovitch frequency band. sedimentology 51, 1323–1342. huber, b.t. & watkins, d.k. 1992: biogeography of campanian–maastrichtian calcareous plankton in the region of the southern ocean: paleogeographic and paleoclimatic implications. in: kennett, j.p. & warnke, d.a. (eds): the antarctic paleoenvironment: a perspective on global change. antarctic research series 56, 31–60. ineson, j.r., buchardt, b., lassen, s., rasmussen, j.a., schovsbo, n.h., schiøler, p., sheldon, e. & surlyk, f. 2004a: palaeontology, stable isotopes and sedimentology of the upper maastrichtian, danish central graben: a record of palaeoclimatic and palaeoceanographic change. danmarks og grønlands geologiske undersøgelse rapport 2004/81, 20 pp. ineson, j.r., buchardt, b., lassen, s., rasmussen, j.a., schovsbo, n.h., schiøler, p., sheldon, e. & surlyk, f. 2004b: on the origin of laminated–bioturbated chalk cycles in the upper maastrichtian, danish central graben. danmarks og grønlands geologiske undersøgelse rapport 2004/82, 22 pp. jarvis, i., mabrouk, a., moody, r.t.j. & de cabrera, s. 2002: late cretaceous (campanian) carbon isotope events, sea-level change and correlation of the tethyan and boreal realms. palaeogeography, palaeoclimatology, palaeoecology 2948, 1–34. olsen, r.k., wright, j.d. & miller, k.g. 2001: paleobiogeography of pseudotextularia elegans during the latest maastrichtian global warming event. journal of foraminiferal research 31, 275–282. pospichal, j.j. & wise, s.w. 1990: maastrichtian calcareous nannofossil biostratigraphy of maud rise odp leg 113 sites 689 and 690, weddell sea. proceedings of the ocean drilling program, scientific results 113, 465–487. schiøler, p., brinkhuis, h., roncaglia, l. & wilson, g.j. 1997: dinoflagellate biostratigraphy and sequence stratigraphy in the type maastrichtian (late cretaceous), enci quarry, the netherlands. marine micropaleontology 31, 65–95. watkins, d.k. 1989: nannoplankton productivity fluctuations and rhythmically-bedded pelagic carbonates of the greenhorn limestone (upper cretaceous). palaeogeography, palaeoclimatology, palaeoecology 74, 75–86. authors’ addresses j.r.i., p.s., n.h.s. & e.s., geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: ji@geus.dk b.b. & f.s., geological institute, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. s.l., 96 settrington road, london sw6 3ba, uk. j.a.r., geological museum, university of copenhagen, øster voldgade 5–7, dk-1350 copenhagen k, denmark. 12 geological survey of denmark and greenland. bulletin 10, 53-56 53 in 2006 an important milestone will be reached in the study of the three-dimensional structure and architecture of the nuussuaq basin in west greenland. the fifth and last of a series of detailed geological profiles through the sedimentary and volcanic rocks of the nuussuaq basin on disko and nuussuaq will be published (fig. 1). at the same time, the last geological map at scale 1:100 000 of the basin area will be completed. these studies have been carried out over more than two decades by a group of scientists within geocenter copenhagen and the technical university of denmark. the five geological profiles are at scale 1:20 000 and have been published as coloured plates in the same format as the geological maps (pedersen et al. 1993, 2002a, 2003, 2005, 2006). in total, the profiles cover about 500 km of cross-sections through a classic sedimentary-volcanic basin and its crystalline basement. this is one of the best exposed basins of its kind on earth, and it serves as a reference area for studies of similar basins on the continental shelves of greenland, north-western europe and elsewhere. the nuussuaq basin during the late mesozoic, a series of linked sedimentary basins were established along the west greenland continental margin. the nuussuaq basin is the only one of these basins that extends into the onshore areas where late cretaceous to paleocene sediments overlain by volcanic rocks can be studied in detail. from the late albian, sandstones and shales were deposited in a fluvial to deltaic environment in eastern disko and central nuussuaq. towards west and north the delta fanned into deeper water. several tectonic phases affected the basin and gave rise to an uplifted rift margin of precambrian gneiss in eastern nuussuaq and a gneiss ridge in central disko (chalmers et al. 1999). in the paleocene around 62 ma (storey et al. 1998), volcanism started on the sea floor in the western part of the area. the volcanic pile rapidly became emergent and the lavas prograded eastwards into the marine embayment and gradually filled it with thick foreset-bedded hyaloclastites capped by subaerial lava flows. thus, most of the early volcanic units exist in both subaerial and subaqueous facies. eventually the marine basin, and also some slightly younger lake basins, was obliterated. the volcanic rocks interfingered with fluvial sandstones and lake sediments in southern nuussuaq and eastern disko, whereas in eastern nuussuaq they lapped onto the precambrian highlands. the volcanic rocks form two formations: the older vaigat formation of thin pahoehoe flows of magnesia-rich picrites and their equivalent hyaloclastites, and the overlying maligât formation of thick, extensive lava flows of basalt and their five slices through the nuussuaq basin,west greenland asger ken pedersen, lotte melchior larsen, gunver krarup pedersen and keld s. dueholm © geus, 2006. geological survey of denmark and greenland bulletin 10, 53–56. available at: www.geus.dk/publications/bull 54°w 52°w 69°30'n 70°30'n 70°n nuussuaq vaigat m ali ga at disko saqqaq pingu ikorfat itilli fig.2 fig.4 fig.3 25 km maligât formation vaigat formation cretaceous–palaeogene sediments basement gneiss fault ice cap uummannaq aaffarsuaq qeqertarsuaq ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ 3 3 4 4 1 1 2 2 5 5 5 fig. 1. index map, with red lines showing the location of the five geological profiles through disko and nuussuaq. profile 1: pedersen et al. (1993); profile 2: pedersen et al. (2002a); profile 3: pedersen et al. (2003); profile 4: pedersen et al. (2005); profile 5: pedersen et al. (2006). equivalent hyaloclastites. a detailed stratigraphy of the volcanic succession has been established based on lithology and geochemical analyses; several distinct units of crustally contaminated rocks form particularly good marker horizons because they are interbedded with the normal lithologies. oil seepages are found in the volcanic rocks in western nuussuaq and northern disko, and the nuussuaq basin is a key area in the exploration for oil both onshore and offshore west greenland. exploration for nickel and platinum has been focused on some of the contaminated volcanic units in which these elements are missing from the surface deposits and may have formed accumulations at depth in magma chambers. methods many mountain walls in the nuussuaq basin are excellently exposed but largely inaccessible. however, they can be photographed from boat or helicopter. the key data for the five geological profiles consists of long series of colour stereo photographs taken with ordinary, but calibrated, small-frame cameras. these photographs have been orientated and measured using multi-model photogrammetry as described by dueholm (1992) and pedersen & dueholm (1992). in combination with field logging, sampling, geochemistry and petrography, this has enabled us to establish a detailed stratigraphical framework for the volcanic rocks and hence to trace the evolution and facies changes of the volcanic and sedimentary units with time. the profiles the individual profiles (fig. 1), at scale 1:20 000, are between 80 km and 131 km long and show altitudes up to 2100 m with no vertical exaggeration. three examples illustrating aspects of the contents and details of the profiles are shown in figs 2-4. figure 2 shows progradation of hyaloclastite breccias and associated lava flows into a marine basin; this structure, with giant foresets in the hyaloclastite breccias, has been widely used as a model for the interpretation of seismic sections in offshore areas. an unusual feature of central nuussuaq is the presence of submarine feeder systems and eruption sites for several of the volcanic units, which make the bedding structures in the hyaloclastites very irregular. the concentration of feeder sites in this small area is due to the presence of a deep fault zone, along which magma ascent from the mantle was focused. figure 3 illustrates late tectonic movements and subsequent dyke intrusion. near the west coast of disko the lava pile is faulted and tilted seawards at low angles that can be read very accurately on the profile. the reading of the dips requires that the strikes are perpendicular to the section which is mostly, but not always, the case; the index maps accompanying each profile sheet show strikes and dips of the lavas along the profiles. figure 4 illustrates sediments and lava flows and their interaction on the flood plain in the eastern part of the basin in north-east disko. fluvial sandstones are interbedded with 54 w e 20 km18 km 23 km point 1613 m point 1350 milugissoq fig. 2. part of the geological section through the aaffarsuaq valley (profile 2), central nuussuaq (pedersen et al. 2002a) at 17-24 km on the section base line. no vertical exaggeration. sediments of the cretaceous atane formation (k1) and the paleocene eqalulik formation (t1) are overlain by several volcanic units of the vaigat formation. the atane formation was faulted and tilted prior to the deposition of the volcanic rocks, and a large fault crosses the profile at 18.5 km west of which the atane formation is below exposure level. during the deposition of the volcanic rocks, subaqueous hyaloclastite breccias and subaerial lava flows prograded into the basin from the west to the east. lava flows and hyaloclastite breccias from the same volcanic unit are shown with respectively darker and lighter colour shades; such subaerial–subaqueous pairs are c2 and c1(a+b); d2 and d1(a+b) (nuuk killeq member), and e2 and e1(a+b) (naujánguit member). the hyaloclastite breccias show east-dipping foreset bedding (d1b) or irregular bedding structures (d1a, e1b) near eruption sites (feeder dykes lined with red). the red unit f1, at around 23-24 km, comprises the pyroclastic rocks of the ilugissoq volcano (asuk member) which erupted on the margin of the shallow marine shelf. the younger units are banked up against the volcanic edifice, and the lavas of the unit i2 (ordlingassoq member) overran and covered it. two units of paleocene black shales, both of which were deposited in large and deep lakes. the paleocene sediments are contemporaneous with volcanic rocks in the western part of the basin; the first volcanic unit to reach so far east was the middle part of the rinks dal member of the maligât formation. the boundaries between the major volcanic units form important near-isochronous surfaces that allow the tracing of regional synand post-volcanic tectonic movements in the nuussuaq basin. for example, the boundary between the upper rinks dal member and the nordfjord member of the maligât formation is tilted below sea level in western disko (fig. 3) and rises eastwards towards the disko gneiss ridge to more than 1600 m altitude in central disko. east of the gneiss ridge the surface is gently tilted towards the south-east by slow synand post-volcanic regional movements, so that in eastern disko (fig. 4) it is situated at 940 m altitude. in eastern nuussuaq the same surface is situated at up to 1800 m altitude (not shown here). 55 11 km 13 kminngissuaq point 639 m nw se fig. 3. part of the geological section along the south-west coast of disko (pedersen et al. 2003) at 10.6-14 km on the section base line (profile 3). no vertical exaggeration. the pile of formerly flat-lying subaerial lava flows is tilted and the lavas dip 2°-4° seawards (to the left), preserving some of the stratigraphically highest lava flows of the maligât formation on the mountain tops. the unit m8.8 is the uppermost part of the rinks dal member in which individual lava flows are indicated with separate colours and annotation (e.g. m8); such individual flows extend typically over 5-15 km and then peter out. units no1 to no2 are crustally contaminated lavas of the nordfjord member, and ni1 to ni4 are crustally contaminated lavas of the niaqussat member, of which ni1 carries native iron (fe). a crater area (cr) with thick, irregular, red-oxidised material is seen in the left part of ni4. the lava pile is cut by younger dykes (δm and δe) of which the eocene δe runs very obliquely to the section. inngigissoq 101 km 103 km t5b nw se fig. 4. part of the geological section across disko, near pingu in eastern disko (pedersen et al. 2005) at 100.6-104 km on the section base line (profile 4). no vertical exaggeration. sediments and lava flows are shown as viewed from the south, but are projected into the section both from the south (upper part) and from the north (lower part below the broken line: exposures along the vaigat coast). fluvial sandstones of cretaceous (k1) and paleocene (t2) age are separated by an interval of uncertain age (t0). two lake complexes each show filling with a coarsening-upwards succession of black mudstones and fluvial sandstones: the pingu member (t3a-t3b) and the assoq member (t5a-t5b). the level marked ’u’ is an unconformity within the sandstones. lava flows invaded the unconsolidated sediments to form three sill-like bodies (invasive lavas, in), and finally the sediments were overrun by entirely subaerial lava flows. the entablature zone (e) of the lowest flow indicates a moist environment. the lava flows are from the maligât formation, upper rinks dal member (m8) and nordfjord member (iron-bearing no1, and no2). perspectives the completion of the five profiles, and the complementary geological maps at scale 1:100 000, has provided a significantly improved understanding of the overall three-dimensional structure and stratigraphy of the southern part of the nuussuaq basin, in particular of the well-exposed volcanic formations. in addition to the published profiles, an extensive web of colour stereo panels has been constructed wherever helicopter logistics allowed the photography, so that the total coverage now exceeds 1500 km of stereo panels. the existence of this web, assisted by complete on-line coverage of vertical aerial photograph models, has opened for a range of quantitative geological studies centred on volcanology, sedimentology, palaeomagnetics and tectonics. using palaeomagnetic information, pedersen et al. (2002b) calculated eruption rates and basin subsidence rates for an early part of the vaigat formation, and found eruption rates to be much in excess of those characterising modern iceland. measurements of lake depths and lateral correlation of subaqueous volcanic units over more than 20 km were instrumental for the understanding of the environment that gave rise to unique subaqueous rootless volcanic cones in the assoq lake (larsen et al. in press). the ability of the photogrammetrical method to identify volcanic eruption sites within the web of stereo panels has been demonstrated by the discovery of a large number of crater sites within the vaigat formation on nuussuaq. of particular significance is the observation that economically interesting crustally contaminated volcanic rocks tend to erupt along older fault zones within the basin. such an example is provided by the ilugissoq graphite andesite volcano (pedersen & larsen in press), which is the largest eruption site within the vaigat formation. it is believed that continued 3-d based work within the nuussuaq basin will be of considerable interest for a broad range of geoscientists from both universities and industry. acknowledgements the work was partly supported by the carlsberg foundation, grant no. 0385/30. references chalmers, j.a., pulvertaft, t.c.r., marcussen, c. & pedersen, a.k. 1999: new insight into the structure of the nuussuaq basin, central west greenland. marine and petroleum geology 16, 197–224. dueholm, k.s. 1992: geological photogrammetry using standard smallframe cameras. in: dueholm, k.s. & pedersen, a.k. (eds): geological analysis and mapping using multi-model photogrammetry. rapport grønlands geologiske undersøgelse 156, 7–17. larsen, l.m., pedersen, a.k. & pedersen, g.k. 2006: a subaqueous rootless cone field at niuluut, disko, paleocene of west greenland. lithos 92, 20–32. pedersen, a.k. & dueholm, k.s. 1992: new methods for the geological analysis of tertiary volcanic formations on nuussuaq and disko, central west greenland, using multi-model photogrammetry. in: dueholm, k.s. & pedersen, a.k. (eds): geological analysis and mapping using multi-model photogrammetry. rapport grønlands geologiske undersøgelse 156, 19–34. pedersen, a.k. & larsen, l.m. 2006: the ilugissoq graphite andesite volcano, nuussuaq, central west greenland. lithos 92, 1–19. pedersen, a.k., larsen, l.m. & dueholm, k.s. 1993: geological section along the south coast of nuussuaq, central west greenland. 1:20 000 coloured geological sheet. copenhagen: geological survey of greenland. pedersen, a.k., larsen, l.m. & dueholm, k.s. 2002a: geological section along the north side of the aaffarsuaq valley and central nuussuaq, central west greenland. 1:20 000 coloured geological sheet. copenhagen: geological survey of denmark and greenland. pedersen, a.k., larsen, l.m., riisager, p. & dueholm, k.s. 2002b: rates of volcanic deposition, facies changes and movements in a dynamic basin: the nuussuaq basin, west greenland, around the c27n–c26r transition. in: jolley, d.w & bell, b.r. (eds): the north atlantic igneous province: stratigraphy, tectonics, volcanic and magmatic processes. geological society (london) special publications 197, 157–181. pedersen, a.k., larsen, l.m., pedersen, g.k., heinesen, m.v. & dueholm, k.s. 2003: geological section along the south and south-west coast of disko, central west greenland. 1:20 000 coloured geological sheet. copenhagen: geological survey of denmark and greenland. pedersen, a.k., larsen, l.m., pedersen, g.k. & dueholm, k.s. 2005: geological section across north central disko from nordfjord to pingu, central west greenland. 1:20 000 coloured geological sheet. copenhagen: geological survey of denmark and greenland. pedersen, a.k., larsen, l.m., pedersen, g.k., sønderholm, m., midtgaard, h.h., pulvertaft, t.c.r. & dueholm, k.s. 2006: geological section along the north coast of the nuussuaq peninsula, central west greenland. 1:20 000 coloured geological sheet. copenhagen: geological survey of denmark and greenland. storey, m., duncan, r.a., pedersen, a.k., larsen, l.m. & larsen, h.c. 1998: 40ar/39ar geochronology of the west greenland tertiary volcanic province. earth and planetary science letters 160, 568–586. 56 authors’ addresses a.k.p., geological museum, university of copenhagen, øster voldgade 5–7, dk-1350 copenhagen k, denmark. e-mail: akp@snm.ku.dk l.m.l., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. g.k.p., geological institute, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. k.s.d., information and mathematical modelling, richard petersens plads, dtu-bygning 321, dk-2800 lyngby, denmark. geological survey of denmark and greenland bulletin 23, 2011, 49–52 49 any major shaking of the earth can be recorded on a seismograph regardless of the nature of the source. earthquakes and large explosions generate waves with similar frequency content. this fact has been used for decades to construct systems to monitor detonations of underground nuclear explosions. the quality of the monitoring system has increased significantly in recent years, and we demonstrate here that the data are useful in danish earthquake research. one important difference between explosions and earthquakes is the depth of the source, most earthquakes occurring at much larger depths than explosions. thus the depth determination is important in both fields. however, accurate depth determination of earthquake hypocentres is a challenge even when it comes to large well-recorded earthquakes. the uncertainty of the calculated depth of a danish earthquake is of the same magnitude as the depth itself when using standard location techniques. a technique utilising crustal phases recorded at large distances has been introduced at the geological survey of denmark and greenland to improve the determination of the hypocentre depths. only the largest earthquakes in denmark and its immediate surroundings produce sufficiently strong signals to be recorded at teleseismic distances, i.e. larger than 3000 km. the signals are discernable at low-noise seismic array stations as far away as north america and africa. some of these stations are operated by the united nations comprehensive nuclear-test-ban treaty organisation (ctbto). data from many of these stations are available for scientific purposes. we demonstrate here how data from canada and niger can significantly improve the depth estimates for two earthquakes, one in skåne, sweden in 2008 and the other in the danish part of the north sea in 2010 (figs 1, 2). ctbto and ims the comprehensive nuclear-test-ban treaty was adopted by the general assembly of the united nations (un) in september 1996. the treaty bans all nuclear explosions on earth whether for military or for peaceful purposes. denmark signed the treaty in 1996, and it was ratified by the parliament of denmark in 1998. the treaty will enter into force once it has been signed and ratified by all nuclear powers of the world. however, the ratification is still pending in several key countries such as china, pakistan, india and united states of america. comprehensive nuclear-test-ban treaty – a peace-keeping initiative with scientific impact tine b. larsen, peter h. voss, trine dahl-jensen and søren gregersen 10°e 14°e 55°n 57°n 100 km sweden denmark germany skåne earthquake north sea earthquake yka norsar tord spits hfs fines arces fig. 1. map of the north atlantic region showing the locations of seismic array stations used by geus to locate earthquakes in denmark and greenland. yk a, canada. spits, norsar and arces, norway. fines, finland. hfs, sweden. tor d, niger. fig. 2. teleseismic array data have been used to locate earthquakes and measure their depths in skåne on 16 december 2008 and in the north sea on 19 february 2010. © geus, 2011. geological survey of denmark and greenland bulletin 23, 49–52. open access: www.geus.dk/publications/bull 5050 significant resources are being allocated to the development of a large international monitoring system (ims), so that all technical systems as well as procedures, manuals and other agreements are in place once the treaty enters into force. the ims is a un-controlled monitoring system based on four technologies: seismology, radio nuclides, hydroacoustics and infrasound. the system consists of a worldwide network of high-quality monitoring stations, supplementing the existing national networks of detectors, and it has improved the detection threshold for explosions as well as earthquakes in large parts of the earth. data from the stations are transmitted via secure satellite links to a un data centre in vienna. all the data are processed at the centre in vienna. the data centre is completely neutral and is not permitted to judge if an event is natural, such as an earthquake or a volcanic eruption, or caused by a man-made explosion. instead the data centre makes raw data as well as processed data available to the individual countries, and then it is up to the national authority in each country to decide whether an event is suspicious or not. should an event be deemed suspicious by a country, any country has the right to request further processing by the ims and ultimately request an on-site inspection at the location of the suspicious event. in recent years, nuclear test explosions have been easy to identify, as the involved nations have openly announced the tests and provided information about location and time of the explosions (pakistan 1998, india 1998, north korea 2006 and 2009). geus and ctbto in denmark, geus houses both the national data centre and is also the national authority for the ctbto. geus is responsible for running two monitoring stations in the ims network. one is a seismograph in kangerlussuaq, west greenland; it is part of the auxiliary (secondary) seismic network. the other is an infrasound station near qaanaaq, north-west greenland, that is a primary ims station. the danish meteorological institute takes part in the daily maintenance of the infrasound station. together with diplomats from the danish embassy in vienna, geus is also involved in the preparatory work on operational manuals and procedures for waveform processing that is carried out at the un centre. this involves discussions on how to tune the detection system to automatically filter out as many earthquake signals as possible, so that the system triggers on explosions only. this part of the system still needs significant improvements. in order to be as familiar as possible with the data from the ims before the treaty enters into force, seismologists at geus make experiments with the incoming data for other purposes. recently we have found that the ims raw seismological data are useful for determining accurate depths of danish earthquakes. the ims seismographs are of a very high quality and it is possible to identify signals from relatively weak earthquakes at distant stations. earthquake depth analysed using ctbto array data for several decades we have supplemented with data from seismic stations in the countries around denmark and greenland to help detect and localise earthquakes. seismic array stations produce data of particularly high quality. a seismic array station consists of a large number of sensors installed in a small area. the ability to detect an earthquake decreases when the strength of the seismic noise increases relative to the strength of the seismic signal. seismic noise can be reduced significantly in earthquake data recorded by an array by summing the signals recorded at the sensors, thus enabling the detection of smaller events than is possible on a station with just one sensor. the closest seismic arrays that contribute to the monitoring of earthquakes in denmark and greenland are the norsar and arces arrays in norway, the hfs array in sweden, the fines array in finland and the spits array at svalbard (fig. 1). previously, array data have been used to locate earthquakes in denmark and greenland from observations of p and s phase travel times only. for the two earthquakes in skåne on 16 december 2008 and in the north sea on 19 february 2010, however, a new technique was used to improve the estimate of the depth of the earthquakes. this fig. 3. the slightly different paths taken by the pand the pp(or sp-) waves can be used to calculate the depth of an earthquake. the p-wave (yellow) travels directly from the hypocentre to the seismograph, whereas ppand sp-waves (green) travel from the hypocentre to the surface near the epicentre and from there ref lected to the seismograph. the paths of the ppand sp-waves differ slightly due to the crustal structures near the earthquake. epicentre seismograph hypocentre p-wave pp-wave 50–70° 51 technique uses teleseismic observations of travel-time differences between the p phase and the pp and/or sp phases to calculate the depth of the earthquake. the pp and sp phases are ref lections at the earth’s surface of the shaking from the earthquake hypocentre. these phases are recorded slightly after the p wave arrival (fig. 3). the technique requires measurements with a high signal-to-noise ratio and good knowledge of the geological structures near the epicentre. the principles of the teleseismic depth-determination technique are very simple. at teleseismic distances the difference in travel length is negligible for the p-wave travelling directly from the hypocentre to the seismograph and the part of the pp-wave travelling from the epicentre to the seismograph (fig. 3). the difference in travel time between the phases is assumed to be caused by the pp-wave travelling almost vertically through the crust from the hypocentre to the surface. if the velocity structure in the crust below the epicentre is well known, the travel time difference between p and pp and/or sp can be converted to a depth. an accurate crustal velocity model is therefore critical for the analysis since errors in the crustal model will give a wrong determination of the depth. a teleseismic recording is needed as the paths of the pp and sp phases must be near vertical at the source. however, the distance between the earthquake and the seismic array must be sufficiently short for the phase not to be effected by the core–mantle boundary. we find that a distance of around 50 to 70 degrees is optimal for this technique. a significant number of the ims stations are seismic arrays. the stations are installed at locations with low ambient noise, in order to record data of high quality. in our analysis we use data from the yellowknife array (yka) in canada and the toridu array (tord) in niger (fig. 1). the yellowknife array consists of 19 short-period sensors and 4 broadband sensors. the sensors are installed in a cross with an aperture of 25 km. the array was installed in 1962 with the main purpose of monitoring underground nuclear explosions (source: natural resources canada). the toridu array is a modern array constructed specifically for the ctbto (estabrook et al. 2009). it consists of 16 broadband sensors deployed in three concentric rings with a central node. the sensors are not radially aligned, as this layout leads to the largest noise reduction (e.g., schweitzer et al. 2002). as described above, the energy release of the majority of the earthquakes in denmark and greenland is too low to generate clear signals even at the best ims stations. the two earthquakes, skåne, 16 december 2008 and the north sea, 19 february 2010, measuring 4.8 and 4.7 on the richter scale, respectively, are our best candidates for this technique (fig. 2). the geological structures are well mapped in denmark where we have a good knowledge of p-wave velocity (thybo 2001). for the s-wave velocity we have used vp = 1.73 × vs to estimate the earthquake depth. using this technique in greenland will be less reliable in most areas, because the crustal structures are not as well mapped. we have analysed the measurements of the skåne earthquake on the yka array (fig. 4). the measurements show a good signal-to-noise ratio and we find a difference in the p and sp travel times of c. 4 sec., equivalent to an earthquake depth of 9 km. the previously calculated depth of this earthquake was 18.1 ± 5.2 km using the standard location method (snsn 2010), and the result from moment-tensor inversion was 8 km (regel 2010). the standard location method is based on an approach that searches for the hypocentre that gives the best fit to measured travel times of pand s-waves within c. 1000 km of the earthquake, using a 1d earth model. the larger depth obtained by snsn might be due to the velocity model, which is not well calibrated for the skåne 19 feb. 2010 21:16:50.0 utc 55 05 15 25 toa2 tob1 tob2 tob3 tob4 tob5 toc1 toc2 toc3 toc4 toc5 toc6 toc7 16 dec. 2008 05:29:31.9 utc sec.36 40 44 48 yka data, vertical component, unfiltered ykb0 ykb1 ykb3 ykb6 ykb7 ykb8 ykb9 ykr1 ykr3 ykr4 ykr5 ykr7 ykw3 tord data, vertical component bandpass filtered 1–5 hz a b plot start time: fig 4. a: the p-wave train from the skåne earthquake on the yellowknife array (yk a). yellow is the direct p phase and green is the sp phase. b: the p-wave train from the north sea earthquake on the toridu array (tor d). yellow is the direct p phase and green is the pp phase. the high number of sensors improves the possibility of identifying different phases. 5252 area (b. lund, personal communication 2010) and the use of measurements far from the epicentre. the north sea earthquake measurements on the yka have a low signal-to-noise ratio on many of the sensors, but on the best five sensors we observe a signal c. 15 sec. after the p phase. interpreting this as the sp phase yields a depth of 35.2 km. the high noise level in the yka data carries a risk of misinterpretation of the data. we therefore supplement with data from the tord array (fig. 4), to verify the depth of this earthquake. from the measurements of the tord array we find a difference in the p and pp travel time of c. 11 sec., corresponding to an earthquake depth of 38.5 km. the previously calculated depth was 38.7 ± 10.3 km using the standard location method. the depth uncertainty is larger than that of the skåne earthquake due the larger distance of the nearest seismometer. the depths of the two earthquakes are comparable with the depths of previous earthquakes in these areas (gregersen et al. 1999). the higher noise level of the north sea event (fig. 4) is a source of error in the analysis. the higher noise level could be due to an energy radiation pattern of the earthquake that is low in the direction of tord or a different frequency content of the released shaking. concluding remarks teleseismic array data have produced consistent depth estimates for two recent earthquakes in the danish area. this raises the possibility that we might find other earthquakes suitable for this technique in the geus database, especially from greenland. the seismological involvement in detection and discrimination of nuclear explosions has spurred significant nordic collaboration since the 1960s, and a yearly nordic seismological meeting is held. geus has made a special contribution together with the uk foreign and commonwealth office, norsar, the swedish national defence research establishment and the university of helsinki to improve data exchange between the international monitoring system and the international seismological centre. this has resulted in the development of a collection of interactive seismological tools for merging and manipulating the two largest and most complete seismological databases (gaspa et al. 2010). in the future this will hopefully help improve and ease the scientific use of the international monitoring system data. references comprehensive nuclear test-ban treaty (www.ctbto.org). estabrook, c., bergsson, b., soumana, s., boureima, o. & moumouni, m. 2009: results from ims seismic array in niger. poster presented at the egu meeting in vienna, april 2009. gaspa, o., bondar, i., harris, j. & storchak, d. 2010: the ctbto link to the isc database. the 41st nordic seminar on detection seismolog y, århus, 6–8 october, 2010. program with abstracts, 14 only. gregersen, s., hjelme, j. & hjortenberg, e. 1998: earthquakes in denrnark. bulletin of the geological society of denmark 44, 115–127. regel, j. 2010: moment tensor of the 16 dec[ember] 2008 earthquake in skåne, sweden. the 41st nordic seminar on detection seismolog y, århus, 6–8 october 2010. program with abstracts, 39 only. schweitzer, j., fyen, j., mykkeltveit, s. & t. kværna, t. 2010: seismic arrays. in: new manual of seismological observatory practice, chapter 9. doi: 10.2312/gfz.nmsop_rl_ch9. snsn 2010: swedish national seismic network (http://snsn.geofys. uu.se/). thybo, h. 2001: crustal structure along the egt profile across the tornquist fan interpreted from seismic, gravity and magnetic data. tectonophysics 334, 155–190. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: tbl@geus.dk mineralogical and thermodynamic constraints on palaeogene palaeotemperature conditions during low-grade metamorphism of basaltic lavas recovered from the lopra-1/1a deep hole, faroe islands 109 mineralogical and thermodynamic constraints on palaeogene palaeotemperature conditions during low-grade metamorphism of basaltic lavas recovered from the lopra-1/1a deep hole, faroe islands william e. glassley the sequene of secondary minerals that are reported for the lopra-1/1a well records progressive zeolite facies to prehnite–pumpellyite-facies mineral progressions consistent with those of other wellstudied hydrothermally altered rock sequences. detailed comparison of the calc–silicate (zeolites and prehnite) mineral distributions of the lopra-1/1a sequence with those from other regions indicates that this sequence exhibits consistently longer down-hole intervals for secondary mineral species than reported elsewhere. when compared to measured down-hole temperatures reported in other hydrothermally altered regions, the results suggest that the lopra-1/1a mineral progression formed under conditions typical of low temperature hydrothermal systems that form shortly after eruption of thick basaltic piles. maximum temperatures achieved at the 3500 m level of the well were at or below 200°c. the implied geothermal gradient was less than 50°c/km. an analysis of prehnite – fluid composition relationships was also conducted in order to determine if results compatible with the paragenetic sequence study could be obtained from thermodynamic constraints. in this case, the limiting temperature for prehnite formation in equilibrium with albite–quartz–calcite–laumontite (the mineral assemblage at the bottom of the hole) was determined for a range of fluid compositions. the resulting calculations suggest temperatures of formation of prehnite in the range of 140°c to 205°c, a conclusion which is broadly consistent with those reached from study of the paragenetic relationships. comparison of these results with other studies of palaeogeothermal gradients of the north atlantic margins suggests a consistent pattern in which relatively low geothermal gradients persisted in the palaeogene rift basin. keywords: north atlantic volcanic province, thermal history, geothermal gradients, low temperature metamorphism, fluid-rock interaction, reactive transport, zeolites, prehnite-pumpellyite _______________________________________________________________________________________________ lawrence livermore national laboratory, livermore, california 94550, usa. e-mail: glassley1@llnl.gov minerals that crystallise from basaltic lavas are unstable with respect to a wide range of hydrous silicates and carbonates when subjected to low temperature conditions (< 300°c) in the presence of h2oand co2-bearing fluids. recrystallisation of basaltic rocks under these physical and chemical conditions results in the development of minerals that characterise the zeolite, prehnite–pumpellyite and greenschist facies. it has been well-documented that the basalts of the east greenland – faroe islands province record extensive development of minerals characteristic of the zeolite and lower prehnite–pumpellyite facies (jørgensen 1984, 1997; neuhoff et al. 1997; larsen et al. 1999). what remains unclear is the temperature history recorded by these mineral assemblages. generally, under the lowest temperature conditions, clays, zeolites and hydrous fe–mg silicates form, giving way to less hydrated minerals at higher temperatures. often this progression is recorded by the presence of a © geus, 2006. geological survey of denmark and greenland bulletin 9, 109–118. available at: www.geus.dk/publications/bull geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19109 110 complex sequence of zeolite minerals that have increasingly smaller amounts of molecular water bound in their structures (bird et al. 1984; neuhoff & bird 2001). in principle, therefore, zeolitic and related minerals can be sensitive indicators of temperature conditions. this temperature sensitivity is complicated by the equally important sensitivity of the zeolites to the composition of coexisting fluids. the thermodynamic properties of the zeolites are affected by substitution between the alkali metals, particularly na, k and ca, and al–si exchange (e.g. neuhoff et al. 1997, 2002, 2003, 2004). the stability fields of the zeolites are also sensitive to the ratio of calcium activity to hydrogen ion activity (i.e. [ca++]/[h+]2) in the coexisting fluid phase (e.g. surdam 1973; bird et al. 1984). hence, fluid chemistry has a strong influence on both the mineral compositions that develop and the specific mineral phases that form during low temperature recrystallisation. the purpose of this paper is to define likely bounds for bottom-hole temperatures and the likely geothermal gradient active at the time of mineral development, based on paragenetic relationships and thermodynamic constraints, taking into account the effects of fluid chemistry. detailed descriptions of the locations, mineralogies and geological settings for the lopra-1/1a and vestmanna-1 boreholes are presented in other chapters in this book and are only summarised here. geology the basalts of the faroe islands were erupted subaerially onto continental crust during opening of the northern north atlantic. the basalts have been divided informally into an upper, a middle and a lower formation. the lower basaltic sequence is more than 3000 m thick (established on the basis of field exposure and the lopra-1/1a drilling programme), and ranges in age from c. 58.8 to 56.5 ma (waagstein et al. 2002). the overlying basalts and sediments (some of the sediments are coal-bearing) are more than 2000 m thick and were erupted between c. 56 and 55.5 ma (larsen et al. 1999). recrystallisation of the lavas took place during subsequent burial, leading to the development of a wide range of zeolites and associated calc–silicate minerals (jørgensen 1984, 1997). the argument that the secondary mineral development results from burial metamorphism, rather than significant tectonic stacking or folding, is based on the relatively flat-lying nature of the basaltic flows and the absence of any kinematic fabric. methods compiled published data published data from active hydrothermal systems where temperatures and mineral associations are recorded, provide the most direct evidence of the conditions under which specific mineral assemblages occur. for this reason, published data from a variety of drilled hydrothermal systems with depths less than 4000 m were analysed to identify temperature constraints that would apply to the mineral associations reported for samples from the lopra-1/1a drilling programme (jørgensen 1984, 1997). the reported lopra-1/1a assemblages were confirmed by the author during independent examination of thin sections. the best available data that correlate downhole temperatures, depth and mineral occurrences are from geothermal systems in iceland (kristmannsdóttir & tomassón 1976), japan (seki et al. 1969; boles 1981), cerro prieto (bird et al. 1984), wairakei (steiner 1977) and toa baja (cho 1991). the reports from iceland and japan discuss secondary mineral development related to alteration of basaltic rocks, which most closely correspond to the lopra1/1a sequence. the cerro prieto locality consists of sedimentary rocks (sandstones, siltstones and mudstones) that are predominately composed of quartz and feldspars. the wairakei and toa baja localities consist of volcanic and volcanoclastic rocks and their associated clastic derivatives. the wairakei rocks are primarily rhyolitic and the toa baja rocks primarily andesitic. this suite of rock types spans the entire range from basalts through andesites to rhyolites, thus encompassing silica-poor to silica-rich compositions with varying abundances of alkali metals. on a whole-rock basis, then, the compositional range from these reported systems bounds that of the faroe island basalts considered here. the different tectonic settings represented by these systems include both rift and convergent margin environments. since these different settings evolved through different thermal histories, it is likely that the possible thermal conditions that may have affected the faroe island basalts, will be represented by at least some of the data recorded in the published studies. the range of fluid compositions at the various sites is broad. the cerro prieto fluids were concentrated solutions with high total dissolved solids and salinities, while many of the solutions reported from the new zealand region, particularly within the broadlands-ohaki (hedenquist 1990) and wairakei areas, included co2-rich and neutral-ph chloride waters and co2-poorer fluids occurred within the iceland system. thus, the published regeus bulletin no 9 7 juli.pmd 07-07-2006, 14:19110 111 ports examined include a range of solutions that are likely to encompass those that may have been present during alteration of the faroe island basalts. clear differences exist between sites with regard to the depth and extent of secondary mineral development, reflecting the effects of these combined intensive and extensive variables (i.e. t, bulk composition, fluid composition etc.). by considering this broad range of systems, it is possible to develop some insight into the extent to which differing geothermal and chemical conditions influenced the development of the mineral associations and how that influence is expressed at the lopra-1/1a site. comparison of the lopra-1/1a suite with these reported mineral parageneses should provide a strong bound to the thermal gradient inferred from these data. in this study, attention is focused on the calc–silicate mineral suite, which is comprised of the components cao–na2o–al2o3–sio2–h2o–co2. although potassium may play an important role in some of these mineral phases, particularly in zeolites where it may substitute for na and ca, it was not considered in this study because it is generally low in abundance in minerals that are characteristically part of the calc–silicate series in basaltic systems. the minerals of interest in the calc–silicate system for the purposes of this study are the zeolites, prehnite, calcite and zoisite–clinozoisite (which are proxies in this study for epidote). this system was selected for detailed consideration because it is the most thoroughly characterised for low-grade mineral development. these minerals possess well-characterised structures and compositions. in addition, there has been a long history of research in the geochemical community to derive thermodynamic data for phases in this system (liou 1971; glassley 1974; frey et al. 1991; neuhoff et al. 1997, 2002; fridriksson et al. 2001; neuhoff & bird 2001). although of immense importance in determining relative conditions in shallow (< 3000 m), low temperature (< 150°c) systems, the clay minerals and chlorites exhibit such structural and compositional complexity that the thermodynamic data available for modelling their behaviour remain inadequate. for that reason, they are not considered further in this report, although work continues on them. consideration of the calc–silicate system also eliminates complexities that arise due to the effects of variable oxygen partial pressures, which can dramatically influence the stability of iron-bearing mineral phases. hence, chlorites, smectites, fe–oxy/hydroxides and related phases are not considered here. two exceptions are considered in this paper. pumpellyite, which is noted in several other studies and documented as a mineral phase of limited distribution at lopra-1/1a, is considered here as part of the paragenetic assemblage, but does not play an important role in establishing the conclusions presented later. prehnite is also considered here and does possess limited solid solution with an fe3+ end member. measured mole fractions in a limited suite of analysed prehnites (unpublished data 1999, r. waagstein) average 0.08, with a range from 0.00 to 0.20 for 18 samples. rose & bird (1987) have shown that solid solution of as little as 10% of the fe end member in al-rich prehnite can significantly affect prehnite stability. although the majority of prehnites analysed in the lopra-1/1a rocks fall below this value, the impact of this effect must be borne in mind and is discussed later in this paper. although the stability fields of many of these minerals are reasonably well established for their ideal compositional end-members, each of these minerals belongs to a solid solution series. generally, there are very little or no quantitative data available regarding the actual compositions of mineral phases in the low-grade rocks described in the referenced reports. in addition, thermodynamic mixing properties of the solid solutions are generally not available. hence, when comparing stability relationships from one locality to another, it must be borne in mind that uncertainties of unknown magnitude are inherent in the comparison due to possible differences in the compositions of the minerals. thermodynamic calculations once mineral assemblages and distributions were compiled, the sensitivity of mineral development to thermal conditions and composition of coexisting fluids was modelled. this effort was undertaken because textural and compositional properties of these secondary minerals attest to the importance of mass transport involving carbonate–bicarbonate-bearing aqueous fluids. the thermodynamic properties of such solutions influence strongly the stability fields of the minerals and can thus be an additional means of placing limits on the physical conditions at the time of mineral growth. the calculations employed the aqueous speciation/reaction progress software eq3/6 (wolery & daveler 1992), using the .com database. the modelling was accomplished by performing speciation calculations over a range of temperatures and compiling the affinities of the possible solid phases that may develop in this system. affinity here is defined as: a = 2.303rt log(q/k) where a is the affinity (in calories), r is the universal gas geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19111 112 constant (1987 calories/mole-degree kelvin), t is temperature (kelvin), q is the activity product for the relevant species in the applicable hydrolysis reaction and k is the equilibrium constant for that same reaction. affinities greater than zero identify mineral phases that are supersaturated in the water at the specified conditions and affinities less than zero identify mineral phases that are undersaturated for those same conditions. positive affinities thus correlate with minerals that would be expected to precipitate from solution or form from mineral reactions in the rock, whereas negative affinities indicate that the respective mineral phase will dissolve, if present. particular attention was given to the development of prehnite since its compositional variability is less than that of the zeolites and its thermodynamic properties are better constrained. the affinities were calculated assuming in all cases that the system was saturated in quartz, laumontite and albite, since these phases coexist with prehnite (see below). these solids were used to constrain the activities of aqueous sio2, al3+ and na+, respectively. the same simulations were repeated assuming that calcite was present as a control for ca++ activity to determine the sensitivity of the results to this change in the system constraints. at the beginning of all of the simulations, it was assumed that the hydrogen ion activity was near neutral at the temperature considered. the initial fluid composition (a dilute, neutral-ph water at the temperature considered) was not in equilibrium with the constraining mineral phases but, for each simulation, was allowed to evolve toward equilibrium with the constraining mineral phases. the equilibrium fluid composition that evolved thus represented the composition of an aqueous fluid in equilibrium with the constraining phases and was the beginning point for further simulations that considered the effects of temperature and other compositional variables. the sensitivity of the results to variations in total cl– and hco3– was also considered. in this case, the simulations were conducted for cl– concentrations between 14 mg/l and 14.410 mg/l, and hco3– concentrations between 10 mg/l and 1000 mg/l. this range of values was selected because it encompasses the vast majority of water compositions from hydrothermal systems around the world (see compilations and discussions in roedder 1972; ellis & mahon 1977; arnorsson et al. 1983; fournier 1985). results the depth intervals over which individual minerals occur at the lopra-1/1a site are summarised in fig. 1. noteworthy in this compilation is that the progression with depth of the zeolite sequence is consistent with that from other localities (see summaries below under ‘compiled data’), and that epidote does not occur, even at the deepest levels. also of significance is that most of the minerals persist over depth intervals that exceed significantly any other reported occurrence for that mineral. compiled data the published temperature–depth data compiled from iceland (kristmannsdóttir & tomassón 1976), japan (seki et al. 1969; boles 1981), cerro prieto (bird et al. 1984), wairakei (steiner 1977) and toa baja (cho 1991) are shown in figs 2–4. for each location, the depth interval over which a mineral occurs is indicated by connected symbols that link the high and low temperature and depth points that define the extent of the mineral phase. figures 2–4 also show the depth intervals over which mesolite, stilbite, heulandite, laumontite and prehnite occur in the lopra-1/1a samples (jørgensen 1984, 1997). the lopra-1/1a depth–temperature relationships were constrained to be consistent with the following criteria: 0 1000 2000 3000 4000 pr eh ni te h eu la nd it e m o rd en it e sc o le ci te m es o lit e st ilb it e a na lc im e t ho m so ni te w ai ra ki te la um o nt it e pu m pe lly it e d ep th ( m et re s be lo w s ur fa ce ) bottom of hole fig. 1. summary of depth distributions for minerals reported in the lopra-1/1a samples (compiled from jørgensen 1984, fig. 4; 1997, fig. 1). zero depth corresponds to the ground surface at the drill site. the bottom of the well is indicated. minerals are arranged along the horizontal axis in a sequence of increasing depth to the right. the depth intervals correspond to the reported occurrences where the individual minerals are most abundant. in some instances, spot occurrences of minerals occur outside the indicated intervals. such occurrences can result from local variations in rock or fluid chemical conditions, or the consequences of locally controlled reaction kinetics, and are not plotted here. geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19112 113 1. coexistence of analcime and albite is constrained by cho (1991) to temperatures less than c. 120°c. since albite is ubiquitous in the lopra-1/1a volcanics, the maximum depth occurrence for analcime (c. 1850 m) is assumed to mark the c. 120°c isotherm. 2. laumontite coexisting with prehnite is constrained to temperatures less than 160°c (varna 1989). since laumontite and prehnite occur together over a depth of more than 1000 m and extend to the bottom of the lopra-1/1a hole, this constraint would place the base of the studied sequence at temperatures less than 160°c. 3. epidote is considered to require minimum temperatures for development of 200°c (bird et al. 1984). the exception to this would be systems rich in fe3+ (varna 1989), which the lopra-1/1a basalts are not. epidote is not reported within the lopra-1/1a rocks, hence the bottom-hole temperature must be less than 200°c. 4. pumpellyite requires temperatures in excess of 125°c for stable growth (evarts & schiffman 1983; bevins fig. 2. temperature–depth distributions reported from active thermal systems for the zeolites chabazite, scolecite–mesolite, mordenite, stilbite and heulandite. lines between points indicate the temperature–depth intervals over which the minerals are reported to occur. data sources are: kristmannsdóttir & tomassón 1976 for iceland; seki et al. 1969 and boles 1981 for japan; bird et al. 1984 for cerro prieto, baja california; steiner 1977 for wairakei, new zealand; cho 1991 for toa baja, puerto rico. the solid line labelled lopra is the geothermal gradient derived in fig. 2, with the depth intervals for lopra mesolite, stilbite and heulandite indicated. thor., thorlakshofn, iceland; reyk., reykjavik, iceland; nesj., nesjavellir, iceland. fig. 3. temperature–depth distribution for laumontite and prehnite. laumontite occurrences are from iceland, japan and toa baja, and prehnite from iceland, toa baja and cerro prieto (see fig. 3 for references and abbreviations). also shown for comparison is the inferred temperature–depth distribution for the same lopra minerals along the derived geothermal gradient (fig. 2). prehnite epidote depth (metres below surface) te m pe ra tu re ( °c ) reyk. toa baja nesj. cerro prieto krafla thor. wairakei 4000 200 100 400 300 0 lo pr a 0 1000 30002000 0 50 100 150 200 250 0 1000 2000 3000 4000 depth (metres below surface) te m pe ra tu re ( °c ) low t limit of epidote high t limit of analcime + albite low t limit of pumpellyite et al. 1991). the first appearance of pumpellyite is at a depth of c. 2300 m, thus constraining the 125°c isotherm to be near this depth. these observations were used to construct a palaeogeotherm (fig. 3). in developing this palaeogeotherm, points 1 (the constraint on analcime and albite coexistence) and 4 (the minimum temperature for pumpellyite development) were accepted without qualification. it was also assumed that the mean annual surface temperature was 10°c and that the bottom-hole temperature was c. 200°c. the 200°c bottom-hole temperature, which exceeds the 160°c constraint inferred from coexistence of prehnite and laumontite (point 2), was used to assure a conservative estimate of maximum thermal conditions and represents a compromise between points 2 and 3. in other words, the temperature gradient developed by this approach will overestimate maximum likely thermal conditions. the resulting geothermal gradient is linear. least squares regression of the data points gives a correlation of fit of 0.9949 and a gradient of 0.05°c/m, or 50°c/km. using this geothermal gradient, the depth intervals for mesolite, stilbite and heulandite were plotted to be consistent with the permissible measured distance over which these minerals occur. laumontite and prehnite were placed to be consistent with the implied thermal gradient and temperature constraints, as described above. geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19113 114 250 200 150 100 50 0 depth (metres below surface) chabazite mordenite stilbite heulandite scolecite-mesolitereyk. toa baja thor. nesj. krafla thor. lo pr a te m pe ra tu re ( °c ) 0 1000 2000 3000 4000 this reconstruction provides a conservative estimate of the temperature gradient only if the extent of surface erosion since mineral development is small and if there has been minimal tectonic rotation of the volcanic sequence. the consequence of these points is elaborated on below. the following observations are significant for reconstructing conditions recorded in the lopra-1/1a samples. 1. the zeolite group of minerals is stable at temperatures throughout the range 40°c to 210°c (figs 2–4). the only reported occurrence of zeolites at higher temperatures is from the wairakei, new zealand, geothermal field, where wairakite is stable at temperatures of 240°c to 250°c, where it coexists with epidote. this is not an assemblage reported from lopra-1/1a. the corresponding geothermal gradients for wairakei range from a high of > 400°c/km to a low of c. 40°c/km. the highest temperature gradients require active volcanic/ magma systems and are not typical of most environments. nevertheless, the stability relationships for minerals from these systems provide useful information for defining thermal stability limits for the minerals being considered. it should be noted, too, that the higher temperature conditions likely reflect convective hydrothermal environments with highly non-linear geothermal gradients. inevitably, lower geothermal gradients result in a particular mineral being observed over a much longer interval. this then implies that, for a given combination of rockand fluid-compositional characteristics, the lower the temperature gradient, the greater will be the depth range of a borehole over which a particular mineral will occur. 2. although local conditions (such as rock composition, coexisting fluid chemistry, local gas chemistry) at each site determine the exact zeolite sequence, the sequence of minerals generally follows one in which zeolites with high contents of molecular water (e.g. chabazite, scolecite, mesolite) are progressively replaced by zeolites with lower contents of molecular water (e.g. heulandite and laumontite) at higher temperatures. 3. in all cases considered, the assemblage prehnite–laumontite formed near the upper stability field of the zeolites and prior to the appearance of epidote. the temperature range for stable laumontite is in the range 70°c to 200°c. as noted by surdam (1973) and bird et al. (1984), prehnite–laumontite relationships are sensitive to the activity ratio [ca++]/[h+]2 in the fluid fig. 5. temperature constraints for the indicated mineral associations or occurrences. see text for sources and assumptions. the straight line is a least squares fit to the data points. the uncertainty bars for the analcime + albite ‘out’ and the pumpellyite ‘in’ data points span 25°c, and are presented only as an inferred, reasonable uncertainty envelope, in the absence of any available analytical data. the bar associated with the epidote lower t limit indicates the range of possible bottom hole metamorphic temperatures, based on the alternative constraint that the maximum temperature for laumontite coexisting with prehnite is 160°c. see text for further details. fig. 4. temperature–depth distribution for prehnite and epidote. epidote occurrences are from iceland, cerro prieto, toa baja and wairakei (see fig. 3 for references). also shown is the inferred temperature–depth distribution for lopra prehnite along the derived geothermal gradient (fig. 2). prehnite laumontitereyk. toa baja cerro prieto nesj. krafla thor. wairakei japan lo pr a depth (metres below surface) te m pe ra tu re ( °c ) 4000 200 100 400 300 0 0 1000 30002000 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19114 115 phase. variation in fluid chemistry is thus the likely cause for the broad temperature interval observed for laumontite stability. 4. in all cases, prehnite first forms at lower temperatures than epidote. however, both occur within the higher temperature range of the zeolites and are stable beyond the zeolite field (fig. 4). prehnite, for example, is reported to be stable in the temperature range 125°c to 340°c in the reports referenced in this study. this temperature interval is the same as reported for the stable presence of epidote, although the lower temperature occurrences of epidote are in systems that have high ca++ and fe3+ activity. the mineral sequence recorded in the lopra-1/1a well (fig. 1) is typical of that reported in other geothermal systems. the zeolite sequence follows the pattern of generally decreasing molecular water content with increasing depth, reflecting the impact of elevated temperatures at deeper levels in the borehole. this observation is generally consistent with the view that the thermal history experienced by these basalts was relatively simple. the highest temperature mineral assemblage that has developed is the prehnite–laumontite assemblage that is reported from the depth interval 2100 m to 3500 m. this assemblage clearly must extend beyond the bottom of the hole to an unknown depth. nevertheless, the 1400 m length of this assemblage is one of the longest such intervals reported anywhere in the world. by comparison, the toa baja prehnite–laumontite zone, the longest interval reported for these minerals, has a total length of about 850 m, and a geothermal gradient of between 50°c/km and 70°c/ km. the inferred temperature interval over which the prehnite–laumontite association formed at lopra-1/1a is inferred to be approximately 120°c to 200°c. epidote does not occur in any of the samples from the lopra-1/1a suite. figure 4 shows that this would require the bottom hole temperature not to exceed c. 250°c to 350°c, which appears to be the temperature interval over which epidote is consistently observed, although lower temperature occurrences have been reported, for example at thorlakshofn and reykjavik in iceland and at toa baja. as noted above, it is inferred that epidote will not form at temperatures less than c. 200°c under conditions of low to moderate fe3+ and ca++ activity. it is thus assumed that the iceland and toa baja occurrences reflect chemical environments that satisfy these conditions. the vestmanna-1 hole, which was also part of the drilling programme (jørgensen 1984, 1997) contains mineral assemblages typical of the shallowest levels of hydrothermal systems and overlap those of the lopra-1/1a sequence. if these mineral assemblages developed simultaneously, the computed geothermal gradient for the lopra-1/1a sequence would have to be considered a maximum. however, uncertainty exists regarding whether these mineral sequences for these two drill holes are coeval. thermodynamic calculations a suite of thermodynamic calculations, using the code eq3/6, was completed to determine the chemical conditions in the fluid phase that would constrain development of the mineral assemblage prehnite–laumontite–quartz– albite–calcite found in the wells. in these calculations, it was assumed that sodium, aluminium, calcium and silica aqueous concentrations are constrained by equilibrium with albite, laumontite, calcite and quartz, respectively. the calculated saturation state of the solution with respect to prehnite was monitored, as temperature and bicarbonate and chloride concentrations were changed. co2 partial pressure was allowed to evolve in response to the equilibrium conditions and monitored to assure that it remained within ‘real world’ bounds. by noting the temperature fig. 6. calculated lower thermal stability limit of prehnite coexisting with albite–calcite–quartz–laumontite, as a function of hco3– and cl– concentrations in the coexisting aqueous phase. contours on the stability limit surface are labelled in degrees centigrade. the mineral assemblage albite–calcite–quartz–laumontite was used in the calculations because it represents the highest temperature mineral assemblage observed in the bottom of the lopra-1/1a hole. 120°c100°c 160°c 140°c 180°c 200°c 220°c cl–(mg/l) 0 1.0 0.8 0.6 0.4 0.2 0 h c o – (m g/ l) 3 3000 15 00012 00090006000 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19115 116 and bicarbonate and chloride concentrations at which the solution became saturated in prehnite, it is possible to delineate those conditions that bound the stability field for the prehnite-bearing mineral assemblage. the results of the calculations are presented in fig. 6, which shows the contoured temperature surface for the stability of prehnite coexisting with a bicarbonate–chloride solution in equilibrium with laumontite–calcite– quartz–albite. the contours map the minimum temperature required for prehnite stability in this system. it must be emphasised that the exact location of these contours is somewhat imprecisely known, due to uncertainty in the thermodynamic data. the uncertainty in the bicarbonate values is approximately ± 50 mg/l, based on interpolations between simulations. these results show that prehnite stability is only slightly sensitive to the solution salinity (as indicated by the effect of variation in the chloride ion, cl–), but is very sensitive to the solution carbonate/ bicarbonate concentration. this behaviour reflects the strong coupling between these variables and ca speciation and ph. the more concentrated the solution in terms of carbonate/bicarbonate, the higher the temperature necessary to achieve prehnite stability. these calculations suggest that the wide range of prehnite thermal stability observed in natural systems (figs 2, 5) is due, at least in part, to differences in fluid composition from one location to another. this probably is true for other minerals in this calc–silicate suite as well. as documented by rose & bird (1987), the redox state and iron content of the fluid will also be an important variable in controlling prehnite stability, due to the effect of fe3+ substitution for al in the prehnite structure. salinities determined from a preliminary fluid inclusion study of the lopra-1/1a samples (konnerup-madsen 1998) gave cl– concentrations of between 0.167 and 1.49 equivalent weight per cent nacl, which is approximately 1000 to 9000 mg/l cl–. the analytical bicarbonate ion concentrations with this salinity in natural solutions in hydrothermal systems and at these temperatures and pressures are usually in the range of 200 to 800 mg/l (see compilations and discussions in roedder 1972; ellis & mahon 1977; arnorsson et al. 1983; fournier 1985) although the actual hco3– concentrations in the reservoirs will be lower than this value and be controlled by co2 fugacity. this implies (fig. 6) that the mineral association prehnite–laumontite–calcite–quartz formed at temperatures within the range of approximately 140°c to 205°c. this temperature interval is contained within the range of prehnite stability noted in other hydrothermal systems (see figs 2, 5) and is thus consistent with natural occurrences of this assemblage. it is also broadly consistent with the inference from phase relationships described above, in which it is suggested that this assemblage spans the temperature interval of approximately 120°c to 200°c. discussion and conclusions secondary mineral assemblages documented for the basalts recovered from the lopra-1/1a well are similar to those reported from other hydrothermal systems. both the specific mineral occurrences and the relative sequence of mineral stabilities define a systematic distribution that records increasing temperature with depth. the absolute length of individual mineral zones, however, is greater than at other well-documented sites, and suggests that the geothermal gradient at the time of mineral development was low. the mineral associations, complemented by thermodynamic calculations of fluid-rock equilibrium relationships, suggest that the temperature at the bottom of the well did not exceed 200°c, implying a maximum thermal gradient of 50°c/km (assuming a surface temperature in the range of 10 to 25°c). this gradient was constructed based on the assumption that the mineral zones are approximately horizontal. there is currently no structural data available to suggest this assumption is far from accurate, but it remains to be established conclusively. furthermore, it is also assumed that the total stratigraphic thickness at the time of mineral development did not greatly exceed that exposed and inferred today. this assumption is reasonable, based on the correlations established by larsen et al. (1999) between the east greenland volcanic complex and the faroe islands. the correlations indicate that the current thickness of basalts in the faroe islands is probably close to that which was originally erupted. it has previously been suggested that mineral development may have occurred in several discrete episodes (jørgensen 1984, 1997). such an interpretation makes more complex the sequence and timing of mineral growth and may change the absolute depth intervals over which specific mineral associations formed within a given time period. this, in turn, would require reconsideration of the temperature history since such an observation could result only in shorter absolute depth intervals for each mineral development period. in this scenario, the currently observed distribution of minerals would represent the sum of the depth intervals over which an individual mineral formed at different time periods, assuming that no single episode of mineral development obliterated evidence of previous distributions of secondary mineral development. nevertheless, the conclusion that the bottom hole temgeus bulletin no 9 7 juli.pmd 07-07-2006, 14:19116 117 perature did not exceed 200°c would still be valid, since that is based on the mineral association calcite–laumontite–prehnite–quartz, the temperature limit of which is constrained by laumontite and prehnite thermal stability and fluid composition effects. comparison of the derived geothermal gradient in the faroes with those reported for the atlantic margin region north of the united kingdom and in east greenland demonstrates a striking consistency that constrains evolution of the geothermal history in this region. green et al. (1999) used fission track data from apatites as well as vitrinite reflectance data from a series of wells in the eastern north atlantic province to determine palaeogeothermal gradients. they reported geothermal gradients of between 35°c/km and 90°c/km, with the vast majority of the region falling within the lower portion of the range. neuhoff et al. (1997) concluded that the zeolite facies metamorphism that affected east greenland flood basalts during initial opening of the northern north atlantic resulted from recrystallisation associated with a geothermal gradient of 40 ± 5°c/ km. the regional heat flow they derived from this conclusion is consistent with that reported from a study of metamorphic recrystallisation (manning et al. 1993). all of these values effectively bracket the inferred geothermal gradient in the faroe islands and argue for early development of relatively low geothermal gradients that persisted for some time in these regions. these results, and those of larsen et al. (1999), provide conceptual constraints on models of the thermal evolution of this part of the northern north atlantic province during early continental separation and basin development and argue for regions of low geothermal gradients that were not overprinted by later high heat-flow periods. as a word of caution, it should be noted that these conclusions are based on the simplifying assumption that linear geothermal gradients existed during mineral growth in this region. there is substantial evidence in geothermal systems, however, that complex geothermal gradients commonly develop, such that temperature reversals or near isothermal conditions may develop in response to the local thermal–hydrological regime, particularly in environments dominated by convection-driven fluid flow. although such features usually develop in regions of high heat flow and are not characteristic of environments such as the faroe islands region where heat flow is inferred to be low, evidence is currently inadequate to rule out this possibility conclusively. to evaluate the extent to which such behaviour occurred in the faroe islands volcanic province, a more detailed examination of mineral composition characteristics and distributions would be required, coupled with a more detailed modelling effort. acknowledgements regin waagstein kindly provided timely access to thin sections, mineral composition data and mineral distribution data, as well as informative discussions. his assistance greatly aided this effort. extensive comments from dennis bird and bruce christenson led to significant improvements in earlier versions of the manuscript, and are gratefully acknowledged. the editorial wisdom of james a. chalmers significantly improved the presentation and style of this paper. references arnorsson, s., gunnlaugsson, e. & svavarsson, h. 1983: the chemistry of geothermal waters in iceland. ii. mineral equilibria and independent variables controlling water compositions. geochimica et cosmochimica acta 47, 547–566. bevins, r.e., rowbotham, g. & robinson d. 1991: zeolite to prehnite–pumpellyite facies metamorphism of the late proterozoic zig-zag dal basalt formation, eastern north greenland. lithos 27, 155–165. bird, d., schiffman, p., elders, w.a., williams, a.e. & mcdowell, s.d. 1984: calc–silicate mineralization in active geothermal systems. economic geology 79, 671–695. boles, j.r. 1981: zeolites in low grade metamorphic rocks. in: mumpton, f.a. (ed.): mineralogy and geology of zeolites. mineralogical society of america reviews in mineralogy 4, 103– 135. cho, m. 1991: zeolite to prehnite–pumpellyite facies metamorphism in the toa baja drill hole, puerto rico. geophysical research letters 18, 525–528. ellis, a.j. & mahon, w.a.j. 1977: chemistry and geothermal systems, 392 pp. new york: academic press. evarts, r.c. & schiffman, p. 1983: submarine hydrothermal metamorphism of the del puerto ophiolite, california. american journal of science 283, 289–340. fournier, r.o. 1985: continental scientific drilling to investigate brine evolution and fluid circulation in active hydrothermal systems. in: raleigh, c.b. (ed.): observation of the continental crust through drilling i, 98–122. berlin: springer-verlag. frey, m., de capitani, c. & liou, j.g. 1991: a new petrogenetic grid for low-grade metabasites. journal of metamorphic geology 9, 497–509. fridriksson t., neuhoof, p.s., arnorsson, s. & bird, d.k. 2001: geological constraints on the thermodynamic properties of the stilbite–stellerite solid solution in low-grade metabasalts. geochimica et cosmochimica acta 65, 3993–4008. glassley, w. 1974: a model for phase equilibria in the prehnite– pumpellyite facies. contributions to mineralogy and petrology 43, 317–332. green, p.f., duddy, i.r., hegarty, k.a. & bray, r.j. 1999: early geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19117 118 tertiary heat flow along the uk atlantic margin and adjacent areas. in: fleet, a.j. & boldy, s.a.r. (eds): petroleum geology of northwest europe, proceedings of the 5th conference, 349– 357. london: geological society. hedenquist, j.w. 1990: the thermal and geochemical structure of the broadlands–ohaaki geothermal system, new zealand. geothermics 19, 151–185. jørgensen, o. 1984: zeolite zones in the basaltic lavas of the faeroe islands. in: berthelsen, o., noe-nygaard, a. & rasmussen, j. (eds): the deep drilling project 1980–1981 in the faeroe islands. annales societatis scientiarum faroensis. supplementum 9, 71–91. jørgensen, o. 1997: zeolites and other secondary minerals in cavities and veins, lopra-1/1a well, faroe islands, 1996, 8 pp. + plates. unpublished report, technical studies prepared for dansk olie og gasproduktion a/s, copenhagen, denmark (in archives of geological survey of denmark and greenland, geus report file 26129). konnerup-madsen, j. 1998: a preliminary examination of fluid inclusions in vug and fracture-filling quartz and calcite from lopra-1/1a, faroe islands, 5 pp. unpublished report, geological survey of denmark and greenland, copenhagen. kristmannsdóttir, h. & tomassón, j. 1976: zeolite zones in geothermal areas in iceland. in: sand, l.b. & mumpton, f.a. (eds): natural zeolites; occurrence, properties, use, 277–284. oxford: pergamon press. larsen, l.m., waagstein, r., pedersen, a.k. & storey, m. 1999: trans-atlantic correlation of the palaeogene volcanic successions in the faeroe islands and east greenland. journal of the geological society (london) 156, 1081–1095. liou, j.g. 1971: synthesis and stability relations of prehnite, ca2al2si3o10(oh)2. american mineralogist 56, 507–531. manning, c.e., ingebritsen, s.e. & bird, d.k. 1993: missing mineral zones in contact metamorphosed basalts. american journal of science 293, 894–938. neuhoff, p.s. & bird, d.k. 2001: partial dehydration of laumontite; thermodynamic constraints and petrogenetic implications. mineralogical magazine 65, 59–70. neuhoff, p.s., watt, w.s., bird, d.k. & pedersen, a.k. 1997: timing and structural relations of regional zeolite zones in basalts of the east greenland continental margin. geology 25, 803–806. neuhoff, p.s., kroeker, s., du, l.s., fridriksson, t. & stebbins, j.f. 2002: order/disorder in natrolite group zeolites: a 29si and 27al mas nmr study. american mineralogist 87, 1307–1320. neuhoff, p.s., stebbins, j.f. & bird, d.k. 2003: si-al disorder and solid solutions in analcime, chabazite, and wairakite. american mineralogist 88, 410–423. neuhoff, p.s., hovis, g.l., balassone, g. & stebbins, j.f. 2004: thermodynamic properties of analcime solid solutions. american journal of science 304, 21–66. roedder, e. 1972: composition of fluid inclusions. in: data of geochemistry. u.s. geological survey professional paper 400jj, 164 pp. rose, n.m. & bird, d.k. 1987: prehnite-epidote phase relations in the nordre aputiteq and kruuse fjord layered gabbros, east greenland. journal of petrology 28, 1193–1218. seki, y., onuki, h., okumura, k. & takashima, i. 1969: zeolite distribution in the katayama geothermal area of japan. japanese journal of geology and geography 40, 63–79. steiner, a. 1977: the wairakei geothermal area, north island, new zealand: its subsurface geology and hydrothermal rock alteration. new zealand geological survey bulletin 90, 136 pp. surdam, r.c. 1973: low-grade metamorphism of tuffaceous rocks in the karmutsen group, vancouver island, british columbia. geological society of america bulletin 84, 1911–1922. varna, c.l. 1989: mineral reactions and controls on zeolite-facies alteration in sandstones of the central transantarctic mountains, antarctica. journal of sedimentary petrology 59, 688– 703. waagstein, r., guise, p. & rex, d. 2002: k/ar and 39ar/40ar whole-rock dating of zeolite facies metamorphosed flood basalts: the upper paleocene basalts of the faroe islands. in: jolley, d.w. & bell, b.r. (eds): the north atlantic igneous province: stratigraphy, tectonic, volcanic and magmatic processes. geological society special publication (london) 197, 219–252. wolery, t.j. & daveler, s.a. 1992: eq6, a computer program for reaction path modeling of aqueous geochemical systems: theoretical manual, user’s guide, and related documentation. lawrence livermore national laboratory ucrl-ma-110662 part iv, 338 pp. manuscipt received 22 december 1999; revision accepted 26 may 2005. geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19118 geological survey of denmark and greenland bulletin 23, 2011, 45–48 45 chloride (cl) from dissolved salt is a major threat to groundwater quality in many regions of the world. in arid regions near present-day coastlines, where old seawater occurs in deeper sediments and where road salt is frequently used, cl can be a significant pollutant (european environmental agency 2009). european union member states have recently reported that next to nitrogen, cl is the most commonly found pollutant and is often responsible for groundwater bodies being at risk or having a poor ecological status (european commission 2010). intrusion of salty groundwater and infiltration by seawater near coastlines are well-known phenomena in danish aquifers (ødum & christensen 1936; bonnesen et al. 2009). saltwater in aquifers may also come from human pollution such as landfills, road salt storage facilities, roads and agricultural activities (panno et al. 2006). since the 1970s, deicing salt applied to roads has been recognised as a significant source of contamination that may deteriorate aquifers that are used as drinking water resources by increasing their cl concentration and by harming stream and lake ecosystems ( jackson & jabbogy 2005). recent studies have suggested that the decade-long usage of road salt is becoming a rising threat to groundwater quality (bester et al. 2006). salt contamination from roads is therefore particularly problematic to aquifers already at risk (lundmark & olofsson 2007). the present paper explores the impact of road salt on groundwater quality in denmark by means of a combination of chemical indicator analysis, temporal and spatial cl analysis and numerical groundwater modelling. the vulnerability of aquifers to road salt depends on the amount of salt applied per kilometre road, the degree of urbanisation and the percentage of salt lost to the subsurface. based on a literature review, the estimated percentage of road salt lost to the groundwater is 10–20% of applied de-icing salt in danish urban areas (kristiansen et al. 2009). the average amount of road salt used during the winter in denmark has risen since the late 1990s, but varies with weather conditions (fig. 1). in comparison, fig. 1 also shows that the atmospheric nacl deposition for the entire danish surface area is about 280 gigagrams (gg) per year, which is tentatively estimated based on actual bulk deposition measurements (t. ellerman, personal communication 2011). thus, the total amount of applied road salt and the total atmospheric salt deposition in denmark are of the same order of magnitude. however, the local surface load of road salt and atmospheric salt deposition vary widely across denmark. the danish road salt project this paper addresses the results from a recent assessment performed under the danish groundwater mapping project in order to evaluate the impact and risk of road salt to the quality of danish groundwater resources (kristiansen et al. 2009). the project used groundwater quality data from the national database jupiter. the data were downloaded in october 2008 and included approximately 140 000 analyses from approximately 24  000 groundwater sampling points corresponding to about one sample per 2 km2. the oldest data are from 1890, the most recent from 2007. data on the historical consumption of road salt were drawn from the danish road directorate and involved municipalities. three different methods were used: (1) evaluation of indicators to separate chloride sources in groundwater chemistry, (2) analysis of the distribution and variation of cl in time and space, and (3) development of a numerical groundwater risk assessment tool in the hydrological modelling system mike she. does road salt affect groundwater in denmark? søren m. kristiansen, flemming d. christensen and birgitte hansen 500 400 300 200 100 0 1970 year 200019901980 s al e o f ro ad s al t p e r w in te r se as o n total sale of road salt in denmark nacl deposition (1 0 0 0 m e tr ic t o n n e s/ ye ar ) fig. 1. sale of road salt for highway use in denmark from 1965/1966 to 2008/2009 in 1000 metric tonnes (gg) per winter season based on data from the danish road directorate. atmospheric nacl deposition in gg per year is a tentative estimate for the entire danish surface area based on bulk deposition measurements by t. ellerman, university of aarhus, 2011. © geus, 2011. geological survey of denmark and greenland bulletin 23, 45–48. open access: www.geus.dk/publications/bull 4646 chloride source indicators geochemical tools with mass ratios of especially the halides have proved useful for identifying different groundwater cl sources (davies et al. 1998). groundwater salt origins were identified by a graphical technique that distinguishes between multiple sources (panno et al. 2006). this approach discriminates sea salt from, for instance, vacuum salt used as road salt. an average of 40% of danish de-icing salt is vacuum salt. both cl and br form stable anions in water, which are usually not affected by sediment–water reactions. in addition, nabr is less soluble than nacl. as a consequence of the production process, vacuum salt has a cl/br mass ratio >1000. sedimentary rock salt, and hence road salt coming from this source, has cl/br mass ratios similar to rain, as well as residual and infiltrating waters with a cl/br mass ratio <400 (davis et al. 1998). based on a literature review and own data analyses, we find that cl/br ratios are appropriate to detect the origin of dissolved cl sources in danish groundwater (kristiansen et al. 2009). the chemical indicator analysis shows that the potential impact of road salt on groundwater can be traced using a combination of cl/br mass and na/cl molecular ratios in groundwater where the na/cl ratio is affected by the exchange of sodium between the solid and liquid phases and the cl/br ratio is affected by the above-mentioned dissolution processes. groundwater chloride sources firstly, a prevalence of br-poor groundwater (cl/br mass ratios >1000) was found in upper groundwater (<80 m below surface), which indicates that anthropogenic cl sources (e.g. vacuum salt from roads, atmospheric deposition, or animal manure from farming) have a general impact on groundwater quality. secondly, groundwater with reversed ionic exchange (na/cl molecular ratio <0.75) was also preferentially found in upper groundwater, which indicates infiltration of nacl containing water into more fresh sediment. thirdly, most chloride in groundwater (mg/l) >600 250–600 125–250 75–125 30–75 <30 50 km 10°e 14°e 55°n 57°n 57°n 55°n fig. 3 fig. 2. geographical distribution of the latest analysed chloride concentration in c. 24 000 danish groundwater sampling points. the highest measured chloride concentration in wells with more than one measuring point is shown. data were downloaded from the national database jupiter in october 2008. 47 of the groundwater with high cl concentrations was found in the upper groundwater with a gradual decrease from the surface to about 80 m below surface. these three different analyses support that the upper groundwater is affected by cl sources at the soil surface. however, the analyses could not identify which specific type of cl source at the surface inf luences groundwater quality. in addition, the analyses showed that the deeper groundwater (>90 m below surface) often had cl/br mass ratios <550; moreover, a gradual increase in cl concentrations with depth indicated that the primary cl source in deeper danish aquifers should be found in the underlying groundwater with much higher cl concentrations. chloride distribution in danish groundwater the cl concentration classes used in fig. 2 are based on statistical analysis of the distribution of all the cl analyses from danish groundwater where four geochemi cal populations are found: <10, 10–30, 30–600 and >600 mg cl/l. background concentrations of cl in danish ground water is below 30 mg/l. groundwater with cl concentrations above the drinking water standard of 250 mg/l is commonly found close to the coastline, especially in the eastern parts of denmark (fig. 2). however, elevated concentrations of cl are also found in inland aquifers. trend analyses of the cl concentration in the groundwater in the greater copenhagen area show that 38% of the wells have experienced significantly increasing concentrations whereas only 9% have seen significantly decreasing concentrations (95% confidence interval) since the 1960s. median cl concentrations in groundwater rose from 40–80 mg/l in 1965–1978 to 80–160 mg/l in 1994–2007. a predominance of inversed ionic exchanged groundwater indicates that infiltration of salt water into a fresher aquifer comes from anthropogenic inf luenced sources such as road salt or intrusion by sea water due to drinking water abstraction. numerical modelling of road salt impact a numerical assessment tool was developed for a large part of the greater copenhagen area (274 km2) in order to evaluate the impact of road salt on groundwater quality. we modelled losses of road salt to the environment at catchment scale from 1967 to 2060 (fig. 3). the tool combines a surface load model with a well-calibrated 3d numerical groundwater model in mike she that simulates water f low and solute transport in the subsurface (kristiansen et al. 2009). the surface load model consists of (1) the historic use of road salt since 2001 distributed on the road network where the type of road has been taken into consideration, (2) estimation of the loss of road salt to the groundwater, and (3) simple 1d modelling of the cl transport through the unsaturated zone. the loss of road salt to the surroundings is difficult to estimate, but tvedt et al. (2001) estimated that 15–30% of the road salt is lost under danish conditions. however, not all the lost road salt infiltrates the groundwater as some percolating water is removed by drainage or sewage. in the modelling, we decided to use a loss of 15% of the road salt to groundwater, which can be considered as a best estimate based on available knowledge. simulations indicate that with a loss of 15% of the applied road salt, the chloride concentrations below urban areas genc h lo ri d e c o n c e n tr at io n (m g/ l) well 250 100 25 12.5 3 km rødovre glostrup albertslund brøndby copenhagen frederiksberg copenhagen vallensbæk abstraction well (fig. 4) model boundary hvidovre nn fig. 3. modelling results of chloride concentrations in the primary aquifer due to leaching of road salt estimated for a steady-state situation in 2060 in the greater copenhagen area. the loss of historically used road salt is put to 15% and all factors are kept constant from 2008 to 2060. the background concentration of chloride is not included. for location see fig. 2. 4848 erally will show a 25–40 mg/l increase, whereas increases can reach 125 mg/l at some major road junctions. simulated breakthrough curves for a shallow well are shown in fig. 4 for different scenarios compared to measured values. a background cl concentration of 80 mg/l is added for the simulated results which contains cl from natural sources as atmospheric deposition and marine residual water. the upper curve, where the current load of road salt is maintained, shows that it takes decades before a steady state situation is reached. the rest of the curves show the development of the groundwater cl concentrations at steady state for different reduction scenarios in relation to current road salt usage. conclusions the results show that the upper groundwater cl concentrations (<80 m below surface) are affected by cl sources such as road salt, atmospheric deposition and animal manure. precise identification of the cl sources at the surface requires more analyses of chemical indicator species in the groundwater. numerical groundwater modelling in the greater copenhagen area shows that road salt can result in a significant increase of the cl concentration in groundwater, particularly near major road junctions. the aquifer used for water supply may be degraded because of the accumulated impact from several cl sources such as road salt, residual salt groundwater and recent seawater intrusion. the applied model assumes that the loss to groundwater of road salt is 15%. but if the loss was 30%, then the resultant cl concentration should be doubled. more precise quantification of the loss of road salt and knowledge on cl sources other than salt applied to public roads are therefore required in order to reduce the uncertainty of the current estimate of the effect of road salt on groundwater quality, for example by establishing study sites in urban areas. acknowledgement the project was supported by the former environmental centres under the danish ministry of the environment. references bester, m.l., friend, e.o., molson, j.w., rudolph, d.l. 2006: numerical investigation of road salt impact on an urban well-field. ground water 44, 165–175. bonnesen, e., larsen, f., sonnenborg, t., klitten, k. & stemmerik, l. 2009: deep saltwater in chalk of north-west europe: origin, interface characteristics and development over geological time. hydrogeolog y journal 17, 1643–1663. davis, s., cecil, d.w., zreda, m. & sharma, p. 1998: uses of chloride/ bromide ratios in studies of potable water. ground water 36, 338–350. european commission 2010: report from the commission in accordance with article 3.7 of the groundwater directive 2006/118/ec on the establishment of groundwater threshold values, 10 pp. brussels: european commission. european environmental agency 2009: water resources across europe – confronting water scarcity and drought, 60 pp. copenhagen: european environmental agency. jackson, r.b. & jabbog y, e.g. 2005: from icy roads to salty streams. proceedings of the national academy of sciences of the united states of america 102, 14487–14488. kristiansen, s.m., christensen, f.d. & hansen, b. 2009: vurdering af danske grundvandsmagasiners sårbarhed overfor vejsalt, 107 pp. københavn: de nationale geologiske undersøgelser for danmark og grønland. lundmark, a. & olofsson, b. 2007: chloride deposition and distribution in soils along a deiced highway – assessment using different methods of measurement. water, air & soil pollution 182, 173–185. ødum, h. & christensen, w. 1936: danske grundvandstyper og deres geologiske optræden. danmarks geologiske undersøgelse iii. række 26, 183 pp. panno, s.v., hackley, k.c., hwang, h.h., greenberg, s.e., krapac, i.g., landsberger, s. & o’kelly, d.j. 2006: characterization and identification of na-cl sources in ground water. ground water 44, 176–187. tvedt, t., randrup, t.b., pedersen, l.b. & gludsted, s. 2001: planter & vejsalt, 19 pp. københavn: trafikministeriet, vejdirektoratet and miljøog energiministeriet, skov & landskab. current average road salt load maintained 25% reduction of current road salt load 50% reduction of current road salt load 130 120 110 100 90 80c h lo ri d e c o n c e n tr at io n ( m g/ l) year 1980 2000 2020 2040 2060 100% reduction of current road salt load no road salt used on highways; current road salt load maintained on other road types observed data fig. 4. modelled and measured chloride concentrations in groundwater in an abstraction well in the greater copenhagen area. for location see fig. 3. breakthrough curves are shown for different scenarios whereby road salt losses to groundwater are reduced. authors’ addresses s.m.k., university of aarhus, department of earth sciences, høegh-guldbergs gade 2, dk8000 aarhus c. e-mail: smk@geo.au.dk f.d.c., rambøll, hannemanns allé 53, dk-2300 copenhagen s, denmark. b.h., geological survey of denmark and greeland, lyseng allé 1, dk-8270 højbjerg, denmark. geological survey of denmark and greenland. bulletin 10, 61-64 the arctic ocean is a landlocked basin, at present covered by perennial sea ice. during the past few decades a significant thinning and shrinking of the sea ice has been observed, and modelling studies indicate that the arctic ocean ice cover could, by the end of this century, almost disappear from most parts of the arctic ocean during peak summer seasons. it remains uncertain, however, whether the environmental changes are an enhanced greenhouse-warming signal or a result of natural (long-term) variability, but palaeoceanographic studies can contribute to our understanding of the natural variability of environmental parameters, e.g. sea-ice cover and oceanographic changes on time-scales of centuries to millennia. as part of the multidisciplinary eu project greenland arctic shelf ice and climate experiment (greenice), sediment coring and seismic reflection measurements have been undertaken in a hitherto unexplored part of the arctic ocean, the margin of the lomonosov ridge in the lincoln sea (fig. 1). the aim of the project was to study the structure and dynamics of the sea-ice cover and attempt to relate these to longer-term records of climate variability retrieved from sediment cores. the main field work was carried out in may 2004 from an ice camp established by a twin otter aircraft on drifting sea ice at 85°n, 65°w, c. 170 km north of alert, arctic canada. the camp was deployed over the shallowest part of the lomonosov ridge off the northern greenland/canada continental margin (fig. 1). the sea-ice drift would normally be between east and south, but persistent easterly winds resulted in a fast drift trajectory towards the wsw, such that the camp drifted a distance of approximately 62 km during the two weeks camp period. at present the study area is heavily ice covered, and forecast models of future shrinking arctic sea-ice cover suggest that this area is one of the least sensitive to warming in the arctic. the results obtained from the greenice project challenge this view. an unexplored area the reduction and thinning of arctic sea ice in recent decades (e.g. rothrock et al. 1999; acia 2004) has drawn attention to whether these environmental changes are an early reaction to global warming, or whether they are part of a long-term variation of the arctic environment. modelling studies of global warming effects indicate that the arctic is radical past climatic changes in the arctic ocean and a geophysical signature of the lomonosov ridge north of greenland naja mikkelsen, niels nørgaard-pedersen,yngve kristoffersen, susanne juul lassen and emma sheldon © geus, 2006. geological survey of denmark and greenland bulletin 10, 61–64. available at: www.geus.dk/publications/bull 500 600 700 800 9001000 1000 11 00 12 00 #11 #10 76°w 74°w 72°w 70°w85°00´ 84°45´ 10 km arctic ocean lincoln sea alert lomonosov ridge fig. 1. upper: the greenice field camp area (marked by a red square) was deployed north of arctic canada and north greenland at the shallowest part of the submarine lomonosov ridge, in a region where no geologic record has hitherto been retrieved. lower: drift path of the field camp is shown by arrow and red line and coring stations by yellow and red dots. 61 likely to show a significant temperature increase, and that sea-ice cover could, by the end of this century, almost disappear during peak summer seasons (johannessen et al. 2004). such a scenario would not only have a dramatic impact on arctic ecosystems, navigation and indigenous people, but could also influence the thermohaline circulation and regional climate in the sub-arctic and north atlantic region. in a discussion of these scenarios, there is an urgent need for high-latitude arctic records of variations in climate, oceanography and sea-ice cover representing long time periods and, in particular, records of natural environmental change during earlier warm periods, which can be used to evaluate presentday changes. in spite of its importance, the recent geological record of many parts of the arctic ocean, including the lincoln sea, are still poorly known and hampered by difficult access. reduced ice cover during interglacial periods seismic data and sediment cores were collected from the drifting greenice station in this normally inaccessible area of the lincoln sea. during the camp period, 15 gravity core stations were established (figs 1, 2), and the retrieved cores were subsequently subjected to a wide array of investigations including ams-14c dating, faunal analysis of nannofossils and benthic and planktonic foraminifers, and stable isotope and geochemical analysis. the two longest cores, greenice core 10 (176 cm) and greenice core 11 (64 cm), show several characteristic colour cycles previously recorded in other parts of the arctic ocean (fig. 3; phillips & grantz 1997; nørgaard-pedersen et al. 1998; jakobsson et al. 2000; polyak et al. 2004; spielhagen et al. 2004). the stratigraphy of core 11 is based on nannoplankton, benthic foraminiferal assemblages and ams-14c dates and provides a record of the last c. 130 000 years, including the last interglacial period (eemian). preliminary investigations indicate that the longer core 10 contains a record of the last c. 200 000 years. planktonic foraminiferal assemblages are used as a key palaeoceanographic proxy, and a surprisingly large variability of these foraminifers was observed for an interior arctic ocean site. the discovery of abundant numbers of the small subpolar foraminifers turborotalita quinqueloba in two core sections, corresponding to the last interglacial and a younger warm interstadial (fig. 3), is an enigma, as this species indicates fairly strong subsurface atlantic water advection and possibly a much reduced summer sea-ice cover in the area compared to present-day conditions. the youngest part of the retrieved sediment record is condensed, but samples taken from close to the surface, representing holocene and recent conditions, lack the subpolar foraminifer species and thus indicate a consistent thick perennial sea-ice cover in accordance with present-day conditions (nørgaard-pedersen et al. in press) the results support the concept that interglacial conditions in the interior arctic ocean can vary considerably. at present, however, it is not known whether the influx of subpolar foraminifers was related to an ice-margin or polynyatype setting, or whether it reflects a generally reduced sea-ice cover of the interior arctic ocean. ongoing work aims to explore whether the observed trends can be traced to other key sites in the arctic ocean. seismic investigations and active faulting a 62 km long seismic reflection profile was collected during the drift of the greenice field camp (figs 1, 4). seismic reflection data were obtained from the shallowest part of the 62 a b fig. 2. a: lightweight gravity coring equipment (constructed by j. boserup, geus) used during the drift of the greenice camp. b: sediment cores were retrieved through a hole drilled in the ice. submarine lomonosov ridge facing the canadian/greenlandic continental margin, and comprise two parallel single channel lines (kristoffersen & mikkelsen 2006). the data reveal that the top of lomonosov ridge is bevelled at a water depth of 550 m and that only a thin sediment cover (less that 50 m) overlies the acoustic basement. pre-pleistocene sediments were probably eroded by a grounded marine ice sheet extending north from ellesmere island, and/or by deep draft icebergs. in the deep passage between the lomonosov ridge and the lincoln sea continental margin, more than 1 km of sediment is present. the uppermost 300 m of this succession reflects a significant sediment drift possibly related to 63 fig. 3. the greenice sediment cores show marked colour cycles. greenice core 11 covers a time span of c. 130 000 years and includes the eemian interglacial marine isotope stage 5e. abundant subpolar foraminifers (turborotalita quinqueloba) in eemian deposits indicate open water conditions not far from the greenice site. this is in contrast to holocene sediments that show a total dominance of polar species (neogloboquadrina pachydermal). 0 5 10 15 20 25 30 35 40 45 50 55 60 65 holocene polarí species subpolar’ species planktonic foraminifers nos/g sediment core 11 n. pachyderma (sin.) % t. quinqueloba nos/g sediment eemian interglacial 0 4000 8000 12000 16000 0 4000 80000 20 40 60 80 100 d e p th ( c m ) 1.0 1.5 2.0 2.5 3.0 2000 1500 1000 shot point 500 20 km t im e ( se c .) middle/upper pliocene – pleistocene upper cretaceous – neogene cretaceous upper jurassic – lower cretaceous basement sw ne lomonosov ridge fig. 4. seismic line retrieved during the ice drift over the lomonosow ridge north of canada and greenland (adapted from kristoffersen & mikkelsen 2006). 64 increased plio-pleistocene sediment input, and the underlying 700 m of sediment onlap a subsiding ridge slope. blocks of older margin sediments may represent the acoustic basement in the area. a basal unconformity, which may correspond to the hauterivian break-up unconformity of embry & dixon (1994), caps a series of nw–se-trending grabens, and several of the main graben faults extend to the sea bed and appear to have been active until recent times. acknowledgements the greenland arctic shelf ice and climate experiment (greenice) was supported by eu-grant evk2-2001-00280. references acia, 2004: impacts of a warming arctic – arctic climate impact assessment, 144 pp. cambridge: cambridge university press. embry, a.f. & dixon, j. 1994: the age of the amerasian basin. in: thurston, d.k. & fujita, k. (eds): 1992 proceedings, international conference on arctic margins, 289–294. anchorage, alaska, usa: u. s. department of the interior, minerals management service. jakobsson, m., løvlie, r., al-hanbali, h., arnold, e., backman, j.& mörth, m. 2000: manganese and color cycles in arctic ocean sediments constrain pleistocene chronology. geology 28, 23–26. johannessen, o.m. et al. 2004: arctic climate change: observed and modelled temperature and sea-ice variability. tellus a 56, 559–560. kristoffersen, y. & mikkelsen, n. 2006: on sediment deposition and nature of the plate boundary at the junction between the submarine lomonosov ridge, arctic ocean and the continental margin of arctic canada /north greenland. marine geology 225, 265–278. nørgaard-pedersen, n., spielhagen, r.f., thiede, j. & kassens, h. 1998: central arctic surface ocean environment during the past 80,000 years. paleoceanography 13, 193–204. nørgaard-pedersen. n., mikkelsen, n., lassen, s.j., kristoffersen, y. & sheldon, e. in press: arctic ocean sediment cores off northern greenland reveal reduced sea-ice concentrations during the last interglacial period. paleoceanography. phillips, r.l. & grantz, a. 1997: quaternary history of sea ice and paleoclimate in the amerasia basin, arctic ocean, as recorded in the cyclical strata of northwind ridge. geological society of america bulletin 109, 1101–1115. polyak, l., curry, w.b., darby, d.a., bischof, j. & cronin, t.m. 2004: contrasting glacial/interglacial regimes in the western arctic ocean as exemplified by a sedimentary record from the mendeleev ridge. palaeogeography, palaeoclimatology, palaeoecology 20, 73–93. rothrock, d.a., yu, y. & maykut, g.a. 1999: thinning of the arctic seaice cover. geophysical research letters 26, 3469–3472. spielhagen, r.f., baumann, k.-h., erlenkeuser, h., nowaczyk, n.r., nørgaard-pedersen, n., vogt, c. & weiel, d. 2004: arctic ocean deepsea record of northern eurasian ice sheet history. quaternary science reviews 23, 1455–1483. authors’ addresses n.m., n.n.-p., s.j.l. & e.s., geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350 copenhagen k, denmark; e-mail: nm@geus.dk y.k., department of earth science, university of bergen, allegaten 41, n-5007 bergen, norway. geological survey of denmark and greenland bulletin 6, 41-56 41geological survey of denmark and greenland bulletin 6, 41–56 © geus, 2004 the caledonian thin-skinned thrust belt of kronprins christian land, eastern north greenland a.k. higgins, n.j. soper, m. paul smith and jan a. rasmussen kronprins christian land in the extreme north of the east greenland caledonides, exposes a thin-skinned thrust belt up to 50 km wide developed in ordovician–silurian platform limestones and dolostones of the iapetus passive margin. this thrust belt is characterised by a series of ssw–nne-trending and east-dipping caledonian thrusts with westward displacements of generally a few kilometres each. it passes westwards into undisturbed autochthonous foreland. based on a line and area restoration, total displacement along a well-exposed wnw–ese section through the thrust belt amounts to 17.6 km, which represents a shortening of 45% in the line of section. biostratigraphic control in the limestone and dolostone succession is based on conodonts and macrofossils. the alteration colours of the conodonts provide estimates of maximum burial temperatures, which show that the thickness of the overlying thrust sheets ranged from about 6 to 12.5 km from west to east across the thrust belt. since the estimated former thickness of the vandredalen thrust sheet above the thin-skinned parautochthonous thrust belt is insufficient to yield the temperatures attained, higher thrust sheets must once have extended across the region. keywords: caledonides, conodonts, greenland, ordovician, thrust tectonics a.k.h. & j.a.r., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: akh@geus.dk n.j.s., gams bank, threshfield, skipton bd23 5np, uk. also affiliated with: department of geology, university college, galway, ireland. m.p.s., lapworth museum, school of geography, earth and environmental sciences, university of birmingham, edgbaston, birmingham b15 2tt, uk. the east greenland caledonides extend for 1300 km along the coastal region of east greenland between latitudes 70° and 82°n, in a belt up to 300 km wide. it can be broadly divided into an eastern thick-skinned thrust belt, and a western marginal thrust belt that in places is thin-skinned (fig. 1). the western marginal thrust belt is characterised by the presence of foreland windows, in most of which a thin lower palaeozoic sequence is preserved beneath the bordering thrusts demonstrating that the thrusting episode is postordovician (higgins et al. 2001a). the thrust sheets overlying the foreland windows incorporate substantial units of reworked basement gneisses, derived from the thick-skinned thrust belt to the east. the greenland inland ice obscures the western parts of the marginal thrust belt along most of its length, and the transition between the caledonian orogenic belt and the autochthonous foreland is only completely exposed in kronprins christian land (79°30′–82°n). here the transition zone takes the form of a thin-skinned parautochthonous thrust belt, which is the subject of this paper. geus bulletin 6.pmd 10-02-2005, 09:5441 42 ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ c a l e d o n id e s greenland 70ºn 74ºn 78ºn 82ºw 35ºw wandel sea centrumsø 100 km jameson land scoresby sund 25 w traill ø wollaston forland bessel fjord danmarkshavn lambert land peary land station nord k ro np rin s c hr ist ian l an d nørreland window kronprins christian land thin-skinned thrust belt (parautochthonous foreland) palaeogene basalts palaeogene intrusions wandel sea basin: carboniferous–palaeogene sediments east greenland basins: carboniferous–cretaceous sediments devonian – continental sediments late to post-kinematic granites neoproterozoic–ordovician sediments (east greenland) neoproterozoic–silurian sediments (eastern north greenland) palaeo-mesoproterozoic sediments and basalts (eastern north greenland) crystalline complexes and sediments (archaean–mesoproterozoic) neoproterozoic–silurian sediments (north greenland) palaeo-mesoproterozoic sediments and basalts (eastern north greenland) mainly crystalline rocks – parautochthonous windows thrust fault/shear zone tectonic zone boundary post-caledonian late to post-caledonian caledonian orogenic belt caledonian foreland ▲ ▲ fig. 2 hamberg gletscher foreland dronning louise land charcot land window målebjerg window gåseland window c a le d o n ia n so le t h r u st in la n d ic e m a r g in a l t h r u s t b e l t t h ic k s k in n e d t h r u s t b e l t eleonore sø window ▲ ▲ ▲ fig. 1. general geological map of the east greenland caledonides, illustrating the division into western marginal and eastern thick-skinned thrust belts (modified from higgins et al. 2001a). the main foreland windows along the length of the fold belt are shown, with the kronprins christian land area in the extreme north. the frame indicates the area of fig. 2. geus bulletin 6.pmd 10-02-2005, 09:5442 43 geological setting throughout most of its length, the east greenland caledonides are dominated by crystalline orthogneiss complexes (fig. 1) that retain much of their ‘basement’ character despite caledonian reworking. the protolith age of the orthogneisses has been determined as archaean or proterozoic on the basis of numerous isotopic ages (e.g. steiger et al. 1979; kalsbeek et al. 1993, 1999). isotopic mineral ages are generally caledonian, testifying to widespread mediumto highgrade caledonian metamorphism (e.g. dallmeyer & strachan 1994; dallmeyer et al. 1994; brueckner et al. 1998). proterozoic sedimentary successions overlying the crystalline gneiss complexes are widespread in the southern half of the caledonides. an older late mesoproterozoic to early neoproterozoic succession (krummedal supracrustal sequence and equivalents; higgins 1988) preserves isotopic evidence of a pre-caledonian (~ 930 ma) thermal event, and in many areas hosts ~ 930 ma augen granite intrusions (jepsen & kalsbeek 1998; kalsbeek et al. 2000; watt et al. 2000; leslie & nutman 2000, 2003). the younger, neoproterozoic, eleonore bay supergroup is conspicuous in the fjord region of east greenland (72°–74°30′n), where it is unconformably overlain by the vendian tillite group and lower palaeozoic sediments, forming a succession up to 18.5 km thick. both sedimentary successions are variably affected by caledonian metamorphism and deformation, and both host caledonian granites (kalsbeek et al. 2001a, b). in the northern part of the east greenland caledonides, latest palaeoproterozoic to mesoproterozoic supracrustal successions are represented by the independence fjord group and associated volcanic rocks (figs 1, 2; see also below). these are widely exposed in the caledonian foreland west of danmark fjord, and are also conspicuously developed within the caledonian thrust complexes of kronprins christian land, where they are overlain by the neoproterozoic rivieradal group siliciclastic succession and hagen fjord group (fig. 2; see also stratigraphy section below). early work in southern kronprins christian land by fränkl (1954, 1955) established many of the principal structural features of this part of the east greenland caledonides. while subsequent interpretations of the frontal thrust systems were explained by hurst & mckerrow (1981a, b, 1985) in terms of three nappes, later systematic survey work has considerably simplified this view. the vandredalen thrust sheet is now recognised as the westernmost major allochthonous tectonic unit along the entire > 200 km long thrust front in kronprins christian land (fig. 2; rasmussen & smith 1996). the vandredalen thrust displaces the neoproterozoic rift succession now known as the rivieradal group (smith et al. 2004a, this volume) across the parautochthonous foreland succession (higgins et al. 2001b). the thin-skinned thrust belt west of, and structurally underlying, the vandredalen thrust sheet is developed in an ordovician to lower silurian succession, that continues westwards into the undisturbed foreland sequences west of danmark fjord. the succession in this 30–50 km wide, parautochthonous thrust belt is disrupted by a series of east-dipping and ssw–nne-trending thrusts and associated belts of folding (fig. 2). a thin-skinned deformation style was also suggested in the earliest studies by fränkl (1954, 1955), and peel (1980) distinguished numerous significant thrusts in an w–e traverse through the belt in kronprins christian land west of romer sø. observations by peel indicated that the westernmost thrusts extend almost to danmark fjord. regional mapping of the southern part of kronprins christian land, including the parautochthonous thrust belt, was carried out during the 1993–1995 expeditions by the former geological survey of greenland (ggu; henriksen 1994a, b, 1995, 1996; higgins 1995). the vandredalen thrust climbs a steep ramp along the hekla sund – spærregletscher lineament, that is well exposed at the bay marmorvigen (m on fig. 2), is almost continuously exposed along the west side of hekla sund and extends northwards to the east side of brede spærregletscher (bs on fig. 2). west of the ramp, the thrust follows a long flat in the ordovician wandel valley formation, that is continuously exposed along the west side of sæfaxi elv, the river draining into marmorvigen. the > 200 km long vandredalen thrust sheet front has a general ssw–nne trend, and is traceable from west of blåsø through the east end of centrumsø to west of romer sø (fig. 2). this trend line coincides with another ramp that cuts up through the ordovician–silurian platform limestones and dolomites and carries the vandredalen thrust sheet up to overlie silurian turbidites of the lauge koch land formation at present-day exposure levels. the root zone of the vandredalen thrust sheet, along the ssw–nne-trending hekla sund – spærregletscher lineament, coincides approximately with the west margin of the original rift basin (hekla sund basin) in which the rivieradal group succession accumulated (higgins et al. 2001b). geus bulletin 6.pmd 10-02-2005, 09:5443 44 wandel sea basin sequence (post-caledonian) samuelsen høj formation lauge koch land formation odins fjord formation turesø formation wandel valley formation kap holbæk formation crystalline basement thrust fault børglum river and sjælland fjelde formations fyns sø, kap bernhard, campanuladal fms hagen fjord gp rivieradal group independence fjord gp and basaltic formations vandredalen thrust hagen fjord group    vandredalen thrust sheet    ▲ ▲ ▲ ▲ ro m er sø d an m ar k fj or d amdrup land holm land hovgaard ø kap bernhoft dijmphna sund cen tru ms ø s k a l l in g e n syd vej da l rivieradal 20°w 81°n blåsø nio gha lvfje rdsf jord en sæ faxi elv h ek la su nd ingolf fjo rdbs h fl m va nd re da le n ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ 80°n sp t sp t ▲ ▲ c a le d o n id es greenland 25 km geus bulletin 6.pmd 10-02-2005, 09:5444 45 east of the hekla sund – spærregletscher lineament a broad zone of latest palaeoproterozoic to mesoproterozoic clastic and volcanic rocks crops out, and still farther east crystalline basement rocks extend to the eastern coast of kronprins christian land (fig. 2). these broad regions are bounded by steeply inclined shear zones, some of which probably represent major thrusts. the crystalline basement rocks underlying the post-caledonian wandel sea basin succession in the coastal zone incorporate eclogitic enclaves that testify to deep burial during the caledonian orogeny, followed by rapid exhumation (e.g. gilotti & ravna 2002; gilotti et al. 2003). the pronounced ssw–nne lineament that can be traced from hovgaard ø through western holm land to amdrup land, is generally not well exposed, but appears to have a complex history. this feature is often viewed as a northward continuation, or a splay, of the major, sinistral, storstrømmen shear zone, described from hertugen af orléans land (78°n) by strachan & tribe (1994). the latest movements on the lineament in kronprins christian land are post-caledonian, with eastward downthrow of the wandel sea basin succession. however, in southern hovgaard ø and lambert land jones & escher (1995) record a series of late caledonian ductile shear zones along the lineament, that preserve evidence of both sinistral and east-side-up displacement. in lambert land these shear zones post-date foreland-propagating thrust-stacking events, that place thrust sheets of high-grade crystalline gneisses (with eclogitic enclaves) above thrust sheets comprising independence fjord group sandstones. it is considered likely that the high grade basement gneisses of hovgaard ø and holm land form part of major, thick-skinned thrust sheets that once projected westwards, structurally above the strongly sheared and folded independence fjord group west of the hovgaard ø – amdrup land lineament (see also fig. 5). stratigraphy the autochthonous and parautochthonous foreland comprises thick latest palaeoproterozoic to mesoproterozoic successions (hekla sund formation, aage berthelsen gletscher formation, independence fjord group, zig-zag dal basalt formation) and associated mafic intrusions (midsommersø dolerite formation); see also sønderholm & jepsen (1991). these are overlain by neoproterozoic shelf sediments (hagen fjord group: comprising the jyske ås, campanuladal, kap bernhard and fyns sø formations). there is a hiatus between the fyns sø formation dolostones and the overlying sandstones of the kap holbæk formation with local developments of palaeokarst (smith et al. 1999). another hiatus occurs between the kap holbæk formation (early cambrian) and the overlying ordovician–silurian carbonate and siliciclastic rocks. the neoproterozoic rivieradal group is represented only in the allochthonous vandredalen thrust sheet, and its deposition can be linked to an episode of extensional rifting (higgins et al. 2001b). all these units were involved to some extent in the caledonian folding and thrusting, but in the thin-skinned parautochthonous belt the thrusts are essentially confined to the ordovician–silurian sequence. the best exposed sections through the thin-skinned thrust belt follow the sides of centrumsø and the valleys which branch off the west end of this lake. this is the only area where there is sufficient relief and ground control to permit reconstruction of a restorable section (see below). other good partial sections occur in valleys to the north and south. the extensive plateau areas between valleys are often poorly exposed, and here mapping was carried out by spot checks of the sporadic exposures, supplemented by sampling and conodont studies (rasmussen & smith 2002). the main formations represented on the maps and cross-sections are listed in fig. 3, and are briefly described below. hekla sund formation, aage berthelsen gletscher formation, independence fjord group, midsommersø dolerite formation, zig-zag dal basalt formation with the exception of the tholeiitic basalts of the hekla sund formation and aage berthelsen gletscher formation, the type areas of these proterozoic divisions were established on the caledonian foreland west of facing page: fig. 2. geological map of southern and central kronprins christian land. the frame outline centred on centrumsø indicates the position of the cross-section and geological map presented in fig. 4; the extension of the section line beyond the frame is that of the cross-section in fig. 5. the lineament traceable from hovgaard ø through western holm land to amdrup land, marked by a dashed line, has a complex history (see text). bs, brede spærregletscher; fl, finderup land; h, hjørnegletscher; m, marmorvigen; spt, spærregletscher thrust. modified from higgins et al. (2001a). geus bulletin 6.pmd 10-02-2005, 09:5445 46 danmark fjord (sønderholm & jepsen 1991). the independence fjord group comprises a more than 2 km thick succession of mainly clastic alluvial deposits, dominantly white-weathering quartzitic sandstones (collinson 1980, 1983). the midsommersø dolerite formation consists of the widespread doleritic sheets, sills and dykes which invade the independence fjord group sandstones (jepsen 1971; kalsbeek & jepsen 1983). the zig-zag dal basalt formation comprises at least 1350 m of lava flows which overlie the independence fjord group (jepsen et al. 1980; kalsbeek & jepsen 1984); they are considered to be the extrusive equivalents of the midsommersø dolerite formation. highly deformed quartzitic sandstones, doleritic dykes and basaltic lava sequences which crop out in the alpine region of eastern kronprins christian land within the caledonian orogenic belt have traditionally been regarded as equivalents of the foreland divisions. however, the survey’s regional mapping revealed that the basaltic sequences found in the thrust complexes of kronprins christian land do not overlie the independence fjord group, but are interbedded with the lower levels of the quartzite succession. these basalfig. 3. summary stratigraphic scheme of proterozoic and palaeozoic units depicted on the maps, and their relationships to iapetus opening (modified from smith et al. 1999). non-deposition or erosion is depicted by vertical ruling. silurian ordovician cambrian vendian sturtian riphean lauge koch land formation samuelsen høj formation odins fjord formation turesø formation børglum river formation sjælland fjelde formation wandel valley formation kap holbæk formation hagen fjord group fyns sø fm kap bernhard fm campanuladal fm jyske ås fm zig-zag dal basalt formation independence fjord group hekla sund fm, aage berthelsen gletscher fm, & interbedded quartzites thermal subsidence extensional rifting and block tilting extensional riftingrivieradal group (allochthonous vandredalen thrust sheet only) post-rift thermal subsidence baltica collision thrust loaded flysch basin tectonic setting depositional environment stratigraphy lapetus passive margin lapetus opening pre-lapetus rift-sag cycle intracratonic extensional events thermal subsidence block tilting zz if hs/ab kh rg    geus bulletin 6.pmd 10-02-2005, 09:5446 47 tic sequences are distinguished as the hekla sund formation and aage berthelsen gletscher formation (pedersen et al. 2002). shrimp isotopic studies on rhyolites of the hekla sund formation yielded an age of 1740 ma (kalsbeek et al. 1999). this result implies that either the age range of the independence fjord group must be extended downwards to the later part of the palaeoproterozoic, or there are two superficially indistinguishable quartzite sequences, of which the older unnamed succession is interbedded with the hekla sund and aage berthelsen gletscher formations. the first alternative is adopted here. quartzitedyke-basalt associations similar to the foreland succession are presumed to underlie the entire parautochthonous region. rivieradal group the succession of sandstones, mudstones, conglomerates and some carbonate rocks first mapped by fränkl (1954, 1955), and assigned by hurst & mckerrow (1981a, b) to a single sequence that they referred to as the ‘rivieradal sandstones’, has been formally defined as the rivieradal group (smith et al. 2004a, this volume). the rivieradal group is restricted to the vandredalen thrust sheet, where it is overlain conformably by units of the hagen fjord group. fränkl had recognised that the neoproterozoic rivieradal group was not represented on the foreland, and introduced the term ‘hekla sund basin’ for its area of deposition. field work by ggu in 1993–1995 demonstrated that the rivieradal group is 7.5–10 km thick. it was also shown that the sediments of the rivieradal group had accumulated in an east-facing, half-graben rift-basin, bounded to the west by extensional faults; this basin was estimated to have been at least 200 km long and 50 km wide (higgins et al. 2001b). during the caledonian orogeny the rivieradal group was displaced westwards across the western margin of the rift basin as the vandredalen thrust sheet. the root zone of this thrust sheet and the remnants of the original rift basin can be traced in a narrow belt through the centre of the alpine region along the hekla sund – spærregletscher lineament (fig. 2). hagen fjord group (and kap holbæk formation) representatives of the hagen fjord group are preserved in the frontal portions of the vandredalen thrust sheet, resting conformably on the rivieradal group. in the foot wall of the vandredalen thrust, as elsewhere in eastern north greenland, the hagen fjord group rests directly on independence fjord group lithologies, locally with an intervening basal clastic unit. the hagen fjord group is thus viewed as a transgressive, post-rift sequence, and its presence in both the hanging wall and foot wall of the vandredalen thrust enables the displacement on the vandredalen thrust to be estimated at 35–50 km (higgins et al. 2001b). the jyske ås formation (fig. 3) at the base of the group occurs only west of danmark fjord in the foreland, and is not considered further here. in the parautochthonous region with which this paper is concerned, four formations are recognised in addition to the basal clastic unit, although the uppermost unit (the kap holbæk formation) is now formally excluded from the hagen fjord group (see below). 1. basal clastic unit. this dominantly conglomeratic unit directly overlies independence fjord group quartzitic sandstones, and is overlain by siltstones and mudstones ascribed to the campanuladal formation. the unit was first recorded at hjørnegletscher (h on fig. 2) on the north side of inner ingolf fjord (jepsen & kalsbeek 1981) where it is a few metres thick. in 1993 two additional developments of the unit, respectively 35 m and 0–60 m thick, were located along the margin of the alpine region north of sæfaxi elv (jepsen et al. 1994). 2. campanuladal formation. dominated by green and red fine-grained sandstones, siltstones and mudstones, it is about 110–175 m thick in the foreland areas west of the head of danmark fjord (clemmensen & jepsen 1992). in the parautochthonous region between inner ingolf fjord and sæfaxi elv, jepsen & kalsbeek (1985) reported 0–80 m of mudstone and sandstone of the formation overlying either the basal conglomeratic unit or the independence fjord group. 3. kap bernhard formation. this comprises reddishbrown limestones with minor amounts of silt, and is about 150 m thick at the head of danmark fjord (clemmensen & jepsen 1992). the formation is up geus bulletin 6.pmd 10-02-2005, 09:5447 48 to 400 m thick in the frontal region of the vandredalen thrust sheet. 4. fyns sø formation. at its type locality at the head of danmark fjord (craig & jepsen 1995), it is made up of 356 m of spectacular, cliff-forming, yellowweathering dolostones, characteristically preserving well-formed stromatolites. a similar thickness (~ 400 m) is seen in both the foot wall and the hanging wall of the vandredalen thrust. 5. kap holbæk formation. this was originally the upper formation of the hagen fjord group (clemmensen & jepsen 1992). recognition that the formation is early cambrian, and that the hiatus between it and the underlying fyns sø formation covers the entire vendian (fig. 3), led smith et al. (2004b, this volume) to formally exclude it from the hagen fjord group. the formation was recognised in the parautochthonous belt in the inner parts of ingolf fjord in 1994 (jepsen & sønderholm 1994), and here is up to 180 m thick; it comprises variegated mudstones at the base overlain by a light and dark coloured sandstone succession. sandstone-filled fissures and cave-like lenses in the upper surface of the underlying fyns sø formation, first recorded by fränkl (1954, 1955), have been interpreted as palaeokarst (smith et al. 1999). the kap holbæk formation was recognised in the hanging wall of the vandredalen thrust by hurst & mckerrow (1981a, b), who placed it in their ‘finderup land nappe’. lower palaeozoic platform the lower palaeozoic platform strata of eastern north greenland are the easternmost representatives of the franklinian basin succession, which is exposed in a broad, 900 km long belt across north greenland (higgins et al. 1991). the earliest lower palaeozoic platform strata in the parautochthonous belt of eastern kronprins christian land are the early ordovician limestones and dolostones of the wandel valley formation (rasmussen & smith 1996; smith et al. 2004b, this volume), which rest unconformably on the fyns sø formation or kap holbæk formation. uplift of eastern north greenland and subsequent erosion have resulted in a progressive overstep of the early ordovician from west to east across north greenland (peel & smith 1988). there is also a north–south component to the overstep, since south of kronprins christian land, in lambert land, the hagen fjord group is missing and the wandel valley formation rests directly on independence fjord group lithologies (smith et al. 1999; smith 2000). a fuller stratigraphical description of the lower palaeozoic platform limestone and dolostone succession is given by smith et al. (2004b, this volume). the following formations are distinguished on the maps and cross-sections of this paper. 1. wandel valley formation (upper ibexian – middle whiterockian). three limestone and dolostone members are present in the parautochthonous belt, all very similar in their development to their counterparts on the foreland around danmark fjord, and with a total thickness of about 335 m. 2. sjælland fjelde formation (upper whiterockian). about 100 m thick, it is divided into a lower dark grey burrow-mottled limestone and dolostone unit and an upper grey dolostone unit. the vandredalen thrust follows a long flat in the middle part of the formation, well seen along the west side of sæfaxi elv, before climbing a ramp to another flat in the upper dolomite unit. near the head of ingolf fjord, about 70 km to the north, the vandredalen thrust occupies the same stratigraphic level. 3. børglum river formation (mohawkian – upper cincinatian). the formation is widespread in the parautochthonous belt, where it comprises a thick succession of dominantly dark, nodular, burrowmottled limestones with abundant fossils. a complete section through the unit is not seen in the parautochthonous belt, but is probably close to the thickness of 430 m measured in the autochthonous foreland areas further to the north-west (smith et al. 1989). facing page: fig. 4. geological map and restored cross-section of the thinskinned thrust belt in the centrumsø region. a: geological map and location of section line; see also frame in fig. 2. base camp indicated by filled triangle. b: cross-section with calculated displacements on individual thrusts in kilometres (e.g. 2.75) based on a line and area balance; only the sjælland fjelde formation is given a distinctive ornament, with other formations indicated by two-letter abbreviations (see legend on map of fig. 4a). note the gently eastwardsdipping floor thrust at the base of the wandel valley formation. c: model section with thrusts restored; note reproduced at a smaller scale than the cross-section in b. in both b and c the thrusts are indicated by thicker lines. geus bulletin 6.pmd 10-02-2005, 09:5448 4 9 ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ce nt ru m sø section line 0 5 km 0 5 km 0 5 km n lauge koch land odins fjord turesø sjælland fjelde fyns sø kap bernhard rivieradal group thrust lk of tu br sf fs wv wv kb rg wandel valley børglum river ▲ ▲ base camp a b c lk of of tu br wv lk tu tu br br br br br wv wv br wv lk of tu lk lk of lk lk of oftu tubr br fs kb rg wv br of tu tu wv 0.05 0.55 0.4 0.9 0.95 0.751.8 1.0 2.85 5.4 km 1.0 km 2.75 2.75 4.9 0.8 9.15 km 8.45 km 22.4 km g e u s b u lle tin 6 .p m d 1 0 -0 2 -2 0 0 5 , 0 9 :5 4 4 9 50 4. turesø formation (upper cincinnatian – lower llandovery). the formation spans the ordovician– silurian boundary (armstrong 1990), and where measured 7 km west of centrumsø comprises about 200 m of variably coloured dolostones and limestones (see fig. 6a). the colour variations make the formation conspicuous and easily recognisable. towards the eastern end of centrumsø, just west of the vandredalen thrust sheet front, the formation thickens to at least 350 m; here trains of tight folds are developed in the dolostone-dominated intervals (see fig. 6b). 5. odins fjord formation (mid-llandovery). the formation is widely exposed in southern kronprins christian land close to the vandredalen thrust sheet front, where it is at least 220 m thick, although deformation and poor exposure make this estimate uncertain. christie & peel (1977) estimated a thickness of 320 m in south-east peary land. the transition from the underlying turesø formation is marked by a change in colour from pale grey to pale brown, and in lithology from dolostone to limestone rich in tabulate corals and stromatoporoids. 6. samuelsen høj formation (upper llandovery). developed as conspicuous reefs, the formation is represented by several major bodies in northern kronprins christian land; those in southern areas are generally smaller and mainly occur in a belt just west of the vandredalen thrust sheet front (fig. 2). only one small body is known south of centrumsø, and there are none in the line of section (fig. 4). 7. lauge koch land formation (uppermost llandovery – wenlock). the silurian flysch of kronprins christian land was assigned by hurst & surlyk (1982) to fränkl’s ‘profilfjeldet shales’, which was given member rank within the lauge koch land formation. the sequence is widely involved in the major thrusts of northern kronprins christian land, where a maximum thickness of 400 m was estimated (hurst & surlyk 1982). further south the formation crops out mainly in a zone just west of the vandredalen thrust sheet front. only two thrust-bounded inliers occur south of centrumsø; here the lower 50 m of the formation is characterised by black shaly siltstones interbedded with dark grey to black bituminous and nodular carbonate rocks (smith et al. 2004b, this volume). structure the most important thrusts within the 30–50 km wide thin-skinned thrust belt of kronprins christian land are depicted in figs 2 and 4. they make up a major imbricate stack beneath a former extension of the vandredalen thrust sheet. individual thrusts dip eastwards at angles varying from about 30° to 70°, although the steeper thrusts appear to represent over-steepening arising from further thrust displacement in the foot wall succession. many thrusts can be followed for several tens of kilometres, some for as much as 75 km along strike. major folding accompanied the thrusting, although this is normally conspicuous only in certain formations. about 25 km south of centrumsø several major thrusts die out. further south, only one major thrust has been traced for 30 km west of the vandredalen thrust front, and this divides into two thrusts west of blåsø (fig. 2). all the ordovician–silurian stratigraphic units from the wandel valley formation to the lauge koch land formation are involved in the thrusting. individual thrust movements range from a few hundred metres to several kilometres. despite topographic relief of 1000 m, matching foot wall and hanging wall cut-offs are rarely observed. estimates of thrust displacements therefore rely on the construction of a restorable crosssection. the best exposed sections are, in the north, the valley system west of romer sø (described by peel 1980) and, in the south, the valley system containing centrumsø with which this paper is mainly concerned. a restorable cross-section through the centrumsø area constructed perpendicular to the thrust trends is presented in fig. 4. prior to attempting to restore the cross-section, a series of cross-sections (not reproduced here) were constructed along profile lines north and south of centrumsø to gain an impression of the possible range of displacements. the section line of fig. 2 was chosen because of the excellent exposures on the cliff walls north and south of the lake, and because of the generally good ground control. initial section construction was at a scale of 1:50 000, on the basis of enlarged copies of the survey’s 1:100 000 topographic maps. thrust trajectories and fold shapes were projected into the line of section using the best available thickness estimates for formations as noted above. the maximum observed thickness estimate of 400 m for the lauge koch land formation was used. in respect of the turesø formation, the 200 m thickness was used in the west, and 350 m in the eastern part of the section. geus bulletin 6.pmd 10-02-2005, 09:5450 51 balancing was attempted initially assuming that a single floor thrust in the parautochthonous belt followed the base of the børglum river formation (as the wandel valley and sjælland fjelde formations were not visibly involved in the thrusting along the line of profile). however, all attempts at a balance with this constraint produced an unrealistic undulating floor thrust (not illustrated here). the floor thrust was then reassigned downwards to the base of the wandel valley formation with, in addition, a major thrust at the base of the børglum river formation. this change is justified on the grounds that: (1) the wandel valley and sjælland fjelde formations are both involved in the thrusting in northern kronprins christian land (see fig. 1 in peel 1980); (2) along sæfaxi elv, immediately north of the eastward extension of the centrumsø cross-section, several highly disturbed bedding-parallel shear zones were observed near the base of the wandel valley formation. the restoration of the centrumsø cross-section achieved on this basis (fig. 4b), exhibits a very gentle eastward inclination for the floor thrust at the base of the wandel valley formation. in this model all the thrusts west of the end of centrumsø root into the floor thrust, whereas the thrusts exposed along the margins of centrumsø all root into the slightly higher flat thrust following the base of the børglum river formation. the section restoration presented in fig. 4 involved resolution of several problems. at the west end of the section there is a very broad mapped expanse of børglum river formation between two observed major thrusts (see map fig. 4a). the 4.5 km long valley section shows the sequence dipping at moderate angles eastwards, with locally some dislocation and associated folding. however, since the maximum thickness of the børglum river formation is probably about 430 m, restoration could only be achieved assuming the formation to be repeated in a duplex with displacements of 400–1800 m on the individual thrusts. the positions of the duplex thrusts were not identified during the field work, mainly because the significance of the over-thickened section was not appreciated; thus, while depicted on the cross-sections (fig. 4b, c), these thrusts are not shown on the map (fig. 4a). a further problem concerned a long central segment of the cross-section which exhibits a syncline at the west end (see fig. 6a) and a broad flat anticline in the centre with the lowest levels of the børglum river formation exposed at valley level. this could only be satisfactorily accommodated by introducing a ramp duplicating the wandel valley and sjælland fjelde formations over a distance of 5.4 km (central part of section in fig. 4b). in the cliff north of the base camp at the west end of centrumsø, a long flat thrust brings the børglum river formation above a thin sequence of the turesø formation. south of centrumsø the same thrust changes levels and takes the turesø formation above the odins fjord formation on an equally long flat thrust. similar long thrust flats are interpreted to exist at the eastern end of the section, with the largest displacement on an individual thrust estimated at 4.9 km. intense folding at the eastern end of the section, just west of the vandredalen thrust sheet front (see fig. 6b), and the implications of such internal distortion in other parts of the section, cannot be accurately depicted. total displacement on the basis of the model restoration in fig. 4b is estimated at 17.6 km. the thrusts depicted in the east part of the section along centrumsø have a total displacement of 8.45 km rooting into the thrust at the base of the børglum river formation, which merges with the vandredalen thrust at the vandredalen thrust front. the thrusts west of centrumsø root into a floor thrust following the base of the wandel valley formation and have an estimated total of 9.15 km displacement; this thrust merges with the vandredalen thrust east of the line of section in the vicinity of marmorvigen (fig. 2). the restoration implies that an original 43 km wide segment of the parautochthonous belt has been reduced to about 25.4 km in the line of section, a shortening of approximately 45%. the restored section depicted in fig. 4b demonstrates that the model chosen is realistic. it invokes only two major flat thrusts, both of which merge eastwards with the vandredalen thrust. conodont geothermometry epstein et al. (1977) demonstrated that colour variations of conodont elements are principally related to temperature. they erected a scale of conodont alteration indices (cai 1–5) ranging from pale yellow through shades of brown to black, corresponding to a temperature range from < 50°–300°c. higher alteration indices (cai 6–8), in which the conodont elements progressed from black through grey to white, were calibrated by rejebian et al. (1987) as corresponding to a temperature range from 300°c to over 600°c. a regional description of conodont geothermometry geus bulletin 6.pmd 10-02-2005, 09:5451 52 in the kronprins christian land area has been presented by rasmussen & smith (2001). conodonts studied in kronprins christian land were recovered from stratigraphic units ranging in age from mid-early ordovician (wandel valley formation) to llandovery (lauge koch land formation). lithologies varied from unaltered platform dolostones and limestones to their highly sheared equivalents underlying the vandredalen thrust sheet. whereas the degree of internal shearing and deformation had a significant effect on the morphological character of the conodont elements, it had no apparent effect on the colour alteration indices. the cai isothermal zones run parallel to the thrust trends and the vandredalen thrust sheet front in southern kronprins christian land. cai values of 2–3 were seen west of danmark fjord. a broad zone of cai 3 extends eastwards to approximately the west limit of the cross-section in fig. 4. most of the cross-section is within the zone of cai 4, rising to cai 5 at the eastern end adjacent to the front of the vandredalen thrust sheet. the limestones and dolostones beneath the vandredalen thrust sheet, exposed along sæfaxi elv, are in cai zone 5 increasing to cai 5–6 in the easternmost exposures at marmorvigen. the cai temperatures indicate the maximum thickness of the caledonian overburden, comprising the vandredalen thrust sheet and possible higher thrust units. the thickness was determined from estimates of geothermal gradients and the thermal conductivity of the rock units involved (see rasmussen & smith 2001, for details). the results imply that the approximate thickness of the maximum overburden in the area of the cross-section (fig. 5), ranged from about 6 km at the west end of the cross-section to 10.7 km farther east at the front of the vandredalen thrust sheet (fig. 6c). the highest cai values at marmorvigen point to an overburden of 12.5 km (rasmussen & smith 2001). the assumed extent and thickness of the vandredalen thrust sheet formerly present above the parautochthonous zone are also indicated in fig. 5. the hagen fjord group in the hanging wall exhibits a cut-off against the vandredalen thrust along much of the vandredalen thrust sheet front on the west side of vandredalen. thus, the former extent of the vandredalen thrust sheet across the parautochthonous zone must have consisted essentially of a packet of ordovician–silurian carbonate and siliciclastic rocks. the thickness of this packet was probably not much greater than 2 km (fig. 5). the only uncertainty in this estimation of the thickness concerns the contribution of turbidites of the lauge koch land formation. a maximum thickness of 400 m has been assumed for this unit in the cross-section, being the maximum thickness preserved in present-day exposures (hurst & surlyk 1982). the silurian turbidites of north greenland were derived from erosion of the rising caledonian mountain chain. the thickness of the turbidite succession that may have accumulated in the western part of present kronprins christian land before it was over-ridden by the westward-propagating caledonian thrust sheets is unknown. between 3 and 10 km of additional overburden above the vandredalen thrust 0 km 5 0 22 km 6 km 12.5 km 50 km ? 100 km ? or d.– sil st 18 km wsw ese vt spt 50 km e s t i m at e d ov e r b u r d e n f r o m c o n o d o n t a lt e r at i o n ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ crystalline basement rivieradal group hagen fjord group ordovician – silurian independence fjord group and associated volcanics fig. 5. simplified cross-section through the caledonian fold belt in kronprins christian land, from higgins et al. (2001b); for section line see fig. 2. the maximum overburden deduced from conodont alteration indices (indicative of eastward increase in temperature) is also shown. spt, spærregletscher thrust; st, caledonian sole thrust; vt, vandredalen thrust. geus bulletin 6.pmd 10-02-2005, 09:5452 53 of of tu tu rg vt a b c fig. 6. a: syncline in line of cross-section looking north, 7 km west of the centrumsø base camp. of, odins fjord formation; tu, turesø formation. cono-donts have cai values of 4, indicative of a former overburden of about 6.8 km. summit at centre is 500 m above the valley floor. photo: j. lautrup. b: intense folding in variegated dolomites of the turesø formation (tu). north side of centrumsø, about 3 km west of the vandredalen thrust front. conodonts have cai values of 4–5, indicative of an overburden of about 8–9 km. plateau is about 750 m above the lake level (foreground). photo: j. lautrup. c: outlier of rivieradal group (rg) conglomerates and sandstones in the vandredalen thrust sheet, overlying ordovician carbonates of the odins fjord formation (of) on the west side of vandredalen. the vandredalen thrust (vt) follows the marked discordance. conodonts from the carbonates of the odins fjord formation have cai values of 5, indicative of a former overburden of about 10.7 km. summit is 850 m above the valley floor in the foreground. geus bulletin 6.pmd 10-02-2005, 09:5453 54 sheet would be required to reach the temperatures demonstrated by the conodont alteration pattern, and it is considered unlikely that this can be accounted for by substantially increasing only the contribution of the lauge koch land formation turbidites. it is more probable that higher, westward-propagating thrust sheets were formerly present above the vandredalen thrust sheet. these are likely to have comprised units such as the independence fjord group quartzitic sandstones with associated dolerite dykes and sills, and the hekla sund formation basalts (representatives of which crop out in the mountainous region east of the hekla sund – spærregletscher lineament). these units would have been transported westwards on the spærregletscher thrust (spt in figs 2, 5). lower palaeozoic formations may also have been present in the proximal parts of this thrust sheet. all the cai zones are based on sample collections from the parautochthonous zone structurally underlying the vandredalen thrust sheet. this zone is part of a thin-skinned thrust belt, and therefore the most likely setting to account for the increased temperatures would be burial of the parautochthonous zone beneath a pile of westward-directed caledonian thrust sheets. allowing for subsidence of the parautochthonous zone that resulted from the weight of the overlying thrust burden, the thrust sheets must still have made up a substantial mountain chain, increasing in altitude eastwards where summits may have attained altitudes of about 3–4 km. conclusions the rock units which constitute the up to 50 km wide thin-skinned thrust belt west of the vandredalen thrust front extend westwards into undisturbed foreland. the thrust belt is therefore viewed as parautochthonous. the deformation associated with the eastward-dipping thrusts of the parautochthonous zone involves only ordovician–silurian rock units and is essentially thinskinned in style. a line-and-area restoration along the best exposed section through the thrust belt, i.e. along centrumsø and adjacent valleys, can be achieved assuming that the observed thrusts root into two flat thrusts. one is depicted as the caledonian floor or sole thrust, in this region located at the base of the wandel valley formation; the second slightly higher thrust is assumed to lie at the base of the børglum river formation. both thrusts are assumed to merge eastwards with the vandredalen thrust. total displacement of 17.6 km on the two flat thrusts in the model restoration implies that an original 43 km wide segment of the parautochthonous belt has been reduced to 25.4 km, a shortening of 45% in the line of section. the colour changes experienced by conodont elements reflect variations in temperature which can be linked to the maximum thickness of overburden during the caledonian orogeny. overburden estimates increase systematically from 6 km at the west end of the cross-section to 10.7 km at the vandredalen thrust front, and farther east to 12.5 km at marmorvigen (fig. 5). as the vandredalen thrust sheet overlying the parautochthonous zone was probably not much more than 2 km thick, the remainder of the estimated overburden must have comprised higher thrust sheets, since eroded, that projected westwards across the parautochthonous belt. acknowledgements the field and conodont studies of j.a.r. were financially supported by the carlsberg foundation (grant no. 950164/20-1292). the helpful comments of the two reviewers, robin strachan and brian chadwick, are gratefully acknowledged. references armstrong, h.a. 1990: conodonts from the upper ordovician – lower silurian carbonate platform of north greenland. bulletin grønlands geologiske undersøgelse 159, 151 pp. brueckner, h.k., gilotti, j.a. & nutman, a.p. 1998: caledonian eclogite-facies metamorphism of early proterozoic protoliths from the north-east greenland eclogite province. contributions to mineralogy and petrology 130, 103–120. christie, r.l. & peel, j.s. 1977: cambrian–silurian stratigraphy of børglum elv, peary land, eastern north greenland. rapport grønlands geologiske undersøgelse 82, 48 pp. clemmensen, l.b. & jepsen, h.f. 1992: lithostratigraphy and geological setting of upper proterozoic shoreline-shelf deposits, hagen fjord group, eastern north greenland. rapport grønlands geologiske undersøgelse 157, 27 pp. collinson, j.d. 1980: stratigraphy of the independence fjord group (proterozoic) of eastern north greenland. rapport grønlands geologiske undersøgelse 99, 7–23. collinson, j.d. 1983: sedimentology of unconformities within a fluvio-lacustrine sequence; middle proterozoic of eastern north greenland. sedimentary geology 34, 145–166. craig, l.e. & jepsen, h.f. 1995: late proterozoic hagen fjord group: stratigraphic relationships between the fyns sø forgeus bulletin 6.pmd 10-02-2005, 09:5454 55 mation and kap holbæk formation – including a new reference section through the fyns sø formation. in: higgins, a.k. (ed.): express report: eastern north greenland and northeast greenland 1995, 53–57. unpublished report, geological survey of greenland, copenhagen. dallmeyer, r.d. & strachan, r.a. 1994: 40ar/39ar mineral age constraints on the timing of deformation and metamorphism, north-east greenland caledonides. in: higgins, a.k. (ed.): geology of north-east greenland. rapport grønlands geologiske undersøgelse 162, 153–162. dallmeyer, r.d., strachan, r.a. & henriksen, n. 1994: 40ar/39ar mineral age record in ne greenland: implications for tectonic evolution of the north atlantic caledonides. journal of the geological society (london) 151, 615–628. epstein, a.g., epstein, j.b. & harris, l.d. 1977: conodont color alteration – an index to organic metamorphism. professional paper united states geological survey 995, 27 pp. fränkl, e. 1954: vorläufige mitteilung über die geologie von kronprins christians land (ne-grönland, zwischen 80°–81°n und 19°–23°w). meddelelser om grønland 116(2), 85 pp. fränkl, e. 1955: weitere beiträge zur geologie von kronprins christians land (ne-grönland, zwischen 80° und 80°30′n). meddelelser om grønland 103(7), 35 pp. gilotti, j.a. & ravna, e.j.k. 2002: first evidence for ultrahighpressure metamorphism in the north-east greenland caledonides. geology 30, 551–554. gilotti, j.a., nutman, a.p, brueckner, h.k. & mcclelland, w.c. 2003: devonian collision along the northeastern margin of laurentia, greenland caledonides. geological society of america: abstracts with programs 35, n. 3. henriksen, n. (ed.) 1994a: express report: eastern north greenland and north-east greenland 1994, 126 pp. unpublished report, geological survey of greenland, copenhagen. henriksen, n. 1994b: eastern north greenland 1993–1995 – a new 1:500 000 mapping project. rapport grønlands geologiske undersøgelse 160, 47–51. henriksen, n. 1995: eastern north greenland 1994, the 1:500 000 mapping project. rapport grønlands geologiske undersøgelse 165, 53–58. henriksen, n. 1996: conclusion of the 1:500 000 field mapping in eastern north greenland. bulletin grønlands geologiske undersøgelse 172, 42–48. higgins, a.k. 1988: the krummedal supracrustal sequence in east greenland. in: winchester, j.a. (ed.): later proterozoic stratigraphy of the northern atlantic regions, 86–96. glasgow & london: blackie and son ltd. higgins, a.k. (ed.) 1995: express report: eastern north greenland and north-east greenland 1995, 171 pp. unpublished report, geological survey of greenland, copenhagen. higgins, a.k., ineson, j.r., peel, j.s., surlyk, f. & sønderholm, m. 1991: lower palaeozoic franklinian basin of north greenland. in: peel, j.s. & sønderholm, m. (eds): sedimentary basins of north greenland. bulletin grønlands geologiske undersøgelse 160, 71–139. higgins, a.k., leslie, a.g., smith, m.p. & rasmussen, j.a. 2001a: neoproterozoic – lower palaeozoic stratigraphical relationships in the marginal thin-skinned thrust belt of the east greenland caledonides: comparisons with the foreland in scotland. geological magazine 138(2), 143–160. higgins, a.k., soper, n.j., leslie, a.g., smith, m.p., rasmussen, j.a. & sønderholm, m. 2001b: the neoproterozoic hekla sund basin, eastern north greenland: a pre-iapetan extensional sequence thrust across its rift shoulders during the caledonian orogeny. journal of the geological society (london) 158, 487–489. hurst, j.m. & mckerrow, w.s. 1981a: the caledonian nappes of eastern north greenland. nature, london 290, 772–774. hurst, j.m. & mckerrow, w.s. 1981b: the caledonian nappes of kronprins christian land, eastern north greenland. rapport grønlands geologiske undersøgelse 106, 15–19. hurst, j.m. & mckerrow, w.s. 1985: origin of the caledonian nappes of north-east greenland. in: gee, d.g. & sturt, b.a. (eds): the caledonide orogen – scandinavia and related areas, 1065–1069. chichester: john wiley & sons. hurst, j.m. & surlyk, f. 1982: stratigraphy of the silurian turbidite sequence of north greenland. bulletin grønlands geologiske undersøgelse 145, 121 pp. jepsen, h.f. 1971: the precambrian, eocambrian and early palaeozoic stratigraphy of the jørgen brønlund fjord area, peary land, north greenland. meddelelser om grønland 192(2), 42 pp. jepsen, h.f. & kalsbeek, f. 1981: non-existence of the carolinidian orogeny in the prinsesse caroline-mathilde alper of kronprins christian land, eastern north greenland. rapport grønlands geologiske undersøgelse 106, 7–14. jepsen, h.f. & kalsbeek, f. 1985: evidence for non-existence of a carolinidian fold belt in eastern north greenland. in: gee, d.g. & sturt, b.a. (eds): the caledonide orogen – scandinavia and related areas, 1071–1076. chichester: john wiley & sons. jepsen, h.f. & kalsbeek, f. 1998: granites in the caledonian fold belt of east greenland. in: higgins, a.k. & frederiksen, k.s. (eds): caledonian geology of east greenland 72°–74°n: preliminary reports from the 1997 expedition. danmarks og grønlands geologiske undersøgelse rapport 1998/28, 73–82. jepsen, h.f. & sønderholm, m. 1994: sedimentological studies of the hagen fjord group and ‘rivieradal sandstones’ (late proterozoic), eastern north greenland. in: henriksen, n. (ed.): express report: eastern north greenland and north-east greenland 1994, 39–48. unpublished report, geological survey of greenland, copenhagen. jepsen, h.f., kalsbeek, f. & suthren, r.j. 1980: the zig-zag dal basalt formation, north greenland. rapport grønlands geologiske undersøgelse 99, 25–32. jepsen, h.f., escher, j.c., friderichsen, j.d. & higgins, a.k. 1994: the geology of the north-eastern corner of greenland – photogeological studies and 1993 field work. rapport grønlands geologiske undersøgelse 151, 21–33. jones, k.a. & escher, j.c. 1995: an e–w traverse across the caledonian fold belt from lambert land to norske øer. in: higgins, a.k. (ed.): express report: eastern north greenland and north-east greenland 1995, 23–41. unpublished report, geological survey of greenland, copenhagen. kalsbeek, f. & jepsen, h.f. 1983: the midsommersø dolerites geus bulletin 6.pmd 10-02-2005, 09:5455 56 and associated intrusions in the proterozoic platform of eastern north greenland – a study of the interaction between intrusive basic magma and sialic crust. journal of petrology 24, 605–634. kalsbeek, f. & jepsen, h.f. 1984: the late proterozoic zig-zag dal basalt formation of eastern north greenland. journal of petrology 25, 644–664. kalsbeek, f., nutman, a.p. & taylor, p.n. 1993: palaeoproterozoic basement province in the caledonian fold belt of northeast greenland. precambrian research 63, 163–178. kalsbeek, f., nutman, a.p., escher, j.c., friderichsen, j.d., hull, j.m., jones, k.a. & pedersen, s.a.s. 1999: geochronology of granitic and supracrustal rocks from the northern part of the east greenland caledonides: ion microprobe u-pb zircon ages. geology of greenland survey bulletin 184, 31–48. kalsbeek, f., thrane, k., nutman, a.p. & jepsen, h.f. 2000: late mesoproterozoic metasedimentary and granitic rocks in the kong oscar fjord region, east greenland caledonian fold belt: evidence for grenvillian orogenesis? journal of the geological society (london) 157, 1215–1225. kalsbeek, f., jepsen, h.f. & nutman, a.p. 2001a: from source migmatites to plutons: tracking the origin of c. 435 ma granites in the east greenland caledonian orogen. lithos 57, 1– 21. kalsbeek, f., jepsen, h.f. & jones, k.a. 2001b: geochemistry and petrogenesis of s-type granites in the east greenland caledonides. lithos 57, 91–109. leslie, a.g. & nutman, a.p. 2000: episodic tectono-thermal activity in the southern part of the east greenland caledonides. geology of greenland survey bulletin 186, 42–49. leslie, a.g. & nutman, a.p. 2003: evidence for neoproterozoic orogenesis and early high temperature scandian deformation events in the southern east greenland caledonides. geological magazine 140, 309–333. pedersen, s.a.s., craig, l.e., upton, b.g.j., rämö, o.t., jepsen, h.f. & kalsbeek, f. 2002: palaeoproterozoic (1740 ma) riftrelated volcanism in the hekla sund region, eastern north greenland: field occurrence, geochemistry and tectonic setting. precambrian research 114, 327–346. peel, j.s. 1980: geological reconnaissance in the caledonian foreland of eastern north greenland with comments on the centrum limestone. rapport grønlands geologiske undersøgelse 99, 61–72. peel, j.s. & smith, m.p. 1988: the wandel valley formation (early– middle ordovician) of north greenland and its correlatives. in: peel, j.s. (ed.): cambrian–jurassic fossils, trace fossils and stratigraphy from greenland. rapport grønlands geologiske undersøgelse 137, 61–92. rasmussen, j.a. & smith, m.p. 1996: lower palaeozoic carbonates in eastern north greenland, and the demise of the ‘sæfaxi elv nappe’. bulletin grønlands geologiske undersøgelse 172, 49–54. rasmussen, j.a. & smith, m.p. 2001: conodont geothermometry and tectonic overburden in the northernmost east greenland caledonides. geological magazine 138, 687–698. rejebian, v.a., harris, a.g. & huebner, j.s. 1987: conodont color and alteration. an index to regional metamorphism, contact metamorphism and hydrothermal alteration. bulletin geological society of america 99, 471–479. smith, m.p. 2000: cambro-ordovician stratigraphy of bjørnøya and north greenland: constraints on tectonic models for the arctic caledonides and the tertiary opening of the greenland sea. journal of the geological society (london) 157, 459–470. smith, m.p., sønderholm, m. & tull, s.j. 1989: the morris bugt group (middle ordovician – silurian) of north greenland and its correlatives. rapport grønlands geologiske undersøgelse 143, 5–20. smith, m.p., soper, n.j., higgins, a.k., rasmussen, j.a. & craig, l.e. 1999: palaeokarst systems in the neoproterozoic of eastern north greenland in relation to extensional tectonics on the laurentian margin. journal of the geological society (london) 156, 113–124. smith, m.p., higgins, a.k., soper, n.j. & sønderholm, m. 2004a: the neoproterozoic rivieradal group of kronprins christian land, eastern north greenland. in: higgins, a.k. & kalsbeek, f. (eds): east greenland caledonides: stratigraphy, structure and geochronology. geological survey of denmark and greenland bulletin 6, 29–39 (this volume). smith, m.p., rasmussen, j.a., robertson, s., higgins, a.k & leslie a.g. 2004b: lower palaeozoic stratigraphy of the east greenland caledonides. in: higgins, a.k. & kalsbeek, f. (eds): east greenland caledonides: stratigraphy, structure and geochronology. geological survey of denmark and greenland bulletin 6, 5–28 (this volume). sønderholm, m. & jepsen, h.f. 1991: proterozoic basins of north greenland. in: peel, j.s. & sønderholm, m. (eds): sedimentary basins of north greenland. bulletin grønlands geologiske undersøgelse 160, 49–69. steiger, r.h., hansen, b.t., schuler, c., bär, m.t. & henriksen, n. 1979: polyorogenic nature of the southern caledonian fold belt in east greenland. journal of geology 87, 475–495. strachan, r.a. & tribe, i.r. 1994: structure of the storstrømmen shear zone, eastern hertugen af orléans land, north-east greenland. in: higgins, a.k. (ed.): geology of north-east greenland. rapport grønlands geologiske undersøgelse 162, 103–112. watt, g.r., kinny, p.d. & friderichsen, j.d. 2000: u-pb geochronology of neoproterozoic and caledonian tectonothermal events in the east greenland caledonides. journal of the geological society (london) 157, 1031–1048. geus bulletin 6.pmd 10-02-2005, 09:5456 geological survey of denmark and greenland bulletin 1, 9-20 9 the jurassic of denmark is mainly known from subsurface data including numerous boreholes and a dense net of seismic lines in the offshore areas. exceptions to this include the island of bornholm in the baltic sea and adjacent areas of skåne, southern sweden, where the jurassic is exposed in many small outcrops. the jurassic of greenland, in contrast, can be studied in extensive outcrops and the succession forms the walls and tops of mountains and plateaus over wide areas. the two regions were once part of the same large-scale system of extensional basins in the northwest european – north atlantic region (fig. 1), but are today located on two different plates separated by a thousand kilometres of ocean. the aim of this introductory paper is to compare and contrast the stratigraphic evolution of the two regions based primarily on the detailed studies included in this book; the focus is on the timing and nature of tectonic events and on the overall stratigraphic trends. the goal is to provide a broad evolutionary framework for the jurassic of denmark and greenland to set the scene for the succeeding papers. for comprehensive reviews of the north atlantic mesozoic rift system, the the jurassic of denmark and greenland: key elements in the reconstruction of the north atlantic jurassic rift system finn surlyk and jon r. ineson the jurassic succession of denmark is largely confined to the subsurface with the exception of exposures on the island of bornholm in the baltic sea. in east greenland, in contrast, the jurassic is extensively exposed. comparison of basin evolution in the two regions, which now occur on two separate plates, thus relies on highly different datasets. it is possible nevertheless to construct an integrated picture allowing testing of hypotheses concerning basin evolution, regional uplift, onset and climax of rifting, relative versus eustatic sea-level changes and sequence stratigraphic subdivision and correlation. on a smaller scale, it is possible to compare the signatures of sequence stratigraphic surfaces as seen on well logs, in cores and at outcrop and of sequences recognised and defined on the basis of very different data types. breakdown of the successions into tectonostratigraphic megasequences highlights the high degree of similarity in overall basin evolution and tectonic style. an important difference, however, lies in the timing. major events such as late early – middle jurassic uplift, followed by onset of rifting, basin reorganisation and rift climax were delayed in east greenland relative to the danish region. this has important implications both for regional reconstructions of the rift system and for the understanding and testing of classical sequence stratigraphic concepts involving eustatic versus tectonic controls of basin evolution and stratigraphy. keywords: denmark, greenland, jurassic, correlation, parallel evolution f.s., geological institute, university of copenhagen, geocenter copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: finns@geo.geol.ku.dk j.r.i., geological survey of denmark and greenland, geocenter copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: ji@geus.dk geological survey of denmark and greenland bulletin 1, 9–20 (2003) © geus, 2003 reader is referred to ziegler (1988, 1990), doré (1992), doré et al. (1999), skogseid et al. (2000) and brekke et al. (2001). sequence stratigraphy – a conceptual note much of the research presented in this book is based on sequence stratigraphic analysis and it is pertinent in this introduction to comment briefly on the conceptual basis for these studies. as stressed by many workers (e.g. carter et al. 1991; posamentier & james 1993; miall 1997), sequence stratigraphy may be applied in two fundamentally different ways, either involving construction of age models based on correlation with the so-called global cycle chart of haq et al. (1987) or lithology prediction based on the interpretation of cyclicity in the rock record (posamentier & james 1993). these two distinct paradigms were termed the ‘global– eustasy paradigm’ and the ‘complexity paradigm’ by miall & miall (2001). it is significant that few of the authors of the individual studies presented here use the ‘global–eustasy paradigm’ but prefer the ‘complexity’ model which deals with the stratigraphic architecture and predictability of sequences and their components. emphasis is on the recognition, interpretation and dating of key surfaces and on the geometry and environmental nature of successive systems tracts. there is, in contrast, little reference to ‘global cycle charts’ and to the potential use of sea-level curves as dating tools. rather, the ages and significance of key surfaces and derived sea-level curves are used to construct robust genetic stratigraphies, to chart basin evolution and to highlight the importance of timing of tectonic events and pulses of sediment input. this approach is in marked contrast to that adopted by most authors in the compilation by de graciansky et al. (1998) in which the ‘global–eustasy paradigm’ is prevalent. tectonostratigraphy subdivision of the jurassic successions of both regions into tectonostratigraphic packages (sensu surlyk 1991) shows that the tectonic evolution and corresponding stratigraphic signals are broadly similar, although the timing of the transition from pre-rift uplift to onset of rifting and of rift culmination appears to be delayed in east greenland compared to the north sea region. the sedimentary environments and facies are also rather similar for the successive tectonostratigraphic units. the early pre-rift succession (rhaetian–sinemurian) of east greenland is wholly non-marine, however, contrasting with the marine late triassic – early jurassic record of much of the danish region. conversely, the aalenian– callovian early syn-rift sediments of the north sea and the danish basin are more proximal and terrestriallydominated than the correlatives in east greenland which are almost exclusively marine. the investigated time interval includes the uppermost triassic and the lowermost cretaceous in order to cover a complete set of genetically related units. this stratigraphic interval in denmark and greenland can be broadly compared in terms of two megasequences, an upper triassic – middle jurassic pre-rift megasequence and a middle jurassic – lowermost cretaceous syn-rift megasequence, separated by a regional uplift event (fig. 2). detailed correlation between the two regions allowing comparison of short-term sea-level cycles is not yet possible. the pre-rift biostratigraphy is based to a large extent on dinocysts (poulsen & riding 2003, this volume), which are stratigraphically rather long ranging and commonly show different ranges in the two regions. correlation by ammonites can only be done at a few levels, notably in the pliensbachian. dating of the syn-rift succession is based mainly on dinocysts in the north sea – danish basin region but on ammonites supported by dinocysts in east greenland (callomon 2003, this volume; surlyk 2003, this volume). faunal provincialism was strongly developed for much of the middle and late jurassic. pre-rift megasequence in east greenland, the rhaetian – early bajocian time interval was characterised by regional subsidence following rift events in the late permian and early triassic (surlyk 1990, 2003, this volume). the depositional basin was centred over jameson land and stratigraphic units have a more or less basinwide extent and sheet-like geometry, reflecting the relatively uniform subsidence and the absence of major faulting (dam & surlyk 1995, 1998). in general, however, individual units are thickest in the basin centre. a similar development is seen in denmark, the upper triassic – aalenian succession recording a phase of relatively uniform regional subsidence following rift events in the late carboniferous – early permian and the early–middle triassic. the sedimentary record is fragmentary, however, as lower jurassic rocks are missing 10 11 60˚n 55˚n 50˚n 45˚n pa la eo la tit ud e 500 km wollaston forland kuhn ø andøy jameson land milne land mid north sea high cg united kingdom denmark db skåne bornholm in tr ari ft hi gh middle jurassic land normal fault igneous activity inferred structural high deltaic/shallow marine sandstone offshore marine mudstone marine carbonate ? greenland norway sweden baltic shield laurentian shield ringkøbing–fyn high fig. 1. schematic middle jurassic reconstruction showing the regional tectonic elements and jurassic seaways in the north sea region and between greenland and norway. for location of intrabasinal structural elements (danish basin, danish central graben) named in the text, the reader is referred to michelsen et al. (2003, this volume). map based on ziegler (1988, 1990), doré (1992) and surlyk (2003, this volume). cg, central graben; db, danish basin. from large parts of the area, particularly the central graben, due to erosion following early middle jurassic uplift (e.g. ziegler 1990; underhill & partington 1994; andsbjerg et al. 2001; andsbjerg & dybkjær 2003, this volume; nielsen 2003, this volume). the erosional remnants, which are located marginal to and outside the main uplifted areas, are indicative of laterally extensive and sheet-like sedimentary packages, similar to those described from east greenland. this architectural style is recorded, in particular, by the marine lower jurassic fjerritslev formation, which is recognised both in the danish sector of the central graben and in the danish basin (michelsen et al. 2003, this volume). over much of the danish area, the depositional environments and facies are more offshore marine and finer-grained than in the land-locked jameson land basin of east greenland although the paralic successions on bornholm and in skåne display alternating lacustrine, estuarine and shoreface deposits that closely resemble the jameson land succession and show a comparable overall transgressive trend (ahlberg et al. 2003, this volume; frandsen & surlyk 2003, this volume; michelsen et al. 2003, this volume). the pre-rift succession in east greenland can be subdivided into a rhaetian–sinemurian fluvial–lacustrine part and a pliensbachian – early bajocian estuarine – offshore marine part (dam & surlyk 1995, 1998; surlyk 2003, this volume). although a similar gross subdivision, reflecting an overall transgressive trend, can be demonstrated in the lower jurassic of denmark, the timing of the marine inundation of non-marine/paralic settings can only be compared in detail with that of east greenland in the most proximal areas (skagerrak–kattegat platform, skåne, bornholm). here, the rhaetian–hettangian succession was deposited in terrestrial environments succeeded by paralic sinemurian and offshore marine pliensbachian conditions. in the danish central graben and the axial parts of the danish basin, marine conditions were already established in late triassic – earliest jurassic times (fig. 2). a composite regressive event took place in the danish basin in the rhaetian, corresponding broadly to a hiatus in the danish central graben (fig. 2); the subsequent hettangian–sinemurian period was a time of stepwise deepening and expansion of the open marine environment, reaching bornholm in the latest sinemurian (surlyk et al. 1995; nielsen 2003, this volume, fig. 31). hence, inundation of the nonmarine jameson land basin at the sinemurian–pliensbachian boundary was broadly coeval with a long-term maximum transgression in the danish area (fig. 2). in the danish basin, the toarcian records the onset of regression and progressive basin restriction, heralding regional uplift and erosion and the reversion to terrestrial conditions in the middle jurassic. a comparable phase of basin restriction in east greenland, albeit somewhat later (latest toarcian – aalenian), appears to be indicated by evidence of brackish water conditions in the lower part of the offshore marine sortehat formation (dam & surlyk 1998; koppelhus & hansen 2003, this volume). this event may be attributable to progressive tectonic isolation of the jameson land basin due to regional uplift farther north. basin evolution in both east greenland and denmark was thus highly similar with regional subsidence by thermal contraction following rift events in the latest palaeozoic and earliest mesozoic. a marked transgressive trend characterised deposition in both areas; marine conditions were restricted to the axial parts of the seaways in the late triassic and earliest jurassic, spreading to the basin margins (e.g. skåne, bornholm) and the most proximal depocentres (e.g. jameson land basin) by the latest sinemurian – early pliensbachian. stepwise regression and basin restriction in the danish basin in the middle–late toarcian probably resulted from progressive uplift of the ringkøbing–fyn high, heralding the regional mid-jurassic uplift event (nielsen 2003, this volume). mid-jurassic regional uplift and erosion in east greenland, the rhaetian – lower bajocian prerift megasequence is restricted to the jameson land basin, which contains a relatively complete succession. the youngest strata beneath the unconformity that caps the megasequence are of early bajocian age based on dinocysts (underhill & partington 1994; koppelhus & hansen 2003, this volume) and supported by sr-isotope data (m. engkilde, personal communication 2000). a detailed ammonite zonation has been established for the shallow marine pelion formation overlying the unconformity but the ammonites are strictly boreal and the bajocian–bathonian interval cannot be directly correlated with european zonations. however, the immediate predecessor of the oldest of the boreal middle jurassic ammonites, cranocephalites borealis, is the subgenus defonticeras of the genus sphaeroceras from the north-eastern pacific which is confidently dated to the uppermost lower bajocian stephanoceras humphriesianum chronozone (callomon 1985). the great resemblance of sphaeroceras (defonticeras) oblatum and c. borealis suggests that the age difference 12 between them is small and the age of the c. borealis zone and of the basal onlapping strata is thus early late bajocian. there is a short hiatus between the sortehat and pelion formations and combined evidence from dating by sr-isotopes, dinocysts and ammonites suggests that it covers an interval across the lower–upper bajocian boundary. the hiatus is associated with a complete change in basin configuration and drainage pattern marking the onset of rifting in east greenland. the overlying deposits of the pelion formation and its correlatives show extensive onlap onto basin margins and northwards up the axis of the new rift (alsgaard et al. 2003, this volume; engkilde & surlyk 2003, this volume; larsen et al. 2003, this volume). the base of this early syn-rift succession youngs to the north and onlaps progressively older rocks from upper triassic through lower triassic and upper permian to crystalline basement in a northwards direction (surlyk 2003, this volume). the absence of lower jurassic rocks north of jameson land has been interpreted to reflect large-scale, possibly domal, uplift of northern east greenland in late early jurassic time (surlyk 1977a, b; surlyk et al. 1993). a similar situation is known from the norwegian side of the rift complex where large areas were uplifted in late early jurassic time; the stratigraphy on andøy on the conjugate margin of northern east greenland thus shows the same development as in wollaston forland, i.e. crystalline basement draped by a thin veneer of upper palaeozoic carbonates is directly overlain by middle jurassic sandstones (dalland 1981). the reality of early jurassic uplift to the north of jameson land originally suggested on stratigraphic grounds has recently been corroborated on the basis of apatite fission track thermochronology by johnson & gallagher (2000). in contrast, the jameson land area shows no evidence of early jurassic uplift and cooling (mathiesen et al. 2000). data from the norwegian shelf show that wide areas were uplifted in late early jurassic time (doré 1992). it has long been known that major uplift took place in the north sea in late early – early middle jurassic times (whiteman et al. 1975; hallam & sellwood 1976; eynon 1981; ziegler 1988; underhill & partington 1993, 1994). the uplifted area is generally referred to as the ‘midnorth sea dome’ and has been interpreted as having been caused by pre-rift heating and uplift followed by volcanism and rifting. the uplifted area underwent strong erosion and gradually deflated, being onlapped and subsequently flooded during middle and late jurassic times. underhill & partington (1993, 1994) demonstrated that the strata subcropping the erosional unconformity became gradually older approaching the centre of the uplift while the onlapping strata became younger in the same direction. more recent work has shown that the uplifted area was not a simple well-defined dome but involved the ringkøbing–fyn high, much of the danish basin and the fennoscandian border zone (nielsen 1995, 2003, this volume; andsbjerg et al. 2001). in the north sea, the main unconformity is typically constrained to the mid-aalenian in marginal areas. in the sorgenfrei–tornquist zone of the danish basin, for example, lower aalenian strata both underlie and overlie the unconformity and, based on dinoflagellate data, the unconformity appears to lie within the upper levels of the lowermost aalenian l. opalinum chronozone (nielsen 2003, this volume). as in east greenland, however, the limitations of the biostratigraphic data should be acknowledged since dating of the dominantly terrestrial sediments of the strata overlying the unconformity in the north sea is notoriously difficult. although the uplift and especially the onset of rifting and the associated radical basin reorganisation appear to have occurred earlier in the danish region than in east greenland, the main onlap phase onto the regional unconformity was broadly coeval, from the late bajocian to the early oxfordian (underhill & partington 1993, 1994; andsbjerg et al. 2001; andsbjerg & dybkjær 2003, this volume; nielsen 2003, this volume; surlyk 2003, this volume). it is noteworthy that this northwards delay in initial uplift from the danish region to east greenland is mirrored passing southwards from the danish area to the dutch sector of the central graben where the uplift – rift onset hiatus spans the mid-bajocian – mid-callovian (herngreen et al. 2003, this volume). regional uplift, erosion and subsequent subsidence, onset of rifting and onlap of the previously uplifted area thus took place in both east greenland and denmark in late early – early middle jurassic times. a common cause can be envisaged for both regions but the succession of events seems to be delayed in east greenland compared to the central north sea. syn-rift megasequence the regional uplift event at the early–middle jurassic transition was succeeded by the onset of a long-term rifting episode, which began in the middle jurassic, peaked in the late jurassic and persisted into the earliest cretaceous. rifting was not continuous but comprised phases of more intense rifting and block rotation 13 alternating with more tranquil periods of regional subsidence. the syn-rift succession can be subdivided into a number of tectonostratigraphic units marked by rift events followed by more gradual subsidence. seven regional tectonostratigraphic sequences have been recognised for the aalenian–valanginian stratigraphic interval in the central and northern north sea (uk and norwegian sectors) by rattey & hayward (1993); the evolution of the danish central graben in the aalenian–ryazanian described by andsbjerg & dybkjær (2003, this volume) is broadly compatible with the regional framework of rattey & hayward (1993) although megasequences were not defined in the danish central graben study. the seven north sea tectonostratigraphic sequences of rattey & hayward (1993) are equivalent to six sequences for the correlative interval in east greenland (surlyk & noe-nygaard 2000; surlyk 2003, this volume). the main difference between the two regions seems to be the delayed onset and culmination of rifting in east greenland compared to the north sea and the apparent lack of a tectonostratigraphic sequence boundary roughly at the oxfordian–kimmeridgian boundary in east greenland. otherwise the sequences correspond broadly to each other in timing and stratigraphic development, and it is not always clear if the differences, i.e. the slightly older positions of the boundaries in the north sea, are real. they may also reflect dating by ammonites in greenland and by dinocysts in the north sea, respectively, and uncertainties in the correlation between the two zonations. it has been noted by a few workers that the base of dinocyst zones tend to occur at progressively higher levels compared to ammonite zone boundaries in a north sea – east greenland – north greenland tran14 ryazanian volgian berriasian tithonian kimmeridgian oxfordian callovian bathonian bajocian aalenian toarcian pliensbachian sinemurian hettangian rhaetian c re ta ce o us ju ra ss ic tr ia ss ic lo w er lo w er u pp er m id dl e u pp er u m l u l u m l u m l u m l u l u m l u m l u l u l 210 200 190 180 170 160 150 140 chronostratigraphyma nesw danish central graben rfhrfh stz skp sw ne danish basin sy nri ft m eg as eq ue nc e pr eri ft m eg as eq ue nc e sy nri ft m eg as eq ue nc e pr eri ft m eg as eq ue nc e sect (smelror 1993; s. piasecki, personal communication 2002). the northwards younging of tectonostratigraphic boundaries may thus be real, possibly reflecting progressive northward propagation of the rift system as suggested by surlyk & clemmensen (1983), or apparent, reflecting correlation problems at a time of marked ammonite provinciality or northward migration of indicator dinocysts with respect to the more finely-tuned ammonite zonation that forms the basis for jurassic chronostratigraphy. early syn-rift sedimentation (late aalenian – bajocian) in the danish basin and the danish central graben was confined to narrow subsiding grabens and the succession is probably incomplete with a number of inferred unconformities within the bajocian–bathonian part. it is noteworthy that a prominent unconformity is recorded in the uppermost bathonian of the northern danish central graben, recording a marked shift in subsidence patterns during early rifting (andsbjerg 2003, this volume). although loosely constrained biostratigraphically, a hiatal surface is also inferred at this level in the danish basin (fig. 2; nielsen 2003, this volume). this event is not detected in the east greenland sedimentary record where the bathonian–callovian transition is characterised by transgression and progressive backstepping of sedimentary systems (fig. 2); minor hiatuses are recorded at this stratigraphic level but these resulted from condensation and non-deposition in offshore settings. the syn-rift successions of denmark and east greenland are suggestive of a northward younging diachroneity of rift phases. the rift climax occurred in the early oxfordian – middle middle volgian in the danish sector of the central graben, albeit with an important lull in the late kimmeridgian characterised 15 no data no data s n source rock estuarine/lagoonal sandstones, heteroliths, mudstones and coal beds hiatus/condensed jameson land wollaston forland – kuhn ø s n w e lacustrine deltas, sand-dominated lacustrine mudstones alluvial/delta plain – paralic, sand-dominated fluvial and estuarine sandstones, conglomerates floodplain mudstones shallow marine sandstones offshore/basinal mudstones, heteroliths organic-rich offshore/basinal mudstones deep marine sandstones deep marine conglomerates coal sy nri ft m eg as eq ue nc e pr eri ft m eg as eq ue nc e sy nri ft m eg as eq ue nc e fig. 2. chronostratigraphic scheme of the uppermost triassic – lowermost cretaceous of the danish central graben, the danish basin and east greenland showing the main lithologies, depositional environments and tectonostratigraphic sequences. simplified from andsbjerg & dybkjær (2003, this volume), nielsen (2003, this volume) and surlyk (2003, this volume); time-scale after gradstein et al. (1994). rfh, ringkøbing–fyn high; skp, skagerrak–kattegat platform; stz, sorgenfrei–tornquist zone. by regression and shoreface progradation (andsbjerg & dybkjær 2003, this volume; johannessen 2003, this volume; møller & rasmussen 2003, this volume). the late middle and late volgian saw a general waning in rift activity in the danish central graben resulting in the development of more symmetrical sub-basins, associated with a general reduction in the overall sedimentation rate. indeed, the upper volgian – lower ryazanian in the central graben is characterised by a relatively condensed stratigraphic package of organic-rich ‘hot shales’, associated locally with basin floor sands (donovan et al. 1993; ineson et al. 2003, this volume) an oxfordian – early volgian rift climax seems to be applicable to the jameson land basin at the southern end of the east greenland rift basin where chaotic deepwater sandstones of the upper oxfordian – lower volgian hareelv formation mark the rift climax (surlyk & noe-nygaard 2001; surlyk 2003, this volume). it was succeeded by rapid progradation and basin infill in middle and late volgian times as rift activity waned. in wollaston forland at the northern end of the rift basin, however, the late oxfordian – early volgian was characterised by gentle block tilting, whereas the rift climax accompanied by strong block tilting took place in the middle volgian. taken at face value, therefore, the stratigraphic synrift histories of the two regions are broadly similar but the main events appear to have started earlier in the south. conclusions unravelling the complexities of the jurassic rifted seaway in the north atlantic region continues to be a subject of major research interest, not least due to the hydrocarbon potential of jurassic basins on both sides of the atlantic ocean. the basins of east greenland and denmark represent important pieces in this jigsaw puzzle and the studies reported in the following papers will help to further constrain regional models of rift development, and to better understand jurassic stratigraphic development in general. comparison of the jurassic evolution of these areas makes it possible to construct an integrated picture of the long, relatively narrow seaways, allowing testing of ideas concerning basin evolution, domal versus regional uplift, and timing of the onset and climax of rifting. in addition to this regional perspective, parallel research into the jurassic of the east greenland and danish basins allows comparison of the signatures of sequence stratigraphic surfaces as seen on well logs, in cores and at outcrop, and of sequences recognised and defined on the basis of very different data types. furthermore, experience gleaned from the extensive outcrops of east greenland aids interpretation of restricted outcrops on bornholm and in skåne and allows them to be placed within a regional framework. the tectonostratigraphic summary presented above shows that the main tectonic events and stratigraphic trends in east greenland, denmark and adjacent areas are highly similar but apparently somewhat out of phase for the syn-rift successions (fig. 3). the rhaetian – early jurassic was characterised by regional subsidence following late palaeozoic and early mesozoic rift events and the detailed stratigraphic signature reflects relative sealevel changes superimposed on a long-term sea-level rise. major regional uplift heralding the onset of rifting took place broadly at the early–middle jurassic boundary and the uplifted areas underwent marked erosion. subsequent subsidence began in the aalenian in the north sea and in the late bajocian in east greenland concomitant with the onset of rifting, resulting in major regional onlap and transgression. continued relative sea-level rise, reflecting the early rifting, took place in the bathonian; deltas and shallow marine sandy systems were drowned almost everywhere by the end of the callovian. rifting culminated in early oxfordian – volgian times with major block tilting and deposition of fault-scarp aprons and basin-floor fans. the rift climax was delayed in northern east greenland compared to areas further south. the timing and style of tectonic events thus exerted the main control on the long-term trends in stratigraphic evolution. in the early jurassic, however, relative sealevel changes that were unrelated to local tectonics seem to have exerted the main control on the depositional motifs (dam & surlyk 1995, 1998; andsbjerg & dybkjær 2003, this volume; nielsen 2003, this volume; surlyk 2003, this volume). the late jurassic deepening and transgressive trend, on the other hand, appears to reflect accelerated regional subsidence, increased tilting of fault blocks, eustatic sea-level rise or a combination of these factors, and isolation of the dominant control is difficult without comparison with successions on other lithospheric plates. acknowledgements this introductory paper is based mainly on the detailed studies reported in this book; we acknowledge the authors and thank peter r. dawes, peter n. johannessen, michael larsen and lars h. nielsen for useful comments. 16 17 lo ca lis ed f au lt r eac ti va ti o n r eg io na l th er m al su bs id en ce u pl ift a nd de ep e ro si o n fa ul tco nt ro lle d su bs id en ce o f ea st er n d c g m in o r up lif t (s ø gn e b as in ) r eg io na l ba ck st ep pi ng m aj o r ha lfgr ab en de ve lo pm en t r ift h ia tu s, se di m en ta ry pr og ra da tio n sh el f dr ow ni ng sh el f dr ow ni ng sh el f dr ow ni ng sh el f dr ow ni ng r en ew ed r ift s ub si de nc e – m ar ke d ba si n se gm en ta ti o n an d bl o ck r o ta ti o n pe ak tr an sg re ss io n u pl ift o f r fh , n eti lt in g o f ba si n, de ep e ro si o n to s w fa ul tco nt ro lle d su bs id en ce o f st z r eg io na l ba ck st ep pi ng r en ew ed r eg io na l su bs id en ce , in cl ud in g r fh m ar in e in un da tio n o ve ra ll tr an sg re ss iv e tr en d m in o r up lif t, ba si n re o rg an is at io n g en tl e bl o ck r o ta ti o n, in it ia l s ed im en ta ry pr o gr ad at io n r eg io na l ba ck st ep pi ng d ee pe ni ng – p er si st en t re gi o na l s ub si de nc e (b lo ck r o ta ti o n) pr og ra da tio n of sh el f sy st em s u pl ift a nd in ci si o n in fil l/d ra pe o f er os io na l r el ie f b as in s eg m en ta ti o n an d bl o ck r o ta ti o n u pl ift /e ro si o no nl ap o nt o pr eju ra ss ic ba se m en t, se di m en ta ry pr og ra da tio n g en tl e bl o ck ro ta ti o n r eg io na l ba ck st ep pi ng sy nri ft p ha se pr eri ft p ha se u pl ift fa ul tco nt ro lle d su bs id en ce ( m in o r/ m aj o r) d en m ar k ea st g re en la nd ja m es o n la nd – m iln e la nd w o lla st o n fo rl an d – k uh n ø c en tr al g ra be n d an is h b as in r ift cl im ax ?u pl ift r ift cl im ax r ift cl im ax r eg io na l th er m al su bs id en ce r eg io na l th er m al su bs id en ce c hr o no st ra ti gr ap hy m a r ya za nia n vo lg ia n b er ri as ia n t it ho nia n k im m er id gi an o xf o rd ia n c al lo vi an b at ho ni an b aj o ci an a al en ia n to ar ci an pl ie ns ba ch ia n si ne m ur ia n h et ta ng ia n r ha et ia n cretaceous jurassic triassic lower lowerupper middle upper u m l u l u m l u m l u m l u l u m l u lm u l u l 21 0 20 0 19 0 18 0 17 0 16 0 15 0 14 0 f ig . 3 . sc h e m e s h o w in g t h e m ai n t e ct o n ic e v e n ts a n d t re n d s in b as in e v o lu ti o n i n t h e d an is h c e n tr al g ra b e n , th e d an is h b as in a n d e as t g re e n la n d p lo tt e d o n a t im e a x is . t im e sc al e a ft e r g ra d st e in e t a l. 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(2007) using xrf. the modal composition of the sand as well as the chemical composition of the individual mineral grains have been analysed using computer-controlled scanning electron microscopy (ccsem), where each grain is classified as a specific mineral on the basis of its chemical composition (keulen et al. 2008). this method was applied in order to discern whether the samples could be differentiated based on their glauconite composition and to test if injected sand could be identified by its glauconite composition. the >45 μm fraction of the sand was used for the analyses. oil was extracted by toluene, and detergent applied to remove the oily drilling mud and disintegrate the slightly lithified sand. differentiation of palaeogene sand by glauconitic and geochemical fingerprinting, siri canyon, danish north sea mette olivarius, christian knudsen and johan b. svendsen 0° 0° 8°e 58°n 58° germany uk north denmark 250 km norway siri canyon sea 8° fig. 1. map of the north sea region showing the location of the ne–sworiented siri canyon with the tyr and kolga members under investigation in the nini oil field. dashed lines: national borders. © geus, 2011. geological survey of denmark and greenland bulletin 23, 17–20. open access: www.geus.dk/publications/bull 1818 bulk geochemical analyses were carried out at acmelabs, vancouver, on 14 core samples and 73 cuttings samples. major and several minor elements were determined by inductively coupled plasma emission spectrometry (icp-es) on fused glass discs, whereas trace elements, including ree, were identified by icp-ms also on fused glass discs. the modal content of minerals in 10 core samples and 16 samples of the cuttings mounted in epoxy were determined at geus by ccsem on a philips xl40sem (keulen et al. 2008). approximately 1200 grains were analysed per sample. the method integrates backscattered electron micrographs with energy dispersive x-ray spectrometry (edx) to measure the element composition of each grain. the major element weight percentages (wt%) were measured as oxides. the analysis is performed by sweeping over the entire grain, and hence the chemical analysis represents an average of the whole grain and not a point. this is important because the glauconite grains are inhomogeneous. grain size and shape parameters were also measured at the cut surface in the polished section. the fragile nature of the glauconite grains made crushing of the more consolidated parts of the sand inexpedient, so a new application of the ccsem method was developed with measurement of chemical composition in points defined by a grid. this was done in five additional core samples. geochemistry chondrite-normalised ree spectra of the tyr and kolga members are quite similar (fig. 2), except for a positive cerium anomaly in the kolga member. the ree concentrations are moreover higher in the kolga member. the ree spectra of the cuttings samples fit very well with the kolga member (fig. 2d). however, the wells from which the cuttings were sampled have some intervals with high resistivity, and these are generally characterised by a lower content of cerium and an enlarged negative europium anomaly. the lower content of trace elements in the tyr member than in the kolga member makes the sand distinguishable by a number of factors. for example, th and ce in the tyr member are below 6 ppm and 70 ppm, respectively, whereas the concentration is higher in the kolga member. all samples of the cuttings except four are, on this basis, interpreted as kolga member. the four outliers are diluted by either calcite cementation or organic matter, which is seen as high values of calcium and loss on ignition (loi), respectively. glauconite composition the glauconite grains show a wide range in chemical composition, which is ref lected in green to brown colours. green grains are usually rounded and well preserved, whereas brown grains show some structural and chemical resemblance to clay minerals. the roundness of the grains could either be caused by their formation process or by subsequent physical abrasion (odin & matter 1981). the best preserved grains are usually those with the highest iron content. zonation seen in many glauconite grains with light centres and dark rims is apparently related to outward decreasing magnesium content. la ce pr nd pm sm eu gd tb dy ho er tm yb lu 1000 100 10 1 100 10 100 10 100 10 s am p le / r e e c h o n d ri te core samples from the kolga member core samples from the tyr member a b c d cuttings samples interpreted as kolga member kolga member tyr member kolga member (interpreted) fig. 2. r ee spectra measured by icp-ms and normalised to the chondrite composition of boynton (1984). a: the tyr member has lower r ee concentrations than the kolga member. b: the kolga member is characterised by a small positive cerium anomaly. c: r ee spectra from cuttings samples from intervals without infiltration by drilling mud or clayey deposits and with normal resistivity. d: composite diagram with r ee spectra from a, b and c indicating that the known and interpreted intervals of the kolga member are idential and that they are different from those of the tyr member. 19 compositional variation is recorded in the glauconite in every sample. however, this variation range is different in the tyr and kolga members. the glauconite in core samples from the tyr member is characterised by a broad scatter and high iron content (fig. 3a), which is distinctly different from the glauconite of the kolga member. the kolga member shows positive correlation between iron and potassium (fig. 3b), which represents a substitution series with aluminium. the kolga member is moreover distinguishable by a high siderite content compared to the tyr member. all the cuttings samples of unknown stratigraphy are interpreted as kolga memcore samples from the kolga member b fe2o3 (wt%) c cuttings samples interpreted as kolga member 0 2 4 6 8 10 12 14 16 18 0 10 20 30 40 50 60 70 80 90 100 core samples from the tyr member a k 2 o ( w t% ) k 2 o ( w t% ) k 2 o ( w t% ) 0 2 4 6 8 10 12 14 16 18 0 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 12 14 16 18 0 10 20 30 40 50 60 70 80 90 100 quartz feldspar barite glauconite carbonate titanite rutile leucoxene ilmenite ti-magnetite chlorite white mica dark mica clinoamphibole/-pyroxene orthoamphibole/-pyroxene siderite pyrite garnet tourmaline zircon fig. 3. fe-k composition of the minerals expressed as fe 2 o 3 versus k 2 o measured by ccsem. a: the tyr member shows a broad glauconite composition without a linear trend. b: the kolga member is characterised by a narrow glauconite composition. c: the sand from the cuttings samples has a glauconite composition that closely resembles that of the kolga member. c u m u la ti ve w t% b c 0 50 100 1 10 100 1000 core samples from the tyr member grain diameter (μm) a 1 10 100 1000 1 10 100 1000 0 50 100 0 50 100 c u m u la ti ve w t% c u m u la ti ve w t% core samples from the kolga member cuttings samples interpreted as kolga member fig. 4. grain-size distribution curves for the minerals measured by ccsem. a: the grain-size distribution of the tyr member has only been measured in one sample, where the glauconite shows a smaller grain size than quartz. b: quartz and glauconite grains in the kolga member are of medium size. c: the cuttings samples have undergone severe crushing and hence the origin of the sand is difficult to determine from the grain-size distribution alone. for legend see fig. 3. 2020 ber on the basis of mineralogy, as their glauconite compositions and siderite contents fit well with this sand (fig. 3c). a large amount of barite is found in many of the cuttings samples, but at least some of it comes from the drilling mud. five of the six samples from the cored tyr member have been measured in single points instead of whole grains because of the extensive cementation, so the results are not entirely reliable. however, the measured glauconite compositions fit well with the broad scatter measured in the un-cemented sample. grain curves the quartz of both the tyr and kolga members is well-sorted, and the variation in grain-size distributions is small (fig. 4). the heavy minerals are finer grained than the light minerals, showing that hydraulic sorting has occurred. the average grain size of the glauconite and quartz grains is almost equal in the kolga member, but the sorting of glauconite is poorer than quartz due to a broad, fine-grained tail, which may be caused by crushing of the fragile glauconite grains. the glauconite in the kolga member is coarser grained than in the tyr member. however, the grain size of the tyr member has only been measured in one sample because of the cementation in the other samples. siderite is silt-sized, and the almost straight grain curves in most samples show that the siderite is authigenic (weibel et al. 2010). cores and cuttings are dominated by quartz grains of about the same size (fig. 4), but the cuttings also contain a fine-grained tail (fig. 4c) which may have been generated by crushing during the drilling process. the glauconite grains are especially susceptible to crushing because of their fragile nature, and this explains why glauconite from cuttings samples is more fine grained than from core samples. concluding remarks the samples of the cuttings collected from the horizontal wells are interpreted as kolga member on the basis of trace element concentrations, ree spectra, glauconite compositions and siderite contents. this implies that remobilisation is restricted to intra-strata processes, rather than between strata. modelling of the injected part of the field is therefore likely to be comparable to that of the in situ parts, as the original composition of the sand is the same. icp-ms and ccsem have proved useful in characterising sand types, and from these observations it was possible to identify the origin of the intrusive sand bodies. especially the ree spectra measured by icp-ms and the glauconite compositions measured by ccsem have enhanced the understanding of the sediments. acknowledgements this study was conducted in cooperation with the partnership of licence 4/95 in the danish north sea, operated by dong energ y. the partnership is thanked for permission to publish the results. references boynton, w.v. 1984: geochemistry of the rare earth elements: meteorite studies. in: henderson, p. (ed.): rare earth element geochemistry, 63–114. amsterdam: elsevier. friis, h., poulsen, m.l.k., svendsen, j.b. & hamberg, l. 2007: discrimination of density f low deposits using elemental geochemistry – implications for subtle provenance differentiation in a narrow submarine canyon, palaeogene, danish north sea. marine and petroleum geolog y 24, 221–235. hamberg, l., dam, g., wilhelmson, c. & ottesen, t.g. 2005: paleocene deep-marine sandstone plays in the siri canyon offshore denmark, southern norway. in: doré, a.g. & vining, b.a. (eds): petroleum geolog y: north-west europe and global perspectives, 1185–1198. proceedings of the 6th petroleum geolog y conference. london: geological society. keulen, n., frei, d., bernstein, s., hutchison, m.t., knudsen, c. & jensen, l. 2008: fully automated analysis of grain chemistry, size and morpholog y by ccsem: examples from cement production and diamond exploration. geological survey of denmark and greenland bulletin 15, 93–96. odin, g.s. & matter, a. 1981: de glauconiarum origine. sedimentolog y 28, 611–641. poulsen, m.l.k., friis, h., svendsen, j.b., jensen, c.b. & bruhn, r. 2007: the application of bulk rock geochemistry to reveal heavy mineral sorting and f low units in thick, massive gravity f low deposits, siri canyon palaeocene sandstones, danish north sea. developments in sedimentolog y 58, 1099–1121. schiøler, p. et al. 2007: lithostratigraphy of the palaeogene – lower neogene succession of the danish north sea.  geological survey of denmark and greenland bulletin 12, 77 pp. weibel, r., friis, h., kazerouni, a.m., svendsen, j.b., stokkendal, j. & poulsen, m.l.k. 2010: development of early diagenetic silica and quartz morphologies – examples from the siri canyon, danish north sea. sedimentary geolog y 228, 151–170. authors’ addresses m.o. & c.k., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: mol@geus.dk j.b.s., dong energy, exploration and production, agern allé 24 –26, dk-2970 hørsholm, denmark. geological survey of denmark and greenland bulletin 11, 1-7 1 geological survey of denmark and greenland bulletin 11 · 2006 precambrian crustal evolution and cretaceous–palaeogene faulting in west greenland edited by adam a. garde and feiko kalsbeek geological survey of denmark and greenland danish ministry of the environment 2 geological survey of denmark and greenland bulletin 11 keywords archaean, cretaceous–palaeogene, deformation, faulting, geochronology, kangâmiut dykes, nagssugtoqidian, rinkian, west greenland cover flat-lying, grey archaean orthogneisses cut by palaeoproterozoic dolerite dykes (black), which have been deformed and rotated into nearparallellism with their host rocks during the nagssugtoqidian orogenesis. the whole succession is cut by lateto postkinematic nagssugtoqidian pegmatites (pink). south coast of island 11 km east of aasiaat in the northern nagssugtoqidian orogen. the nagssugtoqidian deformation of archaean rocks in this region is the main subject of mazur et al. (this volume) and van gool & piazolo (this volume). photo: adam a. garde. frontispiece: facing page archaean, synto postkinematic granitic sheets cutting grey orthogneiss and variably folded with their host. coastal exposure on the north coast of saqqarput 30 km south-east of kangaatsiaq, within an archaean block in the northern nagssugtoqidian orogen that has largely escaped palaeoproterozoic deformation. compare with the cover photograph displaying an example of palaeoproterozoic deformation, and see articles by mazur et al. and thrane & connelly (this volume). photo: adam a. garde. chief editor of this series: adam a. garde editorial board of this series: john a. korstgård, geological institute, university of aarhus; minik rosing, geological museum, university of copenhagen; finn surlyk, geological institute, university of copenhagen scientific editors of this volume: adam a. garde and feiko kalsbeek editorial secretary: esben w. glendal referees: steffen bergh (norway), clark friend (uk), john grocott (uk), karen hanghøj (usa), paul martin holm (denmark), åke johansson (sweden), graham leslie (uk), kenneth j.w. mccaffrey (uk), allen p. nutman (australia), chris pulvertaft (denmark), andrew saunders (uk) and three anonymous referees illustrators: adam a. garde, eva melskens and henrik klinge-pedersen digital photographic work: benny m. schark graphic production: knud gr@phic consult, odense, denmark printers: schultz grafisk, albertslund, denmark receipt/acceptance dates of manuscripts: see end of individual articles printed: 5 december 2006 issn 1604-8156 isbn-10: 87-7871-188-6 isbn-13: 978-87-7871-188-5 geological survey of denmark and greenland bulletin the series geological survey of denmark and greenland bulletin replaces geology of denmark survey bulletin and geology of greenland survey bulletin. citation of the name of this series it is recommended that the name of this series is cited in full, viz. geological survey of denmark and greenland bulletin. if abbreviation of this volume is necessary, the following form is suggested: geol. surv. den. green. bull. 11, 204 pp. available from geological survey of denmark and greenland (geus) øster voldgade 10, dk-1350 copenhagen k, denmark phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: geus@geus.dk or geografforlaget aps rugårdsvej 55, dk-5000 odense c, denmark phone: +45 63 44 16 83, fax: +45 63 44 16 97, e-mail: go@geografforlaget.dk © danmarks og grønlands geologiske undersøgelse (geus), 2006 3 4 contents preface a.a. garde and f. kalsbeek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 evolution of neoarchaean supracrustal belts at the northern margin of the north atlantic craton, west greenland j.a. hollis, m. keiding, b.m. stensgaard, j.a.m. van gool and a.a. garde. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 pre-nagssugtoqidian crustal evolution in west greenland: geology, geochemistry and deformation of supracrustal and granitic rocks north-east of kangaatsiaq j.-f. moyen and g.r. watt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 a lead isotope study of an archaean gold prospect in the attu region, nagssugtoqidian orogen, west greenland h. stendal, r. frei and b.m. stensgaard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 origin and evolution of the kangâmiut mafic dyke swarm, west greenland k.r. mayborn and c.e. lesher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 zircon geochronology from the kangaatsiaq–qasigiannguit region, the northern part of the 1.9–1.8 ga nagssugtoqidian orogen, west greenland k. thrane and j.n. connelly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 207pb-206pb dating of magnetite, monazite and allanite in the central and northern nagssugtoqidian orogen, west greenland h. stendal, k. secher and r. frei . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 new hornblende and muscovite 40ar/39ar cooling ages in the central rinkian fold belt, west greenland a.-s. sidgren, l. page and a.a. garde . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 presentation and interpretation of structural data from the nagssugtoqidian orogen using a gis platform: general trends and features j.a.m. van gool and s. piazolo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 the nordre strømfjord shear zone and the arfersiorfik quartz diorite in arfersiorfik, the nagssugtoqidian orogen, west greenland k. sørensen, j.a. korstgård, w.e. glassley and b.m. stensgaard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 structural analysis of the northern nagssugtoqidian orogen, west greenland: an example of complex tectonic patterns in reworked high-grade metamorphic terrains s. mazur, s. piazolo and g. i. alsop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 magnetic anomalies and metamorphic boundaries in the southern nagssugtoqidian orogen, west greenland j.a. korstgård, b.m. stensgaard and t.m. rasmussen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 faults and fractures in central west greenland: onshore expression of continental break-up and sea-floor spreading in the labrador – baffin bay sea r.w. wilson, k.e.s. klint, j.a.m. van gool, k.j.w. mccaffrey, r.e. holdsworth and j. a. chalmers . . . . . . . . . . 185 5 preface the present volume marks the completion of a large research project by the geological survey of denmark and greenland (geus), focused on the northern part of the palaeoproterozoic nagssugtoqidian orogen of central west greenland, and carried out by a team of danish and international participants. the project comprised geological mapping as well as structural, geochronological, geochemical and economic geological studies. this volume contains reports on both archaean and palaeoproterozoic geology as well as a study of neotectonic brittle structures. the field work was carried out in 2000–2003 in the region between nordre strømfjord and jakobshavn isfjord (see e.g. van gool & piazolo 2006, this volume, fig. 1). the project had two immediate purposes, namely to establish an overview of the mineral resource potential of supracrustal rocks in the region between 66° and 70°15′n, and produce four new geological sheets in the survey’s 1:100 000 map series. the first collection of papers about the nagssugtoqidian orogen, published by the geological survey of greenland (ggu, now part of geus), dates back to 1979 (korstgård 1979). the investigations in this period were mainly based on field descriptions and structural analysis of coastal areas in the southern and central parts of the orogen, combined with limited petrographical, palaeomagnetic and geochronological studies; the results also comprised the first 1:100 000 geological map from within the nagssugtoqidian orogen (olesen 1984). the proterozoic age of the orogen had been established, but it was believed that most, if not all of the quartzofeldspathic basement gneisses were of archaean origin. subsequent work in the nagssugtoqidian orogen by ggu in the 1980s showed that besides archaean orthogneisses and supracrustal rocks, the central part of the orogen also comprises the root zone of a palaeoproterozoic magmatic arc and associated panels of palaeoproterozoic volcanic and metasedimentary rocks (kalsbeek et al. 1987). these results were confirmed during further investigations by the danish lithosphere centre (dlc) in 1994–1999, and the plate-tectonic collisional history of the southern and central nagssugtoqidian orogen was described in detail (van gool et al. 2002). however, these studies added little to previous knowledge of the northern parts of the orogen in the kangaatsiaq–aasiaat–qasigiannguit region, knowledge that was largely based on coastal reconnaissance by henderson (1969) at the time when the entire orogen was still believed to consist of archaean rocks. another project preceding the present work was carried out by ggu in 1988–1991 immediately north of the nagssugtoqidian orogen, in the southernmost part of the likewise palaeoproterozoic rinkian fold belt (disko bugt project, kalsbeek 1999). it was shown that also the latter region comprises palaeoproterozoic (meta)sedimentary rocks, and that most of the archaean basement is strongly overprinted by palaeoproterozoic structures that were formed during overall wor nw-directed lateral tectonic transport. although these structures might be related to similar structures in the nagssugtoqidian orogen, the relationship between the nagssugtoqidian orogen and the rinkian fold belt remained speculative. the only previous economic geological study of regional extent in central west greenland was an airborne reconnaissance study supplemented by local field work, which was carried out in the early 1960s by kryolitselskabet øresund a/s. this work resulted in the discovery of a massive sulphide deposit at naternaq (lersletten), which was studied again in some detail in 2001 by the survey (østergaard et al. 2002) but not reported on in the present volume. the present volume comprises 12 papers with topics ranging geochronologically from mid-archaean to palaeogene, and geographically from the southern nagssugtoqidian foreland to the central part of the rinkian fold belt. many of the papers deal with the northern part of the nagssugtoqidian orogen and are related to the recent field work in that region, while a few contributions are rooted in dlcor other projects. the papers have been arranged in approximate chronological order and are grouped in terms of their main subjects. the two first papers, by hollis et al. and moyen & watt, deal with archaean supraand infracrustal rocks in the northern nagssugtoqidian orogen: their origin, ages, and structural and metamorphic evolution. these papers provide insight into the age and origin of the continental crustal orthogneisses and granites that underlie most of the region, and discuss the relationships between the supracrustal and plutonic components, using zircon u-pb age determinations and major and trace element geochemical characteristics. also the question of palaeoproterozoic tectonic overprint is discussed, with the conclusion © geus, 2006. geological survey of denmark and greenland bulletin 11, 5–7. available at: www.geus.dk/publications/bull 6 from both study areas that most of the observed structures are archaean. the third paper with focus on archaean geology, by stendal et al., describes a small gold prospect at attu likewise in the northern nagssugtoqidian orogen, and discusses the age of the prospect and its host rocks using pbpb geochronology of magnetite. it is concluded that the host rocks at attu may be as old as 3162 ± 43 ma, and that the gold prospect itself is around 2650 ma in age. the fourth paper, by mayborn & lesher, is a thorough review of the kangâmiut dyke swarm in the southern nagssugtoqidian orogen and its foreland. it includes new whole-rock and mineral chemical data, and a list of sampling sites and corresponding field data. the emplacement mechanism and depth of the dyke swarm are discussed in detail, and it is concluded that the dykes were emplaced during the initial rifting prior to the nagssugtoqidian collision and that they are unrelated to subduction processes (contrary to the belief by some previous authors). the next three papers provide geochronological constraints on the ages of supraand infracrustal rocks and the deformation and metamorphism in the northern nagssugtoqidian orogen, and on late orogenic uplift in the central rinkian fold belt. in the first of these papers thrane & connelly employ zircon u-pb age determinations (mainly using the laser icp-ms method), and for the first time provide unequivocal documentation that the naternaq supracrustal belt is of palaeoproterozoic age. other zircon age data from a synkinematic granite southeast of kangaatsiaq show that the large fold structures in this region are of archaean age. the subsequent paper by stendal et al. presents pb-pb ages and isotopic signatures of magnetite in amphibolites; the obtained ages are younger than 1800 ma and are related to cooling of the orogen. stepwise leaching pb-pb ages of monazite and allanite in pegmatites fall in the range of 1750–1800 ma, and are interpreted to date the emplacement of these rocks. the third paper in this group, by sidgren et al., deals with new 40ar/39ar ages of around 1790 ma (hornblende) and 1680 ma (muscovite) from archaean and palaeoproterozoic rocks in the central rinkian fold belt, which are interpreted as orogenic cooling ages. the hornblende ages are significantly older than such hornblende ages previously obtained from the central and northern nagssugtoqidian orogen, pointing to different uplift histories in the two regions. this may in turn suggest that the rinkian continental collision preceded that in the nagssugtoqidian orogen. four of the remaining five papers deal with the nagssugtoqidian structural evolution. in the first of these, van gool & piazolo present a new method of structural analysis, where a geographical information system (gis) is used as a framework for visualisation and analysis of large amounts of structural data. the paper graphically presents an overview of thousands of data points within an area of approximately 160 × 180 km in the central and northern parts of the nagssugtoqidian orogen. this interesting data set points directly towards the two next papers, where crustal-scale structures in the same region and their origin are discussed: sørensen et al. address the prominent nordre strømfjord shear zone just south of this block, and describes the structural and metasomatic transition into the shear zone by means of aeromagnetic and lithological map patterns and geochemical data. another paper, by mazur et al., addresses a prominent break in the structural pattern within the kangaatsiaq–aasiaat area, where the southern part acted as a rigid block during the nagssugtoqidian orogeny and thus preserved its archaean structure. the fourth paper in this group, by korstgård et al., combines rock and aeromagnetic data to discuss the relationship between structure, metamorphic facies and total magnetic field intensity anomalies in the southern nagssugtoqidian orogen. the authors show that static metamorphic boundaries are gradual, whereas boundaries along deformation zones are abrupt. the last paper, by wilson et al., is a novel remote sensing and field geological analysis of onshore brittle structures related to the complex ungava fault zone in the davis strait, which developed during the cretaceous–palaeogene opening of the labrador sea – davis strait – baffin bay seaway. the study area is located in the central nagssugtoqidian orogen, and the authors carefully establish a distinction between old nagssugtoqidian and younger structures in the basement rocks and identify five main sets of young lineaments. they conclude that the onshore fault patterns are predominantly of strike-slip nature, and that they reflect the stress fields that governed the opening of the seaway. acknowledgements the editors are grateful to the 14 external reviewers, each of whom reviewed one or more of the individual papers, for their thorough and constructive work. 7 references henderson, g. 1969: the precambrian rocks of the egedesminde–christianshåb area, west greenland. rapport grønlands geologiske undersøgelse 23, 37 pp. kalsbeek, f. (ed.) 1999: precambrian geology of the disko bugt region, west greenland. geology of greenland survey bulletin 181, 179 pp. kalsbeek, f., pidgeon, r.t. & taylor, p.n. 1987: nagssugtoqidian mobile belt of west greenland: a cryptic 1850 ma suture between two archaean continents – chemical and isotopic evidence. earth and planetary science letters 85, 365–385. korstgård, j.a. (ed.) 1979: nagssugtoqidian geology. rapport grønlands geologiske undersøgelse 89, 146 pp. olesen, n.ø. 1984: geological map of greenland, 1:100 000, agto 67 v.1 nord. copenhagen: geological survey of greenland. østergaard, c., garde, a.a., nygaard, j., blomsterberg, j., nielsen, b.m., stendal, h. & thomas, c.w. 2002: the precambrian supracrustal rocks in the naternaq (lersletten) and ikamiut areas, central west greenland. geology of greenland survey bulletin 191, 24–32. van gool, j.a.m. & piazolo, s. 2006: presentation and interpretation of structural data from the nagssugtoqidian orogen using a gis platform: general trends and features. in: garde, a.a. & kalsbeek, f. (eds): precambrian crustal evolution and cretaceous–palaeogene faulting in west greenland. geological survey of denmark and greenland bulletin 11, 125–144 (this volume). van gool, j.a.m., connelly, j.n., marker, m. & mengel, f.c. 2002: the nagssugtoqidian orogen of west greenland: tectonic evolution and regional correlation from a west greenland perspective. canadian journal of earth sciences 39, 665–686. adam a. garde and feiko kalsbeek geological survey of denmark and greenland bulletin 35, 2016, 47-50 47© 2016 geus. geological survey of denmark and greenland bulletin 35, 47–50. open access: www.geus.dk/publications/bull marine interglacial deposits are fairly common and widespread in denmark, but so far none have been reported from the herning area in central jylland. in 2014, the geological survey of denmark and greenland (geus) received samples at one metre intervals from a borehole at 55°59.3´n, 8°56.6́ e (elevation 27.56 m above sea level), at hesselvigvej 7 near kibæk in central jylland (fig. 1). the succession consisted of miocene and quaternary deposits. the quaternary part was dominated by glaciofluvial sand and a single till bed, but it also contained a marine clay unit (16–21 m depth, 6.5–11.5 m a.s.l.). this marine clay contained spines of the sea-urchin echinocardium cordatum, a boreal species known from eemian and holocene deposits from denmark, but unknown from interstadial deposits. a lacustrine unit between 26 and 33 m depth (5.5 m b.s.l. to 1.5 m a.s.l.) consisted of clay, calcareous-rich gyttja and diatomite. because quaternary marine deposits are unexpected in this part of denmark, we report here on analyses of pollen from the lacustrine unit and foraminifera from the marine unit, and we compare these with some interglacial records from jylland. the analysed samples were treated with standard laboratory methods. middle pleistocene interglacial deposits near herning, jylland, denmark bent v. odgaard, karen l. knudsen, ole bennike and henrik j. granat fig. 1. a: map of denmark showing the location of the herning area (red rectangle) and selected interglacial sites. 1: harboøre (dgu 43.75), 2: kås hoved (dgu 45.759), 3: holstebro nord (dgu 64.248), 4: hoven (dgu 103.1011), 5: vorbasse (dgu 123.1217). b: map of the herning area showing interglacial sites. c: simplified lithological log of the core at kibæk (dgu 95.2875), with two interglacial units. b lind 10°e 100 km sweden jylland germany 57°n 55°n a dgu 95.2875 (kibæk) 1 2 3 4 5 b interglacial lake deposits interglacial marine clay glaciofluvial sand glaciofluvial sand glaciofluvial sand glaciofluvial sand miocene sand miocene clay clayey till c d e p th b e lo w t e rr ai n s u rf ac e ( m ) 0 10 20 30 40 50 60 70 herning harreskov 9°e 56°n 5 km core open sections denmark 4848 the lacustrine unit pollen data from two samples (at 31 and 30 m depth) from the organic lacustrine (gyttja) unit clearly show that this is an interglacial deposit with thermophilous taxa such as tilia (lime) and buxus (box). the lack of carpinus (hornbeam) is noteworthy and makes a correlation with the holstenian or eemian periods unlikely. in 2003 a core was secured through a thick interglacial deposit at nearby lind, 14 km north of the kibæk borehole (kronborg & odgaard 2004; fig. 1). the pollen record of the interglacial part of the lind core shows a clear correlation to the harreskovian (andersen 1965), with absence of carpinus, presence of picea (spruce) throughout the series and traces of celtis (hackberry; fig. 2). an ordination (principal component analysis, pca) on the lind interglacial pollen samples with the kibæk pollen spectra as supplementary samples shows that the bottom kibæk sample correlates well with a level of 28.4 m of the lind core and the upper kibæk sample with lind at 23.4 m (figs 2, 3). this indicates that a full, but thin interglacial lacustrine succession is present at kibæk. the reason for the thin succession could be that the core site is located near the margin of the former lake basin. the marine unit the foraminiferal assemblages from the marine unit (fig. 4) are dominated by elphidium excavatum, with ammonia beccarii second in abundance. the species composition indicates subtidal, inner-shelf conditions with a gradual shallowing of the water depth and deposition during a full interglacial period. the species ammonia beccarii currently has a northern geographical range limit along southern norway, and it is not present in interstadial deposits such as the bølling and allerød in denmark. ammonia beccarii immigrated with the marine transgression in the early holocene. a principal component analysis (pca) on selected interglacial foraminiferal stratigraphies from central and northfig. 2. simplified percentage pollen diagram from the interglacial deposit at lind with indication of the stratigraphical correlation of the two pollen samples from kibæk (dgu 95.2875; purple lines). fig. 3. principal component analysis (pca) biplot of the interglacial pollen sequence of lind with the two kibæk samples as supplementary samples not inf luencing the geometry of the plot. the percentage values were log-ratio transformed prior to the analysis. pca is an ordination technique, which reduces a multidimensional space (here of pollen types) with associated frequencies to fewer dimensions (pca axes) in such a way that the new dimensions are determined by the directions of largest variation in the original data set. the technique also allows easy comparison between samples of multivariate data such as those derived from microfossil analysis. 23 24 25 26 27 28 29 30 0 20 0 20 40 0 20 40 0 20 0 20 0 20 0 20 0 20 0 0 0 0 20 0 20 percentages pin us d e p th ( m ) be tul a sa lix pic ea aln us qu erc us co ryl us ulm us to ta l til ia cor da ta ty pe ta xu s ce ltis dr yop ter is t yp e po ac ea e fraxi alnus quercus tilia ulmus corylus taxus bruckenthalia calluna fraxinus poaceae filipendula pinus picea betula artemisia salix –1.1 kibæk samples species cyperaceae lind – 1 .0 1 .0 1.1 49 western jylland shows the kibæk samples to be intermediate between two long records from kås hoved and holstebro (fig. 5). this position probably reflects an intermediate facies of the kibæk deposit between the relatively shallow kås hoved facies with haynesina orbiculare as an important species, and the more open marine environment at holstebro with elphidium margaritaceum as one of the indicators of relatively high salinity. the kibæk foraminiferal assemblages are closely similar to two samples from harboøre and vorbasse, and the species composition found in a sample from an additional nearby interglacial deposit at hoven (fig. 1; semi-quantitative data) is also very close to those from kibæk. elphidium excavatum is dominant and ammonia beccarii is common in all the comparative records. age estimate the unusual presence of a lacustrine, as well as a marine sequence in one pleistocene series provides a minimum age of the bottom till and a maximum age of the marine deposit. the danish harreskovian interglacial pollen record can be correlated to the record at hunteburg in germany (hahne et al. 1994). a palaeomagnetic reversal at the base of the hunteburg series may indicate the presence of the brunhes–matuyama boundary, in which case the hunteburg interglacial series would correspond to marine isotope stage (mis) 19, almost 800 ka bp. the till at 39–45 m depth at kibæk would then belong to one of the till units identified in the lower part of the lind core (kronborg & odgaard 2004), deposited during one of the oldest pleistocene glaciations recorded from denmark. the marine unit represents a full interglacial period, but it was not possible to relate it to a specific interglacial. the deposit is, however, older that the eemian interglacial (mis 5e), because of the lack of lusitanian elements that charfig. 4. percentage distribution of selected foraminifera in the marine unit of the kibæk core (dgu 95.2875). note the different scales. fig 5. principal component analysis (pca) biplot of foraminiferal assemblages from kås hoved (knudsen et al. 2014), holstebro nord (kronborg et al. 2002), harboøre (knudsen 1987), vorbasse (k.l. knudsen, unpublished data), and kibæk (this study). a similar assemblage was also found in a sample from a core near hoven (dgu 103.1011; semiquantitative data in geus’ jupiter database). for locations see fig. 1. the percentage values were log-ratio transformed prior to the analysis. 17 18 19 20 21 0 0 0 0 0 0 0 0 elp hid ium ex cav atu m am mo nia be cca rii bu lim ina m arg ina ta elp hid ium m ag ella nic um elp hid ium al biu mb ilic atu m elp hid ium ge rth i ha yne sin a g erm an ica fo ra m in ife ra p er 1 00 g 20 40 60 80 1010 10 101010 200 400 600 percentages number d e p th ( m ) inat a. beccarii h. orbiculare h. germanica e. gerthi e. albiumbilicatum e. magellanicum –1.0 kibæk samples species kås hoved 2 holstebro n vorbasse harboøre – 1 .0 1 .0 1.0 b. marginata e. margaritaceum e. excavatum 5050 acterise eemian assemblages in denmark (e.g. knudsen 1994). the assemblages from the marine unit are close to those related to holsteinian interglacial (mis 11) deposits in denmark (fig. 4), but the actual ages of these deposits are also uncertain. a stratigraphical correlation of the interglacial sediments at kås hoved with mis 11 was discussed by knudsen et al. (2014), but further development of optically stimulated luminescence (osl) dating or other absolute dating methods are needed for more exact age estimates of marine pre-eemian interglacial records in denmark. during the late early and the middle pleistocene, foraminiferal assemblages would be expected to be almost identical during similar marine environmental conditions. some of the danish records that are traditionally related to the holsteinian, could thus be from any warm interglacial period with high sea-level during the late early or middle pleistocene. the stratigraphical position of the marine unit in the kibæk core indicates a middle pleistocene age. it has been suggested that mis 11 was an exceptionally long and relatively warm interglacial (e.g. candy et al. 2014) and peak global sea level may have reached 8.0–11.5 m higher than today (chen et al. 2014). however, most temperature proxies for mis 11 give values similar to the holocene (candy et al. 2014), and according to bowen (2010) sea levels were close to the present sea level. because of the orbital similarity between mis 11 and mis 1, these are even used as analogues of warm intervals in climatic studies (berger & loutre 2003). the temperature indication of interglacial foraminiferal assemblages in denmark, which is related to the holsteinian, is also comparable with the holocene and present day temperatures in the region. it is remarkable that the middle pleistocene marine interglacial records at kibæk, vorbasse and hoven in central jylland are found several metres above sea level, whereas the harboøre and holstebro records in north-western jylland are found at more than 30 m b.s.l. a comparison of the core sites with the pre-quaternary surface map of denmark (binzer & stockmarr 1994) shows that kibæk, vorbasse and hoven are located in areas with a high-lying pre-quaternary surface, whereas harboøre and holstebro represent an area with a low-lying pre-quaternary surface. although glacial tectonics may have displaced some of the interglacial marine records the general elevational pattern of these sediments indicates that the central part of jylland may have experienced a tectonic uplift during the quaternary. references andersen, s.t. 1965: interglacialer og interstadialer i danmarks kvartær. meddelelser fra dansk geologisk forening 15, 486–506. berger, a. & loutre, m.-f. 2003: climate 400,000 years ago, a key to the future? american geophysical union geophysical monograph 137, 17–26. binzer, k. & stockmarr, j. 1994: geologisk kort over danmark. 1:500 000. prækvartæroverf ladens højdeforhold. danmarks geologiske undersøgelse kortserie 44. bowen, d.q. 2010: sea level ~400 000 years ago (mis 11): analogue for present and future sea level? climate of the past 6, 19–29. candy, i., schreve, d.c., sherriff, j & tye, g.j. 2014: marine isotope stage 11: palaeoclimate, palaeoenvironments and its role as an analogue for the current interglacial. earth-science reviews 128, 18–51. chen, f., friedman, s., gertler, c.g., looney, j., o’connell, n., sierks, k. & mitrovica, j.x. 2014: refining estimates of polar ice volumes during the mis 11 interglacial using sea level records from south africa. journal of climate 27, 8740–8746. hahne, j., mengeling, h., merkt, j. & gramann, f. 1994: die hunteburg-warmzeit (“cromer-komplex”) und ablagerungen der elster-, saaleund weichsel-kaltzeit in der forschungsbohrung hunteburg ge 58 bei osnabrück. geologisches jahrbuch a134, 117–166. knudsen, k.l. 1987: elsterian-holsteinian foraminiferal stratigraphy in the north jutland and kattegat areas, denmark. boreas 16, 359– 368. knudsen, k.l. 1994: the marine quaternary in denmark: a review of new evidence from glacial-interglacial studies. bulletin of the geological society of denmark 41, 203–218. knudsen, k.l., ditlefsen, c., penney, d.n., kristensen, p., kronborg, c. & eiríksson, j. 2014: elsterian-holsteinian deposits at kås hoved, northern denmark: sediments, foraminifera, ostracods and stable isotopes. boreas 43, 251–271. kronborg, c. & odgaard, b.v. 2004. nyt om danmarks ældste kvartære af lejringer. dgf kvartærgeologisk møde november 2004. geologisk tidsskrift 2004(2), 23–24. kronborg, c., nielsen, o.b., sørensen, j. & kragelund, a. 2002: ringk øbing amt, holstebro nord, boring dgu nr. 64.1248. geologisk institut, aarhus universitet, report 02rk–01, 39 pp. authors’ addresses b.v.o. & k.l.k., department of geoscience, aarhus university, høegh-guldbergs gade 2, dk-8000 aarhus c, denmark. e-mail: bvo@geo.au.dk o.b. & h.j.g., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. geological survey of denmark and greenland bulletin 1, 585-609 585 the lower–middle jurassic of the anholt borehole: implications for the geological evolution of the eastern margin of the danish basin ole b. nielsen, marit-solveig seidenkrantz, niels abrahamsen, birthe j. schmidt, eva b. koppelhus, helle ravn-sørensen, uffe korsbech and k. gynther nielsen this study of upper pliensbachian – bajocian/bathonian deposits in a borehole drilled on the island of anholt, denmark incorporates sedimentology, biostratigraphy (palynomorphs and foraminifera), palaeomagnetism and coal petrology. the studied succession records a gradual change from marine inner shelf storm-influenced clays to mainly terrestrial sands, clays, and lignite containing a flora of mainly freshwater algae and pollen. the regression was initiated at the pliensbachian–toarcian boundary and marine influence ceased during bajocian–bathonian times; the regression thus took place earlier at anholt than in the centre of the danish basin. the sediments in the anholt borehole are referred to the fjerritslev and haldager sand formations. although the lower–middle jurassic boundary is commonly placed at the boundary between the two formations, our data indicate that at anholt the upper fjerritslev formation (member f-iv) is of aalenian age. the lower–middle jurassic boundary occurs close to the boundary between members f-iii and f-iv of the fjerritslev formation. in contrast to other lower–middle jurassic successions in the north sea region, smectites of inferred volcanic origin are preserved in the anholt section, suggesting limited burial and hence less intense diagenetic illitisation or chloritisation of smectites. a down-hole increase in diagenetic influence is reflected by the increase down-section both in the thermal stability of kaolinite and in the vitrinite reflectance. kaolinite of inferred authigenic origin forms a white powder in the quartz-dominated sands of the haldager sand formation; this kaolinite is thermally very unstable and is interpreted to be of late diagenetic, post-uplift origin. the vitrinite reflectance data indicate that the jurassic formations have been exposed to thermal maturation corresponding to burial to a depth of 1000–1200 m below their present depth. post-maturation uplift of the order of 1 km probably occurred partly during late cretaceous – paleocene inversion in the kattegat area and partly during oligocene–recent regional uplift, the latter being the most important of the two uplift phases. palaeomagnetic data indicate that the main carrier of magnetic remanence is fine-grained magnetite. the stable remanence shows a pronounced inclination shallowing, which is attributed to post-depositional compaction. keywords: danish basin, fennoscandian border zone, lower–middle jurassic, anholt borehole, biostratigraphy, palaeomagnetics, sedimentology, clay mineralogy, organic petrology, geochemistry o.b.n. & m.-s.s., department of earth sciences, university of aarhus, c.f. møllers allé, dk-8000 århus c, denmark. e-mail: geololen@aau.dk n.a., department of earth sciences, university of aarhus, finlandsgade 6–8, dk-8200 århus n, denmark. b.j.s., statoil, exploration division, forushagen, n-4035 stavanger, norway. e.b.k., geological survey of denmark and greenland, geocenter copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. present address: royal tyrrell museum of palaeontology, box 7500, drumheller t0j 0y0, alberta, canada. h.r.-s., samfundsteknik a/s, vesterballevej 4–6, fredericia miljøcenter, dk-7000 fredericia, denmark. present address: bascon a/s, åboulevarden 21, p.o. box 510, dk-8100 århus c, denmark. u.k. & k.g.n.*, ørsted-dtu, building 327, technical university of denmark, dk-2800 lyngby, denmark. *retired. geological survey of denmark and greenland bulletin 1, 585–609 (2003) © geus, 2003 586 during early and middle jurassic times, a major depositional basin, the danish basin, extended across most of denmark and into the modern north sea. it was demarcated by the baltic shield to the north and northeast and by the ringkøbing–fyn high to the south, and was linked with the danish–polish trough to the southeast (sorgenfrei & buch 1964; michelsen 1978; liboriussen et al. 1987). previous studies have shown that the upper part of the lower jurassic fjerritslev formation was characterised by a transgressive phase followed by a regressive phase, from open marine conditions during the pliensbachian – early toarcian to a more restricted marine setting during the late toarcian (michelsen 1978, 1989a). during the middle jurassic, the prograding deltaic or braided river sediments of the haldager sand formation were deposited in the northeastern part of the basin (michelsen 1978, 1989b; koch 1983; michelsen et al. 2003, this volume). this study presents a lower–middle jurassic section from a 306 m deep borehole, drilled in 1990 on anholt, a small danish island in the centre of the kattegat (fig. 1). during the jurassic, anholt was situated near the eastern margin of the danish basin. a composite section was attained by means of three boreholes, anholt ii, iii, and iv, spaced less than 20 m apart. only the latter two extended into jurassic sediments. the boreholes penetrated 104 m of quaternary sediments before reaching the jurassic. the drilling site has an elevation of about 2 m above present-day sea level. all depths noted are referred to this point. the aims of the study were to evaluate the age, the palaeoenvironmental setting and the post-depositional history of the jurassic succession. to achieve this goal, studies were carried out in biostratigraphy, sedimentology, coal petrography, and palaeomagnetism. the material from 104–230 m consists largely of ditch cutkattegat sweden anholt jylland denmark uglev-1 frederikshavn city-1 skagen-3 50 km 2 km 8°e 57°n 55°n 12°e terne-1 gassum-1hobro-1 stenlille wells bornholm skåne skagerrak ringkøbing– fyn high danish basin skagerrak–kattegat platform sorgenfrei–tornquist zone dpt ø resund well normal fault areas of late cretaceous and early tertiary inversion basement high børglum-1 fig. 1. map showing the structural outline of the fennoscandian border zone (sorgenfrei–tornquist zone and skagerrak–kattegat platform) and the danish basin, and the location of boreholes and outcrops mentioned in the text (structural outline from petersen et al. 2003, this volume). the inset map of anholt shows the location of the investigated borehole. dpt, danish–polish trough. 587 tings, together with the few available core samples, whereas the samples from below 230 m are all core samples (fig. 2). below 250 m, core recovery was almost 100%, whereas the interval above 250 m is only represented by few, incomplete cores. the latter cores seem mainly to represent clay or silt-rich lithologies, whereas levels with sand are less commonly represented, and primary sedimentary structures might have been destroyed. in ditch cuttings samples, the proportion of clay-sized particles is probably under-represented, as part of the only slightly consolidated clay-rich layers was incorporated with the drilling fluid during coring. 11.0 48.3 9.5 14.1 24.9 150 200 250 300 1 3 5 7 0 40 80 li th o st ra ti gr ap hy to ta l o rg an ic ca rb o n (t o c ) (w t% ) r ew o rk ed pa ly no m o rp hs (% ) pa ly no m o rp h zo ne s fo ra m in ife ra l zo ne s d ep th (m b .s .) h al da ge r sa nd f o rm at io n fj er ri ts le v fo rm at io n fiii m em be r fiv m em be r pd b ar re n m id dl e ju ra ss ic lo w er ju ra ss ic pc fd fc fb pb fapa quat. c hr o no st ra ti gr ap hy fig. 2. chronostratigraphy, biostratigraphical zonation, total organic carbon (toc) content, and reworked palynomorphs of the lower 200 m of the anholt borehole (slightly modified from seidenkrantz et al. 1993). quat., quaternary; m b.s., metres below surface. biostratigraphy the age of the sediments is based on the biostratigraphical analysis. this part of the study has been previously reported in detail (seidenkrantz et al. 1993) and here we only present a synopsis of that study. the preparation of the samples was undertaken using standard techniques (meldgaard & knudsen 1979; dybkjær 1988; poulsen et al. 1990) and the analysis resulted in the establishment of four palynological and four benthic foraminiferal zones (fig. 2). microfauna foraminifera are only present in the lower part of the section and cannot be correlated with faunas from other deposits in the region. with the exception of the lowermost zone (fa), the assemblages almost exclusively consist of agglutinated species (seidenkrantz et al. 1993), whereas jurassic foraminiferal assemblages in surrounding areas are dominated by calcareous species, mainly nodosarids (nørvang 1957; bang 1968a, b, 1971, 1973; norling 1972). in general, the foraminiferal assemblages have a very low diversity and several samples are barren. the lower foraminiferal zone (fa) mainly contains nodosarid genera such as astacolus and planularia. the deposit also contains ammonite fragments, bivalves, and gastropods. in contrast, zone fb (304–288 m) is dominated by the agglutinated genera ammobaculites, bulbobaculites, kutsevella, and haplophragmoides. the fauna of zone fc is essentially restricted to one species of ammobaculites, whereas zone fd yields ammobaculites, bulbobaculites and a few kutsevella (seidenkrantz et al. 1993). the foraminifera are of a boreal affinity not previously found this far to the south (nagy & seidenkrantz in press). palynology the palynomorph assemblages allow close correlation to other sections from denmark, germany, and britain (fig. 3; schulz 1967; lund 1977; bertelsen 1979; woollam & riding 1983; hoelstad 1985; dybkjær 1991; riding & thomas 1992; koppelhus & nielsen 1994; koppelhus & batten 1996). palynomorph zone pa based on the presence of nannoceratopsis spp., luehnda spinosa morgenroth 1970, and mendicodium reticulatum morgenroth 1970. this assemblage correlates well with zone c3 in the hobro-1 borehole in central jylland (bertelsen 1979) and the top of the cerebrocellenites macrooverrucosus zone in the gassum-1 borehole in central jylland (dybkjær 1991) from the danish basin and with the luehndea spinosa zone in the british part of the north sea (riding & thomas 1992). further possible correlations are with the luehnda spinosa zone and the uppermost chasmatosporites zone, both from the bagå formation of bornholm (koppelhus & nielsen 1994) in the danish–polish trough and from the rya formation in the øresund area (fig. 3; koppelhus & batten 1996). recent palynological study of the neill klinter group, jameson land, east greenland (koppelhus & dam 2003, this volume) permits correlation of zone pa from anholt with assemblage zone 2 of the neill klinter group at the albuen section. the combined evidence suggests a late pliensbachian age for zone pa. palynomorph zone pb based on the acme of spheripollenites together with corollina, ischyosporites variegatus (couper) schulz 1967 and manumia delcourtii (pocock) dybkjær 1991. the zone is correlated with zone c4 from the hobro-1 borehole (bertelsen 1979) and the spheripollenites – leptolepidites zone in the stenlille boreholes (dybkjær 1991) of the danish basin. it can also be correlated with zone i of the bagå formation (hasle klinkerfabrik clay pit of bornholm; hoelstad 1985) and the nannoceratopsis gracilis and spheripollenites –leptolepidites zones from the bagå formation (korsodde section, bornholm; koppelhus & nielsen 1994) in the danish – polish trough. the spheripollenites –leptolepidites zone is also known from the rya formation in the øresund area (koppelhus & batten 1996) and from assemblage zone 5 in the neill klinter group in east greenland (koppelhus & dam 2003, this volume). the age is considered to be toarcian. palynomorph zone pc based on abundant perinopollenites elatoides couper 1958 together with callialasporites turbatus (balme) 588 589 m id dl e ju ra ss ic b at ho ni an b aj o ci an a al en ia n to ar ci an lo w er ju ra ss ic se ri es st ag e m ic he ls en 19 89 b an d th is s tu dy m ic he ls en 19 75 lu nd 1 97 7; d yb kj æ r 19 91 fjerritslev formation n o re co rd s pe ri no po lle ni te s el at oi de s z o ne po o r re co rd s c al lia la sp or ite s– pe ri no po lle ni te s z o ne b er th el se n 19 79 h o el st ad 19 85 r id in g & t ho m as 1 99 2 k o pp el hu s & n ie ls en 1 99 4 k o pp el hu s & b at te n 19 96 se id en kr an tz e t al . 1 99 3 an d th is s tu dy b ar re n z o ne ll l z o ne ll z o ne l sp he ri po lle ni te s– le pt ol ep id ite s z o ne o . a de nt ic ul at a– n . ( n .) si m pl ex z o ne c er eb ro po lle ni te s m ac ro ve ru co ss us z o ne sp he ri po lle ni te s– le pt ol ep id ite s z o ne c ha sm at os po ri te s z o ne lu eh nd ea sp in os a z o ne lu eh nd ea sp in os a z o ne m en di co di ni um re tic ul at um z o ne fd pd? p c pb pa fc f b fa n an no ce ra to ps is gr ac ili s z o ne n an no ce ra to ps is gr ac ili s z o ne d c 4 c 3 h al da ge r sa nd fo rm at io n u pp er pl ie ns ba ch ia n c hr o no st ra ti gr ap hy li th o st ra ti gr ap hy o st ra co ds sp o re s/ po lle n d in o fla ge lla te s fo ra m in ife ra pa ly no m o rp hs m io sp o re s b io st ra ti gr ap hi ca l z o na ti o ns f-iii memberf-iv mb ababcde f ig . 3 . c o rr e la ti o n o f th e a n h o lt p al y n o m o rp h a n d f o ra m in if e ra l zo n at io n w it h t h e c h ro n o an d l it h o st ra ti g ra p h y a n d w it h s e le ct e d b io st ra ti g ra p h ic al z o n at io n s fr o m p re v io u s st u d ie s in t h e r e g io n . 590 dev 1961, nannoceratopsis gracilis alberti emend. van helden 1977, and nannoceratopsis senex van helden 1977. this palynomorph assemblage correlates with the perinopollenites elatoides zone from the stenlille boreholes in the danish basin (dybkjær 1991), zone ii from the bagå formation at the hasle klinkerfabrik clay pit, bornholm (hoelstad 1985) and the lower part of the callialasporites –perinopollenites zone from the bagå formation in borehole 107 and the korsodde section, bornholm (koppelhus & nielsen 1994). the zone is also recognised in the rya formation in the øresund area (fig. 3; koppelhus & batten 1996) and from assemblage zone 6 in the neill klinter group, east greenland (koppelhus & dam 2003, this volume). this correlation suggests an aalenian age for zone pc. palynomorph zone pd characterised by perinopollenites elatoides, callialasporites turbatus, c. dampieri (balme) dev 1961, c. microvelatus schulz 1966, c. minus (tralau) guy 1971, densoisporites scanicus tralau 1968, neoraistrickia gristhorphensis (couper) tralau 1964, sestrosporites pseudoalveolatus (couper) dettmann 1963, gleicheniidites conspiciendus (bolchovitina) krutzsch 1959, and g. senonicus ross 1949. this assemblage suggests a correlation with zone d in hobro-1 (bertelsen 1979), with zone iii from the bagå formation (hasle klinkerfabrik clay pit; hoelstad 1985), and with the upper part of the callialasporites –perinopollenites zone, also from the bagå formation on bornholm (bagå beds, section 1; koppelhus & nielsen 1994). the age of the assemblage is considered to be middle jurassic, probably within the bajocian/bathonian interval. palaeomagnetic studies the continuous record of palaeomagnetic anomalies derived from the deep-sea record only reaches back to the late middle jurassic (base of m29 of the top callovian; harland et al. 1990). older reversal chronology therefore relies upon palaeomagnetic polarity studies of individual stratigraphical sections (ogg et al. 1984; steiner et al. 1985, 1987; gradstein et al. 1994). the aim of the present palaeomagnetic study was to contribute to the gradually increasing knowledge of reversals in mesozoic times. this palaeomagnetic study is the first of its kind in the danish area, as previous studies from the area focussing upon pre-quaternary strata are few (e.g. abrahamsen 1994; ali et al. 1994), and none of these were from the jurassic. magnetic methods and results a total of 122 samples were collected for magnetic studies from the cored sections in anholt iii and iv. the samples were obtained by pressing one-inch cylindrical polystyrene holders into argillaceous parts of the stiff sediment. most of the samples are from the toarcian (78 samples), whereas 17 are from the aalenian, and 27 are from the bajocian/bathonian section. all samples were routinely measured in a molspin ltd. spinner magnetometer and subsequently step-wise demagnetised in 5, 10, 20, and 30 mt alternating fields (af) (three orthogonal directions inside metal shields) and remeasured after each step. in order to determine the carriers of the magnetic remanence, eight samples were treated in step-wise increasing pulse-magnetic fields up to 0.6 t (fig. 4). the 159.61 m 189.27 m 249.49 m 252.33 m 121.01 m 160.54 m 121.32 m 186.93 m 0.0 0.1 0.2 0.3 0.4 0.5 0.6 180 160 140 120 100 80 60 40 20 0 field (t) in te ns it y (m a /m ) fig. 4. irm (isothermal remanent magnetisation) performed on eight samples, which show saturation between 0.2 and 0.3 t, suggesting magnetite to be the carrier of the remanence. 591 irm (induced remanent magnetisation) typically saturates in fields between 0.2 and 0.3 t, indicating that the magnetic carriers are dominated by magnetite rather than hematite or goethite. as the mdf (median destructive field) for most samples is well above 30 mt, this suggests that the magnetic minerals are dominated by singleor pseudosingle-domain magnetites, probably of detrital origin. the nrm (natural remanent magnetisation) intensity is low, typically 1–2 ma/m, with extremes of about 0.4 and 4.5 ma/m (fig. 5). the magnetic declination is not known, as the cores were not oriented in azimuth. the af cleaned inclination (30 mt) is shown in figure 6. the present latitude of anholt is 56.7°n, which is equivalent to a central axial dipole inclination of i0 = 71.8°. however, nearly all the inclinations are much closer to 0° than expected (fig. 6). only 16 out of the 122 samples show inclinations more than ± 30° from 0°. during the jurassic, the danish area had a latitudinal position not significantly south of today (press & siever 1982), indicating that this pronounced inclination shallowing cannot be due to plate drift alone, but rather was caused by either remagnetisation or compaction (abrahamsen 1992). as both polarities are found, secondary magnetisation is unlikely to be the cause. the inclination shallowing in the sediment is thus probably due to compaction. on account of the presence of several major gaps in sampling caused by lithological variation (coarse-grained sections were either not recovered or not sampled for palaeomagnetic studies) as well as due to the dominant shallow inclinations, the reversal chronology based upon the material from anholt is poorly constrained. a tentative interpretation is shown in figure 6, but a more detailed magnetostratigraphical correlation to other palaeomagnetic records such as the detailed sequence from the bajocian–bathonian of south spain (steiner et al. 1987) is not justified at present. 0 1 2 3 4 5 100 120 140 160 180 200 220 240 260 280 300 b at ho ni an –b aj o ci an a al en ia n to ar ci an d ep th ( m b .s .) intensity (ma/m) fig. 5. nrm (natural remanent magnetisation) intensity vs. depth. most nrm intensities are between 0.5 and 2.5 ma/m, with an average of 1.5 ma/m. m b.s., metres below surface. -30-60-90 0 inclination (degrees) 30 60 90 100 120 140 160 180 200 220 240 260 280 300 b at ho ni an –b aj o ci an a al en ia n to ar ci an d ep th ( m b .s .) ? ? ? ? ? fig. 6. suggested polarity interpretation of the jurassic inclination record from the anholt borehole. black, normal polarity; white, reversed polarity; grey, intervals in which polarity is mixed or undetermined; zigzag line, significant intervals in which polarity data is lacking; m b.s., metres below surface. lithology a preliminary sediment description was performed during the drilling operation. a more detailed description was made subsequently, both of cores and cuttings samples, and black-and-white and colour photographs of the cores were taken. x-ray photographs were taken of selected 1 cm thick slices of the core material. immediately after drilling, a sng-log (spectral natural gamma-ray log) was obtained from the anholt iv borehole. preliminary results were published by nielsen (1992). methods the following analyses were carried out: 1. grain-size analysis using wet sieving (> 63 µm fraction) and settling in andreassen tubes (< 63 µm fraction). 2. bulk sediment geochemistry comprising toc (total organic carbon) and sulphur analysis measured in a leco induction furnace, as well as measurements by atomic absorption spectrophotometry (aas) of the content of the main elements: si, al, fe, ca, mg, mn, na, and k. 3. mineralogical composition of both bulk samples and of the clay fraction using x-ray diffraction (xrd). samples for bulk mineralogy were dried in a furnace at 105°c for 16 hours, and ground in a mortar. the powder was mounted in the sample holder without preferred orientation. samples for clay mineralogy were dispersed in distilled water, sieved through a 63 µm mesh, and the < 2 µm fraction was obtained by repeated decantation in distilled water. the < 2 µm fraction was smeared onto glass plates in order to obtain preferred orientation of the clay minerals. the glass plates with the clay film were x-rayed in various conditions: air-dried, ethyleneglycol-treated and after heating to different temperatures (nielsen et al. 1989). 4. some of the samples were heated at a rate of 2°c per minute in a differential thermal analysis/thermal gravimetry (dta/tg) instrument in order to determine the temperatures for oxidation of organic compounds and to release the oh-groups of the phyllosilicate minerals. the change in weight from these processes was determined. the analyses were performed both on bulk samples and on the clay fractions (0–2 µm, 0–1 µm, and 1–2 µm) and were followed by heating to 468°c. this temperature was kept constant for 8 hours and the weight loss from the release of ohgroups as a function of time was recorded. a temperature of 468°c was chosen, because the dta/tg curve indicated that approximately 465°c was the threshold temperature for the dehydroxylation process at the heating rate used. the time in minutes for the release of half of the oh-groups was calculated. 5. the same samples were exposed to heating in steps of 25°c from 450–600°c followed by xrd analysis in order to observe the decomposition of the crystal structure in kaolinite. results and discussion sedimentary facies the clays and sands from 306–201 m are referred to the fjerritslev formation (figs 2, 7; michelsen 1978). in the lower part (c. 306–231 m), the sng-log is rather uniform and the sediment consists of a relatively homogeneous, greyish green clay with a low median grain-size (fig. 8). this interval is equivalent to member f-iii of the fjerritslev formation (michelsen 1978). the lowermost c. 6 m are characterised by a slightly sandy and bioturbated clay (figs 7, 8) with ammonites. pure clay lithologies make up 50–70% of each core, the remainder comprising silty clay layers and fine-grained sand laminae. above this basal unit, the clay is commonly non-bioturbated and contains less than 1% sand, except for very thin laminae of fine-grained sand of inferred storm origin. silty clays form between 1 and 30% of each core, whereas pure clay makes up 70–99% of each core. upwards, especially above 260 m, the storm sand layers become coarser and thicker, up to a few millimetres, and the sand content in the clay layers increases to 4–6% (fig. 8). some sand laminae are cross-laminated. at 231 m, a carbonate-cemented lignite conglomerate (fig. 9) marks the lower boundary of member f-iv of the fjerritslev formation (michelsen 1978). this member continues up to 201 m and is characterised by sandier sediments with more numerous and thicker sand layers intercalated with the clay layers. the sand layers show an upwards increase in the content of very fine pebbles from 1.6–8.5% in the lower part to 11–23% in the upper part (fig. 8). the upper part of the jurassic succession (201–104 m) is referred to the haldager sand formation (michelsen 592 593 100 300 250 200 150 306 fiii m em be r fiv m em be r upper pliens. quat. m id dl e ju ra ss ic lo w er ju ra ss ic to ar ci an h al da ge r sa nd f o rm at io n fj er ri ts le v fo rm at io n b aj o ci an /b at ho ni an a al en ia n lithostrat. chronostratigraphy lithology th (ppm) u (ppm) k % total gr log u/th th/k u/k comments 0 0 4 m b.s. 20 5 0 bedding tilted (up to 20°) horizontal bedding calcite-cemented lignite conglomerate siderite concretions siderite concretions siderite concretions pyrite and siderite concretions siderite concretions burrows horizontal bedding concretions silt clay till carbonate lignite clasts gravel coarse-grained sand medium-grained sand fine-grained sand silty sand silty clay fig. 7. integrated log combining lithostratigraphical and lithological data with the spectral natural gamma-ray log (sng). quat., quaternary; pliens., pliensbachian; m b.s., metres below surface. 594 1978). this part has a markedly higher content of sand with brown coal fragments. the lithology of the haldager sand formation shows a cyclic variation which is also evident on the gamma-ray log (fig. 7). intervals (1–10 m thick) of medium-grained sand with lignite fragments alternate with 1–5 m thick units of silty clay with high toc contents (fig. 2). lignite layers, a few centimetres thick, also occur locally. the observed variations in lithology might be explained by lateral migration of channels in a delta-plain or floodplain setting. sng-log analysis the thorium (th), uranium (u), potassium (k), and integrated gamma-ray signals from the spectral natural gamma-ray log (sng-log; fig. 7) obtained from the anholt iv borehole show some significant variations throughout the jurassic section. the main carrier of potassium is believed to be phyllosilicates (clay minerals and mica), as almost no potassium feldspar was observed. uranium is normally concentrated in layers rich in organic matter but may also be present in some heavy minerals. the th-content is somewhat greater in kaolinite than in other clay minerals, but some heavy minerals contain relatively high concentrations of th (see below). the log signal is very uniform in member f-iii of the fjerritslev formation. the only exceptions are characteristic negative peaks where carbonate and pyrite concretions and sand laminae are present (fig. 7). the lower gamma-ray values probably indicate a lower concentration of th, u and k in the carbonate concretions than in the surrounding compacted clay, suggesting that carbonate cementation took place shortly after deposition and prior to significant concentration of k, th and u due to compaction of the clays. the log signature of member f-iv is markedly different from that of the haldager sand formation, mainly due to variations in lithology. the fine-grained layers are enriched in k-containing phyllosilicates and u-containing organic matter relative to the coarser layers. part of the th content is probably also related to kaolinite particles, which are more common in the finer size fractions. uranium and thorium anomalies in the sng-log some thin layers in member f-iv of the fjerritslev formation and in the lowermost part of the haldager sand formation (around 195 m) have higher concentrations of th, and to some extent also u (fig. 7). the smaller th and u anomalies are all located within the coarsening-upwards marine member f-iv, whereas the two strong anomalies are located within the lower levels of the generally non-marine haldager sand formation (environmental interpretations from michelsen 1978, 1989a). the k content is constant or even relatively low in these layers (see also the element ratios in fig. 7). 10 000 1000 100 10 1 90 115 140 165 190 215 240 265 290 315 m ed iu m g ra in s iz e (µ m ) depth (m b.s.) fjerritslev fmhaldager sand fmquat. fig. 8. median grain-size values; note the logarithmic scale on the y-axis. some reservations should be made concerning the results of the grain-size analysis of the f-iv member (231–201 m), as no cores were recovered from this interval. the sediments are only slightly consolidated, and the more fine-grained parts might therefore have been incorporated in the drilling fluid. m b.s., below surface. the base-level of the gamma-ray signal is relatively high in the clay lithologies of the fjerritslev formation, but considerably lower in the haldager sand formation. low gamma signals are normal for sand layers. ditch cuttings samples and samples from the very few cores from these low gamma-ray intervals are dominated by sand thus supporting the log interpretation. however, the very poor core recovery in this section of the borehole did not allow very precise sampling of undisturbed th-rich intervals, so the reason for the high concentrations of this element is unclear. similar peaks of th and u are found in jurassic, cretaceous and miocene deposits in other danish boreholes (korsbech & nielsen 1991; korsbech 1992). the same phenomenon is seen in sections with excellent core recovery of lower cretaceous fine-grained sand in the skagen-3 borehole. here, the coarse silt fraction contains a considerable proportion of heavy minerals (mainly zircons; h. friis, personal communication 1992). the same observation has been made by conner & kelland (1975a, b) in a jurassic sandstone in a north sea well; zircons and other heavy minerals such as monazite, rutile and epidote commonly contain a substantial amount of th, and it was suggested that this might be the source for the relatively high content of this element. the same explanation may be applicable to the jurassic in the anholt cores. an examination of some older borehole logs indicates that layers enriched in heavy minerals may be a common phenomenon in jurassic sandstones in denmark. although sng-logs were not run in these old boreholes, we propose that some of the peaks observed on natural gamma-logs in the jurassic and lower cretaceous sediments of the frederikshavn city-1 and børglum-1 boreholes are due to a high content of heavy minerals. larsen (1966) detected several samples with zircon contents of up to 60% of the non-opaque, nonmicaceous heavy fraction. higher gamma signals are normally found in these layers. the concentrations of th and u between 198 and 190 m are shown on figure 10; note that the u and th peaks are displaced slightly (5–10 cm) relative to one another. the scales were chosen in order to equate the heights of the th and u peaks at 193.9 m. the ratio between the th and u concentrations here is 5:1. in contrast, the th:u ratio for the peaks at 195 m is about 10:1; note that minor fluctuations occur within these peaks at 195 m. this variation in the th:u ratio may imply that some separation of the heavy minerals has taken place, probably based on differences in grain size and density. bulk mineralogy the mineralogical composition of the jurassic succession of the anholt borehole is relatively simple; it comprises only stable, detrital minerals and a few authigenic/diagenetic minerals. the detrital minerals are quartz, clay minerals (including mica) and very little feldspar; the authigenic/diagenetic minerals are pyrite, calcite and siderite. authigenic feldspars have been 595 fig. 9. core photograph of part of the interval from 232.6–231.1 m b.s., fjerritslev formation, f-iii member, uppermost toarcian. opposing faces of a single slabbed core piece are illustrated. the dark clasts are lignite fragments, up to 7 cm in length, in a matrix of calcite-cemented clayey, silty sandstone. width of core is 10 cm. 596 reported in middle jurassic sediments elsewhere in the north sea basin (nielsen & friis 1985), but were not observed in this borehole. the mineralogical variation mainly reflects the grainsize variation and the location of pyrite and carbonate concretions of predominantly sideritic composition. the boundary to the overlying quaternary sediments is clearly marked by a distinct increase in feldspars and amphiboles, i.e. minerals with a relatively low resistance to chemical weathering. clay mineralogy the non-clay minerals of the < 2 µm fraction are dominated by quartz, but the quartz content is much lower in fractions below 1 µm. chlorite is only present in small quantities with a slight tendency to decrease upwards (fig. 11), presumably due to the diagenetic origin of this mineral. illite is a common mineral although the measured illite content in the coarser layers is presumed to also include muscovite (identified macroscopically), as it is difficult to distinguish between these two very similar minerals by xrd. kaolinite is the dominant clay mineral in the coarser sediments. in sands from the haldager sand formation, macroscopic examination revealed a white powder, identified as pure kaolinite by xrd. in finer grades of the clay fraction, the kaolinite content is notably lower, due to its normally larger grain-size relative to other clay minerals. smectites are present in the lower, fine-grained layers (figs 11, 12), but decrease in proportion up-section, rel0 0 190 198 50th (ppm) 10u (ppm) d ep th ( m b .s .) th u fig. 10. thorium (th) and uranium (u) concentrations between 198 and 190 m b.s. the relative concentrations (th/u) differ for the two peaks, probably reflecting sorting processes during sedimentation. m b.s., below surface. 100 90 80 70 60 50 40 30 20 10 0 95 104 201 305 % ( cu m ul at iv e) quat. haldager sand fm fjerritslev fm kaolinite chlorite illite smectite fig. 11. clay mineralogy of the < 2 µm fraction. sum of clay minerals = 100%. the analyses are displayed in stratigraphic order but the horizontal scale is not directly proportional to depth; the depth to the main lithostratigraphic divisions is indicated (in metres below surface). 597 ative to the total clay fraction, corresponding to the overall increase in grain size up-section (fig. 11). the presence of smectite in the fjerritslev formation should be noted as smectite is absent in jurassic and lower cretaceous sediments in most wells in the danish basin and the danish central graben (nielsen 1979, 1985; clausen 1982; nielsen & friis 1985; schmidt 1985a; krabbe 1986; lindgreen 1991). we believe that the dominance of illite and the presence of illite/smectite mixedlayer minerals in jurassic sediments in most boreholes, excepting anholt, is the result of substantial diagenetic illitisation of original smectites due to greater burial depths and thus exposure to higher temperatures. the transformation of smectites to illites via mixedlayer phases is primarily dependent on burial history, temperature and time (dunoyer de segonzac 1970). the transformation is thus seen at different depths and ages in different basins. the process mainly happens within a temperature range of 80–115°c, normally corresponding to a burial depth of 2–4 km in the north sea (środoń & eberl 1984). values of these magnitudes have never been reached for the anholt sediments. the 4. 76 50 5. 00 87 5. 29 86 5. 61 14 5. 75 71 7. 15 54 10 .0 77 7 14 .0 04 6 16 .7 46 3 18 .6 32 7 20 .6 92 5 22 .6 58 3 33 .9 07 6 5. 02 90 7. 24 62 9. 63 58 10 .1 59 2 13 .2 70 3 14 .6 67 4 16 .8 91 2 18 .3 54 4 22 .1 24 6 30 .4 39 6 32 .6 14 4 ill ill chl chl sm ka/chl heat-treated eth.-treated fig. 12. x-ray diffractogram of the clay fraction of a sample from the fjerritslev formation (294.24–294.21 m b.s.). heattreated, x-rayed after heating to 500°c for 1 hour; eth.-treated, x-rayed after treatment with ethyleneglycol vapour for 16 hours at 60°c. reflection peaks: chl, chlorite; ill, illite; ka, kaolinite; sm, smectite. the figures represent crystal lattice spacings in ångstrøms. 598 illitisation process starts in sediments with vitrinite reflectance values of approximately 0.5 %ro, possibly already at 0.40–0.45 %ro (pevear et al. 1980), and burtner & warner (1986) proposed on the basis of rock-eval analysis that the process takes place in sediments with tmax values between 430° and 440°c, possibly already at 425°c. in deeply-buried jurassic successions, such as in the børglum-1 and uglev-1 wells, the vitrinite reflectance values for sediments of the fjerritslev formation are 0.40–0.50 %ro (schmidt 1985b), i.e. considerably higher than the values from anholt (0.25–0.40 %ro, see below). the percentage of smectite normally increases with decreasing particle size and towards the basin centre. because of the marginal location of the anholt borehole, it is possible that the sediments contain less detrital smectite than contemporaneous sediments in other wells in the danish basin prior to diagenetic alteration. geochemistry the toc values are shown in figure 2 and the s, fe2o3 and k2o values in figure 13. peak values of toc in the haldager sand formation are related to brown coal layers. intermediate values of toc are usually found in brownish/black layers dominated by silt-sized particles, normally with relatively abundant muscovite, or in sand layers with scattered lignite clasts, such as in the middle of the fjerritslev formation section. low toc values are mainly restricted to layers dominated by clay or coarse-grained quartz sand. the k2o content generally reflects the amount of illite, whereas s and fe2o3 reflect the pyrite and to some extent the siderite contents. the percentage of fe, excluding that incorporated in pyrite or siderite, is relatively uniform. the analyses were used to calculate a normative mineralogical composition, which was then compared with the xrd mineralogy and used to improve the quantification of the bulk mineralogy from the xrd data. the anholt borehole is well-suited to such a procedure as: (1) many core-samples have been analysed, (2) the number of different minerals is limited, and (3) the minerals present are rather stable. differential thermal analysis (dta) and step-heated xrd the result of the step-wise heating of the sediment for one hour followed by xrd is shown in figure 14. in samples from the top of the jurassic section down to a depth of about 230 m, the 7å kaolinite peak on x-ray diffractograms is totally destroyed by heating to 500°c for one hour; indeed, kaolinite from sand layers in the haldager sand formation is already destroyed at a temperature of 450°c. from 230 m down to the base of the borehole at 306 m, the kaolinite structure is only partly destroyed by heating for one hour. the higher the heating temperature and the longer the sample is exposed to this temperature, the greater the destruction. measurements of different size fractions clearly demonstrated that larger grains were more heat resistant than smaller grains, probably due to a greater proportion of grains with crystal lattice imperfections amongst the smaller size fractions; such size-dependent thermal stability has been noted in many previous studies (e.g. norton 1939). with the exception of a single sample at about 250 m, there is a slight tendency for kaolinites in member f-iii to be more heat resistant with increasing depth, even if the total amount of kaolinite decreases (figs 11, 15) and the particle size of the mineral grains decreases (fig. 8). figure 15 shows the relationship between core depth and time to destruction of half of the kaolinite particles at 468°c, i.e. the release of oh-groups corresponding to half of the weight loss observed at this temperature. generally, the time needed for this destruction increases with increasing depth. this tendency towards a down-section increase in thermal resistance of kaolinite has been observed elsewhere in mesozoic sediments of the north sea basin. holdridge & vaughan (1957) found the temperature for the onset of dehydroxylation to be 477°c for kaolinites (average of 48 samples) and 522.5°c for pure dickite (average of 18 samples) through measurement on differential temperature analysis (dta) equipment at a heating rate of 10°c per minute. the lower threshold temperature observed in these anholt data (468°c), is probably due to the lower heating rate (2°c/min.) used in the present study. the crystal order presumably increases with the influence of progressive diagenesis. in deeper diagenesis/incipient metamorphism, kaolinites may convert to dickite and further to nacrite with the same chemical composition as kaolinite, but with a higher degree of order in the crystal lattice (dunoyer de segonzac 1970). the results of the analysis of the thermal stability of kaolinites from the anholt borehole indicate that the thermal stabilisation of kaolinites during progressive diagenesis is a gradual process. the process seems to initiate at a relatively early diagenetic stage; thermal stabilisation is detectable at diagenetic stages reached 599 at a depth of approximately 1 km. it also seems possible to differentiate the thermal stability of kaolinites within a depth range of 100–200 m. kaolinite in sands of the haldager sand formation is commonly seen as a whitish powder on the quartz grains. the very low thermal resistance of this kaolinite might be explained by a later, probably post-uplift, formation in the pore spaces of the sand. the formation of kaolinite is possibly due to reactions between a migrating diluted acidic porewater and feldspar grains (nielsen & friis 1985). organic petrology and geochemistry a total of 46 samples from the anholt borehole were selected for toc and rock-eval screening. the samples were selected mainly from the darker grey, brownish or black sediment levels where higher organic contents were expected. from the screening results, 23 samples were selected for organic petrographical analyses, i.e. measurements of vitrinite reflectance and fluorescence, and compositional description. 35 30 25 20 15 10 5 0 90 110 130 150 170 190 210 230 250 270 290 310 depth (m b.s.) pe rc en t quat. haldager sand fm fjerritslev fm k2o fe2o3 s fig. 13. the content (%) of k2o, fe2o3, and s determined from the bulk geochemical analysis. quat., quaternary; m b.s., metres below surface. fig. 14. peak ratios (peak height of heated samples/peak height of ethyleneglycol-treated samples) for 7å kaolinite heated to 500°c, 525°c and 550°c. m b.s., metres below surface. 220 0.00 0.02 0.04 0.06 0.08 0.10 r at io 0.12 0.14 0.16 230 240 250 260 270 depth (m b.s.) 280 290 300 310 500°c/glycol 525°c/glycol 550°c/glycol 600 toc and rock-eval screening most of the samples are very poor in total organic carbon (toc). the hydrocarbon potential (hc) is also low (s2 values are low; table 1). s2 values (s2: hydrocarbons generated during rock-eval pyrolysis) of < 0.5 mg hydrocarbon (hc)/g rock are considered to give unreliable tmax values (tmax: temperature of maximum hydrocarbon generation during rock-eval pyrolysis). the highest toc values are from the upper sandy section of the haldager sand formation from a depth of about 190–105 m, whereas the values from the underlying greenish clays of the fjerritslev formation are low to very low. the varying content of organic/coaly debris in the sediments is confirmed by the wide range of variation in toc values. the highest value (38%) was obtained from a thin lignite layer. the tmax varies in the range 410–433°c, with most of the values around 420–425°c (table 1). the lowest value of 387°c from the brown coal bed is considered to be unreliable. the highest value of 433°c is most likely due to the presence of slightly oxidised or reworked material and not due to maturation. the dominant tmax values of about 420–425°c are within the expected range for sediments with the measured vitrinite reflectance values (see below) of about 0.4 %ro (tissot et al. 1987). the hi (hydrogen index) below or just above 100 mg hc/gtoc (table 1) is typical of kerogen types iii–iv. only one sample yielded a higher hi value (276 mg hc/g toc). coal petrography the samples selected for coal petrographic description were embedded in cold synthetic resin, and were ground and polished after hardening. all samples were studied in normal reflected light combined with blue lightinduced fluorescence. the organic material was described and the maceral composition was estimated semi-quantitatively in the following groups: vitrinite, pseudovitrinite, inertinite and liptinite. the main focus was on the degree of oxidation and the liptinite composition. point counting was not performed; the results of the coal petrographic analysis are given in table 2. the organic material in all samples is, in general, dominated by terrestrial material. most samples are characterised by humic material (vitrinite) showing varying degrees of oxidation and/or reworking (pseudovitrinite and inertinite). samples 3 and 8, from 121.6 m and 170.9 m respectively, are composed entirely of large fragments of ulminitic vitrinite with almost no indication of oxidation. in contrast, sample 10 (184.48 m) contains humic material composed almost entirely of oxidised inertinite, mainly tiny small fusinite fragments, or pseudovitrinite. in general, the liptinitic content is low, but the identifiable part shows a high abundance of macerals of terrestrial origin, such as sporinite, resinite and cutinite, sometimes even with possible fluorinite. only very few algae were identified. in the upper part of the section, a few of the botryococcus-type occur, indicating deposition in (or derivation from) fresh to brackish water, and a tasmanites was observed in sample 10 (184.48 m). marine organic material, such as tiny fragments of dinocysts or acritarchs, is present only in the lowermost 100 120 140 160 180 depth (m b.s.) m in ut es a t 46 8° c k ao lin it e (% ) 200 220 240 260 280 60 50 40 30 20 10 0 1/2 weight at 468°c kaolinite 100 90 80 70 60 50 40 30 20 10 0 fig. 15. the proportion of kaolinite (%) relative to the total clay mineral content of the clay fraction (< 2 µm) and the time taken in minutes for the release of half of the oh-groups in kaolinite at 468°c, measured by differential thermal gravimetry. m b.s., metres below surface. part of the succession. a very small amount of bituminite was also recognised in these samples. sample 22 (300.88 m) has the highest proportion of what may be considered to be marine material. the organic material in the uppermost part of the fjerritslev formation is of very poor quality compared to data from other wells in the danish area (thomsen et al. 1987). vitrinite reflectance and fluorescence data reflectance measurements were performed on the same polished specimens as used for description of the organic composition. the photomultiplier attached to the ‘zeiss photomicroscope’ was calibrated by measurements on a polished optical glass standard of constant known 601 1 113.6 0.30 52 2 119.82–119.85 11.00 417 1.08 12.17 0.08 1.10 111 0.33 51 3 121.59–121.60 38.00 387 5.70 31.07 0.16 3.05 82 0.32 63 4 124.6–127.6 3.74 427 0.19 3.15 0.06 0.28 84 0.33 39 130.6–133.6 2.02 426 0.11 1.25 0.08 0.11 62 5 133.6–136.6 2.11 423 0.07 0.97 0.07 0.09 46 0.37 49 137.4–139.6 0.17 424 0.01 0.01 0.50 0.00 6 142.6–145.6 0.17 404 0.03 0.05 0.38 0.01 30 145.6–147.1 1.35 425 0.01 0.11 0.08 0.01 8 147.1–148.6 2.43 424 0.05 0.91 0.05 0.08 37 6 149.90 0.70 426 0.12 1.94 0.06 0.17 276 0.35 50 154.6–157.6 2.44 423 0.03 0.23 0.12 0.02 9 7 159.59–159.74 2.40 424 0.13 1.74 0.07 0.16 73 0.35 52 8 170.8–170.90 5.89 410 0.35 2.67 0.12 0.25 45 0.32 55 9 175.55 1.81 423 0.03 0.79 0.04 0.07 44 0.43 43 184.09–184.10 0.77 427 0.01 0.24 0.04 0.02 31 10 184.80 9.50 427 0.46 5.94 0.07 0.53 63 0.34 7 184.98 1.73 421 0.07 1.32 0.05 0.12 76 11 187.82 1.50 418 0.03 0.59 0.05 0.05 39 0.34 30 12 189.65 0.49 431 0.00 0.07 14 0.32 27 194.6–197.6 0.12 0.01 0.00 13 206.6–209.6 0.63 424 0.03 0.36 0.08 0.03 57 0.34 30 209.6–210.3 0.38 425 0.03 0.15 0.17 0.01 40 212.6–215.6 0.31 422 0.03 0.13 0.19 0.01 42 14 218.6–221.6 0.31 425 0.05 0.13 0.28 0.01 42 0.32 50 221.6–224.6 0.28 422 0.05 0.11 0.31 0.01 40 15 230.53 1.19 422 0.03 0.50 0.05 0.05 50 0.33 51 234.36 0.16 431 0.00 0.07 44 16 239.28 0.72 429 0.01 0.42 0.02 0.04 58 0.31 14 244.15 1.20 427 0.01 1.31 0.01 0.11 109 17 249.68 0.24 429 0.00 0.17 69 0.29 8 255.16 0.22 432 0.00 0.07 32 260.59 0.21 434 0.00 0.13 61 264.20 0.28 420 0.00 0.17 60 18 270.70 0.50 420 0.01 0.25 0.04 0.02 50 274.80 0.19 419 0.00 0.07 38 19 280.09 0.17 414 0.01 0.07 0.13 0.01 41 285.70 0.20 416 0.00 0.07 36 20 290.08 0.45 420 0.01 0.30 0.03 0.03 67 0.31 8 21 295.08 0.42 416 0.01 0.25 0.04 0.02 59 22 300.08 1.08 420 0.05 1.01 0.05 0.09 94 0.34 38 23 304.08 0.66 423 0.01 0.34 0.03 0.03 52 0.35 36 sample depth (m) toc (wt%) tmax (°c) s1 (mg hc/g rock) s2 (mg hc/g rock) pi pc (wt%) hi %ro n table 1. rock-eval screening results and vitrinite reflectance toc : total organic carbon. tmax: temperature of maximum hydrocarbon generation during pyrolysis. s1: thermally-extracted hydrocarbons. s2: hydrocarbons generated during rock-eval pyrolysis. pl: production index [s1/(s1+s2)], derived from rock-eval pyrolysis. pc: pyrolysable carbon [0.083 (s1+s2)]. hl: hydrogen index [100 x s2/toc]. %ro: vitrinite reflectance. n: number of measurements. reflectance. the reflectance measurements are reported as the percentage (%ro) of the incident light reflected from the plane surface of the vitrinite surface when immersed in oil. the abundance of vitrinite particles is good for reflectance measurements, even in the lean samples, as most samples are dominated by humic material. in general, as many measurements as allowed by the available material were performed, and the quality of the data was noted. the average values shown in table 1 are based on reflectance measurements that were considered to be reliable. the most reliable data are considered to be from the coaly samples where the particles are so large that a detailed maceral identification is possible, and therefore the results are more reliable compared with samples containing fine-grained dispersed organic matter. in sample 3 (121.6 m), the organic material is represented entirely by large particles of woody tissue and the measurements were performed on texto-ulminite. the range of values is very narrow (0.25–0.40 %ro) with an average of 0.32 %ro from a total of 62 measurements. reflectance values from corpohuminite, which is also common, have the same range and almost the same average (0.31 %ro). the range of values in the other samples is somewhat larger, though still between 0.2 and 0.5 %ro. the best data quality is generally obtained from the upper coaly samples, whereas the quality decreases in some of the lowermost samples where the particle size of the 602 table 2. composition of the organic material v it ri ni te ps eu do vi tr in it e in er ti ni te li pt in it e sample maximum depth (m) organic content maceral composition liptinite composition d in o fla ge lla te s/ ac ri ta rc hs ta sm an ite s bo tr yo co cc us b it um in it e li pt o de tr in it e sp o ri ni te c ut in it e fl uo ri ni te r es in it e 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 113.6 119.85 121.60 127.60 136.60 149.90 159.70 170.90 175.55 184.48 187.82 189.65 209.60 221.60 230.53 239.28 249.68 270.70 280.09 290.08 295.08 300.88 304.08 moderate high very high moderate moderate moderate moderate high moderate high moderate low low low low low low very low very low low low low low xxxx xxx xxxxx xx x xxx xxx xxxxx xxx x xxxx xxx xxx xxxx xx xxxx xxx xxxx xxx x x xx xxx x xx xx xxx xx xx xx xx x x xx x xx x x x x xx xx x xx x x xx xx x x x x xxxx x x x x xx x x x xx xx x x x x x x x x x xx x xx xxx x x x x x x x x x x x x x xx x x x x xx x x x xx xx x xx x x x x x x x x x x xx xx x x xx xx x xx x x x x x xx x: abundance, ranked in terms of relative abundance (x–xxxxx). : observed. vitrinite is smaller and the morphological affinity of the vitrinite less obvious. the poorer quality is indicated by the wider range of the reflectance data. in samples 18, 19 and 21, it was not possible to perform measurements but the range of reflectance data in table 1 is considered reliable, due to the relatively large number of measurements on each sample. spectral fluorescence measurements were performed on a leitz orthoplan microscope equipped with a hamamatsu photomultiplier and a ploemopak for measurements and observations. the spectra were measured and their q value recorded (q = relative fluorescence intensity at 650 nm / relative fluorescence intensity at 500 nm). it was only possible to make fluorescence measurements on a few samples containing alginite, i.e. samples 4, 6, 7, 10, 21 and 22. the mainly yellowish-green fluorescence colours of the algal bodies indicate their degree of immaturity and correspond to their vitrinite reflectance values. all average q values are between 0.4 and 0.5, corresponding to the measured vitrinite reflectance values (schmidt 1989). uplift the increase in vitrinite reflectance down-section is the result of chemical processes controlled by time and temperature; the increase is linear with respect to time and exponential with respect to temperature (waples 1985). the changes to the chemical structure of the vitrinite are irreversible, and therefore the vitrinite reflectance reflects the maximum temperature to which the sediment has been exposed during burial. uplift will consequently not cause any change in the vitrinite reflectance. a difference between measured reflectance values from a certain depth and estimated reflectance values for that depth can therefore be used as an indication of the magnitude of uplift. a reflectance value of 0.20 %ro is normal for zero coalification at the depositional surface (teichmüller & teichmüller 1979). reflectance values above 0.3 %ro may first be expected at a depth of at least 1000 m in areas of the north sea with no uplift but a similar temperature history (hansen & thomsen 1990; schmidt 1990). the range of reflectance values slightly above 0.3 %ro suggests that some uplift and erosion has taken place. the uplift is estimated to have been about 1000 m; a comparable value (975 m) was obtained by petersen et al. (2003, this volume) who utilised the reflectance data reported here but applied a coalification curve derived from the danish basin. study of the organic material has thus indicated that: 1. the degree of diagenetic maturation is relatively low, but higher than expected for sediments at a depth range of approximately 100–300 m. 2. the ranges of tmax, vitrinite reflectance and q values suggest that the deposits have been exposed to temperatures that are commonly present at c. 1000 m depth. 3. the hi values and the coal petrographic interpretation indicate a terrestrial origin for most of the organic material. 4. the content of marine organic material is very low, and restricted to the lowermost few metres of the cored section. discussion palaeoenvironment nodosarid foraminifera, such as those found in the lowermost part of the borehole in foraminiferal zone fa from 306–304 m, referred to member f-iii of the fjerritslev formation, were typical of normal marine shelf conditions during the jurassic period (e.g. nagy et al. 1990). the nodosarid assemblage combined with the abundant dinoflagellate cysts of low diversity, the occurrence of ammonites, fish remains, bioturbation, the alternating clay and fine-grained sand lithology, and the low toc content (below 1%; fig. 2) suggest that a marine, inner shelf environment with well-oxygenated bottom conditions prevailed during the late pliensbachian (seidenkrantz et al. 1993; nagy & seidenkrantz in press). storm sands are common and relatively coarse-grained in the lowermost levels of the borehole (306–300 m). in contrast to this basal interval, the storm sands become less abundant and finer-grained above 300 m, although their abundance and grain-size varies, with a slight tendency to become more abundant and coarser upwards between 300 m and 260 m. in the uppermost pliensbachian – toarcian, bioturbation is less prominent and the clay-rich sediment contains an upwards increasing proportion of storm sand laminae, especially from 260 m. the thickness and grain size of the sand laminae also increase upwards, suggesting a gradual decrease in water depth through the toarcian. this is supported by the low abundance of 603 marine dinoflagellates, decreasing up-section, and the low-diversity agglutinated foraminiferal fauna (seidenkrantz et al. 1993; nagy & seidenkrantz in press). such foraminiferal assemblages may reflect low salinity, oxygen deficiency, turbulent conditions or rapid sedimentation and were characteristic of deltaic or prodeltaic environments in the jurassic (løfaldli & nagy 1980; nagy et al. 1988, 1990, 1995). thus, the dominance of ammobaculites, bulbobaculites, kutsevella and haplophragmoides, as well as the low diversity (cf. nagy et al. 1984, 1990; nagy 1992) suggest that the uppermost pliensbachian – toarcian sediments at anholt record progressive shallowing of the environment. the presence of a few ammonite fragments and some dinoflagellate cysts show that marine influence persisted. the absence of ostracods, the scarcity of burrows and the relatively common occurrence of haplophragmoides may reflect reduced oxygen conditions at the sea floor. during the following main part of the toarcian succession (upper palynomorph zone pb, 288–231 m) the sparse agglutinated foraminifera (ammobaculites and bulbobaculites) and the marine dinoflagellate cysts gradually disappear. upwards, storm-generated sand layers become more frequent, thicker and coarser and, especially above 260 m, these sands have erosional bases and show cross-lamination. this supports the interpretation of a progressive shallowing, indicated by the palaeobiological data. in the upper part of the interval, the presence of scattered lignite clasts and the increased proportion of reworked palynomorphs suggest an increasing supply of particles from a shallower part of the coastal zone, temporarily exposed to erosion, and/or from a neighbouring coastal plain. the coal petrographic interpretation indicates that most of the organic material has a terrestrial origin. member f-iv of the fjerritslev formation (231–201 m) is broadly referred to the aalenian stage. there are only few cores in this section, but the presence of layers with relatively low total gamma-ray signals, indicates that substantial parts of the unit consist of sand and silty sand and were deposited under higher energy conditions than the sediments below. the palynomorph assemblage contains a significant proportion of freshwater algae (palynomorph zone pc), which, combined with the occurrence of brackish-marine dinoflagellates and acritarchs, indicates a brackish-marine influence in the deltaic environment. the remaining part of the jurassic section, the uppermost aalenian – bajocian/bathonian haldager sand formation (201–104 m), represents a delta plain environment with only occasional brackish water influence in the lower part. this is shown by the absence of foraminifera and dinoflagellates, by the occurrence of acritarchs only in the lower part, and by the presence of brackish to freshwater algae throughout the section. the coal petrographic analysis indicates a marked dominance of terrestrial material, commonly with a varying degree of oxidation of the organic material. the cyclic alteration of sand, pebbly sand, clay, and lignite supports the delta plain interpretation. in the lowermost haldager sand formation, however, discrete thin finegrained sand beds are significantly enriched in th and u (fig. 7), probably reflecting concentration of heavy minerals under high-energy (beach?) conditions. comparison with the central danish basin our data indicate that at anholt most of the toarcian period was characterised by decreasing water depths. in the lower part of the toarcian section, evidence of shallowing is less pronounced, but is very distinct in the mid-toarcian section. in the central danish basin, much of the toarcian was characterised by an increase in water depth (michelsen 1978, 1989a), which may be correlated with a global sea-level rise (hallam 1988). the sea-level rise led to the establishment of stagnant bottom conditions (pedersen 1986; michelsen 1989a). in the central part of the danish basin, the shallowing of the basin first began in the late toarcian (michelsen 1989a, b). although the biostratigraphic data from anholt does not prove the presence of a complete toarcian section, we believe that most of the toarcian stage is represented, at least within the section of complete recovery below 248 m, as no indications of hiatuses have been observed here. it is deemed likely, therefore, that the regressive, shallowing event was initiated earlier at anholt than in the central parts of the danish basin. we suggest that such an early regressive tendency at anholt may be explained by the palaeogeographical position of the site. anholt is located in a marginal position relative to the danish basin and it is possible that progradation of the delta plain that characterised the entire danish basin in the middle jurassic (michelsen 1978), may have influenced anholt earlier than elsewhere in the basin. another possible explanation may be sought in local tectonic uplift in the fennoscandian border zone, but we have no other indications of such an early jurassic uplift in the area. the boundary between the fjerritslev and haldager sand formations in the danish basin has previously been considered to coincide with the lower–middle jurassic 604 boundary (michelsen 1978, 1989b) although michelsen & nielsen (1991) suggested that the uppermost part of the fjerritslev formation may be aalenian in age. our analyses have shown that member f-iv of the fjerritslev formation was deposited in aalenian time. at anholt, the toarcian–aalenian boundary (i.e. the lower–middle jurassic boundary) is thought to correspond broadly to the boundary between members f-iii and f-iv of the fjerritslev formation (fig. 3). post-depositional history and diagenesis the depth interval with vitrinite reflectance data is only about 200 m thick and a depth-related trend in reflectance is not evident. nevertheless, a tentative estimate of uplift has been derived, suggesting that about 1000 m of overburden are missing; this figure is compatible with that derived by petersen et al. (2003, this volume). this indicates that the maximum post-depositional subsidence of the jurassic sediments at anholt was about 1100–1300 m. this value is not very accurate, but the range seems to fit well with data obtained from other methods for quantification of uplift and erosion such as shale compaction, where sonic and density logs are used to estimate the magnitude of uplift (strømnes 1991; japsen 1992; jensen & michelsen 1992; jensen & schmidt 1992, 1993; lykke-andersen et al. 1993). the range of uplift values is compatible with values estimated from the northernmost part of jylland (japsen 1992; jensen & michelsen 1992; jensen & schmidt 1992, 1993). together they define a regional uplift trend almost parallel to the fennoscandian border zone. the regional trend in uplift for the danish area shows that no uplift or erosion has occurred in the central graben, whereas increasing uplift took place in a northeasterly direction towards the norwegian–swedish coast, reaching a maximum of about 1500 m. figure 16 shows how the data from anholt fit into this overall trend. though the magnitude of uplift estimated from differ605 0 m 500 m 1000 m 800 m 1200 m 1500 m ? ? ? ? neogene depocentre 1.0 1.5 2.0 n dk g nl 58°n 4°e 6°e 8°e 10°e 12°e 57°n 56°n anholt denmark sweden norway iso-uplift contours of the regional neogene uplift neogene depocentre: two-way time (sec.) to base of neogene major fault (reverse, normal) well used in this study, magnitude of uplift in metres iku shallow borehole iso-uplift contours of the late cretaceous – early tertiary inversion 0 200 400 1000600 800 ■■ ■■ ■■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ▲ ▲ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ■■ ▲ ▲ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ 400 900 700 700 800 800 800 800 1000 1200 1200 1200 1700 2000 1000 1000 1500 1500 100 km ▲ ■■ 1.0 fig. 16. iso-uplift map of the danish basin. modified from jensen & michelsen (1992). north sea sectors: dk, denmark; g, germany; n, norway; nl, the netherlands. 606 ent methods differs somewhat (japsen 1992, 1993), the overall trend in regional uplift superimposed by inversion along the sorgenfrei–tornquist zone is clear. anholt is situated close to the sorgenfrei–tornquist zone which was inverted during late cretaceous – early tertiary times. this zone is characterised by very high total uplift values reaching about 2000 m (e.g. for the terne-1 well; b.j. schmidt and l.n. jensen, personal communications 1994) representing an addition of 600–700 m to the regional uplift. however, the uplift at anholt does not reach a magnitude which demands a contribution from late cretaceous – early paleocene uplift within the inversion zone (fig. 16). a structural map of the top chalk group (ter-borch 1987) shows that upper cretaceous sediments are found at depths of 150–250 m below sea level both to the ne and sw of anholt. on anholt, lower–middle jurassic sediments occur at this depth, indicating differential uplift of the anholt site of at least this magnitude relative to the areas to the ne and sw. this uplift might have taken place during the inversion of the sorgenfrei–tornquist zone. thus, part of the uplift probably took place during the late cretaceous – paleocene inversion, but the main uplift of the area took place in oligocene–recent times as part of the regional uplift of scandinavia. the mineralogical composition, dominated by detrital quartz, muscovite/illite and kaolinite, with a subordinate smectite contribution increasing down-section, indicates that the source areas for the jurassic sediments had been exposed to intense weathering. diagenetic minerals such as chlorite are present in the lower part, but the presence of smectite demonstrates that the illitisation process, seen in most other wells in the danish basin, has not been significant. this is in accordance with the relatively minor post-jurassic subsidence of the anholt area. the thermal stability of the kaolinite increases down-section. the well-crystallised authigenic kaolinite in the sand layers of the haldager sand formation is less thermally stable than the detrital kaolinite. this indicates that the authigenic kaolinite formed after or during the late cretaceous – tertiary uplift and thus was not thermally stabilised during the subsidence-related progressive diagenesis. the spectral natural gamma-ray log has enabled better definition of the lithological boundaries, especially in sections with poor core recovery. in the transition between the marine clays and the non-marine sands, very high concentrations of th and u are present in relatively thin and well-defined layers. the origin of these layers is not yet fully known, but concentration of thand u-rich heavy minerals in a beach setting is thought to have been the dominant process. conclusions the present study has shown that member f-iii of the fjerritslev formation in the anholt borehole is of pliensbachian–toarcian age, member f-iv is of aalenian age and the haldager sand formation is of latest aalenian – bajocian/bathonian age. the sediments of the fjerritslev formation are mostly marine clays with varying proportions of storm sand laminae that generally increase up-section in abundance, thickness and grain-size. the haldager sand formation consists of an alteration of non-marine sand, clay and a few lignite layers. the sand layers are dominated by quartz and muscovite and, in the haldager sand formation, authigenic kaolinite and lignite clasts. the clays are dominated by kaolinite and illite with subordinate smectite, increasing in proportion down-section, and muscovite. in the lowermost haldager sand formation, the presence of heavy mineral-enriched fine-grained sand layers is inferred from geochemical anomalies. siderite and pyrite are commonly present as concretions, whereas calcite is only found in one concretion. the sand layers are unconsolidated and the clays still plastic. the diagenetic maturation of the organic material indicates that the sediments have been buried to a depth of about 1100–1300 m, and later uplifted to their present position, probably partly during late cretaceous – paleocene inversion and partly during the post-eocene regional uplift of parts of scandinavia. the detrital kaolinite exhibits a greater thermal stability (increasing down-section) than that expected in kaolinite at depths between 100 and 300 m. it is believed that the increased thermal stability was reached during progressive diagenesis, resulting from burial to a depth of 1200–1400 m. the progressive diagenesis did not reach the stage of complete illitisation of the original detrital smectite minerals. the lowermost part of the section, member f-iii of the fjerritslev formation, was deposited in a storminfluenced, marine, well-oxygenated environment. the influence of storms decreased somewhat in the latest pliensbachian and earliest toarcian, and the bottom conditions became more oxygen-deficient. throughout the remaining part of the toarcian, anoxic conditions prevailed and the environment shallowed progressively, probably due to localised, marginal high sedimentation rates despite the regional relative sea-level rise. deltaic environments dominated in latest toarcian – aalenian times, represented by the uppermost part of member f-iii and member f-iv of the fjerritslev formation. the bajocian/bathonian haldager sand formation is interpreted as a delta-plain deposit. acknowledgements we thank henrik friis for critically reading the manuscript, jette gissel nielsen who processed the foraminiferal samples and drafted some of the illustrations, bitten larsen and yvonne desezar for processing the palynological samples, and ulla bjerring, jette grejs pedersen, bente winsløv jensen and terese k. rasmussen for performing the sediment-analysis. lis olesen is thanked for drafting assistance. this work was supported by the danish natural science research council (geokat and magkat projects and an ole rømer stipendium to m.-s.s.) and the 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(eds): petroleum geology of north west europe, 375–388. london: graham & trotman. tissot, b.p., pelet, r. & ungerer, p. 1987: thermal history of sedimentary basins, maturation indices and kinetics of oil and gas generation. american association of petroleum geologists bulletin 71, 1445–1466. waples, d.w. 1985: geochemistry in petroleum exploration, 232 pp. boston: international human resources development corporation. woollam, r. & riding, j.b. 1983: dinoflagellate cyst zonation of the english jurassic. institute of geological sciences report 83/2, 42 pp. london: her majesty’s stationery office. 609 manuscript received 2 september 1994; revision accepted 13 may 1997. geological survey of denmark and greenland bulletin 35, 2016, 59-62 59© 2016 geus. geological survey of denmark and greenland bulletin 35, 59–62 . open access: www.geus.dk/publications/bull for more than 80 years the skaergaard intrusion, 68°n in southern east greenland, has been a foremost natural laboratory for the study of the crystallisation and fractionation of basaltic magma. this process has been of prime importance in the evolution of the earth and other stony planets. models that have been developed and refined during numerous studies of this particular intrusion have been part of the foundation for petrogenetic modelling for decades. in later years, vast amounts of new data have been added, due to systematic sampling in the field and from analysis of exploration drill cores. methods for the study on grain-size scale have advanced, and the quest for a wellsupported genetic model for the pge-au mineralisation of the intrusion has intensified. the new data and insight question the applicability of conventional petrogenetic modelling, and as a consequence, increasing importance is placed on in situ crystallisation and fractionation in mush zones at the roof, walls and floor of the intrusion. the skaergaard intrusion the skaergaard intrusion (wager & brown 1968) is a comparatively small but well-preserved and well-exposed layered gabbro intrusion (fig. 1a). it is 56 ma old (wotzlaw et al. 2012) and was emplaced during the opening of the north atlantic. it is 7 × 11 km in surface exposure, has a total structural height of c. 4 km, and, dependent on the chosen modelling paradigm, has a box-like (nielsen 2004) or ellipsoid shape (irvine et al. 1998, svennevig & guarnieri 2012) and a volume of c. 300 km3. the intrusion crystallised concentrically inward from the margins (fig. 1b) with the layered series (ls, lz, mz and uz) in the bowl-shaped floor, the marginal border series (mbs) on the walls, and upper border series (ubs) below the roof. the ubs and ls meet at the sandwich horizon (sh). all three series are subdivided on the basis of a parallel evolution in liquidus parageneses (salmonsen & tegner 2013 and references therein). new research initiatives petrogenetic modelling of the skaergaard gabbros and the evolution of the melt in the intrusion have traditionally rested on the textural interpretation of the gabbros as rocks composed of liquidus crystals, continued growth of these in situ fractionation and inward migration of the solidification front in the skaergaard intrusion, east greenland troels f.d. nielsen enewsw sh sh no vertical exaggeration 2 km mbsmbs sea level uzc uzb uza mz lzc lzb lza+hz ubsubs mbsmbs fault upper zone greenland 5 km miki fjord watkins fjord a b 31°25´w 68°15´n sediment other gabbros skaergaard intrusion flood basalts basement gneiss ubs uz mzmbs lz upper border series middle zonemarginal border series lower zonelayered series l ay e re d s e ri e s ls fig. 1. a: geological setting of the skaergaard intrusion between basement gneisses, sediments, other gabbros and f lood basalts. location in greenland in insert. b: reconstructed cross-section (nielsen et al. 2015). the upper and lower zones of the layered series are subdivided on the basis of liquidus paragenesis (see text). sea level and present topography are shown in black lines. 6060 crystals in equilibrium with the bulk liquid (adcumulus growth), and crystallisation of solids from trapped liquids. sorting of crystals on the magma chamber floor has been likened to processes established for clastic sediments, including stratification of crystal mushes in matrix-supported mass flows. despite challenges these models have remained robust, and most researchers are faithful to this classic cumulus paradigm and the modelling tools developed therefrom. research initiatives in the later decades of the 20th century (mcbirney 1996 and references therein) provided much new information and were accompanied by investigations facilitated by the exploration of pge-au mineralisation in the intrusion (e.g. bird et al. 1991). notable outcomes of this research include the development of double diffusive convection models (mcbirney & noyes 1979), evaluation of the petrogenetic importance of immiscibility between fe-rich and si-rich silicate melts (jakobsen et al. 2011 and references therein), as well as evidence for isotopic disequilibrium and tight age controls on the emplacement and solidification of the intrusion (see wotzlaw et al. 2012, and references therein). the studies of the skaergaard intrusion surged in 2000 with access to assay data and up to 1200 m long drill cores. the data in the public domain allowed calibration of structural models for the interior of the intrusion (nielsen 2004), erection of compaction models (tegner et al. 2009; mckenzie 2011), and studies of the mineralisation (nielsen et al. 2005, 2015; andersen 2006; rudashevsky et al. 2015 and references therein; holwell et al. 2015; keays & tegner 2015). petrographic studies focused, e.g. on compositional variations in plagioclase (namur et al. 2014) and on clinopyroxene-filled dihedral angles between plagioclase crystals (e.g. holness 2015 and references therein). changes in dihedral angles give indications for, e.g. the arrival of new phases on the liquidus of the silicate melts and changes in permeability, and thus for the controls on the mobility of elements of economic interest. c o re -m an tl e t ra n si ti o n m an tl e -r im t ra n si ti o n core mantle rim (b) 40 45 50 55 a n -c o n te n t (% ) 0 50 100 150 200 250 300 350 distance (μm) fig. 2. compositional variation in lzb plagioclase crystal with small core (liquidus) and broad mantle crystallised during in situ fractionation involving mush melt, and rim crystallised during buffered crystallisation (after namur et al. 2014). a plag plag s s s ol ol ol s s s s plag cpx cpx mt ilm ilm cpx feti b s fig. 3. a: transmitted light image (c. 13 × 9 mm) showing interconnected magnetite and ilmenite that crystallised from interstitial mush melt. b: electron microprobe backscatter image (see nielsen et al. 2015). symplectites (s) formed by reaction between plagioclase and reactive fe-rich mush melt that crystallised most of the magnetite and ilmenite in the view. cpx: clinopyroxene (with exsolutions in fig. 3b). feti: feti-oxides. ilm: ilmenite. mt: magnetite. plag: plagioclase. ol: olivine. s: symplectitic intergrowths. scale at base of the image. 61 the importance of in situ fractionation modelling based on the classic cumulate paradigm suggests that the proportion of trapped liquid decreased from 30– 50 per cent to only a few per cent during the solidification of the intrusion (tegner et al. 2009). this is, however, in conflict with reactions between liquidus minerals and ferich silicate melts (holness et al. 2011) and the occurrence of immiscible melt droplets throughout much of the floor cumulates (jakobsen et al. 2011 and references therein). they are supposed to result from extended in situ crystallisation and fractionation (langmuir 1989) in crystal mush, long residence time, and ineffective compaction. this is supported by the very common zonation in plagioclase (an example is shown in fig. 2, namur et al. 2014) and the distribution of magnetite crystallised from interstitial melt (fig. 3a; nielsen et al. 2015). toward a new solidification model a magma chamber will always be hot in the middle and crystallisation will always occur in the crystal mush between solidified gabbro and the remaining melt, unless the system is affected by vigorous convection. in the skaergaard intrusion this seems unlikely due to the concentric solidification (nielsen 2004). all gabbro samples have recorded a temperature interval on the line of liquid descent and all have witnessed the inward migration of the crystallisation front, fronts with new phases on the liquidus of the mush liquid, and the solidification front. the mushy layer is a sub-chamber of crystal mush migrating inwards, and the samples we collect reflect only processes within the mush itself and the bulk composition of the liquid that was processed in the mush (fig. 4). any sample of the gabbros is composed of minerals left behind by the inward-migrating mush layer. in broad terms, the composition of the floor gabbro is equal to bulk liquid minus what rose out of the floor, e.g., low density melt, and that of the roof gabbro is equal to what remained under the roof, e.g. low density minerals and melt (salmonsen & tegner 2013; nielsen et al. 2015). roof and floor series are complementary, and neither series represents the evolution of the bulk magma, but their weighted average does. the modelling of the evolution of layered intrusions is commonly only based on exposed floor cumulates, and the common neglect of complementary successions in the lost roof of the intrusions may therefore lead to erroneous petrogenetic conclusions. undoubtedly, future research in the skaergaard intrusion and its mineralisation will focus on very detailed petrography, mineralogy, in situ mineral chemistry and isotope geochemistry, and on unravelling of the complexities of the solidification processes. petrogenetic modelling on the basis of bulk rock chemistry without detailed petrographic information is prone to lead to significant oversimplification and unwarranted confirmation of the chosen models. references andersen, j.c.ø. 2006: postmagmatic sulphur loss in the skaergaard intrusion: implications for the formation of the platinova reef. lithos 92, 198–221. bird, d.k., brooks, c.k., gannicott, r.a. & turner, p.a. 1991: a goldbearing horizon in the skaergaard intrusion, east greenland. economic geology 86, 1083–1092. holness, m.b. 2015: plagioclase growth rates control three-grain junction geometry in dolerites and gabbros. journal of petrology 56(11), 2117–2144. holness, m.b., stripp, g., humphreys, m.c.s., veksler, i.v., nielsen, t.f.d. & tegner, c. 2011: silicate liquid immiscibility within the crystal mush: late-stage magmatic microstructures in the skaergaard intrusion, east greenland. journal of petrology 52, 175–222. holwell d.a., keays, r.r., mcdonald, i. & williams, m.r. 2015: extreme enrichment of se, te, pge and au in cu sulfide microdroplets: evidence from la-icp-ms analysis of sulfides in the skaergaard intrusion, east greenland. contributions to mineralogy and petrology 170:53, http://dx.doi.org/10.1007/s00410-015-1203-y irvine, t.n., andersen, j.c.ø. & brooks, c.k. 1998: included blocks (and blocks within blocks) in the skaergaard intrusion: geological relations and the origins of rhythmic modally graded layers. geological society of america bulletin 110, 1398–1447. jakobsen, j.k., veksler, i.v., tegner, c. & brooks, c.k. 2011: crystallization of the skaergaard intrusion from an emulsion of immiscible ironand silica-rich liquids: evidence from melt inclusions in plagioclase. journal of petrology 52, 345–373. keays, r.r. & tegner, c. 2015: magma chamber processes in the formation of the low-sulphide magmatic au–pge mineralization of the hot and liquid interior only tiny crystals no significant crystal settling host rocks inward-migrating mush zone subjected to in situ fractionation and crystallisation solid gabbro with crystallisation in trapped liquid fig. 4. principles of the proposed model of inward migration of mush zone and liquidus front. the inward-migrating mush zone is shown in orange. the residual bulk liquid in the centre has only small and suspended crystals of liquidus phases. the remaining bulk melt is always at liquidus due to feedback from the mush zone (see nielsen et al. 2015 for details of model). 6262 platinova reef in the skaergaard intrusion, east greenland. journal of petrology 56, 2319–2340. langmuir, c. h. 1989: geochemical consequences of in situ crystallization. nature 340, 199–205. mcbirney, a.r. 1996: the skaergaard intrusion. in: cawthorn, r.g. (ed.): layered intrusions, 147–180. amsterdam: elsevier. mcbirney,a,r. & noyes, r.m. 1979: crystallization and layering of the skaergaard intrusion. journal of petrololgy 20(3), 487–554. mckenzie, d. 2011: compaction and crystallization in magma chambers: towards a model of the skaergaard intrusion. journal of petrology 52(5), 905–930. namur, o., humphreys, m.c.s. & holness, m.b. 2014: crystallization of interstitial liquid and latent heat buffering in solidifying gabbros: skaergaard intrusion, greenland. journal of petrology 55(7), 1389–1427. nielsen, t.f.d. 2004: the shape and volume of the skaergaard intrusion, greenland: implications for mass balance and bulk composition. journal of petrology 45(3), 507–530. nielsen, t.f.d., andersen, j.c.ø. & brooks, c.k. 2005: the platinova reef of the skaergaard intrusion. in: mungall, j.e. (ed.): exploration for platinum-group element deposits, 431–455. mac short course 35. ottawa: mineralogical association of canada. nielsen t.f.d., andersen j.c.ø., holness, m.b., keiding, j.k., rudashevsky, n.s., rudashevsky, v.n., salmonsen, l.p., tegner, c. &. veksler, i.v. 2015: the skaergaard pge and gold deposit: the result of in situ fractionation, sulphide saturation, and magma chamber-scale precious metal redistribution by immiscible fe-rich melt. journal of petrology 56(8), 1643–1676. rudashevsky, n.s., rudashevsky, v.n. & nielsen, t.f.d. 2015: intermetallic compounds, copper and palladium alloys in au–pd ore of the skaergaard pluton, greenland. geology of ore deposits 57(8), 674–690. salmonsen, l.p. & tegner, c. 2013: crystallization sequence of the upper border series of the skaergaard intrusion: revised subdivision and implications for chamber-scale magma homogeneity. contributions to mineralogy and petrology 165, 1155–1171. svennevig, k. & guarnieri, p. 2012: from 3d mapping to 3d modelling: a case study from the skaergaard intrusion, southern east greenland. geological survey of denmark and greenland bulletin 26, 57–60. tegner, c., thy, p., holness, m.b., jakobsen, j.k. & lesher, c.e. 2009: differentiation and compaction in the skaergaard intrusion. journal of petrology 50(5), 813–840. wager, l.r. & brown, g.m. 1968: layered igneous rocks. edinburgh and london: oliver & boyd, 588 pp. wotzlaw, j.-f., bindeman, i.n., schaltegger, u., brooks, c.k. & naslund, h.r. 2012: high-resolution insights into episodes of crystallization, hydrothermal alteration and remelting in the skaergaard intrusive complex. earth and planetary science letters 355–356, 199–212. author’s address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark; e-mail: tfn@geus.dk geological survey of denmark and greenland bulletin 35, 2016, 35-38 35© 2016 geus. geological survey of denmark and greenland bulletin 35, 35–38. open access: www.geus.dk/publications/bull roskilde fjord is a characteristic n–s-trending geomorphological element in north-east sjælland (fig. 1). the eastern coastline of the fjord forms a nearly straight, sse– nnw-trending lineament from the town of roskilde to the coastal areas at kattegat. due to the records from wells, it has long been known that a fault zone has to be present along this lineament (bondesen 1979). the fault is named after the fjord: the roskilde fjord fault (fig. 2). however, a detailed analysis of the well data in the roskilde area has shown that a number of minor faults are present, superposed by various landscape elements. these are the inner fjord and valley distributary at roskilde, the kornerup å valley, the inlet of lejre vig and its contributory, and the peninsula of bognæs (figs 1, 2). in this paper we propose a lithostratigraphic division of the cenozoic deposits and their dynamic development in the roskilde area. a distribution of the faults with estimated maximum displacements is presented, and their relations to the geomorphological features are outlined. the description is based on several years’ studies of the roskilde fjord fault complex and presented here due to the recent interest in neotectonics in denmark and environmental considerations focused on roskilde fjord (gravesen & pedersen 2005). stratigraphy of the roskilde area the palaeogene and quaternary stratigraphy of the area is briefly outlined here based on well data and a few sand and gravel pit outcrops (gravesen & pedersen 2005). the palaeogene deposits in the area include danian and selandian formations (65.5 to 58.7 ma). the late danian københavn kalk formation consists of calcisiltitic and calcarenitic yellow-white limestone with some thick chert layers (thomsen 1995). the overlying, early selandian deposits were laid down after a period of erosion and often begin with glauconitic conglomerate and greensand of the lellinge greensand formation followed by olive grey glauconitic silty limestone, sand and clay (clemmensen & thomsen 2005). the pre-quaternary unconformity thus truncates danian as well as selandian units. the oldest quaternary deposits are probably from the late saalian (150–130 ka bp). the clayey tills and sand layers are found in deep buried valleys down to 80 m below the surface. the deposits are known from wells but are difficult to date precisely. jacobsen (1985) also suggested that saalian deposits were the oldest quaternary deposits in the area. from the early middle weichselian thin and fragmented sand layers were deposited in rivers and lakes, and the surficial processes possibly initiated the valley formation c. 70–55 ka bp. a middle weichselian ice stream from the east, the 55–50 ka bp old baltic ice stream, deposited the ristinge klint till formation, characterised by reddish staining of the clayey and sandy tills (houmark-nielsen 2010). the late weichselian himmelev formation consists of cross-bedded meltwater sand and gravel deposited by braided streams from the north (jacobsen 1985), indicattectonic control on the formation of roskilde fjord, central sjælland, denmark stig a. schack pedersen and peter gravesen bognæs eskilsø sjælland kattegat le jre v ig k or ne ru p å himmelev kirke såby veddelev roskilde risø fig. 1. terrain model of the roskilde area and index map of denmark showing the location of the area in focus. note the strong s–n-trending lineament including the linear coast lines of roskilde fjord. 3636 ing deposition at the southern front of the melting kattegat ice stream at c. 26 ka bp. this unit is overlain by the grey to brown, massive mid danish till formation deposited by the ice stream from north-east during the last glacial maximum (houmark-nielsen 1987, 2010). the mid danish till formation is overlain by the hedeland formation, which is a very coarse-grained, cross-bedded sand/gravel formation deposited as a proximal sandur and in meltwater channels (jacobsen 1985). the last ice advance, the young baltic ice advance, was separated into two. the first, the east jylland advance from the south-east and east deposited the east jylland till formation of grey and brown clayey till at 19–18 ka bp (houmark-nielsen 2010). in the following period, which was free of ice cover, glaciolacustrine sediments were deposited. the last advance from the east and south-east deposited the brown, clayey bælthav till formation (18–17 ka bp). during the final melting of the last glaciers the vindinge formation consisting of fine-grained sand, silt and clay was deposited in a dead ice landscape. marine holocene sand and mud deposits are found along the coast of roskilde fjord, while freshwater deposits occur along small streams and in lakes. method of cross-section construction the analysis of the subsurface geology in the roskilde fjord area was carried out by the construction of a large number of mainly e–w-trending cross-sections perpendicular to the interpreted strike of fault features. the cross-sections were constructed in arcgis©, using well data from the jupiter database along chosen sections with a bandwidth of 1 km. maps were constructed from a selection of these wells, providing information on the depth to the pre-quaternary unconformity and the local lithology at the pre-quaternary surface (fig. 2). the pre-quaternary unconfomity map was produced by an integration over the well data points using arcgis©. depth to the pre-quaternary unconformity the map of the depth to the pre-quaternary unconformity (fig. 2) shows that the surface forms a high plateau to the east of roskilde, reaching a level above 30 m a.s.l. along the drainage creek to the south-eastern arm of roskilde fjord and along the eastern coastline, the structural contours of the surface of the pre-quaternary unconformity are closely spaced and trend n–s, indicating an escarpment parallel to the east coast of the roskilde fjord. below the central part of the southern depression of roskilde fjord, where the peninsula of bognæs is located, the depth to the pre-quaternary unconformity is more than 40 m b.s.l. thus, the level change from east to the central part of roskilde fjord is almost 80 m. the south-western corner of the roskilde fjord is dominated by two strong lineaments parallel to the geomorphic features kornerup å and lejre vig, where two buried val0 -30 -20 -20 -20 -20 -10 -40 10 10 -5 0 20 40 -40 0 -10 -4 0 -5 0 -2 0 0 -10 30 0 -10 0 -10 60 -6 0 -70 -30 -30 -2 0-3 0 -2 0 -20 -20 -1 0 -20 30 -10 -3 0 -10 10 -40 -40 r is ø fa ul t h o rn sh er re d fa ul t le jr e v ig f au lt g ev ni ng e f au lt r o skilde fjo rd fault h erslev fault kattinge vig graben sønde rsø g raben sønde rsø g raben la ng ho lm h o rs t k o rn er up g ra be n ågerup block rosk ilde fjord 5 kmn normal fault lineament paleocene deposits danian limestone w ew e himmelev block fig. 2. geological map of the formations occurring on the pre-quaternary unconformity surface and location of the cross-section shown in fig. 4. the contour lines show the depth in metres to the pre-quaternary unconformity based on well data. roskilde forkastning risø fault ågerup block himmelev block veddelev block c. 100 m c. 1 km roskilde fjord fault fig. 3. the block diagram illustrates the relay faults along the east side of roskilde fjord. 37 leys are eroded to a depth of more than 70 m b.s.l. (fig. 1). between the lineaments the pre-quaternary unconformity has an elevation of 0–10 m b.s.l., and farther to the west and south-west at kirke såby the surface forms a plateau at about sea level (fig. 2). to the north the roskilde fjord changes from a broad basin to a narrow fjord arm extending northwards. the shift is located to the area around eskilsø, and the broad basin depression to the south is interpreted as the interference between the roskild fjord lineaments and the e–w-trending søndersø graben (fig. 2). this graben system is interpreted as partly tectonically controlled but mainly mirrors a tunnel-valley drainage system to the west related to the baltic ice advance. block faulting of danian limestone and paleocene limestone and clay only two formations are distinguished at the pre-quaternary unconformity surface: danian limestone and paleocene limestone and clay (fig. 2). their distribution follows two rules: danian limestone either appears where a trench has been carved down to a depth below the base of the paleocene limestone, greensand and clay, or it appears on elevated plateaux above the paleocene deposits. the latter is the case east of roskilde, whereas carved trenches are seen below the kornerup å valley and the lejre vig buried valley (figs 1, 2). the broad, e–w-trending søndersø graben belongs in the first group representing a buried valley sandur. the faults are relay faults (korstgård 1996). this means that they have a hinge point where the displacement is negligible, and from where the displacement increases along strike (fig. 3). a culmination of the displacement occurs about 1–4 km from the hinge point, and then the displacement decreases to another hinge point at the opposite termination of the fault. in the roskilde fault complex the maximum displacement is calculated to about 60 m, but most faults have displacements only in the range of 10–30 m. the marker horizon used for estimation of the displacement is the boundary between the danian limestone and the selandian deposits. this boundary is believed to have been an almost horizontal plane, given that both units are marine successions deposited in the broad shelf environment that dominated the danish basin in the palaeogene. w e gl. lejre kornerup å glim vor frue 2 km 0 -10 -20 -30 -40 -50 m bælthavs till fm weichselian saalian paleocene east jutland till fm hedeland fm mid danish till fm himmelev till fm ristinge till fm undifferentiated glaciofluvial deposits undifferentiated glaciofluvial till fm selandian limestone, greensand and clay unconformity danian limestone fault fig. 4. e–w cross-section of the area south of roskilde fjord (location shown in fig. 2). below the geological cross-section, two back-stripped cross-sections illustrate the early fault and landscape evolution. grey vertical lines represent wells. 3838 glaciodynamic development of the quaternary succession the interpretation of the dynamic development includes a palinspastic reconstruction shown in fig. 4. the interpreted cross-section also illustrates two former structural steps in the development. the first of these goes back to an unconformity that is interpreted as a peneplanation in the main part of the middle-late weichselian. the second step is a further back-stripping to the supposed eemian peneplanation after the saalian glaciation; this scenario illustrates the interpreted faulting of the boundary between the danian limestone and selandian unit. evidently, at this time the roskilde fault complex had already been active. furthermore, a deep incised valley along the kornerup å lineament was probably initiated in the neogene prior to the late pleistocene. we suggest that deep valley erosion in the elsterian was succeeded by infill into the valley of meltwater sand and tilly material in the saalian (fig. 4). during the middle weichselian the ristinge advance deposited meltwater sand and the ristinge till formation on a succession that had been faulted. in the beginning of the late weichselian, the last glacial maximum initiated the swedish ice advance (pedersen 2012), which resulted in meltwater streams eroding into the surfaces of downthrown blocks. renewed erosion and deposition took place in the kornerup å valley, and new valleys were formed in the blocks to the east and to the west along fault lineaments. after the meltwater sand of the himmelev formation had filled the valleys to form a relatively even outwash plane surface, the mid danish till formation covered the area with a more than 10 m thick clayey basal till. after the deposition of the mid danish till formation, a new phase of faulting occurred along the roskilde fault. this resulted in a relative uplift of the block to the east and the total vertical displacement by c. 60 m. during the young baltic ice advance in the late weichselian the mid danish till formation and the underlying himmelev formation were eroded away from the elevated area to the east, whereas the sequence was preserved in a down-faulted block to the west. the young baltic ice advance had oscillating advances and retreats including the east jutland ice advance and the bælthav ice advance (houmark-nielsen 2010). at this time the main part of eastern denmark became covered by a huge outwash plane. at roskilde this resulted in the deposition of the hedeland formation which is the main source for gravel exploitation in the roskilde area (the previous interpretation of the hedeland formation by jacobsen 1985 is now considered redundant). thin beds of till are commonly present in this meltwater succession, representing the oscillating ice conditions. before the final erosion of the valleys and fjord arms the bælthav till formation was deposited shaping the present hummocky moraine plateau landscape. conclusions the geomorphology of the roskilde area mirrors a number of tectonic and depositional elements in the subsurface. the fault zones responsible for several terrain lineaments are relay faults that outline an imperfect en échelon pattern. the fault displacements can be calculated from the position of the boundary between the danian limestone and the selandian unit. neotectonic displacement was active shortly after the deposition of the mid danish till formation. the deepest buried valleys were probably eroded out during the elsterian glaciation and filled with sand and till during the saalian glaciation. these valleys were buried during the weichselian glaciodynamics. references bondesen, e. 1979: roskilde, by og landskab – geologi og samfund. in: birkebæk, f.a. (ed.): 13 bidrag til roskilde byog egnshistorie. roskilde museums 50 års jubilæumsskrift, 20–41. roskilde: roskilde museum. clemmensen, a. & thomsen, e. 2005: palaeoenvironmental changes across the danian–selandian boundary in the north sea basin. palaeogeography, palaeoclimatology, palaeoecology 219, 351–394. gravesen, p. & pedersen, s.a.s. 2005: de geologiske forhold ved risø. redegørelse udarbejdet på basis af eksisterende data. danmarks og grønlands geologiske undersøgelse rapport 2005/30, 40 pp. houmark-nielsen, m. 1987: pleistocene stratigraphy and glacial history of the central part of denmark. bulletin geological society of denmark, 36, 189 pp. houmark-nielsen, m. 2010: extent, age and dynamics of marine isotope stage 3 glaciations in the southwestern baltic basin. boreas 39, 343–359. jacobsen, e.m. 1985: en råstofgeologisk kortlægning omkring roskilde. dansk geologisk forening, årsskrift for 1984, 65–78. korstgård, j.a. 1996: ekstensionsforkastninger. geologisk tidsskrift 1, 1–24. pedersen, s.a.s. 2012: glaciodynamic sequence stratigraphy. in: huuse, m. et al. (eds): glaciogenic reservoirs and hydrocarbon systems. geological society, london, special publications 368, 29–51. thomsen, e. 1995: kalk og kridt i den danske undergrund. in: nielsen, o.b. (ed.): danmarks geologi fra kridt til i dag. aarhus universitet geokompendier 1, 32–67. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: sasp@geus.dk a reconnaissance study of fluid inclusions in fracture-filling quartz and calcite from the lopra-1/1a well, faroe islands 119© geus, 2006. geological survey of denmark and greenland bulletin 9, 119–122. available at: www.geus.dk/publications/bull a reconnaissance study of fluid inclusions in fracture-filling quartz and calcite from the lopra-1/1a well, faroe islands jens konnerup-madsen fracture-filling calcite and quartz from the lopra-1/1a well (at 2380 m and 3543 m depth) contains both aqueous low-salinity fluid inclusions and hydrocarbon-dominated fluid inclusions. microthermometry indicates that the aqueous fluids contain 0.2 to 1.4 equivalent weight% nacl and occasionally contain traces of hydrocarbons. homogenisation to liquid occurred between 90°c and 150°c. modelling based on these fluid inclusion observations indicates that during burial the basaltic section was subjected to temperatures of 160°c and 170°c, occasional pressures of 600–700 bars and the simultaneous percolation of aqueous and hydrocarbon fluids. these fluid conditions may also be relevant to the formation of zeolite observed in the lopra-1/1a well. keywords: basalts, faroe islands, fluid inclusions, hydrocarbons, veins, zeolites __________________________________________________________________________________________________________________________________________ geological institute, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k., denmark. e-mail: jenskm@geol.ku.dk fluid inclusions in cements or minerals filling vugs and fractures in buried sedimentary and volcanic rocks may provide important information on the chemical and physical nature and origin of mineral-precipitating fluids, on the potential interplay between migrating hydrocarbon and aqueous fluids, and on the temperatures and pressures of precipitation (e.g. bodnar 1990; jensenius & burruss 1990). a reconnaissance study was undertaken of fluid inclusions in vugand fracture-filling quartz and calcite from samples taken from the basalts penetrated by lopra1/1a. the two samples studied are from core 1 (2380 m) and sidewall core 1 (3543 m). the fluid inclusions were examined by ordinary microscopy, fluorescence microscopy and with a chaixmeca heating and freezing stage. types and setting of fluid inclusions in selected samples the samples were selected by examining about 40 thin sections taken between 2204 m and 3543 m depth in the lopra-1/1a well. only two samples, from 2380 m and 3543 m depth, were found to contain fracture-filling quartz and calcite with fluid inclusions suitable for further study. sample 2380 m (lopra-1, core 1) is a sparsely plagioclase-glomerophyric olivine-clinopyroxene basalt with almost complete alteration of plagioclase and olivine. the quartz and calcite studied occur in mm-wide veins. the veins are rimmed by chlorite, calcite and quartz that appear to have been precipitated contemporaneously. according to jørgensen (2006, this volume) the zeolites characterising this level in the core are laumontite, prehnite and pumpellyite. sample 3543 m (lopra-1a, sidewall core 1) is a nearaphyric lapilli-tuff with extensively altered plagioclase, olivine and clinopyroxene phenocrysts in a cryptocrystalline groundmass. the irregular veins contain laumontite, prehnite, calcite and rare quartz. the veins are rimmed by chlorite. again, calcite and quartz appear to have been precipitated contemporaneously, although quartz precipitation might have been slightly later. geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19119 120 0 1 2 3 50 100 150 200 homogenisation temperature, °c sa lin it y, w t% n ac l group a group b data on fluid inclusions in quartz from lopra-1/1a altered basalt field for aqueous fluid inclusions in calcite types of fluid inclusions in quartz and calcite two types of fluid inclusions were observed using fluorescence and ordinary light microscopy: (1) aqueous twophase (liquid-vapour) inclusions with about 5 vol.% vapour at room temperature, and (2) one or two-phase hydrocarbon inclusions with fluorescence emission colours that vary from orange-yellow to green. with ordinary light microscopy it is difficult to distinguish between the twophase liquid-vapour hydrocarbon and aqueous inclusions, although the latter seem to be characterised by a (perhaps) slightly lower vol.% vapour than the former. no clear relative chronology between the two fluid inclusion types could be established. examples of typical morphologies and phase proportions of fluid inclusions observed in quartz are shown in fig. 1. in general, the fluid inclusions are characterised by immature morphologies and occur in irregular groupings or in curved internal planar arrangements, suggesting periods for their entrapment which do not markedly postdate the growth of the host mineral. the liquid-vapour ratio in individual groupings varied slightly, most probably and mainly as a result of necking down of the inclusions after entrapment, because liquid-only inclusions could occasionally be observed together with the aqueous two-phase liquid-vapour inclusions. all inclusions indicative of having been influenced by necking down were avoided during the heating and freezing stage work. microthermometry results on aqueous fluid inclusions the results of microthermometry of fluid inclusions in quartz and calcite are summarised in fig. 2. fluid inclusions in quartz incipient melting of ice was observed at temperatures around –32°c, indicating the presence of additional ions such as ca2+, mg2+ and/or fe2+ in solution rather than chlorides of na+ and/or k+ (konnerup-madsen 1979). final melting temperatures were observed in the range –0.1°c to –0.9°c, corresponding to salinities from 0.167 to 1.49 equivalent weight% nacl, respectively (average: 0.62 equivalent weight% nacl) (bodnar et al. 1989), but with no clear difference between the two samples. temperatures of homogenisation occurred between 94°c and 150°c and bimodality in temperature is suggested from the data (see fig. 2, groups a and b). group a and group b inclusions gave average homogenisation temperatures of 108°c and 141°c, respectively. group b inclusions in quartz showed in three cases clear indications (ragged outline of meniscus between vapour and liquid) of the formation of a clathrate hydrate after initial ice melting, indicating the presence of trace amounts of volatiles such as hydrocarbons in the entrapped group b fluids. however, although no temperature of dissolution of the hydrate could be obtained and hence the identity of the volatile component could not be established, its formation suggests that the higher temperatures of homogenisation obtained for group b inclusions may reflect trace concentrations of hydrocarbons in the vapour phase of these inclusions. fig. 1. examples of typical morphologies of aqueous liquid-vapour fluid inclusions in quartz from core 1 (2380 m) from lopra-1/1a. fig. 2. salinity versus liquid homogenisation temperatures of aqueous inclusions in quartz from lopra-1/1a. 10 µm geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19120 121 fluid inclusions in calcite only very few measurements were made on inclusions in calcite, as most inclusions occurred along well-defined healed fracture-planes so are secondary in origin. final melting temperatures varied between –0.2°c and –0.7°c, corresponding to salinities of 0.33 to 1.16 equivalent weight% nacl. homogenisation temperatures varied from 101°c to 186°c (fig. 2). however, the higher homogenisation temperatures might conceivably reflect partial decrepitation (stretching) of the inclusions during heating (e.g. bodnar & bethke 1984). two-phase (liquid-vapour) hydrocarbon inclusions were observed in fluorescence microscopy in both calcite and quartz. the abundance of hydrocarbon inclusions appears to be relatively higher in calcite and only very few were observed in quartz. the emission colours, from orangeyellow to green, may be interpreted roughly in terms of compositions corresponding to api gravities of 20–35 (lang & gelfand 1985). no successful heating and cooling runs were, however, obtained on the hydrocarbon inclusions in the two samples. interpretation of fluid inclusion data an interpretation in terms of pressures and temperatures for entrapment of the fluid inclusions in quartz is shown in fig. 3. isochores corresponding to group a and b inclusions (brown 1989) in quartz are shown in fig. 3, assuming them to be pure aqueous fluids with salinities as indicated by the final ice melting temperatures (fig. 2). no indications of the entrapment of boiling aqueous fluids were observed during this study and the homogenisation temperatures for the fluid inclusions observed are thus considered to be minimum temperatures of fluid entrapment and host mineral formation. a comparison with geothermal gradients of 20°c/100 bars and 20°c/226 bars that are considered relevant for lopra-1/1a and that reflect hydrostatic and lithostatic conditions, respectively, has been made in fig. 3. if hydrostatic conditions prevailed, group a inclusions would indicate entrapment at around 140°c at pressures of around 600 bars. microthermometry indicated that group b inclusions may contain traces of hydrocarbons and the isochores shown in fig. 3 are therefore not strictly applicable because they assume an aqueous-only composition. as trace concentrations of hydrocarbons are present in group b inclusions, pressures at homogenisation will be considerably higher than indicated by the isochores drawn in fig. 3. the presence of only a few parts per thousand methane in solution would shift homogenisation pressures to values of 400–600 bars at the observed temperatures of homogenisation (hanor 1980). the actual isochoric path for group b inclusions should therefore be shifted to a setting essentially parallel to that shown but starting at the bubble-point curve for the actual aqueous-hydrocarbon system at around 400 bars (fig. 3, point a). if this interpretation is valid, both groups of inclusions in quartz indicate minimum entrapment of fluids slightly different in composition at conditions of about 400 bars and 140°c. assuming hydrostatic conditions, probable entrapment of both group a and b aqueous fluids low in salts (average 0.61 equivalent weight% nacl) and containing occasional traces of hydrocarbons occurred at around 600–700 bars at temperatures of 160°c to 170°c. however, more data would be needed to substantiate this conclusion. concluding remarks although it is of a reconnaissance nature, the present study of fluid inclusions in fracture-filling quartz and calcite indicates that the basaltic sections represented by the samples examined were subjected to temperatures of 160°c to 170°c and pressures of 600–700 bars at stages during their burial. during these burial conditions, precipitation of quartz and calcite in fractures (and vugs?) occurred in the presence of low-salinity aqueous fluids containing occasional traces of hydrocarbons. similar p–t-fluid-char0 500 1000 1500 2000 0 100 200 300 temperature, °c pr es su re , ba rs hydrostatic gradient 20°c/226 bars hydrostatic gradient 20°c/100 bars bubble-point curve for h 2 o–0.2 mole % ch 4 a group a group b isochore for aqueous inclusions fig. 3. pressure-temperature diagram with isochores for groups a and b inclusions in quartz from lopra-1/1a. the open and filled circles show pressure and temperature at homogenisation for pure aqueous and aqueous-0.2 mole%ch4 fluids in group b inclusions, respectively. bubble-point curve from hanor (1980). see text for further comments. geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19121 122 acteristics may also be of relevance to the formation of e.g. zeolites in these rocks. although no clear evidence for the simultaneous existence and migration of hydrocarbon and aqueous fluids was observed, such simultaneity is suggested by the occasional presence of hydrocarbons in the entrapped aqueous fluids and the hydrocarbon-dominated inclusions observed especially in calcite. references bodnar, r.j. 1990: petroleum migration in the miocene monterey formation, california, usa: constraints from fluid-inclusion studies. mineralogical magazine 54, 295–304. bodnar, r.j. & bethke, p.m. 1984: systematic stretching of fluid inclusions. fluorite and sphalerite at one atmosphere confining pressure. economic geology 79, 141–146. bodnar, r.j., sterner, s.m. & hall, d.l. 1989: salty: a fortran program to calculate compositions of fluid inclusions in the system nacl-kcl-h2o. computers & geosciences 15, 19–41. brown, p.e. 1989: flincor: a microcomputer program for the reduction and investigation of fluid inclusion data. american mineralogist 74, 1390–1393. hanor, j.s. 1980: dissolved methane in sedimentary brines: potential effect on the pvt properties of fluid inclusions. economic geology 75, 603–617. jensenius, j. & burruss, r.c. 1990: hydrocarbon-water interactions during brine migration: evidence from the composition of hydrocarbon inclusions in calcite from danish north sea oil fields. geochemica cosmochemica acta 54, 705–713. jørgensen, o. 2006: the regional distribution of zeolites in the basalts of the faroe islands and the significance of zeolites as palaeotemperature indicators. geological survey of denmark and greenland bulletin 9, 123–156 (this volume). konnerup-madsen, j. 1979: fluid inclusions in quartz from deepseated granitic intrusions, south norway. lithos 12, 13–23. lang, w.h. & gelfand, j.c. 1985: the evaluation of shallow potential in a deep field wildcat. log analyst 26, 13–22. manuscipt received 15 december 1999; revision accepted 29 june 2001. geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19122 geological survey of denmark and greenland bulletin 23, 2011, 65–68 65 this paper describes structural data collected during field work in southern east greenland, a region characterised by a complex tectonic history. here, 3d photogeology based on aerial and oblique photographs using high-resolution photogrammetry of a 150 km2 area in sødalen in southern east greenland shows ese–wnw-trending faults cross-cutting paleocene rift structures and f lexure-related normal faults. the kinematic analysis highlights oblique and left-lateral strike-slip movements along faults oriented 120°. strike-slip and dip-slip kinematic indicators on the walls of the chilled contacts between alkaline e–w-oriented dykes and the volcanic host rocks suggest that the faults and dykes formed at the same time, or maybe the faults were re-activated at a later stage. palaeostress analysis, performed by inversion of fault-slip data, shows the presence of three different tectonic events. coupling the 3d photogeological tool with structural analysis at key localities is a fundamental way to understand better the tectonic history of such a large area. geological setting the blosseville kyst in southern east greenland is characterised by a thick sequence of f lood basalts and mafic intrusions (fig. 1). the skaergaard layered gabbro, the miki fjord macrodyke and dolerite sill complexes were formed during the continental break-up and the initial opening of the north–east atlantic ocean at 55 ma (nielsen 1975; karson & brooks 1999; tegner et al. 2008). in the sødalen region pre-basaltic sediments characterise the kangerlussuaq basin and the lower part of the blosseville group (wager 1947; nielsen et al. 1981). sedimentological studies recognise different facies associations of late aptian to late paleocene age (larsen, m. et al. 1999). the youngest part of the basin comprises interfingering paleocene volcanic units. based on stratigraphy, geochemistry and petrography, the lavas of the blosseville group have been divided into two main series: (1) a 2 km thick sequence of volcanic rocks that formed in a continental rift environment (nielsen et al. 1981), and (2) a 6 km thick sequence of plateau basalts (larsen, l.m. et al. 1989). furthermore, the blosseville kyst is characterised by different generations of dykes and sills, partly related to the break-up and post-break-up history (wager 1947; hanghøj et al. 2003). southern east greenland is a type example of a volcanic rifted margin (geoffroy 2005). the geological evolution of the margin is interpreted as the result of a ne–sw-oriented late cretaceous rifting phase that led to the onset of oceanic spreading in the late paleocene – early eocene (c. 55 ma) after a period of syn-rift continental tectonism and volcanism. the general south-east dip of the basalts, the presence of landwarddipping normal faults and the coastal dyke swarm suggest a regional lithosphere f lexure (larsen, h.c. & saunders 1998). sødalen region sødalen is an 8 km long, nw–se-oriented, u-shaped glacial valley extending se–nw up to the ‘sødalengletscher’ (fig. 2a). the bedrock of the area is characterised by gneiss basement, locally overlain by syn-rift sedimentary and volcanic rocks that form a monocline that dips south-eastwards. the late paleocene syn-rift sedimentary rocks crop out along the western side of the valley; they are unconformably overlain by sedimentary rocks belonging to the vandfaldsdalen formaanalysis of palaeogene strike-slip tectonics along the southern east greenland margin (sødalen area) pierpaolo guarnieri sø d ale n ‘sødalengletscher’ 68°15´n 31°w miki fjord skaergaard intrusion m ac ro d yk e fig. 2a greenland mainly palaeogene volcanic rocks palaeogene gabbro mesozoic–palaeogene sedimentary rocks precambrian basement 10 km b l o s s e v i l l e k y s t fig. 1. simplified geological map of the sødalen region in southern east greenland. © geus, 2011. geological survey of denmark and greenland bulletin 23, 65–68. open access: www.geus.dk/publications/bull 6666 main strike-slip fault faults and dykes bedding structural locality 1 10 sill miki fjord macrodyke mikis fm lava flows breccias hyaloclastite volcaniclastics schjelderup member precambrian basement vandfaldsdalen formation 300 2 0 0 400 5 0 0 1 0 0 7 0 0 8 0 0 6 0 0 700 6 0 0 5 0 0 500 3 0 0 500 900 60 0 60 0 800 800 400 4 0 0 80 070 0 300 200 900 8 7 4 8 5 9 7 19 20 22 10 15 10 900 sødalen 1 km 68°14´n 68°12´n 68°14´n 68°12´n 31°25´w 31°20´w 31°20´w31°25´w a b c d lake ice cap quaternary deposits ‘s ød a le n gl et sc h er ’ 5 2 4 3 1 faults (outcrop data) dykesfaultsfaults and dykes (vertical photographs) reverse faultsnormal faults left-lateral faults all faults (n = 92) n nnn s1> s2> n = 111 max = 13% n = 66 max = 18% n = 82 max = 17% n = 92 max = 15% (oblique photographs) right-lateral faults s3 n nn phase 1 phase 2 phase 3 67 tion (nielsen et al. 1981). the unconformity may be related to pre-volcanic uplift, coeval with the ne–sw-oriented rifting, followed by a rapid subsidence that accommodated the volcanism (larsen, m. et al. 1999). the continental breakup is contemporaneous with the emplacement of layered gabbro bodies dated to c. 55 ma, which formed at c. 2 km depth in the continental crust. the skaergaard intrusion and the miki fjord macrodyke (nielsen et al. 1981; tegner et al. 2008) are contemporaneous with the up to 6 km thick sequence of plateau basalts (larsen, l.m. et al. 1989). structural data a total of 350 measurements for structural analysis were collected, from two sources: (1) from outcrops (metre scale) at five sites used for kinematic analysis and (2) from 3d photo geology to evaluate strike and dip direction and cross-cutting relationships of faults and dykes using vertical aerial photographs (kilometre scale) and oblique photographs (100 m scale). a new tool for photogeology and mapping is developed and implemented at geus to collect geological features as 3d polylines with a descriptive gis database suitable for 3d modelling (vosgerau et al. 2010). dykes – three main generations of dykes are found in the area. their relative ages can be established from cross-cutting relationships, which show that the oldest generation (d 1 ) is mainly ne–sw-oriented, orthogonal to bedding or landward-dipping; the trend is parallel to the miki fjord macrodyke. the average trend of the second generation (d 2 ) is ene–wsw and these dykes are almost vertical (fig. 2b). the third generation of dykes found in the area (d 3 ) trends e–w (fig. 2b). faults – two main trends of fault traces, up to 2 km long, can be followed on the vertical aerial photographs (fig. 2b). the oldest generation (f 1 ) is characterised by ene–wsworiented normal faults. these faults are mainly landwarddipping and are interpreted as f lexure-related faults (wager 1947; nielsen et al. 1981). at site 3 (fig. 2a), the miki fjord macrodyke contact is downfaulted by a landward-dipping (f 1 ) normal fault with an average vertical offset of 400 m. the youngest (f 2 ) faults trend ese–wnw. south-east of localities 2 and 4 (fig. 2a), the fault traces are curved in planar view typical of strike-slip fault systems. kinematic analysis field data suitable for fault-slip analysis include measurements of fault plane orientations, slip directions, senses of slip and bedding orientations. the slip direction of faults is determined using slickensides and calcite fibres on the fault plane. sense of slip indicators include tails and scratches and crescentic marks formed by intersection of the fault plane with secondary fractures such as: r, r’, p and t (petit 1987). data collected in the canyon at locality 2 (fig. 2a) define the kinematics of a 120°-trending fault corresponding to a major left-lateral strike-slip fault that cuts the basalts. the fault zone is c. 50 m wide and contains a >50 cm thick calcite vein. double movement along the fault plane with well developed dip-slip and strike-slip slickensides and calcite fibres suggests a reactivation of the fault (fig. 3). the estimated vertical offset, based on the tectonic contact between two stratigraphic markers, is around 250 m, whereas the horizontal offset is estimated to 500 m. this results in a more than 50–150 m wide, 120°-trending, rhomb-shaped fault zone, 1 km long in map view (fig. 2a, locality 2) and with a negative f lower structure in cross-section. to the south-east, the fault trace disappears below an ice cap and to the north-west it is covered by the moraine in front of ‘sødalengletscher’, but it is exposed on the western side of sødalen, where a well facing page: fig. 2. structural data analysis. a: geological map of the sødalen area (modified from nielsen et al. 1981). arrows show the direction of movement along strike-slip faults; contour lines 100 m. b: rose diagrams for orientation of faults and dykes. c: lower hemisphere stereographic projection of faults grouped by kinematics; arrows show the slip vector. d: palaeostress analysis of 92 fault-slip measurements. black arrows indicate maximum horizontal shortening/extension; σ1, σ2, σ3 = principal axes of stress. visualisation of the right dihedral method (red = pressure, blue = tension) shows planes that are likely to have been re-activated (the three diagrams to the right). dip slipdip slip strike-slipstrike-slipstrike-slip dip slip fig. 3. evidence of multiple re-activation of a fault testified by well-developed dip-slip and strike-slip slickensides on a fault plane (locality 2 in fig. 2a). 6868 developed vertical cleavage, locally with strike-slip slickensides, cross-cuts the miki fjord macrodyke. at locality 5 (fig. 2a), a 4 km long e–w-oriented dyke crosses sødalen; it is an example of the latest dyke generation (d 3 ). slickensides are found on the chilled margins of the dyke, which show that both dip-slip and strike-slip movements have taken place. the trend of the dykes, coupled with evidence of multiple reactivation of the contact, suggests a relationship between strike-slip faults and dykes in which normal faults intruded by dykes were re-activated as leftlateral faults in a nne–ssw extensional regime associated with the ese–wnw-trending shear-zone (fig. 2a). palaeostress analysis palaeostress analysis of the heterogeneous fault-slip data set was performed using integrated software for structural analysis (žalohar 2009). more than 90 fault-slip measurements were taken at five sites (localities 2a–c) and used for inversion to obtain palaeostress values. the gauss method associated with visualisation of p&t dihedra (žalohar 2009) distinguishes three superimposed tectonic phases in the area (fig. 2d): (1) a phase with strike-slip regime and a 20–30° trending maximum horizontal shortening interpreted as oblique rifting; (2) a phase with a sse–nnw-trending maximum horizontal extension that corresponds to the coastal f lexure and (3) a phase with strike-slip regime and a 95°-trending maximum horizontal shortening that caused the inversion and uplift of the entire area. conclusions the structural data collected in sødalen indicate the presence of strike-slip faults related to two tectonic events separated in time by the coastal f lexure. the youngest structures and dykes (phase 3; fig. 2d) are associated with a nw–se left-lateral shear zone that cross-cuts the paleocene rift and the structures related to the coastal f lexure of the continental margin (phase 2). the evidence of dyke intrusions related to n–s extension compatible with the strike-slip tectonic regime of phase 3, suggests a coexistence of the two phenomena as a superficial expression of deep-seated crustal structures. the oldest structures and dykes of phase 1 show a maximum horizontal extension coherent with the trend of the miki fjord macrodyke. this strike-slip tectonic regime could be related to an oblique rifting stage in paleocene time. finally, the accuracy of the 3d photogeological tool is tested over a range of kilometre to metre scale (fig. 2b) showing the power of this method developed at the survey. acknowledgement chevron is thanked for interest and financial support. references geoffroy, l.: 2005. volcanic passive margins. comptes rendus geoscience 337, 1395–1408. hanghøj k., storey m. & stecher o. 2003: an isotope and trace element study of the east greenland tertiary dyke swarm: constraints on temporal and spatial evolution during continental rifting. journal of petrolog y 44, 2081–2112. karson, j.a. & brooks, c.k. 1999: structural and magmatic segmentation of the tertiary east greenland volcanic rifted margin. in: ryan, p.d. (ed.): continental tectonics. geological society special publications (london) 164, 313–338. larsen, h.c. & saunders a.d. 1998: tectonism and volcanism at the southeast greenland rifted margin: a record of plume impact and later continental rupture. proceedings of the ocean drilling program, scientific results 152, 503–534. larsen, l.m., watt, w.s. & watt, m. 1989: geolog y and petrolog y of the lower tertiary plateau basalts of the scoresby sund region, east greenland. bulletin grønlands geologiske undersøgelse 157, 164 pp. larsen, m., hamberg, l., olaussen, s., nørgaard-pedersen, n. & stemmerik, l. 1999: basin evolution in southern east greenland: an outcrop analog for cretaceous–paleogene basins on the north atlantic volcanic margins. aapg bulletin 83, 1236–1261. nielsen,t.f.d. 1975: possible mechanism of continental breakup in the north atlantic. nature 253, 182–184. nielsen, t.f.d., soper, n.j., brooks, c.k., faller, a.m., higgins, a.c. & matthews, d.w. 1981: the pre-basaltic sediments and the lower basalts at kangerdlugssuaq, east greenland: their stratigraphy, litholog y, palaeomagnetism and petrolog y. meddelelser om grønland geoscience 6, 3–25. petit, j.p. 1987: criteria for the sense of movement on fault surfaces in brittle rocks. journal of structural geolog y 9, 597–608. tegner, c., brooks, c.k., duncan, r.a., heister, l.e. & bernstein, s. 2008: 40ar-39ar ages of intrusions in east greenland: rift-to-drift transition over the iceland hotspot. lithos 101, 480–500. vosgerau h., guarnieri p., weibel r., larsen m., dennehy, c., sørensen, e.v. & knudsen, c. 2010: study of a palaeogene intrabasaltic sedimentary unit in southern east greenland: from 3-d photogeolog y to micropetrography. geological survey of denmark and greenland bulletin 20, 75–78. wager, l.r. 1947: geological investigations in east greenland, part iv: the stratigraphy and tectonics of knud rasmussens land and the kangerdlugssuaq region. meddelelser om grønland 134(5), 62 pp. žalohar, j. 2009: t-tecto 3.0 professional. integrated software for structural analysis of fault-slip data. department of geolog y, si-1000 ljubljana, slovenia. author’s address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: pgua@geus.dk geological survey of denmark and greenland bulletin 11, 179-184 179 magnetic anomalies and metamorphic boundaries in the southern nagssugtoqidian orogen, west greenland john a. korstgård, bo møller stensgaard and thorkild m. rasmussen within the southern nagssugtoqidian orogen in west greenland metamorphic terrains of both archaean and palaeoproterozoic ages occur with metamorphic grade varying from low amphibolite facies to granulite facies. the determination of the relative ages of the different metamorphic terrains is greatly aided by the intrusion of the 2 ga kangâmiut dyke swarm along a nne trend. in archaean areas dykes cross-cut gneiss structures, and the host gneisses are in amphibolite to granulite facies. along itilleq strong shearing in an e–w-oriented zone caused retrogression of surrounding gneisses to low amphibolite facies. within this itivdleq shear zone kangâmiut dykes follow the e–w shear fabrics giving the impression that dykes were reoriented by the shearing. however, the dykes remain largely undeformed and unmetamorphosed, indicating that the shear zone was established prior to dyke emplacement and that the orientation of the dykes here was governed by the shear fabric. metamorphism and deformation north of itilleq involve both dykes and host gneisses, and the metamorphic grade is amphibolite facies increasing to granulite facies at the northern boundary of the southern nagssugtoqidian orogen. here a zone of strong deformation, the ikertôq thrust zone, coincides roughly with the amphibolite–granulite facies transition. total magnetic field intensity anomalies from aeromagnetic data coincide spectacularly with metamorphic boundaries and reflect changes in content of the magnetic minerals at facies transitions. even the nature of facies transitions is apparent. static metamorphic boundaries are gradual whereas dynamic boundaries along deformation zones are abrupt. keywords: aeromagnetic data, magnetic anomalies, metamorphic facies, nagssugtoqidian orogen, west greenland __________________________________________________________________________________________________________________________________________________________ j.a.k., department of earth sciences, university of aarhus, høegh-guldbergsgade 2, dk-8000 århus c, denmark. e-mail: john.korstgard@geo.au.dk b.m.s. & t.m.r., geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350 copenhagen k, denmark. the establishment of the palaeoproterozoic nagssugtoqidian orogen in west greenland (ramberg 1949) is based on the deformation and metamorphism of the kangâmiut dykes, dated at 2.04 ga by nutman et al. (1999). south of the southern nagssugtoqidian front (snf in fig. 1), in the southern nagssugtoqidian foreland, kangâmiut dykes are undeformed and cross-cut gneiss structures. north of the front, gneisses and dykes have been metamorphosed and deformed together during the nagssugtoqidian orogeny. here, gneiss structures and dyke margins are concordant and dykes transformed into amphibolites. this is the simple story upon which ramberg (1949) based his definition of the ‘nagssugtoqides’. ramberg also divided the nagssugtoqidian orogen into three metamorphic complexes based on the metamorphic grade of the rocks. thus the egedesminde complex was the northernmost amphibolite facies complex, the isortoq complex the central granulite facies complex, and the ikertôq complex the southernmost amphibolite facies complex. the current division of the orogen (fig. 1) is based on structural criteria, and division boundaries now follow major structural features (marker et al. 1995). the current division therefore deviates considerably from ramberg’s original division for the northern and central nagssugtoqidian orogen, whereas the © geus, 2006. geological survey of denmark and greenland bulletin 11, 179–184. available at: www.geus.dk/publications/bull 180 50 km inland ice ? ? snf cno nno aasiaataasiaat kangerlussuaqkangerlussuaq sno nordre strømfjord shear zone nordre isortoq steep belt southern nagssugtoqidian foreland sø nd re str øm fjo rd nordre strømfjo rd aasiaat kangerlussuaq nordre strømfjo rd arfersiorfik fig. 3 fig. 2 sisimiut ikertôq thrust zone itivdleq shear zone 54° 67° 68° 51° surficial deposits quaternary north atlantic craton granodioritic-granitic gneiss (northern parts reworked) orthogneiss (largely unreworked) metasedimentary rocks (palaeoproterozoic, may include archaean components) nagssugtoqidian orogen sisimiut charnockite (palaeoproterozoic) arfersiorfik quartz diorite (palaeoproterozoic) orthogneiss (archaean, reworked) metasedimentary rocks (archaean, may include proterozoic components) amphibolite anorthosite and ultrabasic rocks 500 km greenland fig. 1. schematic geology of the southern part of the nagssugtoqidian orogen and adjacent forelands (modified from escher & pulvertaft 1995 and marker et al. 1995). sno, southern nagssugtoqidian orogen; cno, central nagssugtoqidian orogen; nno, northern nagssugtoqidian orogen; snf, southern nagssugtoqidian front. the locations of thrust and shear zones are defined from trends observed in the aeromagnetic data; note that the e–wtrending thrust zone with question marks north of kangerlussuaq is uncertain, as this structure has not been confirmed by geological mapping. black frames show the locations of figs 2, 3. southern nagssugtoqidian orogen corresponds almost exactly to ramberg’s original ikertôq complex. the southern nagssugtoqidian orogen (sno in fig. 1) in the coastal region between sisimiut and itilleq consists mainly of quartzofeldspathic gneisses of granodioritic to tonalitic composition. several supracrustal layers occur, particularly in the northern part of the sno. the supracrustal rocks are mainly garnet-biotite schists, rusty weathering biotite gneisses and amphibolites. the metamorphic grade is low amphibolite facies to granulite facies, and due to the fortunate timing of the intrusion of the kangâmiut dykes it is possible to assign relative ages to the different metamorphic terrains in the region. pre-dyke metamorphism and deformation south of and immediately north of itilleq, the kangâmiut dykes are largely undeformed, unmetamorphosed and 181 [nt] 526 424 365 319 282 247 216 189 164 140 1189673523211–7 –26 –46 –68 –89 –110 –131 –150 –168 –185 –202 –222 –245 –266 –283 –305 –327 –352 –377 –398 –409 –436 52°30'52°30'53°30'53°30' 66 °5 0' 66 °5 0' 66 °4 0' 66 °4 0' 66 °3 0' 53°53° a b c d dd e e f f g g h h i sisimiut 10 km qeq erta lik qeq erta lik itilleqitilleq kkaanngg eerrlluuaa rrssuukk iikkeerrttooooqq mm aalliiggaaaaqq j a b 52°30'53°30' 66 °5 0' 66 °4 0' 66 °3 0' 53° a b c d d d e e f f g g h h isisimiut 10 km qeq erta lik itilleq kang erlua rsuk ikertooq m aligaaq post-dyke (nagssugtoqidian) granulite facies post-dyke (nagssugtoqidian) amphibolite facies pre-dyke (archaean) granulite facies pre-dyke (archaean) amphibolite facies pre-dyke amphibolite facies j fig. 2. correlation between metamorphic facies and aeromagnetic anomaly patterns in the itilleq–ikertooq region. white lines indicate approximate metamorphic facies boundaries based on geological field work; labels a–j are explained in the text. a: distribution and relative ages of metamorphic facies. b: total intensity magnetic field anomaly map. shadow of magnetic field pattern modelled from a light source with inclination 45° and declination 315°. cross-cut gneiss structures. the main dyke direction is nne–ssw, and a subordinate direction is e–w to ese– wnw (fig. 1). upon entering the itilleq area, the dyke trends are e–w, parallel to the fjord. this change in trend also corresponds to a change in foliation trend in the host gneisses. however, the dykes are still largely undeformed and unmetamorphosed within this e–w trend. the metamorphic grade of host gneisses north and south of itilleq is granulite facies in western parts and amphibolite facies in eastern parts (fig. 2a). however, all along the e–w trend in itilleq, gneisses are in low amphibolite facies. the dyke behaviour in the itilleq region led to the interpretation that prior to intrusion of the kangâmiut dykes the area was stabilised in amphibolite-granulite facies with a variable northerly trend of the foliation (grocott 1979; korstgård 1979). at some point prior to dyke intrusion an e–w zone of strong deformation was established along itilleq, downgrading gneisses to low amphibolite facies (epidote-muscovite). within this itivdleq shear zone, dykes intruded along the shear fabrics and show a variety of primary pinch-and-swell structures (nash 1979). outside the shear zone, dyke margins are straight-sided indicating that dykes intruded along brittle fractures. 182 post-dyke metamorphism and deformation farther north of itilleq, from kangerluarssuk and northwards (fig. 2a), dykes are thoroughly deformed and parallel to country rock structures. both dykes and country rock structures are in amphibolite facies. foliation trends are variable ene–wsw around west-plunging fold axes. continuing northwards the metamorphic grade increases and reaches granulite facies north of ikertooq fjord (fig. 2a). in addition, gneiss structures and metamorphosed dykes take on a pervasive e–w orientation (ikertôq thrust zone, fig. 1) with a steeply n-dipping foliation and nplunging stretching lineations. the interpretation of field observations in the northern sno is that the metamorphism and deformation are post-dyke, the metamorphic transition is prograde, and the ikertôq thrust zone represents a zone of southward ductile thrusting whereby deeper-seated rocks are brought up from the north. facies transitions within the itilleq–ikertooq region four types of facies transitions or boundaries are recognised. two of these are prograde and two are associated with strong deformation in ductile shear zones. the amphibolite–granulite facies transition in the archaean areas around itilleq is prograde and static in the sense that the boundary was not established as a result of a deformational event, but reflects static equilibration of the mineral assemblages to the conditions that prevailed when the rocks were at their deepest crustal level. during later uplift the rocks escaped any significant metamorphic changes due to the absence of deformation, and the metamorphism reflects their initial archaean state. the granulite to low amphibolite facies and amphibolite to low amphibolite facies transitions along itilleq are retrograde and dynamic in the sense that they were established as a direct consequence of the deformation along the itivdleq shear zone. mineral assemblages in the shear zone were equilibrated to the metamorphic conditions of a higher crustal level than reflected in the surrounding gneisses, and the shearing triggered this re-equilibration. the amphibolite–granulite facies transition north of ikertooq is both prograde and dynamic. it can be considered as a displaced prograde and static transition brought up into a sub-vertical position by the overthrust movement along the ikertôq thrust zone (fig. 1). magnetisation comparing the magnetic anomaly map for the area (fig. 2b) with the metamorphic map (fig. 2a) a striking coincidence of magnetisation and metamorphic boundaries is evident. more information on the magnetic field data and the geological interpretations can be found in rasmussen & van gool (2000), nielsen (2004) and nielsen & rasmussen (2004). strong magnetisation in pre-dyke archaean granulite facies areas just north of itilleq (a in fig. 2b) is attributed to a higher content of magnetite or other magnetic minerals. a likely explanation for this is production of magnetite by the breakdown of hydrous (fe, mg)-al-silicates (e.g. biotite, amphibole) during the transition from amphibolites to granulite facies according to the general reaction: hydrous (fe, mg)-al-silicates ± sio 2 ± o 2 = kfeldspar + (fe, mg)-silicates ± magnetite + h 2 o. the lower magnetisation in pre-dyke archaean amphibolite facies areas (b in fig. 2b) relative to pre-dyke archaean granulite facies areas indicates no additional production of magnetite. the gradual increase in magnetic intensity (c in fig. 2b) marks the gradual prograde facies transition. the elongate low magnetic anomaly coincident with the itivdleq shear zone (d in fig. 2b) is caused by extensive breakdown of magnetic minerals. this may be due to chemical breakdown during metamorphic retrogression to pre-dyke amphibolite facies aided by circulating fluids in the shear zone, and mechanical destruction of the magnetic mineral grains. the abrupt changes in anomaly patterns from d to a (fig. 2b) across the metamorphic facies transition and deformation boundary are a response to the dynamic nature of this boundary. previously suggested possible shearing south of ikertooq (e in fig. 2b; grocott 1979; korstgård 1979) contemporaneous with the shearing at itilleq (d in fig. 2b) is supported by similarities in the character of the anomaly patterns. the post-dyke amphibolite facies areas at, and south of, ikertooq (f in fig. 2b) indicate the palaeoproterozoic retrogression to amphibolite facies and deformational reworking. the boundary between the pre-dyke archaean amphibolite facies and the post-dyke amphibolite facies areas does not have a well-defined magnetic signature (between b and f in fig. 2b). the increase in magnetisation north of ikertooq (g in fig. 2b) corresponds to rocks metamorphosed under granulite facies conditions after dyke intrusion and brought up by overthrusting. the offset between the mapped facies boundary north of ikertooq (fig. 2a) and the boundary between high and low magnetisation (h in fig. 2b) can be explained as partially due to non-exposed post-dyke 183 granulite facies rocks, and partially to the effect of stacked thrust panels of post-dyke amphibolite and granulite facies rocks with alternating low and high magnetic intensity anomalies (i in fig. 2b). isolated high intensity anomalies can be correlated with distinct lithologies or intrusives (e.g. an anorthosite complex at j in fig. 2b). the presence or absence of kangâmiut dykes is not reflected in the aeromagnetic data. the observed correlations between metamorphic facies, deformation and magnetisation can be extended to other areas of the sno (fig. 3) provided that the background gneisses are lithologically fairly homogeneous, as is generally the case in the southern nagssugtoqidian orogen. where gneiss lithologies are more variable, such as in the nordre isortoq steep belt (fig. 1) and the nordre strømfjord shear zone (sørensen et al. 2006, this volume) correlations tend to depend on lithology rather than metamorphic grade. acknowledgements the authors thank graham leslie and chris pulvertaft for their concise and constructive reviews. references escher, j.c. & pulvertaft, t.c.r. 1995: geological map of greenland, 1:2 500 000. copenhagen: geological survey of greenland. grocott, j. 1979: controls of metamorphic grade in shear belts. in: korstgård, j.a. (ed.): nagssugtoqidian geology. rapport grønlands geologiske undersøgelse 89, 47–62. korstgård, j.a. (ed.) 1979: nagssugtoqidian geology. rapport grønlands geologiske undersøgelse 89, 146 pp. marker, m., mengel, f., van gool, j. & field party 1995: evolution of the palaeoproterozoic nagssugtoqidian orogen: dlc investigations in west greenland. rapport grønlands geologiske undersøgelse 165, 100–105. nash, d. 1979: an interpretation of irregular dyke forms in the itivdleq shear zone, west greenland. in: korstgård, j.a. (ed.): nagssugtoqidian geology. rapport grønlands geologiske undersøgelse 89, 77–83. nielsen, b.m. 2004: crustal architecture and spatial distribution of mineral occurrences in the precambrian shield of central west greenland based on geophysical and geological data. danmarks og grønlands geologiske undersøgelse rapport 2004/26, 63 pp., 8 appendices. ph.d. thesis 2004. department of earth sciences, university of aarhus, denmark. nielsen, b.m. & rasmussen, t.m. 2004: mineral resources of the precambrian shield of central west greenland (66° to 70°15′n). part fig. 3. total intensity magnetic field anomaly map of the south-eastern part of the nagssugtoqidian orogen and its foreland, with the location of the itilleq–ikertooq region (white frame, fig. 2). abbreviations as for fig. 1; shadow on magnetic data as for fig. 2. the e–w-trending thrust zone with question marks north of kangerlussuaq is uncertain, as this structure has not been confirmed by geological mapping. sn f southern nagssugtoqidian foreland (north atlantic craton) n ag ss ug to qi di an o ro ge n no rdr e is ort oq ste ep bel t sou the rn cn o iker tôq thr ust zo ne itiv dle q she ar z one c n o sn o 50°50°52°52° 66 °4 0' 66 °4 0' 67 °0 5' 67 °0 5' 66 °1 5' 66 °1 5' sø nd re str øm fjo rd sø nd re str øm fjo rd sisimiutsisimiut kangerlussuaqkangerlussuaq itilleqitilleq ikerto oq ikerto oq qeqertalikqeqertalik kangerluarsukkangerluarsuk fig. 2 53°53° [nt] ?? 50 km 536 407 334 284 243 209 178 151 125 76 54 32 11 –9 –30 –50 –72 –91 –110 –127 –145 –161 –176 –190 –204 –219 –234 –264 –282 –303 –326 –354 –386 –416 –461 –535 184 3. implications of potential field data for the tectonic framework. danmarks og grønlands geologiske undersøgelse rapport 2004/ 21, 165 pp. nutman, a.p., kalsbeek, f., marker, m., van gool, j.a.m. & bridgwater, d. 1999: u-pb zircon ages of kangâmiut dykes and detrital zircons in metasediments in the palaeoproterozoic nagssugtoqidian orogen (west greenland): clues to the pre-collisional history of the orogen. precambrian research 93, 87–104. ramberg, h. 1949: on the petrogenesis of the gneiss complexes between sukkertoppen and christianshaab, west greenland. meddelelser fra dansk geologisk forening 11, 312–327. _____________________________________________________________________________________________________________________________________________________________ manuscript received 10 november 2004; revision accepted 1 november 2005 rasmussen, t.m. & van gool, j.a.m. 2000: aeromagnetic survey in southern west greenland: project aeromag 1999. geology of greenland survey bulletin 186, 73–77. sørensen, k., korstgård, j.a., glassley, w.e. & stensgaard, b.m. 2006: the nordre strømfjord shear zone and the arfersiorfik quartz diorite in the inner arfersiorfik, the nagssugtoqidian orogen, west greenland. in: garde, a.a. & kalsbeek, f. (eds): precambrian crustal evolution and cretaceous–palaeogene faulting in west greenland. geological survey of denmark and greenland bulletin 11, 145–161 (this volume). geological survey of denmark and greenland bulletin 17, 2009, 41-44 groundwater mapping in denmark has high priority. it was initiated in the 1990s when the pressure on groundwater resources increased due to urban development and pollution from industrial and agricultural sources. in some areas, the groundwater mapping included survey drillings, modelling based on existing knowledge and geophysical mapping with newly developed methods that made area coverage on a large scale possible. the groundwater mapping that included development of new geophysical methods showed promising results, and led to an ambitious plan to significantly intensify the hydrogeological mapping in order to improve the protection of the danish groundwater resources. in 1999 the danish government initiated the national groundwater mapping programme with the objective to obtain a detailed description of the aquifers with respect to localisation, extension, distribution and interconnection as well as their vulnerability to pollution (thomsen et al. 2004). this mapping programme covers around 40% of the area of den mark designated as particularly valuable water abstraction areas. water consumers fi nance the mapping programme by paying 0.04 € per cubic metre of consumed water. at the end of the programme in 2015, the total cost is estimated to be about 250 000 000 € with a significant part spent on geophysical mapping. the mapping programme is administered by seven local offices under the ministry of environment, but most of the practical work is carried out by private consulting companies, and involves the use of geophysical survey methods, survey drillings, well logging, water sampling and hydrological mapping, as well as geological and groundwater modelling. in major parts of the particularly valuable water abstraction areas, it is important to obtain spatially dense geophysical data covering large continuous areas. geophysical methods used in the hydrogeological mapping the choice of geophysical methods depends on the geological setting of the aquifers. those of interest for drinking water are primarily found within the upper 250 m of the subsurface. the aquifers can be grouped into three main types. in © geus, 2009. geological survey of denmark and greenland bulletin 17, 41–44. available at: www.geus.dk/publications/bull 41 fig. 1. areal extent of data collected by the end of 2008. a: areas with tem and skytem soundings, b: areas with paces profiles, c: cves profiles. d: seismic profiles. geophysical methods and data administration in danish groundwater mapping ingelise møller, verner h. søndergaard and flemming jørgensen c d jylland sjælland fyn a b 50 km fig. 3 rosa_2008:rosa-2008 01/07/09 15:48 side 41 the western part of denmark, extensive quaternary and prequaternary sand deposits dominate. in the central part, the most important groundwater resources are located in qua ternary sand deposits often found in quaternary valley structures deeply eroded into palaeogene clay deposits. in the northern and eastern parts of the country, most of the important aquifers are found in upper cretaceous and danian limestone. the most important geophysical methods are electrical and electromagnetic methods, combined with reflection seismic profiling and borehole logging at selected localities. differences in electrical properties between sandy aquifers and clay sediments favour the use of the electrical and electromagnetic methods (sørensen et al. 2005), but the ability of seismic methods to reveal detailed internal structures within the aquifers is also important. the most commonly used geophysical method in the groundwater mapping programme is the airborne transient electromagnetic method, skytem (sørensen & auken 2004), which is one of the new methods that has been developed to improve and optimise groundwater mapping. the first skytem groundwater mapping project was carried out in 2003. since then the skytem method has been developed further and has proved faster and more powerful than the groundbased, single-site transient electromagnetic method, tem, which was previously widely used. the skytem method is used for mapping to a maximum depth of 250–300 m. nu me rous buried valleys have been mapped in denmark by the tem method, in particular in the central parts of the country, where highly impermeable and low-resistive palaeogene clay layers form the lower boundaries of the aquifers and the valleys are easily detected. at the end of 2008, tem and skytem data cover an area of more than 11 000 km2 (fig. 1a), which is about one quarter of the area of denmark. electrical methods are used for near-surface mapping purposes. the pulled array continuous electrical sounding meth od (paces; sørensen 1996) has been extensively used to map layers within the upper 20–30 m. this method works well in combination with tem measurements, and the combined methods provide data from the surface down to 200–300 m. this combination of methods has mainly been used in eastern jylland and on fyn. a total of around 9000 effective line kilometres of paces data have been collected, corresponding to a coverage of more than 3000 km2 (fig. 1b). the continuous vertical electrical sounding method (cves; e.g. dahlin 1996) is used in areas where it is unne cessary to map deeper layers, and where the subsurface resistivity values are too high for the skytem method. about 4000 line kilometres have been collected, mainly in the central part of jylland and on the eastern part of sjælland (fig. 1c). the reflection seismic method is also of great value as a geophysical groundwater mapping tool, particularly following the development of a land-streamer and a new vibroseismic system (e.g. vangkilde-pedersen et al. 2006). although the reflection seismic method is expensive, it can be successfully combined with skytem measurements, and the decision about where to acquire seismic data can be based on the skytem results (jørgensen et al. 2003). successful mapping of the outline of buried valleys and their internal structures has been based on the interpretations of seismic profiles; skytem data do not allow such interpretations. the reflection seismic method has also been used successfully to map palaeogene and neogene sediments in the western part of denmark (rasmussen et al. 2007), where thick and extensive layers of sandy deposits constituting important aquifers are bounded by thinner layers of clayey deposits, and to map faults in danian and cretaceous limestone in the eastern part of denmark. around 1400 km of seismic lines have been collected, particularly in the western and central parts of jylland (fig. 1d). borehole logs are crucial for the geological and hydrological interpretation of boreholes. it is now common practise to log boreholes following survey drilling, and older water supply wells have also been logged. particularly in areas with chalk and limestone or neogene groundwater reservoirs log stratigraphy has provided valuable information. about 1500 boreholes have been logged. administration of the geophysical data the groundwater mapping programme is split up into many smaller areas to ease the administrative handling and to be able to meet priority criteria. careful and standardised treatment of data is required to ensure that the resulting ‘patchwork’ is of high and uniform quality and has no visible seams. therefore, standards and guidelines are worked out for geophysical data acquisition, calibration of instruments, data processing, interpretation (e.g. hydrogeophysics group 2007a) and geological modelling (jørgensen et al. 2008). without a predefined system of archiving the geophysical data and modelling results, the data logistics of the groundwater mapping programme would be overwhelming. the national geophysical relation database (gerda; http:// gerda.geus.dk) hosted at the geological survey of denmark and greenland (geus), is used for archiving these geophysical data. the development of the database began more than ten years ago. the database contains geophysical data of various types such as wenner profiles, schlumberger soundings, pulled array continuous electrical soundings, continuous vertical electrical soundings and induced polarisation, transient electromagnetic data including the airborne skytem data, 42 rosa_2008:rosa-2008 01/07/09 15:48 side 42 frequency domain electromagnetic data, reflection seismic profiles and borehole logs. various kinds of 1-d models and 2-d models resulting from inversion of electrical and electromagnetic data are also saved, securing an immediate use of the results. all information about data acquisition, data processing and inversion can be stored, which facilitates reprocessing of data and makes the inversion and interpretation of data transparent. geus also hosts another database (jupiter; http://jupiter. geus.dk) for borehole data. jupiter contains information on, for example, geological and lithological descriptions, groundwater level and water quality observations. both the jupiter and gerda databases have web-based graphical user interfaces, where any user can search for and download data free of charge. geophysical data are handled from data processing to ge ological interpretation in an integrated system formed by the gerda and the jupiter databases and two software packages, the aarhus workbench and the geoscene3d in combination with a geological model database hosted at geus (fig. 2; møller et al. in press). the aarhus workbench (hydro geophysics group 2007b) has modules for handling, processing, inverting, interpreting and visualising electrical and electromagnetic data, all combined on a common gis platform and a common database. the aarhus workbench enables anybody to work with the geophysical data in the gerda database without having to know the complicated data model of gerda or to be able to carry out a database query. by using the gis platform at the aarhus workbench it is easy to produce various types of maps compiled from the geophysical data. the different maps are entered into the 3-d visualisation and modelling tool geoscene3d (i-gis, http://www.i-gis.dk) together with all the geophysical data stored in gerda and the borehole information stored in jupiter, and the geophysical data are ready to be used in the geological modelling process carried out in geoscene3d. an example of the strength of the integrated data handling system is illustrated for a 50 × 60 km2 area in eastern jylland (fig. 3). large parts of this area are covered by tem soundings (c. 83 000 soundings), collected during more than 90 mapping campaigns (fig. 3b) and with five different tem methods (fig. 3c) over a time span of more than ten years. figure 3a shows a map of the surface of the deepest low-resistive model layer based on interpretation of all the tem soundings in the area. the deepest low-resistive model layer represents palaeogene clay deposits except in the north-eastern corner, where it represents salty pore water in danian limestone. the most prominent features found in the area are a large number of buried valleys incised into the palaeogene clay deposits. the buried valleys show no direct correlation to the overall topography. even though the data have been acquired by different companies, with different instruments and methods, and at different times, the data can be combined without showing any discrepancies at survey borders. concluding remarks geophysical measurements play an important role in the national groundwater mapping programme and have contributed significantly to the mapping of aquifers in den mark. in heterogeneous regions the data density needs to be high in order to provide acceptable mapping results. geo physical methods like tem/skytem and electrical methods can provide sufficient data density and reflection seismic profiles can resolve internal structures in specific areas in combination with detailed borehole information such as litho logical descriptions, geophysical logs, data on water chem43 gerda jupiteraarhus workbench data processing raw electrical and electromagnetic data inversion preparation of data to gerda 3-d visualisation data quality control geological modelling geological models hydrostratigraphical models groundwater models borehole information location lithology waterlevel water chemistry wenner seismic data, borehole logs cves schlumberger ip tem paces skytem em3x hem seismics borehole logs 1-d models 2-d models reprocessing re-interpretation visualisation on maps, profiles advanced data analysis advanced data interpretation geoscene 3d modeldb hydrogeological data fig. 2. sketch of the integrated system of databases and program packages handling geophysical data and geological modelling. the arrows show the flow of data between the geophysical database gerda, the borehole database jupiter, the aarhus workbench program package, the geoscene3d visualisation and modelling tool and the geological model database modeldb. rosa_2008:rosa-2008 01/07/09 15:48 side 43 44 istry and hydraulic parameters. these data form the basis for detailed hydrogeological models. an integrated data hand ling system makes it possible to merge geophysical data acquired over long periods by different companies with different instruments. this is of great value for future mapping and administrative purposes. references dahlin, t. 1996: 2d resistivity surveying for environmental and engineering applications. first break 14, 275–283. hydrogeophysics group 2007a: guide to processing and inversion of skytem data. version 1.2. århus: department of earth sciences, uni ver sity of aarhus. http://www.hgg.geo.au.dk/hggsoftware/work-bench/ workbench_skytem.pdf. hydrogeophysics group 2007b: aarhus workbench a-z reference, ver sion 2.2. århus: department of earth sciences, university of aarhus. http://www.hgg.geo.au.dk/hggsoftware/workbench/workbench_az_reference.pdf. jørgensen, f., lykke-andersen, h., sandersen, p.b.e., auken, e. & nør mark, e. 2003: geophysical investigations of buried quaternary valleys in denmark: an integrated application of transient electromagnetic soundings, reflection seismic surveys and exploratory drillings. journal of applied geophysics 53, 215–228. jørgensen, f., kristensen, m., højberg a.l., klint, k.e.s, hansen, c., jordt, b.e., richardt, n & sandersen, p. 2008: opstilling af geologiske modeller til grundvandsmodellering. geo-vejledning 3, 176 pp. copen hagen: geological survey of denmark and greenland. møller, i., søndergaard, v.h., jørgensen, f., auken, e. & christiansen, a.v. in press: integrated management and utilisation of hydrogeophysical data on a national scale. near surface geophysics. rasmussen, e.s., vangkilde-pedersen, t. & scharling, p. 2007: prediction of reservoir sand in miocene deltaic deposits in denmark based on highresolution seismic data. geological survey of denmark and greenland bulletin 13, 17–20. sørensen, k. 1996: pulled array continuous electrical profiling. first break 14, 85–90. sørensen, k.i. & auken e. 2004: skytem – a new high-resolution helicopter transient electromagnetic system. exploration geophysics 35, 191–199. sørensen, k.i., auken, e., christensen, n.b. & pellerin l. 2005: an integrated approach for hydrogeophysical investigations. new technologies and a case history. in: butler, d. (ed.): near-surface geo physics part ii, seg investigations in geophysics series 13, 585–603. tulsa: society of exploration geophysicists. thomsen, r., søndergaard, v.h & sørensen, k.i. 2004: hydrogeologi cal mapping as a basis for establishing site-specific groundwater protection zones in denmark. hydrogeology journal 12, 550–562. vangkilde-pedersen, t., dahl, j. f. & ringgaard, j. 2006: five years of ex perience with landstreamer vibroseis and comparison with conventional seismic data acquisition. proceedings of the 19th annual sageep sym posium on the application of geophysics to engineering and en vironmental problems, seattle, usa, 2–6 april, 2006. (published on cdrom, 1086–1093). authors’ address geological survey of denmark and greenland, lyseng allé 1, dk-8270 højbjerg, denmark. e-mail: ilm@geus.dk fig. 3. data coverage and results from an area in eastern jylland. for location see fig. 1. a: map showing the elevation of the surface of the deepest low-resistive layer in the area relative to sea level. b: the data come from 94 different mapping projects (shown by different colours). c: five diffe rent tem methods were used to produce map a. århus 10 km –200 –100 500 tem 40 hmtem 1 hmtem 2 patem skytem ca b elevation (m) rosa_2008:rosa-2008 01/07/09 15:48 side 44 geological survey of denmark and greenland. bulletin 10, 57-60 57 earthquake seismology is a rapidly evolving field that has provided a wealth of new information about deep geological structures on a regional scale over the last decade as well as information about dynamic processes in the earth. a major leap forward was the development of portable digital broad band (bb) seismographs around 1990. without any changes in configuration, these are able to record the signals from large distant earthquakes, as well as the signals from weak local events. bb seismographs typically cover a frequency range from 0.0083 hz to 50 hz, making them useful for studies ranging from the high frequency signals from explosions to the very low frequency oscillations following major earthquakes. the first seismological observatory in greenland was established in 1907 in qeqertarsuaq (gdh) and was in service for about five years (hjelme 1996). later, seismographs were established in ivittut (1927) and illoqqortoormiut (1928; sco), and the network has been regularly upgraded and expanded ever since (fig. 1). prior to the development of bb seismographs, each station was equipped with a set of seismographs with different frequency sensitivities in an attempt to cover both distant and local earthquakes. now just one small instrument is needed at each location. the geological survey of denmark and greenland (geus) operates four permanent bb seismographs in greenland (fig. 1), two of them in collaboration with foreign institutions. in addition to the permanent network, there are currently 13 temporary bb seismographs active in greenland, of which eight are operated by geus. three of the temporary seismograph stations were established as part of the danish continental shelf project (marcussen et al. 2004), and the remainder in connection with research projects. three temporary seismographs were deployed during 2005 as part of a research project aiming to resolve very deep regional structures in north greenland: the citronen fjord station (cfj, continental shelf project), and the stations in kullorsuaq (kul) and daneborg (dbg). the seismological service in greenland the study of earthquakes is international by nature. large earthquakes can be recorded world wide, and a good coverage of high quality data is crucial for an accurate determination of an epicentre. epicentral determination for large earthquakes is carried out at international data centres through collaboration of seismic services in almost all countries of the world. the primary task for the seismology group at geus is to maintain the seismological service for denmark and greenland (see gregersen et al. 2004). the seismological service runs the permanent network of seismographs, that collects high quality continuous data, analyses the data, and reports registered earthquake signals (phases) for local earthquakes as well as for regional and teleseismic events. the © geus, 2006. geological survey of denmark and greenland bulletin 10, 57–60. available at: www.geus.dk/publications/bull earthquake seismology in greenland – improved data with multiple applications tine b. larsen,trine dahl-jensen, peter voss,thomas møller jørgensen, søren gregersen and hans peter rasmussen n dag sco sfj ale nrs upn nuk attu sisimiut ivittut sum ffb cfj kia ass kulang kangerlussuaq is3 kag gdh umm asi ill ngr paa dy2 dbg is1 is2 soe hjo tule ilg nor greenland summer station active summer 2000 station deployed in 2005 long-term station long-term station currently not active permanent station abandoned analog site 250 km 60° 70° 80° 50° 40° 30° 90° 50°60°70°80° 40° 30° 20° 10° 0° 10° fig. 1. seismograph stations in greenland. 58 continuous digital waveform data are freely available directly from a geus server, as well as through international data centres. due to greenland’s size and geographical location, data from greenland are particularly important to the international seismological community. currently, the kangerlussuaq (sfj) seismograph and the seismograph at the summit ice camp (sum) are the only two in greenland with real-time data transmission. data from other stations are available with varying time delay. the phase readings are reported to international data centres such as the united states geological survey (usgs) and the international seismological centre (isc) through the weekly bulletin and the revised monthly bulletin. in 2005, geus reported a total of 3999 earthquake signals from the permanent seismograph network in greenland, including many of the aftershocks that continued for several months after the sumatra earthquake on 26 december, 2004, as well as the devastating 7.6 richter scale kashmir earthquake on 8 october, 2005 (fig. 2). the seismograph in kangerlussuaq was moved 300 m in february 2005 to a vault protected from local radar antenna disturbances. this was carried out in order to serve better the needs of the comprehensive test ban treaty organisation (ctbto). ctbto financed the move, and provides in addition the real-time satellite transmission of the continuous data. the instrumentation was supplemented in 2005 with an extra bb seismograph. the ctbto is an organisation under the united nations, and its goal is to detect nuclear explosions of more than 5 kg fissionable material anywhere on earth. an important tool for the organisation is seismological surveillance carried out by a primary and a secondary global network of designated secure seismograph stations. the kangerlussuaq seismograph is part of the secondary network, and was officially certified by ctbto on 24 november 2005. geus is denmark’s national authority for the ctbto. several minor earthquakes occurred in greenland in 2005. geus received reports that earthquakes were felt in qeqertarsuaq (gdh) on 30 march, in sisimiut on 23 july, at station nord (nor) on 30 august, and in attu on 23 october. tasiilaq (ang) is normally the place in greenland where most earthquakes are felt; however, no earthquakes were reported in 2005. including the reports of felt earthquakes noted above, geus has so far registered 20 earthquakes in greenland in 2005 (fig. 3). this number may increase when the preliminary earthquake catalogue is quality controlled and revised, and data from the temporary seismographs are recovered and included. studies on deep crustal and mantle structures denmark ratified the united nations convention on the law of the sea (unclos) in november 2004. after ratification of unclos, a country has ten years to collect the appropriate information and submit a claim for an extended continental shelf beyond 200 nautical miles. one of the potential claim areas is the continental shelf north of greenland (marcussen et al. 2004). three bb seismographs have been placed along the north greenland coast (fig. 1) with the aim of learning more about the thickness and structure of the crust of north greenland through receiver function analysis. this method has previously been used at many sites in greenland during the glatis (greenland lithosphere analysed teleseismically on the ice sheet) project, but all bb seismographs used in previous studies were located further south (dahl-jensen et al. 2003). the stations at frankfield bugt (ffb) and aftenstjernesø (ass) have been in operation since 2004, whereas the citronen fjord station (cfj) started recording data in 2005. these stations record signals from distant (teleseismic) earthquakes that can be processed to obtain information about crustal structure, e.g. depth to moho and even deeper structures. the data retrieved so far are of excellent quality. normally it is necessary to record data for more than a year in order to obtain a reliable estimate for the depth to moho, but for the aftenstjernesø station a depth to moho of 41 km and a vp/vs of 1.71 was determined using just a few months of data. the relatively sco hh z sco hh n minutes 0 10 20 30 40 50 60 sco hh e fig. 2. seismograms for the richter scale 7.6 kashmir earthquake on 8 october, 2005 recorded at illoqqortoormiut. the top seismogram shows the vertical motion, the middle seismogram motion in the north–south direction, and the bottom seismogram motion in the east–west direction. 59 large depth to moho at aftenstjernesø indicates that the station is on the rim of the precambrian shield area (fig. 3), and data from other locations are therefore necessary to resolve the question of crustal thickness in the franklinian basin that extends along the north greenland coastal region. surface waves from teleseismic earthquakes can provide information on deep geological structures between two seismographs recording the same earthquake. provided that two seismographs are located on the same great circle as the epicentre, differences in the signal recorded on the two instruments will reflect the geology affecting the wave propagating between the two stations. a dense web of epicentres and station pairs will make it possible to construct a seismic velocity model from depths of about 60 km to about 300 km. this kind of analysis was successfully carried out during the glatis project (darbyshire et al. 2004). similar studies were made previously by gregersen (1970, 1982) for the crust, using various kinds of seismic waves. in addition to the studies of velocity structure in the mantle, measurements of amplitude attenuation have been carried out (jørgensen 2005), resulting in preliminary maps of differences in the wave absorption properties of the deep structures. in order to take full advantage of the seismographs along the north coast of greenland and improve coverage inland north of 72°n, it was necessary to deploy two extra seismographs, one in the settlement of kullorsuaq (kul), and another at daneborg (dbg) that was previously used by the glatis project (fig. 1). both seismographs were installed in 2005 and will remain in operation until 2007. it is expected that a first-order model of the very deep velocity structures inland in north greenland can be constructed within the framework of the project. in 2006 another deep-structure seismological project will deploy a short profile of five bb seismographs across the safartoq kimberlite region south-east of sisimiut. the aim of this project is to reveal the crustal thickness in the area. the safartoq project will be initiated as a pilot study of the area in order to facilitate a proposal for a large-scale deep structure study with international partners. a larger array of instruments is necessary for studies of the deep lithospheric structures. glacial earthquakes glacial earthquakes are a peculiar type of seismological event primarily located in greenland. they were first described by ekström et al. (2003). the signals are dispersive, lack the characteristic pand swaves known from ordinary earthquakes and all signals appear to have their source beneath large glaciers. the focal mechanisms that can be calculated for the earthquakes are consistent with a large mass of ice moving abruptly downhill over an elastic medium (landslide model). in 2005 geocenter copenhagen funded a joint research project on glacial earthquakes involving geus and the institute of geography, university of copenhagen. through the glatis project geus possesses a unique seismological data set for greenland, previously used only for structural studies. when the majority of bb seismographs in greenland were installed, the existence of glacial earthquakes had not been recognised. however, after the start of the glacial earthquake project in 2005, it has become clear that the bb seismological data from greenland are a unique data set for the study of glacial earthquakes. 500 km north atlantic ocean permanent ice upper cretaceous – palaeogene sediments and basalts devonian–palaeogene sediments caledonian orogenic belt proterozoic sediments and volcanic rocks palaeoproterozoic orogenic belts archaean craton offshore basins with substantial sediment thicknesses major faults and thrusts lower palaeozoic sediments, franklinian basin n 5.0 4.0 3.0 2.0 fig. 3. map of earthquake locations in and around greenland for 19702005. only earthquakes with a magnitude of 2.0 or more on the richter scale are shown. the map is compiled from the geus earthquake database, supplemented with epicentre locations from the geological survey of canada, the united states geological survey and norsar in norway. glacial earthquakes have not previously been studied extensively using a local data set (fig. 4). one purpose of the project is to significantly improve the location accuracy for the earthquakes, and to improve the detection threshold by an order of magnitude from 4.7 on the richter scale to 3.7. detecting smaller earthquakes opens the possibility of revealing unknown ice streams within the greenland ice sheet. the occurrence of glacial earthquakes shows strong seasonal variation, with most earthquakes occurring during summer. this implies that the glacial earthquakes could contribute information as to how variations in climate parameters affect ice sheet dynamics. gps fieldwork is planned for summer 2006, when glacial earthquakes will be recorded simultaneously on both seismographs and differential gps. the objective of the project is to shed light on the mechanisms controlling the glacial earthquakes, with the possibility that glacial earthquakes can be used as a surveillance tool to study greenland ice sheet dynamics. acknowledgements geoforschungszentrum-potsdam (gfz), germany provides instrumentation and technical support to the seismograph in danmarkshavn, and together with the incorporated research institutions for seismology (iris), usa to the seismograph in kangerlussuaq. the bureau of minerals and petroleum, government of greenland, provided financial support to several of the projects described in this paper. geocenter copenhagen provides financial support for the project on glacial earthquakes. references dahl-jensen, t., larsen, t.b., woelbern, i., bach, t., hanka, w., kind, r., gregersen, s., mosegaard, k., voss, p. & gudmundsson, o. 2003: depth to moho in greenland: receiver-function analysis suggests two proterozoic blocks in greenland. earth and planetary science letters 205, 379–393. darbyshire, f.a., larsen, t.b., mosegaard, k., dahl-jensen, t., gudmundsson, o., bach, t., gregersen, s., pedersen, h.a. & hanka, w. 2004: a first detailed look at the greenland lithosphere and upper mantle, using rayleigh wave tomography. geophysical journal international 158, 267–287. ekström, g., nettles, m. & abers, g.a. 2003: glacial earthquakes, science 302, 622–624. gregersen, s. 1970: surface wave dispersion and crust structure in greenland. geophysical journal of the royal astronomical society 22, 22–39. gregersen, s. 1982: seismicity and observations of lg wave attenuation in greenland. tectonophysics 89, 77–93. gregersen, s., glendrup, m., larsen, t.b., voss, p. & rasmussen, h.p. 2004: seismology: neotectonics and structure of the baltic shield. bulletin of the geological survey of denmark and greenland 7, 25–28. hjelme, j. 1996: history of seismological stations in denmark and greenland. in: wahlström, r. (ed.) seismograph recording in sweden, norway – with arctic regions, denmark – with greenland, and finland. proceedings from the uppsala wiechert jubilee seminar, 49–57. uppsala: seismological department, uppsala university, sweden. jørgensen, t.m., 2005: attenuation of rayleigh waves in greenland, 78 pp. unpublished m.sc. thesis, university of copenhagen, denmark. marcussen, c., christensen, f.g., dahl-jensen, t., heinesen, m., lomholt, s., møller, j.j. & sørensen, k 2004: exploring for extended continental shelf claims off greenland and the faroe islands. bulletin of the geological survey of denmark and greenland 4, 61–64. authors’ address geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: tbl@geus.dk 60 time ale ang borg dag frb gdh hjo kbs kono nuk soe sum stack ang is3 soe hjo kul a b fig. 4. a: seismogram envelopes for a glacial earthquake, that occurred on 20 october, 2000. signal from the earthquake is shown in blue. the bottom seismogram is a stack of the twelve seismograms, relative to a chosen test epicentre. when the test epicentre is close to the true epicentre, stacking will produce a strong signal. for location of greenland stations see fig. 1. ale: alert, arctic canada. borg: borganes, iceland. frb: frobisher bay, arctic canada. kbs: kingsbay, svalbard; kono: kongsberg, norway. b: correlation for the signal in the stack, with the best correlation in blue. many test epicentres are modelled before the true epicentre can be determined, in this case centred in kangerlussuaq in east greenland (see fig. 1). geological survey of denmark and greenland bulletin 12, 16-23 16 core samples have been available. as the use of stratigraphic lowest occurrences (lo) of taxa in cuttings samples may be hampered due to downhole caving, the event succession comprises almost exclusively stratigraphic highest occurrences (ho) of taxa (a single significant lo is included in the succession). the event succession is shown in fig. 5a–c; its correlation with international and north sea biozones is shown in fig. 6a–c. seismic sections from the 2-d and 3-d seismic surveys cgd85, dk-1, rtd81–re94, ucg96 and ucge97 have been used to further support the well correlation and to map the stratigraphic units in areas with only scattered well coverage. the combined results from the correlation and mapping procedures are presented as isochore maps for individual stratigraphic units. inspection of cuttings samples from 16 key wells supplemented with sedimentological studies of cored intervals from 23 wells have formed the basis for the lithological and sedimentological descriptions of the units. the well depths mentioned in the lithostratigraphy section are loggers’ depths measured either from rotary table (mdrt) or kelly bushing (mdkb). supplementary data for new type and reference wells are provided in table 1. the names assigned to the new lithostratigraphic units defined herein are derived from nordic mythology and thus follow the nomenclatural tradition previously established for the norwegian north sea (isaksen & tonstad 1989). it should be noted that the micropalaeontology-based palaeoenvironmental terminology used herein was originally developed for a passive margin situation (e.g. the terms ‘neritic’ and ‘bathyal’ to indicate the physiographic zones ‘shelf ’ and ‘shelfslope’, respectively). its application herein to the epicontinental north sea basin solely relates to depositional depth. offshore and onshore lithostratigraphic nomenclature there is a high degree of lithological similarity between the palaeogene–neogene mudstone succession in danish offshore boreholes and that in onshore exposures and boreholes. however, the status of the danish onshore units is quite varied since many units were named before a standard for description of a lithostratigraphic unit was established; some fulfil these requirements, whereas others are still informal. if a previously established onshore unit and an offshore unit can be demonstrated to be identical (e.g. the holmehus formation and the new ve member proposed herein), the name of the onshore unit theoretically has priority over the name of the offshore unit (salvador 1994). in other cases, names of offshore units can be argued to have priority over onshore units (e.g. sele and balder formations over ølst formation). however, in order to acknowledge the traditional distinction between offshore and onshore stratigraphic nomenclature, the two sets of nomenclature are kept separate herein. whenever possible, comments are given in the text to explain the relationship between offshore and onshore danish stratigraphic nomenclature. a correlation between the two sets of nomenclature is shown in fig. 2. chronostratigraphy and biostratigraphy age assessment of the lithostratigraphic units in the north sea sedimentary succession is based on correlation between key biostratigraphic events encountered in the units and the calibrated standard chronostratigraphy published by berggren et al. (1995), with modification for the paleocene–eocene boundary following ratification of its position by the international union of geological scientists (aubry et al. 2002). the key events are from biostratigraphic zonation schemes established for the north sea area. planktonic and benthic microfossils are covered by the zonation schemes of king (1983, 1989; figs 5a–c, 6a–c). dinoflagellates from the paleocene and eocene epochs are covered by the zonation scheme of mudge & bujak (1996b; fig. 6a, b); the oligocene and miocene epochs are covered by the zonation schemes of costa & manum (1988) with modifications by köthe (1990, 2003; fig. 6b, c). key events from these schemes used in this study are listed in fig. 5a–c. for the dinoflagellate events, geochronological calibration has been largely established using age estimates from hardenbol et al. (1998), munsterman & brinkhuis (2004) and williams et al. (2004). for events not mentioned in these three publications, the works of mudge & bujak 17 p2 p9 p7 p6 b a p5 p4 c p8 np13 np12 np10 np9 np11 b a b a p3 c b a p1 pα + p0 np8 np6 np5 np4 np3 np2 np1 np7 abathomphalus mayaroensis cc26 cc25 (pars) pseudotextularia elegans p6 p5 p4 p3 p2 p1 e1a e2a e2b e2c e3a e3b l e1c e1be o ce ne ( pa rs ) pa le o ce ne c re ta ce o us (p ar s) np14 (pars) e3c 50 60 55 65 nsp6 (pars) nsp5b nsp4 nsb4 (pars) nsb3a nsb2 nsp5a nsb3b nsp3 nsp2 nsp1 nsb1 65.0 ypresian (pars) lo w er ( pa rs ) u pp er lo w er 55.5 60.0 thanetian selandian danian u pp er ( pa rs ) maastrichtian (pars) 57.9 54.5 sparnacian c b a b c a planktonic microfossils benthic microfossils dinoflagellate cysts planktonic microfossils calcareous nannofossils north sea biozonesstandard biozones chronostratigraphy (berggren et al. 1995) stageseries berggren & miller (1988), berggren et al. (1995) mudge & bujak (1996b) martini (1971) king (1989) geochronology ma a fig. 6. biostratigraphic correlation charts showing approximate correlation of calibrated standard planktonic foraminifer and nannofossil biozones with north sea microfossil and dinoflagellate biozones. calibration of the standard biozones follows hardenbol et al. (1998). relationships between the north sea biozones are approximate and their correlation with the standard zones may deviate from that of the original authors (for discussion, see text). a: paleocene–eocene biostratigraphic correlation chart. b: eocene–oligocene biostratigraphic correlation chart. c: oligocene – middle miocene biostratigraphic correlation chart. p17 e6b np14 p9 p7 p8 np13 np12 np11 e2a e2b e2c e3a e3b e1c e1b e3c nsp6 nsp5b nsb4 nsb3ansp5a nsb3b p18 p16 p15 np23 (pars) np22 np21 np19–20 np18 p14 p12 p11 p10 p13 np17 np16 np15 e3d e4a e4b e4c e4d e5a e5b e6a e6c e7a e7b e8b e8a d13 mudge & bujak (1996b) costa & manum (1988), köthe (1990) planktonic microfossils benthic microfossils dinoflagellate cysts planktonic microfossils calcareous nannofossils north sea biozonesstandard biozones p19 (pars) 35 40 50 45 o lig o ce ne (p ar s) lo w er ( pa rs ) eo ce ne ( pa rs ) u pp er m id dl e lo w er ( pa rs ) nsb7ansp9b nsp9a nsb6b nsp8c nsb6a nsp8b nsb5c nsp8a nsp7 nsb5b nsb5a p6 b a np10 (pars) nsp4 (pars) nsb2 (pars) e1a (pars) geochronology ma chronostratigraphy (berggren et al. 1995) stageseries berggren & miller (1988), berggren et al. (1995) costa & manum (1988), köthe (1990), mudge & bujak (1996b) martini (1971) king (1989) rupelian (pars) priabonian 41.3 lutetian ypresian (pars) 49.0 37.0 33.7 bartonian b fig. 6b. eocene–oligocene biostratigraphic correlation chart. 18 m7 m9 m12 m8 m11m10 m6 m5 m3 m2 m4 m1 b a p22 p21 b a p20 p19 p18 nn5 nn6 nn9a– nn7 nn4 nn3 nn2 nn1 np25 np24 np23 np22 np21 (pars) d13 d14 d15 d16 d17 d18 d19 tortonian (pars) burdigalian aquitanian m io ce ne ( pa rs ) lo w er chattian u pp er rupelian (pars) lo w er ( pa rs ) o lig o ce ne ( pa rs ) m id dl e langhian serravallian 28.5 23.8 20.5 16.4 14.8 11.2 15 20 30 25 u pp er (p ar s) nsp9a (pars) nsb6b (pars) nsp14b nsb13a nsp14a nsb12c nsp13 nsb12b nsb12a nsp12 nsb11 nsp11 nsp10 nsb10 nsb9 nsp9c nsb8c nsb8b nsb8a nsb7b nsb7a nsp9b m13a (pars) nn9b (pars) planktonic microfossils benthic microfossils dinoflagellate cysts planktonic microfossils calcareous nannofossils north sea biozonesstandard biozones chronostratigraphy (berggren et al. 1995) stageseries berggren & miller (1988), berggren et al. (1995) costa & manum (1988), köthe (1990), martini (1971) king (1989) geochronology ma c fig. 6c. oligocene – middle miocene biostratigraphic correlation chart. 19 20 (1996b), dybkjær (2004), piasecki (2005) and schiøler (2005) have been consulted. however, whereas hardenbol et al. (1998) and williams et al. (2004) used the timescale of berggren et al. (1995), mudge & bujak used the slightly older timescale from haq et al. (1987) for calibration of their events. therefore, the ages of events only listed by mudge & bujak have been recalibrated herein to conform to the timescale of berggren et al. (1995). king (1989) calibrated his planktonic and benthic microfossil zone markers with the standard chronostratigraphic scale of berggren et al. (1985a, b). however, king noted that only a few first-order correlations were possible; most of the calibrations were made using dinoflagellates, planktonic foraminifers and nannoplankton from onshore sections in the north sea basin (king 1989 p. 420); the correlation of the lower miocene is particularly uncertain (king 1989 p. 446). paleocene and eocene key planktonic and benthic microfossil events from king (1989) were subsequently correlated with the north sea dinoflagellate events by mudge & bujak (1996b). by using the above-mentioned recalibration of key dinoflagellate events from mudge & bujak (1996b), it is feasible to indirectly correlate king’s north sea microfossil events with the timescale of berggren et al. (1995). this has been attempted in fig. 5a–c. figure 6a–c shows the relationships between the north sea biozones and their correlation with the standard planktonic foraminifer and calcareous nannofossil zones. however, it should be noticed that in a few cases the correlation of the north sea microfossil and dinoflagellate zones with the standard zones in fig. 6a–c is at variance with that of the authors of the same zones. this is an effect of improved age determinations of the standard zones and the dinoflagellate events used to calibrate the north sea microfossil zones. the section below outlines the current status for the palaeogene and neogene chronostratigraphic units covered by the studied succession and lists key biostratigraphic events used for chronostratigraphic correlation of the succession. paleocene the bases of the selandian and thanetian stages, which together constitute the upper paleocene series, have yet to be formally defined. however, ongoing work in the international subcommission on palaeogene stratigraphy indicates that the global standard stratotype-section and point (gssp) of the base of the selandian stage will probably be close to the p2–p3a or the p3a–p3b standard planktonic foraminifer zone boundary, while the gssp for the thanetian stage will probably be at the base of magnetochron c26n (gradstein & ogg 2002). hardenbol et al. (1998) followed berggren et al. (1995) in placing the base of the selandian stage at the base of zone p3a, at the lowest occurrence of the planktonic foraminifer morozovella angulata. however, many of the microfossil species that characterise the danian–selandian boundary interval in the international zonation schemes, including m. angulata, are extremely rare or absent in the north sea basin thereby hampering chronostratigraphic correlation of the boundary. based on a study of core material from the type area for the danian and selandian stages, clemmensen & thomsen (2005) concluded that the danian–selandian stage boundary is located in the upper part of the np4 standard nannofossil zone, close to the np4–np5 zone boundary, approximately at the p3a– p3b zone boundary, at c. 60 ma on the timescale of hardenbol et al. (1998). they further concluded that there is a hiatus between the danian and selandian stages in the danish area outside the central graben due to truncation of the danian limestones of the ekofisk formation (fig. 5a; clemmensen & thomsen 2005). hence, the danian–selandian stage boundary is herein placed just below the downhole reappearance (provisional ho) of planktonic foraminifers and the ho of the dinoflagellate alisocysta reticulata, but above the closely spaced events marked by the ho of the planktonic foraminifers subbotina trivialis and globanomalina cf. compressa (e.g. jones 1999; mudge & bujak 2001). the selandian–thanetian stage boundary is herein approximated by the ho of the dinoflagellate palaeoperidinium pyrophorum, at the base of the p5 dinoflagellate zone of mudge & bujak (1996b). this level is close to the base of magnetochron c26n, according to hardenbol et al. (1998). eocene the base of the eocene is at the base of the negative carbon isotope excursion (cie) at 55.5 ma (berggren & aubry 1996; aubry et al. 2002). this position is below the base of the ypresian stage, the lowermost eocene stage. therefore it has been proposed to reintroduce the sparnacian stage as the new basal eocene stage between the cie and the base of the ypresian (aubry et al. 2003). the cie has been correlated with the proliferation of the dinoflagellate genus apectodinium, an event recognised globally (e.g. knox 1996; crouch et al. 2001). onshore denmark, the cie and the proliferation of apectodinium coincides precisely with the laminated stolle klint clay in the 21 2900 m 3000 2900 m 3000 2000 m 2100 2700 m 2900 m horda fm balder fm sele fm lista fm bue mb r o ga la nd g ro up st ro ns ay g ro up ve mb vile mb våle fm chalk group 3000 2800 kim-1 gr sonic gr sonic gr sonic gr sonic gr sonic kim-1 mona-1 cleo-1 gulnare-1 e-8 e-8 lowermost part of the haslund member of the ølst formation (heilmann-clausen & schmitz 2000; willumsen 2004). in the north sea basin, the acme of apectodinium is located in the lowermost, laminated part of the sele formation (sensu deegan & scull 1977, see below) according to knox (1996). as the event is a lo, its position cannot be determined with certainty in wells in which this interval is covered only by cuttings samples. in the north sea basin, however, this stratigraphic level is characterised by a prominent excursion on the gamma-ray log near the base of the sele formation which therefore can be used as an approximation for the base of the eocene series. the remaining stages of the eocene series, the ypresian, lutetian, bartonian and priabonian stages, lack basal boundary gssps for the present. in this paper, we follow mudge & bujak (1996b) and approximate the bases of the three latter stages by using three key dinoflagellate events: the base of the lutetian stage is at the ho of common eatonicysta ursulae, the base of the bartonian stage is close to the ho of diphyes colligerum, and the base of the priabonian stage is close to the ho of heteraulacacysta porosa. the base of the classic ypresian stage is at the lo of the calcareous nannoplankton species tribrachiatus digitalis. as yet, there is no commonly recognised ho index event at that level in the north sea basin, but the boundary between the sparnacian and the ypresian stages may be placed below the hos of common cerodinium wardenense and apectodinium augustum (fig. 5a), both dinoflagellate species. oligocene the gssp for the eocene–oligocene boundary is in the massignano section (central italy), at the highest occurrence of the planktonic foraminifer genera hantkenina and cribrohantkenina, immediately above the p17–p18 planktonic foraminifer zone boundary (premoli silva & jenkins 1993). however, hantkeninids have not been observed from the north sea basin and alternative zone markers have therefore been used here. in the north sea basin, the planktonic foraminifer globigerinatheka index and the benthic foraminifer cibicidoides truncanus have their hos in the uppermost eocene (king 1989), and the two events may be used to approximate the eocene–oligocene boundary. a palynological marker of the lowermost oligocene is the ho of the dinoflagellate areosphaeridium diktyoplokum (brinkhuis & biffi 1993; brinkhuis & visscher 1995), which is widespread in the north sea basin. the three latter events in combination serve as useful markers for bracketing the eocene–oligocene boundary in the north sea basin. the principal criterion for the rupelian–chattian (lower–upper oligocene) boundary has not yet been defig. 7. log panel illustrating the thickness variation of the rogaland group formations in the danish central graben. 22 cided by the subcommission on palaeogene stratigraphy. indications are that the boundary may be positioned at the base of the p21b planktonic foraminifer zone (premoli silva 2005), at 28.5 ma (hardenbol et al. 1998). however, the defining boundary event cannot be recognised in the north sea basin and its exact correlation with the north sea biostratigraphic event succession remains uncertain. instead, most north sea biostratigraphers recognise the rupelian–chattian stage boundary at the ho of the benthic foraminifer rotaliatina bulimoides. this event marks the top of the nsb7 zone of king (1983, 1989; fig. 5c) and the nsr7 zone of gradstein et al. (1994). the ho of r. bulimoides is at 29 ma in the northern north sea according to gradstein & bäckström (1996), slightly older than the 28.5 ma for the rupelian–chattian stage boundary quoted by hardenbol et al. (1998). the rupelian–chattian stage boundary may also be approximated by the ho of the dinoflagellate rhombodinium draco. in the north sea wells reported herein, where both the hos of r. bulimoides and r. draco have been recorded, these events are largely contemporaneous. however, in the type area of the rupelian and chattian stages, r. draco has its ho above r. bulimoides in the type chattian (van simaeys et al. 2004). therefore, it may be inferred that the two latter events probably bracket the rupelian–chattian boundary (fig. 5c). ve mb tyr mb bue mb log depth core depth våle fm lista fm bor mb gr soni c cecilie-1 clay si. vf. f. m. sand c. vc. p p p p p p p p p ? s 5o 2240 2250 2260 2270 2280 2240 2250 2260 2270 2280 vile mb fig. 8. core log showing intrusive sandstones in the våle and lista formations in the cecilie-1 well. for legend, see fig. 9. the two intervals marked by grey bars in the core depth column are shown as core photographs in fig. 10. 23 lithology sedimentary structures sandstone intrusions mudstone clasts chert siderite calcite concretions trace fossils sandstone mudstone marl chalk carbonate cement (non-calcitic) calcite cement pyrite glaucony parallel lamination faint parallel lamination water-escape pipes (large) load cast dish structures and pipes deformed/slumped bedding fractures/faults bed boundary cross-lamination sandstone intrusions flow structures stylolites zoophycos helminthopsis planolites thalassinoides chondrites low moderate intense degree of bioturbation p g s c miocene the oligocene–miocene series boundary is bracketed by a number of hos at its type section (lemme-carosio, north-west italy). unfortunately, none of the foraminifer events are believed to be true stratigraphic tops (facies dependent), and reworking in the section hampers the use of nannofossil tops (steininger et al. 1997). however, the dinoflagellate succession from the lemme-carosio section has been documented in detail by powell (1986), brinkhuis et al. (1992) and zevenboom (1995, 1996), and provides a means for direct correlation to the north sea basin (munsterman & brinkhuis 2004). the ho of distatodinium biffii is below the chattian–aquitanian boundary in its type section and the ho of chiropteridium spp. is above. this succession of events can be recognised in many north sea wells, and the chattian–aquitanian boundary is positioned between the two. supporting microfossil events that characterise the lowermost miocene include the ho of the diatom aulacodiscus insignis quadrata (small morphotype, same as diatom sp. 3 of king 1983, 1989), a widespread event in the north sea basin, and the ho of the benthic foraminifer brizalina antiqua (king 1989). the ho of the planktonic foraminifer paragloborotalia nana marks uppermost chattian strata. the principal criteria for the aquitanian–burdigalian, burdigalian–langhian and langhian–serravallian stage boundaries are as yet undecided. most authors place the three boundaries at microfossil zone boundaries or magnetochron boundaries at 20.5, 16.4 and 14.8 ma, respectively (hardenbol et al. 1998; williams et al. 2004). the correlation of the three boundaries to the north sea basin is feasible using the dinoflagellate zonation scheme of de verteuil & norris (1996), established for us east coast sections and the review of dinoflagellate index events published by williams et al. (2004). the former zonation scheme is correlated directly with the zonation schemes of berggren et al. (1995) and the miocene timescale by means of calcareous nannofossils and foraminifers. the aquitanian–burdigalian boundary is positioned just above the ho of the dinoflagellate caligodinium amiculum. the burdigalian–langhian boundary is placed between the ho of the dinoflagellates hystrichokolpoma cinctum and pyxidinopsis fairhavenensis, two events that bracket the boundary level. the langhian–serravallian boundary is slightly above the ho of the dinoflagellate cousteaudinium aubryae. in this study, these four events have been used to approximate the three stage boundaries. fig. 9. legend for core logs (figs. 8, 11, 18, 27, 30 and 39); the lithological colour scheme is also adopted on well sections (e.g. fig. 13). geological survey of denmark and greenland bulletin 6, 5-28 5 lower palaeozoic stratigraphy of the east greenland caledonides m. paul smith, jan audun rasmussen, steve robertson, a.k. higgins and a. graham leslie the lower palaeozoic stratigraphy of the east greenland caledonides, from the fjord region of north-east greenland northwards to kronprins christian land, is reviewed and a number of new lithostratigraphical units are proposed. the slottet formation (new) is a lower cambrian quartzite unit, containing skolithos burrows, that is present in the målebjerg and eleonore sø tectonic windows, in the nunatak region of north-east greenland. the unit is the source of common and often-reported glacial erratic boulders containing skolithos that are distributed throughout the fjord region. the målebjerg formation (new) overlies the slottet formation in the tectonic windows, and comprises limestones and dolostones of assumed cambrian–ordovician age. the lower palaeozoic succession of the fjord region of east greenland (dominantly limestones and dolostones) is formally placed in the kong oscar fjord group (new). amendments are proposed for several existing units in the kronprins christian land and lambert land areas, where they occur in autochthonous, parautochthonous and allochthonous settings. keywords: early palaeozoic, north-east greenland, stratigraphy. m.p.s., lapworth museum, school of geography, earth and environmental sciences, university of birmingham, edgbaston, birmingham b15 2tt, uk. e-mail: m.p.smith@bham.ac.uk j.a.r. & a.k.h., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. s.r. (deceased) & a.g.l., british geological survey, murchison house, west mains road, edinburgh eh9 3la, uk. the east greenland caledonides extend for over 1300 km between scoresby sund (70°n) and kronprins christian land (81°30′n), cropping out in an ice-free coastal strip of variable width (fig. 1). in the south, the exposed width of the orogen is 300 km, but in the north this is reduced to less than 100 km. the orogen has been the subject of a series of systematic mapping programmes by the survey since 1968, supplementing and revising work by other groups, most notably lauge koch’s long series of geological expeditions between 1926 and 1958 (see haller 1971). this paper documents the key stratigraphical observations on lower palaeozoic rocks made during expeditions from 1993 to 1995 by the former geological survey of greenland (ggu) to kronprins christian land and lambert land (78°–82°n), and the 1997–1998 field work by the survey in the kong oscar fjord region (72°–75°n). a number of new lower palaeozoic lithostratigraphical units are proposed on the basis of this work and amendments are proposed for some existing units. the lower palaeozoic sediments of kronprins christian land and lambert land (fig. 2) were deposited on a subtidal to peritidal platform that constituted the south-easternmost part of the franklinian basin (higgins et al. 1991), and lay at a marked inflexion of the laurentian margin where it turns through 90° between the present-day e–w-trending coast of north greenland and the n–s-trending coast of east greenland. the stratigraphy erected in the caledonian foreland of eastern north greenland (peary land and western kronprins christian land; peel 1985; higgins geological survey of denmark and greenland bulletin 6, 5–28 © geus, 2004 geus bulletin 6.pmd 10-02-2005, 09:535 6 ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ c a l e d o n id e s greenland 70°n 74°n 78°n 82°w 35°w wandel sea centrumsø 100 km jameson land scoresby sund 25°w traill ø wollaston forland bessel fjord danmarkshavn lambert land peary land station nord k ro np rin s c hr ist ian l an d nørreland window kronprins christian land thin-skinned thrust belt (parautochthonous foreland) palaeogene basalts palaeogene intrusions wandel sea basin: carboniferous–palaeogene sediments east greenland basins: carboniferous–cretaceous sediments devonian – continental sediments late to post-kinematic granites neoproterozoic–ordovician sediments (east greenland) neoproterozoic–silurian sediments (eastern north greenland) palaeo-mesoproterozoic sediments and basalts (eastern north greenland) crystalline complexes and sediments (archaean–mesoproterozoic) neoproterozoic–silurian sediments (north greenland) palaeo-mesoproterozoic sediments and basalts (eastern north greenland) mainly crystalline rocks – parautochthonous windows thrust fault/shear zone tectonic zone boundary post-caledonian late to post-caledonian caledonian orogenic belt caledonian foreland ▲ ▲ fig. 8 fig. 2 c a le d o n ia n so le t h r u st in la n d ic e m a r g in a l t h r u s t b e l t t h ic k s k in n e d t h r u s t b e l t gåseland window charcot land window eleonore sø window målebjerg window hamberg gletscher foreland dronning louise land ▲ ▲ ▲ fig. 1. geological map of the east greenland caledonides, showing location of the foreland windows in the western marginal thrust belt. modified from higgins & leslie (2000). frames indicate the regions shown at larger scales in figs 2 and 8. geus bulletin 6.pmd 10-02-2005, 09:536 7 et al. 1991; smith & bjerreskov 1994) can, to a significant degree, be applied to the successions farther to the east and south within the study area (figs 2, 3), although many of the units differ in detail. this region is the only part of the franklinian basin to have been subsequently affected by the caledonian orogeny, and the lower palaeozoic units described here occur both in the foreland and in the thin-skinned parautochthonous fold-and-thrust belt beneath the vandredalen thrust sheet (fig. 2; higgins et al. 2001b). the lower palaeozoic successions of the fjord region of the southern parts of north-east greenland (72°–74°30′n; see fig. 8) have been the subject of a more protracted research effort that extends back to the 19th century. the cambrian–ordovician of the fjord region has become one of the classic reference areas for this stratigraphical interval, but it was only during the 1997–1998 survey field seasons that the tectonic context was fully elucidated (higgins et al. 2004a). it is now clear that the cambrian–ordovician of the fjord region, together with the underlying, neoproterozoic tillite group and eleonore bay supergroup, make up the upper part of the highest thrust sheet in the orogen, which has been transported several hundred kilometres from the east-south-east (higgins & leslie 2000; higgins et al. 2004a). furthermore, notably different developments of lower palaeozoic rocks were discovered cropping out in tectonic windows adjacent to the inland ice; the successions within these windows are disturbed by caledonian deformation, and are interpreted as autochthonous to parautochthonous representatives of the foreland (smith & robertson 1999a, b; higgins et al. 2004a, b, this volume). the latter are fully documented for the first time here, and provide data critical for interpreting the lower palaeozoic evolution of the iapetus passive margin and its subsequent deformation during the caledonian orogeny. kronprins christian land the lower palaeozoic units cropping out over a c. 5000 km2 area in southern kronprins christian land, eastern north greenland (figs 2, 3), were mapped and documented in 1993–1995 as part of the 1:500 000 mapping programme carried out by ggu. within the thin-skinned parautochthonous fold-and-thrust belt forming much of this region (higgins et al. 2004b, this volume) exposure is often poor due to an extensive cover of recent glacio-fluvial sediments, and the best exposures are on the slopes of the main valleys, with more scattered outcrops on the plateaus. the discontinuous exposure is disrupted by a series of eastward-dipping thrusts with displacements of several hundred metres to a few kilometres. correlation of superficially similar middle ordovician to silurian sediments in alternating units of peritidal dolostone and subtidal burrow-mottled limestones required detailed sedimentary facies analysis. macrofaunal biostratigraphy in the field was supplemented by the biostratigraphic analysis of conodonts, which in almost all cases verified the field determinations (rasmussen & smith 2001). cambrian sediments are restricted to the sandstones of the kap holbæk formation (see below), scattered representatives of which occur in autochthonous, parautochthonous and allochthonous settings. kap holbæk formation revised history. the kap holbæk formation was first documented by adams & cowie (1953) during a geological reconnaissance around the head of danmark fjord, and was informally divided into five members. fränkl (1954) demonstrated that the unit was also present in kronprins christian land around sæfaxi elv, and hurst & mckerrow (1985) interpreted it as occurring within thrust sheets north of romer sø. initial biostratigraphical determinations (peel & vidal 1988) concluded that, on the basis of acritarchs, the unit was of latest vendian (late ediacaran) age. clemmensen & jepsen (1992) revised the hagen fjord group of haller (1961) to encompass a phase of neoproterozoic shallow marine sedimentation which succeeds the palaeoproterozoic–mesoproterozoic independence fjord group and the mesoproterozoic zigzag dal basalt formation, and pre-dates franklinian basin sedimentation. since the kap holbæk formation was thought to be of vendian age, the formation was considered to be representative of the youngest phase of sedimentation in the hagen fjord group basin. however, two schemes of possible stratigraphic correlation could still be used to express the relationship of the kap holbæk formation to the underlying fyns sø formation, with radically different consequences in terms of basin evolution models and correlation with east greenland. these alternatives were outlined by sønderholm & jepsen (1991): geus bulletin 6.pmd 10-02-2005, 09:537 8 ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲▲ ▲ ▲ ▲ ro m er sø i n go lf fjor d amdrup land holm land hovgaard ø kap bernhoft dijmphna sund h ek la sund cen tru ms ø s k a l l in g e n sy dv ejd al r ivie r a d a l 20°w 80°n 81°n blåsø sk jo ld un ge el v nio gha lvfje rdsf jord en gr æs elv sæ faxi elv d an m ar k fj or d va nd re d al en th ru st v an dr ed al en kap holbæk p c m a hj lambert land m fl h wandel sea basin sequence (post-caledonian) samuelsen høj formation lauge koch land formation odins fjord formation turesø formation wandel valley formation kap holbæk formation crystalline basement thrust fault shear zone børglum river and sjælland fjelde formations fyns sø, kap bernhard, campanuladal fms hagen fjord gp rivieradal group independence fjord gp and basaltic formations vandredalen thrust hagen fjord group ▲ ▲ ▲ ▲ vandredalen thrust sheet ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲▲ ▲ ▲ c a le d o n id es greenland d p 25 km geus bulletin 6.pmd 10-02-2005, 09:538 9 1. the late ediacaran kap holbæk formation could rest conformably on the fyns sø formation, in which case the whole of the hagen fjord group would probably be of vendian age (sønderholm & jepsen 1991, fig. 18b). 2. the formation could rest disconformably on the fyns sø formation; the latter could then be representative of the late riphean to sturtian carbonate developments that characterise the north atlantic area. in this case, a substantial hiatus would span the vendian, and the hagen fjord group would be of riphean to sturtian age (sønderholm & jepsen 1991, fig. 18a). the kap holbæk formation overlies stromatolitic dolostones of the fyns sø formation at kap holbæk with a well-defined, but in detail obscured, contact. clues that might have helped to differentiate between these two hypotheses include the occurrence of a single clast of fyns sø formation-like lithology in the morænesø formation, a glacially influenced deposit of presumed varanger age in central peary land (collinson et al. 1989; sønderholm & jepsen 1991). an additional indication was provided by fränkl (1955) who had interpreted the kap holbæk formation as being the fill of karstic cavities in the top of the fyns sø formation at a single locality in sæfaxi elv. field work in sæfaxi elv in 1994 confirmed and expanded on fränkl’s observations. the uppermost part of the fyns sø formation was found to contain cave systems, infilled with sandstone, which are of typical phreatic character (smith et al. 1999). the fyns sø formation is unconformably overlain by the wandel valley formation, which is sandy at the base but passes upwards into typical dolomitic lithofacies of the danmark fjord member. confirmation of the lithostratigraphical relationships came from a locality at the junction of hjørnegletscher and ingolf fjord; here the fyns sø formation is overlain by the kap holbæk formation but infilled caves are preserved in the uppermost fyns sø formation (smith et al. 1999). deep channels are incised into the top of the latter and both the caves and the channels are infilled by lithofacies that can be directly matched to the lower part of the kap holbæk formation (smith et al. 1999). the channels and caves constitute one of the most spectacular and well-preserved examples of pre-carboniferous palaeokarst recorded to date. the demonstration of a hiatus between the fyns sø and kap holbæk formations lends support to correlation alternative 2 above (scheme a of sønderholm & jepsen 1991), which invokes a major time gap between the two units (fig. 3). further support comes from the interpretation of bjørnøya (western svalbard) as a detached north greenland terrane (smith 2000). on bjørnøya, a carbonate unit similar to the fyns sø formation is overlain by a sparse diamictite interpreted as a glacial horizon by harland et al. (1993), indicating that the carbonate is pre-vendian. the glacial unit, the sørhamna formation, is unconformably overlain by the ‘younger dolomite’, a peritidal dolostone containing a mid-early ordovician fauna that is closely comparable with the wandel valley formation (smith 2000). efforts to internationally standardise the position of the vendian–cambrian boundary have produced a wealth of biostratigraphic data in recent years. the redefined boundary has the effect of including a considerable time interval, the nemakit–daldyn (544–535 ma), within the early cambrian that was previously included within the neoproterozoic. furthermore, deep skolithos burrows are now known to have a first appearance in the tommotian (mid-early cambrian). their presence close to the base of the kap holbæk formation means that the unit is of early cambrian age, and is thus a probable correlative of the buen formation of north greenland, as originally postulated (peel 1980; peel et al. 1981; see fig. 7). because of the substantial time gap between the fyns sø formation and the kap holbæk formation, probably corresponding to the whole of the vendian, the younger unit is here removed from the hagen fjord group. type section. kap holbæk, a headland close to the head of danmark fjord on its western side (fig. 2). thickness. estimates of the thickness of the kap holbæk formation in the vicinity of danmark fjord range from 135 m (adams & cowie 1953) to 150 m (clemfacing page: fig. 2. geological map of kronprins christian land and lambert land; see inset outline map and fig. 1 for location. the region shows the well-exposed transition from autochthonous foreland in the west around kap holbæk and danmark fjord, eastwards through a thin-skinned fold-andthrust belt, to the allochthonous vandredalen thrust sheet and higher thrust sheets. fl, finderup land; h, harefjeld; hj, hjørnegletscher; m, marmorvigen; pcma, prinsesse caroline-mathilde alper. on inset map of greenland; d, daugaard-jensen land; p, peary land. geus bulletin 6.pmd 10-02-2005, 09:539 10 mensen & jepsen 1992). farther to the east, in the inner part of ingolf fjord, the formation is 180 m thick but thins southwards, along the western flanks of the prinsesse caroline-mathilde alper, to zero around sæfaxi elv. at sæfaxi elv, the ordovician wandel valley formation rests unconformably on the fyns sø formation and kap holbæk sediments are present only as the fill of palaeokarst cavities (smith et al. 1999). the allochthonous vandredalen thrust sheet does, however, contain the kap holbæk formation (see below), indicating that the formation was present farther to the east prior to thrusting (higgins et al. 2001b). the thinning of the formation to zero is coincident with the position of the rift shoulder of the hekla sund basin, the name given by fränkl (1955) to the half-graben rift basin in which the neoproterozoic rivieradal group accumulated (see also smith et al. 1999; higgins et al. 2001b; smith et al. 2004, this volume), suggesting that the structure continued to exert an influence on sedimentation into the earliest palaeozoic. boundaries. at the type locality, the kap holbæk formation disconformably overlies the fyns sø formasilurian ordovician cambrian vendian sturtian riphean lauge koch land formation samuelsen høj formation odins fjord formation turesø formation børglum river formation sjælland fjelde formation wandel valley formation kap holbæk formation hagen fjord group fyns sø fm kap bernhard fm campanuladal fm jyske ås fm zig-zag dal basalt formation independence fjord group hekla sund fm, aage berthelsen gletscher fm, & interbedded quartzites thermal subsidence extensional rifting and block tilting extensional riftingrivieradal group (allochthonous vandredalen thrust sheet only) post-rift thermal subsidence baltica collision thrust loaded flysch basin tectonic setting depositional environment stratigraphy lapetus passive margin lapetus opening pre-lapetus rift-sag cycle intracratonic extensional events thermal subsidence block tilting zz if hs/ab kh rg    fig. 3. pre-caledonian stratigraphy and tectonic history of kronprins christian land and lambert land. modified from smith et al. (1999). geus bulletin 6.pmd 10-02-2005, 09:5310 11 tion with a hiatus that probably corresponds to most of the vendian. it is disconformably overlain by the wandel valley formation, which is mid-early ordovician in age at the base (smith 1991; smith & bjerreskov 1994). these relationships pertain throughout the outcrop area, including the palaeokarst localities (smith et al. 1999). distribution. the kap holbæk formation crops out around the southern end of danmark fjord, extending southwards along the western side of skjoldungeelv to the inland ice (fig. 2). farther east, it crops out along the western side of ingolf fjord south of hjørnegletscher and along the western flanks of the prinsesse caroline-mathilde alper. at the junction of hjørnegletscher and ingolf fjord it additionally occurs infilling fossil caves in the fyns sø formation, and this is the only context in which it occurs around sæfaxi elv. the formation is also present in the frontal part of the vandredalen thrust sheet in finderup land, north of romer sø, where it was first described in the context of the ‘finderup land nappe’ (hurst & mckerrow 1981a, b; hurst et al. 1985). biota and age. peel & vidal (1988) noted a low diversity palynomorph assemblage from the formation and considered that the flora ‘in general suggests an age older than cambrian’. however, as noted above, the base of the cambrian has now been extended significantly downwards. the sandstones of the kap holbæk formation also contain deep skolithos burrows which extend vertically for many tens of centimetres (clemmensen & jepsen 1992, fig. 29) and occur to within 30 m of the base (adams & cowie 1953). the presence of deep skolithos burrows indicates a tommotian (early cambrian) or younger age (crimes 1992a). sf wv ab sæfaxi elv fig. 4. harefjeld viewed from the south showing steep or cliff-forming burrow-mottled limestones of the amdrup member and danmarks fjord member of the wandel valley formation (wv), which unconformably overlie the fyns sø formation (fs). the recessive pale weathering cap of the hill is the lower part of the alexandrine bjerge member (ab). sæfaxi elv in the foreground is 200–400 m wide. slightly modified from rasmussen & smith (1996). geus bulletin 6.pmd 10-02-2005, 09:5311 12 ryder gletscher group wandel valley formation remarks. the development of the wandel valley formation in southern and eastern kronprins christian land is very similar to that documented in the northern and western parts by peel & smith (1988). in the sæfaxi elv – vandredalen area, the danmarks fjord member (21 m) is overlain by 200 m of highly strained burrow-mottled lime mudstones (amdrup member) in which the burrows are considerably stretched. this unit is in turn overlain by 115 m of recessive dolostones of peritidal origin (alexandrine bjerge member). extensive conodont sampling has verified this lithostratigraphic interpretation. the three members of the wandel valley formation can be traced along the whole length of sæfaxi elv to a point opposite harefjeld (fig. 4), the type locality of the ‘harefjeld formation’ of hurst (1984). the latter unit was considered to be a deep-water equivalent of the lower palaeozoic platform succession that was present only in a single thrust sheet, the ‘sæfaxi elv nappe’, with a postulated displacement of over 100 km (hurst & mckerrow 1981a, b, 1985; hurst et al. 1985). however, a number of sections examined around harefjeld in 1994–1995 demonstrated an identical succession to that in sæfaxi elv with sandy danmarks fjord member overlying the fyns sø formation, and in turn overlain by burrow-mottled lime mudstones of the amdrup member. harefjeld is capped by poorly exposed, but distinctive, recessive buff dolostones assigned to the alexandrine bjerge member (fig. 4). the ‘thrust’ at the base of the ‘sæfaxi elv nappe’ of hurst & mckerrow (1981a, b, 1985) was recognised to be an unconformity with associated palaeokarst development (rasmussen & smith 1996; smith et al. 1999; see kap holbæk formation above). the succession differs from that in the remainder of kronprins christian land only in exhibiting particularly high levels of strain. rasmussen & smith (1996) therefore proposed the abandonment of the ‘harefjeld formation’. the lower member of the wandel valley formation, the danmarks fjord member, varies in thickness from 12 m around inner danmark fjord (smith & peel 1986) to 20–21 m at marmorvigen and the inner parts of ingolf fjord. the upper part of the unit is strongly brecciated by evaporitic collapse at ingolf fjord and marmorvigen (up to 10 m in thickness), whereas a 2.5 m thick breccia occurs in the middle part of the member on the east side of inner danmark fjord. east of vandredalen, the danmarks fjord member is overlain by highly strained burrow-mottled lime mudstones (200 m) in which the burrows are considerably stretched (fig. 5). these have yielded conodonts of late early ordovician age and are assigned to the amdrup member of the wandel valley formation. this member is in turn overlain by recessive dolostones of peritidal origin (115 m) containing whiterockian (middle ordovician) conodonts, together indicative of the alexandrine bjerge member (fig. 4). in summary, all three members of the wandel valley formation in the sæfaxi elv – harefjeld – ingolf fjord area are very similar to their development in the danmark fjord area on the foreland. intervals with shallower water lithofacies in the southernmost repa b fig. 5. a: stylolites in highly strained burrow-mottled facies of the amdrup member (wandel valley formation) on harefjeld. the stylolites are concentrating the buff-weathering, dolomitic burrow fills, and other burrows are highly stretched and flattened. b: highly strained wavy laminated facies in the basal part of the wandel valley formation, probably representing the danmarks fjord member, in westernmost lambert land. bedding parallel, cylindrical, dolomite-filled burrows are seen in cross-section. lens cap for scale; from rasmussen & smith (1996). geus bulletin 6.pmd 10-02-2005, 09:5312 13 resentatives of the formation in western lambert land (see section on lambert land below) suggest that a southern or eastern margin of the platform is being approached. sjælland fjelde formation remarks. the sjælland fjelde formation in the type section near danmark fjord is around 100 m thick and comprises a lower dark grey, burrow-mottled dolostone/limestone unit and an upper, grey dolostone unit (ineson et al. 1986). the thickness and character of the formation are maintained in the eastern and southern parts of kronprins christian land. east of vandredalen, the vandredalen thrust follows a long flat in the upper alexandrine bjerge member before ramping up westwards to a flat in the upper dolostone unit of the sjælland fjelde formation. the formation has been traced northwards along strike from sæfaxi elv as far as the western side of hjørnegletscher, a distance of around 70 km, and the vandredalen thrust maintains both the same topographic level and the same stratigraphic level within the sjælland fjelde formation. the southernmost exposure of the sjælland fjelde formation is close to the inland ice, 30 km west of centrumsø. the alexandrine bjerge member is there overlain by 36 m of highly fossiliferous limestones that may be equivalent to the ‘opikina limestone’ of scrutton (1975). the remainder of the interval beneath the børglum river formation is covered, but the likely overall thickness of the sjælland fjelde formation at this locality is around 110 m. morris bugt group børglum river formation remarks. the børglum river formation comprises lithologically monotonous, burrow-mottled lime mudstones and wackestones. the formation is generally highly fossiliferous in the upper part with abundant stromatoporoids, corals, gastropods and cephalopods together with rarer brachiopods and trilobites. a distinctive 10 m thick dolostone horizon occurs 20 m below the top of the formation and constitutes a useful marker horizon in sections where the overlying turesø formation is intensely deformed. substantial areas of børglum river formation were mapped in 1995, and the formation remains uniform throughout the mapping area. it is difficult to provide an accurate estimate of the thickness since, owing to tectonics and exposure, no sections were found in which both the upper and lower boundaries were exposed. the value of 430 m estimated by smith et al. (1989) seems, however, to be a reasonably valid one. turesø formation remarks. previous to the 1993–1995 mapping programme, the turesø formation was known to show a marked increase in thickness from around 150 m in peary land to over 200 m in northern kronprins christian land (peel 1985). this trend is maintained southwards, and a section measured 5 km west of centrumsø (fig. 6) had a thickness of 320 m in which subtidal burrow-mottled intervals of lime mudand wackestone are more dominant than farther to the west in peary land. this produces a distinctive black and white striped appearance which is of considerable utility in identifying the formation from a distance. the uppermost ordovician(?) – lowermost silurian succession in the western part of vandredalen shows a slightly different development to the area west of centrumsø. the tectonically deformed succession, in a major footwall ramp of the vandredalen thrust, comprises a lower dolostone unit, a middle burrow-mottled unit and an upper dolostone unit. the lower unit is a minimum of 20 m thick (the base is unexposed) and comprises alternating dolostone beds and burrow-mottled limestones. it is succeeded by about 90 m of burrow-mottled limestones containing a diverse macrofauna, which includes brachiopods, tabulate corals, cephalopods and stromatoporoids. the 130 m thick upper dolostone member is made up of whiteweathering dolostone beds and interbedded dark grey limestones that give the unit a distinctive, striped appearance. the upper dolostone unit is generally poor in macrofossils, but does contain sparse stromatoporoids and brachiopods. the southernmost occurrence of the turesø formation is 10 km to the north-west of blåsø, and the unit is here thinner (around 200 m) than farther north in kronprins christian land (around 300 m). the base is marked by a 30 m thick, pale grey dolostone unit. the lowest occurrence of pentamerid brachiopods is about 140 m above the formation base, but it is probgeus bulletin 6.pmd 10-02-2005, 09:5313 14 able that the ordovician–silurian boundary occurs well below this level. washington land group odins fjord formation remarks. although the odins fjord formation is widely exposed across the area, it is rather uniformly developed, and was examined in detail only at its most southerly occurrence west of blåsø. the minimum thickness in this part of southern kronprins christian land is 220 m. this compares with a thickness of 200 m in southern peary land, which increases northwards to around 300 m approaching the shelf margin in central peary land (hurst 1984). the transition from the turesø formation to the odins fjord formation at blåsø is marked by a change in weathering colour from pale grey to pale brown. at the same level, the lithology alters from dolostonedominated to limestones rich in tabulate corals and stromatoporoids. the lower 100 m are dominated by brown-weathering, burrow-mottled limestones, some of which are floatstones. a very distinctive pale dolostone interval occurs 70–103 m above the base, and contains abundant calcite-cemented vugs, probably representing pseudomorphed evaporitic nodules. the pale weathering, dark grey limestones are notably bituminous. this interval is at approximately the same level within the odins fjord formation as the peritidal sediments of the melville land member in peary land (hurst 1984) and it is likely that they are broadly correlative. the interval was not initially recognised in the centrumsø area, but a much thinner development at around 100 m above the base may be the correlative. as with the wandel valley formation, the presence of intervals with shallower water lithofacies in southernmost kronprins christian land suggests that a southern or eastern margin of the platform is being approached. samuelsen høj formation remarks. although reefs of the samuelsen høj formation had previously been documented on the northern side of centrumsø (fränkl 1954; hurst 1984), they had not previously been recognised farther to the south. however, in 1994–1995 a single small reef was located within a thrust sheet that extends southwards from the western end of centrumsø for around 10 km along the eastern side of græselv. the small reef directly overlies stromatoporoidal biostrome facies of the odins fjord formation. the reef, approximately 50 m in diameter and 20 m high, is typical of the forfig. 6. folded middle ordovician – silurian carbonates within the parautochthonous thrust belt, 5 km to the west of centrumsø, looking northwards. br, børglum river formation; tu, turesø formation; of, odins fjord formation. note the distinctive striped character of the turesø formation and the cliffforming nature of the odins fjord formation. the profile is 500 m high. geus bulletin 6.pmd 10-02-2005, 09:5314 15 mation, with a massive, unbedded core facies and radially dipping flank beds. peary land group lauge koch land formation remarks. the southernmost occurrence of the lauge koch land formation in kronprins christian land is in the parautochthonous fold-and-thrust belt immediately to the south of centrumsø. in contrast to the typical development of the samuelsen høj formation reef in this area, that of the overlying flysch is atypical. hurst & surlyk (1982) assigned all of the silurian flysch in kronprins christian land to the ‘profilfjeldet shales’ of fränkl (1954), and the unit was given member rank within the lauge koch land formation. in the type section on the west side of vandredalen, the lower part of the profilfjeldet member is dominated by quartz conglomerates and sandstone turbidites. locally, black mudstones with rare starved ripples and thin-bedded muddy siltstones are developed up to a thickness of a few metres. in distinct contrast, the lower part of the section south of centrumsø contains approximately 50 m of black siltstones and sandstones with interbedded carbonates overlying the odins fjord formation and the samuelsen høj formation reef. the black siltstones and fineto medium-grained sandstone beds are 5– 30 cm thick and contain planar lamination. in places a rhythmic alternation of 1 cm sandstone with 1–3 cm shaly siltstone can be seen. the interbedded carbonates are very dark grey to black, bituminous, nodular and burrow-mottled with calcite concretions; there are abundant black silty partings. the abundant macrofauna includes graptolites, cephalopods and gastropods. the interbedding of turbiditic clastic sediments with burrow-mottled carbonates is somewhat unusual, but presumably represents intermittent distal turbidite deposition in a deep subtidal setting which, during times of low clastic influx, allowed the re-establishment of carbonate deposition and a burrowing infauna. above the lower black shale/carbonate unit, the lauge koch land formation is more typically developed. a 25 m thick interval of green-weathering, very thinly bedded, shaly siltstones and sandstones is overlain by cliff-forming sandstone turbidites. the latter contain t a–c,e and t b–e units and 4 m thick, massive channel fills are present. coarseningand thickeningupward 20–30 m cycles are also present. the thrusttruncated thickness is approximately 150 m, well within the maximum thickness of 400 m cited for the member (hurst & surlyk 1982). lambert land prior to the 1993–1995 mapping programme, the wandel valley formation was not known to crop out south of kronprins christian land. escher & jones (1994), however, pointed to the possible presence of early palaeozoic carbonates in westernmost lambert land, north-east greenland (fig. 2), resting unconformably upon independence fjord group quartzites. examination of the quartzite-carbonate boundary near the inland ice margin in westernmost lambert land demonstrated that the carbonates unconformably overlie independence fjord group quartzites, with a very slight angular discordance. the basal 25 m of the carbonates constitute a generally pale weathering unit, which is made up of current laminated dolostones with scours and some ripple lamination, together with darker wavy laminated dolostones containing ripples and drapes (fig. 5b). some cyclicity is evident, and the top of one cycle contains probable pseudomorphed evaporite nodules. this lower unit is overlain by highly strained, dark-weathering wavy laminated and burrow-mottled carbonates, dolomitised to greater or lesser degrees. the current laminated dolostones are absent above 25 m. taking into account the lithofacies present, the unconformable relationship with the independence fjord group, and the recovery of fragmentary conodonts, the lambert land carbonates are assigned to the wandel valley formation. it is probable that the lower 25 m unit represents the danmarks fjord member and that the overlying carbonates are part of the amdrup member. the thickness of the upper unit in lambert land is difficult to estimate due to structural complications, but it does not exceed the 200 m seen in the amdrup member in kronprins christian land. the presence of the wandel valley formation resting unconformably on the independence fjord group demonstrates that the progressive overstep of the early ordovician from west to east across north greenland (peel & smith 1988, fig. 6) continues into kronprins christian land, where it rests on the kap holbæk formation in the west and the fyns sø formation in the east, and southwards to lambert land (fig. 7). the pattern is suggestive of a strong n–s component in addition to the well-documented west to east overgeus bulletin 6.pmd 10-02-2005, 09:5315 16 step, and perhaps indicates that maximum pre-wandel valley formation uplift was farther to the south than hitherto anticipated. the depositional environments are broadly comparable with the development to the north, but the burrow-mottled upper unit in lambert land seems to be of slightly shallower water origin than the amdrup member, suggesting proximity to a southern and/or eastern margin to the franklinian platform in lambert land. dronning louise land the extensive nunatak region of dronning louise land (fig. 1) was first documented geologically during the 1952–1954 british north greenland expedition (peacock 1956, 1958). the region was not re-investigated in detail until the systematic mapping programme conducted by ggu in 1989–1990 (friderichsen et al. 1990; holdsworth & strachan 1991; strachan et al. 1994). dronning louise land is divided by a n–s-trending imbricate zone into an autochthonous foreland area to the west, and parautochthonous to allochthonous palaeoproterozoic gneiss complexes with interbanded metasedimentary rocks to the east, transported westwards as thrust sheets. the foreland area comprises crystalline basement orthogneisses overlain by sequences of sedimentary rocks assigned to the ‘trekant’ and ‘zebra series’. the older ‘trekant series’ and underlying basement gneisses are intruded by dolerite dykes, and are overlain unconformably by the ‘zebra series’. the ‘zebra series’ is also present in the imbricate zone where it overlies pale grey-green sandstones that are intruded by metadolerites. 200 km morris bugt group ryder gletscher group brønlund fjord group tig m kh hagen fjord group independence fjord group buen formation plf/kcm wsw ese ese snw n wandel valley formation rg fs portfjeld formation crystalline basement daugaardjensen land peary land la m be rt l an dkronprins christian land m m l l ve nd ia n r ip h. st ur . pr o te ro zo ic c am br ia n o rd o v. u fig. 7. proterozoic – middle ordovician stratigraphic relationships on the platform area of north and north-east greenland, showing the extent and magnitude of the sub-wandel valley unconformity. maximum uplift and associated erosion was in lambert land, at the extreme right hand side of the diagram. the locations of daugaard-jensen land and peary land are indicated on the inset map of greenland in fig. 2. fs, fyns sø formation (hagen fjord group); kh, kap holbæk formation; m, glacial sediments of the morænesø formation; plf/kcm, quartz arenite sandstone sheet assigned to the permin land formation and the kap coppinger member; rg, rivieradal group (see smith et al. 2004, this volume); tig, tavsens iskappe group. modified from smith (2000). facing page: fig. 8. geological map of north-east greenland 71°50′– 74°30′n, showing location of the eleonore sø, målebjerg, and charcot land windows. the legend depicts the units contained in the two thrust sheets and franz joseph allochthon, which overlie the windows. ael, arnold escher land; es, eleonore sø; g, gemmedal; hb, albert heim bjerge; kfjf, kejser franz joseph fjord; m, målebjerg; ml, j.l. mowinckel land; on, c.h. ostenfeldt nunatak; s, slottet. geus bulletin 6.pmd 10-02-2005, 09:5316 17 ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i ▲ ▲ ▲ ▲ ▲ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ eleonore sø window hamberg gletscher foreland målebjerg window charcot land window nathorst land hudson land ella ø suess land andrée land lyell land stauning alper kong oscar fjord kfjf ael es s ml m g cecilia nunatak hb on neoproterozoic–ordovician post-caledonian caledonian granite 930 ma granite palaeoproterozoic–ordovician krummedal sequence krummedal sequence palaeoproterozoic orthogneiss archaean–palaeoproterozoic orthogneiss ▲ ▲ ▲ ▲ franz joseph allochthon foreland hagar bjerg thrust sheet niggli spids thrust sheet detachment extensional fault thrust ▲ ▲ i i ■ ■ ■ ■ 72º72º 73º 74º 27º 100 km geus bulletin 6.pmd 10-02-2005, 09:5317 18 in the foreland of north-west dronning louise land, the ‘zebra series’ comprises 3–10 m of basal pebble conglomerates, overlain by 10–15 m of purple-white striped quartzites. these pass upwards into yellowwhite mediumto coarse-grained quartzites (5–30 m) and interbanded magnetite sandstones, siltstones and mudstones (10 m; friderichsen et al. 1990). these clastic rocks are overlain by around 10 m of fine-grained grey-black limestones. deep skolithos burrows are found in situ in the quartzites demonstrating, as with the kap holbæk formation, that the ‘zebra series’ is no older than cambrian. the quartzites are thus correlative with the kap holbæk formation of kronprins christian land, the slottet formation of the eleonore sø and målebjerg windows (see below), and the kløftelv formation (kong oscar fjord group – see below) of the franz joseph allochthon. a similar succession is present within the ‘zebra series’ of the imbricate thrust zone where, in central dronning louise land, friderichsen et al. (1990) recorded 2 m of pale green sandstones with thin lensoid pebble beds up to 20 cm thick at the base, overlain by 45 m of white to rusty weathering medium-grained quartzites with abundant tabular cross-bedding. these beds are overlain by a heterogeneous 50 m package of interbedded grey-green siltstone, dark mudstone, thin quartzites, yellow sandstones and limestones. the base of this latter unit contains ichnofossils assigned to cruziana sp. (strachan et al. 1994), which indicate a maximum age of atdabanian (mid-early cambrian; crimes 1992b). the quartzites are overlain by about 120 m of grey dolomitic limestones – a stratigraphic signature that is very similar to the successions in the eleonore sø and målebjerg windows (see below). the precise age of the dolomitic limestones at the top of the ‘zebra series’ in both the foreland and imbricate zone is uncertain, but they must be of cambrian–ordovician age. nunatak region 71°50′′′′′n–74°30′′′′′n the presence of in situ lower palaeozoic sediments in the western nunatak region of the southern part of the east greenland caledonides (fig. 8) had not been demonstrated prior to the 1997–1998 survey mapping programme. however, several clues had been noted, namely the presence of erratic carbonate blocks containing early ordovician conodonts on cecilia nunatak (72°30′n; j.s. peel in higgins et al. 1981), and the abundant occurrence of quartz arenite blocks containing skolithos throughout the caledonides (see e.g. haller 1971, fig. 48). two tectonic windows through thrust sheets (leslie & higgins 1998, 1999) discovered in 1997 revealed the presence of vendian tillites, cambrian sandstones and cambrian–ordovician carbonates in the footwall immediately underlying the bordering thrusts; these distinctive successions record the effects of caledonian deformation, and have been interpreted as representing autochthonous to parautochthonous caledonian foreland (higgins et al. 2001a). while the strain levels in these units are high, sufficient sedimentary detail can be observed to allow confident interpretation and correlation. slottet formation new formation history. the ‘slottet quartzite’ was first described by katz (1952) from the eleonore sø region (74°n), and was included within a group of rocks that was correlated with the upper part of what is now the nathorst land group (lower eleonore bay supergroup). subsequently, haller (1971), following a suggestion of wenk (1961), assigned the quartz-arenite unit to his ‘basal series’ of the eleonore bay supergroup. this complex of rocks included a wide variety of lithologies, and it is now clear that a wide range of ages is also represented (leslie & higgins 1998, 1999). as part of the systematic re-mapping programme of 1997–1998, the eleonore sø region was revisited, and it was recognised that the rock units were located within a major facing page: fig. 9. a: quartzites of the slottet formation (sf) a few hundred metres north of the type section, overlying a clastic unit that includes diamictites (vt). the light coloured quartzites of the slottet formation are clearly visible in the cliffs of målebjerg in the background. a few metres of carbonate (not visible) represent the målebjerg formation, with the niggli spids thrust (nst) marking the upper limit of the unit. view looking south to målebjerg (1873 m high), the summit of which is about 1500 m above the ice-dammed lake and glacier. b: skolithos burrows in quartzite from the slottet formation of the eleonore sø window. distortion of the upper part of the burrows, along bedding planes, is a consequence of westward displacement of the overriding caledonian thrust sheets. c: highly strained, parallel laminated dolostones and burrow-mottled limestones of the målebjerg formation at the type section, to the north of målebjerg, in the målebjerg window. geus bulletin 6.pmd 10-02-2005, 09:5318 19 geus bulletin 6.pmd 10-02-2005, 09:5319 20 window through a caledonian thrust sheet. when the effects of caledonian deformation were restored, it became clear that haller’s (1971) supposed ‘basal series’ in this region is a complex of volcanic and sedimentary rocks deposited in a rift setting and unconformably overlain by the slottet formation (leslie & higgins 1998). the older group of rocks was informally termed the ‘eleonore sø complex’, while the discovery of skolithos burrows in the younger ‘slottet quartzite’ indicated the cambrian age of the unit (leslie & higgins 1998; smith & robertson 1999b). further outcrops of the ‘slottet quartzite’ were located 70 km east of the eleonore sø region at the foot of målebjerg, in another smaller tectonic window through a caledonian thrust, now known as the målebjerg window. these outcrops were originally mapped by haller (1953), and their resemblance to the ‘slottet quartzite’ was pointed out by haller (1971) who also placed them in his ‘basal series’ of the eleonore bay supergroup. name. the formation is named after the promontory of slottet (‘the castle’) to the south of eleonore sø, where the unit crops out spectacularly and was first described by katz (1952). type section. the north side of the ice-dammed lake in gemmedal, north of målebjerg (fig. 9a). thickness. at the type section, the formation is 143 m thick (fig. 10). in the vicinity of slottet, photogrammetric calculations suggest that the unit is considerably thicker, of the order of 350 m (see photograph on front cover of this volume) although this is much less than the > 1000 m estimate derived from katz’s observations that was quoted by haller (1971). lithology. in the type section north of målebjerg (figs 9a, 10), the lower 10 m comprise structureless or planar laminated, fineto coarse-grained quartz arenites in 10–30 cm beds. from 10–36 m, the maximum grain size diminishes, and fineto medium-grained sandstones occur in 0.2–1.6 m beds. the quartz arenites are parallel laminated and cross-bedded, the latter sometimes being of very large scale, with sets up to 1.6 m. some beds are lenticular at outcrop scale, and shaly interbeds are sometimes present. above 36 m, the fine-grained quartz arenites are in beds of 0.3– 1.5 m thickness, and are either structureless or crossbedded with sets up to 1 m and very low angle foresets. the beds are mainly tabular, but some are seen to fig. 10. composite log of the slottet and målebjerg formations at the type locality in the målebjerg window. the lenticular clastic succession beneath the slottet formation, with two diamictite levels, occupies a depression in the gneissic basement, and is interpreted as a vendian tillite. c am b. -o rd . c am br ia n v en di an t ill it e pr ev en di an b as em en t vf m vcc f c la y gr an ul e pe bb le co bb le bo ul de r sa nd si lt a ge u ni t li th o lo gy st ru ct ur e m ål eb je rg f . sl o tt et f o rm at io n m 200 150 100 50 0 thrust ? ? gneiss sandstone mudstone-siltstone limestone dolostone large scale cross-bedding ripple-lamination skolithos burrow-mottling scours planar lamination igneous or metamorphic clast sedimentary clast   geus bulletin 6.pmd 10-02-2005, 09:5320 21 wedge out at outcrop scale. interbeds of thin sandstones and sandy shales up to 0.4 m thick occur. current directions determined from foreset orientation are predominantly towards the south-east. at 79 m, there is a conspicuous change from golden brown-weathering quartz arenites to a rusty weathering alternation of interbedded quartz arenites and sandy shales. this unit is 50 m thick (79–129 m) although above 112 m the mud content falls off. the quartz arenites are in beds of < 15–60 cm and are largely structureless, although hints of cross-bedding do occur. the sandy shales comprise mudstones (now slaty) with lenticular sand bodies up to a few centimetres thick and traces of ripple lamination. in some places, mud drapes were observed on foreset laminae. the formation is capped by a 14 m thick massive quartz arenite that is structureless and virtually unbedded. boundaries. north of målebjerg, in the type section on the north side of the ice-dammed lake in gemmedal (fig. 8), the slottet formation lies unconformably on gneisses of probable palaeoproterozoic age. however, a few hundred metres farther north the gneisses are overlain by a lenticular tillite unit with a maximum thickness of 31 m (figs 9a, 10). the unit contains two beds of diamictite separated and overlain by platy quartzites, phyllites and semi-pelites. this unit can be seen to gradually wedge out southwards, and occupies a hollow on a peneplaned surface of basement gneisses. the lower part of the lower diamictite bed (1.4 m) comprises clast-supported pebbles and cobbles resting on sheared granitic gneiss, but within 30 cm there is a gradation up into matrix-supported diamictites. the matrix is composed of fine sand which in places is micaceous and phyllitic. the upper diamictite bed is up to 7.6 m thick, but thickens and thins markedly along strike. the clasts are dominated by fineto coarse-grained granitic lithologies but also include metasandstones and carbonates, with the latter up to 6 × 1.5 × 1 m in size. the unit is considered to be of varanger age and is disconformably overlain by the slottet formation. distribution. the slottet formation occurs around the margins of the eleonore sø and målebjerg tectonic windows. within the eleonore sø window, the formation is present in j.l. mowinckel land, arnold escher land and around eleonore sø itself, and in the målebjerg area it crops out on either side of the n–strending glacier that bisects the window. fauna and age. the slottet quartzite is characterised by the presence of skolithos burrows that attain lengths of several tens of centimetres (fig. 9b). the first unequivocal appearance in the type section is at the base of the rusty weathering unit (79 m), but more equivocal examples are present as low as 45 m. as noted in the discussion of the kap holbæk formation, the presence of deep skolithos indicates an age for the unit that is no older than tommotian (mid-early cambrian). målebjerg formation new formation history. katz (1952) recognised and mapped a carbonate unit above his ‘slottet quartzite’ in the eastern eleonore sø region, but considered it to represent mylonitised eleonore bay supergroup. in the 1997– 1998 field seasons it was recognised that the carbonate unit, although highly strained, conformably overlies the slottet formation and lies in the footwall of the thrust that bounds the eleonore sø and målebjerg windows (leslie & higgins 1998; smith & robertson 1999b). name. named after the mountain målebjerg, which lies immediately to the south of the type section. type section. the type section of the målebjerg formation is a continuation of the slottet formation type section, on the northern side of the ice-dammed lake in gemmedal, north of målebjerg (fig. 10). a better exposed, but less accessible, reference section is present on a nunatak (73°41′n, 28°40′w) south of j.l. mowinckel land, within the eleonore sø window. thickness. in the type section (fig. 10), 32 m of sediment are preserved beneath the thrust that terminates the section. in the reference section, the formation is 45 m thick, and a similar thickness is present wherever it crops out within the eleonore sø window. lithology. in both of the measured sections, the slottet formation is overlain by 1.5 m of sandy dolostones. in the type section the next 20 m are poorly exposed, but dark grey weathering medium grey dolostones and pale grey weathering pale grey dolostones with current lamination were observed. the uppermost 9 m comprise buff-weathering, parallel laminated dolostones (fig. 10) interbedded with dark grey limestones geus bulletin 6.pmd 10-02-2005, 09:5321 22 with buff dolomite burrow fills. in places these can be seen to be shallowing-upward, subtidal burrowmottled limestone – peritidal dolostone cycles similar to those that commonly occur elsewhere in the laurentian cambrian–ordovician. in the reference section in j.l. mowinckel land, the basal sandy dolostones become progressively less sandy upwards; parallel lamination and ripple lamination with dolomitic mud drapes are present. this unit is overlain by 3.5 m of dolostones in which 2–3 cm beds of fine-grained dolostone alternate with 0.5 cm beds of coarser, sand-grade, dolomite. the latter are parallel laminated and low amplitude ripples are also developed. from 5–20 m, massive buff-weathering pale grey dolostones occur in beds up to 2.5 m thick. for the most part these beds are structureless but traces of burrow-mottling are present in places, as are fenestral, laminated dolostones and current lamination. more thinly bedded dolostones make up the interval from 20–40 m; these are predominantly structureless or current laminated, and extensively veined with quartz and carbonate. the uppermost 5 m comprise dark, burrow-mottled limestones with buff burrow fills that become increasingly strained and mylonitised towards the thrust that terminates the section. boundaries. in both sections, the basal sandy dolostones overlie the slottet formation with no angular discordance and the succession is truncated by the thrust that bounds the tectonic windows. distribution. as with the slottet formation, the carbonate unit is restricted to the margins of the eleonore sø and målebjerg windows. however, because it is markedly thinner and less resistant to weathering it crops out less frequently. fauna and age. there is, to date, no fauna recorded from the målebjerg formation, although its tectonic context and the presence of bioturbation in the form of burrow-mottling, together with its conformable boundary with the underlying slottet formation, suggest a cambrian–ordovician age. fjord region 71°36′′′′′–74°17′′′′′n the presence of cambrian–ordovician sediments within the outer fjord region of north-east greenland (71°36′–74°17′n; fig. 8) has been known since the early work of lauge koch and christian poulsen. their good exposure and relative ease of access has resulted in more research than areas to the north (for reviews see cowie & adams 1957; henriksen & higgins 1976; smith & bjerreskov 1994; stouge et al. 2001). the tectonic setting has, however, remained rather more enigmatic since, although clearly incorporated within the caledonian orogen, the units are relatively undeformed. mapping of the underlying eleonore bay supergroup in 1997–1998 has clarified this relationship, and it is now apparent that the lower palaeozoic rocks of the fjord region are part of the highest level thrust sheet in this sector of the orogen, and have been transported several hundreds of kilometres from the eastsouth-east (smith & robertson 1999a, b; higgins & leslie 2000; higgins et al. 2004a) before involvement in synto post-orogenic collapse (hartz & andresen 1995; andresen et al. 1998). the cambrian–ordovician formations are here incorporated within the newly erected kong oscar fjord group (fig. 11). kong oscar fjord group new group history. recorded observations of the lower palaeozoic rocks of the fjord region extend back to karl koldewey’s expedition of 1869–1870 when palaeozoic sediments similar to the ‘hekla hoek formation’ of spitsbergen were documented (toula & lenz 1874). palaeontological confirmation of this stratigraphical determination came from a.g. nathorst’s expedition of 1899, which re-visited kejser franz joseph fjord and recovered ‘silurian’ and devonian fossils (nathorst 1901). the lower palaeozoic was further examined by the cambridge expedition of 1926 under the leadership of j.m. wordie (wordie 1927), and in the same year lauge koch led the first of a series of expeditions that were to make a major impact on the understanding of east greenland caledonian geology. the latter expeditions continued until 1958 with breaks only for the war years. towards the end of this programme, p.j. adams and j.w. cowie carried out a detailed investigation of the lower palaeozoic, and the ensuing monograph (cowie & adams 1957) remains a key publication. k. swett and co-workers carried out some sedimentological work in the early 1970s, including comparisons with coeval successions in north-east spitsbergen and north-west scotland (e.g. geus bulletin 6.pmd 10-02-2005, 09:5322 23 swett & smit 1972). extensive logging and sample collecting for conodont work was carried out by p. frykman in 1977, and by m.p. smith and j.s. peel in 1988. this has resulted inter alia in a refinement of biostratigraphical constraints, particularly in the late cambrian – ordovician part of the group (smith 1985, 1991; smith & bjerreskov 1994; huselbee 1998). additional field work has been carried out in the succession by stouge et al. (2001, 2002), and documentation of early cambrian small shelly faunas was undertaken, with subsequent biostratigraphic refinements, by skovsted (2003). name. named after kong oscar fjord, at the head of which lies the island of ella ø with the most easily accessible and most studied outcrops of the group (fig. 12a). type area. in view of the above, the most suitable type area is ella ø. important reference areas, which contain the only complete sections through the two youngest formations, are present in the north of the outcrop belt at albert heim bjerge and c.h. ostenfeld nunatak (fig. 8; cowie & adams 1957; frykman 1979; hambrey et al. 1989; smith 1991; smith & bjerreskov 1994; stouge et al. 2002). thickness. on ella ø, the group is 2625 m thick (cowie & adams 1957; smith & bjerreskov 1994) including a revised thickness of 1161 m for the cape weber formation (smith 1991). the upper part of the group thickens northwards (and perhaps also eastwards), and frykman (1979) recorded an apparently unfaulted thickness of 1750 m for the cape weber formation on c.h. ostenfeld nunatak. in addition, frykman (1979) estimated a thickness of 1200 m for the heimbjerge formation on c.h. ostenfeld nunatak, rather than the maximum 320 m recorded beneath devonian red beds on albert heim bjerge (cowie & adams 1957). the kong oscar fjord group in the northernmost part of 450 460 470 480 490 500 510 520 530 540 545 ma cape weber cape weber narwhale sound narwhale sound heimbjerge albert heim bjerge devonian antiklinalbugt antiklinalbugt dolomite pointdolomite point hyolithus creek c am br ia n o rd o vi ci an c ar ad o c b ri ti sh s er ie s m o ha w ki an n o rt h a m er ic an s er ie s w hi te ro ck ia n ib ex ia n a re ni g t re m ad o c u pp er m id dl e lo w er ll an vi rn ella island bastion kløftelv hyolithus creek ella island bastion kløftelv ? ? devonian ella ø fig. 11. correlation chart of units within the kong oscar fjord group on ella ø and albert heim bjerge, showing component formations of upper cambrian – ordovician age. the age of the base of the kløftelv formation is uncertain. the absolute ages of chronostratigraphic boundaries are compiled from tucker & mckerrow (1995), cooper (1999) and encarnacíon et al. (1999). stratigraphic dates for the unit boundaries are based on henriksen & higgins (1976), pickerill & peel (1990), smith & bjerreskov (1994) and huselbee (1998). geus bulletin 6.pmd 10-02-2005, 09:5323 24 geus bulletin 6.pmd 10-02-2005, 09:5324 25 the outcrop belt is thus likely to be around 4500 m thick, its maximum within the region. dominant lithology. the lower part of the group (kløftelv formation and bastion formation) is dominated by quartz arenites that fine upwards into glauconitic sandstones, and sandy micaceous and ferruginous shales. clastic supply wanes in the upper bastion formation, and the remainder of the group is carbonate-dominated. the ella island formation is limestone-dominated, but the succeeding two units, the hyolithus creek formation and dolomite point formation, are dolostone-dominated. the ordovician units comprise an alternation of thick, pale grey, homogeneous subtidal limestones (cape weber formation and heimbjerge formation), with more thinly bedded units in which subtidal or subtidal–peritidal shallowing-upwards sequences are developed on the scale of 1–5 m (antiklinalbugt formation and narwhale sound formation). significant developments of thrombolitic–stromatolitic reefs are present in the basal part of the antiklinalbugt formation on ella ø (fig. 12c) and the lower 100 m of the cape weber formation on albert heim bjerge and c.h. ostenfeld nunatak (hambrey et al. 1989; stouge et al. 2001). boundaries. the kong oscar fjord group overlies the tillite group. at outcrop scale, the boundary appears to be sharp but conformable. however, northwards along strike the uppermost unit of the tillite group, the spiral creek formation (maximum thickness 55 m) wedges out and the kløftelv formation rests on the underlying canyon formation (fig. 12b; hambrey & spencer 1987; hambrey et al. 1989). it is thus probable that a regional hiatus and/or low angle unconformity is present at the base of the kløftelv formation. stouge et al. (2001, 2002) inferred the presence of a significant disconformity or condensed interval at the antiklinalbugt formation – cape weber formation boundary. the antilklinalbugt formation contains early ibexian macroand microfaunas, and a cephalopod identified as ?cyptendoceras sp. indet. recovered from the basal beds of the cape weber formation was considered to be of late ibexian age. together with the absence of a middle ibexian macrofauna, this evidence was used to invoke the presence of a disconformity or condensed interval spanning the middle ibexian. however, closely spaced conodont samples throughout the interval from the upper dolomite creek formation to the top of the cape weber formation (smith 1985, 1991; huselbee 1998) demonstrate that there is a complete succession, and that there is no significant disconformity or condensed interval present. the upper part of the group is cut by the caledonian erosion surface, and is overlain by devonian molasse of the kap kolthoff group. on ella ø, the erosion level is within the middle part of the narwhale sound formation, and on albert heim bjerge it cuts through the lower part of the heimbjerge formation, whereas on c.h. ostenfeld nunatak a much thicker section in the latter unit is preserved. complete sections through the narwhale sound formation and the overlying heimbjerge formation are thus present only in the northern part of the outcrop belt. distribution. the group is present in a narrow belt that extends from canning land (71°36′n) through the fjord region to c.h. ostenfeld nunatak (74°17′n), and is confined to the franz joseph allochthon. the main outcrop forms part of the neoproterozoic–ordovician division shown in fig. 8; the detached outcrops on canning land lie 90 km east-south-east of the south-east corner of fig. 8. geological age. early cambrian – upper whiterockian (middle ordovician – upper llanvirn sensu fortey et al. 1995). subdivision. the kong oscar fjord group contains nine formations: kløftelv formation, bastion formation, ella island formation, hyolithus creek formation, dolomite point formation, antiklinalbugt formation, cape weber formation, narwhale sound forfacing page: fig. 12. a: the kong oscar fjord group on ella ø, showing upper cambrian – ordovician formations. af, antiklinalbugt formation; cw, cape weber formation; dp, dolomite point formation. the highest summit visible is 500 m above the tent in the foreground. b: the kong oscar fjord group on albert heim bjerge, showing lower cambrian formations, with the lowermost kløftelv formation (kf) unconformably overlying the neoproterozoic canyon formation (cf) of the tillite group. bf, bastion formation; ei, ella island formation; hc, hyolithus creek formation. tent at lower right for scale. the height of the profile is c. 600 m. c: thrombolitic– stromatolitic reefs in the basal part of the antiklinalbugt formation on ella ø. the oval to rounded thrombolites are about 25 cm in diameter. geus bulletin 6.pmd 10-02-2005, 09:5325 26 mation and the heimbjerge formation (fig. 11). the cambrian–ordovician boundary occurs within the uppermost part of the dolomite point formation (miller & kurtz 1979; huselbee 1998). the lower palaeozoic units of the east greenland foreland, observed in the parautochthonous setting of the eleonore sø and målebjerg tectonic windows (slottet formation and målebjerg formation formally erected above), are specifically excluded from the group because of the significantly different depositional context, located high on the craton in an attenuated neoproterozoic – lower palaeozoic succession. acknowledgements we are grateful to the referees, j.s. peel and j.e. repetski, whose perceptive comments greatly improved the manuscript. references adams, p.j. & cowie, j.w. 1953: a geological reconnaissance of the region around the inner part of danmarks fjord, northeast greenland. meddelelser om grønland 111(7), 24 pp. andresen, a., hartz, e. & vold, j. 1998: a late orogenic extensional origin for the infrastructural gneiss domes of the east greenland caledonides (72º–74ºn). tectonophysics 285, 353–369. clemmensen, l.b. & jepsen, h.f. 1992: lithostratigraphy and geological setting of upper proterozoic shoreline-shelf deposits, hagen fjord group, eastern north greenland. rapport grønlands geologiske undersøgelse 157, 27 pp. collinson, j.d., bevins, r.e. & clemmensen, l.b. 1989: post-glacial mass flow and associated deposits preserved in palaeovalleys: the late precambrian morænesø formation, north greenland. meddelelser om grønland geoscience 21, 26 pp. cooper, r.a. 1999: the ordovician time scale – calibration of graptolite and conodont zones. acta universitas carolinae – geologica 43(1/2), 1–4. cowie, j.w. & adams, p.j. 1957: the geology of the cambroordovician rocks of east greenland. 1. meddelelser om grønland 153(1), 193 pp. crimes, t.p. 1992a: the record of trace fossils across the proterozoic–cambrian boundary. in: lipps, j.h. & signor, p.w. 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(eds): geology of greenland, 182– 246. copenhagen: geological survey of greenland. higgins, a.k. & leslie, a.g. 2000: restoring thrusting in the east greenland caledonides. geology 28, 1019–1022. higgins, a.k., friderichsen, j.d. & thyrsted, t. 1981: precambrian metamorphic complexes in the east greenland caledonides (72°–74°n) – their relationships to the eleonore bay group and caledonian orogenesis. rapport grønlands geologiske undersøgelse 104, 5–46. higgins, a.k., ineson, j.r., peel, j.s., surlyk, f. & sønderholm, m. 1991: the franklinian basin in north greenland. in: peel, j.s. & sønderholm, m. (eds): sedimentary basins of north greenland. bulletin grønlands geologiske undersøgelse 160, 71– 139. geus bulletin 6.pmd 10-02-2005, 09:5326 27 higgins, a.k., leslie, a.g. & smith, m.p. 2001a: neoproterozoic – lower palaeozoic stratigraphical relationships in the marginal thin-skinned thrust belt of the east greenland caledonides: comparisons with the foreland in scotland. geological magazine 138, 143–160. higgins, a.k., smith, m.p., soper, n.j., leslie, a.g., rasmussen, j.a. & sønderholm, m. 2001b: caledonian inversion of the hekla sund basin, eastern north greenland: a pre-iapetan rift sequence displaced across its rift shoulders during the caledonian orogeny. journal of the geological society (london) 158, 487–499. higgins, a.k. et al. 2004a: the foreland-propagating thrust architecture of the east greenland caledonides 72°–75°n. journal of the geological society (london) 161, 1009–1026. higgins, a.k., soper, n.j., smith, m.p. & rasmussen, j.a. 2004b: the caledonian thin-skinned thrust belt of kronprins christian land, eastern north greenland. in: higgins, a.k. & kalsbeek, f. (eds): east greenland caledonides: stratigraphy, structure and geochronology. geological survey of denmark and greenland bulletin 6, 41–56 (this volume). holdsworth, r.e. & strachan, r.a. 1991: interlinked system of ductile strike slip and thrusting formed by caledonian sinistral transpression in northeastern greenland. geology 19, 510– 513. hurst, j.m. 1984: upper ordovician and silurian carbonate shelf stratigraphy, facies and evolution, eastern north greenland. bulletin grønlands geologiske undersøgelse 148, 73 pp. hurst, j.m. & mckerrow, w.s. 1981a: the caledonian nappes of eastern north greenland. nature 290, 772–774. hurst, j.m. & mckerrow, w.s. 1981b: the caledonian nappes of kronprins christian land, eastern north greenland. rapport grønlands geologiske undersøgelse 106, 15–19. hurst, j.m. & mckerrow, w.s. 1985: origin of the caledonian nappes of eastern north greenland. in: gee, d.g. & sturt, b.a. (eds): the caledonide orogen – scandinavia and related areas, 1065–1069. london: john wiley & sons. hurst, j.m. & surlyk, f. 1982: stratigraphy of the silurian turbidite sequence of north greenland. bulletin grønlands geologiske undersøgelse 145, 121 pp. hurst, j.m., jepsen, h.f., kalsbeek, f., mckerrow, w.s. & peel, j.s. 1985: the geology of the northern extremity of the east greenland caledonides. in: gee, d.g. & sturt, b.a. (eds): the caledonide orogen – scandinavia and related areas, 1047– 1063. london: john wiley & sons. huselbee, m.y. 1998: late cambrian to earliest ordovician (ibexian) conodont evolution and biogeography of greenland and northwest scotland, 296 pp. unpublished ph.d. thesis, university of birmingham, uk. ineson, j.r., peel, j.s. & smith, m.p. 1986: the sjælland fjelde formation: a new ordovician formation from eastern north greenland. in: peel, j.s. (ed.): north greenland lower palaeozoic palaeontology and stratigraphy: short contributions. rapport grønlands geologiske undersøgelse 132, 27–37. katz, h.r. 1952: ein querschnitt durch die nunatakzone ostgrönlands (ca. 74° n.b.). ergebnisse einer reise vom inlandeis (in zusammenarbeit mit den expéditions polaires françaises von p.-e. victor) ostwärts bis in die fjordregion, ausgeführt im sommer 1951. meddelelser om grønland 144(8), 65 pp. leslie, a.g. & higgins, a.k. 1998: on the caledonian geology of andrée land, eleonore sø and adjacent nunataks (73º30′– 74ºn), east greenland. in: higgins, a.k. & frederiksen, k.s. (eds): caledonian geology of east greenland 72°–74°n: preliminary reports from the 1997 expedition. danmarks og grønlands geologiske undersøgelse rapport 1998/28, 11–27. leslie, a.g. & higgins, a.k. 1999: on the caledonian (and grenvillian) geology of bartholin land, ole rømer land and adjacent nunataks, east greenland. in: higgins, a.k. & frederiksen, k.s. (eds): geology of east greenland 72°–75°n, mainly caledonian: preliminary reports from the 1998 expedition. danmarks og grønlands geologiske undersøgelse rapport 1999/19, 11–26. miller, j.f. & kurtz, v.e. 1979: reasssigment of the dolomite point formation of east greenland from the middle cambrian(?) to the lower ordovician based on conodonts. geological society of america abstracts with programs 10, 219 only. nathorst, a.g. 1901: bidrag til nordöstra grönlands geologi. geologiska föreningens i stockholm förhandlingar 23, 275– 306. peacock, j.d. 1956: the geology of dronning louise land, n.e. greenland. meddelelser om grønland 137(7), 38 pp. peacock, j.d. 1958: some investigations into the geology and petrography of dronning louise land, n.e. greenland. meddelelser om grønland 157(4), 139 pp. peel, j.s. 1980: geological reconnaissance in the caledonian foreland of eastern north greenland, with comments on the centrum limestone. rapport grønlands geologiske undersøgelse 99, 61–72. peel, j.s. 1985: cambrian–silurian platform stratigraphy of eastern north greenland. in: gee, d.g. & sturt, b.a. (eds): the caledonide orogen – scandinavia and related areas, 1077– 1094. london: john wiley & sons. peel, j.s. & smith, m.p. 1988: the wandel valley formation (early– middle ordovician) of north greenland and its correlatives. in: peel, j.s. (ed.): cambrian–jurassic fossils, trace fossils and stratigraphy from greenland. rapport grønlands geologiske undersøgelse 137, 61–92. peel, j.s. & vidal, g. 1988: acritarchs from the kap holbæk formation, north greenland. in: peel, j.s. (ed.): cambrian–jurassic fossils, trace fossils and stratigraphy from greenland. rapport grønlands geologiske undersøgelse 137, 42 only. peel, j.s., ineson, j.r., lane, p.d. & armstrong, h.a. 1981: lower palaeozoic stratigraphy around danmark fjord, eastern north greenland. rapport grønlands geologiske undersøgelse 106, 21–27. pickerill, r.k. & peel, j.s. 1990: trace fossils from the lower cambrian bastion formation of north-east greenland. in: peel, j.s. (ed.): lower cambrian trace fossils from greenland. rapport grønlands geologiske undersøgelse 147, 5–43. rasmussen, j.a. & smith, m.p. 1996: lower palaeozoic carbonates in eastern north greenland, and the demise of the ‘sæfaxi elv nappe’. bulletin grønlands geologiske undersøgelse 172, 49–54. rasmussen, j.a. & smith, m.p. 2002: conodont geothermometry and tectonic overburden in the northernmost east greenland caledonides. geological magazine 138, 687–698. geus bulletin 6.pmd 10-02-2005, 09:5327 28 scrutton, c.t. 1975: corals and stromatoporoids from the ordovician and silurian of kronprins christian land, northeast greenland. meddelelser om grønland 171(4), 43 pp. skovsted, c.b. 2003: the early cambrian fauna of north-east greenland. unpublished thesis, uppsala university, sweden. smith, m.p. 1985: ibexian–whiterockian (ordovician) conodont palaeontology of east and eastern north greenland, 372 pp. unpublished ph.d. thesis, university of nottingham, uk. smith, m.p. 1991: early ordovician conodonts of east and north greenland. meddelelser om grønland geoscience 26, 81 pp. smith, m.p. 2000: cambro-ordovician stratigraphy of bjørnøya and north greenland: constraints on tectonic models for the arctic caledonides and the tertiary opening of the greenland sea. journal of the geological society (london) 157, 459–470. smith, m.p. & bjerreskov, m. 1994: the ordovician system in greenland. correlation chart and stratigraphic lexicon. international union of geological sciences special publication 29a, 46 pp. smith, m.p. & peel, j.s. 1986: the age of the danmarks fjord member, eastern north greenland. in: peel, j.s. (ed.): north greenland lower palaeozoic palaeontology and stratigraphy: short contributions. rapport grønlands geologiske undersøgelse 132, 7–13. smith, m.p. & robertson, s. 1999a: the nathorst land group (neoproterozoic) of east greenland – lithostratigraphy, basin geometry and tectonic history. in: higgins, a.k. & frederiksen, k.s. (eds): geology of east greenland 72°–75°n, mainly caledonian: preliminary reports from the 1998 expedition. danmarks og grønlands geologiske undersøgelse rapport 1999/19, 127–143. smith, m.p. & robertson, s. 1999b: vendian – lower palaeozoic stratigraphy of the parautchthon in the målebjerg and eleonore sø windows. in: higgins, a.k. & frederiksen, k.s. (eds): geology of east greenland 72°–75°n, mainly caledonian: preliminary reports from the 1998 expedition. danmarks og grønlands geologiske undersøgelse rapport 1999/19, 169–182. smith, m.p., sønderholm, m. & tull, s.j. 1989: the morris bugt group (middle ordovician – silurian) of north greenland and its correlatives. rapport grønlands geologiske undersøgelse 143, 5–20. smith, m.p., soper, n.j., higgins, a.k. & rasmussen, j.a. 1999: palaeokarst systems in the late proterozoic of eastern north greenland and their stratigraphic and tectonic significance. journal of the geological society (london) 156, 113–124. smith, m.p., higgins, a.k., soper, n.j. & sønderholm, m. 2004: the neoproterozoic rivieradal group of kronprins christian land, eastern north greenland. in: higgins, a.k. & kalsbeek, f. (eds): east greenland caledonides: stratigraphy, structure and geochronology. geological survey of denmark and greenland bulletin 6, 29–39 (this volume). sønderholm, m. & jepsen, h.f. 1991: proterozoic basins of north greenland. in: peel, j.s. & sønderholm, m. (eds): sedimentary basins of north greenland. bulletin grønlands geologiske undersøgelse 160, 49–69. stouge, s., boyce, d.w., christiansen, j., harper, d.a.t. & knight, i. 2001: vendian – lower ordovician stratigraphy of ella ø, north-east greenland: new investigations. geology of greenland survey bulletin 189, 107–114. stouge, s., boyce, d.w., christiansen, j.l., harper, d.a.t. & knight, i. 2002: lower–middle ordovician stratigraphy of north-east greenland. geology of greenland survey bulletin 191, 117– 125. strachan, r.a., friderichsen, j.d., holdsworth, r.e. & jepsen, h.f. 1994: regional geology and caledonian structure, dronning louise land, north-east greenland. in: higgins, a.k. (ed.): geology of north-east greenland. rapport grønlands geologiske undersøgelse 162, 71–76. swett, k. & smit, d.e. 1972: paleogeography and depositional environments of the cambro-ordovician shallow marine facies of the north atlantic. bulletin of the geological society of america 83, 3223–3248. toula, f. & lenz, o. 1874: geologie ostgrönlands zwischen dem 73. und 76.° nordl. br. in: geographisches gesellschaft in bremen: die zweite deutsche nordpolarfahrt in den jahren 1869 und 1870. 2, 475–496. tucker, r.d. & mckerrow, w.s. 1995: early paleozoic chronology: a review in light of new u-pb ages from newfoundland and britain. canadian journal of earth sciences 32, 368–379. wenk, e. 1961: on the crystalline basement and the basal part of the pre-cambrian eleonore bay group in the southwestern part of scoresby sund. meddelelser om grønland 168(1), 54 pp. wordie, j.m. 1927: the cambridge expedition to east greenland in 1926. appendix v. geology. geographical journal 70, 252– 253. geus bulletin 6.pmd 10-02-2005, 09:5328 geological survey of denmark and greenland bulletin 3, 24-97 24 the danish late quaternary marine molluscs the record of shell-bearing danish late quaternary marine molluscs has been established on the basis of finds made during the systematic geological mapping since 1888, as presented in the publications from the geological survey of denmark, mainly in the i. række covering the descriptions for the map sheets. furthermore, special papers on holocene and late pleistocene marine molluscs have been included. most of them have been listed in one of the preceding chapters on works on danish sites with marine sediments. 1. the bælt sea area 2. the baltic sea area 3. the kattegat area with fjords 4. the limfjord area 5. the north sea coastal area 6. the vendsyssel area 7. the skagen area the regions are figured on the map (fig. 2) and follow the outline of the geological map sheets except the skagen area. it should be especially noted that the southern limit during the holocene of the north sea coastal region is at blåvands huk. although this area from varde to the german border has been mapped, no descriptions have been published. however, studies of the eemian from this region have been published and will be commented upon when presenting the eemian records from the above-mentioned areas. the bælt sea area has been taken as the region between the kattegat region and the baltic, here following ekman (1953) saying that the boundary between the bælt sea and the baltic proper is the threshold between gedser and darss and the southern end of the øresund, see fig. 1. the reason for including the øresund north of saltholm (northern and middle øresund sensu jensen & knudsen 1995) in the kattegat region is that regarding the water from the baltic the øresund is a sound – a passage – for the brackish water flowing north, but regarding the salt-water from the kattegat, the øresund is a fjord down to the threshold between amager and limhamn, to quote thorson (1944a, p. 42). the subfossil shell-bearing molluscs are presented on the background of the annotated check list of recent marine molluscs of danish waters by jensen & knudsen (1995). furthermore, general information has been taken from jensen & spärck (1934), lemche (1948), nordsieck (1968, 1969), fretter & graham (1976–1978, 1980–1982, 1984), fretter et al. (1986) and poppe & goto (1991, 1993) (which will not be quoted throughout the text, listing the many species and their environment). only the synonyms mentioned in texts on danish molluscan finds are included. a list of these synonyms is found heading the index of species. the investigations carried out by scientists in the northern atlantic have given a good base for the evaluation of the danish late quaternary molluscan fauna. these studies have been published mainly in papers on the zoology of east greenland, the godthaab expedition 1928, the zoology of iceland, and the zoology of the faroes. however, the zoology of greenland has been supplemented by contributions from macpherson (1971), lubinsky (1980), the 6. og 7. thule expedition til sydøstgrønland 1931–33 under the leadership of knud rasmussen and the treaarsexpeditionen til christian den x’s land 1931–34 under the leadership of lauge koch. in the two last-mentioned contributions, especially the animal ecology and the arctic communities have been treated, which form a very important part in the discussion of the danish late quaternary molluscan assemblages. the following publications on molluscs can be mentioned: 1. from greenland: spärck (1933), thorson (1933, 1944b, 1951), thorson & ussing (1934), madsen (1936), bertelsen (1937), lemche (1941a, b), ockelmann (1958), kramp (1961, 1963). 2. from iceland: spärck (1937), lemche (1938), thorson (1941), knudsen (1949a, b), madsen (1949). 3. from the faeroes: lemche (1928), thorson & spärck (1928), spärck & thorson (1931), petersen (1968), knudsen (1970). as to the community concept as worked out by c.g.j. petersen, references have already been given to petersen & jensen (1911), petersen (1913, 1914, 1915, 1918), and thorson (1957). the regional division of the northern european seas in to arctic, subarctic, boreal and lusitanian is from the zoogeographical division of the geus bulletin no 3.pmd 28-06-2004, 08:4524 25 northern european seas as given by feyling-hanssen (1955, fig. 5) and símonarson et al. (1998), as seen on figs 4 and 5 respectively. the molluscan genera and species are presented in groups within class, subclass and order mainly following the presentation of recent marine molluscs of danish waters as given by jensen & knudsen (1995). when there is no subfossil record at hand the information is taken from the recent data as given by poppe & goto (1991, 1993), jensen & knudsen (1995) and others as listed previously. to facilitate the use of the index of all molluscan species, a list of synonyms is given as mentioned earlier including the species mentioned in danish mollusc literature. class polyplacophora order neoloricata among the seven species recorded in the recent danish fauna only one, tonicella marmorea, has been found subfossil in the vendsyssel area from the younger weichselian deposits. it is a circumboreal species which in europe is known from northern scandinavia south to denmark and recorded from around iceland (knudsen 1949a, b) down to ireland (poppe & goto 1991). it is common in danish waters, being known from the central part of the kattegat and the øresund region (muus 1959), e.g. subarctic–boreal–lusitanian species. habitat. common in shallow water of less than 20 m, otherwise recorded from 0–183 m (muus 1959). the lack of information on subfossil finds may reflect difficulty in determination when the species is found in the subfossil state of preservation with the shell parts apart. polyplacophora do occur as seen from the skagen well where finds have been recognised at the 70.10–70.30 m and the 37.0–37.25 m levels, viz. during the subboreal and the subatlantic respectively. among the other – only recent – finds of polyplacophora, leptochiton asellus is widely found from the arctic to the lusitanian. hanleya hanleyi, ischnochiton albus and the above-mentioned tonicella marmorea are all found in the subarctic, boreal and lusitanian regions. the last three species, callochiton septemvalvis, lepidochitona cinereus and tonicella rubra, are all restricted to the boreal–lusitanian region. class gastropoda subclass prosobranchia order archaeogastropoda scissurella crispata fleming 1828 fig. 6 distribution. w greenland, s and w iceland, spitsbergen, norway north of lofoten, and south to the mediterranean. occurrence. the subarctic (not in true arctic water), boreal and lusitanian regions (according to thorson 1941). habitat. in the waters around iceland (thorson 1941, p. 4), the living specimens have often been found at depths greater than 500 m on clay bottom. however, poppe & goto (1991, p. 64) write that the species lives on stones, shelly sand and clay bottoms between 15 and 600 m. fretter & graham (1976, pp. 2–4) stated that the species is always sublittoral, even in the extreme northerly limits of its range, and occurs from 8– 2000 m. it is not recorded from danish waters although fretter & graham mentioned it from the norwegian and swedish coasts of the skagerrak. only subfossil finds. during the eemian in the kattegat region. fig. 6. scissurella crispata fleming 1828. anholt ii, 78.06–78.09 m b.s. × 20. mguh 25316. geus bulletin no 3.pmd 28-06-2004, 08:4525 26 patella vulgata linnaeus 1758 distribution. faeroes, norway off the lofoten islands, and south to the straits of gibraltar (thorson 1941). occurrence. boreal–lusitanian. habitat. intertidal, rocky shores or man-made hard substrates. however, it also occurs with seaweed. only one recent individual has been found at løkken, while empty shells are often found on the skagerrak coast (knudsen 1993). subfossil finds. the limfjord region, holocene, in a ‘køkkenmødding’ (kitchen midden) at bulbjerg (petersen 1888). helcion pellucidum (linnaeus 1758) distribution. west and south iceland, northern norway north of lofoten, and south to portugal (thorson 1941). also found in the øresund, but absent from the baltic and the limfjord. occurrence. boreal and lusitanian. habitat. lives on seaweeds at depths from 0 to 27 m. petersen (1888) points to this habitat as a reason why it is rarely found. subfossil finds. the limfjord region and vendsyssel, holocene. lepeta caeca (müller 1776) distribution. from northern scandinavia, n and s iceland and spitsbergen (thorson 1941) south to scotland. it is not present in the baltic, the north sea and the channel, but occurs in the azores. this species, according to poppe & goto (1991), prefers cold temperatures and lives at greater depths in the southern part of its range. in this way it exemplifies the tropical submerge. it is present in the øresund region and has been reported from single finds in the kattegat (petersen 1888). occurrence. subarctic and boreal. subfossil finds. none. iothia fulva (müller 1776) distribution. northern scandinavia and s and w iceland south to the irish sea, and like lepeta caeca in deep water off the azores. it is found in the øresund region, but with rare and single finds in the kattegat (petersen 1888). occurrence. boreal and lusitanian. habitat. offshore between 5 and 600 m on hard substrates like lepeta caeca. subfossil finds. the limfjord region, holocene. acmaea tessulata (müller 1776) distribution. east greenland, around iceland (thorson 1941) and in scandinavia according to petersen (1888). the limfjord (petersen 1986a). common in the øresund, but absent in the baltic. extends southwards to the north of the british isles and northern ireland. occurrence. arctic, subarctic, boreal, and lusitanian. habitat. lower part of the intertidal zone. in the south connected with zostera. subfossil finds. the limfjord region, holocene. acmaea virginea (müller 1776) distribution. northern scandinavia and around iceland (thorson 1941), south to the cape verde islands. common in the kattegat and øresund, but not found in the baltic. occurrence. subarctic, boreal, lusitanian. habitat. on hard substrate at depths from 0 to 100 m. subfossil finds. the limfjord and vendsyssel regions, holocene. emarginula fissura (linnaeus 1758) distribution. scandinavia and south to the mediterranean, according to petersen (1888) taken alive from the øresund, dead shells in the northern kattegat. geus bulletin no 3.pmd 28-06-2004, 08:4526 27 occurrence. boreal and lusitanian. habitat. from the low tide line to a depth of 700 m on hard substrate. subfossil finds. none. puncturella noachina (linnaeus 1771) distribution. spitsbergen and around iceland (thorson 1941), scandinavia south to portugal. also found in the skagerrak and kattegat including øresund. occurrence. arctic, subarctic, boreal and lusitanian. habitat. between 10 and 200 m on rock and stones. subfossil finds. none. margarites helicinus (phipps 1774) distribution. from northern scandinavia, spitsbergen and around iceland (thorson 1951) south to the british isles. a few records from the skagerrak and kattegat. occurrence. arctic, subarctic, boreal and northern part of the lusitanian region. habitat. from the intertidal zone to 400 m deep on seaweeds and under stones. subfossil finds. the limfjord region, holocene. gibbula cineraria (linnaeus 1758) distribution. from northern scandinavia north of lofoten, and w and s iceland (thorson 1941) south to morocco. according to petersen (1888) known from the kattegat including øresund, the bælt sea and the limfjord area. occurrence. boreal–lusitanian. habitat. intertidal to 130 m deep on rocks and seaweeds. subfossil finds. the limfjord, the north sea and vendsyssel, holocene. recorded from the north sea during the eemian. gibbula tumida (montagu 1803) distribution. from northern norway north of lofoten, and s and w iceland (thorson 1941), south to spain. known from the kattegat, including the øresund, but not so common as gibbula cineraria. the species does not occur in the limfjord (petersen 1986a, table 1). occurrence. boreal–lusitanian. habitat. on gravel bottoms from below low tide to depths of 1200 m. subfossil finds. the limfjord and vendsyssel area, holocene. jujubinus clelandi (w. wood 1828) distribution. from the lofoten islands south into the mediterranean. found in the kattegat region, including the øresund, but rare. occurrence. boreal–lusitanian. habitat. on various types of bottom from depths of 35 m to 800 m. subfossil finds. none. calliostoma formosa (mighels 1842) distribution. along the norwegian coast, w and s iceland (thorson 1941), and south to the british isles but not on the west side. occurrence. boreal. habitat. dredged at depths between 19 and 1000 m – the species is never littoral. subfossil finds. none. calliostoma zizyphinum (linnaeus 1758) distribution. from the lofoten islands south to the azores. in the skagerrak. occurrence. boreal–lusitanian. geus bulletin no 3.pmd 28-06-2004, 08:4527 28 habitat. intertidal to 300 m deep – lives on all types of bottoms. subfossil finds. none. skenea serpuloides (montagu 1808) distribution. from the british isles south to portugal and into the mediterranean. occurrence. lusitanian. habitat. from the intertidal zone down to 50 m deep. intertidal on weeds and stones, and sublittoral dredged from shelly and gravelly sand. only subfossil finds. the limfjord area, holocene. skenea basistriata (jeffreys 1877) distribution. atlantic coast of europe, but not in the north sea and the baltic. occurrence. boreal–lusitanian. habitat. on soft bottom – never in shallow water or littoral sequences, deep water 90–2400 m. subfossil finds. the limfjord region, holocene. theodoxus fluviatilis (linnaeus 1758) distribution. from the pyrenees and the british isles east towards the caucasus, including northern sweden and the coasts of finland. occurrence. lusitanian–boreal. habitat. the primary habitat of this species is rivers. in the baltic sea the form littoralis becomes a common littoral animal (fretter & graham 1978a, p. 105). the species is also recorded from the fjords bordering the kattegat region today. subfossil finds. the kattegat and limfjord regions, holocene. the archaeogastropoda are represented by 16 species in the recent marine fauna, out of which ten have been recorded from the past. only two species, skenea serpuloides and scissurella crispata, are not found in the recent fauna. there is a total number of subfossil finds among the archaeogastropoda of 12 species, with two from the eemian and ten from the holocene. order mesogastropoda littorina littorea (linnaeus 1758) distribution. from northern norway north of lofoten, and south to spain. common along all the danish coasts but not in the baltic and on the more exposed sandy coasts (petersen 1888). recent records from the baltic as far as bornholm (fretter & graham 1980, p. 256). occurrence. boreal and lusitanian. habitat. the intertidal zone, abundant on rocky shores, might be found to a depth of 60 m. subfossil finds. the bælt sea, baltic, kattegat, limfjord, the north sea and vendsyssel regions, holocene. the bælt sea, baltic, kattegat and north sea regions in the eemian. melaraphe (littorina) neritoides (linnaeus 1758) distribution. from western norway south to morocco and the mediterranean. a scattered occurrence in the kattegat (jensen & knudsen 1995). the species is recorded from the limfjord (petersen 1986a). occurrence. boreal and lusitanian. habitat. lives high on the rocky shores (splash zone). subfossil finds. none. littorina mariae sacchi & rastelli 1966 distribution. from northern scandinavia south to the mediterranean, extending through the kattegat into the bælt sea. occurrence. the boreal and lusitanian. habitat. in the tidal zone on weeds. subfossil finds. none. (the species may have been confused with littorina obtusata.) geus bulletin no 3.pmd 28-06-2004, 08:4528 29 littorina obtusata (linnaeus 1758) distribution. w greenland, s and w iceland (thorson 1941), northern scandinavia north of lofoten, and south to the mediterranean. the species extends through the limfjord and kattegat into the bælt sea (fretter & graham 1980). occurrence. subarctic, boreal and lusitanian. habitat. intertidal, lives on weeds. subfossil finds. the bælt sea, kattegat, limfjord, north sea and vendsyssel regions, holocene. during the eemian recorded from the north sea. littorina saxatilis (olivi 1792) distribution. from greenland, spitsbergen, around iceland and the atlantic coasts of europe. common in the fjords bordering the kattegat, including the limfjord (petersen 1986a). occurrence. the arctic, subarctic, boreal and lusitanian. habitat. intertidal. subfossil finds. the bælt sea, kattegat, limfjord, north sea and vendsyssel regions, holocene. the north sea during the eemian, and the vendsyssel area in the late weichselian. littorina tenebrosa (montagu 1803) distribution. off southern iceland and the atlantic coasts of europe. the species is found in the limfjord, and penetrates also into the baltic, with finds off møn and stevns (petersen 1888). occurrence. the boreal and lusitanian. habitat. intertidal. subfossil finds. the bælt sea, baltic, kattegat, limfjord and vendsyssel regions, holocene. lacuna pallidula (da costa 1778) fig. 7a, b distribution. from spitsbergen, around iceland and along the atlantic coast down to the gulf of biscay. enters the danish waters, including the limfjord, the øresund and the bælt sea. occurrence. the arctic, subarctic, boreal and lusitanian. habitat. intertidal to 70 m deep on weeds. subfossil finds. the bælt sea, limfjord, north sea and vendsyssel regions, holocene. in the skagen well from the subatlantic. lacuna crassior (montagu 1803) distribution. from the arctic seas to the british isles. only records from the north sea and from the nw coast of sweden. occurrence. the arctic, subarctic and boreal. habitat. sublittoral to 90 m deep on soft bottoms with stones and shells (fretter & graham 1980, p. 248). subfossil finds. none. fig. 7. a, b: lacuna pallidula (da costa 1778). skagen 4, 30.8– 30.5 m b.s., lab. no. 355,93. × 20. mguh 25317. geus bulletin no 3.pmd 28-06-2004, 08:4529 30 lacuna parva (montagu 1803) distribution. from norway off the lofoten, and south to spain, found in the kattegat region with fjords, but few records, and not found in the limfjord. occurrence. boreal and lusitanian. habitat. intertidal extending sublittorally to around 50 m as lacuna vincta (fretter & graham 1980, p. 250) and living on seaweeds. subfossil finds. the limfjord, north sea and vendsyssel regions, holocene. from the north sea during the eemian. lacuna vincta (montagu 1803) distribution. from w greenland around iceland, norway and south to spain. in the danish waters, including the limfjord, found into the bælt sea (fretter & graham 1980). occurrence. subarctic, boreal and lusitanian. habitat. intertidal to 60 m deep living on seaweeds. subfossil finds. the bælt sea, kattegat, limfjord, north sea and vendsyssel regions, holocene. in the north sea region found during the eemian. in the vendsyssel area recorded from the eemian, and also from the early/middle and late weichselian (older and younger yoldia sea respectively). hydrobia neglecta muus 1963 distribution. the british isles, ireland and the north sea. occurrence. boreal and lusitanian. habitat. shallow-water environments on the soft substratum or the vegetation. subfossil finds. none. hydrobia ulvae (pennant 1777) fig. 8 distribution. norway off lofoten south to the mediterranean. in all the danish waters including the baltic. occurrence. the boreal and lusitanian. habitat. the intertidal zone, but has been found as deep as 20 m, on soft substrate, most often on intertidal banks of firm mud or muddy sand (fretter & graham 1978a, p. 122). subfossil finds. the bælt sea, baltic, kattegat, limfjord, north sea and vendsyssel regions, holocene. in the skagen well from the subatlantic. during the eemian recorded from the bælt sea, baltic, kattegat and the north sea regions. hydrobia ventrosa (montagu 1803) distribution. norway off lofoten, south to the mediterranean. in all the danish waters including the baltic. occurrence. the boreal and lusitanian regions. habitat. the intertidal zone, on soft substratum like hydrobia ulvae, but prefers lower salinities (fretter & graham 1978a, p. 126). the two species may occur together, so quantitative analyses must be undertaken to designate any changes in the environment (petersen 1993). subfossil finds. the baltic, kattegat, limfjord and the north sea regions, holocene. potamopyrgus antipodarum (gray 1853) distribution. from scandinavia to spain and in danish waters into the baltic, a late immigrant according to jensen & knudsen (1995). occurrence. the boreal and lusitanian regions. fig. 8. hydrobia ulvae (pennant 1777). skagen 4, 25.0–25.5 m b.s., lab. no. 350,93. × 20. mguh 25318. geus bulletin no 3.pmd 28-06-2004, 08:4530 31 habitats. in all kinds of brackish and freshwater habitats. much like the distribution of hydrobia ventrosa in brackish waters (fretter & graham 1978a, p. 132). subfossil finds. none. skeneopsis planorbis (fabricius 1780) distribution. w greenland, around iceland and norway, south to the mediterranean. known from few places in danish waters. occurrence. the subarctic, boreal and lusitanian regions. habitat. intertidal down to a depth of 70 m, lives on seaweeds. only subfossil finds. the limfjord and the vendsyssel regions, holocene. barleeia unifasciata (montagu 1803) fig. 9 distribution. from the shetlands south into the mediterranean. occurrence. the boreal and lusitanian regions. habitat. shallow waters, intertidal, lives on seaweeds on rocky shores. only subfossil finds. the skagen well from the subatlantic. alvania abyssicola (forbes 1850) distribution. from northern norway to the mediterranean. the species extends into the skagerrak and kattegat, including the øresund. occurrence. the boreal and lusitanian regions. habitat. on muddy bottom in sublittoral areas at depths of 15–100 m. subfossil finds. the vendsyssel area from the eemian. alvania jeffreysi (waller 1864) distribution. s and w iceland, norway, south to the mediterranean. found in the skagerrak, but not in the north sea. occurrence. the boreal and lusitanian regions. habitat. always sublittoral from 50 to 600 m on sandy bottom. subfossil finds. none. alvania lactea (michaud 1830) distribution. from the channel islands south to morocco and the mediterranean. occurrence. the lusitanian region. habitat. sublittorally under stones and amongst algae. only subfossil finds. the limfjord and vendsyssel areas, holocene. alvania cimicoides (forbes 1844) distribution. sw and nw iceland (empty shells), norway, north of lofoten, and south to the mediterranean; probably absent from the channel and the north sea. occurrence. the boreal and lusitanian regions. habitat. sublittoral, from the laminarian zone downwards, but mainly in deeper water down to 500 m. fig. 9. barleeia unifasciata (montagu 1803). skagen 3, 33.90– 34.20 m b.s., lab. no. 709,93. × 20. mguh 25319. geus bulletin no 3.pmd 28-06-2004, 08:4531 32 usually found on soft bottoms (fretter & graham 1978b). only subfossil finds. the vendsyssel area, holocene. alvania punctura (montagu 1803) distribution. norway south of lofoten (including lofoten) and south to the mediterranean. it extends to the swedish west coast, but is absent from the øresund, the baltic, the eastern shores of the north sea and the eastern basin of the channel (fretter & graham 1978b). however, according to jensen & knudsen (1995) alvania punctura is found in the northern and central parts of the øresund. occurrence. the boreal and lusitanian regions. habitat. sublittoral to depths of c. 100 m, on both finer and coarser substrata. subfossil finds. the limfjord and the vendsyssel regions, holocene. alvania cruenta odhner 1915 distribution. arctic canada, west greenland and svalbard (thorson 1951; macpherson 1971). occurrence. the arctic and subarctic. habitat. from 19 to 234–254 m on mud (macpherson 1971). only subfossil finds. the early/middle weichselian in the vendsyssel region. alvania jan mayeni (friele 1886) distribution. e and w greenland, spitsbergen, ne iceland, and norway north of lofoten (thorson 1941). occurrence. the arctic and subarctic with boreal outposts. habitat. off iceland between 94–442 m in deep on clay with many stones (thorson 1941). only subfossil finds. the early/middle weichselian (older yoldia clay) in vendsyssel. alvania scrobiculata (möller 1842) distribution. e and w greenland, spitsbergen, n and e iceland, and norway north of lofoten (thorson 1941). occurrence. the arctic and subarctic with boreal outposts. habitat. from 22 m at e greenland to 342 m in the northern arctic sea on a bottom of sand and with algae (thorson 1941). only subfossil finds. from the early/middle weichselian (older yoldia clay) in vendsyssel. cingula semistriata (montagu 1808) distribution. from lofoten and south along the west coast of norway to the mediterranean (rare in the north). it extends into the kattegat, but is absent from the eastern shores of the southern north sea and the limfjord. occurrence. the boreal and lusitanian regions. habitat. on rocky shores in the intertidal zone and sublittorally to 100 m, fond of silty places (fretter & graham 1978b). subfossil finds. the limfjord and the vendsyssel areas, holocene. cingula turgida (jeffreys 1870) distribution. from norway north of lofoten to the south into kattegat. occurrence. the boreal region. habitat. on muddy bottoms down to c. 1000 m. subfossil finds. the north sea region, holocene. obtusella alderi (jeffreys 1858) distribution. from norway to spain, not on the eastern shores of the north sea and in the baltic; however, found in the kattegat, including the northern part of the øresund. occurrence. the boreal and lusitanian regions. geus bulletin no 3.pmd 28-06-2004, 08:4532 33 habitat. sublittoral to a depth of 60 m amongst algae and on sandy or gravelly bottoms. subfossil finds. none. onoba aculeus (gould 1841) distribution. from spitsbergen, w greenland, around iceland and along the coast of norway into the kattegat, including the øresund. also found at localities off ireland. occurrence. the arctic, subarctic, boreal and lusitanian regions. habitat. found to about 200 m on algae. subfossil finds. none. onoba semicostata (montagu 1803) distribution. around iceland, along the coast of norway and south to the mediterranean. absent from the eastern north sea coasts, but extends through the limfjord and kattegat, including the øresund, into the bælt sea and the most saline parts of the baltic (fretter & graham 1978b). occurrence. the subarctic, boreal and lusitanian regions. habitat. from the intertidal region to depths of 100 m. found under stones, amongst weeds, mussels and tunicates in shelly gravel, but only where there are quantities of silt (fretter & graham 1978b). subfossil finds. the bælt sea, kattegat, limfjord and vendsyssel regions, holocene. onoba proxima (forbes & hanley 1850) distribution. from the western coast of britain south to the mediterranean. occurrence. the lusitanian region. habitat. from 10 to 170 m on bottoms of muddy sand. only subfossil finds. the limfjord region, holocene. onoba vitrea (montagu 1803) fig. 10 distribution. from norway off lofoten and south to the mediterranean, extends through skagerrak into the kattegat, including the øresund, but absent from the limfjord. occurrence. the boreal and lusitanian regions. habitat. muddy bottoms at depths of 10–50 m in the northern parts of its range, but extending to 120 m in the south. further notes on onoba species in fretter & graham (1978b, p. 170). subfossil finds. the kattegat, limfjord, north sea, vendsyssel and skagen areas, holocene. in the skagen well recorded from the atlantic, the subboreal and the subatlantic. during the eemian recorded from the north sea. rissoa albella lovén 1846 fig. 11 distribution. from norway off the lofoten islands, and south to the mediterranean, extending into the limfjord and the kattegat with the danish fjords, including the øresund and the bælt sea. occurrence. the boreal and lusitanian regions. habitat. on rocky shores amongst weeds, sublittoral to 15 m. it is tolerant of some brackishness (fretter & graham 1978b). subfossil finds. the bælt sea, baltic, kattegat, limfjord, north sea, vendsyssel and skagen well from the subfig. 10. onoba vitrea (montagu 1803). skagen 3, 67.0–67.25 m b.s., lab. no. 720,93. × 9.6. mguh 25320. geus bulletin no 3.pmd 28-06-2004, 08:4533 34 atlantic, holocene. from the eemian recorded from the north sea. rissoa inconspicua alder 1844 distribution. from northern norway, north of lofoten, and south to the mediterranean. occurring in the limfjord, øresund and bælt sea. occurrence. the boreal and lusitanian regions. fretter & graham (1978b, p. 200) indicate that the species is found to the arctic. however, it is not recorded from iceland and the faroes but only from norway north of lofoten (thorson 1941, table ii, p. 141). habitat. typically sublittoral living on algae, and on sandy gravel to depths of about 100 m. tolerant of slightly brackish conditions. subfossil finds. the bælt sea, baltic, kattegat, limfjord, north sea and vendsyssel, holocene. during the eemian recorded from the bælt sea, kattegat and north sea regions. rissoa membranacea (j. adams 1800) distribution. from norway off lofoten and south to the canary islands. extends into the limfjord, kattegat, bælt sea and the westernmost part of the baltic (the rügen island). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone sublittorally to about 15 m associated with zostera or on weeds with the same habit, extending into brackish water. subfossil finds. the bælt sea, baltic, kattegat, limfjord, north sea and vendsyssel areas, holocene. during the eemian in the bælt sea and north sea regions. rissoa parva (da costa 1779) distribution. from norway, north of lofoten and the faeroes, south to the mediterranean, found in the limfjord (petersen 1986a) and the northern part of the øresund but not in the baltic according to fretter & graham (1978b). however, bondesen (1975) includes the species in the baltic, but excludes it from the bælt sea. petersen (1888, p. 93) regarded the species as being limited to the central part of the kattegat, depending on sufficient salt content – therefore the information of the occurrences in the baltic given by bondesen (1975) is surprising. occurrence. the boreal and lusitanian regions. habitat. from the tidal zone to about 25 m on fronds, smaller weeds and under stones. in the faeroes from the rock pools and the beach to a depth of 20 m (spärck & thorson 1931). subfossil finds. the limfjord and vendsyssel areas, holocene. during the eemian recorded from the bælt sea, north sea and vendsyssel regions. rissoa violacea desmarest 1814 fig. 12 distribution. rissoa violacea is not at all recorded from iceland (thorson 1941) and the faroes (spärck & thorson 1931) but from norway off the lofoten islands and south. both of the recent subspecies are recorded from the kattegat, including the øresund region. bonfig. 12. rissoa violacea desmarest 1814. skagen 4, 27.0– 27.5 m b.s., lab. no. 352,93. × 20. mguh 25322. fig. 11. rissoa albella lovén 1846. skagen 4, 30.0–30.5 m b.s., lab. no. 355,93. × 20. mguh 25321. geus bulletin no 3.pmd 28-06-2004, 08:4534 35 desen (1975) has rissoa violacea sensu lato from the skagerrak, the kattegat and the limfjord regions. occurrence. the boreal and lusitanian regions. habitat. in the tidal zone to about 50 m on weeds and amongst sandy gravel. subfossil finds. the limfjord, north sea, vendsyssel and skagen areas, holocene. in skagen recorded from the subatlantic. the species occurred during the eemian in the kattegat region. assiminea grayana fleming 1828 distribution. the species is confined to the north sea coasts. in danish waters it extends south to blåvands huk. occurrence. the boreal region. habitat. the species is limited to the upper parts of the salt-marsh areas on the vegetation. subfossil finds. none. caecum glabrum (montagu 1803) distribution. from norway off lofoten south to the mediterranean. it extends into kattegat, where it has been reported from the northern part (jensen & knudsen 1995), but not from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. sublittorally to about 250 m on sandy and sandy–muddy bottoms. subfossil finds. the limfjord, north sea and vendsyssel regions, holocene. recorded from the bælt sea and the north sea during the eemian. tornus exquisitus (jeffreys 1883) distribution. within the danish waters recorded from northern kattegat (jensen & knudsen 1995), but no record is given by fretter & graham (1978b, p. 232) so the species is not treated further. habitat. unknown for this species. subfossil finds. none. bittium reticulatum (da costa 1778) fig. 13 distribution. from off lofoten in norway south to the mediterranean. it is found through the skagerrak, limfjord, kattegat, including the øresund, and into the bælt sea, but not from the southern coastal part of the north sea. occurrence. the boreal and lusitanian regions. habitat. common in shallow sublittoral water, but recorded to 250 m. found on soft bottoms in association with weeds. subfossil finds. the species is recorded from all regions during the holocene. from skagen recorded from the subatlantic. from the eemian found in the bælt sea, kattegat, north sea, and vendsyssel regions. turritella communis risso 1826 fig. 14 distribution. from the lofoten islands south to the mediterranean. the species extends into all the danish waters as far as the øresund. occurrence. the boreal and lusitanian regions. habitat. from 10 to 200 m depths on soft bottoms. subfossil finds. the limfjord, north sea, vendsyssel and skagen areas, holocene. in the skagen area refig. 13. bittium reticulatum (da costa 1778). geus collection. vejlager xiv, denmark. × 9.6. mguh 25323. geus bulletin no 3.pmd 28-06-2004, 08:4535 36 corded from the subboreal and subatlantic. during the eemian recorded from the baltic, kattegat, north sea and vendsyssel regions. turritella erosa couthouy 1838 distribution. west and east greenland (thorson 1944b, p. 40), svalbard and on the northern coast of russia (macpherson 1971). occurrence. the arctic and subarctic regions. habitat. from 10 to 350 m on soft bottoms. subfossil finds. recorded from the vendsyssel region in early/middle weichselian. aporrhais pespelicani (linnaeus 1758) fig. 15 distribution. on the southern and western part of iceland, norway off lofoten with a questionable occurrence north of lofoten (thorson 1941), and south to the mediterranean. it does not occur off the west coast of denmark nor in its fjords, except the limfjord. it extends through the kattegat, including øresund (fretter & graham 1981, p. 297). empty shells are found in kieler bucht (arntz et al. 1976). occurrence. the boreal and lusitanian regions. habitat. sublittoral to depths of 180 m on mud, muddy sand and sand. subfossil finds. the baltic, limfjord, north sea, vendsyssel and skagen areas, holocene. in the skagen region from the subatlantic. during the eemian recorded from the bælt sea, baltic, north sea, and vendsyssel regions. aporrhais serresianus (michaud 1828) distribution. from southern and western iceland, norway off lofoten and south to the mediterranean. according to fretter & graham (1981) absent from the skagerrak and all danish seas; however, jensen & knudsen (1995) note a single record from the central kattegat. occurrence. the boreal and lusitanian regions. habitat. from sublittoral (as aporrhais pespelicani) down to 1000 m on finer muds. subfossil finds. none. crepidula fornicata (linnaeus 1758) distribution. c. fornicata is a late immigrant to europe (first recorded in the british isles late in the 19th century). the present distribution is from norway south to portugal. it reached the limfjord in 1934. in 1949– 50 it was found in the northern part of kattegat but has not spread further south (jensen & knudsen 1995). fig. 15. aporrhais pespelicani (linnaeus 1758). skagen 3, 0.0–30.0 m b.s. (washed sample). × 4.8. mguh 25325. fig. 14. turritella communis risso 1826. skagen 3, 73.10–73.30 m b.s., lab. no. 722,93. × 4.8. mguh 25324. geus bulletin no 3.pmd 28-06-2004, 08:4536 37 occurrence. the boreal–lusitanian regions within its european distribution. crepidula fornicata was transferred by man as seen also for species like mya arenaria. habitat. sublittoral to depths of c. 10 m. the animals live in chains, the oldest attached to a substrate which might be an oyster. the species was actually transported to europe with oysters (fretter & graham 1981, p. 311). subfossil finds. obviously none. capulus ungaricus (linnaeus 1758) distribution. empty shells recorded from sw and nw iceland and living specimens from norway north of lofoten south to the mediterranean. the record from greenland mentioned in fretter & graham (1981) cannot be sustained in the literature (thorson 1944b, 1951). occurrence. the boreal and lusitanian regions. habitat. usually sublittorally to 805 m attached to stones or the host animal. subfossil finds. none (young date from the north sea). lamellaria perspicua (linnaeus 1758) distribution. sw and nw iceland, norway from lofoten and south to the mediterranean. it occurs in the skagerrak but not on the danish coasts. occurrence. the boreal and lusitanian regions. habitat. from the tidal zone and downwards to depths of 1200 m, especially in the southern parts of its range on rocky shores and under stones. subfossil finds. none. velutina plicatilis (müller 1776) distribution. from east greenland and spitsbergen, southern and western iceland, norway north of lofoten and south to northern spain. it extends into the skagerrak, kattegat and the northern part of the north sea. occurrence. the arctic, subarctic, boreal and lusitanian regions. habitat. from 10 to c. 375 m deep on hard bottoms, usually in association with ascidians and hydroids. subfossil finds. none. velutina velutina (müller 1776) distribution. from spitsbergen, e and w greenland, around iceland and norway south to the mediterranean. it extends into the skagerrak and kattegat, including øresund. occurrence. arctic, subarctic, boreal and lusitanian regions. habitat. sublittoral extending to 1000 m on hard bottoms associated with tunicates. subfossil finds. none. trivia arctica (pulteney 1799) distribution. from norway off lofoten and south to the mediterranean. it extends into the skagerrak and kattegat (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. sublittoral to about 100 m, in southerly latitudes to about 1000 m. it is associated with ascidians. subfossil finds. none. trivia monacha (da costa 1778) distribution. from the british isles south to the mediterranean. the recent distribution in the north sea is questioned, and the species is not recorded from scandinavia (fretter & graham 1981, p. 329). occurrence. the lusitanian region. habitat. on rocky shores and under stones associated with ascidians. subfossil finds. the vendsyssel region, holocene. geus bulletin no 3.pmd 28-06-2004, 08:4537 38 amauropsis islandicus (gmelin 1791) distribution. from spitsbergen, e and w greenland, around iceland and norway. it extends into the skagerrak and kattegat, including øresund, although it is rare there (jensen & knudsen 1995). occurrence. the arctic, subarctic and boreal regions. habitat. sublittorally to about 80 m deep on sandy clay bottoms. subfossil finds. none (late date from the north sea). lunatia alderi (forbes 1838) fig. 16 distribution. from southern and western iceland and norway off the lofoten islands south to the mediterranean (thorson 1941). it extends into the skagerrak, kattegat and øresund, but the species is not recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. sublittoral between 10 and 50 m, extending to 2000 m. infaunal on sandy shores, clean sand and some admixture of mud. according to petersen (1888), it is common on mixed bottoms in the kattegat. subfossil finds. the limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen area recorded from the atlantic, subboreal and subatlantic. from the eemian recorded from the baltic, kattegat, north sea, vendsyssel and skagen regions. lunatia catena (da costa 1778) distribution. from the skagerrak and kattegat, including øresund but not the limfjord, south to the mediterranean (fretter & graham 1981, p. 339). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone down to about 125 m on sandy bottoms. subfossil finds. the limfjord, north sea and vendsyssel regions, holocene. lunatia montagui (forbes 1838) fig. 17 distribution. from w and s iceland, norway north of the lofoten islands, and south to the mediterranean. it occurs in the skagerrak and kattegat, including øresund, however, rare in the sound as the presiding species according to jensen & knudsen (1995). occurrence. the boreal and lusitanian regions. habitat. from 15 to 200 m depth on sandy and muddy bottoms. subfossil finds. recorded from the skagen well from the subatlantic. fig. 16. lunatia alderi (forbes 1838). skagen 4, 26.0–26.5 m b.s., lab. no. 351,93. × 20. mguh 25326. fig. 17. lunatia montagui (forbes 1838). skagen 4, 20.0–20.5 m b.s., lab. no. 345,93. × 4.8. mguh 25327. geus bulletin no 3.pmd 28-06-2004, 08:4538 39 lunatia pallida (broderip & sowerby 1829) distribution. from spitsbergen, e and w greenland, around iceland and norway, south to the north sea, skagerrak and the kattegat, including the øresund. occurrence. the arctic, subarctic and boreal regions. habitat. from 10 to 2000 m on clay bottoms – the greatest depths in the most southerly parts of its range (fretter & graham 1981). in greenland waters common in the arctic macoma community (thorson 1944b). subfossil finds. the vendsyssel region during the early/ middle weichselian and late weichselian (the older and younger yoldia sea respectively). natica affinis (gmelin 1790) distribution. from spitsbergen, w and e greenland, around iceland and norway south to the mediterranean. however, within the lusitanian region the species lives in deep water (fretter & graham 1981, p. 345). the species is recorded from danish waters (jensen & knudsen 1995). occurrence. the arctic, subarctic, boreal and lusitanian regions. habitat. from about 4 m depth in high latitudes to well over 2000 m in low ones on sandy, muddy and clay bottoms. as mentioned for other species with a wide geographical distribution this is a ‘tropical submerge’ which is quite common for cold-water animals which in the northern regions inhabit the surface water to occur mainly or exclusively in deeper zones in the southern seas (ekman 1953, p. 112). the species is found in the arctic macoma community (spärck 1937). subfossil finds. recorded from the vendsyssel area during the early/middle weichselian (the older yoldia sea), and the late weichselian (the younger yoldia sea). order heterogastropoda triphora adversa (montagu 1803) distribution. from norway off the lofoten islands and south to spain. it extends into the kattegat, including øresund and the bælt sea, but not recorded from the limfjord. occurrence. the boreal and lusitanian regions. habitat. sublittorally to 100 m under stones, algae or associated with sponges. subfossil finds. the bælt sea, kattegat, limfjord, north sea and vendsyssel areas, holocene. recorded from the bælt sea and the north sea during the eemian. cerithiella metula (lovén 1846) distribution. s and w iceland, norway north of lofoten, and south to the mediterranean. recorded from the danish waters (jensen & knudsen 1995), although rare in the skagerrak and not occurring in the kattegat (fretter & graham 1982, p. 377). occurrence. the boreal and lusitanian regions. habitat. from 40 to 400 m depth on soft bottoms. subfossil finds. none. cerithiopsis barleei jeffreys 1867 distribution. according to fretter & graham (1982), from sw england south to the mediterranean. however, the species is recorded from danish waters, i.e. the øresund area, although as rare (jensen & knudsen 1995), but is not found in the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. sublittorally associated with sponges. subfossil finds. the limfjord region, holocene. geus bulletin no 3.pmd 28-06-2004, 08:4539 40 cerithiopsis tubercularis (montagu 1803) distribution. from norway off the lofoten islands and south to the mediterranean. recorded from the swedish west coast, but not in danish waters (fretter & graham 1982). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone and sublittorally to 100 m. the species is found on sponges. only subfossil finds. the limfjord region, holocene, and the north sea during the eemian. epitonium clathratulum (kanmacher 1797) distribution. from norway and south to the mediterranean. it extends into the kattegat, including the øresund. occurrence. the boreal and lusitanian regions. habitat. from 30 to 100 m deep on sandy–muddy bottoms. subfossil finds. none. epitonium clathrus (linnaeus 1758) distribution. from norway off the lofoten islands and south to the mediterranean. the species extends into the kattegat and øresund (jensen & knudsen 1995), but does not enter the danish fjords (fretter & graham 1982, p. 387). occurrence. the boreal and lusitanian regions. habitat. sublittorally from 5 to 70 m on sandy–muddy bottoms. subfossil finds. the limfjord, north sea and vendsyssel regions, holocene. recorded from the bælt sea and the north sea during the eemian. epitonium trevelyanum (johnston 1841) fig. 18 distribution. from norway off the lofoten islands and south to the mediterranean. the species extends into the kattegat, including the øresund. occurrence. the boreal and lusitanian regions. habitat. from 30 to 200 m depth on sandy–muddy bottoms. subfossil finds. the skagen area, holocene, recorded from the subboreal and the subatlantic. epitonium turtonis (turton 1819) distribution. from norway off the lofoten islands (thorson 1941) and south to the mediterranean. occurring in the kattegat (fretter & graham 1982) and øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from 5 to 20 m deep on sandy–muddy bottoms. subfossil finds. the limfjord and vendsyssel regions, holocene. aclis ascaris (turton 1819) distribution. from norway off lofoten and south to the mediterranean. the species extends into the skagerrak and kattegat, including the øresund. occurrence. the boreal and lusitanian regions. habitat. from 10 to 50 m deep on soft sandy bottoms. subfossil finds. the north sea, holocene. fig. 18. epitonium trevelyanum (johnston 1841). skagen 3, 58.5– 60.0 m b.s., lab. no. 98,93. × 9.6. mguh 25328. geus bulletin no 3.pmd 28-06-2004, 08:4540 41 aclis minor (brown 1827) fig. 19 distribution. from norway off the lofoten islands and south to the mediterranean. the species is recorded from the southern kattegat and øresund. occurrence. the boreal and lusitanian regions. habitat. from 15 to 150 m deep on bottoms of sand, muddy sand or gravel. subfossil finds. the limfjord, north sea and skagen areas, holocene; in the skagen well recorded from the atlantic, subboreal and subatlantic. aclis walleri jeffreys 1867 distribution. from norway off the lofoten islands and south to the mediterranean. recorded from north of skagen (petersen 1888) and the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. according to fretter & graham (1982), at greater depths than the other aclis ssp. – down to 550 m on soft bottoms. subfossil finds. the north sea, holocene. eulima bilineata (alder 1848) distribution. from norway north of lofoten, south to the mediterranean. in the danish waters recorded from the southern kattegat. occurrence. the boreal and lusitanian regions. habitat. from 20 to 250 m deep on soft bottoms associated with ophiuroids. subfossil finds. none. haliella stenostoma (jeffreys 1858) distribution. off west greenland, around iceland, norway off the lofoten islands, and south to the mediterranean. occurrence. the subarctic, boreal and lusitanian regions. habitat. sublittoral from about 70 to 3000 m on soft bottoms. the species has its main occurrence at rather great depths (thorson 1941), but is also recorded from danish waters (jensen & knudsen 1995). subfossil finds. none. polygireulima sinuosa (sacco 1836) fig. 20 distribution. from the kattegat and south to the mediterranean. occurrence. the boreal and lusitanian regions. habitat. sublittoral from 30 to 150 m on soft bottoms. subfossil finds. the skagen area, holocene, recorded from the subatlantic. fig. 19. aclis minor (brown 1827). skagen 3, 55.1–55.3 m b.s., lab. no. 716,93. × 20. mguh 25329. fig. 20. polygireulima sinuosa (sacco 1836). skagen 3, 38.19–38.24 m b.s., core sample k-6. × 9.6. mguh 25330. geus bulletin no 3.pmd 28-06-2004, 08:4541 42 polygireulima monterosatoi (monterosato 1890) distribution. norway south of the lofoten islands, and south to the mediterranean. occurrence. the boreal and lusitanian regions. habitat. from 20 to 120 m deep on sandy muddy or gravelly bottoms. however, as fretter & graham (1982, p. 421) say: “presumably these animals attack echinoderms like their relatives, but which is not known”. subfossil finds. none. vitreolina collensi (sykes 1903) fig. 21 distribution. from the west coast of britain and ireland to the mediterranean. fig. 21. vitreolina collensi (sykes 1903). skagen 3, 70.10–70.30 m b.s., lab. no. 721,93. × 20. mguh 25331. fig. 22. a, b: vitreolina philippii (rayneval & pouzi 1854). skagen 4, 21.0–21.5 m b.s., lab. no. 346,93. × 20. mguh 25332. occurrence. the lusitanian region. habitat. sublittorally to 35–40 m on soft bottoms. only subfossil finds. the skagen area, holocene, recorded from the subboreal and the subatlantic. vitreolina philippii (reyneval & ponzi 1854) fig. 22a, b distribution. from norway off the lofoten islands and south to the mediterranean. according to petersen (1888), very common in danish waters from the skagerrak, the kattegat and the øresund, and the bælt sea, but not recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from the lowest part of the tidal zone to a depth of 200 m on soft bottoms. fretter & graham (1982, p. 422) hold it as perhaps the most common local eulimid and like other eulimids an intermittent parasite of echinoderms. subfossil finds. the limfjord, vendsyssel and skagen areas, holocene, recorded from the subatlantic in the skagen well. occurring in the eemian in the vendsyssel region. graphis albida (kanmacher 1798) fig. 23 distribution. from southern norway south to the mediterranean. the species has a record from the limfjord (petersen 1986a). geus bulletin no 3.pmd 28-06-2004, 08:4542 43 occurrence. the boreal and lusitanian regions. habitat. from low in the tidal zone to 30 m deep on muddy and sandy bottoms. only subfossil finds. the skagen well area, holocene, recorded from the subatlantic. melanella lubrica (monterosato 1891) fig. 24 distribution. from norway south to iberia. the species is recorded from the danish waters south into the øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from 14 to 100 m on soft bottoms of muddy sand and gravel. the species is an intermittent ectoparasite (fretter & graham 1982). subfossil finds. the skagen area, holocene, recorded from the atlantic and subatlantic. melanella alba (da costa 1778) fig. 25 distribution. from norway off the lofoten islands and south to the mediterranean. occurrence. the boreal and lusitanian regions. habitat. from 16 to 135 m deep on muddy sand and gravel bottoms, an ectoparasite of holothurians. only subfossil finds. the skagen well area, holocene, recorded from the subboreal. hemiaclis ventrosa (jeffreys ms fricle 1874) fig. 26 distribution. from west and south iceland, norway off the lofoten islands, and south to the bay of biscay. occurrence. the boreal and lusitanian regions. habitat. from 100 to 300 m deep on soft bottoms. only subfossil finds. the skagen well area, holocene, recorded from the subatlantic. fig. 23. graphis albida (kanmacher 1798). skagen 4, 25.0–25.5 m b.s., lab. no. 350,93. × 40. mguh 25333. fig. 24. melanella lubrica (monterosato 1891). skagen 3, 83.73– 83.83 m b.s., lab. no. 512,93. × 40. mguh 25334. fig. 25. melanella alba (da costa 1778). skagen 3, 74.89–75.00 m b.s., lab. no. 509,93. × 40. mguh 25335. geus bulletin no 3.pmd 28-06-2004, 08:4543 44 pelseneeria stylifera (turton 1826) distribution. from norway off the lofoten islands and south to the mediterranean. few recorded from the skagerrak and kattegat, including øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. the animals are confined to the surface of regular sea urchins (fretter & graham 1982, p. 431). subfossil finds. none. enteroxenos oestergreni bonnevie 1902 distribution. recorded from scandinavia, a single danish record (jensen & knudsen 1995). occurrence. the boreal region. habitat. a parasite in the holothurian stichopus tremulus (jensen & knudsen 1995). subfossil finds. none. order neogastropoda nucella lapillus (linnaeus 1758) distribution. w greenland, around iceland, norway from north of lofoten, and south to the straits of gibraltar. the species reaches into the skagerrak, but it is uncommon in danish waters (fretter & graham 1984). however, it occurs on breakwaters along the north sea and skagerrak coasts. there are a few records from the southern kattegat and øresund (jensen & knudsen 1995). occurrence. the subarctic, boreal and lusitanian regions. habitat. intertidal on rocky shores and extends, albeit rarely, to depths of 30 to 40 m. it avoids very weedy shores and seems to stand only limited reduction of salinity (fretter & graham 1984, p. 445). subfossil finds. the kattegat, limfjord (exposed towards the skagerrak), north sea and vendsyssel regions, holocene. boreotrophon clathratus (linnaeus 1767) distribution. spitsbergen, e and w greenland, around iceland, the faroes and the coast of norway south to the skagerrak and kattegat. occurrence. the arctic, subarctic and boreal regions. habitat. from 8 m to over 1000 m on soft bottoms. subfossil finds. the vendsyssel area, late weichselian (the younger yoldia sea). boreotrophon truncatus (ström 1768) distribution. spitsbergen, e and w greenland, around iceland, norway south to the biscay. the species extends in to danish waters south to the øresund. occurrence. the arctic, subarctic, boreal and lusitanian regions. habitat. from the laminarian zone to depths of about 200 m on bottoms of a stony, gravelly or muddy nature. subfossil finds. none. ocenebra erinacea (linnaeus 1758) distribution. from the southern coasts of britain south to the mediterranean. however, the few records from fig. 26. hemiaclis ventrosa (jeffreys ms fricle 1874). skagen 4, 30.0–30.5 m b.s., lab. no. 355,93. × 20. mguh 25336. geus bulletin no 3.pmd 28-06-2004, 08:4544 45 danish waters might have been introduced with oysters (jensen & knudsen 1995). occurrence. the lusitanian region. habitat. sublittoral to 150 m deep on stony bottoms. subfossil finds. none. trophonopsis barvicensis (johnston 1825) distribution. w and s iceland, norway and south to the british isles, and further south (france) at greater depths. in danish waters from the kattegat, including the øresund, although rare (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. sublittoral at a few metres’ depth at the northern end of its range to 300–400 m at the southern end. subfossil finds. none. buccinum undatum linnaeus 1758 fig. 27 distribution. spitsbergen, w greenland, around iceland, norway and south to the bay of biscay (thorson 1944b). the species extends into the kattegat, limfjord, and the bælt sea with the mecklenburger bucht as the easternmost position. occurrence. the subarctic, boreal and lusitanian regions. habitat. sublittorally to about 1200 m deep usually on soft bottoms. subfossil finds. the kattegat, limfjord, north sea, vendsyssel and skagen areas, holocene, recorded as a fragment from the skagen well from the subatlantic. during the eemian in the kattegat, north sea, and vendsyssel regions. from the vendsyssel area found during the late weichselian (the younger yoldia sea). buccinum cyaneum bruguière 1792 distribution. spitsbergen, w and e greenland around iceland and norway north of lofoten. occurrence. the arctic, subarctic and northern part of the boreal regions. habitat. from 0 to 392 m on all sorts of bottoms – sand, clay, stones and algae (thorson 1944b). only subfossil finds. from the vendsyssel area recorded during the late weichselian (the younger yoldia sea). colus gracilis (da costa 1778) distribution. s and w iceland (empty shells), norway off the lofoten islands and south to portugal. the species extends into the kattegat. occurrence. the boreal and lusitanian regions. habitat. usually from 30 to 800 m deep (less common and deeper in the south). subfossil finds. none. colus jeffreysianus (fischer 1868) distribution. from norway south to the mediterranean. the species extends through the skagerrak to the kattegat, including the northern part of the øresund. occurrence. the boreal and lusitanian regions. habitat. from 30 to 2000 m deep on soft bottoms. subfossil finds. none.fig. 27. buccinum undatum linnaeus 1758. geus collection. limfjord, denmark. height 70 mm. mguh 25337. geus bulletin no 3.pmd 28-06-2004, 08:4545 46 colus sabini (gray 1824) distribution. from w greenland (empty shells) and s and w iceland, northern north sea and extending into the skagerrak (jensen & knudsen 1995). occurrence. the boreal region. (a subarctic extension is not considered, since only empty shells have been found off w greenland and no occurrences on n and e iceland (thorson 1941, 1944b).) habitat. from 35 to 1500 m deep on muddy bottoms. subfossil finds. none. liomesus ovum (turton 1825) distribution. from greenland, the faeroes and the coasts of norway. according to fretter & graham (1984, p. 465), the species is not recorded from the skagerrak or kattegat; however, jensen & knudsen (1995) mentioned this species as occurring in danish waters. furthermore, the species liomesus ovum cannot be found in thorson (1944b), who has buccinum ovum middendorff, which is not the same according to fretter & graham (1962), and the occurrence off the faeroes cannot be confirmed in spärck & thorson (1931). occurrence. the boreal region with only uncertain outposts into the subarctic and lusitanian regions. habitat. from 70 to 400 m deep on soft bottoms. subfossil finds. none. neptunea antiqua (linnaeus 1758) distribution. from southern norway south to the bay of biscay. the species extends into the kattegat, øresund (jensen & knudsen 1995), and the bælt sea as far east as lübecker bucht. the species has also been recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from 15 to 1200 m on all kinds of bottom, mainly soft. subfossil finds. the vendsyssel area, holocene. neptunea despecta (linnaeus 1758) distribution. from spitsbergen, e and w greenland, around iceland and the coasts of norway, south to the seas off denmark according to fretter & graham (1984), but not mentioned by jensen & knudsen (1995) in their annotated check list of recent marine molluscs of danish waters. occurrence. the arctic, subarctic and boreal regions. habitat. from 6 to 1400 m on soft bottoms. only subfossil finds. the vendsyssel region during the late weichselian (the younger yoldia sea). turrisipho moebii (dunker & metzger 1874) distribution. from the coasts of northern and southern norway and the faeroes (sipho sarsi in spärck & thorson 1931). the species extends into the skagerrak. occurrence. the boreal region. habitat. from 200 m to 1000 m deep on soft bottoms. subfossil finds. none. hinia incrassata (ström 1768) distribution. s and w iceland, norway north of lofoten, and south to the mediterranean (thorson 1941). the species extends into the kattegat and øresund, although rare in this place (jensen & knudsen 1995), and it has not been found in the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. rocky coasts in the lower part of the tidal zone. mainly found in the shallow sublittoral, but may extend to about 200 m. subfossil finds. the limfjord and vendsyssel regions, holocene. recorded from the vendsyssel region during the eemian. hinia pygmaea (lamarck 1822) fig. 28 distribution. from norway off the lofoten islands and geus bulletin no 3.pmd 28-06-2004, 08:4546 47 south to the mediterranean. it extends into danish waters such as the skagerrak, limfjord and kattegat and øresund. occurrence. the boreal and lusitanian regions. habitat. from 1 m to about 200 m on sandy bottoms. subfossil finds. the limfjord, north sea, vendsyssel and skagen areas, holocene. recorded from the subatlantic in the skagen well material. found in the bælt sea, kattegat and north sea regions during the eemian. hinia reticulata (linnaeus 1758) fig. 29 distribution. from norway off lofoten and south to the mediterranean. in danish waters within the limfjord and kattegat with fjords, the øresund and the bælt sea. occurrence. the boreal and lusitanian regions. habitat. from the tidal zone to about 15 m deep on soft bottoms. subfossil finds. the bælt sea, baltic, kattegat, limfjord, north sea, vendsyssel and skagen regions, holocene. in the skagen well material recorded from the subatlantic. from the bælt sea, baltic, kattegat, north sea and vendsyssel regions recorded from the eemian. troschelia bernicensis (king 1846) distribution. from norway north of lofoten and south to the west coast of scotland and the dogger bank. recorded from danish waters by jensen & knudsen (1995). occurrence. the boreal and lusitanian (northern part) regions. habitat. lives on the continental shelves and upper slopes, between 90 and 2700 m (poppe & goto 1991). subfossil finds. none. cytharella coarctata (forbes 1840) distribution. from norway off the lofoten islands (thorson 1941: mangelia costata) and south to the mediterranean. the species is recorded from the skagerrak and kattegat where it extends into the øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone to 250 m deep on sandy bottoms. subfossil finds. the vendsyssel area, holocene. during the eemian in the north sea region. oenopota incisula (verrill 1882) distribution. the species is known from the boreal zone of the east coast of north america, and is comfig. 28. hinia pygmaea (lamarck 1822). skagen 4, 12.0–12.5 m b.s., lab. no. 337,93. × 9.6. mguh 25338. fig. 29. hinia reticulata (linnaeus 1758). skagen 3, 55.10–55.30 m b.s., lab. no. 716,93. × 4.8. mguh 25339. geus bulletin no 3.pmd 28-06-2004, 08:4547 48 mon off west greenland (posselt & jensen 1898), but it is not recorded from iceland or the coasts of the north-east atlantic (thorson 1941). occurrence. the arctic, subarctic, and in north america into the boreal regions. habitat. in the canadian north-east region the species has been collected from 6–7 to 140 m deep on clay (macpherson 1971). only subfossil finds. from the vendsyssel region recorded during the eemian and early/middle weichselian (the older yoldia clay). oenopota trevelliana (turton 1834) distribution. spitsbergen, e and w greenland, around iceland (thorson 1941: bela trevelliana (turton)), norway from north of lofoten, and south to the british isles. the species extends south to the kattegat, including øresund. occurrence. the arctic, subarctic, boreal and lusitanian (northern part) regions. habitat. sublittorally from 25 m to depths over 300 m on fine sand. subfossil finds. the vendsyssel area during the eemian. oenopota turricola (montagu 1803) fig. 30 distribution. greenland, iceland, faeroes, norway south to scotland (spärck & thorson 1931). the species extends into the limfjord and kattegat (fretter & graham 1984) and the øresund (jensen & knudsen 1995). occurrence. the arctic, subarctic and boreal regions. habitat. sublittoral from 20 to 200 m on sandy bottoms. subfossil finds. the limfjord, vendsyssel and skagen areas, holocene. from the skagen well recorded from the subatlantic. found in the vendsyssel area from the late weichselian (the younger yoldia sea). oenopota violacea (mighels & adams 1842) distribution. e and w greenland, spitsbergen, around iceland and south along the coast of norway, but not reaching the british isles (thorson 1941). occurrence. the arctic, subarctic and boreal regions. habitat. from 1 m to 761 m on mud and stones. only subfossil finds. the vendsyssel area during the eemian. bela exarata g.o. sars 1878 distribution. e and w greenland, spitsbergen, around iceland, the faeroes, and norway from north of lofoten and west of ireland. the species is also recorded west of iceland, where it has been found at depths down to 2214 m (thorson 1941). occurrence. the arctic, subarctic, boreal regions with lusitanian outposts. habitat. in the northern part of its range it belongs to the shallow-water species (norway and e greenland from 3 m) (thorson 1941). only subfossil finds. from the eemian in the vendsyssel area. mangelia attenuata (montagu 1803) distribution. from norway off the lofoten islands and fig. 30. oenopota turricola (montagu 1803). skagen 4, 21.0– 21.5 m b.s., lab. no. 346,93. × 9.6. mguh 25340. geus bulletin no 3.pmd 28-06-2004, 08:4548 49 south to the mediterranean. the species extends into the skagerrak and kattegat, including the øresund. occurrence. the boreal and lusitanian regions. habitat. from 5 to 150 m deep on sand or clay bottoms. subfossil finds. none. mangelia brachystoma (philippi 1844) fig. 31 distribution. from norway off the lofoten islands and south to the mediterranean. the species extends into the skagerrak and kattegat, including the øresund. occurrence. the boreal and lusitanian regions. habitat. sublittorally from 4 m to 60 m deep on bottoms of sand and sandy mud. subfossil finds. the skagen area, holocene, recorded from the subatlantic in the skagen well cores. during the eemian found in the vendsyssel region. mangelia nebula (montagu 1803) distribution. norway off the lofoten islands and south to the mediterranean. the species is recorded a few times from the kattegat and extends into the øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from 10 to 50 m deep on sandy bottoms. subfossil finds. none. raphitoma purpurea (montagu 1803) distribution. from northern norway off the lofoten islands south into the mediterranean. occurrence. the boreal and lusitanian regions. habitat. from 10 to 100 m deep on sandy, gravelly and stony bottoms. only subfossil finds. the limfjord region, holocene. raphitoma asperrima (brown 1827) distribution. from the coast of norway south to the mediterranean, extending into the kattegat, including the øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from 20 to 100 m deep on sandy bottoms. subfossil finds. none. raphitoma leufroyi (michaud 1821) distribution. from the coast of norway off the lofoten islands and south to the mediterranean, extending into the skagerrak and with a few records from the northern kattegat (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone to 150 m deep on sandy, shelly and stony bottoms. subfossil finds. none. raphitoma linearis (montagu 1803) distribution. sw and nw iceland, norway from north of lofoten and south to the mediterranean. the species extends into the skagerrak and kattegat and øresund, although rare (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. fig. 31. mangelia brachystoma (philippi 1844). skagen 3, 58.04– 58.25 m b.s., lab. no. 717,93. × 9.6. mguh 25341. geus bulletin no 3.pmd 28-06-2004, 08:4549 50 habitat. from 10 to 200 m deep on sandy, shelly and stony bottoms. subfossil finds. the limfjord and vendsyssel area, holocene. during the eemian found in the vendsyssel area (the turritella terebra zone in the skærumhede sequence). taranis borealis bouchet & warén 1980 distribution. so far as known, this species is confined to waters off western norway and the skagerrak (fretter & graham 1984, p. 548). occurrence. the boreal region. habitat. from 150 m to nearly 2000 m deep on soft bottoms. subfossil finds. none. taranis moerchi (malm 1861) distribution. from norway north of lofoten south to the mediterranean, extending into the kattegat. occurrence. the boreal and lusitanian regions. habitat. from 80 m deep near the northern limits of its range to over 2000 m elsewhere on soft bottoms. subfossil finds. none. admete viridula (fabricius 1780) distribution. spitsbergen, e and w greenland, around iceland, empty shells from off the faeroes, norway from north of the lofoten islands, and south to the northern borders of the north sea. included in the recent danish fauna (jensen & knudsen 1995). occurrence. the arctic, subarctic and boreal regions. habitat. from a few metres to depths of 1000 m, the greatest depths in the south of its range (fretter & graham 1984, p. 507) on soft bottoms. subfossil finds. recorded from the early/middle weichselian (the portlandia arctica zone in the skærumhede sequence) in the vendsyssel region. subclass heterobranchia order heterostropha omalogyra atomus (philippi 1841) distribution. w greenland, around iceland and norway, south to the mediterranean. known from only a few places in danish waters. occurrence. the subarctic, boreal and lusitanian regions. habitat. from the lower part of the shore to a depth of 20 m, occurring on seaweeds. only subfossil finds. the limfjord region, holocene. brachystomia carozzai van aartsen 1987 distribution. from the southern part of norway (spärck & thorson 1931) and south to the mediterranean. the species extends into the kattegat and limfjord. as commented on by fretter et al. (1986, p. 605) and jensen & knudsen (1995), the determination of these small snails living ectoparasitically on other marine organisms is still in progress, so the actual situation for the record of subfossil material should be taken with great precaution. occurrence. the boreal and lusitanian regions. habitat. from the tidal zone, where it occurs in crevices, to depths of about 70 m. subfossil finds. none. brachystomia eulimoides hanley 1844 distribution. from norway off the lofoten islands and south to the mediterranean. recorded from the limfjord, according to jensen & knudsen (1995) the only danish record, following fretter et al. (1986, p. 602). occurrence. the boreal and lusitanian regions. habitat. most frequently found on living animals of pecten, chlamys, oysters and turritella to depths of 120 m. subfossil finds. the kattegat, limfjord, north sea and geus bulletin no 3.pmd 28-06-2004, 08:4550 51 vendsyssel regions, holocene. from the north sea region during the eemian. odostomia scalaris macgillivray 1843 distribution. from southern norway south to the mediterranean. the species extends into the limfjord, through the kattegat, including the øresund, and the bælt sea into the kiel bay (fretter et al. 1986, p. 600). occurrence. the boreal and lusitanian regions. habitat. associated primarily with banks of mytilus edulis, but also recorded from other hosts (fretter et al. 1986, p. 600). subfossil finds. the limfjord and vendsyssel regions, holocene. from the bælt sea and north sea during the eemian. chrysallida decussata (montagu 1803) fig. 32 distribution. mainly southern distribution, with the shetlands as the northernmost post, but recorded from the øresund (jensen & knudsen 1995) and there are older records from east of scotland (fretter et al. 1986). occurrence. the boreal and lusitanian regions. habitat. from 14 to 40 m deep on sandy and shelly bottoms. subfossil finds. the limfjord and skagen areas, holocene, in the skagen well recorded from the subatlantic. chrysallida eximia (jeffreys 1849) distribution. sw and nw iceland, norway north of lofoten, and south to western scotland. there is no record from danish waters. occurrence. the boreal and lusitanian (northernmost) region. habitat. from 20 m to more than 1000 m, the greater depths in the southern part of its range, on soft gravelly bottoms. only subfossil finds. the limfjord region, holocene. from the vendsyssel area during the eemian. chrysallida indistincta (montagu 1808) distribution. from norway off the lofoten islands (thorson 1941) and south to the mediterranean. it extends into the kattegat and øresund (jensen & knudsen 1995), but is not recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from 7 to 100 m deep on sandy bottoms. subfossil finds. the limfjord, north sea and vendsyssel areas, holocene. recorded from the north sea during the eemian. chrysallida obtusa (brown 1827) distribution. from norway off the lofoten islands and south to the mediterranean. the species extends into the limfjord and through the kattegat into the øresund (fretter et al. 1986, p. 562). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone in rock pools to 90 m deep in stony places, associated with oysters (fretter et al. 1986, p. 562). subfossil finds. the limfjord and vendsyssel regions, holocene. from the bælt sea and north sea regions during the eemian. fig. 32. chrysallida decussata (montagu 1803). skagen 4, 15.0– 15.5 m b.s., lab. no. 340,93. × 20. mguh 25342. geus bulletin no 3.pmd 28-06-2004, 08:4551 52 chrysallida spiralis (montagu 1803) distribution. from norway north of lofoten and south to the mediterranean. according to fretter et al. (1986, p. 574), the species extends into the kattegat and øresund, but it is absent from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone to about 120 m deep, often abundant in the neighbourhood of tubes of sedentary polychaetes (fretter et al. 1986). subfossil finds. the kattegat, limfjord, north sea and vendsyssel regions, holocene. the bælt sea, kattegat, and north sea regions during the eemian. ebala nitidissima (montagu 1803) distribution. from south of norway to the mediterranean. recorded from the kattegat region with fjords and the øresund and the bælt sea regions as far as kiel bay (fretter et al. 1986, p. 630), but absent from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from 5 to 50 m deep on muddy sand or shelly bottoms. subfossil finds. the limfjord and vendsyssel regions, holocene. from the bælt sea and north sea areas during the eemian. eulimella laevis (brown 1827) distribution. from norway off the lofoten islands and south to the mediterranean. it has not been recorded from danish waters except the øresund region (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from 20 to 400 m deep on muddy sand. subfossil finds. the limfjord, north sea and vendsyssel regions, holocene. eulimella scillae (scacchi 1835) fig. 33 distribution. from norway off the lofoten islands, but empty shells only off sw iceland (thorson 1941), and south to the mediterranean. it extends into the kattegat along the swedish west coast (fretter et al. 1986), but occurs in the øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from 20 to 400 m deep on muddy sand or sand. subfossil finds. the limfjord and skagen areas, holocene, recorded in the skagen well from the atlantic and subboreal. from the vendsyssel area found during the eemian. ondina divisa (j. adams 1797) distribution. from s and w iceland, northern norway (w finmarken) (thorson 1941) and south to the biscay. the species extends through the kattegat to the øresund (fretter et al. 1986, p. 582). occurrence. the boreal and lusitanian regions. habitat. from 18 to 200 m deep on sandy and gravelly mud. subfossil finds. the limfjord region, holocene. from the vendsyssel area found during the eemian. fig. 33. eulimella scillae (scacchi 1835). skagen 3, 82.34–82.50 m b.s., lab. no. 729,93. × 9.6. mguh 25343. geus bulletin no 3.pmd 28-06-2004, 08:4552 53 ondina obliqua (alder 1884) distribution. according to fretter et al. (1986, p. 586) from southern scandinavia to biscay. however, spärck & thorson (1931) only mentioned scotland. furthermore, only western localities have been reported from the british isles (fretter et al. 1986), and it is doubtful whether the danish records actually refer to this species. therefore, the species is here considered to be lusitanian and should not be taken as present in the recent danish fauna, although recorded by jensen & knudsen (1995). habitat. from 30 to 60 m deep in gravelly or sandy mud. subfossil finds. none. ondina diaphana (jeffreys 1848) distribution. according to spärck & thorson (1931), present from southern norway and south to the mediterranean. in danish waters the kattegat and the øresund. occurrence. the boreal and lusitanian regions. habitat. from 20 to 90 m deep on soft bottoms. subfossil finds. the limfjord and north sea regions, holocene. liostomia clavula (lovén 1846) distribution. from southern norway south to the mediterranean. extends through the kattegat to the øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from 30 to 90 m deep on soft bottoms associated with pennatula (fretter et al. 1986, p. 590). subfossil finds. none. liostomia afzelii warén 1991 this species, newly established, will not be considered further. odostomia acuta jeffreys 1848 distribution. from norway north of lofoten and south to the mediterranean. the species is found in the skagerrak, kattegat and øresund (fretter et al. 1986, p. 613). occurrence. the boreal and lusitanian regions. habitat. from 20 to 30 m deep. perhaps associated with bryozoans. subfossil finds. the limfjord region, holocene. odostomia conoidea winckworth 1932 fig. 34 distribution. from norway off the lofoten islands and south to the mediterranean. recorded from the skagerrak (fretter et al. 1986) and the øresund (jensen & knudsen 1995), but not from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from 10 to 150 m deep, usually in association with the starfish astropecten irregularis (fretter et al. 1986, p. 617). subfossil finds. the bælt sea, limfjord, north sea, vendsyssel and skagen regions, holocene. in the skagen area recorded from the subatlantic. fig. 34. odostomia conoidea winckworth 1932. skagen 3, 48.90– 49.10 m b.s., lab. no. 714,93. × 40. mguh 25344. geus bulletin no 3.pmd 28-06-2004, 08:4553 54 odostomia turrita hanley 1844 distribution. from norway north of lofoten and south to the mediterranean. the species extends through the kattegat to the øresund (fretter et al. 1986, p. 612), but is not recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone to 100 m deep on weed and clay bottoms. subfossil finds. the limfjord and vendsyssel regions, holocene. recorded from the vendsyssel area during the eemian. odostomia albella lovén 1846 distribution. empty shells recorded from spitsbergen, sw and nw iceland, norway north of lofoten and south to the mediterranean. the species occurs in the skagerrak (fretter et al. 1986), the øresund area (jensen & knudsen 1995), and the limfjord region (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone to depths of about 100 m on boulders, associated with growth of pomatoceros (fretter et al. 1986). subfossil finds. the limfjord, north sea and vendsyssel regions, holocene. from the north sea region during the eemian. odostomia plicata (montagu 1803) distribution. from the southern part of scandinavia (not southern norway (spärck & thorson 1931)) and south to the mediterranean (fretter et al. 1986, p. 610). the species extends into the kattegat, including the øresund (jensen & knudsen 1995), but is not recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. in the tidal zone associated with pomatoceros triqueter (fretter et al. 1986). subfossil finds. the limfjord and vendsyssel regions, holocene. odostomia umbilicaris (malm 1863) fig. 35 distribution. from southern norway (spärck & thorson 1931) to the british isles. the species extends to the swedish west coast but not further into the kattegat (fretter et al. 1986, p. 620). occurrence. the boreal and lusitanian (northern part) regions. habitat. from 20 to 275 m deep, found on the bivalve mytilus adriaticus (fretter et al. 1986). subfossil finds. the skagen area, holocene, recorded from the atlantic and subatlantic. turbonilla crenata (brown 1827) distribution. from norway off the lofoten islands (thorson 1941) and south to the mediterranean. the species extends into the kattegat and øresund (fretter et al. 1986), but is absent from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from 15 to 350 m deep on fine sand. subfossil finds. the limfjord and north sea regions, holocene. recorded from the bælt sea and north sea during the eemian. fig. 35. odostomia umbilicaris (malm 1863). skagen 3, 82.34–82.50 m b.s., lab. no. 725,93. × 20. mguh 25345. geus bulletin no 3.pmd 28-06-2004, 08:4554 55 turbonilla delicata monterosato 1884 fig. 36 distribution. from the south-western part of the british isles to the mediterranean (fretter et al. 1986, p. 636). however, recorded from the northern kattegat and northern øresund although, rare (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. on soft bottoms, but at uncertain depths (fretter et al. 1986, p. 636). subfossil finds. the limfjord, north sea and skagen regions, holocene. from the skagen area recorded from the subatlantic. turbonilla lactea (linnaeus 1758) distribution. from northern norway and south to the mediterranean. present although uncommon in danish waters (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone to depths of about 80 m, occurring under stones in silty places in the tidal zone and on soft, muddy and sandy bottoms sublittorally (fretter et al. 1986, p. 634). subfossil finds. the limfjord, north sea and vendsyssel regions, holocene. recorded from the bælt sea, kattegat, and north sea regions during the eemian. subclass opisthobranchia order bullomorpha acteon tornatilis (linnaeus 1758) distribution. w and s iceland, norway off the lofoten islands and south to the mediterranean (lemche 1938). the species extends into the kattegat, including the øresund (petersen 1888, p. 78), but it is not recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone down to 250 m in sand, usually in sheltered areas (poppe & goto 1991, p. 192). subfossil finds. the limfjord, north sea and vendsyssel regions, holocene. recorded from the north sea and vendsyssel areas during the eemian. haminoea navicula (da costa 1778) distribution. from the british isles south to the mediterranean. occurrence. the lusitanian region. habitat. lives in the zostera beds in sheltered areas (poppe & goto 1991, p. 196). only subfossil finds. the bælt sea, kattegat, and north sea regions during the eemian. cylichna cylindracea (pennant 1777) distribution. w and s iceland, norway off the lofoten islands and south to the mediterranean. the species extends into the limfjord and kattegat, including øresund (petersen 1888, p. 78; jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from 40 to 200 m deep, in sand. according to lemche (1938) associated with the boreal amphiura filiformis community in deeper water south of iceland, corresponding to its occurrence in danish waters. subfossil finds. the limfjord and vendsyssel regions, holocene. fig. 36. turbonilla delicata (monterosato 1874). skagen 4, 20.0– 20.5 m b.s., lab. no. 345,93. × 20. mguh 25346. geus bulletin no 3.pmd 28-06-2004, 08:4555 56 cylichna alba (brown 1827) fig. 37 distribution. w and e greenland, around iceland, norway north of lofoten and south to the bay of biscay at greater depth (lemche 1938, p. 9). the species extends into the north sea and skagerrak (lemche 1928, p. 4). occurrence. the arctic, subarctic, boreal and lusitanian regions. habitat. according to lemche (1928), this species is also widely distributed in depth, being found in low water to depths down to 2700 m, on clay bottom (faeroes). subfossil finds. the limfjord, north sea and skagen areas, holocene. in the skagen well recorded from the subatlantic. also found in the vendsyssel area from the early/middle and late weichselian (the older and younger yoldia sea respectively). cylichna occulta (mighels 1841) distribution. e and w greenland, n and e iceland, norway north of lofoten (lemche 1938). occurrence. the arctic, subarctic and boreal (northernmost part) regions. will be referred as an arctic and subarctic species. habitat. from 10 to 388 m deep (iceland), especially found within the macoma calcarea community, and might also occur within the yoldia hyperborea community (lemche 1938). only subfossil finds. recorded from the kattegat region during the early/middle weichselian and the vendsyssel region during the early/middle and late weichselian (the older and younger yoldia sea respectively). scaphander lignarius (linnaeus 1758) distribution. from s and w iceland, the faeroes, norway off the lofoten islands and south to the mediterranean. occurrence. the boreal and lusitanian regions. habitat. from 60 to 700 m deep. the species is associated with the boreal spisula elliptica community on sandy plateaus south and west of iceland (lemche 1938, p. 7). subfossil finds. none. scaphander punctostriatus (mighels & adams 1841) distribution. e and w greenland, s and w iceland, the faeroes, norway north of lofoten and south to the mediterranean. occurrence. the arctic, subarctic, boreal and lusitanian regions. habitat. recorded from depths between 10 and 3000 m, this probably having some relation to its wide horizontal distribution. around the faeroes the species may be expected to be found on the great, sandy plateaus (lemche 1928, p. 4). subfossil finds. none. philine aperta (linnaeus 1767) distribution. from the faeroes, western norway off lofoten, and south to the mediterranean (lemche 1928). the species extends through kattegat and øresund, into the bælt sea as far as kieler bugt (petersen 1888, p. 83), and it is also recorded from the limfjord (petersen 1986a). fig. 37. cylichna alba (brown 1827). skagen 3, 44.88–45.00 m b.s., lab. no. 499,93. × 9.6. mguh 25347. geus bulletin no 3.pmd 28-06-2004, 08:4556 57 occurrence. the boreal and lusitanian regions. habitat. the species prefers shallow water but has been found at depths down to 100 m off the faeroes (lemche 1928) on sandy bottoms. in danish waters recorded from 10 to 30 m, also on sandy bottoms (petersen 1888). subfossil finds. the limfjord and vendsyssel regions, holocene. recorded from the bælt sea and the north sea during the eemian. philine angulata jeffreys 1867 this species is mentioned by jensen & knudsen (1995), but only on the basis of one broken shell found in the zoological museum in copenhagen; difficult to identify; occurrence uncertain. so in the light of “the difficult problem of the relation between punctata and angulata”, as treated by lemche (1948, p. 67), this find will be omitted, also that no subfossil species have been found. philine catena (montagu 1803) fig. 38 distribution. from norway off the lofoten islands and south to the mediterranean. occurrence. the boreal and lusitanian regions. habitat. from low water-mark to 76 m (forbes & hanley 1853) subfossil finds. the skagen region during the eemian. philine denticulata (adams 1800) distribution. from norway south to the mediterranean. occurrence. the boreal and lusitanian regions. subfossil finds. none. philine punctata (adams 1800) distribution. the faeroes, southern part of the west coast of norway, and south to the mediterranean. lemche (1928) also mentioned occurrences from greenland, which, however, was not repeated in later papers (lemche 1941a, b). jensen & knudsen (1995) report occurrences from the øresund, although rare, and petersen (1888) has a single find from the bælt sea and petersen (1986a) from the limfjord. occurrence. the boreal and lusitanian regions. habitat. at the faeroes the species is recorded from depths down to 240 m (lemche 1928). subfossil finds. the limfjord and vendsyssel regions, holocene. philine quadrata (wood 1839) distribution. w greenland, around iceland, norway north of lofoten, and south to the mediterranean. recorded from the øresund, but rare (jensen & knudsen 1995). occurrence. the subarctic, boreal and lusitanian regions. habitat. the vertical range of the species is about 35 m down to 2150 m (lemche 1938). subfossil finds. none. philine scabra (müller 1776) distribution. s and w iceland, the faeroes, norway north of lofoten, and south to the mediterranean. the species extends into the kattegat, including the øresund (petersen 1888, p. 84). occurrence. the boreal and lusitanian regions.fig. 38. philine cf. catena (montagu 1803). skagen 3, 180.77– 180.89 m b.s., lab. no. 798,93. × 40. mguh 25348. geus bulletin no 3.pmd 28-06-2004, 08:4557 58 habitat. off the coasts of w and s iceland from 20– 216 m on sandy bottom (lemche 1938, p. 11); however, in danish waters (kattegat) from 20–40 m on mixed bottom (petersen 1888, p. 84). subfossil finds. none. philinoglossa helgolandica hertling 1932 distribution. from the north sea – helgoland – and south to the mediterranean, the species might occur in danish waters (jensen & knudsen 1995, p. 29). occurrence. the boreal and lusitanian regions. habitat. probably in shell gravel (jensen & knudsen 1995). subfossil finds. none. order anaspidea diaphana minuta brown 1827 distribution. e and w greenland, around iceland, the faeroes, norway north of lofoten, and south to the mediterranean. the species extends into the kattegat and øresund (petersen 1888; jensen & knudsen 1995). occurrence. the arctic, subarctic, boreal and lusitanian regions. habitat. in general from the tidal zone to 770 m, but is said to prefer sandy clay at depths of 20–40 m (lemche 1928). this is very much the same as for the kattegat, where petersen (1888) says that the species prefers mixed bottom at a depth of about 19–38 m. subfossil finds. the limfjord and vendsyssel regions, holocene. retusa obtusa (montagu 1803) distribution. e and w greenland, around iceland, the faeroes, norway north of lofoten, and south to the british isles (shetland and scotland) (lemche 1928). the species is found in the limfjord and is common in the fjords and bays bordering the kattegat, including the øresund, and extends into the bælt sea and the western part of the baltic (petersen 1888, p. 81). occurrence. the arctic, subarctic and boreal regions. habitat. from the intertidal zone down to 300 m deep in mud or fine sand. in danish waters petersen (1888) points to the observed differences in depth, i.e. in the kattegat region around 20 m while 60 m deep in the baltic. the species is connected with the arctic macoma community (lemche 1941a, b). subfossil finds. the bælt sea, kattegat, limfjord, north sea and vendsyssel regions, holocene. also recorded from the vendsyssel area during the early/middle weichselian and the late weichselian (the older yoldia sea and the younger yoldia sea respectively). retusa truncatula (bruguière 1792) fig. 39 distribution. the faeroes, norway north of lofoten, and south to the mediterranean (lemche 1928, 1938). the species extends through the kattegat, including the øresund, and into the bælt sea, and it is also recorded from the limfjord (petersen 1888, p. 80). occurrence. the boreal and lusitanian regions. habitat. in general the species lives from the tidal zone down to 200 m (poppe & goto 1991). however, in danish waters, according to petersen (1888), it lives in shallow water down to only about 20 m deep on sandy bottoms with zostera. subfossil finds. the bælt sea, baltic, kattegat, limfjord, north sea, vendsyssel and skagen regions, holocene. fig. 39. retusa truncatula (bruguière 1792). skagen 3, 67.34–67.39 m b.s., core sample k-25. × 9.6. mguh 25349. geus bulletin no 3.pmd 28-06-2004, 08:4558 59 recorded from the skagen area from the subboreal and subatlantic. from the bælt sea and the north sea recorded during the eemian. retusa umbilicata (montagu 1803) fig. 40 distribution. from norway north of lofoten (lemche 1928) and south to the mediterranean (poppe & goto 1991). the species extends into the kattegat and øresund (petersen 1888; jensen & knudsen 1995), but is not recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from depths of about 20 to 30 m on mixed bottoms (petersen 1888). subfossil finds. the limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subboreal and subatlantic. from the bælt sea, north sea, and vendsyssel regions found during the eemian. rhizorus acuminatus (bruguière 1792) distribution. from western and southern norway south to the mediterranean, in danish waters from the southern kattegat. occurrence. the boreal and lusitanian regions. habitat. from the tidal zone to 800 m deep. subfossil finds. none. akera bullata o.f. müller 1776 distribution. the faeroes, norway north of lofoten, and south to the mediterranean (lemche 1928). the species extends into the limfjord, the kattegat, including the øresund, and the bælt sea as far as the kieler bugt (petersen 1888). occurrence. the boreal and lusitanian regions. habitat. in sheltered bays down to 370 m deep (poppe & goto 1991). common in shallow water with zostera (petersen 1888). subfossil finds. the bælt sea, kattegat, limfjord and vendsyssel regions, holocene. in the bælt sea and kattegat regions recorded from the eemian. order thecosomata limacina retroversa (fleming 1823) fig. 41 distribution. e and w greenland, around iceland, norway north of lofoten, and south to ireland (lemche 1938). it is common in the north sea and skagerrak, penetrating into the kattegat, occasionally even into the bælt sea (kramp 1961). occurrence. the arctic, subarctic, boreal and lusitanian (northernmost) regions. habitat. pelagic. subfossil finds. recorded from the vendsyssel and skagen regions during the eemian and from the vendsyssel region during the late weichselian (the younger yoldia sea). fig. 40. retusa umbilicata (montagu 1803). skagen 3, 70.10–70.30 m b.s., lab. no. 721,95. × 20. mguh 25350. fig. 41. limacina retroversa (fleming 1823). skagen 3, 180.57– 180.70 m b.s., lab. no. 797,93. × 20. mguh 25351. geus bulletin no 3.pmd 28-06-2004, 08:4559 60 order gymnosomata clione limacina (phipps 1774) fig. 42 distribution. e and w greenland, around iceland, the faeroes, norway north of lofoten (lemche 1938), and south to the west coast of england. common in the northern part of the north sea and in the skagerrak, occasionally penetrating into the kattegat (kramp 1961). rare occurrences in the øresund (jensen & knudsen 1995). occurrence. the arctic, subarctic, boreal and lusitanian (northern part) regions. habitat. pelagic. subfossil finds. recorded (imprint) from the skagen well during the late weichselian (the younger yoldia sea). subclass pulmonata order basommatophora ovatella myosotis (draparnaud 1801) distribution. from scandinavia along the coast of western europe, south to the mediterranean (steenberg 1911, p. 204). in danish waters recorded from the bælt sea and the baltic (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. lives on sea wrack along the coasts (steenberg 1911). subfossil finds. none. lymnaea (radix) peregra (müller 1774) f. baltica linné distribution. lymnaea peregra is found all over europe: iceland, the faeroes, norway north of lofoten, and south to the mediterranean (mandahl-barth 1938). the species occurs in the baltic and southern øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. lymnaea peregra f. baltica linné and l. p. f. succinea nilsson are brackish water forms tolerating up to 8‰ salt (mandahl-barth 1949, p. 74). subfossil finds. the bælt sea and baltic regions, holocene. class scaphopoda order siphonodentalioida cadulus subfusiforme (m. sars 1865) fig. 43 distribution. western iceland, the faeroes, norway north of lofoten, and south to the mediterranean (knudsen 1949b). in danish waters taken in the skagerrak (muus 1959). occurrence. the boreal and lusitanian regions. habitat. from 80 to 1300 m deep on mud bottoms. in danish waters at a depth of 230 m on clay bottom (muus 1959). subfossil finds. recorded from the skagen well during the eemian. fig. 42. clione limacina (phipps 1774). skagen 3, 115.07–115.15 m b.s., lab. no. 749,93. × 20. mguh 25352. fig. 43. cadulus subfusiforme (m. sars 1865). skagen 3, 180.77– 180.89 m b.s., lab. no. 798,93. × 20. mguh 25353. geus bulletin no 3.pmd 28-06-2004, 08:4560 61 siphonodentalium lobatum (sowerby 1860) fig. 44 distribution. e and w greenland, n and e iceland (knudsen 1949b), the faeroes, norway north of lofoten, and south to portugal. the species might be found in norske rende. in norway often found in glacial deposits (muus 1959). occurrence. the main areas are the arctic, subarctic and boreal regions, but the species extends into the lusitanian region. habitat. from 36 to 3116 m on mud (knudsen 1949b). only subfossil finds. recorded from the skagen well in the late weichselian (the younger yoldia sea) and from the eemian. entalina tetragona (brocchi 1814) fig. 45 distribution. from northern norway south to the bay of biscay and the mediterranean. from danish waters in the north sea and skagerrak (muus 1959). occurrence. the boreal and lusitanian regions. habitat. it is a deep-water species preferring mud bottoms (poppe & goto 1993). in the danish waters known from 100 to 480 m on mixed bottom (muus 1959) connected with the amphilipis norvegica/pecten vitreus community at depths of 250–700 m. subfossil finds. recorded from the skagen well during the eemian. order dentalioida antalis agile g.o. sars 1878 distribution. s and w iceland, norway off the lofoten islands, and south to the mediterranean. in the danish waters the species extends from the north sea into the skagerrak and kattegat. occurrence. the boreal and lusitanian regions. habitat. from 55 m down to 1250 m. in scandinavian waters rarely at depths less than 70 m (muus 1959). subfossil finds. none. antalis entalis (linnaeus 1758) distribution. w greenland, iceland, the faeroes, norway north of lofoten, and south to the mediterranean (knudsen 1949b). common in the danish waters, extending into the kattegat (muus 1959) although rare in the øresund (jensen & knudsen 1995). occurrence. the subarctic, boreal and lusitanian regions. habitat. from 20 to 400 m in the kattegat region, and in the north sea between 30 and 200 m (muus 1959). however, the vertical range in general goes from 6– 3200 m (knudsen 1949b). subfossil finds. the skagen well during the eemian. fig. 44. siphonodentalium lobatum (sowerby 1860). skagen 3, 114.64–? m b.s., core sample k-57. × 9.6. mguh 25354. fig. 45. entalina tetragona (brocchi 1814). skagen 3, 183.77– 184.00 m b.s., lab. no. 799,93. × 9.6. mguh 25355. geus bulletin no 3.pmd 28-06-2004, 08:4561 62 dentalium vulgare da costa 1778 fig. 46 distribution. from the british isles and south to the mediterranean. might be found in the southern north sea. occurrence. mainly the lusitanian region. habitat. sublittorally from 1 m and down to 50 m on mud and sandy bottoms. only subfossil finds. recorded from the skagen well during the eemian. class bivalvia subclass palaeotaxodonta order nuculoida nucula nitidosa winckworth 1930 fig. 47 distribution. from norway off the lofoten islands and south to the mediterranean (madsen 1949). the species extends from the more shallow part of the north sea and skagerrak into the kattegat, including the øresund. very common in the western part of the limfjord (jensen & spärck 1934, p. 23). occurrence. the boreal and lusitanian regions. habitat. in general from 7 to 250 m deep on fine sand or sand/mud bottoms (poppe & goto 1993). however, according to jensen & spärck (1934) the species is often found at depths of 6–10 m in the limfjord and 10–30 m in the kattegat region. subfossil finds. the limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subatlantic. during the eemian found in the bælt sea, baltic and north sea regions. nucula nucleus (linnaeus 1767) fig. 48 distribution. from norway off the lofoten islands, the faeroes, and south to the mediterranean (madsen 1949). posselt & jensen (1898) have but few records from west greenland. the species extends from the north sea into the kattegat, including the øresund (jensen & spärck 1934), and is recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. lives from the tidal zone down to 150 m on gravel and mud bottoms. in danish waters common between 20 and 100 m. subfossil finds. the limfjord, north sea, vendsyssel fig. 46. dentalium vulgare da costa 1778. skagen 3, 181.17– 181.21 m b.s., core sample k-99. × 9.6. mguh 25356. fig. 47. nucula nitidosa winckworth 1930. skagen 4, 21.0–21.5 m b.s., lab. no. 346,93. × 9.6. right valve. mguh 25357. fig. 48. nucula nucleus (linnaeus 1767). skagen 4, 9.0–9.5 m b.s., lab. no. 334,93. × 4.8. right valve. mguh 25358. geus bulletin no 3.pmd 28-06-2004, 08:4562 63 and skagen regions, holocene. recorded in the skagen well from the subatlantic. in the eemian recorded from the baltic and vendsyssel regions. nucula sulcata (bronn 1831) distribution. norway off the lofoten islands and south to the mediterranean. in danish waters common in the deeper parts of the kattegat and øresund (jensen & knudsen 1995), and it is also recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from 10 to 400 m deep, on mud or clay bottoms, and down to 2250 m (poppe & goto 1993). in kattegat from 50 to 100 m deep on silty bottom (jensen & spärck 1934). subfossil finds. the north sea, holocene. from the bælt sea, north sea and vendsyssel regions recorded from the eemian. nuculoma hanleyi winckworth 1931 distribution. from the british isles south to spain (poppe & goto 1993). recorded from the northern kattegat (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from 30 to 90 m deep on mud and gravel bottoms. subfossil finds. none. nuculoma tenuis (montagu 1808) distribution. w and e greenland, spitsbergen, around iceland, the faeroes, norway north of lofoten, and south to the mediterranean (madsen 1949). the species extends from the deeper part of the skagerrak into the kattegat, øresund, and bælt sea (jensen & spärck 1934). occurrence. the arctic, subarctic, boreal and lusitanian regions. habitat. from off-shore down to 300 m on muddy bottoms (poppe & goto 1993). the species is more littoral in the northern latitudes than in the south (jensen & spärck 1934). subfossil finds. from the limfjord and north sea regions, holocene. recorded from the vendsyssel area during the eemian, and from the kattegat and vendsyssel area during the early/middle weichselian (the older yoldia sea), and furthermore from the vendsyssel region during the late weichselian (the younger yoldia sea). nuculana minuta (müller 1776) fig. 49 distribution. se and w greenland, around iceland, the faeroes, norway north of lofoten, and south to the british isles. according to ockelmann (1958), lacking in the most high-arctic seas. in south-western europe only at depths greater than 400 m (madsen 1949). the species extends from the north sea and skagerrak into the kattegat and øresund (jensen & spärck 1934). occurrence. the subarctic and boreal regions. habitat. from 10 to 190 m. however, recorded from 2000 m on mud, sand and gravel bottoms (poppe & goto 1993). in danish waters common on silty bottom (jensen & spärck 1934). subfossil finds. the skagen region, holocene. recorded from the skagen well during the subboreal and subatlantic. from the vendsyssel region found during the eemian and in the skagen area during the late weichselian (the younger yoldia sea). fig. 49. nuculana minuta (müller 1776). geus collection. læsø, denmark. × 4.8. right valve. mguh 25359. geus bulletin no 3.pmd 28-06-2004, 08:4563 64 nuculana pernula (müller 1776) fig. 50 distribution. e and w greenland, around iceland, the faeroes, norway north of lofoten, and south to the bay of biscay. however, in sw europe only at depths greater than 400 m (madsen 1949). in danish waters the species extends from the north sea, skagerrak, and into the kattegat, øresund, and bælt sea region north of femern (jensen & spärck 1934). occurrence. the arctic, subarctic and boreal regions. habitat. lives off-shore between 80 and 900 m deep, especially in mud bottoms (poppe & goto 1993). however, in danish waters the species is found from a depth of 20 m (kattegat) to 200 m (skagerrak) according to jensen & spärck (1934), and in the arctic (east greenland) from 3–9 m (ockelmann 1958), being mostly littoral in the arctic. subfossil finds. recorded from the vendsyssel and skagen regions during the eemian. from the kattegat, vendsyssel and skagen regions during the early and middle weichselian (the older yoldia sea). from the vendsyssel and skagen regions during the late weichselian (the younger yoldia sea). yoldia hyperborea lovén 1859 fig. 51 distribution. e and w greenland, spitsbergen, around iceland and norway north of lofoten (madsen 1949). occurrence. the arctic, subarctic and boreal (northern part – high-boreal) regions. habitat. from about 5 to 675 m on clay or mud, in few cases sand (madsen 1949). only subfossil finds. recorded from the vendsyssel and skagen areas during the early and middle weichselian (the older yoldia sea) and from the skagen well also during the late weichselian (the younger yoldia sea). portlandia arctica (gray 1824) fig. 52 distribution. according to ockelmann (1958, p. 26): “widely distributed in high-arctic seas”. occurrence. north greenland, east greenland, spitsbergen, the barents sea, novaya zemlya, the kara sea, the siberian ice sea, viz: arctic and subarctic regions. habitat. from 2 m to 340 m deep, however, the species is most common at depths between 10 and 50 m on a muddy or clayey bottom (ockelmann 1958, p. 25). fig. 50. nuculana pernula (müller 1776). geus collection. læsø, denmark. × 4.8. right valve. mguh 25360. fig. 51. yoldia hyperborea lovén 1859. geus collection. nordre strømfjord, greenland. × 4.8. right valve. mguh 25361. fig. 52. portlandia arctica (gray 1824). geus collection. disko, greenland, 46 m a.s.l. × 4.8. specimen seen from the right. mguh 25362. geus bulletin no 3.pmd 28-06-2004, 08:4564 65 only subfossil finds. recorded from the kattegat, vendsyssel, and skagen areas during the early and middle weichselian (the older yoldia sea) and from the same areas during the late weichselian (the younger yoldia sea). yoldiella lucida (lovén 1846) distribution. w greenland, around iceland, norway north of lofoten (madsen 1949), and south over the british isles to the mediterranean. in the danish waters found in the deeper part of the skagerrak (jensen & spärck 1934). occurrence. the subarctic, boreal and lusitanian regions. habitat. from about 20 m to about 1400 m (iceland), in the skagerrak from about 200 m to more than 600 m on clayey bottoms. subfossil finds. from the vendsyssel area during the eemian. yoldiella lenticula (möller 1842) fig. 53 distribution. e and w greenland, spitsbergen, siberian sea, norway north of the lofoten islands, south to the british isles. further south only at depths greater than 400 m (madsen 1949). occurrence. the arctic, subarctic and boreal regions. habitat. most common at depths between 20 and 200 m (east greenland) on rather pure clay or mud (ockelmann 1958). only subfossil finds. recorded from the vendsyssel area during the eemian, early/middle weichselian (the older yoldia sea) and late weichselian (the younger yoldia sea). found in the skagen area from the late weichselian (the younger yoldia sea). yoldiella frigida (torell 1859) fig. 54 distribution. e and w greenland, spitsbergen, around iceland, norway from north of lofoten, and south to the mediterranean (madsen 1949). in the danish waters found in the deeper parts of the skagerrak (jensen & spärck 1934). however, this is questioned by ockelmann (1958), who says that the main distribution is high-arctic and therefore the recent finds in danish waters should be referable to yoldiella nana. however, according to the old information, the species must have a wide distribution. occurrence. the arctic and subarctic regions, boreal and lusitanian. habitat. most common at depths between 30 and 150 m on bottoms consisting of clay, mud, and clay mixed with sand and gravel (ockelmann 1958). subfossil finds. following the distribution of portlandia frigida sensu jensen & spärck (1934), the species has been recorded from the vendsyssel and skagen areas during the eemian and from the early and middle weichselian (the older yoldia sea) and the late weichselian (the younger yoldia sea). fig. 53. yoldiella lenticula (möller 1842). skagen 3, 121.39– 121.50 m b.s., lab. no. 759,93. × 20. specimen seen from the left. mguh 25363. fig. 54. yoldiella frigida (torell 1859). skagen 3, 127.39–127.50 m b.s., lab. no. 763,93. × 20. specimen seen from the right. mguh 25364. geus bulletin no 3.pmd 28-06-2004, 08:4565 66 yoldiella philippiana (nyst 1845) distribution. from norway off the lofoten islands and south to the mediterranean. occurrence. the boreal and lusitanian regions. habitat. lives to a depth of about 135 m (poppe & goto 1993); however, found at depths of 2500 m (jensen & spärck 1934). only subfossil finds. recorded from the vendsyssel area during the eemian. yoldiella nana (m. sars 1846) distribution. considering the discussion by ockelmann (1958) on distinguishing between portlandia frigida and yoldiella nana, where the latter “at least in part” should be referable to p. fraterna, it is not possible to give any information on the distribution of yoldiella nana mentioned by jensen & knudsen (1995) as being part of the recent danish fauna. subfossil finds. none. malletia obtusa (g.o. sars 1872) distribution. from norway off the lofoten islands and south to sw europe. the occurrences around the british isles and in the mediterranean are at depths greater than 400 m (madsen 1949). occurrence. the boreal and lusitanian regions. habitat. this species has a wide range of depths according to madsen (op. cit.) from 20–3200 m deep. in danish waters only from the deeper part (> 300 m), and in the skagerrak mostly at a depth of 600 m (jensen & spärck 1934). subfossil finds. none. subclass pteriomorphia order arcoida acar nodulosa (müller 1766) distribution. s and w iceland, the faeroes, norway north of lofoten, and south to the mediterranean. the species has been taken on the dogger bank, but not in the inner danish waters. occurrence. the boreal and lusitanian regions. habitat. from the tidal zone down to 1000 m fixed with its byssus to hard substrates (poppe & goto 1993). subfossil finds. none. bathyarca glacialis (gray 1824) fig. 55 distribution. w and e greenland, spitsbergen, and around iceland. the occurrences from sw europe are of dead shells and from deep water (ockelmann 1958). occurrence. mainly the arctic and subarctic regions; however, the occurrences from southern iceland imply extension into the boreal region as well. habitat. from 6–10 m down to 425 m (east greenland), but most abundant below 40 m on clay bottoms with stones and gravel, where the astarte crenata community occurs. only subfossil finds. recorded from the vendsyssel (not in the skærumhede sequence) and skagen regions during the early/middle weichselian and the late weichselian respectively. bathyarca pectunculoides (scacchi 1834) distribution. w and e greenland, around iceland, norway north of lofoten, and south to the mediterranean. in the danish waters the species is rather common in the deeper part of the skagerrak between 300–700 m (jensen & spärck 1934). fig. 55. bathyarca glacialis (gray 1824). skagen 3, 114.64–? m b.s., core sample-57. × 9.6. fragments of left valve. mguh 25365. geus bulletin no 3.pmd 28-06-2004, 08:4566 67 occurrence. the arctic, subarctic, boreal and lusitanian regions. habitat. from 50 m (the shetland isles) to more than 2000 m (the mediterranean) (madsen 1949). subfossil finds. none. order mytiloida mytilaster lineatus (gmelin 1791) distribution. a mediterranean species according to jensen & spärck (1934) but also found in the neighbouring atlantic (poppe & goto 1993). occurrence. the lusitanian region. habitat. intertidal, attached to rocks. only subfossil finds. the eemian in the kattegat and north sea regions. mytilaster solidus form minimus (poli 1795) distribution. from bretagne and south into the mediterranean. occurrence. the lusitanian region. habitat. intertidal, attached to rocks or algae. subfossil finds. recorded from the bælt sea during the eemian. mytilus edulis linnaeus 1758 fig. 56 distribution. w and e greenland, but only along the south-eastern coast (ockelmann 1958), around iceland, the faeroes, norway north of lofoten, and south to the mediterranean. known from all parts of the danish waters, including the baltic. occurrence. the subarctic, boreal and lusitanian regions. habitat. intertidal to 40 m deep, but in danish waters common as an epifaunal element down to a depth of 10 m; however, in the baltic as deep as 40 m (jensen & spärck 1934). subfossil finds. the bælt sea, baltic, kattegat, limfjord, north sea, vendsyssel and skagen regions, holocene. recorded in the subatlantic from the skagen well. in the eemian records from the bælt sea, baltic, kattegat, north sea and vendsyssel regions. in the late weichselian also recorded from the vendsyssel region (the younger yoldia sea). modiolula phaseolina (philippi 1844) distribution. from sw and nw iceland, the faeroes, norway north of lofoten, and south to the british isles (petersen 1968) and the mediterranean. the species extends from the north sea and skagerrak into the kattegat and øresund (jensen & knudsen 1995), but is not recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone and down to 160 m, attached by its byssus to rocks or on the base of the larger seaweeds (poppe & goto 1993), but also recorded from depths of 1000 m. subfossil finds. the bælt sea, limfjord and vendsyssel regions, holocene. recorded from the bælt sea and the north sea regions during the eemian. modiolus adriaticus (lamarck 1819) distribution. recorded from the southern part of the british isles and denmark (petersen 1968) south to the mediterranean. in danish waters taken in the kattegat, including the øresund (jensen & spärck 1934), but fig. 56. mytilus edulis linnaeus 1758. skagen 4, 18.7–18.8 m b.s., lab. no. 311,95. × 4.8. fragment of left valve. mguh 25366. geus bulletin no 3.pmd 28-06-2004, 08:4567 68 not observed in the limfjord (petersen 1986a). it might have been passed over in many places, as mentioned by petersen (1888, p. 127). occurrence. the boreal and lusitanian regions. habitat. sublittoral between 14 and 75 m on mud bottoms. subfossil finds. the limfjord and vendsyssel region, holocene. modiolus modiolus (linnaeus 1758) distribution. around iceland, the faeroes, norway north of lofoten, and south to the british isles (petersen 1968) and the bay of biscay (poppe & goto 1993). in danish waters, including the limfjord, the species extends into the bælt sea (jensen & spärck 1934) and the øresund (jensen & knudsen 1995). occurrence. the subarctic, boreal and lusitanian regions. habitat. from the extreme low tide down to 150 m attached with its byssus to rocks or gravel (poppe & goto 1993). in danish waters the species replaces mytilus edulis as the dominating epifaunal element in deeper water (jensen & spärck 1934). subfossil finds. the bælt sea, limfjord and vendsyssel regions, holocene. recorded from the baltic and north sea during the eemian. musculus discors (linnaeus 1767) fig. 57 distribution. e and w greenland, around iceland and spitsbergen (madsen 1949), norway from north of lofoten (petersen 1968) and south to the mediterranean. in danish waters the species extends into the bælt sea and øresund (jensen & spärck 1934), but it has not been observed in the limfjord (petersen 1986a). occurrence. the arctic, subarctic, boreal, and lusitanian regions. habitat. from the intertidal zone on algae (poppe & goto 1993) and rarely on water deeper than about 200 m (jensen & spärck 1934). subfossil finds. the bælt sea, kattegat, limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subatlantic. musculus laevigatus (gray 1824) distribution. e and w greenland, around iceland and norway north of lofoten. occurrence. the arctic, subarctic and boreal regions. habitat. from the infralittoral zone down to 83 m (poppe & goto 1993). only subfossil finds. recorded from the early/middle weichselian (the older yoldia sea, but not in the skærumhede sequence) and the late weichselian (the younger yoldia sea) in the vendsyssel region. musculus niger (gray 1824) distribution. e and w greenland, around iceland, the faeroes, norway north of lofoten, and south to the north sea and the irish sea (madsen 1949; petersen 1968). in danish waters the species extends from the north sea into the kattegat, øresund and bælt sea as far as warnemünde (jensen & spärck 1934; jensen & knudsen 1995). occurrence. the arctic, subarctic and boreal regions. habitat. most often found in danish waters at water depths of more than 25 m (jensen & spärck 1934). poppe & goto (1993) indicate from 7 m deep down to about 135 m. however, off the east greenland coast the species is rarely met with at depths exceeding 40 m (ockelmann 1958). fig. 57. musculus discors (linnaeus 1767). skagen 4, 28.0–28.5 m b.s., lab. no. 353,93. × 20. left valve. mguh 25367. geus bulletin no 3.pmd 28-06-2004, 08:4568 69 subfossil finds. recorded from the vendsyssel region during the eemian, the early and middle weichselian (the older yoldia sea) and the late weichselian (the younger yoldia sea). modiolaria tumida (hanley 1843) distribution. the british isles and the shetlands, and south to the mediterranean (madsen 1949). in danish waters the species is very common in the limfjord, but also in the other fjords, and it extends into the bælt sea (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. it is a common shallow-water species in danish waters (jensen & spärck 1934), but goes down to 60 m (poppe & goto 1993) associated with tunicates and echinoderms. subfossil finds. the limfjord and vendsyssel regions, holocene. recorded from the north sea region during the eemian. crenella decussata (montagu 1803) distribution. e and w greenland, around iceland, norway north of lofoten and south to the british isles (madsen 1949; petersen 1968). in danish waters the species is found in the kattegat, including the øresund. occurrence. the arctic, subarctic and boreal regions. habitat. from 4 to 200 m deep on all kinds of bottoms (poppe & goto 1993). according to jensen & spärck (1934), most common in danish waters between 15 and 30 m. subfossil finds. recorded in the kattegat during the holocene and from the early and middle weichselian (the older yoldia sea) in the vendsyssel region. adipicola simpsoni (marshall 1900) distribution. from southern iceland and south to portugal and the mediterranean. might be found in danish waters (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. as mentioned by poppe & goto (1993, p. 48): “the species has been collected repeatedly on the skulls of whales, where it lies, attached in the sutures, by its byssus”. subfossil finds. none. order pteroida chlamys islandica (o.f. müller 1776) distribution. se and w greenland, around iceland, spitsbergen, norway north of lofoten, and south to the shetlands and the orkney islands (rare) (petersen 1968). occurrence. the subarctic and boreal regions. habitat. around iceland one of the most common bivalves present from nearly all localities along the nw, n and e coast, both in the fjords and on the outer part of the shelf, at depth from a few metres to 300 m (madsen 1949). common in danish waters from 10 to 100 m (jensen & spärck 1934) on rocks and gravel bottoms. lives attached to hard substrates with its byssus (poppe & goto 1993). only subfossil finds. recorded from the vendsyssel region during the early and middle weichselian (the older yoldia sea) and the late weichselian (the younger yoldia sea). aequipecten opercularis (linnaeus 1758) distribution. norway from north of lofoten, and south to the mediterranean (petersen 1968). in danish waters the species extends into the kattegat and øresund, but is not recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone down to 400 m on all types of bottoms except rocky ones (poppe & goto 1993). subfossil finds. the limfjord and vendsyssel regions, holocene. recorded from the north sea region during the eemian. geus bulletin no 3.pmd 28-06-2004, 08:4569 70 chlamys varia (linnaeus 1758) fig. 58 distribution. norway off the lofoten islands, and south to the mediterranean (petersen 1968). in danish waters the species occurs in the limfjord (jensen & spärck 1934) and has been recorded juvenile from the øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. intertidal to 83 m, attached by its byssus (poppe & goto 1993). subfossil finds. the limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subatlantic. recorded from the north sea during the eemian. delectopecten vitreus (gmelin 1791) fig. 59 distribution. w greenland, w iceland, spitsbergen, norway north of lofoten, and south to the british isles (madsen 1949), and according to poppe & goto (1993) also into the mediterranean. in danish waters from the skagerrak (jensen & spärck 1934). occurrence. the subarctic, boreal and lusitanian regions. habitat. between 30 and 600 m, fixed by its byssus to hard substrates (poppe & goto 1993). the species lives in the deeper part of the skagerrak, from 400 to 600 m, according to jensen & spärck (1934). subfossil finds. the limfjord, holocene. recorded from the eemian in the skagen well. palliolum greenlandicum (sowerby 1842) fig. 60 distribution. e and w greenland, n and e iceland, spitsbergen, and norway north of lofoten (madsen 1949). however, at depths greater than 400 m the species has been found off the faeroes and the british isles. occurrence. the arctic, subarctic and boreal regions. habitat. in the arctic seas living in shallow water from 5 m, but most common between 20 and 70 m on clay bottoms containing stones or shells (ockelmann 1958). only subfossil finds. recorded from the vendsyssel region and the skagen well during the early/middle weichselian (the older yoldia sea). fig. 58. chlamys varia (linnaeus 1758). skagen 3, 32.85–32.90 m b.s., core sample-2. × 20. right valve. mguh 25368. fig. 59. delectopecten cf. vitreus (gmelin 1791). skagen 3, 183.17–183.40 m b.s., lab. no. 9e+05. × 9.6. mguh 25369. fig. 60. palliolum greenlandicum (sowerby 1842). geus collection. east greenland. × 4.8. right valve. mguh 25370. geus bulletin no 3.pmd 28-06-2004, 08:4570 71 palliolum striatum (müller 1776) distribution. from s and w iceland, the faeroes, norway north of lofoten, and south to the mediterranean. the species extends from the north sea and skagerrak into the kattegat, including øresund. occurrence. the boreal and lusitanian regions. habitat. from shallow water around 5 m to more than 800 m deep on all types of bottom (poppe & goto 1993). the vertical range off iceland is indicated to lie between 100 and 260 m (madsen 1949). subfossil finds. the limfjord region, holocene. palliolum tigerinum (müller 1776) distribution. from nw, w and s iceland, the faeroes, norway north of lofoten, and south to morocco. in danish waters from the north sea and skagerrak into the kattegat, including the øresund. occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone down to 400 m, but deeper in the southern part of its range on sandy bottoms (poppe & goto 1993). subfossil finds. the limfjord region, holocene. pecten maximus (linnaeus 1758) distribution. norway off the lofoten islands and south to spain. in danish waters rarely found living in the kattegat and only shells have been recovered from the øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone down to 250 m on sand and gravel bottoms (poppe & goto 1993). subfossil finds. recorded from the vendsyssel region, holocene. pseudamussium septemradiatum (müller 1776) distribution. s iceland, norway from north of the lofoten islands, and south to the mediterranean. in danish waters the species extends from the skagerrak and becomes common in the southern kattegat with finds also in the øresund (jensen & spärck 1934; jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. in general living between 60 and 600 m deep on muddy bottoms (poppe & goto 1993). in danish waters often found between 30 and 60 m. subfossil finds. recorded from the vendsyssel region during the eemian. similipecten similis (laskey 1811) distribution. s and w iceland, the faeroes, norway north of lofoten, and south to the mediterranean (petersen 1968). the species extends into the kattegat from skagerrak. occurrence. the boreal and lusitanian regions. habitat. sublittorally between 4 and 250 m deep on sand and fine gravel bottoms (poppe & goto 1993). in danish waters from 30 to 80 m deep (jensen & spärck 1934). however, the vertical range around iceland is 200–320 m (madsen 1949). subfossil finds. recorded from the vendsyssel area during the eemian. pododesmus patelliformis (linnaeus 1761) distribution. s and w iceland, the faeroes, norway off the lofoten islands, and south to the mediterranean (madsen 1949). the species extends from the north sea into the kattegat, including the øresund, and occurs also in the limfjord (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. intertidal to 50 m deep on gravel or rock bottoms, often attached to shells (poppe & goto 1993). subfossil finds. the limfjord and vendsyssel regions, holocene. pododesmus squama (gmelin 1791) distribution. around the british isles and from danish waters the occurrences in the kattegat and øresund geus bulletin no 3.pmd 28-06-2004, 08:4571 72 are questioned, although larvae occur (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone to 75 m deep on all types of bottoms attached to hard substrates (poppe & goto 1993). subfossil finds. none. anomia ephippium linnaeus 1758 distribution. from the british isles, including the orkney islands, and south to the mediterranean. occurrence. mainly the lusitanian region. habitat. from the intertidal zone down to 150 m on all kinds of hard substrates. only subfossil finds. the limfjord and the vendsyssel region, holocene. heteranomia squamula (linnaeus 1758) fig. 61 distribution. around iceland, the faeroes, norway north of lofoten, and south to the bay of biscay. the species extends into the kattegat, øresund, and occurs in the limfjord (jensen & spärck 1934). occurrence. the subarctic, boreal and lusitanian regions. habitat. from 5 to 110 m deep fixed on hard substrates, but also on algae and crustaceans (poppe & goto 1993). subfossil finds. the kattegat, limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subatlantic. during the eemian recorded from the bælt sea and the north sea regions. crassostrea gigas (gmelin 1791) this oyster species from the portuguese–spanish region (poppe & goto 1993) has been introduced in 1972 as spat for commercial production (jensen & knudsen 1995) and is not considered here, although mentioned as now part of the danish molluscan fauna. no subfossil records either. ostrea edulis linnaeus 1758 fig. 62a, b distribution. from the southern part of the west coast of norway south to the mediterranean. in danish waters only common in the western part of the limfjord, although stray specimens are found in the northern north sea, skagerrak and northern kattegat (jensen & spärck 1934; jensen & knudsen 1995). fig. 61. heteranomia squamula (linnaeus 1758). skagen 4, 21.0– 21.5 m b.s., lab. no. 346,93. × 20. left valve. mguh 25371. fig. 62. a, b: ostrea edulis linnaeus 1758. skagen 4, 8.0–8.5 m b.s., lab. no. 333,93. × 9.6. left valve of juvenile specimen (exterior and interior, respectively). mguh 25372. geus bulletin no 3.pmd 28-06-2004, 08:4572 73 occurrence. the boreal and lusitanian regions. habitat. from the tidal zone down to 90 m on all types of bottoms. in danish waters the species can be found at depths of 3 to 7 m in the limfjord, but also deeper elsewhere (jensen & spärck 1934). subfossil finds. the bælt sea, kattegat, limfjord, north sea, vendsyssel and skagen regions, holocene. recorded from the subatlantic in the skagen well. finds from the bælt sea, kattegat, and north sea regions during the eemian. limaria hians (gmelin 1791) distribution. norway north of lofoten, the orkney islands and south to the mediterranean (petersen 1968). a few records from the northern and central parts of the kattegat (jensen & knudsen 1995). already jensen & spärck (1934) mentioned that the species then known from the deeper parts of the north sea might occur in danish waters. occurrence. the boreal and lusitanian regions. habitat. lives from the low tide mark zone down to 100 m on coarse sand and gravel bottoms (poppe & goto 1993). subfossil finds. none. limaria loscombi (sowerby 1832) distribution. norway off the lofoten islands, the faeroes and south to the mediterranean (petersen 1968). poppe & goto (1993) mentioned occurrences of l. hians and l. loscombi off iceland which, however, cannot be found in the other literature. in danish waters the species has been found in the kattegat, including the øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. lives from 35 to 100 m deep on fine sand and sand–mud bottoms (poppe & goto 1993). in danish waters it is characteristic in the south-eastern part of kattegat together with pseudamussium septemradiatum (jensen & spärck 1934). subfossil finds. none. limatula subauriculata (montagu 1808) distribution. se and w greenland, n and e iceland, norway north of lofoten, and south to the mediterranean (petersen 1968). in the danish waters only shells have been recorded from the northern kattegat (jensen & knudsen 1995). occurrence. the subarctic, boreal and lusitanian regions. habitat. especially living on the continental shelves. however, records ranges from 4 to 2000 m (poppe & goto 1993). subfossil finds. none. subclass heterodonta order veneroida chama gryphoides linnaeus 1767 this lusitanian species (up to the coasts of portugal) has only one record from danish waters (jensen & knudsen 1995), and this is considered to have been dropped by a ship. therefore it will not be discussed. no subfossil records. lucinella divaricata (linnaeus 1758) distribution. from the english channel and southern part of the north sea south to the mediterranean. occurrence. mainly the lusitanian region. habitat. from the tidal zone down to a depth of 60 m in fine sand and/or mud (poppe & goto 1993). only subfossil finds. the eemian in the bælt sea, kattegat, and north sea regions. lucinoma borealis (linnaeus 1758) distribution. the faeroe islands, norway from off lofoten, and south to the mediterranean (petersen 1968). in danish waters the species occurs in the kattegat, including the øresund, but is not recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. geus bulletin no 3.pmd 28-06-2004, 08:4573 74 habitat. from the intertidal zone down to 500 m deep on gravel bottoms and in pure sand and/or mud (poppe & goto 1993). in danish waters between 20 and 50 m (jensen & spärck 1934). subfossil finds. the limfjord and vendsyssel regions, holocene. myrtea spinifera (montagu 1803) distribution. from norway south to morocco. in danish waters recorded from the northern kattegat (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from 7 to 250 m deep on sand, mud and gravel bottoms (poppe & goto 1993). subfossil finds. none. axinopsida orbiculata (g.o. sars 1878) distribution. e and w greenland, around iceland, the faeroes, and norway north and just south of the lofoten islands (petersen 1968). the species occurs off the north western part of scotland. occurrence. the arctic, subarctic and boreal regions. habitat. from 2 to 50 m deep on sand, clay and mud around iceland (madsen 1949). north of the hebrides occurring at depths down to 900 m (jensen & spärck 1934). only subfossil finds. the vendsyssel region from the early and middle weichselian (the older yoldia sea) and the late weichselian (the younger yoldia sea). thyasira croulinensis (jeffreys 1847) distribution. w greenland, around iceland, the faeroes, norway north of lofoten (petersen 1968), and south to the mediterranean (poppe & goto 1993). in danish waters taken in the north sea and skagerrak. occurrence. the subarctic, boreal and lusitanian regions. habitat. about 40 to 2500 m off the faeroes on gravel and clay (petersen 1968). in danish waters the species is found in the deeper water (jensen & spärck 1934). subfossil finds. none. thyasira equalis (verrill & bush 1898) distribution. it is questioned by nordsieck (1969, p. 79) if t. equalis should be thyasira flexuosa var. rotunda. there are no subfossil finds under the name of t. equalis, so this species will not be considered any further. however, as discussed by ockelmann (1958, p. 100) a species, t. equalis, does occur in the arctic, while t. flexuosa has a boreo-lusitanian main distribution. thyasira flexuosa (montagu 1803) fig. 63 distribution. e and w greenland, spitsbergen, around iceland, the faeroes, norway north of lofoten, and south to the mediterranean. in the danish waters it is very common and extends into the øresund (jensen & knudsen 1995), but is not recorded from the limfjord (petersen 1986a). occurrence. the arctic, subarctic, boreal and lusitanian regions (see comments under t. equalis). habitat. from 10 to 2000 m deep on sand and mud bottoms (poppe & goto 1993). in danish waters from 20 m to around 100 m deep on clay bottoms (jensen & spärck 1934). from the north sea recorded at 30 to 200 m depths on mixed bottom in the trenches around the dogger bank (petersen 1977). subfossil finds. the limfjord, north sea, vendsyssel fig. 63. thyasira flexuosa (montagu 1803). skagen 3, 35.90– 36.00 m b.s., lab. no. 496,93. × 9.6. left valve. mguh 25373. geus bulletin no 3.pmd 28-06-2004, 08:4574 75 and skagen regions, holocene. from the skagen well recorded from the subatlantic. from the north sea during the eemian and in the vendsyssel region recorded from the late weichselian (the younger yoldia sea). thyasira sarsi (philippi 1845) distribution. from novaja semlja along the coast of norway south to the skagerrak region. the species extends into the kattegat, including the øresund (jensen & knudsen 1995). occurrence. the arctic, subarctic and boreal regions. habitat. from 100 m to deep water. subfossil finds. none. leptaxinus ferruginosus (forbes 1844) distribution. w greenland, w iceland, spitsbergen, norway off the lofoten islands, and southwards to madeira (madsen 1949). jensen & spärck (1934) mentioned the species from the deeper part of the skagerrak, but jensen & knudsen (1995) have no further record of this species as belonging to the recent danish fauna. occurrence. the arctic, subarctic, boreal and lusitanian regions. habitat. about 20 m to more than 3000 m. the vertical range off iceland is 320–560 m. so here is another example of tropical submerge (see order mesogastropoda natica affinis). subfossil finds. recorded from the vendsyssel region during the eemian. mysella bidentata (montagu 1803) fig. 64 distribution. around iceland, the faeroes, norway from north of lofoten, and south to west africa (petersen 1968). the species has a common distribution in danish waters, including the limfjord, south to the bælt sea by warnemünde (arntz et al. 1976), and the øresund (jensen & spärck 1934). also found in the north sea (petersen 1977). occurrence. the subarctic, boreal and lusitanian regions. habitat. intertidal zone down to 2500 m, often in commensal association with other animals. in the north sea it is recorded from 20 to 90 m as a commensal on for example, acrocnida brachiata (petersen 1977). subfossil finds. the bælt sea, kattegat, limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well, records from the preboreal–boreal, subboreal and subatlantic. from the bælt sea, baltic, north sea and vendsyssel regions also recorded from the eemian. mysella tumidula (jeffreys 1867) distribution. this species is recorded by jensen & knudsen (1995) as being part of the danish fauna, although it seems to have a purely lusitanian distribution (poppe & goto 1993). the species has no subfossil occurrence. montacuta substriata (montagu 1803) distribution. w iceland, the faeroes, norway north of lofoten, and south to the mediterranean. in danish waters rarely found in the north sea, skagerrak and kattegat. occurrence. the boreal and lusitanian regions. habitat. off iceland the vertical range is between 31 and 165 m (madsen 1949). in danish waters out to depths of around 700 m (skagerrak) reported as a commensal on spatangus purpureus (jensen & spärck 1934) and from the north sea also on echinocardium flavesens at depths from 30 to 100 m (petersen 1977). subfossil finds. none. fig. 64. mysella bidentata (montagu 1803). skagen 4, 27.0–27.5 m b.s., lab. no. 352,93. × 9.6. to the left a specimen seen from the right, and to the right a left valve. mguh 25374. geus bulletin no 3.pmd 28-06-2004, 08:4575 76 tellimya ferruginosa (montagu 1803) fig. 65 distribution. around iceland, the faeroes, norway north of lofoten, and south to the mediterranean. in danish waters the species extends from the north sea, limfjord, and skagerrak into the kattegat and øresund (jensen & spärck 1934). occurrence. the subarctic, boreal and lusitanian regions. habitat. in general the species is most common just below the tidal zone, which according to poppe & goto (1993) is the preferred habitat of echinocardium with which t. ferruginosa is often associated. however, the species is also found on brissopsis lyrifera or living by itself (jensen & spärck 1934). accordingly, the depth range may vary, around iceland being between 32 and 80 m (madsen 1949). subfossil finds. the limfjord, north sea, vendsyssel and skagen regions, holocene. the records from the skagen well are from the subboreal and subatlantic. furthermore, the species has been recorded from the bælt sea and north sea during the eemian. mysella dawsoni (jeffreys 1864) distribution. petersen (1888, p. 154) mentioned a single find from the limfjord, and the species is mentioned by petersen (1986a) on the basis of the tables on molluscan finds in the limfjord from danmarks fiskeriog havundersøgelser (petersen 1976). however, it is not cited among the recent danish species by jensen & knudsen (1995). the species is mentioned from w greenland (thorson 1951) and south to the mediterranean (poppe & goto 1993), and also from spitsbergen and the west coast of norway (jensen & spärck 1934). occurrence. the arctic, subarctic, boreal and lusitanian regions. habitat. deep-living species, but mentioned from a depth of 5 m by posselt & jensen (1898) and in sandy bottom in west greenland. subfossil finds. none. tellimya tenella (lovén 1846) cited only from the kattegat, including the øresund, by jensen & knudsen (1995). no subfossil finds. will not be considered further. turtonia minuta (fabricius 1780) fig. 66 distribution. w greenland, around iceland, the faeroes, norway north of lofoten, and south to the mediterranean. occurrence. the subarctic, boreal and lusitanian regions. habitat. lives in the tidal zone among plants and algae on rocks (poppe & goto 1993). off iceland in the tidal zone all around the island, but also down to a depth of 50 m (petersen 1968). only subfossil finds. the limfjord, vendsyssel and fig. 65. tellimya ferruginosa (montagu 1803). skagen 4, 27.0– 27.5 m b.s., lab. no. 352,93. × 9.6. to the left interior of a right valve, and to the right a specimen seen from the left. mguh 25375. fig. 66. turtonia minuta (fabricius 1780). skagen 3, 39.85– 40.02 m b.s., lab. no. 711,93. × 40. right valve. mguh 25376. geus bulletin no 3.pmd 28-06-2004, 08:4576 77 skagen regions, holocene. recorded from the subatlantic in the skagen well. lepton nitidum (turton 1822) distribution. from the faeroes, western norway, and south to the mediterranean (jensen & spärck 1934; madsen 1949). only recently recorded from the northern kattegat and øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from 18 to 216 m, commensal on the crustaceans upogebia deltaura and gebia stellata (nordsieck 1969, p. 89). subfossil finds. the limfjord, north sea and vendsyssel regions, holocene. recorded from the eemian in the bælt sea and north sea areas. lepton squamosum (montagu 1803) distribution. from the west coast of norway and south to spain. only shells have been found in danish waters (northern kattegat) mentioned by jensen & knudsen (1995). occurrence. the boreal and lusitanian regions. habitat. from 10 to 120 m deep it lives in and around the burrows of the crustaceans (upogebia deltaura and u. stellata) on mud or gravel bottoms (poppe & goto 1993). subfossil finds. none. devonia perrieri (malard 1904) distribution. from the british isles south to spain. in danish waters recorded from the northern kattegat (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. this species is a commensal on leptosynapta inhaerens (nordsieck 1969, p. 95). subfossil finds. none. kellia suborbicularis (montagu 1803) distribution. s and w iceland, the faeroes, norway off the lofoten islands and south to the mediterranean. in danish waters recorded from the northern kattegat and øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. intertidal to 120 m deep in crevices, shells or in borings made by other species (poppe & goto 1993). subfossil finds. recorded from the vendsyssel region, holocene. potidoma dorkiae (clark 1852) this species has been recorded only in a single find by jensen & knudsen (1995), and there are no subfossil finds from the literature, so it will not be considered further. astarte sulcata (da costa 1778) distribution. se and w greenland, s and w iceland, the faeroes, norway north of lofoten, and south to the mediterranean. the species extends from the north sea into the kattegat, but is not common (jensen & spärck 1934). occurrence. the subarctic, boreal and lusitanian regions. habitat. sublittorally from 20 m and deeper on sand, mud and gravel bottoms. subfossil finds. none. tridonta borealis schumacher 1817 distribution. this species is found in all regions of the north atlantic except the british isles (madsen 1949). however, according to petersen (1968) the species has not been recorded from the faeroes. in the danish waters the species extends from the deeper part of the northern north sea (single finds) into the kattegat, including the øresund and the bælt sea, becoming very common in the baltic (jensen & spärck 1934). occurrence. the arctic, subarctic and boreal regions. geus bulletin no 3.pmd 28-06-2004, 08:4577 78 habitat. from below the tidal zone down to 250 m on mud, sand and gravel bottoms. the species is “a common member of all the zones of the arctic macoma community, and the gomphina fluctuosa community” (ockelmann 1958, p. 83). subfossil finds. the bælt sea and limfjord regions, holocene. recorded from the vendsyssel region both in the early/middle weichselian (not in the skærumhede sequence) and the late weichselian (the older yoldia sea and the younger yoldia sea respectively). tridonta elliptica (brown 1827) distribution. this species is found in all regions of the north atlantic, including the british isles (madsen 1949). petersen (1968) specified the occurrence of this species to be in the clyde sea and off the isle of man only. in the danish waters it occurs in the kattegat, øresund, the bælt sea and the baltic, where it becomes as common as t. borealis (jensen & spärck 1934). occurrence. the arctic, subarctic and boreal regions. considering the occurrences on the west coast of britain it is also in the northern part of the lusitanian region, but here probably mostly in deeper water. habitat. the vertical range for this species is off iceland 6 to 300 m (madsen 1949), and off the east greenland coast it is most often taken between about 5 and 50 m, being abundant locally within the arctic macoma community (ockelmann 1958). subfossil finds. recorded from the north sea during the eemian, and in vendsyssel during the early/middle weichselian, being part of the older yoldia sea found in the skærumhede sequence (jessen et al. 1910). tridonta montagui (dillwyn 1817) distribution. e and w greenland, around iceland, spitsbergen, the faeroes, norway form north of lofoten, and south to the clyde sea and isle of man (petersen 1968), also recorded from the bay of biscay. it is present in the north western part of the north sea (petersen 1977) and common in the kattegat, øresund and extending into the bælt sea (jensen & spärck 1934). occurrence. the arctic, subarctic, boreal and lusitanian regions. habitat. the vertical range off iceland is 7–150 m (madsen 1949) and in the north sea sampled at depths between 40 and 75 m on mixed bottom in the trenches around the dogger bank (petersen 1977, p. 226). subfossil finds. recorded from the north sea region during the eemian and from the vendsyssel area during the early/middle weichselian (the older yoldia sea). acanthocardia echinata (linnaeus 1758) fig. 67 distribution. s and w iceland, norway north of lofoten, and south to the mediterranean (madsen 1949). in danish waters the species extends from the north sea (petersen 1977) into the skagerrak, limfjord, and kattegat regions and the øresund (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. from 4 to 350 m deep on mud, sand and gravel bottoms (poppe & goto 1993). subfossil finds. the kattegat, limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subboreal and subatlantic. there are eemian records from the bælt sea, kattegat, north sea and vendsyssel regions. parvicardium exiguum (gmelin 1791) distribution. norway north of lofoten and south to the mediterranean (madsen 1949). in danish waters common in bays and fjords, including the limfjord. considering all the variations belonging to the same species it extends into the bælt sea (petersen 1888). occurrence. the boreal and lusitanian regions. fig. 67. acanthocardia echinata (linnaeus 1758). skagen 4, 27.0–27.5 m b.s., lab. no. 352,93. × 20. right valve. mguh 25377. geus bulletin no 3.pmd 28-06-2004, 08:4578 79 habitat. in general occurring from low tide to about 55 m deep (poppe & goto 1993); however, according to rasmussen (1973) the species has its main occurrence along the shores and is associated with vegetation. subfossil finds. the bælt sea, baltic, kattegat, limfjord, north sea and vendsyssel regions, holocene. recorded also from the bælt sea, kattegat, and north sea regions during the eemian. parvicardium hauniense (petersen & russell 1971) distribution. this newly established species has been recorded from recent danish waters, but no subfossil records are at hand. parvicardium ovale (sowerby 1840) distribution. around iceland, norway north of lofoten, and south to the mediterranean (madsen 1949). in danish waters the species is found in all the regions except the baltic extending only to darss (jensen & spärck 1934). occurrence. the subarctic, boreal and lusitanian regions. habitat. according to the icelandic records (madsen 1949) found between 5 to 350 m on bottoms such as mud, sand, clay and shell gravel with stones. subfossil finds. the bælt sea, limfjord, north sea and vendsyssel regions, holocene. from the north sea and vendsyssel regions also recorded from the eemian. parvicardium scabrum (philippi 1844) distribution. from norway north of the lofoten islands, and south to the mediterranean (madsen 1949). in danish waters common in the limfjord (jensen & spärck 1934) and recorded from the kattegat, but questioned, as there may be two separate species (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone to several hundred metres deep on sand, mud and gravel bottoms (poppe & goto 1993). subfossil finds. the bælt sea, kattegat, limfjord, north sea and vendsyssel regions, holocene. recorded from the north sea during the eemian. plagiocardium papillosum (poli 1795) distribution. from the english channel south into the mediterranean (poppe & goto 1993). occurrence. the lusitanian region. habitat. from 1 to 60 m deep on rough sand and gravel bottoms. only subfossil finds. recorded from the eemian in the north sea region. parvicardium minimum (philippi 1836) fig. 68 distribution. s and w iceland, the faeroes, norway north of lofoten, and south to the mediterranean at greater depths. in danish waters common in the deeper part of the skagerrak extending into the kattegat, including the øresund (petersen 1888). the occurrence in the limfjord is questioned (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from 4 to 161 m on mud, sand and gravel bottoms (poppe & goto 1993). however, according to madsen (1949) the species has around iceland only been found at depths of more than 75 m, and the bottoms are recorded as sand with shells and stones or as ooze and clay. in danish waters the species prefers fig. 68. parvicardium minimum (philippi 1836). geus collection. north of skagen, denmark. × 9.6. specimen seen from the right. mguh 25378. geus bulletin no 3.pmd 28-06-2004, 08:4579 80 depths of more than about 30 m, and it occurs at the greatest depth (petersen 1888). subfossil finds. the north sea and skagen regions, holocene. recorded from the skagen well during the preboreal–boreal, the atlantic, subboreal and subatlantic. from the vendsyssel region recorded from the eemian. cerastoderma edule (linnaeus 1758) distribution. norway north of the lofoten islands, and south to the mediterranean (madsen 1949). in danish waters found in all regions (petersen 1888, p. 136 – who already stressed that it is a very variable species). occurrence. the boreal and lusitanian regions. habitat. this is a shallow-water infaunal species – intertidal to few metres deep, but in the baltic occurring also at 20–30 m depths (jensen & spärck 1934) on sandy bottoms. subfossil finds. the bælt sea, baltic, kattegat, limfjord, north sea and vendsyssel regions, holocene. from the eemian recorded in the bælt sea, baltic, kattegat and north sea regions. cerastoderma glaucum (poiret 1789) distribution. from the west coast of norway south to the mediterranean (poppe & goto 1993, pp. 95–96). in danish waters the species extends into the baltic (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. this is a shallow-water species on sand and mud bottoms. however, according to studies on subfossil material (rasmussen 1973, p. 298–302), the associated fauna indicates a tidal estuarine environment for the danish material of an ertebølle age in the isefjord. subfossil finds. the baltic, kattegat and limfjord regions, holocene. however, the species identifications on the subfossil material recorded through time should be taken with some reservation on the basis of the great difficulties connected with recent species identifications. clinocardium ciliatum (fabricius 1780) distribution. w and e greenland, spitsbergen, around iceland and norway north of the lofoten islands. from the faeroes only at depths exceeding 400 m (petersen 1968). occurrence. the arctic, subarctic and boreal (highboreal) regions. habitat. from the tidal zone down to 700 m, off iceland occurring on ooze, mud, clay, sand and mixed bottoms (madsen 1949). mainly found in the arctic macoma community (ockelmann 1958). only subfossil finds. from the vendsyssel region recorded both from the eemian and from the early/middle weichselian (the older yoldia sea). laevicardium crassum (gmelin 1791) distribution. from norway north of the lofoten islands and south to the mediterranean. in danish waters only recorded from the north sea (petersen 1977) and the northern part of the kattegat (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone down to 183 m deep on sand, mud or gravel bottoms. subfossil finds. the vendsyssel region, holocene. from the eemian recorded in the kattegat region. serripes groenlandicus (bruguière 1798) distribution. w and e greenland, spitsbergen, around iceland and norway north of lofoten. from the faeroes only at depths exceeding 400 m (petersen 1968). occurrence. the arctic, subarctic and boreal (highboreal) regions. habitat. from 0 to 1 m to 120 m deep on clay and mud, but also sand and gravel are recorded (madsen 1949). subfossil finds. from the vendsyssel area during the eemian and early/middle weichselian. geus bulletin no 3.pmd 28-06-2004, 08:4580 81 mactra stultorum (linnaeus 1758) fig. 69 distribution. from the british isles and denmark south to the mediterranean (petersen 1968). in the danish waters the species is common in the north sea and skagerrak, extending into the limfjord (petersen 1986a), kattegat and øresund, although here only juveniles are present (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone down to 60 m in clean sand. subfossil finds. the limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subatlantic. during the eemian recorded from the bælt sea region. lutraria lutraria (linnaeus 1758) distribution. norway off the lofoten islands and south to the mediterranean. since 1990 live specimens have been taken in danish waters near frederikshavn and at the skagerrak coast (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. intertidal down to 100 m, lives at depths up to 35 cm, burrowing in sand, sand–mud or gravel bottoms (poppe & goto 1993). subfossil finds. the limfjord and vendsyssel regions, holocene. spisula elliptica (brown 1827) distribution. around iceland, the faeroes, norway north of lofoten, and south to the english channel and gibraltar. the species occurs in the north sea, extending into the limfjord and kattegat and the øresund (jensen & knudsen 1995). occurrence. the subarctic, boreal and lusitanian regions. habitat. between 20 and 200 m deep in mud, sand and gravel bottoms. subfossil finds. the limfjord, north sea and vendsyssel regions, holocene. from the bælt sea region recorded during the eemian. spisula solida (linnaeus 1758) distribution. s and w iceland, and south to the mediterranean (petersen 1968). in danish waters very common offshore from the west coast of jylland (jensen & knudsen 1995 – as recorded by petersen 1977, fig. 25). the species extends into the limfjord (petersen 1986a) and kattegat, including the øresund and the bælt sea regions (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone down to 100 m on sandy bottoms. in the north sea found at 15–40 m depths in coarse sand (petersen 1977). subfossil finds. the limfjord, north sea and vendsyssel regions, holocene. recorded from the kattegat during the eemian. spisula subtruncata (da costa 1778) fig. 70a, b distribution. norway north of the lofoten islands, and south to the mediterranean (petersen 1968). in danish waters the species extends from the north sea into the kattegat, where it is also common. the species has been recorded both from the øresund and the bælt sea (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone down to 200 m deep fig. 69. mactra stultorum (linnaeus 1758). skagen 4, 15.0–15.5 m b.s., lab. no. 340,93. × 4.8. hinges of two right valves. mguh 25379. geus bulletin no 3.pmd 28-06-2004, 08:4581 82 in mud and sand (poppe & goto 1993). in danish waters common at depths out to 20–30 m in sand (jensen & spärck 1934). subfossil finds. the bælt sea, limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded from the atlantic, subboreal and subatlantic; in the subatlantic occurring in huge quantities. from the eemian recorded from the bælt sea, baltic and kattegat regions. solecurtus chamasolen (da costa 1778) distribution. norway off the lofoten islands, and south to the mediterranean. in the danish waters shells have been found near frederikshavn (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from 5 to 400 m deep on muddy bottoms. subfossil finds. none. solecurtus scopula (turton 1822) distribution. from the british isles and south to the mediterranean. shells recorded from the northern kattegat (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. mainly offshore to 110 m deep in muddy sand and on clean gravel bottoms (poppe & goto 1993). subfossil finds. none. ensis americanus gould 1870 distribution. at present occurring down to the øresund. however, the species has recently accidentally been transported to western europe from the east coast of north america (jensen & knudsen 1995), so it will not be further considered. ensis arcuatus (jeffreys 1865) distribution. the faeroes, the british isles and south to spain. in danish waters shells have been recorded from the kattegat region, including the øresund. occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone to 40 m deep in sand and gravel bottoms. subfossil finds. none. ensis ensis (linnaeus 1758) distribution. the faeroes, norway north of lofoten, and south to the mediterranean (petersen 1968). the species extends from the north sea east to the limfjord and kattegat regions, including the øresund (jensen & spärck 1934; jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone to about 80 m deep, burrowing in fine sand (poppe & goto 1993). from the north sea mainly recorded from depths of 20–30 m on the dogger bank and along the west coast of jylland (petersen 1977, fig. 40). fig. 70. a: spisula subtruncata (da costa 1778). skagen 4, 15.0–15.5 m b.s., lab. no. 340,93. × 4.8. right valve interior. mguh 25380. b: spisula subtruncata (da costa 1778). skagen 4, 15.0–15.5 m b.s., lab. no. 340,93. × 20. serrated surfaces of paired right valve laterals. mguh 25380. geus bulletin no 3.pmd 28-06-2004, 08:4582 83 subfossil finds. the limfjord, north sea and vendsyssel areas, holocene. during the eemian recorded from the bælt sea, north sea and the vendsyssel regions. ensis siliqua (linnaeus 1758) distribution. norway from north of lofoten, and south to the mediterranean. in danish waters, the species is recorded from the north sea, kattegat and øresund (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone to about 70 m deep in fine sand. subfossil finds. none. phaxas pellucidus (pennant 1777) fig. 71 distribution. norway off the lofoten islands, and south to the mediterranean (madsen 1949). in danish waters the species extends into the limfjord and kattegat, øresund and bælt sea regions (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. found offshore between 4 and 150 m deep in sand, mud and gravel bottoms (poppe & goto 1993). in the north sea it is abundant in the whole area, mainly from depths of 30–50 m (petersen 1977). subfossil finds. the limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subboreal and subatlantic. during the eemian found in the north sea and vendsyssel regions. angulus tenuis (da costa 1778) fig. 72 distribution. norway off the lofoten islands, and south to the mediterranean (madsen 1949). in danish waters the species extends from the north sea, where it is common in shallow waters, into the kattegat and limfjord regions (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. common in shallow water down to 10–20 m deep in fine sand. subfossil finds. the bælt sea, limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subatlantic. during the eemian found in the bælt sea and north sea regions. arcopagia crassa (pennant 1778) distribution. from norway south to west africa. only one record from danish waters other than empty shells (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone down to 150 m deep in sand, mud and shell gravel bottoms (poppe & goto 1993). subfossil finds. none. fig. 71. phaxas pellucidus (pennant 1777). skagen 4, 27.0–27.5 m b.s., lab. no. 352,93. × 9.6. view of the inside of a left valve above and a right valve below (valves not paired). mguh 25381. fig. 72. angulus tenuis (da costa 1778). skagen 4, 6.0–6.5 m b.s., lab. no. 331,93. × 4.8. view of the inside of a right valve. mguh 25382. geus bulletin no 3.pmd 28-06-2004, 08:4583 84 tellina donacina linnaeus 1758 distribution. from the shetlands over the british isles and south into the mediterranean (poppe & goto 1993). the species occurs in the southern north sea and has been recorded off edinburgh (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. from the low-tide mark to 200 m deep in sand, mud and gravel bottoms. only subfossil finds. recorded from the north sea during the eemian. fabulina fabula (gmelin 1791) fig. 73a, b distribution. norway of the lofoten islands, and south to the mediterranean (madsen 1949). the species extends into danish waters from the north sea to the kattegat and limfjord regions (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone to 50 m deep in fine sand. in danish waters common on sand between 5– 25 m, but it has been taken at depths of 40 m (jensen & spärck 1934). subfossil finds. the limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subatlantic. from the eemian recorded from the north sea. tellina pygmaea (lovén 1846) fig. 74 distribution. the faeroes, norway north of lofoten, and south to the mediterranean (madsen 1949). the species extends from the north sea into the kattegat and øresund (jensen & knudsen 1995). uncertain in the records from the limfjord (collin 1884, p. 113). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone to depths of 100 m. in the north sea found at depths of 30–50 m on hard bottoms (petersen 1977). subfossil finds. from the skagen well recorded from the subatlantic. gastrana fragilis (linnaeus 1758) distribution. from the british isles including the shetlands, and south to the mediterranean. fig. 73. a: fabulina fabula (gmelin 1791). skagen 4, 6.0–6.5 m b.s., lab. no. 331,93. × 4.8. view of the inside of a right valve. mguh 25383. b: × 4.8. right valve exterior with diagonal lines running from the upper right to the lower left superimposed upon sculpture of concentric lines. mguh 25383. fig. 74. tellina pygmaea (lovén 1846). skagen 4, 27.0–27.5 m b.s., lab. no. 352,93. × 40. right valve. mguh 25384. geus bulletin no 3.pmd 28-06-2004, 08:4584 85 occurrence. mainly the lusitanian region. habitat. from below the tidal zone to a depth of 750 m in sand, mud and gravel bottoms (poppe & goto 1993). subfossil finds. recorded from the bælt sea, kattegat and the north sea during the eemian. macoma balthica (linnaeus 1758) distribution. w greenland, norway from north of lofoten, and south to the british isles (petersen 1968) and spain (poppe & goto 1993). the species is found in all the regions and extends far into the baltic, but it is not common in the north sea region from blåvandshuk and north to skagen (jensen & spärck 1934). occurrence. the subarctic, boreal and lusitanian regions. habitat. this is a shallow-water species, but in the baltic occurs also at depths of more than 50 m on soft bottoms (muus 1967, p. 163). the species is also the characterising animal of the petersen macoma balthica community so often found in the inner danish waters. however, muus (op. cit., pp. 215–217) discussed the problem concerning this community in further detail and concluded that petersen’s community can be considered a serviceable way of giving a brief description of a faunal region for other marine biologists. subfossil finds. the bælt sea, baltic, kattegat, limfjord, north sea and vendsyssel regions, holocene. recorded from the bælt sea, baltic, and the north sea during the eemian, and from the vendsyssel area during the late weichselian. macoma calcarea (gmelin 1791) distribution. w and e greenland, spitsbergen, around iceland, the faeroes, norway from north of lofoten (madsen 1949), and south into the north sea, kattegat, bælt sea and baltic (jensen & spärck 1934). occurrence. the arctic, subarctic and boreal regions. habitat. from the intertidal zone down to several hundred metres in the southern part of the distribution area. the species is the characteristic animal of the arctic macoma community (thorson 1957). subfossil finds. from the vendsyssel region, holocene. recorded from the baltic and the vendsyssel regions during the eemian, from the kattegat and vendsyssel regions during the early/middle weichselian (the older yoldia sea stage), and finally from the vendsyssel region also during the late weichselian (the younger yoldia sea stage). macoma torelli (steenstrup) jensen 1904 distribution. e and w greenland and spitsbergen. according to ockelmann (1958) this species is regarded as having a high-arctic main distribution and being restricted to the n atlantic sector. occurrence. the arctic region. habitat. recorded rarely from greenland sublittorally out to 90 m deep on clay and gravel (ockelmann 1958). subfossil finds. recorded from the vendsyssel region during the late weichselian (the younger yoldia sea). macoma loveni (steenstrup) jensen 1904 distribution. w and e greenland and spitsbergen. according to ockelmann (1958), the main distribution is high-arctic with low-arctic outposts. occurrence. the arctic and subarctic regions. habitat. at east greenland the vertical range of the species has been recorded from 4–5 m to 207 m, and the species has been taken from various types of bottoms: clay, mud, sand, gravel and stony ones (ockelmann 1958). subfossil finds. the vendsyssel region during the late weichselian (the younger yoldia sea). donax vittatus (da costa 1778) fig. 75 distribution. norway off the lofoten islands, and south to the mediterranean (madsen 1949). this species is found on the southern part of the dogger bank and along the west coast of jylland (petersen 1977) but not in the inner danish waters (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. geus bulletin no 3.pmd 28-06-2004, 08:4585 86 habitat. from the tidal zone down to 20 m in clean sand. one of the few molluscan species well suited to live in the coastal zone of sandy beaches. subfossil finds. the limfjord on old beach ridges facing the skagerrak (petersen 1976), north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subatlantic. found in the north sea during the eemian. gari depressa (pennant 1777) distribution. norway off the lofoten islands, and south to the mediterranean. occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone down to about 50 m in sand, mud and gravel bottoms. subfossil finds. the vendsyssel region, holocene. gari fervensis (gmelin 1791) fig. 76 distribution. w greenland, the faeroes, norway north of lofoten, and south to the mediterranean (petersen 1968). in the north sea the species is most common on the dogger bank (petersen 1977) and extends through the skagerrak into the kattegat and øresund (jensen & spärck 1934). occurrence. the subarctic, boreal and lusitanian regions. habitat. from the tidal zone to a depth of 110 m in coarse sand and shell gravel bottoms (poppe & goto 1993). in danish waters on mixed bottoms and sand at depths of 15–40 m (jensen & spärck 1934). subfossil finds. the limfjord, vendsyssel and skagen regions, holocene. recorded from the subatlantic in the skagen well. gari tellinella (lamarck 1818) distribution. s and w iceland, the faeroes, norway north of lofoten, and south to the mediterranean. the species has been taken from the northern kattegat (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone to a depth of 460 m in coarse sand, gravel and stone bottoms. subfossil finds. none. scrobicularia plana (da costa 1778) distribution. norway off the lofoten islands, and south to the mediterranean (madsen 1949). the species extends into the bælt sea at kiel and warnemünde (jensen & spärck 1934), and is also recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone to about 30 m in clay or muddy bottoms, often in estuaries (poppe & goto 1993). jensen & knudsen (1995) point to the occurrences in the wadden sea and to the sensitivity to severe winters, living in such shallow-water environments. fig. 75. donax vittatus (da costa 1778). geus collection. holland. × 4.8. view of the inside of a right valve. mguh 25385. fig. 76. gari fervensis (gmelin 1791). skagen 4, 23.0–23.5 m b.s., lab. no. 348,93. × 4.8. right valve. mguh 25386. geus bulletin no 3.pmd 28-06-2004, 08:4586 87 subfossil finds. the bælt sea, baltic, kattegat, limfjord, north sea and vendsyssel regions, holocene. during the eemian recorded from the bælt sea, baltic, kattegat, and north sea regions. abra alba (wood 1802) fig. 77 distribution. norway off the lofoten islands, and south to the mediterranean (madsen 1949). in danish waters it is found most abundantly in the shallow-water parts of the north sea (petersen 1977) and extends through the skagerrak, limfjord and kattegat and øresund into inner danish waters such as the bælt sea and the baltic to neustadt, where it is the typical bottom animal (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. from the infralittoral zone to a depth of 65 m in sand, mud or muddy gravel (poppe & goto 1993). in danish waters common at depths of 3–8 m and out to 15–20 m in soft bottoms (jensen & spärck 1934). subfossil finds. the bælt sea, kattegat, limfjord, north sea, vendsyssel and skagen regions, holocene. in the skagen well recorded from the subboreal and subatlantic. during the eemian recorded from the bælt sea, north sea and vendsyssel regions. abra nitida (müller 1776) fig. 78 distribution. recorded from s and w iceland, the faeroes, norway north of lofoten, and south to the mediterranean (madsen 1949). in danish waters recorded from the north sea, skagerrak, limfjord and kattegat (jensen & spärck 1934), including the øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. mainly offshore to depths of 200 m in sandy mud, mud or gravel bottoms (poppe & goto 1993). however, in danish waters such as the north sea on soft to mixed bottoms at depths of 40–70 m (petersen 1977) and in the skagerrak at depths of 100–300 m extending into the kattegat, including the øresund, on soft bottoms (jensen & spärck 1934). subfossil finds. the limfjord, north sea, vendsyssel and skagen regions, holocene. in the skagen well recorded from the subboreal and subatlantic. during the eemian recorded from the vendsyssel region. abra prismatica (montagu 1803) fig. 79 distribution. s and w iceland, the faeroes, norway north of lofoten, and south to the mediterranean (madsen 1949). in the danish waters the species extends from the north sea and skagerrak into the kattegat and øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the infralittoral zone to 400 m deep in sand or muddy sand (poppe & goto 1993). in the north sea most abundant at depths deeper than 50 m on mixed bottoms (petersen 1977). subfossil finds. the limfjord, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subboreal and subatlantic. during the eemian refig. 77. abra alba (wood 1802). geus collection. storebælt, denmark. × 4.8. specimen seen from the left. mguh 25387. fig. 78. abra nitida (müller 1776). geus collection. hellebæk, denmark. × 4.8. specimen seen from the left. mguh 25388. geus bulletin no 3.pmd 28-06-2004, 08:4587 88 corded from the bælt sea, kattegat, north sea, and vendsyssel regions. abra segmentum (récluz 1843) distribution. from the west coast of france into the mediterranean. occurrence. the lusitanian region. habitat. in the infralittoral zone in sandy mud (poppe & goto 1993). it seems to be connected with the shallow-water environment, also with brackish water (jensen & spärck 1934). only subfossil finds. recorded from the bælt sea and the north sea during the eemian. arctica islandica (linnaeus 1767) fig. 80 distribution. around iceland, the faeroes, norway north of lofoten, and south to the bay of biscay. in the danish waters, including the limfjord, the species extends from the north sea and skagerrak as far as the baltic (to bornholm) (jensen & spärck 1934). occurrence. the subarctic, boreal and (lusitanian) regions. however, the species tends to live more deeply in the southern part of its range (poppe & goto 1993). habitat. intertidal to 482 m in mud, sand or gravel bottoms. in the north sea mainly from depths deeper than 40 m and from mixed bottoms (petersen 1977). in inner danish waters often at depths from 10–15 to 50–60 on clay or clayey bottoms (jensen & spärck 1934). according to badarsson (1920), fishermen say that the species occurs in very shallow water, just below the low-water mark, in winter living deeply burrowed in the substrate, but in the summer often lying in abundance on the bottom. subfossil finds. the kattegat, limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded in the subatlantic. in the bælt sea, baltic and north sea (there are (single find) records from the eemian and the vendsyssel region during the late weichselian (the younger yoldia sea). kelliella miliaris (philippi 1844) fig. 81 distribution. from norway off the lofoten islands, and south to the mediterranean. from danish waters recorded from the skagerrak. according to jensen & spärck (1934), very common in the deeper part of the skagerrak. jensen & knudsen (1995) mentioned a single finding from the southern kattegat. fig. 79. abra prismatica (montagu 1803). geus collection. iceland. × 4.8. specimen seen from the left. mguh 25389. fig. 80. arctica islandica (linnaeus 1767). geus collection. læsø rende, denmark. × 4.8. juvenile specimen, beaks directed forwards. mguh 25390. fig. 81. kelliella miliaris (philippi 1844). skagen 3, 185.04–185.06 m b.s., core sample-102. × 20. two specimens seen from the left. inside the corroded specimen to the left, pyrite is seen. mguh 25391. geus bulletin no 3.pmd 28-06-2004, 08:4588 89 occurrence. the boreal and lusitanian regions. habitat. from 134 to 700 m deep (nordsieck 1969). subfossil finds. recorded from the eemian in the vendsyssel and skagen regions. glossus humanus (linnaeus 1758) distribution. s and w iceland, norway off the lofoten islands, and south to the mediterranean. in danish waters recorded from the north sea and kattegat, where shells are common (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. offshore beyond 7 m on bottoms of sand, sandy mud or soft mud (tebble 1966). subfossil finds. none. chamelea striatula (da costa 1778) fig. 82 distribution. the faeroes, norway north of lofoten, and south to the mediterranean (madsen 1949). in danish waters the species extends from the north sea, limfjord and skagerrak into the kattegat and øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the infralittoral zone to 55 m deep on sand and mud bottoms (poppe & goto 1993). in the north sea mainly from 20 to 40 m on sand to mixed bottoms (petersen 1977). in the skagerrak at depths of more than 100 m, but in the kattegat at depths of less than 50 m, since the sand bottom is not to be found at deeper levels (jensen & spärck 1934). subfossil finds. the limfjord, north sea, vendsyssel and skagen areas, holocene. from the skagen well recorded from the subboreal and subatlantic. during the eemian recorded from the bælt sea, north sea and vendsyssel regions. clausinella fasciata (da costa 1778) distribution. the faeroes, norway off the lofoten islands, and south to the mediterranean. from the north sea the species extends into the kattegat (petersen 1888). occurrence. the boreal and lusitanian regions. habitat. from 4 to 110 m deep in sand, mud and gravel bottoms (poppe & goto 1993). in the north sea in hard sand (petersen 1977), and in the kattegat in gravel and sand between 15 and 30 m (petersen 1888, p. 143). subfossil finds. the limfjord, north sea and vendsyssel areas, holocene. paphia aurea (gmelin 1791) distribution. norway off the lofoten islands, and south to the mediterranean. the finds closest to danish waters are from southern norway (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone down to 36 m deep in sand, mud and gravel bottoms. only subfossil finds. the bælt sea, kattegat, limfjord, north sea and vendsyssel regions, holocene. recorded from the kattegat region during the eemian. paphia aurea senescens (cocconi 1873) distribution. the only one of our quaternary molluscs which does not live at present. also found in quaternary deposits in italy (jensen & spärck 1934). regarded as a lusitanian species according to nordmann (1913). however, poppe & goto (1993) regard the fossil valves found, for example along the coast of the netherlands and belgium, as a subspecies in which the differences fig. 82. chamelea striatula (da costa 1778). skagen 4, 21.0– 21.5 m b.s., lab. no. 346,93. × 4.8. left valve. mguh 25392. geus bulletin no 3.pmd 28-06-2004, 08:4589 90 from extant ones are minimal, and they propose that the relationship between the fossil and recent shells be restudied. from nordmann (1913) and cerulli-irelli (1908) it seems right that tapes senescens doederl. and tapes aureus var. eemiensis are identical. but as the relationship between t. senescens and t. aureus sensu stricto at the time of nordmann (1913) was not clear, the position as a not extant subspecies given by poppe and goto is followed here. only subfossil finds. the bælt sea, kattegat, and north sea regions during the eemian. tapes decussatus (linnaeus 1758) distribution. norway off the lofoten islands, and south to the mediterranean. closest to danish waters the species occurs off western norway (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. from the tidal zone to a depth of few metres in sand or muddy-gravel bottoms. only subfossil finds. the kattegat, limfjord, north sea and vendsyssel regions, holocene. recorded from the north sea region during the eemian. timoclea ovata (pennant 1777) fig. 83a, b distribution. s and w iceland, the faeroes, norway north of lofoten, and south to the mediterranean (madsen 1949). in danish waters the species extends from the north sea into the kattegat and øresund (jensen & knudsen 1995), but has not been recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. at depths between 4 and 200 m on all types of bottoms (poppe & goto 1993). in the north sea usually deeper than 50 m and on soft bottoms (petersen 1977). subfossil finds. the limfjord, north sea, vendsyssel and skagen regions, holocene. in the skagen well recorded from the subatlantic. during the eemian found in the bælt sea, kattegat and north sea regions. venerupis rhomboides (pennant 1777) distribution. the faeroes, norway off the lofoten islands (madsen (1949) does not mention any norwegian occurrence), and south to the mediterranean (petersen 1968). one pair of united valves recorded from the northern kattegat (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone to 180 m deep (poppe & goto 1993) in gravel and mud bottoms. subfossil finds. the limfjord and vendsyssel regions, holocene. venerupis pullastra (montagu 1803) distribution. norway from north of the lofoten islands, and south to the mediterranean (madsen 1949). from danish waters recorded from the limfjord and kattefig. 83. a: timoclea ovata (pennant 1777). skagen 4, 27.0–27.5 m b.s., lab. no. 352,93. × 40. left valve. mguh 25393. b: timoclea ovata (pennant 1777). geus collection. herthas flak, denmark. × 4.8. right valve. mguh 25394. geus bulletin no 3.pmd 28-06-2004, 08:4590 91 gat regions (jensen & spärck 1934) and the øresund (jensen & knudsen 1995). the species has a common occurrence in the isefjord (rasmussen 1973). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone to 40 m deep in hard sand and muddy gravel (poppe & goto 1993). rasmussen (1973, p. 303): considers “its present common occurrence there [in the isefjord] to be a result of the disappearance of the zostera since 1933–45, as the lack of a continuous vegetation caused a change in the bottom conditions to the benefit of venerupis pullastra. undoubtedly the species has lived in interior danish waters since the stone age, being, however, rare in recent times up to 1933–34”. subfossil finds. the bælt sea, kattegat, limfjord, north sea and vendsyssel regions, holocene. recorded from the north sea region during the eemian. dosinia exoleta (linnaeus 1758) distribution. norway off lofoten, and south to the mediterranean. the species extends from the north sea (petersen 1977) into the northern kattegat (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone to 73 m deep, burrowing deeply in sand, mud and gravel bottoms (poppe & goto 1993). in the north sea found at depths of 30– 100 m, on hard bottoms around the dogger bank (petersen 1977). subfossil finds. the north sea and vendsyssel regions, holocene. dosinia lincta (montagu 1803) distribution. s and w iceland, the faeroes, norway north of lofoten, and south to the mediterranean (petersen 1968). the species extends from the north sea into the kattegat and øresund (petersen 1888). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone to 200 m deep in pure sand and fine gravel bottoms (poppe & goto 1993). in the north sea sampled at 10–100 m on soft to mixed bottoms (petersen 1977). from the kattegat recorded on mixed bottoms between 18 and 56 m (petersen 1888). subfossil finds. the north sea and vendsyssel regions, holocene. recorded from the bælt sea and the north sea during the eemian. gouldia minima (montagu 1803) distribution. the faeroes, norway off the lofoten islands, and south to the mediterranean (petersen 1968). occurrence. the boreal and lusitanian regions. habitat. from below the tidal zone to depths of over 200 m in sand, mud and fine gravel bottoms (poppe & goto 1993). only subfossil finds. recorded from the bælt sea and the north sea during the eemian. petricola pholadiformis (lamarck 1822) distribution. this species in an immigrant introduced in to europe, probably with oysters, at the end of the last century (poppe & goto 1993). according to jensen & knudsen (1995), the species occurred in 1906 in the wadden sea; the skagerrak 1905; the kattegat 1931; and the bælt sea 1943. it will not be considered any further in this work. mysia undata (pennant 1777) distribution. the faeroes, norway north of the lofoten islands, and south to the mediterranean (petersen 1968). in danish waters the species extends from the north sea (petersen 1977) into the kattegat and øresund (jensen & knudsen 1995). it is not recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from below the tidal zone to depths of 55 m in muddy sand and gravel bottoms (poppe & goto 1993). in the north sea found at depths of 40–70 m on soft to mixed bottoms (petersen 1977). subfossil finds. the limfjord and vendsyssel regions, holocene. during the eemian recorded from the north sea region. geus bulletin no 3.pmd 28-06-2004, 08:4591 92 order myoida mya arenaria linnaeus 1758 distribution. norway from north of the lofoten islands, south to the british isles (petersen 1968). the species extends from the north sea into the limfjord and the inner danish waters, including the baltic (jensen & spärck 1934). it is a late immigrant, known from europe in the plio-pleistocene (strauch 1972, pp. 135– 137) having been transferred from north america by man, presumably the vikings, and dated back to the 13th century, i.e. well before columbus (petersen et al. 1992b). occurrence. mainly in the boreal region, but with new finds further to the south on the east coast of north america (rasmussen & heard 1994). habitat. from the tidal zone down to 6–7 m deep in sandy bottoms, the species avoids high-energy coastal environments (jensen & spärck 1934). subfossil finds. the records from the bælt sea and vendsyssel might be of recent dates; only the occurrences at jerup halfway up to the skagen spit have been dated and included in the skagen area from the subatlantic. mya truncata linnaeus 1758 distribution. w and e greenland, spitsbergen, around iceland, the faeroes, norway from north of lofoten, and south to the bay of biscay (madsen 1949; poppe & goto 1993). the species extends from the north sea into the limfjord and the inner danish waters as far as the bælt sea (kiel and warnemünde) (jensen & spärck 1934). occurrence. the arctic, subarctic, boreal and lusitanian regions. habitat. from the intertidal zone down to about 75 m deep (poppe & goto 1993). however, in danish waters often at depths between 10 and 20 m (jensen & spärck 1934). in the north sea found at depths of 37– 70 m on soft mixed bottoms (petersen 1977). in east greenland the species belongs to the arctic macoma community (ockelmann 1958). however, according to jensen (1900) the typical mya truncata is not found in the arctic (g.h. petersen, personal communication 1998). subfossil finds. the bælt sea, kattegat, limfjord, north sea and vendsyssel regions, holocene. recorded from the eemian in the bælt sea, baltic, north sea and vendsyssel areas. from the early/middle weichselian in the kattegat and vendsyssel regions, and from the vendsyssel region also in the late weichselian. corbula gibba (olivi 1792) fig. 84 distribution. norway north of lofoten, and south to the mediterranean (petersen 1968). the species extends from the north sea into the inner danish waters, including the limfjord, as far as the westernmost part of the baltic region at møn (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. from the low intertidal zone to 250 m deep anchored by a byssus on silty sand and muddy-gravel bottoms (poppe & goto 1993). however, in danish waters rarely at depths of more than about 50 m (jensen & spärck 1934). in the north sea sampled at 35–50 m depths on mixed bottoms (petersen 1977). subfossil finds. the bælt sea, baltic, kattegat, limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subboreal and subatlantic. during the eemian recorded from the bælt sea, baltic, kattegat, north sea and vendsyssel regions. fig. 84. corbula gibba (olivi 1792). skagen 3, 37.00–37.25 m b.s., lab. no. 710,93. × 9.6. to the upper left a specimen seen from the left, and to the right a view of the inside of a right valve. mguh 25395. geus bulletin no 3.pmd 28-06-2004, 08:4592 93 hiatella arctica (linnaeus 1758) fig. 85 distribution. w and e greenland, spitsbergen, around iceland, the faeroes, norway from north of lofoten, and south to the mediterranean (madsen 1949). following jensen & spärck (1934) who regard the records of hiatella as one species, it is widely spread but not always common in all the danish waters, it extends to kiel in the bælt sea. occurrence. the arctic, subarctic, boreal and lusitanian regions. habitat. “from the intertidal zone down to almost 1400 m fixed by its byssus on or in all kinds of substrate on all types of bottoms. also found in holes previously bored by other species” (poppe & goto 1993, p. 130). however, petersen (1977, p. 228) states: “both the systematics and nomenclature are insufficiently investigated for this genus”. so with regard to the subfossil finds, the questions on species are even more difficult, as seen from petersen (1986b, figs 2, 3), where forms with different habitat such as hiatella cf. byssifera are found fixed on a stone taken as a grab sample in kejser franz josephs fjord, east greenland, and as traces of hiatella arctica in the saxicava sand of late weichselian age in vendsyssel. however, here símonarson et al. (1998) is followed, relating the more widely used and less specific name hiatella arctica. subfossil finds. the bælt sea, limfjord, north sea, vendsyssel and skagen areas, holocene. from the skagen well records from the subboreal and subatlantic. from the eemian recorded from the kattegat, north sea, vendsyssel and skagen regions. in the kattegat and vendsyssel regions finds from the early/middle weichselian (the older yoldia sea) and in the vendsyssel region from the late weichselian (the younger yoldia sea). hiatella rugosa (linnaeus 1758) distribution. jensen & knudsen (1995) include this as a separate species and take it as part of the recent danish shell-bearing fauna. records from the literature on subfossil finds are therefore considered here. according to poppe & goto (1993), found from norway south to the mediterranean. ockelmann (1958, p. 135 ff.), discussing the hiatella taxonomy at some length, concludes that reservations must be made as to future separations of the hiatella forms (h. arctica incl. of h. gallicana and h. pholadis) occurring in the northern hemisphere into valid species. occurrence. the arctic, subarctic, boreal and lusitanian regions. subfossil finds. the kattegat and vendsyssel regions, holocene. saxicavella jeffreysi winckworth 1930 fig. 86 distribution. norway off the lofoten islands, and south to the mediterranean (madsen 1949). the species extends into the kattegat and øresund, although rare (jensen & knudsen 1995). it has been recorded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. offshore between 7 and 240 m deep in sand, mud or gravel bottoms (poppe & goto 1993). in the fig. 85. hiatella arctica (linnaeus 1758). skagen 3, 37.00–37.25 m b.s., lab. no. 710,93. × 20. left valve. mguh 25396. fig. 86. saxicavella jeffreysi winckworth 1930. skagen 4, 20.0– 20.5 m b.s., lab. no. 345,93. × 4.8. right valve. mguh 25397. geus bulletin no 3.pmd 28-06-2004, 08:4593 94 danish waters often at depths between 25–50 m (jensen & spärck 1934). subfossil finds. the limfjord, north sea, vendsyssel and skagen regions, holocene. in the skagen well recorded from the subatlantic. during the eemian recorded from the north sea region. panomya arctica (lamarck 1818) distribution. s and w iceland, norway from north of lofoten, and south to the british isles and denmark (madsen 1949). however, petersen (1968) refers to empty shells from n iceland and occurrences in the clyde sea and off the isle of man. in danish waters only once taken alive near skagen, otherwise shells only, but found as far south as øresund (jensen & knudsen 1995). occurrence. mainly boreal, but outposts into the subarctic (subfossil?) and lusitanian regions (strauch 1972). habitat. from the intertidal zone down to 300 m buried in mud or sand (poppe & goto 1993). subfossil finds. none. barnea candida (linnaeus 1758) fig. 87 distribution. norway off the lofoten islands, and south to the mediterranean (madsen 1949). in the danish waters, including the limfjord, the species extends into the bælt sea as far as kiel (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. from the low intertidal zone to about 30 m deep, the species bores in semi-hard substrates such as clay (poppe & goto 1993). subfossil finds. the bælt sea, limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subatlantic. during the eemian found in the bælt sea and north sea regions. pholas dactylus linnaeus 1758 fig. 88a, b distribution. norway off the lofoten islands, and south to the mediterranean (madsen 1949). in danish waters only found to frederikshavn and the limfjord (petersen 1986a; jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone to a depth of 10 m boring in different substrates, preferring clay bottoms (poppe & goto 1993). subfossil finds. the limfjord, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subatlantic. zirfaea crispata (linnaeus 1758) distribution. around iceland, norway from north of the lofoten islands, and south to the bay of biscay (madsen 1949). in the danish waters, including the limfjord, extending into the bælt sea as far as kiel (jensen & spärck 1934). occurrence. mainly boreal with outposts into the lusitanian region. habitat. from the low tide line to about 7 m deep, boring in semi-hard substrates (poppe & goto 1993). in the danish waters the species has a wide extension, depending on the bottom substrates (jensen & spärck 1934): in the north sea and skagerrak peat and chalk; in the limfjord cementstone, mo-clay, chalk, peat and clay; and the bælt sea clayey bottoms. subfossil finds. the bælt sea, limfjord, north sea and vendsyssel regions, holocene. from the bælt sea region recorded from the eemian and from the vendsyssel region during the late weichselian (the younger yoldia sea). fig. 87. barnea candida (linnaeus 1758). geus collection. off rubjerg knude, denmark. × 4.8. left valve. mguh 25398. geus bulletin no 3.pmd 28-06-2004, 08:4594 95 xylophaga dorsalis turton 1822 distribution. s and w iceland, norway from north of lofoten, and south to the mediterranean. recorded from the øresund region (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. according to madsen (1949) the occurrences at iceland have been from depths between 140–230 m found in sunken pieces of wood. subfossil finds. none. teredo navalis linnaeus 1758 distribution. norway off the lofoten islands (petersen 1968), and south to the mediterranean (madsen 1949). the species is found into the bælt sea (jensen & spärck 1934). occurrence. the boreal and lusitanian regions. habitat. specialised wood-borers. subfossil finds. none. nototeredo norvegica (spengler 1792) distribution. s and w iceland, norway north of lofoten, and south to the mediterranean (madsen 1949). the species extends from the north sea (in driftwood) into the bælt sea as far as kiel (jensen & spärck 1934), and was recorded from the limfjord by collin (1884). occurrence. the boreal and lusitanian regions. habitat. in driftwood. subfossil finds. none. psiloteredo megotara (forbes & hanley 1848) distribution. w greenland, spitsbergen, around iceland, norway north of lofoten, and south to the mediterranean (madsen 1949). in danish waters common on the west coast of jylland and recorded from the kattegat, including øresund (jensen & knudsen 1995). occurrence. the arctic, subarctic, boreal and lusitanian regions, although rare in the last region. habitat. only in driftwood (jensen & knudsen 1995). subfossil finds. none. subclass anomalodesmata order pholadomyoida pandora glacialis leach 1819 distribution. w and e greenland and spitsbergen (madsen 1949). occurrence. the arctic and subarctic regions. habitat. from 2 to 205 m deep on mixed bottoms (ockelmann 1958). only subfossil finds. from the vendsyssel region during early/middle and late weichselian (the older yoldia sea and the younger yoldia sea respectively). fig. 88. a: pholas dactylus linnaeus 1758. skagen 4, 20.0–20.5 m b.s., lab. no. 345,93. × 9.6 fragment with umbonal reflection with septa. mguh 25399. b: pholas dactylus linnaeus 1758. geus bulletin no 3.pmd 28-06-2004, 08:4595 96 lyonsia norwegica (gmelin 1791) distribution. s and w iceland, the faeroes, norway off the lofoten islands, and south to the mediterranean. in danish waters recorded from the kattegat. occurrence. the boreal and lusitanian regions. habitat. from 20 to 250 m deep in sand, silty sand and mud bottoms. subfossil finds. recorded from the skagen region, holocene. in the skagen well recorded from the preboreal and boreal. lyonsia arenosa (möller 1842) distribution. w and e greenland, spitsbergen, and norway north of the lofoten islands. main distribution in the arctic and subarctic regions. habitat. from 3 to about 200 m on mixed bottoms (ockelmann 1958). subfossil finds. recorded from the vendsyssel region during the early/middle weichselian and the late weichselian (the older yoldia sea and the younger yoldia sea respectively). cochlodesma praetenue (pulteney 1799) fig. 89a, b distribution. s and w iceland, the faeroes, norway off the lofoten islands, and south to gibraltar (petersen 1968). the species is rare in danish waters and has only once been taken live in the kattegat (jensen & spärck 1934), although shells are found in the øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from the intertidal zone down to 110 m in sand, mud and gravel bottoms. subfossil finds. the north sea and skagen regions, holocene. from the skagen well recorded from the subatlantic. during the eemian recorded from the skagen region. thracia convexa (wood 1815) distribution. the faeroes, norway off the lofoten islands, and south to the mediterranean (madsen 1949). in danish waters recorded from the kattegat (jensen & knudsen 1995). occurrence. the boreal and lusitanian zones. habitat. offshore down to over 800 m in mud and sand bottoms (poppe & goto 1993). in the danish waters taken between 30–80 m (jensen & spärck 1934). subfossil finds. none. thracia phaseolina (lamarck 1818) fig. 90 distribution. s and w iceland, norway off the lofoten islands, and south to the mediterranean (madsen 1949). the species extends from the north sea (petersen 1977) into the kattegat and øresund, although with few records (jensen & knudsen 1995), and it has been refig. 89. a: cochlodesma praetenue (pulteney 1799). skagen 3, 43.19–43.24, core sample-9. × 9.6. view of the inside of a fragmented right valve. mguh 25401. b: cochlodesma praetenue (pulteney 1799). geus collection. læsø rende, denmark. × 4.8. detailed view of the inside of a right valve showing the resilifer. mguh 25402. geus bulletin no 3.pmd 28-06-2004, 08:4596 97 corded from the limfjord (petersen 1986a). occurrence. the boreal and lusitanian regions. habitat. from the low intertidal zone down to 50 m in fine sand, mud or gravel bottoms (poppe & goto 1993). subfossil finds. the limfjord, north sea, vendsyssel and skagen regions, holocene. from the skagen well recorded from the subatlantic. during the eemian found in the bælt sea and north sea regions. thracia gracilis (jeffreys 1865) distribution. recorded from the atlantic (nordsieck 1969). from the danish waters found in the northern kattegat (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. subfossil finds. none. thracia villosiuscula (macgillivray 1827) distribution. s and w iceland, the faeroes, norway off the lofoten islands, and south to the british isles (petersen 1968). according to poppe & goto (1993) also found in the mediterranean. occurrence. the boreal and lusitanian regions. habitat. in the north sea sampled at depths between 20 and 50 m on hard sand (petersen 1977). subfossil finds. recorded from the north sea region during the eemian. cuspidaria cuspidata (olivi 1792) distribution. norway off the lofoten islands, and south to the mediterranean. in the danish waters found in the kattegat (jensen & spärck 1934) and øresund (jensen & knudsen 1995). occurrence. the boreal and lusitanian regions. habitat. from 20 m to 250 m deep in muddy sand and gravel bottoms (poppe & goto 1993). in danish waters at depths between 30 and 60 m (jensen & spärck 1934). subfossil finds. none. cuspidaria obesa (lovén 1846) distribution. e and w greenland, spitsbergen, around iceland, norway north of the lofoten islands, and south to the mediterranean; however, to the south only at depths greater than 400 m (madsen 1949). in danish waters recorded from the skagerrak and kattegat. occurrence. the arctic, subarctic and boreal regions. habitat. at depths from 40 to 2500 m according to madsen (1949), but in danish waters fairly common in the deeper part of the skagerrak. subfossil finds. none. fig. 90. thracia phaseolina (lamarck 1818). skagen 4, 14.0– 14.5 m b.s., lab. no. 339,93. × 9.6. fragment of left valve. mguh 25403. geus bulletin no 3.pmd 28-06-2004, 08:4597 geological survey of denmark and greenland. bulletin 10, 65-70 the kenya coastline extends 600 km from the border of tanzania in the south to the border of somalia in the north (fig. 1). the kenyan coast features a diverse marine environment, including estuaries, mangroves, sea grass beds and intertidal reef platforms and coral reefs, which are vital for the reproduction of marine organisms. these coastal ecosystems are regarded as some of the most valuable in kenya but face serious threats from the ever increasing human pressure of tourism, industrial pollution, destructive fishing, mangrove logging and other unsustainable uses of marine resources. another serious threat is the maritime transportation activities along the coast and at the ports. it is estimated that at any given time more than 50 ships operate in the major shipping lanes off the kenyan coast, of which about nine are oil tankers with capacities ranging from 50 000 to 250 000 tonnes. furthermore, the harbour of mombasa serves as the major port for countries in east africa. in recognition of the risks posed by oil pollution the government of kenya and the commercial petroleum industry agreed to develop a national oil spill response contingency plan (nosrcp) with the purpose of enabling a speedy and effective response to any oil spill within the territorial waters of kenya. an important element of this plan was the mapping of the coastal resources and the development of an environmental sensitivity atlas showing the vulnerability of the coast to marine oil spills. in 2004, the government of kenya approached the united nations development program (undp) in kenya for financial support to develop an environmental sensitivity atlas. the project was approved and forwarded for funding by the danish consultancy trust fund administrated by united nations operational program (unops) in copenhagen. the project was announced in denmark, and the kensea group headed by the geological survey of denmark and greenland (geus) was awarded the contract. the project comprises four phases: (1) data compilation and development of the kensea database, (2) development of a coastal classification for kenya, (3) development of the sensitivity index jointly with a group of stakeholders, and (4) compilation of the kensea environmental sensitivity atlas (tychsen 2006). development of the kensea database in the 1990s the eastern africa coastal and marine resources database and atlas (unep 1998) was developed by the united nations environmental programme. this database contains a variety of datasets covering bioscience, geoscience and human use, which have been incorporated either directly or as guidelines for further investigations in the kensea database (kenseabase). however, the unep atlas has been produced at the scale of 1:250 000, implying a lower degree of spatial resolution than the scale of 1:50 000 requested for the kensea project. kensea – development of an environmental sensitivity atlas for coastal areas of kenya john tychsen, ole geertz-hansen and jesper kofoed © geus, 2006. geological survey of denmark and greenland bulletin 10, 65–68. available at: www.geus.dk/publications/bull 65 mombasa 50 km kenya africa 39°e 40°e 41°e 5°s 4°s 3°s 2°s kenya tanzania indian ocean somalia fig.3 fig. 1. the coastal area of kenya (red frame on index map) showing coverage of the kensea coastal sensitivity map (ruled area). green frame, location of maps shown in fig. 3. 66 following a kick-off seminar with all stakeholders, the team from the kensea group visited a large number of government agencies, ministries, private companies and national as well as international non-governmental organisations to collect additional and updated data. all collected data were digitised and included in the kenseabase, and preliminary maps were printed. based on these preliminary maps, a field programme for data verification and additional data collection was developed and carried out. the results were integrated into the kenseabase and logistic and topographic maps and coastal resource maps were produced. development of a coastal classification for kenya many attempts have been made worldwide to classify coastlines with respect to their vulnerability to oil pollution. these classifications are usually based on the geomorphology, the degree of exposure to wind and waves, and other relevant conditions. most of these classifications were inspired by gundlach & hayes (1978) and baker et al. (1994). the classification adopted for the kensea project is a further development of these classifications to meet the conditions in kenya. in addition to coastal geomorphology and degree of exposure, the ecological value and biodiversity of this particular stretch of coastline is taken into account, as well as the ability of the particular coastal types to facilitate selfcleaning and the conditions for removing a potential oil spill. the resulting classification comprises seven categories, each of which can be described in terms of its geomorphology, ecological value and vulnerability to an oil spill (tychsen 2006). rocky coast much of the kenyan coast is formed by 4–6 m high pleistocene coral limestone cliffs (fig. 2). at present-day sea level they are exposed to wave erosion, resulting in an irregular and rugged appearance. in the upper part of the intertidal zone biological activity is sparse. subtidal rocks and man-made hard-surface structures such as piers and wharfs may develop a richer flora and fauna, resembling the conditions found on reefs. the exposed cliffs are regarded as less sensitive to oil pollution than most other habitats because of the sparse biological activity, and because the exposure to waves makes the surface to some extent self-cleaning. sandy beaches and dunes two types of sandy shores are present along the kenyan coast: (1) gentle to steep sandy beaches without protection from a reef. the beach is often backed by one or a series of windblown sand dunes. the sand may be of terrestrial origin and supplied by the larger rivers. (2) gently sloping beaches sheltered behind a reef are common along the coast and the sand is often white calcareous sand of marine origin (coral sand). species diversity on sandy beaches is usually low. above the high-water line, only a few burrowing crabs and amphipods are usually found. the density and diversity of crabs, bivalves, polychaetes and other marine invertebrates increases in the intertidal zone, but remains low compared to most other habitats. fine-grained sandy beaches are less sensitive to oil pollution due to their relatively sparse biological activity. furthermore, they are relatively easy to clean since oil does not penetrate deep and can be removed either manually or by use of machinery. on the other hand, coarse sand or gravel is more sensitive as the oil can sink deep into it, and the oil may therefore be impossible to remove. coral reefs and reef flats most of the kenya coastline is fringed by a major barrier reef complex that includes the most diverse ecosystems in the marine environment. the up to 2 km wide shallow-water reef flats between the coastal cliffs and the reef crest comprise fossil reefs currently eroded by wave action. active reef growth occurs at the reef crest and on the slope facing the ocean where coral reef growth occurs to depths between 20 and 25 m. the main part of the reefs are subtidal, and are therefore sheltered from direct contact with a possible oil slick. however, reef crests are usually exposed at low tide and the intertidal corals will be killed immediately by contact with oil. the deeper parts of the reef may also be endangered as waves break on the crest and fine oil droplets become dispersed in the water column. recovery of damaged coral reefs may take several decades, and restoration techniques are usually not very successful. fig. 2. pleistocene coral limestone cliffs typical of the kenyan coast. rias rias are drowned river valleys or estuaries. the typical ria has a steep slope or a sheltered cliff, often with a narrow subtidal muddy beach with a few mangrove trees. the sheltered environment of the ria has only little self-cleaning capacity, although it is often possible to clean from the seaward side because of its narrow extent. river mouths and estuaries the rivers in the area form large, gently sloping floodplains with extensive estuarine zones characterised by fluctuating salinity. the mouths of smaller rivers are often hidden behind mangrove creeks. few plant species apart from mangroves are adapted to low or fluctuating salinities. the biodiversity is therefore low within the estuaries, although the density is usually very high due to the continuous supply of food and nutrient from the river. the high density of bivalves, snails and other benthic invertebrates usually attracts many birds. tidal currents can carry any oil pollution far into the estuary and thus into contact with a high density of food items. therefore the sensitivity is very high. flushing and self-cleaning is limited to the seasonal high flow situations. mangroves mangroves have a high productivity as they profit from nutrients from both land and sea, and mangrove detritus is often the main source of energy fuelling the estuarine food webs. mangroves are favoured by fine-grained nutrient-rich sediment, and are therefore often associated with estuaries and other freshwater outlets. while the diversity of mangrove tree species is limited, they create a multitude of niches suitable for a vast diversity of other organisms. oil can be acutely toxic to the mangrove as clogging of the aerial roots by oil may hinder proper ventilation 67 human use major town town settlement water intake historical/cultural site hotel ferry crossing biological resources turtle, high priority turtle, low priority forest bird wader, high sensitivity wader, moderate sensitivity wader, low sensitivity coral mangrove priority coral forest or thicket plantation papyrus swamp important bird area sand or mud seasonal swamp sensitivity index line level 1 (low) level 2 level 3 level 4 level 5 (high) coastal types mangrove sheltered rias tidal mud flats sheltered sand exposed sand rock coral environmental sensitivity map coastal resource map fish traps fish landing site air strip main road road track fig. 3. examples of a coastal resource map (left) and an environmental sensitivity map (right) from the kensea environmental sensitivity atlas (see fig. 1 for location). 68 of subsurface parts and lead to suffocation and stress, and eventually death. clean-up operations may prove extremely difficult due to the low energy environment of mangrove forests. intertidal mud flats sheltered mangroves in creeks or bays are often fringed by a broad intertidal mudflat. these are characterised by a high density of marine invertebrates such as mussels, snails and crustaceans. although diversity is usually low they are important feeding grounds for aquatic birds. the mudflats are sensitive to oil spills since they are difficult to clean mechanically without mixing the oil into the sediment. where mangrove forests are associated with mudflats the clean-up is even more difficult for both habitats. development of a sensitivity index the oil spill sensitivity ranking is designed to help decisionmakers to prioritise the available resources and to focus the emergency response on the most vulnerable areas, both (1) during the pre-spill planning, in order to prepare appropriate response strategies and (2) during an oil spill combat in order to plan and continuously optimise the response strategy under the given conditions and limitations (oil type, weather, equipment, crew, etc.). planning the clean-up operation and avoiding post-spill damage the goal of oil spill response is to minimise the overall impacts on natural and economic resources as well as cultural assets, but some aspects will be of greater concern than others. the sensitivity ranking for a given stretch of coastline therefore includes the actual sensitivity of the present resources or assets, and a more subtle evaluation of importance or value. the ranking should integrate a multitude of data such as geomorphological and geological properties, wave exposure, biological diversity and productivity, oil behaviour, ease of clean-up, human use and cultural assets. although these properties are not directly comparable or quantifiable the outcome should ideally be a simple statement, a numerical index value, or a colour code. the comparison and evaluation of incomparable properties is a matter of balancing often conflicting interests, and no perfect system can be devised. a complicated system is not necessarily better or more accurate than a simple system or qualified judgments. therefore, it is essential that the amount of detail matches the purpose, and leaves the decision-makers with some alternatives. the total sensitivity index developed for the kensea atlas embraces three main themes: (1) coastal type, (2) biological resource, and (3) human use. for each theme an index value that incorporates the index values for the various attributes encompassed by the particular theme has been allocated for a particular stretch of coastline. the index value for the individual attributes used in each of the themes and the formula for calculating the total index were developed during a seminar with participants from government agencies, ministries, private sector as well as national and international ngos. this joint development of the formula is crucial for the future use of the sensitivity index. the sensitivity index line has been reproduced on the environmental sensitivity maps (fig. 3). environmental sensitivity atlas the atlas covers the entire coastline and comprises three types of maps, each of which have been produced in 16 map sheets at scale 1:50 000 (fig 1; tychsen 2006). references baker, j.m., spalding, m.d., moore, j. & tortell, p. 1994:. sensitivity mapping for oil spill response. imo/ipieca report series 1, 24 pp. gundlach, e.r. & hayes, m.o. 1978: vulnerability of coastal environments to oil spill impacts. marine technology society journal 12, 18–27. tychsen, j. 2006 (ed.): kensea – environmental sensitivity atlas for coastal area of kenya, 76 pp. copenhagen: geological survey of denmark and greenland. unep 1998. eastern africa atlas of coastal resources, kenya, 119 pp. nairobi: unep. authors’ address j.t., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: jt@geus.dk o.g.-h., aquasim, slagslunde bygade 37, dk-3660 stenløse, denmark. j.k., geoquest, gyldenløvesgade 16, dk-1369 copenhagen k, denmark. geological survey of denmark and greenland bulletin 1, 631-656 631 early and middle jurassic mires of bornholm and the fennoscandian border zone: a comparison of depositional environments and vegetation henrik i. petersen, lars h. nielsen, eva b. koppelhus and henning s. sørensen suitable climatic conditions for peat formation existed during early–middle jurassic times in the fennoscandian border zone. autochthonous peat and allochthonous organic matter were deposited from north jylland, south-east through the kattegat and øresund area, to skåne and bornholm. the increase in coal seam abundance and thickness from north jylland to bornholm indicates that the most favourable peat-forming conditions were present towards the south-east. peat formation and deposition of organic-rich muds in the early jurassic coastal mires were mainly controlled by a continuous rise of relative sea level governed by subsidence and an overall eustatic rise. watertable rise repeatedly outpaced the rate of accumulation of organic matter and terminated peat formation by lacustrine or lagoonal flooding. organic matter accumulated in open-water mires and in continuously waterlogged, anoxic and periodically marine-influenced mires. the latter conditions resulted in huminite-rich coals containing framboidal pyrite. the investigated lower jurassic seams correspond to peat and peaty mud deposits that ranged from 0.5–5.7 m in thickness, but were generally less than 3 m thick. it is estimated that on bornholm, the mires existed on average for c. 1200 years in the hettangian–sinemurian and for c. 2300 years in the late pliensbachian; the early jurassic (hettangian–sinemurian) mires in the øresund area existed for c. 1850 years. aalenian uplift of the ringkøbing–fyn high and major parts of the danish basin caused a significant change in the basin configuration and much reduced subsidence in the fennoscandian border zone during the middle jurassic. this resulted in a more inland position for the middle jurassic mires which on occasion enabled peat accumulation to keep pace with, or temporarily outpace, watertable rise. thus, peat formation was sometimes sustained for relatively long periods, and the mires may have existed for up to 7000 years in the øresund area, and up to 19 000 years on bornholm. the combination of the inland position of the mires, a seasonal climate, and on occasion a peat surface above groundwater level caused temporary oxidation of the peat surfaces and formation of inertinite-rich coals. the spore and pollen assemblages from coal seams and interbedded siliciclastic deposits indicate that the dominant plant groups in both the early and middle jurassic mires were ferns and gymnosperms. however, significant floral differences are evident. in the lower jurassic coals, the palynology testifies to a vegetation rich in cycadophytes and coniferophytes (taxodiaceae family) whereas club mosses were of lesser importance. conversely, in the middle jurassic coals, the palynology indicates an absence of cycadophytes, a minor proportion of coniferophytes (taxodiaceae) and a significant proportion of club mosses. these variations are probably related to adaptation by different plants to varying environmental conditions, in particular of hydrological character. keywords: danish basin, fennoscandian border zone, bornholm, lower–middle jurassic, coal distribution, coal petrography, sedimentology, palynology, mire environments, mire vegetation, peat accumulation rates, sea-level change h.i.p., l.h.n., e.b.k.* & h.s.s.**, geological survey of denmark and greenland, geocenter copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: hip@geus.dk present addresses: *royal tyrrell museum of paleontology, box 7500, drumheller t07 0y0, canada. **danfoss a/s, l7-s38, dk-6430 nordborg, denmark. geological survey of denmark and greenland bulletin 1, 631–656 (2003) © geus, 2003 632 in contrast to the permo-carboniferous and cenozoic, the jurassic is not considered to be a time of major peat formation. however, the jurassic succession of northwest europe, and in particular the middle jurassic, contains significant coal-bearing strata showing that favourable conditions for peat formation were fulfilled at many times. in the danish area, coal-bearing strata are generally restricted to the central graben in the north sea and the fennoscandian border zone. well-developed lower–middle jurassic coals are found from the øresund area to the island of bornholm in the baltic sea indicating climatic and geological conditions suitable for the accumulation and preservation of organic matter (fig. 1). the importance of coal beds in stratigraphic analysis is emphasised by the fact that coal seams may represent a considerable proportion of the time represented by coal-bearing successions. thus, this paper views the peat-forming environments on bornholm and in the fennoscandian border zone in a broad geological perspective and discusses the variability in peat-forming conditions in the area in an attempt to explain the principal compositional differences between the lower and middle jurassic coal seams. in addition, the paper presents palynological data from the coals and adjacent sediments and discusses the palynological evidence of the peat-forming vegetation compared to the evidence from the coal composition. geological setting the fennoscandian border zone is a major tectonic structure that separates the baltic shield from the danish basin and polish trough (fig. 1). the border zone is divided into the stable skagerrak–kattegat platform and the highly block-faulted sorgenfrei–tornquist zone, which has been tectonically active at least since late palaeozoic times (sorgenfrei & buch 1964; norling & bergström 1987; eugeno-s working group 1988; michelsen & nielsen 1991, 1993; mogensen 1994). towards the south-east, the sorgenfrei–tornquist zone continues into the teisseyre–tornquist zone via the rønne graben, west of bornholm in the baltic sea. the rønne graben pull-apart basin was formed by late carboniferous – early permian dextral wrench-faulting (vejbæk 1985; liboriussen et al. 1987). continued triassic jylland børglum fault frederikshavn-3 skagen-2 100 km ringkøbing–fyn high bornholm skåne danish basin fjerritslev fault skagerrak–kattegat platform sorgenfrei–tornquist zone well normal fault erosion limit of triassic–jurassic areas of late cretaceous and early tertiary inversion basement high r øn ne g ra be n skagerrak kattegat 56°n 57°n 55°n east north sea high 5 15 7 18 haldager fault øresund wells øresund 13 8°e 10°e 12°e12°e 14°e fig. 1. map showing the structural outline of the fennoscandian border zone and the location of bornholm and the øresund, skagen-2 and frederikshavn-3 wells. modified from liboriussen et al. (1987) and eugeno-s working group (1988). 633 – early cretaceous wrench faulting resulted in faultcontrolled subsidence and tilting of fault blocks in the sorgenfrei–tornquist zone. compressional tectonism in the late cretaceous – palaeogene led to inversion of fault blocks in the sorgenfrei–tornquist zone and regional neogene–pleistocene uplift resulted in erosion of the mesozoic sediments (gry 1969; michelsen & nielsen 1991, 1993; japsen 1993; petersen et al. 2003, this volume). northwards transgression from the tethys during early jurassic times due to an overall rise in sea level combined with continued subsidence of the north sea area and the danish basin, created an extensive epicontinental sea in northwest europe (hallam 1988, 1992; ziegler 1988). the north-eastern margin of the sea coincided with the fennoscandian border zone. coastal and delta plains were established along the margin of the sea, and hettangian–sinemurian coal-bearing strata were deposited on bornholm (rønne formation), in the øresund area, skåne (helsingborg member), and in the kattegat and north jylland (gassum formation; troedsson 1951; gry 1969; bertelsen 1978; gravesen et al. 1982; pieńkowski 1991; petersen 1993, 1994; nielsen 1995; surlyk et al. 1995). fully marine conditions were established across the entire area in the early pliensbachian, but due to a late pliensbachian regression, deposition of coal-bearing strata (sorthat formation) was resumed on bornholm until an early toarcian transgression terminated peat formation (fig. 2–3; koppelhus & nielsen 1994; petersen & nielsen 1995). in the danish basin, deposition of marine clays and sands continued until the aalenian (michelsen 1989; michelsen & nielsen 1991; nielsen 1995). continental conditions were re-established during the middle jurassic and coal-bearing strata were deposited in lake-dominated peatlands and small alluvial fans on bornholm (bagå formation; gry 1969; gravesen et al. 1982; petersen 1993; koppelhus & nielsen 1994), in lake-dominated peatlands in the øresund area (petersen 1994), and in deltaic environments in skåne (fuglunda member; rolle et al. 1979; norling et al. 1993). thin coaly muds, lacustrine clays and fluvial sands were deposited in north jylland (haldager sand formation; koch 1983; nielsen 1995). u m l u l u l u m l u l u l ø re su nd -7 ø re su nd -5 ø re su nd -1 5 ø re su nd -1 8 ø re su nd -1 3 m ar ie da l f m a f vilhelmsfält fm fortuna marl glass sand mb fuglunda mb r ya f m h ö ga nä s fm helsingborg mb döshult mb pankarp mb katslösa mb rydebäck mb röddinge fm ? sorthat fm bagå fm hasle fm galgeløkke mb sose bugt mb munkerup mb r ø nn e fm gassum fm fjerritslev fm haldager sand fm hettangian sinemurian pliensbachian toarcian aalenian bajocian bathonian callovian (part) m id dl e lo w er ju ra ss ic system stage sw ne nw se danish basin bornholm onshore øresund wells (the measured parts) skåne ? ?? ? fig. 2. the lower and middle jurassic stratigraphy in the study area; af, annero fm. compiled from michelsen (1978), gravesen et al. (1982), sivhed (1984), ahlberg et al. (2003, this volume) and michelsen et al. (2003, this volume). note that the age range of the øresund-5 and -7 wells is poorly constrained. 634 early–middle jurassic climate establishment of peat-forming mires and preservation of peat are mainly controlled by a complex interaction of climate, subsidence and eustasy. the breakup of pangea and northwards drift of laurasia during the mesozoic into a warm-temperate to subtropical climatic zone at approximately 40°n, and the creation of a large epicontinental sea in northern europe in the jurassic, resulted in a substantial increase in humidity and rainfall compared to the hot and arid conditions that had dominated the permian and most of the triassic periods (parrish et al. 1982; ziegler 1982; hallam 1984; scotese 1994). the interaction of precipitation and temperature, and in particular seasonality of rainfall, has a strong influence on peat formation, because probably the single most important factor controlling peat distribution is continuity in rainfall (ziegler et al. 1987; calder & gibling 1994; lottes & ziegler 1994). seasonally wet conditions north of tethys (western europe) in jurassic times has been suggested by hallam (1985), and reconstructed rainfall maps for the pliensbachian suggest a moderate rainfall in the danish region (parrish et al. 1982). plant fossil assemblages from the rhaetian and lower jurassic of sweden, germany, bornholm and jameson land, east greenland, indicate that the climate was sufficiently uniform to establish a northern floral province with relatively uniform plant communities (harris 1937; florin 1958). warm conditions are suggested by the large number of plant species from jameson land, and thin cutinised leaves of podozamites and equisetales comparable in size to modern subtropical bamboos are thought to reflect favourable conditions for plant growth (harris 1937). investigations of clay mineralogy and palaeosols of the jurassic on bornholm indicate a warm, humid climate (graff-petersen & bondam 1963; arndorff 1993), and the taxonomic composition of miospore assemblages from the hettangian–sinemurian sose bugt section on bornholm lends support to the interpretation rønne– hasle fault block nyker block rønne graben arnager–sose fault block gudhjem trough bornholm high 5 6 3 4 2 1 10 km cretaceous lower–middle jurassic sorthat formation and middle jurassic bagå formation lower jurassic hasle formation lower jurassic rønne formation upper triassic kågeröd formation lower palaeozoic precambrian crystalline basement fault n fig. 3. geological map of bornholm showing the location of the studied localities: 1, coastal exposures, munkerup member; 2, sose bugt succession, sose bugt member; 3, galgeløkke cliff succession, galgeløkke member; 4, korsodde coastal cliff, sorthat formation; 5, levka-1 well, sorthat formation; 6, hasle klinkerfabrik clay pit, bagå formation. modified from gravesen et al. (1982). 635 lake & swamp lake lagoon shallow submerged inter-fluvial areas crevasse delta shoreface swamp & lake lake lagoon lagoon fluvial channel 20 m 30 40 50 60 70 80 90 seam 15 seam 12/13 seam 9 leaves branch stem coal particles fragm ents fossils iron concretions pyritic concretions carbonaceous detritus lithology mudstone siltstone silty sandstone sandstone coal biogenic structures degree of bioturbation teichichnus diplocraterion equilibrichnia horizontal burrows rootlets sedimentary structures erosional surface horizontal bedding/ lamination cross-bedding with mud drapes cross-lamination wave ripples low-angle cross-bedding small-scale hummocky cross-stratification flaser and wavy bedding lenticular and silt-streaked bedding load structure small-scale water escape structures synaeresis cracks disturbed bedding – lagoon y y y shallow submerged inter-fluvial areas three stacked fluvial channel fills three stacked fluvial channel fills stacked crevasse deltas & swamps fluvial channel crevasse delta lake & swamp lake fluvial channel lagoon m 120 130 140 150 160 clay gamma-ray gamma-ray si sand 2 4 8 mm clay si sand 2 4 8 mm levka-1 y y yy y y y yy y yyyy yy y yyyy y y yy y swamp lagoon seam 6 seam 4/5 seam 2 seam 3 110 100 fig. 4. sedimentological core-log of the upper pliensbachian – lower toarcian part of the sorthat formation in the levka-1 well (reference level: metres below surface). the investigated coal seams are indicated. the accompanying legend refers also to figs 5, 10, 11, 14, 15. intervals with no core recovery (lithology shown only) are interpreted on the basis of gamma-log data. modified from koppelhus & nielsen (1994). 636 of a wetter climate, in particular compared to areas further to the west, for example around the british isles (batten et al. 1994). however, seasonal variations are indicated by annual rings in tree trunks from the rhaetian of skåne (ahlberg & arndorff 1994), in gymnospermous wood from jameson land (harris 1937), and in tree-stumps from the hettangian and bajocian–bathonian on bornholm (höhne 1933; nielsen 1995; surlyk et al. 1995). parts of the hettangian–sinemurian succession in the øresund-18 and -15 wells are characterised by thinly-stratified light grey silty claystones and dark grey claystones or thin graded layers with a silty base and a darker, more clayey upper part. the thin layering may reflect seasonal fluctuations in sedimentation rates, possibly due to unevenly distributed rainfall through the year, as suggested by hamilton & tadros (1994) for similar stratified lacustrine mudstones with coal seams in the gunnedah basin, australia. lower jurassic coal-bearing strata sorthat formation, bornholm fully marine conditions prevailed in early jurassic times over most of the danish basin (michelsen 1975). on bornholm, however, coastal plain environments lasted until the late sinemurian; a transgression caused deposition of marine sandstones in the early pliensbachian (gravesen et al. 1982; surlyk et al. 1995). a late pliensbachian regression re-established a coastal plain environment with peat-forming mires on bornholm until the regional early toarcian sea-level rise caused a renewed transgression (koppelhus & nielsen 1994). the upper pliensbachian – lower toarcian sediments of the levka-1 well and the lower part of the korsodde section (included in the sorthat formation) were deposited in an overall coastal plain environment (figs 3–5; koppelhus & nielsen 1994; petersen & nielsen 1995; michelsen et al. 2003, this volume). the levka-1 well section represents fluvial channels, floodplain areas with shallow lakes and lagoons, and small crevasse deltas (fig. 4). coalified wood fragments and stems occur frequently. coal seams 2, 3, 6 and 9 represent peat-forming mires established on top of abandoned sandy channel fills and on heavily rooted crevasse and lake deposits in shallow inter-fluvial areas. seams 4 and 5 represent peat accumulation on top of lagoonal sediments showing wave-ripples, wavy and flaser bedding, bioturbation and transported equisetites stems. a well-oxidised palaeosol that developed upon the fill of a coastal lake, is overlain by seams 12 and 13 which are separated by a thin sandy, rooted parting. the clay of the lake-fill contains a palynomorph assemblage dominated by spores and pollen, together with a few acritarchs and tasmanites. seam 15 is interpreted to represent an infilled-lake peat mire. the lower 133 m of the korsodde section consists of fluvial channel sand interbedded with heterolithic fining-upwards units of clay and silt and laminated to seam 4 seam 3 clay si sand 8 mm42 86 90 92 m 88 lakes & swamps 118 120 122 124 m seam 5 estuarine channel lagoon lagoon korsodde section clay si sand 8 mm42 fig. 5. sedimentological log of selected coal-bearing intervals from the korsodde coastal cliff succession (sorthat formation); reference level: metres above base of section. modified from koppelhus & nielsen (1994); for legend, see fig. 4. 637 almost massive clay beds topped by coal seams that overlie rooted horizons (fig. 5). the fining-upwards units contain pyrite nodules, coalified wood fragments, and mixed palynomorph assemblages of spores, pollen, acritarchs, freshwater algae and marine dinoflagellate cysts, and were deposited in small coastal lakes and protected lagoons (batten et al. 1994; koppelhus & nielsen 1994). coal seam composition and peat-forming environments the studied coal seams of the sorthat formation are between 0.08 and 0.57 m thick (figs 4, 5). those from the levka-1 well and seam 4 from the korsodde section are dominated by very high contents of huminite (seam-average ranges from 80–90 vol.%), and only minor amounts of inertinite, liptinite and minerals (petersen & nielsen 1995). pyrite occurs in several of the seams. seams 3 and 5 from the korsodde section differ in petrographic composition from the rest of the investigated seams. seam 3 contains significant amounts of minerals (seam-average 37 vol.%) and seam 5 contains a high proportion of inertinite (seam-average 30 vol.%). both seams contain pyrite. reflected-light microscopic analysis of a sample from seam 2 in levka-1 reveals that it contains 2 vol.% pyrite and 6 vol.% of other minerals (petersen & nielsen 1995). the composition of the inorganic components in the sample was further investigated by computer controlled scanning electron microscopy (ccsem). inorganic parunclassified rutile gypsum/ al-silicate gypsum quartz kaolinite illite quartz/ pyrite clay/pyrite pyrite 0 10 20 30 40 50 wt% (mineral basis) m in er al s sorthat fm, seam 2 bagå fm, seam 6 fig. 6. composition (wt% on a mineral basis) of the mineral matter in the upper part of seam 2, sorthat formation (levka-1 well) and in seam 6 (interval 125–135 cm) in the upper bagå formation. the group ‘unclassified’ includes minerals which constitute less than 1 wt% of the inorganic fraction. lower delta plain upper delta plain strand plain piedmont plain back barrier tree density increases 0.0 1.0 2.0 3.0 4.0 0.1 10 1 tissue preservation index g el ifi ca ti o n in de x lower jurassic : sorthat formation; levka-1 well and korsodde coastal cliff : rønne formation, galgeløkke member; galgeløkke coastal cliff : øresund area; øresund-13, -15 and -18 wells 100 fig. 7. coal samples from the lower jurassic of bornholm and the øresund area plotted on the tissue preservation index (tpi) vs. gelification index (gi) diagram of diessel (1986). the strand plain area is after kalkreuth & leckie (1989; see also diessel 1992). notable are the low gi values of the galgeløkke member coal suggesting oxidizing conditions during deposition of the peat (domed bog), and the very high gi values of the upper pliensbachian – lower toarcian sorthat formation coals suggesting anoxic, waterlogged conditions during peat deposition. 638 fig. 8. colour photomicrographs of pyrite (reflected white light, oil immersion, scale bar c. 30 µm, except a2: scale bar c. 20 µm). a1: framboidal pyrite (p) in ulminite in coal seam 2, sorthat formation. note how the sporinite (arrows) ‘flows’ around the pyrite, suggesting precipitation of the pyrite (syngenetic) prior to compaction (seam 2, sample 291934; levka-1 well). a2: framboidal pyrite (p) in the same sample. b: pyrite (p) filling cleats in ulminite in seam 8 in the upper bagå formation, suggesting epigenetic pyrite precipitated after gelification of the organic matter (seam 8, sample b-9.2, hasle klinkerfabrik clay pit). c: pyrite (p) filling cleats in macrinite in seam 8 in the upper bagå formation, suggesting epigenetic pyrite precipitated after gelification and oxidation of the organic matter (seam 8, sample b-9.2, hasle klinkerfabrik clay pit). d: pyrite (p) precipitated in cell lumens in fusinite in seam 5, upper part of the bagå formation (seam 5, sample b-6.3, hasle klinkerfabrik clay pit). a1 p p p p pp b d c a2 ticles below 1 µm and organically bound elements are not detected. the ccsem analysis indicates that the inorganic fraction is dominated by 45 wt% quartz with subordinate pyrite and minor proportions of gypsum and clay minerals (fig. 6). in general, the quartz is in the size range of clay and silt with the major part being fine-grained silt (4–16 µm). the pyrite crystals are mainly within the size limits of silt followed by very fine-grained and fine-grained sand. framboidal aggregates may account for the larger particles. the peats accumulated mainly in anoxic and fully water-saturated freshwater mires as indicated by the very high content of humified organic matter in all of the seams in the levka-1 section (high gelification index values, gi = huminite/inertinite, fig. 7; petersen & nielsen 1995). the high content of humocollinite and the abundance of hopanoids in the coals indicate pronounced bacterial activity reflecting abundance of nutrients and a relatively high ph level (teichmüller 1989; waples & machihara 1991; peters & moldowan 1993). the significant amounts of pyrite in seams 2 and 4 and minor amounts in several other seams suggest occasional brackish – marine influence on the mires (cohen et al. 1984; phillips & bustin 1996a). the pyrite occurs in association with fusinite and inertinite, and as framboidal aggregates and minute crystals in huminite (fig. 8a). it is interpreted to be mainly syngenetic. however, some of the pyrite, e.g. in seam 4, occurs infilling cleats in huminite and macrinite, thus suggesting that precipitation of pyrite also took place after gelification. the very small grain size of the mineral matter (clay to fine-grained silt) suggests that the mineral matter was deposited from suspension or may have been windborne. three coal seams, seams 3, 4 and 5, from the korsodde succession have been investigated in detail (fig. 5; petersen & nielsen 1995). seam 4 is petrographically very similar to the seams from the levka-1 well and represents a wet, anoxic, and probably rheotrophic, nutrient-rich peat-forming environment. the seam overlies sediments from a shallow, vegetated coastal lake, that occasionally was flooded by the sea. seam 3 also overlies coastal lake deposits, and the high mineral content in the seam reflects the development of the lake into a frequently inundated open mire. a peat mire failed to develop although rootlets indicate that in situ plants contributed to peat accumulation. seam 5 overlies a lagoonal unit and constitutes the final, regressive phase in the evolution of an estuarine complex. the precursor peat was subjected to desiccation, possibly linked to a decreased rate of watertable rise. palynological evidence of the peat-forming vegetation palynological analyses were carried out on five coal samples from seams 2 and 15 in levka-1 and three samples from the sediment immediately below the coal seams. although the parent plant affinities of palynomorphs from the jurassic are uncertain in most cases, it has been possible to discriminate several groups of plants: ferns (pteridophytes) of the order filicales (class: filicopsida), cycadophytes of the order cycadales (class: gymnospermopsida), coniferophytes of the order coniferales (class: gymnospermopsida), mosses (division: bryophyta), and microplankton-like acritarchs, marine green-algae (tasmanites spp.) and a freshwater greenalgae (botryococcus spp.; table 1). the palynomorph assemblage of the sediment sample below seam 2 in the levka-1 well is dominated by cycadalean pollen (c. 25%, chasmatosporites hians, c. minor, c. apertus) and jurassic species of the family pinaceae (c. 50%, mainly cerebropollenites thiergartii) (table 1). the content of ferns is likewise pronounced (18%). moving up to the two coal samples, several pollen types that have affinities with conifers disappear, while chasmatosporites hians, whose affinity lies with the order cycadales (van konijnenburg-van cittert 1971), and cerebropollenites thiergartii, whose affinity lies with the family pinaceae, increase significantly in number upwards in the seam (cycadales and pinaceae pollen increases to 14% and 19% in the uppermost sample, respectively). however, the pollen corollina torosus, the affinity of which is considered to lie with the large conifer cheirolepidaceae (srivastava 1976) and which constituted an important part of the jurassic coniferous forests (stewart 1983), appears in the lower coal sample. the occurrence of these larger gymnospermous plants is in agreement with the considerable content of the maceral subgroup humotelinite in the lower coal sample. the diversity of spores whose affinities lie with the ferns, in particular the family osmundaceae, increases from the underlying sediment up into the coal. in the lower coal sample, the proportion of ferns reaches 56%, suggesting a mire with a pronounced herbaceous vegetation. the generally high content of degraded organic matter (humodetrinite) in both coal samples correlates with a high proportion of these small plants. spores related to mosses constitute a significant proportion of the coal assemblages. the palynomorph diversity is lower in the uppermost coal sample, possibly due to the influence of marine water as interpreted from the coal petrology and the occur639 640 locality seam sample sampletype filicopsida % lycopsida % cycadales gymnosperms % coniferales p* t† g‡ microplankton§ % bryophyta % n � øresund-13 øresund-18 levka-1 bagå clay pit 1 2 cm below seam 1 4 cm above seam 1 1 1 1 1 2 cm below seam 1 4 cm below seam 1 2 2 2 cm below seam 2 2 2 3 cm below seam 2 15 15 15 2 cm below seam 15 3 cm below seam 15 1 2 3 3 4 5 6 few cm below 6 247943 6371 6373 6372 6369 247944 247945 6375 6374 247947 clay/silt coal coal coal coal light clay light clay coal coal dark clay 5.1 16.0 23.7 41.7 0 73.9 71.4 61.4 46.0 20.3 6.2 2.5 1.7 0 0 0 0 2.6 9.8 8.8 1.1 7.3 5.1 16.7 0 4.3 4.4 1.3 2.0 14.7 10.7 14.1 8.5 0 40.0 0 1.1 18.6 6.9 10.4 14.1 25.6 30.5 8.3 0 0 3.3 1.3 2.0 4.7 4.6 0.5 1.7 12.5 ¶ 0 14.4 4.4 0 1.0 5.1 0 0.5 5.1 4.2 20.0 1.5 4.4 0 0 0 178 206 59 24 5 69 91 75 102 193 291934 291932 247938 6386 6383 6379 247940 247941 coal coal coaly clay coal coal coal clay clay 10.8 56.1 18.0 33.3 24.5 28.9 43.5 43.4 13.5 8.4 24.6 28.5 40.0 42.0 11.9 18.2 18.9 6.3 50.2 12.4 11.1 8.1 33.7 31.5 0 6.3 0.6 4.9 3.3 1.6 2.0 0.5 32.5 12.5 6.6 19.7 14.4 11.3 8.9 6.4 5.4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 18.9 10.4 0 1.2 6.7 8.1 0 0 37 48 167 81 90 62 202 203 b-1.1 b-2.1 b-3.2 b-3.1 b-4.1 b-6.9 b-7.2 b-7.1 coal coal coal coal coal coal coal black clay 62.7 31.3 50.9 54.1 53.3 24.7 30.7 36.2 13.2 9.7 10.5 16.2 22.3 31.1 3.6 21.3 14.2 25.7 12.3 2.7 22.2 24.6 19.8 27.5 0 8.3 0 2.7 0 0 0 0 5.5 20.8 24.6 21.6 2.2 19.6 45.9 12.5 0 0 0 2.7 0 0 0 0 0 0 0 0 0 0 0 0 4.4 4.2 1.7 0 0 0 0 2.5 91 144 57 37 45 61 111 80 6368 247948 64.3 14.0 5.1 4.2 3.5 13.5 11.2 19.2 0.5 8.2 15.4 37.9 0 3.0 0 0 196 209 table 1. peat-forming plants based on palynological evidence coal black clay ¶ three dinoflagellates. � number of palynomorphs counted. ‡ other gymnospermous pollen. § mainly acritarchs, some tasmanites and botryococcus. * pinaceae. † taxodiaceae. 58.2 33.5 23.7 16.6 40.0 5.9 11.0 14.8 32.3 36.0 0 10 20 30 40 50 60 70 80 90 100 27.10 27.20 27.30 27.40 27.50 m levka-1 well, seam 15 27.60 81 90 n 62 202 203 ferns (filicopsida) cycadophytes (cycadales) coniferophytes (coniferales) coal interpreted plant groups lithology mudstone gymnosperms, other mosses (bryophyta) % (cumulative) fig. 9. the succession of main plant groups in seam 15, levka-1 well, as suggested by the botanical affinities of palynomorphs and their abundance in percentages. n, number of palynomorphs counted. 641 rence of a probable acritarch species (lecaniella foveata; batten et al. 1994; petersen & nielsen 1995). the clay samples taken immediately below seam 15 in the levka-1 well contain a significant content of the same pollen species identified in seam 2 whose affinities lie with the order cycadales and jurassic species of the family pinaceae (fig. 9; table 1). fern spores are present below seam 15 in considerable amounts (43%, mainly deltoidospora spp.), and the diversity of spores related to ferns is greater than in the sediment sample below seam 2. the most pronounced changes in the palynomorph assemblages in seam 15 compared to the underlying sediment are a significant decrease in the proportion of pollen whose affinities are with the family pinaceae, a decrease in the amount of fern spores, and a considerable increase in the proportion of pollen whose affinities are with the cycadophytes (fig. 9; table 1). despite differences in types and amounts of the recorded pollen species among the three coal samples in seam 15, they display a rather uniform composition. the coal petrographic composition is also uniform, conforming with studies on recent peat deposits, which have shown a correlation between peat vegetation and peat composition (cohen & spackman 1977; phillips & bustin 1996b). thus, the mire vegetation may have been dominated by gymnospermous plants and a secondary proportion of ferns characterised by the genera dicksonia or coniopteris and the family osmundaceae (tralau 1968; van konijnenburg-van cittert 1978). this might correlate with the dominance of humotelinite over humodetrinite in the seam. the lowermost coal sample has both the smallest amount of gymnospermous pollen and the lowest proportion of humotelinite of the three coal samples. in general, the palynomorph assemblages suggest that the peat-forming vegetation of seam 15 was of higher diversity than that of seam 2, which may be explained by the influence of saline water in the precursor mire of seam 2. duration of peat formation the compaction ratio for peat to bituminous coal varies between 4.1:1 and 30:1 (ryer & langer 1980). a peat:coal compaction ratio of 10:1 may be assumed for the subbituminous coals in this study (see also mccabe 1991). the tropical batang hari river peat deposit in sumatra has an accumulation rate of c. 1.8 mm/yr, whereas the cold temperate peat deposit in maine has been accumulating at a rate of c. 0.6 mm/yr (cameron et al. 1989). an average accumulation rate of 1 mm/yr may thus be a reasonable assumption for the warm temperate to subtropical jurassic climate. using this assumption, the late pliensbachian – early toarcian peat-forming mires on bornholm existed between 800 and 5700 years, with an average of c. 2300 years. other lower jurassic coal-bearing strata in the fennoscandian border zone hettangian–sinemurian mires are represented by coal and coaly mudstones within the munkerup member and the sose bugt member of the arnager–sose fault block on the south coast of bornholm (figs 2, 3). the poorly exposed munkerup member consists primarily of lake deposits (gry 1969; gravesen et al. 1982; koppelhus 1991). periodically, the lacustrine environment developed into mires. increasing deoxygenation of the lakes and encroachment of vegetation is evident sose bugt member galgeløkke member rønne formation m 10 5 0 seam a seam b seam c seam d m 25 20 15 clay si sand clay si sand fig. 10. sedimentological log of the coastal sose bugt succession (hettangian–sinemurian sose bugt member) and galgeløkke cliff section (sinemurian galgeløkke member). after gravesen et al. (1982); section heights refer to the original sections of gravesen et al. (1982). for legend, see fig. 4. from the gradual transition from clayey, rooted sediments to the overlying coaly mudstones. the coaly mudstones are inertinite-rich, contain pyrite, and are to a large extent allochthonous, reflecting deposition in freshwater to brackish, open water environments (petersen 1993). the sose bugt member consists of lacustrine, fluvial, lagoonal, and restricted marine shoreface to offshore sediments (figs 2, 3, 10; surlyk et al. 1995). the occurrence of marine palynomorphs at certain levels within the terrestrial part of the succession indicates occasional marine incursions. the four 0.12–0.30 m thick, mainly allochthonous, mineral-rich coaly mudstones were deposited in shallow lakes on a coastal plain (petersen 1993; surlyk et al. 1995). the mires developed largely under freshwater conditions, but may have periodically been influenced by marine water. in the neighbouring rønne–hasle fault block, the rønne formation is dominated by lagoonal units with coal seams deposited in an overall coastal plain environment (nielsen 1995). the exposed section of the sinemurian galgeløkke member consists of sandy and muddy lagoonal, tidal flat and tidal channel complex deposits (figs 3, 10; sellwood 1972; gravesen et al. 1982). an inertinite-rich coal seam, 0.10–0.35 m thick, overlies wavyand flaser-bedded tidal flat heteroliths. the seam represents a dominantly freshwater peat bog 642 lagoon or restricted brackish bay lagoon or restricted brackish bay sparsely vegetated open water environment. limnic facies. mainly allochthonous deposition. a øresund-13 well m 88 clay silt sand 89 90 91 92 93 94 upper part: densely vegetated rheotrophic infilled lake swamp. telmatic freshwater facies. lower part: sparsely vegetated open water lake. limnic facies. mainly allochthonous deposition. freshwater lake upper part: mesotrophic to ombrotrophic domed bog. (telmatic to) terrestrial freshwater facies. lowermost part: densely vegetated rheotrophic infilled lake swamp. telmatic freshwater facies. freshwater lake b øresund-18 well m 10 seam 2 11 12 ? 13 14 15 16 clay seam 1 siltsilt sand densely vegetated rheotrophic swamp. slightly brackish wet telmatic facies. restricted brackish shallow water lake c øresund-15 well m 101 ? clay siltsilt sand 102 103 104 105 fig. 11. a: sedimentological core-log of the studied hettangian–sinemurian part of the øresund-13 well. b: sedimentological core-log of the studied hettangian–sinemurian part of the øresund-18 well. c: sedimentological core-log of the studied sinemurian part of the øresund-15 well. modified after petersen (1994); reference level: metres below sea level. for legend, see fig. 4. with a domed surface (fig. 7, gi values < 1), implying a significant change from the tidal flat environment that prevailed prior to peat formation (petersen 1993), and the possible presence of a diastem below the coal seam. siliciclastic deposition may have occurred contemporaneously nearby, but the elevated peat surface hindered flooding of the peat deposit (e.g. staub & esterle 1994; phillips & bustin 1996b). the high content of well-preserved pyrofusinite, which represents fossil charcoal (scott 1989), indicates that wildfires occurred in the bog. this resulted in a high inertinite content in the seam as shown by low gi values in the tpi versus gi diagram (fig. 7). the coal seam contains small amounts of pyrite towards the top, which probably was precipitated due to migration of sulphate ions into the peat from the overlying brackish sediments after peat formation was terminated. similar paralic depositional environments existed in the øresund area in hettangian–sinemurian times (fig. 1). the bioturbated heteroliths underlying a 0.18 m thick, inertiniteand mineral-rich coal seam in the øresund-13 well represent deposition in a shallow, restricted bay or lagoon (fig. 11a ; petersen 1994). after the shallow area was filled, it became vegetated and accumulation of mainly allochthonous organic matter resistant to degradation during transportation took place in an open freshwater mire. both seams 1 (0.25 m) and 2 (0.15 m) in the øresund-18 well overlie lake fill sediments (fig. 11b; petersen 1994). the presence of rooted claystones below the seams demonstrates that the gradual fill of the lakes promoted plant growth. both seams represent rheotrophic, probably nutrient-rich freshwater mires, although the precursor peat of seam 1 may temporarily have evolved to a more domed state. sinemurian coal-bearing strata occur in the øresund-15 well, and the claystones underlying the coal seam were deposited in a shallow, weakly brackish lake situated in a coastal plain (fig. 11c). the preserved stratification and absence of trace fossils suggest a poorly oxygenated sediment. the 0.16 m thick, huminite-dominated coal seam represents an occasionally slightly brackish, nutrient-rich swamp established on top of the lake-fill. a c. 3 cm thick coaly mudstone occurs in the uppermost lower jurassic in the skagen-2 well in north jylland (referred to as the fjerritslev formation by michelsen 1978). the coaly mudstone represents an allochthonous deposit, which is emphasised by the high content of the mineral-rich microlithotype carbominerite (71 vol.%), microlaminated detrital macerals, and macerals resistant to degradation during transportation (inertinite: 39 vol.%; liptinite: 9 vol.%). oxidised cutinites may reflect oxidation of the organic matter during transportation. the occurrence of pyrite (2 vol.%) suggests that the open water environment was brackish or periodically influenced by marine water. the peat mire was situated in a coastal environment, consistent with the position of the bed within a thin unit that correlates with transgressive marine mudstones further to the west (i.e. basinwards; nielsen 1995). palynological evidence of the peat-forming vegetation in the øresund area a total of twelve samples were analysed from the øresund-13 and -18 wells; these comprise seven coal samples, four samples from the sediment immediately below the coal seams, and one sample immediately above a seam. in addition to the plant groups mentioned from the sorthat formation coals, club mosses (class: lycopsida) were identified in these coals (table 1). a sample was taken from the coal seam in the øresund-13 well and from the black clay about 2 cm below the seam. the latter shows a higher diversity than the coal sample. acritarchs (lecaniella foveata, leiosphaeridia spp. and a possible cymatiosphaera spp.), tasmanites spp. and a possible dinoflagellate cyst (? mancodinium semitabulatum) occur only in the sediment sample. this is consistent with the interpretation of the sedimentary environment as a lagoon or brackish restricted bay and the seam as a freshwater deposit (petersen 1994). spores related to ferns, in particular deltoidospora spp., whose affinities lie with the two fern genera coniopteris or dicksonia (tralau 1968), are common in the clay. however, coniferalean and cycadalean pollen are more abundant. bisaccate species and a pollen of unknown affinity are also abundant. in combination, the pollen related to gymnosperms constitute 78% of the palynomorph assemblage in the clay sample (table 1). in contrast, in the coal sample the proportion of gymnosperm pollen is only 31%. in particular, the proportions of the species chasmatosporites hians and perinopollenites elatoides, whose affinities are with the cycadales and the coniferophyte family taxodiaceae (guy-ohlsson 1986) respectively, are significantly lower. however, spores whose affinities lie with the order lycopodiales, the fern genera dicksonia and the fern family osmundaceae (van konijnenburg-van cittert 1978) are more abundant. in total, the proportion of fernrelated spores increases to approximately 64% in the coal sample. thus, the palynomorphs indicate a change 643 644 in the composition of the vegetation from the siliciclastic environment to the mire environment. the sparse mire vegetation probably consisted to a large extent of herbaceous plants. the sediment samples below seam 1 in the øresund-18 well are dominated by fern spores (71–74%, mainly deltoidospora spp.) and up to 15% acritarchs (fig. 12; table 1). upwards through the coal seam, spores related to ferns decrease and constitute only 16% in the uppermost sample. club mosses (retitriletes clavatoides) were probably present in the late peat stages corresponding to slightly wetter conditions. most notable compared to the underlying clay is the significant content of taxodiaceous pollen (perinopollenites elatoides) and bisaccate pollen related to unknown gymnosperm plants. pollen and spores also show that plants belonging to the cycadales (chasmatosporites hians, c. apertus), the pinaceae (pinuspollenites minimus, cerebropollenites macroverrucosus, c. thiergartii), and the bryophyta constituted parts of the original mire vegetation (fig. 12; table 1). an evolutionary link between the parent plant of c. macroverrucosus and the extant tsuga has recently been suggested, although the parent plant of the former probably became extinct during the cretaceous (batten & dutta 1997). acritarchs and dinoflagellates are present. the composition of the vegetation cannot be directly correlated to the maceral composition of the seam, which may be due to the high proportion of oxidised organic matter (inertinite), particularly inertodetrinite. the occurrence of club mosses in the upper part of the seam may correspond to a return to more wet and nutrient-rich conditions, which would be consistent with the increased content of mineral matter. in contrast, the occurrence of microplankton in the seam is of particular interest. no indications of saline water influence, such as pyrite, have been observed in the seam, and the sediments have been interpreted as freshwater deposits (petersen 1994). however, the occurrence of acritarchs suggests, at least temporarily, brackish conditions. on the basis of the palynomorph assemblage, the mire may have been covered with a dominantly gymnospermous vegetation and a significant, subordinate proportion of ferns and club mosses. spores (mainly deltoidospora spp.) probably derived from ferns increase from c. 20% in the dark clay immediately below seam 2 in the øresund-18 well to 61% in the upper part of the seam, whereas the proportions of cycadalean pollen and pollen with unknown gymnosperm affinities decrease significantly upwards (table 1). the contribution of the taxodiaceae family was much less important in the precursor mire of seam 2 than in that of seam 1. the mire may have been characterised by a prominent herbaceous vegetation, and the highest proportion of spores derived from club mosses occurs in the lower part of the seam representing wet, 12.00 12.10 12.20 12.30 12.40 m 178 206 59 24 69 91 n øresund-18 well, seam 1 0 10 20 30 40 50 60 70 80 90 100 % (cumulative) ferns (filicopsida) club mosses (lycopsida) cycadophytes (cycadales) coniferophytes (coniferales) coal interpreted plant groups lithology mudstone siltstone carbonaceous detritus gymnosperms, other microplankton (mainly acritarchs) mosses (bryophyta) fig. 12. the succession of main plant groups in seam 1, øresund-18 well, as suggested by the botanical affinities of palynomorphs and their abundance in percentages. n, number of palynomorphs counted. open-water conditions. the contribution of plant tissue from ferns together with club mosses in the precursor mire is compatible with the high content of detrital organic matter (humodetrinite) in the coal. duration of peat formation the coaly mudstones from the sose bugt member are very low in rank (petersen et al. 2003, this volume), and a compaction ratio of 4:1 for peat:lignite (esterle & ferm 1994) may provide a better estimate than that adopted for the sub-bituminous coals (see above). using this value and ignoring the relatively high content of mineral matter, the original carbonaceous deposits were between 0.5 and 1.2 m thick, and organic matter accumulation lasted for about 500–1200 years. the hettangian munkerup member is located in the same fault block as the hettangian–sinemurian sose bugt member. the boundary between the two members is not exposed (gry 1969; gravesen et al. 1982), but the thickness of the sediment package between the seams of the two members is insignificant with regard to coalification. thus, although the munkerup member coals yield higher reflectance values than the sose bugt member seams (petersen et al. 2003, this volume), the 4:1 compaction ratio is also applied to the munkerup member coals. using this compaction ratio, the original peat deposits of the munkerup member were also between 0.5 and 1.2 m thick, and peat accumulation lasted for about 500–1200 years. the original peat deposit represented by the coal seam in the galgeløkke coastal cliff section in the rønne graben had a maximum thickness of 3.5 m (peat:coal compaction ratio: 10:1), corresponding to 3500 years of peat accumulation. on average, the mires represented by the investigated seams in the rønne formation thus existed for c. 1200 years. assuming a 10:1 compaction ratio for the lower jurassic coal seams in the øresund area, the original peat thickness was 1.5–2.5 m and the duration of peat accumulation was 1500–2500 years. on average, the peat mires existed for 1850 years. middle jurassic coal-bearing strata bagå formation, bornholm the lower to middle part of the bagå formation in the hasle klinkerfabrik clay pit is a heterogeneous, clayrich succession about 60 m thick that is characterised by stacked units (c. 10 m thick) of laminated, grey – dark grey clay with silt and sand laminae and subordinate beds of cross-bedded or laminated sandstones, often showing rootlets (koppelhus & nielsen 1994). these units are separated by coaly mudstones or coal seams, associated with rooted horizons that record the periodic establishment of peat-forming mires. fossil plant fragments, small logs, stems, and leaves are common in the clay. the palynomorph assemblages are all non-marine and dominated by pteridophyte spores and gymnosperm pollen (hoelstad 1985; koppelhus & nielsen 1994), and the total sulphur content in the coaly mudstones and coal seams is generally less than 0.80 wt%, indicating a freshwater environment (casagrande 1987). thus, the clay was deposited in freshwater lakes, which were gradually filled and transformed into openwater or peat-forming freshwater mires. the sand beds represent crevasse splays and channel deposits. the upper part of the bagå formation becomes more sandy, with some very poorly sorted sand beds, occasionally with large kaolinised granite boulders deposited by debris flows that originated from the granite horst located immediately to the east (gry 1969; gravesen et al. 1982; nielsen 1995). pyrite nodules are common in the sand beds. based on the clastic facies and the proximity to the major graben fault against the granitic basement, a small alluvial fan environment with deposition from sheet wash and mud flows is envisaged. coal seam composition and peat-forming environments eight coal seams, 0.05–1.90 m thick, have been investigated in the upper part of the bagå formation (seams 1–8 of petersen 1993). the seams are petrographically complex, with varying amounts of inertinite (1–72 vol.%; 74% of the studied coal samples contain 20–60 vol.%) and huminite (16–89 vol.%; 71% of the studied samples contain more than 30 vol.%), and often a considerable content of minerals (2–57 vol.%; 57% of the studied samples contain 10–20 vol.%; petersen 1993). fusinite is a prominent component of the inertinite maceral group (up to 41 vol.%). pyrite occurs in seven of the eight seams. framboidal pyrite has not been observed, although in several of the seams significant amounts of pyrite (up to 36 vol.%) fill cell-lumens of fusinite, occur as massive pyrite or fill cleats in gelified organic matter (fig. 8b, c, d; petersen 1993). analysis of a sample from seam 5 by ccsem shows that the inorganic fraction is dominated by pyrite (46 wt%), 645 646 followed by quartz (19 wt%), clay associated with pyrite (13 wt%) and kaolinite (10 wt%; fig. 6). the majority of the quartz is in the grain-size range of silt (in particular coarse silt, 32–64 µm), to fine-grained sand, whereas most of the pyrite is of fine-grained sand grade. the eight coal seams from the upper part of the bagå formation were formed in freshwater swamps, that occasionally were established on the alluvial plain. the occurrence of several well-defined root horizons below a thick coal seam (seam 5 of petersen 1993) indicates repeated episodes of siliciclastic deposition followed by colonisation of the sediments by plants. a level coloured by humus substances below each root horizon was possibly formed by a low-standing watertable, which together with the petrography of seam 5 imply an unstable watertable. most of the samples from seam 5 plot in the field of the piedmont plain in the tpi versus gi diagram (fig. 13), consistent with the alluvial fan interpretation. varying amounts of detrital minerals in the seams is attributed to periodic outwash from the nearby granitic horst. in addition to pyrite and clay associated with pyrite, the inorganic fraction in the 125–135 cm interval in seam 5 is characterised by quartz, primarily of coarse silt to fine-grained sand size, and kaolinite. the comparatively high content of kaolinite is probably related to the proximity of the mires to the weathered granitic basement of the bornholm high to the east. a large proportion of impure coals and an abundance of inertinite-rich lithotypes occur in piedmont coal seams in the springhill coalfield of nova scotia, where peatlands were nourished by groundwater discharge from alluvial fans and basin-margin fault-fed springs (calder 1993, 1994). a similar small-scale scenario is envisaged for the sand-dominated, upper part of the bagå formation. formation of dull coals due to severe oxidation in the piedmont plain setting has also been noted by diessel (1986), and most of the upper bagå formation coals contain much inertinite. the inertinite may have formed due to a fluctuating watertable in the precursor mires, an inertinite-forming process known from recent peat-forming environments (cohen & stack 1996; moore et al. 1996). fluctuations were probably related to seasonality as indicated by the occurrence of annual rings in wood from the coal seams in the bagå formation (höhne 1933). a peat-forming flora dominated by cellulose-rich plants (shrubs, herbs) is suggested by the maceral composition. palynological evidence for the peat-forming vegetation seven coal samples and one clay sample were analysed from coal seams 1–6 (petersen 1993) in the upper part of the bagå formation. it is possible to discriminate several plant groups: ferns (order: filicales; class: lower delta plain upper delta plain strand plain piedmont plain back barrier tree density increases 0 1.0 2.0 3.0 4.0 5.0 0.1 100 10 1 tissue preservation index g el ifi ca ti o n in de x middle jurassic : bagå formation (uppermost part); hasle klinkerfabrik clay pit : øresund area; øresund-5 and -7 wells fig. 13. coal samples from the middle jurassic on bornholm and the øresund area plotted on the tpi vs. gi diagram (fig. 7). most of the samples from the upper bagå formation plot within the field of the piedmont plain. filicopsida), club mosses (class: lycopsida), coniferophytes (order: coniferales; class: gymnospermopsida) and mosses (division: bryophyta; table 1). pollen related to cycadophytes were not found, although höhne (1933) identified cycadophytes in the coals. a sample from the lowermost part of seam 1 is characterised by a high diversity of spores, which are related to ferns of the family osmundaceae and the genera dicksonia or coniopteris (tralau 1968; van konijnenburgvan cittert 1978), to the orders lycopodiales and selaginellales, and to bryophytes. fern-related spores constitute 63% and club mosses 13% of the assemblage (table 1). pollen whose affinities lie with the cheirolepidaceae and pinaceae are also present. compared to seam 1, seam 2 is characterised by a higher diversity and a larger proportion of pollen whose affinities are with the families pinaceae, taxodiaceae, and other gymnosperms (table 1). the spore assemblage has a different composition from that of seam 1 and makes up a smaller proportion of the total palynomorphs. it implies, however, a rather similar overall composition of the herbaceous vegetation. based on coal petrography, petersen (1993) suggested that the vegetation in the mires represented by seams 1 and 2 was generally small-sized and consisted of abundant herbaceous plants, small trees, shrubs and tree ferns. palynological evidence of tree ferns has not been found in the coals, and the abundance of spores whose affinities are with herbaceous plants indicates that ferns and club mosses were more common in these mires than deduced from the maceral composition, which has a rather high content of humotelinite. the rest of the samples from seams 3–6 are rather similar. the diversity of spores related to ferns is considerably lower than in seams 1 and 2; however, they still constitute up to 54% of the assemblages (table 1). ferns in particular seem to have been abundant in the mires represented by seams 3 and 4. the most abundant is deltoidospora spp., whose affinity is with the genera dicksonia or coniopteris (tralau 1968). the proportion of club mosses was significant in the mires, and the spores (mainly retitriletes austroclavatoides, r. clavatoides, r. semimuris, sestrosporites pseudoalveolatus) amount to 22% and 31% in seams 4 and 5, respectively. these spores are particularly associated with mineral-rich levels in the coals implying that the plants favoured wetter and more nutrient-rich conditions. the pollen species cerebropollenites macroverrucosus which is related to the gymnosperm genus tsuga of the family pinaceae (tralau 1968; batten & dutta, 1997), is abundant. in the coal sample from seam 6, the pollen vitreisporites pallidus is abundant. the affinity of this pollen is with the caytoniales (van konijnenburg-van cittert 1971), a gymnosperm order of uncertain relationship (stewart 1983). a peat-forming vegetation consisting of abundant herbaceous and shrubby plants and some larger trees was suggested by petersen (1993). to some extent this is supported by the palynomorph assemblages, but the proportion of gymnospermous trees may have been greater than deduced from the maceral composition. plants belonging to the family pinaceae were present. reconstruction of the gymnospermous vegetation in the mires is difficult due to the high proportion of pollen of unknown affinity (table 1). duration of peat formation assuming a peat accumulation rate of 1 mm/yr and a peat:coal compaction ratio of 10:1 (see above), the original peat deposits represented by the coal seams in the upper part of the bagå formation were between 0.5 and 19.0 m thick, and peat accumulation occurred in the mires for between 500 and 19 000 years. other middle jurassic coal-bearing strata in the fennoscandian border zone several seams, 0.16–0.70 m thick, are present in the øresund-5 and -7 wells, overlying parallel-laminated to homogeneous claystones deposited in freshwater lakes (figs 14, 15; petersen 1994). the abundance of coalified plant remains and the upwards-increasing content of organic matter, coal particles, coal streaks and rootlets in the claystones towards the coal seams record the gradual fill of the lakes and deterioration of the oxygen supply in the mires. the lower part of the øresund-5 seam represents a drier mire environment, whereas the upper part of the seam is a carbonaceous claystone deposited in an open freshwater environment. this indicates that the rising groundwater level gradually outpaced organic matter accumulation, and peat formation was terminated by lacustrine flooding. seams 1, 3 and 4 in the øresund7 well contain a higher inertinite content as shown by low gi values (fig. 13), and they represent bogs that were probably subjected to a fluctuating watertable (petersen 1994). the mire represented by seam 2 was also established after a lake had been filled with sediment. however, the mire was continuously water-saturated and anoxic, and probably nutrient-rich and rheotrophic. 647 648 the middle jurassic peat-forming freshwater mires in the øresund area were thus located in an overall lakedominated wetland with a prolific flora indicated not only by the coal seams but also by the abundance of coalified leaves and branches in the claystones. there is no evidence of marine influence, and the continental sedimentation kept pace with the subsidence-induced base-level rise. in north jylland, thin coal seams and carbonaceous mudstones are present in the middle jurassic haldager sand formation. analysis of a 4 cm thick seam in the frederikshavn-3 well shows that it is inertiniteand mineral-rich (75 vol.% and 17 vol.%, respectively), which may indicate an allochthonous origin. however, black carbonaceous clay and rootlets below the seam indicate a gradual change to oxygen deficient, low energy conditions and the establishment of vegetation. degraded liptinite components suggest fungal and/or bacterial attack under well-oxidised conditions. this and the scarcity of huminite (1 vol.%) may imply that the seam was severely oxidised, possibly due to a fall in the watertable following the accumulation of the organic matter. minerals are easily incorporated into a thin layer of organic matter, and the carbonaceous seam is probably autochthonous and was deposited in a shallow, slightly brackish area, as suggested by the presence of pyrite (4 vol.%). the seam is overlain by coaly matter associated with quartz grains, and poorly sorted darkbrown clay and sand, indicating a gradually rising watertable. duration of peat formation the original peat deposits in the øresund area were between 1.6 and 7.0 m thick and the peat-forming environments existed for between 1600 and 7000 years using the assumptions discussed above. although some clay sand sandsilt øresund-5 well upper part: open freshwater lake. limnic to limnotelmatic facies. mainly allochthonous deposition. lower part: mesotrophic to ombrotrophic domed bog. terrestrial facies. shallow freshwater lake freshwater lake m 52 55 56 57 58 m 45 47 48 49 50 53 54 59 clay silt 46 51 fig. 14. sedimentological core-log of the jurassic succession of the øresund-5 well. modified after petersen (1994); reference level: metres below sea level. for legend, see fig. 4. 649 of the mires were rather short-lived, the data demonstrate that certain of the middle jurassic peat mires in the øresund area were able to exist for longer periods than the early jurassic mires in the same area. discussion factors controlling peat formation peat formation occurred in the fennoscandian border zone from north jylland, through øresund and skåne to bornholm during early–middle jurassic times. the conditions for peat accumulation were most favourable to the south-east as indicated by an increase in number and thickness of the seams from north jylland to bornholm. the upper pliensbachian – lower toarcian sorthat formation coals differ from the bathonian upper bagå formation coals in terms of composition, thickness and palynological content. the lower jurassic coal seams represent peat accumulation in low-lying interchannel and abandoned channel mires on a lower coastal plain in an overall transgressive setting (petersen & nielsen 1995). in paralic settings, rising relative sea-level causes a rise in the groundwater table and a more landwards ponding of coarse sediments, which may result in the formation of extensive peatlands (diessel 1994; petersen & andsbjerg 1996; petersen et al. 1998). peat accumulation in the sorthat precursor mires was favoured by a continuously high-standing watertable and anoxic conditions, and only small amounts of very fine-grained detrital mineral particles reached the mires. the mires were probably rheotrophic and periodically saline-water influenced, and the resulting coals are generally very huminite-rich. the limited thickness of the seams (up to 0.57 m, but generally between 0.08 m and 0.26 m) reflects a rather short duration of peat accumulation (average for all seams of 2300 years), determined by a fairly rapid relative sea-level rise. the sea-level rise was governed by an overall eustatic rise (hallam 1988; haq et al. 1988) and a subsidence rate of c. 30 m/my (petersen clay sand sandsilt øresund-7 well lower to upper part: densely vegetated mesotrophic swamp. telmatic to terrestrial freshwater facies. lowermost part: densely vegetated rheotrophic infilled lake swamp. limnotelmatic to telmatic freshwater facies. freshwater lake densely vegetated mesotrophic swamp. telmatic freshwater facies. densely vegetated mesotrophic to ombrotrophic domed bog. (telmatic to) terrestrial freshwater facies. shallow freshwater lake densely vegetated rheotrophic infilled lake swamp. limnotelmatic to telmatic freshwater facies. shallow freshwater lake shallow freshwater lake possibly ombrotrophic raised bog. terrestrial facies. seam 1 seam 4 seam 3 seam 2 m 50 51 52 53 54 55 56 m 45 46 47 48 49 coal ? clay silt 44 fig. 15. sedimentological core-log of the jurassic succession of the øresund-7 well. modified after petersen (1994); reference level: metres below sea level. for legend, see fig. 4. & nielsen 1995). most of the coal seams represent the boundary between two succeeding lake/lagoonal successions, i.e. they were deposited during the transition from a period of relatively slow rise in the watertable to a period during which the watertable rose more rapidly. peat formation began when the lake/lagoon or abandoned channel was filled and turned into lowlying mires. peat accumulation probably continued during the initial phase of the succeeding faster rise in watertable, as accumulation of organic matter may have been favoured by sediment starvation due to upstream ponding of clastic sediments. peat formation was terminated by lacustrine or lagoonal flooding of the mires, when the watertable rise outpaced the rate of organic matter accumulation. similarly, the formation and duration of the hettangian–sinemurian coastal mires in the fennoscandian border zone was strongly controlled by a relative sea-level rise, and the peats obtained thicknesses of only 0.5–3.5 m. on average, the investigated mires in the rønne formation existed for c. 1200 years and the mires in the øresund area for 1850 years. the principal controlling factor on the development of the early jurassic mires in the fennoscandian border zone was thus a general rise of the groundwater table that favoured the development of waterlogged, possibly rheotrophic and nutrient-rich mires, and hindered the development of domed bogs in most cases. this resulted in the dominance of huminite-rich coals and carbonaceous claystones. a similar mechanism has been presented for the westphalian a in the warrior basin, alabama, where domed peat formation may have been hindered due to extremely rapid basin subsidence in spite of a suitably warm and humid climate (eble et al. 1994). hunt (1989) suggested that eastern australian permian delta plain coals are consistently high-vitrinite coals, because the peats formed under high watertables principally controlled by a high subsidence rate. during the middle jurassic, the subsidence rate was much lower as clearly shown by thinner middle jurassic sediment packages (up to 200 m in c. 21 ma; gradstein et al. 1994) in the danish basin and fennoscandian border zone compared to those in the lower jurassic (up to 1000 m in c. 26 ma). the marked change in subsidence rate and basin configuration was caused by uplift of the ringkøbing–fyn high and the danish basin south-west of the sorgenfrei–tornquist zone (nielsen 1995, 2003, this volume). these changes may have been related to thermal doming centrally in the north sea area (underhill & partington 1993) and to an important middle jurassic volcanic event in central skåne that was possibly associated with, or preceded by, uplift in the form of a rift dome (f. surlyk, personal communication 1997). the reduced subsidence rate coupled with a more stable eustatic sea level (hallam 1988; haq et al. 1988) resulted in a more inland position for the middle jurassic mires in the fennoscandian border zone and on bornholm than that for the early jurassic mires. the proximity of the bathonian mires (upper bagå formation) on bornholm to granitic basement is reflected in the coarser grain size of the quartz particles and a much higher kaolinite content than observed in the sorthat formation coals. the thickest of the upper bagå formation coal seams (1.9 m) corresponds to a precursor peat thickness of 19 m and an estimated 19 000 years of peat accumulation. from the øresund area, a maximum of 7000 years is estimated. this suggests that on occasion peat accumulation was able to keep pace with the increase in accommodation space for a relatively long period of time. at other times, the rate of peat accumulation may have outpaced the rate of watertable rise resulting in the development of domed peats. as noted above, this style of peat development probably resulted from the combination of a low subsidence rate and a stable eustatic sea level, which worked together to limit flooding controlled by relative sea-level rise. the coal petrography indicates that most of the investigated middle jurassic mires were exposed to fluctuations in the groundwater table, probably controlled by a seasonal climate; such periodic falls in the watertable level favoured oxidation of the peat surfaces. in contrast, the seasonal climate probably had a more limited influence on the level of the watertable in the early jurassic coastal mires, where a high-standing watertable was governed by a more or less continuous rise of relative sea level. oxidation of the organic matter on the middle jurassic peat surface implies that the estimates of peat accumulation periods may be a rough minimum. the combined effect of a seasonal climate and possibly peat accretion above the watertable level resulted in coal seams with a higher content of inertinite. a low subsidence rate has been similarly inferred to account for oxidation of the precursor peats of permian high-inertinite coals in eastern australia (hunt 1989; hunt & smyth 1989). the fluctuating watertable in the middle jurassic mires may have favoured wildfire frequency and the formation of fire-derived inertinite; however, the nature of the inertinite, particularly in the coals from the øresund area, is indicative of derivation by oxidation. the presence of inertinitic maceral precursors formed by oxidation in recent peat deposits (cohen & stack 1996; moore et al. 1996), makes this suggestion likely. 650 the peat-forming vegetation based on palynological evidence the palynological evidence of the peat-forming vegetation suggests a lower jurassic flora with a prominent proportion of ferns together with cycadophytes, coniferophytes from the families pinaceae and taxodiaceae, unknown gymnospermous plants, and bryophytes. although the overall composition of the plant communities seems to have been rather uniform, variations in the composition of the palynomorph assemblages (and coal composition) in the seams and between seams may reflect variations in the peat-forming plant communities. these variations are probably related to specific environmental conditions in the mires as demonstrated in recent peat systems (cohen 1973; esterle & ferm 1994; phillips & bustin 1996b). the limited knowledge of the ecology and environmental tolerance of the plants restricts the understanding of the palaeoecological differences between the mire systems as indicated by various palynomorph assemblages. the middle jurassic seams from the upper bagå formation are characterised by the common occurrence of spores whose affinities lie with the order lycopodiales and the absence of pollen related to the order cycadales. club mosses are particularly abundant in mineral-rich levels corresponding to wet, nutrient-rich conditions in the precursor mires, or common inundations. bryophytes seem to have been present, together with ferns and coniferophytes. of particular note is the absence of pollen related to cycadales in the middle jurassic coals, particularly in view of their common occurrence in the lower jurassic samples. according to lapo & drozdova (1989), cycadophytes are rarely found in jurassic coals because they preferred drier habitats. however, höhne (1933) noted the presence of cycadophytes in the bagå formation coals, although this may have been stratigraphically lower in the succession. it is notable that the genus nilssonia, considered to represent the foliage of cycadophytes, occurs in lower jurassic claystones on bornholm (möller 1903). hence the palynomorphs from the lower jurassic seams whose affinities are with the cycadales could have originated from vegetation outside the mires. in general, there is a relatively good correspondence between the interpretation of the peat-forming vegetation based on macerals and the palynological evidence of the peat-forming vegetation. in order to strengthen the interpretations based on macerals, however, it is necessary to acquire specific knowledge of the peat-forming plants, i.e. the stature, structure and the wood content of the tissues; furthermore, the degradational conditions should also be considered (pierce et al. 1995). biological aspects of the parent plants should be incorporated, if possible, in particular to account for the variation in spore/pollen production by different species, but also to account for spores and pollen that may have been transported into the mires from the hinterland. it is clear that multidisciplinary studies of coals integrating palaeobotanical data with petrographic results provide the most detailed picture of the mire floras (see discussion by scott 1991; dimichele & phillips 1994). origin and environmental significance of pyrite in the coals of the sorthat and bagå formations the framboidal pyrite in the sorthat formation coals is interpreted to be syngenetic. framboidal pyrite is normally considered to indicate the influence of saline water during peat formation because organic sulphur inherited from the peat-forming flora only accounts for low contents of sulphur and pyrite in freshwater environments (cohen et al. 1984; casagrande 1987; phillips & bustin 1996a). however, the nature of the pyrite in the bagå formation coals and the lack of other evidence for marine influence suggest that this pyrite is mainly epigenetic in origin. it is therefore necessary to identify an external source of sulphur to account for the high content of pyrite in fairly well-defined intervals in the coals and the abundant pyrite concretions in the sand beds. the coal-bearing strata are faulted against the graben bounding fault, and sulphate-enriched porewater expelled from deeper levels may have migrated up through the fault zone and into the highly permeable sand beds and coal seams. sulphate-rich porewater is associated with anhydrite deposits, and zechstein and triassic deposits with anhydrite and a very low content of organic matter are present in the rønne graben. sulphate-rich porewater is known from triassic strata in the danish basin (gustafson & anderson 1979; laier 1982). the pyrite nodules in the sand beds in the bagå beds are often associated with coal particles. this suggests that the reduction of the sulphate and the precipitation of pyrite occurred where the local environment was reducing due to enrichment in organic matter. in the coal seams, pyrite is often found associated with fusinite, suggesting that precipitation was favoured by the higher porosity of the fusinite compared to the huminite (fig. 8d). an analogous situation has been described from carboniferous coal seams in a non651 marine succession from nova scotia, canada, where epigenetic pyrite fills fusain lenses, fractures and cleats (beaton et al. 1993). the carboniferous coal measures are in fault contact with rocks containing gypsum, anhydrite, carbonates, halite and potash salts, which are interpreted to be the source of the sulphur. conclusions the development of the early–middle jurassic mires in the fennoscandian border zone occurred in a humid, warm-temperate to subtropical, weakly seasonal climate. during the early jurassic, mires were established on coastal plains facing the open sea to the west. peat formation was mainly controlled by an overall fairly rapid rise of relative sea level governed by the general eustatic rise and a relatively high subsidence rate causing repeated lacustrine or lagoonal flooding of the mires. the early jurassic mires were relatively short-lived, averaging 1200 years (rønne formation), 1850 years (øresund area) and 2300 years (sorthat formation), because watertable rise outpaced the rate of peat accumulation. the lower jurassic coals and coaly mudstones in the fennoscandian border zone and on bornholm represent peat deposits that were between 0.5 and 5.7 m thick, but generally were less than 3 m thick. the upper pliensbachian – lower toarcian sorthat formation coals originated in continuously waterlogged, anoxic mires, and the high-standing watertable and the periodic marine influence on the mires favoured the formation of huminite-rich coals and the precipitation of framboidal pyrite. in addition to pyrite, the mineral matter is dominated by clay and fine-grained silt-sized quartz. uplift of the ringkøbing–fyn high and the main part of the danish basin south of the sorgenfrei–tornquist zone in aalenian times changed the basin configuration and influenced the accumulation of peat. the uplift, which may have been related to the formation of a large thermal dome in the central north sea, and possibly also in skåne, caused a strongly reduced subsidence rate within the fennoscandian border zone. the low subsidence rate coupled with a relative stable eustatic sea level, resulted in a general regression such that the middle jurassic mires developed farther inland than those of the early jurassic. the setting enabled peat accumulation in the middle jurassic mires to keep pace with and occasionally outpace the watertable rise. thus, some of the middle jurassic peat mires existed for relatively long periods. it is inferred from coals in the øresund area that peat accumulation occurred for up to 7000 years and upper bagå formation coals testify that at certain times during the bathonian, peat accumulation may have occurred on bornholm without significant interruption for up to 19 000 years. the combination of an inland position of the middle jurassic mires, a seasonal climate, and periodic peat accretion above the groundwater level caused temporary oxidation of the peat surfaces and the formation of inertiniterich coals. watertable fluctuations within the upper bagå formation mires on bornholm may further have been promoted by the generally sandy substrate of the alluvial plain. the proximity of these mires to the granitic basement areas to the east on bornholm is reflected by a larger grain size of quartz particles and a higher kaolinite content than observed in the sorthat formation coals. the pyrite in the upper bagå formation coals is interpreted to be mainly epigenetic in origin, precipitated out of sulphate-enriched porewater expelled from underlying zechstein–triassic strata. palynological data indicate variations in the peatforming plant communities between coal seams. variations within individual seams also suggest subtle changes in the mire environment, probably mainly of hydrological character, reflecting the evolution of the mire. the hettangian–sinemurian mires represented by the seams in the øresund-18 well were characterised by an abundance of ferns, cycadophytes and at certain levels significant proportions of coniferophytes of the family taxodiaceae. club mosses were also represented. the late pliensbachian – early toarcian mires (seams 2 and 15 in the levka-1 well, sorthat formation) were also characterised by an abundance of ferns. in contrast to the sinemurian mires in the øresund area, however, cycadophytes were more abundant, while coniferophytes of the family taxodiaceae were much less common and club mosses were probably absent. the bathonian mires represented by the seams in the upper bagå formation differ in particular from the early jurassic mires by the complete absence of cycadophytes and the abundance of club mosses, and by the rare occurrence of coniferophytes of the family taxodiaceae. ferns were significant components of the mires, as were jurassic species of pinaceae. it is tempting to relate the difference in the plant communities of the mires represented by the sorthat and bagå formation coal seams to the distinctly different depositional settings represented by these seams. the early jurassic mires were waterlogged, anoxic and periodically marine-influenced, whereas the bathonian mires developed under fresh652 water conditions and were situated inland, where in particular the seasonal climate was important in promoting a fluctuating watertable. in general, there appears to be a relationship between the petrographic composition of the coals and the composition of the peatforming vegetation, as deduced from palynological evidence. thus, the overall coal seam composition was controlled not only by allogenic factors but also by differences in vegetational input from the various peat-forming plant communities, which may account for the more subtle petrographic variations in the coal seams. acknowledgement the paper benefited significantly from constructive reviews by d.j. 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(ed.): coal and coal-bearing strata: recent advances. geological society special publication (london) 32, 25–49. ziegler, p.a. 1982: geological atlas of western and central europe, 130 pp. the hague: elsevier for shell internationale petroleum maatschappij. ziegler, p.a. 1988: evolution of the arctic – north atlantic and the western tethys. american association of petroleum geologists memoir 43, 179 pp. manuscript received 12 january 1996; revision accepted 13 january 1998. geological survey of denmark and greenland bulletin 6, 99-112 99geological survey of denmark and greenland bulletin 5, 99–112 © geus, 2004 jurassic dinoflagellate cyst stratigraphy of store koldewey, north-east greenland stefan piasecki, john h. callomon and lars stemmerik the jurassic of store koldewey comprises a middle jurassic succession towards the south and an upper jurassic succession towards the north. both successions onlap crystalline basement and coarse sediments dominate. three main lithostratigraphical units are recognised: the pelion formation, including the spath plateau member, the payer dal formation and the bernbjerg formation. rich marine macrofaunas include boreal ammonites and the successions are dated as late bathonian – early callovian and late oxfordian – early kimmeridgian on the basis of new collections combined with material in earlier collections. fine-grained horizons and units have been analysed for dinoflagellate cysts and the stratigraphy of the diverse and well-preserved flora has been integrated with the boreal ammonite stratigraphy. the dinoflagellate floras correlate with contemporaneous floras from milne land, jameson land and hold with hope farther to the south in east greenland, and with peary land in north greenland and svalbard towards the north. the middle jurassic flora shows local variations in east greenland whereas the upper jurassic flora gradually changes northwards in east greenland. a boreal flora occurs in peary land and svalbard. the characteristic and stratigraphically important species perisseiasphaeridium pannosum and oligosphaeridium patulum have their northernmost occurrence on store koldewey, whereas taeniophora iunctispina and adnatosphaeridium sp. extend as far north as peary land. assemblages of dinoflagellate cysts are used to characterise significant regional flooding events and extensive sequence stratigraphic units. keywords: ammonites, boreal, dinoflagellate cysts, jurassic, north-east greenland, store koldewey s.p. & l.s., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: sp@geus.dk j.h.c., department of chemistry, university college london, 20 gordon street, london wc1h 0aj, uk. jurassic sediments are well exposed in the east greenland basin from milne land (70°n) in the south to hochstetter forland (75°n) in the north. yet farther to the north, jurassic sediments are restricted to isolated outliers (ravn 1911; stemmerik & piasecki 1990) until the more extensive outcrops of jurassic deposits in the wandel sea basin in eastern north greenland are reached (81°n–83°n; fig. 1). the geographical gap between the jurassic outcrops of the wandel sea basin (peary land) and the well-studied ones of the east greenland basin corresponds to the zone covering the transition from the strictly boreal dinoflagellate cyst flora of peary land to the subboreal hybrid flora of east greenland. accordingly, dinoflagellate data from store koldewey are important since they improve correlation between these two floral provinces. the jurassic exposures on the island of store koldewey are also stratigraphically important because they provide the nearest accessible record in guiding the evaluation of the hydrocarbon potential of the extensive offshore shelf areas in the northern region. the mesozoic of store koldewey was first described by ravn (1911) and koch (1929) on the basis of data collected by members of ‘danmarks expeditionen’ in 1906–1908. store koldewey was then not visited by geologists until the summer of 1989, when several fieldgeus bulletin no 5.pmd 29-10-2004, 11:1499 100 18 w 18ºw 20 km 76º30'n 76ºn store koldewey danmarkshavn undifferentiated, mostly glacial deposits cretaceous kap arendt ravn pynt trækpasset sydlige gneisnæs jurassic caledonian crystalline basement fault n kløft i kløft ii greenland 500 km 5 4 3 2 1 6 1: milne land 2: jameson land 3: hold with hope 4: hochstetter forland 5: store koldewey 6: peary land/ wandel sea basin fig. 1. simplified geological map of store koldewey. geus bulletin no 5.pmd 29-10-2004, 11:14100 101 parties from the geological survey of greenland (ggu; since 1995 part of the geological survey of denmark and greenland) studied the geology of the island as part of regional mapping projects (stemmerik & piasecki 1990; henriksen 1997). other areas mapped as palaeozoic and mesozoic sediments by haller (1983) were also visited at the same time but most of these appeared to be glacial deposits (stemmerik & piasecki 1990). however, some new, very small outcrops of jurassic sediments were found, protected from erosion on the downthrown side of basement faults (piasecki et al. 1994). geological setting the elongated shape of store koldewey reflects a north–south-oriented crystalline basement ridge. mesozoic sediments are exposed only in low coastal cliffs along the east side of the island (fig. 1). they include four distinct stratigraphic units (i–iv) that are preserved in small structural basins separated by basement highs (fig. 1). the lithology is generally of mud to fine-grained sand grade and the units are highly fossiliferous. the stratigraphic units are of middle jurassic (i), late jurassic (ii) and early cretaceous ages (iii–iv). the southernmost outcrop at ravn pynt consists of a middle jurassic succession more than 60 m thick, the trækpasset formation (koch 1929; figs 1, 2). upper jurassic sediments crop out in two gullies, kløft i and kløft ii, in the northern part of the island (fig. 1). the sediments in the first (northern) af these gullies have been referred to the kløft i formation (koch 1929) based on the description by ravn (1911) of material collected by members of the ‘danmarks ekspeditionen’ in 1906–1908. ravn (1911) proposed a callovian age for the trækpasset formation and a ‘sequanian’ (kimmeridgian) age for the kløft i formation based on ammonites. the sandstone of the kløft i formation was later found in the kløft ii locality to be overlain with a sharp boundary by grey laminated mudstones of the bernbjerg formation (piasecki et al. 1994). samples and methods the palynological samples were prepared by standard preparation methods including treatment with hydrochloric and hydrofluoric acids, oxidation and filtration with 20 micron mesh. the stratigraphical position of the middle jurassic samples is marked on the sedimentological log from ravn pynt (fig. 2). this succession is well dated by ammonites and the recorded occurrences and distributions of dinoflagellate cysts are mainly used to improve the precision of middle jurassic dinoflagellate cyst stratigraphy in east greenland. this has involved new palynological analyses of ammonite-dated samples from jameson land for confirmation of the new stratigraphical results from store koldewey. these new data are not published yet, but are referred to in this paper. the new ammonite records are not yet published in detail but are utilised in this paper. the position of the upper jurassic samples is marked on the sedimentological log from kløft ii (see fig. 5). the record of dinoflagellate cysts is then used to date the regionally recorded transition from shallow marine sandstone to the shale of the bernbjerg formation. the dinoflagellate assemblages are correlated with older ammonite data, but the samples were not themselves directly associated with ammonites. a number of new species have been described and defined separately (piasecki 2001). middle jurassic lithostratigraphy the middle jurassic succession on store koldewey, the trækpasset formation of koch (1929), is a lateral equivalent in part of the geographically widespread pelion formation, and as there is little reason to maintain a separate stratigraphy for store koldewey, it is herewith re-assigned to the pelion formation. the upper part of the exposed succession is of early to middle callovian age and biostratigraphically equivalent to the new spath plateau member on hold with hope (vosgerau et al. 2004, this volume) where the same two ammonite zones are recorded. this part of the store koldewey succession provides dinoflagellate cyst data from an interval that is not so well documented in jameson land (milner & piasecki 1996). ammonites and dinoflagellate cysts in the succession at ravn pynt may indicate a depositional break between the bathonian and the callovian parts of the pelion formation (figs 3, 4). the basal callovian comprises the only significant mudstone in this succession. this shift in depositional facies is associated with the appearance of callovian ammonites and several of the uppermost bathonian ammonite zones are not recorded beneath the facies shift. the absence of these zones geus bulletin no 5.pmd 29-10-2004, 11:14101 102 40 0 10 20 30 50 m structure fossils lithology sand sand with gravel mud clay clasts calcareous concretions hardened bed lamination lenticular lamination planar cross-bedding shell bed thalassinoides isp. curvolithos isp. planolites isp. monocraterion isp. diplocraterion isp. boreal ammonite fauna horizon belemnite bivalve pinna sp. serpulid oyster 360691 wood 360691 360694 360695 360696 360697 360699 360392 360393 360394 360395 360396 360397 360398 360399 360400, 401 360700 360698 360692, 693 mud sand gravel 16 16 26 31 31 19a ggu sample numbers fig. 2. sedimentological log of the exposed middle jurassic succession at ravn pynt. levels of the analysed palynological samples are indicated. geus bulletin no 5.pmd 29-10-2004, 11:14102 103 may indicate a hiatus in the sedimentary succession or simply no preservation of fauna and flora in that specific part of the section. some of the absent ammonite faunas, however, have been collected just south of ravn pynt on store koldeway. ammonites the jurassic succession contains abundant ammonites in well-separated faunal horizons and the stratification is generally preserved despite some solifluction. the sedimentological succession was studied in a ravine at ravn pynt and four ammonite horizons were collected here in situ and directly correlated with the fine-grained palynological samples (fig. 2). these ammonites represent the arcticoceras ishmae zone (horizon 16), the arcticoceras cranocephaloide zone (horizon 19a including topotypes of kepplerites tychonis ravn), the cadoceras apertum zone (horizon 26) and the proplanulites koenigi zone (horizon 31) of the standard boreal ammonite biostratigraphy of jameson land (callomon 1993). the age of the succession is then midbathonian to callovian based on the ammonite faunas. dinoflagellate cysts the organic matter in the middle jurassic succession is dominated by black and brown woody material. the abundance of dinoflagellate cysts is generally low but the diversity is fair (65 recorded species, including a few acritarchs). the assemblages are dominated by proximate cysts accompanied by few cavate cysts but are basically barren of chorate cysts. specimens from the pareodinia/paraevansia/evansia and the escharisphaeridium/sentusidinium groups are the most abundant cysts. successive species appear regularly upwards in the succession but the highest number of appearances is in ggu sample 360698 at 19.60 m (fig. 4) at the base of a 13 m thick fine-grained interval (fig. 2). this may reflect a hiatus in the succession below the sample and/or a shift to a more open marine depositional environment. since the middle jurassic succession is dated in detail by ammonites, the distribution of the dinoflagellate cysts can be used to increase the precision of their ranges in the boreal jurassic as previous recorded in other regions in east greenland (jameson land and hold with hope). sirmiodinium grossii, gonyaulacysta pectinigera, paragonyaulacysta retiphragmata and chytroeisphaeridia hyalina are the stratigraphically important species that occur throughout the investigated succession. s. grossii appears in the arctocephalites arcticus chronozone in milne land (larsen et al. 2003) and becomes more frequent from approximately the arctocephalites cranocephaloide chronozone and upwards to the cadoceras apertum chronozone (milner & piasecki 1996). this increase in abundance of s. grossii is not observed here because no samples were collected from this part of the section. in milne land, g. pectinigera is recorded as becoming abundant from the a. cranocephaloide chronozone upwards into the c. apertum chronozone but again, this increase in abundance is not represented in the present section. in jameson land, p. retiphragmata has its earliest appearance in the a. cranocephaloide chronozone but at store koldewey it clearly appears already in the arcticoceras ishmae chronozone. c. hyalina appeared earliest in the cadoceras calyx chronozone in jameson land (milner & piasecki 1996). the present material, in combination with new data from jameson land, show that c. hyalina is present already in the a. ishmae chronozone and becomes abundant from the c. apertum zone. aldorfia aldorfensis appears in the a. cranocephaloide chronozone precisely where it is expected from its range in jameson land (milner & piasecki 1996). the morphologically variable species ctenidodinium thulium is recorded throughout the succession, having a much more extensive range than that recorded elsewhere in east greenland. towards the south, in milne land, it is restricted to the interval above the a. cranocephaloide chronozone and below the paltoceras athleta chronozone (larsen et al. 2003). this upper range is confirmed in these northern regions by data from hold with hope where it is recorded in strata just below the p. athleta chronozone (piasecki et al. 2004, this volume). many of the less frequent species seem to occur in a rather random way that makes their presence and especially their absence less stratigraphically useful. crussolia perireticulata is a good example of this. in milne land, it occurs in the bathonian a. arcticus chronozone and again higher in the callovian part of the succession (larsen et al. 2003). in jameson land, it appears one ammonite zone higher than in milne land, the bathonian arctocephalites greenlandicus chronozone and is then not recorded again until it reappears in the basal callovian, top c. apertum chronozone. there are no records of this species from the bathonian or the callovian of store koldewey and hold with hope. this could indicate a southern affinity of this geus bulletin no 5.pmd 29-10-2004, 11:14103 104 species as the depositional settings of these localities are comparable overall. however, a callovian range is reported from the present arctic regions of the sverdrup basin and svalbard (smelror 1993). some exceptionally early occurrences of ambonosphaera calloviana and gonyaulacysta helicoidea in the a. ishmae chronozone and of pareodinia stegasta and paraevansia brachythelis in the c. apertum chronozone are recorded in the present succession. the dinoflagellate cysts in the middle jurassic succession are divided into an upper bathonian and a lower callovian dinoflagellate cyst assemblage. the boundary is placed at 19.2 m, above which level a significant number of new species appear (figs 2, 4). most species in the upper bathonian assemblage also occur in the lower callovian assemblage and the composition of the bathonian assemblage varies significantly between the few samples studied. the younger, boreal ammonite zonation lithostratigraphy erymnoceras coronatum succession south of ravn pynt succession at ravn pynt kosmoceras jason sigaloceras calloviense proplanulites koenigi cadoceras nordenskjoeldi spath plateau member pe lio n fo rm at io ncadoceras apertum b a t h o n ia n c a ll o v ia n cadoceras calyx cadoceras variabile arcticoceras cranocephaloide arcticoceras ishmae arctocephalites greenlandicus arctocephalites arcticus fa u n a h o r iz o n s 31 22 26 20 19 16 15 hiatus ? fig. 3. schematic stratigraphical classification of the middle jurassic succession on store koldewey. geus bulletin no 5.pmd 29-10-2004, 11:14104 10 5 sa m pl e he ig ht m et re 50 25 0 g g u s am pl e no . 57.00 43.80 39.40 38.60 31.80 29.50 26.50 23.00 19.80 12.40 4.60 3.60 360400 54.50 360401 360397 360395 360394 360393 360392 360700 360699 360698 360696 360694 360693 sy st em ju ra ss ic ( m id dl e) st ag e c al lo vi an b at ho ni an f o rm at io n pe lio n fo rm at io n 1 pa ra ev an si a sp p. 2 pa re od in ia s co pa eu s 3 a m bo no sp ha er a ca llo vi en se 4 va le ns ie lla o vu la 5 g on ya ul ac ys ta ju ra ss ic a 6 va le ns ie lla d ic ty di a 7 g on ya ul ac ys ta p ec tin ig er a 8 pa ra go ny au la cy st a re tip hr ag m at a 9 ev an si a ja ne ae 10 m ei ou ro go ny au la x sp on gi os a 11 c hy tr oe is ph ae ri di a hy al in a 12 a to po di ni um h ar om en se 13 r hy nc ho di ni op si s cf . c la do ph or a 14 si rm io di ni um g ro ss ii 15 c ad do sp ha er a ha lo sa 16 m ei ou ro go ny au la x sp p. 17 c hl am yd op ho re lla c f. ec to ta bu la ta 18 d ur ot ri gi a da ve yi 19 g on ya ul ac ys ta h el ic oi de a 20 ba tia ca sp ha er a sp p. 21 sc ri ni od in iu m s pp . 22 se nt us id in iu m sp p. 23 c hy tr oe is ph ae ri di a ch yt ro eo id es 24 c ym at io sp ha er a sp p. 25 se nt us id in iu m p el io ne ns e 26 k al lo sp ha er id iu m s pp . 27 c te ni do di ni um t hu liu m 28 pa re od in ia a rc tic a 29 va lv ae od in iu m le ne ae 30 es ch ar is ph ae ri di um r ud is 31 d ur ot ri gi a cf . d av ey i 32 pa re od in ia p ac hy ce ra s 33 k al lo sp ha er id iu m h yp or na tu m 34 po ly st ep ha no ph or us c f. pa ra ca la tu s 35 va le ns ie lla s p. f en so m e 36 va le ns ie lla s pp . 37 c hy tr oe is ph ae ri di a sp p. 38 fr om ea t or na lis 39 g on ya ul ac ys ta c f. ce nt ri co nn at a 40 ev an si a pe ri re tic ul at a 41 pa re od in ia s te ga st a 42 n . p le ga s va r. d ic ty or na tu s 43 a ld or fia a ld or fe ns is 44 d is si lio di ni um sp p. 45 pa ra ev an si a br ac hy th el is 46 k al lo sp ha er id iu m p ra us si i 47 pa ra go ny au la cy st a sp p. 48 pa re od in ia g ra nu la ta 49 pa re od in ia p ro lo ng at a 50 sc ri ni od in iu m c f. lu ri du m 51 se nt us id in iu m sp . d f en so m e 52 a to po di ni um p ol yg on al is 53 fr om ea s pp . 54 pa re od in ia s pp . 55 pa re od in ia c f. sc op ae us 56 es ch ar is ph ae ri di um s pp . 57 ja ns on ia sp p. 58 so lis ph ae ri di um a nk yl et on 59 le pt od in iu m sp p. 60 si rm io di ni op si s sp p. 61 g on ya ul ac ys ta s pp . 62 pa re od in ia c f. gr oe nl an di cu m 63 es ch ar is ph ae ri di um s pp . 64 li th od in ia sp p. 65 a m bo no sp ha er a cf . c al lo vi an a 66 g on ya ul ac ys ta c f. he lic oi de a alphabetical species list 43 aldorfia aldorfensis 3 ambonosphaera calloviana 65 ambonosphaera cf. calloviana 12 atopodinium haromense 52 atopodinium polygonalis 20 batiacasphaera spp. 15 caddosphaera halosa 17 chlamydophorella cf. ectotabulata 23 chytroeisphaeridia chytroeoides 11 chytroeisphaeridia hyalina 37 chytroeisphaeridia spp. 27 ctenidodinium thulium 24 cymatiosphaera spp. 44 dissiliodinium spp. 31 durotrigia cf. daveyi 18 durotrigia daveyi 63 escharisphaeridium spp. 30 escharisphaeridium rudis 56 escharisphaeridium spp. 9 evansia janeae 40 evansia perireticulata 53 fromea spp. 38 fromea tornalis 39 gonyaulacysta cf. centriconnata 66 gonyaulacysta cf. helicoidea 19 gonyaulacysta helicoidea 5 gonyaulacysta jurassica 7 gonyaulacysta pectinigera 61 gonyaulacysta spp. 57 jansonia spp. 33 kallosphaeridium hypornatum 46 kallosphaeridium praussii 26 kallosphaeridium spp. 59 leptodinium spp. 64 lithodinia spp. 10 meiourogonyaulax spongiosa 16 meiourogonyaulax spp. 42 n. plegas var. dictyornatus 45 paraevansia brachythelis 1 paraevansia spp. 8 paragonyaulacysta retiphragmata 47 paragonyaulacysta spp. 48 pareodinia granulata 28 pareodinia arctica 62 pareodinia cf. groenlandicum 55 pareodinia cf. scopaeus 32 pareodinia pachyceras 49 pareodinia prolongata 2 pareodinia scopaeus 54 pareodinia spp. 41 pareodinia stegasta 34 polystephanophorus cf. paracalatus 13 rhynchodiniopsis cf. cladophora 50 scriniodinium cf. luridum 21 scriniodinium spp. 25 sentusidinium pelionense 51 sentusidinium sp. d fensome 22 sentusidinium spp. 60 sirmiodiniopsis spp. 14 sirmiodinium grossii 58 solisphaeridium ankyleton 6 valensiella dictydia 4 valensiella ovula 35 valensiella sp. fensome 36 valensiella spp. 29 valvaeodinium leneae store koldewey ravn pynt >50 specimens 20–50 specimens 5–19 specimens 1–4 specimens fig. 4. distribution chart of the dinoflagellate cysts in the middle jurassic succession at ravn pynt on store koldewey. g e u s b u lle tin n o 5 .p m d 2 9 -1 0 -2 0 0 4 , 1 1 :1 4 1 0 5 106 lower callovian assemblage is characterised by abundant chytroeisphaeridia hyalina and pareodinia pachyceras, together with many species not present below e.g. pareodinia stegasta, aldorfia aldorfiense and paraevansia brachythelis. middle jurassic correlation the dinoflagellate cyst assemblage of the lower part of the succession (bathonian) correlates with assemblages of the a. arcticus – a. cranocephaloide chronozones from both milne land (assemblages 2 and 3 in: larsen et al. 2003) and jameson land (milner & piasecki 1996) in central east greenland. the assemblages from the charcot bugt formation in milne land are very poor, both in diversity and density, but have stratigraphically significant species such as s. grossii, c. hyalina, kallosphaeridium hypornatum and evansia janeae in common with the present assemblage. in the same stratigraphical interval in the fossilbjerget formation of jameson land, new species appear for the first time in abundance and have many species in common with the assemblage from store koldewey. differences in occurrence and first appearances of significant species between the two areas are discussed above. the dinoflagellate cyst assemblage of the higher part of the succession (lower callovian) on store koldewey also correlates well with assemblages from the charcot bugt formation in milne land, whereas the contemporaneous assemblages from the fossilbjerget formation in jameson land are poor and not so well documented. in contrast, dinoflagellate cyst assemblages from the pelion formation, spath plateau member, on hold with hope (piasecki et al. 2004, this volume) correlate well with assemblages from store koldewey. the assemblages in the charcot bugt formation (assemblages 4 and 5 in: larsen et al. 2003) are not precisely dated but are not older than the a. cranocephaloide chronozone (bathonian) and not younger than the erymnoceras coronatum chronozone (top middle callovian). discussion the correlation of the pelion formation on store koldewey with the charcot bugt, the fossilbjerget and the pelion formations in southern parts of the jurassic east greenland basin complex shows that time-equivalent sedimentary successions exist regionally in different lithostratigraphical units. the middle jurassic dinoflagellate assemblages vary with depositional environments but the overall characters can be recognised and correlated over long distances. the main problem is the interdependence of deposition of relatively fine-grained sediments and preservation of dinoflagellate cysts, giving relatively few horizons with rich assemblages in the generally coarsegrained middle jurassic successions, i.e. the pelion and charcot bugt formations. upper jurassic lithostratigraphy the upper jurassic succession on store koldewey was defined as the kløft i formation (koch 1929). its lower sandstone-dominated part is equivalent to the recently defined payer dal formation (alsgaard et al. 2003) from hold with hope, kuhn ø and hochstetter forland further to the south, and the overlying mudstones are equivalent to the geographically extensive bernbjerg formation (fig. 5). for convenience and simplification of the lithostratigraphy, the kløft i formation is not used here and the succession is referred to the payer dal and bernbjerg formations (fig. 5). 0 5 10 15 m 360497 360498 360496 360493 360494 360495 mud sand b er nb je rg f m pa ye r d al fm fig. 5. sedimentological log of the exposed upper jurassic succession at kløft ii with the levels of analysed samples marked. for legend, see fig. 2. geus bulletin no 5.pmd 29-10-2004, 11:14106 107 ammonites the old ammonite collections from the kløft i formation (payer dal formation) described by ravn (1911) were recently correlated more precisely with the british ammonite succession, confirming a late oxfordian to early kimmeridgian age, equivalent to the amoeboceras serratum, a. rosenkrantzi and aulacostephanoides mutabilis zones (fig. 6; sykes & surlyk 1976; sykes & callomon 1979). new ammonite finds indicate a similar age. these ammonites are not precisely located but most probably came from the sandstones referred here to the payer dal formation. the samples analysed for dinoflagellate cysts are from the top of this formation and from the overlying bernbjerg formation (fig. 6). dinoflagellate cysts the organic content of the upper jurassic samples is dominated by brown and black woody material and the abundance and diversity of the dinoflagellate cyst floras are low. the richest samples are from the base of the bernbjerg formation, probably representing a flooding event. the dinoflagellate cysts are better preserved in the payer dal formation than in the bernbjerg formation. the composition of the dinoflagellate cyst flora is clearly in favour of proximate cysts, with a minority of chorate specimens and species. the upper jurassic succession comprises two assemblages, which intermingle at the transition from payer dal to bernbjerg formation (fig. 7). the lower assemblage is characterised by gonyaulacysta dualis, adnatosphaeridium sp. (a. hartzi in: piasecki 1980), taeniophora iunctispina, ambonosphaera calloviana and paragonyaulacysta capillosa. this assemblage is well known from oxfordian/kimmeridgian strata in milne land in east greenland (piasecki 1980; piasecki 1996), hochstetter forland (piasecki & stemmerik 2004, this volume) and in peary land, north greenland (håkansson et al. 1981; piasecki 1994). the upper assemblage is characterised by paragonyaulacysta capillosa, occisucysta sp., perisseiasphaeridium pannosum, rhynchodiniopsis sp. and rhynchodiniopsis cf. pennata. this assemblage is known from kimmeridgian strata in milne land with a slightly different frequency of the species involved (piasecki 1996), and from peary land, north greenland (piasecki 1994) and svalbard (århus 1988). the earliest paragonyaulacysta capillosa on milne land appears in the basal kimmeridgian, rasenia cymodoce chronozone, shortly before the earliest perisseiasphaeridium pannosum and avellodinium cf. falsificum at the base of the a. mutabilis chronozone. these two events are recorded within an assemblage of abundant adnatosphaeridium sp. (a. hartzi in: piasecki 1980), taeniophora iunctispina, gonyaulacysta jurassica/dualis and ambonosphaera calloviana that dominates from the late oxfordian (a. rosenkrantzi based on dinoflagellate cysts based on ammonites chronozones k im m er id gi an o xf o rd ia n lithostratigraphy formations bernbjerg payer dal aulacostephanoides mutabilis rasenia cymodoce pictonia baylei amoeboceras rosenkrantzi amoeboceras regulare amoeboceras serratum amoeboceras glosense chronostratigraphyfig. 6. schematic stratigraphical classification of the upper jurassic succession on store koldewey. geus bulletin no 5.pmd 29-10-2004, 11:14107 10 8 2 5 0 18.00 11.00 4.00 3.00 1.00 360495 360494 360493 360496 360497 ju ra ss ic k im m er id gi an o xf o rd ia n– k im m er id gi an b er nb je rg pa ye r d al 1 r hy nc ho di ni op si s cl ad op ho ra 2 pi lo si di ni um m yr ia tr ic hu m 3 n um m us s pp . 4 a dn at os ph ae ri di um s p. 5 a m bo no sp ha er a ca llo vi an a 6 pa ra go ny au la cy st a ca pi llo sa 7 le pt od in iu m s ub til e 8 se nt us id in iu m p el io ne ns e 9 g on ya ul ac ys ta c f. he lic oi de a 10 le io sp ha er id ia s pp . 11 ep ip lo sp ha er a sp p. 12 g on ya ul ac ys ta d ua lis 13 c ri br op er id in iu m g ra nu lig er a 14 pa re od in ia h al os a 15 te nu a hy st ri x 16 c hy tr oe is ph ae ri di a hy al in a 17 ep ip lo sp ha er a bi re tic ul at a 18 c irc ul od in iu m sp p. 19 es ch ar is pa ha er ia la ev ig at a 20 c ad do sp ha er a cf . h al os a 21 o cc is uc ys ta a ff. m on oh eu ri sk os 22 ta en io ph or a iu nc tis pi na 23 a m bo no sp ha er a sp . 24 si rm io di ni um g ro ss ii 25 pa re od in ia s pp . 26 sc ri ni od in iu m ir re gu la re 27 a to po di ni um h ar om en se 28 pe ri ss ei as ph ae ri di um p an no su m 29 av el lo di ni um c f. fa ls ifi cu m 30 es ch ar is ph ae ri di a po co ck ii 31 r hy nc ho di ni op si s sp p. 32 r hy nc ho di ni op si s cf . p en na ta 33 o cc is su cy st a sp p. 34 ba rb at ac ys ta p ilo sa 35 pr ol ix os ph ae ri di um g ra nu lo su m 36 es ch ar is pa ha er ia c f. la ev ig at a 37 tu bo tu be re lla c f. eg em en ii 38 te nu a sp p. 39 c irc ul od in iu m d ow ni ei 40 c irc ul od in iu m c f. do w ni ei 41 pa ra go ny au la cy st a cf . c ap ill os a 42 o lig os ph ae ri di um p at ul um 43 a pt eo di ni um s pp . 44 c ri br op er id in iu m c f. pe rf or an s 45 pa re od in ia b or ea lis 46 pe ri ss ei as ph ae ri di um c f. pa nn os um 47 a cr it ar ch s pe ci es alphabetical species list 23 ambonosphaera sp. 47 acritarch species 4 adnatosphaeridium sp. 5 ambonosphaera calloviana 43 apteodinium spp. 27 atopodinium haromense 29 avellodinium cf. falsificum 34 barbatacysta pilosa 20 caddosphaera cf. halosa 16 chytroeisphaeridia hyalina 40 circulodinium cf. downiei 39 circulodinium downiei 18 circulodinium spp. 44 cribroperidinium cf. perforans 13 cribroperidinium granuligera 17 epiplosphaera bireticulata 11 epiplosphaera spp. 36 escharispahaeria cf. laevigata 19 escharispahaeria laevigata 30 escharisphaeridia pocockii 9 gonyaulacysta cf. helicoidea 12 gonyaulacysta dualis 10 leiosphaeridia spp. 7 leptodinium subtile 3 nummus spp. 33 occisucysta spp. 21 occisucysta aff. monoheuriskos 42 oligosphaeridium patulum 45 pareodinia borealis 6 paragonyaulacysta capilosa 41 paragonyaulacysta cf. capilosa 14 pareodinia halosa 25 pareodinia spp. 46 perisseiasphaeridium cf. pannosum 28 perisseiasphaeridium pannosum 2 pilosidinium myriatrichum 35 prolixosphaeridium granulosum 32 rhynchodiniopsis cf. pennata 1 rhynchodiniopsis cladophora 31 rhynchodiniopsis spp. 26 scriniodinium irregulare 8 sentusidinium pelionense 24 sirmiodinium grossii 22 taeniophora iunctispina 15 tenua hystrix 38 tenua spp. 37 tubotuberella cf. egemenii sa m pl e he ig ht m et re g g u s am pl e no . sy st em st ag e f o rm at io n store koldewey kløft ii >50 specimens 20–50 specimens 5–19 specimens 1–4 specimens fig. 7. distribution chart of the dinoflagellate cysts in the upper jurassic succession at kløft ii on store koldewey. g e u s b u lle tin n o 5 .p m d 2 9 -1 0 -2 0 0 4 , 1 1 :1 4 1 0 8 109 chronozone) to the earliest kimmeridgian (pictonia baylei and r. cymodoce chronozones). a similar order of appearances occurs in the upper jurassic succession of store koldewey and the presence of occisucysta sp. in these strata also supports a stratigraphical level equivalent to the r. cymodoce chronozone by comparison with the assemblages from milne land. p. pannosum becomes abundant in milne land in the a. mutabilis chronozone and dominates the dinoflagellate assemblages throughout the a. eudoxus zone until oligosphaeridium patulum becomes the totally dominant species in the a. autissiodorensis chronozone. the assemblage on store koldewey contains perisseiasphaeridium pannosum most abundantly at the transition between the two formations and oligosphaeridium patulum follows rapidly at the base of bernbjerg formation. none of the two species are abundant at higher levels in the bernbjerg formation at kløft ii. upper jurassic correlation the upper jurassic dinoflagellate cyst assemblages on store koldewey closely resemble the boreal assemblages from the jurassic ladegårdsåen formation of peary land (piasecki 1994), and to some degree also the assemblage in the janusfjellet formation, svalbard (århus 1988). however, the restricted ammonite faunas in these two formations do not allow precise dating of the dinoflagellate assemblages on peary land and svalbard. the most significant difference between these assemblages is the presence of p. pannosum and o. patulum only at store koldewey. adnatosphaeridium sp. and taeniophora iunctispina occur as far north as peary land but are not reported from svalbard. the stratigraphically highest occurrence of gonyaulacysta dualis, atopodinium haromense, occisucysta sp. in peary land, in an assemblage with abundant escharisphaeridium pocockii, rhynchodiniopsis sp., taeniophora iunctispina and adnatosphaeridium sp. is associated with the appearance of paragonyaulacysta capillosa and cribroperidinium perforans. this assemblage and associated stratigraphic events in peary land are directly comparable with the dinoflagellate cyst assemblage at the transition from the payer dal formation to the bernbjerg formation on store koldewey. the age of this assemblage is interpreted to be early kimmeridgian (r. cymodoce – a. mutabilis chronozones). a comparable event has not been recorded in the kimmeridgian of svalbard (janusfjellet formation) where only paragonyaulacysta capillosa seems to have stratigraphical potential, with a consistently relative short range (århus 1988). there, p. capillosa appears after a poor to barren interval in the upper oxfordian to lowermost kimmeridgian, above a poor ammonite record of rasenia sp. and at a level where bioturbated mudstones are followed by laminated mudstones, just as on store koldewey and in milne land. the appearance of p. capillosa and its associated assemblage may therefore reflect a relative sea-level rise. the presence of p. capillosa and its associated dinoflagellate cyst assemblage may be used as a general indication of the stratigraphical level from the r. cymodoce chronozone into the a. mutabilis (a. eudoxus?) chronozone. the few other associated species in the janusfjellet section are the stratigraphically long-ranging species paragonyaulacysta borealis, lanterna saturnalis and tubotuberella apatela, the typical borealis assemblage (brideaux & fisher 1976) which also occurs in east and north greenland. the dinoflagellate cyst assemblages in peary land and svalbard provide no clear upper stratigraphical limits, except for the disappearance of p. capillosa. p. capillosa occurs commonly up to the a. autissiodorensis chronozone (top kimmeridgian) in milne land but is also recorded scattered throughout the volgian. the successions at store koldewey, peary land and svalbard within the range of abundant p. capillosa are therefore considered to be of kimmeridgian (pre-volgian) age. discussion despite the similarity in composition and abundance of specific species in the geographically widespread assemblages described above, there are also clear differences reflecting the latitudinal distance between the compared localities. the upper jurassic dinoflagellate cyst assemblage on store koldewey is a mixture of species with subboreal or boreal preference but with a clear affinity to the boreal region. p. pannosum and o. patulum are abundant and long-ranging in northwest europe, they are abundant with a more restricted stratigraphical range in east greenland, and they appear in low numbers with a limited stratigraphical range in store koldewey. this is probably close to the northern limit of these species as they do not appear farther to the north in peary land (piasecki 1994) and svalbard (århus 1988). on store koldewey, the occurrence of these species so far north is associated with the most geus bulletin no 5.pmd 29-10-2004, 11:14109 110 significant relative sea-level rise recorded in the upper jurassic of east greenland, in the r. cymodoce to a. mutabilis (a. eudoxus) chronozones of the kimmeridgian. sequence stratigraphic implications studies of the jurassic ammonite and dinoflagellate cyst stratigraphy integrated with sedimentological studies and sequence stratigraphical interpretations in east greenland lead towards an integrated genetic model in which the units can be identified by their content of dinoflagellate cysts. the present study of the dinoflagellate cyst assemblages on store koldewey contributes to the study of this complex problem. the middle jurassic succession deposited directly on crystalline basement on store koldewey correlates with contemporaneous and stratigraphically similar successions from the lower part of the fossilbjerget formation in jameson land (p5 and p6 third-order sequences of engkilde & surlyk 2003), the charcot bugt formation in milne land (larsen et al. 2003) and the pelion formation at hold with hope (vosgerau et al. 2004, this volume). both in milne land and on hold with hope, the middle jurassic successions represent the earliest evidence of the jurassic transgression of the margins of the sedimentary basins. the ammonite fauna from the a. ishmae chronozone is among the most widespread faunas in the arctic (callomon 1993) and marks the considerable extent of this circum-arctic second-order marine transgression represented also in most areas of east greenland. the third-order depositional sequence p5 in jameson land is limited by sequence boundaries located in the a. ishmae and c. calyx chronozones, respectively (engkilde & surlyk 2003). the p6 depositional sequence is confined to the c. apertum, c. nordenskjoeldi and basal p. koenigi chronozones. stratigraphically, p5 and p6 correspond to the two sedimentological units identified in the middle jurassic of store koldewey and their content of dinoflagellate cysts correlates as well. in milne land, the charcot bugt formation also contains ammonites from the a. ishmae and the a. cranocephaloide zones (larsen et al. 2003). the associated dinoflagellate cyst assemblages correlate well with assemblages from the corresponding lower pelion succession on store koldewey. dinoflagellate cysts from the higher pelion formation, the spath plateau member, at store koldewey (c. apertum chronozone to the basal p. koenigi chronozone) correlate with those from assemblage 4 from the charcot bugt formation. on hold with hope, the pelion formation comprises two sedimentological units: a lower sandstone unit followed by the spath plateau member (vosgerau et al. 2004, this volume). ammonites indicating the c. apertum zone and the p. koenigi zone occur in the basal strata of spath plateau member. dinoflagellate cyst assemblages equivalent to the assemblages from the corresponding spath plateau member on store koldewey have been recorded in this succession (piasecki et al. 2004, this volume). thus, two distinct dinoflagellate cyst assemblages of bathonian and callovian age characterise the two sedimentological units that have been identified as third-order depositional sequences and are found to be extensively distributed throughout east greenland. as already mentioned above, the upper jurassic succession on store koldewey, consisting of the payer dal and bernbjerg formations, correlates excellently with contemporaneous successions from eastern peary land and svalbard in the north to milne land in the south. the overall transgressive trend from the upper oxfordian to maximum flooding in the kimmeridgian is represented by sedimentary deposits throughout east and north greenland that can be correlated in detail on the basis of both ammonites and dinoflagellate cysts. a succession of distinct dinoflagellate cyst assemblages characterises the stepwise progress of relative sea-level rise and can be recognised throughout the sedimentary basins of east greenland. conclusion the jurassic succession of store koldewey is divided into the pelion, payer dal and bernbjerg formations. abundant boreal ammonites date the succession in detail and associated floras of dinoflagellate cyst provide supplementary data. the pelion formation is dated as late bathonian – early callovian, in the middle jurassic, and the payer dal and bernbjerg formations are dated as late oxfordian – early kimmeridgian in the late jurassic. the middle jurassic succession consists of a bathonian and a callovian part. they can be correlated with contemporaneous sedimentary successions on hold with hope, in jameson land and in milne land to the south, where corresponding dinoflagellate cyst assemblages have been recorded. ranges of individual dinoflagellate species are given in relation to the boreal ammonite stratigraphy. geus bulletin no 5.pmd 29-10-2004, 11:14110 111 the upper jurassic succession is correlated with corresponding successions in hochstetter forland, hold with hope and milne land to the south and with those of peary land, north greenland, and svalbard to the north. passing northwards from east greenland via north greenland to svalbard, the upper jurassic dinoflagellate cyst floras show a transition from dominantly subboreal species in central east greenland to a distinct boreal flora in svalbard. the stratigraphic ranges of many species and their abundance decrease towards the north. in contrast, species with boreal affinity range southwards to milne land. the assemblages in store koldewey are transitional in composition. the sedimentological units of store koldewey are placed in the sequence stratigraphic framework developed for the jurassic in east greenland, and the associated dinoflagellate cyst assemblages are used to characterise and to identify these sequence stratigraphic elements. acknowledgements work began as part of the project ‘resources of the sedimentary basins of north and east greenland’, supported by the danish research councils. the work was completed with support from the carlsberg foundation (carlsbergfondet) ans. 980089/20-262. the authors are grateful to dr. a. wierzbowski and dr. g.f.w. herngreen for careful comments and constructive suggestions. references alsgaard, p.c., felt, v.l., vosgerau, h. & surlyk, f. 2003: the jurassic of kuhn ø, north-east greenland. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 865–892. århus, n. 1988: palynostratigraphy of some bathonian–hauterivian sections in the arctic, with emphasis on the janusfjellet formation type section, spitsbergen. institutt for kontinentalsokkelundersøkelser (iku) report 23.1252.11/01/88, 139 pp. brideaux, w.w. & fisher, m.j. 1976: upper jurassic – lower cretaceous dinoflagellate assemblages from arctic canada. geological survey of canada bulletin 259, 1–53. callomon, j.h. 1993: the ammonite succession in the middle jurassic of east greenland. bulletin of the geological society of denmark 40, 83–113. engkilde, m. & surlyk, f. 2003: shallow marine syn-rift sedimentation: middle jurassic pelion formation, jameson land, east greenland. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 813–863. håkansson, e., birkelund, t., piasecki, s. & zakharov, v. 1981: jurassic–cretaceous of the extreme arctic (peary land, north greenland). bulletin of the geological society of denmark 30, 11–42. haller, j. 1983: geological map of northeast greenland 75°– 82°n lat. meddelelser om grønland 200(5), 22 pp. henriksen, n. 1997: geological map of greenland 1:500 000, sheet 10, dove bugt. copenhagen: geological survey of denmark and greenland. koch, l. 1929: stratigraphy of greenland, 124 pp. dr. scient thesis, university of copenhagen, denmark. larsen, m., piasecki, s. & surlyk, f. 2003: stratigraphy and sedimentology of a basement-onlapping shallow marine sandstone succession, the charcot bugt formation, middle–upper jurassic, east greenland. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 893–930. milner, p.s. & piasecki, s. 1996: boreal middle jurassic dinoflagellate cyst stratigraphy of jameson land, east greenland. in: piasecki, s. et al. (eds): formation of source and reservoir rocks in a sequence stratigraphic framework, jameson land, east greenland. energy research programme efp-93, projects 1313/93-0010 and 0017. danmarks og grønlands geologiske undersøgelse rapport 1996/30, vol. i and ii, 46 pp. piasecki, s. 1980: middle to late jurassic dinoflagellate cyst stratigraphy from milne land (east greenland) correlated with ammonite stratigraphy, 167 pp. unpublished ph.d. thesis, university of copenhagen, denmark. piasecki, s. 1994: biostratigraphy of the jurassic – lower cretaceous ladegårdsåen formation, peary land. in: håkansson, e. (ed.): wandel sea basin: basin analysis. efp-91, project no. 0012, 1–14. piasecki, s. 1996: boreal dinoflagellate cyst stratigraphy of middle to upper jurassic sediments of milne land, east greenland. in: piasecki, s. et al. (eds): formation of source and reservoir rocks in a sequence stratigraphic framework, jameson land, east greenland. energy research programme efp-93, projects 1313/93-0010 and 0017. danmarks og grønlands geologiske undersøgelse rapport 1996/30, vol. i and ii, 100 pp. piasecki, s. 2001: three new middle jurassic dinoflagellate cysts of east greenland. neues jahrbuch für geologie und paläontologie. abhandlungen 219(1–2), 15–31. piasecki, s. & stemmerik, l. 2004: jurassic dinoflagellate cysts from hochstetter forland, north-east greenland. in: stemmerik, l. & stouge, s. (eds): the jurassic of north-east greenland. geological survey of denmark and greenland bulletin 5, 89–97 (this volume). piasecki, s., stemmerik, l., friderichsen, j.d. & higgins, a.k. 1994: stratigraphy of the post-caledonian sediments in the germania land area, north-east greenland. rapport grønlands geologiske undersøgelse 162, 183–190. piasecki, s., larsen, m., therkelsen, j. & vosgerau, h. 2004: jurassic dinoflagellate cyst stratigraphy of hold with hope, geus bulletin no 5.pmd 29-10-2004, 11:14111 112 north-east greenland. in: stemmerik, l. & stouge, s. (eds): the jurassic of north-east greenland. geological survey of denmark and greenland bulletin 5, 73–88 (this volume). ravn, j.p.j. 1911: on jurassic and cretaceous fossils from northeast greenland. meddelelser om grønland 45(10), 437–500. smelror, m. 1993: biogeography of bathonian to oxfordian (jurassic) dinoflagellates: arctic, nw europe and circum-mediterranean regions. palaeogeography, palaeoclimatology, palaeoecology 102, 121–160. stemmerik, l. & piasecki, s. 1990: post-caledonian sediments in north-east greenland between 76° and 78°30′n. rapport grønlands geologiske undersøgelse 148, 123–126. sykes, r.m. & callomon, j.h. 1979: the amoeboceras zonation of the boreal upper oxfordian. palaeontology 22(4), 839– 903. sykes, r.m. & surlyk, f. 1976: a revised ammonite zonation of the boreal oxfordian and its application in north-east greenland. lethaia 9, 421–436. vosgerau, h., larsen, m., piasecki, s., therkelsen, j. & surlyk, f. 2004: a new middle–upper jurassic succession on hold with hope, north-east greenland. in: stemmerik, l. & stouge, s. (eds): the jurassic of north-east greenland. geological survey of denmark and greenland bulletin 5, 51–71 (this volume). geus bulletin no 5.pmd 29-10-2004, 11:14112 geological survey of denmark and greenland bulletin 17, 2009, 49-52 in 2008, the geological survey of denmark and greenland began a project in collaboration with the bureau of minerals and petroleum of greenland with the aim to publish a webbased, seamless digital map of the precambrian bedrock between 61°30´ and 64°n in southern west greenland. such a map will be helpful for the mineral exploration industry and for basic research. producing an updated digital map requires additional field work revisiting key localities to collect samples for geochemistry, geochronology and metamorphic petrology. the new data will help us to test and refine existing models and improve general understanding of the geological evolution of the area. here we summarise some results from the 2008 field activities between ame ralik in the north and frederikshåb is blink in the south (fig. 1). the area was mapped in the 1960s and 1970s, and although the 1:100 000-scale maps are of excellent quality, they do not include more recent developments in geochro nology, thermobarometry and geochemistry. a notable exception is the fiske næsset complex (fig. 1), which has re ceived considerable attention after it was first mapped (ellitsgaard-ras mus sen & mouritzen 1954; wind ley et al., 1973; windley & smith, 1974; myers 1985). new tectonic models have been developed since the original 1:100 000 maps were produced, and the tectonic evolution has been com monly ex plained in terms of terrane accretion (friend et al. 1996). friend’s model de fines a number of boundaries that separate terranes of different age and origin and which might have contrasting tectono-metamorphic histories prior to terrane accretion. the current project area includes the northern part and proposed boundary of the tasiusarsuaq terrane, which was amalgamated with the terranes to the north at 2.72 ga, when regional metamorphism affected the region (friend et al. 1996). in addition, windley & garde © geus, 2009. geological survey of denmark and greenland bulletin 17, 49–52. available at: www.geus.dk/publications/bull geological observations in the southern west greenland basement from ameralik to frederikshåb isblink in 2008 nynke keulen, anders scherstén, john c. schumacher, tomas næraa and brian f. windley 49 mainly upper crustal zone lower crustal zone prograde amphibolite facies retrograde amphibolite facies granulite facies quaternary deposits block boundary inferred thrust transition between lower and upper crustal zones late kinematic ttg plutons and granitic rocks orthogneiss metavolcanic belt eoarchaean gneiss anorthosite complex tasiusarsuaq western terrane boundary 64°n 62°n52°w 48° 50 km bjø rne sun d ikk att oq fre der iks håb isb link tre br ød re ter ran e fiskenæsset complex utqqôrqqqq uuuuur tttttuuuuuôrqqutôrqutqutqutqutq tttqôôôqôôôôôqqq tetnitang aggraninnran ttg teg ngran teetei rtalikrtvev alikkkkkkiillrriilllllliiiiii talikkee ttavertaaerta kkkki t li qôrqut granite bu kse fjor den am era lik græ def jord ikk att up n un aa sermilik bjørnesund kvanefjord nuuk paamiut qa rlii t n un aat th rus t qi lan nga ars uit qi lan nga ass ua tasiusarsuaq terrane ma joq qap qa ava inland ice ilivertalik granite davis strait greenland fig. 1. simplified geological map of the central part of the north atlantic craton in southern west greenland showing the main rock com ponents, patterns of metamorphic facies and three crustal blocks (modified after windley & garde 2009). rosa_2008:rosa-2008 01/07/09 15:48 side 49 (2009) proposed a model in which a series of blocks represent crustal sections that (except for the sermilik block; fig. 1) display a systematic metamorphic progression from amphibolite facies to granulite facies rocks from south to north. each block represents a number of island and continental arcs that were amalgamated by collision into the growing north atlantic craton. in their model, the project area consists of the sermilik, bjørnesund and kvanefjord blocks, where each block represents a combination of lateral and vertical crustal growth. however, contrary to the terrane model, two blocks can have a common origin. quartzo-feldspathic rocks grey tonalite-trondhjemite-granodiorite-type gneiss es (ttg) have intrusive ages of 2.92–2.84 ga that represent the main crust-generating period (schiøtte et al. 1989; næraa & scher stén 2008). there is growing evidence from zircon u-pb-hf geochronology for an older previously unrecognised meso archaean crustal component within the tasiusarsuaq terrane (næraa & scherstén, unpublished data). the extent of the older component is currently unclear, but it is apparently most widespread in the northern part of the terrane. in addition, a number of strongly deformed and veined tonalitic gneisses of presumed early neoarchaean age are younger, about 2.72 ga, and formed from older pre-existing crust. granite (sensu lato) intrusions are variably deformed but post-date the majority of the grey gneisses. the main granite, the ilivertalik augen granite, has feldspar megacrysts, and is in some places orthopyroxene-bearing and has been dated to 2.8 ga (pidgeon & kalsbeek 1976; næraa & scherstén, unpublished data). the main volume of this granite intrudes the sermilik block, but satellite intrusions, including the type locality at ilivertalik mountain, are found in the bjørnesund block, implying that these blocks were a single crustal unit by 2.8 ga. at ilivertalik mountain, kalsbeek & myers (1973) suggested that the intrusion was charnockitic and was emplaced under granulite-facies conditions. mica schists, commonly with garnet or sillimanite, occur throughout the area. these were originally mapped as having sedimentary protoliths. to our knowledge, all recognised structures in these rocks are tectono-metamorphic, and their supracrustal origin seems to have been mostly inferred from their common relationship with amphibolites or their aluminium-rich or quartzitic compositions. amphibolites and metagabbro-anorthosites supracrustal rocks with a range of compositions occur throughout the area, but are dominated by amphibolites. preservation varies, with readily identified primary textures in 50 temperature (°c) 400 500 600 700 800 900 1000 1100 1200 1 0 2 3 4 5 6 7 8 9 10 p (k ba r) d epth (km ) calculated geotherms facies boundaries reaction boundaries metamorphic conditions consistent with field observations in 2008 possible p-t trajectory of a plagioclase lherzolite boudin (fig. 3) reaction of olivine+plagioclase to orthoand clinopyroxene in plagioclase lherzolite boudin am gn sil ky and melting in quartzfeldspar rocks melting of ultramafic rocks q z m u s sil kfs opx cpx ol plg bio qz o px kfs l t spinel lhz plagioclase lhz ~2.7 ga ~3.2 ga ~2.56 ga ~3.0 ga 3 2 4 1 eb ea s u dil os eti n ar g d e ar ut as -l a gs 35 25 15 5 fig. 2. ranges of p–t estimates from previous work by wells (1979), griffin et al. (1980) and riciputi (1990); geotherms based on measured and estimated contents as a function of time of radiogenic elements in basaltic and felsic green land rocks using methods of kamber et al. (2005). the calculations are based on a crustal thickness of 40 km and a two-layer model with 10 km of mafic rocks at the base of the crust overlain by 30 km of felsic rocks. depths in kilometres are based on an average crustal density of 2.75 g/cm3. parameters: man tle heat flow: 20 mw/m2; mafic and felsic rockheat production are: 0.262 and 3.478 µw/m3 at 3.2 ga (possible maximum age for this part of the terrane), 0.244 and 3.254 µw/m3 at 3.0 ga, 0.220 and 2.945 µw/m3 at 2.7 ga, 0.210 and 2.811 µw/m3 at 2.56 ga (age of the qôrqut granite). the numbered blue fields represent the ranges of p–t estimates: 1 = sermilik (griffin et al. 1980); 2 = sermilik and qilan ngaassua (riciputi et al. 1990); 3 = sermilik (wells 1979); 4 = qilanngaarsuit (wells 1979). am, amphibolite facies; and, andalusite; bio, biotite; cpx, clinopyroxene; ea, epidoteamphibolite facies; eb, epidote-blueschist facies; gn, granulite facies; gs, greenschist facies; kfs, k-feldspar; ky, kyanite; l, liquid; lhz, lherzolite; mus, muscovite; ol, olivine; opx, orthopyroxene; plg, plagioclase; qz, quartz; sil, sillimanite. rosa_2008:rosa-2008 01/07/09 15:48 side 50 some areas and amphibolite lenses in others. the ikkattup nunaa belt on the islands in the ikkattoq fjord just north of frederikshåb isblink (fig. 1) is one of the best-preserved volcanic belts in the region (andersen & friend’s 1973 ravns storø belt). pillow lavas and volcanic bombs are well preserved here, and these rocks likely formed in shallow water with partly explosive volcanism. rocks with calc-alkaline basaltic to andesitic compositions predominate (k. szilas et al., unpublished data 2009), and analytical results suggest a convergent margin setting with an age of 2.91 ± 0.01 ga (nutman et al. 2004). in 2008 we discovered that some major amphibolite belts at majoqqap qaava (fig. 1) contain two components, namely lithic tuff-dominated, metavolcanic rocks and massive homogeneous amphibolite sheets, which are similar to the two main components of the ikkattup nunaa belt, thus a common arc origin is likely. the fiskenæsset complex is a layered igneous complex containing ultramafic rocks, gabbros, leucogabbros, anorthosites and chromitites, which formed largely by cumulate processes (myers 1985). in 2008, we established that the lower main ultramafic unit, best exposed at majoqqap qaava, consists of a succession of layered dunites intruded by a major sill complex that comprises more than 25 clinopyroxene-hornblende sills, some of which are up to 10 m thick. the sills contain xenoliths of dunite, send apophyses into adjacent dunites and have discordant contacts against layered dunites. this observation means that the early history of the fiskenæsset complex involved intrusion of a second, hydrous magma batch into earlier crystallised, olivine-rich cumulates. meta-gabbros and meta-anorthosites of the fiskenæsset complex are closely associated with amphibolites of supra crustal origin, and they could be part of the same magmatic system. escher & myers (1975) believed that the fiskenæsset complex was intrusive into the amphibolites. however, the observed contacts are tectonic, and direct evidence for primary intrusive relationships is lacking. clearly, discordant anor thosite dykes cross-cut strongly deformed metagabbros within the complex (e.g. at 63.1156°n, 50.7155°w). these dykes consist of plagioclase and orthopyroxene and likely post-date all deformation. tectono-metamorphic development the qarliit nunaat thrust forms the boundary between the tre brødre and tasiusarsuaq terranes (fig. 1; friend et al. 1996). south of buksefjorden there is a very high-strain, high-grade shear zone several kilometres wide between the færingehavn and the tasiusarsuaq terranes (stainforth 1977; crowley 2002). however, on either side of this shear zone, the tectono-metamorphic styles are different; to the north of buksefjorden we found no evidence for a metamorphic or structural discontinuity. here, rocks previously considered to be part of the tre brødre terrane might therefore be part of the tasiusarsuaq terrane. an abrupt change in metamorphic grade, from amphibolite facies just south of grædefjord to granulite facies a little farther south, within the tasiusarsuaq terrane, is associated with intensive shearing as predicted in the crustal block model of windley & garde (2009). confirmation of the model comes from the fact that in 2008 we discovered that the boundary is occupied by a north-dipping, over 250-mwide shear zone with a down-dip lineation, which contains augen gneisses, cataclasites and mylonites. the boundary separates amphibolite facies gneiss with granulite facies relicts to the south from prograde amphibolite facies gneisses to the north, as also predicted by kalsbeek (1976). pressure –temperature (p–t) estimates are sparse in the present field area and focused on pyroxene-garnet assemblages (amphibolites) that are restricted to upper amphibolite and granulite facies. figure 2 shows the locations of estimated geotherms for a 40 km thick crust. the geotherms that bracket the (3.0–2.7 ga) metamorphism suggest pressures of 5–6 kbar for the conditions of the amphibolite facies to granulite facies transition. these p–t-t (t = time) conditions are consistent with field observations, e.g. the only aluminosilicate phase found in 2008 was sillimanite, and the observed peak assemblages are consistent with conditions near the amphibolite facies and granulite facies transition at intermediate pressure. granulite-facies rocks occur more rarely than suggested on the current 1:100 000 scale maps, although, in the area around the fiskenæsset complex granulite-facies rocks are 51 1 cm fig. 3. spinel-bearing plagioclase lherzolite showing the breakdown of olivine and plagioclase to form coronas of clinopyroxene and orthopyroxene. the stability limits of the plagioclase lherzolite are below c. 9 kbar and 1200ºc, and the reaction would have occurred between about 700°c, 4 kbar and 870ºc, 7 kbar. location at 63.932ºn, 51.219ºw. rosa_2008:rosa-2008 01/07/09 15:48 side 51 52 abundant. some of the area designated as granulite facies contains amphibolite-facies assemblages, but is interpreted to have once attained granulite-facies conditions. however, part of the rocks previously considered retrograde from granulitefacies rocks might better be interpreted as prograde amphibolite-facies rocks that never reached granulite-facies con ditions. full analysis of the p–t–t trajectories will require detailed textural and chemical analysis of these rocks. garnet-bearing mica schists and amphibolites from ame ralik fjord and frederikshåb isblink suggest garnet growth at the expense of plagioclase, which is consistent with a metamorphic event dominated by pressure increase. these observations are best explained by thrust tectonics. evidence for isobaric or near-isobaric cooling was observed in reaction textures of the plagioclase lherzolite from north of buksefjorden described in fig. 3. the lherzolite occurs as a boudin within a refolded zone of amphibolite and ultramafic rocks in grey gneiss. ultramafic boudins are associated with pegmatite dykes, and this resulted in alteration of the ultramafic rocks. similar corona textures were noted at majoqqap qaava and were interpreted as late igneous or early metamorphic reactions by myers & platt (1977). cataclastic structures are abundant in the area between ameralik and frederikshåb isblink (e.g. stainforth 1977). brittle deformation occurs as an overprint of earlier ductile structures. pseudotachylytes were observed at a few localities, although cohesive fault rocks (cataclasites) are more common. references andersen, l.s. & friend, c. 1973: structure of the ravns storø amphibolite belt in the fiskenæsset region. rapport grønlands geologiske undersøgelse 51, 37–40. crowley, j.l. 2002: testing the model of late archaean terrane accretion in southern west greenland: a comparison of timing of geological events across the qarliit nunaat fault, buksefjorden region. pre cam brian research 116, 57–79. ellitsgaard-rasmussen, k. & mouritzen, m. 1954: an anorthosite occurrence from west greenland. meddelelser fra dansk geologisk for ening 12, 436–442. escher, j.c. & myers, j.s. 1975: new evidence concerning the original relationships of early precambrian volcanics and anorthosites in the fiskenæsset region, southern west greenland. rapport grønlands geologiske undersøgelse 75, 72–76. friend, c.r.l., nutman, a.p., baadsgaard, h., kinny, p.d. & mcgregor, v.r. 1996: timing of late archaean terrane assembly, crustal thickening and granite emplacement in the nuuk region, southern west green land. earth and planetary science letters 142, 353–365. griffin, w.l., mcgregor, v.r., nutman, a.p., taylor, p. n. & bridgwater, d. 1980: early archaean granulite-facies metamorphism south of ame ralik, west greenland. earth and planetary science letters 50, 59– 74. kalsbeek, f. 1976: metamorphism in the fiskenæsset region. rapport grønlands geologiske undersøgelse 73, 34–41. kalsbeek, f & myers, j.s. 1973: the geology of the fiskenæsset region. rapport grønlands geologiske undersøgelse 51, 5–18. kamber, b.s., whitehouse, m.j., bolhar, r. & moorbath, s. 2005: volcanic resurfacing and the early terrestrial crust: zircon u–pb and ree constraints from the isua greenstone belt, southern west greenland. earth and planetary science letters 240, 276–290. myers, j.s. 1985: stratigraphy and structure of the fiskenæsset complex, southern west greenland. bulletin grønlands geologiske under søgelse 150, 72 pp. myers, j.s. & platt, r.g., 1977: mineral chemistry of layered archaean anorthosite at majorqap qâva, near fiskenæsset, southwest greenland. lithos 11, 59–72. næraa, t. & scherstén, a. 2008: new zircon ages from the tasiusarsuaq terrane, southern west greenland. geological survey of denmark and greenland bulletin 15, 73-76. nutman, a.p., friend, c.r.l., barker, s.l.l. & mcgregor, v.r. 2004: inventory and assessment of palaeoarchaean gneiss terrains and detrital zircons in southern west greenland. precambrian research 135, 281–314. pidgeon, r.t. & kalsbeek, f. 1978: dating of igneous and metamorphic events in the fiskenaesset region of southern west greenland. cana dian journal of earth sciences 15, 2021–2025. riciputi, l.r., valley, j.w. & mcgregor, v.r. 1990: conditions of archean granulite metamorphism in the godthab-fiskenaesset region, southern west greenland. journal of metamorphic geology 8, 171–190. schiøtte, l., compston, w. & bridgwater, d. 1989: u-pb single-zircon age for the tinissaq gneiss of southern west greenland: a controversy resolved. chemical geology 79, 21–30. stainforth, j.g. 1977: the structural geology of the area between ameralik and buksefjorden, southern west greenland, 480 pp. unpublished ph.d. thesis, exeter university, uk. wells, p.r.a. 1979: chemical and thermal evolution of archaean sialic crust, southern west greenland. journal of petrology 20, 187–226. windley, b.f. & garde, a.a. 2009: arc-generated blocks with crustal sections in the north atlantic craton of west greenland: crustal growth in the archean with modern analogues. earth-science reviews 93, 1–30. windley, b.f. & smith, j.v. 1974: the fiskenæsset complex, west green land, part ii. general mineral chemistry from qeqertarssuatsiaq. bulle tin grønlands geologiske undersøgelse 108, 54 pp. windley, b.f., herd, r.k. & bowden, a.a. 1973: the fiskenæsset complex, west greenland, part i. a preliminary study of the stratigraphy, petrology, and whole rock chemistry from qeqertarssuatsiaq. bulletin grønlands geologiske undersøgelse 106, 80 pp. authors’ addresses n.k., a.s.1 & t.n., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: ntk@geus.dk j.c.s., department of earth sciences, university of bristol, bristol bs8 1rj, uk. b.f.w., department of geology, university of leicester, leicester le1 7rh, uk. 1present address: department of geology, lund university , sölvegatan 12, s-223 62 lund, sweden. rosa_2008:rosa-2008 01/07/09 15:48 side 52 geological survey of denmark and greenland bulletin 17, 2009,57-60 57 geological maps are of vital importance for documenting and advancing geological knowledge and they are a prerequisite for any meaningful evaluation of economic resources. in greenland, mapping is taking place on the mainland – that for two centuries has been the traditional exploration target – and offshore, where only in the last decades has hydrocarbon exploration moved to the continental shelves. greenland with its 2 166 000 km2 is the largest island in the world. however, the land is overwhelmed by ice. a central ice sheet – the inland ice – blankets some 81% of the country reducing rock outcrop to a coastal fringe 0 to 300 km wide (fig. 1). the continental shelves comprise a little more than twice the area of this fringe, c. 830 000 km2. this preamble serves to emphasise that greenland’s three physiographic units – exposed fringe, offshore and inland ice – are of very different size and that mapping has focused on the smallest acreage. piecing together the composition of the largest, and hitherto unexplored, unit constitutes the next chapter of greenland mapping. historical perspective and aim of this paper in the last 25 years, great strides have been made in geolo gical understanding as can be seen from two 1:2 500 000 maps (escher 1970; escher & pulvertaft 1995). apart from the progress recorded in the ice-free fringe, the 1995 map provides a first interpretation of the offshore, and it also includes information of sub-ice bedrock although this is but a single blob of colour at borehole gisp 2 (fig. 1). this paper’s aim is to provide a first graphic interpretation of the bedrock under the inland ice and to review data sources. its four-page limit does not allow citation of specific sources; these will be covered in a forthcoming paper. this state-of-the-art map is naturally rudimentary in approach with all boundaries arbitrary but it has the prospect of directing attention to future data assembly. the state of knowledge 2008 present knowledge of sub-ice geology is based on six main sources, each discussed below with emphasis on its use in compilation of the geological map shown in fig. 1. drill sites drilling through the ice is the ultimate way of determining substratum composition. however, the only in situ rock sampled is from borehole gisp 2 – an archaean granitoid rock reactivated during the palaeoproterozoic (fig. 1). other ice cores have revealed information about rock debris, for example, camp century (fountain et al. 1981). nunataks nunataks are restricted to the inland ice margin within c. 30 km of the nearest land. most expose locally known rocks and are important for piecing together structural make-up. of importance for the new map is the 120 km long n–s string of nunataks west of dronning louise land, north-east greenland. they infer larger sub-ice occurrences of meso proterozoic sediments than exist on the neighbouring land. coast to coast correlation greenland’s tapering form enables precambrian rocks to be correlated across its southern tip and, by extrapolation farther north, under the ice. the presence on both coasts of archae an rocks flanked north and south by palaeo pro ter o zoic orogenic belts allows the sub-ice projection of the north atlantic craton although its southern and northern boundaries are hidden for 250 km and 500 km, respectively. this correlation is strengthened by aeromagnetic data (fig. 2). the disappearance of palaeogene extrusives on both sides of the inland ice might suggest a single province. however, both coasts are eruption sites connected to continental breakup but since the role of plumes and hot-spots is still unclear, basalts cannot be excluded from central greenland. glacial erratics the inland ice is a relic of a vast pleistocene ice cover and the surrounding land is strewn with rocks dropped as the ice retreated. broadly speaking, erratic suites from southern greenland represent extensively exposed precambrian and late phanerozoic provinces whereas farther north, exotic precambrian–palaeozoic suites relate to sub-ice occurrences that are unknown or not exposed locally. moreover, even the © geus, 2009. geological survey of denmark and greenland bulletin 17, 57–60. available at: www.geus.dk/publications/bull the bedrock geology under the inland ice: the next major challenge for greenland mapping peter r. dawes rosa_2008:rosa-2008 01/07/09 15:48 side 57 58 r i n k i a n c a l e d o n i a n camp century washington land gisp 2 e l l e s m e r e – i n g l e f i e l d c o m m i t t e e – m e l v i l l e peary land dronning louise land v i c t o r i a e l l e s m e r i a n north atlantic craton n a g s s u g t o q i d i a n nuuk m elville b ugt tasiusaq victoria fjord k e t i l i d i a n ? ? ? nares strait f r a n k l i n i a n baffin island labrador grenville orogen ellesmere island c a n a d a g r e e n l a n d labrador sea baffin bay mesoproterozoic intrusions precambrian shield ellesmerian (devonian) caledonian (silurian) phanerozoic basins devonian–palaeogene cambrian–silurian proterozoic basins with basalts mesoproterozoic– ?neoproterozoic mesoproterozoic, porphyries, redbeds ?mesoproterozoic, redbeds gardar palaeo–neoproterozoic sub-ice basins basalts and intrusions phanerozoic fold belts palaeogene volcanic province palaeoproterozoic palaeoproterozoic, with reworked archaean mainly archaean (palaeoproterozoic overprint) archaean incl. palaeoarchaean (palaeoproterozoic overprint) meso-neoarchaean archaean including eoarchaean thrust deep borehole 250 km kronprins frederik land k nu d r as mu sse n l and margin of inland ice fig. 1. geological map of greenland with interpretation of sub-ice bedrock in terms of major provinces. ice-free geology (in dark colour shades) modified from henriksen (2008); dashed, grey line, division of proterozoic crust from dahl-jensen et al. (2003). small map, canadian– greenland correlations in the precambrian shield showing the palaeozoic franklinian basin blanketing its northern margin. rosa_2008:rosa-2008 01/07/09 15:48 side 58 59 absence of particular erratics can be informative, for example, this author has no knowledge of erratics that might indicate a late palaeozoic – mesozoic sub-ice source. information from five erratic suites is incorporated into fig. 1. glacial drift across the proterozoic–phanerozoic platform of north greenland is characterised by shield blocks – granitoid rocks, gneisses and associated rocks. most of these need laboratory work to cast light on their age and use in reflecting hidden provinces (see 1 below) but some rocks are ready-made indicators (2, 3). farther south, exotic suites occur on the shield terrain of the west and east coasts (4, 5). 1. the shield erratics isotopically dated are from peary land and environs and they suggest sub-ice archaean crust affected by strong palaeoproterozoic overprint. 2. banded iron formation (bif) characterises the neo archaean committee–melville orogen of baffin is land and north-west greenland. bif erratics in north green land suggest an extension of this terrane far to the east. 3. erratics of porphyries and basalt, with rare sandstone, in washington land indicate a sub-ice volcanic–redbed province (fig. 3a). preliminary isotopic work points to a meso proterozoic age. 4. red sandstone and siltstone erratics around tasiusaq and farther north in north-west greenland point to extensive sub-ice sources (fig. 3b). 5. erratics along the east greenland ice margin were emphasised by haller (1971, fig. 48): proterozoic sandstone and basalt, cambrian quartzite with skolithos and ordovician limestone infer extensive sub-ice sources. detrital provenance studies age and palaeoflow history of detritus within sedimentary rocks – rock clasts and crystals – can be relevant for sub-ice geology. however, minerals like zircon can be transported thousands of kilometres before deposition and identifying sub-ice geology on grains alone is problematical. thus, the clast–grain couplet of the tilloidal neoproterozoic morænesø formation in southern peary land is relevant, particularly so with its south-westerly provenance (kirkland et al. 2009). clasts are of local mesoproterozoic sandstone and dolerite, with less frequent granitoid rocks, bif and porphyry, suggesting proximal sub-ice sources of neoarchaean and meso proterozoic ages. age estimates of zircons from granitoid clasts are 2.7 ga with overprinting at 1.25 ga. zircon crystals range from palaeo archaean to mesopro terozoic with strong palaeo proterozoic peaks suggesting large sub-ice areas. a minor 3.3 ga peak is an obvious link to the substratum (victoria fjord complex) that contains the only known rocks of this age in greenland (nutman et al. 2008). moreover, the subsidiary status of these grains compared to neoarchaean also exists in sequential mesoproterozoic and cambrian strata implying that palaeo archaean rocks form but a minor com ponent of the complex. kirkland et al. (2009) favour two south-western sources for meso proterozic detritus: proximal sub-ice gren ville-overprinted rocks and the type grenvillian of labrador, more than 2000 km distant. a third source is suggested by fig. 1: the sub-ice volcanic province that may also source the rare porphyry clasts. geophysics geophysical methods – satellite, airborne or ice based – undoubtedly have great potential for mapping the sub-ice geology. preliminary interpretations about structure and fig. 2. grids of total magnetic field over southern greenland and offshore based on verhoef et al. (1996, low resolution maanaoala data, geol ogical survey of canada) and white frame, high resolution aeromag data (geological survey of denmark and greenland). stippled lines, geol ogical trends by b.m. stensgaard (personal communication 2009). fig. 3. glacial erratics from sub-ice provinces unknown in outcrop. a: feldspar porphyry from washington land, western north greenland, ggu 425204. other porphyry erratics are illustrated in dawes et al. 2000, fig. 3. b: coarse-grained, cross-bedded sandstone from tasiusaq area, north-west greenland, ggu 457508. photos: jakob lautrup. 553 289 181 103 50 10 -23 -54 -86 -119 -158 -206 -326 363 174 111 70 42 16 -7 -30 -52 -77 -105 -141 -210 a b rosa_2008:rosa-2008 01/07/09 15:48 side 59 crustal thickness can be made from regional magnetic and gravity surveys. the power of aeromagnetics is illustrated by verhoef et al.’s (1996) compilation of reconnaissance data that shows arcuate coast to coast anomalies coinciding with tectonic segments of the nagssugtoqidian orogen, while mergence with high-resolution coastal data allows some structural subdivision of the shield (fig. 2). radar and remote-sensing techniques provide physiographic details about the sub-ice landscape, for example, legarsky et al.’s (1998) work used to locate the volcanic province in knud rasmussen land (fig. 1). many tectonic provinces display distinct physiographical characteristics and thus 3-d imagery is vital for mapping sub-ice geology. mountains, plains, plateaux and lowlands are not the only geological indicators, but hills and valleys affect ice dynamics and control water flow, two primary parameters for determining provenances of erratics and detrital material. conclusions, future research, ice recession and economic potential a main conclusion must be that while mapping below the ice is in its infancy, the status of the geus databases has promising potential for planning research, whether sampling, drill ing or geophysics. one dire need is for low-altitude and ice-based geophysical surveys to facilitate deductions about spatial relationships of sub-ice provinces. the new map leads to eight conclusions, but being conjectural, it raises important questions – too many to discuss in this short paper. 1. provinces unknown in outcrop occur below the ice. 2. where it is widest, in the north, the inland ice hides the most variable geology: palaeoarchaean, neoarchaean, pala eoproterozoic, mesoproterozoic and palaeozoic pro vinces. 3. archaean crust underlies kronprins frederik land but its eastern connection is unknown. 4. whether the ellesmere–inglefield juvenile crust links genetically and structurally (or at all) with palaeo pro ter ozoic rocks within the caledonian fold belt remains open. 5. the volcanic province of knud rasmussen land reinforces the profusion of proterozoic rift-related magmatism along the rim of the north american craton. 6. mesoproterozoic–ordovician rocks are widespread be yond the caledonian front linking northern foreland outcrops to sub-ice occurrences in central east greenland. 7. the potential for sub-ice basins of late palaeozoic – mesozoic age is limited. 8. the presence of palaeogene volcanic rocks in central greenland cannot be dismissed. currently, greenland plays centre stage in the global climate debate, its recessive ice margin with spectacular, shrinking glaciers being international attractions. with this coveted popularity come startling prophecies, for example, “as its huge ice sheets begin to melt, it [greenland] could find itself sitting on a fortune in oil and gems” (barkham 2008). be this as it may, before the rocks of the hidden 81% have been mapped, assessments of economic potential – often judged poor compared with neighbouring canada despite common geology (fig. 1) – remains equivocal. references barkham, p. 2008: beyond the ice. the guardian, 11 december 2008, electronic version. london: guardian news & media. dahl-jensen, t., larsen, t.b., woelbern, i., bach, t., hanka, w., kind, r., gregersen, s., mosegaard, k., voss, p. & gudmundsson, o. 2003: depth to moho in greenland: receiver-function analysis suggests two proterozoic blocks in greenland. earth and planetary science letters 205, 379–393. dawes, p.r., thomassen, b. & andersson, t.i. 2000: a new volcanic province: evidence from glacial erratics in western north greenland. geology of greenland survey bulletin 186, 35–41. escher, a. 1970: geological/tectonic map of greenland, 1:2 500 000. copenhagen: geological survey of greenland. escher, j.c. & pulvertaft, t.c.r. 1995: geological map of greenland, 1:2 500 000. copenhagen: geological survey of greenland. fountain, j., usselman, t.m., wooden, j. & langway, c.c. 1981: evidence of the bedrock beneath the greenland ice sheet, near camp century, greenland. journal of glaciology 27(95), 193–197. haller, j. 1971: geology of the east greenland caledonides, 413 pp. new york: interscience publishers. henriksen, n. 2008: geological history of greenland, 272 pp. copen hagen: geological survey of denmark and greenland. kirkland, c.l., pease, v., whitehouse, m.j. & ineson, j.r. 2009: pro venance record from mesoproterozoic–cambrian sediments of peary land, north greenland; implications for the ice-covered shield and laurentian palaeogeography. precambrian research 170, 43–60. legarsky, j., wong, a., akins, t. & gogineni, s.p. 1998: detection of hills from radar in central-northern greenland. journal of glaciology 44(146), 182–184. nutman, a.p., dawes, p.r., kalsbeek, f. & hamilton, m.a. 2008: palaeoproterozoic and archaean gneiss complexes in northern greenland: palaeoproterozoic terrane assembly in the high arctic. precambrian research 161, 419–451. verhoef, j., macnab, r., roest, w.r. & arjani-hamed, j. 1996: magnetic anomalies of the arctic and north atlantic oceans and adjacent land areas. geological survey of canada, open file report 3125a, 225 pp. author’s address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: prd@geus.dk 60 rosa_2008:rosa-2008 01/07/09 15:48 side 60 geological survey of denmark and greenland bulletin 12, 46-57 46 sharp and characterised by prominent shifts on both the sonic and density logs (figs 29, 33). it is often difficult to identify the boundaries on the gamma-ray log alone. depositional environment. although the sandstones of the rind member were deposited from highly concentrated gravity flows, their present appearance largely records postdepositional liquefaction and fluidisation processes. age. thanetian. correlation. the rind member may be contemporaneous with parts of the lithologically dissimilar østerrende clay encountered in the storebælt region (fig. 1), with sandstones in the higher parts of the heimdal formation (hardt et al. 1989) and with the upper balmoral sandstone of the mey sandstone member of knox & holloway (1992). however, the rind member is not contiguous with those sandstone units and has a different source area. sele formation history. the sele formation was established by deegan & scull (1977) for the dark grey to greenish grey, laminated and carbonaceous, tuffaceous, montmorillonite-rich shales and siltstones that overlie the non-laminated and nontuffaceous shales of the lista formation in some areas, or arenaceous sediments belonging to a variety of different units in other areas. the original definition of the sele boundary is followed herein. this implies that the base of the sele formation is located at the base of the “laminated tuffaceous shales” that overlie the “non-laminated, nontuffaceous shales” of the lista formation (deegan & scull 1977; see boundaries section under the lista formation for further details). sandstones occur in the sele formation in the danish sector; these are established as a new member, the kolga member. type well. british sector well 21/10-1, 2131–2100 m mdkb. bue mb rind mb vile mb ve mb balder fm horda fm lark fm sele fm lista fm våle fm 1800 1900 2000 2004.8 2066.3 2100 m sandra-1 gr sonic neutron/density fig. 33. sandra-1, reference well for the rind member. black bar shows cored section. 47 danish reference wells. siri-1, 2072.6–2047.5 m mdkb (fig. 14; plates 1, 4); tabita-1, 2958.8–2941.4 m mdkb (fig. 34; plate 2). distribution and thickness. the sele formation is recognised from a large number of north sea wells and it has a basinwide distribution. in the danish sector, the thickness varies from 5 to 54 m (fig. 35). lithology. the sele formation consists of medium to dark grey, brownish or black laminated mudstones. thin tuff layers occur in the upper part of the formation. it contains three or more well-laminated intervals where dark mudstone beds alternate with lighter coloured mudstone beds. the well-laminated intervals are enriched in organic material resulting in a high gamma-ray response, primarily due to increased uranium content. the most organic-rich, and often darkest, most well-laminated interval is found in the basal part of the formation (fig. 36). the mudstones of the sele formation show an overall upward increase in the silt fraction. in the upper half of the formation, the mudstones may be interbedded with thin, very fine-grained sandstone laminae and thin sandstone beds (fig. 37). the sandstone beds are up to 12 cm thick, normally graded and display parallel lamination. locally, and dominantly in the upper part of the formation, graded tuff laminae less than 1 cm thick are present. in cores, the tuff laminae have a light purple colour. small calcite concretions are present, but rare. in the siri canyon, the sele formation is interbedded with sandstones or it grades upwards into a succession of thinly interbedded sandstones and mudstones. thin sandstone intrusions occur, but only in the lower part of the formation. log characteristics. the sele formation is characterised by high gamma-ray readings throughout, with a number of gamma-ray peaks. on the gamma-ray log, the base of the sele formation is generally marked by a conspicuous upward shift to consistently higher gamma-ray readings than those of the underlying bue member (figs 38, 39). in most wells, a pronounced gamma-ray peak follows a short distance above the base of the sele formation (e.g. augusta-1 and e-8; fig. 38). in wells to the north and west of the danish sector, the stratigraphic distance between the shift to higher gamma-ray readings at the base of the sele formation and the gamma-ray peak is considerably greater (e.g. in the norwegian well 2/7-1; fig. 25). in some wells in the danish sector (and in most siri canyon wells), the basal high gamma-ray interval is missing and the base of the sele formation is marked by the pronounced gamma-ray peak (e.g. cleo-1 and nini-3; figs 38, 39). boundaries. the lower boundary is characterised by a change from the light to dark grey and greyish black mudstones with thin sandstone laminae of the bue member (lista formation), to dark grey to black well-laminated mudstones without sandstone laminae of the sele formation (fig. 36). the upper boundary is at the base of the balder formation. subdivision. knox & holloway (1992) suggested an informal threefold subdivision of the sele formation based fig. 35. isochore map of the sele formation in the study area. the positions of the two danish reference wells, siri-1 and tabita-1, are indicated in the figure. siri-1 tabita-1 10 20 30 40 50 thickness (m) sele formation 25 km fig. 34. tabita-1, danish reference well for the sele formation. horda fm balder fm sele fm lista fm vile mb ve mb bue mb våle fm chalk gp 2900 3000 m tabita-1 2941.4 2958.8 gr sonic 48 in figs 24, 26 and 38), whereas other lithological changes are more subtle. the subdivision is outlined below. unit s1 this unit comprises a lower subdivision s1a and an overlying subdivision s1b. subdivision s1a is identical to the bue member of the lista formation and the stratigraphic interval from the base of the sele formation (sensu deegan & scull 1977) up to the base of the lowermost conspicuous gamma-ray peak within that formation (fig. 38). that peak is associated with relatively low sonic values. subdivision s1b has its base at the gamma-ray peak and its top at the base of the next gamma-ray peak. the gamma-ray response decreases up through s1b. unit s1 consists of brownish grey to dark grey and black, well-laminated mudstones. unit s2 the base of the unit is at the base of the second gamma-ray peak. this peak can be differentiated from the gamma-ray peak at the base of s1b by its association with high sonic values. unit s2 can be divided into a lower subdivision (s2a) characterised by a relatively high gamma-ray response level and an overlying subdivision (s2b) with a lower gamma-ray response (fig. 38). the two subdivisions are separated by a gammaray low. unit s2 consists of light grey to brownish dark grey, laminated to well-laminated mudstones. both the lamination and the colour of the two subdivisions are very similar in the cores encountered in this study and it is almost impossible to distinguish the two subdivisions on lithology alone. knox & holloway (1992) observed tuff layers in the basal part of unit s2b in the british wells; tuffs were not observed in the danish wells.. unit s3 this unit is characterised by high and increasingupwards gamma-ray values. the base of the unit is defined by a sharp increase in gamma-ray readings (fig. 38). there is no significant colour difference between the mudstones of units s2 and s3 in the danish wells, but lamination seems to be better developed in unit s3 than in unit s2. tuff layers were observed in unit s3 in the british wells studied by knox & holloway (1992). similar tuff layers have been observed in wells from the siri canyon, and may further be used to distinguish unit s3 from the upper part of unit s2. 0 10 20 30 40 50 60 70 80 90 100 cm 2888 m 2889 m augusta-1 2890 m sele fm b ue m b fig. 36. core photographs of the lista–sele formation boundary interval in the augusta-1 well. the upper part of the bue member (lista formation) consists of mudstones with thin sandand siltstone laminae superficially resembling mudstone-in-mudstone lamination. at 2890.35 m, the bue member is overlain sharply by the laminated mudstones of the sele formation. depths are core depths. on the gamma-ray log signature. this subdivision can also be recognised on petrophysical logs from most wells in the danish sector (the subdivision is shown in five wells 49 0 10 20 30 40 50 60 70 80 90 100 cm 1689 m 1690 m nini-3 1692 m 1693 m the sele formation includes a sandstone unit (kolga member, new) in the danish north sea sector. macroand ichnofossils. fish scales and skeletal fragments are common in cores from the sele formation. bioturbation is very rare, but chondrites ispp. has been observed locally. microfossils and palynomorphs. benthic foraminifers are rare in the sele formation. the lo of an acme of the dinoflagellate genus apectodinium and the coeval lo of the shortranged a. augustum mark a level at, or a few centimetres above the base of the sele formation. the ho of a. augustum is located in the lower part of the sele formation. the ho of an influx of the dinoflagellate cerodinium wardenense marks a level in the upper part of the sele formation. the ho of an influx of the diatoms fenestrella antiqua and coscinodiscus morsianus is located in the uppermost part of the sele formation. throughout, the formation contains abundant spores and pollen, in particular pollen of the genus inaperturopollenites. depositional environment. the mudstones of the sele formation represent a mixture of pelagic fallout and dilute, low-density mud turbidites. the well-laminated character of the sediment, the high content of organic material and uranium, and the general lack of trace fossils and benthic foraminifers indicate starved sedimentation under dysoxic to anoxic bottom conditions. common diatoms indicate a high nutrient level in the water mass. the tuffs of the sele formation are evidence of extensive volcanism in the region. the significant depauperation of the benthic microfaunas during the deposition of the sele formation was most likely caused by isolation of the north sea basin (schmitz et al. 1996). the restriction and isolation of the basin was the result of a sea-level fall, possibly combined with (or caused by) tectonic uplift to the north-west (knox et al. 1981). based on microfossils, the palaeoenvironment has been suggested to represent an upper bathyal setting with a palaeodepth estimate of around 300 m (mitlehner 1996). the palynomorph assemblage indicates a marine environment characterised by a massive influx of terrestrial palynomorphs. age. sparnacian (sensu aubry et al. 2003) – early ypresian, with the lowermost level possibly of thanetian age. correlation. the sele formation corresponds to the haslund member of the ølst formation (heilmann-clausen et al. 1985). its upper part correlates with the haslund member-equivalent diatomitic knudeklint member of the fig. 37. core photographs from the nini-3 well showing the upper, arenaceous part of the sele formation. the interval belongs to the s2a subunit of the sele formation (see text for further explanation). stratigraphic position of the figured interval is shown in fig. 39. depths are core depths. fur formation in north-west jylland (danielsen & thomsen 1997). the lower boundary of the sele formation correlates with the boundary between the østerrende clay and the haslund member onshore denmark. 50 2760 2740 m 2780 s3 s2b s2a s1b s1a 2900 cleo-1 augusta-1 e-8 horda fm balder fm sele fm lista fm bue mb ve mb 2880 2040 2860 2020 m m gr sonic gr sonic gr sonic cleo-1 e-8 the lower part of the sele formation, consisting of laminated, dark grey to black mudstones, correlates with the lithologically very similar, 15 m thick informal unit stolle klint clay that constitutes the lower part of the haslund member, onshore denmark (heilmann-clausen 1995). this unit is known from throughout the north sea (hardt et al. 1989; knox & holloway 1992) and constitutes most or all of the sele s1b unit of knox & holloway (1992). kolga member new member history. the kolga member consists of sandstone deposits within the sele formation. these sandstones were previously recognised by a stratigraphic working group at statoil norway in the mid-1990s and were informally referred to the hermod formation of hardt et al. (1989). derivation of name. after the goddess kolga. type well. danish sector well siri-3, 2066.4–2036.1 m mdrt (fig. 24; plate 4). reference well. danish sector well nini-3, 1717.2–1700.4 m mdrt (figs 26, 39; plate 4). distribution and thickness. the kolga member has a restricted distribution in the siri canyon in the northern part of the danish sector (fig. 20c). it reaches a thickness of up to 30 m. lithology. the member consists primarily of fine-grained to very fine-grained, olive-green to greenish grey, well-sorted, quartz-rich sandstones (fig. 39). rounded and translucent quartz grains dominate the mineralogical assemblage, but the content of glaucony grains is high (15– 25%). mica and small pyrite concretions are present in small amounts. locally, the sandstones are partly cemented by calcite and chlorite. the member usually includes one thick unit composed of amalgamated sandstone beds and a number of thinner sandstone beds interbedded with mudstones that are lithologically comparable to the sele formation mudstones described above. log characteristics. the kolga member is clearly defined on the gamma-ray log by a blocky pattern with intermediate values. this pattern differs from the high gamma-ray readings that normally characterise the lower sele formation. the kolga member may show a gradual upward decrease in gamma-ray response in its lower part (e.g. in the well nini-3; figs 26, 39). however, this does not reflect grain-size change, judging from core examination. the density log shows a blocky pattern with low density fig. 38. correlation diagram of the sele formation showing the sele units s1–3 of knox & holloway (1992). 51 v v v sele fm lista fm kolga mb bue mb grsonic 1700 1690 1710 1720 1700 1710 1720 nini-3 clay si. vf. f. m. sand c. vc. log depth core depthfig. 39. core log of the sandstonedominated kolga member encased in the sele formation mudstones in the nini-3 well. for legend, see fig. 9. intervals marked by grey bars in the core depth column are shown as core photos in fig. 37. values for the kolga member sandstones and relative high values for the interbedded mudstones (fig. 24). boundaries. the boundaries between the sandstones of the kolga member and the mudstones of the sele formation are sharp and characterised by prominent shifts on the gamma-ray and sonic logs (figs 24, 26). microfossils and palynomorphs. the kolga member is characterised by an abundance of apectodinium spp., including a. augustum. depositional environment. the sandstones of the kolga member were deposited from highly concentrated gravity flows, although the present character of the kolga member mainly reflects postdepositional liquefaction and fluidisation processes. primary sedimentary structures are common in the kolga member in some wells (e.g. sandra-1), however, indicating that the member has experienced less postdepositional remobilisation in certain areas. age. sparnacian (sensu aubry et al. 2003) possibly including the latest thanetian. correlation. the kolga member is contemporaneous with parts of the sele formation onshore denmark. it possibly correlates with the forties sandstone member (knox & holloway 1992) in the central graben and with the teal and skadan sandstone members (knox & holloway 1992) in the southern viking graben. however, the kolga member is not contiguous with those units and has another source area. fur formation history. the fur formation is a marine diatomite with numerous ash layers. it was formally established by pedersen & surlyk (1983) with a type section in the coastal cliff knudeklint on the island of fur, denmark. its lower boundary was revised by heilmann-clausen et al. (1985). the characteristic lithology of the fur formation was subsequently recognised by thomsen & danielsen (1995; danielsen & thomsen 1997) in cuttings samples from three offshore wells located in the north-eastern part of the danish sector of the north sea, as well as in one well in the norwegian sector. 52 350 450 m k-1 gr sonic balder fm horda fm fur fm sele fm lista fm våle fm chalk group 398.9 402.2 400 m 485.5 697.1 795.3 810.7 500 600 700 800 900 dufa mb horda fm balder fm lark fm sele fm fur fm lista fm våle fm chalk gp inez-1 gr sonic type section. the coastal cliff knudeklint, the island of fur, onshore denmark (for location map, see pedersen & surlyk 1983). reference sections. silstrup south cliff, skarrehage, feggeklit, harhøj, stolleklint (for location maps, see pedersen & surlyk 1983). danish reference wells. danish sector wells k-1, 402.2– 398.9 m mdkb (fig. 40; plate 5); inez-1, 810.7–795.3 m mdkb (fig. 41; plates 1, 5). distribution and thickness. onshore denmark, the fur formation is distributed in a limited area in north-west jutland. it is c. 61 m thick in its type section. offshore, the formation occurs in a belt stretching from the northwestern coast of jutland, continuing into the norwegian sector parallel to the southern coast of norway (thomsen & danielsen 1995 text-fig. 6; fig. 42). it reaches a thickness of 15.4 m in the inez-1 well, 7.9 m in the c-1 well and 3.3 m in the k-1 well (figs 40–42). lithology. the lithology of the fur formation was described from its onshore exposures by pedersen (1981) and pedersen & surlyk (1983). it is a clayey, porous, dark grey diatomite with numerous volcanic ash layers. diatom frustules constitute 65 wt% of the rock, clay particles constitute 35 wt% (pedersen 1981). tests of coscinodiscus spp. and stephanopyxis are the major constituent of the diatomite fraction (thomsen & danielsen 1995). fine lamination is the primary sedimentary structure, but at some fig. 41. inez-1, reference well for the fur formation and type well for the dufa member. fig. 40. k-1, reference well for the fur formation. 53 25 km k-1x 3.3 15.4 7.9 inez-1 c-1 57°00' 6°00' 8°00' 56°00' 55°00' ? ? ? ? fur formation levels the lamination has been destroyed by bioturbation. the ash layers are black, graded and consist of volcanic glass particles. individual layers range from 1–20 cm in thickness but are fairly uniform in thickness over a limited area (pedersen & surlyk 1983). the diatomite recognised in cuttings samples from north sea wells by thomsen & danielsen (1995) is a similar lithology to that of the onshore sections studied by pedersen (1981) and pedersen & surlyk (1983). log characteristics. the fur formation is identified by the combination of a low gamma-ray response and low sonic readings within an interval of higher sonic readings characterising mudstones below and above (thomsen & danielsen 1995; danielsen & thomsen 1997; figs 40, 41; plates 1, 5). boundaries. in the c-1 and k-1 wells, the fur formation is enveloped by the balder formation. in inez-1, the formation is bounded by the sele and balder formations (figs 40, 41; plates 1, 5). it should be noted, however, that thomsen & danielsen (1995 text-fig. 4) and danielsen & thomsen (1997 fig. 5) placed the fur formation entirely within the sele formation in the k-1 well. the discrepancy between the interpretation herein and that of the former authors is due to different interpretations of the position of the balder–sele boundary in the well. the boundary of the fur formation with the balder and sele formations is characterised by a change from laminated or structureless diatomite with ash layers to the dark mudstones of the balder and sele formations. this lithological change is reflected on the sonic log by an abrupt increase in velocity (figs 40, 41; plates 1, 5). subdivision. onshore denmark, the fur formation is divided into the lower, laminated knudeklint member that contains relatively few, widely spaced ash layers and the upper, mainly structureless silstrup member with numerous ash layers (pedersen & surlyk 1983). macroand ichnofossils. the macrofossil assemblage described from onshore exposures of the fur formation encompasses fish, birds, turtles, snakes, starfish, shellfish, snails, mussels, crabs, pteropods, insects, fossil wood, leaves and fructifications (bonde 1966, 1979, 1987, 2003; pedersen 1981; pedersen & surlyk 1983; kristoffersen 2001). ichnofossils from onshore exposures include planolites ispp., teichichnus ispp., chondrites ispp. and taenidium ispp. (pedersen & surlyk 1983). microfossils and palynomorphs. diatom frustules are rockforming in the fur formation (pedersen 1981). silicofig. 42. distribution map of the fur formation with formation thickness (m) indicated for three wells. flagellates are present (perch-nielsen 1976) whereas calcareous microfossils are absent. the formation contains abundant dinoflagellates and sporomorphs (hansen 1979; heilmann-clausen 1982; willumsen 2004). depositional environment. the deposition of the fur formation diatomites took place in a long, narrow zone under upwelling conditions (bonde 1974, 1979). the upwelling was controlled by northerly winds (bonde 1974, 1979) or it may have been created by a combination of bottom currents and bottom topography (pedersen & surlyk 1983). age. early ypresian. correlation. onshore denmark, the knudeklint and silstrup members are largely contemporaneous with the upper part of the haslund member and the overlying værum member of the ølst formation (heilmannclausen et al. 1985), respectively, and correlate with the 54 upper part of the sele formation and the lower unit b1 (see below) of the balder formation (heilmann-clausen 1995; knox 1997 fig. 3). balder formation history. deegan & scull (1977) established the balder formation for the succession of variegated, fissile and laminated shales with interbedded tuff layers that lie between the sele and horda formations. type well. norwegian sector well 25/11-1, 1780–1705 m mdkb. danish reference wells. mona-1, 2945.0–2930.8 m mdkb (fig. 43; plate 1). siri-3, 2016.8–1998.8 m mdrt (fig. 24; plate 4). distribution and thickness. the balder formation extends over most of the central and northern north sea. in the danish sector, it reaches a thickness of more than 20 m in the siri-3 and frida-1 wells on the western part of the ringkøbing–fyn high (fig. 1) and 20 m in gwen-2 in the northern part of the danish sector of the central graben. the balder formation thins to less than 5 m towards the south-west and to less than 10 m in the eastern part of the danish sector of the north sea. the balder formation is lacking in the danish well s-1 (michelsen et al. 1998). an isochore map of the balder formation is shown in fig. 44. lithology. the balder formation is composed of laminated, dominantly grey, fissile shales with interbedded dark and light grey, purple, buff and green sandy tuffs (fig. 45). the tuffs are normally graded and less than 5 cm thick. locally the tuff beds are slumped. the tuff layers may be cut by irregular, vertical, calcite-filled cracks up to 20 cm long (fig. 45). similar cracks have been reported from the balder formation in the grane field, norwegian sector of the north sea (haaland et al. 2000). sandstone beds, interpreted as intrusive sandstone bodies, occur locally in the balder formation. log characteristics. the balder formation is characterised by a relatively high gamma-ray values in its lower and higher parts, but shows low values in its middle part. the change in gamma-ray response is normally gradual, but relatively steep. the gamma-ray motif is mirrored by a gradual increase in sonic readings commencing at the formation base, culminating at or slightly below the level of minimum gamma-ray values in the middle part of the fig. 44. isochore map of the balder formation in the study area. the positions of the two danish reference wells, mona-1 and siri-3, are indicated in the figure. siri-3 mona-1 balder formation 5 10 15 20 thickness (m) 25 km fig. 43. mona-1, danish reference well for the balder formation. 3000 2900 m 2930.8 2945.0 horda fm balder fm sele fm lista fm våle fm vile mb ve mb bue mb chalk gp mona-1 gr sonic 55 2013 m siri-3 2012 m 2014 m 2015 m 0 10 20 30 40 50 60 70 80 90 100 cmformation, followed by a gradual decrease towards the top of the formation where the lowest sonic reading is reached. the gamma and sonic motifs together create a characteristic barrel-shaped log pattern (e.g. figs 24, 33, 38, 43; plates 1–5). boundaries. in general, the boundary with the underlying sele formation is gradational, although it can be sharp in some wells. where gradational, it is placed where the tuff layers become prominent (e.g. fig. 45). on petrophysical logs, the lower boundary is identified at a significant upward decrease in gamma-ray response accompanied by an increase in sonic readings (e.g. figs 24, 33, 38, 43). the upper boundary is at the base of the horda formation. subdivision. knox & holloway (1992) subdivided the balder formation into a lower, laminated and tuff-rich unit (b1) and a poorly laminated upper unit (b2). this subdivision can be recognised in a number of danish wells west of cecilie-1, but the b2 unit seems to be absent from danish north sea wells north-east of, and including, the cecilie-1 well. macroand ichnofossils. macrofossils have not been observed. the balder formation is non-bioturbated to moderately bioturbated. ichnofossils comprise chondrites ispp., phycosiphon ispp., planolites ispp. and thalassinoides ispp. microfossils and palynomorphs. the sele–balder boundary interval is characterised by the ho of common fenestrella antiqua and coscinodiscus morsianus (both diatoms). this event is located in the uppermost part of the sele formation but may be used as a biostratigraphic guide to locate the boundary. the diatom fenestrella antiqua characterises the balder formation and has its ho at the formation top. the dinoflagellate deflandrea oebisfeldensis shows an acme at the top of the balder formation. as observed in the underlying sele formation, the balder formation contains high numbers of spores and pollen, in particular pollen of the genus inaperturopollenites spp., and the top of the balder formation is marked by the ho of common representatives of that genus. in contrast to the overlying horda formation, calcareous benthic foraminifers are virtually absent in the balder formation. depositional environment. a restricted marine palaeoenvironment at upper bathyal depths with dysoxic to anoxic bottom conditions is suggested for the balder formation. this is based on the scarcity of calcareous microfossils and agglutinated foraminifers combined with common to abundant siliceous microfossils, especially diatoms. the fig. 45. core photographs of tuffaceous balder formation mudstones from the siri-3 well. the tuff layers are seen as light coloured, graded intervals (e.g. at 2012.42–2012.40 m). the boundary with the underlying sele formation is placed where tuffs become common, at 2015.5 m (large arrow); two tuff layers may be seen in the uppermost sele formation, at 2015.66 and 2015.90 m (small arrows). two small, lightning-shaped cracks are seen at 2015.4 m. depths are core depths. 56 2363.5 2930.8 1598.3 horda fm h2 h1 h3 l2 l3 l4 lark fm nordland gp balder fm sele fm lista fm våle fm chalk gp 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500 2600 2700 2800 2900 3000 m mona-1 gr sonic fig. 46. mona-1, danish reference well for the horda and lark formations. the figure shows the tripartite subdivision of the horda formation and the l2–4 units of the lark formation. the l1 unit is absent in the mona-1 area. presence of abundant terrestrial palynomorphs further supports a restricted, marginal marine depositional setting. a petrographic and geochemical study of the balder formation in the grane field, norwegian north sea sector, shows that the tuffs can be classified as representing sub-alkaline basalts and basaltic andesites of intra-plate origin (haaland et al. 2000). the tuffs are similar to the contemporaneous lower basalts in east greenland, the rockall trough and the middle series of the faeroe islands, all linked to the opening of the north atlantic (haaland et al. 2000). the volcanic phase took place at 55–52 ma. age. early ypresian. correlation. although unit b2 of knox & holloway (1992) is apparently lacking in wells in the north-eastern part of the danish sector, both units b1 and b2 can be correlated with strata onshore denmark, although unit b2 is very thin. unit b1 corresponds to the lithologically similar værum member of the widespread ølst formation onshore denmark and with the diatomaceous silstrup member of the fur formation in north-west jylland (knox 1997 fig. 3). the lower boundary of the værum and silstrup members is placed at ash layer no. +1 in the tephrachronology of bøggild (1918). the ash chronology has not been identified in the type section of the balder formation and precise correlation with the lower boundary of the værum and silstrup members is therefore uncertain. however, judging from the abundance of thick ash layers in the balder formation and the scarcity of ash layers in the underlying sele formation, it is likely that the base of the balder formation approximately correlates with ash layer no. +1, i.e. with the base of the værum and silstrup members. according to knox (1997 fig. 3), unit b2 probably correlates with the knudshoved member of the røsnæs clay formation (heilmann-clausen et al. 1985). this member has a very restricted distribution in north-west jylland where it overlies the silstrup member of the fur formation. the knudshoved member consists of a lower dark grey, pyritic clay unit rich in pyritised diatoms, and an upper greenish clay unit (heilmann-clausen et al. 1985). only a few, thin volcanic ash layers are present in the member (håkansson & sjørring 1982). based on lithological comparison, it is suggested that at least the lower, 57 pyritic part of the knudshoved member may correlate with the upper, tuff-poor unit b2 of the balder formation. stronsay group knox & holloway (1992) replaced the hordaland group of deegan & scull (1977) with two new groups: the stronsay group succeeded by the westray group (fig. 3). the two groups together comprise the light grey, green and brown coloured, soft, fissile, marine shales with thin limestone streaks that overlie the rogaland group and underlie the nordland group. these groups each contain two formations, one representing sandy shelf lithofacies and the other representing basinal mudstone lithofacies. in the central north sea, and in the danish sector, the stronsay group is represented by its mudstone facies, the horda formation (knox & holloway 1992). sandstone units of varying thickness occur at many levels in the stronsay and westray groups along the basin margin in the norwegian and british sectors, and many of these have been defined as formations or members (deegan & scull 1977; hardt et al. 1989; knox & holloway 1992). a sandstone unit also occurs in the horda formation on the ringkøbing–fyn high in the danish sector and is described here as a new member (hefring member). horda formation history. knox & holloway (1992) established the horda formation for the greenish grey basinal mudstone facies of their stronsay group that overlies the grey tuffaceous mudstones of the balder formation and underlies the greenish grey to brown mudstones of the lark formation (knox & holloway 1992). type well. british sector well 22/1-1a, 2379.5–1992 m mdkb. danish reference wells. mona-1, 2930.8–2363.5 m mdkb (fig. 46); siri-1, 2037.9–1916.5 m mdkb (fig. 47). distribution and thickness. the horda formation extends over the central and northern north sea and is present in 1916.5 2037.9 horda fm chalk gp lark fm balder fm sele fm lista fm våle fm 1900 2000 2100 2200 m siri-1 gr sonic rind mb idun mb tyr mb vile mb ve mb bue mb bue mb horda formation siri-1 mona-1 floki-1 100 200 300 400 500 600 700 800 900 thickness (m) 25 km fig. 47. siri-1, danish reference well for the horda formation. black bars show cored sections. fig. 48. isochore map of the horda formation in the study area. the positions of the two danish reference wells for the horda formation, mona-1 and siri-1, are indicated on the map. the position of floki-1, the type well for the hefring member, is also indicated. geological survey of denmark and greenland bulletin 12, 63-73 63 the lower part of the overlying main body of greenish and greyish mudstones in the offshore succession can be correlated with the coeval and lithologically similar upper part of the lillebælt clay formation. the upper part of the horda formation can be correlated with the søvind marl formation, which consists of grey marls. the highest part of the horda formation, only observed in central graben wells, may be correlated with the viborg formation on biostratigraphic evidence. hefring member new member history. the hefring member consists of sandstone deposits within the horda formation. these sandstones have not previously been recognised as a separate unit in the danish sector. derivation of name. after the goddess hefring. type well. danish sector well floki-1, 1793.4–1731.3 m mdrt (fig. 53). distribution and thickness. the hefring member is only known from the floki-1 well located in the northern part of the danish sector. as the unit currently cannot be identified on seismic sections, its further distribution is unknown. in the floki-1 well, the member is 62 m thick. lithology. the hefring member consists of greenish grey, fine-grained, immature sandstones with glaucony grains. log characteristics. the hefring member is characterised by a conspicuous blocky signature on the gamma-ray, sonic and density logs (fig. 53). gamma-ray responses are lower than those of the enveloping horda formation mudstones. the hefring member can also be recognised from a combination of the density and neutron logs as the presence of pure sandstones results in a ‘cross-over’ of the two log curves (fig. 53). boundaries. the boundaries with the mudstones of the horda formation are sharp and characterised by prominent shifts on the gamma-ray and sonic logs (fig. 53). depositional environment. no cores have been taken in the hefring member, but the sandstones were probably deposited from concentrated gravity flows, based on log similarity with the other fine-grained sandstone bodies in the nearby siri canyon. age. lutetian (middle eocene) based on the age of the associated horda formation mudstones. correlation. based on biostratigraphic data, the hefring member may be contemporaneous in part with the lillebælt clay formation onshore denmark, with the lower part of the grid sandstone member (knox & holloway 1992) in the viking graben and with the upper part of the tay sandstone member (knox & holloway 1992) in the northern part of the central graben. westray group the westray group is the upper of the two groups established by knox & holloway (1992) to replace the hordaland group of deegan & scull (1977; fig. 3). in the central north sea and in the danish sector of the north sea, the westray group is represented by the lark formation. lark formation history. the lark formation was established by knox & holloway (1992) for the brownish grey mudstone-dominated lithofacies of the westray group that overlies the more variable association of red and green-grey mudstones, silty mudstones and sandstones of the horda formation and underlies the grey, sandy and shelly mudstones, siltstones and sandstones of the nordland group of deegan & scull (1977; fig. 3). the lark formation is also recognised in the danish sector although its lithology is more variable than that given in the original description. type well. british sector well 21/10-4, 1867–1217 m mdkb. danish reference wells. mona-1, 2363.5–1598.3 m mdkb (fig. 46); siri-1, 1916.5–819.3 m mdkb (fig. 54). distribution and thickness. the lark formation extends over the central and northern north sea and is probably present in the entire danish sector of the north sea. its depocentre is in the central and northern part of the danish sector, along the eastern boundary of the danish central graben, where it reaches a thickness of 1194 m in the siri-3 well. the lark formation thins west to a thickness of 389 m in the tordenskjold-1 well in the central graben, and east to a thickness of 240 m in the s-1 well on the ringkøbing–fyn high (fig. 55). 64 lithology. the lower lark formation (l1–3, see below) is dominated by dark, greenish grey, non-fissile mudstones in most wells; in some wells subordinate intervals of brownish grey mudstones are also present. thin layers of white or reddish brown carbonate are also recorded in the upper levels of the lower lark formation. the upper lark formation (l4, see below) is dominated by pale to dark brownish grey mudstones with subordinate intervals of greenish grey mudstones in its lower levels. the uppermost 50–100 m of the formation consist of yellowish grey to light brown mudstones. in eastern and northern parts of the danish sector, discrete sandstone interbeds and thin sandstone stringers occur throughout the formation. log characteristics. the lower part of the lark formation is characterised by an overall stable gamma-ray log signature, whereas the upper part of the formation has a more unstable signature (figs 46, 54). this change in gammaray log signature coincides approximately with the change from lithologies dominated by greenish grey mudstones to lithologies dominated by dark to light brownish grey mudstones at the base of unit l4 (see below). boundaries. the base of the lark formation is marked by a change from fissile, greenish grey mudstones of the horda formation to non-fissile, greenish grey mudstones of the lark formation. this change in lithology coincides with an abrupt increase in gamma-ray values to a consistently higher level than that displayed by the horda formation (figs 46, 51, 54). wells in the eastern part of the danish central graben and on the ringkøbing–fyn high show a conspicuous log break on the gamma-ray log at the formation boundary, whereas the log break is less pronounced in wells from the central and western parts of the danish central graben (fig. 51). although the actual increase in gamma-ray response may be limited in the latter wells, the offset is usually sharp and well defined. on the sonic log, the boundary between the horda formation and the lark formation is characterised by a transition from a stable sonic signature to one characterised by numerous fluctuations. the lark formation is overlain by the undifferentiated nordland group of deegan & scull (1977). over most of the area, the boundary seems conformable and is represented by a change from yellowish grey and light brown mudstones to medium to dark grey mudstones characte1916.5 819.3 horda fm lark fm nordland gp l4 l3 l2 l1 balder fm sele fm lista fm våle fm chalk gp 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 m siri-1 gr sonic no log data fig. 54. siri-1, danish reference well for the lark formation. the units l1–4 are all present in this well. black bars show cored sections. 65 rised by intervals with shell-hash and coarse-grained sands. this boundary is marked by a conspicuous gamma-ray peak at the base of a 20–40 m thick interval with elevated gamma-ray values in the lowermost nordland group (figs 46, 51). this interval is further characterised by a marked double peak on the gamma-ray log. in the north-eastern parts of the danish sector (nini-1, vanessa-1, cecilie-1 and siri-1; figs 1, 51, 54), sediments of the nordland group rest unconformably on the lark formation. in this area the uppermost lark formation and the lowermost nordland group are missing, probably due to erosion and/or non-deposition. the distinct gamma-ray peak that marks the top of the lark formation as well as the double gamma-ray peak in the lowermost nordland group are lacking in these wells, and therefore the top of the lark formation is more difficult to identify on petrophysical logs. subdivision. the lark formation can be subdivided into four major mudstone packages, l1–l4, based on seismic and log evidence (figs 46, 49, 51, 54, 56; plates 1–5). these units are described below; isochore maps of the units are shown in fig. 57a–d. l1 (figs 51, 56a, b, 57a; plates 1, 4, 5) this unit has been recognised in the north-eastern part of the danish sector only (fig. 57a). it is bounded beneath by the th marker and above by the tl1 marker (fig. 56a, b). it is characterised by downlapping reflectors and represents a south-westwards prograding mudstone succession. on the gamma-ray log, the l1 unit is characterised by a relatively high and relatively stable response. in most wells, it shows a weakly concave pattern, going from a relatively high gamma-ray response at its base, over a gamma-ray low halfway through the unit to a level close to starting level at the top of the unit (e.g. ida-1, inez-1, k-1, f-1 and sandra-1; plates 1, 4, 5). in the siri-1 and siri-3 wells, near the south-western limit of the l1 unit, the gamma-ray log motif instead appears slightly convex (figs 51, 54; plates 1, 4). the l1 unit consists predominantly of greenish grey mudstones but also includes yellowish brown and dark grey mudstones. l2 (figs 46, 51, 56a, b, 57b; plates 1–5) the unit is recognised over the entire study area. on the gamma-ray and sonic logs the unit is characterised by a stable log signature. the gamma-ray log shows two to three slightly concave patterns with signatures similar to that of the l1 unit (fig. 51; plates 1, 4). the lithology is characterised by dark beige-grey to greenish grey mudstones, greenish colours becoming dominant towards the top of the unit. l3 (figs 46, 51, 56a, b, 57c; plates 1–5) this unit is encountered in the northern and eastern parts of the danish sector, east of the central graben (fig. 57c) but is not recognised on logs or seismic sections in the central graben area. it is characterised by stable gamma-ray and sonic log signatures (figs 46, 51; plates 1–4). the unit consists almost invariably of dark, greenish grey mudstones. l4 (figs 46, 51, 56a, b, 57d; plates 1–5) the unit is recognised over the entire study area (fig. 57d). the interval is characterised by a slightly more unstable gamf-1 inez-1 siri-1 francisca-1 frida-1 tordenskjold-1 s-1 mona-1 25 km 200 300 400 500 600 700 800 900 1000 1100 1200 1300 freja member distribution dufa member distribution lark formation thickness (m) fig. 55. isochore map of the lark formation in the study area. the positions of the two danish reference wells, mona-1 and siri-1, are indicated in the figure. the map also shows the distribution of the sandstones of the dufa and freja members and the location of their type and reference wells, inez-1 and f-1, and francisca-1 and frida-1, respectively. 66 fig. 56. a: sw–ne-trending seismic section (rtd81-re94-22a) showing the complex architecture of the lark formation and its subdivision into l1–4 units. the vertical white line indicates change in section direction. the locations of the two seismic sections are shown on fig. 1; abbreviations as in figs 49 and 51. 0 500 1000 1500 2000 2500 3000 3500 0 500 1000 1500 2000 2500 3000 3500 tordenskjold-1 f-1 tabita-1 cecilie-1 siri-3 sw ne horda fmhorda fm l2l2 lark fmlark fm l4 horda fm l2 aa l2l2 l1 lark fmlark fm l4 l3 l1 10 km lark fm lark fm l4 l3l3l3 l4 l3 uou tl2 th tb tc tl tf uou tl2 tl uou tl2 tl1 th tb tc twt (msec) twt (msec) 67 25 50 75 100 125 thickness (m) l1 25 km 25 km 100 200 300 400 thickness (m) l2 100 200 300 400 500 600 700 800 thickness (m) 100 200 300 400 500 600 700 800 thickness (m) l3 l4 a b c d fig. 57. isochore maps of lark formation subunits. a: l1. b: l2. c: l3. d: l4. a and d are at the same scale, b and c are at the same scale. 1500 2000 2500 3000 3500 twt (msec) 20 km nini-2 d-1 nolde-1 nw se tl uou tl2 tl1 tb tc l1 l2l2 l3 l4 l1 l2 l3 l4 bb fig. 56. b: nw–se-trending seismic section (rtd81-re94-14a) showing subdivision of the lark formation and marked thinning of this formation towards the south-east. the locations of the two seismic sections are shown on fig. 1; abbreviations as in figs 49 and 51. 68 ma-ray and sonic log signature than that of the underlying units (figs 46, 51; plates 1–5). it is dominated by brown to yellowish brown mudstones, but in some wells an interval of greenish grey mudstones occurs in its lower part. in wells to the east and north, thin sandstones are interbedded with the mudstones and become more frequent towards the top of the unit. two thick sandstone units occur in the lark formation on the ringkøbing–fyn high and are described here as two new members (dufa and freja members). macroand ichnofossils. only observed in cores taken in the freja member (see below). microfossils and palynomorphs. farthest to the north and east the basal part of the formation includes the downhole succession of ho areosphaeridium diktyoplokum and ho a. michoudii indicating a late priabonian (late eocene) age for the base of the formation in this area. in the central graben area, the base of the lark formation is significantly younger. here it contains an event succession characteristic of the middle and lower rupelian (lower oligocene) stage (hos of phthanoperidinium amoenum, achilleodinium biformoides and phthanoperidinium comatum). the top of the lark formation is bracketed by a number of conspicuous biostratigraphic events: the uppermost part contains the hos of the benthic foraminifers asterigerina staeschei and elphidium inflatum followed downhole by the ho of uvigerina tenuipustulata. dinoflagellate events near the top of the lark formation include the hos of apteodinium spiridoides and cousteaudinium aubryae. the lowermost part of the overlying nordland group contains the hos of the calcareous microfossils bolboforma clodiusi, bolboforma spiralis and bolboforma metzmacheri, the ho of the benthic foraminifer bulimina elongate, and the ho of the dinoflagellate cyst cannosphaeropsis passio. a large number of hos characterise the lark formation; key events are listed in fig. 5c. depositional environment. the l1 unit is characterised by abundant agglutinated foraminifers dominated by rhabdammina discreta and similar tubular taxa, together with haplophragmoides spp. and recurvoides spp. the microfaunal assemblage indicates that the unit was predominantly deposited in an open marine, dysoxic palaeoenvironment at upper bathyal depths. the l2 unit and most of the l3 unit are characterised by an increasing abundance and diversity of calcareous benthic and planktonic foraminifers. the relative proportions of agglutinated, calcareous planktonic and benthic foraminifers vary considerably from well to well, indicating pronounced lateral changes in the depositional environment. the calcareous plankton/benthos ratio is usually low, indicating a neritic setting for most of the succession, but in a few restricted intervals it may reach 1:2 or even 1:1 indicating an outer neritic setting. thus, the foraminifer assemblage indicates an open marine, neritic to outer neritic setting with well-oxygenated bottom conditions for the lower to middle part of the lark formation. the microfossil assemblage in the uppermost part of the l3 unit as well as the l4 unit is dominated by calcareous benthic foraminifers, and agglutinated foraminifers are generally rare. epifaunal and shallow infaunal foraminifers are more common than deep infaunal taxa, indicating oxic bottom conditions during this interval. in general, the microfaunal assemblage in this part of the lark formation suggests that it was deposited in a neritic, probably middle neritic, palaeoenvironment over most of the study area. the palynofacies assemblage in the lark formation is characterised by a rich dinoflagellate assemblage and abundant dispersed terrestrial matter (phytoclasts, spores and pollen), indicating an open marine environment with considerable influx from nearby land areas. stratigraphic variations in the relative abundance of terrestrial palynomorphs in the lark formation suggest successive pulses of progradation and backstepping of the palaeocoastline. age. the lark formation is of priabonian to serravallian (late eocene to middle miocene) age with eocene sediments being present in the l1 unit only. the l1 unit is priabonian to early rupelian (early oligocene) in age, the base of the unit being oldest farthest to the north and east and younging towards the south and west. the age of the l2 unit is rupelian; the l3 unit is rupelian in age in its lower part and chattian (late oligocene) in its upper part. the rupelian–chattian boundary is located in the lower part of the unit. the chattian–aquitanian (oligocene– miocene) boundary is located just above the top of the l3 unit. in some wells, a hiatus is indicated at this level by the clustering of hos. the chattian–aquitanian, aquitanian–burdigalian, burdigalian–langhian and langhian–serravallian stage boundaries are all located in the l4 unit. the uppermost part of the lark formation is of midserravallian age. correlation. based on biostratigraphic correlation, the lowermost l1 unit is probably largely coeval with the viborg formation onshore denmark, and with sequence 4.1 of michelsen et al. (1998). the l2 unit may be corre69 lated with the linde clay onshore denmark (informal mudstone unit described by heilmann-clausen 1995). intervals in the l3 unit may be correlated with the branden clay (ravn 1906) onshore denmark, based on lithological similarities and biostratigraphy. intervals in the lark formation around the l3–l4 boundary (around the chattian–aquitanian boundary) may be correlated with the two lowermost, clay-rich units of the onshore vejle fjord formation (the brejning clay and vejle fjord clay of larsen & dinesen 1959). the uppermost part of the lark formation possibly correlates with the onshore arnum formation (sorgenfrei 1958) and the hodde formation onshore denmark (rasmussen 1961), based on biostratigraphy. dufa member new member history. the dufa member comprises a thick sandstonedominated unit that occurs within unit l3 of the lark formation in the northern and eastern part of the danish sector of the north sea. the unit has not been previously described. derivation of name. after the goddess dufa. type well. danish sector well inez-1, 697.1–485.5 m mdkb (figs 41, 58; plates 1, 5). reference well. danish sector well f-1, 337.5–324.3 m mdkb (figs 58, 59; plate 5). distribution and thickness. the dufa member is present in the north-eastern part of the danish sector of the north sea (fig. 55). in its type well, the dufa member is 210 m thick and consists of three major sandstone units with thicknesses 30–120 m (fig. 41). the sandstone units are separated by mudstone intervals up to 20 m thick. towards the north, in the f-1 well, the lower sandstone units are fig. 58. n–s-trending composite seismic section (rtd81-re94-45/rtd81-re94-09). blue-coloured lines indicate the outline of the dufa member. the gamma-ray logs from the inez-1 and f-1 wells are inserted (see figs 55 and 59 for depth-converted gamma-ray logs for the two wells). the horda formation is thin in this area and the top horda reflector (th) is therefore indistinguishable from the top balder reflector (tb). the location of the seismic section is shown in fig. 1; abbreviations as in fig. 49. inez-1f-1 0 500 1000 twt (msec) tf tl2 tb/th n s dufa mb dufa mbdufa mb 5 km 70 well, the lower sandstone intervals of the dufa member show the presence of a number of 5–10 m thick sandstone packets showing blocky, decreasing-upwards gamma-ray log signatures suggesting coarsening-upwards sand bodies. these sandstones are separated by intervals of fig. 60. francisca-1, type well for the freja member. black bars show cored sections. 1400 1500 1600 1700 1800 m 1562.8 1840.7 freja mb lark fm francisca-1 gr sonic missing (figs 58, 59). the dufa member is absent in wells west of f-1. lithology. the lower sandstone units predominantly consist of coarsening-upwards successions of very fine-grained to fine-grained, greenish brown, muddy sandstones. the upper sandstone unit fines upwards and consists of mediumto coarse-grained, quartzitic, relatively pure sand with intervals rich in glaucony. lignite has been observed in cuttings samples. log characteristics. the member is characterised by an overall blocky signature on the gamma-ray log. in the type fig. 59. f-1, reference well for the dufa member. dufa mb lark fm 300 400 500 600 m f-1 324.3 337.5 gr sonic 71 mudstones with higher gamma-ray response. the upper unit is characterised by an overall blocky signature with minor gamma-ray peaks and trends suggesting a number of fining-upwards intervals, 10–20 m thick, and a few coarsening-upwards intervals, 5–10 m thick (fig. 41). boundaries. the upper and lower boundaries of the member with the mudstones of the lark formation are sharp and characterised by prominent shifts on the gamma-ray log (figs 41, 59). depositional environment. judging from seismic evidence, the dufa member is positioned partly on the offlap break, partly seaward of it (fig. 58). based on this palaeosetting and the presence of lignite in cuttings samples, the dufa member sandstones are interpreted to represent deltaic, shallow-marine sediments, probably deposited in pulses during an overall relative sea-level low. age. rupelian, based on the age of the enveloping mudstones. correlation. there are no danish onshore correlatives to the dufa member. the correlation with the norwegian offshore successions is currently uncertain. freja member new member history. the freja member is a conspicuous sandstonedominated unit that occurs within the upper levels (l4) of the lark formation in the northern and central parts of the danish sector of the north sea. the unit has not previously been described. derivation of name. after the goddess freja. type well. danish sector well francisca-1, 1840.7–1562.8 m mdrt (figs 60, 61). reference well. danish sector well frida-1, 1623.5–1487.7 m mdrt (fig. 62; plate 4). distribution and thickness. the freja member is present in the northern and central parts of the danish sector of the north sea (fig. 55). in its type well, the freja member spans a stratigraphic interval of c. 280 m and includes major sandstone units separated by subordinate intervals of mudstones (fig. 60). in the cecilie-1 well, the member is c. 150 m thick whereas in the frida-1 well the member attains c. 130 m (fig. 62). lithology. in its type well, the lower half of the freja member consists of very fine-grained to fine-grained quarzitic sandstones with many thin mudstone interbeds. the member becomes less muddy in the upper third of this interval. the upper third of the freja member consists largely of relatively pure quarzitic, very fine-grained sandstones with mudstone interbeds becoming frequent towards the top (fig. 60). between these two major sandstone units is a c. 60 m thick interval dominated by mudstones but with carbonate-cemented, sandstone-dominated packets in its upper part. log characteristics. the freja member has an overall blocky gamma-ray log signature. in the type well, its lowermost part (1840.7–1750 m) can be split into a number of smaller units with blocky or increasing-upwards gamma-ray log signatures separated by gamma-ray peaks. in comparison, the overlying sandstones (1750–1720 m) display a more stable, low gamma-ray log pattern with few gamma-ray log spikes (fig. 60). the mudstone-dominated interval (1720–1660 m) separating the two sandstone-dominated units in the type well generally shows high gamma-ray values: thin calcite-cemented sandstone packets are intercalated with the mudstones in this interval (e.g. 1680– 1670 m) and show decreasing-upwards gamma-ray values. boundaries. the lower boundary of the freja member with the lark formation mudstones is sharp and characterised by prominent shifts on the gamma-ray and sonic logs. in the type well, where the upper levels of the freja member are characterised by interbedded mudstones and sandstones, the upper boundary of the member is less prominent. in this well, it is placed at the top of the uppermost discrete sandstone bed, at 1562.8 m (fig. 60). macroand ichnofossils. intervals with shell debris have been observed in core sections of the freja member in the francisca-1 well. ichnofossil genera from the freja member comprise chondrites ispp., phycosiphon ispp., planolites ispp., terebellina ispp., thalassinoides ispp. and zoophycos ispp. depositional environment. the freja member represents stacked successions of thickand thin-bedded turbidite sands deposited in submarine channels and proximal levee environments (figs 60, 62). the upper parts of the turbidite successions show transitions from normally graded turbidites, deposited in slightly more distal levee environ72 francisca-1 w e n s 2 km 0 500 1000 1500 2000 2500 3000 twt (msec) freja memberfreja memberfreja member horda fmhorda fm lark fmlark fm lark fmlark fm horda fm lark fm l3l3 l2l2 l4l4 lark fm tl tf uou tl2 th tb ments and minor turbidite channels, to mainly silty turbidite deposits that represent distal levee and fan fringe environments and the transition to the open slope. the source of the sand was probably a marginal marine shelf environment, judging by the abundance of the marginal marine acritarch paralecaniella indentata. age. in the type well, the freja member is chattian to aquitanian in age, based on the age of mudstones within and bounding the member. in the frida-1 well, the freja member is entirely chattian in age. correlation. the freja member is broadly contemporaneous with the vejle fjord formation onshore denmark, with the vade formation (hardt et al. 1989) in the norwegian central graben and with the skade formation (hardt et al. 1989) in the viking graben. thick, coarsening-upward sandstone bodies are present above the dufa memfig. 61. composite seismic section (dk1–5623a re94/dk1–0448b re94) with the freja member indicated between the reflectors uou and tf. the gamma-ray log from the francisca-1 well is indicated on the figure (see fig. 60 for depth-converted gamma-ray log). the vertical white bar indicates where the section changes direction. the location of the seismic section is shown on fig. 1; abbreviations as in fig. 49. 73 1487.7 1623.5 freja mb lark fm 1400 1500 1600 1700 m frida-1 gr sonic ber in the inez-1 well (shown as unnamed sandstones in fig. 2); these sandstones may be contemporaneous or even contiguous with those of the freja member. however, confident correlation on the basis of log and seismic data is not possible at present. acknowledgements aage bach sørensen (geus) is thanked for help with seismic interpretations. yvonne desezar, johnny e. hansen and birthe amdrup are thanked for preparation of microfossil and palynology samples. the referees robert w.o’b. knox (british geological survey) and paul van veen (conocophilips norway) are thanked for their constructive criticism of the manuscript; the editorial contributions of adam a. garde, jon r. ineson and martin sønderholm are gratefully acknowledged. this work was made possible through grants from the danish energy authority, under the energy research project framework 2000. fig. 62. frida-1, reference well for the freja member. black bar shows cored section. references ahmadi, z.m., sawyers, m., kenyon-roberts, s., stanworth, c.w., kugler, k.a., kristensen, j. & fugelli, e.m.g. 2003: paleocene. in: evans, d. et al. (eds): the millenium atlas: petroleum geology of the central and northern north sea, 235–259. london: geological society. armentrout, j.m., malecek, s.j., fearn, l.b., sheppard, c.e., nayler, p.h., miles, a.w., desmarais, r.j & dunay, r.e. 1993: log-motif analysis of paleogene depositional systems tracts, central and northern north sea: defined by sequence stratigraphic analysis. in: parker, j.r. (ed.): petroleum geology of northwest europe: proceedings of the 4th conference, 45–57. london: geological society. aubry, m.-p. et al. 2002: proposal: global standard stratotype-section and point (gssp) at the dababiya section (egypt) for the base of the eocene series, 58 pp. unpublished report, international subcommision on paleogene stratigraphy. aubry, m.-p. et al. 2003: chronostratigraphic terminology at the paleocene/eocene boundary. geological society of america, special paper 369, 551–566. berggren, w.a. & aubert, j. 1975: paleocene benthonic foraminiferal biostratigraphy, paleobiogeography and paleoecology of atlantic– tethyan regions; midway-type fauna. palaeogeography, palaeoclimatology, palaeoecology 18, 73–192. geological survey of denmark and greenland bulletin 1, 543-554 543 an offshore transgressive–regressive mudstone-dominated succession from the sinemurian of skåne, sweden nils frandsen and finn surlyk a sinemurian mudstone-dominated succession was exposed until recently in the gantofta quarry in skåne, southern sweden. the deposits are placed in the döshult and pankarp members of the sinemurian–aalenian rya formation. similar facies of the same age are widespread in the danish basin where they constitute the f-ib unit (f-i member) of the fjerritslev formation. the gantofta succession thus represents the easternmost extension of the environment characteristic of the fjerritslev formation and is essentially the only locality where it has been possible to study the facies of this formation in outcrop. sedimentation seems to have taken place under relatively quiet tectonic conditions except for the possible fault-control of the basin margin. the lower part of the gantofta section is of early and early late sinemurian age. it represents the upper part of the döshult member and consists of muddy, lower shoreface sandstones, abruptly overlain by dark, bioturbated, fossiliferous mudstones with thin storm siltstones and sandstones. they are overlain by the upper sinemurian pankarp member which comprises red-brown, restricted marine calcareous mudstones with an upwards increasing number of storm siltstones and sandstones reflecting general shallowing and shoreline progradation. the succession spans the greater part of two simple sequences with a distal sequence boundary located at the boundary between the döshult member and the pankarp member. the exposed part of the lower sequence includes a thick transgressive systems tract and a very thin highstand systems tract. the upper sequence is represented by an undifferentiated transgressive and highstand systems tract. an early sinemurian sea-level rise, a late early sinemurian highstand, an early late sinemurian fall and a late sinemurian minor rise and a major fall are recognised. nearby boreholes show evidence for an end-sinemurian – early pliensbachian major rise. this evolution corresponds well with trends recorded in the subsurface fjerritslev formation of the danish basin. comparison with published european and british jurassic sea-level curves show similar overall trends, but exhibit differences in the precise ages of sequence boundaries and maximum flooding surfaces. this may reflect poor biostratigraphical resolution of the gantofta section, differences in sequence stratigraphic interpretation, real differences in the age of sequence stratigraphic key surfaces, or the basin marginal position of gantofta in the fennoscandian border zone. keywords: skåne, southern sweden, lower jurassic, sinemurian, facies analysis, sequence stratigraphy, sedimentary environments, sea-level change n.f., dong, agern allé 24–26, dk-2970 hørsholm, denmark. e-mail: nfr@dong.dk f.s., geological institute, university of copenhagen, geocenter copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. geological survey of denmark and greenland bulletin 1, 543–554 (2003) © geus, 2003 544 jurassic sedimentary rocks occur in great thicknesses in the subsurface of denmark and southern sweden (michelsen 1978; norling et al. 1983; nielsen 2003, this volume). they are, however, only exposed in a few relatively small outcrops on bornholm in the baltic sea, and in skåne, southern sweden, in the fennoscandian border zone (fig. 1; sellwood 1972; rolle et al. 1979; gravesen et al. 1982; norling et al. 1983; surlyk & noenygaard 1986; ahlberg et al. 2003, this volume). this intensely block-faulted zone forms the north-eastern boundary of the danish basin. detailed facies, biostratigraphic and sequence stratigraphic studies of exposed units are thus of outstanding importance in obtaining a more detailed picture of the sedimentary environments prevailing during jurassic time in southern scandinavia. the aims of the present paper are to interpret the facies and sequence stratigraphy of the sinemurian offshore marine deposits exposed in the gantofta quarry in skåne, southern sweden, to place the succession in its regional context, and to compare the derived sealevel curve with the sea-level curves of haq et al. (1988), hallam (1988) and hesselbo & jenkyns (1998). geological setting and stratigraphy gantofta is located close to the nw–se-trending western margin of the fennoscandian border zone (fig. 1). the margin is characterised by a major faulted flexure formed by late cretaceous – palaeogene tectonic inversion which marks the transition to the major depocentre of the danish basin to the south-west (norling 1981, fig. 37). the locality is a small clay pit (150 x 100 m) which was abandoned some years ago and the section is thus no longer easily accessible. the ammonites from the succession were described by reyment (1969a, b), the foraminifera by norling (1972), the palynology by lund (1977), the ostracodes by sivhed (1977, 1980, 1981) and the sedimentary facies and environments by frandsen (1977), rolle et al. (1979) and pieńkowski (1991a, b). the succession is 70 m thick and consists of sandstones and mudstones of the lower – lower upper sinemurian döshult member and the upper sinemurian pankarp member, which constitute the two lower members of the sinemurian–aalenian rya formation (sivhed 1984; ahlberg et al. 2003, this volume). the whole succession is tilted, and the strata strike 140° and dip 30° sw (fig. 2). vomb trough fyledalen fault gantofta 25 km höganäs basin malmö trough hanö bay kullen i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i ii i i i i i i i i i i i i i i i i sweden dk bornholm i i i rhaetian and jurassic present distribution fault active in the jurassic post-jurassic fault n norway ängelholm basin fig. 1. map showing the location of gantofta in the fennoscandian border zone of southern skåne. important jurassic structural features are indicated; note that jurassic normal faults were subsequently inverted in the late cretaceous – palaeogene. based on norling & bergström (1987). dk, denmark. 545 a foraminifer fauna from the middle part of the döshult member at the base of the exposure indicates an early sinemurian age (norling 1972). an ammonite fauna including asteroceras obtusum (sowerby) and promicroceras planicostatum (sowerby) from a level 2 m below the base of the overlying pankarp member is of early late sinemurian obtusum chronozone, planicostatum subzone age (reyment 1969a). k. hoffman (in: bölau 1959) reported the occurrence of the birchi subzone (top of the turneri chronozone) immediately below the base of the pankarp member. the ostracode faunas of the döshult member indicate a latest early sinemurian to late sinemurian age (sivhed 1977). norling (1972) suggested that the succession spans the time interval of the semicostatum to obtusum chronozones. a new find of the ammonite euagassiceras cf. lundgreni reyment in the basal muddy sandstone of the section suggests a mid early sinemurian semicostatum chronozone age for this level (probably resupinatum subzone). this is in agreement with bölau (1973). correlative strata are widely distributed in the danish basin where they form the f-ib unit (f-i member) of the thickly developed, uniform mudstone package of the fjerritslev formation (michelsen 1975, 1978, 1989; pedersen 1985, 1986; michelsen et al. 2003, this volume; nielsen 2003, this volume). the succession of the gantofta quarry consists of similar facies and thus essentially represents the only locality where it has been possible to study the characteristic facies of the otherwise deeply buried fjerritslev formation in outcrop. sedimentology a detailed sedimentological log of the succession was measured in 1975–1976 by frandsen (1977). special emphasis was placed on recording primary sedimentary structures, body and trace fossils, and details of concretions and other diagenetic features were also noted. five sedimentary facies are recognised and are described below followed by an interpretation of the depositional processes and environments. sedimentary facies muddy sandstone (facies 1) this facies consists of fineto very fine-grained quartz sandstone with a mud-rich matrix. it is only known fault n a b ba i i i i i i i i i i i i i i i i i i katslösa mb pankarp mb coal seam mudstone sandstone gantofta quarry fault i i 200 m upper sinemu rian lower sinemu rian 200 m döshult mb fig. 2. geological map and section (a–b) of the gantofta area. modified from sivhed (1981). 546 se m ic os ta tu m c hr o no zo ne (? re su pi na tu m s ub zo ne ) ob tu su m c hr o no zo ne (p la ni co st at um s ub zo ne ) trace fossils chondrites isp. rhizocorallium isp. diplocraterion isp. planolites isp. skolithos isp. pyritic tube teichichnus isp. bioturbation increasing density body fossils bivalves, suspension feeders bivalves, deposit feeders bivalve fragments gastropods ammonites belemnites scaphopods serpulids brachiopods echinoid spines shark teeth ostracodes foraminifers sequence stratigraphy sequence boundary maximum flooding surface transgressive surface of erosion transgressive systems tract highstand systems tract parasequence sb mfs tse tst hst ps tse tst mfs hst tst hst d ö sh ul t m b pa nk ar p m b d ö sh ul t m b lithology mudstone calcareous mudstone silty and sandy mudstone siltand sandstone carbonate cemented conglomerate structures parallel lamination parallel lamination with siltstone lenses cone-in-cone structures clay ironstone concretions c la y si lt sa nd vf f c la y si lt sa nd vf f 35 30 25 20 15 10 5 0 1 3 2 2 2 2&3 2&3 2&3 2&3 2 2 2 2 2&3 3 ps ps ps ps ps ps ps 70 m m 65 60 55 50 45 40 35 2 4 5 sb fa ci es se q. st ra t. fig. 3. sedimentological section showing the biostratigraphy, chronostratigraphy and sequence stratigraphy of the sinemurian succession at gantofta. from the base of the section (fig. 3). shelly coquinas with quartz granules occur at some levels. the colour varies from light grey to dark grey. the sandstone is almost totally bioturbated and the original structures are commonly difficult to recognise. however, fine biogenic lamination caused by high densities of the trace fossil teichichnus isp. is a characteristic feature of the facies. siderite is the dominant cement, whereas the most indurated beds have a calcitic cement. the trace fossils include teichichnus isp., diplocraterion isp., rhizocorallium isp., chondrites isp., planolites isp. and zapfella isp.; the last of these occurs as elongate borings in shells of the bivalve liogryphaea arcuata. the facies contains a fully marine fauna of body fossils which occur in rather high densities. frandsen (1977) compiled a list of the fauna and documented the presence of species described from other localities by troedsson (1951). a taxonomic revision has not been attempted. the fauna includes the bivalves liogryphaea arcuata, chlamys textoria, chlamys interpunctata, entolium sp., and oxytoma sinemuriensis, the ammonite euagassiceras cf. lundgreni reyment, and indeterminate belemnites, echinoids, serpulids, ostracodes and nodosariid foraminifera. coalified wood occurs as scattered pieces up to 6 cm long. the preservation of the shells is quite variable. some are well-preserved and unworn, while others occur in coquinas and have clearly undergone some transport and destruction. the combination of marine body and trace fossils, intense bioturbation, shelly coquinas and a sand-dominated grain size indicates deposition under well-oxygenated marine conditions with normal salinity and relatively low sedimentation rates, periodically interrupted by higher energy events resulting in erosion, reworking and transport of shells. the taphonomic conditions suggest that the fauna can be considered a neighbourhood assemblage representing a fauna which lived in the area and which underwent only limited transport. the muddy nature of the sandstone suggests that the original facies was a sand-dominated, possibly flaserbedded heterolith, but the very high degree of bioturbation does not allow a detailed process interpretation. dark grey mudstone (facies 2) the mudstone of this facies characterises the bulk of the exposed part of the döshult member (fig. 3). it has a high content of silt and fine sand. silt and clay are roughly equally abundant, and the clay is dominated by kaolinite with some illite and chlorite. coaly detritus, muscovite, very small shells and shell fragments, and framboidal pyrite nodules (0.1–0.3 mm in diameter) are characteristic constituents. a few intervals, up to 1 m thick, have a relatively higher content of sand and can be classified as muddy sandstones. the mudstone is laminated with light coloured laminae of coarse silt, 1 mm thick. clay ironstone is a characteristic component and occurs as bedding-parallel siderite impregnated layers, 5 cm thick, with ellipsoidal concretions, 5–20 cm long. thin conglomerate beds consisting of reworked clay-ironstone concretions are found at the 35.05 m and 38 m levels (fig. 3). carbonate concretions with cone-in-cone structures occur at several levels. the facies is strongly bioturbated, especially in the sandier portions, but several recognisable trace fossils were noted, including diplocraterion isp., skolithos isp., rhizocorallium isp. (which has only been recorded from the clay-ironstone conglomerate) and chondrites isp. pyritic tubes, 0.2–1.0 mm in diameter, probably representing burrows of small deposit feeders, and ?planolites isp. occur throughout. this facies and the laminated siltstone–sandstone facies (facies 3) contain a rich shelly fauna. the two facies and their faunas are closely related and their faunas are described together here. the carbonate shells have undergone dissolution and are mainly poorly preserved, but wear due to transport appears to be negligible. liogryphaea arcuata is relatively rare and the specimens are smaller than those of facies 1. two species of chlamys and minute specimens of oxytoma sinemuriensis have been found. a major difference in faunal composition compared to facies 1 is the abundance of deposit-feeding bivalves of the nuculanacea (nuculana, palaeoneilo, rollieria, leda) and nuculacea (nucula). bivalves belonging to cardinia, astarte, homomya and pleuromya or related genera also occur, but the determinations are uncertain. small, high-spired gastropods representing a number of different genera are very common. poorly preserved scaphopods, brachiopods, ammonites and rare shark teeth occur at several levels. the fine-grained muds were deposited from suspension in an offshore open marine environment. the content of silt and sand probably represents material transported to the area during storms. bioturbation then resulted in mixing of the fine and coarser fractions, and destruction of primary current-produced structures. the high density and diversity of body and trace fossils show that the water was of normal salinity and well547 oxygenated. the abundance of deposit feeders is a common characteristic of fine-grained, nutrient-rich sediments, whereas the abundant small-sized gastropods suggest the presence of a marine vegetation. the clay ironstone layers were formed under conditions of negative eh, low concentration of sulphide ions, high activity of ferrous ions, and the presence of bicarbonate ions. following sellwood (1971) it is suggested that iron was transported to the marine environment and deposited as insoluble ferrioxide which was adsorbed on clay minerals. the siderite nodules contain undeformed trace fossils and the mudstone shows compaction features around the nodules which were thus formed after burrowing but before compaction. laminated siltstone–sandstone (facies 3) this facies varies in grain size from coarse silt to fine sand, but grains up to granule size occur set in a muddy matrix. it forms beds up to 1–2 m thick and is commonly interbedded with facies 2. more than 95% of the grains consist of quartz. other components are plagioclase, muscovite and coaly grains. nodules of framboidal pyrite with a diameter of 0.1 mm occur locally. the cement consists mainly of calcite. the facies is parallel laminated, but structureless intervals are also observed and primary structures are commonly obliterated by bioturbation. laminae are normally 1–2 mm thick, and may be graded from fine sand to coarse silt. thin laminae of shell hash occur locally. the facies is strongly bioturbated. recognizable trace fossils include rare skolithos isp., chondrites isp., rhizocorallium isp. with protrusive spreiten, and ?pygospioides isp. which is very similar to chondrites, but more closely resembles pygospioides isp. as described from the hettangian of niedersachsen by häntzschel & reineck (1968). ?planolites isp. traces occur throughout the facies. body fossils are described under facies 2 (see above). the coarse siltstones and sandstones of this facies probably represent distal offshore storm deposits (pedersen 1985), but the pervasive bioturbation precludes an unequivocal interpretation. variegated mudstone (facies 4) this facies and facies 5 characterise the pankarp member in the upper part of the section (fig. 3). it differs from facies 2 in the red-brown colour and a finer grain size dominated by clay and silt. some levels are light-grey with a greenish tinge. the colour difference from facies 2 is associated with a greater content of iron; the red variety is richer in ferric and poorer in ferrous compounds than the greenish variety. the facies shows some lamination and upwards in the succession thin lenticular silt ripples start to appear. a few indeterminate bivalves and some pyrite-impregnated nodosariid foraminifers have been found. the facies was deposited under low energy conditions, probably in a marginal marine environment as inferred from the impoverished fauna and the scarcity of bioturbation compared to facies 2 and 3. calcareous siltstone and mudstone (facies 5) the facies consists of intimately interbedded, soft, variegated claystone and siltstone of the same type as facies 4, and harder light grey coarse siltstone and very fine sandstone. up to 60–70% of the sediment consists of calcite while quartz, clay and some muscovite constitute the remaining part. the calcite occurs as recrystallized cement and grains of uncertain origin. comminuted coaly fragments occur throughout. the facies shows an almost varve-like grading with 5–17 mm thick beds. the graded beds pass from light grey, calcite-rich clay into red clay, poor in calcite. the lower boundaries of the graded beds are sharp and the tops are flat or gently undulating. some of the thicker, coarser-grained beds show parallel lamination passing into low-amplitude hummocky cross-stratification. these beds also display load structures, groove casts, flatlying folds and wrinkle marks on their upper surfaces. the wrinkle marks are very similar to the kinneya ripples of reineck & singh (1980). trace fossils are scarce, typically represented by scattered 3–4 mm wide subhorizontal burrows, whereas teichichnus isp. and subhorizontal rhizocorallium isp. with protrusive spreiten are found in the upper coarsergrained part of the succession. body fossils are only represented by scattered shell fragments. the fine grain size and the scarcity of trace and body fossils suggest deposition under very low energy conditions in a marginal or high stress marine environment. the graded beds probably represent deposition from storm-induced suspension clouds (pedersen 1985). the upwards increase in grain size and in the frequency of beds displaying parallel lamination and hummocky cross-stratification indicate increasingly storm-influenced 548 deposition. the sum of characters thus indicates deposition under low energy conditions interrupted by sudden influxes of storm-derived sediments. the environment may have been distant offshore or more likely a relatively protected shallow marine area where the available grain sizes were very fine and where the effects of storm events were relatively subtle. the red coloration and the presence of kinneya-type wrinkle marks lend some credence to the latter hypothesis. the wrinkle marks may have been caused by a strong wind blowing over a cohesive, fine-grained sediment covered by only a thin veneer of water, possibly with a microbial mat growing on the sea floor under environmentally stressed conditions (reineck & singh 1980). they are thus indicative of near emergent conditions. as indicated on the geological map (fig. 2), a coal seam is situated slightly above the studied section. this also suggests that facies 5 was deposited in a marginal to non-marine environment. depositional environment facies 1–5 form a regular vertical succession with facies 1 at the base and facies 5 at the top, and interbedding only occurs between facies 2 and 3. the section thus includes a basal muddy sandstone, a lower dark grey unit and an upper unit dominated by light grey and redbrown colours. the sedimentary structures and grain sizes do not show any marked changes and the main mechanisms of transport and deposition seem to have been rather uniform. the whole succession is thus considered to represent an association of genetically related facies. the basal part of the association consists of muddy sandstone (facies 1; only 1.2 m exposed). it is followed with a sharp boundary by a unit dominated by dark grey mudstone with clay-ironstone layers (facies 2), 37.7 m thick, with numerous intercalations of thin siltstone and sandstone beds (facies 3). this unit is overlain with a sharp contact by a variegated mudstone unit, 14.9 m thick, (facies 4), which gradually gives way to a succession of calcareous mudstones and siltstones (facies 5); 15.9 m of this last unit was exposed in the 1970s. the succession is interpreted to reflect changes in relative sea level in an area with uniform subsidence and relatively constant sediment influx. thus, facies 1 represents slow deposition in a well-aerated shallow shelf sea. the muddy sand was originally deposited as alternating thin layers of mud and thicker layers of sand which were thoroughly mixed by bioturbation in the offshore transition to lower shoreface zone close to wave-base. the sharp boundary to the overlying mudstones of facies 2 is interpreted as a ravinement surface caused by combined drowning and transgressive erosion when coarser clastic material was trapped in estuaries and other inshore environments. the main part of the succession represented by mudstone with coarser-grained intercalations (facies 2 and 3) was deposited in deeper offshore areas with periodic influxes of silt and sand from storm-generated suspension clouds. most of the silt and sand beds were thoroughly bioturbated and their identity as storm deposits became less obvious. the unit shows an upwards decrease in the density and diversity of body fossils culminating at the almost barren 35 m level (fig. 3). the top 4 m of the unit are again rich in body fossils. this trend is interpreted to have resulted from transgression and increasing water depth associated with a decrease in oxygenation followed by a regression combined with increasing oxygenation at the sea floor. the variegated mudstones of facies 4 and 5 overlie the dark grey mudstone with a sharp contact (38.9 m in fig. 3) and are somewhat difficult to interpret environmentally. they have the finest grain size of the whole succession indicating very low energy conditions during deposition. the red colour and the occurrence of wrinkle marks or kinneya ripples suggest well-oxygenated, very shallow water conditions. the sediments were possibly derived from erosion of finegrained red beds of triassic age exposed in a nearby source area. the upwards increase in storm siltstones and sandstones suggests coastal progradation, whereas the scarcity of body and trace fossils suggests a marginal marine or high stress environment. the generally fine grain size points to deposition in a sheltered, somewhat enclosed area. the variegated mudstones with storm siltstones and sandstones of facies 4 and 5 thus seem to have been rapidly deposited in a very shallow marine, restricted environment under the influence of storms. sequence stratigraphy the döshult member can be divided into six or seven coarsening-upwards units, about 2–8 m thick, with sharp upper boundaries (fig. 3). they are typical examples of distal parasequences (van wagoner et al. 1990). thin fining-upwards units, 10–20 cm thick, are not assigned any sequence stratigraphic significance but are interpreted as bioturbated storm siltstones and sand549 stones. the parasequences stack into a parasequence set which shows a subtle overall fining-upwards trend accompanied by a distinct decrease in density and diversity of body and trace fossils (0–25 m in fig. 3). the trend is interpreted as an overall backstepping stacking pattern which culminates in the poorly fossiliferous interval between 25 m and 35 m in the upper part of the döshult member (fig. 3). a few thin conglomerates rich in body and trace fossils occur between 35 m and 38.9 m. the dark mudstones of the döshult member (facies 2) are overlain by the pankarp member with a sharp conglomeratic boundary at 38.9 m. this unit comprises about 30 m of variegated, and red-brown, almost unfossiliferous mudstones which contain an upwards increasing number of thin storm siltstones and sandstones. the slowly deposited fully marine muddy sandstones at the base of the section are interpreted to belong to the lower part of the transgressive systems tract. they are capped by a sharp erosional drowning or ravinement surface formed by transgressive marine erosion (tse in fig. 3). the overlying dark mudstones form the upper part of the transgressive systems tract (tst in fig. 3). lowstand deposits cannot be recognised and were probably not deposited in the area. the transgressive marine erosion surface corresponds to the lithostratigraphic boundary between units f-ia and f-ib (both f-i member) of the fjerritslev formation but is slightly younger than in most of the danish basin. the age of the erosion surface is close to the semicostatum–turneri chronozone boundary. a distinct maximum flooding surface cannot be identified on the basis of the available data but a maximum flooding zone is interpreted to occur at about 34 m (mfs in fig. 3). the upper part, from 34 m to the top of the section may represent a simple highstand systems tract. the siderite pebble conglomerate at 38.9 m is not easy to interpret in terms of sequence stratigraphy. it occurs at a marked facies change from dark fossiliferous mudstones (facies 2) to variegated and redbrown almost non-fossiliferous mudstones (facies 4, 5). this change seems to represent a significant environmental change associated with a marked seawards shift in facies and it is possible that it represents a distal sequence boundary. if this is the case then the highstand systems tract of the underlying sequence is a maximum of 5 m thick and consists of dark, uniform mudstones at the top of the döshult member (34–38.9 m in fig. 3). this interpretation is tentatively preferred here and the exposed döshult member thus includes a lower transgressive systems tract (tst), a transgressive surface of erosion (tse), a thick upper transgressive systems tract (tst), a maximum flooding surface or zone (mfs) and a thin highstand systems tract (hst) topped by a distal sequence boundary (sb; fig. 3). the overlying pankarp member probably represents poorly differentiated transgressive and highstand systems tracts. the fossiliferous siderite pebble conglomerate at the döshult–pankarp member boundary may be interpreted as reworked hiatus concretions formed when sediment supply to the basin was shut off during maximum flooding (hesselbo & palmer 1992). this interpretation is, however, considered unlikely due to the marked facies change, the seawards shift in facies and the associated inferred major drop in water depth across the boundary. correlation to the contemporaneous sose bugt member (rønne formation) on bornholm in the baltic sea is hampered by the paralic, poorly fossiliferous nature of that unit (surlyk et al. 1995). dating of the gantofta succession is based on ammonites, ostracodes and foraminifera, whereas the sose bugt member is dated on the basis of pollen in the lower part and a few dinoflagellates in the upper part. a major sequence boundary is situated close to the hettangian–sinemurian boundary in the sose bugt section. this correlates well with a sequence boundary at the base of the döshult member in skåne, below the gantofta section (surlyk et al. 1995). two minor sequence boundaries are identified in the sose bugt section in the lower sinemurian and in the middle upper sinemurian, respectively. the lower sequence boundary occurs at a level roughly corresponding to the top of the muddy sandstone (facies 1) at the base of the gantofta section (1.2 m in fig. 3), whereas the upper one may correlate with the interpreted sequence boundary at the sharp break between dark mudstones (facies 2) and variegated mudstones (facies 4) at gantofta (döshult member – pankarp member boundary; 38.9 m in fig. 3). this correlation may corroborate the interpretation of the erosional boundary between the döshult and pankarp members as representing the distal expression of a sequence boundary. it is remarkable that highstand systems tract deposits are almost absent in the sinemurian sose bugt section which mainly consists of transgressive systems tract deposits. this is thought to be typical of the more proximal, basin margin areas (surlyk et al. 1995) and may also account for the thinly-developed highstand deposits at gantofta which occupied an intermediate basinal position between the paralic setting of the sose bugt member and the offshore danish basin. higher parts of the pankarp member are known from boreholes situated close to the gantofta quarry. the red-brown, var550 551 iegated and light grey mudstones of facies 4 and 5 are overlain by 10–17 m of bluish-grey mudstone. this is followed by about 5 m of sand with an allochthonous coal seam, 5–15 cm thick, representing a marked regression (sivhed 1980). the sand is overlain by about 15 m of red-brown or bluish-grey mudstone. the pankarp member spans the upper sinemurian oxynotum and most of the raricostatum chronozones. the nature of the lower boundary of the sand bed is not known and a sequence stratigraphic interpretation cannot be undertaken on the basis of the available data. a relative sea-level curve constructed on the basis of the sedimentary evolution as interpreted here is shown on figure 4. it is compared with the jurassic eustatic sea-level curves of haq et al. (1988) and hesselbo & jenkyns (1998). the overall trends of the curves are remarkably similar, but the exact ages of the main highs and lows differ somewhat. the haq et al. (1988) and hesselbo & jenkyns (1998) curves show the highest degree of similarity although the latter is more detailed and shows more candidate sequence boundaries and maximum flooding surfaces. the two curves show major sequence boundaries in the uppermost hettangian, uppermost lower sinemurian and uppermost sinemurian, and maximum flooding surfaces in the middle lower sinemurian and middle upper sinemurian. the gantofta curve is simpler due to a combination of uniform facies development and lower biostratigraphical resolution. it differs from the curve of hesselbo & jenkyns (1998) in that they place the main sinemurian sequence boundary at the base or immediately below the base of the obtusum chronozone whereas it occurs within this chronozone at gantofta. the mismatch between the gantofta curve and the two other curves may be due to the basin marginal position and the lack of lowstand deposits at gantofta. the low biostratigraphic resolution prevents identification of possible hiatuses in the mudstone-dominated succession. the eustatic signal may thus be overprinted by tectonism in the fennoscandian border zone, by higher sediment input during transgression and condensation and bypass during regression. hallam (1988) did not give any detailed zonal data for his transgressive and regressive events and his curve is thus difficult to compare with the other curves. conclusions until recently, a lower jurassic, sinemurian marine succession, 70 m thick, was exposed at the gantofta locality in north-western skåne, southern sweden. gantofta represents the only place where it has been possible to study exposed strata of the same facies as the deeplyburied contemporaneous fjerritslev formation of the danish basin. the succession comprises the upper part sb sb sb sbsb sb sb sb mfs mfs mfs mfs mfs high low high low high low after haq et al. (1988) after hesselbo & jenkyns (1998) this paper, gantofta 200 195 ma jamesoni chronozones raricostatum oxynotum obtusum turneri semicostatum bucklandi angulata u pp er u pp er lo w er lo w er pliensbachian stages sea-level changes sinemurian hettangian fig. 4. relative sea-level curve constructed for the gantofta succession compared with the jurassic sea-level curves of haq et al. (1988) and hesselbo & jenkyns (1998); the time scale is after gradstein et al. (1994). an ammonite from the basal muddy sandstone at gantofta suggests a mid-semicostatum chronozone age for this level. the level of the obtusum chronozone is well located and the lower part of the succession has a general early sinemurian age. the age of the postobtusum chronozone beds is not wellknown but ostracode data suggest a late sinemurian age (sivhed 1980). mfs, maximum flooding surface; sb, sequence boundary. of the döshult member and the lower part of the pankarp member, both belonging to the sinemurian–aalenian rya formation. the basal 1.2 m of the gantofta section exposed the uppermost levels of the sand-dominated lower sinemurian part of the lower döshult member. this overall transgressive, fluvial and lacustrine to shallow marine succession is known from temporary exposures at nearby örby where it is 32 m thick (erlström et al. 1999). five genetically related facies are recognised. the lower half of the gantofta section, representing the upper döshult member, is composed of three facies (1–3). the lowermost 1.2 m consists of lower sinemurian bioturbated, richly fossiliferous muddy sandstones (facies 1), interpreted as having been deposited relatively slowly in an offshore to transition zone environment. they are followed with a sharp contact by lower – lower upper sinemurian, dark grey, bioturbated, fossiliferous mudstones (facies 2) with intercalations of siltstones and sandstones (facies 3). the mudstones represent slow, fair-weather deposition below wave base under offshore shelf conditions interrupted by deposition of thin silts and sands from storm-generated suspension clouds. the general low sedimentation rate and the distal, thin nature of the storm deposits is reflected by the pervasive bioturbation and mixing of both facies. the succeeding upper sinemurian succession, referred to the lower pankarp member, comprises marginal marine, variegated mudstones and red-brown calcareous mudstones (facies 4, 5) with an upwards increasing number of storm siltstones and sandstones reflecting general shallowing and progradation of the coastline associated with restriction of the marine circulation. a fossiliferous siderite pebble comglomerate occurs at the boundary between the döshult and pankarp members. the succession encompasses the greater part of two, relatively simple depositional sequences. the basal muddy sandstone is interpreted as belonging to the lower transgressive systems tract of the lower sequence. it is topped by a ravinement surface formed by transgressive marine erosion overlain by a backstepping parasequence set representing the upper transgressive systems tract. a maximum flooding zone is identified close to the top of the dark döshult member mudstones. it is overlain by a thinly developed highstand systems tract topped by an erosion surface marked by the siderite pebble conglomerate. the erosion surface is tentatively interpreted as a distal sequence boundary and the overlying variegated and red-brown pankarp member mudstones belong to the poorly differentiated transgressive and highstand systems tracts of the second sequence. comparison with the sequence stratigraphy of the contemporaneous sose bugt member (rønne formation) of bornholm lends some credence to this interpretation. the gantofta succession records an early sinemurian sea-level rise, a mid-sinemurian highstand, an early late sinemurian sea-level fall followed by a late sinemurian minor rise and subsequent major fall. data from nearby boreholes indicate an end sinemurian – early pliensbachian major rise. the sea-level curve constructed on the basis of the gantofta section is compared with the sea-level curves of haq et al. (1988) and hesselbo & jenkyns (1998) in figure 4. it is remarkable that the three curves show similar overall trends but the sequence boundaries and maximum flooding surfaces are delayed in the gantofta curve compared to the two other curves. this may reflect the basin marginal position of the gantofta section in the fennoscandian border zone with higher sedimentation rates during sea-level rise and condensation or bypass during fall. furthermore, the gantofta curve is much simpler than the hesselbo & jenkyns (1998) curve. this is probably a direct result of the poor biostratigraphic resolution of the gantofta section and the implicit difficulty in identifying hiatuses in the mudstone-dominated succession. acknowledgements we thank ulf sivhed for useful comments, lars b. clemmensen for critically reading an early manuscript version and referees stephen p. hesselbo and gunver k. pedersen for constructive criticism. the study was supported by the carlsberg foundation and the danish natural science research council. references ahlberg, a., sivhed, u. & erlström, m. 2003: the jurassic of skåne, southern sweden. in: ineson, j.r. & surlyk, f. 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(eds): mesozoic and cenozoic sequence stratigraphy of european basins. sepm (society for sedimentary geology) special publication 60, 561–581. hesselbo, s.p. & palmer, t.j. 1992: reworked early diagenetic concretions and the bioerosional origin of a regional discontinuity within british jurassic marine mudstones. sedimentology 39, 1045–1065. lund, j.j. 1977: rhaetic to lower liassic palynology of the onshore south-eastern north sea basin. danmarks geologiske undersøgelse ii. række 109, 129 pp. michelsen, o. 1975: lower jurassic biostratigraphy and ostracods of the danish embayment. danmarks geologiske undersøgelse ii. række 104, 287 pp. michelsen, o. 1978: stratigraphy and distribution of jurassic deposits of the norwegian–danish basin. danmarks geologiske undersøgelse serie b 2, 28 pp. michelsen, o. 1989: log-sequence analysis and environmental aspects of the lower jurassic fjerritslev formation in the danish subbasin. danmarks geologiske undersøgelse serie a 25, 23 pp. michelsen, o., nielsen, l.h., johannessen, p.n., andsbjerg, j. & surlyk, f. 2003: jurassic lithostratigraphy and stratigraphic development onshore and offshore denmark. in: ineson, j.r. & surlyk, f. 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revision accepted 13 october 1999. geological survey of denmark and greenland bulletin 1, 115-144 115 this paper attempts a further integration and standardisation of the jurassic dinoflagellate cyst zonation schemes established for the british and danish areas (fig. 1; davey 1979, 1982; woollam & riding 1983; nøhr-hansen 1986; riding & thomas 1988, 1992; poulsen 1991, 1992, 1994a; koppelhus & nielsen 1994). in addition, the relationships between the zonation and palaeoecology are discussed, particularly with respect to the appearance and disappearance of species in relation to changes in sea level and palaeotemperature. dinoflagellates dinoflagellates are primarily motile single-celled algae. about half are autotrophic, phytosynthetic species, the reminder being non-photosynthetic consumers that ingest other organisms or particulate organic matter as predators, symbionts, parasites or decomposers. they have been a major component of marine phytoplankton since their diversification in the late triassic and became important in non-marine environments during the early cretaceous (batten & lister 1988). the dinoflagellates have diversified into a wide range of ecological habitats and many of them are sensitive to environmental physical/chemical changes. the understanding of the response of extant dinoflagellates to environmental stress is not well-advanced. the prediction of environment, temperature, water depth and other parameters based on certain species, however, can be made with some accuracy (wall et al. 1977; de vernal et al. 1992). the jurassic dinoflagellate cyst zonation of subboreal northwest europe niels e. poulsen and james b. riding with an appendix by bjørn buchardt: oxygen isotope palaeotemperatures from the jurassic in northwest europe the jurassic dinoflagellate cyst zonation for the british–danish area is revised and discussed in relation to palaeoenvironmental factors, in particular, eustatic changes and fluctuations in palaeotemperature. the stepwise evolution of dinoflagellate cyst assemblages as defined by inceptions and apparent extinctions was largely controlled by sea-level change, particularly during intervals with significant short-term eustatic fluctuations. during times characterised by less pronounced, or longer term, sea-level change, fluctuations in oceanic palaeotemperatures appear to have influenced dinoflagellate evolution. differences in the ranges of certain taxa between denmark and the united kingdom may be partly related to differences in palaeotemperature. keywords: subboreal northwest europe, jurassic, dinoflagellate cyst zonation, palaeotemperatures and biotic provincialism, dinoflagellate palaeoecology n.e.p., geological survey of denmark and greenland, geocenter copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: nep@geus.dk j.b.r., british geological survey, keyworth, nottingham ng12 5gg, uk. b.b., geological institute, university of copenhagen, geocenter copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. geological survey of denmark and greenland bulletin 1, 115–144 (2003) © geus, 2003 dinoflagellate cysts represent the non-motile dormant stage in the life cycle, resulting from sexual fusion (evitt 1985); it is not known, however, whether encystment is related solely to sexual reproduction. cysts are generally resistant to adverse conditions, whereas the motile thecate stage is quickly destroyed after death or encystment. most resting cysts act as sedimentary particles and eventually sink to the sea floor, although many of them have adaptations to floating such as processes, an oil-rich cellular content or becoming entangled with floating debris (sarjeant et al. 1987). the cyst distribution pattern is therefore not only dependent on ecological factors but also on sedimentary history. knowledge of the major factors controlling the distribution patterns of jurassic dinoflagellate cysts cannot be obtained by analogy to modern taxa. however, detailed studies of pre-neogene fossil dinoflagellates during the last 60 years have revealed distinctive distribution patterns of provincialism related to palaeosalinity, palaeotemperature and palaeowater-depth gradients. geological framework during the latest triassic and the earliest jurassic, denmark, the united kingdom, and the north sea basin were part of the subboreal province (fig. 2). the biogeographical affiliations of parts of this area changed, however, as the tethyan realm periodically expanded northwards, and occasionally retreated southwards. the main reasons for this are thought to be variations in seafloor spreading, the migration routes of faunas and floras or a combination of these factors. in general, the true boreal realm consisted of east greenland (jameson land and adjacent areas), the greenland sea (northernmost atlantic), the boreal sea, northern siberia, the arctic islands and northern canada (enay 1972, 1980). the norwegian–danish basin, the british isles and the central graben are termed the subboreal province (fig. 2). this province may be further divided into: (1) a southern part including southern england and the southern central graben, termed the northwest european subprovince, and (2) a northern part, or transitional area, i.e. the 116 poland dknorth sea germanynetherlands atlantic ocean ireland norway sweden england scotland celti c se a wealddorset east midlands london– brabant massif moray f irth hebrides skagerrak– k attegat platform yorkshire (cleveland) brora bornholm skånejylland central graben baltic shield ? ?jurassic strata, outcrop/subsurface 500 km norwegian–danish basin 0° 16°e 32°e8°w16°w 58°n 50°n 8°e fig. 1. generalised distribution of jurassic strata in northwest europe, both at outcrop and in the subsurface. compiled from brooks & chesher (1975), czaplicka (1976), michelsen (1978), cope et al. (1980a, b), guy-ohlson (1986), guy-ohlson & norling (1988), ziegler (1988), andrews et al. (1990), cameron et al. (1992), hamblin et al. (1992), rattey & hayward (1993), stoker et al. (1993), erlström et al. (1994), hamann (1994), koppelhus & nielsen (1994), vejbæk & britze (1994) and japsen et al. (2003, this volume). dk, denmark. norwegian–danish basin, northern united kingdom and the northern central graben, referred to as the boreal– subboreal subprovince (fig. 2; enay 1972, 1980). following deposition of the mainly continental triassic succession, jurassic sedimentation was largely marine and clastic-dominated. a number of major depocentres developed during the jurassic in the subboreal area, including the celtic sea, weald, east midlands, cleveland, moray firth, hebrides, central graben and danish– norwegian basins (fig. 1). large parts of the north sea region were affected by the late toarcian – aalenian central north sea thermal or volcanic doming (sellwood & hallam 1974; whiteman et al. 1975; eynon 1981; ziegler 1988; underhill & partington 1993). following resumed subsidence and initial (middle jurassic) paralic/deltaic sedimentation, the north sea region accumulated a thick marine succession dominated by the mud-rich deposits of the kimmeridge clay formation and its correlatives. during the jurassic period, representing some 70 ma of earth history, the sedimentary successions attained (post-compaction) thicknesses in excess of 1600 m in onshore uk (hallam 1992a), over 1200 m in the danish basin (the danish part of the norwegian–danish basin, see fig. 1; nielsen 2003, this volume) and over 4000 m in the deepest parts of the danish central graben (møller 1986; sundsbø & megson 1993; japsen et al. 2003, this volume). methods the ranges for the stratigraphical index dinoflagellate cyst species are based on those recorded in both the british 117 boreal realm tethys 2 month polar winter night volgian toarcian pliensbachian arctic canada g re en la nd se a siberia polish subprovince northwest european subprovince subboreal province boreal–subboreal subprovince present day land land in jurassic times position of jurassic north poles c. 1000 km fig. 2. biogeographical realms, provinces and subprovinces (modified from poulsen 1996, based on enay 1972, 1980). the approximate geographical extent of the pliensbachian and volgian two-month polar night is indicated, assuming that precession was of the same order in the mesozoic as at the present-day. and danish areas. the zonation represents an idealised succession of bioevents, which takes into account factors such as local hiatuses, palaeoenvironmental/facies control on sediment distribution and ranges of taxa, natural variability and sampling problems. range extension using graphical correlation (shaw 1964; edwards 1984, 1989) was not undertaken. significant differences in ranges are not generally observed, although occasional exceptions have been recorded and are indicated on the composite range charts (see figs 3–5). the middle jurassic of the danish central graben and the danish basin consists mainly of coarse-grained, non-marine strata deposited during the aalenian–bathonian regressive event, or is represented by hiatuses. it contains few stratigraphic levels with marine intercalations and dinoflagellate cysts from this part of the middle jurassic are extremely rare (for further discussion, see poulsen 1992, 1996). the dinoflagellate cyst ranges for the middle jurassic are therefore based on ranges determined from the united kingdom. facies control may have influenced the dinoflagellate cyst assemblages, making them variable in composition inter-regionally. the principal aim here is to present a zonation for the subboreal area that is tested against other faunal zonations, such as those for ammonites and ostracods, and in which apparent variations in ranges have been taken into account, thus giving the best overall regional correlations. as a result of variations in sample availability, inadequate data in certain intervals means that the exact correlation of dinoflagellate cyst zonal boundaries to ammonite zonal boundaries may be uncertain. in such cases, the boundaries are deemed to be coincident, although this methodology may introduce certain minor errors. the ammonite zones are chronostratigraphical units (wimbledon & cope 1978; callomon 1984; cox 1990; page 2003, this volume) and are thus referred to by the species name alone, in roman type (e.g. tenuicostatum zone). this is the convention followed by working groups of the international subcommission on jurassic stratigraphy (isjs) and the international commission on stratigraphy (ics). the base of the jurassic is taken at the inception of the ammonite genus psiloceras, which marks the base of the planorbis zone as recommended by warrington et al. (1994; for further discussion, see page 2003, this volume). the dinoflagellate cyst zones are indicated by the generic and specific names of the index taxon in italics, e.g. dapcodinium priscum zone. only the taxa which are useful for identifying each zone or subzone are cited; accessory forms are consistently present but these are not usually biostratigraphically diagnostic. stratigraphic palynology davey & riley (1978) and morbey & dunay (1978) presented a summary of knowledge of upper triassic and jurassic dinoflagellate cyst biostratigraphy in northwest europe. williams & bujak (1985) subsequently published an extensive synthesis of dinoflagellate cyst zonation schemes for the triassic to quaternary interval. riding & thomas (1992) and riding & ioannides (1996) outlined the history of study of jurassic dinoflagellate cyst biostratigraphy. poulsen (1991, 1992, 1993, 1994a, b, 1996, 1998) demonstrated the utility of the british jurassic dinoflagellate cyst zonations of woollam & riding (1983) and riding & thomas (1992) in denmark and poland. this paper attempts further emendation, integration and standardisation of jurassic dinoflagellate cyst zonal schemes. the zonation presented herein (table 1) is an integrated zonation for denmark and the united kingdom based on the zonations presented by davey (1979, 1982), woollam & riding (1983), nøhr-hansen (1986), riding & thomas (1988, 1992) and poulsen (1991, 1992, 1994b, 1996). the british and danish zonations are in general identical, with the exception of certain new subzones and other emendations that resulted from simultaneous, independent revisions by poulsen (1992) and riding & thomas (1992); these differences are integrated and standardised here. only the necessary emendations and other pertinent comments for unifying the british and danish zonations are given below. it should be noted that the middle–upper jurassic dinoflagellate cyst zones have been recognised in poland (poulsen 1992, 1993, 1994a, 1996, 1998). these zones are also widely recorded in the jurassic deposits in europe and adjacent regions, for example in onshore united kingdom (the wessex, east midlands, cleveland, hebrides and onshore moray firth basins), the danish basin and in the danish sector of the north sea central graben. the zones have been named following biostratigraphical tradition and international stratigraphical guidelines and recommendations, with the zonal name related to an index species, for example, the acanthaulax senta zone. following international rules, zonal names change to conform with any valid changes to the name of the index species (hedberg 1976; salvador 1994); for example, the acanthaulax senta zone of woollam & riding (1983) became the liesbergia scarburghensis zone of riding & thomas (1992) and is now the trichodinium scarburghensis zone. further118 119 zonation formal zonal name reference# (this study) dsk2 endoscrinium pharo subzone (or gochteodinia villosa zone, subzone c) 1 (2 6) dsk1 rotospaheropsis thula subzone (or gochteodinia villosa zone, subzone b (pars)) 1 9 (2 6) dsj39 gochteodinia villosa zone, subzone b (pars) 9 (6) dsj38 exmontodinium expiratum subzone (pars) or gochteodinia villosa zone, subzone a 1 6 9 dsj37 dingodinium spinosum zone 1 dsj36 dichadogonyaulax culmula zone, subzone b (pars) 1 2 5 6 9 dsj35 dichadogonyaulax culmula zone, subzone a 1 2 5 6 dsj34 glossodinium dimorphum zone, subzone e 6 dsj33 glossodinium dimorphum zone, subzone d 6 dsj32 glossodinium dimorphum zone, subzone c 6 dsj31 glossodinium dimorphum zone, subzone b 6 dsj30 glossodinium dimorphum zone, subzone a 6 dsj29 endoscrinium luridum zone, perisseiasphaeirdium pannosum subzone 5 dsj28 endoscrinium luridum zone, stephanelytron scarburghense subzone 5 dsj27 scriniodinium crystallinum zone, subzone d 4 6 dsj26 scriniodinium crystallinum zone, subzone c 4 6 dsj25 scriniodinium crystallinum zone, subzone b 4 6 dsj24 scriniodinium crystallinum zone, subzone a (pars) 9 (6) dsj23 scriniodinium crystallinum zone, subzone a (pars) 9 (6) dsj22 trichodinium scarburghense zone, subzone b 9 (2) dsj21 trichodinium scarburghense zone, subzone a 9 (2) dsj20 wanaea fimbriata zone 2 6 dsj19 wanaea thysanota zone 2 6 dsj18 ctenidodinium continuum zone 6 (2) dsj17 ctenidodinium sellwoodii zone, subzone c 6 (2) dsj16 ctenidodinium sellwoodii zone, subzone b 6 (2) dsj15 ctenidodinium sellwoodii zone, subzone a 6 (2) dsj14 cribroperidinium crispum zone, subzone b 6 9 (2) dsj13 cribroperidinium crispum zone, subzone a 6 9 (2) dsj12 nannoceratopsis gracilis zone, subzone e 6 dsj11 nannoceratopsis gracilis zone, subzone d 6 dsj10 parvocysta nasuta zone (stat. nov.) (pars), (nannoceratopsis gracilis zone, subzone c) 9 (5 6) dsj9 parvocysta nasuta zone (stat. nov.) (pars), (nannoceratopsis gracilis zone, subzone b) 9 (5 6) dsj8 mancodinium semitabulatum zone (emend. nov.) 9 (2 5 6) dsj7 luehndea spinosa zone, subzone b 6 dsj6 luehndea spinosa zone, subzone a, or luehndea spinosa zone, subzone b 6 or 8 dsj5 nannoceratopsis senex zone (new), (luehndea spinosa zone, subzone a) 9 (8) dsj4 mendicodinium reticulatum zone, (liasidinium variabile zone, subzone b) 7 (2) dsj3 liasidinium variabile zone, subzone a 2 dsj2* dapcodinium priscum zone, subzone b 2 5 dsj1* dapcodinium priscum zone, subzone a 2 5 dstr rhaetigonyaulax rhaetica zone 2 table 1. jurassic dinoflagellate cyst zonation # references: 1: davey (1978, 1982) 2: woollam & riding (1983) 3: nøhr-hansen (1986) 4: riding & thomas (1988) 5: poulsen (1991, 1992) 6: riding & thomas (1992) 7: koppelhus & nielsen (1994) 8: poulsen (1994a) 9: this study * note that in the united kingdom it is not possible to separate these two zones, hence they are termed zone dsj1–2 more, riding & thomas (1992) used a three-letter abbreviation for their jurassic dinoflagellate cyst zones (e.g. lsc for the liesbergia scarburghensis zone). calcareous nannoplankton, foraminiferal and other biozones are often denoted by an alphanumeric code in which the first letter indicates the respective fossil group, for example n for (calcareous) nannoplankton, and the second letter indicates a period or epoch – p for palaeogene and n for neogene. each zone is thus enumerated np24, np25, nn1, nn2, nn3 etc. this method results in abbreviations (e.g. nn9) which are easier and more convenient to use, especially for nonpalaeontologists; this methodology is adopted here. the dinoflagellate cyst zones evaluated in this study are thus given a similar code e.g. zone dsj13, (d for dinoflagellate cysts, s is added to emphasise that it is a subboreal zonation, tr for triassic, j for jurassic and k for cretaceous, see table 1). the jurassic and cretaceous are numbered, whereas only one zone is recognised for the triassic. as almost every jurassic dinoflagellate cyst zone is divided into subzones, the subzones are generally taken as the basic numbered biounits in this study. the zonation is, where possible, defined both by species with first occurrences and last appearances coincident with the zonal boundaries. dinoflagellate cyst zonation the zonation presented below is an attempt to further refine the work of r.j. davey, h. nøhr-hansen, n.e. poulsen, j.b. riding, j.e. thomas, r. woollam and others, and to integrate and standardise the jurassic dinoflagellate cyst zonation scheme (table 1). accounts of the ranges of the index species can be found in raynaud (1978), davey (1979, 1982), fisher & riley (1980), woollam (1980), riding (1982, 1984a, b, 1987), riley & fenton (1982), woollam & riding (1983), riding et al. (1985), riding & sarjeant (1985), nøhr-hansen (1986), riding & thomas (1988, 1992, 1997), riley et al. (1989), poulsen (1991, 1992, 1993, 1996), riding et al. (1991), partington et al. (1993) and j.b. riding, j.e. thomas and i.p. wilkinson (in: richards et al. 1993). triassic zonation dstr ; upper triassic (rhaetian) a single zone, dstr, is established for the upper triassic (rhaetian). the dstr zone corresponds to the rhaetogonyaulax rhaetica zone of woollam & riding (1983), which is based on the common/abundant presence of rhaetogonyaulax rhaetica (fig. 3). this zone may locally be further divided into two or three new zones defined on the abundance, presence and/or absence of sverdrupiella spp., heibergella spp., suessia spp. and rhaetogonyaulax rhaetica. these relatively high diversity associations are most likely to occur in the peripheral regions of the subboreal province. jurassic – lowermost cretaceous zonation dsj1, dsj2; uppermost triassic – lower sinemurian (turneri zone) the dsj1 and dsj2 zones are equivalent to the dapcodinium priscum zone of woollam & riding (1983); the lower part of the dsj1 zone spans the triassic–jurassic boundary. subzones a and b of the dapcodinium priscum zone are herein named the dsj1 and dsj2 zones, respectively (fig. 3). in denmark, the dsj1 zone is coincident with the range of d. priscum in the uppermost triassic and lower sinemurian; the index species is absent in the dsj2 zone. the range top of the index species, d. priscum, appears to become younger in more southerly areas relative to the northern subboreal province. as stated above, in the danish embayment the d. priscum zone may be subdivided into two subzones, the upper of which is characterised by the absence of d. priscum. in the united kingdom, d. priscum has been recorded in the lower sinemurian turneri zone (riding 1984a), thereby negating the bipartite subzonal division of the d. priscum zone in the united kingdom initially advocated by woollam & riding (1983). in the united kingdom, the zones established here are termed the dsj1–2 zones to indicate that the d. priscum zone is not subdivided. further south, in portugal, davies (1985) recorded d. priscum from the lower pliensbachian. dsj3; upper sinemurian (obtusum–raricostatum zones) this zone corresponds to the liasidium variabile zone, subzone a of woollam & riding (1983) and riding & thomas (1992) and coincides with the total range of the index species (fig. 3). 120 dsj4; lower pliensbachian (jamesoni – davoei (pars) zones) the dsj4 zone is characterised by the presence of mendicodinium reticulatum or is marked by the absence of dinoflagellate cysts. koppelhus & nielsen (1994) erected the equivalent lower pliensbachian mendicodinium reticulatum zone below the luehndea spinosa zone. the mendicodinium reticulatum zone is equivalent to subzone b of the liasidium variabile zone of woollam & riding (1983) and riding & thomas (1992). dsj5–7; lower pliensbachian – lower toarcian (davoei (pars) – tenuicostatum zones) the upper pliensbachian luehndea spinosa zone of woollam & riding (1983) was expanded into the lowermost toarcian and subdivided into subzones a and b by riding & thomas (1992) and poulsen (1994a). however, the subzones were defined differently by these authors and subzone b of poulsen (1994a) corresponds to subzone a of riding & thomas (1992). a three-fold division of the luehndea spinosa zone is thus proposed below. dsj5; lower pliensbachian (davoei zone (pars)) the dsj5 zone corresponds to the luehndea spinosa zone, subzone a of poulsen (1994b) and is here formally renamed the nannoceratopsis senex zone. the zone is defined in poulsen (1994a) as the interval from the inception of n. senex to the first occurrences of l. spinosa and other species of nannoceratopsis (fig. 3). dsj6; pliensbachian (margaritatus, spinatum zones) this interval corresponds to the luehndea spinosa zone, subzone a of riding & thomas (1992) and subzone b of poulsen (1994a). the zone is defined as subzone a in riding & thomas (1992) and additional species are used to define the base of subzone b of poulsen (1994b). it is therefore defined herein as the interval from the inceptions of l. spinosa, mancodinium semitabulatum, maturodinium inornatum, nannoceratopsis gracilis, n. raunsgaardii, n. ridingii, n. triceras and valvaeodinium armatum to the range tops of m. inornatum and v. armatum. dsj7; lowermost toarcian (tenuicostatum zone) the dsj7 zone corresponds to the luehndea spinosa zone, subzone b of riding & thomas (1992) and was defined as the interval from the apparent extinction of maturodinium inornatum and valvaeodinium armatum, to the range top of luehndea spinosa (fig. 3). dsj8; lower toarcian (falciferum, bifrons (pars) zones) the dsj8 zone broadly corresponds to the mancodinium semitabulatum subzone of poulsen (1992) and subzone a of the nannoceratopsis gracilis zone of riding & thomas (1992; table 1). the dsj8 zone also forms part of the mancodinium semitabulatum zone, subzone a of woollam & riding (1983). dsj9–10; lower toarcian – lowermost aalenian (bifrons (pars) – opalinum zones) the parvocysta nasuta range subzone of poulsen (1992) is herein raised in status to that of a zone and is formally divided into two subzones, a and b, corresponding to subzones b and c, respectively, of the nannoceratopsis gracilis zone of riding & thomas (1992). the inceptions of nannoceratopsis dictyambonis, phallocysta elongata, and susadinium scrofoides define the boundary between subzones a and b, which are equivalent to the dsj9 and dsj10 zones, respectively (fig. 3). the stratigraphically important species nannoceratopsis ambonis, nannoceratopsis dictyambonis, scriniocassis priscus and scriniocassis weberi are not found in the danish basin, although they are characteristic elements both in the united kingdom (woollam & riding 1983; riding 1987) and germany (prauss 1989). dsj11, dsj12; aalenian – lower bajocian (murchisonae–sauzei zones) the dsj11 and dsj12 zones correspond precisely to subzones d and e, respectively, of the nannoceratopsis gracilis zone of riding & thomas (1992; fig. 4, table 1). dsj13, dsj14; lower–upper bajocian (humphriesianum–parkinsoni zones) the dsj13 and dsj14 zones are equivalent to the acanthaulax crispa zone of riding & thomas (1992). the acanthaulax crispa zone of riding & thomas (1992) 121 122 210 205 200 195 190 185 180 sv er dr up ie lla m ut ab ili s h ei be rg el la k en de lb ac hi a su es si a sw ab ia na va lv ae od in iu m d ia cr or ha et iu m be au m on te lla ? ca m in us pi na r ha et og on ya ul ax r ha et ic a d ap co di ni um p ris cu m li as id iu m v ar ia bi le m en di co di ni um r et ic ul at um n an no ce ra to ps is s en ex m at ur od in iu m in or na tu m va lv ae od in iu m a rm at um lu eh nd ea s pi no sa sc rin io ca ss is w eb er i m an co di ni um s em ita bu la tu m n an no ce ra to ps is g ra ci lis pa rv oc ys ta " su it e" pa rv oc ys ta n as ut a ph al lo cy st a eu m ek es ju ra ss ic t ri as si c la te t ri as si c r ha et ia n h et ta ng ia n si ne m ur ia n ea rl y ju ra ss ic pl ie ns ba ch ia n t o ar ci an pe ri o d ep o ch a ge t im e in m a sc rin io ca ss is p ris cu s o va lic ys ta h ia ta su sa di ni um s cr of oi de s n an no ce ra to ps is d ic ty am bo ni s ph al lo cy st a el on ga ta 123 210 205 200 195 190 185 180 t im e in m a r. rhaetica planorbis liasicus dstr r. rhaetica r. rhaetica dsj1 dsj2 dsj3 dsj4 dsj5 dsj6 dsj7 dsj8 dsj9 dsj10 p. nasuta p. nasuta l. spinosa l. spinosa l. spinosa m. semitabulatum n. gracilis m. reticulatum l. variabile l. variabile l. variabile d. priscum d. priscum d. priscum c hr o no zo ne s z o ne s (t hi s st ud y) d sz o ne s z o ne s, d en m ar k su bz o ne s, d en m ar k z o ne s, g re at b ri ta in su bz o ne s, g re at b ri ta in lo ng -t er m e us ta ti c cu rv e af te r h aq e t al . ( 19 87 ) sh o rt -t er m e us ta ti c cu rv e af te r h aq e t al . ( 19 87 ) pa la eo te m pe ra tu re cu rv e (° c ) angulata levesquei thouarsence variabilis bifrons falciferum tenuicostatum spinatum margaritatus davoei ibex jamesoni raricostatum oxynotum obtusum turneri semicostatum bucklandi n. senex m. semitabulatum m. semitabulatum b a b b a a a a a b b b c se ale ve l c ur ve af te r h al la m ( 19 88 ) 20100 m100sea-level rise fig. 3. composite range chart for the key marker dinoflagellate cyst species in the lower jurassic of the subboreal region. in figs 3–5, the eustatic sea-level curves are from haq et al. (1987) and hallam (1988), the palaeotemperature curve is courtesy of b. buchardt (appendix 1) and the time-scale is from haq et al. (1987). note that danish jurassic ammonite recovery is sporadic and that only certain chronostratigraphic zones can be identified using macrofossils (poulsen 1996). is renamed the cribroperidinium crispum zone to accommodate the change in name of the index species (hedberg 1976; salvador 1994). the acanthaulax crispa (cribroperidinium crispum) zone was divided into subzones a and b by riding & thomas (1992) and the dsj13 and dsj14 zones correspond precisely to subzones a and b, respectively. dsj15–18; bathonian – middle callovian (zigzag–coronatum zones) zones dsj15, dsj16 and dsj17 correspond respectively to subzones a, b and c of the ctenidodinium sellwoodii zone of riding & thomas (1992; fig. 4). the latter biozone largely equates to the ctenidodinium combazii – 124 155 160 165 170 175 ju ra ss ic m id dl e ju ra ss ic a al en ia n b aj o ci an b at ho ni an c al lo vi an pe ri o d ep o ch a ge t im e in m a m en di co di ni um r et ic ul at um n an no ce ra to ps is s en ex sc rin io ca ss is w eb er i m an co di ni um s em ita bu la tu m n an no ce ra to ps is g ra ci lis pa rv oc ys ta ‘s ui te ’ pa rv oc ys ta n as ut a ph al lo cy st a eu m ek es sc rin io ca ss is p ris cu s o va lic ys ta h ia ta su sa di ni um s cr of oi de s n an no ce ra to ps is d ic ty am bo ni s ph al lo cy st a el on ga ta d ur ot rig ia d av ey i c rib ro pe rid in iu m c ris pu m va lv ae od in iu m s pi no su m li th od in ia c ay to ne ns is ‘g ro up ’ c te ni do di ni um c on tin uu m c ar pa th od in iu m p re da e a ld or fia a ld or fe ns is c te ni do di ni um c om ba zi i d ic ha do go ny au la x se llw oo di i ‘ gr o up ’ g on ya ul ac ys ta ju ra ss ic a ad ec ta n an no ce ra to ps is p el lu ci da im pl et os ph ae rid iu m v ar is pi no su m r ig au de lla a em ul a c te ni do di ni um o rn at um si rm io di ni um g ro ss i c om po si to sp ha er id iu m p ol on ic um g on ya ul ac ys ta e is en ac ki i st ep ha ne ly tr on s ca rb ur gh en se g on ya ul ac ys ta c en tr ic on na ta li m bo di ni um a bs id at um w an ae a th ys an ot a tr ic ho di ni um s ca rb ur gh en se sc rin io di ni um c ry st al lin um ctenidodinium sellwoodii zone of woollam & riding (1983). the dsj18 zone is coeval with the ctenidodinium continuum zone of riding & thomas (1992), which is broadly coincident with the ctenidodinium ornatum – ctenidodinium continuum zone of woollam & riding (1983). dsj19; upper callovian (athleta, lamberti zones) the dsj19 zone corresponds to the wanaea thysanota zone of riding & thomas (1992), formerly the wanaea thysanota zone (subzones a and b) of woollam & riding (1983). the subdivision of the wanaea thysanota zone, based on the range base of trichodinium scar125 155 160 165 170 175 t im e in m a c hr o no zo ne s z o ne s (t hi s st ud y) d sz o ne s z o ne s, d en m ar k su bz o ne s, d en m ar k z o ne s, g re at b ri ta in su bz o ne s, g re at b ri ta in lo ng -t er m e us ta ti c cu rv e af te r h aq e t al . ( 19 87 ) sh o rt -t er m e us ta ti c cu rv e af te r h aq e t al . ( 19 87 ) pa la eo te m pe ra tu re c ur ve ( °c ) se ale ve l c ur ve af te r h al la m ( 19 88 ) zigzag discus dsj13 n. gracilis c. crispum n. gracilis a. crispa c. continuum w. thysanota w. thysanota lamberti athleta jason calloviense koenigi herveyi coronatum aspidoides hodsoni subcontractus progracilis tenuiplicatus morrisi parkinsoni garantiana subfurcatus humphriesianum sauzei loeviusculo discites dsj11 dsj12 dsj14 dsj15 dsj16 dsj17 dsj19 concavum murchisonae p. nasuta dsj10opalinum not zoned p. nasuta not zoned m. semitabulatum c d e a b a b c c. continuum dsj18 c. sellwoodii c. sellwoodii 20100 m100sea-level rise fig. 4. composite range chart for the key marker dinoflagellate cyst species in the middle jurassic of the subboreal region. burghensis, was discontinued by riding & thomas (1992). dsj20; lowermost oxfordian (mariae zone) the dsj20 zone equates to the wanaea fimbriata zone of woollam & riding (1983) and riding & thomas (1992). the definition of the upper boundary of the dsj20 zone is given below, in the text pertaining to the dsj21 and dsj22 zones. dsj21, dsj22; lower–middle oxfordian (cordatum, densiplicatum zones) the name of the liesbergia scarburghensis zone of riding & thomas (1992), originally the acanthaulax senta zone of woollam & riding (1983), is changed to the trichodinium scarburghensis zone due to the name change of the index species (hedberg 1976; salvador 1994). the inception of forms belonging to the systematophora areolata group was used to redefine the lower boundary of this zone by riding & thomas (1992). the distribution of the systematophora areolata group in the united kingdom and the danish embayment appears to be palaeoenvironmentally controlled (poulsen 1992, 1996; riding & thomas 1992) and this group is therefore excluded from the revised definition, given below. dsj21; lower oxfordian (cordatum zone) the base of this zone is defined by the range base of leptodinium subtile (fig. 5). the top of the dsj21 zone is defined by the range tops of gonyaulacysta centriconnata, limbodinium absidatum and wanaea thysanota and the inception of endoscrinium luridum. the age of the zone corresponds to the cordatum zone; poulsen (1996) presented a detailed discussion of the dinoflagellate cyst zonations at the middle–upper jurassic boundary. dsj22; middle oxfordian (densiplicatum zone) the base of this zone is defined by the last occurrences of gonyaulacysta centriconnata, limbodinium absidatum and wanaea thysanota and the range base of endoscrinium luridum (fig. 5). the top of zone dsj22 is defined by the range top of the lithodinia caytonensis group, and the inceptions of glossodinium dimorphum and scriniodinium inritibile. dsj23–27; middle oxfordian – lowermost kimmeridgian (tenuiserratum–baylei zones) the gonyaulacysta jurassica – scriniodinium crystallinum dinoflagellate cyst zone of woollam & riding (1983) is herein divided into five dsj zones. the zone and its three subzones were defined by woollam & riding (1983) and emended by riding & thomas (1988, 1992); the upper boundary of the zone was emended by poulsen (1991). by introducing further subdivision, a redefinition of the zone and its constituent subzones is therefore required here (fig. 5). dsj23; middle oxfordian (tenuiserratum zone) the base of zone dsj23 is defined by the range top of the lithodinia caytonensis group and the inceptions of glossodinium dimorphum and scriniodinium inritibile. the top of zone dsj23 is defined by the last occurrences of rigaudella aemula and trichodinium scarburghensis. zone dsj23 is coeval with the lsc (c) subzone of riding & thomas (1992). dsj24; upper oxfordian (glosense zone) the base of the dsj24 zone is defined by the apparent extinctions of rigaudella aemula and trichodinium scarburghensis; the top is defined by the range top of compositosphaeridium polonicum. it is equivalent to the scr (a) subzone of riding & thomas (1992). dsj25; upper oxfordian (serratum, regulare zones) the base of the dsj25 zone is defined by the range top of compositosphaeridium polonicum. the top is defined by the last occurrence of gonyaulacysta jurassica subsp. adecta and the first appearances of dingodinium tuberosum and occisucysta balia. the dsj25 zone is equivalent to the scr (b) subzone of riding & thomas (1992). dsj26; upper oxfordian (rosenkrantzi zone) the base of the dsj26 zone is defined by the range top of gonyaulacysta jurassica subsp. adecta and the first appearances of dingodinium tuberosum and occisucysta balia. the top of the zone is defined by the last occurrence of ctenidodinium ornatum and the inception of senoniasphaera jurassica. the dsj26 zone equates to the scr (c) subzone of riding & thomas (1992). 126 dsj27; lower kimmeridgian (baylei zone) the base of the dsj27 zone is defined by the range top of ctenidodinium ornatum and the inception of senoniasphaera jurassica. the top of the zone is defined by the last occurrences of gonyaulacysta eisenackii, nannoceratopsis pellucida and scriniodinium crystallinum, and the first appearances of cribroperidinium? longicorne and oligosphaeridium patulum. the dsj27 zone equates to the scr (d) subzone of riding & thomas (1992). dsj28, dsj29; kimmeridgian (cymodoce–autissiodorensis zones) a bipartite subdivision of the endoscrinium luridum zone (formerly the scriniodinium luridum zone) of woollam & riding (1983) was introduced by nøhrhansen (1986); the zone was subsequently expanded and emended by riding & thomas (1988) and poulsen (1991). the definition of the lower boundary of the endoscrinium luridum zone of riding & thomas (1992), and thus the dsj28 zone, is here extended to include the last occurrence of gonyaulacysta eisenackii. the definitions of the top of zone dsj28 (or the stephanelytron scarburghense subzone of nøhr-hansen 1986) and the base and top of zone dsj29 (or the perisseiasphaeridium pannosum subzone) follow poulsen (1991). the definition of the top of zone dsj29 is emended to include the first appearances of egmontodinium polyplacophorum and systematophora daveyi (fig. 5). dsj30–34; lower–middle volgian (elegans–fittoni zones) the dsj30–34 zones correspond respectively to subzones a to e of the glossodinium dimorphum (gdi) zone of riding & thomas (1992). these units are coeval with subzones b and c of the glossodinium dimorphum – dingodinium tuberosum zone of woollam & riding (1983). dsj35–37; middle volgian (albani–anguiformis zones) the dsj35, dsj36 and dsj37 zones are the equivalent of the dichadogonyaulax culmula and dingodinium? spinosum zones of davey (1979). the latter are also equivalent to the dichadogonyaulax? pannea zone of riding & thomas (1992; formerly the ctenidodinium culmulum – ctenidodinium panneum zone of woollam & riding 1983). in this zonation for the entire british– danish area, the subdivision of the dichadogonyaulax culmula and dingodinium? spinosum zones of davey (1979, 1982) is used, and the dichadogonyaulax culmula zone is further subdivided into two zones (dsj35 and dsj36; fig. 5). it should be noted that the boundary between the dichadogonyaulax culmula zone (dsj36) and the dingodinium? spinosum zone (dsj37) is herein placed at the top of the glaucolithus zone, rather than at the top of the okusensis zone, where this boundary was placed by poulsen (1991, 1992, 1996). dsj35; middle volgian (albani zone) the base of the dsj35 zone is defined by the range base of consistent dichadogonyaulax culmula and the apparent extinction of occisucysta balia. the zone is the equivalent of the dpa (a) subzone of riding & thomas (1992). dsj36; middle volgian (glaucolithus zone) the base of the dsj36 zone is defined by the youngest occurrences of leptodinium subtile and scriniodinium inritibile. dsj37; middle volgian (okusensis–anguiformis zones) the base of the dsj37 zone is defined by the range base of dingodinium? spinosum. within this zone, or at the top, the range top of senoniasphaera jurassica is observed. this apparent extinction appears to occur in older strata in the british area than in the danish onshore area. dsj38–dsk2; middle volgian – upper ryazanian (oppressus–icenii zones) the pareodinia dasyforma and gochteodinia villosa zones of davey (1979, 1982) were subdivided into three subzones. the names of the egmontodinium expiratum, rotosphaeropsis thula, and endoscrinium pharo subzones of davey (1979, 1982) have been changed to follow the international guidelines whereby zonal names are changed in order to conform with any changes in the name of the index species (hedberg 1976; salvador 1994). the broadly equivalent gochteodinia villosa zone of woollam & riding (1983) and riding & thomas (1992) 127 was divided into subzones a to c by woollam & riding (1983) and riding & thomas (1992). the boundaries between subzones a to c of riding & thomas (1992) are different to those of the egmontodinium expiratum, rotosphaeropsis thula and endoscrinium pharo subzones of davey (1979, 1982) and adopted by poulsen (1991, 1992, 1996). the top of the gochteodinia villosa zone equivalent is herein regarded as being coincident with the top of the icenii zone. this is one chronozone lower than in the subdivisions of davey (1979, 1982), woollam & riding (1983), riding & thomas (1992) and poulsen (1996). the oppressus to icenii zone interval is herein subdivided into a four-fold subdivision, the dsj38, dsj39, dsk1 and dsk2 zones (fig. 5). 128 130 135 140 145 150 li th od in ia c ay to ne ns is ‘g ro up ’ c te ni do di ni um c on tin uu m d ic ha do go ny au la x se llw oo di i ‘ gr o up ’ g on ya ul ac ys ta ju ra ss ic a ad ec ta n an no ce ra to ps is p el lu ci da r ig au de lla a em ul a c te ni do di ni um o rn at um si rm io di ni um g ro ss i c om po si to sp ha er id iu m p ol on ic um g on ya ul ac ys ta e is en ac ki i st ep ha ne ly tr on s ca rb ur gh en se g on ya ul ac ys ta c en tr ic on na ta li m bo di ni um a bs id at um w an ae a th ys an ot a tr ic ho di ni um s ca rb ur gh en se sc rin io di ni um c ry st al lin um w an ae a fim br ia ta g on ya ul ac ys ta ju ra ss ic a ju ra ss ic a le pt od in iu m s ub til e en do sc rin iu m lu rid um sc rin io di ni um in rit ib ile g lo ss od in iu m d im or ph um a ld or fia d ic ty ot a py ru m o cc is uc ys ta b al ia d in go di ni um t ub er os um se no ni as ph ae ra ju ra ss ic a c rib ro pe rid in iu m ? lo ng ic or ne o lig os ph ae rid iu m p at ul um sy st em at op ho ra a re ol at a su bt ili sp ha er a? in af fe ct a su bt ili sp ha er a? p ae m in os a pe ris se ia sp ha er id iu m p an no su m d ic ha do go ny au la x pa nn ea eg m on to di ni um p ol yp la co ph or um sy st em at op ho ra d av ey i pe ri o d ep o ch a ge t im e in m a ju ra ss ic la te j ur as si c o xf o rd ia n k im m er id gi an v o lg ia n r ya za ni an v al . c re ta ce o us ea rl y c re ta ce o us eg m on to di ni um e xp ira tu m r ot os ph ae ro ps is t hu la m ud er on gi a si m pl ex k le ith ria sp ha er id iu m p or os is pi nu m d ic ha do go ny au la x cu lm ul a d in go di ni um ? sp in os um g oc ht eo di ni a vi llo sa ba tio la di ni um r ad ic ul at um o cc is uc ys ta s p. a o f d av ey 1 98 2 ps eu do ce ra tiu m p el lif er um dsj38; middle–upper volgian (oppressus, primitivus zones) the base of the dsj38 zone is defined by the youngest occurrences of dichadogonyaulax? pannea, dingodinium tuberosum and glossodinium dimorphum and the oldest consistent occurrence of gochteodinia villosa. this zone is therefore equivalent to subzone a of the gochteodinia villosa zone of riding & thomas (1992) and the lower part of the egmontodinium expiratum subzone of davey (1979, 1982). dsj39; upper volgian – lower ryazanian (preplicomphalus–runctoni zones) the base of the dsj39 zone is defined by the range top of egmontodinium polyplacophorum. this zone spans the jurassic–cretaceous boundary and is equiv129 lo ng -t er m e us ta ti c cu rv e af te r h aq e t al . ( 19 87 ) sh o rt -t er m e us ta ti c cu rv e af te r h aq e t al . ( 19 87 ) pa la eo te m pe ra tu re c ur ve ( °c ) se ale ve l c ur ve af te r h al la m ( 19 88 ) c hr o no zo ne s z o ne s (t hi s st ud y) d sz o ne s z o ne s, d en m ar k su bz o ne s, d en m ar k z o ne s, g re at b ri ta in su bz o ne s, g re at b ri ta in t. scarburghense s. crystallinum s. crystallinum not zoned t. scarburghense e. luridum e. luridum g. dimorphum g. dimorphum d. culmula d. spinosum d. spinosum d. culmula g. villosa g. villosa g. villosa d. pannea g. dimorphum e. luridum s. crystallinum t. scarburghense s. scarburghense p. pannosum dsj37 dsj39 paratollia albidum stenumphalus icenii kochi runctonii lamplughi preplicomphalus primitivus oppressus anguiformis kerberus okusensis glaucolithus albani fittoni rotunda pallasioides pectinatus hudlestoni wheatleyensis scitulus elegans autissiodorensis eudoxus mutabilis cymodoce baylei rosenkrantzi regulare serratum glosense tenuiserratum densiplicatum cordatum mariae w. fimbriata w. fimbriatadsj20 dsj21 dsj22 dsj23 dsj24 dsj26 dsj27 dsj28 dsj29 dsj30 dsj31 dsj32 dsj33 dsj34 r. thula e. pharo dsj35 dsj36 dsj38 dsk1 dsk2 130 135 140 145 150 t im e in m a dsj25 e. expiratum not zoned d c b a b a a b b c d e a a a a a a b b b b b b c c c c c d d e 20100 m100sea-level rise fig. 5. composite range chart for the key marker dinoflagellate cyst species in the upper jurassic – lowermost cretaceous of the subboreal region. alent to the majority of subzone b of the gochteodinia villosa zone of riding & thomas (1992) and the upper part of the egmontodinium expiratum subzone and the lower rotosphaeropsis thula subzone of davey (1979, 1982). dsk1; lower ryazanian (kochi zone) the top of the dsk1 zone is defined by the youngest occurrence of rotosphaeropsis thula. this zone is equivalent to the upper part of subzone b of the gochteodinia villosa zone of riding & thomas (1992) and the upper part of the rotosphaeropsis thula subzone of davey (1979, 1982). dsk2; upper ryazanian (icenii zone) the base of the dsk2 zone is defined by the youngest occurrence of rotosphaeropsis thula and the oldest appearance of occisucysta sp. a of davey (1982). the top of this zone is defined by the oldest appearance of pseudoceratium pelliferum. the range top of systematophora daveyi is present at the lower boundary of this zone in the danish basin and the danish north sea. in the united kingdom, this species occurs in younger strata. the dsk2 zone is equivalent to the lower part of subzone c of the gochteodinia villosa zone of riding & thomas (1992) and the lower part of the endoscrinium pharo subzone of davey (1979, 1982). the jurassic dinoflagellate cyst zonation as proxy for palaeoenvironmental changes the causal background for the spatial and temporal distributions of fossil and modern biotas is a function of the interplay of many factors. among these parameters, salinity and water temperatures have direct importance in dinoflagellate cyst distribution patterns, whereas changes in sea level have an indirect influence by changing coastal to shelf environments (wall et al. 1977; stover et al. 1996). before considering the palaeoecological implications of jurassic dinoflagellate distributions, it is instructive to briefly outline the established palaeoclimatic and palaeo-oceanographic scenario for jurassic times in subboreal northwest europe. jurassic sea-level change jurassic sea-level changes are well-established in the literature and several high-resolution sea-level curves have been published (e.g. haq et al. 1987; hallam 1988, 1992b). furthermore, stratigraphic analyses of sedimentary basins via the recognition of genetically-related stratal packages bounded by unconformities (sequences) have recently been developed by many workers such as partington et al. (1993), andsbjerg & dybkjær (2003, this volume) and nielsen (2003, this volume). jurassic palaeoclimates and ammonite provincialism jurassic palaeoclimates were characterised by weaker temperature gradients and more uniform seawater temperatures than at present (berggren & hollister 1974; gordon 1975). furthermore, the polar regions were significantly warmer than today without indications of continental glaciation (arkell 1956; donn 1982; valdes & sellwood 1992). the numerical general circulation model presented by valdes & sellwood (1992) may indicate somewhat lower palaeotemperatures for the kimmeridgian than for other intervals of the jurassic. however, the latter estimates appear to be inconsistent with other measurements and the geological record (see below). organisms demanding a warm climate lived closer to the polar regions than today, even when continent migration due to plate tectonics is taken into account. for example, hermatypic corals have been reported from the bathonian of east greenland (håkansson et al. 1971), a remarkable record as the northern proto-atlantic ocean was isolated from the tethys ocean during bajocian and bathonian times (birkelund & perch-nielsen 1976; callomon 1985, 2003, this volume). stahl & jordan (1969) measured palaeotemperatures between 18°c and 24°c from isotopic studies of ammonites from the german aalenian and an average palaeotemperature of 13°c (with a range of 8–22°c) from studies of septa in a callovian ammonite from poland. tan et al. (1970) determined palaeotemperatures of 19–25°c from early callovian belemnites from staffin bay, skye, north-west scotland. these authors also demonstrated middle callovian palaeotemperatures of 21–24°c using belemnites, although ammonites from the same horizons revealed palaeotemperatures of 28–30°c; tan et al. (1970) noted, however, that the middle callovian ammonites are enriched in 13c, thereby giv130 131 ing slightly higher calculated palaeotemperatures. measurements of palaeotemperature based on material originating from palaeoenvironments with lower than fully marine palaeosalinities may give erroneously high values, some 2–3°c higher than normal (donn 1982). the subboreal sea during the jurassic exhibited significant palaeosalinity fluctuations (hallam 1969; fürsich & sykes 1977), which may explain the slightly higher measurements of tan et al. (1970). isotopic studies on coccoliths from the kimmeridge clay of westbury, wiltshire, england revealed a palaeotemperature of 20–30°c throughout the early kimmeridgian (salinas 1984). although the jurassic was characterised by less pronounced global marine temperature gradients than those of the present-day, palaeoecological studies and palaeothermometry have demonstrated that jurassic palaeoclimatic variations were nevertheless significant. the palaeotemperature curve for the jurassic in figure 6 has been compiled by b. buchardt (table 2, appendix 1). it suggests that the early jurassic was characterised by a general cooling until the latest pliensbachian, followed by a rise which terminated at the aalenian–bajocian boundary. there followed a rapid palaeotemperature fall during the bajocian, succeeded by minor fluctuations for the remainder of the middle jurassic. the late jurassic was characterised by a steady temperature rise until the middle volgian, after which time there was a period of cooling to the jurassic–cretaceous boundary (fig. 6; appendix 1). enay (1980) and hallam (1983) stated that jurassic palaeoclimates had a relatively minor influence on jurassic provincialism, the biotic endemism observed being largely controlled by isolation related to plate tectonic events and sea-level changes. similarly, fürsich & sykes (1977) found that factors such as regional palaeotemperature and/or palaeosalinity gradients cannot alone explain the existence of the boreal realm durpalaeotemperature (°c) 242220181614121086 hettangian sinemurian pliensbachian toarcian aalenian bajocian bathonian callovian oxfordian volgian kimmeridgian polewards direction equatorial cosmopolitan dinoflagellate cyst flora boreal and tethyan dinoflagellate cyst provincialism boreal, australian and tethyan dinoflagellate cyst provincialism cosmopolitan dinoflagellate cyst flora mediterranean and euro-caucasian ammonite provincialism cosmopolitian ammonite fauna reduced boreal ammonite diversity boreal ammonite provincialism tethyan ammonite impoverishment and boreal ammonite isolation subboreal ammonite province and migration tethyan ammonite migration boreal ammonite invasions boreal ammonite expansion tethyan ammonite migration tethyan ammonite migration palaeodepositional temperature la te j ur as si c m id dl e ju ra ss ic ea rl y ju ra ss ic fig. 6. jurassic palaeotemperature curve, courtesy of b. buchardt (appendix 1). the heavy black line connects the average isotopic temperature for each stage, whereas the grey envelope shows the scatter of individual isotopic results. true palaeotemperatures are believed to fall inside the grey envelope. ing the oxfordian. the late jurassic palaeotemperature rises, however, appear to have controlled the migration of tethyan faunas into the boreal realm. furthermore, falling palaeotemperatures during the jurassic caused boreal faunal expansions or invasions into the tethyan realm (see below). ammonites were cosmopolitan during the earliest jurassic (hettangian and sinemurian), but in the early pliensbachian and throughout the remainder of the jurassic, ammonite provincialism was well-developed (hallam 1971, 1973; enay 1972, 1980; callomon 1985, 2003, this volume; cariou et al. 1985; page 2003, this volume; zeiss 2003, this volume). the mediterranean and euro-caucasian provinces were developed during the pliensbachian and by the close of the stage a boreal fauna made its first southerly incursion into the tethyan realm. the establishment of ammonite provincialism was coincident with falling palaeotemperatures and the following ‘boreal expansion’ corresponds to the early jurassic temperature minimum (fig. 6). during the toarcian to early bajocian period, boreal ammonite faunas became less diverse as they expanded into the tethyan realm; this phenomenon is related to rising palaeotemperatures. furthermore, doming in the central north sea interrupted the passage from the boreal ocean to the tethyan area (sellwood & hallam 1974; whiteman et al. 1975; eynon 1981; ziegler 1988; underhill & partington 1993). during the bathonian, tethyan ammonite migration northwards towards the boreal ocean coincided with the opening of the passage through the united kingdom and the north sea, together with rising palaeotemperatures. the boreal cardioceratid ammonite fauna developed during the late bathonian and callovian and several boreal ammonite ‘expansions’ have been recorded. these early incursions coincide with falling palaeotemperatures at this time. in the latest callovian to kimmeridgian, palaeotemperatures rose and tethyan ammonite faunas migrated into the boreal realm. several boreal ammonite ‘expansions’ also occurred at this time. although the average palaeotemperature rose during this period, the maximum temperature fell during the latest callovian – late oxfordian (fig. 6); this probably explains biotic migration from both the boreal and tethyan realms. from the late oxfordian to the early middle volgian, the palaeotemperature rose and thereafter fell. during the kimmeridgian, palaeotemperatures rose and a subboreal ammonite fauna was developed which migrated towards both the boreal and tethyan realms. finally, during the volgian, falling palaeotemperatures resulted in isolation of the boreal realm, and tethyan impoverishment was recorded by the ammonite faunas (hallam 1971, 1973; enay 1972, 1980; sykes & callomon 1979; imlay 1980; callomon & birkelund 1982; birkelund & callomon 1985; callomon 1985, 2003, this volume; cariou et al. 1985; wierzbowski 1989; page 2003, this volume; zeiss 2003, this volume). jurassic dinoflagellate palaeoecology jurassic dinoflagellate cyst provincialism is almost negligible compared to ammonite endemism (enay 1972, 1980; davies & norris 1981). globally, jurassic dinoflagellate cyst assemblages are of broadly similar generic/specific composition and a large number of species are cosmopolitan. furthermore, they exhibit marked similarities in stratigraphic ranges throughout the world (riding & ioannides 1996). it appears that during the early jurassic, dinoflagellate cyst assemblages throughout northwest europe were broadly non-provincial. however, during the aalenian pre-rift central north sea (ziegler 1988; underhill & partington 1993), a land barrier blocked north sea marine communications and the dinoflagel132 stage average range number of references# temperature °c data points °c* volgian no data kimmeridgian 18 15–20 22 1, 2, 3, 5 oxfordian 16 13–18 18 1, 2 callovian+ 17 14–20 18 8 callovian‡ 8 6–18 13 2, 3, 4, 7 bathonian 12 8–17 8 1, 4, 9, 10 bajocian 15 10–18 20 1, 2, 3, 4, 6 aalenian 22 17–24 17 2, 3, 4, 7, 9, 10 toarcian 18 12–23 39 1, 2, 3, 4, 9, 10 pliensbachian 15 10–18 21 1, 2, 3, 4, 9, 10 sinemurian 17 13–21 6 2 hettangian 19 15–23 5 2 table 2. oxygen isotope palaeotemperatures for the jurassic of northwest europe * isotope palaeoptemperatures calculated from oxygen isotope values according to the equation given by craig (1965). + data from scotland, uk. ‡ data from germany. # references: 1: bowen (1961a, b) 2: fritz (1964) 3: jordan & stahl (1970) 4: kunz (1973) 5: salinas (1984) 6: spaeth et al. (1971) 7: stahl & jordan (1969) 8: tan et al. (1970) 9: veizer (1974) 10: veizer & fritz (1976) late cyst assemblages were consequently differentiated into the boreal and tethyan provinces (smelror 1993; riding & ioannides 1996). this barrier became submerged by rising sea levels during the callovian, and late callovian and oxfordian dinoflagellate cyst assemblages are cosmopolitan throughout europe and adjacent regions (raynaud 1978; smelror 1993; riding & ioannides 1996). however, during the kimmeridgian and volgian stages, tethyan and boreal–australasian floras became established (helby et al. 1987; riding & ioannides 1996). the assemblage diversity in the northern hemisphere also followed general ecological principles, with higher diversities in equatorial regions. for example, the early toarcian dinoflagellate cyst assemblages of southern germany appear to be more diverse than coeval associations from the united kingdom (riding 1987; riding & ioannides 1996). other palaeoecological factors, however, clearly controlled dinoflagellate cyst diversity, as the late triassic and the toarcian–aalenian floras from the sverdrup basin, arctic canada are both significantly more diverse than their european counterparts (davies 1983; riding & ioannides 1996). dinoflagellate cyst associations were affected by a number of inter-related factors such as latitude, climate (temperature), water depth, marine currents, nutrient supply, inter-basin seaways, barriers, distance from shoreline and salinity. for much of the jurassic, dinoflagellate cyst assemblages in the subboreal realm appear to have been influenced by these parameters, particularly palaeotemperature/climate, palaeobathymetry (sealevel fluctuations) and seaways. the distribution patterns of late jurassic dinoflagellate cysts with low and high surface relief are related to cold and warm water, respectively, according to dörhöfer (1977). lentin & williams (1980) established that high relief cyst surfaces and processes are a flotation adaptation necessary in warm water (the specific gravity of water is 1.00000 at 4°c, falling to 0.99567 at 30°c). this palaeoecological trend in the jurassic was noted by wierzbowski & århus (1990), smelror (1993) and riding & ioannides (1996); these authors found that complex process-bearing forms are more common in the middle–upper jurassic of the tethyan realm compared to the boreal realm. the seasonal variation in day length is another important ecological factor which is rarely considered in studies of phytoplankton provincialism (reid 1973). figure 2 illustrates the position of the pliensbachian, toarcian and volgian north poles, in addition to the approximate geographical extent of the pliensbachian and volgian two-month polar night, giving seasonal variations in day length and sunlight intensity. such variations will have increased towards the poles, independent of climate and climatic zones. this must have been an important factor in a period during which heat-demanding plants and animals lived at higher latitudes compared to the present. the seasonal variations in day length and sunlight intensity would have had a major influence on phytoplankton during jurassic times and thereby also on higher links in the food chain (hallam 1973; reid 1973). the position of the two-month polar night moved during the jurassic from a position in the jurassic arctic sea near north-east siberia to a position between siberia and alaska (fig. 2). this may have reduced biotic migration between the proto-arctic ocean and the pacific, especially in the latest jurassic, thereby compounding increasing provincialism in the latest jurassic caused by falling temperatures in the kimmeridgian–volgian (figs 2–6). biozonation, palaeotemperature and sea-level changes in the late sinemurian, eustatic fluctuations appear to have been critical for dinoflagellate cyst floras. at this time, a sea-level rise (fig. 3) appears to have controlled the earliest occurrence of liasidium variabile; this species is considered to be related to deeper marine conditions. its occurrence may be related to migration as a consequence of the rising sea-level. the latest sinemurian sea-level fall (fig. 3) may have caused the apparent extinction of liasidium variabile. cooling during the earliest jurassic may explain the apparent earlier extinction of dapcodinium priscum in the danish basin than in the united kingdom (see dsj1–2 zones, fig. 3). furthermore, dapcodinium priscum ranges up to the lowermost toarcian in portugal (davies 1985). dapcodinium priscum was apparently a temperature-sensitive species which was confined to a relatively narrow palaeotemperature window. thus it continued to live under warmer conditions in portugal, although it disappeared from the subboreal province in the early sinemurian due to palaeoenvironmental factors (riding & thomas 1992). the middle–late pliensbachian sea-level highstand corresponds to the inception of the genus nannoceratopsis, as manifested by the first appearance of nannoceratopsis senex. during the late pliensbachian – middle toarcian sea-level rise, several dinoflagellate cyst species appeared including other species of nannoceratopsis (dsj5–6 zones, fig. 3). several of these forms 133 have apparent extinctions in the earliest toarcian, possibly caused by a fall in sea level (fig. 3), and the latest pliensbachian palaeotemperature minimum (fig. 6). the lower toarcian (dsj7–8 zones) is marked by widespread indications of restricted marine conditions resulting from a rapid sea-level rise (gorin & feistburkhardt 1990). the succeeding middle toarcian to earliest aalenian short-term sea-level changes are reflected in the united kingdom by a greater degree of zonal subdivision (dsj8–10) than in the danish basin where zones dsj9 and dsj10 cannot be differentiated (figs 3, 4). the inception of the marker species nannoceratopsis dictyambonis, which defines the boundary between the dsj9 and dsj10 zones, and the biostratigraphically important species nannoceratopsis ambonis, scriniocassis priscus and scriniocassis weberi, are not observed in the danish basin (poulsen 1992, 1996), although they are characteristic elements both in the united kingdom (woollam & riding 1983; riding 1987) and germany (prauss 1989). sea-level change in more proximal (i.e. shallow-water) parts of the north sea region may have been an important controlling factor, especially in the danish basin, where ammonites and ostracods are also absent in the toarcian (sorgenfrei & buch 1964; michelsen 1975; poulsen 1996). furthermore, the palaeotemperature rises influenced changes in the carbon reservoir and may have had a controlling effect on the palaeoenvironment (gorin & feist-burkhardt 1990). this effect may especially have influenced the environment in denmark during the toarcian. palaeotemperatures rose weakly during the aalenian, fell sharply in the bajocian and weakly in the bathonian – middle callovian before rising again in the latest callovian (fig. 6). this is reflected in the northward migration of tethyan floras from the aalenian to the bajocian. this migration ceased later in the bajocian and bathonian (see below). the middle jurassic thermal doming in the north sea started in the late toarcian and led to non-marine to marginal marine sedimentation in the north sea area (underhill & partington 1993; nielsen 2003, this volume). the dinoflagellate cyst record is interrupted in denmark above the dsj10 zone. in the united kingdom, the zonation may be interpreted as an interaction between variations in palaeotemperature and sea level. the nannoceratopsis gracilis zone (dsj11–12 zones) broadly corresponds to the middle aalenian – early bajocian sea-level rise (fig. 4). the following sea-level maximum and fall (fig. 4) correlates to the dsj13–16 zones with the dsj14–15 zonal boundary corresponding to the middle bathonian shortterm sea-level minimum (fig. 4). the dsj17–20 zonal boundaries do not appear to have been related to known sea-level changes (fig. 4). fenton & fisher (1978) demonstrated that the bathonian transgressive phase controlled dinoflagellate cyst migrations from germany and southern england to eastern england and the central graben in the north sea. these authors also compared the aspidoides zone in the united kingdom, france, east greenland and spain and found that although certain species are consistently present, there are significant compositional differences in these assemblages. fenton & fisher (1978) noted that species of ctenidodinium in the united kingdom were more common south of the london– brabrant massif than to the north, with c. combazii and c. ornatum dominant, and that c. combazii was not recorded north of the massif. in the aquitane basin, south-west france, the assemblages comprise approximately 90% c. combazii, whereas to the north, in the paris basin near poitiers, the assemblages are dominated by acritarchs with only relatively rare representatives of ctenidodinium (including c. combazii) and lithodinia (valensi 1953; dupin 1965; fenton & fisher 1978). in eastern england, bathonian dinoflagellate cyst assemblages are dominated by species of chytroeisphaeridia, ctenidodinium, lithodinia and sentusidinium. fenton & fisher (1978) concluded that highly sculptured species were common in the southern region, whereas the boreal assemblages include many smooth forms and that the callovian transgression resulted in a northern spread of sculptured forms (fig. 7). investigations of the bathonian–callovian from northwest germany (gocht 1970; fenton 1981), the netherlands (herngreen & de boer 1978) and the united kingdom (sarjeant 1959, 1976; neves & selley 1975; lam & porter 1977; muir & sarjeant 1978; fenton et al. 1980; woollam 1980, 1982; riding 1982; riding et al. 1991) have identified significant differences between the tethyan ctenidodinium-dominated assemblages and their boreal counterparts. the latter include shallowwater, proximal assemblages with ctenidodinium continuum, c. ornatum, dichadogonyaulax sellwoodii, lithodinia spp., nannoceratopsis spp., pareodinia spp. and valensiella ovula. it appears that the tethyan floras migrated northwards from southern england during the latest bajocian – earliest bathonian. a mixed tethyan–boreal flora is recognised further north in oxfordshire and cambridgeshire, central england, in the upper bathonian – lower callovian and in scotland in the middle callovian. the northwards migration of ctenidodinium combazii and related species appears to have been in response to warming during the late 134 bajocian – middle bathonian (figs 6, 7). this northerly incursion of tethyan floras ceased in the middle bathonian and a mixed flora is present in central and northern england; this event coincides with falling palaeotemperatures as well as falling sea-level in the bajocian – middle callovian. the middle jurassic floras with common nannoceratopsis gracilis and valensiella ovula may be indicative of shallow-water, relatively nearshore settings, rather than these associations having boreal affinities. this assemblage type was displaced by a more diverse tethyan flora due to rising sea-levels in the bajocian (fig. 4). nannoceratopsis gracilis has been described as a euryhaline species, tolerant of reduced palaeosalinities (fisher 1980; bucefalo palliani & riding 1997). it was described by fensome (1979) as a dominant species in a restricted marine palaeoenvironment (see also surlyk et al. 1973). this taxon has been reported from shallow-water marine to deltaic swamp facies of yorkshire by hancock & fisher (1981). davey (1979), however, described n. gracilis as being abundant in normal marine sediments together with valensiella ovula and related forms. valensiella ovula was deemed to be a boreal species by norris (1975), although it has been reported from bulgaria (dodekova 1975) which was within the tethyan realm. furthermore, this species has not been recorded from northern north america. in east greenland, it was recorded by fensome (1979) in a shallow shelf palaeoenvironment (surlyk et al. 1981). palmer & jenkyns (1975) described the bathonian palaeoenvironment in the area north of the london– brabrant massif in england as fresh to brackish water lagoons (the oxfordshire shallows). towards the south, these lagoons became gradually more marine and were replaced by fully marine carbonate shelf palaeoenvironments in dorset, southern england. not only did the 135 500 km ? ? ? ? 40°n 0° 10°e10°w land paralic/deltaic siliciclastics coastline probable coastline speculative northward migration of tethyan dinoflagellate cyst flora middle callovian late bathonian middle bathonian early bathonian fig. 7. palaeogeographical map of the north sea area during the middle jurassic (modified slightly from callomon 2003, this volume) showing the progressive northwards migration of tethyan dinoflagellate cysts. facies change in relation to palaeotemperature variations, but also from non-marine to marginal marine and further to fully marine. the oxfordian and kimmeridgian stages were characterised by rising palaeotemperatures and relatively minor, short-term, sea-level changes (figs 5, 6). the dinoflagellate cyst zonation appears to be a reflection of both of these factors. provincialism was developed in the kimmeridgian–volgian interval. falling palaeotemperatures and repeated, short-term eustatic changes in the volgian appear to be expressed in the zonation. in the danish basin, lowermost middle oxfordian marine deposits succeed fluviatile middle jurassic deposits (poulsen 1992, 1996; nielsen 2003, this volume). at this time, the distribution of dinoflagellate cysts became uniform over the entire british–danish area (poulsen 1996). raynaud (1978) compared the callovian to volgian (tithonian) dinoflagellate cyst record in the united kingdom and the north sea and found broad similarities between the areas, although quantitative differences were discerned. these differences were most pronounced in the kimmeridgian to volgian (tithonian) interval. according to raynaud (1978), late callovian – early oxfordian floras were uniform throughout arctic canada, east greenland, europe and svalbard (beju 1971; johnson & hills 1973; tan & hills 1978; bjærke 1980; poulsen 1984). the rising palaeotemperatures during the late callovian and oxfordian, together with the marine connection between the boreal and tethyan oceans, appear to have created a cosmopolitan floral province during this interval in the northern hemisphere. the majority of upper jurassic dinoflagellate cyst zonal boundaries were probably influenced by late jurassic eustatic oscillations (fig. 5). for example, the dsj28–29 zonal boundary coincides with the short-term sea-level fall following the mid-kimmeridgian maximum. in contrast, the dsj29–30 zonal boundary (the top of the endoscrinium luridum zone) corresponds approximately to the sea-level maximum in the latest kimmeridgian. similarly, many of the boundaries of the dsj30–38 zones correlate broadly with sea-level minima or maxima of the short-term eustatic curve of haq et al. (1987; fig. 5). the upper boundary of the glossodinium dimorphum zone (the dsj34–35 zonal boundary) approximates to a short-term sea-level maximum. the boundary between the dingodinium? spinosum and the gochteodinia villosa zones (dsj37–38) coincides with the short-term sea-level maximum at the close of the volgian (fig. 5). most of the zonal boundaries that correlate broadly with eustatic events have been recorded slightly later than the sea-level minima and maxima, and may be related to shifts in sedimentary facies from clay to sand (e.g. from the kimmeridge clay to portland sand formations or from the børglum to frederikshavn formations in dorset and jylland, respectively). kimmeridgian – early volgian dinoflagellate cyst assemblages are rich; the high diversities reflect correspondingly high sea levels. rich nearshore assemblages of latest kimmeridgian – earliest volgian age have been recorded in denmark at the margin of the baltic shield (poulsen 1996), indicating the maximum extent of the børglum formation (kimmeridge clay formation equivalent) over the baltic shield. marine conditions existed continuously in denmark during the volgian to ryazanian, although non-marine phases occurred near the margin of the baltic shield (poulsen 1996). poulsen (1992; 1996) considered volgian and ryazanian palaeoenvironments and identified floral events in denmark which were thought to reflect eustatic changes. these events are more readily identified in shallow shelf deposits than in the deeper water succession of the central graben. low diversity dinoflagellate cyst assemblages in the lower part of the dsj39 zone were recorded in denmark by poulsen (1996), who related them to eustatic rise and fall during the latest jurassic. the rich assemblages within the upper part of the dsj39 zone correspond to the sea-level rise at the jurassic–cretaceous boundary (poulsen 1996). less diverse assemblages recorded from the lowermost cretaceous (dsk1–2 zones) are related to successive marine highstands and lowstands (poulsen 1996). the richer assemblages from the overlying pseudoceratium pelliferum subzone have been related to the succeeding sea-level rise (poulsen 1996). the lowermost cretaceous of denmark is characterised by rich dinoflagellate cyst assemblages which include a variety of pareodiniacean dinoflagellate cysts, thereby suggesting affinities to the boreal realm (poulsen 1996). this corresponds to falling palaeotemperatures close to the jurassic–cretaceous boundary (fig. 6). late ryazanian assemblages are characterised by a decrease in the abundance and diversity of dinoflagellate cysts in the dsk2 zone and younger strata. lott et al. (1989) also noted this phenomenon and related the differences to a latest ryazanian transgression. it is believed, therefore, that the dinoflagellate cyst diversity and abundance fluctuations correspond well to both the sealevel changes at the jurassic–cretaceous boundary proposed by haq et al. (1987), and to the model of rawson & riley (1982). 136 137 conclusions the stepwise evolution of dinoflagellate cyst assemblages, as defined by inceptions and apparent extinctions, appears to have been largely controlled by sea-level changes, particularly during intervals with significant short-term eustatic fluctuations. in times of less pronounced, or more long-term sea-level changes, fluctuations in the marine palaeotemperature seem to have influenced dinoflagellate evolution. differences in the ranges of certain taxa between denmark and the united kingdom are ascribed to minor palaeotemperature differences. the early jurassic was characterised by a general cooling until the late pliensbachian. the zonation can be related to sea-level changes, although the slightly different ranges of some of the index species in denmark compared to the united kingdom can be explained by minor palaeotemperature differences. the late toarcian – aalenian thermal doming event in the north sea resulted in non-marine to marginal marine sedimentation during late aalenian – bathonian times in the north sea and denmark, such that the dinoflagellate cyst zonation is often difficult to apply in this stratigraphic interval. in the united kingdom, however, the zonation can be interpreted to reflect the interaction between the general falling palaeotemperature and sea-level changes. the oxfordian–kimmeridgian was characterised by warming and short-term sea-level changes. the dinoflagellate cyst zonation appears to record both these factors, sometimes together, sometimes singly. the falling palaeotemperature and the short-term sea-level changes in the volgian are expressed in the zonation, in addition to increased provincialism. comparison of the zonation scheme with the shortterm sea-level curve demonstrates that the ds zones in the subboreal province (subzones in the earlier zonation scheme for the british–danish area, see figs 3–5) often correlate with the short-term sea-level minima of haq et al. (1987). however, many of the zonal boundaries in the earlier british–danish zonation scheme correlate with short-term sea-level maxima on the haq et al. (1987) sea-level curve. hallam (1983) stated that jurassic palaeoclimates had only a minor influence on jurassic provincialism, and that any biotic endemism was largely controlled by plate tectonic events and sea-level changes. however, increases in jurassic palaeotemperatures allied to palaeooceanographic factors appear to have controlled the migration of tethyan biotas northward into the boreal realm. furthermore, falling jurassic palaeotemperatures caused boreal spreads or invasions southwards into the tethyan realm. acknowledgements we wish to express our sincere thanks to colleagues at our respective institutes for their help and interest, and to the referees, roger j. davey and don g. benson, for their constructive reviews. j.b.r. publishes with the permission of the british geological survey. references including references cited in appendix 1 andrews, i.j., long, d., richards, p.c., thomson, a.r., brown, s., chesher, j.a. & mccormac, m. 1990: united kingdom offshore regional report: the geology of the moray firth, 106 pp. london: her majesty’s stationery office for the british geological survey. andsbjerg, j. & dybkjær, k. 2003: sequence stratigraphy of the jurassic of the danish central graben. in: ineson, j.r. & surlyk, f. 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(ed.): triassic–jurassic rifting; continental breakup and the origin of the atlantic ocean and passive margins. developments in geotectonics 22, 711–755. amsterdam: elsevier. manuscript received 9 june 1997; revision accepted 7 july 1999. 143 appendix 1: oxygen isotope palaeotemperatures from the jurassic in northwest europe (by bjørn buchardt) the oxygen isotope palaeotemperature curve presented in figure 6 of this paper was first constructed as part of a basin modelling project (b. buchardt in: yükler & speers 1988); note that the term palaeotemperature is used here to refer to the temperature registered by organisms living at the time of deposition (epstein et al. 1951; epstein & lowenstam 1953). the curve was compiled from previously published data, predominantly from older literature. the data reflect the state-of-the-art in isotope analyses in the 1960s and 1970s, at which time palaeotemperature studies were mainly based on macrofossils collected at outcrop. a brief description is given here of the principles behind, and the background of, the palaeotemperature curve. an oxygen isotope palaeotemperature is a numerical value calculated from the oxygen isotopic composition of a carbonate shell according to the equations formulated by epstein et al. (1951) and craig (1965) for calcite and horibe & oba (1972) for aragonite, and expressed in degrees celsius (°c). interpretation of this value as a ‘true’ palaeotemperature is limited by several factors such as: (1) vital effects of the actual organisms (shell carbonate precipitated out of equilibrium with the surrounding water), (2) seasonal-selective shell formation, (3) variations in the oxygen isotope composition of the ambient water, and (4) postdepositional alteration of the shell. of these factors, the last is deemed to be the most important. vital effects are well-known among large groups of calcareous-shelled organisms that should be avoided for palaeotemperature work. however, molluscs are known to exhibit vital effects to only a small degree (epstein et al. 1951, fritz & poplawski 1974, buchardt & weiner 1988) and are eminently suitable for palaeotemperature studies. among the molluscs, belemnites and ammonites are believed to have had a nektonic to nektobenthonic habitat, where seasonal variations in seawater temperatures probably were of less importance. they are therefore more suited for palaeotemperature work than, for example oysters, which lived closer to the coast, in waters probably affected by seasonality. calculation of isotopic palaeotemperatures presumes knowledge of isotopic compositions of both shell carbonate and ambient seawater. as the last parameter cannot be measured directly, indirect assessments are necessary. the world’s oceans can be viewed as a homogeneous reservoir with a constant oxygen isotope composition in space, but not in time. the amount of 18o-depleted water bound in glacial ice affects the isotopic composition of the oceans globally. oceans today have an oxygen isotope composition of 0‰ on the ä-scale relative to the smow standard (standard mean ocean water). during preglacial times, this value was lowered by at least 1‰ (shackleton & kennett 1975), and consequently an average seawater ä18o-value of -1‰ has been applied in the present calculations. this correction amounts to a calculated temperature difference of approximately 4°c (craig 1965). unfortunately, seawater oxygen isotope homogeneity is also affected by any mixing with freshwater from rivers and streams discharging into the sea. river water is normally depleted in 18o to a highly variable degree. each estuary system thus has its own characteristic salinity/ä18o relationship (mook 1968; israelson et al. 1994). during the jurassic period in northwest europe, palaeo-oceanographic conditions were complex, and local isotopic effects from river discharge were probably common (salinas 1984; nøhr-hansen 1986). however, by mainly using nektobenthonic organisms such as belemnites and ammonites, these effects should be minimised. isotopic palaeotemperatures calculated from analyses of belemnites have been claimed by several authors to be unreliable (longinelli 1969; spaeth et al. 1971). this critique has focused on possible postdepositional alteration of belemnite guards (stahl & jordan 1969; spaeth et al. 1971; veizer 1974). the controversy has never been resolved, and belemnite oxygen isotope palaeotemperatures should only be applied when the volume of belemnite data is large enough to allow cross-checks between different areas and lithologies. stahl & jordan (1969) pointed out that the metastable aragonite phase in fossils is more reliable for isotopic studies than calcite because recrystallization processes invariably lead to the modification of aragonite to calcite and therefore can easily be identified. well-preserved aragonite in fossil shells can thus be taken as indication of minimal recrystallization and therefore of an unmodified isotopic signal. therefore, aragonite from ammonites can be viewed as a more reliable source for oxygen isotope palaeotemperatures than calcite from belemnites. however, the number of jurassic ammonite analyses reported in the literature are few, and it is not possible to compile a palaeotemperature curve solely from published ammonite data. consequently, data from both belemnites and ammonites has been compiled, although belemnite data are excluded where differences in isotopic composition between ammonites and belemnites are significant. oxygen isotope data from jurassic fossils in northwest europe (e.g. britain, germany and poland) have been published by several authors (bowen 1961a, b; fritz 1964; longinelli 1969; stahl & jordan 1969; tan et al. 1970; jordan & stahl 1971; kunz 1973; tan & hudson 1974; veizer 1974; veizer & fritz 1976; salinas 1984). these reports form the database for the oxygen isotope palaeotemperature curve presented in figures 3–6 of this paper. only data from ammonites and belemnites have been included. in most cases, stratigraphic resolution of the data is possible to zonal level. the curve is constructed from average values (solid line) and entire ranges (shaded area) of isotopic results for each stratigraphic 144 level. in table 2, the oxygen isotope palaeotemperatures have been calculated for each stage as an average and a range. the isotope palaeotemperature curve as shown in figures 3–6 is one method of displaying an oxygen isotope dataset for a heterogeneous selection of ammonites and belemnites from the jurassic deposits of northwest europe. the fact that the calculated palaeotemperatures fall within a credible range (8–26°c), supports the validity of the data and the compilation of information from different geographical areas. the only major discrepancy in the dataset is in the callovian, where extremely low values (minimum 8°c) in germany and poland (jordan & stahl 1971; kunz 1973) contrast with results from scotland (maximum 25°c; tan et al. 1970). in this study, the scottish results are excluded because they probably reflect the influence of 18o-depleted freshwater in a large estuarine system (tan & hudson 1974). the curve demonstrates isotopic variations which probably represent cold seawater conditions during the pliensbachian and the bajocian–callovian in northwest europe. these cold intervals are in contrast to warmer seawater conditions during the sinemurian, the toarcian–aalenian and the oxfordian–kimmeridgian. the maximum palaeotemperatures occurred at the early–middle jurassic transition and during the early kimmeridgian. geological survey of denmark and greenland bulletin 11, 101-114 101 207pb-206pb dating of magnetite, monazite and allanite in the central and northern nagssugtoqidian orogen, west greenland henrik stendal, karsten secher and robert frei pb-isotopic data for magnetite from amphibolites in the nagssugtoqidian orogen, central west greenland, have been used to trace their source characteristics and the timing of metamorphism. analyses of the magnetite define a pb-pb isochron age of 1726 ± 7 ma. the magnetite is metamorphic in origin, and the 1726 ma age is interpreted as a cooling age through the closing temperature of magnetite at ~600°c. some of the amphibolites in this study come from the naternaq supracrustal rocks in the northern nagssugtoqidian orogen, which host the naternaq sulphide deposit and may be part of the nordre strømfjord supracrustal suite, which was deposited at around 1950 ma ago. pb-isotopic signatures of magnetite from the arfersiorfik quartz diorite in the central nagssugtoqidian orogen are compatible with published whole-rock pb-isotopic data from this suite; previous work has shown that it is a product of subduction-related calc-alkaline magmatism between 1920 and 1870 ma. intrusion of pegmatites occurred at around 1800 ma in both the central and the northern parts of the orogen. pegmatite ages have been determined by pb stepwise leaching analyses of allanite and monazite, and source characteristics of pb point to an origin of the pegmatites by melting of the surrounding late archaean and palaeoproterozoic country rocks. hydrothermal activity took place after pegmatite emplacement and continued below the closure temperature of magnetite at 1800– 1650 ma. because of the relatively inert and refractory nature of magnetite, pb-isotopic measurements from this mineral may be of help to understand the metamorphic evolution of geologically complex terrains. keywords: pb isotopes, magnetite, nagssugtoqidian orogen, palaeoproterozoic, pegmatites, pb stepwise leaching, supracrustal rocks ______________________________________________________________________________________________________________________________________________________________________________ h.s. & k.s., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: hst@geus.dk r.f., geological institute, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. as part of the research programme 2000–2003 in the nagssugtoqidian orogen of west greenland by the geological survey of denmark and greenland (geus), an assessment was made of the mineral resource potential of the region between maniitsoq (sukkertoppen; 66°n) and the southern part of nuussuaq (70°15′n; stendal et al. 2004). the present study comprises pb-isotopic analyses of magnetite from amphibolites, hydrothermally altered amphibolites, the arfersiorfik quartz diorite (see below), skarn, ultramafic rocks and pegmatites. magnetite was chosen as a medium for analysis because of its abundance in amphibolites, even though the concentration of pb in magnetite is generally low. in addition, an attempt was made to date monazite and allanite from pegmatites by the pb stepwise leaching (pbsl) technique (frei & kamber 1995). the pb-isotopic study of the amphibolites covers the attu, kangaatsiaq and qasigiannguit regions (fig. 1). the analysed pegmatites are from the nordre © geus, 2006. geological survey of denmark and greenland bulletin 11, 101–114. available at: www.geus.dk/publications/bull 102 strømfjord (nassuttooq), attu and qasigiannguit areas. the aims of the study were (1) to use pb-isotopic signatures of magnetite in an attempt to outline the metamorphic history of the region; (2) to characterise the hydrothermal overprinting in terms of its timing and pb source; and (3) to place the results within the evolutionary frame of the nagssuqtoqidian orogen. regional geological setting the study region comprises the palaeoproterozoic nagssugtoqidian orogen, a major collisional belt situated just north of the north atlantic craton (van gool et al. 2002), as well as the southernmost part of the contemporaneous rinkian fold belt (garde & steenfelt 1999; connelly et al. 2006). most of the region consists of archaean orthogneisses, variably reworked during the nagssugtoqidian and rinkian tectonothermal events. several thin belts of supracrustal rocks occur within the reworked archaean gneiss terrain of the nagssugtoqidian orogen (fig. 1). granitoid rocks and numerous pegmatites intrude the gneisses. formations of palaeoproterozoic age are limited to the sisimiut igneous suite, arfersiorfik quartz diorite, and minor supracrustal sequences including the naternaq supracrustal belt (connelly et al. 2000; thrane & connelly 2006, this volume). the metamorphic grade is amphibolite facies, except for an area south of ataneq in the south-western part of the northern nagssugtoqidian orogen (nno; fig. 1) and in most of the central nagssugtoqidian orogen (cno), where granulite facies rocks predominate. the gneisses are intensely folded and show a general e–w to ne–sw strike. deformation of the archaean gneisses in the nno greenland inland ice greenland canada 51° us sui tnordre strømfjord arfersiorfik aasiaat qasigiannguit kangaatsiaq attu sisimiut kangerlussuaq naternaq n ag ss u gt o q id ia n o ro ge n sn o c n o nssz itz n n o inland ice 0 50 km t t t t t t ttt disko bu gt 68° jakobshavn isfjord kangersuneq ataneq quaternary surficial deposits basalt metasedimentary rocks palaeoproterozoic palaeogene quaternary sisimiut charnockite arfersiorfik quartz diorite archaean, variably reworked granodioritic and granitic gneiss orthogneiss dioritic gneiss metasedimentary rocks amphibolite (including proterozoic components) t t thrust 457785457785 481049481049 481058481058 484883484883 484890484890 446633446633 446632446632 446626446626 481087481087 446603-04446603-04 44662344662320017362001736 485178485178 485179485179485193485193 223736223736 225348225348 223746223746 481070481070 fig. 1. geological map of central west greenland, modified from van gool et al. (2002). red dots with numbers refer to samples analysed. cno, central nagssugtoqidian orogen; nno, northern nagssugtoqidian orogen; sno, southern nagssugtoqidian orogen; itz, ikertôq thrust zone; nssz, nordre strømfjord shear zone. 103 decreases gradually northwards, from high-strain to more open structures in the archaean rocks. steeply and shallowly dipping shear and fault zones are common in contact zones between different rock types. major fault and shear zones generally strike nne–ne. the gneisses of the nno are late archaean, with ages between 2870 and 2700 ma (kalsbeek & nutman 1996; connelly & mengel 2000; thrane & connelly 2006, this volume). however, older rocks with ages ~3150 ma appear to be present in the attu area (stendal et al. 2006, this volume). only a few younger palaeoproterozoic ages have been obtained from the nno, including an undeformed pegmatite between attu and aasiaat with an intrusion age of about 1790 ma (connelly & mengel 2000). the geological history of the study area can be summarised as follows (van gool et al. 2002): • deposition of supracrustal rocks: 2200–1950 ma • continental breakup – the kangâmiut dyke swarm: 2040 ma • drifting – sediment deposition (supracrustal rocks) in the nordre strømfjord area: 2000–1920 ma • subduction – calc-alkaline magmatism, giving rise to the sisimiut and arfersiorfik igneous suites: 1920–1870 ma • peak metamorphism during collision (d1 and d2): 1860–1840 ma • large scale folding (d3): ~1825 ma • shearing in steep belts (d4): ~1775 ma • slow cooling following the shearing, with closing temperature of rutile (420°c) at around 1670 ma (connelly et al. 2000). based on 40ar-39ar and u-pb data for several minerals, willigers et al. (2001) estimated cooling temperatures around 500°c at ~1700 ma, 410°c at ~1640 ma, and 200°c at ~1400 ma. previous investigations the geological survey, university research groups as well as exploration companies have been working in central west greenland for decades and have collected significant amounts of data on the mineral potential of the region (stendal et al. 2002, 2004; stendal & schønwandt 2003; schjøth & steenfelt 2004; steenfelt et al. 2004). whole-rock pb-pb, rb-sr and sm-nd isotopic data from the study area have been presented by kalsbeek et al. (1984, 1987, 1988), taylor & kalsbeek (1990) and whitehouse et al. (1998), while e.g. kalsbeek & nutman (1996), connelly & mengel (2000), connelly et al. (2000), hollis et al. (2006, this volume) and thrane & connelly (2006, this volume) have published zircon u-pb geochronological data. pb-isotopic work has been carried out on sulphide separates, mainly pyrite, from a mineralisation in the disko bugt region north of the study area (stendal 1998). in the latter study, two distinct mineralisation types in the archaean rocks were identified – a syngenetic, and at least one epigenetic type of ore formation. pb-isotopic data of sulphides from proterozoic rocks yield a well-defined linear trend in a pb-pb isochron diagram, with a slope corresponding to an age of ~1900 ma, and indicative of a primitive (i.e. low µ) source character of pb in that mineralisation. local geology and descriptions of the investigated rocks during this study pb-isotopic analyses were carried out on magnetite from amphibolite (four samples), banded iron formation (one sample), hydrothermally altered amphibolite and calc-silicate skarn rock (four samples), the arfersiorfik quartz diorite (three samples), magnetite skarn (one sample), ultramafic rock (one sample) and pegmatite (one sample). in addition, one amphibolite, one altered amphibolite and one sample of banded iron formation were subjected to pbsl procedures (frei & kamber 1995), and allanite (two samples) and monazite (three samples) from pegmatites were analysed by pbsl in an attempt to date their emplacement. brief descriptions of the investigated rocks are given below. amphibolitic rocks amphibolites occur together with garnet-mica schists/ gneisses in supracrustal sequences, interlayered with orthogneiss. some amphibolite layers in the gneiss terrain can be followed continuously along strike for up to tens of kilometres. they are heterogeneous in composition. they are found in three associations: (1) rusty weathering, medium-grained garnet amphibolite layers (c. 0.5 m thick) folded together with the orthogneisses, (2) dark, fine-grained amphibolite, occurring as layers up to 10 m thick, and (3) medium-grained, commonly garnetiferous, layered amphibolite. layered amphibolites are the most common, and occur as units up to 200 m thick, although layers only 10–20 m thick are more common. the three different types of amphibolite form separate outcrops and do not occur together. the pb-isotopic analyses reported in this paper refer to magnetite from the layered amphibolites (type 3). 104 the supracrustal sequences consist of garnet-mica schist/gneiss, together with amphibolite (fig. 2a) and rusty weathering layers c. 1 m thick of quartz-garnet rich gneiss with some iron sulphides (1 vol.%). within the layered amphibolite sequences, magnetite-bearing horizons 1–10 m thick occur. the magnetite occurs in laminae 1–10 mm thick, alternating with quartz-feldspar laminae of the same thickness. alteration is common within the layered amphibolites. altered amphibolite some amphibolites have been hydrothermally altered and sulphide mineralised and may contain calc-silicates. this type of amphibolite is dominated by layered garnet-rich amphibolite, interlayered with magnetite-bearing and rusty weathering layers, with disseminated pyrite (fig. 2b). the layers are generally 0.5–2 m thick; in some cases layered amphibolite is intercalated with rusty weathering layers 10–30 cm thick, consisting of quartz-bearing mica schist with iron sulphides and staining of malachite. within the altered amphibolite calc-silicate minerals are found in zones 1–2 m thick or as smaller lenses, comprising hornblende, diopside, garnet and magnetite. a b fig. 2. amphibolite (a) and hydrothermally altered amphibolite (b) from the attu area. 105 banded iron formation at naternaq the supracrustal belt at naternaq (fig. 1) consists of metavolcanic rocks interlayered with pelitic and psammitic schists and gneisses, marble units, exhalites and chert-rich layers with minor quartzite and banded iron formation. in total, these units define a supracrustal sequence up to 3 km thick, which is folded into a major shallowly dipping wsw-trending antiform. the supracrustal sequence can be traced for approximately 30 km along strike and is intruded by granite sheets and pegmatite veins. østergaard et al. (2002) and stendal et al. (2002) give detailed descriptions of the stratigraphy of the supracrustal rocks. the banded iron formation (fig. 3) occurs locally associated with the amphibolite in zones composed of centimetre-thick layers of magnetite and siderite quartz and calcsilicates. the depositional environment is of a sedimentary type comprising true sediments, submarine volcanic rocks and exhalites. a range of variably altered conformable horizons of very fine-grained siliceous and sulphide rich lithologies associated with either amphibolite or marble are interpreted as volcanogenic-exhalitic rocks (østergaard et al. 2002; stendal et al. 2002). arfersiorfik quartz diorite the arfersiorfik quartz diorite (kalsbeek et al. 1987) is located in the eastern part of the fjord arfersiorfik (fig. 1) and covers several hundreds of square kilometres. within the quartz diorite body, magnetite occurs in hornblenderich rocks (hornblende, quartz, feldspar, and chlorite) and often shows paragenetic relation with iron sulphides (predominantly pyrrhotite). the arfersiorfik quartz diorite was emplaced in the period 1920–1870 ma (kalsbeek et al. 1987; connelly et. al. 2000). ultramafic rocks near qasigiannguit an ultramafic body 300 × 300 m large is located on the north side of kangersuneq, forming rusty weathered hills. on its eastern and western sides the ultramafic body is bounded by fault zones, invaded by pegmatites. on its northern and southern sides it is bordered by amphibolite and garnet amphibolite, respectively. because of the penetrative weathering it is difficult to sample fresh material from the ultramafic body. in its centre, an intensely rusty weathered and eroded ‘joint’ zone cuts the ultramafic rocks. this contains 1–10 vol.% magnetite. magnetite-rich skarn at qasigiannguit near qasigiannguit a skarn rock is found in the contact zone striking 66° and dipping 77°se between mica schist and quartzite and a marble-calc-silicate sequence. it comprises magnetite skarn (0.5 m thick) in close contact with the mica schist and quartzite. towards the south-east the magnetite skarn is followed by alternating layers of calcsilicate rocks and marble (including a quartzitic, sulphiderich layer), followed by a pegmatite body. fig. 3. banded iron formation sequence from the naternaq area. 106 a b fig. 4. pegmatites and minerals analysed. a: pink discordant pegmatite and allanite (inset) from the attu area. b: white pegmatite and monazite (inset) from the nordre strømfjord (nassuttooq) area. 107 pegmatites pink pegmatites. throughout the study area, especially in the outer fjord zone from south of attu northward to kangaatsiaq, the country rocks are intruded by granite and by pink pegmatites with alkali feldspar crystals commonly more than 10 cm in size. the pegmatites occur mostly as discordant decimetreto metre-thick bodies within the gneisses, at contacts between major lithological units, and within supracrustal rocks where they are clearly cross-cutting. the dominant minerals in the pink pegmatite are alkali feldspar, quartz, biotite and subordinate allanite, titanite, apatite, magnetite and fe-sulphides (fig. 4a). zonation is occasionally seen with quartz-rich centres bounded by alkali feldspar-rich parts. white pegmatites. white pegmatites are generally concordant (but locally discordant) to the foliation of the adjacent country rocks, typically grey gneiss and supracrustal rocks. the pegmatites are 5–20 m wide and 50–200 m long with a general trend of nw–se all over the nordre strømfjord and ussuit areas. gradational contacts to the host rocks are common. quartz and feldspar dominate the white pegmatites, with garnet, biotite, monazite, magnetite and zircon as characteristic minor constituents. monazite is found as 0.5–5 mm orange crystals that mainly occur in plagioclaseand biotite-rich pegmatites (fig. 4b). monazite crystals are euhedral and occur in lens-shaped layers accompanied by biotite, set in a granoblastic matrix of primarily plagioclase (secher 1980). analytical methods pb isotope analyses for this study were carried out at the danish centre for isotope geology, geological institute, university of copenhagen. mineral fractions were separated from dry split aliquots of crushed and sieved (100– 200 µm) rock powders using a hand magnet, a frantz isodynamic separator and heavy liquid techniques. no further purification was carried out, and the mineral fractions may contain minor proportions of foreign minerals. pb was separated conventionally on 0.5 ml glass columns charged with anion exchange resin, followed by a clean up on 200 µl teflon columns. a standard hbr-hcl solution recipe was applied in both column steps. total procedural blanks for pb amounted to < 120 pg which is considered insignificant for the measured pb-isotopic results, relative to the amount of sample pb estimated from the mass spectrometer signal intensities. isotope analyses were magnetite from amphibolite and banded iron formation 446626 ataneq 68°.061 53°.510 amphibolite 18.815 0.026 15.549 0.022 44.971 0.068 0.973 0.953 446632 ataneq 68°.047 53°.179 amphibolite 28.204 0.042 16.518 0.026 38.467 0.066 0.971 0.906 446623 attu 67°.837 53°.408 amphibolite 17.522 0.025 15.404 0.024 38.344 0.066 0.961 0.880 481070 attu 67°.915 53°.231 amphibolite 17.388 0.019 15.376 0.018 41.241 0.053 0.978 0.936 484883 naternaq 68°.398 51°.941 bif in amphibolite 54.587 0.028 19.316 0.012 36.871 0.030 0.942 0.886 magnetite from altered amphibolite and calc-silicate rock 446633 niaqornaarsuk 68°.217 53°.028 altered amphibolite 26.387 0.505 16.465 0.316 47.423 0.908 0.998 0.999 446603 attu 67°.927 53°.622 altered amphibolite 18.398 0.030 15.620 0.026 41.710 0.074 0.978 0.956 446604 attu 67°.927 53°.622 altered amphibolite 18.256 0.046 15.638 0.042 40.443 0.122 0.930 0.845 484890 naternaq 68°.408 51°.935 calc-silicates (skarn) 16.534 0.009 15.372 0.010 35.562 0.028 0.957 0.913 magnetite from the arfersiorfik quartz diorite 485178 arfersiorfik 67°.970 50°.430 quartz diorite 17.790 0.016 15.469 0.016 36.703 0.049 0.919 0.782 485179 arfersiorfik 67°.967 50°.412 quartz diorite 18.071 0.018 15.498 0.016 36.343 0.041 0.975 0.954 485193 arfersiorfik 67°.956 50°.594 hornblenditic rock 17.007 0.013 15.456 0.013 37.124 0.037 0.959 0.902 magnetite from pegmatite 481087 attu 67°.890 53°.517 pegmatite 28.393 0.043 16.602 0.026 189.024 0.311 0.982 0.971 magnetite from ultramafic rock and skarn 481049 qasigiannguit 68°.801 50°.973 ultramafic rock 25.827 0.039 16.103 0.025 51.334 0.084 0.979 0.949 481058 qasigiannguit 68°.800 51°.169 magnetite skarn 35.124 0.024 17.028 0.013 38.847 0.035 0.968 0.929 table 1. pb isotope ratios of magnetite from different rock types bif: banded iron formation. * errors are 2σ absolute (ludwig 1990). ** r1 = 206pb/204pb versus 207pb/204pb error correlation (ludwig 1990). † r2 = 206pb/204pb versus 208pb/204pb error correlation (ludwig 1990). sample locality latitude longitude rock 206pb ± 2σ* 207pb ± 2σ 208pb ± 2σ r1 ** r2† n w 204pb 204pb 204pb 108 magnetite, banded iron formation within amphibolite 484883, locality 68°.398 n, 51°.941 w [1] 1 n hbr 30' 48.234 0.030 18.615 0.014 37.418 0.032 0.968 0.919 [2] 1 n hbr 1 h 120.002 0.091 26.407 0.022 3.862 0.005 0.978 0.760 [3] 4 n hbr 3 h 94.120 0.363 23.247 0.090 37.841 0.149 0.995 0.987 [4] 8 n hbr 6 h 30.176 0.239 16.809 0.134 35.387 0.282 0.994 0.994 [5] 8 n hbr 12 h 18.799 0.062 15.506 0.052 34.534 0.116 0.991 0.987 [6] hf 12 h 18.799 0.124 15.539 0.103 35.013 0.233 0.995 0.993 magnetite, amphibolite 446632, locality 68°.047 n, 53°.179 w [1] 1 n hbr 30' 19.932 0.026 15.621 0.021 37.462 0.055 0.970 0.920 [2] 1 n hbr 1 h 38.765 0.032 17.639 0.016 39.167 0.040 0.978 0.946 [3] 4 n hbr 3 h 35.439 0.060 17.098 0.030 42.830 0.079 0.982 0.948 [4] 8 n hbr 6 h 37.099 0.150 17.595 0.072 36.972 0.154 0.993 0.979 [5] 8 n hbr 12 h 40.431 0.219 18.100 0.099 34.544 0.189 0.994 0.994 [6] hf 12 h 28.265 0.083 16.910 0.051 34.598 0.106 0.987 0.977 magnetite, altered amphibolite 446633, locality 68°.217 n, 53°.027 w [1] 1 n hbr 30' 25.206 0.021 16.298 0.015 45.932 0.047 0.971 0.914 [2] 1 n hbr 1 h 27.276 0.170 16.492 0.104 47.555 0.300 0.993 0.990 [3] 4 n hbr 3 h 25.359 0.022 16.261 0.016 45.944 0.049 0.975 0.948 [4] 8 n hbr 6 h 26.018 0.024 16.333 0.016 46.646 0.051 0.968 0.936 [5] 8 n hbr 12 h 27.705 0.073 16.539 0.046 48.236 0.138 0.965 0.937 allanite, pegmatite 2001-736, locality 67°.883 n, 53°.523 w [1] 1 n hbr 30' 22.579 0.029 15.860 0.021 137.787 0.193 0.982 0.960 [2] 1 n hbr 1 h 21.528 0.013 15.728 0.011 123.978 0.101 0.971 0.939 [3] 4 n hbr 3 h 79.398 1.929 22.265 0.542 1360.842 33.070 0.999 1.000 [4] 8 n hbr 6 h 2527.779 37.253 295.424 4.391 52501.990 774.512 0.992 0.999 [5] 8 n hbr 12 h 7804.112 133.916 882.216 15.164 161163.864 2767.112 0.999 1.000 [6] hf 12 h 551.839 2.322 74.260 0.322 11002.171 46.823 0.973 0.994 [7] hf 2 d 111.336 0.543 25.175 0.136 1948.881 9.628 0.901 0.991 table 2. pb-pb step leaching data for magnetite, allanite, and monazite in banded iron formation, amphibolite and pegmatites in the nagssugtoqidian orogen code acid time 206pb/204pb ± 2σ * 207pb/204pb ± 2σ * 208pb/204pb ± 2σ * r1 r2 * errors are 2σ absolute (ludwig 1990). for explanations of r1 and r2, see table 1. allanite, pegmatite 457785, locality 68°.834 n, 51°.226 w [1] 1 n hbr 30' 36.910 1.617 17.616 0.772 538.548 23.595 1.000 1.000 [2] 1 n hbr 1 h 44.614 0.389 18.318 0.160 714.245 6.237 0.998 0.999 [3] 4 n hbr 3 h 26.321 0.210 16.341 0.130 270.923 2.164 0.998 0.999 [4] 8 n hbr 6 h 21966.303 527.491 2410.934 57.939 328786.908 7897.797 0.999 1.000 [5] 8 n hbr 12 h 26.193 0.574 17.165 0.390 161.467 3.639 0.964 0.972 [6] hf 12 h 15.058 1.448 15.006 1.443 39.562 3.805 1.000 1.000 [7] hf 2 d 27.000 0.230 15.806 0.207 186.650 2.183 0.651 0.729 monazite, pegmatite 223736, locality 67°.680 n, 52°.565 w [1] 1 n hbr 30' 136.776 2.665 28.301 0.574 6619.883 131.103 0.960 0.984 [2] 1 n hbr 1 h 222.475 3.796 37.330 0.643 12548.515 214.343 0.991 0.999 [3] 4 n hbr 3h 219.227 2.039 36.918 0.346 12871.792 120.474 0.992 0.995 [4] 8 n hbr 6 h 184.897 2.055 33.259 0.373 10581.910 118.035 0.993 0.997 [5] 8 n hbr 12 h 89.680 0.811 23.046 0.213 3554.756 32.275 0.979 0.998 [6] hf 12 h 39.412 0.038 17.328 0.018 88.489 0.099 0.980 0.957 [7] hf 2 d 261.196 1.366 41.737 0.220 175.006 0.931 0.994 0.987 monazite, pegmatite 223746, locality 67°.674 n, 52°.456 w [1] 1 n hbr 30' 20.955 0.097 15.264 0.071 156.248 0.733 0.995 0.994 [2] 1 n hbr 1 h 26.768 0.169 16.158 0.103 315.778 2.010 0.997 0.997 [3] 4 n hbr 3h 215.079 2.560 37.781 0.451 5263.963 62.733 0.997 0.999 [4] 8 n hbr 6 h 2978.834 188.060 343.540 21.694 75533.892 4768.946 1.000 1.000 [5] 8 n hbr 12 h 6392.913 99.502 721.057 11.259 157988.821 2460.811 0.997 1.000 [6] hf 12 h 468.603 5.974 66.525 0.919 10731.171 137.428 0.923 0.996 [7] hf 2 d 2161.547 97.250 254.541 11.458 51062.309 2297.561 1.000 1.000 monazite, pegmatite 225348, locality 67°.833 n, 52°.323 w [1] 1 n hbr 30' 139.662 2.160 29.676 0.459 1656.012 25.630 1.000 1.000 [2] 1 n hbr 1 h 140.039 1.416 29.481 0.299 1544.411 15.642 0.996 0.999 [3] 4 n hbr 3h 877.104 4.121 108.678 0.517 12440.807 58.889 0.990 0.997 [4] 8 n hbr 6 h 25.459 0.418 16.750 0.456 225.146 4.515 0.604 0.820 [5] 8 n hbr 12 h 40549.054 1970.494 4458.008 222.550 602889.998 29313.071 0.973 1.000 [6] hf 12 h 8037.949 261.731 893.317 29.098 122611.734 3993.108 1.000 1.000 [7] hf 2 d 4389.260 60.969 493.058 6.880 66031.253 918.275 0.996 0.999 109 carried out on a vg sector 54-it instrument. fractionation for pb was controlled by repetitive analysis of the nbs 981 standard (values of todt et al. 1993) and amounted to 0.103 ± 0.007% / amu (2 σ; n = 11). stepwise pb leaching (pbsl) experiments followed methods described in frei & kamber (1995). the programmes and parameters of ludwig (1990) were used for the isochron calculations. model first-stage µ 1 values were calculated using 4.55 ga for the age of the earth. all age and isotope data in this paper are given with 2 σ precisions. results the pb-isotopic results are given in tables 1–3. the uranogenic pb-isotopic composition of magnetite from the amphibolites (four samples; squares in fig. 5) together with the banded iron formation (naternaq; one sample outside the range of fig. 5) define an isochron with an age of 1726 ± 7 ma (2 σ; mswd = 1.4; model µ 1 = 7.89 ± 0.02), which corresponds to a late stage in the metamorphic evolution of the nagssugtoqidian orogen (cf. willigers et al. 2002). this isochron intercepts the stacey & kramers (1975) pb-isotopic growth curve at ~2140 ma. four mineral separates from altered amphibolite, represented by calc-silicate rich phases and by hydrothermally altered and mineralised samples, have pb-isotopic compositions that plot above the 1726 ma isochron (diamonds in fig. 5). this more radiogenic pb-isotopic composition indicates admixture of a more evolved pb component into the alteration fluids. the pb-isotopic compositions of magnetite from an ultramafic rock and a magnetite skarn from the qasigiannguit area plot below the isochron (out5 samples amphibolite/bif magnetite bulk 1726 6.5 1.38 2140 7.89 0.02 484883 bif magnetite pbsl 1756 36 8.70 2401 7.7 0.11 223736 pegmatite monazite pbsl 1797 13 4.44 2925 7 0.05 223746 pegmatite monazite pbsl 1816 16 41.7 2784 7.24 0.12 225348 pegmatite monazite pbsl 1787 11 76.9 2271 7.81 1.00 447783 pegmatite allanite pbsl 1785 9.2 12.9 2335 7.76 0.00 2001-736 pegmatite allanite pbsl 1818 12 53.8 2453 7.66 0.02 bif: banded iron formation; pbsl: pb step leaching. table 3. pb isotope ages, µ1-values, and intercepts with the stacey & kramers (1975) pb-isotopic growth curve for magnetite, allanite, and monazite from amphibolite, bif and pegmatites sample rock mineral method age (ma) ± 2σ mswd intercept (ma) with µ1 ± 2σ stacey & kramers (1975) 1915 16 17 18 20 7 p b/ 20 4 p b 206pb/204pb 15.2 15.3 15.4 15.5 15.6 2000 1600 1200 800 400 0magnetite amphibolite altered amphibolite arfersiorfik this study arfersiorfik kalsbeek et al. (1987) arfersiorfik whitehouse et al. (1998) age = 1726 ± 7 ma mswd = 1.4 fig. 5. 206pb/204pb-207pb/204pb diagram. squares, pb isotope ratios of magnetite from amphibolites; diamonds, magnetite from altered amphibolites (data from sample 446632 outside the range of fig. 5, see table 1). arfersiorfik quartz diorite: circles, this study; crosses, data from kalsbeek et al. 1987; filled triangles, data from whitehouse et al. 1998. the isochron intercepts the stacey & kramers (1975) pbisotopic growth curve (blue) at ~2140 ma. 110 side the range of fig. 5; see table 1), suggesting a slightly more primitive pb source. the uranogenic vs. thorogenic isotopic patterns (not shown in a figure) are complex and do not add to a better understanding of the uranogenic pb-isotopic data. as expected, they reflect differences in u/th ratios among the different samples analysed. the arfersiorfik quartz diorite has been dated at ~1920 ma (kalsbeek et al. 1987). three magnetite samples from this igneous suite have been included in the present study. the uranogenic pb-isotopic compositions of these magnetites (circles in fig. 5) are similar to the whole-rock pbisotopic signatures (crosses in fig. 5; data from kalsbeek et al. 1987). four additional whole-rock analyses (filled triangles in fig. 5; data of whitehouse et al. 1998) show wider scatter than the data of kalsbeek et al. (1987) and the results of this study. the pbsl data obtained on magnetite from three of these samples are shown in fig. 6. a regression for the steps defined by the sample of banded iron formation, 484883 (excluding step 3; table 1) yields a best-fit line with a slope corresponding to an age of 1756 ± 36 ma (mswd = 8.70; model µ 1 = 7.70 ± 0.11; lower intercept with the stacey & kramers pb-isotopic growth curve at ~2400 ma), similar to the age obtained from the amphibolites. pbsl analyses of two other samples (446632, amphibolite and 446633, altered amphibolite) are closely scattered around the 1756 correlation line. pbsl data obtained on allanite from a pink pegmatite (sample 2001-736) resulted in a well-defined errorchron with an age of 1818 ± 12 ma (mswd = 53.8; model µ 1 = 7.66 ± 0.02; lower intercept with the stacey & kramers pb-isotopic growth curve at ~2450 ma; fig. 7a). the thorogenic vs. uranogenic isotopic pattern (fig. 7b) reveals that essentially only one phase has dominantly contributed pb to the leaching acids, as a nearly perfect linear relationship is indicated by the data points. this points to a more or less constant th/u in the recovered pb fractions. for this reason, the age of 1818 ± 12 ma can be interpreted with great confidence to represent the emplacement age of the pegmatite. the pb-isotopic composition of magnetite (sample 481087, table 1) from this pegmatite plots on the allanite isochron (fig. 7a), indicating preservation of isotopic equilibrium between these two phases. pbsl data on monazite from a white pegmatite (sample 223736) also yield an errorchron, the slope of which corresponds to an age of 1797 ± 13 ma (mswd = 4.44; model µ 1 = 7.00 ± 0.05; lower intercept with the stacey & kramers pb-isotopic growth curve at ~2925 ma; fig. 8a). the thorogenic vs. uranogenic isotopic pattern (fig. 8b) again indicates a predominantly single phase that contributed pb to the leaching acids, as the data points define a near perfect linear relationship. consequently, with great confidence, the age of 1797 ± 13 ma is interpreted as the intrusion age of this pegmatite. 12 16 20 24 28 484883 486632 486633 intercept ~ 2401 ma banded iron formation 484883 altered amphibolite 486633 amphibolite 486632 age = 1756 ± 36 ma mswd = 8.70 magnetite step leaching 1200 20 40 1401008060 20 7 p b/ 20 4 p b 206pb/204pb fig. 6. 206pb/204pb-207pb/204pb diagram of step leaching results of magnetite for three samples. the errorchron intercepts the stacey & kramers (1975) pb-isotopic growth curve (blue) at ~2400 ma. 111 three more step-leaching experiments were performed on allanite (1) and monazite (2) separates from other pegmatites (fig. 9). the ages defined by the respective errorchrons are similar to the ones presented above, and are close to 1800 ma. results of the isochron calculations are listed in table 3. discussion the age defined by the pb-isotopic compositions of magnetite from the amphibolites (1726 ± 7 ma) is younger than the latest major tectonometamorphic event in the region (d4, strike-slip shearing and granite intrusion at 1780– 1770 ma; see connelly et al. 2000 and van gool et al. 2002), and may be interpreted as a cooling age after the d4 event. metamorphic conditions in the cno reached temperatures above 650°c at 1800 ma and approximately 540°c by c. 1740 ma (connelly & mengel 2000; connelly et al. 2000; willigers et al. 2001). slow cooling followed with closing temperatures of rutile (420°c) around 1670 ma (connelly et al. 2000). based on 40ar-39ar and u-pb data of several minerals, willigers et al. (2001) estimated cooling temperatures around 500°c at ~1700 ma, 410°c at ~1640 ma and 200°c at ~1400 ma. a continuous magnetite-ulvöspinel solid solution series exists, with exsolution taking place below 600°c (deer et al. 1966; ramdohr 1969). thus, the ages of the magnetite may date 20 7 p b/ 20 4 p b 10 30 50 70 allanite 2001-736 magnetite age = 1812 ± 12 ma mswd = 54 20 8 p b/ 20 4 p b 206pb/204pb 0 4000 2000 8000 10000 0 100 200 300 400 500 600 magnetite a b fig. 7. step leaching 206pb/204pb-207pb/204pb and 208pb/204pb-206pb/ 204pb diagrams of allanite from red pegmatite (sample 2000736). the errorchron intercepts the stacey & kramers (1975) pb-isotopic growth curve (blue) at ~2925 ma. 20 7 p b/ 20 4 p b 10 20 30 40 50 monazite 223736 age = 1797 ± 13 ma mswd = 4.4 20 8 p b/ 20 4 p b 206pb/204pb 0 4000 12000 16000 0 100 200 300 a b fig. 8. step leaching 206pb/204pb-207pb/204pb and 208pb/204pb-206pb/ 204pb diagrams of monazite from white pegmatite (sample 223736). the errorchron intercepts the stacey & kramers (1975) pb-isotopic growth curve (blue) at ~2453 ma. 112 the timing where exsolution in magnetite ceased (< 1800 ma), that is, after peak metamorphic conditions. model first-stage µ 1 values associated with pb-pb isochrons have been used elsewhere in greenland to judge the influence of pb from archaean sources on the pbisotopic characteristics of palaeoproterozoic igneous rocks (e.g. kalsbeek & taylor 1985). rocks derived from proterozoic sources commonly have model µ 1 values around 8, while contamination with pb from archaean sources tends to lower the µ 1 values. the high µ 1 value (7.89; table 3) obtained for the amphibolite isochron and the lower intercept with stacey & kramers (1975) pb-isotopic growth curve at 2140 ma suggest a mainly palaeoproterozoic pb source for the amphibolites. this source is probably also related to the origin of the supracrustal rocks. detrital zircon u-pb ages of metasedimentary rocks of the nordre strømfjord suite (2200–1950 ma; nutman et al. 1999) and the naternaq supracrustal belt (c. 1950– 1900 ma, thrane & connelly 2006, this volume) indicate erosion of a predominantly palaeoproterozoic hinterland. it implies that the stratabound, semi-massive sulphide deposits associated with banded iron formation at naternaq (stendal et al. 2004) were also deposited during palaeoproterozoic time. the results of allanite and monazite pbsl experiments indicate pegmatite formation around 1800 ma in both the cno (at nordre strømfjord) and nno (at attu and qasigiannguit). this is in agreement with ages reported by kalsbeek & nutman (1996) and connelly et al. (2000), which are slightly younger (1780–1770 ma) or within error overlapping those reported here. the pegmatites were emplaced after post-collisional deformation, large scale folding, and shear zone formation (d3) which ended around 1825 ma (van gool et al. 2002). the wide range in model µ 1 values (7.00–7.81) and lower intercepts with the stacey & kramers (1975) pbisotopic growth curve (2271–2925 ma) indicate variable contributions of archaean and palaeoproterozoic country rocks to the petrogenesis of the pegmatites: pegmatite sample 223736 (µ 1 = 7.00; lower intercept at 2925 ma) may largely consist of remelted archaean country rock, whereas sample 225348 (µ 1 = 7.81; lower intercept at 2271 ma) appears to be mainly derived from palaeoproterozoic sources. hydrothermal activity in the region probably continued after the time of pegmatite emplacement and after the magnetite had cooled through its closing temperature (~600°c), which means that the temperatures of the hydrothermal fluids ranged from 650°c to 400°c in the period 1800–1650 ma. the pb-isotopic signatures of the ultramafic rock and 20 7 p b/ 20 4 p b 206pb/204pb 0 100 150 300 200 250 50 0 c monazite 223746 age = 1816 ± 16 ma mswd = 41.7 400 800 1200 1600 2000 2400 2800 20 7 p b/ 20 4 p b 15 16 17 18 19 allanite 457785 age = 1785 ± 9.2 ma mswd = 12.9 206pb/204pb 0 ma 800 1600 a 15 25 35 45 20 8 p b/ 20 4 p b 206pb/204pb 0 200 400 600 800 1000 b 0 2000 4000 6000 8000 monazite 225348 age = 1787 ± 11 ma mswd = 77 fig. 9. step leaching 206pb/204pb-207pb/204pb diagrams of monazite from white pegmatite (samples 225348 and 223736) and allanite from pink pegmatite (sample 447783). the errorchron intercepts of the stacey & kramers (1975) pb-isotopic growth curve (blue) are given. 113 the magnetite skarn from the qasigiannguit area do not lend themselves to deduce whether these formations were formed during the palaeoproterozoic or represent remnants of archaean origin. it has been suggested that many of the epigenetic gold and copper occurrences in the ataa area north-east of disko bugt, about 75 km north of jakobshavn isfjord (fig. 1), are contemporaneous with the peak metamorphism at ~1900 ma in that area (stendal 1998). this 1900 ma metamorphic-hydrothermal event is not reflected in the magnetite pb-isotopic data of the present study area. conclusions pb-isotopic data of magnetite can be related to the general geological evolution of the nagssugtoqidian orogen and are thus a useful tool for studying the metamorphic history of palaeoproterozoic events in west greenland. a drawback of magnetite pb-isotopic analysis, however, is the generally low pb concentration in this mineral, which makes analysis difficult. magnetite in the amphibolites was formed during several stages of metamorphism. the isochron age of ~1726 ma probably represents a cooling age after a prominent late tectonometamorphic event in the region dated at ~1775 ma. the isotopic data suggest a palaeoproterozoic (mantle?) source for the pb in the amphibolites. the nordre strømfjord supracrustal suite, formed by erosion of a similar juvenile palaeoproterozoic hinterland, was deposited between 2000 and 1920 ma. it is suggested that the naternaq sulphide deposit is part of this supracrustal suite. calc-alkaline magmatism related to subduction (1920– 1870 ma; connelly et al. 2000) gave rise to the formation of the arfersiorfik quartz diorite. the pb-isotopic signature of magnetite from these rocks is comparable with that of whole-rock samples. allanite and monazite pbsl analyses yield pegmatite formation ages of ~1800 ma for both the nordre strømfjord, attu and qasigiannguit regions. the formation of pegmatites is therefore post-collisional. the pegmatites were formed by melting of the local country rocks; pbisotopic data indicate that variable proportions of late archaean and palaeoproterozoic age contributed to their petrogenesis. hydrothermal activity continued after pegmatite emplacement and after closure of magnetite, at 1800–1650 ma. acknowledgements the authors acknowledge f. kalsbeek for inspiring suggestions, and p.m. holm and an anonymous reviewer for further improvements of the manuscript. this paper also contains contributions from several colleagues at geus, all of whom are acknowledged for their work. a special thanks goes to k. markussen, attu, for information about the allanite-bearing pegmatite south of the village. references connelly, j.n. & mengel, f.c. 2000: evolution of archean components in the paleoproterozoic nagssugtoqidian orogen, west greenland. geological society of america bulletin 112, 747–763. connelly, j.n., van gool, j.a.m. & mengel, f.c. 2000: temporal evolution of a deeply eroded orogen: the nagssugtoqidian orogen, west greenland. canadian journal of earth sciences 37, 1121–1142. connelly, j.n., thrane, k., krawiec, a.w., & garde, a.a. 2006: linking the palaeoproterozoic nagssugtoqidian and rinkian orogens through the disko bugt region of west greenland. journal of the geological society, london 163, 319–335. deer, w.a., howie, r.a. & zussman, j. 1966: an introduction to the rock-forming minerals, 528 pp. london: longman. frei, r. & kamber, b.s. 1995: single mineral pb-pb dating. earth and planetary science letters 129, 261–268. garde, a.a. & steenfelt, a. 1999: precambrian geology of nuussuaq and the area north-east of disko bugt, west greenland. geology of greenland survey bulletin 181, 6–40. hollis, j.a., keiding, m., stensgaard, b.m., van gool, j.a.m. & garde, a.a. 2006: evolution of neoarchaean supracrustal belts at the northern margin of the north atlantic craton, west greenland. in: garde, a.a. & kalsbeek, f. 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(eds): precambrian crustal evolution and cretaceous– palaeogene faulting in west greenland. geological survey of denmark and greenland bulletin 11, 87–99 (this volume). todt, w., cliff, r.a., hanser, a. & hofmann, a.w. 1993: re-calibration of nbs lead standards using a 202pb + 205pb double spike. terra abstracts 5, supplement 1. van gool, j.a.m., connelly, j.n., marker, m. & mengel, f. 2002: the nagssugtoqidian orogen of west greenland: tectonic evolution and regional correlations from a west greenland perspective. canadian journal of earth sciences 39, 665–686. whitehouse, m.j., kalsbeek, f. & nutman, a.p. 1998: crustal growth and crustal recycling in the nagssugtoqidian orogen of west greenland: constraints from radiogenic isotope systematics and u-pb zircon geochronology. precambrian research 91, 365–381. willigers, b.j.a., krogstad, e.j. & wijbrans, j.r. 2001: comparison of thermochronometers in a slowly cooled granulite terrain: nagssugtoqidian orogen, west greenland. journal of petrology 42, 1729– 1749. __________________________________________________________________________________________________________________________________________________________________________________ manuscript received 28 october 2004; revision accepted 19 december 2005 larsen 2023: geus bulletin 54. 8347. https://doi.org/10.34194/geusb.v54.8347 1 of 2 preface preface rune berg-edland larsen* department of geoscience and petroleum, norwegian university of science and technology (ntnu), trondheim, norway *correspondence: rune.larsen@ntnu.no received: 02 feb 2023 accepted: 10 feb 2023 published: 27 jul 2023 keywords: igneous complex, magma chamber processes, mineralisation, platinum group elements, skaergaard intrusion abbreviations: au: gold pge: platinum group elements ntnu: norwegian university of science and technology geus bulletin (eissn: 2597-2154) is an open access, peer-reviewed journal published by the geological survey of denmark and greenland (geus). this article is distributed under a cc-by 4.0 licence, permitting free redistribution, and reproduction for any purpose, even commercial, provided proper citation of the original work. author(s) retain copyright. edited by: catherine jex (geus, denmark) reviewed by: none. preface to: rudashevsky et al. 2023 (this volume) funding: none. competing interests: none. additional files: none. in this special issue of geus bulletin, the many riddles regarding the platinum group elements and gold (pge-au) mineralisation of the east greenland skaergaard intrusion are untangled and discussed. the skaergard pge-au mineralisation, as defined in this study, embodies an enigmatic and rich ore formation that arguably could have been an economic resource, had it not been for its ice-locked position in central east greenland. the authors of this study (rudashevsky et al. 2023, this volume) characterise the systematic variability in the precious metal mineralogy from the contact towards the interior of the intrusion based on the analysis of more than 4000 individual pge-au grains. this variability is interpreted in the light of 90 years of research and over 1000 publications pertaining to magma chamber processes in the skaergaard intrusion. with such an impressive library of knowledge, on a comparatively simple magmatic system such as the skaergard intrusion, we should have discovered a few islands of truth in igneous petrology and ore-deposit formation. and indeed, we have. but we are also enriched with an evolving story, where answering one question only serves to raise three new questions. this study demonstrates the variability of pge-au phases throughout the ore-forming zone of the skaergaard intrusion. as previously observed, pge-au mineralisation in the central parts is divided into several layers over 30–40 m of the cumulus stratigraphy with increasing pd/pt ratios upwards, an au-rich upper part and a low sulphide content throughout all layers. close to the contact, the precious metal zonation is less pronounced, and it is significantly more sulphide rich. the pge mineralogy deviates significantly from the centre to the margin. these complex lateral and vertical variations cannot be explained by one genetic model but require an intricate combination of igneous processes including silicate-melt liquid immiscibility, sulphide-melt immiscibility, sulphide-melt resorptions, precious metal transport by volatile-rich fluids and, finally, the solidification rate of the cumulus mushes. for other well-preserved pge-au deposits throughout the world, we observe a great variation of ore-forming models. remarkably, most of these models may be applied to various parts of the skaergaard mineralisation. the authors suggest that the skaergaard intrusion preserves different steps in pge-au ore genesis, which in many other intrusions are obliterated by later https://doi.org/10.34194/geusb.v54.8347 https://orcid.org/0000-0002-0117-1106 mailto:rune.larsen@ntnu.no larsen 2023: geus bulletin 54. 8347. https://doi.org/10.34194/geusb.v54.8347 2 of 2 w w w . g e u s b u l l e t i n . o r g igneous events. therefore, the legacy of the skaergaard mineralisation is the preservation of igneous ore-forming events that may also precede the genesis of other pge-au deposits in the world. after the last conclusion, i guarantee that you will be confused and perhaps a bit triggered but hopefully also inspired and bursting with new questions on the genesis of pge-au deposits in mafic and ultramafic igneous complexes. in light of the recent study, you may even be encouraged to look at your favourite pge-au deposit with fresh eyes. this study beautifully demonstrates that turning the next page in the book of magma chamber processes is more important than seeing ‘the end’. rune b. larsen professor, economic geology, ntnu, norway reference rudashevsky, n.s., nielsen, t.f.d. & rudashevsky, v.n. 2023: the pge-au mineralisation of the skaergaard intrusion: precious metal minerals, petrography and ore genesis. geus bulletin 54 (this volume), 8306. https://doi.org/10.34194/v.54.8306 https://doi.org/10.34194/geusb.v54.8347 http://www.geusbulletin.org https://doi.org/10.34194/v.54.8306 geological survey of denmark and greenland bulletin 38, 2017, 1-8 1 geological survey of denmark and greenland bulletin 38 • 2017 review of survey activities 2016 edited by adam a. garde and ole bennike geological survey of denmark and greenland danish ministry of energy, utilities and climate 22 geological survey of denmark and greenland bulletin 38 key words geological survey of denmark and greenland, survey organisations, current research, denmark, greenland. cover photographs from left to right 1. the traditional spear auger remains a principal tool in mapping danish quaternary deposits, but can now be combined with short-range electromagnetic methods for specific purposes such as 3d delineation of contaminated landfill sites. photograph: jakob lautrup 2. elevation map around the stream of hagens møllebæk in north-west jylland with the positions of measuring stations to determine the nitrate runoff from agricultural fields at different times of the year. 3. the monitoring of the surface conditions of the greenland ice sheet by geus is an important tool fo understanding global climate change. photograph: baptiste vandecrux. 4. rescuing primary seismic data from the north sea obtained by private exploration companies to a national electronic database at geus. photograph: peter warna-moors. frontispiece: facing page surface of qagssimiut ice lobe ablation area, southern greenland ice sheet, after a period of extended clear sky conditions that enabled a strong dark ice algal bloom registered in satellite imagery presented in box et al. (2017, this volume). aerial oblique photo near 61°11.006́ n, 46°42.333´w, 820 m elevation. photo: jason e. box, 23 august 2014. chief editor of this series: adam a. garde editorial board of this series: john a. korstgård, department of geoscience, aarhus university; minik rosing, geological museum, university of copenhagen; finn surlyk, department of geosciences and natural resource management, university of copenhagen scientific editors: adam a. garde and ole bennike editorial secretary: jane holst referees (numbers refer to first page of reviewed article): nicolaj k. larsen & lars nielsen, dk (9); anonymous & ole silkjær, dk (13); peter k. engesgaard & bo v. iversen, dk (17); john korstgård & lars nielsen, dk (21); thomas balstrøm & nicolaj k. larsen, dk (25), niels balling & reinhard kirsch, dk (29); anonymous & allan mahler, dk (33); mikael erlström, se & maciej i. kotarba, pl (37); jakob keiding, no & vesa nykänen, fi (41); christopher harrison, ca & martin sønderholm, dk (45); michael k. engkilde & ida l. fabricius, dk (49); xavier fettwis, be & teruo aoki, jp (53); james h. lever, us & christopher j. ries, dk (57); anonymous & jacob c. yde, no (61); asger k. pedersen, dk & daniel sopher, se (65); christian holmegaard, dk & martin l. nayembil, uk (69); jens havskov, no & christopher j. ries, dk (73). illustrations: benny m. schark, allan lindy, stefan sølberg and susanne rømer layout and graphic production: jane holst and carsten e. thuesen printer: rosendahls-schultz grafisk a/s, albertslund, denmark manuscripts received: 12 january – 28 march 2017 final versions approved: 15 march – 19 may 2017 printed: 31 july 2017 issn (print) 1604-8156, isbn (print) 978-87-7871-469-5 issn (online) 1904-4666, isbn (online) 978-87-7871-470-1 citation of the name of this series it is recommended that the name of this series is cited in full, viz. geological survey of denmark and greenland bulletin. if abbreviation of this volume is necessary, the following form is suggested: geol. surv. den. green. bull. 38, 76 pp. available from geological survey of denmark and greenland (geus), øster voldgade 10, dk-1350 copenhagen k, denmark phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: geus@geus.dk and at www.geus.dk/publications/bull © de nationale geologiske undersøgelser for danmark og grønland (geus), 2017 for the full text of the geus copyright clause, please refer to www.geus.dk/publications/bull 3 44 25 karst sinkhole mapping using gis and digital terrain models p.b. sørensen, h. lykke-andersen, p. gravesen and b. nilsson 29 towards a geothermal exploration well in the gassum formation in copenhagen h. vosgerau, u. gregersen, l. kristensen, s. lindström, a. mathiesen, c.m. nielsen, m. olivarius and l.h. nielsen 33 pre-drilling geothermal assessment of porosity and permeability of the bunter sandstone formation, onshore denmark m.l. hjuler and l. kristensen 37 generation and origin of natural gas in lower palaeozoic shales from southern sweden n.h. schovsbo and a.t. nielsen thailand bangladesh vietnam cambodia greenland kenya ethiopia nigeria cameroon malawi tanzania denmark swedeniceland russia ghana 7 review of survey activities 2016 f.g. christiansen 9 optimising geological mapping of glacial deposits using high-resolution electromagnetic induction data k.e.s. klint, i. møller, p.k. maurya and a.v. christiansen 13 buried valleys in denmark and their impact on the subsurface geological architecture p.b.e. sandersen and f. jørgensen 17 nitrate transport pathways in riparian zones of the hagens møllebæk catchment, northern denmark b. nilsson, a.l. højberg and p. jensen 21 structures and stratigraphy of danian limestone, eastern sjælland, denmark p.r. jakobsen, m.m. rohde and e. sheldon 5 dark grey indicates countries where geus has ongoing or recently completed projects. orange indicates countries with geus projects described in this volume. 41 prospectivity mapping for orogenic gold in southeast greenland b.h. heincke and b.m. stensgaard 45 inversion structures as potential petroleum exploration targets on nuussuaq and northern disko, onshore west greenland e.v. sørensen, j.r. hopper, g.k. pedersen, h. nøhr-hansen, p. guarnieri, a.k. pedersen and f.g. christiansen 49 potential hydrocarbon reservoirs of albian– paleocene age in the nuussuaq basin, west greenland m.l. hjuler, n.h. schovsbo, g.k. pedersen and j.r. hopper 53 greenland, canadian and icelandic land-ice albedo grids (2000–2016) j.e. box, d. van as, k. ste�en and the promice project team 57 new programme for climate monitoring at camp century, greenland w. colgan, s.b. andersen, d. van as, j.e. box and s. gregersen 61 asynchronous ice-sheet development along the central east greenland margin: a glanam project contribution l.f. pérez and t. nielsen 65 �e rescue of seismic �eld data from exploration activities in the danish north sea m.m. hansen and n. rinds 69 an integrated public database for geology, groundwater and drinking water in denmark m. hansen and c.t. �omsen 73 arctic geopolitics and the beginning of earthquake monitoring in denmark and greenland a.l.l. jacobsen thailand bangladesh vietnam cambodia greenland kenya ethiopia nigeria cameroon malawi tanzania denmark swedeniceland russia ghana 66 7 review of survey activities 2016 flemming g. christiansen deputy director 2016 was a year of transition in the international geological society. like previous years, it was still a period with lots of reorganisation and cut-backs in the energy and mineral industry but also with obvious signs of an even more complex business pattern where well-organised geological data and easy access to geological knowledge will be strongly needed. compared to the industry, and also to some of the authorities that are regulating the use of natural resources, geus has a high degree of continuity of both activities and personnel; in these years with strong focus on key strategic goals. this creates and develops a corporate memory that can be easily applied even with sudden shifts of a political or business agenda. this also establishes geus as the starting point for getting access to geological information from denmark and greenland, and makes geus a natural collaboration partner nationally as well as internationally. publication of results, both internationally and in our own series is a key factor for keeping a high scientific standard and for documentation of this towards society, authorities and industry. this issue of geus’ review of survey activities shows like in previous years a broad spectrum with a total of 17 papers covering many different activities. the papers give a good overview in their own right but with systematic references to background reports and other papers, they also provide an easy way to dig deep into the important work that geus is carrying out. eight papers are on denmark, six on greenland and three on other themes. activities in denmark geus works on many different – and often closely interrelated – topics in denmark such as the use of water, energy, and mineral resources, protection of nature under significant climatic changes, and by making up-to-date geological and geophysical data and information easily available for all sorts of purposes. the use of groundwater is very important for denmark, and geus carries out many studies on water resources and their protection in connection with climate changes, environmental impact and domestic use. systematic geological and geophysical studies provide not only specific water data, but also give a much better understanding of the geological models that can be used to predict resources and regulate their use. one paper with a case study from samsø describes how traditional geological mapping can be optimised by using high-resolution electromagnetic induction data. another paper gives an overview of buried valleys in denmark, their geological architecture and very significant length, which has great implications for the groundwater resources in many parts of denmark. a third paper gives a detailed description of nitrate transport pathways in one catchment area in northern jylland where results from year-around monitoring can be used for planning and regulating to meet the demands of the eu water framework directive. in many areas in denmark, chalk and limestone are directly exposed or found near terrain surface with only a thin cover of quaternary deposits. such deposits are important as a mineral resource for many different purposes and due to their groundwater resources and they may also control structures in overlying sediments. one paper documents the structures and stratigraphy of danian limestone on eastern sjælland, whereas another study uses gis and digital terrain models to map karst sinkholes in areas of jylland and to interpret the geological and climatic conditions and anthropogenic activities that influence their development. denmark has a large potential for subsurface geothermal energy and for heat and energy storage. following the recent launching of the geothermal webgis portal with all geological and geophysical data relevant for geothermal exploration, geus has continued with more detailed studies of specific areas and on specific parameters. one paper gives a summary of a eudp-supported project on the planning of exploration in urban areas of copenhagen by targeting on shallower reservoirs in the gassum formation and by using smaller drilling rigs. another paper has focus on the porosity and permeability variation of the bunter sandstone formation that is a potential geothermal reservoir in large onshore areas of southern denmark. shale-gas production has been a major game changer in the energy sector for quite some years, and we have seen © 2017 geus. geological survey of denmark and greenland bulletin 38, 7–8. open access: www.geus.dk/publications/bull 88 many studies of the resource potential and some exploration in europe, including denmark and southern sweden. one paper gives a detailed description of the gas composition and discuss biogenic versus thermogenic origin of gas in lower palaeozoic shales from scientific core holes in southern sweden. activities in greenland once again there was a high level of geological and glaciological activities in greenland in 2016, both traditional studies with focus on the mineral and petroleum potential and exploration studies as well as monitoring and research related to climate changes and their effect. geus has been active with regional mapping and research in south-east greenland for quite some years, and some of the geo-datasets are important for identifying exploration targets. one paper argues for the possibility of orogenic gold deposits by using aeromagnetic and stream sediment geochemistry data in a minerals systems model. a large number of data and proxies maps have been applied to construct a final prospectivity map pointing towards the most interesting possibilities in the tasiilaq area. the nuussuaq basin in west greenland has served as an analogue geological model for offshore petroleum exploration for decades but there may also be an onshore potential. as preparation for both offand onshore licensing rounds, geus has compiled key data in a gis model and re-studied especially the large-scale structures in more detail using photogrammetric mapping. one paper describes a very large inversion anticline on central nuussuaq that could be an interesting drilling target. a revised migration pathway model is proposed; this could explain distribution of both oil and gas seeps outside the traditional area with common seepage. another paper describes the reservoir properties of quite a number of sedimentary and volcanic successions of aptian to paleocene age in the nuussuaq basin. monitoring programmes of the greenland ice sheet and research based on local ground truth data from stations on the ice – and from fjords and nearby offshore areas – are very important contributions from geus to global climate models. one paper gives an example of albedo grids measured from satellite and checked with local data to give a much better de-noising and bias correlation. another paper outlines a new climate monitoring and radar mapping programme in the camp century area in northern greenland that will be managed by geus; some historical information and background models are also presented. a third paper describes the ice-sheet development along the central east greenland margin in late miocene to recent time where thick and different types of glacigenic deposits are interpreted using seismic data. other themes as the national geological data center geus has a strong obligation to make all data available to authorities, educational and research institutes and to private enterprises. the ever accelerating changes in technology make this a great challenge in terms of competence, capacity and economic resources, both for collection and quality control of the actual data and for the database and distribution systems. the value for society is, however, very high and there is a strong focus on digitalisation strategy in denmark these years. one paper describes the tremendous effort that was made to rescue most of the seismic field data from exploration activities in the 1980s and 1990s in the danish north sea and how successfully this worked in collaboration with the operators. another paper introduces jupiter, the integrated public database for geology, groundwater and drinking water in denmark, and describes the data systems, agreements and management behind it. finally, the last paper presents the early history of earthquake monitoring in denmark and greenland, and discusses how this was as geopolitically important more than a century ago as it is today. geological survey of denmark and greenland bulletin 15, 2008, 89-92 reconstructing past secular environmental variations is an important issue in palaeoclimate research. however, most key variables for palaeoclimate reconstructions cannot be measured directly, and reconstructions are therefore based on proxy data. here, we demonstrate the potential of bivalve shells as an archive of environmental parameters. the geo lo gical survey of denmark and greenland (geus) has developed a fast and reliable method for chemical analyses of shell material by laser ablation inductively coupled plasma mass spectrometry (la-icp-ms), and here we present some ex amples of the use of this method. in tropical and subtropical waters, corals can provide century-long archives of past water chemistry with annual resolution. a comparable archive for temperate and arctic waters would be highly useful in climate research, and therefore it has been examined whether this can be provided by bivalve shells (e.g. schoene et al. 2005). long-lived species may provide archives with annual resolution extending over several hundred years, whereas short-lived, fast-growing species can provide archives with a seasonal or in some cases daily resolution over a period of a few years. most bivalves are sessile, and shells are commonly preserved as fossils. there are, however, a number of challenges related to the use of bivalves as proxy archives: (1) many proxies show species specific behaviour (seed 1980); (2) only very few proxies are dependent on a single variable (wefer et al. 1999); and (3) the effects of biology and ontogeny on the uptake of trace elements and stable isotope fractionation in shell carbonate are largely unknown and have to be evaluated empirically. therefore, any potential proxy must be calibrated individually for each species of interest before it can be used. a large number of chemical analyses are needed to calibrate a proxy. these are commonly obtained by solution icp-ms, in which sample preparation is time-consuming and labour-intensive. the use of la-icp-ms is therefore a considerable advance in bivalve shell proxy research, as it greatly reduces the effort needed for sample preparation. at the same time, the method requires less material for analysis, thus providing better spatial and hence temporal resolution. proxies based on bivalve shell carbonate can be used in present-day environmental monitoring, and for environmental reconstructions from shells found as fossils. shells from museum collections and shells found in archaeological middens can give information on historic and prehistoric environmental conditions (e.g. carrell et al. 1987), and fossil shells can be used as archives of environmental parameters on geological timescales (e.g. hendry et al. 2001). shell mineralisation bivalve shells consist mainly of calcium carbonate with im purities in the form of various elements substituting for calcium in the crystal structure. calcium carbonate represents 95–99% by weight of the shell, the remaining 1–5% being organic matrix, which is dominated by proteins (marin & luquet 2004). the shell material is deposited sequentially in growth increments that are often visible in polished sections studied by computer-controlled scanning electron micro scopy (ccsem). as a consequence of the growth pattern the increments occur in chronological order, and a relative time line for chemical analyses can be established. a section with the different layers of the shell of the common blue mussel (mytilus edulis) is shown in fig. 1, where internal growth increments are also illustrated. figure 2 shows an image of the actual shell structure. the elements needed for shell mineralisation come from the water or from particles that the bivalve ingests. in order to be included in the shell, the elements have to cross two biological membranes, the outer and inner mantle epithelium. these membranes actively discriminate against certain elements, but for some elements this discrimination is influenced by external stimuli (e.g. klein et al. 1996). 89 laser ablation analysis of bivalve shells – archives of environmental information maiken hansen klünder, dorothee hippler, rob witbaard and dirk frei © geus, 2008. geological survey of denmark and greenland bulletin 15, 89–92. available at: www.geus.dk/publications/bull aragonite calcite periostracum hemolymph m an tl e sh el l inner extrapallial fluid (epf) outer extrapallial fluid epithelium (inner/outer) fig. 1. section through the margin of shell and mantle of a mytilus edulis. the crystalline shell consists of two separate layers: a prismatic layer of calcite and an aragonitic layer of nacre. the outermost layer is a protective organic layer (periostracum). the shell is secreted in growth increments in the area be tween the shell and the mantle. the la-icp-ms method many previous studies of bivalve shells have utilised wet chemical analysis. samples often consist of powder drilled from the shell with dentist drills and other microdrilling tools. powder samples are routinely analysed by solution icp-ms. la-icp-ms combines an analytical precision comparable to that of solution icp-ms with a significantly shorter and easier sample preparation process. the laser technique is not only time-saving – the fewer steps needed in sample preparation also reduce the risk of contamination. furthermore, the spatial resolution is much higher, as laser ablation in shell samples can be undertaken with a beam diameter of 30–65 µm, as opposed to the 200–300 µm diameter of a microdrill. sample preparation any sample of bivalve shell material can be analysed by laicp-ms, but cross-sections through entire valves are preferred in order to constrain the growth history. the shell must be cleaned of soft tissues, epibionts or adhering sediment. the shell material is embedded in epoxy resin to prevent it from fracturing during handling. the shell is then cut with a diamond-tipped rock saw to produce a cross-section, and polished to show the shell structure (fig. 3). shells longer than 5 cm may have to be divided into two or more sections to fit into the sample chamber of commercially available laser ablation systems. after polishing, the section is cleaned with alcohol and treated ultrasonically to remove possible surface contamination. analytical techniques the la-icp-ms equipment at geus is a finnigan el ement2 high resolution icp-ms connected to a new wave research up213 laser ablation system. for shell analyses, the nist 612 and nist 614 glasses are used as standard materials. the elemental concentrations for the standard glasses published by pearce et al. (1997) are used for concentration calculations. there are potential problems in using nonmatrix-matched standards, but at ablation times of less than 80 seconds, these problems are not significant in analyses carried out on calcium carbonate (vander putten et al. 1999). as an internal standard in the samples, calcium (43ca) is suitable for the measurement of several trace and minor elements in calcite (longerich et al. 1996), and sem analyses of m. edulis have shown that the calcium content in the calcite layer is uniform. we use the glitter software package for final concentration calculations from the time-resolved raw data. relative age and growth rate an advantage of calibrating a proxy on bivalve shells taken from laboratory or field culturing experiments is that measurements of the shell length can be made during the experiment, so that the chemical analyses can be time constrained. when applying the proxy to fossil shells, it is of course im possible to carry out multiple shell length measurements on the live individual, so other methods must be used. many species form annual growth increments that can be used to set the relative age of a specimen. furthermore, all species show micro-increments that are visible in a microscope. these narrow growth increments are not always regular, but in a number of species the increments show a periodicity related to moon phases or diurnal or tidal shifts. utilising what is known about the periodicity of increment formation in the species analysed, one can assign relative ages to chemical analyses and calculate approximate growth rates for the analysed shell. examples mg/ca thermometry the use of the ratio between mg and ca in shells as a temperature proxy was first suggested because it was found that the mg/ca ratio in marine carbonates varies according to lat90 5 µm 1 cm fig. 2. sem image of a mytilus edulis shell in cross-section, showing aragonitic nacre (left side of image) and prismatic calcite (right side of image). the image illustrates the differences in structure between these two shell layers, and the direction of the growth increments. fig. 3. computer scan of shell sample mytilus edulis b218 prepared for laicp-ms analysis. itude (see henderson 2002). using calcite from m. edulis taken from field culturing experiments in the wadden sea, we found shell mg/ca ratios to be temperature dependent. the mg/ca ratio of m. edulis shells from svendborg sund, denmark was then used to calculate seawater temperatures. the temperature was calculated from the mg/ca ratio using the equation t = 2.22 + 18.2 log (mg/ca) (unpublished data, m.h. klünder). the calculated temperatures have been compared with water temperatures measured by the national en vironmental research institute (fig. 4). it is seen that the mg/ca thermometer gives a fair estimate of temperature changes during a summer. lead pollution the concentration of pb in shell increments of the bivalve mya arenaria is a function of the pb concentration in the water (pitts & wallace 1994), and hence the former concentration of pb in the water can be calculated from the lead concentration in m. arenaria shells. shell samples from a fouryear old specimen from limfjorden, denmark, collected in 2005, have been analysed. the results indicate that the pb concentration in limfjorden has varied from 20 to 280 pmol/kg water over the sampled time span (fig. 5). hence analysing a single water sample may give a misleading picture of the pb level. the concentration of pb in limfjorden is comparable to that found in the relatively uncontaminated cape cod bay, eastern usa; it is up to ten times higher than pre-industrial levels in the boston area, as calculated from the pb content of sub-fossil shells from shell middens, and ten times lower than in boston harbour (pitts & wallace 1994). the pb proxy has also been applied to data from an arctica islandica individual that was transferred from the baltic sea to a dutch harbour (fig. 5). the proxy has not yet been calibrated for a. islandica, and the results can only be regarded as qualitative. however, it is seen that the pb concentration in shell material secreted after transplantation to the harbour is significantly higher than in that secreted in the baltic. these results indicate that shells of a. islandica can be used to monitor pb contamination of seawater. shell mn/ca and ba/ca – a link to primary production? it has been suggested that the content of mn and/or ba in bivalve shells can be correlated with primary production (e.g. stecher et al. 1996). this would suggest that mn/ca or ba/ca ratios are related to phytoplankton blooms, providing a proxy 91 0 5 10 15 20 25 0 50 100 150 200 jan/1 mar/1 may/1 jul/1 sep/1 nov/1 jan/1 calculated temperature measured temperature t em pe ra tu re ( °c ) analysis number 0 100 200 300 400 020406080100120140160 0 10 20 30 40 50 60 pm o l p b/ kg w at er analysis no. a545 analysis no. 025 10 0 20 30 40 50 c hl -a , n o nac id ifi ed μm o l b a/ m o l c a 0.5 1 1.5 2 2.5 3 3.5 4 10 0 20 30 40 50 0.05 0.10 0 0.15 sep/1 jan/1 may/1 sep/1 jan/1 c hl -a , n o nac id ifi ed μm o l m n/ m o l c a a b fig. 4. temperatures in svendborg sund, denmark in the summer of 2005 calculated from mg/ca ratios in mytilus edulis (red line) and compared to measured water temperatures (blue line). the calculated temperatures provide a fair estimate of the actual temperature. fig. 5. pb content in seawater calculated from shell pb concentration using the equation of pitts & wallace (1994). one specimen of mya arenaria (blue line, limfjorden) and one specimen of arctica islandica (red line, baltic sea, transplanted to the netherlands) were analysed. the arrow shows the time of the transplantation. fig. 6. ba/ca and mn/ca ratios of four mytilus edulis specimens compared with the chlorophyll-a concentrations (red line) of the seawater. a: ba/ca ratios in m. edulis shells from the dutch wadden sea. b: mn/ca measured in the same shells. for the timing and size of such events. to test this theory, m. edulis shell samples from an aquaculture field experiment site in the wadden sea were analysed at geus and compared to the chlorophyll-a concentration of the ambient water (fig. 6). the results are not conclusive, but they suggest that the relationships between the mn/ca or ba/ca ratios and the chlorophyll-a concentration are not simple linear functions. the ba/ca ratio in the shells seems to increase with the chlorophyll-a concentration in the water, but continues to remain at an elevated level after the end of the bloom; however, mn/ca seems to have a correspondence with the peaks of some less intensive algae blooms, but is quite low during the most pronounced bloom recorded in may. clearly, further research is needed to better understand the link between mn/ca and ba/ca ratios in shell material and phytoplankton blooms. final remarks the la-icp-ms method is a reliable and advantageous technique for the analysis of a wide range of trace elements in carbonates. the combination of relatively high precision, low detection limits, high spatial resolution, straightforward sample preparation and fast analysis makes the method especially suited for research and application of calcium carbonate based proxies. further development of biogenic carbonate proxies will have benefits for both palaeo-climate research and investigation into the processes of biomineralisation, as well as for environmental studies. acknowledgements we would like to thank m. sejr for assistance and j. v. iperen for the chlorophyll-a data. this paper is a contribution to the euroclimate project 04 eclim fp08 casiopeia. the work has been supported financially by the european science foundation under the eurocores programme euroclimate and the danish research agency for science, technology and innovation (fnu). references carell, b., forberg, s., grundelius, e., henrikson, l., johnels, a., lindh, u., mutvei, h., olsson, m., svärtström, k. & westermark, t. 1987: can mussel shells reveal environmental history? ambio 16, 2–10. henderson, g.m. 2002: new oceanic proxies for paleoclimate. earth and planetary science letters 203, 1–13. hendry, j.p., perkins, w.t. & bane, t. 2001: short-term environmental change in a jurassic lagoon deduced from geochemical trends in aragonite bivalve shells. geological society of america bulletin 113, 790–798. klein, r.t., lohmann, k.c. & thayer, c.w. 1996: bivalve skeletons record sea-surface temperature and δ18o via mg/ca and 18o/16o ratios. geology 24, 415–418. longerich, h.p., günther, d. & jackson, s.e. 1996: elemental fractionation in laser ablation inductively coupled plasma mass spectrometry. fresenius’ journal of analytical chemistry 355, 538–542. marin, f. & luquet, g. 2004: molluscan shell proteins. comptes rendus palevol 3, 469–492. pearce, n.j.g., perkins, w.t., westgate, j.a., gorton, m.p., jackson, s.e., neal, c.r. & chenery, s.p. 1997: a compilation of new and published major and trace element data for nist srm 610 and nist srm 612 glass reference materials. geostandards newsletter 21, 115–144. pitts, l.c. & wallace, g.t. 1994: lead deposition in the shell of the bivalve mya arenaria: an indicator of dissolved lead in seawater. estuarine, coastal and shelf science 39, 93–104. schoene, b.r., fiebig, j., pfeifer, m., gless, r., hickson, j., johnson, a.l.a., dreyer, w. & oschmann, w. 2005: climate record from a bivalved methuselah (arctica islandica, mollusca, iceland). palaeo geography, palaeoecology, palaeoclimatology 228, 130–148. seed, r. 1980: shell growth and form in the bivalvia. in: rhoads, d.c. & lutz, r.a. (eds): skeletal growth of aquatic organisms, biological records of environmental change, 23–67. new york: plenum press. stecher, h.a., krantz, d.e., lord, c.j., luther, g.w. & bock, k.w. 1996: profiles of strontium and barium in mercenaria mercenaria and spisula solidissima shells. geochimica et cosmochimica acta 60, 3445–3456. vander putten, e., dehairs, f., andré, l. & bayens, w. 1999: quantitative in situ microanalysis of minor and trace elements in biogenic calcite using infrared laser ablation – inductively coupled plasma mass spectrometry: a critical evaluation. analytica chimica acta 378, 261–272. wefer, g., berger, w.h., bijma, j. & fischer, g. 1999: clues to ocean history: a brief overview of proxies. in: fischer, g. & wefer, g. (eds): use of proxies in paleoceanography: examples from the south atlantic, 1–68. berlin: springer. 92 authors’ addresses m.h.k. & d.f., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: mhk@geus.dk d.h., faculty of earth and life sciences, vrije universiteit amsterdam, de boelelaan 1085, 1081 hv amsterdam, the netherlands. r.w., royal netherlands institute for sea research (nioz), p.o. box 59, 1790 ab den burg (texel), the netherlands. geological survey of denmark and greenland bulletin 35, 2016, 51-54 51© 2016 geus. geological survey of denmark and greenland bulletin 35, 51–54. open access: www.geus.dk/publications/bull the chemical composition of chalk and marl reflects the mixture of carbonate particles and clastic input deposited on the seabed together with growth of authigenic minerals and diagenesis. the rørdal quarry in jylland (fig. 1) is known for its alternating chalk–marl succession (surlyk et al. 2010) and the aim of this article is to investigate how this cyclicity is reflected in the geochemical signature of the sequence and test if this has implications for the interpretation of the depositional environment as well as the chemostratigraphy in the chalk. the observed variation in the benthic fauna and the cyclic character of the chalk–marl succession may reflect an environmental response to orbital forcing. the benthic fauna shows higher species diversity and density in the chalk than the marl layers, suggesting more favourable living conditions in the former (lauridsen & surlyk 2008), whereas no differences in environmental stress between the two environments could be derived from a study of the trace fossils (lauridsen et al. 2011). the c. 10 m thick rørdal member was established as a lithostratigraphic unit by surlyk et al. (2010) and recognised as an expression of a late maastrichtian cooling event. x-ray diffraction (xrd) analysis indicates that the marly layers represent a relative increase in smectite clays and illite together with some quartz and analcime. the inorganic geochemical evolution in maastrichtian chalk was investigated by jørgensen (1986) who noted changes in sr/ca and mn/ca ratios towards the end of the maastrichtian in the north sea central graben, leading to the conclusion that geochemistry is a “conceivable tool in basin analysis in the lithologically rather monotonous chalk sequence” (p. 267). however, a systematic geochemical analysis of the chalk has never been undertaken and this work is an attempt to look into the potential of understanding the geology of the chalk by analysing a wide range of elements in chalk and marl. chemical variability related to clay content sixty-three samples from the rørdal quarry were ground, digested in aqua regia and analysed for 66 elements using the elan 6100 quadrupole icp-ms at the geological survey of denmark and greenland (geus). the data reduction was based on totalquant software with emphasis on the trace element analysis. the analytical procedure follows larsen et al. (2009). the cyclicity and the alternation between chalk and marl are easily recognised in the geochemical profile (fig. 2) with an increase in the concentration of major and minor elements such as al, si, fe, mg and k in the marly layers caused by the presence of clay. the eight peaks in fig. 2 can be correlated to the eight peaks in the marly layers of the rørdal member which can be identified in the gamma log in a nearby well (surlyk et al. 2010). the gamma-radiation in the well log can be explained by the increased content of k in the marl (fig. 2a). iron is the element after al with the highest increase in concentration in the marly layers indicating that the clay minerals are rich in fe. magnesium also shows an increase in the marly layers (fig. 2a), and the combined clay minerals in the marl – which according to surlyk et al. (2010) consist of smectite and illite – must be rich in fe, k and mg. the content of al, fe and k is about three times higher in the marl than in the chalk. geochemistry of the maastrichtian rørdal member, jylland, denmark: ce anomaly as a palaeo-redox proxy christian knudsen and bodil w. lauridsen denmark sweden 50 kmgermany jylland møns klint stevns klint rørdal quarry n lake profile 1 km 10°e 55° 57°n a l o w e r u p p e r m aa st ri c th ia n p al e o c e n e d an ia n fiskeler mb rørdal mb c b fig. 1. a: location of the rørdal quarry, stevns klint and møns klint in denmark. b: map of the rørdal quarry with the profile where the samples were collected. c: stratigraphic section with rørdal and fiskeler members. 5252 the concentration of many trace elements, including the rare-earth elements (ree), is also elevated in the marly layers (fig. 2b). if all ree were located in clay the increase would be three times higher, as is the case with al, k and fe, but the content of ree in the marl is ‘only’ 1.5 times higher than in the chalk. this suggests that although the ree concentration is higher in the clay than in the chalk a substantial fraction of the rees is located in the carbonate component of both chalk and marl. lanthanum and nd follow parallel tracks (fig. 2b), whereas ce crosses both tracks with relatively high ce in the marl. light ree (la, ce, pr, nd and sm) are more abundant than heavy ree (er, tm, yb and lu) in the marl compared to the chalk, which can also be seen as higher la/lu ratios (figs 3e, 4). lithophile elements such as th, cs, rb, be, cr, sc and li increase in concentrations in the marl (of which rb and li are shown in figure 2c) and are c. 2.5 to 3 times higher in the marl than in the chalk, similar to the behaviour of al and k. this suggests that these elements are almost entirely located in the clay. chalcophile elements such as pb, as, zn and cu (fig. 2d) are c. 1.5 times higher in the marl than in the chalk similar to the ree mentioned above. the content of most elements in the succession varies with the clay content. however, this is not the case for nb, zr, mn and ti (fig. 3a). mica and clay commonly contain some ti, zr and nb, elements that also occur in mafic volcanic material. these elements are difficult to leach out of minerals and generally follow clay and mica in sedimentary environments. if the clay was clastic or volcanogenic one would expect that the content of elements such as ti, zr and nb would be elevated in the marl. however, this is not the case, suggesting that a fraction of the clay may be of authigenic origin. manganese is probably hosted in the carbonate and its concentration is relatively stable throughout the analysed section. there is a decrease in the ba content in the rørdal member (fig. 3b) relative to the underlying hvidskud member with the lowest contents in its middle part. there is an increase in sr content in the overlying sigerslev member. jørgensen (1986) observed a similar increase in the sr content in chalk from the north sea basin and this may be regional. ce anomaly as a proxy for redox potential the ree commonly occur as cations with a valency of three and the different ree have similar geochemical behaviour in the sedimentary environment. however, one of the elements, ce, can also occur as ce4+ with a very low solubility in marine environments as compared to ce3+. where no fractionation of ce relative to the other ree has occurred, the distribution would be seen as a straight line on fig. 3d. to quantify the fractionation of ce, the term ce anomaly (ce/ce*) has been introduced; ce is the measured cerium concentration and ce* is what the ce content would have been without fractionation, based on the contents of la and nd. the ce anomaly is calculated: ce/ce* = 3cen/(2lan + ndn) where reen is the measured concentration normalised relative to chondrite (boynton 1984). in this paper a ce anomaly is referred to as negative when ce is depleted relative to the other ree and as positive if ce is enriched relative to the other ree. in 0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 k m g f e a l s i a ppm 1 .0 1 0 b y b d y g d s m n d p r c e l a 0 .1 1 .0 1 0 c r b g a c r vs c l i 0 .1 1 0 1 .0 d p b a s c u n i c o z n 0 5 10 15 m ( h e ig h t) u p p e r m aa st ri c h ti an r ø rd al m b s ig e rs le v m b h v id sk u d m b fig. 2. chemical profiles through the rørdal member including the uppermost part of the hvidskud member and the lowermost part of the sigerslev member. marly layers are shown as grey shaded bands. a: major and minor elements. b: ree; logarithmic scale. c: lithophile trace elements; logarithmic scale. d: chalcophile elements with ni and co; logarithmic scale. stratigraphy from surlyk et al. (2013). 53 the modern marine environment, a negative ce anomaly is indicative of oxic conditions (german & elderfield 1990) which, in turn, is caused by the low solubility of ce4+ and low availability of ce. this feature offers the possibility to look into variations in the redox conditions during deposition of the chalk (jeans et al. 2015). in fig. 4 it can be seen that there is a negative ce anomaly both in the chalk and in the marl in the rørdal quarry as well as in the chalk and the fish-clay at stevns. there is also a negative eu anomaly which is probably caused by the source of the ree being slightly depleted in eu (frei & frei 2002). the negative ce anomaly in the chalk at stevns is more pronounced than in the chalk at rørdal (fig. 4) suggesting that the environment during deposition of the chalk at stevns was more oxic than at rørdal. the chalk at stevns has a higher stratigraphic position (in the sigerslev member) and the change in the ce anomaly with time could suggest that the oxygen availability in the chalk sea increased with time during the late maastrichtian. alternatively, this could suggest that the chalk at stevns was deposited in a shallower sea. the ce concentration at rørdal changes with lithology and stratigraphic position in the section (fig. 3d); it is lower in the chalk than in the marl, indicating that the environment was more oxic in the chalk than in the marl. the ree (including ce) are located in the carbonate component as well as in the clay as mentioned above. accordingly, the ce anomaly reflects the combined effect of the composition of the seawater where the coccoliths and where the clay were formed. surlyk et al. (2010) suggested that the clay in the rørdal member is derived from volcanic eruptions. such clay, derived from alteration of volcanic glass, is likely to have an overall resemblance to the ree distribution in the source. however, the transformation from glass to clay in the marine environment could be the cause of the negative ce anomaly found in the marl. the fish-clay at stevns also has this negative ce anomaly which is indicative of formation of clay in a marine environment (kastner et al. 1984; frei & frei 2002). the question is then whether the clay was (trans)formed from volcanic glass in the free water masses or in the seabed. the seabed is likely to have been less oxic than the free water mass, and formation of the clay in the seabed would explain the difference in the redox potential compared to the chalk formed in the free water mass. finally, the composition of the clay minerals could have been modfied during diagenesis in the presence of organic material affecting the ce anomaly. 0 .0 1 1 .0 1 0 0 a n b z r r b m n t i ppm 0 2 0 4 0 b b a 0 5 0 0 1 0 0 0 1 5 0 0 c s r 0 0 .2 0 .4 0 .6 d ce anomaly 4 0 8 0 1 2 0 e l a/ l u 0 10 15 m ( h e ig h t) 5 u p p e r m aa st ri c h ti an r ø rd al m b s ig e rs le v m b h v id sk u d m b fig. 3. chemical profiles in the rørdal member. same stratigraphy as fig. 1. marly layers are shown as grey shaded bands. a: nb, zr, rb, mn and ti; logarithmic scale. b: ba. c: sr. d: ce anomaly. e: la/lu ratio; logarithmic scale. fish clay, stevns chalk, stevns marl, rørdal chalk, rørdal la ce nd sm gd dy er yb lupr pm eu tb ho tm 1 0 s am p le /r e e c h o n d ri te 1 0 0 fig. 4. chondrite-normalised ree distribution patterns for the rørdal samples compared with ree data from stevns klint (frei & frei 2002). 5454 summary and outlook the chemical composition of the chalk–marl sequence at rørdal in jylland reflects the varying proportions of carbonate and clay. the content of major and minor elements such as si, al, fe and k is proportional to the clay content, with a threefold increase in the marly layers relative to the chalk layers. it is suggested that these elements are located in clay minerals together with lithophile trace elements such as li, ga, rb, cs and th which likewise increase threefold in the clay relative to the chalk. other elements such as pb, as, zn and cu and the ree are found in c. 1.5 times higher concentrations in the marl, and these elements are located both in the clay and the carbonate component of the succession. the clay has a light ree enrichment compared to the chalk. formation of the clay as authigenic minerals may explain why large ion lithophile elements such as zr and nb, as well as ti, are not incorporated in the clay. the content of ba in the rørdal member is low relative to the underand overlying strata, and the deposition of ba could be tested as a chemo-stratigraphic marker and environmental proxy. the ree distribution shows a negative ce anomaly both in the chalk and in the marl, suggesting that the environment was oxic throughout the deposition, and as the ce anomaly is more pronounced in the chalk, the environment was more oxic where the carbonate was formed than in the clay. this observation matches the observation that there is higher species diversity and density in the chalk than in the marl (lauridsen & surlyk 2008). if the clay and the carbonate were formed in the same water mass, the observed alternating redox level would be indicative of changing conditions in the sea. however, if the main part of the clay was formed in the seabed as authigenic minerals or was affected by diagenesis, then the alternating redox levels indicated by the ce anomaly reflects changes in redox conditions at or in the seabed. the ce anomaly in chalk from stevns is larger than in chalk from rørdal, suggesting that the environment was more oxic in the chalk sea towards the end of the maastrichtian. these differences could be related to changes in temperature over time. a recent study by thibault et al. (2016) suggests a global cooling with superimposed cool/warm fluctuations in the last 8 ma of the maastrichtian including e.g. the rørdal and sigerslev members. it is suggested that the ce anomaly can be used as a palaeo-redox indicator or proxy to compare environments across chalk basins. in this context it is interesting to analyse both carbonate and clay components from the marl. acknowledgement we wish to thank lars stemmerik for constructive comments on earlier versions of the manuscript. references boynton, w.v. 1984: cosmochemistry of the rare earth elements: meteorite studies. in: henderson, p. (ed.): rare earth element geochemistry, 63–114. amsterdam: elsevier. frei, r. & frei, k.m. 2002: a multi-isotopic and trace element investigation of the cretaceous–tertiary boundary layer at stevens klint, denmark – inferences for the origin and nature of siderophile and lithophile element geochemical anomalies. earth and planetary science letters 203, 691–708. german, c.r & elderfield , h. 1990: application of the ce anomaly as a paleoredox indicator: the ground rules. paleoceanography 5, 823–833. jeans, c.v., wray, d.s. & williams, c.t. 2015: redox conditions in the late cretaceous chalk sea: the possible use of cerium anomalies as palaeoredox indicators in the cenomanian and turonian chalk of england. acta geologica polonica 65, 345–366. jørgensen, n.o. 1986: geochemistry, diagenesis and nannofacies of chalk in the north sea central graben. sedimentary geology 48, 267–294. kastner, m., asaro, f., michel, h.v., alvarez, w. & alvarez, l.w. 1984: the precursor of the cretaceous–tertiary boundary clays at stevns klint, denmark, and dsdp hole 465a. science 226 (4671), 137–143. larsen, l m., heaman, l.m., creaser, r.a., duncan, r.a., frei, r. & hutchinson, m. 2009: tectonomagmatic events during stretching and basin formation in the labrador sea and the davis strait: evidence from age and composition of mesozoic to palaeogene dyke swarms in west greenland, journal of the geologicla society (london) 166, 999–1012. lauridsen, b.w. & surlyk, f. 2008: benthic faunal response to late maastrichtian chalk–marl cyclicity at rørdal, denmark. palaeogeography, palaeoclimatology, palaeoecology 269, 38–53. lauridsen, b.w., surlyk, f. & bromley, r.g. 2011: trace fossils of a cyclic chalk–marl succession; the upper maastrichtian rørdal member, denmark. cretaceous research 32, 194–202. surlyk, f., stemmerik, l., ahlborn, m., harlou, r., lauridsen, b.w., rasmussen, s.l., schovsbo, n., sheldon, e. & thibault, n.r. 2010: the cyclic rørdal member – a new lithostratigraphic unit of chronostratigraphic and palaeoclimatic importance in the upper maastrichtian of denmark. bulletin of the geological society of denmark 58, 89–98. surlyk, f., rasmussen, s.l., boussaha, m., schiøler, p., schovsbo, n.h., sheldon, e., stemmerik, l. & thibault, n.r. 2013: upper campanian–maastrichtian holostratigraphy of the eastern danish basin. cretaceous research 46, 232–256. thibault, n., harlou, r., schovsbo, n.h., stemmerik, l., surlyk, f. 2016: late cretaceous (late campanian–maastrichtian) sea surface temperature record of the boreal chalk sea. climate of the past 12, 429–438. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark, e-mail: ckn@geus.dk geological survey of denmark and greenland bulletin 6, 57-66 57geological survey of denmark and greenland bulletin 6, 57–66 © geus, 2004 palaeoproterozoic age of a basement gneiss complex in the charcot land tectonic window, east greenland caledonides kristine thrane the charcot land tectonic window exposes crystalline basement gneisses, which form part of the foreland of the east greenland caledonides. these gneisses were previously believed to be archaean in age, on the basis of imprecise k-ar analyses carried out in the early 1980s on hornblende from amphibolitic bands and inconclusive rb/sr isotope data. new u-pb singlezircon ion microprobe analyses on the gneisses of the window yield upper intercept ages of 1916 ± 21 and 1928 ± 11 ma, and are interpreted to represent the age of crystallisation of the igneous protolith. the foreland gneisses of the charcot land window are similar in age to parts of the allochthonous gneiss complexes of structurally overlying thrust sheets, but the two terranes have different lithological and structural characteristics. no archaean rocks have been identified with certainty in any of the east greenland caledonian foreland windows. keywords: caledonides, east greenland, geochronology, palaeoproterozoic geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. present address: geological institute, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. email: kthrane@geol.ku.dk the charcot land window is located between latitudes 71°45′n and 72°15′n in the south-western part of the 1300 km long east greenland caledonides (fig. 1). it is one of a series of tectonic windows, interpreted to expose parautochthonous foreland (higgins & leslie 2000), found along the western border of the caledonian orogen. the gåseland window is exposed to the south at c. 70°n (wenk 1961; phillips et al. 1973), and the målebjerg and eleonore sø windows to the north between latitudes 73°30′–74°15′n (leslie & higgins 1998; higgins & leslie 2000, 2004, this volume). further to the north, the foreland basement is also exposed in western dronning louise land (76°–77°n; e.g. strachan et al. 1992), and in the small nørreland window (78°40′n; hull & friderichsen 1995). apart from these restricted areas the foreland of the east greenland caledonides is not well known, as it is largely concealed beneath the inland ice to the west. the charcot land window (fig. 2) exposes a basement complex of grey gneisses with amphibolite bands, overlain by a cover of low to medium-grade supracrustal rocks including carbonates, volcanic rocks and siliciclastic sediments (charcot land supracrustal sequence; steck 1971). both basement and cover are cut by major palaeoproterozoic granite intrusions (hansen et al. 1981). structurally overlying the charcot land window are caledonian thrust sheets comprising crystalline gneiss complexes (flyverfjord infracrustal complex) and overlying high-grade metasedimentary rocks (krummedal supracrustal sequence; henriksen & higgins 1969, 1976). the crystalline gneisses making up the flyverfjord infracrustal complex in hinks land, south-east of charcot land (fig. 2), are of late archaean age (c. 2700 ma; rex & gledhill 1974; thrane 2002). the flyverfjord infracrustal complex extends both southwards and northwards (fig. 1); however, north of 72°50′n very similar looking orthogneisses have yielded palgeus bulletin 6.pmd 10-02-2005, 09:5457 58 ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ c a le d o n ia n f o ld b el t in l a n d ic e palaeogene basalts palaeogene intrusions wandel sea basin: carboniferous–palaeogene east greenland basin: carboniferous–cretaceous sediments devonian – continental sediments crystalline basement thrust fault/shear zone post-caledonian late to post-caledonian caledonian fold belt caledonian foreland 70° 74° 78° 35° wandel hav 100 km jameson land scoresby sund 25° traill ø bessel fjord kejser franz joseph fjord kong oscar fjord dronning louise land fig. 2 danmarkshavn w es te rn li m it of de fo rm at io n ▲ ▲ peary land k ro np ri ns c hr is tia n la nd caledonian granites neoproterozoic–ordovician sediments (east greenland) palaeo-mesoproterozoic sediments and basalts (north greenland) neoproterozoic–silurian sediments (north greenland) neoproterozoic–silurian sediments (north greenland) crystalline gneisses and volcano-sedimentary complexes palaeo-mesoproterozoic sediments and basalts (north and north-east greenland) high-grade metasediments (krummedal supracrustal sequence) charcot land window gåseland window eleonore sø window målebjerg window 25° 15° 15° 35° 82° ▲ ▲ ▲ fig. 1. geological map of the east greennland caledonides. frame indicates study area shown at larger scale in fig. 2. geus bulletin 6.pmd 10-02-2005, 09:5458 59 aeoproterozoic ages (c. 1900 ma; rex & gledhill 1981; kalsbeek et al. 1993; thrane 2002). the krummedal supracrustal sequence, that overlies the flyverfjord infracrustal complex as well as the similar gneiss complexes between latitudes 70° and 76°n, was deposited later than 1100 ma ago, and underwent high grade metamorphism with generation of granites c. 940 ma ago (kalsbeek et al. 2000). the contact between the krummedal supracrustal sequence and the structurally overlying neoproterozoic–ordovician sedimentary succession is a shear zone, interpreted as an extensional detachment or locally a thrust (escher & jones 1998; leslie & higgins 1998). the western border of the main neoproterozoic–ordovician outcrop in the fjord region from 72°–75°n is a late orogenic extensional fault system (e.g. hartz & andresen 1995). the c. 13 km thick neoproterozoic eleonore bay supergroup succession (sønderholm & tirsgaard 1993) together with the vendian tillite group (800–1000 m) and cambro-ordovician shelf sequence (up to 4 km), constitute the highest part of the uppermost caledonian thrust sheet (higgins et al. 2004). in 1968, the southern part of the charcot land area was mapped by the geological survey of greenland (henriksen & higgins 1969, 1976; steck 1971), during a systematic regional mapping project in the scoresby sund region (70°–72°n). during the 1997 and 1998 survey expeditions to the kong oscar fjord region (72°–75°n), the northern part of charcot land was mapped by friderichsen & thrane (1998). sample collections were made for ion microprobe zircon studies, the results of which are reported here. geological setting the foreland rock units exposed within the charcot land window include crystalline basement orthogneisses with interleaved amphibolite bands, that are overlain by a c. 2000 m thick succession of various metasedimentary rocks (including white marble) and metamorphosed basic extrusive and intrusive rocks (charcot land supracrustal sequence). these units are cut by two major granitoid intrusions which crop out widely in central charcot land (fig. 2); one is a hornblende-biotite quartz diorite to granodiorite body and the other a pegmatitic muscovite granite. in southernmost charcot land a hornblende gabbro body intrudes the basement gneisses. tillit nunatak in south-west charcot land takes its name from a sheared tillite resting unconformably on the granodiorite intrusion. this tillite has been correlated with the vendian tillites of the fjord zone (moncrieff 1989), as has a similar tillite in the gåseland window. the charcot land tillite is very little deformed but does contain a planar cleavage. the charcot land supracrustal sequence of southernmost charcot land is characterised by greenschist facies metamorphism. metamorphic grade increases towards the north-east and reaches upper amphibolite facies at ~ 72°n latitude (steck 1971). further to the north, the metamorphic grade again decreases (friderichsen & thrane 1998). the eastern and western boundaries of the charcot land window are marked by major caledonian thrusts (fig. 2). the western thrust dips gently to the t t overlying thrust units tillit nunatak formation metasediments marble thrust fold trend metavolcanics hornblende gabbro 30˚ 72˚ 30˚ charcot land c ha rc o t la nd se qu en ce an tillit nunatak daugaar d-jen sen gle tsc he r nvf hinks land 426040 1928 ± 11 ma 29˚ muscovite granite quartz diorite basement gneiss and amphibolite 426041 1916 ± 21 ma 10 km 29˚ fig. 2. geological map of the charcot land window, showing major lithological divisions and sample locations. modified from henriksen & higgins (1976). the rock types of the overlying thrust sheets are undifferentiated, and include gneisses of the flyverfjord infracrustal complex and the krummedal supracrustal sequence. an, alfabet nunatakker; nvf, nordvestfjord. geus bulletin 6.pmd 10-02-2005, 09:5459 60 west and is only exposed on the alfabet nunatakker, while the eastern thrust dips to the east and can be traced for more than 25 km in western hinks land (higgins 1982). north-east of charcot land, on the north-east side of innermost nordvestfjord, a very large-scale, recumbent, west-vergent isoclinal anticline makes up the eastern boundary of the window (fig. 3). this fold nappe is sitting in the hanging wall and is made up by the cover rocks from outside of the window. the nappe, first recognised by eduard wenk and helge backlund in 1934 (backlund in koch 1955; wenk 1956), is outlined by a conspicuous white marble unit that has an isoclinal fold closure some 25 km north-west of its first appearance opposite the front of daugaard-jensen gletscher. however, the narrow closure that wenk and backlund observed from fjord level accounts for less than half of the magnitude of this fold nappe. over its entire length, the structure could easily accommodate a translative movement of the proportions necessary to form the charcot land window, a minimum of 40 km displacement (friderichsen & thrane 1998). structures the broad structure of the charcot land window is an elongate n–s-trending dome (fig. 2). within the window, foliation trends have a general nw–se strike and dip at shallow angles to the east. lineations plunge at moderate angles eastwards, between north-east and south-east. major folds have trends between e–w and nw–se, while minor folds have more variable trends and plunge directions. the crystalline basement terrain east and north-east of charcot land, that forms part of the structurally overlying thrust sheet, exhibits a different pattern of structures. friderichsen & thrane (1998) mapped a broad area of the allochthonous gneisses north-east of charcot land. they record the general foliation trends in eastern parts of their area as ne–sw to n–s with an eastwards dip, with linear elements plunging at moderate to shallow angles to the east or southeast; these were interpreted as caledonian structures. the presence of major, recumbent, nw-verging folds suggests the ne–sw trends might be a response to caledonian compression, while the n–s trends may relate to caledonian extension, mainly seen as ductile top-down-to-the-east faults. in the western part of their area, friderichsen & thrane (1998) noted the structural pattern as more diffuse, perhaps due to a fig. 3. part of the major, recumbent, west-verging isoclinal fold that defines the eastern boundary of the charcot land window (hanging wall). the isocline is outlined by the two white marble bands (m) which form a closure just beyond the left side of the photograph. the black units are amphibolite. north-east of innermost nordvestfjord (see fig. 2); profile height about 1000 m. geus bulletin 6.pmd 10-02-2005, 09:5460 61 less intense caledonian overprinting of older and more complex pre-caledonian structures. in general the foliation trends are ne–sw, with nw-plunging lineations. although the general foliation trends within the charcot land window are also broadly nw–se, like those in the eastern areas of the overlying thrust sheets, the structures in charcot land are not interpreted as caledonian. lineations in charcot land also have much steeper eastward dips than in the thrust sheets. further evidence that the caledonian overprint within the window was generally weak is that the large palaeoproterozoic granite intrusions cutting the basement gneisses in charcot land show no evidence of deformation. the only certain caledonian structures are the planar cleavage in the diamictites of the vendian tillit nunatak formation. the major thrust along the east side of the charcot land window is well-defined in north-west hinks land (fig. 2), but its northward continuation on the northeast side of nordvestfjord was previously uncertain (henriksen & higgins 1976). on the basis of their 1997 studies, friderichsen & thrane (1998) proposed that the movement might have been taken up by the major nappe-like fold on the north-east side of the charcot land window (fig. 3). the trend and westward sense of overturning of this nappe-like fold support the viewpoint that it is a caledonian structure, although no other comparable structures were observed within the window. a thick low-grade succession of dark phyllitic shales observed in the crest of the fold has also been traced in the western nunataks of charcot land, substantially increasing the possible extent of the structure. in addition a thrust associated with this nappe-like major fold suggests that the total displacement was probably significantly more than the 40 km proposed by henriksen & higgins (1976) and henriksen (1986). previous geochronological studies hansen et al. (1981) analysed hornblende from amphibolite bands within the charcot land basement gneisses, and obtained k-ar ages of 2097 ± 105 ma and 2855 ± 145 ma. these were regarded as minimum ages for the amphibolite units of the crystalline complex. rb-sr whole rock analyses on samples of the gneisses were undertaken by hansen (1976), but while the results did not yield any exact ages, there were indications that the gneisses might be more than 2200 ma old. based on lithology and age an archaean origin comparable to that of the flyverfjord basement gneisses was thought likely. rb-sr whole rock analyses were also undertaken on samples of the widespread pegmatitic muscovite granite body, that intrudes both the basement gneisses and the supracrustal rocks in charcot land (hansen et al. 1981); an age of c. 1850 ma was considered to indicate the approximate time of intrusion. k-ar analyses on large muscovite crystals from the same granite yielded ages of 1760 ± 60 and 1870 ± 60 ma, interpreted as a minimum age of emplacement (hansen et al. 1981). based on field observations, steck (1971) argued that the granite was intruded after the main metamorphism of the supracrustal rocks, which was suggested to have taken place about 1900–1850 ma ago (hansen et al. 1981). a young rb-sr biotite age of 402 ± 10 ma from an amphibolite, together with a biotite-feldspar-wholerock isochron age of 402 ± 8 ma for samples of the pegmatitic granite, were considered to reflect a caledonian greenschist facies metamorphic overprint (hansen et al. 1981). isotopic data from orthogneiss units in some of the other foreland areas exposed along the margin of the caledonian orogen in east greenland have yielded palaeoproterozoic protolith ages, e.g. kalsbeek et al. (1993) and tucker et al. (1993) obtained palaeoproterozoic ages for basement gneisses from the western part of dronning louise land (77°n, 25°w) and quartz porphyry bodies and grey granites within the eleonore sø window have yielded similar ages (higgins & leslie 2004, this volume). none of the so far dated foreland rock units have yielded convincing archaean ages. geochronology samples two representative samples from the basement gneiss complex were studied. sample 426040 is a fine-grained, light grey, granodioritic orthogneiss, and sample 426041 a dark grey, coarse-grained, granodioritic orthogneiss (fig. 4). both rock units exhibit a penetrative gneissosity and mineral lineation, and are cut by deformed light-coloured granite veins and undeformed pegmatitic muscovite granite veins. in the field, the age relationships between the two orthogneisses are very clear; the fine-grained orthogneiss (426040) intrudes and cuts the coarse-grained orthogneiss (426041). the limited field work undertaken in charcot land in 1997, and that undertaken earlier during the 1968– geus bulletin 6.pmd 10-02-2005, 09:5461 62 1972 scoresby sund expeditions (henriksen 1986), indicate both gneiss types to be part of the regional basement gneiss complex, the oldest rocks exposed in charcot land. analytical methods for the ion microprobe study u-pb dating of zircons was undertaken using the cameca ims 1270 ion probe at the nordsim laboratory, swedish museum of natural history, stockholm. approximately 50 zircon grains from each sample were hand-picked, and mounted in a transparent epoxy resin together with reference zircons 91500 (from ontario, canada, with a weighted average 207pb/206pb age of 1065 ma; wiedenbeck et al. 1995). the zircon grains were polished sufficiently to expose any potentially older cores. the mounts were examined by reflected light microscopy and by backscatter imaging in a scanning electron microscope and then coated with c. 30 nm of gold. analytical procedures are similar to those described by schuhmacher et al. (1994) and whitehouse et al. (1997). calibration of pb/u ratios follows procedures similar to those used by the ion probe group at the australian national university (williams 1998), and is based on observed relationships between pb/u and uo 2 /u, during the same analytical run. results are given as discordia line intercept ages. the ages were calculated using isoplot/ex (ludwig 1999). analytical results the u-pb zircon data (table 1) are presented in conventional concordia diagrams (fig. 6; 1 f error ellipses). sample 426041 most of the zircons in sample 426041 are elongate, prismatic and clear, with sizes ranging from 100 to 400 mm, most commonly between 200 and 250 mm. they contain solid homogenous cores, some of which show oscillatory zonation. the rims are broad, metamict and show zonation. from the backscatter images, it is not clear whether the rims are metamorphic or simply alteration rims (fig. 5). however, there is a clear chemical variation, with the rims having much lower th/u ratios (0.02–0.07) than the cores (0.19– 0.36), and also containing more common lead (table 1). the variation in the th/u ratios indicates that the rims may have a metamorphic origin, while the higher common lead content may be a result of alteration of the rims. in the concordia diagram (fig. 6a), all the analyses (rims as well as cores) fall on the same discordia line. the upper intercept age is 1916 ± 21 ma and the lower intercept date of 443 ± 25 ma (mswd = 10.9), where the upper intercept is interpreted as the best approximation of the crystallisation age of the gneiss protolith. most of the rims plot on the discordia line, indicating that they must have a palaeoproterozoic origin very close in age to the protolith, e.g. the rock must have been exposed to metamorfig. 4. dark grey orthogneiss (426041) cut by a broad dyke of light grey orthogneiss (426040). both are cut by later pegmatitic granite veins. water flowing from right to left produces the colour differences between wet and dry rocks. fig. 5. backscatter image of zircon number 7 from sample 426041. the circles indicate the ion probe analysis sites. geus bulletin 6.pmd 10-02-2005, 09:5462 6 3 table 1. sims u-th-pb analytical data and derived ages sample/ u pb th th/u f % 207pb ±σ 207pb 206pb ±σ disc. ages (ma) spot# ppm ppm ppm meas. common 206pb % 235u % 238u % % 207pb ±σ 207pb ± 206pb ±σ 206pb 235u 238u 426040 9c 351 137 86 0.25 0.08 0.1170 0.29 5.275 0.82 0.327 0.77 –5.3 1911 5 1865 7 1824 12 6c 473 148 134 0.28 0.07 0.1125 0.33 4.041 0.82 0.261 0.75 –21.1 1840 6 1642 7 1493 10 5c 717 192 279 0.39 1.10 0.1034 0.46 2.713 0.92 0.190 0.79 –36.3 1686 8 1332 7 1123 8 1c 1583 245 727 0.46 1.29 0.0998 0.55 1.739 1.00 0.126 0.83 –55.8 1620 10 1023 6 767 6 3c 628 122 190 0.30 1.14 0.0996 0.92 2.243 1.26 0.163 0.87 –42.7 1616 17 1195 9 975 8 4c 856 158 362 0.42 0.18 0.0971 0.42 2.062 1.14 0.154 1.06 –44.1 1569 8 1136 8 923 9 2c 752 134 194 0.26 1.49 0.0958 0.59 2.007 1.12 0.152 0.96 –43.8 1543 11 1118 8 912 8 7r 7482 463 250 0.03 4.80 0.0527 5.96 0.425 6.01 0.058 0.77 15.9 317 130 359 18 366 3 426041 2c 302 110 83 0.27 0.09 0.1165 0.40 4.883 0.93 0304 0.83 –11.6 1904 7 1799 8 1711 13 13c 247 93 88 0.36 0.11 0.1143 0.49 4.857 1.19 0.308 1.09 –8.3 1869 9 1795 10 1732 17 14c 503 138 94 0.19 0.40 0.1115 0.42 3.635 0.93 0.236 0.83 –27.7 1824 8 1557 7 1368 10 4c 364 107 123 0.34 0.21 0.1107 0.41 3.707 0.97 0.243 0.87 –25.1 1810 7 1573 8 1402 11 2r 475 127 106 0.22 0.24 0.1086 0.39 3.424 0.95 0.229 0.87 –27.9 1775 7 1510 8 1328 10 7c 780 212 162 0.21 0.16 0.1067 0.25 3.415 0.96 0.232 0.93 –25.3 1745 5 1508 8 1345 11 9c 618 136 175 0.28 0.53 0.1057 0.45 2.711 1.15 0.186 1.06 –39.4 1727 8 1332 9 1100 11 1c 683 134 192 0.28 0.36 0.0999 0.41 2.288 0.93 0.166 0.84 –41.9 1621 8 1208 7 991 8 7r 3705 594 95 0.03 0.40 0.0935 0.29 1.827 0.88 0.142 0.83 –45.8 1498 5 1055 6 854 7 8r 3445 514 73 0.02 0.83 0.0924 0.33 1.727 0.90 0.136 0.83 –47.3 1475 6 1019 6 820 6 9r 2780 289 132 0.05 0.69 0.0750 0.58 0.992 1.09 0.096 0.92 –46.7 1068 12 700 6 591 5 15r 3761 349 159 0.04 1.59 0.0732 0.63 0.867 1.05 0.086 0.84 –49.8 1019 13 634 5 531 4 3r 3824 354 93 0.02 0.80 0.0693 0.52 0.823 0.98 0.086 0.83 –43.2 909 11 609 5 532 4 11r 3622 294 108 0.03 1.67 0.0598 0.80 0.630 1.16 0.076 0.85 –21.2 597 17 496 5 475 4 5r 3622 280 255 0.07 2.27 0.0548 0.87 0.542 1.22 0.072 0.86 –11.4 403 19 440 4 447 4 errors on ratios and ages are quoted at 1 σ level. f % common is the fraction of common 206pb estimated from the measured 204pb. disc. % refers to the degree of discordance of the zircon analysis. σ u pb th % σ σ σ σ σ 1911 5 1865 7 1824 12 1840 6 1642 7 1493 10 1686 8 1332 7 1123 8 1620 10 1023 6 767 6 1616 17 1195 9 975 8 1569 8 1136 8 923 9 1543 11 1118 8 912 8 317 130 359 18 366 3 1904 7 1799 8 1711 13 1869 9 1795 10 1732 17 1824 8 1557 7 1368 10 1810 7 1573 8 1402 11 1775 7 1510 8 1328 10 1745 5 1508 8 1345 11 1727 8 1332 9 1100 11 1621 8 1208 7 991 8 1498 5 1055 6 854 7 1475 6 1019 6 820 6 1068 12 700 6 591 5 1019 13 634 5 531 4 909 11 609 5 532 4 597 17 496 5 475 4 403 19 440 4 447 4 g e u s b u lle tin 6 .p m d 1 0 -0 2 -2 0 0 5 , 0 9 :5 4 6 3 64 phism soon after crystallisation of the protolith, and these rims have later suffered pb loss. only a few rims cluster around the lower intercept and could reflect the time when the gneiss suffered caledonian metamorphism. sample 426040 the morphologies of the zircons in 426040 are very similar to those in sample 426041. most have long prismatic shapes, but stubby grains also occur. the zircons are clear and range in size from 100 to 250 mm. both homogenous and oscillatory zoned cores are present, while the rims are often metamict. in this study mostly cores were analysed. they plot on a discordia line (fig. 6b) yielding intercept ages of 1928 ± 11 ma and 467 ± 18 ma (mswd = 0.74). two rims were analysed; these do not plot on the discordia line, but one of them plots on the concordia line, yielding a 206pb/ 238u age of 366 ± 3 ma. discussion the two analysed samples of basement gneisses from the charcot land window yield identical upper intercept ages for the protolith within error, 1928 ± 11 and 1916 ± 21 ma. the fact that the two orthogneisses yield the same age demonstrates that several distinct magma pulses were emplaced during this time period. if the rb-sr whole-rock age of c. 1850 ma reported by hansen et al. (1981) for the undeformed muscovite granite is valid, then the time of deformation and gneissification is bracketed between c. 1920 and 1850 ma. the palaeoproterozoic metamorphic effect seen in the growth of rims on zircons in sample 426041 might have been caused by the palaeoproterozoic intrusive activity. the lower concordia intercepts suggesting caledonian ages are indicative of some pb loss and alteration of the zircons (fig. 6), and can be linked to burial of the foreland beneath a several kilometre thick pile of caledonian thrust sheets. within the charcot land window limited caledonian deformation is recorded, e.g. development of a planar cleavage in the diamictites of the vendian tillit nunatak formation, and associated folding in the underlying basement gneisses (moncrieff 1989). however, caledonian deformation was not pervasive and, as noted above, the palaeoproterozoic muscovite granite body has no internal fabric. the new age determinations reported here indicate that the protolith of the basement gneiss complex in charcot land is palaeoproterozoic, rather than archaean as suggested by hansen (1976) and hansen et al. (1981). at the current state of knowledge there is, in fact, no convincing isotopic evidence of the presence of archaean basement rocks in any of the foreland windows along the western margin of the caledonian orogen. volcano-sedimentary sequences of palaeoproterozoic age are known in the charcot land and eleonore sø windows (higgins et al. 2001), but are not known in the allochthonous thrust sheets that overlie the foreland windows. similarly, the late mesoproterozoic – early neoproterozoic krummedal supracrustal sequence that is widely represented in the thrust sheets 0.4 0.3 0.2 0.1 0.4 0.3 0.2 0.1 0.0 0 1 2 3 4 5 6 7 400 800 1200 1600 2000a 426041 grey orthogneiss cut by 426040 8 9r 5 5 3 4 7r 1 9c 2r 1511 3 14 13 7c 4 2c intercepts at 443 + 25 & 1916 + 21 ma (mswd = 10.9, n = 15) 20 6 p b / 23 8 u 0.0 0 1 2 3 4 5 6 7 400 800 1200 1600 2000b 426040 grey orthogneiss intruding 426041 intercepts at 467 + 18 & 1928 + 11 ma (mswd = 0.74, n = 6) 20 6 p b / 23 8 u 207pb / 235u 2 1 7 6 9 fig. 6. u-pb concordia diagrams for the two samples of orthogneiss from charcot land. a: sample 426041. b: sample 426040. error ellipses show 1 σ errors and errors on the intercept ages are 2 σ. geus bulletin 6.pmd 10-02-2005, 09:5464 65 structurally above these windows is not present within them. it could, therefore, be argued that the known archaean rock units, such as the allochthonous flyverfjord infracrustal complex south of latitude 72°50′n, represent a terrain that was accreted onto the palaeoproterozoic foreland. there remain many uncertainties in making regional assessments. for example, modern isotopic age data are still lacking for the crystalline basement rocks of the southern gåseland window, while metasedimentary rocks found as infolded layers within the allochthonous crystalline basement gneisses north of latitude 72°n (friderichsen & thrane 1998; thrane & friderichsen 1999) are of uncertain age. the assumption that these infolded metasedimentary layers are related to the thick developments of the late mesoproterozoic – early neoproterozoic krummedal sequence is not proven, and it cannot be excluded that they are equivalents of the palaeoproterozoic charcot land supracrustal sequence. the absence of representatives of the krummedal supracrustal sequence in the foreland windows could be considered as support for the view that this sequence was deposited far away from the flyverfjord crystalline basement and that these units were juxtaposed during the caledonian orogeny (watt & thrane 2001). the ages obtained from the basement gneiss complex in the charcot land foreland window are not dissimilar from the ages obtained on the allochthonous crystalline basement complexes north of 72°50′n (rex & gledhill 1981; kalsbeek et al. 1993; thrane 2002), although the lithological make-up of the two basement complexes is different. characteristic features of charcot land include the spectacular palaeoproterozoic granitoid intrusions, which occur both as netveining dykes and as major undeformed plutons. such characteristic features are uncommon in the allochthonous palaeoproterozoic crystalline basement rocks to the north. it is the author’s opinion that the grey orthogneisses in the allochthonous crystalline basement north of 72°50′n originally had much the same appearance as the charcot land orthogneisses, but that the former suffered much more intense deformation during the caledonian orogeny. thus, the charcot land basement gneisses and the allochthonous basement gneiss complexes north of 72°50′n could once have been parts of the same terrain prior to separation by caledonian thrusting, with the major nappelike structure on the north-east side of the charcot land window taking up the thrust movement. alternatively, the two palaeoproterozoic basement terrains may originally have been unrelated, and with different histories, but have been brought into close proximity by thrusting during the caledonian orogeny. acknowledgements the isotope data described in this paper were acquired at the nordsim laboratory at the swedish museum of natural history, stockholm. critical comments on the manuscript by johan d. friderichsen, adam a. garde, a.k. higgins and feiko kalsbeek are greatly appreciated. this project was based on funding from the danish natural science research council. david gee and clark friend are thanked for constructive reviews of the manuscript. references escher, j.c. & jones, k.a. 1998: caledonian thrusting and extension in frænkel land, east greenland (73°–73°30′n): preliminary results. in: higgins, a.k. & frederiksen, k.s. 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(eds): geology of east greenland 72°–75°n, mainly caledonian: preliminary reports from the 1998 expedition. danmarks og grønlands geologiske undersøgelse rapport 1999/19, 37–41. tucker, r.d., dallmeyer, r.d. & strachan, r.a. 1993: age and tectonothermal record of laurentian basement, caledonides of ne greenland. journal of the geological society (london) 150, 371–379. watt, g.r. & thrane, k. 2001: early neoproterozoic events in east greenland. precambrian research 110, 165–184. wenk, e. 1956: alpines und ostgrönländisch-kaledonisches kristalline, ein tektonish-petrogenetischer vergleich. verhandlungen des naturforscher gesellschaftes in basel 67, 75–102. wenk, e. 1961: on the crystalline basement and the basal part of the pre-cambrian eleonore bay group in the south-west part of scoresby sund. meddelelser om grønland 168(1), 54 pp. whitehouse, m.j., claesson, s., sunde, t. & vestin, j. 1997: ion microprobe u-pb zircon geochronology and correlation of archaean gneisses from the lewisian complex of gruinard, north-western scotland. geochimica et cosmochimica acta 61, 4429–4438 wiedenbeck, m., allé, p., corfu, f., griffin, w.l., meier, m., oberli, f., von quardt, a., roddick, j.c. & spiegel, w. 1995: three natural zircon standards for u-th-pb, lu-hf, trace element and ree analyses. geostandards newsletter 19, 1–23. williams, i.s. 1998: u-th-pb geochronology by ion microprobe. in: mckibben, m.a., shanks iii, w.c. & ridley, w.i. (eds): applications of microanalytical techniques to understanding mineralizing processes. reviews in economic geology 7, 1–35. geus bulletin 6.pmd 10-02-2005, 09:5466 geological survey of denmark and greenland bulletin 17, 2009, 37-40 the danish landscape is characterised by low relief and consequently the risk of soil erosion is low compared to many central and southern european countries with more variable terrain (european environment agency 2000; van der knijff et al. 2000). however, even in countries with less intensive erosion, water-induced soil erosion is recognised as an increasingly important environmental issue due to its role in the transport of nutrients, pesticides and other contaminants to rivers, lakes and coastal waters (e.g. stone 2000). there are relatively few monitoring programmes of sediment erosion in denmark and those that exist typically only cover the last few decades (veihe et al. 2003). therefore, it is difficult to identify long-term trends and baseline conditions. however, the geological record provides insight into patterns and rates of soil erosion through time. lake and fjord sediment archives are especially useful because they can provide continuous and undisturbed sediment successions that can be ana lysed at high temporal resolution. these sediment records can be examined using a variety of approaches that include sedimentological, geochemical and biological analyses and thus generate important insight into baseline states, trajectories and responses to forcing mechanisms over long timescales, which would otherwise be difficult to obtain. the records are typically limited to yielding insight only into the average rate of erosion and they often provide little information about the spatial extent or distribution of erosional processes within a catchment area. in this paper we present an example of a long-term erosional record from gudme sø, fyn (fig. 1). numerous archae ological excavations have been undertaken near gudme sø, and the geological survey of denmark and greenland has carried out analyses of sediments from the lake to provide a continuous picture of landscape changes. sediment accumulation rates of minerogenic matter and pollen analysis are here used to ex plore the erosional response to changes in land-use. study site and methods gudme sø is located on south-east fyn c. 5 km from the sea in a gently undulating terrain with surface deposits consisting of clay till (fig. 1). the lake has a surface area of 9 ha, a mean water depth of 0.5 m, and a catchment area of 48 ha. it has no major natural inlets or outlets. an 11.8 m long sediment core of slightly humic gyttja with low calcareous content and varying silt and clay contents was retrieved from the lake. age determination was provided by radiocarbon dating, and the chronology at the top of the core was further refined by linear interpolation, using the first occurrence of spheroidal carbonaceous fly-ash particles and the date of the sediment surface (i.e. the year of coring) as bracketing ages (fig. 2). sediment accumulation rates of minerogenic matter (sar-min in mg/cm2 per year) were calculated and used as prox ies of soil erosion from the catchment area to the lake (e.g. mackereth 1966). the changes in sar-min values were compared to pollen-inferred changes in vegetation and landuse from the same sediment core. the increases and decreases in non-arboreal pollen (nap) were used as a record of changes in the proportion of open land. it is assumed that the variation in the sum of taxa of cultivated plants and plantago lanceolata (ribwort plantain) reflects changes in the extent of arable land, and pastures or meadows, respectively (behre 1981; gaillard 2007). the record of colonies of the green algae pediastrum sp. is used as proxy evidence for in-lake productivity (bradshaw et al. 2005). soil erosion and land-use change during the last six millennia recorded in lake sediments of gudme sø, fyn, denmark peter rasmussen and jesper olsen © geus, 2009. geological survey of denmark and greenland bulletin 17, 37–40. available at: www.geus.dk/publications/bull 37 fig. 1. aerial photograph of gudme sø seen from the south-east. the lake size is c. 490 × 250 m. today the lake catchment area (48 ha) consists of 50% tilled, 25.8% natural and 24.2% built-up area. photograph courtesy of the royal danish air force. rosa_2008:rosa-2008 01/07/09 15:48 side 37 results and discussion chronology the 14c dates from the gudme sø sediment core are based on bulk sediment samples and may overestimate their actual ages due to the hard-water effect (björck & wohlfarth 2001). however, the caco3 content of the sediments is very low and the ages of key-pollen, stratigraphical levels at gudme sø are in agreement with other independent ages from corresponding levels in danish bogs where the dated peat is unaffected by hard water (table 1). hence, we consider the gudme sø age–depth model to be reasonably accurate and reliable within c. 100 years. in the following, all ages are given in calendar years bc/ad. incipient landscape disturbance in fig. 3 the history of the last c. 6000 years of soil erosion to the gudme sø basin is compared with contemporary changes in vegetation and land-use. coincident increases in total nap and taxa of cultivated plants and in sar-min suggest a causal link between agricultural activities and soil loss. the low sar-min values in the late mesolithic (c. 4200– 3900 bc) suggest a low level of soil disturbance, which is in good agreement with the pollen data. very low nap values (c. 2%) indicate that the landscape was dominated by closedcanopy forests with only a sparse field layer vegetation (iver sen 1973). during the mesolithic, anthropogenic impact on the vegetation appears to have been negligible, and landscape disturbance was driven by natural agencies, implying that the sediment flux to the lake at this time represents a ‘natural’ baseline state. in denmark the cultural shift from the mesolithic (hunting-fishing-gathering) to the neolithic (farming) way of living took place c. 3900 bc. approximately 200 years later (c. 3650–3500 bc) a marked increase in both sar-min and nap values at gudme sø indicate an erosional event clearly triggered by deforestation that was associated with incipient agricultural activities. at that time the first pollen types unambiguously indicative of crop cultivation and pastoral farming occurred (cereals and plantago lanceolata, respectively). interestingly, the data indicate that catchment disturbance and agricultural activities precede accelerated erosion rates by c. 150–200 years, thus showing a delay or threshold effect in the system’s response. between c. 3350 and 3200 bc soil erosion rates increased again, although this time not correlated with pollen evidence of land clearance or intensified agriculture. low soil erosion rates between c. 3200 and 2650 bc and low nap values indicate catchment stability. at about 2650 bc a renewed and short-lived (c. 2650–2550 bc) deforestation was accompanied by intensified agricultural activities reflected in high percentages of nap, plantago lanceolata and cultivated taxa. despite the apparent intensity of this brief land clearance episode, the erosional response was moderate. this might be 38 20001000010002000300040005000 age (calendar years bc/ad) d ep th b el o w s ed im en t su rf ac e (c m ) k-5839 k-6022 k-5840 k-6023 k-5771 k-6024 k-5770 k-6025 k-5841 k-6026 k-5842 k-5769 k-5768 200 300 400 500 600 700 800 900 1000 1100 1200 100 table 1. 14c dates of pollen-analytical levels in gudme sø and three danish raised bogs gudme fuglsø abkær holmegaard sø mose mose mose data partly from odgaard (1994). 1st centaurea cyanus (cornflower) ad 1320 ad 1360 ad 1240 ad 1350 1st secale cereale (rye) 170 bc 80 bc 80 bc 80 bc fagus sylvatica (beech) 3–5% 960 bc 890 bc 240 bc 920 bc fagus sylvatica (beech) > 0.5–1% 1460 bc 1320 bc 1320 bc 1400 bc 1st plantago lanceolata (ribwort plantain) 3650 bc 3630 bc 3000 bc 3800 bc elm decline 3990 bc 3830 bc 3870 bc 3500 bc fig. 2. age–depth model for the gudme sø sediment succession based on 13 calibrated 14c dates, the date of the first occurrence of spheroidal carbonaceous fly-ash particles (blue dot at ad 1900; odgaard 1993) and the age of the sediment surface (red dot at ad 1989). the k-numbers are the laboratory numbers for the dated samples. the small diagrams show probability distributions of the calibrated ages. the age–depth model was established using the programme bpeat (blaauw & christen 2005). rosa_2008:rosa-2008 01/07/09 15:48 side 38 due to the type of land-use at a time when subsistence economy most likely was predominantly based on pastoral farming. in contrast to arable farming, such land-use implies the maintenance of permanently grass-covered pasture that would be less prone to erosion than cultivated fields (veihe et al. 2003). after 2550 bc, low soil erosion rates indicate a long period of relative stability in the catchment area, which lasted until the middle of the bronze age at c. 1000 bc. landscape transformation for c. 150 years, between 1000 and 850 bc, the landscape around gudme sø changed drastically and became far more open than previously as suggested by the increase in nap. extensive forest clearance and expansion of areas used for livestock grazing and crop cultivation led to comprehensive landscape disturbance and a marked increase in erosion rates to the lake. the contemporary increase in pediastrum sp. indicates a larger nutrient loss from the catchment area to the lake due to soil in-wash, which enhanced the in-lake productivity. after c. 200 years, the sediment influx to the lake gradually declined and stabilised, despite a continued high an thro pogenic impact on the landscape as indicated by the continued high nap values. in the iron age around 100 bc, the erosion rates in creased slightly and remained almost constant until c. ad 400. thereafter, there was a short-lived disturbance period around ad 400–500 with intensified arable farming (in creased abundances of cultivated taxa), accelerated soil erosion, and higher lake productivity (raised percentages of pediastrum sp.). high percentages of cannabis-type pollen in this period (not shown) indicate that the lake was used for retting hemp, a process in which stems are soaked in water to free their bast fibres from the surrounding tissue in order to produce fibres for example for cloth and rope making. hemp-retting in the lake most likely contributed to the increased input of minerogenic material, as plants for retting may have been placed in the lake with roots; this could also have contributed to the nutrient enrichment of the lake at that time (odgaard 1994). between c. ad 600 and 900 the soil erosion rate to the lake decreased, in agreement with the reduced anthropogenic impact on the landscape as reflected in the decreasing nap values. at this time, the use of the lake for hemp-retting almost ceased and the percentage value of pediastrum sp. declined. between ad 950 and 1050, i.e. in the second half of the viking age, the pollen data suggest renewed deforestation followed by greatly intensified arable farming (elevated percentages of cultivated taxa). this marked change in landuse led to an unprecedented increase in soil erosion that likely caused eutrophication of the lake involving blooms of pedia strum sp. the nutrient enrichment of the lake may have been further intensified by resumption of hemp-retting in the lake, a procedure which continued to around ad 1900. during the medieval period, the anthropogenic impact on the landscape increased significantly as land clearance in 39 2000 m es ol ith ic n eo lit hic br on ze a ge iro n ag e m ed iev al m od er n 40 20 sa r -m in ( m g/ cm 2 pe r yr ) 10% 1500% 1000% 500% 10% 4000 3500 3000 2500 2000 1500 1000 500 5000 1000 1500 60 40 20 age (calendar years bc/ad) n a p (% ) sar-min sar-min x 10 nap (%) ∑ pollen from cultivated taxa pediastrum sp. plantago lanceolata a b c d fig. 3. a: sediment accumulation rate of mine ro genic matter (sar-min; proxy of soil erosion rate) and non-arboreal pollen (nap; proxy for open land). the results of the pollen analysis are presented as percentages of the total sum of pollen and spores from terrestrial plants. b: pollen percentages of the sum of cultivated taxa. c: pollen percentages of plantago lanceo lata (ribwort plantain). d: percentages of the green algae pediastrum sp. (calculated on the basis of the terrestrial pollen and spore sum). for b, c and d the dark-coloured curves are percentages and the light-coloured areas represent 10 times exaggeration. rosa_2008:rosa-2008 01/07/09 15:48 side 39 40 creased and crop cultivation intensified. the cultivation of large new areas was facilitated by the introduction of new farming technology such as the mouldboard plough and ridge-and-furrow. at gudme sø, the intensive arable farming in the middle ages led to steadily increasing sediment yields. the abundance of pediastrum sp. at this time suggests continued eutrophication. in modern time (ad 1536 to the present) the area around the lake was further cultivated at the expense of woodland. from c. ad 1500 to 1950, nap values increased from c. 30% to 55% indicating widespread agricultural activities predominantly characterised by crop cultivation. the high and in creasing human impact during this period corresponds closely to a dramatic and unprecedented increase in soil erosion, which peaked around ad 1950 contemporaneously with the highest nap values in the entire record. a rapid and marked increase in the percentage of pediastrum sp. at the beginning of the 18th century signifies the onset of a major nutrient enrichment of the lake. concluding remarks the investigation of the lake sediments from gudme sø provides a 6000-year-record of soil erosion rates as well as contemporary pollen-inferred changes in vegetation and land-use. the study demonstrates a close correlation between changes in agricultural activity and rates of soil erosion in the catchment area of the lake. prior to the late viking age, erosion to the lake occurred in pulses triggered by episodes of land clearance followed by periods of relative stability in the catchment area. after the late viking age, soil erosion accelerated continuously and reached a peak in the mid-20th century with erosion rates approximately 30 times higher than the pre-disturbance rates in the mesolithic. the study dem onstrates that after the introduction of agriculture, soil erosion was mainly caused by human activity rather than cli mate. this general result has also emerged from other lake-based studies of long-term erosion in denmark (ras mussen & bradshaw 2005) and southern sweden (dearing 1991). according to current climate models we can expect an in crease in precipitation, more rainfall in the winter season and a higher frequency of extreme precipitation events in the future (christensen et al. 2006). given these predictions, climate will undoubtedly be of growing significance as a forcing mechanism for soil erosion. acknowledgement the gudme sø investigation is part of an archaeological research project funded by a.p. møller og hustru chastine mc-kinney møllers fond til almene formaal. references behre, k.-e. 1981: the interpretation of anthropogenic indicators in pollen diagrams. pollen et spores 23, 225–245. björck, s. & wohlfarth, b. 2001: 14c chronostratigraphic techniques in paleolimnology. in: last, w.m. & smol, j.p. (eds): tracking environmental change using lake sediments: basin analysis, coring, and chronological techniques 1, 205–245. blaauw, m. & christen, j.a. 2005: radiocarbon peat chronologies and environmental change. journal of the royal statistical society, series c (applied statistics) 54, 805–816. bradshaw, e.g., rasmussen, p., nielsen, h. & anderson, n.j. 2005: midto late-holocene land-use change and lake development at dallund sø, denmark: trends in lake primary production as reflected by algal and macrophyte remains. the holocene 15, 1130–1142. christensen, j.h., christensen, o.b., guldberg, a. & stendel, m. 2006: modeller for klimaets udvikling. in: søndergaard, m., kronvang, b., pejrup, m. & sand-jensen, k. (eds): vand og vejr om 100 år – klima forandringer og det danske vandmiljø, 40–54. højbjerg: forlaget hovedland. dearing, j.a. 1991: erosion and land use. in: berglund, b.e. (ed.): the cultural landscape during 6000 years in southern sweden. ecological bulletins 41, 283–292. european environment agency 2000: down to earth: soil degradation and sustainable development in europe. a challenge for the 21st century. environmental issue series 16, 32 pp. luxembourg: office for official publications of the european communities. gaillard, m.-j. 2007: pollen methods and studies – archaeological applications. in: elias, s.a. (ed.): encyclopedia of quaternary science 3, 2570–2595. oxford: elsevier science. iversen, j. 1973: the development of denmark’s nature since the last glacial. danmarks geologiske undersøgelse v. række 7-c, 126 pp. mackereth, f.j.h. 1966: some chemical observations on post-glacial lake sediments. philosophical transactions of the royal society of london, series b, 250, 165–213. odgaard, b.v. 1993: the sedimentary record of spheroidal carbonaceous fly-ash particles in shallow danish lakes. journal of paleolimnology 8, 171–187. odgaard, b.v. 1994: the holocene vegetation history of northern west jutland, denmark. opera botanica 123, 171 pp. rasmussen, p. & bradshaw, e. 2005: midto late-holocene land-use change and lake development at dallund sø, denmark: study aims, natural and cultural setting, chronology and soil erosion history. the holocene 15, 1105–1115. stone, m. (ed.) 2000: the role of erosion and sediment transport in nutrient and contaminant transfer. international association of hydro logical sciences publication 263, 308 pp. van der knijff, j.m., jones, r.j.a. & montanarella, l. 2000: soil erosion risk assessment in europe, 34 pp. eur 19044 en. ispra: european soil bureau, joint research centre and space applications institute. veihe, a., hasholt, b. & schiøtz, i.g. 2003: soil erosion in denmark: processes and politics. environmental science & policy 6, 37–50. authors’ addresses p.r., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: per@geus.dk j.o., department of earth sciences, aarhus university, høegh-guldbergs gade 2, dk-8000 århus c, denmark. rosa_2008:rosa-2008 01/07/09 15:48 side 40 geological survey of denmark and greenland bulletin 1, 21-59 stratigraphy previous page: lower jurassic ammonites (platypleuroceras caprarium) from bornholm, denmark – see donovan & surlyk (2003, this volume). photo: kristian kloth-jørgensen. 23 the lower jurassic of europe: its subdivision and correlation kevin n. page the lower jurassic sub-system comprises four stages, in chronological order, the hettangian, sinemurian, pliensbachian and toarcian. each stage is subdivided into a sequence of ‘standard zones’ (= chronozones) and subzones – each correlated primarily on the basis of its ammonite fauna. a further increase in stratigraphical resolution is available by the use of intra-subzonal units known collectively as ‘horizons’. the close link between ammonites and chronostratigraphy means that faunal provincialism may determine which zonal framework, and therefore which subdivision of the lower jurassic, applies in different regions of europe. such provincialism is of minor importance in the early jurassic (hettangian – lower pliensbachian) but increases significantly in the upper pliensbachian and into the toarcian where at least three ammonoid faunal provinces are distinguishable. the standard zonal schemes for each relevant faunal area are discussed here, with greatest emphasis being placed on the northwest european province, which is characteristic of much of northern europe throughout most of the early jurassic. intra-subzonal units have only been described in certain regions for parts of the lower jurassic but where recognisable these are introduced. keywords: europe, lower jurassic, ammonite zonal biostratigraphy department of geological sciences, university of plymouth, drake circus, plymouth, devon pl4 8aa, uk. e-mail: kevinp@bello-page.fsnet.co.uk contents d’orbigny’s stages, oppel zones and the lower jurassic chronostratigraphy: stages, standard zones, subzones, chronozones and ammonites intra-subzonal units: biohorizons and zonules ammonoid provincialism in the lower jurassic of europe: consequences for correlation hettangian stage the base of the hettangian stage and the jurassic system hettangian correlative schemes and ammonoid provincialism northwest european province (britain, ireland, france, germany, etc.) planorbis chronozone liassicus chronozone angulata chronozone mediterranean province (austria) calliphyllum chronozone megastoma chronozone marmorea chronozone 25 25 26 26 27 27 28 29 29 30 30 31 31 31 31 geological survey of denmark and greenland bulletin 1, 23–59 (2003) © geus, 2003 sinemurian stage the base of the sinemurian stage sinemurian correlative schemes and ammonoid provincialism northwest european province (britain, ireland, france, germany, switzerland, etc.) lower sinemurian substage bucklandi chronozone semicostatum chronozone turneri chronozone upper sinemurian substage obtusum chronozone oxynotum chronozone raricostatum chronozone mediterranean province (austria, italy) pliensbachian stage the base of the pliensbachian stage pliensbachian correlative schemes and ammonoid provincialism northwest european province (britain, france, germany, northern spain, etc.) lower pliensbachian substage jamesoni chronozone ibex chronozone davoei chronozone northwest european province: lusitanian ?sub-province (portugal) subboreal province (britain, northern germany, etc.) upper pliensbachian substage margaritatus chronozone spinatum chronozone submediterranean province (southern france, northern spain, etc.) mediterranean province (austria, italy, southern spain) toarcian stage the base of the toarcian stage toarcian correlative schemes and ammonoid provincialism subboreal province (northern britain) lower toarcian substage tenuicostatum chronozone serpentinum chronozone bifrons chronozone submediterranean province (southern england, france, germany, northern spain, etc.) lower toarcian substage tenuicostatum chronozone serpentinum chronozone bifrons chronozone northwest european province (britain, france, germany, northern spain, etc.) upper toarcian substage variabilis chronozone thouarsense chronozone dispansum chronozone pseudoradiosa chronozone aalensis chronozone mediterranean province (italy, austria, southern spain, north africa, etc.) lower toarcian substage polymorphum chronozone levisoni chronozone bifrons chronozone upper toarcian substage gradata chronozone bonarellii chronozone speciosum chronozone meneghini chronozone aalensis chronozone references 24 31 31 32 32 32 32 34 34 34 34 36 36 37 38 38 38 39 39 39 39 41 41 41 41 41 43 43 43 43 44 44 45 45 45 46 46 47 47 47 48 48 49 49 49 50 50 51 51 51 51 51 52 52 52 52 52 52 53 53 53 the jurassic system takes its name from the jura mountains of eastern france and switzerland, first recognised as having rocks of a distinctive geological division by alexander von humbolt in 1795. it was not until 1829, however, that the term ‘jurassique’ was introduced by brongniart (1829), although in a restricted sense essentially for what is now known as the middle jurassic (torrens & getty 1980). inclusion of what is now lower and upper jurassic was soon made and by 1842, with the publication of alcide d’orbigny’s ‘palaeontologie française, terrains jurassique’ (1842–1849), a system of subdivision of a modern-looking jurassic system into stages was well under way (arkell 1933; rioult 1974). d’orbigny’s stages, oppel zones and the lower jurassic the stages introduced by d’orbigny (1842–1849) were designed to be of worldwide use and were based on the assumption that periodic mass extinctions followed by rapid re-establishments of new faunas characterised stage boundaries (arkell 1933, p. 9). the duration of the existence of a particular ‘fauna’ therefore correlated rocks belonging to a specific stage. for what is now considered to be lower jurassic, he recognised three successive stages: sinémurien (after semur-en-auxois in burgundy, eastern france), liasien (derived from the old lithological or lithostratigraphical term ‘lias’) and toarcien (after thouars in western france). d’orbigny (1842–1849) included in each of his stages a series of fossil ‘zones’, using the term in a purely palaeontological sense to indicate the general stratigraphic range of particular taxa. the term ‘zone’ was refined by albert oppel (1856–1858), who developed a sequence of such divisions for the entire jurassic system. oppel also apparently firmly established the use of lower jurassic (‘unterer jura’) in a modern sense, as being equivalent to the earlier essentially lithostratigraphical division known as ‘lias’. although not specifically using d’orbigny’s stages, oppel referred to zonengruppen or etagen. for the lower jurassic he recognised three successive divisions of this type: semur-gruppe (equivalent to d’orbigny’s sinémurian), pliensbach-gruppe (equivalent to liasien, named after pliensbach in württemberg, germany) and thouars-gruppe (equivalent to toarcian). very importantly, oppel established the ‘zone des ammonites planorbis’ as marking the base of the jurassic. this convention still stands, as does oppel’s general framework of zones, the only significant subsequent change being the creation of the hettangian stage by renevier (1864) for the first two zones of oppel’s original scheme. many other stage names have been proposed for parts of the lower jurassic in europe, some have continued to be used for divisions at the level of substage, but most are now redundant. a full list of such terms was provided by arkell (1933), together with extensive discussion of the origins of the various schemes for subdividing the jurassic system. conventionally the sinemurian, pliensbachian and toarcian stages are divided into an upper and a lower substage (dean et al. 1961), generally used without a specific identifying name. nevertheless, substage names are occasionally used and these are introduced in the relevant sections below. chronostratigraphy: stages, standard zones, subzones, chronozones and ammonites chronostratigraphy is the establishment of a series of subdivisions of geological time, using actual rock units as standards for reference. there is much discussion of this method and it is not necessary to develop it further here (see, for example, hedberg 1976; callomon 1984; harland et al. 1990; salvador 1994; remane et al. 1996). chronostratigraphic divisions are defined only at their base in a suitable stratotype section, the top of the unit being identified by the actual or correlated base of the next equivalent ranked division of the scale. chronostratigraphical divisions form a hierarchy with systems, series and stages being three divisions of decreasing rank (although the term series is almost never used in jurassic stratigraphy). the definitions of stages and systems is now regulated by the international commission on stratigraphy (ics), a project of iugs/unesco, through subcommissions focused on single systems. the aim is to formally recognise an internationally agreed global stratotype section and point (gssp) for the base of every system and for every stage of every system (cowie et al. 1986; salvador 1994). several such proposals have now been ratified by iugs, including the sinemurian stage of the lower jurassic, and several others are likely to be agreed within the next few years. below the level of stage, subdivisions at the level of chronozone and ultimately zonule can be used, but are not formally regulated through the international subcommission on jurassic stratigraphy (isjs) or the ics. in the jurassic, the often great abundance of ammonites and their wide geographical distribution has led to their 25 use for correlating sequences of standard zones. as discussed at great length elsewhere (callomon 1965, 1984; callomon & donovan 1974; cox 1990), these standard zones are chronozones and should therefore be treated as such – a fact ignored by some authors (e.g. whittaker et al. 1991) who confuse jurassic ammonite zones with biozones, where the use of fossils in correlation is not explicitly linked to geological time. as discussed by the former authors, although the names of the zonal units are derived from species names, they are by convention quoted non-italicised (e.g. jamesoni chronozone or jamesoni [standard] zone and not uptonia jamesoni zone or biozone). this is the convention followed by working groups of the international subcommission on jurassic stratigraphy. other fossil groups, especially microfossil, have been used to construct true biozonal schemes for the marine jurassic but the resolution of these schemes is usually inferior to the ammonite scale. indeed, the latter scale is typically used as a ‘standard’ against which biozonal schemes are correlated. for this reason, only the ammonite-based standard zonations for europe will be considered further here; microfossil schemes for the jurassic of northwest europe were reviewed by cox (1990) and dommergues (1997), based on dinocysts (woollam & riding 1983; falconnier 1997), calcareous nannofossils (bown et al. 1988; gardin 1997), foraminifera (copestake & johnson 1989; bassoullet 1997; ruget & nicollin 1997) and ostracods (bate & coleman 1975; lord 1978; park 1984; bodergat 1997; colin 1997). tables 71 and 72 in dommergues (1997) provide a recent cross-correlation between these various schemes, and others based on macrofossil groups – the latter including belemnites (based on doyle 1990; combémorel 1997), brachipods (based on alméras et al. 1997) and echinoderms (based on thierry et al. 1997). intra-subzonal units: biohorizons and zonules most jurassic chronozones are divided into subchronozones, largely for historical reasons, as the creation of new subchronozones within existing chronozones achieves a degree of nomenclatural stability at a chronozonal level. smaller divisions than subchronozones, however, are also used in jurassic ammonite stratigraphy and their use to further refine correlations again avoids ‘tampering’ with an established standard zonation. such divisions are generally known collectively (and sometimes confusingly) as ‘horizons’ although including two conceptually different types of unit (page 1995a). the first type of horizon, known as a zonule (as adopted by phelps (1985) following hedberg (1976), is the smallest subdivision of a chronostratigraphical scale. it should therefore be defined, as with higher divisions, by a basal boundary stratotype. the second type of unit is a biohorizon and is defined as “a bed or series of beds, characterised by a fossil assemblage, within which no further stratigraphical differentiation of the fauna or flora can be distinguished” (callomon 1984, p. 624). the earlier term hemera, proposed by buckman (1893), is considered to be the chronological equivalent of biohorizon (cf. callomon 1984), i.e. as period is the time equivalent of system. biohorizons are the smallest palaeontologically correlatable segments of geological time using ‘guide fossils’ and unlike ‘normal’ chronozones are effectively defined at both their bases and tops. their duration is typically geologically very short but a significant time gap may exist between each successive unit and is shown as an interval on any correlation diagram (page 1992, 1995a; dommergues et al. 1994a). the use of biohorizons is rather like events in event stratigraphy, as they enable the correlation of virtually isochronous time lines between successions at different localities (callomon 1984, 1985). by convention, zonules are quoted in a similar fashion to zones and subzones with a non-italicised specific name (e.g. planorbis zonule) but biohorizons typically retain an italicised specific epithet (e.g. planorbis biohorizon). biohorizonal and zonule schemes have been derived in different regions for different parts of the jurassic and relevant lower jurassic schemes are introduced below. they represent the ultimate in resolvable chronology for the jurassic, and the average zonule or biohorizon plus interval duration is potentially less than 200 000 years in the lower jurassic of northwest europe (page 1995a). ammonoid provincialism in the lower jurassic of europe: consequences for correlation ammonoids, like any group of organisms, frequently show distinctive geographical distribution patterns, reflecting ecological and physical controls on individuals and populations. such patterns are characterised as biogeographical provinces and the inevitable consequence of using ammonites for correlation purposes is that every province, almost by definition, will have a different scheme of standard zones. these differences can inevitably make interprovincial correlations at zonal, and especially subzonal and horizon level, difficult. up to four 26 contemporaneous faunal provinces can be recognised in the lower jurassic of europe. most are geographically adjacent and inter-provincial correlations are thus usually fairly good, although the southernmost faunas of the mediterranean province are sometimes sufficiently distinct as to present significant correlation problems when compared to better known successions further north. as discussed by page (1996), the main faunal provinces recognised in the lower jurassic of europe are: 1. northwest european province. the province was characteristic of much of europe from the hettangian to the early pliensbachian and again in the late toarcian, when great faunal uniformity characterised most of the region. faunal affinities are virtually entirely from southern or tethyan areas (i.e. the mediterranean province) and direct connection to the arctic or boreal sea was lacking (except perhaps in the earlier late toarcian). zonal schemes of the northwest european province are well-developed reflecting the long history of research on the area. at times in the pliensbachian, and also earlier, faunas in the lusitanian basin (portugal) developed a separate character from those of the rest of the northwest european province (dommergues & mouterde 1987), thereby creating some correlation problems. a separate sequence of ‘horizons’ has consequently been recognised for this area for the lower pliensbachian, but whether full province or simply sub-province status is warranted is unclear. 2. mediterranean province. this was characteristic of deeper water areas of southern and south-eastern europe (italy, austria, southern spain, etc.) throughout the jurassic. faunal sequences of the province are often less well-known in detail than those of more northerly areas, and zonations therefore tend to be relatively crude in comparison, but with considerable potential for refinement. 3. subboreal province. the establishment of direct marine connections with the boreal sea in the late pliensbachian and toarcian enabled some mixing of arctic province faunas and the previously separated faunas of northwest europe (see fig. 2). the abundance of boreal taxa alongside more southerly forms distinguishes the province in the more northerly areas of europe (such as northern britain). the zonation is well-established and correlates fairly well with more southerly areas as a result of faunal overlap. 4. submediterranean province. the province developed in parallel with the subboreal province in the late pliensbachian in regions between the former and the mediterranean province (e.g. in mid to southern france). boreal taxa are usually infrequent and an independent zonation is used in the lower toarcian, but with significant similarities to that of subboreal areas. the following sections summarise and correlate available zonal schemes for each of the faunal provinces or sub-provinces recognised in europe. the emphasis is on the northwest european and subboreal schemes as these are most appropriate for northern european areas (including britain, northern france, northern germany and denmark). stratotypes are only identified when clearly described in the literature. it would be premature to propose such definitions for other units, pending a reassessment of taxal ranges and surviving localities. only the taxa which are useful for correlating each subzone are cited; other forms will be present but these are not always chronologically diagnostic. hettangian stage the hettangian stage as originally proposed by renevier (1864) corresponded to the first two zones of the schemes proposed by oppel (1856–1858) for the jurassic, namely those of ammonites [psiloceras] planorbis and ammonites [schlotheimia] angulatus. this interpretation remains essentially unchanged, the only difference being the later creation of a liasicus ‘zone’ for the lower part of the original angulatus zone. the base of the hettangian stage and the jurassic system the jurassic colloquium in luxembourg in 1962 recommended that the planorbis ‘zone’ should form the lowest part of the hettangian stage (mauberge 1964); this zone, as conventionally interpreted, marks the first occurrence of ammonites in northwest europe, after the re-establishment of fully marine conditions towards the end of the triassic period. the type locality of the index fossil of the first subchronozone and the first chronozone of the jurassic of the northwest european province (i.e. psiloceras planorbis (j. de c. sowerby 1824)) is on the coast of west somerset near watchet in south-west england. a proposal 27 in 1967 to the 2nd luxembourg colloquium on the jurassic system recommended that a type section for the zone should actually be selected in this region (d.t. donovan, p.e. kent and h.c. ivimey-cook in: morton 1971). there has been much subsequent discussion as to where exactly the boundary should be drawn (e.g. torrens & getty 1980; warrington & ivimey-cook 1990), culminating in the proposal of warrington et al. (1994) to establish a section at st audries bay, east of watchet as a gssp. the issue as to whether the region is in fact suitable for such a definition has not, however, been thoroughly addressed (page 1994; page et al. 1994). the latter proposal placed the base of the subchronozone and chronozone at the then first recorded occurrence of ammonites in bed a21 of palmer (1972; equivalent to beds 13–15 of whittaker & green 1984). ammonites had not previously been recorded any lower in the immediate area and, indeed, characteristically triassic ammonoids are entirely lacking in britain (although there is a problematic record of an indeterminate, and therefore completely undiagnostic psiloceratid, from presumed latest triassic deposits elsewhere in the region; donovan et al. 1989). this definition, therefore, relies to a certain extent on negative evidence, as emphasised by the subsequent discovery of earlier ammonites at the same locality by hodges (1994) in beds a18 and a19 (beds 8 and 9 of whittaker & green 1984) and the author, westwards along the coast in doniford bay nearer watchet. further work on the sections has revealed a succession of ammonite faunas, previously unrecognised, which correlates well with faunas recovered from the wilkesley borehole in cheshire in north-west england (bloos & page 1997, 2000a; page & bloos 1998). the lowest fauna in the borehole is characterised by the ribbed psiloceratid, psiloceras erugatum (phillips), as already noted by d.t. donovan (in: poole & whiteman 1966, pp. 50, 140). re-examination of the higher faunas reveals the presence of neophyllites and the subchronozonal index p. planorbis itself. the same sequence is present in somerset with bed 8 now known to yield p. erugatum (bloos & page 1997, 2000a; page & bloos 1998). no ammonites are presently known from demonstrably lower levels in britain. in response to the new discoveries in somerset, warrington & ivimey-cook (1995) modified their original proposal and placed the base of the jurassic system at the base of bed a18 (bed 8 of whittaker & green 1984). as discussed by bloos & page (1997, 2000a), however, elsewhere in europe the erugatum fauna has not yet been positively identified, the earliest ammonites typically belonging to neophyllites (bloos 1999) or p. ex grp sampsoni (portlock)/psilonotum (quenstedt), indicating a degree of diachroneity in the first occurrence of ammonites. even where late triassic choristoceras ammonite faunas are present below psiloceratids, such as in mediterranean regions, there remains an ‘ammonite gap’, and the earliest ‘jurassic’ ammonites also appear to represent later species close to the p. sampsoni/psilonotum group (bloos 1985; hallam 1990). more complete sequences of ammonoid faunas from the uppermost triassic (rhaetian stage) to the lowermost jurassic are known, however, elsewhere in the world and two have been proposed as candidate gssps in new york canyon, nevada, usa (guex 1980, 1982; guex et al. 1997) and northern peru (von hillebrandt 1994, 1997). whether a ‘new world’ definition for the base of the jurassic system is acceptable on historical grounds remains to be determined, but it is clear that at the present state of knowledge, it is not possible to accurately correlate these sections with any in europe (bloos & page 2000a). the st audries bay section remains the best exposed triassic–jurassic boundary section in britain, although the ammonite faunas are better preserved in doniford bay along the somerset coast to the west. the erugatum fauna itself, however, is very rare and poorly preserved in somerset, but much better developed, both in terms of abundance and preservation, in cheshire and north yorkshire in northern england, although only known in situ in boreholes (bloos & page 2000a). none of these localities is, therefore, ideal as a gssp, not least due to the absence of triassic ammonoids below in a continuous open marine sequence, but also due to the present lack of clear records of p. erugatum outside britain. if the latter could be identified elsewhere, however, for instance amongst some of the early and poorly characterised psiloceratids in new york canyon, a final agreement on the selection of a suitable gssp for the base of the jurassic system would be much closer. hettangian correlative schemes and ammonoid provincialism hettangian faunas are remarkably similar globally, reflecting the relatively small number of available ammonoid taxa, so soon after the late triassic mass extinctions. no direct boreal links existed in europe, so a simple pattern of a northern northwest european province and a southern and deeper water mediterranean province is recognisable (fig. 1). 28 29 northwest european province (britain, ireland, france, germany, etc.) the origins of the standard zonation for the hettangian of the region go back to the original scheme presented by oppel (1856–1858) with the later addition of a liassicus zone by collenot (1869). the zonation as presently employed is that established by d.t. donovan (in: dean et al. 1961) with later additions by elmi & mouterde (1965) and bloos (1979, 1983), summarised diagrammatically by mouterde & corna (1991) and reviewed by mouterde & corna (1997). mouterde & corna (1991, 1997) presented a scheme of zonules which are here integrated with a sequence of biohorizons established as a result of recent studies in south-west england by page (1994, 1995b, 2002a), page & bloos (1998) and bloos & page (2000a, b). few of the units summarised below have established or proposed stratotypes, with the notable exception of the planorbis subchronozone (and therefore the planorbis chronozone) at the base of the stage and hence the jurassic system. cox (1990) has suggested reference sections for each zone, although these are not equivalent to basal boundary stratotypes; some of these proposals would require revision, however, based on new information on the succession of ammonite faunas both at the proposed localities and elsewhere. planorbis chronozone index. psiloceras planorbis (j. de c. sowerby 1824). author. oppel (1856). planorbis subchronozone index. as planorbis chronozone (see above). author. trueman (1922). stratotype. proposed by warrington et al. (1994), modified by warrington & ivimey-cook (1995); base of bed 8 (= a18), st audries bay, west somerset, england (see discussion above). correlating fauna. dominated by smooth whorled species of ‘psiloceras’ and neophyllites (sensu lange pseudomoreana depressa striatissima complanata similis extranodosa amblygonia hadroptychus laqueolus laqueus schroederi portlocki hagenowi prometheus intermedium johnstoni caloceras sp.2 caloceras sp.1 plicatulum sampsoni α planorbis antecedens imitans erugatum marmorea/depressa ? extranodosa ? storthoceras/ alsatites, etc. tenerum calliphyllum ‘psilonotum’ marmorea megastoma calliphyllum depressa complanata extranodosa hadroptychus liassicus laqueus portlocki belcheri johnstoni plicatulum sampsoni planorbis depressa complanata extranodosa laqueus portlocki johnstoni planorbis angulata liassicus planorbis chronozone subchronozone zonule biohorizon faunas chronozone northwest european province mediterranean province fig. 1. hettangian subdivisions and correlations: northwest european and mediterranean provinces. for explanation, see text. the double lines separating the biohorizons on this and later figures indicate the stratigraphic interval conceptually present between each successive division of this kind (see discussion in text). 1941) but with ribbed psiloceras erugatum at the base of the subchronozone. included subdivisions. planorbis zonule (including psiloceras erugatum, neophyllites imitans, n. antecedens and psiloceras planorbis biohorizons), sampsoni [= psilonotum] zonule (including psiloceras sampsoni α biohorizon), plicatulum zonule (including plicatulum biohorizon) (mouterde & corna 1991, 1997; page 1994; page & bloos 1998; bloos & page 2000a, b). comment. buckman (1930 in: buckman 1909–1930) first proposed a plicatus hemera, subsequent raised to the status of ‘horizon’ (= zonule) by elmi & mouterde (1965) and ultimately a subzone by von hillebrandt (1990). status as a zonule is provisionally retained here, however, pending an assessment of ammonite faunas in south-west england, where circumstantial evidence suggests that at least three, maybe four, correlatable biohorizons could ultimately be recognisable, potentially lending support to raising the status of the unit to subchronozone. johnstoni subchronozone index. caloceras johnstoni (j. de c. sowerby 1824). author. von schloenbach (1863) as a zone, trueman (1922) as a subzone (but see discussion by d.t. donovan in: dean et al. 1961, p. 444). correlating fauna. early species of caloceras. included subdivisions. johnstoni zonule (including caloceras sp. 1, caloceras sp. 2 and c. johnstoni biohorizons), belcheri zonule (including c. intermedium biohorizon) (mouterde & corna 1991, 1997; page 1994). liassicus chronozone index. alsatites liassicus (d’orbigny 1844). author. collenot (1869). portlocki subchronozone index. waehneroceras portlocki (wright 1881). author. lang (1924). correlating fauna. early species of waehneroceras including w. (curviceras), also psilophyllites. included subdivisions. portlocki zonule (including w. (curviceras) prometheus, psilophyllites hagenowi, waehneroceras portlocki and w. schroederi biohorizons) (mouterde & corna 1991, 1997; page 2002a). laqueus subchronozone index. laqueoceras laqueus (quenstedt 1856). author. reynès (1879). correlating fauna. laqueoceras is typical, with alsatites above, in association with common late waehneroceras spp. (= ‘saxoceras’) and late caloceras at higher levels. included subdivisions. laqueus zonule (including laqueoceras laqueus biohorizon), liassicus zonule (including alsatites laqueolus biohorizon), hadroptychus zonule (including w. hadroptychus biohorizon) (mouterde & corna 1991, 1997). angulata chronozone index. schlotheimia angulata (schlotheim 1820). author. oppel (1856). extranodosa subchronozone index. schlotheimia extranodosa (waehner 1886). author. lange (1922) as germanica zone (name changed due to apparent synonymy by donovan 1952). correlating fauna. early species of schlotheimia. included subdivisions. extranodosa zonule (including schlotheimia amblygonia and s. extranodosa biohorizons) (bloos 1984; mouterde & corna 1991, 1997). complanata subchronozone index. schlotheimia complanata von koenen 1902. author. spath (1942) replacing the stenorhyncha zone of lange (1922). correlating fauna. schlotheimia spp. including relatively compressed and smooth whorled macroconchs, with giant forms at higher levels. the rare early arietitid schreinbachites is locally recorded. included subdivisions. complanata zonule (including s. similis, s. complanata and s. striatissima biohorizons) (bloos 1984; mouterde & corna 1991, 1997; page 1995b; bloos & page 2000b). depressa subchronozone index. schlotheimia depressa (waehner 1886). author. bloos (1983). correlating fauna. the index species and its allies, especially s. ex grp pseudomoreana (spath). ?paracaloceras is also known, but is very rare. included subdivisions. depressa zonule (including s. depressa and s. pseudomoreana biohorizons) (bloos & page 2000b; page 2002a). comment. the depressa subchronozone was established by bloos (1983, 1984) but was reduced in status to a zonule by mouterde & corna (1991, 1997). in britain, the subchronozone is well-developed, although has only recently been recognised; it 30 includes the pseudomoreana and ‘schlotheimia sp. 2’ biohorizons of page (1995b) (page & bloos 1998; bloos & page 2000b). mediterranean province (austria) the subdivision of the hettangian mediterranean province is not well-developed despite the presence of considerably richer ammonoid faunas than in northwest european areas. a sequence of three zones, calliphyllum, megastoma and marmorea, was recognised by waehner (1886) and used again by lange (1952). blind (1963) subdivided the calliphyllum ‘zone’ and attempted to subdivide the higher zones, although bloos (1984) considered that these schemes were not entirely satisfactory. the marmorea chronozone has been the subject of some discussion as to its meaning and indeed whether it ranges into the sinemurian (taylor 1986), but in a european sense at least, a wholly hettangian age is most likely (bloos 1983, 1984). calliphyllum chronozone index. psiloceras calliphyllum neumayr 1879. author. waehner (1886). correlating fauna. species of psiloceras, especially the index, and early waehneroceras (= curviceras) at higher levels. included subdivisions. the psilonotum and calliphyllum faunas (= zones i–ii of blind 1963; bloos 1984). megastoma chronozone index. ?kammerkarites megastoma (waehner 1886). author. waehner (1886). correlating fauna. species of kammerkarites, waehneroceras (sensu lato), alsatites and caloceras. included subdivisions. the tenerum, storthoceras/alsatites and extranodosa faunas (blind 1963; bloos 1984). marmorea chronozone index. schlotheimia marmorea (oppel 1856). author. waehner (1886). correlating fauna. species of schlotheimia with common early arietitidae (paracaloceras, etc.). included subdivisions. includes an s. marmorea/s. depressa fauna at the top of the chronozone (as indicated by bloos 1984). sinemurian stage the sinemurian stage corresponds to the zonal range suggested by oppel (1856) minus the hettangian of renevier (1864), i.e. with a bucklandi chronozone at the base and a raricostatum chronozone at the top. additional zones have been added subsequently, but the modern interpretation remains essentially unchanged. although the lower sinemurian substage has no common alternative name, the term lotharingian (from ‘lorraine, france’) is often used in france for the upper sinemurian (after haug 1910 in: haug 1908–1911 but sensu spath 1942 as haug’s stage included the turneri zone, now considered to be lower sinemurian; dean et al. 1961). the base of the sinemurian stage the base of the stage is drawn at the base of the conybeari subchronozone, the lowest division of the bucklandi chronozone. d.t. donovan (in: morton 1971) proposed that the stratotype for the stage should be established on the dorset–devon coast, near lyme regis. in this area, the relatively well-preserved and first obvious sinemurian fauna (i.e. dominated by arietitid ammonites, including metophioceras) occurs in nodules on the base of bed 19 of lang (1924) although traces of vermiceras have now been found about 0.25 m lower, in bed 18 (author’s unpublished data), and 0.25 m above the last schlotheimia seen on the surface of bed 17 (page 1992); this is c. 0.75 m lower than donovan’s original designation of the base of bed 21 for the base of the stage. recent study of other sections on the coast of the neighbouring county of somerset has revealed a considerably expanded hettangian–sinemurian succession, more than four times thicker than that at lyme regis (palmer 1972; whittaker & green 1984; page 1992, 1995b). in particular, it has been possible to demonstrate that near lyme regis the faunal record is incomplete (page 1992, 1995b; bloos & page 2000b). the dorset section is not therefore a suitable stratotype let alone a candidate gssp, whereas the somerset section has great potential and was proposed as such by page et al. (2000) and ratified by iugs at the rio de janeiro symposium in august 2000 – the first lower jurassic gssp to be formally approved (bloos & page 2002). it is the faunal completeness and expanded succession (c. 14 m for the earliest sinemurian conybeari subzone alone) which makes the locality unusual in europe. elsewhere, for 31 instance in germany and south-east france, successions are usually much thinner and much less complete. the base of the sinemurian at east quantoxhead is taken at the first occurrence of abundant arietitid ammonites 70 cm above the base of bed c100/145 (palmer 1972; whittaker & green 1984) and only 20 cm above the last common hettangian schlotheimia. this fauna, with vermiceras quantoxense (bloos & page) and v. palmeri (bloos & page), underlies an assemblage including metophioceras ex grp brevidorsale (quenstedt) and m. conybearoides (reynes) which is normally the earliest recorded in the sinemurian elsewhere in europe (bloos 1997; bloos & page 2000a; page et al. 2000). sinemurian correlative schemes and ammonoid provincialism sinemurian provincialism is essentially the same as in the hettangian, with a broad northwest european province over much of europe, and a mediterranean province in south-easternmost areas. some endemism or geographic restriction of genera and species in portugal at times in the late sinemurian probably indicates some links with north africa (i.e. the ethiopian province sensu page 1996; figs 2, 3). northwest european province (britain, ireland, france, germany, switzerland, etc.) the subdivision of the stage into chronozones and subchronozones, as started by oppel (1856–1858) and developed through the work of w.d. lang and l.f. spath (lang et al. 1923; lang 1924; spath 1924, 1942; lang & spath 1925b), was eventually stabilised by d.t. donovan (in: dean et al. 1961). the only subsequent changes have been in the name of zonal indices as a result of the identification of senior synonyms. ivimeycook & donovan (1984) proposed the removal of the bucklandi subchronozone and lowering of the base of the semicostatum zone to include most of the former subzone. page (1992), however, retained a bucklandi subchronozone as the unit forms a significant and important stratigraphical unit that is readily recognisable internationally. corna et al. (1997) provided a recent review of the zonation of the stage and the zonules therein, essentially reproducing the scheme presented diagrammatically by corna et al. (1991). bloos (1985) proposed a sequence of ‘horizons’ for the basal part of the stage, the divisions identified being very similar to those of the earliest part of a zonule scheme described by corna (1987). page (1992) introduced a sequence of biohorizons for the entire sinemurian, the upper sinemurian part of which was correlated with french successions in burgundy (dommergues 1993) to produce the revised biohorizonal scheme of dommergues et al. (1994a). additional biohorizons in the lower sinemurian, especially the conybeari subchronozone were recognised by page (1995a, b), bloos & page (2000b) and page et al. (2000). reference sections for each zone were suggested by cox (1990), but now require some modification based on new faunal information from various regions. lower sinemurian substage bucklandi chronozone index. arietites bucklandi (j. sowerby 1818). author. oppel (1858). conybeari subchronozone index. metophioceras conybeari (j. sowerby 1816). author. tutcher (1918) as a zone, trueman (1922) as a subzone. stratotype. level 0.7 m above the base of bed c100/145, east quantoxhead, somerset, uk (see discussion above). correlating fauna. species of metophioceras, with early vermiceras and epammonites. giant charmasseiceras typical. included subdivisions. latisulcatum zonule (including vermiceras quantoxense, metophioceras sp. 2, and m. conybearoides biohorizons), rotarium zonule (including epammonites rotarius, m. rouvillei, coroniceras rotator and v. elegans biohorizons), conybeari zonule (including metophioceras conybeari biohorizon) (corna 1987; corna et al. 1991; page 1992, 1995a, b; bloos & page 2000b, 2002; page et al. 2000). rotiforme subchronozone index. coroniceras rotiforme (j. de c. sowerby 1824). author. collenot (1879) as a zone, trueman (1922) as a subzone. correlating fauna. evolute and strongly ribbed species of coroniceras, with occasional charmasseiceras at certain levels. included subdivisions. hyatti zonule (including epammonites silvestrei, coroniceras cf. defneri, c. rotiforme, c. aff. rotiforme and c. caprotinum biohorizons), 32 33 ‘schloenbachi’ zonule (including c. aff. kridion biohorizon) (corna 1987; corna et al. 1991, 1997; page 1992, 1995b). bucklandi subchronozone index. as bucklandi chronozone (see above). author. spath (1942) as a subzone. correlating fauna. large and massive whorled arietitidae (arietites) typical with coroniceras at certain levels. early arnioceras and charmasseiceras present, the former in the upper part of the subchronozone. 31: cf. bordoti 30: subturneri 29: birchi 28: pseudobonnardi 27: obtusiformis 26: hartmanni 25: brooki 24: sulcifer 23: cf. semicostatum 22: alcinoeiforme 21: euagassiceras 20: cf. resupinatim 19: pseudokridion 18: acuticarinatum 17b: alcinoe 17a: paracoroniceras sp 16: bodleyi 15b: cf. charlesi 15a: lyra 14: multicostatum 13: cf. scunthorpense 12: isis 11: aff. isis 10: scylla 9: kridion 8: caprotinum 7b: aff. rotiforme 7a: rotiforme 6: cf. defneri 5c: silvestrei 5b: conybeari 5a: elegans 4: rotator 3b: rouvillei 3a: rotarius 2b: conybearoides 2a: metophioceras sp.b 1: quantoxense bordoti turneri brooki sauzeanum nodulatum scipionanum alcinoe crossi charlesi lyra bisulcatus isis coronaries schloenbachi hyatti conybeari rotarium ‘latisulcatum’ birchi brooki sauzeanum scipionanum lyra bucklandi rotiforme conybeari turneri semicostatum bucklandi chronozone sub-chronozone zonule biohorizon ceratoides ? part rotiforme fauna northwest european province mediterranean province ? fig. 2. lower sinemurian subdivisions and northwest european horizons. for explanation, see text. included subdivisions. coronaries zonule (including vermiceras scylla biohorizon, previously included in the rotiforme subzone by page 1992 but placed at the base of the bucklandi subchronozone by corna et al. 1997), isis zonule (including arietites aff. isis, a. isis and a. aff. scunthorpense biohorizons), bisulcatus zonule (including coroniceras multicostatum biohorizon) (corna 1985; corna et al. 1991, 1997; page 1992, 1995b). semicostatum chronozone index. arnioceras semicostatum (young & bird 1829). author. judd (1875). lyra subchronozone index. paracoroniceras lyra (hyatt 1867). author. buckman (1918) as gmuendense zone, changed to reynesi subzone by d.t. donovan (in: dean et al. 1961, after a junior synonym of p. lyra, subchronozone renamed accordingly by guérin-franiatte 1966). equivalent to the charlesi subzone of mouterde & tintant (1980). correlating fauna. species of paracoroniceras and ‘pararnioceras’, with common arnioceras at certain levels. included subdivisions. lyra zonule (including coroniceras lyra (sensu stricto) biohorizon), charlesi zonule (including p. cf. charlesi [= c. lyra in page 1992] and arnioceras bodleyi biohorizons), crossi zonule (probably includes the paracoroniceras sp. biohorizon of page 1992), alcinoe zonule (including the ‘pararnioceras’ alcinoe biohorizon; included in the scipionanum subzone by corna 1987 and corna et al. 1991, 1997) (corna 1987; corna et al. 1991; page 1992). scipionanum subchronozone index. agassiceras scipionanum (d’orbigny 1844). author. tutcher (1918). correlating fauna. species of agassiceras and arnioceras. may include early euagassiceras (e. striaries (quenstedt)) in the higher part of the subchronozone (teste corna et al. 1997). included subdivisions. scipionanum zonule (including arnioceras acuticarinatum biohorizon), nodulatum zonule (including arnioceras pseudokridion biohorizon) (corna 1987; corna et al. 1991, 1997; page 1992). resupinatum subchronozone index. euagassiceras resupinatum (simpson 1843). author. tutcher (1918) as a zone, trueman (1922) as a subzone. correlating fauna. euagassiceras and arnioceras. included subdivisions. sauzeanum zonule (including e. cf. resupinatum, ‘euagassiceras’ sp., ‘pararnioceras’ alcinoeiforme and arnioceras cf. semicostatum biohorizons) (corna et al. 1991, 1997; page 1992). turneri chronozone index. caenisites turneri (j. de c. sowerby 1824). author. wright (1860). brooki subchronozone index. caenisites brooki (j. sowerby 1818). author. lang (1914, w.d. lang in: lang et al. 1923). correlating fauna. early species of caenisites and some arnioceras and ‘sulciferites’ (i.e. late charmasseiceras). included subdivisions. brooki zonule (including sulciferites sulcifer, c. brooki and arnioceras hartmanni biohorizons) (corna et al. 1991, 1997; page 1992). birchi subchronozone index. microderoceras birchi (j. sowerby 1820). author. collenot (1869) as a zone, spath (1942) as a subzone. correlating fauna. species of microderoceras, caenisites ex grp turneri, early epophioceras locally and common early promicroceras at higher levels. included subdivisions. turneri zonule (including caenisites obtusiformis, epophioceras pseudobonnardi, microderoceras birchi and caenisites subturneri biohorizons), bordoti zonule (including caenisites cf. bordoti biohorizon) (corna et al. 1991, 1997; page 1992). upper sinemurian substage obtusum chronozone index. asteroceras obtusum (j. sowerby 1817). author. oppel (1856). obtusum subchronozone index. as obtusum chronozone (see above). author. spath (1942) as a subzone of ‘promicroceras planicosta or obtusum (sensu stricto)’ (= planicosta zone of lang 1914). correlating fauna. early species of asteroceras, with promicroceras (but not p. planicosta), xipheroceras and occasionally late arnioceras. 34 35 tardecrescens meigeni boehmi crassicostatum raricostatum rhodanicum edmundi delicatum oxynotum gagateum aff. glaber fowleri blakei stellare confusum apianatum macdonelli raricostatum densinodulum oxynotum simpsoni denotatus stellare obtusum raricostatum oxynotum obtusum xl: aplanatum/tardecrescens xxxix: recticostatum xxxviii: aureolum xxxvii: macdonnelli xxxvi: meigeni xxxv: subplicatum xxxiv: boehmi xxxili: cf. intermedium xxxil: crassicostatum xxxi: raricostatum xxx: rhodanicum xxix: ‘echioceras’ sp.3 xxviii: radiatum xxvii: grp armatum xxvi: bispinigerum xxv: lymense xxiv: subplanicosta xxiii: delicatum xxii: doris xxi: bifer xx: grp oxynotum xix: driani xviii: gagateum xvii: exortum xvi: aff. glaber xv: denotatus xiv: fowleri xiii: cf. undaries xii: sagittarium xi: aff. arnouldi x: blakei s.s. ix: stellare viii: cf. landrioti vii: margaritoides vi: aff. margaritoides v: ‘galaticeras’ iv: obtusum iii: semicostatoides ii: cf. confusum i: aff. confusum tardecrescens/romanicum oosteri/gruenae meigeni/macdonnelli meigeni meigeni/charpentieri liciense favrei boehmi raricostatoides quenstedti rigidum salisburgense glaber eparietites suevicum ceratoides (part) chronozone subchronozone zonule biohorizon biohorizon northwest european province mediterranean province ? grp oxynotum aff. saltriense retusum fig. 3. upper sinemurian (‘lotharingian’) subdivisions and northwest european horizons. for explanation, see text. included subdivisions. confusum zonule (including asteroceras aff. confusum, as. cf. confusum, arnioceras semicostatoides and as. obtusum biohorizons) (corna et al. 1991, 1997; page 1992; dommergues et al. 1994a). as. confusum is here preferred to as. obtusum as an index for a zonule, as the latter is relatively rarely recorded and the former is more typical of this level in northwest europe. stellare subchronozone index. asteroceras stellare (j. sowerby 1815). author. buckman (1910) as a zone, lang (1914) as a subzone. correlating fauna. late species of asteroceras, also promicroceras, xipheroceras, some epophioceras with early aegasteroceras at the top of the subchronozone. included subdivisions. stellare zonule (including ‘galaticeras’ [=? bouhamidoceras], asteroceras aff. margaritoides, as. margaritoides, epophioceras cf. landrioti and as. stellare biohorizons), blakei zonule (including aegasteroceras blakei, arnioceras aff. arnouldi and aegasteroceras sagittarium biohorizons) (corna et al. 1991, 1997; page 1992; dommergues et al. 1994a). denotatus subchronozone index. eparietites denotatus (simpson 1855). author. buckman (1918) as a hemera; buckman (1919 in: buckman 1909–1930) in a zonal context. correlating fauna. species of eparietites, with aegasteroceras (grp simile) at lower levels. included subdivisions. fowleri zonule (including eparietites cf. undaries, ep. fowleri and ep. denotatus biohorizons), glaber zonule (including ep. aff. glaber biohorizon) (corna et al. 1991, 1997; page 1992; dommergues et al. 1994a). oxynotum chronozone index. oxynoticeras oxynotum (quenstedt 1843). author. oppel (1856). simpsoni subchronozone index. oxynoticeras simpsoni (simpson 1843). author. buckman (1918) as a hemera, spath (1942) as a subzone. correlating fauna. o. ex grp simpsoni and gagaticeras. included subdivisions. gagateum zonule (including gagaticeras exortum, g. gagateum and paroxynoticeras driani biohorizons) (corna et al. 1991, 1997; page 1992; dommergues et al. 1994a). oxynotum subchronozone index. as oxynotum chronozone (see above). author. buckman (1918) as a hemera, spath (1942) as an alternative name for his bifer subzone. correlating fauna. oxynoticeras grp oxynotum, bifericeras and some palaeoechioceras. included subdivisions. oxynotum zonule (including o. ex grp oxynotum, bifericeras ex grp bifer and gleviceras doris biohorizons) (corna et al. 1991, 1997; page 1992; dommergues et al. 1994a). raricostatum chronozone index. echioceras raricostatum (zieten 1831). author. oppel (1856). densinodulum subchronozone index. crucilobiceras densinodulum buckman 1923. author. buckman (1923 in: buckman 1909–1930) as a hemera. w.d. lang (1926 in: lang & spath 1926) as a subzone. correlating fauna. crucilobiceras, eoderoceras, gleviceras and at restricted levels, early echioceratids (including ‘plesechioceras’ [= ‘paltechioceras’ sensu lato] etc.). included subdivisions. delicatum zonule (including ‘plesechioceras’ delicatum biohorizon), edmundi zonule (including crucilobiceras subplanicosta, oxynoticeras lymense, eoderoceras bispinigerum and eoderoceras ex grp armatum biohorizons), radiatum zonule nov. (including echioceras radiatum and echioceras [= paltechioceras sensu lato] sp. 3 biohorizons) (corna et al. 1991, 1997; page 1992; dommergues et al. 1994a). raricostatum subchronozone index. as raricostatum chronozone (see above). author. buckman (1918) as a raricostatoides hemera, spath (1942) as a subzone (e. raricostatoides is generally considered to be a junior synonym of e. raricostatum). correlating fauna. raricostate echioceras spp., with some crucilobiceras, eoderoceras and gleviceras. included subdivisions. rhodanicum zonule (including echioceras rhodanicum biohorizon), raricostatum zonule (including e. raricostatum biohorizon), crassicostatum zonule (including e. crassicostatum biohorizon), boehmi zonule (including ‘paltechioceras’ cf. intermedium and ‘p.’ boehmi biohorizons) (corna et al. 1991, 1997; page 1992; dommergues et al. 1994a). 36 macdonnelli subchronozone index. leptechioceras macdonnelli (portlock 1943). author. buckman (1918) as a hemera, w.d. lang (1926 in: lang & spath 1926) as a zone, spath (1942) as a subzone. correlating fauna. leptechioceras spp., with some eoderoceratids (including epideroceras in more southerly areas) and early radstockiceras. included subdivisions. meigeni zonule (including leptechioceras subplicatum, l. meigeni and l. macdonnelli biohorizons) (corna et al. 1991, 1997; page 1992; dommergues et al. 1994a). aplanatum subchronozone index. paltechioceras aplanatum (hyatt 1889). author. buckman (1918) as a hemera, lang (1926) as a zone, spath (1942) as a subzone. correlating fauna. late species of paltechioceras, with eoderoceras and epideroceras, the latter typically in more southerly areas. included subdivisions. tardecrescens zonule (including paltechioceras aureolum, p. rectiradiatum and p. aplanatum/tardecrescens biohorizons) (corna et al. 1991, 1997; page 1992; dommergues et al. 1994a). comment. the eoderoceras donovani and vicininodiceras simplicicosta biohorizons were provisionally included in the sinemurian by page (1992) and dommergues et al. (1994a). new information from north yorkshire, however, suggests that at least the former is best considered to be of basal pliensbachian age. the latter remains stratigraphically problematic, however, and is consequently no longer used as a biohorizonal index, pending clarification of the precise position of the specimens recorded by donovan (1990) on raasay, scotland. mediterranean province (austria, italy) the basic northwest european chronozonal and subchronozonal framework is generally used in mediterranean areas, for example by donovan (1990), dommergues et al. (1995), blau (1998) and especially blau & meister (1999). at zonule/biohorizonal level, however, correlation is typically less precise as many species appear to be different and the relative generic composition is also often distinct in mediterranean areas. in the lower sinemurian, only generalised correlations seem to be possible (corna et al. 1991, 1997), but in the upper sinemurian, there are considerably more links, and in the raricostatum chronozone in particular, some biohorizons are even correlatable between provinces, as demonstrated by blau & meister (1999; fig. 3). summarising from figures 2–4 of blau & meister (1999), the following is a generalised and provisional composite sequence of biohorizons or faunas for the mediterranean province in the upper sinemurian: 1. obtusum chronozone, obtusum subchronozone (confusum zonule, may include elements of the arnioceras ceratoides fauna of the apennines, italy); stellare subchronozone (stellare zonule, including asteroceras retusum and as. aff. saltriense (part?) faunas/biohorizons (adnet, austria); blakei zonule, including as. aff. saltriense (?part) (adnet) and as. suevicum (lienz, austria) faunas/biohorizons); denotatus subchronozone (fowleri zonule, including eparietites fauna/biohorizon (lienz, austria); glaber zonule (including e. glaber fauna/biohorizon (lienz and adnet, austria)). 2. oxynotum chronozone, simpsoni subchronozone (gagateum zonule, no recorded faunas in blau & meister 1999), oxynotum subchronozone (oxynotum zonule, including oxynoticeras ex grp oxynotum (adnet, austria) and paroxynoticeras salisburgense (lienz, austria) faunas/biohorizons). 3. raricostatum chronozone, densinodulum subchronozone (delicatum–edmundi zonules, part?, including g. rigidum fauna/biohorizon, part?); raricostatum subchronozone (rhodanicum zonule, including echioceras quenstedti biohorizon; raricostatum zonule, including e. raricostatoides biohorizon; crassicostatum zonule, no confirmed records in blau & meister 1999; boehmi zonule, including paltechioceras boehmi biohorizon (apennines, italy)); macdonelli subchronozone (meigeni zonule, including ‘paltechioceras’ favrei, ‘p.’ liciense, leptechioceras meigeni/p. charpentieri, l. meigeni and l. meigeni/l. macdonnelli biohorizons (lienz, austria)); aplanatum subchronozone (tardecrescens zonule, including paltechioceras oosteri/miltoceras gruenae (lienz, austria) and p. tardecrescens/p. romanicum biohorizons (apennines, italy and lienz, austria)). localities and faunas are described by dommergues et al. (1994b; apennines, italy), dommergues et al. (1995; adnet, austria) and blau (1998; lienz, austria). 37 pliensbachian stage the stage name was first used by oppel (1856) as ‘pliensbach-gruppe’, with a zonal composition identical to that still used throughout europe. pliensbach is near boll in württemberg, southern germany. oppel’s stage is essentially the same as d’orbigny’s earlier nongeographically named (and hence rejected) ‘liasien’ (d’orbigny 1842). ‘charmouthian’ is another early synonym attributed to mayer-eymar (1864) but considered by dean et al. (1961) as having been first published by renevier (1874). unlike other lower jurassic stages, the pliensbachian is often subdivided into named substages, the lower pliensbachian corresponding to the carixian substage (after ‘carixa’ = charmouth, dorset, england; lang 1913) and the upper pliensbachian corresponding to the domerian substage (after monte domaro in the lombardy alps, italy; bonarelli 1894). the base of the pliensbachian stage the first zone of oppel’s original ‘pliensbach-gruppe’ is still used as the first of the stage, namely the jamesoni ‘zone’ (oppel 1856), now with a taylori subchronozone forming its lowest unit. d.t. donovan (in: morton 1971) discussed the base of the stage and indicated that the taylori subzone was first recognised on the coast of southern england in dorset near charmouth. the base of the stage at that locality (= base of bed 105 of lang 1928) lies immediately above a non-sequence which omits the highest two subzones of the sinemurian. the locality is not suitable, therefore, for defining the base of the stage, according to ics guidelines. a non-sequence at the base of the stage is also widespread throughout much of northern europe, including at pliensbach itself (geyer 1964; morton 1971). where more complete sinemurian–pliensbachian successions are exposed, however, for instance in robin hood’s bay (north yorkshire, england; tate & blake 1876; dommergues & meister 1992; page 1992; hesselbo & jenkins 1995) and the isle of raasay (western scotland; oates 1978; donovan 1990; page 1992), drawing a suitable base can be somewhat problematic. in robin hood’s bay, above the last typical sinemurian-type ammonites (paltechioceras) is a fauna with a small eoderoceratid described by dommergues & meister (1992) as ‘bifericeras’ donovani. at this level occur the first, rare apoderoceras, a genus more characteristic of the taylori subzone than the index phricodoceras taylori itself, but it is not until slightly higher in the yorkshire succession that the latter genus is recorded. on raasay, however, above the last paltechioceras and below common apoderoceras, donovan (1990) reported a fauna with a rare liparoceratid, vicininodiceras. this fauna was included in the sinemurian by donovan and also by page (1992), but its assignment to the stage is somewhat problematic, especially as its stratigraphical relationship to ‘bifericeras’ donovani is presently unknown. recent work on the robin hood’s bay sections by the pliensbachian working group of the isjs (in 1999) has confirmed the presence of small (?juvenile) apoderoceras in association with ‘bifericeras’ donovani (= donovani biohorizon or zonule), that this level is therefore suitable for marking the base of the pliensbachian stage and that the fauna is typical of a conventional pliensbachian and not the terminal sinemurian as implied by dommergues et al. (1994a, 1997). the section has now yielded results from other stratigraphical techniques, including microfossil assemblages and chemostratigraphy, leading to a formal proposal as a gssp in late 2002 (meister et al. 2002), the base of the stage being drawn at the base of bed 73 (or 1011) of dommergues & meister (1992). pliensbachian correlative schemes and ammonoid provincialism early pliensbachian faunas show a great deal of uniformity throughout northern europe and most of the region is included in a northwest european province. mediterranean province faunas, although differing in taxonomic detail, are sufficiently well-correlated with those further north and west that the same standard zonation is used for both provinces, but faunal successions are nevertheless distinguishable at horizonal level (figs 4, 5). in the upper part of the lower pliensbachian and throughout the upper pliensbachian, however, the establishment of direct connections with boreal regions resulted in a faunal spectrum developing across europe from assemblages dominated by boreal taxa in the northern areas (characterising a subboreal province) through faunas dominated by mediterranean faunas in central and western areas (submediterranean province) to true mediterranean province faunas in the south. no true arctic province faunas (sensu page 1996) are recognisable in europe, however. inter-provincial faunal links facilitate good correlations and it is possible to use the 38 same standard zonation throughout europe, but faunal sequences may be very different at horizon level. the development of endemism in the early pliensbachian of portugal has necessitated the establishment of a different sequence of horizons from adjacent submediterranean areas and sub-provincial or full provincial status may therefore be justifiable. northwest european province (britain, france, germany, northern spain, etc.) the zonal and subzonal framework of the province is used throughout europe and is based on oppel’s original scheme (oppel 1856). for convenience, the province is here equated temporally with the lower pliensbachian substage (equivalent to the first three zones of oppel’s scheme) and a description of the upper pliensbachian zonation of northern areas is included under the heading of subboreal province. the subzonal framework follows d.t. donovan (in: dean et al. 1961) as reviewed by dommergues et al. (1997). reference sections for each chronozone were proposed by cox (1990) but some need modification in the light of new information on faunal successions elsewhere. a number of systems of horizons, primarily in the sense of zonules, have been proposed for the early part of the stage in the province and include the schemes of dommergues (1979) and phelps (1985), with later revisions by dommergues & meister (1987), dommergues (1987, 1997) and dommergues et al. (1991). lower pliensbachian substage jamesoni chronozone index. uptonia jamesoni (j. de c. sowerby 1827). author. oppel (1856). taylori subchronozone index. phricodoceras taylori (j. de c. sowerby 1826). author. spath (1923). stratotype. proposed by meister et al. (2002): base of bed 73/1011, robin hood’s bay, north yorkshire, uk (see discussion above). correlating fauna. species of apoderoceras, with rarer phricodoceras and radstockiceras. tetraspidoceras is common in southern areas (dommergues et al. 1997). included subdivisions. donovani zonule, nodogigas/grp aculeatum zonule, taylori zonule (dommergues et al. 1991, 1997; meister et al. 2002). comment. the basal unit of the stage characterised by bifericeras donovani is here quoted as a ‘zonule’ for consistency with higher subdivisions of the pliensbachian. in meister et al. (2002), however, the unit is treated as a ‘biohorizon’. polymorphus subchronozone index. polymorphites polymorphus (quenstedt 1845). author. buckman (1918) as a hemera, spath (1923) as a subzone. correlating fauna. species of polymorphites, with early platypleuroceras in the upper part of the subchronozone. radstockiceras and epideroceras also locally present. included subdivisions. polymorphus zonule (dommergues et al. 1991, 1997). brevispina subchronozone index. platypleuroceras brevispina (j. de c. sowerby 1827). author. von seebach (1864) as part of a larger zone, buckman (1918) as a hemera, spath (1923) as a subzone. correlating fauna. platypleuroceras ex grp brevispina and spp. radstockiceras and tragophylloceras also present, with metaderoceras in more southerly areas. included subdivisions. brevispina zonule, submuticum zonule (dommergues et al. 1991, 1997). jamesoni subchronozone index. as jamesoni chronozone (see above). author. buckman (1918) as a hemera, d.t. donovan (in: dean et al. 1961) as a subzone. correlating fauna. uptonia ex grp jamesoni and spp. tragophylloceras and coeloceras also typical locally. included subdivisions. jamesoni zonule, pettos zonule (dommergues et al. 1991, 1997). ibex chronozone index. tragophylloceras ibex (quenstedt 1843). author. oppel (1856). masseanum subchronozone index. tropidoceras masseanum (d’orbigny 1844). author. buckman (1918) as a hemera, spath (1923) as a subzone. correlating fauna. tropidoceras spp., tragophylloceras frequent, especially in more southerly areas. included subdivisions. masseanum zonule (dommergues 1979; phelps 1985; dommergues et al. 1991, 1997). 39 valdani subchronozone index. acanthopleuroceras valdani (d’orbigny 1844). author. collenot (1869) as a zone, buckman (1918) as a hemera, spath (1942) as a subzone. correlating fauna. acanthopleuroceras spp., with tragophylloceras, liparoceras, and beaniceras at higher levels. included subdivisions. arietiforme zonule, maugenesti zonule, valdani zonule, actaeon zonule, alisiense zonule (dommergues 1979; phelps 1985; dommergues et al. 1991, 1997). luridum subchronozone index. beaniceras luridum (simpson 1855). 40 figulinum angulatum crescens capricornus lataecosta maculatum sparsicosta luridum crassum rotundum alisiense actaeon valdani maugenesti arietiforme masseanum pettos jamesoni submuticum brevispina polymorphus taylori nodogigas/grp aculeatum donovani figulinum capricornus maculatum luridum valdani masseanum jamesoni brevispina polymorphus taylori dilectum ? demonense aenigmaticum davoei ibex jamesoni beirense amaltheiforme splendens polymorphoides renzi maugenesti carinatum uptonia sp. bronni–lata bronni–jamesoni acanthobronnii muellensis costatus biruga dayiforme caprariforme chronozone subchronozone northwest european province mediterranean province zonule (nw european s.s.) zonule (lusitanian) zonule chronozone (spain) d ay ic er o id es costicillatum volubile–pantanellii dilectum aff. dilectum catriense ? mediterraneum flandrini erythreum ? sellae ? fig. 4. lower pliensbachian (‘carixian’) subdivisions and correlations: northwest european and mediterranean provinces. for explanation, see text. author. d.t. donovan (in: dean et al. 1961). correlating fauna. beaniceras grp luridum with liparoceras spp. and tragophylloceras. included subdivisions. rotundum zonule, crassum zonule, luridum zonule (dommergues 1979; phelps 1985; dommergues et al. 1991, 1997). davoei chronozone index. prodactylioceras davoei (j. sowerby 1822). author. oppel (1856). maculatum subchronozone index. androgynoceras maculatum (young & bird 1822). author. lang (1936) as a zone, spath (1938) as a subzone. correlating fauna. a. ex grp maculatum and liparoceras. included subdivisions. sparsicosta zonule, maculatum zonule (dommergues 1979; phelps 1985; dommergues et al. 1991, 1997). capricornus subchronozone index. androgynoceras capricornus (schlotheim 1820). author. wright (1863) used the index for a zone equivalent to the davoei zone of oppel; retained as a subzone by d.t. donovan (in: dean et al. 1961). correlating fauna. a. lataecosta, a. grp capricornus, etc. with liparoceras (including l. (becheiceras)) and, at certain levels, prodactylioceras. included subdivisions. lataecosta zonule, capricornus zonule, crescens zonule (dommergues 1979; phelps 1985; dommergues et al. 1991, 1997). figulinum subchronozone index. oistoceras figulinum (simpson 1855). author. lang (1936). correlating fauna. oistoceras spp. with liparoceras (becheiceras), tragophylloceras and prodactylioceras at certain levels. included subdivisions. angulatum zonule, figulinum zonule (dommergues 1979; phelps 1985; dommergues et al. 1991, 1997). northwest european province: lusitanian ?sub-province (portugal) faunal differentiation in the early pliensbachian has resulted in some correlation difficulties at intra-subzonal level between portuguese faunas and those elsewhere in europe. general affinities are however northwest european. local subdivisions as tabulated by dommergues et al. (1991, 1997, based on dommergues 1987) are shown in figure 4, and include: 1. jamesoni chronozone, taylori subchronozone (unnamed interval, caprariforme zonule, dayiforme zonule); polymorphus subchronozone (biruga zonule, costatus zonule); brevispina subchronozone (muellensis zonule, acanthobronni zonule); jamesoni subchronozone (bronni–jamesoni zonule, bronni– lata zonule, uptonia sp. zonule – ?part). 2. ibex chronozone, masseanum subchronozone (uptonia sp. zonule – ?part); valdani subchronozone (dayiceroides zonule, including acanthopleuroceras carinatum and a. maugenesti ?biohorizons, renzi zonule, polymorphoides zonule, splendens zonule, amaltheiforme zonule, beirense zonule and unnamed interval); luirdum subchronozone and davoei chronozone as northwest european province. subboreal province (britain, northern germany, etc.) increased faunal polarisation between southern and northern pliensbachian faunas in the upper pliensbachian (= domerian substage) makes intra-subzonal correlations difficult or impossible. subboreal faunas in particular, are dominated by amaltheidae with only very rare representation of mediterranean hildocerataceae. the former dominate in the south, however, and correlate detailed horizonal sequences. the basic zonal/subzonal framework employed is nevertheless identical to that used elsewhere in europe and follows m.k. howarth (in: dean et al. 1961). significantly, howarth (1991–1992) has proposed definitions for the bases of the subzones of the substage using northern english sites, all falling within the scope of the subboreal province as interpreted here. no complete system of biohorizons has been specifically proposed for the province, but the sequence of zonules used by dommergues et al. (1997) can be applied. full descriptions of faunas and successions can be found in howarth (1955, 1956, 1957, 1991–1992). upper pliensbachian substage margaritatus chronozone index. amaltheus margaritatus (de montfort 1808). author. oppel (1856). 41 stokesi subchronozone index. amaltheus stokesi (j. sowerby 1818). author. lang (1936). defined base. base of bed 1, hawsker bottoms or bed 12, staithes, staithes sandstone formation, north yorkshire, england (howarth 1955, 1991–1992; cox 1990). correlating fauna. amaltheus ex grp stokesi with rare protogrammoceras. tragophylloceras and liparoceras (becheiceras) present, especially in more southerly areas. included subdivisions. occidentale zonule, monestieri zonule, nitescens zonule, celebratum zonule (dommergues 1979; phelps 1985; dommergues et al. 1991, 1997). comment: the zonules of dommergues et al. (1997) are recognised largely on the basis of protogrammoceras which is typically very rare or absent in more northerly areas, thereby making the recognition of such units increasingly difficult from south to north. subnodosus subchronozone index. amaltheus subnodosus (young & bird 1828). author. spath (1942) as a nodifer subzone; name changed to subnodosus by howarth (1955) for reasons of synonym. defined base. base of bed 18, hawsker bottoms or bed 26, staithes, cleveland ironstone formation, north yorkshire, england (howarth 1955, 1991–1992). correlating fauna. amaltheus ex grp subnodosus with rare protogrammoceras. included subdivisions. normanianum zonule, unnamed interval (dommergues et al. 1991, 1997). comment: the normanianum zonule of dommergues et al. (1997) is recognised on the basis of protogrammoceras which is typically very rare or absent in more northerly areas, thereby making recognition of the unit increasingly difficult from south to north. 42 hawskerense lotti solare transiens salebrosum ? ruthense algovianum bertrandi (il) kurrianus ugdulenai macrum ragazzonii boscense depressum celebratum nitescens monestieri occidentale elisa emaciatum imitator solare levidorsatum meneghinii ? accuratum canavarii ugdulenai bertrandi (l) ragazzonii cornacaldense celebratum marianii isseli/ brevispiratum lavinianum/ portisi elisa solare levidorsatum meneghenii accuratum bertrandi ragazzonii cornacaldense emaciatum algovianum lavinianum hawskerense elaboratum solare transiens salebrosum (unnamed interval) algovianum (unnamed interval) normanianum celebratum nitescens monestieri occidentale hawskerense apyrenum gibbosus subnodosus stokesi spinatum margaritatus chronozone subchronozone zonule zonule zonule (austria–italy–spain) subchronozone(spain) chronozone (spain) mediterranean province submediterranean province subboreal province isseli brevispiratum lavinianum portisi fig. 5. upper pliensbachian (‘domerian’) subdivisions and correlations: subboreal, submediterranean and mediterranean provinces. for explanation, see text. gibbosus subchronozone index. amaltheus gibbosus (schlotheim 1820). author. buckman (1918) as a hemera, kuhn (1935) as a zone, spath (1942) as a subzone. defined base. base of bed 21, hawsker bottoms or bed 32, staithes, cleveland ironstone formation, north yorkshire, england (howarth 1955, 1991–1992). correlating fauna. amaltheus ex grp gibbosus, and rare protogrammoceras. included horizons. unnamed interval, algovianum zonule, unnamed interval. comment. the algovianum zonule of dommergues et al. (1997) is recognised on the basis of protogrammoceras which is typically very rare or absent in more northerly areas, thereby making the recognition of the unit increasingly difficult from south to north. spinatum chronozone index. pleuroceras spinatum (bruguière 1789). author. oppel (1856). apyrenum subchronozone index. pleuroceras apyrenum (buckman 1911). author. spath (1942). defined base. base of bed 25, hawsker bottoms, cleveland ironstone formation, north yorkshire (howarth 1955, 1991–1992; non cox 1990). correlating fauna. pleuroceras ex grp solare (phillips), p. apyrenum, etc. and occasional amaltheus ex grp margaritatus. included subdivisions. salebrosum zonule, transiens zonule, solare zonule (dommergues et al. 1991, 1997). hawskerense subchronozone index. pleuroceras hawskerense (young & bird 1928). author. buckman (1922) as a hemera, spath (1942) as a subzone. defined base. base of bed 38, hawsker bottoms, or bed 32, staithes, cleveland ironstone formation, north yorkshire (howarth 1955, 1991–1992). correlating fauna. pleuroceras ex grp hawskerense and occasional pseudamaltheus engelhardti (d’orbigny). included subdivisions. elaboratum zonule, hawskerense zonule (dommergues et al. 1991, 1997). submediterranean province (southern france, northern spain, etc.) the submediterranean province developed in parallel with the subboreal and is also therefore primarily a phenomenon of the upper pliensbachian (= domerian). faunas are dominated by hildocerataceae, with some dactylioceratidae but amaltheidae are usually much less common than in subboreal areas. in consequence, a separate sequence of zonules is recognised for the upper pliensbachian of the submediterranean province (meister 1989; dommergues et al. 1991, 1997) as follows: 1. margaritatus chronozone, stokesi subchronozone (as subboreal province); subnodosus subchronozone (depressum zonule, boscense zonule); gibbosus subchronozone (ragazzonii zonule, macrum zonule, ugdulenai zonule, kurrianus zonule, bertrandi zonule (ii), algovianum zonule, ruthense zonule, unnamed interval). 2. spinatum chronozone, apyrenum subchronozone (as subboreal province); hawskerense subchronozone (lotti zonule, hawskerense zonule). mediterranean province (austria, italy, southern spain) faunas in the province are commonly so different from those of northern europe that it is remarkable that the same standard zonation can often be used. the presence of interprovincial correlative tie-lines is very important in linking northern and southern areas, but many problems still remain, leading to the introduction by braga et al. (1982) and braga (1983) of a new zonal scheme for the mediterranean province, as correlated by dommergues et al. (1997) with submediterranean and northwest european schemes and reproduced here on figures 4 and 5. several sequences of ‘horizons’ are also recognised within the mediterranean province for the pliensbachian stage and schemes for austria/italy and spain are also tabulated on figures 4 and 5 (after braga 1983; meister 1987; ferreti 1990; dommergues et al. 1991, 1997; meister et al. 1994). toarcian stage the stage name was derived by d’orbigny (1842–1849) from the town of thouars in central western france (poitou) where the division is well-developed and rich in ammonites. unlike those of the earlier lower jurassic stages, all the zones of the modern toarcian stage postdate oppel’s simple scheme of 1856 (with a ‘zone der 43 posidonia bronni’, followed by a ‘zone des ammonites jurensis’). as for the pliensbachian, the toarcian is divided into two substages. both these substages have names, the lower toarcian corresponding to the whitbian (after whitby in north yorkshire, north-east england; buckman 1910) and the upper toarcian to the yeovilian (after yeovil in somerset, south-west england; buckman 1910). the original definition of whitbian included the variabilis zone but was redefined by m.k. howarth (in: dean et al. 1961) to exclude that zone which was reassigned as the lowest of the yeovilian. unlike for the pliensbachian, however, these geographical names for substages have fallen into disuse. the base of the toarcian stage the base of the lower zone of oppel’s toarcian, (with the bivalve ‘posidonia’ bronni as index) corresponds to the changeover in northwest europe from typical pliensbachian ammonite faunas with pleuroceras to typical toarcian faunas with abundant dactylioceras. the base of the stage in the type region (submediterranean province as used here) corresponds to the base of the tenuicostatum chronozone. this zone, however, has its type locality on the coast of northern england (north yorkshire; buckman 1910, subboreal province), and this has led to various proposals or assumptions that this latter area should include the basal boundary stratotype of the stage (e.g. m.k. howarth in: morton 1971; cox 1990; howarth 1991–1992). the lower part of the tenuicostatum chronozone as used in both provinces is a paltum subchronozone, the base of which was defined by howarth (1991–1992) as the base of bed 26, kettleness, or the base of bed 58, staithes (basal grey shales member, whitby mudstone formation), both in north yorkshire (sections as described by howarth 1955, 1973). the use of this stratigraphic division dates back to buckman (1922) with reference to a fauna in the highly condensed middle–upper lias ‘junction bed’ of dorset, southern england (buckman 1910; jackson 1926). the characteristic protogrammoceras fauna of buckman’s paltus hemera is abundant in dorset, but does not occur as part of a clear faunal succession due to the highly condensed and lenticular nature of the uppermost pliensbachian – lower toarcian ‘junction bed’. in yorkshire, however, the fauna is much rarer, although the rock succession itself is considerably expanded. nevertheless, as noted by howarth (1992, p. 5 in: howarth 1991–1992), p. paltum is probably not a good index, but was selected as it is restricted to this level in britain. further south in europe, similar protogrammoceras (or ‘paltarpites’) occur at higher and lower levels (howarth 1992, p. 7 in: howarth 1991–1992). in addition, the earliest toarcian dactylioceras, in association with p. paltum, are abundant and characteristic in southern areas but virtually absent in britain. the association of the former, including dactylioceras (eodactylites) mirabilis fucini and d. (e.) simplex fucini, with p. paltum in spain (e.g. goy & martinez 1990) and even in southern germany (schlatter 1985) presents a better scenario, however, for defining the base of the stage (cf. elmi 1997; elmi et al. 1997). detailed correlations between the northern european tenuicostatum chronozone and the unit of the same name in southern areas is not yet established in detail, due to apparent differences in the dactylioceratid faunas (cf. elmi et al. 1997). nevertheless, it is very unlikely that sections in britain will be suitable candidate gssps as they are faunally impoverished when compared to southern europe and hence have a more limited international correlation potential. toarcian correlative schemes and ammonoid provincialism early toarcian faunas show similar distribution patterns to those of the late pliensbachian, as boreal connections appear to have persisted throughout the substage. as in the pliensbachian, a subboreal to submediterranean to mediterranean province transition is recognisable. unlike the pliensbachian, however, separate zonal schemes exist for all three provinces (fig. 6). there are very close links, however, between submediterranean and subboreal faunas, so whether a distinct zonal/subzonal scheme is needed is debatable. even at intra-subzonal level, similarities are sufficient that many cross-correlations are possible. in the late toarcian, these similarities are so great that only one zonal scheme is justifiable in northwest europe and only one scheme is therefore reviewed here for a northwest european province (fig. 7). rare boreal links include occasional pseudolioceras, mainly in northern britain. this unified scheme combines elements of the british standard of w.t. dean (in: dean et al. 1961) and howarth (1980) with the french schemes of gabilly et al. (1971, 1974), gabilly (1976) and elmi et al. (1991, 1994, 1997). 44 subboreal province (northern britain) a restricted subboreal province is most characteristic of northern england and scotland in the lower toarcian (from late tenuicostatum to bifrons chronozones) when faunas are dominated by dactylioceratids with less common hildocerataceae, especially in scotland. the presence at certain levels of boreal hildocerataceans, such as tiltoniceras, elegantuliceras, ovaticeras and pseudolioceras, is typical. further south in britain, faunas become more submediterranean in character and late dactylioceratids of the bifrons chronozone are rare in dorset and somerset. the following scheme for the lower toarcian is that of m.k. howarth (in: dean et al. (1961) as modified by howarth (1973) and defined by howarth (1991–1992). the included biohorizons are described more fully elsewhere (page 2002b) and are based on observations by the author and records by howarth (1962, 1973, 1978, 1991–1992). the system of zonules for the ‘north west european’ province of elmi et al. (1997; essentially the submediterranean province as used here) is applicable, at least in part, to the subboreal province and is utilised below. lower toarcian substage tenuicostatum chronozone index. dactylioceras tenuicostatum (young & bird 1822). author. buckman (1910) replacing the annulatus zone of tate & blake (1876) (the latter with a stratigraphically incorrectly placed index; see m.k. howarth in: dean et al. 1961). paltum subchronozone index. protogrammoceras paltum (buckman 1922). author. buckman (1922) as a hemera, howarth (1973) as a subzone. defined base. provisionally defined (see comment) as base of bed 55, staithes, ketteness member, cleveland ironstone formation, north yorkshire, england (howarth 1955, 1973, 1991–1992; cox 1990). correlating fauna. protogrammoceras paltum, and very rare early dactylioceras (including d. pseudocommune fucini). included subdivisions. paltum zonule (including protogrammoceras paltum biohorizon). comment. although useful for correlating the base of the toarcian in a subboreal/uk sense, howarth’s north yorkshire reference section is not a ratified gssp (see discussion above). 45 crassum–semipolitum crassum–bifrons vortex braunianus turriculatum athleticum commune ovatum falciferum pseudoserpentinum elegans exaratum elegantulum antiquum semicelatum tenuicostatum clevelandicum crosbeyi paltum crassum fibulatum commune falciferum exaratum semicelatum (l) tenuicostatum clevelandicum paltum bifrons serpentinum tenuicostatum bifrons serpentinum tenuicostatum bifrons levisoni polymorphum bifrons sublevisoni falciferum? levisoni ‘semicelatum’ (il) mirabile semipolitum bifrons apertum lusitanicum tethysi sublevisoni striatus paltarpites bifrons sublevisoni falciferum elegantulum ‘semicelatum’ (ll) paltum semipolitum bifrons apertum lusitanicum tethysi sublevisoni douvillei pseudoserpentinum strangewaysi elegantulum ‘semicelatum’ tenuicostatum crosbeyi paltum chronozone subchronozone biohorizon zonule subchronozone chronozone chronozone subchronozone zonule subboreal province submediterranean province mediterranean province fig. 6. lower toarcian subdivisions and correlations: subboreal, submediterranean and mediterranean provinces. for explanation, see text. clevelandicum subchronozone index. dactylioceras clevelandicum howarth 1973. author. howarth (1973) = dactylioceras sp. nov. horizon of m.k. howarth (in: dean et al. 1961). defined base. base of bed 18, grey shales member, whitby mudstone formation, north yorkshire coast (e.g. kettleness/port mulgrave), england (howarth 1973, 1991–1992). correlating fauna. d. grp clevelandicum. included subdivision. crosbeyi zonule (including dactylioceras crosbeyi and d. clevelandicum biohorizons). tenuicostatum subchronozone index. as tenuicostatum chronozone (see above). author. buckman (1930 in: buckman 1909–1930) as a hemera, m.k. howarth (in: dean et al. 1961) as a ‘horizon’, howarth (1973) as a subzone. defined base. base of bed 20, grey shales member, whitby mudstone formation, north yorkshire coast (kettleness/port mulgrave), england (howarth 1973, 1991–1992). correlating fauna. d. tenuicostatum. included subdivisions. tenuicostatum zonule (including dactylioceras tenuicostatum biohorizon). semicelatum (i) subchronozone index. dactylioceras semicelatum (simpson 1843). author. m.k. howarth (in: dean et al. 1961) as ‘d. semicelatum horizon’, howarth (1973) as a subzone. the index has been used by mauberge (1948, 1952) for a tenuicostatum–semicelatum zone and a semicelatum zone, effectively as a synonym of the tenuicostatum chronozone as a whole. defined base. base of bed 28, grey shales member, whitby mudstone formation, north yorkshire coast (e.g. kettleness/port mulgrave area), england (howarth 1973, 1991–1992). correlating fauna. d. semicelatum and tiltoniceras antiquum (wright). included subdivisions. semicelatum zonule (including dactylioceras semicelatum and tiltoniceras antiquum biohorizons). comments. the semicelatum subchronozone of the subboreal province is as restricted by howarth (1973). in the submediterranean and mediterranean provinces, however, a ‘semicelatum subzone’ is also used but broadly equates to the clevelandicum, tenuicostatum and semicelatum subchronozones combined. clearly, different names are needed to distinguish the two units, but pending a full revision the two subchronozones are here distinguished as semicelatum (i) and semicelatum (ii), respectively. serpentinum chronozone index. harpoceras serpentinum (schlotheim 1813). author. oppel (1856) suggested the use of ammonites serpentinum as an alternative index to posidonia bronni. reynès (1868) restricted a serpentinus zone to the lower part of the lower toarcian (below a bifrons zone) and its use was restricted further by the recognition of a basal tenuicostatum zone. the use of h. serpentinum as an index has priority over h. falciferum (j. sowerby 1820) first used as a zonal index by haug (1885) and subsequently by most british authors (e.g. m.k. howarth in: dean et al. 1961; howarth 1991–1992). exaratum subchronozone index. cleviceras exaratum (young & bird 1828). author. buckman (1910) as a zone, arkell (1956) as a subzone. defined base. base of bed 33, mulgrave shale member, whitby mudstone formation, north yorkshire coast (e.g. rosedale wyke to lingrow knock or saltwick bay area, whitby), england (howarth 1962, 1991–1992; cox 1990). correlating fauna. elegantuliceras, cleviceras and early harpoceras in succession. dactylioceras (nodicoeloceras) and hildaites ex grp levisoni present. included subdivisions. elegantulum zonule (including elegantuliceras elegantulum biohorizon), strangewaysi zonule (including cleviceras exaratum and c. elegans biohorizons). falciferum subchronozone index. harpoceras falciferum (j. sowerby 1820). author. haug (1885) as a broader zone (including the exaratum subzone), buckman (1930 in: buckman 1909–1930) as a hemera, arkell (1933) as a subzone. defined base. base of bed 41, mulgrave shale member, whitby mudstone formation, north yorkshire coast (e.g. saltwick bay area, rosedale wyke to lingrow knock, etc.) england (howarth 1962, 1991–1992). correlating fauna. harpoceras ex grp falciferum. included subdivisions. pseudoserpentinum zonule (including harpoceras pseudoserpentinum biohorizon), douvillei zonule (including h. falciferum biohorizon). bifrons chronozone index. hildoceras bifrons (bruguière 1789). author. reynès (1868) as a zonal index. 46 commune subchronozone index. dactylioceras commune (j. sowerby 1815). author. wright (1863) as a zone in a broad sense, and equivalent to lower toarcian, m.k. howarth (in: dean et al. 1961) as a restricted subzone. equivalent to the ‘communis beds’ or subcarinata zone of thompson (1910). suggested re-defined base. base of bed 47, whitby, alum shale member, whitby mudstone formation, north yorkshire, england (sections described by howarth 1962, 1991–1992). this definition is modified from that of howarth (1991–1992) and cox (1990) to include the ovatum biohorizon. it is suggested that this modification is necessary to equate the base of the bifrons chronozone in the subboreal province with that in the submediterranean and mediterranean provinces where faunas with hildoceras ex grp sublevisoni are taken to indicate the lower part of the chronozone (abundant h. ex grp sublevisoni occurs with rare ovaticeras ovatum near ilminster in southern england; unpublished observations by the author). correlating fauna. dactylioceras, including d. commune and d. athleticum (simpson), also ovaticeras. hildoceras spp., including h. lusitanicum meister are usually uncommon. included subdivisions. sublevisoni zonule (including ovaticeras ovatum biohorizon), tethysi zonule (including dactylioceras commune biohorizon), lusitanicum zonule (including d. athleticum biohorizon). fibulatum subchronozone index. peronoceras fibulatum (j. de c. sowerby 1823). author. thompson (1910). defined base. base of bed 60, alum shale member, whitby mudstone formation, whitby, north yorkshire, england. correlating fauna. peronoceras, zugodactylites and porpoceras spp. with some hildoceras (including h. bifrons). included subdivisions. apertum zonule (including peronoceras turriculatum and zugodactylites braunianus biohorizons), bifrons zonule (part, including porpoceras vortex biohorizon). crassum subchronozone index. catacoeloceras crassum (young & bird 1828). author. corroy & gérard (1933). defined base. 1.5 m above the base of bed 72, whitby or the base of bed xiiv, alum shale member, whitby mudstone formation, ravenscar, north yorkshire, england (howarth 1962, 1978, 1991–1992). correlating fauna. abundant catacoeloceras with less frequent hildoceras including h. semipolitum buckman. included subdivisions. bifrons zonule (part, including catacoeloceras crassum – h. bifrons biohorizon), semipolitum zonule (including c. crassum – h. semipolitum biohorizon). submediterranean province (southern england, france, germany, northern spain, etc.) although strong links exist between northern and southern regions, faunas of submediterranean areas in the lower toarcian are usually richer in hildocerataceae, sometimes to the virtual exclusion of dactylioceratidae. the separate chronozonal schemes historically used in britain and france are not entirely necessary as the greatest faunal changes actually occur within britain, between southern england (dorset and somerset) and northern england (north yorkshire) and scotland (isle of raasay). the chronozonal framework employed in france is identical in zonal composition to that in britain, but differs at the level of subzones and horizons due to faunal differentiation. the scheme summarised here follows elmi et al. (1991, 1994, 1997) and is largely based on gabilly et al. (1971) and gabilly (1976). lower toarcian substage tenuicostatum chronozone index and author. as subboreal province (see above). paltum (or paltus) subchronozone index, author and defined base. as subboreal province (see above). correlating fauna. protogrammoceras paltum and, in certain areas, dactylioceras (eodactylites) spp., neolioceratoides and lioceratoides. included subdivisions. paltum [paltus] zonule (gabilly et al. 1974; gabilly 1976; elmi et al. 1991, 1994, 1997). semicelatum (ii) subchronozone index and author. as subboreal province, but used here in a less restricted sense (sensu gabilly et al. 1971; see comments below). 47 correlating fauna. dactylioceras spp. including d. semicelatum, and rarer hildoceratids, including protogrammoceras and neolioceratoides. included subdivisions. crosbeyi zonule, tenuicostatum zonule, semicelatum zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). comments. the exact relationship of the submediterranean semicelatum subchronozone to the subboreal subchronozone of the same name is problematic as both the crosbeyi and tenuicostatum subchronozones are difficult to recognise outside their type area. the conventional usage continued here is to draw the base of the submediterranean division at the first occurrence of abundant dactylioceras (orthodactylites) – this would therefore equate with the base of the clevelandicum subchronozone of subboreal areas. as the definition of the subchronozone in that region has been stabilised by formal definition (howarth 1991–1992, see above), it is necessary to rename the submediterranean division. as suggested above in discussion of the subchronozone in the subboreal province, pending full revision the two units are here distinguished as ‘semicelatum’ (i) (subboreal) and ‘semicelatum’ (ii) (submediterranean and mediterranean). serpentinum chronozone index and author. as subboreal province (see above). elegantulum subchronozone index. elegantuliceras elegantulum (young & bird 1828) author. gabilly (1976) as a subzone, equivalent to his earlier strangewaysi zone. correlating fauna. elengantuliceras, harpoceras ex grp serpentinum, cleviceras, hildaites and dactylioceratids including ‘nodicoeloceras’. included subdivisions. elegantulum zonule, strangewaysi zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). comment. the subchronozone is probably exactly equivalent to the subboreal exaratum subchronozone as it appears to have a coincident base (the definition of howarth 1991–1992 cited above could also therefore apply to this subchronozone; indeed, this is necessary if the serpentinus chronozone is to be used in both provinces). falciferum subchronozone index and author. as subboreal province (see above). correlating fauna. harpoceras ex grp falciferum, hildaites and dactylioceratids including nodicoeloceras. included subdivisions. pseudoserpentinum zonule, douvillei zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). comments. the subchronozone as used in submediterranean areas is probably equivalent to that of subboreal regions. a common defined base is therefore necessary if the same name is to be used in both provinces and that of howarth (1991–1992) may be appropriate. bifrons chronozone index and author. as subboreal province (see above). sublevisoni subchronozone index. hildoceras sublevisoni fucini 1922. author. donovan (1958). correlating fauna. abundant hildoceras spp. including hi. ex grp sublevisoni, harpoceras ex grp falciferum, dactylioceras ex grp commune, etc. included subdivisions. sublevisoni zonule, tethysi zonule, lusitanicum zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). comments. see discussion on subboreal province commune subchronozone regarding equilibration with the submediterranean scheme. howarth (1992, p. 177 in: howarth 1991–1992) includes faunas with hi. sublevisoni within a falciferum subchronozone sensu anglico. as harpoceras ex grp falciferum persists into the sublevisoni subchronozone, however, this interpretation would conflict with the established interpretation of french authors in the type region of the bifrons chronozone (e.g. gabilly et al. 1971) where the first appearance of primitive hildoceras (i.e. hi. ex grp sublevisoni) is regarded as marking the base of the zone. this latter convention is followed here. bifrons subchronozone index and author. as bifrons chronozone (see above). correlating fauna. hildoceras bifrons and allied species abundant, with rarer harpoceras subplanatum (oppel), phymatoceras and dactylioceratids, including zugodactylites and catacoeloceras. included subdivisions. apertum zonule, bifrons zonule, semipolitum zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). comments. a semipolitum subchronozone has been used in submediterranean province areas (e.g. in elmi et al. 1991, 1994), after donovan (1958), but was reduced to the status of ‘horizon’ (= zonule) by elmi et al. (1997). 48 49 northwest european province (britain, france, germany, northern spain, etc.) in the upper toarcian, good faunal links throughout most of more northerly areas of europe suggest that only one zonal scheme for the region is justifiable (fig. 7). faunas are richer in more southerly areas, especially in phymatoceratidae, but the bulk of the correlatively important grammoceratinae (hildoceratidae) are very widespread. the following scheme is based on the french systems of gabilly et al. (1971, 1974) and elmi et al. (1991, 1994, 1997), taking into account the earlier british zonation of w.t. dean (in: dean et al. 1961) as modified by howarth (1980). all intrasubzonal units are here used as zonules, no complete schemes of biohorizons presently being available for the province. upper toarcian substage variabilis chronozone index. haugia variabilis (d’orbigny 1845). author. buckman (1888 in: buckman 1887–1907) as a subzone of larger jurensis zone. first used as a zone by welsch (1903). variabilis subchronozone index. as variabilis chronozone (see above). author. buckman (1925 in: buckman 1909–1930) as a hemera, used as a horizon by gabilly et al. (1971) and a subzone by gabilly (1976). correlating fauna. haugia ex grp variabilis, denckmannia and catacoeloceras dumortieri (de brun). included subdivisions. navis zonule, jugosa zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). comment. interpretation of the base of the variabilis chronozone differs between britain and france depending on whether the last occurrence of hildoceras semipolitum/catacoeloceras spp. or the first occurrence of haugia is taken as a guide (the former would indicate bifrons chronozone, crassum subchronozone in britain and the latter variabilis chronozone, variabilis subchronozone in france). the base of the conventional variabilis chronozone is therefore drawn at a lower level in france than in britain as all three taxa are recorded together. this latter convention is followed here. illustris subchronozone index. haugia illustris (denckman 1887). buckmani lugdunensis celtica mactra tectiforme pseudoradiosa munieri insignisimilis gruneri pachu cappucinum fallaciosum fascigerum thouarsense doerntense bingmanni vitiosa phillipsi illustris jugosa navis aalensis pseudoradiosa dispansum thouarsense variabilis fluitans mactra pseudoradiosa levesquei gruneri insigne fallaciosum (l) fascigerum striatulum bingmanni vitiosa illustris variabilis ? fluitans flamandi mactra meneghinii subregale aratum aalensis meneghinii speciosum bonarellìi gradata chronozone chronozonesubchronozonesubchronozone mediterranean provincenorthwest european province zonule zonule fluitans mactra ? reynesi speciosum fallaciosum (ll) mediterraneum alticarinatus ? gemma fig. 7. upper toarcian subdivisions and correlations: northwest european and mediterranean provinces. for explanation, see text. author. stolley (1909) as a zone, gabilly et al. (1971) as a horizon, gabilly (1976) as a subzone. correlating fauna. haugia grp illustris, h. phillipsi (simpson), etc. (including haugiella), hammatoceras spp., denckmannia. included subdivisions. illustris zonule, phillipsi zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). vitiosa subchronozone index. haugia vitiosa (buckman 1909). author. gabilly (1976) as a subzone. correlating fauna. haugia grp vitiosa, denckmannia, hammatoceras, pseudogrammoceras. included subdivisions. vitiosa zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). thouarsense chronozone index. grammoceras thouarsense (d’orbigny 1844). author. brasil (1896) as a zone. comment. in britain, only two subchronozones are conventionally recognised in the thouarsense chronozone (e.g. dean et al. 1961; howarth 1980). the lower or striatulum subchronozone corresponds broadly to the combined bingmanni, striatulum and fascigerum subchronozones of the scheme used here. the upper or fallaciosum subchronozone is probably more or less equivalent to the division of the same name used here. bingmanni subchronozone index. pseudogrammoceras bingmanni (denckman 1887). author. gabilly et al. (1971) as a zone, gabilly (1976) as a subzone. correlating fauna. p. bingmanni and p. struckmanni with rarer podagrosites, etc. included subdivisions. bingmanni zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). striatulum subchronozone index. grammoceras striatulum (j. de c. sowerby 1823). author. buckman (1888 in: buckman 1887–1907). correlating fauna. grammoceras spp. including the index and g. thouarsense with some pseudogrammoceras, etc. included subdivisions. doerntense zonule, thouarsense zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). comment. use of g. striatulum as an index by buckman (1888 in: buckman 1887–1907) has priority over the use of g. thouarsense (used first as a zone by brasil 1896) and also by elmi et al. (1997). fascigerum subchronozone index. esericeras fascigerum (buckman 1888 in: buckman 1887–1907). author. gabilly et al. (1971) as esericeras subzone, guex (1975) as fascigerum subzone. correlating fauna. e. fascigerum and e. spp., pseudogrammoceras differens (ernst) and grammoceras penestriatulum (buckman), etc. included subdivisions. fascigerum zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). fallaciosum (i) subchronozone index. pseudogrammoceras fallaciosum (bayle 1878). author. nicklès (1907), probably as a broader division; replaces the struckmanni subzone of w.t. dean (in: dean et al. 1961) due to the latter’s stratigraphically incorrectly placed index (howarth 1980). correlating fauna. p. grp fallaciosum, osperlioceras, etc. included subdivisions. fallaciosum zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). comment. as a fallaciosum subchronozone is also used in mediterranean province areas, but may not be exactly time equivalent, the northwest european unit is here designated ‘fallaciosum (i)’. dispansum chronozone index. phlyseogrammoceras dispansum (lycett 1860). author. buckman (1889) as dispansum beds, buckman (1910) as dispansum zone. comment. the dispansum chronozone as used here corresponds to the dispansum subzone of the levesquei zone of british authors (e.g. w.t. dean in: dean et al. 1961; howarth 1980). insigne subchronozone index. hammatoceras insigne (zieten 1830). author. welsch (1897) as a zone, theobald & mauberge (1949) as a subzone. correlating fauna. h. ex grp insigne, phlyseogrammoceras dispansum, etc. included subdivisions. cappucinum zonule, pachu zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). gruneri subchronozone index. gruneria gruneri (dumortier 1874). author. gabilly et al. (1971) as a ‘horizon’ (= zonule), used as a subzone by elmi et al. (1991, 1994). correlating fauna. gruneria ex grp gruneri, hammatoceras perplanum prinz, etc. included subdivisions. gruneri zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). 50 51 pseudoradiosa chronozone index. dumortieria pseudoradiosa (branco 1879). author. haug (1892). levesquei subchronozone index. dumortieria levesquei (d’orbigny 1844). author. benecke (1901) as a broader ‘levesqueischichten’, buckman (1925 in: buckman 1909–1930) as a hemera, later as a subzone (spath 1942). correlating fauna. d. ex grp levesquei, catulloceras. included subdivisions. insignisimilis zonule, munieri zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). comment. broadly equivalent to the levesquei subzone of the levesquei zone of british authors (e.g. w.t. dean in: dean et al. 1961; howarth 1980). pseudoradiosa subchronozone index. as pseudoradiosa chronozone (see above). author. used as a subzone by gabilly et al. (1971). correlating fauna. d. ex grp pseudoradiosa including d. explanata buckman, huddlestonia, etc. included subdivisions. pseudoradiosa zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). comments. broadly equivalent to the moorei subzone of w.t. dean (in: dean et al. 1961) although d. moorei was later found to co-occur with the first pleydellia and therefore placed in the aalensis zone, mactra subzone by gabilly (1976). aalensis chronozone index. pleydellia aalensis (zieten 1832). author. reynès (1868). comment. broadly equivalent to the aalensis subzone of w.t. dean (in: dean et al. 1961). mactra subchronozone index. pleydellia mactra (dumortier 1874). author. mouterde (1952) informally as a ‘horizon’, elmi (1967) as a horizon, as a subzone by gabilly et al. (1971). correlating fauna. p. ex grp mactra and the last dumortieria ex grp moorei (lycett) with rarer pseudammatoceras, etc. included subdivisions. tectiforme zonule, mactra zonule, celtica zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). fluitans subchronozone index. pleydellia fluitans (dumortier 1874). author. elmi et al. (1991, 1994). correlating fauna. p. fluitan, p. lugdunensis (dumortier), p. buckmani mauberge, rarer pseudammatoceras, etc. included subdivisions. lugdenensis zonule, buckmani zonule (gabilly 1976; elmi et al. 1991, 1994, 1997). comments. the subzone was created by elmi et al. (1991) as a replacement for the aalensis subzone as p. aalensis itself was considered to be a primitive form of the mactra subzone. the buckmani subzone of gabilly (1976) was also reduced to the status of a ‘horizon’ (= zonule). mediterranean province (italy, austria, southern spain, north africa, etc.) the closest correlations between mediterranean and submediterranean areas are in the bifrons and aalensis chronozones. at other levels, the degree of faunal differentiation has necessitated the creation of the zonal schemes of donovan (1958), elmi et al. (1974), guex (1973) and other authors. a number of horizons (probably mainly with the status of zonules) are tabulated by elmi et al. (1991, 1994) and summarised again by elmi et al. (1997), as reproduced here on figures 6 and 7. lower toarcian substage polymorphum chronozone index. dactylioceras polymorphum fucini 1919. author. jimenez & rivas (1979). equivalent to the mirabile zone of guex (1973; index: d. mirabile fucini). mirabile subchronozone index. dactylioceras mirabile fucini 1919. author. colo (1961) as a ‘horizon’ or ‘niveau’, used as a subzone by guex (1973). correlating fauna. dactylioceras (eodactylites) spp., protogrammoceras (= paltarpites), lioceratoides, etc. included subdivisions. ‘paltarpites’ fauna (?part; elmi et al. 1991, 1994, 1997). semicelatum (ii) subchronozone index and author. as subboreal province (see above), but used in the sense of the submediterranean province. broadly equivalent to the ‘niveau à protogrammoceras madagascariense’ of colo (1961) and the madagascariense subzone of guex (1973; index: protogrammoceras madagascariense (thevenin 1908)). correlating fauna. dactylioceras spp. including d. semicelatum, also protogrammoceras madagascariense thevenin, etc. included subdivisions. ‘paltarpites’ fauna (?part), ‘striatus’ fauna (?part; elmi et al. 1991, 1994, 1997). levisoni chronozone index. hildaites levisoni (simpson 1843). author. guex (1973). levisoni subchronozone index. as levisoni chronozone (see above). author. guex (1973). correlating fauna. hildaites spp. including h. levisoni, also dactylioceras spp., etc. included subdivisions. the ‘striatus’ fauna (?part; elmi et al. 1991, 1994, 1997). falciferum subchronozone index and author. as subboreal province (see above). correlating fauna. harpoceras grp falciferum, mercaticeras, etc. included subdivisions. none (elmi et al. 1991, 1994, 1997). bifrons chronozone index and author. as subboreal province (see above). sublevisoni subchronozone index and author. as submediterranean province (see above). correlating fauna. hildoceras grp sublevisoni, etc. included subdivisions. sublevisoni zonule, tethysi zonule (elmi et al. 1991, 1994, 1997). bifrons subchronozone index and author. as submediterranean province (see above). correlating fauna. hildoceras grp bifrons. included subdivisions. lusitanicum zonule, apertum zonule, bifrons zonule, semipolitum zonule (elmi et al. 1991, 1994, 1997). comment. the semipolitum zonule has been previously used as a full subchronozone (see note under submediterranean province above). upper toarcian substage gradata chronozone index. brodieia gradata (merla 1932). author. atrops & elmi (1971) as a subzone. gemma subchronozone index. gabyllites [collina] gemma (bonarelli 1893). author. gallitelli-wendt (1970). correlating fauna. peronoceras, podagrosites, pseudopolyplectus, etc. included subdivisions. none (elmi et al. 1991, 1994, 1997). alticarinatus subchronozone index. merlaites alticarinatus (merla 1932). author. mouterde (1967) as a ‘niveau’, atrops & elmi (1971) as a subzone. correlating fauna. crassiceras spp., phymatoceras, pseudogrammoceras, polyplectus, etc. included subdivisions. aratum ?zonule, subregale ?zonule (elmi et al. 1991, 1994, 1997). bonarellii chronozone index. hammatoceras bonarellii parisch & viale 1906. author. elmi et al. (1991, 1994) as a replacement, in part, for the rivierense zone of elmi (1986; index osperlioceras rivierense (monestieri)). mediterraneum subchronozone index. pseudogrammoceras mediterraneum rivas 1975. author. used as a subzone by elmi et al. (1991, 1994). correlating fauna. pseudogrammoceras sp. including p. cf. bingmanni, also polyplectus, oxyparoniceras, etc. included subdivisions. none (elmi et al. 1991, 1994, 1997). fallaciosum subchronozone index and author. as northwest european province (see above). correlating fauna. pseudogrammoceras fallaciosum, polyplectus, oxyparoniceras, erycites, etc. included subdivisions. none (elmi et al. 1991, 1994, 1997). speciosum chronozone index. hammatoceras speciosum jamensch 1902. author. used as a zone by elmi et al. (1991, 1994). speciosum subchronozone index. as speciosum zone (see above). author. used as a subzone by elmi et al. (1991, 1994). correlating fauna. hammatoceras insigne, osperlioceras, pseudogrammoceras pachu. included subdivisions. none (elmi et al. 1991, 1994, 1997). reynesi subchronozone index. osperlioceras reynesi (monestier 1921). 52 author. j. mattei (in: gabilly et al. 1971) as ‘assises à pseudogrammoceras reynesi’. correlating fauna. o. reynesi and spp., hammatoceras perplanum, etc. included subdivisions. none (elmi et al. 1991, 1994, 1997). meneghini chronozone index. dumortieria meneghinii haug 1887. author. donovan (1958). correlating fauna. d. meneghinii with catulloceras grp perroudi, osperlioceras, hammatoceras, erycites etc. included subdivisions. meneghinii ?zonule, unnamed interval (elmi et al. 1991, 1994, 1997). aalensis chronozone index and author. as northwest european province (see above). mactra subchronozone index and author. as northwest european province (see above). correlating fauna. pleydellia grp mactra etc. included subdivisions. mactra zonule, flamandi zonule (elmi et al. 1991, 1994, 1997). fluitans subchronozone index and author. as northwest european province (see above). correlating fauna. pleydellia spp. including p. fluitans. included subdivisions. fluitans zonule, unnamed interval (elmi et al. 1974, 1991, 1994, 1997). references alméras, y., boullier, a. & laurin, b. 1997: brachiopodes. in: cariou, e. & hantzpergue, p. 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(1975b) and sørensen (1983), and is a main subject of this paper. the nordre strømfjord shear zone was recognised by previous authors as a sinistral shear zone mainly on the basis of deflection of fabrics and lithologies. a general observation was that open structures outside the zone become closed and brought into parallelism within the zone. this is apparent both in the field and especially so on regional geological maps and aerial photographs. a systematic change in the orientation of planar fabrics across the shear zone indicated that the zone is wedge-shaped in vertical profile, suggesting that the zone narrows upwards, © geus, 2006. geological survey of denmark and greenland bulletin 11, 145–161. available at: www.geus.dk/publications/bull 146 disko bugt 69° –0.844 –0.230 –0.147 –0.108 –0.082 –0.064 –0.049 –0.037 –0.027 –0.019 –0.011 –0.004 0.004 0.013 0.024 0.039 0.059 0.087 0.128 0.210 1.736 attu arfe rs iorfik 25 km inland ice b [nt/m] b aasiaat attu nordre strømfjord shear zone nordre strømfjo rd arfersiorfik fig. 1b fig. 2 agto map sheet 54° 68° a 50 km inland ice 53°53° 51°51° 50°50°52°52° 51° 50°52° 67°30'67°30' 53° 67°30' 51° 68°68°68° arfe rs iorfik 68° arfe rs iorfikattuattu 500 km greenland surficial deposits quaternary basalt palaeogene metasedimentary rocks (may include archaean components) nagssugtoqidian orogen sisimiut charnockite arfersiorfik quartz diorite orthogneiss (archaean, reworked) archaean metasedimentary rocks (may include palaeoproterozoic components) amphibolite anorthosite and ultrabasic rocks fig. 1. a: simplified geological map of the nagssugtoqidian orogen. index map of greenland shows the location of fig. 1a. black frames, locations of the agto map sheet (olesen 1984) and the inner arfersiorfik region investigated during field work in 2002 (fig. 2). b: aeromagnetic map of the nordre strømfjord shear zone from the coast to the western margin of the inland ice (shown as the vertical gradient of the total magnetic field intensity, nt/ m). anticlockwise rotation of lithologies into the shear zone is shown by curved stippled lines. the established and inferred boundaries of the high-strain part of the shear zone (full and stippled lines) are positioned where these rotating lithologies attain orientations which are indistinguishable from those within the central part of the shear zone itself. the magnetic anomaly field was obtained by subtracting the regional aeromagnetic data from the international geomagnetic reference field (rasmussen & van gool 2000). nominal flight altitude of the survey: 300 m above sea level, with gentle drape flying over areas with high relief. the survey was flown along n–s flight lines 500 m apart and along orthogonal tielines at 5 km intervals. nt = nanotesla (magnetic flux density). 147 and conversely widens deeper in the crust. this interpretation is supported by the observation that the deepest part of the shear zone, which is exposed in the west near the coast, is more than twice as wide as its more high-level, eastern end near the inland ice (bak et al. 1975a, b). the western part of the nordre strømfjord shear zone was mapped in detail within the agto map sheet (olesen 1984). in this paper we report an investigation of its eastern part, conducted in 2002 in the inner part of the fjord arfersiorfik. our investigations were in part intended to resolve conflicting interpretations of the nature of the shear zone. although all previous published work on the shear zone had reached similar conclusions regarding its magnitude and structural character, a different hypothesis was presented in a subsequent reconnaissance study by hanmer et al. (1997a, b), who re-interpreted the pre-existing data and purported that the shear zone was smaller than previously mapped and accommodated less lateral displacement than previously accepted. our premise was that detailed field work aimed at resolving the spatial relationships of structural elements, rather than relying on previously collected data, would expand our knowledge of the characteristics of the shear zone and would enable rigorous testing of the two previous hypotheses. the early work (bak et al. 1975a, b; sørensen 1983) showed the shear zone to be a large-scale synmetamorphic, sinistral transcurrent zone with a distinct wedge shape in its western, syn-granulite facies part. in that area, the shear zone is c. 15 km wide. it was also suggested that the shear zone deformation occurred simultaneously with large-scale metasomatism (sørensen & winter 1989). prior to the present study, the general outline and extent of the nordre strømfjord shear zone between the agto map sheet and the inland ice was drawn by bak et al. (1975b) and sørensen (1983), based on work by henderson (1969) and interpretation of aerial photographs. now, the extent of the zone of high strain between the coast and the inland ice can be demonstrated to correlate with anticlockwise rotation of lithologies into the shear zone, which is clearly visible on a new aeromagnetic data set (nielsen & rasmussen 2004). the age of the shear zone seems to be bracketed by the 1.85 ga age of regional metamorphism (hickman & glassley 1984; connelly et al. 2000) and postkinematic pegmatite ages of 1.76 ga (connelly et al. 2000; stendal et al. 2006, this volume). apart from the shear zone, the area we investigated in 2002 also encompasses a major part of the arfersiorfik quartz diorite (aqd), first observed by noe-nygaard & ramberg (1961) and later described by henderson (1969). the latter author visited the area in connection with reconnaissance work leading to the publication of the 1:500 000 scale geological map nussuaq – søndre strømfjord (escher 1971). the arfersiorfik quartz diorite was subsequently studied by kalsbeek et al. (1984, 1987) and kalsbeek (2001), who interpreted it as a subduction-related calc-alkaline intrusive suite and obtained an age of intrusion of 1.92 ga (see also the section on petrology). along its shores, the arfersiorfik fjord system offers excellent exposures of the shear zone and its surroundings. the authors spent three weeks in the region in the summer of 2002, conducting their investigations from a single camp with transport by inflatable dinghy, supplemented by half a day’s helicopter reconnaissance in the area between inner arfersiorfik and the inland ice. the area covered during the field work is shown in fig. 2. the main aims of the field work were to investigate the shear zone in the inner part of arfersiorfik and to investigate the relationships between the shear zone and the arfersiorfik quartz diorite; as can be seen from fig. 2, the shear zone constitutes the northern boundary of the aqd for a distance of at least 35 km between the inland ice and inner arfersiorfik. laboratory investigations of the approximately 110 samples collected during field work have not yet been finalised, and this account is therefore of preliminary nature. a transect through the shear zone the lithology and structure of the shear zone are illustrated by way of a schematic profile covering the area between akunnaaq and sarfaarsuk (fig. 3), a distance of c. 8 km, corresponding to a distance of c. 7 km as measured perpendicular to the shear zone trend. the shear zone is expressed by two principal characteristics: lithological units are all planar and vertically oriented, and the lithological variability per unit length across strike is much more pronounced than in the surrounding rocks north and south of the zone. in the field, these features are best displayed along the eastern shore of the small fjord orlerfik (fig. 2). lithologically, the shear zone can be described as a succession of supracrustal schist and gneiss units alternating with siliceous and intermediate orthogneisses of the aqd. the profile of fig. 3 is described in the following from south to north. further details about the aqd are described in a later section. to the south of the shear zone (within the area of investigation, fig. 2) the aqd is seen to rest with low-angle boundaries on siliceous gneisses, often with an intervening screen of schist. we agree with van gool et al. (1999) that this surface is of tectonic, probably thrust or ductile 148 thrust nature. farther to the south, in the area between the heads of nordre strømfjord and arfersiorfik, a thin (up to 500 m) sheet of aqd with tectonic contacts occurs with archaean siliceous gneisses both above and below the aqd sheet (the ussuit unit; manatschal et al. 1998; van gool et al. 1999). the geometry of this bounding surface is interpreted as outlining a series of folds. only the northern limb of the northernmost synformal structure is contained within the composite profile of fig. 3. folding of the aqd was observed by henderson (1969) and later elaborated upon by passchier et al. (1997) and van gool et al. (1999). at the localities outside the shear zone where the aqd can be seen in contact with the structurally underlying siliceous gneisses (localities 01702, arfers iorfik inner arfersiorfik b a orle rfik sarfaarsuk nue rsor fik 12702 01703 03706 13705 13704 01704 15705 15703 15702 51° 68° 50°30' 51°30' major outwash plains fault (inferred) structural trend line 10 km polonia gletscher highly deformed, chemically altered and pegmatite-invaded part of the aqd ('pencil gneiss'), mapped and inferred arfersiorfik quartz diorite (aqd), mapped and inferred supracrustal schist units, mapped and inferred siliceous gneisses (probably orthogneisses), mapped and inferred nuussuaqtunertoq inland ice 18702 05702 ak un na aq 05701 ks fig. 2. simplified geological map of the inner arfersiorfik region, showing the authors’ 2002 field work along full-coloured coasts (see also fig. 1). compare the mapped geology with the magnetic patterns on fig. 7, shown at the same scale. red lines, structural trend lines mainly from aeromagnetic data. ks, kangimut sammisoq (near map centre). five digit numbers, locality numbers mentioned in the text. two antiformal folds east of the inferred fault along inner arfersiorfik are outlined by the aqd contact overlying siliceous gneisses north of localities 05702 and 03706. the axial trace of the intervening synformal fold meets the coast near loc. 01703. tent symbol, position of camp during 2002 field work. inland geology near nuersorfik from van gool & marker (2004). 127020170201703 (cumulate) 02701 02702 08703 08704 18702 metadolerite locality aqd ba sse nnw (31 km south) 1 km 'hornblende gneiss rich in microcline' of henderson (1969): lineated and fine grained with abundant pegmatite sheets nordre strømfjord shear zone granitic orthogneiss amphibolites mafic enclaves hornblendebearing orthogneiss gneisses with abundant inclusions massive coarse-grained aqd homogeneous gneisses with few inclusions neosome increases three metadolerites 4th supracrustal unit 5th supracrustal unit 3rd supracrustal unit 2nd supracrustal unit 1st supracrustal unit fig. 3. schematic profile a–b through the nordre strømfjord shear zone in the inner arfersiorfik from akunnaaq in the south to sarfaarsuk in the north (figs 2, 7). localities and lithologies have been projected onto the profile plane along the strike direction of the shear zone. locality numbers mentioned in the text appear beneath the profile. for colour code, consult caption to fig. 2. 149 01704, 03706, 05701, figs 2, 3), the contacts are all tectonised, and with a well-developed, folded planar fabric. original intrusive features have been obliterated except at loc. 05702 (fig. 2), where xenoliths of pelitic schist can be seen within the aqd, clearly indicating intrusion of the quartz diorite into a pre-existing metamorphosed sedimentary sequence. from loc. 01702 (fig. 3) and towards the north, siliceous gneisses become progressively more deformed and contain an increasing amount of granitic material. for a distance of almost 1 km to the south of the first supracrustal schist unit, the gneisses display a subvertical planar fabric and contain abundant layers of leucocratic, in places pegmatitic, material. these gneisses appear highly strained. the transition within these gneisses, from 01701 to 02702 (fig. 3), is the best exposed transition zone developed in siliceous gneisses in the area that we have visited. the structural development of these gneisses is illustrated in fig. 4a–c. the first supracrustal unit (fig. 3) comprises a predominant lithology of mafic schists with calc-silicate and ultramafic lenses. pelitic schists are subordinate. at locality 08703, a second thin supracrustal unit of pelitic schist (thickness 25 m) occurs along the boundary to the aqd. the gneisses to the north of the first supracrustal unit contain abundant layers of homogeneous amphibolite, a c b b d fig. 4. siliceous gneisses between localitiess 17701 and 02702 (figs 2–3) illustrating progressive deformation towards the first supracrustal unit. a: coarsely banded biotite gneiss, loc. 17701 (knife 10 cm long). b: finely banded gneiss with generally steeply oriented foliation, but apparently variable deformation intensity at outcrop scale, loc. 02701 (compass 10 cm long). c: extreme planar fabric and fine-scale layering in siliceous gneiss near the first supracrustal schist unit, loc. 02702. d: detail from the same locality with lenticular ultramafic inclusions (knife 10 cm long). 150 with locally preserved discordant relationships to the host gneiss structures. these discordant amphibolites were undoubtedly originally dolerite dykes. farther to the north, the gneisses are nearly devoid of amphibolites and are characterised by wavy and folded migmatitic structures without the pronounced planar fabric seen in the gneisses adjacent to the first supracrustal unit. the contact between the second supracrustal unit and the aqd is vertical. coarse-grained segregations of granitic pegmatite in the schist appear to be smeared out and pulled apart. the aqd near this contact is syntectonically recrystallised and displays layering on a centimetre scale. the aqd farther to the north of the contact becomes relatively coarse grained and in places preserves undeformed magmatic structures (see a later section with more details on the petrology of the aqd). these relatively coarse-grained aqd rocks become progressively tectonised towards the north, developing a very pronounced ltectonite fabric. pegmatite sheets also become abundant, and the aqd itself becomes progressively more leucocratic. henderson (1969 p. 7) describes this transition with these words: “in the inner part of arfersiorfik a zone of basic gneiss of a type not found elsewhere in the area was encountered. this is a hornblende gneiss rich in microcline. it contains numerous pegmatites”, and further, “a large folded quartz diorite body dominates the inner part of arfersiorfik ... on its northern side it is in contact with the hornblende gneiss rich in microcline mentioned previously” (henderson 1969, p. 11). we interpret the “hornblende gneiss rich in microcline” as the northernmost, most highly deformed (and most chemically altered) equivalent of the much less deformed and more igneous appearing aqd to the south of the shear zone. nevertheless, the aqd to the south of the shear zone is in most places also a tectonite; a mineral lineation is nearly always present in the rock. textures viewed on sections perpena b fig. 5. arfersiorfik quartz diorite. a: coarsegrained metamorphosed quartz diorite with pervasive linear fabric. a minor dextral shear zone deforms the linear fabric (compass 10 cm long). b: extreme linear fabric developed in aqd close to its northern boundary (‘pencil gneiss’; knife 20 cm long). 151 dicular to the lineation appear igneous, while a pronounced tectonic lineation is seen in other orientations (fig. 5). the transition from the more magmatic appearing aqd to the “hornblende gneiss rich in microcline” is gradual, and the continuity of these rocks is evident on either side of arfersiorfik. between the third and fourth supracrustal units siliceous gneisses of varying heterogeneity and apparent degree of shear zone deformation occur, all with a vertical planar structure. basic inclusions are common in this gneiss unit. the fourth supracrustal unit as exposed on the eastern shore of orlerfik is a lithologically variable assemblage of pelitic schists and gneisses, amphibolitic schists, and calcsilicate gneiss. overall, the rocks appear highly deformed. the pelitic rocks typically contain numerous layers and lenses of pegmatitic material up to 8 m thick. cordierite was observed in the schists, and a lens of tourmalinite was also found. near the inland ice, at loc. 15703 (fig. 2), a centimetre-thick marble layer, the only occurrence of marble seen during field work, was observed in a pelitic schist thought to be the merged equivalent of the third and fourth supracrustal units at orlerfik. the gneisses between the fourth and fifth supracrustal a b fig. 6. pelitic and mafic schists from supracrustal unit near the inland ice visited during helicopter reconnaissance, loc. 15705 (fig. 2). a: two-mica sillimanite schist with abundant ‘winged’ feldspar blasts indicating sinistral sense of shear. long dimension of photo c. 75 cm. b: amphibolitic schist with boudins of garnet-bearing ultramafic rock (hammer c. 50 cm long). 152 units are quartzofeldspathic. a rather homogeneous, granitic orthogneiss 1 km wide occurs immediately to the north of the fourth supracrustal unit. it contains a few mafic inclusions which appear to be metadolerites. this gneiss, although foliated, has not developed the typical shear zone fine layering, and it is clearly an orthogneiss. towards the north, quartzofeldspathic gneisses with numerous granitic layers and bands form the boundary towards the fifth supracrustal unit. the finely banded shear zone planar structure is developed in places. the gneisses between the fourth and fifth supracrustal unit thus appear to be progressively deformed towards the north. the fifth supracrustal unit is well exposed at orlerfik and along the western shore of the nuussuaq peninsula. on nuussuaq, this unit forms an elongate ridge of strongly rusty weathering rocks. in fresh exposures in the tidal zone, the rusty weathering rock can be seen to be a fine-grained graphiteand sulphide-bearing darkish grey gneiss. in this unit, finely banded amphibolitic schists are prominent, along with pelitic sillimanite-bearing schists. calc-silicate rocks are seen as well, as also described by henderson (1969). pegmatitic layers are abundant. we were unable to confirm the marble layer occurring on the western half of the nuussuaq peninsula on henderson’s (1969) map. we found, instead, a complex of light-coloured, in some places greenish, anthophyllite-phlogopite-diopside-bearing metamorphosed ultramafic rocks. it appears that all the supracrustal units, although structurally continuous, change lithologically along strike, consisting of various combinations of pelitic schists and gneisses, graphite-sulphide gneisses, calc-silicate rocks, mafic schists and ultramafic lenses. in all the supracrustal units deformation appears to be intense. both pelitic and mafic rocks are finely schistose (fig. 6). ultramafic and skarn lenses may be rather massive and homogeneous, but they are small in size and volumetrically minor. overall, the supracrustal units are schistose throughout, and differ in this way from the intervening siliceous gneisses, which are heterogeneously deformed on a 100 m scale. to the north of the fifth supracrustal unit only scattered exposures of gneiss are found at orlerfik. along several localities near the northern boundary of the shear zone, at orlerfik and along the south coast of tunertoq, a homogeneous, hornblende-bearing orthogneiss is encountered. in places it is reminiscent of the aqd. farther north of the shear zone in the area around sarfaarsuk, gneisses with a complex history occur, as indicated by several generations of granitic and pegmatitic veins and layers, and mafic and ultramafic layers and lenses. at locality 12702 (fig. 2), a number of mafic layers are clearly folded metadolerites, and at this locality it can be seen how new layering develops concomitantly with deformation. along this layering the thin metadolerites can be seen to be displaced, and it seems evident that new layering develops in the siliceous gneisses at small angles to the older layering. without the metadolerites it would be impossible to discriminate between new and old layering. aeromagnetic data the entire nordre strømfjord shear zone and adjacent areas are covered by regional aeromagnetic data (figs 1b, 7) acquired during the project aeromag 1999 (see text to fig. 1b and rasmussen & van gool 2000). the aeromagnetic map proved very useful for delineation of lithologies and structures in the field, and in general there is a very clear correlation between observed surface geology and the aeromagnetic anomaly patterns. the arfersiorfik quartz diorite is associated with a variable magnetic signature. the best exposed part of the aqd is located in inner arfersiorfik just north of polonia gletscher (fig. 7). this part is denoted the core zone of the aqd complex and is characterised by a distinct positive anomaly (300–490 nt). here an unusually large amount of magnetite was found, both as millimetre-scale magnetite needles and as magnetite grains 1–3 cm large. a pronounced decrease in the magnetic intensity of the aqd is observed just north-west of the core zone. the magnetic signature of the aqd changes towards the shear zone, where the fine-grained, pegmatite-bearing and strongly linear aqd (the ‘pencil gneiss’) that forms the northernmost 1–2 km of the body exhibits strong negative anomalies. these changes in magnetic signature appear to reflect metamorphic and metasomatic processes associated with the shear zone development. the demagnetising effects reflect the formation of titanite and biotite at the expense of fe-ti-oxides, which is synchronous with shear zone evolution. detailed thin section observations show that the modal abundances of titanite and magnetite/ilmenite are strongly negatively correlated. comparison of titanite-rich samples and magnetite/ilmenite-rich samples with the vertical gradient of the magnetic anomaly field (obtained from the map shown in fig. 7) shows that the titanite-rich samples consistently occur within negative changes in the gradient, while the magnetite/ilmenite-rich samples occur within positive gradients. further work is underway to evaluate the reliability of this correlation. in general, the supracrustal schist units are associated with negative anomalies in the total magnetic field intensity. within the shear zone, the schist units are characterised by pronounced, linear short-wavelength negative ano153 malies (–150 to –300 nt). at kangimut sammisoq (ks on fig. 7) and towards the west-south-west the aqd and juxtaposed schists form a coherent negative anomaly, which can be traced for a considerable distance towards west-south-west into the agto map sheet area (olesen 1984). within the latter area the anomaly reflects supracrustal rocks only. the negative anomalies of the supracrustal schists probably reflect the absence of fe-ti oxides and the abundance of iron sulphides and graphite, which yields a weak magnetic response. in general, gneiss lithologies in the area are expressed as positive magnetic anomalies. because of their greater volume, the gneisses are associated with broader wavelength anomalies than the supracrustal units. however, the shape of the anomalies associated with the gneiss units within the shear zone are of short wavelength and elongate (fig. 7). where a significant strain gradient in the siliceous gneisses is observed, e.g. northwards from akunnaaq along the western shore of inner arfersiorfik (from loc. 01702 to 02702, fig. 3), this transition is not visible in the magnetic field (a on fig. 7). in general, it appears that even large changes in strain adjacent to and within the shear zone do not have a clear magnetic signature in the siliceous gneisses. while the magnetic lows associated with supracrustal units are in general persistent along strike, the highs associated with the siliceous gneisses in places outline lenticular structures, the most obvious example being the magnetic high which can be seen to coincide with the orthogneisses between the fourth and fifth unit (b on fig. 7). the general map structure although we have not carried out regional mapping, some map scale observations follow from our work. from the inland ice and for a distance of at least 35 km towards the south-west (i.e. in the area between the inland ice and the bend of arfersiorfik towards south-east west of nuussuaq), the aqd is bounded to the north by the shear zone, and probably with a continuous screen of supracrustal schists along its northern boundary. towards this bounding schist, the aqd becomes progressively deformed, developing a pronounced linear fabric and undergoing a number of [nt] 5 2 4 2 0 7 1 4 4 1 0 4 7 2 5 0 3 2 1 86 – 6 – 1 5 – 2 4 – 3 2 – 4 0 – 4 8 – 5 6 – 6 4 – 7 1 – 7 9 – 8 6 – 9 3 – 1 0 0 – 1 0 8 – 1 1 5 – 1 2 2 – 1 2 9 – 1 3 7 – 1 4 4 – 1 5 1 – 1 5 9 – 1 6 7 – 1 7 5 – 1 8 4 – 1 9 2 – 2 0 2 – 2 1 4 – 2 2 7 – 2 4 5 – 2 7 5 – 4 0 2 ks e b a c 51°30' 50°30' 68° d 51° inland ice polonia gletscher inner arfersiorfik ak un na aq orle rfik arfers iorfik nue rsor fik qaam asuuo q sarfarsuuk nuussuaq tunertoq 10 km fig. 2 fig. 7. total magnetic field intensity map of the study area. a, akunnaaq; ks, kangimut sammisoq; b, magnetic high coinciding with the orthogneisses between the fourth and fifth supracrustal units; c–d, lithological boundary between siliceous gneisses and supracrustal schists; e, possible magnetic expression of merged fourth and fifth supracrustal units. the position of the camp site used during the field work is shown with a tent symbol. compare the magnetic patterns with the mapped geology on fig. 2 (white frame), shown at the same scale. nt: nanotesla, a unit of magnetic flux density. 154 mineralogical changes, described below. these mineralogical changes are reflected in a change in magnetic signature. the change is less dramatic to the east of arfersiorfik than it is to the west of the fjord, and this signature can be followed from the fjord to the inland ice and beneath the ice for at least another 30 km. based on aeromagnetic data covering the entire greenland including the inland ice, nielsen (2004) and nielsen & rasmussen (2004) suggest a 125 km eastward extension of the aqd beneath the ice. the outcrop pattern and orientations of the boundary between the aqd and the structurally underlying schists and gneisses are in accord with a structural model involving relatively open folding, as marked on fig. 2. on henderson’s (1969) map, a ‘tongue’ of siliceous gneisses projects from the eastern shore of the fjord 20 km eastwards into the aqd. during helicopter reconnaissance by us, this eastward-reaching gneiss was nowhere to be seen. along the shores of arfersiorfik, there is an antiformal closure of aqd over siliceous gneisses with an intervening schist screen, but this cannot extend inland for more than 2 km. the entire triangular area bounded by arfersiorfik, the shear zone, and the inland ice is most likely only underlain by aqd. the map pattern west of inner arfersiorfik differs from the pattern described above. along the shoreline south of kangimut sammisoq the southern boundary of the aqd is vertical, and south of the boundary, gneisses and the schists of the first supracrustal unit are also vertically oriented and possess a well-developed planar shear zone fabric. we interpret this difference in map pattern as reflecting intersections with the shear zone boundary at two different levels. petrology arfersiorfik quartz diorite the arfersiorfik quartz diorite was first mapped in the study area by henderson (1969), who noted that it varies from a homogeneous, coarse-grained igneous rock in its central region which lacks evidence of deformation, to a compositionally banded gneiss near its margins. further work by kalsbeek et al. (1984, 1987) and kalsbeek (2001) supported the general descriptions of henderson and provided a considerable body of evidence regarding the age and chemical composition of the body. our observations expand on these earlier results. within the ‘greater aqd igneous complex’ we have observed a number of lithologies indicative of a complex igneous history (fig. 8). at loc. 01703 (fig. 2) we observed a locally developed layered cumulate sequence (fig. 8a) in gradational igneous contact with quartz diorite that contains blocks of more mafic igneous rocks. the cumulate sequence consists of numerous cycles of pyroxene-olivine cumulate layers grading into plagioclase-pyroxene anorthositic layers. this rhythmic layering grades upward into massive dioritic and quartz-dioritic rocks that contain plagioclase-porphyritic mafic xenoliths. at the same structural level, but farther north at loc. 08704, mafic enclaves (fig. 8b) occur within leucocratic quartz diorite. in places, these enclaves contain plagioclase-porphyritic xenoliths similar to those observed at loc. 01703. we interpret these enclaves to be evidence of mixing of magmas, similar to that reported for other igneous bodies (e.g. gagnevin et al. 2004; healy et al. 2004; janousek et al. 2004). the presence of both cumulate rocks and mixed mafic magmas at approximately the same structural level suggests that these sites represent the lower levels of the igneous complex that makes up the aqd suite. at loc. 13705 clear evidence of at least two separate magmas in an undeformed state is preserved, with a later diorite exhibiting well-developed chilled margins against an earlier quartz diorite (fig. 8d). whether this implies that the aqd is actually a collection of numerous smaller intrusions or a major igneous body with local, small and rare later intrusive phases can only be resolved with more detailed field work. at loc. 18702 (fig. 2) we have also observed a finely banded rock, apparently developed by extreme deformation of a sequence of pillow lavas (fig. 8d). this latter occurrence was found close to the northern boundary of the aqd and may represent the upper part of the ‘greater aqd igneous complex’. within the thin sheet of aqd to the south of the localities that we examined, an occurrence of metavolcanic rocks was reported by manatschal et al. (1998), which supports the interpretation that exposures of the aqd suite represent a variety of deep to near-surface original positions. in thin section, the mineralogy of the aqd suite is invariably modified by metamorphic recrystallisation. textural features suggest that the aqd originally consisted of hornblende and pyroxene diorites and quartz diorites. in those rocks with primary pyroxenes, the orthoand clinopyroxenes are partially to completely recrystallised to intergrowths of plagioclase, hornblende, quartz, magnetite, ilmenite and sometimes biotite. in instances where the pyroxene is completely replaced by amphibole, the amphibole is densely filled with inclusions of magnetite/ ilmenite. in the hornblende diorites and quartz diorites the original igneous amphiboles are generally inclusionfree and tend to have more brownish pleochroic colours. in some cases, plagioclase crystals exhibit well-preserved 155 igneous oscillatory zoning, but usually this is partially to completely replaced by metamorphic zoning. cummingtonite-hornblende intergrowths are relatively common and are identical to similar features described from dioritic rocks affected by amphibolite facies metamorphism in other parts of the world, e.g., tanzania (haslam & walker 1971), usa (new hampshire, brady 1974; the grand canyon, clark 1978), and australia (new south wales, stephensen & hensel 1979). recrystallisation of the aqd occurred within middle to upper amphibolite facies, as indicated by the hornblende-biotite-plagioclase ± garnet association, the instability of orthoand clinopyroxene with amphibole, and the development of cummingtonitehornblende intergrowths. the chemical variability of the aqd suite (fig. 9) is typical of that of other calc-alkaline igneous complexes, as noted previously by kalsbeek et al. (1987) and kalsbeek (2001) who demonstrated similarities between these rocks and the sierra nevada batholith. including their data, we have expanded the comparison to that of the cascades of washington state, usa, the mt lassen complex of california, and the southwest pacific island arc a b b c d fig. 8. extent of lithological variation within the ‘greater arfersiorfik quartz diorite complex’. a: igneous layering at loc. 01703 (fig. 2), where an assemblage of undeformed cumulates and related rocks from the aqd suite is set in a host of tectonised (lineated) aqd (pencil c. 15 cm long). b: igneous textured aqd with hornblende-rich pods indicating fractionation or magma mingling. observe light grey xenolith within hornblende rich phase immediately north-east of centre of photo (fist for scale). c: dark coloured igneous rock (left) chilling against lighter coloured rock (right), loc. 13705 (fig. 2; compass 10 cm long). d: part of a pegmatite sheet (right) within a banded amphibolitic rock (left) interpreted as strongly deformed pillow lava (hammer handle c. 50 cm long). 156 system. the compositional range of the aqd suite is large, varying from ultramafic (within the cumulate complex) to quartz-dioritic and quartz-monzonitic. the compositional evolution of the magma appears to have been controlled by crystal fractionation of olivine and/or pyroxenes when the cumulates were forming, but eventually reaching the stage where hornblende fractionation dominated the chemical evolution of the magma (fig. 10). the one sample that deviates from these trends is labelled m-aqd. this is a fine-grained biotite-plagioclase-quartz mylonite produced by local granulation of coarse-grained aqd. further study of this sample is underway to understand the controls on this alteration process. we noted that in the near vicinity of the nordre strømfjord shear zone chemical modification of the aqd appears to be significant. development of k-feldspar-rich mineral assemblages is common, and often accompanied by the association calcite-titanite. these rocks occur in the same region in which henderson (1969) noted the presence of k-feldspar-rich gneisses. the magnitude, extent and significance of these chemically unusual rocks are under investigation. metasomatism at the aqd margin and minor shear zones within the aqd were described by kalsbeek et al. (1987). included in figs 9, 10 are four analyses (labelled lb) from samples of large boulders in outwash from glacial deposits, collected several hundred metres east of our camp (see fig. 2). in the field, the samples bear striking similarity to aqd lithologies. as is evident from the figures, these rocks are chemically indistinguishable from the aqd suite, supporting evidence from aeromagnetic data discussed above that the aqd extends under the ice for some distance. late garnet granite the southernmost samples collected (loc. 13704, fig. 2) are from a site at which peraluminous garnet granite exhibits classic intrusive relationships into granodioritic to quartz-dioritic gneisses of the aqd. this granite contains stoped blocks of gneisses within the upper 30 m of its upper boundary zone (fig. 11), and dykes and sills from the granite invade the gneiss. the granite itself contains lb lb mt lassen new zealand and tonga-kermadec aqd suite aqd (kalsbeek 2001) mt stuart batholith fe2o3 + feo mgona2o + k2o m-aqdm-aqd skaergaard fig. 9. afm diagram comparing arfersiorfik quartz diorite chemistry (including the large boulder samples labelled ‘lb’) to that of other calc-alkaline systems. the trend for the skaergaard igneous complex is shown for comparison. mt stuart data from erikson (1977). all other trends from best (1982). the sample labelled m-aqd is the mylonitised quartz diorite sample mentioned in the text. lblb aqd cumulate suite aqd plutonic suite aqd (kalsbeek 2001) al-na-k fe + mgca m-aqdm-aqd cordierite biotite anorthite clinopyroxene hornblende fig. 10. acf atomic triangular diagram showing the chemical variation in the arfersiorfik quartz diorite based on our data (including the boulder samples lb and data reported by kalsbeek 2001). red symbols, samples collected within cumulate localities. blue and green symbols, collected by us and kalsbeek (respectively) from the non-layered igneous complex. note the kink in the trend of chemical evolution and the overlap between the non-layered and cumulate rocks of the arfersiorfik quartz diorite. red arrowed line, the trend of magmatic evolution implied by the cumulate samples, reflecting fractionation of some combination of olivine and/or orthopyroxene with clinopyroxene in the most primitive cumulate suite. blue arrowed line, that suite of samples for which chemical variability can be ascribed to hornblende fractionation. yellow box: outline of the range of likely hornblende compositions. m-aqd, mylonitised quartz diorite sample mentioned in the text. 157 delicate, primary muscovite rosettes and myrmekitic intergrowths with no evidence of deformation. the intrusive relationships and the preservation of delicate primary igneous structures suggest that the granite invaded postkinematically, and that it could provide excellent samples for establishing a minimum age for the time of cessation of tectonic activity in the region. late stage, low-grade metamorphism a suite of samples from the aqd in the region south of the nordre strømfjord shear zone contain postkinematic mineral assemblages of the prehnite-pumpellyite and lower greenschist facies overprinting the higher grade metamorphic mineral assemblages that define the amphibolite facies metamorphism. this late-stage, low-grade metamorphism is associated with brittle fracturing and veining, and local piemontite and base metal mineralisation. the timing of this low-grade metamorphism remains unresolved. strain variation within the nordre strømfjord shear zone earlier work within the agto map sheet (fig. 1; bak et al. 1975b; sørensen 1983) concluded that the nordre strømfjord shear zone reflects sinistral transcurrent movement. it was also concluded from the fanning of planar structures that the shear zone is wedge-shaped within the agto map sheet. the present work has shown that in the inner part of arfersiorfik such fanning is not obvious, perhaps because the zone here is only half as wide as near the coast in the agto map sheet area. the planar structures within the shear zone are vertical (fig. 3) with an extremely limited variation of dips (fig. 12), and linear structures are horizontal. the justification for drawing the schematic profile (fig. 3) with vertical lithological boundaries throughout the shear zone is evident from the stereograms of fig. 12. the horizontal orientation of linear structures is also in accordance with a horizontal movement direction and with the orientation of linear structures in the western part of the shear zone (bak et al. 1975b). the sinistral shear sense, already inferred by bak et al. (1975b) and further discussed and analysed by sørensen (1983), is obvious from the large-scale anticlockwise rotation seen in fig. 11. peraluminous garnetand muscovite-bearing granite at loc. 13704 (fig. 2) intruding into arfersiorfik quartz diorite and interpreted as the roof zone of a pluton with rafts of country rock and sheets of granite above. looking north-north-east. height of section c. 150 m. 158 the aeromagnetic data (figs 1, 7). small-scale shear sense indicators confirm this pattern (fig. 6). they do not occur abundantly, and as the large-scale features of the entire shear zone from the coast to the inland ice leave no doubt about the sinistral nature of movement, we have made no systematic investigations of small-scale shear sense indicators. it was suggested by sørensen (1983, fig. 14) that the shear zone between arfersiorfik and the inland ice could be divided into an central part bounded by two marginal zones. he furthermore speculated (p. 3432) that the strain profile at the inland ice was suggestive of superposition of two mechanisms, one responsible for most of the deformation in the marginal zones, and another responsible for the major part of the strain in the central part of the shear zone. the rotation on which this suggestion was based is also evident, for example, on the aeromagnetic data between labels c and d on fig. 7, and from there b a c d e f n = 85 n = 25 n = 52 n = 12 n = 37 n = 23 c.i. = 3.0 % / 1 % area south of the shear zone within the shear zone north of the shear zone planar structures linear structures fig. 12. stereograms of planar and linear structures from within and outside the nordre strømfjord shear zone. while linear structures (d–f) outside and within the shear zone do not differ in orientation, planar structures (a–c) within the shear zone are seen to be extremely concentrated as opposed to the wider spread of planar structures along girdles perpendicular to the linear structures outside the zone. equal area lower hemisphere projections. contour interval = 3% of plotted points per 1% of stereogram area. 159 farther towards the west-south-west. our field work demonstrates that this line is in fact a lithological boundary between siliceous gneisses and supracrustal schists. a corresponding boundary may be placed at the boundary between the ‘pencil type’ aqd and the schist that we have termed the third supracrustal unit on fig. 3, and thus like the northern line of rotation coincides with a lithological boundary. throughout the shear zone all the supracrustal units are highly and penetratively deformed, whereas the intervening orthogneisses are heterogeneously deformed. furthermore, where visited by the authors, the boundaries to the central part of the shear zone do in fact correspond to lithological boundaries involving supracrustal schists. in addition, the intervening siliceous gneisses, as judged from the aeromagnetic map, may in places form augenlike features, as for example, immediately north of e on fig. 7. the eastern tip of this positive magnetic anomaly was visited by helicopter (loc. 15702). immediately east of this locality the fourth and fifth supracrustal units can be seen to be separated by a few tens of metres of siliceous gneiss, a unit which is almost 2 km wide along orlerfik 15 km to the west. to the east of this locality, a wide negative magnetic anomaly can be seen to underlie unexposed ground (e on fig. 7). we interpret this as the magnetic expression of the merged supracrustal units four and five. our work in arfersiorfik therefore suggests a model for strain variation that is fundamentally different from the model developed by sørensen (1983) for the western, lower crustal and most high-grade part of the shear zone. where the latter model suggests continuity of lithologies from wall to wall of the shear zone, our observations in arfersiorfik indicate that adiscontinuitiesy in strain may be associated with boundaries between schists and orthogneisses. it is furthermore suggested by the aeromagnetic data that the intervening siliceous gneisses may form augen-like features. the change in deformation mechanism suggested by sørensen (1983) may therefore reflect ductility contrasts between the supracrustal schist units and the siliceous gneisses and not the superposition of two different deformation mechanisms. mineral occurrences two dominating types of mineral occurrences have been found in the inner part of arfersiorfik: (1) occurrences of disseminated to massive pyrrhotite in supracrustal mica schist units and (2) occurrences of iron sulphides in the contact/fault zones between the aqd and juxtaposed supracrustal units. the former type is associated with strongly foliated amphibolite, biotite ± graphite ± sillimanite schist and paragneiss. the pyrrhotite is found either as horizons up to 0.5 m thick or as lenticular bodies or pods up to 1 × 2 m in outcrop size. this type of occurrence is only found in the supracrustal rock units within the shear zone. similar occurrences exist west of the investigated area all the way to the outer coast just north of the mouth of nordre strømfjord. this occurrence type is interpreted as syn-genetic volcanic-associated exhalative sulphide deposited in a volcanic arc environment. the highest analytical values of gold and base metals obtained from samples of disseminated sulphides in pelitic schist are the following figures: 38 ppb au, 45 ppm as, 497 ppm zn, 3813 ppm cu and 456 ppm ni. all samples have elevated mn concentrations, up to 2.9 wt% mn. the second type of mineral occurrence is widespread in the inner part of arfersiorfik, both within and outside the shear zone. the zones hosting the sulphides are often associated with alteration, and in many cases a high degree of silicification is observed. it is unknown if this type is strictly epigenetic, caused by hydrothermal activity along the contact or in the fault zones between the aqd and the minor supracrustal units, or if it is a product of hydrothermal remobilisation of syngenetic iron sulphides in the supracrustal rock units. for more details and description of mineral occurrences in central west greenland see steenfelt et al. (2004) and stendal et al. (2004). conclusions our investigations of the nordre strømfjord shear zone in the eastern part of arfersiorfik suggest that deformation and displacement at this crustal level are primarily a function of lithology, with large displacements effected by ductile flow in the supracrustal sequences. the large mass of arfersiorfik quartz diorite between arfersiorfik and the inland ice is bordered to the north by the shear zone, probably with a supracrustal schist unit along this boundary. the latter is indicative of the extreme deformation that can be taken up in the supracrustal rocks. towards this boundary the tectonite fabric of the aqd becomes further accentuated, and near its northern boundary the aqd differs both chemically, mineralogically and structurally from the aqd to the south of the shear zone. we have both found cumulate rocks originating from near the base of the original magmatic aqd complex and metavolcanic rocks interpreted as belonging to its top part, whose less deformed equivalents are most probably covered by the inland ice. the chemical variation of the aqd suite is wide and comparable to that of cenozoic calcalkaline igneous suites. 160 acknowledgements concise reviews by graham leslie and chris pulvertaft and financial support by the carlsberg foundation are gratefully acknowledged. the air greenland helicopter pilot and the crew on board m/s milandt (aasiaat) are thanked for efficient transport and practical help. chemical analyses were carried out by xrf on glass discs at the department of earth sciences, university of aarhus, denmark. references bak, j., grocott, j., korstgård, j.a., nash, d., sørensen k. & watterson, j. 1975a: tectonic implications of precambrian shear belts in western greenland. nature 254, 566–569. bak, j., korstgård, j.[a.] & sørensen, k. 1975b: a major shear zone within the nagssugtoqidian of west greenland. tectonophysics 27, 191–209. best, m.g. 1982: igneous and metamorphic petrology, 630 pp. san francisco: w.h. freeman. brady, j.b. 1974: coexisting actinolite and hornblende from west-central new hampshire. american mineralogist 59, 529–535. clark, m.d. 1978: amphibolitic rocks from the precambrian of grand canyon: mineral chemistry and phase petrology. mineralogical magazine 42, 199–207. connelly, j.n., van gool, j.a.m. & mengel, f.c. 2000: temporal evolution of a deeply eroded orogen: the nagssugtoqidian orogen, west greenland. canadian journal of earth sciences 37, 1121–1142. erikson, e.h. jr. 1977: petrology and petrogenesis of the mount stuart batholith – plutonic equivalent of the high-alumina basalt association?. contributions to mineralogy and petrology 60, 183–207. escher, a. 1971: geological map of greenland, 1:500 000, søndre strømfjord – nûgssuaq, sheet 3. copenhagen: geological survey of greenland. gagnevin, d., daly, j.s. & poli, g. 2004: petrographic, geochemical and isotopic constraints on magma dynamics and mixing in the miocene monte capanne monzogranite (elba island, italy). lithos 78, 157–195. hanmer, s., mengel, f., connelly, j. & van gool, j.[a.m.] 1997a: significance of crustal-scale shear zones and synkinematic dykes in the nagssugtoqidian orogen, sw greenland: a re-examination. journal of structural geology 19, 59–75. hanmer, s., mengel, f., connelly, j. & van gool, j.[a.m.] 1997b: significance of crustal-scale shear zones and synkinematic dykes in the nagssugtoqidian orogen, sw greenland: a re-examination. (corrigendum). journal of structural geology 19, i. haslam, h.w. & walker, b.g. 1971: a metamorphosed pyroxenite at nero hill, central tanzania. mineralogical magazine 38, 58–63. healy, b., collins, w.j. & richards, s.w. 2004: a hybrid origin for the lachlan s-type granites: the murrumbidgee batholith example. lithos 78, 197–216. henderson, g. 1969: the precambrian rocks of the egedesminde–christianshåb area (sheets 68v.1 and 68v.2). rapport grønlands geologiske undersøgelse 23, 1–37. hickman, m.h. & glassley, w.e. 1984: the role of metamorphic fluid transport and the rb-sr isotopic resetting of shear zones: evidence from nordre strømfjord, west greenland. contributions to mineralogy and petrology 87, 265–281. janousek, j., braithwaite, c.j.r., bowes, d.r. & gerdes, a. 2004: magma-mixing in the genesis of hercynian calc-alkaline granitoids: an integrated petrographic and geochemical study of the sazava intrusion, central bohemian pluton, czech republic. lithos 78, 67– 99. kalsbeek, f. 2001: geochemical comparison between archaean and proterozoic orthogneisses from the nagssugtoqidian orogen, west greenland. precambrian research 105, 165–181. kalsbeek, f., taylor, p.n. & henriksen, n. 1984: age of rocks, structures and metamorphism in the nagssugtoqidian mobile belt – field and pb-isotopic evidence. canadian journal of earth sciences 21, 1126–1131. kalsbeek, f., pidgeon, r.t. & taylor, p.n. 1987: nagssugtoqidian mobile belt of west greenland: a cryptic 1850 ma suture between two archaean continents – chemical and isotopic evidence. earth and planetary science letters 85, 365–385. manatschal, g., ulfbeck, d. & van gool, j.[a.m.] 1998: change from thrusting to syncollisional extension at a mid-crustal level: an example from the palaeoproterozoic nagssugtoqidian orogen (west greenland). canadian journal of earth sciences 35, 802–819. nielsen, b.m. 2004: crustal architecture and spatial distribution of mineral occurrences in the precambrian shield of central west greenland based on geophysical and geological data. danmarks og grønlands geologiske undersøgelse rapport 2004/26, 63 pp., 8 appendices. ph.d. thesis, department of earth sciences, university of aarhus, denmark. nielsen, b.m & rasmussen, t.m. 2004: mineral resources of the precambrian shield of central west greenland (66° to 70°15′n). part 3. implications of potential field data for the tectonic framework. danmarks og grønlands geologiske undersøgelse rapport 2004/ 21, 165 pp., 1 cd-rom. noe-nygaard, a. & ramberg, h. 1961: geological reconnaissance map of the country between latitudes 69°n and 63°45′n, west greenland. meddelelser om grønland 123, 1–9. olesen, n.ø. 1984: geological map of greenland, 1:100 000, agto, 67 v.1 nord. copenhagen: geological survey of greenland. passchier, c.w., den brok, s.w.j., van gool, j.a.m., marker, m. & manatschal, g. 1997: a laterally constricted shear zone system – the nordre strømfjord steep belt, nagssugtoqidian orogen, w. greenland. terra nova 9, 199–202. ramberg, h. 1949: on the petrogenesis of the gneiss complexes between sukkertoppen and christianshaab, west greenland. meddelelser fra dansk geologisk forening 11, 312–327. rasmussen, t.m. & van gool, j.a.m. 2000: aeromagnetic survey in southern west greenland: project aeromag 1999. geology of greenland survey bulletin 186, 73–77. sørensen, k. 1983: growth and dynamics of the nordre strømfjord shear zone. journal of geophysical research 88, 3419–3437. 161 sørensen, k. & winter, j.d. 1989: deformation and mass transport in the nordre strømfjord shear zone, central west greenland. in: bridgwater, d. (ed.): fluid movements – element transport and the composition of the deep crust, 171–185. amsterdam: kluwer academic publishers. steenfelt, a., stendal, h., nielsen, b.m. & rasmussen, t.m. 2004: gold in central west greenland – known and prospective occurrences. geological survey of denmark and greenland bulletin 4, 65–68. stendal, h., nielsen, b.m., secher, k. & steenfelt, a. 2004: mineral resources of the precambrian shield of central west greenland (66° to 70°15′n). part 2. mineral occurrences. danmarks og grønlands geologiske undersøgelse rapport 2004/20, 212 pp. stendal, h., secher, k. & frei, r. 2006: 207pb-206pb dating of magnetite, monazite and allanite in the central and northern nagssugtoqidian orogen, west greenland. in: garde, a.a. & kalsbeek, f. (eds): precambrian crustal evolution and cretaceous–palaeogene faulting in west greenland. geological survey of denmark and greenland bulletin 11, 101–114 (this volume). stephensen, n.c.n. & hensel, h.d. 1979: intergrown calcic and femg amphiboles from the wongwibinda metamorphic complex, n.s.w., australia. canadian mineralogist 17, 11–23. van gool, j.a.m., kriegsman, l.m., marker, m. & nichols, g.t. 1999: thrust stacking in the inner nordre strømfjord area, west greenland: significance for the tectonic evolution of the palaeoproterozoic nagssugtoqidian orogen. precambrian research 93, 71–86. van gool, j.a.m., connelly, j.n., marker, m. & mengel, f.c. 2002: the nagssugtoqidian orogen of west greenland: tectonic evolution and regional correlations from a west greenland perspective. canadian journal of earth sciences 39, 665–686. van gool, j.a.m. & marker, m. 2004: geological map of greenland, 1:100 000, ussuit, 67 v.2 nord. copenhagen: geological survey of denmark and greenland. __________________________________________________________________________________________________________________________________________________________________________________ manuscript received 5 november 2004; revision accepted 1 november 2005 162 geological survey of denmark and greenland bulletin 17, 2009, 45-48 the european union’s water frame work directive aims to achieve a ‘good’ ecological status for groundwater bodies, for groundwater-dependent terrestrial ecosystems, and for aquatic surface water bodies by the year 2015. in denmark, this goal will most likely not be fulfilled within such a short time frame due to the current poor ecological condition of danish lakes (søndergaard et al. 2008). however, public concern about the protection of aquatic environments has increased, and so has interest in improving lake water quality by reducing nutrient loading. effective and sustainable lake restoration and conservation depend on the ability to (1) point out sensitive catchment areas for the lake, (2) estimate its total water and nutrient budgets and (3) relate observed differences in seepage rates to the abundance and distribution of macrophytes in the lake and to the topography and land-use of the surrounding terrain. in seepage lakes, i.e. lakes without inlets or outlets, the influence of the surrounding terrain, regional hydrogeology and lake geometry on the overall lake water budget has been studied in some detail (krabbenhoft et al. 1990; anderson & cheng 1993; cheng & anderson, 1994; kratz et al. 1997; water budget of skærsø, a lake in south-east jylland, denmark: exchange between groundwater and lake water bertel nilsson, peter engesgaard, jacob kidmose, sachin karan, majken caroline looms and mette cristine schou frandsen © geus, 2009. geological survey of denmark and greenland bulletin 17, 45–48. available at: www.geus.dk/publications/bull 45 fig. 1. a: location of skærsø east of the main stationary line in jylland. b: lake area in summer (dark blue) and winter (light blue). c: map of the lake skærsø area showing the groundwater level of the regional aquifer and the water level of skærsø. black dots show the locations of wells used to construct the map. 9°16.5’e skærsø 55°35’n contours (1 m interval) lake in summer lake in winter 500 m 50 m 4849 44 45 4647 66–67 m cb a 150 m 9°16.5’e 43 m 55°35’n weichselian deposits saalian deposits outwash plains marine deposits aeolian deposits freshwater deposits 50 km main stationary line rosa_2008:rosa-2008 01/07/09 15:48 side 45 winter 1999; townley & trefry 2000). however, little effort has been made to understand and quantify how riparian zones (wetlands) surrounding lakes may control the water flow and nutrient transport to the lakes. although groundwater inflow to seepage lakes is suspected to be smaller than inflow from drainage ditches, it may still account for a significant nutrient influx. this paper focuses on field work carried out 2007 and 2008 at skærsø, a lake in the upper part of the kolding å catchment area in south-east jylland (fig. 1a). field studies at skærsø have shown that seepage can vary on different scales in both space and time. the purpose of this study is to link measurements of lake seepage rates and lake precipitation or evaporation to the catchment hydrogeology. the project is conducted by the centre for lake restoration, which includes participants from university of southern denmark, national en vironmental research institute, university of copenhagen and geological survey of denmark and greenland. towards a lake typology the centre for lake restoration is developing a typological classification of danish lakes using a multidisciplinary ap proach that integrates interactions between groundwater and lake water. the classification is based on geological, hydrological, hydrogeological, geomorphological, botanical and chemical aspects. the botanical part focuses on plant indicator species in the lakes, and the chemical part addresses water and sediment chemistry. two or three main lake types are currently distinguished on the basis of geological, hydrological, hydrogeological and geomorphological criteria. new lake types will probably be defined in the coming years as biolo gical and chemical indicators are also included in the classification. location and setting of skærsø skærsø is located a few kilometres east of the main stationary line that formed during the last glacial maximum around 20 000 years ago. the lake is situated in the upper part of the 46 medium k low k high k 4 77 44 17 19 39 medium k low k high k k = hydraulic conductivity a b unsaturated zone lake lake fig. 2. a: preliminary model of the water balance of skærsø. grey arrows show influx, black arrows loss. numbers in per cent. b: conceptual hydrogeological model of a perched lake disconnected from the underlying aquifer. a a sand sand gyttjagyttja sandsand multiplesmultiples sandsand sand gyttja sand multiples 50 m 8 0 2 4 6 d ep th ( m ) sand bbb fig. 3. a: mapping of lake sediments using reflection ground penetrating radar (gpr). the radar equipment is contained in the grey rubber boat. b: an example of a gpr reflection profile with a preliminary interpretation. rosa_2008:rosa-2008 01/07/09 15:48 side 46 kolding å catchment area (fig. 1a) that is dominated by glacial and glaciofluvial deposits. around skærsø a 2–7 m thick sand layer overlies an approximately 10 m thick clayey till that is underlain by a regional sandy aquifer. the riparian zone around skærsø has a width of 30–50 m and a thickness of 0.1–0.5 m, and consists of organic-rich fine sand and silt. the water table of the lake varies seasonally about 0.5 m, and in the winter or early spring the riparian zone around the lake is flooded (fig. 1b). during flooding, organic particles and solutes are transported to the lake and cause a significant decrease in the transparency of the water. below skærsø, the groundwater table of the regional sand aquifer is 48–49 m above sea level, whereas the surface of the lake is 66–67 m above sea level. this difference indicates that there is a hydraulic connection between the lake and the regional aquifer (see below and fig. 1c). the area of skærsø is approximately 16 ha , and its average water depth is 1.5 m, with a maximum depth of about 8 m. it is characterised as a mesotrophic, low-alkaline, clear-water lake. until the 1980s, skærsø was a clear-water heath lake, dominated by submerged macrophytes including lobelia dortmanna that grew to a depth of 1.5 m. at the end of the 1980s, skærsø suffered from organic-rich, acidic, unclear water, resulting in almost complete disappearance of the submerged macrophytes. after almost 19 years of unsuccessful attempts at lake restoration, the conditions in skærsø are still deteriorating. a recent study showed that changes in light conditions in the lake are not as strongly coupled to changes in the external nutrient loading as expected (frandsen & stæhr 2007). changes in the hydrology of the riparian zone have led to a seasonal flush of dissolved coloured organic matter into the lake which causes decreased water transparency, decreased light penetration and release of nutrients. however, the mechanisms that affect water transparency require further investigation. hydrogeological model the hydrogeological model of the lake is characterised by the setting of shore and wetland (the riparian zone) with an upper, local groundwater aquifer in sediments of low to moderate permeability showing low hydraulic gradients. the deeper part of the lake is probably connected to a lower permeable layer with high hydraulic gradients (fig. 1c). because the surface of skærsø is almost 20 m above the hydraulic head of the regional sand aquifer, we expect leakage of water from the lake through its bottom into the underlying regional aquifer. the water supply to skærsø is dominated by precipitation (77%) and inflow from the catchment area (19%). a limited portion (4%) comes from the shallow, local groundwater aquifer. water flux from the lake is dominated by outflow via outlets (44%; mainly an artificial ditch) and evaporation (39%). we suggest that the remaining 17% is lost by leakage to the underlying aquifer (fig. 2a). thus skærsø can be conceptualised as a perched lake, a lake which is disconnected from the underlying aquifer by an unsaturated zone between the lake bottom and the aquifer (fig. 2b). ground penetrating radar in order to investigate the structure and thickness of the sedi ments below the lake, a ground penetrating radar survey was carried out (fig. 3a). thick layers of organic-rich sediments such as lake mud (gyttja) or peat generally reduce ground water seepage, whereas sandy sediments can promote inter action between groundwater and lake water (fig. 3b). ground penetrating radar can help to identify areas of potential groundwater seepage, which may then be verified using more traditional point measurements such as coring. the appli cation of ground penetrating radar to map lake sediments is new in denmark, and the interpretation of the radar profiles is still uncertain and needs to be checked against data from coring. however, according to our preliminary interpretation of the radar data, sandy sediments are widespread below the lake, whereas gyttja is probably restricted to a small area (fig. 3b). multidisciplinary approach to estimate the groundwater flux seepage to or from skærsø to the upper, local groundwater aquifer was measured using various tracers (heat, stable isotopes), direct measurements of water flux, as well as nutrients sampled from piezometer transects. the combined use of different tracers and methods at different scales provides a good understanding of the physical, chemical and biological behaviour of the entire lake. figure 4 shows three types of field equipment that were used to quantify the flux from the local aquifer to skærsø, and the estimated groundwater fluxes (specific discharges) to skærsø are summarised in table 1. the flux values estimated by the three different methods are not consistent. the highest estimated fluxes (using the darcy 47 method flux specific discharge (m/sec) seepage meter q seep 10–7 – 3 × 10–7 temperature q t 10–8 – 10–7 darcy1 q d 10–7 – 10–6 table 1. groundwater discharge into skærsø 1 q d = k × i, where k is the saturated hydraulic conductivity of the lake-shore sediment (i.e. fine sand and silt in the upper 2 m) equiv alent to k = 10–4 – 10–5 m/sec, and i is the hydraulic gradient measured by a potentiomanometer to about ± 0.01. rosa_2008:rosa-2008 01/07/09 15:48 side 47 (transect) method) are 10–100 times higher than the lowest estimated fluxes (using the temperature method). despite this difference, the data indicate a low inflow from the shallow groundwater aquifer and, as mentioned above, we suggest that 4% of the inflow to the lake comes from the shallow aquifer, based on the average value obtained by the applied methods. we have no data on leakage through the lake bottom to the underlying aquifer, but we consider this process likely and suggest a flux value of 17% based on the difference between the other fluxes. however, this figure is highly uncertain. especially the figure for the evaporation from the lake may be underestimated if investigations of other lakes in jylland are considered. nevertheless, we conclude that exchange between groundwater and lake water plays an important role in the water budget of lake skærsø. acknowledgement villum kann rasmussen fonden is gratefully acknowledged for funding the centre for lake restoration (clear), which is a villum kann rasmussen centre of excellence. references anderson, m.p. & cheng, x. 1993: longand short-term transience in a groundwater/lake system in wisconsin, usa. journal of hydrology 145, 1–18. cheng, x. & anderson, m.p. 1994: simulating the influence of lake position on groundwater fluxes. water resources research 30, 2041–2049. frandsen, m.c.s. & stæhr, a.p. 2007: differentieret analyse af lysmiljøet i skærsø, 24 pp. unpublished report, freshwater biological laboratory, university of copenhagen, hillerød, denmark. krabbenhoft, d.p., bowser, c.j., anderson, m.p. & valley, j.w. 1990: estimating groundwater exchange with lakes. 2. calibration of a threedimensional, solute transport model to stable isotope plume. water resources research 26, 2455–2462. kratz, t.k., webster, k.e., bowser, c.j., magnuson, j.j. & benson, b.j. 1997: the influence of landscape position on lakes in northern wisconsin. freshwater biology 37, 209–217. lee, d.r. 1977: a device for measuring seepage flux in lakes and estuaries. limnology and oceanography 22, 140–147. nilsson, b., engesgaard, p., kidmose, j. & karan, s. 2008: groundwater – lake exchange at lake skærsø in western denmark. proceedings of 36th iah congress, october 2008, toyama, japan. integrating groundwater science and human well-being. extended abstract on cd-rom. schmidt, c., bayer-raich, m. & schirmer, m. 2005: characterization of spatial heterogeneity of groundwater – stream water interactions using multiple depth streambed temperature measurements at the reach scale. hydrology and earth system sciences 10, 849–859. søndergaard, m., liboriussen, l., pedersen, a.e. & jeppesen, e. 2008: lake restoration by fish removal: shortand long-term effects in 36 danish lakes. ecosystems 11, 1291–1305. townley, l.r. & trefry, m.g. 2000: surface water – groundwater interaction near shallow circular lakes: flow geometry in three dimensions. water resources research 36, 935–949. winter, t.c. 1999: relation of streams, lakes, and wetlands to groundwater flow systems. hydrogeology journal 7, 28–45. winter, t.c., labaugh, j.w. & rosenberry, d.o. 1988: the design and use of a potentiomanometer for direct measurement of differences in hydraulic head between groundwater and surface water. limnology and oceanography 33, 1209–1214. authors’ addresses b.n., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: bn@geus.dk p.e., j.k., s.k. & m.c.l., department of geography and geology, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. m.c.s.f., freshwater biological laboratory, biological institute, university of copenhagen, helsingørsgade 51, dk-3400 hillerød, denmark. 48 a b c fig. 4. equipment used for field determination of groundwater seepage. a: modified 1 m long potentiomanometer used to measure the water pressure in the subsurface (winter et al. 1988). b: multi-level, 1.25 m long temperature probe used to measure the temperature at multiple levels in the sediment (schmidt et al. 2005). c: a steel drum seepage meter, 0.5 m in dia meter, used to measure the flow of ground water through the lake bottom (lee 1977). from nilsson et al. (2008). rosa_2008:rosa-2008 01/07/09 15:48 side 48 the regional distribution of zeolites in the basalts of the faroe islands and the significance of zeolites as palaeotemperature indicators 123 the regional distribution of zeolites in the basalts of the faroe islands and the significance of zeolites as palaeotemperature indicators ole jørgensen the first maps of the regional distribution of zeolites in the palaeogene basalt plateau of the faroe islands are presented. the zeolite zones (thomsonite-chabazite, analcite, mesolite, stilbite-heulandite, laumontite) continue below sea level and reach a depth of 2200 m in the lopra-1/1a well. below this level, a high temperature zone occurs characterised by prehnite and pumpellyite. the stilbite-heulandite zone is the dominant mineral zone on the northern island, vágar, the analcite and mesolite zones are the dominant ones on the southern islands of sandoy and suðuroy and the thomsonite-chabazite zone is dominant on the two northeastern islands of viðoy and borðoy. it is estimated that zeolitisation of the basalts took place at temperatures between about 40°c and 230°c. palaeogeothermal gradients are estimated to have been 66 ± 9°c/km in the lower basalt formation of the lopra area of suðuroy, the southernmost island, 63 ± 8°c/km in the middle basalt formation on the northernmost island of vágar and 56 ± 7°c/km in the upper basalt formation on the central island of sandoy. a linear extrapolation of the gradient from the lopra area places the palaeosurface of the basalt plateau near to the top of the lower basalt formation. on vágar, the palaeosurface was somewhere between 1700 m and 2020 m above the lower formation while the palaeosurface on sandoy was between 1550 m and 1924 m above the base of the upper formation. the overall distribution of zeolites reflects primarily variations in the maximum depth of burial of the basalt rather than differences in heat flow. the inferred thinning of the middle and upper basalt formation from the central to the southern part of the faroes is in general agreement with a northerly source area for these basalts, centred around the rift between the faroes and greenland. the regional zeolite distribution pattern is affected by local perturbations of the mineral zone boundaries that reflect local differences in the temperature, perhaps related to the circulation of water in the underground. the zonal distribution pattern suggests that these temperature anomalies are in part related to nw–se-trending eruption fissures or zones of weakness separating the present islands and are subparallel to transfer zones in the faroe–shetland basin. both the regional and the local distribution of zeolite assemblages are probably a reflection of the basic volcanic-tectonic pattern of the faroe islands. keywords: faroe islands, palaeogene basalt plateau, zeolite zone, palaeotemperature indicators _____________________________________________________________________________________________________________________________________________________________________________________ o.j., scandinavian asbestos & mineral analysis, kildeskovsvej 62, dk-2820 gentofte, denmark. e-mail: oj@oj-sama.dk © geus, 2006. geological survey of denmark and greenland bulletin 9, 123–156. available at: www.geus.dk/publications/bull geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19123 124 the zeolites of the faroe islands have been known for more than 300 years (debes 1673) although the islands remained nearly unknown to mineralogists until the end of the eighteenth century. because of increasing interest in mineralogy in the nineteenth century, the faroe islands were visited by many naturalists. one of these was brewster (1825), who proposed the name levyne for a new zeolite species he discovered at dalsnípa on sandoy. the first modern description of the distribution of faroese minerals was published by currie (1905), who visited the faroe islands and described the minerals at 120 localities. five years later a new description of the faroese zeolites was presented by görgey (1910). interest in the minerals of the faroe islands declined during the following 70 years until betz (1981) visited the islands and reviewed the classic localities. the present author started a literature study to discover, if a system of zeolite zones exists on the faroe islands similar to that described by walker (1960) in east iceland, but concluded that published descriptions were based on minerals from the same set of localities that were known to be rich in mineral species and where large crystals could be collected. this sampling bias meant that it was not possible to decide if zeolite zones existed on the faroe islands, so in 1979 a systematic mapping of the zeolites in the faroe islands was initiated by the present author. during the following 20 years, more than 800 localities were visited and about 3000 rock samples were investigated in the field and in the laboratory. the work was extended by studying samples from the vestmanna-1 and lopra-1 boreholes drilled in 1980 and 1981, respectively (jørgensen 1984; waagstein et al. 1984). in 1996, the lopra-1 borehole was deepened to a total of 3565 m (lopra-1/1a) and the secondary minerals in the deepened part of the lopra well were also described by the present author (jørgensen 1997). the aim of the present paper is to describe the secondary mineral distribution in the exposed parts of the faroe islands and in the lopra-1/1a and vestmanna-1 wells. the results of the mapping are used to estimate the palaeogeothermal gradients and the altitudes of the palaeosurfaces at various places in the faroes basalt succession. the following topics will be discussed: (1) the general conditions for the use of zeolites as palaeotemperature indicators and the statistical distribution of zeolites in a vertical profile, (2) the original thickness of the three basalt formations and the volcanic evolution of the faroese basalt complex, and (3) the regional distribution of the zeolite zones as a function of the thicknesses of the middle and the upper basalt formations. outline of the geology of the faroe islands the faroe islands (62°n, 7°w) have a total area of 1400 km2, an average height of 300 m above sea level and form part of the north atlantic brito-arctic cenozoic igneous province that extends from the british isles to greenland. the faroe islands consist almost exclusively of flood basalts that were erupted about 59–55 ma (waagstein 1988; larsen et al. 1999). the basalts on the exposed part of the faroe islands are divided into a lower, a middle and an upper basalt formation, separated by two horizons termed a and c in fig. 1 (see also fig. 4). according to rasmussen & noe-nygaard (1969, 1970) the volcanic evolution of the faroe islands may be summarised as follows: volcanic activity started west of the present islands with the eruption of the lower basalt formation. with time the production rate of lava slowed to a temporary standstill. during this quiet period, about 10 m of clay and coal bearing sediments were deposited (the a-horizon.). volcanic activity restarted with an explosive phase, resulting in the deposition of coarse volcanic ash and agglomerates. an effusive phase followed during which the middle basalt formation was erupted from sandoy nólsoy skúvoy stóra dímun lítla dímun streymoy kallsoy viðoy fugloy borðoy svinoy eysturoy 62°00'n 7°00'w 20 km0 koltur hestur vágar mykines upper basalt formation middle basalt formation lower basalt formation irregular instrusive bodies and sills coal-bearing sequence dykes suðuroy fig. 1. geological map of the faroe islands. from rasmussen & noe-nygaard (1969). geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19124 125 several vents and small fissures within the present group of islands. finally, volcanic activity moved farther east, away from the present islands, causing the lava flows of the upper basalt formation to transgress the middle basalt formation from the east. the discordant surface between the middle and upper basalt formations is named the chorizon. after the upper basalt formation was formed, the basalt plateau was intruded by dykes and sills. large sills were intruded near the boundary between middle and upper basalt formations in streymoy and eysturoy. tectonic activity continued long after the volcanism ended until the faroese basalt pile acquired its present gentle easterly dip. methodology sampling and mineral identification renewal of a large part of the road system of the faroes just before initiation of the fieldwork made it possible to collect samples in fresh road cuts and new quarries along the roads. after most of the road sites had been examined, the mountains were traversed and samples collected along the old paths between the villages. in addition to the samples collected by the author, the present investigation is based on 500 specimens of faroese zeolites collected privately by k. jørgensen and on the collection of faroese zeolites in the geological museum, copenhagen. the minerals were identified by their crystal morphology, optical properties, and x-ray diffraction (xrd) patterns or by chemical analysis carried out on a scanning electron microscope equipped with an energy dispersive analytical system. the xrd reference patterns were taken from gottardi & galli (1985). mapping of the mineral zones walker (1960, 1970) defined his zeolite zones by seven distinctive amygdale mineral assemblages. each zone was fig. 2. mineral temperature scale. the five zeolite zones are defined by the index minerals chabasite + thomsonite, analcite, mesolite, stilbite + heulandite and laumontite. the temperatures are shown at zone boundaries. abbreviations used for the various minerals are shown in table 1. an: analcite ap: apophyllite ca: calcite ce: celadonite ch: chabasite cl: chlorite cld: chalcedony ed: epidote ep: epistilbite ga: garronite gi: gismondine gy: gyrolite ha: harmotom he: heulandite la: laumontite table 1. abbreviations used for mineral names le: levyne me: mesolite: solid me*: mesolite: hair-like mo: mordenite na: natrolite ok: okemite op: opal ph: phillipsite pr: prehnite pu: pumpellyite qz: quartz sc: scolecite sm: smectites st*: stellerite † source: kristmannsdóttir & tómasson (1978), kristmannsdóttir (1982) and jakobsson & moore (1986) mineral zones approx. temperatures in °c † ch th* th an me* ph le me gy mo st he ep ap la pr pu ed cl ce sm qz cld op ca zeolite free zone 40–60 high temperature zone > 300 laumontite 190–230 stilbite-heullandite 110–130 mesolite 90–100 analcite chabazite-thomsonite 50–70 0 1 2 3 4 5 6 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19125 126 defined by the presence or dominance of certain mineral species, termed index minerals, whose names are used to designate the zones. in addition to the index minerals, other minerals may be present as indicated in fig. 2. walker’s (1960) original zones are the carbonate, chabazitethomsonite, analcite, mesolite, laumontite, prehnite and epidote zones. the original mesolite zone was later subdivided into a mesolite and a stilbite-heulandite zone. this extended zone definition was adopted in the present investigation (fig. 2). the classification of the zeolite zones was normally based on the mineral assemblages of amygdales, and fracture fillings were used only in places without amygdales. classification of the mineral assemblages from samples from the lopra-1/1a and vestmanna-1 boreholes was originally based on the abundance of the individual index minerals expressed as the weight% of the total mass of index minerals (jørgensen 1984). in the present investigation, which is based on about 3000 samples, quantitative analysis was carried out only on two selected mineral assemblages, one from the middle and one from the upper basalt formation. the assemblages from most localities consist of a large number of minerals which makes it difficult to estimate the relative abundance of the different minerals. another complication was the fact that more than one index mineral often occurred at the same locality. the present investigation is therefore based on the first formed index minerals in the amygdales, i.e. the minerals that were deposited nearest to the host rock. where more than one first formed index mineral was present at a locality, the index mineral assumed to have the highest temperature of formation was chosen to map the zones. the mineral zones mapped in this way thus reflect the maximum temperature of mineralisation. this method is different from a mapping based on abundance of the minerals, which shows the distribution of the zeolite zones as the result of the main mineralisation. appendices a and b give the observed paragenesis in the 29 sections and two table 2. relative frequency (in %) of amygdales and mineralised fractures in the exposed part of the faroe islands mineral zeolites: analcite chabazite cowlesite epistilbite garronite gismondine heulandite laumontite levyne mesolite mordenite natrolite scolecite stellerite stilbite phillipsite thomsonite other minerals: apophyllite calcite celadonite chlorite csh gyrolite smectites silica minerals visited localities 32 67 1 <1 4 4 30 11 17 61 8 4 1 45 37 8 64 15 36 19 8 2 12 18 19 61 61 7 0 8 0 51 5 5 56 12 10 2 24 37 17 59 12 37 15 10 5 7 7 29 160 16 65 0 0 0 10 69 6 16 65 0 0 0 55 10 6 45 13 39 13 3 0 3 3 6 85 49 71 0 3 6 0 77 29 23 86 14 9 0 26 74 3 60 29 34 11 3 3 14 36 14 148 33 78 0 0 8 5 60 29 20 63 8 0 0 20 38 3 60 20 43 38 23 0 28 23 20 302 35 76 2 0 8 8 63 3 26 60 19 5 3 13 39 11 75 27 32 27 13 8 29 26 19 235 18 62 0 0 0 3 38 5 8 48 0 3 0 6 33 10 73 3 32 14 5 0 0 16 25 52 15 66 0 0 0 0 38 0 20 50 0 0 0 9 26 15 79 0 32 15 15 21 41 41 abundant minerals in bold face, common minerals in italics and rare minerals in normal type face. csh is calcium silicate hydrates. silica minerals are opal, chalcedony etc. average vágar suðuroy sandoy streymoy eysturoy borðoy viðoy geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19126 127 wells mapped. the most probable temperature range of deposition of the zeolite zones is indicated in fig. 2. the rules of zone classification stated above could not be followed strictly everywhere. in the southern part of suðuroy, mineralised vesicles are rare and, in this area, the mapping had to be based mainly on mineralised fractures. in the lopra-1/1a borehole, the study was based on cuttings. they included fragments of amygdales and mineralised fractures, and the first formed index mineral could be determined only when part of the host rock adhered to the sample. in order to establish a correlation between the zeolite zones and the temperature of formation of the minerals, the vertical distribution of index minerals and temperatures was examined in a number of boreholes in the geothermal areas of iceland (kristmannsdóttir & tómasson 1978; kristmannsdóttir 1982). the result was the mineral–temperature scale shown in fig. 2. examination showed that the temperatures at the boundaries of individual zeolite zones varied from place to place. this is probably caused by the fact that zeolites can be formed within a broad range of temperatures and that variations in the chemical composition of the rock and the hydrothermal solutions can affect the formation temperature of the zeolites (barth-wirsching & höller 1989; breck 1974). another problem that makes it difficult to determine accurately the palaeotemperatures at the zone boundaries is the fact that zone boundaries are not well defined lines, a problem that will be discussed below. the temperatures at the boundaries of the zeolite zones are therefore indicated in fig. 2 at the lowest and highest temperatures that occur at the icelandic zone boundaries. as mentioned above, the original classification of the mineral assemblages of the lopra-1/1a and vestmanna-1 drillholes was based on the most abundant index zeolite. it was therefore necessary to re-classify the mineral assemblages of the two drillholes according to the method used in the present investigation. this had a rather small effect on the zonation of the lopra-1/1a drillhole. however, the first formed minerals from the vestmanna-1 borehole are overgrown by abundant chabazite and thomsonite. neglecting these later deposits, changes the zonation from a simple chabazite-thomsonite zone to an alternation between the mesolite and stilbite-heulandite zones. the distribution of minerals, zones and temperatures frequency of occurrence of minerals table 2 shows the 17 zeolites and 8 associated minerals that were recorded in amygdales and mineralised fractures of the basalt in the islands of suðuroy, sandoy, vágar, streymoy, eysturoy, borðoy and viðoy. in addition to the minerals listed, prehnite, pumpellyite, native copper and pyrite were found in the lopra-1/1a borehole. all the zeolites listed in table 2 have been reported previously from the faroe islands with the exception of garronite, ch te le ph ap gy cl ca me st he la an su sa va st ey bo vi su sa va st ey bo vi su sa va st ey bo vi r el at iv e fr eq u en cy a s % o f lo ca lit ie s r el at iv e fr eq u en cy a s % o f lo ca lit ie s r el at iv e fr eq u en cy a s % o f lo ca lit ie s 100 80 60 40 20 0 80 60 40 20 0 50 20 30 40 10 0 s n s n s n fig. 3. variation diagrams of the relative frequency of minerals on suðuroy (su), sandoy (sa), vágar (vá), streymoy (st), eysturoy (ey), borðoy (bo) and viðoy (vi). contractions for zeolite names are listed in table 1. geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19127 128 c 3500 3000 2500 2000 1500 1000 500 0 up pe r ba sa lt f o rm at io n m id dl e ba sa lt f o rm at io n lo w er ba sa lt f o rm at io n su 1 su 2 su 3 su 9 v a 1 v a 4 v a 7 w es tm an na -1 w el l st 6 w st 6 e sa 5 st 1 0 sa 1 sa 3 ey 1 ey 2 ey 3 ey 4 ey 8 ey 1 0 b o 1 b o 2 b o 3 v i 1 v i 2 st 2 w st 2 e th–ch zone an zone me zone st–he zone altitude of profile a c v i 3 fig. 4. stratigraphic location of the zeolite zones in the 28 sections through the exposed part of the faroe islands. the data shown here are tabulated in table 3. which was found for the first time at several localities during the mapping reported here. the minerals in table 2 were divided into three classes: (1) very frequent minerals that occur at 60% or more of the localities; (2) common minerals that occur at between 15% and 60% of the localities; (3) rare minerals that occur at less than 15% of the localities. the frequency of occurrence is given as percentages of localities examined on each island. from the column named average in table 2, it is seen that chabazite, mesolite and thomsonite are the most frequent secondary minerals within the exposed part of the faroe islands, followed by stilbite, stellerite, heulandite, analcite and calcite. epistilbite and scolecite are rare minerals in the exposed part of the faroe islands, but they are common in the lopra-1/1a well. regional distribution of minerals and zones fig. 3 shows how the relative frequency of a number of index minerals and associated minerals varies from island to island. for most of the minerals, the relative frequency decreases from south to north and from west to east, but for the minerals of the analcite and the chabazite-thomsonite zone, the relative frequency increases in the direction of viðoy (fig. 1). the variation in relative frequency of minerals reflects the regional shift in the distribution of mineral zones. the analcite and mesolite zones are the dominant mineral zones on suðuroy. from sandoy to vágar, the analcite zone is gradually replaced by a stilbiteheulandite zone that becomes widespread on vágar. on streymoy and eysturoy the stilbite-heulandite zone has a less widespread distribution, so that the stilbite-heulandite and the mesolite zones are of equal importance. the areal extent of the mesolite and stilbite-heulandite zones is further reduced on borðoy and viðoy, so the chabazitethomsonite zone becomes the major one on these two islands. description of mineral assemblages and zones figures 5–11 show the geographic distribution of the mineral zones on the islands suðuroy, sandoy, vágar, streymoy, borðoy and viðoy. in order to show the vertical distribution of the mineral zones, 28 local sections were constructed that are also shown on figs 5–11. the sections have been arranged such that it is possible to follow the changes in the mineral zones both geographically and stratigraphically (fig. 4). the data on which the sections are based are shown in appendices a and b, and table 3 gives the thickness of each zone. in contrast to the profiles drilled by the lopra-1/1a and vestmanna-1 boreholes, the profiles from the exposed part of the faroes have been constructed from observations along each section line, so the sections do not represent a single vertical profile through the lava pile. geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19128 129 suðuroy (fig. 5) the distribution of the secondary minerals on suðuroy is remarkably heterogeneous, a feature noted by currie (1905). to the north of section su2 that extends across the island from fámjin to holmssund, nearly all vesicles and fractures of the basalts are mineralised, but to the south of the section, amygdales and mineralised fractures are rare. the boundary (section su2) between the two parts of suðuroy forms a transition zone in which the scattered vesicles are partly mineralised by an analcite assemblage composed of hair-like mesolite, thomsonite, analcite, chabazite, calcite, quartz and chalcedony. this mineral assemblage is found all along section su2, which means that no relationship exists between the secondary minerals and their stratigraphic position within the lava pile. to the north of section su2, the number of mineral species and the degree of mineralisation increases gradually northwards and the area just north of trongisvágsfjørður is in the mesolite zone. despite apparent regularity, the northern part of suðuroy is a mosaic of small areas in which the mineral assemblages vary from place to place. the largest area of this kind occurs around the summit of gluggarnir (443 m). at this locality, nearly all minerals listed in table 2 are present. the southern part of the island is partly devoid of zeolites. the most abundant minerals are quartz, calcite and chalcedony, while mesolite, thomsonite, chabazite, analcite, heulandite and stilbite are less frequent. the mode of mineralisation is also different on the two parts of the island. on the northern part of suðuroy, mineralised fractures and vesicles occur in equal numbers, whereas mineralised fractures are more common than amygdales on the southern part of the island, in spite of the fact that empty vesicles occur at many localities. because of this, section su1 is based mainly on mineralised fractures. despite the weak amount of mineralisation on southsu1+lo su2 su5 su9 vá1 vá4 vá7 st2w st2e vestmanna-1 st6w st6e st10 sa1 sa3 sa5 ey1 ey2 ey3 ey4 ey8 ey10 bo1 bo2 bo3 vi1 vi2 vi3 0 330 798 970 842 1241 1424 1461 1461 795 1799 1799 2344 2252 2545 2594 1831 1650 1745 2039 2080 2098 2084 2263 2091 2237 2140 2188 _ _ _ _ 350 250 219 _ 100 400 125 _ _ 50 _ _ 166 50 _ _ _ _ _ _ _ _ _ _ 530† – 480 373 300 180 463 325 272 200 385 500 340 – 200 280 270 350 300 230 300 180 503 310 150 100 _ 180 430 _ _ _ _ _ 82 50 _ 20 83 _ _ 200 116 _ 125 195 170 190 200 _ 182 190 190 208 200 _ _ _ _ _ _ _ 293 200 _ _ _ _ _ 46 _ _ _ 75 193 149 187 _ 70 415 251 375 400 table 3. stratigraphic position and thickness of mineral zones (see fig. 4) me zone† thickness in metres ch–th zone thickness in metres st-he zone thickness in metres * stratigraphic height within the exposed lava pile of the faroe islands. the mesolite zone is composed of the upper 330 m of the lopra-1 mesolite zone plus the 200 m thick mesolite zone of section su1. base level stratigraphic height in m* section an zone thickness in metres † geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19129 130 fig. 5. distribution of zeolite zones on suðuroy and on sections su1, su2, su5, su9 and in the lopra-1/1a borehole. 7°00'w n 62°00'n 7°00'w20 km 5 km thomsonite–chabasite zone analcite zone mesolite–scolecite zone stilbite–heulandite zone laumontite zone empty vesicles 1000 0 –1000 –2000 –3000 –4000 analcite zone mesolite zone stilbite–heulandite zone laumontite zone ht zone suðuroy sandvik hvalbiarfjørdur skálafjall su2 su5 tempilklettur frodbiarkambur gluggarnir fámjin trongisvágsfjørdur hólmssund hovsfjørdur vágsfjørdur lopra-1/1a spinarnir su1 lambaklettur m et re s ab o ve s ea l ev el su9 su1 + lopra-1/1a su2 su9 su5 geus bulletin no 9 7 juli.pmd 07-07-2006, 15:15130 131 thomsonite–chabasite zone analcite zone mesolite–scolecite zone stilbite–heulandite zone laumontite zone empty vesicles skopun sandur skàlavik husàvik dalsnipa stórafjall hálsur skarvanes tyrilsválur søltuvik sandsvatn pætursfjall dalur sa1 sa3 sa5 1.3° 500 400 300 200 100 0 m et re s ab o ve s ea l ev el th–ch zone an zone me zone st–he zone sandoy 7°00'w n 62°00'n 7°00'w 20 km sa5 sa1 sa3 5 km ern suðuroy, a clear zonation can nevertheless be discerned along section su1, where a 200 m mesolite zone is overlain by a 180 m analcite zone. the mesolite zone continues to a depth of 600 m below sea level in the lopra-1/1a borehole (fig. 5). the most abundant minerals there are mesolite, scolecite, stilbite, heulandite and mordenite. chlorite, mesolite and scolecite were deposited first. mesolite and scolecite are replaced by laumontite as the first formed mineral at a depth of –626 m, indicating the top of the stilbite-heulandite zone. at about –1200 m, epistilbite replaces stilbite as the first formed mineral so that the order of deposition becomes celadonite/chlorite-epistilbite-thomsonite-laumontite or celadonite/chlorite-epistilbite-laumontite-stilbite. since an epistilbite zone has not yet been defined elsewhere, it was decided to include the total interval between –1200 m and –2200 m depth in the laumontite zone. a high temperature assemblage of laumonite, mordenite-prehnite, pumpellyite, chlorite, calcite and quartz is found from about –2200 m to the bottom of the lopra-1a borehole at –3534 m. fig. 6. distribution of zeolite zones on sandoy and on sections sa1, sa3 and sa5. the arrow indicates the apparent dip of the zeolite zones on section sa3. geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19131 132 800 600 400 200 0 me zone st–he zone thomsonite–chabasite zone analcite zone mesolite–scolecite zone stilbite–heulandite zone laumontite zone empty vesicles m et re s ab o ve s ea l ev el eysturtindur akranesskarð vestm annasund hestfalsgjøgv oyragjøgv vá4 vá1 vá7 kvig and alsá br eið á malinstindur sandavágur midvágur sørvágur høgafjall sørvágasfjørdur reyðastiggjatagi rógvukollur skjatlá 4° vágar 7°00'w n 62°00'n 7°00'w 20 km 5 km và1 và4 và7 the uppermost mineral zone preserved in the su1 section is part of an analcite zone. in east iceland, a chabazitethomsonite zone (walker 1960) and in east greenland a zeolite free zone (neuhoff et al. 1997) has been recorded in the uppermost parts of the basalt complexes whose total thicknesses are 700 m and 1400 m, respectively. if equivalent zones have ever existed on the southern part of suðuroy, they must have been considerably thinner than those on iceland and greenland, because the palaeosurface of the lower basalt formation was about 300 m above the ahorizon (see below). sandoy (fig. 6) the southern part of sandoy is strongly mineralised while the mineralisation in the northern part is weak. the area north of a line from søltuvík to skálavík is weakly mineralised by quartz, calcite, chalcedony, chabazite, hair-like mesolite, thomsonite and late formed stilbite or stellerite. nearly all fractures and vesicles are totally mineralised to the south of the line. the most abundant zeolites are analcite, chabazite, heulandite, mesolite, stilbite and thomsonite. no distinct boundary has been observed between the northern and the southern part of the island. sections sa1, sa3 and sa5 (fig. 6) show that four fig. 7. distribution of zeolite zones on vágar and on sections vá1, vá4 and vá7. the dip and strike of the zeolite zones is indicated on the map. geus bulletin no 9 7 juli.pmd 07-07-2006, 15:16132 133 zeolite zones exist on sandoy. in the area between sandur and søltuvik, the uppermost 50 m of a stilbite-heulandite zone are exposed. the stilbite-heulandite assemblage consists of chlorite, heulandite, stilbite, mordenite and occasionally of laumontite and apophyllite. the latter two minerals occur mostly in fractures in the basalt. however, the degree of mineralisation is low in the stilbite-heulandite zone and, by volume, only half of the vesicles are mineralised. the southern and the eastern parts of sandoy are dominated by a mesolite zone. the most abundant minerals are chabazite, heulandite, mesolite (solid or hair-like), stellerite, thomsonite and calcite together with minor gyrolite, gismondine and levyne. heulandite and mesolite are the first deposited minerals. dalsnípa at the south-east coast of sandoy is the type locality of levyne (brewster 1825). a detailed quantitative analysis of the mineral assemblage and the zeolite zones in section sa3 is given below. vágar (fig. 7) in contrast to suðuroy and sandoy, vágar is totally mineralised and the island may be divided into two areas. northeast of a line from sørvágur to sandavágur, a stilbite-heulandite assemblage occurs at 40% of the localities that has not been observed farther south. south-east of the boundary line, the localities are dominated by a mesolite and analcite assemblage. around miðvágur hair-like mesolite with up to 100 mm long crystal needles can be found in larger fractures and cavities in the basalt. the distribution pattern of the mineral assemblages on vágar is controlled by the rise of the stilbite-heulandite zone towards the north-east. a calculation shows that the stilbite-heulandite zone dips from between 1–3°ssw to 0.6°ese, while the basalt flows dip 3–4°ese, i.e. the mineral zones are discordant to the lava stratification. a quantitative analysis of the mineral assemblage and the zeolite zones on section vá1 is given below. streymoy (fig. 8) streymoy can be divided into a northern, a central and a southern area. a stilbite-heulandite assemblage occurs along the coast from tjørnuvík to langasandur in the north. the observed minerals are stilbite, heulandite, thomsonite, compact mesolite, laumontite, gyrolite, okenite, tobermorite, apophyllite, celadonite and smectite. the mineral assemblage in the amygdales changes gradually towards the west. the hydrated calcium silicates, stilbite and laumontite, disappear from the amygdales although they still occur in fractures in the basalt. at saksun near the north-west coast, the stilbite-heulandite assemblage is replaced by a mesolite assemblage, characterised by solid mesolite, thomsonite, heulandite, chabazite, calcite and montmorillionite. gyrolite and stilbite are present, but only in fractures. the distribution pattern is reversed in the central part of streymoy (between langasandur, vestmanna, dalsnipa and kollafjørður). there the stilbiteheulandite assemblage occurs along the west coast from vestmanna to dalsnipa, while a mesolite assemblage is found along the east coast between langasandur and kollafjørður. only the mesolite assemblage is found in the southern part of streymoy. because of the differences in mineral distribution, sections st2 and st6 have been divided into two columns, showing the eastern and the western parts of the sections, respectively (fig. 8). the dip of the zeolite zones in the northern part of streymoy is 2°sw and 2°nne the central area. the distribution of secondary minerals is rather complex at many localities in northern and central streymoy and shows repetitive zoning, i.e. a regular repetition of two mineral zones. for example, on the path from saksun to the summit of borgin (643 m), a mesolite zone is first encountered, then a stilbite-heulandite zone, then, near the summit, a second mesolite zone. repetitive zoning has also been observed at loysingafjall (638 m), where the mesolite zone is overlain by a stilbite-heulandite zone, and along the main road between the villages of vestmanna and kvívík. between vestmanna and kvívík, zones occur within which the vesicles and fractures of the basalt flows are mineralised, either by heulandite, stilbite, mordenite plus minor laumontite, or by compact mesolite, heulandite, stilbite, thomsonite and chabazite. the widths of the zones are from a few hundred metres to about 1 km. repetitive zoning also exists in the vestmanna-1 borehole. the first classification of the vestmanna-1 mineral assemblages was based on the mass concentration of major index minerals. since chabazite and thomsonite are the most abundant minerals, the entire mineral assemblage was classified as a thomsonite-chabazite assemblage. during the reclassification based on the first formed minerals for the present work, it became apparent that the drilled lava succession contains a repetitive zoning of mesolite and stilbite-heulandite assemblages (fig. 8). it is unlikely that repetitive zoning is caused by vertical fluctuations of the geothermal gradient within such relatively short distances, but the repetitive zoning may reflect flows of water of different temperature that changed geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19133 134 streymoy 7°00'w n 62°00'n 7°00'w 20 km thomsonite–chabasite zone analcite zone mesolite–scolecite zone stilbite–heulandite zone laumontite zone empty vesicles tjørnuvik haldarsvik sun din i saksun hvalvik hósvik kollafjørdur kaldbaksfjørdur st2e st2w langasandur tórshavn kvivik givrufelli langafjall borgin saksunardalur loysingfjall vestmanna-1 st6w bøllufjall hundsarabotnur sund hvitanes sundshalsurdalsnipa øksnagjogv kirkjubøur st10 2° 3.4° th–ch zone an zone me zone st–he zone 700 600 500 400 300 200 100 0 m et re s ab o ve s ea l ev el st–he zone 2 me zone 2 st–he zone 1 me zone 1 0 –100 –200 –300 –400 –500 –600 m et re s ab o ve s ea l ev el vestmanna-1 st 2w st 2e st 6w st 6e st 10 4° 3.4° st 2e st 6w st 6e st 10 st 2w saksunardalur loysingfjall bøllufjall hundsarabolnur sundshálsur hvitanes øksnaglógv kirkjubøur vestmanna-1 vestmannasund sund 1.5° 2° 5 km givrufelli langafjall borgin 2° 2° fig. 8. distribution of zeolite zones on streymoy and on sections st2e, st2w, st6e, st6w, st10 and in the vestmanna-1 borehole. the dip and strike of the zeolite zones is indicated on the map. the arrows indicate the calculated strike of the zeolite zones between the sections. geus bulletin no 9 7 juli.pmd 07-07-2006, 15:16134 135 gøtuvik lambavik su n d in i selatrað breiða morskarnes raktangi nes æðuvik rituvik runavik lambareiði stórafjall syðrugøta ritufjall heltnará sandfelli urðará glyvur inran svinár nordskáli litlafelli skerðingur elduvik funningur slættaratindureiði gjógv ey10 ey4 ey8 ey3 ey2 ey1 skálafjørdur th–ch zone an zone me zone st–he zone 700 600 500 400 300 200 100 0 m et re s ab o ve s ea le ve l oyndarfjørdur fuglaflørdur funningsfjørdur oyri kolbanargjógv kambur 5 km 0.8° thomsonite–chabasite zone analcite zone mesolite–scolecite zone stilbite–heulandite zone laumontite zone empty vesicles eysturoy 7°00'w n 62°00'n 7°00'w 20 km ey1 ey2 ey3 ey4 ey10 ey8 1.7° 2° 0.4° 0.8° 2.8° 1.1° 2° 2° 2° 2° 4 ° 4° fig. 9. distribution of zeolite zones on eysturoy and on sections ey1, ey2, ey3, ey8 and ey10. the dip and strike of the zeolite zones is indicated on the map. the arrows indicate the calculated dip of the zeolite zones between the sections. locally the vertical distribution of temperature. alternative explanations for repetitive zoning are: (1) local variations in the chemical composition of the basalt, or: (2) mineralisation in an open and closed system, caused by variations in the percolation speed of the geothermal water (barth-wirsching & höller 1989; gottardi 1989). eysturoy (fig. 9) eysturoy may be divided into two for descriptive purposes. north of a line from norðskáli to fuglafjørður, the stilbite-heulandite assemblage occurs at 64% of localities. south of that line mineral assemblage occurs at only 12% of the localities (fig. 9). the actual strike and dip of the geus bulletin no 9 7 juli.pmd 07-07-2006, 15:17135 136 zeolite zones can be determined by combining the dip of the zeolite zones along the sections with the dips between them. on fig. 9 it can be seen that the strikes and dips change to follow the changes in mineralogy. north of a line from svinár/norðskáli to fuglafjørður, the zeolite zones dip about 2° towards the east. to the south of the line, the dips of the zones shift gradually from 4° to the sw to 2° to the s. this means that the mineral zones are discordant to the lava bedding on the northern part of eysturoy, but nearly concordant to it on the southern part of the island. borðoy (fig. 10) the mesolite, analcite and chabazite-thomsonite zones are the only ones exposed on borðoy. at klakkur (section bo1) the vesicles and fractures in the basalt are mineralised by heulandite, stilbite, mesolite (massive and hairlike), thomsonite (massive and hair-like), chabazite, levyne, phillipsite, montmorillionite and celadonite, but no clear relationship exists between the distribution of mineral and height in the lava pile. since analcite and mesolite are the first deposited minerals in most vesicles, the mineral assemblage of section bo1 was classified as a mesolite zone assemblage. the poor zoning west of borðoyavik suggests 800 600 400 200 0 th–ch zone an zone me zone m et re s ab o ve s ea le ve l h van n asu n d h arald ssu n d bo rd oyavik høgahadd hálgafelli klakkur ánir strond húsadalur norðtoftir depil bo rð oy + v ið oy 2° 1.1° arnafjordur bo3 bo2 bo1 thomsonite–chabasite zone analcite zone mesolite–scolecite zone stilbite–heulandite zone laumontite zone empty vesicles borðoy 7°00'w n 62°00'n 7°00'w 20 km bo 3 bo 1 bo 2 5 km fig. 10. distribution of zeolite zones on borðoy and on sections bo1, bo2 and bo3. the arrow shows the strike of the zeolite zones between bo2 and bo3. the common dip and strike of the zeolite zones on borðoy and viðoy is shown in the upper right corner. geus bulletin no 9 7 juli.pmd 07-07-2006, 15:18136 137 altitude metres table 4. quantitative analysis of section sa3, sandoy. the table shows the number of observed and calculated amygdales containing the index mineral per 25 amygdales 0 25 50 75 100 120 150 180 200 210 220 243 270 320 340 360 375 380 400 420 446 18 18 10 16 0 4 6 2 0 2 1 0 1 1 1 0 0 0 0 0 0 ncalnobs me 0 0 0 0 0 0 2 3 7 14 15 22 22 10 5 0 1 1 0 0 0 0.0 0.0 0.02 0.1 0.3 0.8 1.4 5.9 5.6 2.0 0.7 0.5 0.1 0.0 0.0 ncalnobs me* 14 12 8 5 4 3 3 1 1 0 0 0 0 0 0 0 0 0 0 0 0 9.2 7.2 5.5 4.3 2.8 1.7 1.1 0.9 0.7 0.5 0.2 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.875 ncalnobs th 0 0 0 0 0 0 0 2 3 2 0 3 5 9 10 0 14 14 23 23 23 0.1 0.1 0.1 0.2 0.3 0.5 0.7 1.0 1.5 1.8 2.2 2.8 4.4 8.5 11.2 14.0 16.3 17.1 20.1 22.8 24.6 ncalnobs th* 14 0 11 8 0 8 5 5 4 5 0 3 3 2 1 0 0 0 1 0 0 12.8 11.5 10.2 9.2 8.2 7.4 6.3 5.2 4.5 4.2 3.8 3.3 2.5 1.5 1.1 0.9 0.7 0.7 0.4 0.3 0.3 ncalnobs an 0 0 1 1 0 2 3 0 0 0 6 6 6 8 13 0 0 0 16 0 20 1.1 1.3 1.5 1.8 2.1 2.4 2.7 3.6 4.2 4.4 4.8 5.4 6.7 9.3 11.3 12.0 13.2 13.8 15.4 17.2 19.1 ncalnobs ch † rn,u: correlation coefficient of the regression line inh versus u(nobs). see equation (2). ‡ sh: standard deviation on hcal. in m. see equation (3). 9.1 6.6 4.1 2.4 1.3 1.1 0.6 0.4 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 rn,u† sh ‡ _ _ 0.988 _ _ 0.996 _ _ _ _ 0.991 _ _ 0.982 _ _ 0.952 10.3 13.0 15.9 21.4 24.9 11.9 21.3 18.6 15.5 12.2 44 17 14 32 56 59 13.4 11.3 ncalnobsnobsnobsnobsnobs ncalncalncalncal ch th me he st table 5. quantiative analysis of section vá1, vágar. the table shows the number of observed and calculated amygdales containing the index mineral per 25 amygdales metres altitude 0 0 0 0 0 0 2 2 3 3 6 3 5 6 _ _ 0.2 0.3 0.6 0.7 1.2 1.2 1.4 1.7 2.2 2.4 2.7 3.5 4.8 5.3 0 0 0 3 13 9 15 0 19 18 19 21 0 23 _ _ 0.8 1.7 3.9 3.9 10.1 10.7 12.6 14.8 18.4 19.4 21.1 23.8 25.0 24.8 0 0 0 0 0 1 3 6 7 9 10 0 24 0 _ _ 0.0 0.1 0.3 0.4 1.9 2.2 3.1 4.5 7.6 8.8 11.0 16.1 22.0 23.5 4 9 24 23 15 18 10 7 3 2 1 0 0 0 _ _ 3.7 11.3 22.7 24.8 17.7 16.3 11.9 7.9 3.1 2.2 1.2 0.2 0.0 0.0 3 15 21 0 7 5 0 0 0 0 0 0 0 0 _ _ 3.7 14.3 25.0 23.2 6.7 5.4 2.6 1.1 0.2 0.1 0.0 0.0 0.0 0.0 † rn: correlation coefficient of the regression line inh versus u(nobs). see equation (2). ‡ sh: standard deviation on hcal. in m. see equation (3). 10 100 200 235 340 350 380 410 460 475 500 550 610 630 rn,u† sh‡ 0.987 0.972 0.851 0.837 0.871 58 27 25 26 97 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19137 138 that the area has been affected by several generations of mineralisation. the zoning becomes distinct farther eastwards on sections bo2 and bo3. the exposed part of the mesolite zone is 500 m on bo1, but 300 m on bo2 and 150 m on bo3 (fig.10). the analcite and thomsonite-chabazite zones also appear at higher levels on sections bo2 and bo3. the mineral zones have apparent dips of about 1º towards the north and east. the analcite zone is about the same thickness on both bo2 and bo3, which suggests that the vertical displacement of the two zones reflects differences in altitude of the palaeosurface of the basalt plateau. the lava flows of borðoy dip 1.6º to the se, which means that the zeolite zones are discordant to the lava bedding. viðoy (fig.11) the distribution pattern of the secondary minerals on viðoy is a continuation of that on borðoy. the mineral zones are displaced downwards compared to those of borðoy with the result that only between 100 m and 200 m of the mesolite zone is exposed on sections vi1 and vi2. on section vi3 a lower analcite zone about 200 m thick is exposed, which is separated from the thomsonitechabazite zone by about 130 m of repetitive zoning. the chabazite-thomsonite zone is about 430 m thick, which is the maximum thickness recorded for that zone within the basalts exposed on the faroe islands. quantitative analysis of mineral distributions once the position and temperatures are known of the boundaries of the zeolite zones, the geothermal gradient h van n asu n d th–ch zone 3 an zone 3 th–ch zone 2 an zone 2 th–ch zone 1 an zone 1 me zone m et re s ab o ve s ea le ve l 800 600 400 200 0 malinsfjall tunnafjall enni vl1 vl2 vl3 2.1° 2.1° 2° vi ðo y + bo rð oy thomsonite–chabasite zone analcite zone mesolite–scolecite zone stilbite–heulandite zone laumontite zone empty vesicles 2° vi3 vi2 vi1 vi d vi k 7°00'w n 62°00'n 7°00'w 20 km 5 km viðoy fig. 11. distribution of zeolite zones on viðoy and on sections vi1, vi2 and vi3. the dip and strike of the zeolite zones is indicated on the map. the arrows indicate the strike of the zeolite zones in the profiles. the common dip and strike of the zeolite zones on borðoy and viðoy is shown in the upper left corner. geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19138 139 and the altitude of the palaeosurface of the basalt plateau can be estimated using least squares regression, assuming a linear palaeotemperature gradient. however, in order to make a reliable estimate, the regression must be based on three or more zone boundaries. this requirement is fulfilled only where the lopra-1/1a and su1 sections can be combined. elsewhere, the number of exposed zone boundaries is too small to calculate a geothermal gradient. in order to overcome this limitation, an attempt has been made to estimate the position of unexposed mineral boundaries from a detailed analysis of the distribution of the exposed mineral zones. quantitative analyses carried out on the mineral assemblages of the lopra-1/1a and vestmanna-1 boreholes showed that the relative vertical frequency of the minerals followed a skewed distribution with one or more maxima (jørgensen 1984). this observation has been used to extrapolate non exposed zone boundaries on section vá1 on vágar and sa3 on sandoy. the two sections were chosen because they are through the middle and the upper basalt formations respectively, the distribution of minerals in them is simple and nearly all rocks sampled contain a large number of well developed amygdales. in order to examine the relationship between the thickness of the zeolite zones and the distribution of index minerals, the number of amygdales containing a particular index mineral was recorded for 25 amygdales (see below). to ensure that the amygdales were selected randomly, all amygdales in the samples from each locality were numbered and the 25 amygdales for examination were selected by using a computerised random number generator. after the amygdales had been chosen, the first formed index mineral was determined and the total number of amygdales containing the same index mineral was recorded. these results are presented as columns nobs in tables 4 and 5. trials were carried out using different exponential distribution functions to find the best correlation between altitude and number of amygdales containing the same index minerals. the experiments showed that the best fit between the observed distribution and the calculated distribution was obtained by the log normal distribution function: ni,cal = n0 exp(–½[(lnh – lnh0) / a]2) (1) where: ni,cal is the calculated number of amygdales containing index mineral i. n0 is the total number of amygdales investigated; in this case n0 = 25. h is the altitude of the sample above sea level. h0 is the altitude where the distribution function attains its maximum value. a is a constant. by transforming equation (1) to a linear form and replacing ni,cal by ni,obs, we obtain: lnh = au + lnh0, where u = ± [2 (lnn0 – lnni,obs)]½ (2) the constants a and h0 can be determined by linear regression on u and lnh. the calculated number of amygdales (ni,cal) containing index mineral i is shown in tables 4 and 5. a t-test shows that u and lnh fit a straight line at the 1% confidence level. the distribution curves in figs 12 and 13 give only a best estimate for the height above sea level of the zone boundaries. to assess the degree of uncertainty of these estimates (see below) we calculate the standard deviation of the altitude (h) defined as: sh = [1/(n – 2) s (h – hc)2]½ (3) where: n is number of pairs (h, ni) along the distribution curve. h is the altitude of the sample above sea level. hc is the calculated altitude of a point on the distribution curves corresponding to ni amygdales that contain index mineral i. in equation (3), n is reduced by 2 because of the loss of two degrees of freedom by the least squares estimation of a and h0 in equation (1) (miller & freund 1977). when ni, h0 and a are known, hc can be calculated from equation (1). sh for the distribution curves is shown in tables 4 and 5 and a graphic representation of the calculated distributions of chabazite, thomsonite, mesolite, analcite, heulandite and stilbite on sections sa3 and vá1 is shown in figs 12 and 13. the shape of the curves suggests that a temperature range existed around the altitude h0 in which conditions were favourable for the formation of a particular zeolite. where h < h0, palaeotemperatures decreased away from h0 to where they became too low for the zeolite to form. where h > h0, palaeotemperatures increased away from h0. the zeolite that was most stable at h0 would have been formed in some interval below h0 but, at higher temperatures, formation of the first zeolite would gradually be inhibited and another one would have become stable. so a zeolite will most likely be found between the maximum slopes of its distribution curve versus height, which corresponds to a palaeotemperature interval. geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19139 140 la zone st–he zone me zone th–ch zone zeolite freezonean z o ne la zone st–he zone me zone th–c h zone zeolite freezonean z o ne la zone st–he zone me zone th–ch zone zeolite freezonean z o ne ho analcite–chabazite ho ho 1000800600400200–20 0–400–600–800–1000–1200 0 3 6 9 12 15 18 21 24 solid mesolite–hair-like mesolite solid thomsonite–hair-like thomsonite ch (obs) ch (cal) an (obs) an (cal) n um be r o f am yg da le s co nt ai ni ng a n/ c h pe r 25 a m yg da le s altitude (m above sea level) 1000800600400200–200–400–600–800–1000–1200 0 3 6 9 12 15 18 21 24 altitude (m above sea level) n um be r o f am yg da le s co nt ai ni ng m e/ m e pe r 25 a m yg da le s 1000800600400200–200–400–600–800–1000–1200 0 3 6 9 12 15 18 21 24 altitude (m above sea level) n um be r o f am yg da le s co nt ai ni ng a n/ c h pe r 25 a m yg da le s ho ho me (obs) me (cal) me*(obs) me*(cal) th (obs) th (cal) th*(obs) th*(cal) la zone st–he zone me zone ch zone zeolite freezone la zone st–he zone me zone ch zone zeolite freezone chabasite–mesolite thomsonite–stilbite–heulandite 16001200 140010006004002000–200–400 800 3 6 9 12 15 18 21 24 altitude (m above sea level) n um be r o f am yg da le s co nt ai ni ng c h/ m e pe r 25 a m yg da le s 1000800600400200–200–400–600–800–1000–1200 0 3 6 9 12 15 18 21 24 altitude (m above sea level) n um be r o f am yg da le s co nt ai ni ng a n/ c h pe r 25 a m yg da le s ch (obs) ch (cal) me (obs) me (cal) th (obs) th (cal) he (obs) he (cal) st (obs) st (cal) + + + numbers are small. a zone boundary is defined for mapping purposes to be reproducible with a probability of 95%. the probability (p) of discovering ni,obs objects (amygdales containing the new zeolite i) among n0 objects (amygdales) can be calculated by means of the binomial distribution function (see e.g. kreyszig 1975 or miller & freund 1977). it can be shown that when n0 = 25 and p = 95%, then ni,obs = 3. fig. 12 shows that this reasoning can be applied to define the upper boundaries of the thomsonite-chabazite, analcite and mesolite zones at the heights where the upper end of the appropriate distribution curve intersects the line ni = 3. however, this method cannot be used on the upper boundaries of the stilbite-heulandite and laumontite zones, because stilbite, heulandite and laumontite do not exist as first formed index minerals in section sa3. fig. 12 shows that solid mesolite occurs most commonly in the mesolite zone and thomsonite occurs most commonly in the stilbite-heulandite plus the mesolite zone. if we assume that 95% of the two index minerals occurs within the zones in question, we can define the fig. 12. the calculated distribution of chabazite, analcite, thomsonite (compact and hair-like) and mesolite (compact and hairlike) on section sa3, sandoy. fig. 13. the calculated distribution of chabazite, mesolite, thomsonite, stilbite and heulandite on section vá1, váger. the calculated distribution curves shown in figs 12 and 13 show that the number of amygdales containing a particular zeolite decreases rapidly as |h – h0| increases. this has the practical consequence that it becomes harder to define a zone boundary by field mapping when sample geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19140 141 heights of the lower boundaries of the mesolite and the stilbite-heulandite zones where the lower end of the distribution curves interest the line ni = 3. that 95% of an index mineral occurs within the interval in question can be verified by plotting the accumulated distribution of the index mineral in a probability diagram. analcite occurs only sporadically below 340 m on section vá1 (fig. 13), so the analcite zone cannot be defined on this profile. the other zone boundaries were calculated as described above. estimation of palaeothermal gradients and altitudes of palaeosurfaces if we assume that the palaeothermal gradient was constant with depth, it may be estimated by linear regression on the data from the combined lopra-1/1a plus su1 sections, the mineral zone boundaries obtained by calculation and shown in figs 12 and 13 and the temperatures shown in fig. 2. the resulting estimates are shown in table 6. the new estimate from southern suðuroy is considered more accurate than that in jørgensen (1984), which was based on the mineral distribution in the lopra-1 borehole only. from these palaeogeothermal gradients and assuming a surface temperature of 7°c, the altitudes of the palaeosurface of the basalts has been estimated (table 6). the altitude differences between the estimated palaeosurface and stratigraphic marker horizons a and c is different at the three localities (table 7). on southern suðuroy, the palaeosurface was about 0.7 km (± 0.3 km) above present day sea level, i.e. close to the extrapolated top of the lower basalt formation. on vágar, the palaeosurface was 1.9 ± 0.2 km above the extrapolated top of the lower basalt formation (or 0.5 ± 0.2 km above the top of the middle formation), while on sandoy, the palaeosurface was 1.7 ± 0.2 km above the top of the middle basalt formation. this suggests that the focus of volcanism shifted laterally with time as will be discussed below. zeolite zone temperatures at the zone boundaries zeolite free 40– 60°c st–he 110– 130°c palaeothermal gradient °c/km altitude of palaeosurface m above sea level correlation coefficient r altitude of zone boundaries (m above sea level): lopra-1/1a + su1 vá1 sa3 0.9547 0.9181 0.8689 table 6. estimated palaeothermal gradients and the altitude of the palaeosurfaces at lopra-1/1a and sections su1, vá1 and sa3 ch–th 50– 70°c me 90– 100°c la 190– 220°c –590 380 425 –1200 – 825 –2200 – – 443–983 1760–2080 1150–1524 – 1325 653 – 900 150 66 ± 9 63 ± 8 56 ± 7– – table 7. estimated thicknesses of the basalt formations along various sections across the faroe islands altitude of palaeo surface in m above sea level (table 6) present stratigraphic thickness in m local altitude (m) of aand c-horizons altitude of palaeosurface in m above aor c-horizon 443–983 1760–2080 1150–1525 > 31001 14102 700–9001,3 a-horizon: a-horizon: c-horizon: 1550–1924 sources: 1) larsen et al. 1999, 2) waagstein & hald 1984, 3) waagstein 1988. s. suðuroy w. vágar e. sandoy area section formation lopra-1/1a + su1 vá1 sa3 l. formation m. formation u. formation a-horizon: 700 a-horizon: c-horizon: –400 –257–283 1700–202060 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19141 142 discussion palaeothermometry and zone boundaries the use of zeolites as palaeotemperature indicators is based on the assumptions: (1) that the zeolite zones reflect univariant equilibrium with a high coefficient dp/dt of the clausius-clapeyron equation and: (2) that the formation temperature of the minerals is independent of the chemical composition of the hydrothermal solution. assumption (1) is fulfilled because the properties of condensed systems are nearly independent of pressure, if the pressure is not extremely high and the temperature is below the supercritical temperature (374ºc) of water. we can also estimate the error of the temperature determination when we ignore the external pressure of the system. the coefficient dp/dt is known only for a small number of systems that involve zeolites, but experimental studies of the systems stilbite-laumontite-h2o and laumontitewairakite-h2o show that dp/dt is of the order of 25–33 bars/degree in the range pfluid = 0–2000 bars (liou 1971; jové & hacker 1997). consequently, if the external pressure is equal to the fluid pressure and the original thickness of the lava pile is 2 km, the likely maximum error of the temperature determination is 8°c, disregarding the depth between the boundary of the zeolite zone and the unknown altitude of the palaeosurface. in contrast to the effect of pressure, the chemical composition of the rock and the hydrothermal fluids has a much larger effect on the formation temperature of the minerals. barth-wirsching & höller (1989) studied the formation of zeolites in glasses of different chemical compositions. they found that replacing rhyolitic glass by basaltic glass caused the formation temperature of different zeolites to increase by between 50°c and 100°c. this demonstrates the importance of choosing a reference area for the thermometry that consists of rocks with a chemical composition similar to that of the rocks in the area studied. other factors may also affect the formation of zeolites such as the texture of the rock, the content of glass and the porosity of the rock (gottardi 1989). the geothermal areas on iceland were used as a reference for the thermometry in the present study. the basalts from the faroe islands are all tholeiites, but show large compositional variations that range from picritic to ferrobasaltic (waagstein 1988). most of the icelandic basalts are also tholeiites, but minor amounts of acid rocks (rhyolites, andesites, granophyres, acid tuff ) are found, mainly associated with volcanic centres (sigurdsson 1967). this compositional variation of the icelandic rocks may partly explain the large variation in temperature at the boundaries of the zeolite zones mentioned above (fig. 2). from the description of the sections shown in figs 12 and 13 (and listed in appendix a), it can be seen that the distribution of index minerals varies gradually between successive zeolite zones. an index mineral that defines a zone may thus overlap the boundaries of neighbouring zones which makes it difficult to define the exact boundaries between mineral zones. the problem was solved by statistical analysis on sections sa3 and vá1 from which the boundaries of the zeolite zones could be defined as the locations where 3 out of 25 amygdales contain the appropriate index mineral. the overlap problem occurs in all the sections described in appendix a and, because of the lack of quantitative mineral data, the distributions in sa3 and vá1 were the only ones that could be described by a simple distribution model. on all other sections, the zone division was based on a crude estimate of the abundance of the index minerals around the zone boundaries. figs 12 and 13 show that the overlap between the zeolite zones varies from 100 m to 300 m. which means that, in the worst case, the zone boundaries could be determined with an accuracy of only ± 150 m when the zone boundary localities are based on a subjective estimate of the abundance of index minerals. volcanic and tectonic evolution the average of the three calculated palaeogeothermal gradients is about 60°c/km and there may be a small decrease in the gradient from the lower to the upper basalt formation. if real, this decrease could reflect either a reduction in heat flow with time or a variation in heat flow with locality. rasmussen & noe-nygaard’s (1969, 1970) summary of the volcanic evolution of the faroe islands that volcanic activity started in the west and moved eastwards with the times, must be modified, because evidence from the lopra-1 drillhole indicates that the lavas of the lower formation were erupted from local centres (waagstein 1988) and not from centres situated west of the present islands. this change might explain the change in the palaeogeothermal gradients shown in table 6. the eruption centres of the lower and middle formations were located in the faroe islands and the geothermal gradient was high. movement away to the east during eruption of the upper formation led to a decrease in the gradient. geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19142 143 regional distribution of the zeolite zones at the time when the faroe lava pile was first mineralised, the thermal gradient seems to have been fairly constant, at least regionally and for some time. this is suggested by the rough equality of the calculated palaeogeothermal gradients from the southern, western and central part of the faroes that represent different stratigraphic levels (table 6). the overall regional distribution of zeolites is thus considered to reflect primarily variations in the maximum depth of burial of the basalt rather than differences in heat flow. the inferred palaeosurface on southern suðuroy is close to the extrapolated top of the lower formation (table 7), indicating that the total thickness of middle and upper formation lavas must have been small in this area. in contrast, in eastern sandoy about 50 km farther north where the exposed thickness of the upper formation is of the order of 1 km, the estimated palaeosurface is >1.5 km above the base of the upper formation or stratigraphically approximately 3 km above the lower–middle formation boundary. if we use the palaeogeothermal gradient calculated on sandoy, then the palaeosurface of the upper formation on viðoy may have been at about 1.3 km ± 0.2 km above sea level. these results suggest that the upper formation had a similar or only slightly smaller thickness in the north-eastern part of the faroes compared with the central part of the islands. on the other hand, the upper formation seems to have been much thinner or non existent in both the western and southern parts of the faroes (table 7) and the middle formation must also have been thin in the south. the inferred thinning of the middle and upper formations from the central to southern part of the faroes is consistent with a northerly source area for these basalts, centred on the rift between the faroes and greenland (waagstein 1988; hald & waagstein 1991; larsen et al. 1999). the thinning of the upper formation towards the west is consistent with rasmussen & noe-nygaard’s (1969, 1970) interpretation of an easterly source for this part of lava pile and may suggest a shift in the focus of volcanism. the first order regional zeolite distribution pattern is affected by local perturbations of the mineral zone boundaries (fig. 4). these perturbations show up as shifts in the dip of the zone boundaries within and between neighbouring islands as well as shifts in the degree of mineralisation. the latter effect is clearly seen towards the south. southern sandoy and northern suðuroy are heavily mineralised, although at different temperatures, whereas the vesicles of the basalt in the adjoining areas of northern sandoy and southern suðuroy usually contain no zeolites. on the northern and western islands, the zone distribution shows a tendency to symmetry around the narrow nw–se-trending sounds that separate the islands (figs 7–9). the distributions on the neighbouring north-eastern islands of borðoy and viðoy similarly seem to be mirror imaged, a distribution difficult to explain by variations in depth of burial. it is more likely that the distributions reflect local differences in palaeotemperature, perhaps related to the circulation of water underground with high temperatures in areas of up welling and low temperatures in areas of down welling. the symmetry of the zonal distribution patterns suggests that these temperature anomalies are in part related to nw–se-trending eruption fissures or zones of weakness separating the present islands (noe-nygaard 1968; rasmussen & noe-nygaard 1969, 1970). they are subparallel to the transfer zones in the faroe–shetland basin described by rumph et al. (1993) and later authors, and may indicate the presence of similar deep seated features. both the regional and the local distribution of zeolite assemblages probably reflect the basic volcanic-tectonic systems that led to the development of the faroe islands. acknowledgements i want to express my gratitude to the late arne noe-nygaard and jóannes rasmussen for discussions and support during the first phase of this project. i also want to express my thanks to the geological survey of denmark and greenland for financial support to the present project, to curator ole v. petersen, geological museum, copenhagen for permission to study the collection of zeolites from the faroes and to mrs. kitty jørgensen, næstved, who kindly made her collection of zeolites from the faroes available for my study. finally, i want to thank regin waagstein, james chalmers and kjeld alstrup for discussions and constructive criticism of the various versions of the manuscript. the comments of two anonymous reviewers are likewise greatly acknowledged. references barth-wirsching, u. & höller, h. 1989: experimental studies on zeolite formation conditions. the european journal of mineralogy 1, 498–506. betz, v. 1981: zeolites from iceland and the faroes. mineralogical record 12, 5–26. breck, d.w. 1974: zeolite molecular sieves: structure, chemistry and use. new york: john wiley. geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19143 144 brewster d. 1825: a description of levyne, a new mineral species. edinburgh journal of science 2, 322–334. currie, j. 1905: the minerals of the faroes, arranged topographically. transactions of the edinburgh geological society (session 1905–1906) 9, 1–68. debes, l.j. 1673: færoæ et færoa reserata. hafniæ: suptibus daniels paaulli reg. bibl. (in latin and danish). görgey, r. 1910: ein beitrag zur topographischen mineralogie der färöer. neues jahrbuch der mineralogie und palaeontologie xxix, 269–315. gottardi, g. 1989: the genesis of zeolites. european journal of mineralogy 1, 479–487. gottardi, g. & galli, e. 1985: natural zeolites. in: wyllie, p.j., goresy, a.e., von engelhard, w. & hahn, t. (eds): minerals and rocks no. 18. berlin: springer verlag. hald, n. & waagstein, r. 1991: the dykes and sills of the early tertiary faroe islands basalt plateau. transactions of the royal society of edinburgh: earth sciences 82, 373–388. jørgensen, o. 1984: zeolite zones in the basaltic lavas of the faroe islands. annales societatis scientiarum faroensis. supplementum 9, 71–91. jørgensen, o. 1997: zeolites and other secondary minerals in cavities and veins, lopra-1/1a well, faroe islands, 1996, 8 pp. + plates. unpublished report. technical studies prepared for dansk olie og gasproduktion a/s 1997 (in archives of the geological survey of denmark and greenland, geus report file 26129). jove, c. & hacker, b.r. 1997: experimental investigation of laumontite ® wairakite + h2o; a model diagenetic reaction. american mineralogist 82, 781–789. kreyszig, e. 1975: advanced engineering mathematics, 707–709, 783–787. new york: john wiley. kristmannsdóttir, h. 1982: alteration in the irdp drillhole compared with other drillholes in iceland. journal of geophysical research 87 (b8), 6525–6531. kristmannsdóttir, h. & tómasson, j. 1978: zeolite zones in geothermal areas in iceland. in: sand, l.b. & mumpton, f.a. (eds): natural zeolites, occurrence, properties and use, 277–284. oxford: pergamon press. larsen, l.m., waagstein, r., pedersen, a.k. & storey, m. 1999: trans-atlantic correlation of palaeogene volcanic successions in the faroe islands and east greenland. journal of the geological society (london) 156, 1081–1095. liou, j.g. 1971: stilbite-laumontite equilibrium. contribution to mineralogy and petrology 31, 171–177. miller, i. & freund, j.e. 1977: probability and statistics for engineers, 50–63. englewood, new jersey: prentice-hall. neuhoff, p.s., watt, w.s., brid, d.k. & petersen, a.k. 1997: timing and structural relations of regional zeolite zones in basalts of the east greenland continental margin. geology 25, 803–806. noe-nygaard, a. 1968: on extrusion forms in plateau basalts; shield volcanoes of ‘scutulum’ type. science in iceland 1,10–13. rasmussen, j. & noe-nygaard, a. 1969: beskrivelse til geologisk kort over færøerne i målestok 1:50 000. danmarks geologiske undersøgelse i række 24, 370 pp. + map vol. (in danish with summaries in faroese and english). rasmussen, j. & noe-nygaard, a. 1970: geology of the faroe islands (pre-quaternary). danmarks geologiske undersøgelse i række 25, 142 pp. rumph, b., reaves, c.m., orange, v.g. & robinson, d.l. 1993: structuring and transfer zones in the faroe basin in a regional tectonic context. in: parker, j.r. (ed.): petroleum geology of northwest europe: proceedings of the 4th conference, 999– 1009. london: geological society. sigurdsson, h. 1967: the icelandic basalt plateau and the question of sial. in: björnsson, s. (ed.): iceland and mid-ocean ridges. societas scientiarium islandica xxxviii, 32–46. waagstein, r. 1988: structure, composition and age of the faroe basalt plateau. in: morton, a.c. & parson, l.m. (eds): early tertiary volcanism and the opening of the ne atlantic. geological society (london) special publication 29, 225–238. waagstein, r. & hald, n. 1984: structure and petrography of a 660 m lava sequence from the vestmanna-1 drillhole. in: berthelsen, o., noe-nygaard, a. & rasmussen, j. (eds): the deep drilling project 1980–1981 in the faroe islands. føroya fródskaparfelag, tórshavn, 39–65. walker, g.p.l. 1960: zeolite zones and dike distribution in relation to the structure of the basalts of eastern iceland. journal of geology 68, 515–528. walker, g.p.l. 1970: the distribution of amygdale minerals in mull and morvern (western scotland). in: murty, t.v.v.g.r.k. & rao, s. (eds): studies in earth sciences, west commemoration volume, 181–194. faridibad, india: today & tomorrow’s publishers. manuscipt received 3 july 2001; revision accepted 7 december 2001. geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19144 145 appendix a: locations of sites along the sections discussed in the paper and minerals found in vesicles and fractures at each locality. the mineral zones are defi ned in fig. 2 profi le locality altitude (m) vesicles fractures zone su1 road exposure 0.5 km nor 25 no vesicles. he–me. he–st–ch. an–ch. ca. qz. 2–3 su1 the northern entrance of the sumba tunnel 70 – he–me. he–ch. me–an. ca. ch–an. 2–3 su1 road exposure at the w slope of siglidalur 200 – ch–an. ca. 1–3 su1 road exposure at small stream on the w slope of spinarnir 380 – ch–th*. op. qz. 1–2 su1 288 – ch–an. op. qz. ca. 1–2 su1 road exposure at stórá, 1km se of spinarnir 340 – th*–an. op. qz. ca. 1–2 su1 lambaklettur 235 – as above. 1–2 su2 road exposure 3 km e of øravík 100 empty vesicles. ca. qz. 1–2 su2 road exposure 2.5 km e of øravík 25 ce–an. ch–me*–th*. an. ca. st. 1–2 su2 exposure in dalsá, 1.5 km w of øravík 100 an, me*. ch. ca. cld. cld. qz. 1–2 su2 road exposure just north of høgiklovningur, 2.5 km s of øravík 250 ca–an. ph–th*. cld. me*. 1–2 su2 278 empty vesicles. ca. 1–2 su2 nw slope of nónfjall 360 th*–an–ch. th–th*–an–ch. 1–2 su2 the summit of nónfjall 427 an–me* ca. qz. an. 1–2 su2 road exposure 0.8 km s of the church in fámjin 80 ac. ch. ch. an. qz. 1–2 su2 road exposure 0.5 km s of the church in fámjin 20 an–th. th*–ch. an. st. me*. 1–2 su5 høvdatangi, fr 0–25 empty vesicles. empty fractures. – su5 skarvatangi 60 na–(th, an). me–th. ch. me–me*. me–st. me–an. st–ch. st*–st. 2–3 su5 exposure at the road fr 90 an–st. me–st. th–st. th–me. me*–ch. 2–3 su5 – do – 130 na. ch. me–sc. me–ch. th–ga–ch. na–st*–st. an–th. st–ch. 2–3 su5 – do – 140 an–th*–ch. an–me. st–me–st. me–la, ch. 2–3 su5 – do – 250 me–me*. th–me. an. he–st. op, cld, ca. 2–3 su5 summit of kambur 483 ce–he. me in large acicular crystals like scolecite. ce–me*, ce–an. he. 2–3 su9 hamranes and the southern entrance of the tunnel hvalba–sandvík 0–100 he–st. he–me–ch. an–me. me–me*– gy. me–gy+ap. he–st–ap. me*–la. th–ch; he–(st, la). he–ap. he–la. la–ca. la–gy. 2–3 su9 the southern slope of skálafjall 70 an–he. me–th. cld. as in the vesicles. 2–3 su9 – do – 120 as above. 2–3 su9 – do – 160 scolecite-like me. an–he. me–he. he–me–me*. ca. 2–3 su9 – do – 200 as above. 2–3 su9 – do – 240 me–st. he–st. he–ch. ca–(ch, le). 2–3 su9 – do – 260 me–me*–ch. th–ch. 2–3 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19145 146 profi le locality altitude (m) vesicles fractures zone su9 the southern slope of skálafjall 290 th*–ch. me–me*–ch. ca. 1–3 su9 the summit of skálafjall 374 as above. 1–3 sa1 exposure at the cost line and at road cuttings in søltuvík 0–50 many empty vesicles. he. st. la. ca. la–st–ca. mo–he–st. ca. 2–4 sa1 road exposure at the road sandur–søltuvík, 1.5 km west of sandur 60 he–st. he+me–st. th–st. he+me–st. ca. 2–4 sa1 large quarry at lake sandvatn, 1 km north of sandur 10 no vesicles. st–la–ca. he. st. 2–4 sa1 sprutthol, sandsvágur bay 30 he–me. ch. ca. st. ca. 2–4 sa3 húsavíklið n of húsavík 0–75 he–me. ce–me. th–me. st. 2–3 sa3 road exposure 2 km w of skálavík 78 me–ch. gi. cld. he–st–ca. 2–3 sa3 road exposure at hálsur, 3 km w of skálavík 119 me–th. me–me*. he–th. st–st*. ap. 2–3 sa3 urðarklettar nw of húsavík 120 me–th–ch. an–me–th. 2–3 sa3 húsavíklið n of húsavík 150 me–th–me. an. he. ca. 2–3 sa3 exposure at gravaráin 140 me–th. he–st. he–ch. an. st. la. 2–3 sa3 urðatklettar, nw of húsavík 150 ce–me–th–me*, me–me*–gy. me*. 2–3 sa3 – do – 180 ca–me–me*. an–me. 2–3 sa3 húsavíklið, n of húsavík 180–200 me–th*. an–th–me*. 2–3 sa3 exposure at gravaráin 210–220 me–ca–.me*. an–me*. an–th*. ca–he–st. ca–ap. 1–2 sa3 exposure at stórá 243 me–me*. me–th*–ca. gi. ca–st. 1–2 sa3 summit of heiðafjall 266 he–me*. an–me*–an. th*. 1–2 sa3 exposure at stórá 320–340 me–an–me*. ch. th*. 1–2 sa3 skriðubakki 360–380 th*–ch. me*–ch. me*. 1–2 sa3 – do – 400–420 ch–th*. th*–ch. an. many empty vesicles. 0–1 sa3 the summit of pætursfjæll 447 ch–th*. many empty vesicles. 0–1 sa5 dalsnípa 150 me–an. me–ap–st. th–ap. ch–ap. th–ch. an–ch. le. he–st–ap. cld. 2–3 sa5 the s slope of skúvoyafjall, 0.6 km nw of dalsnipa 280 me–st, me–an, he. 2–3 sa5 the summit of skúvoyafjall 354 ce–ch. ce–th–th*. st. 1–3 sa5 road exposure at the end of the road dalur–skuvoyafjall 308 he–me. th–me*. ch–th*. 1–3 sa5 road exposure 2 km sw of dalur 260 th–ap. st–me–le. th–le. he–me–la. 2–3 sa5 dalur harbour 0–30 ch. ch–le. an–th–th*. he–me–st. ch. le. me–ap–st. me–me*. 2–3 sa5 road exposure at kinnartangi 100 ch. ch–th–ch. st–me–gy. gy–me. 2–3 sa5 the se slope of stórafjall 160 ch. an–me–me*. st–th. ch. st. he. gy. 2–3 sa5 – do – 220 me–me*–ch. th–me. 2–3 sa5 – do – 260 as above. 2–3 sa5 – do – 300 ph. gi–me*. th*–le. me–me*. 1–2 sa5 – do – 340 as above. ch–le. he–me–st–ap. 1–2 sa5 – do – 360 as above. he–le. 1–2 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19146 147 profi le locality altitude (m) vesicles fractures zone sa5 the summit of stórafjall 396 ch+ph. gi–me*. me*–ch. th–ch. 1–2 sa5 the ne slope of stórafjall 310 ch. me*–ch. he. 1–2 sa5 trigonometric station on the ne slope of stórafjall 217 ch. an. me–ch. he–st. he–me–gy. 2–3 sa5 road exposure at tjarnaheyggjur 60 as above. me–ca. 2–3 vá1 reyðastiggajatangi 0–10 he–st, an. cl–st–ca–la. 3–4 vá1 gásadalur, exposure along the path gásadalur–rógvukollur 100 he–st, st–la. cl–st–la. 3–4 vá1 – do – 200 he, st. me, la, an. 3–4 vá1 gásadalur, exposure at the path gásadalur– rógvukollur 235 he–th. la, ca. 3–4 vá1 gásadalur. the pass between knúkarnir– neytaskarð 340 he, st, th, an, cl. 3–4 vá1 grunnadalur, exposure at the branching of small streams 380 cl–he–th, cl–he–st, cl–st–me. st–la–st. 3–4 vá1 rógvukollur , exposure at the w slope 380 he–me, me–ch, th–ch–th, mo–he, mo–ch ± cld. me, ca. 2–3 vá1 neytaskarð, exposure at the se slope 400–420 as above. 2–3 vá1 the summit of rógvukollur 464 he–me, me–he–me, th–me, th–ch, me–ch. 2–3 vá1 djúpidalur (the nw slope of eysturtindur), exposure at stream 470–480 he–me, he–ch, me–ch, th–ch. 2–3 vá1 500 he, me, th, ch. 2–3 vá1 grunnadalur, exposure at the end of small streams 550 th–me*–ch. la, ca. 2–3 vá1 djúpidalur (the nw slope of eysturtindur) 600–610 ce–th–th, ce–ch. st–me–la, ca. 2–3 vá1 the plateau between eysturtindur and akranesskarð 620–640 an, th, me, sm. 2–3 vá4 oyrargjógv ferry harbour and the path to sørvágur 0–136 st–st*. ep–st. la. th. ch. st. la. 3–4 vá4 large quarry 1 km w of sørvágur 10 cl–st–st*. st–la. mo–he. mo–gy. an–gy. me–me*–ch. me–ap±sm. he–st–st*. ep. la, me. 3–4 vá4 sjatlá, 1.5 km n of sørvágsvatn 45–60 cl–he–st. st–la. ap. 2–4 vá4 exposure at n end of small road from sørvágur, just w of sjatlá 114 cl–st–me. cl–an. cl–ch±sm. st–la. ap. 2–4 vá4 – do –, exposure at small tributary of skjatlá 150 cl–he–st. st–ap. cl–me–th. cl–me– ch. me–ap. me–ch. me–ap. an–ap. he–ch. 3–4 vá4 – do – 190 as above. 3–4 vá4 – do – 220 cl–st–st*. cl–he ± la. th. mo–st. 3–4 vá4 end of breiðá (oyrargjógv) 250 ce–me. he–me. 3–4 vá4 – do – 304 ce–me–th. ce–th–ch. gy–me. 2–3 vá4 kvígandalur, exposure at the se tributary of kvígandalsá 250 an. he–le. me–le. an–th–ch. 2–3 vá4 husadalur, exposure at the w? tributary of kirjuá 275 an. me. he. me–an. 2–3 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19147 148 profi le locality altitude (m) vesicles fractures zone vá4 kvígandalur, exposure at the se tributary of kvígandalsá 300–365 an. he. le. ch. 2–3 vá4 the cross between the path oyrargjógv– sørvágur and sandavágur–slættanes 436 me. th. st. ch. 2–3 vá7 road exposure 3 km north of sandavágur 100–120 ce–he–st. ce–st–me. ce–he–th. ce–mo–st. ce–me–st. ce–mo–he. ce–he–st. ce–me*–ch. ce–ap. 2–4 vá7 the western slope of malinstindur 219 as above. 2–4 vá7 – do – 235 ce–he–me. ce–me–gy. st–ca. 2–3 vá7 – do – 280 ce–me–ch.±ca. ±sm. 2–3 vá7 – do – 345 as above. 2–3 vá7 – do – 386 empty vesicles. – vá7 – do – 410 ce–he–me. th–me. th–an. st. ch. 2–3 vá7 – do – 500 as above. 2–3 vá7 – do – 538 he. an. me. th. th*. cld. ca. he–me. me*. cld. 1–2 vá7 – do – 563 me–me*. th*–ph. th*–ch+le. 1–2 vá7 the summit of malinstindur 580 ce–me*. 1–2 vá7 – do – 620 he. me. ph. ch. th. ca. cld. 1–2 vá7 – do – 683 me–he. me*–ch. ph–ch. 1–2 vá7 – do – 690 he. ch. le. th. cld. 1–2 st2w the path saksun–haldarsvík: kvíggjarhamar, saksun 0–100 he. st. th. me. ch. st–ca–st. gy. tb. ok. 2–3 st2w the slope of the mountain between skipá and gellingará 150 he–ch–th. me–st. 2–3 st2w – do – 200 me. ca. 2–3 st2w – do – 250 th–me. he–me. me–ch. st. la. 2–3 st2w – do – 310 as above. 2–3 st2w – do – 325 me. me*. th*–ch. he–me. ok. gy. ca. 2–3 st2w – do – 355 me–me*. th–me*. th*–ch. 2–3 st2w – do – 360 ce–th*. he–me*–sm. 1–2 st2w – do – 380 an–th*. th*–le. me*–ca. 1–2 st2w – do – 407 ce–ph–ch. ce–th*–ch. 1–2 st2w – do – 430 th*–ch. 1–2 st2w – do – 460 empty vesicles. 0–1 st2w – do – 555 le–ch. th–th*. 0–1 st2w víkarskarð 600 ce. th. ch. cld. 0–1 st2w the ne slope of gívrufelli 650 as above. 0–1 st2w the summit of gívrufelli 701 as above. 0–1 st2e víkarnes n of haldarsvík 0–30 he–st. ca. ca–la. 3–4 st2e the se slope of fjallið 100 as above + th. gy. ok. to–gy. la. 3–4 st2e – do – 150 he. me. th. to–st. th–gy–ap. 2–3 st2e the summit of fjallið 180 he–me. he–th*. ca. 2–3 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19148 149 profi le locality altitude (m) vesicles fractures zone st2e the path haldarsvík–saksun: exposure 0.5 km sw of haldarsvík 148 he–st. me. me–th–ch. me–an. ph–le–ch. 2–3 st2e – do –, exposure 1 km sw of haldarsvík 200 he–st. he–me. 2–3 st2e – do –, exposure at the svínstiáir tributaries of kluftá, 1 km sw of haldarsvík 230 me. th. he. st. ca. 2–3 st2e – do –, exposure 1.2 km sw of haldarsvík 250 he. me. mo. he. st. ap. ca. 2–3 st2e – do –, exposure 1.5 km sw of haldarsvík 280 me–th–me–gy–sm. 2–3 st2e – do –, exposure 1.8 km sw of haldarsvík 350 me–th. 2–3 st2e – do –, exposure 2 km sw of haldarsvík 360 me–th. me–ph–ch. 2–3 st2e – do –, exposure 2.3 km sw of haldarsvík 370 me–th. an–me–me*. 2–3 st2e – do –, exposure 2.5 km sw of haldarsvík 400 th*–ch. me–th*. ph–ch. ch + le. 1–2 st2e – do – 410 me–me*. ch–le–ch. 1–2 st2e the se slope of víkartindur 420 me–me*–le. ch–ph–sm. 1–2 st2e – do – 440 .me*. th–th*–ch. 1–2 st2e – do – 500 th*. ch.cld. 0–1 st2e – do – 540 as above. 0–1 st2e – do – 620 as above. 0–1 st6w road exposure at the main road kvívík– stykkið, 1.5 km e of kvívík 50 he. st. la. me. th. ap. he. st. ap. me*. th. ch. an. 2–4 st6w tunnel workplace at the village of leynar 50 me. st. la. 2–4 st6w exposure at leynarvatn along the old road tórshavn-vestmanna 60–125 he. st. wa. la. ce. cld. st. ca. he. st. st*. la. me*, th, le. 2–4 st6w the path leynarvatn–hósvík, exposure 0.3 km ne of leynarvatn 150–190 ce–he–st. ce–me–gy. cld. ph, gy, ap. 2–3 st6w – do –, 0.4 km ne of leynarvatn 210 ce–he–st. ce–me–th. ce–st–la. 2–3 st6w – do –, 0.5 km ne of leynarvatn 260 ce–me–th. ce–he–me. ce–he–th. me–ca. 2–3 st6w the path leynarvatn–hósvík, exposure 0.5 km ne of leynarvatn 300 as above. 2–3 st6w – do –, 0.6 km ne of leynarvatn 340 as above. 2–3 st6w á halsi, 1 km ne of leynarvatn 380 as above. 2–3 st6w – do –, 1.5 km ne of leynarvatn 463 ce–he–me–me*. ce–th–ch. 2–3 st6w – do –, 1.9 km ne of leynarvatn 500 as above. 2–3 st6w – do –, 2 km ne of leynarvatn 510 me–he–me*. me–me*. th*–ch. he–me. 2–3 st6w hósvíksskarð 520–530 th. th*. ph. ch. le. + ce. 2–3 st6w the sw slope of bøllufjall 550 as above. 1–2 st6w the summit of bøllufjall 584 as above. 1–2 st6w the sw slope of gívrufjall 530 as above. 1–2 st6e road exps. between við áir and hosvík 15 he–st*. he–st–ap. he–st–ch. he– th–ch. th–st. th–ch. ga–th. an–ch. an–ap. an–th. an–th–ch±ce. he–ch–st. th–gy+ap. ch–th*–ap. 2–3 st6e the path hosvík–leynar: smørdalsá 160–203 he–me. he–ch–th, me–gy. he–an–th. 2–3 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19149 150 profi le locality altitude (m) vesicles fractures zone st6e the path hosvík–leynar: smørdalsá 240–260 ce–me–he. ce–th–me. cld. me–th–ap–gy. 2–3 st6e – do – 360 as above. ca–la. cld. 2–3 st6e the ne slope between bøllufjall and gívrufjall 436 me–th. he–me–ca. he–th. 2–3 st6e – do – 480 he–me–me*. th–ch. th–th*. 2–3 st6e – do – 500 th–th*–gy. me*–gy. 2–3 st6e the ne slope of bøllufjall 530 th–th*. th–ph, th*–ch. 1–2 st6e the summit of bøllufjall 584 as above. 1–2 st10 large quarry 0.5–1 km nw of sund, kalsbaksfjørður 15 me. me*. th. an. ph. gi. ap. 2–3 st10 exposure at sundá, 1.2 km s of sund 227 he. me. ca. 2–3 st10 – do –, 1.6 km sw of sund 265 me. th. st–he. 2–3 st10 quarry 0.5 km sw of lambafelli at the high road tórshavn–kollafjørður 340 ce–he. ce–ch–le. ce–an. ce–ch. ce–he–sm, ce–he–ch. ce–he–th–ch. 2–3 st10 road exps. 1 km w of sundshálsur along the high road tórshavn–kollafjørður 310 ce–he–me. ce–me–ch. ce–th–me. 2–3 st10 small quarry at end of road to the water reservoir of havnardalur 170 he. me. th. ch. 2–3 st10 road exposure at the road tórshavn– velbastaður, 0.5 km n of velbastaður 160 ce–me. ce–th–ch. 2–3 st10 exposure at the road tórshavn–velbastaður, just n of velbasta ur 123 me–me*. me–ch. me.th–ch. th–me– me*. cld, ca. 2–3 ey1 road exposure at the road eiði–norðskáli, 0.4–0.5 km se of eiði 60–100 ap–gy–me. me–ph. he–gy–me. he– me–ch. st–aå–sm. th–ap. th–st–ap. th–ch–sm. st–la–st*–ca. he–st– ch–sm. 3–4 ey1 localities on the road eiði–funningur: quarry in djúpidalur, 2 km east of eiði 150 st–gy. st–th–gy. th–ga–th. me–th. me–ch. st–la. 3–4 ey1 50 m long road cutting on w slope of slættaratindur, 3.5 km east of eiði 200–230 me–th*–gy. me–th*–ch. me–he–me. he–me. st–st*. la–me*–sm. he–ap. st. cld. qz. 2–3 ey1 road exposure 0.4–0.5 km e of eiðisskarð just at the n slope of vaðhorn 336–346 ce–me–th*. ce–me–ch. 2–3 ey1 the n slope of vaðhorn 410 as above. he–st–st*. mo–st. 2–3 ey1 – do – 435 as above. 2–3 ey1 small quarry at the road fork eiði, funningur, gjógv, 1 km west of funningur (165) 165 he. st. me. me*. ch. 2–4 ey1 exposure at the coast line at funningur 5–10 mo. he. st. me. +ce. st. an. me. cld. 3–4 ey2 exposure at the coast between stórá and marká 0–20 mo. he. st. st. qz. cld. ca. 3–4 ey2 the path svínár–funningur 30–40 he–me. he–st–gy. he–me–gy. 3–4 ey2 – do – 100 me–th–ch. th–gi. th–me*. an–ch. an–th–ch. th–gy–ap. me–ap–st. 2–3 ey2 – do – 212 as above. 2–3 ey2 – do – 280 me. th. an. ch. an–th*–gy. 2–3 ey2 – do – 346 an. me. me*. th. th*. th–ch–sm. 2–3 ey2 – do – 400 ce–th–th*–ch. ce–ch. th–th*–ch. 1–2 ey2 – do – 420 ch–an. ch.gi–th*. an–ph–ch. 1–2 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19150 151 profi le locality altitude (m) vesicles fractures zone ey2 kvígandalsskarð 460 me*. th*. ch. gy. sm. 1–2 ey2 – do – 480 as above. 1–2 ey2 the e slope of skerðingur 500 as above. 1–2 ey2 – do – 525 as above. 1–2 ey2 – do – 450 ce–th*. ce–me–me*–ch. 1–2 ey2 – do – 430 as above. 2–3 ey2 – do – 415 ce–an. ce–qz. cld. 2–3 ey2 – do – 380 me. 2–3 ey2 kvígandalur 363 he–me. he–th. ey2 skipagjógv 180 me–th–th*. ch–gi–th. an–th–ap–gy–sm. cl. ca. 2–3 ey2 – do – 80 he. me. th. ca. 2–3 ey2 – do – 50 gy–he. gy–th–me. 3–4 ey2 skipagjósoyran 0–10 he. st. th. la. gy. he. me–la–st. 3–4 ey3 large quarry 1 km s of oyri 20–30 me–th–sm. me–th–ch–sm. me–gy– me*. cl–he–th–ap. 2–3 ey3 oyrargjógv 100 me–th, me–gy. 2–3 ey3 – do – 210 no vesicles. he. st. me. th. gy. 2–3 ey3 the path oyri–skálafjørður 251 me. th. ch. 2–3 ey3 – do – 300 he–me. th–me. th–ch. 2–3 ey3 – do – 340 an. me*–ch. 1–2 ey3 – do – 350 me*–ch. th–th*. 1–2 ey3 – do – 400 th–st–gy. ch. st. 1–2 ey3 – do – 426 an–th*. an–th*–ca. ch. 1–2 ey3 – do – 495 th*–ch+le. 1–2 ey3 the sw slope of sandfelli 527 ce–th*–ch. ce–cld. he. me. ca. cld. 0–1 ey3 – do – 545 as above. as above. 0–1 ey3 the summit of sandfelli 572 as above. as above. 0–1 ey3 the path on the s slope of skálafjall 440 me–th. he–me. 2–3 ey3 – do – 405 as above. 2–3 ey3 – do –, just at öksnagjógv 200 as above. 2–3 ey4 small quarry just n of morskarnes, about 1 km n of nesá 20 he–th–ch. me–th. he–st. he–ap. ca. 2–3 ey4 the w slope of neshagi, just e of the locality above 140 cl–me–th. he–th. 2–3 ey4 exposure at skotá 194 as above. 2–3 ey4 – do – 230 me–me*. ch. 1–2 ey4 – do – 320 th*. me–me*. ch. he–me. he–st. 1–2 ey4 the se slope of kambur: exposure between the source of skotá and urðará 380 me*. ch, le +ce. 1–2 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19151 152 profi le locality altitude (m) vesicles fractures zone ey4 the se slope of kambur: exposure between the source of skotá and urðará 400 as above. 1–2 ey4 – do – 430 th*. ch. le. ce. 0–1 ey4 – do – 462 ch. many empty vesicles. 0–1 ey4 the path steffanstangi–kambur 480 as above. 0–1 ey4 – do – 500 th–ch–th*. cld. ca. 0–1 ey4 – do – 540 as above. 0–1 ey4 the summit of kambur (trigonometric station) 593 as above. 0–1 ey4 the e slope of heygshagi 440 me*–ch. th*–ch. 1–2 ey4 – do – 400 as above. 1–2 ey4 – do – 250 as above. 1–2 ey4 markrá 250 me–me*. he–th. he–me*. 2–3 ey4 – do – 160 as above. 2–3 ey8 road exposure at the old road lervík– fuglafjørður/norðragøta, about 2 km nw of lervík 80 ce–mo–he–me. ce–ch. he–me–st. 2–3 ey8 localities along kálvadalsá in kálvadalur 200 mo–he–me–me*. an–th–ch. le–ch–le. he–me–st–st*. an–th. 2–3 ey8 – do – 270 as above. 2–3 ey8 – do – 300 he–me*–ch. an–th*–ch. 2–3 ey8 mannsgjógv 400 an–ph–ch. an–th–ch, me*–an. 1–2 ey8 the ne slope of navirnar 300 he–me–st*. he–ch, he–le. an–he. he–st. he–me. 2–3 ey8 the e slope of ritafjall 440 he–me*–ch. an–th*–ch. 1–2 ey8 – do – 490 he–th–ch. me*–st*. 1–2 ey8 – do – 520 th–ch. me*–ch. he. st. ca. 0–1 ey8 the summit of ritafjall 560 th.ch. le. 0–1 ey8 – do – 641 th*. nearly all vesicles are empty. 0–1 ey10 large quarry just n of the road fork skálafjørður–runavík–lambi 60–80 me–st*. th–st*. th–me–an. th–ch–st*. co–th. ha. he–st*. he–th–ca. ph–ch–ph. ha–ca. 2–3 ey10 the sw slope of ritafelli, ne of the locality above 180 no vesicles. he–me–ch–sm. me*–le–ch–sm. an–me*–sm. 2–3 ey10 – do – 200 me–me*. ch. th*. ph. an–me*–sm. me*–ph– le. ap–sm. 1–2 ey10 – do – 230–240 as above. 1–2 ey10 – do – 270 he–th–ch. th*–ph. an–th*, ch–st. an–st. ap–th–ph. ca. st–la. me–ap. 1–2 ey10 the edge of ritafelli 350 st, me*. th*. ph. ch. ce. 1–2 ey10 the sw slope of stórafjall 380 th*. ch. ph. 1–2 ey10 the w edge of stórafjall 440 th. ph. ch. an. ce. an. st. ch. ph. sm. 0–1 ey10 – do – 490 empty vesicles. st, th*. ch. ca. cld. sm. 0–1 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19152 153 profi le locality altitude (m) vesicles fractures zone ey10 the w edge of stórafjall 520 th. many empty vesicles. 0–1 ey10 the summit of stórafjall 567 as above. 0–1 bo1 large quarries at klakkur 60 me–ch. he–me. cld. mo–st–la. ca–st. 2–3 bo1 the ne slope of klakkur 100 mo–an. mo–he. me–ch. ca. 2–3 bo1 – do – 140 me–th*. ga–me. ch–gi–th. as in the vesicles. 2–3 bo1 the ne slope of klakkur 160 th–me*–ph. ph–ch. he–st. ca–st. 1–2 bo1 – do – 210 mo–he–ch. ch–th. th–ph. le–ch. ca–st. 1–2 bo1 – do – 260 me–th–la. an–st–la. an–th–ch. 2–3 bo1 the summit of klakkur 414 ch–th. th–ph. 2–3 bo1 the s slope of klakkur 380 as above. 2–3 bo1 – do – 300 me–th. th*–ch. th–ph–ch. he–st–la. 2–3 bo1 – do – 260 he–me–th. he–th. 2–3 bo1 the ne slope of hálgafelli 280 ce–he–me–st. ce–me–an. 2–3 bo1 – do – 300 as above. 2–3 bo1 – do – 360 as above. 2–3 bo1 – do – 380 ce–mo–he–th. ce–he–me. 2–3 bo1 – do – 400 ce–st–ch. he–th–me–st. 2–3 bo1 – do – 450 as above. 2–3 bo1 – do – 480 an–me–me*. th–ch. 2–3 bo1 the summit of hálgafelli 503 ce–he–me. st–la. 2–3 bo2 exposure at stream 0.6 km sw of norðoyri 20–80 he. me. ch. an. ap. st. cld. ca. 2–3 bo2 the w slope of høgahædd 140 an. me. ch. many empty vesicles. as above. 1–3 bo2 – do – 220 he–st. he–ch–st. th–ph. st. ca. 2–4 bo2 – do – 270 empty vesicles. – bo2 – do – 310 he–me–me*. me–an. me–ch. 2–3 bo2 – do – 320 ch–th*–ch. he–ch.th*. an. 1–2 bo2 – do – 330 me*. th’. ch. ca. 1–2 bo2 – do – 360 as above. ch. th*. ca. 1–2 bo2 – do – 440 th*. ca. op. cld. 1–2 bo2 – do – 474 me. me*. th*. ch. 1–2 bo2 – do – 510 th–th*. ca. cld. many empty vesicles. 0–1 bo2 – do – 550 as above. 0–1 bo2 the summit of høgahædd 563 as above. 0–1 bo3 large quarry between norðdepil and depil 40–50 ce–he–th. ce–he–na–th. ce–th–ch. cl–he–st–ap. cl–th– ap. cl–ph. 2–4 bo3 depilsá 150 me–me*–ch–le. me–me*–ch. he–me. 2–3 bo3 – do – 200 me*–ch, an–ch. 1–2 bo3 – do – 300 he–me*–ch. he–th*–ch. an–ph–ch. +ce. he–st. he–th–ca. 1–2 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19153 154 profi le locality altitude (m) vesicles fractures zone bo3 depilsá 340 as above. 1–2 bo3 e slope of lokki 375 ch–gi–th’. ch–an. 0–1 bo3 – do – 400 ch–th*–ch. ch–le. 0–1 bo3 – do – 450 as above. 0–1 bo3 – do – 470 th. ch. ca. he–st–th–ca. 0–1 bo3 e slope of lokkanøv 460 ce–an–ch. ce–th–ch–th*. many empty vesicles. 0–1 bo3 – do – 580 as above. 0–1 bo3 – do – 700 as above. 0–1 bo3 the summit of lokki (trigonometric station) 754 as above. 0–1 vi1 the starting point of the profi le is the largest stream 0.5 km se of hvannasund 50 ce–me–st. ce–an–th–me. ce–me–ch. ce–he–st–me. ce–cl–st. ce–cl–me– ca. 2–3 vi1 sw slope of enni 120–132 empty vesicles. – vi1 sw slope of enni 180 mo–an. 2–3 vi1 – do – 210 an. ph–ch. an–th. me–me*. he–me– ch. he–me*–ch. he–ph– ch. he–th–me. 2–3 vi1 – do – 225 as above. 1–2 vi1 – do – 240 me*. th*. an. 1–2 vi1 – do – 270 ce–th–th*–ch. ce–ch–le. ce–an– ch. ce–ch–st. ce–he. ce–he–cld. he–st. cld. 1–2 vi1 – do – 310 ch–gi–th*. st–ch. ph–ch. th–th*. 1–2 vi1 – do – 360 ce–ch. ce–ph–ch. ce–th*. ch. 1–2 vi1 – do – 380 ch. th. le. sm. cld. 1–2 vi1 – do – 420 th*–le–ch–sm. op. sm. 0–1 vi1 – do – 550 as above. many empty vesicles. 0–1 vi1 – do – 600 ca and siderite. 0–1 vi1 the summit of enni 651 as above. 0–1 vi2 small quarry at the road hvannasund– viðareiði, 2.6 km n of hvannasund 40–80 ce–he–me. ce–he–th. ce–he– ch–sm. ce–ch–sm. ce–ph–me*. ce–me–me*. he–me–st. 2–3 vi2 w slope of tunnafjall 80–100 he–me–me*. an–th–me. an–th–ch. an–ph–ch. he–st. st–me. 2–3 vi2 – do – 150 as above. 1–2 vi2 – do – 200 as above. 1–2 vi2 – do – 225 me*. th*. ch. ph. an. he. st. ca. 1–2 vi2 – do – 250 me*. th*. ch. 1–2 vi2 – do – 300 th*. ch. 1–2 vi2 – do – 315 as above. 0–1 vi2 – do – 390 an. th’. ch. ph. me*. ph. st. 0–1 vi2 – do – 460 th*. ch. le. sm. st. sm. 0–1 vi2 – do – 520–550 empty vesicles. qz. cld. ca. 0–1 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19154 155 profi le locality altitude (m) vesicles fractures zone vi2 the summit of tunnafjall 593 th. th*. ch. 0–1 vi2 the s slope of myrnafjall 620 no vesicles. th. th*. 0–1 vi2 the summit of myrnafjall (trigonometric station) 688 th. th*. only 20% of the vesicles are mineralised. 0–1 vi3 small quarry at the road viðareiði– hvannasund, 2.5 km south of viðareiði 80 he–th*. me–me*–ch–se. as in the vesicles. 1–2 vi3 the w and the sw slope of malinsfjall 150 he–th*. me–me*–ch. an–me*–ph. 1–2 vi3 – do – 200–220 th*. ch. le. me. me*. th. th*. an. st. 0–1 vi3 – do – 255 th*. ph. an. he–st. 1–2 vi3 the w and the sw slope of malinsfjall 310 th*–ch. 0–1 vi3 – do – 300–330 me–th*. gi–ch. 0–2 vi3 – do – 440 th*. ch. about 50% of the vesicles are empty. an–st. 0–1 vi3 – do – 540 as above. 0–1 vi3 – do – 605 ch–th–le. ca. ca–th–ca. 0–1 vi3 – do – 660 all vesicles are empty. 0–1 vi3 – do – 680 as above 0–1 vi3 – do – 710 scattered mineralisations of th and ch. 0–1 vi3 the summit of malinsfjall 750 as above. 0–1 geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19155 156 max depth min depth vesicles zone lopra-1/1a –3543 –3400 la, pr, ca, cl. ht –3400 –3200 la, mo, pr, cl. ht –3200 –3000 la, mo, pr, sm, qz. ht –3000 –2800 la, pu, qz, cl. ht –2800 –2600 (no data) –2600 –2400 la, ca, pr ,cl. ht –2400 –2200 la, pr, pu. ht –2200 –2000 th, ep, he, la, pr, wa, mo, ca, ce, sm, cl, si. 5–6 –2000 –1800 sc, th, ep, he, la, an, ca, ce, cl, si. 3–5 –1800 –1600 sc, th, st, ep, la, an, ca, ce, sm, cl, si. 3–5 –1600 –1400 sc, th, st, ep, he, la, an, ca, ce, sm, si. 4–5 –1400 –1200 me, th, st, ep, he, la, ce, sm, cl, si. 4–5 –1200 –1000 me, sc, th, ep, he, la. 3–4 –1000 –800 me, sc, th, st, ep, he, la, an, ca, cl, si. 3–4 –800 –600 th, st, ep, he, la, an, cl. 3–4 –600 –400 me, sc, th, ep, he. an. ca. 2–3 –400 –200 me, sc, th, ep, he, an, ca, cl, si. 2–3 –200 0 me, sc, th, st, he, an, mo, ca, cl, si. 2–3 vestmanna-1 –600 –575 he. he–ch. 3–4 –575 –550 he. an. st–st*. ch–sm. 3–4 –550 –525 he–ch. ap. th–ap. ch–sm. 3–4 –525 –500 he. he–ac. th–ch. st–ch. –500 –475 an–th–mt. th–sm. 3–4 –475 –450 an–th–sm. th–sm. 3–4 –450 –425 gy–th–sm. an. an–th–sm. th. sm. 3–4 –425 –400 an. he–la–ch. me–ch. th–sm. ch–sm. 3–4 –400 –375 he–la–ch. me–ap–ch. me–ch+le–sm. ch–sm. 3–4 –375 –350 me. gy–th–sm. th–sm. th*–ch. ch+le. 2–4 –350 –325 ap. th–ap. gy–la. gy–th–st. ph. th*–sm. th*–ch. 1–4 –325 –300 he. he–me. he–la–ch. mo–he–ch, th*–sm. th*–ch, ch–sm. 2–4 –300 –275 he. he–ch. me–he–st. th–ga–ch. th*–ph–ch. th*–ch. ch–sm. 2–4 –275 –250 me. me–th–ch. me–th–ph–ch.. la–me. ap. th–ch–sm. ch–sm. 2–4 –250 –225 th–gy–sm. th–th*–ch. he–th–ap. le–sm. 2–4 –225 –200 –200 –175 he. he–ch–ap–sm. me–ch, th–th*– ch. th–gy–mt. th–ap. an. ap. le–sm. 2–3 –175 –150 me–he–me*. me–he–ap. me–ap. me– he–th–le. me–th–ph–ch. th*–ch –le. na–ch. ch–sm. 2–3 –150 –125 me. me–th–ph–ch. ph–sm. me*–ch an–sm. 2–3 –125 –100 –100 –75 me. me–th–ch–sm. me+na–ap–sm. me*–ch. an–ep–ch. mo–ch. th–ch. 2–3 –75 –50 he. he–th. mo–he. me–th. na–ch. th–ch. me*–ch. ch–sm. 3–4 –50 –25 ch–sm. ep–ch. 3–4 –25 0 me. me*. me–ap. me–th. me*–ch. mo–ch. 2–3 appendix b. minerals found in vesicles within different depth intervals in the lopra-1/1a and vestmanna-1 boreholes geus bulletin no 9 7 juli.pmd 07-07-2006, 14:19156 geological survey of denmark and greenland bulletin 6, 77-93 77geological survey of denmark and greenland bulletin 6, 77–93 © geus, 2004 the eleonore sø and målebjerg foreland windows, east greenland caledonides, and the demise of the ‘stockwerke’ concept a.k. higgins and a. graham leslie recognition of the eleonore sø and målebjerg foreland windows during the 1997–1998 regional mapping expeditions to the east greenland caledonides provided critical evidence for largescale, westward-directed thrusting in the kong oscar fjord region (72°–75°n), a revelation that dealt a final blow to the ‘stockwerke’ concept of an in situ highly mobile infrastructure characterised by rising fronts of caledonian migmatisation and metasomatism. this paper reviews earlier investigations in both the eleonore sø and målebjerg areas, and the misinterpretations of rock units that initially obscured recognition of their foreland affinity. the eleonore sø and målebjerg windows can now be placed in context, as part of the lowest structural level of the foreland-propagating thrust pile of the kong oscar fjord region. keywords: caledonides, east greenland, tectonic windows a.k.h., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. email: akh@geus.dk a.g.l., british geological survey, murchison house, edinburgh eh9 3la, uk. the 1300 km long east greenland caledonides (70°– 81°30′n) can be broadly divided into western marginal and eastern thick-skinned thrust belts (fig. 1; higgins & leslie 2000; higgins et al. 2001, 2004). the western thrust margin of the orogen against the caledonian foreland is largely obscured by the greenland inland ice, with the most continuous foreland exposures west of kronprins christian land in the extreme north. elsewhere foreland areas are locally preserved in the westernmost nunataks and in scattered tectonic windows exposed along the length of the marginal thrust belt (fig. 1). while the foreland windows all exhibit some disturbance due to caledonian deformation, and have therefore been classified as parautochthonous, the similarities of the successions preserved within the various windows and that in the undisturbed foreland, suggest they are only slightly displaced from their original locations (higgins et al. 2001). prior to the survey’s 1997–1998 regional mapping programme, large-scale thrusting had not been demonstrated in the kong oscar fjord region (fig. 2; 72°–75°n). indeed, new investigations in this region (hartz & andresen 1995; andresen & hartz 1998; andresen et al. 1998), had led to interpretations of caledonian orogenesis in terms of upward and lateral movement of light, low viscosity, lower crustal material towards the region of maximum crustal extension, a process compared to haller’s (1953, 1970, 1971) ‘stockwerke’ concept, and that carried the implication that orogenic contraction was negligible. the recognition of the målebjerg and eleonore sø foreland windows during the survey’s 1997–1998 regional mapping provided incontrovertible evidence for large-scale westward-directed caledonian thrusting in the kong oscar fjord region (figs 2, 3). this discovery completely undermined arguments for explaining orogenic development in terms of the in situ ‘stockwerke’ concept or similar processes, and at the same time resolved a number of outstanding problems of east greenland geology. the areas of both geus bulletin 6.pmd 10-02-2005, 09:5477 78 ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ c a l e d o n id e s greenland 70°n 74°n 78°n 82°w 35°w wandel sea centrumsø 100 km jameson land scoresby sund 25°w traill ø wollaston forland bessel fjord danmarkshavn lambert land peary land station nord k ro np rin s c hr ist ian l an d nørreland window kronprins christian land thin-skinned thrust belt (parautochthonous foreland) palaeogene basalts palaeogene intrusions wandel sea basin: carboniferous–palaeogene sediments east greenland basins: carboniferous–cretaceous sediments devonian – continental sediments late to post-kinematic granites neoproterozoic–ordovician sediments (east greenland) neoproterozoic–silurian sediments (eastern north greenland) palaeo-mesoproterozoic sediments and basalts (eastern north greenland) crystalline complexes and sediments (archaean–mesoproterozoic) neoproterozoic–silurian sediments (north greenland) palaeo-mesoproterozoic sediments and basalts (eastern north greenland) mainly crystalline rocks – parautochthonous windows thrust fault/shear zone tectonic zone boundary post-caledonian late to post-caledonian caledonian orogenic belt caledonian foreland ▲ ▲ fig. 2 målebjerg window gåseland window c a le d o n ia n so le t h r u st in la n d ic e t h r u s t b e l t t h ic k s k in n e d t h r u s t b e l t charcot land window eleonore sø window hamberg gletscher foreland dronning louise land ▲ ▲ ▲ m a r g in a l fig. 1. geological map of the east greenland caledonides, showing location of the foreland windows in the western marginal thrust belt. the frame indicates the region between 71°50′ and 74°30′n, shown at a larger scale in fig. 2, which includes the målebjerg and eleonore sø windows. modified from higgins & leslie (2000). geus bulletin 6.pmd 10-02-2005, 09:5478 79 ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i ▲ ▲ ▲ ▲ ▲ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ fjd eleonore sø window hamberg gletscher foreland målebjerg window charcot land window nathorst land hudson land ella ø suess land lbl pd p andrée land lyell land fr f stauning alper kong oscar fjord kfjf es ml m cecilia nunatak fig 3 fjd neoproterozoic–ordovician post-caledonian caledonian granite 930 ma granite palaeoproterozoic–ordovician krummedal sequence krummedal sequence palaeoproterozoic orthogneiss archaean–palaeoproterozoic orthogneiss ▲ ▲ ▲ ▲ franz joseph allochthon foreland hagar bjerg thrust sheet niggli spids thrust sheet detachment extensional fault thrust cross-section line ▲ ▲ i i ■ ■ ■ ■ 72°72° 73° 74° 27° 100 km fig. 2. geological map of north-east greenland 71°50′– 74°30′n, showing location of the eleonore sø, målebjerg and charcot land windows, and the hamberg gletscher foreland. the legend depicts the units contained in the two thrust sheets and franz joseph allochthon overlying the windows. the målebjerg and eleonore sø areas are shown in more detail in figs 5 and 6. es, eleonore sø; fjd, franz joseph detachment; frf, fjord region fault; kfjf, kejser franz joseph fjord; lbl, louise boyd land; m, målebjerg; ml, j.l. mowinckel land; p, petermann bjerg; pd, petermann detachment. the line of the cross-section shown in fig. 3 is indicated. geus bulletin 6.pmd 10-02-2005, 09:5479 80 windows had been investigated prior to the survey’s regional mapping, the eleonore sø area by katz (1952) and the målebjerg area in andrée land by haller (1953). however, while haller (1971) had speculated that the eleonore sø region might be a window (see below), neither katz nor haller identified the lower palaeozoic rock units whose presence clarifies the structural setting beyond any doubt. this paper reviews the history of investigations in the eleonore sø and målebjerg areas, and the early misinterpretations of rock units that obscured their recognition as parts of the caledonian foreland. these misinterpretations were closely linked to the evolution of ideas to explain orogenic developments in east greenland, that culminated in the ‘stockwerke’ concept as elaborated by haller (1970, 1971). haller’s ‘stockwerke’ model was a development of the earlier ideas of backlund (1930, 1933) and wegmann (1935). the crystalline gneiss complexes constituting the central metamorphic complex that underlie, and appear to be interleaved with high grade metasediments, were envisaged by haller as elements of a highly mobile infrastructure formed by the rise of caledonian fronts of migmatisation and metasomatism. associated mechanical and chemical changes were thought to have led to in situ transformation of a succession of sedimentary rocks into the gneissic and granitic rocks of the infrastructure, which was considered ‘entirely rejuvenated’. the mobile migmatite domes of the infrastructure were bordered by and overlain by the more rigid sedimentary suprastructure, with the two levels separated by a thick, often strongly folded, ‘zone of detachment’. the term ‘stockwerke’ refers to the different levels of the growing orogenic belt; in german ‘stockwerke’ refers to the floors or stories of a house. in haller’s map compilations the infrastructure of the central metamorphic complex is depicted as caledonian synorogenic granite (koch & haller 1971), and he remarks that regional thrusting was probably of “no importance in their formation” (haller 1971, p. 179). the spectacular ‘stockwerke’ structures in east greenland, and haller’s drawings, are still presented in modern textbooks (e.g. best 2003) as classic examples of mantled gneiss domes, and metamorphic core complexes. the målebjerg and eleonore sø windows can now be placed in their correct context as parts of the lowest structural level of the foreland-propagating thrust pile in the southern half of the caledonian orogen (70°–75°n; elvevold et al. 2000; higgins et al. 2004). these foreland windows are structurally overlain by a lower niggli spids thrust sheet and an upper hagar bjerg thrust sheet, both with substantial westward displacements (fig. 3). the very thick neoproterozoic to lower palaeozoic succession (eleonore bay supergroup, tillite group, kong oscar fjord group) is distinguished as the franz joseph allochthon, and viewed as an upper detached part of the hagar bjerg thrust sheet. hamberg gletscher foreland boyd bastion fault eleonore sø window målebjerg window fjord region fault 10 km ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ■ ■ ■ ■ ■ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ■ ■ caledonian granite 930 ma granite neoproterozoic–ordovician krummedal sequence krummedal sequence palaeoproterozoic orthogneiss archaean–palaeoproterozoic neoproterozoic–ordovician palaeoproterozoic ▲ ▲ ▲ ▲ ▲ ▲ ■ ■ extensional fault detachment thrust ■ ■ franz joseph allochthon   foreland       hagar bjerg thrust sheet    niggli spids thrust sheet fig. 3. cross-section through the eleonore sø and målebjerg windows showing the foreland windows overlain by two thrust sheets and the franz joseph allochthon. section line is indicated on fig. 2. geus bulletin 6.pmd 10-02-2005, 09:5480 81 geological setting the eleonore sø and målebjerg windows (figs 2, 3) are characterised by thin (< 400 m) neoproterozoic – lower palaeozoic sedimentary successions. the latter comprise a lens-like 31 m thick diamictite in the målebjerg window correlated with the vendian tillite group, a 143–350 m thick quartzite sequence with skolithos ichnofossils of early cambrian age defined as the slottet formation, and a 32–45 m thick dolomite sequence of cambrian–ordovician age defined as the målebjerg formation (smith et al. 2004, this volume). this thin vendian–ordovician foreland succession is in great contrast to the 18.5 km thick, partly equivalent succession, preserved in the structurally overlying franz joseph allochthon. in the eleonore sø window the slottet formation overlies a palaeoproterozoic sedimentary-volcanic assemblage with profound unconformity, and in the målebjerg window unconformably overlies gneisses of presumed palaeoproterozoic age. the niggli spids thrust sheet structurally overlying both windows (fig. 3) incorporates crystalline gneiss complexes and high-grade metasedimentary successions, which were reworked to varying degrees during caledonian orogenesis. ion microprobe studies on zircons from the orthogneisses have yielded archaean and palaeoproterozoic protolith ages (thrane 2002; unpublished data 2004, f. kalsbeek and a.p. nutman), that confirm earlier less precise isotopic ages by other methods (e.g. rex & gledhill 1981). the highgrade metasedimentary rocks of both the niggli spids thrust sheet and the higher hagar bjerg thrust sheets are correlated with the krummedal supracrustal sequence (higgins 1988). the krummedal sequence metasedimentary rocks in the hagar bjerg thrust sheet host a suite of 940–910 ma augen granites generated during an early neoproterozoic thermal event (kalsbeek et al. 2000; watt et al. 2000; watt & thrane 2001). ion microprobe studies of detrital zircons from the krummedal sequence show the youngest detrital zircons are about 1050 ma old, and deposition of the sediments must therefore have taken place in the period c. 1050–940 ma ago (late mesoproterozoic – early neoproterozoic). high-grade regional metamorphism and associated anatexis during the caledonian orogeny led to generation of a new suite of 440–425 ma granites (watt et al. 2000; hartz et al. 2001; kalsbeek et al. 2001a, b). the franz joseph allochthon is made up of the c. 13 km thick neoproterozoic eleonore bay supergroup (riphean–sturtian; post-900 to c. 590 ma), the 800– 1000 m thick vendian tillite group (hambrey & spencer 1987), and the c. 4 km thick cambrian–ordovician kong oscar fjord group (cowie & adams 1957; smith & bjerreskov 1994; smith et al. 2004, this volume). this succession is widely exposed in the central fjord system of the kong oscar fjord region, and also occurs in a more restricted area to the west in louise boyd land and around petermann bjerg (fig. 2). the contact between the eleonore bay supergroup and underlying high-grade krummedal metasediments of the hagar bjerg thrust sheet is a shear zone, in which both extensional and contractional strain have been recorded. in the west the shear zone is known as the petermann detachment (pd, fig. 2; escher & jones 1998, 1999), and in the east the franz joseph detachment (fjd, fig. 2). the latter is only well exposed between northern andrée land and hudson land (leslie & higgins 1998, 1999), and between lyell land and the stauning alper (cf. tindern detachment of white et al. 2002). in most of the fjord region the present-day west limit of the eleonore bay supergroup outcrop is a late-orogenic extensional fault, the ‘fjord region fault’ of this paper (frf, fig. 2). this corresponds to the ‘fjord zone fault’ of larsen & bengaard (1991) and to part of the ‘fjord region detachment’ system of hartz & andresen (1995) and co-workers (andresen et al. 1998; hartz et al. 2000; white et al. 2002). conodonts extracted from the uppermost levels of the ordovician succession exhibit very low conodont alteration indices (smith 1991; stouge et al. 2002), which demonstrate that the franz joseph allochthon in this region cannot have been over-ridden by higher thrust sheets. historical review: the målebjerg and eleonore sø areas the investigations of john haller and others working with lauge koch’s long series of east greenland geological expeditions (1926–1958) more than 40 years ago, essentially predated the era of isotopic age determinations. the first, very few, k-ar ages from east greenland only became available in 1961 (haller & kulp 1962), after the cessation of field work in 1958. the evolution of ideas and the conclusions of their studies were thus almost entirely based on field observations and interpretations. the revolutionary concept of plate tectonics did not make its mark until the late 1960s, and while it was widely accepted by many geus bulletin 6.pmd 10-02-2005, 09:5481 82 geologists, john haller considered that its enthusiastic reception had obscured its shortcomings (see haller 1979). lauge koch’s sledge journeys along the length of the caledonian orogen led him to propose that the greater part of the gneisses that previous expeditions assumed to be archaean were “in reality the nucleus of a caledonian folding range” (koch 1929, p. 60, fig. 20). however, at this time the gneisses of the inner fjords between scoresby sund and kejser franz joseph fjord were still considered to be archaean. meanwhile, british geologists working in the inner part of the kong oscar fjord region compared the gneisses and metasedimentary rocks of the so called ‘central metamorphic complex’ to the lewisian and dalradian of scotland, and concluded that the caledonian orogeny was ‘superficial’ (wordie 1930; parkinson & whittard 1931). helge backlund investigated the same region, but reached a different interpretation (backlund 1930, 1932). he proposed that wordie’s ‘archaean’ granites and gneisses were the result of caledonian granitisation and migmatisation of a varied sedimentary succession, similar to the processes of gneiss formation in fennoscandia. backlund’s views were largely supported by wegmann’s (1935) report on the ‘caledonian orogeny’, in which wegmann speculated that any former basement to the caledonian geosyncline (greenlandian) would have been transformed to such a degree as to be unrecognisable (see also reviews of early work in haller 1971, pp. 6–35). up to 1950 no outcrops of the caledonian foreland had been recognised in east greenland. however, the period 1952–1961 saw the discovery and description of foreland areas in kronprins christian land in the north (fränkl 1954, 1955), in dronning louise land (peacock 1956, 1958), and in western gåseland in the south (wenk 1961; see fig. 1). all of these discoveries were incorporated into haller’s major reviews and map compilations of the east greenland caledonides (haller 1970, 1971, 1983; koch & haller 1971). the area around målebjerg (73°27′n) was first mapped by john haller in 1949–1950 as part of a regional investigation of western andrée land (haller 1953): it was a key area for his development of the ‘stockwerke’ models of the caledonian orogeny. on the basis of his studies in andrée land, haller reached wide-ranging conclusions as to the nature of the caledonian orogeny, elaborating on the earlier interpretations of backlund (1930, 1932) and wegmann (1935). thus haller (1953) stated in his english summary (p. 190) that: “the dispute as to the age of the ‘central metamorphic complex’ is, as far as the region of kejser franz josephs fjord is concerned, finally resolved by the present study, which shows that several stratigraphic subdivisions, recognised in the eleonore bay formation, can be traced also in the gneisses, schists and marbles of the ‘central metamorphic complex’. the crystalline rocks of sedimentary origin represent members of the groenlandium, metamorphosed and metasomatically altered during the caledonian orogeny.” with respect to the area around målebjerg, he correlated the distinctive quartzites and dolomites found there with fränkl’s (1951) ‘alpefjord series’, i.e. the lower levels of the eleonore bay ‘formation’ (haller 1953). the ‘groenlandium’ (also spelt grönlandium, groenlandian or greenlandian) is a now obsolete term that originally encompassed all proterozoic sedimentary (and metasedimentary) rocks of north and east greenland (koch 1930). within the caledonides of east greenland it was considered to be made up entirely of the eleonore bay ‘formation’ and equivalents. thus, haller envisaged the sedimentary rocks of the present-day målebjerg window, together with those of the structurally overlying niggli spids and hagar bjerg thrust sheets and franz joseph allochthon, to form parts of a single stratigraphical succession. the gneisses, which he viewed originally as synorogenic granites, formed parts of the mobilised infrastructure (see below). this basic interpretation remained essentially unchanged in haller’s detailed studies of nearby areas (wenk & haller 1953; haller 1955), and was only slightly modified in his later regional descriptions (haller 1970, 1971, 1983; koch & haller 1971). haller’s early observations in the crystalline rocks of the inner fjords and nunatak region (haller 1953, 1955, 1956; wenk & haller 1953), and those of his coworkers, were all interpreted within the context of the ‘stockwerke’ concept. a series of categorical statements in their published descriptions appear to be aimed particularly at countering the interpretations of british geologists. thus they stated: “the archaean basement of the upper algonkian-ordovician series of deposits has hitherto not been found anywhere in central east greenland” (haller 1956, p. 160); “the geologists participating in the investigations agree that the base of the eleonore bay group is not to be found within the central zone of the caledonides” (wenk 1961, p. 8); “the granitic and migmatitic infrastructure, in its present state of preservation, is not older, but younger, than the pre-cambrian sedimentary cover. geus bulletin 6.pmd 10-02-2005, 09:5482 83 the ascent of the granitic solutions, and associated thermal fronts, represented the most important act of the east greenland orogeny” (wenk & haller 1953, p. 32–33). however, within a few years these early interpretations were modified significantly, with recognition that a ‘basement’ to the metasedimentary rocks was in fact recognisable: “inside the caledonian domain, rock units which were originally from the ancient basement, represent substantial ingredients of the fold belt” (haller & kulp 1962, p. 18). the basement gneiss complexes were, nevertheless, considered to have been petrogenetically rejuvenated over large areas, and were assigned a caledonian age. a sketch map by haller (haller & kulp 1962, fig. 3b; haller 1971, fig. 15b) shows that the ‘niggli spids dome’ and ‘gletscherland migmatite complex’ (two of the units of the ‘central metamorphic complex’), were now to be considered caledonian reworked precambrian basement rocks. however, in respect of the nappe-like convolutions of the so called ‘hagar migmatite sheet’, an entirely caledonian origin was still envisaged. in his description of these nappelike migmatite sheets haller 1971 (p. 179) writes: “they are asymmetrical and have considerable overlaps of up to 25 km. regional thrusting is probably of no importance in their formation.” this is essentially a re-statement of the earlier conclusion of wenk & haller (1953, p. 32): “we cannot believe that these structures are due to far-reaching tectonic transport, produced by tangential compression. their mode of occurrence, especially their diapir-like character, indicates that we are here dealing with mobile masses of the infrastructure, which have ascended and intruded into the covering sedimentary series.” many of the essential principles of the ‘stockwerke’ interpretation of the east greenland caledonides were maintained in haller’s later publications (haller 1971, 1983). haller does express regret, however, that the term ‘synorogenic granite’ had been retained on his maps for the central metamorphic complex gneisses (koch & haller 1971), because it was at variance with the modified views given by haller & kulp (1962) and had thus been misunderstood by many workers. the assumption that all metasedimentary rocks in the southern part of the caledonides were parts of the eleonore bay ‘formation’ or ‘group’ (promoted to a ‘supergroup’ by sønderholm & tirsgaard 1993) was retained in haller’s latest publications (1971, 1983). it was not until the 1968–1972 expeditions by the former geological survey of greenland (ggu) to the scoresby sund region that suspicions grew that the widespread high-grade and often migmatitic metasedimentary rocks might be significantly older than the distinctive succession now known as the eleonore bay supergroup. rb-sr whole rock isochrons and u-pb bulk zircon determinations indicated that some granites emplaced into the metasediments were approximately 1000 ma old (hansen et al. 1978; steiger et al. 1979; rex & gledhill 1981). these presumed older metasedimentary rocks, cut by the c. 1000 ma granite suite, were therefore distinguished as the krummedal supracrustal sequence (e.g. henriksen & higgins 1969; higgins 1974, 1988). convincing proof that the krummedal sequence metasedimentary rocks had experienced an early neoproterozoic thermal event (940– 910 ma) not seen in the eleonore bay supergroup had to await the advent of sophisticated modern geochronology, notably ion microprobe age determinations on individual zircon grains (strachan et al. 1995; jepsen & kalsbeek 1998; kalsbeek et al. 2000; watt et al. 2000; leslie & nutman 2000, 2003). in the mid-1970s a number of reconnaissance investigations were carried out in the general kong oscar fjord region. these extended the general conclusions of the 1968–1972 investigations in the scoresby sund region northwards. the widespread mediumto highgrade metasedimentary successions in the kong oscar fjord region were correlated with the krummedal supracrustal sequence (higgins 1988), and rb-sr whole rock isochrons on the underlying gneisses yielded palaeoproterozoic ages (rex & gledhill 1981). two further important observations were made: (1) the distinctive quartzite in the målebjerg window was mapped in 1976 as resting unconformably on the gneissic basement (tage thyrsted in higgins et al. 1981, fig. 8), and (2) during a survey reconnaissance helicopter flight to the eleonore sø region, it was recorded that the base of the ‘slottet quartzite’ at one locality was an unconformity with a basal conglomerate, rather than the supposed thrust. unfortunately, the regional significance of these observations was not appreciated at the time. målebjerg the målebjerg area was a significant location for haller’s ‘stockwerke’ interpretation, in particular for the magnificent exposures of what was described as the ‘zone of detachment’ between the mobile granitic infrastructure and the more rigid metasedimentary superstructure (haller 1971, photograph 47, p. 138; geus bulletin 6.pmd 10-02-2005, 09:5483 84 see also fig. 4). haller mapped the main lithological units in the målebjerg area including the white quartzite now distinguished as the slottet formation, and recognised that they occupied an anticlinal structure (haller 1953, 1970). he observed that the intensity of metamorphism was weaker than elsewhere and that the stratigraphy was well preserved, but he referred this quartzite and nearby marble units to the ‘basal series’ of the eleonore bay ‘group’ (haller 1971, p. 86). haller’s geological and structural maps of the area around målebjerg show several features marked with thrust symbols, some of which have no obvious significance and appear to be photogeological interpretations, while others can be identified with major structures. the most prominent structure on his maps corresponds to the nw–se-trending, ne-dipping thrust that crosses gemmedal (fig. 5), a major feature now identified as the hagar bjerg thrust at the base of the hagar bjerg thrust sheet. haller’s ‘zone of detachment’ in the cliff of målebjerg is not marked with a thrust symbol on his maps, but the folded quartzites of his ‘zone of detachment’ lie immediately beneath the niggli spids thrust of current usage (nst in fig. 4). there is no evidence that haller considered the målebjerg area to be a foreland window or that he suspected the presence of lower palaeozoic sediments. however, he was aware that a “detailed exploration of this key locality is still lacking” (haller 1971, p. 86), and there is reason to believe that such exploration would have been carried out if lauge koch’s expeditions had not been brought to an unexpected close after 1958. as noted above, reconnaissance investigations in the målebjerg area in 1976 led to recognition of an unconformity at the base of the c. 200 m thick quartzite, with a distinctly diverging foliation in the underlying basement gneisses (t. thyrsted in higgins et al. 1981, fig. 8). detailed studies in 1997–1998 by leslie & higgins (1998) established the presence of a significant foreland window (fig. 5). key observations included: (1) the presence of a local diamictite in depressions in the peneplained gneiss surface, now correlated with the diamictites of the vendian tillite group; (2) a skolithos-bearing quartzite (the early cambrian slottet formation) unconformably overlying the gneisses and the diamictite; (3) a lower palaeozoic fig. 4. the west face of målebjerg in western andrée land (for location see fig. 5). light coloured folded quartzites (< 200 m thick) of the slottet formation (sf) unconformably overlie grey gneisses (g) that are probably of palaeoproterozoic age. the unconformity is strongly folded. a few metres of grey dolomite (målebjerg formation) occur immediately beneath the niggli spids thrust (nst). overlying units of the niggli spids thrust sheet are dominated by massive mica schists with pale coloured carbonate-rich units (krummedal supracrustal sequence). the summit of målebjerg at right is 1873 m high, about 1500 m above the glacier surface in the foreground. geus bulletin 6.pmd 10-02-2005, 09:5484 85 dolomite unit (målebjerg formation) above the slottet formation quartzite; (4) a major thrust at the top of the målebjerg formation (niggli spids thrust). these observations were confirmed by smith & robertson (1999), who made additional detailed observations and measured sections in the diamictite unit (interpreted as a tillite), and in the slottet and målebjerg formations (smith et al. 2004, this volume). eleonore sø investigation of the western nunatak region between 72° and 75°n was for many years limited to the traverse of the eleonore sø area by hans katz in 1951 (katz 1952, 1953), traverses by eduard wenk and john haller west and south of petermann bjerg in 1951 and 1953 (wenk & haller 1953; haller 1956), and extensive aerial reconnaissance by john haller. cautious statements about what might be present in this vast nunatak area thus amounted to speculation on the basis of very limited ground information. reviewing the possibilities subsequent to the discovery of the caledonian foreland areas in dronning louise land (76°n; peacock 1956, 1958) and in gåseland (70°n; wenk 1961), haller (1971, p. 195–196) suggested that the thrusts around the gåseland window (70°n) and near charcot land (72°n; vogt 1965) had only modest displacements (20 km and < 1 km, respectively). recording that no further outcrops of the foreland were known, he further speculated (haller 1971, p. 218): “considering the structure pattern hitherto obtained from this poorly exposed and little known nunatak region, i would not be surprised if future investigators were able to trace relics of early caledonian overthrust tectonics, on which the present pattern of main folding was then superimposed.” he continues: “however, the main caledonian structures displayed in the wellexplored fjord region are definitely not far travelled; on the contrary, they appear to be autochthonous, initiated and caused by the rise of the migmatite front resulting in a ‘stockwerk’ folded belt.” on the basis of his 1951 traverse of the eleonore sø region, katz had observed that the low grade sedimentary rocks at eleonore sø “are of the same type as those of the eleonore bay formation of the fjord zone” ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ målebjerg ge mm ed al g erard de g eer g letscher thrust thrust krummedal metasediments (mesoproterozoic) krummedal metasediments (mesoproterozoic) carbonate (krummedal sequence) målebjerg and slottet formations orthogneiss (palaeoproterozoic) orthogneiss (palaeoproterozoic) orthogneiss (palaeoproterozoic) granite 930 ma or caledonian ▲ ▲ ▲ ▲ h ag ar b je rg th ru st sh ee t n ig gl i s pi ds th ru st sh ee t m ål eb je rg fo re la nd w in do w 5 km 73 30' 27 fig. 5. geological map of the målebjerg area, after maps and interpretations of leslie & higgins (1998, 1999). legend below figure illustrates the new thrust terminology. geus bulletin 6.pmd 10-02-2005, 09:5485 86 fig. 6. geological maps of the eleonore sø area, at the same scale but with slightly different topographic bases. a: redrawn after maps and interpretations of katz (1952), haller (1970, 1971) and koch & haller (1971). note legend below figure assigns all sediments and metasedimentary rocks to the eleonore bay ‘group’. b: redrawn after maps and interpretations of leslie & higgins (1998, 1999), using a modern topographic base. legend at top left distinguishes foreland lithologies from allochthonous thrust units. ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ i i i i i i i i i i i i i i i i i i i i i i i i i i ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ 74° 74° 28° 28° arnold escher land arnold escher land harald grieg fjelde harald grieg fjelde slottet slottet wilkins nunatakker j.l. mowinckel land j.l. mowinckel land wilkins nunatakker louise boyd landlouise boyd l a nd a b eleonore sø pa la eo pr o te ro zo ic fo re la nd w in do w a llo ch th o no us th ru st u ni ts el eo no re b ay ‘g ro up ’ ▲ ▲ palaeogene basalt caledonian granite unconformity caledonian ophiolite (greenstone) caledonian reactivated gneissb as al s er ie s metasediments argillaceous–arenaceous shale carbonate slottet quartzite fault, tick on downthrow side thrust palaeogene basalt caledonian granite unconformity eleonore bay supergroup krummedal metaseds. (mesoproterozoic) orthogneiss (palaeoproterozoic) målebjerg and slottet formations carbonate and shale metavolcanics granite gneiss ▲ ▲ i i 25 km ha m be rg gl et sc he r ha mb er g g let sc he r geus bulletin 6.pmd 10-02-2005, 09:5486 87 (katz 1953, p. 12). the associated volcanic rocks were interpreted as ophiolitic intrusions and of the same age as the tillites of the fjord zone. while katz correctly depicted a thrust at the west side of harald grieg fjelde (fig. 6a), he considered it to be of devonian age (this thrust corresponds to the major thrust contact on the east side of the window above the målebjerg formation dolomites; fig. 6b). the map in katz (1953) also shows a continuous thrust contact at the base of his ‘slottet quartzite’ (fig. 6a), with the internal structure of the quartzite depicted on his crosssections (katz 1953, tafel 4) as discordant to the ‘thrust’ at the base. it was katz’s interpretation of this prominent quartzite unit as equivalent to the lower part of the eleonore bay ‘formation’ that led him to introduce the basal thrust, because the quartzite lay structurally above the sedimentary rocks he viewed as correlateable with the upper part of the eleonore bay ‘formation’. katz’s cross-section of the eleonore sø region (1953, tafel 4) does indicate tectonic contacts at both margins of the present window, but his preferred interpretation was that the rock units occupied a graben. based on the work of katz, haller initially agreed with katz’s interpretation that the eleonore sø sediments, which from aerial observations he had traced southwards through j.l. mowinckel land to hamberg gletscher, occupied a large post-caledonian graben structure (haller 1956, p. 161). most geologists that have worked in east greenland have come across the widespread and often large erratic blocks of skolithosbearing quartzites, and haller (1971, fig. 48) had plotted observations of these quartzites, and inferred that the source areas lay beneath the inland ice. however, he clearly did not make any link between the skolithos erratic boulders and the ‘slottet quartzite’ of katz (1952, 1953), since he placed this latter unit in his ‘basal series’ of the eleonore bay ‘formation’. summarising the situation at eleonore sø, haller writes of the nonmetamorphic dolomites and quartzites at eleonore sø as being associated with greenschists that katz had interpreted as caledonian ophiolites. he notes that the region in which the outcrops are found is bounded on both sides by tectonic lineaments, and he writes (haller 1971, p. 86–87) “it is open to question whether we are concerned here with parts of the overridden caledonian foreland, similar to the gaaseland ‘window’, or not.” the structures distinguished by haller (1970, 1971) in the vicinity of eleonore sø compared to those mapped by leslie & higgins (1998, 1999) are shown in fig. 6. the only thrust correctly depicted by haller, who here followed the usage of katz (1952), is the east-dipping structure on the east side of the window at harald grieg fjelde. at this locality, high-grade metasedimentary rocks in the hanging wall lie structurally above low-grade carbonates and quartzites in the foot wall. in view of the difficulties of access to the region in the 1950s, and the lack of isotopic age determinations, it is not surprising that the ages attributed to the rock units in the eleonore sø region by katz and haller have since proved to be incorrect. however, the thrust that marks the west side of the window is depicted on haller’s maps as a major normal fault, whereas the other thrusts shown on haller’s interpretation (fig. 6a) correspond to the unconformity at the base of the ‘slottet quartzite’, the presentday slottet formation. it is, perhaps, surprising that katz did not apparently examine the base of the quartzite unit, which is an obvious unconformity in the field, and often has a basal conglomerate. his erroneous interpretation of this unconformity as a thrust contact does give the impression of an arched thrust on haller’s structural maps (e.g. haller 1971, fig. 58), and has been taken by some authors as evidence that haller ‘discovered’ the window (cf. hartz et al. 2001). however, as noted above, haller (1971) considered it “open to question”. only a few geologists have visited the eleonore sø region since katz’s 1951 visit, but it was not until the survey’s 1997–1998 regional mapping expedition that detailed field studies led to the regional delineation of the basal unconformity of the ‘slottet quartzite’. the authors of this article retraced one of katz’s traverses eastwards towards harald grieg fjelde, and observed that the basal contact of the quartzite was in fact conformable to the bedding within the quartzite rather than discordant as in katz’s profiles (katz 1952). the quartzites were observed to contain well-preserved sedimentary structures, and the first in situ finds of skolithos were found just west of the thrust at harald grieg fjelde. the unconformity surface, subsequently studied at several localities, proved to be a clean undisturbed contact (fig. 7) with a basal conglomerate up to 1.5 m thick often present. in nearly every section of the quartzites examined, in situ long skolithos burrows were observed, and these demonstrate that the sequence now termed the slottet formation (smith et al. 2004, this volume) is of lower cambrian age (crimes 1992). a cambrian–ordovician age can therefore be assumed for the thin dolomite sequence of the målebjerg formation, which conformably overlies geus bulletin 6.pmd 10-02-2005, 09:5487 88 the slottet formation and immediately underlies the thrust (leslie & higgins 1998, 1999; smith et al. 2004, this volume). on the west side of the window, the west-dipping thrust contact is well exposed and associated with thick developments of mylonites. a clear definition of the entire thrust system bordering the window was established for the first time during the 1997–1998 mapping (fig. 6b). finds of low grade volcanic rocks in eastern j.l. mowinckel land have extended the known distribution of their occurrence considerably, such that the eastern marginal thrust of the window can now be placed parallel to the glacier to the east of j.l. mowinckel land. exposures of characteristic rock types (low-grade volcanic rocks and skolithos-bearing quartzites) observed as far north as nunataks at 74°25′n (fig. 6b) show that the nne– ssw extent of the eleonore sø window is at least 125 km. the volcanic succession (pillow lavas and tuffs) and associated sedimentary rocks (thick dolomites and dolomite breccias, sandstones and shales) that are unconformably overlain by the slottet formation quartzites are intruded locally by quartz porphyry bodies, dated by shrimp analyses of zircon to c. 1950 ma (f. kalsbeek, personal communication 2000). the eleonore sø volcano-sedimentary rocks are thus palaeoproterozoic or older in age, and can be broadly compared with the volcano-sedimentary rocks of the charcot land window at c. 72°n and the foreland exposures of the hamberg gletscher complex (volcanic rocks and associated gabbros) at c. 73°n (fig. 1; higgins et al. 2001). discussion the exceptional exposures in the extensive fjord system and nunataks of the kong oscar fjord region (72°– 75°n), and the long series of geological expeditions led by lauge koch (1926–1958), have deservedly led to recognition of the east greenland caledonides as a spectacular example of an orogenic belt. this is in large part a tribute to the superb compilations of data presented by john haller (haller 1970, 1971; koch & haller 1971). development of new models for the east greenland caledonides, to replace the ‘stockwerke’ concept, has been a gradual process extending over a period of some 30 years (1968–1998), during which the entire 1300 km length of the orogen has been remapped as part of the survey’s regional 1:500 000 mapping project. during this extended period of refig. 7. the nunatak slottet in the eleonore sø window, looking northwards. the white (lower) and dark (upper) quartzites of the lower cambrian slottet formation (sf: 350 m thick) rest unconformably on dark coloured palaeoproterozoic clastic sediments of the eleonore sø volcano-sedimentary complex (es). the highest summit of slottet is 1933 m high, about 600 m above the glacier surface. geus bulletin 6.pmd 10-02-2005, 09:5488 89 search, most of the assumptions built into haller’s (1970, 1971) ‘stockwerke’ concept of an in situ caledonian orogenic belt have been queried or refuted, and the new interpretations confirmed by increasingly sophisticated isotopic age determinations. prior to the survey’s 1997–98 expeditions the existence of far-travelled thrust sheets had not been demonstrated in the kong oscar fjord region. with discovery of the eleonore sø and målebjerg windows, and distinction of a thrust pile with hundreds of kilometres of west-north-west thrust displacement (henriksen 1998, 1999; leslie & higgins 1998, 1999; elvevold et al. 2000; higgins et al. 2004), the ‘stockwerke’ concept of in situ caledonian orogenesis can finally be pronounced dead and laid to rest. restoration of the thrust sheets to their approximate original locations implies that the focus of caledonian orogenesis, i.e. the collision of laurentia with baltica, took place several hundred kilometres east-south-east of the orogenic belt now preserved onshore in east greenland. wordie (1930) and parkinson & whittard (1931) were, in fact, partly correct when they compared the crystalline gneisses of the inner fjord region of east greenland to the archaean lewisian gneisses of scotland. the former have yielded archaean and proterozoic protolith ages, with archaean gneiss complexes extending throughout the inner part of the scoresby sund region and northwards to southern suess land (72°50′n). farther north the orthogneisses have yielded palaeoproterozoic protolith ages which relate to an important episode of regional palaeoproterozoic crustformation well documented throughout the northern half of the east greenland caledonides (kalsbeek et al. 1993, 1999). it follows that haller (1953) was wrong in attributing the formation of the orthogneisses to rising fronts of caledonian migmatisation that transformed metasedimentary rocks of the eleonore bay ‘formation’. haller’s later re-interpretation of these gneisses as caledonian reworked basement rocks was close to the present-day interpretation (haller & kulp 1962; haller 1971). john haller was of swiss nationality, educated in switzerland, and obviously familiar with the major thrusts and fold nappes of the alpine orogenic belt. his earliest 1949–1951 studies in east greenland were in andrée land (haller 1953), and his main conclusions were presented as a confirmation and elaboration of the interpretations of h.g. backlund and c.e. wegmann. he was already committed to the idea of widespread transformation of a single metasedimentary succession (eleonore bay ‘group’) by the vertical rise of mobile migmatitic bodies, a view that was developed during his subsequent field work, and elegantly presented as the ‘stockwerke’ concept (haller 1970, 1971). haller’s wide-ranging observations on the ground and from the air, and katz’s observations around eleonore sø, were all interpreted within the context of the basic ‘stockwerke’ model. thus the palaeoproterozoic volcano-sedimentary succession of the eleonore sø window and the thin lower palaeozoic successions of the målebjerg and eleonore sø windows were referred to the eleonore bay ‘group’. an unconformity at the base of the ‘slottet quartzite’ in the eleonore sø window, presumably not examined very closely, was interpreted as a major thrust in order to force the stratigraphy to fit into the model. the displacements on the major thrusts that were recognised were grossly underestimated, perhaps in order not to upset the assumption that “the main caledonian structures displayed in the well-explored fjord region are definitely not far travelled; on the contrary, they appear to be autochthonous” (haller 1971, p. 218). while the ‘stockwerke’ model of intense in situ granitisation is no longer tenable, the caledonian orogeny in east greenland was certainly not the ‘superficial’ orogeny envisaged by the early british geologists. the precambrian orthogneiss complexes, together with the overlying metasedimentary successions, have experienced high-grade caledonian metamorphism and intense reworking during the regional caledonian compressive deformation that produced major westward propagating thrust sheets. caledonian granites generated by melting of mesoproterozoic sediments are widespread in the hagar bjerg thrust sheet, but absent in the lower niggli spids thrust sheet. the dominant fabric in the archaean and palaeoproterozoic orthogneisses of the thrust sheets is today interpreted in many areas to be essentially caledonian, which as a concept is not greatly different from the ‘caledonian petrogenetic rejuvenation’ envisaged by haller & kulp (1962, p. 18). however, despite caledonian reworking, the orthogneisses of the crystalline complexes still yield archaean and palaeoproterozoic protolith ages, and in low strain areas relicts of the precambrian foliation cut by discordant amphibolite dykes are preserved (higgins et al. 1981, p. 37–38). the assumption that all metasedimentary rocks in the southern half of the east greenland caledonides were variably transformed parts of the eleonore bay ‘group’, was not questioned until ggu’s work in the scoresby sund region in 1968–1972. although then geus bulletin 6.pmd 10-02-2005, 09:5489 90 based on imprecise rb-sr and u-pb ages (rex & gledhill 1974; hansen et al. 1978; steiger et al. 1979), ggu’s investigations led to distinction of two sedimentary successions (henriksen & higgins 1969, 1976; higgins 1974, 1988). the widespread high-grade metasedimentary rocks that hosted c. 1000 ma augen granites were ascribed to the krummedal supracrustal sequence, whereas the high-grade to non-metamorphic eleonore bay supergroup appeared to be affected only by caledonian metamorphism and deformation. this viewpoint did not go unchallenged, and diverging interpretations have continued to be expressed (peucat et al. 1985; hartz & andresen 1995; andresen & hartz 1998; hartz et al. 2000). recent ion microprobe zircon studies have now confirmed the widespread distribution of a distinctive 940–910 ma granite suite hosted by the high-grade, commonly migmatitic, krummedal sequence of the hagar bjerg thrust sheet (jepsen & kalsbeek 1998; kalsbeek et al. 2000; leslie & nutman 2000; watt et al. 2000; watt & thrane 2001). a later granite suite, hosted by both the krummedal sequence and the lowest part of the eleonore bay supergroup, is caledonian in age (rex & gledhill 1981; hartz et al. 2001; kalsbeek et al. 2001a, b; white et al. 2002). the most dramatic revelation of the recent survey mapping is that the 18.5 km thick neoproterozoic– ordovician succession preserved in the franz joseph allochthon of the hagar bjerg thrust sheet structurally overlies a partly equivalent < 400 m thick sequence preserved in the målebjerg window (fig. 4). higgins et al. (2001, fig. 8) demonstrated the similarities of the restricted foreland succession of the målebjerg window with that in the eleonore sø window and other foreland areas preserved along the western margin of the east greenland caledonides. it follows that the allochthonous and very thick eleonore bay supergroup – tillite group – kong oscar fjord group succession must have been laid down in a completely different sedimentary environment a substantial distance to the east of the restricted sequence deposited on the foreland craton. the succession preserved in the franz joseph allochthon of east greenland exhibits broad similarities with the major neoproterozoic – lower palaeozoic sedimentary successions of svalbard, nw scotland and newfoundland that were deposited along the western passive margin of the iapetus ocean (e.g. swett & smit 1972; soper 1994). in east greenland the preserved remnants of this basin were displaced at least 200 km, and possibly as much as 400 km, westnorth-west across the laurentian margin to structurally overlie their thin foreland equivalents, a caledonian shortening across the orogenic belt estimated at 40–60% (higgins & leslie 2000; higgins et al. 2001, 2004). as noted above, restoration of the thrust sheets to their approximate original locations implies that the collision of laurentia with baltica took place several hundred kilometres east-south-east of the orogenic belt now preserved onshore in east greenland. the models of the caledonian orogen presented by hartz & andresen (1995) and andresen et al. (1998), which invoked upward and lateral movement of light, low viscosity, lower crustal material towards the region of maximum crustal extension, a process compared to haller’s ‘stockwerke’ concept, neglect the significance of caledonian thrusting. following the survey’s demonstration of the existence of the foreland windows and the presence of major thrusts at caledonian symposiums held in copenhagen (frederiksen & thrane 1998, 1999), a considerably revised model for the orogen was presented by hartz et al. (2001). while the thrust terminology employed by hartz et al. (2001) has similarities with that of elvevold et al. (2000), there are many differences in interpretation. some boundaries on their map (hartz et al. 2001, fig.1) appear to have been adopted from koch & haller’s (1971) obsolete maps, and, for example, the west-dipping thrust of the eleonore sø window is incorrectly indicated as an east-dipping extensional fault (cf. fig. 6). john haller’s contributions to the understanding of the east greenland caledonides are considerable (see e.g. henriksen & higgins 1993; schwarzenbach 1993). however, although he did not discover the målebjerg and eleonore sø windows or identify the lower palaeozoic rock units, many of his observations, in retrospect, support such an interpretation. unfortunately, haller’s emphasis on the autochthonous in situ origin of the crystalline complexes led him to deny that significant thrusting was involved in the central fjord zone, and to underestimate displacements on the thrusts that were observed in gåseland, near charcot land, around eleonore sø, and around målebjerg in andrée land. acknowledgements the helpful comments of the two reviewers, brian chadwick and arild andresen, are gratefully acknowledged, and have resulted in correction of a number of errors and improvements to the original text. geus bulletin 6.pmd 10-02-2005, 09:5490 91 references andresen, a. & hartz, e.h. 1998: basement–cover relationships and orogenic evolution in the central east greenland caledonides. gff 120, 191–198. stockholm: geological society of sweden. andresen, a., hartz, e. & vold, j. 1998: a late orogenic extensional origin for the infrastructural gneiss domes of the east greenland caledonides (72°–74°n). tectonophysics 285, 353–369. backlund, h.g. 1930: contributions to the geology of northeast greenland. meddelelser om grønland 74(11), 207–296. backlund, h.g. 1932: das alter des ‘metamorphen komplexes’ von franz josef fjord in ost-grönland. meddelelser om grønland 87(4), 119 pp. best, m.g. 2003: igneous and metamorphic petrology (2nd edit.), 729 pp. oxford: blackwell publishing. cowie, j.w. & adams, p.j. 1957: the geology of the cambroordovician rocks of central east greenland. part 1. stratigraphy and structure. meddelelser om grønland 153(1), 193 pp. crimes, t.p. 1992: the record of trace fossils across the proterozoic–cambrian boundary. in: lipps, j.h. & signor, p.w. 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wager & brown 1968; mcbirney 1996; nielsen 2004). the intrusion is c. 54.5 ma old and was formed during the palaeogene opening of the north atlantic ocean, intruding into the base of the east greenland flood basalts. the intrusion is relatively small with a volume of c. 300 km3 (nielsen 2004). spectacular magmatic layering and systematic evolution in the compositions of liquidus phases and estimated melt compositions (e.g. wager & brown 1968) have made the intrusion the most studied example of the development of the ‘fenner trend’ of iron enrichment in basaltic liquids (e.g. thy et al. in press; veksler in press). the identification in the late 1980s of significant platinum-group elements (pge) and gold (au) occurrences in the intrusion (e.g. bird et al. 1991; nielsen et al. 2005) has led to continued investigation and exploration drilling. the skaergaard intrusion is suggested to hold c. 33 million ounces (1000 tonnes) of pge and c. 13 million ounces (400 tonnes) of au (nielsen et al. 2005). the mineralised zone is located in a c. 100 m thick zone of anomalous pge and au enrichment in the upper part of the middle zone (bird et al. 1991; nielsen et al. 2005) of the layered series. the mineralised zone consists of a succession of bowl-shaped, stratiform and very tightly controlled levels of palladium (pd) enrichment referred to as pd1 to pd5 (fig. 2; nielsen et al. 2005). the bottom level, pd5, is developed from margin to margin of the intrusion, whereas the overlying levels pd4 to pd1 are increasingly restricted in width, and the entire succession of pd levels is only developed in the central part of the intrusion. the structure of the mineralised zone can be compared to a set of bowls with upward-decreasing diameters. gold is always concentrated in the uppermost palladium levels or in a level above the top palladium level, irrespective of the number of developed pd levels. more detailed descriptions are provided by nielsen et al. (2005). the exploration drill cores provide material and structural information from previously inaccessible parts of the intrusion (nielsen et al. 2005). the 3-d image presented in fig. 4 is based on drill-core information (petrographical, petrophysical, geochemical etc.) and surface information. it allows an unprecedented insight into the internal structure of the upper part of the intrusion and offers a possibility of refinement of volume estimates and quantitative modelling of the developing a 3-d model for the skaergaard intrusion in east greenland: constraints on structure, mineralisation and petrogenetic models troels f.d. nielsen, símun d. olsen and bo m. stensgaard © geus, 2009. geological survey of denmark and greenland bulletin 17, 61–64. available at: www.geus.dk/publications/bull 61 fig. 2. characteristic variation in whole-rock pd concentration in the central parts of the skaergaard mineralised zone (core ddh 90-22, from bernstein & nielsen 2004). fig. 1. the skaergaard intrusion is located in the kangerlussuaq region in the palaeogene magmatic province in east greenland. kangerlussuaq iceland inland ice 100 km skaergaard intrusion blo sse vil le k ys t tasiilaq illoqqortoormiut /scoresbysund palaeogene intrusive centre pre-cretaceous sedimentary rocks cretaceous–palaeogene sed. rocks palaeogene basalt greenland 69°n 66° 32°w 24° d ep th in c o re d d h 9 022 ( m ) 0 1000 2000 3000 concentration (ppb) gold palladium pd5 pd4 pd3 pd2 pd1 pd1/au au+1980 990 1000 1010 1020 1030 1040 rosa_2008:rosa-2008 01/07/09 15:48 side 61 zones and subzones of the intrusion. a constrained structural model will in turn allow evaluation and revision of crystallisation models for the basaltic liquid in the magma chamber. 3-d modelling of the intrusion and the mineralised zone the initial aim of the 3-d modelling was a visualisation of the intrusion and the associated pge and au mineral occurrences. geographical information system software was used for the compilation of the surface data used for the model. these data, together with subsurface data, were subsequently imported into modern 3-d mining and resource software (gemcom gems®), which was used for the construction of the 3-d model of the intrusion and its mineralised zone. the detailed topographical model needed for the modelling (fig. 3) was constructed from satellite aster data (resolution 30 × 30 m). aster scenes and the 1:20 000 scale geol ogical map of the intrusion and adjacent area were draped on the terrain model. forty-one cores with a total length of 23 425 m have been drilled since 1989. the deepest holes reached levels of c. 1200 m below the collars of the drill holes. the petrographic variation in all these cores is described in drill-hole logs in company reports in the archives of the geological survey of denmark and greenland. these logs were digitalised and compiled. the courses of the drill holes (taking azimuth and dip into account) were visualised in 3-d, and assays for pge and au displayed together with the petrographic information. all the information was subsequently assessed for each drill hole, and the delineation of specific lithologies and mineralised sections was interpolated manually by the geologist software operator from one drill hole to another and from drill holes to surface exposures of the mineralised zone. triangulation surfaces were constructed mathematically by the gems software from the delineations and united into wire-frames that represent 3-d solids (geological bodies). the delineation and resulting solids were validated by the software. dykes in the intrusion were also modelled as solids. mapped-out fault planes were visualised as 3-d surfaces. in intrusion-wide images the mineralised zone is a very narrow structure. the 3-d model is best seen ‘live’, and we have chosen, as examples, to show the initial results of the imaging of the mineralised zone in two vertical 2-d panels through the intrusion (figs 4, 5). in fig. 5 the mineralised zone is shown as the zone between the lower boundary of the lowermost pd-levels (pd5, cut-off at c. 1 gram per tonne pd) and the top of the au-rich part of the mineralised zone (pd1/au or au + 1 levels, cut-off at c. 0.8 gram per tonne au). 62 fig. 3. aster satellite image with topography (1.5 × vertical exaggeration; see text for explanation). the green line shows the outer boundary of the skaergaard intrusion, and the blue dots show the locations of the collars of drill holes. 2 km mbs uz southsouth easteast northnorth westwest south ubs east mbs uznorth mzlz mbs west fig. 4. satellite image showing the area of the mineralised zone so far covered by the 3-d model (purple area) with the geological boundaries transferred from the geological map of the skaergaard intrusion (mcbirney 1989). mbs, marginal border series (wall rocks); ubs, upper border series (roof rocks); layered series (ls; floor rocks) consisting of lz, lower zone; mz, middle zone; uz, upper zone. islands in ubs: the younger basistoppen sill. the two white lines show the location of the 2-d cross-sections (fig. 5). abbreviations also apply to table 1 and fig. 6. rosa_2008:rosa-2008 01/07/09 15:48 side 62 results the west –east section of fig. 5a shows the mineralised zone to be bowl-shaped with a central depression of c. 400 m. the magnitude of the depression is in broad agreement with the margin-to-margin depression of c. 700 m modelled by nielsen (2004) and nielsen et al. (2005). the difference in the magnitude of the depression reflects that the 3-d model does not reach all the way to the margins of the intrusion. as expected, the imaging also shows that the vertical distance between the lower and upper boundaries of the mineralised zone increases towards the centre of the intrusion, in agreement with the structure of the mineralised zone proposed by nielsen et al. (2005). the demonstrated bowl-shape of the mineralised zone, and thus the layered gabbros, corroborates the model suggesting concentric crystallisation of the gabbro on the floor, walls and below the roof of the intrusion (nielsen 2004). the north–south section (fig. 5b) shows the general 20° dip of the layered gabbros and the mineralised zone. application of 3-d modelling to the evolution of the skaergaard intrusion nielsen (2004) developed a structural model for the intrusion solely on the basis of field observations and analogies. compared to the classic and traditional accumulation models, the apparent concentric crystallisation in the 300 km3 magma chamber reduces the volumes of the most evolved zones and subzones in the intrusion and thus the proportions of the products of the crystallisation process. the model was used for a mass balance-based estimate of the bulk composition of the intrusion, which turned out to be a composition very similar to that of the contemporaneous flood basalts. the data in nielsen (2004) can also be used for the calculation of the line of liquid descent (lld) of the bulk liquid (fig. 6; table 1). toplis & carroll (1995) modelled the lld for the skaergaard intrusion on the basis of experimental investigations. as shown in fig. 6 the trend of the supposed skaergaard liquid of toplis & carroll (1995) has the same shape as the one calculated using mass balance (table 1). the data in fig. 6 are projected from the sio2 corner above the plane in the figure, and the difference between the toplis & carroll (1995) and the lld suggested here is a reflection of differences in the starting compositions. 63 west eastsea level terrain surface mineralised zone north southsea level mineralised zone terrain surface 1 km 1 km b a fig. 5. west–east (a) and north–south (b) cross-sections through the skaer gaard intrusion. the blue and green lines show the lower and upper boundaries of the skaergaard mineralised zone (see text for definition). the bowl-shape and the increasing stratigraphic width of the mineralised zone towards the centre of the intrusion are seen (see also nielsen et al. 2005). table 1. compositions of liquids during the fractionation of the skaergaard magma bulk l1 l2 l3 l4 l5 l6 l7 sk-tfdn lzb lzc mz uza uzb uzc mg % solidified 0.00 32.74 55.26 62.56 75.81 85.57 93.43 95.00 sio 2 47.88 47.03 45.92 46.52 48.19 50.73 58.45 62.08 tio 2 3.03 3.74 4.86 4.63 3.74 2.65 1.40 1.07 al 2 o 3 13.87 11.93 11.24 11.15 10.75 10.42 11.35 12.39 fe 2 o 3 2.00 2.34 2.70 2.72 2.80 2.78 2.12 1.63 feo 13.32 15.63 17.97 18.12 18.64 18.53 14.13 10.88 mno 0.22 0.26 0.29 0.30 0.32 0.34 0.29 0.20 mgo 6.29 6.18 4.62 4.15 3.16 1.83 0.56 0.63 cao 10.16 9.62 8.78 8.55 7.89 7.37 5.89 4.64 na 2 o 2.56 2.48 2.61 2.71 2.94 3.18 3.78 4.18 k 2 o 0.40 0.44 0.55 0.61 0.79 1.07 1.63 1.99 p 2 o 5 0.27 0.35 0.47 0.54 0.78 1.10 0.42 0.31 sum 100.00 100.00 100.01 100.00 100.00 100.00 100.02 100.00 mg no. 0.457 0.413 0.314 0.290 0.232 0.150 0.066 0.094 based on bulk liquid sk-tfdn in nielsen (2004). the composition of the liquid as it evolves is calculated by subtraction of average compositions of correlated ls, mbs and ubs subzones (mcbirney 1989) in the mass proportions in nielsen (2004). the spread sheet with the calculation is available on request. the composition of the liquid of a specific zone refers to the composition of the liquid at the base of the indicated zone. bulk composition is corrected so that the end-result matches the composition of average melanogranophyre (mg). fe 2 o 3 /feo has been set at 0.15. the abbreviations are explained in fig. 4. rosa_2008:rosa-2008 01/07/09 15:48 side 63 64 the lld of the skaergaard intrusion is of utmost scientific interest. well-constrained deviations from the expected can be reflections of processes that have not been taken into account in the modelling of the fractionation process. the lack of balance in the sio2 distribution, as reflected in the common quartz-normative compositions of the upper bor der series of the intrusion (naslund 1984), was suggested to reflect chemical stratification of the cooling magma (hoover 1989). but what process would have been responsible for the chemical stratification? sio2-enrichment in the upper part of the magma chamber could be due to liquid immiscibility (e.g. jakobsen et al. 2005) or dynamic conditions. only with well-constrained mass balances and geophysical models for the shape of the magma chamber can numeric models for the evolution of the skaergaard intrusions be developed and the relative importance of all the suggested processes in the evolution of the melt evaluated. all well-constrained internal boundaries and the details of the mineralised zone (bulk chemistry, lithologies and mine ralogy) in the skaergaard intrusion will be included in the 3-d model in the coming years. this will allow refinement of the 3-d distributions and volumes of different lithologies, including the mineralised zone, lead to more advanced massbalance models for the skaergaard intrusion, and provide more general constraints for modelling of the crystallisation and fractionation processes in basaltic magma chambers. references bernstein, s. & nielsen, t.f.d. 2004: chemical stratigraphy in the skaer gaard intrusion. danmarks og grønlands geologiske under søgelse rapport 2004/123, 31 pp. + 1 cd. bird, d.k., brooks, c.k., gannicott, r.a. & turner, p.a. 1991: a goldbearing horizon in the skaergaard intrusion, east greenland. econo mic geology 86, 1083–1092. hoover, j.d. 1989: petrology of the marginal border series of the skaer gaard intrusion. journal of petrology 30, 399–439. jakobsen, j.k., veksler, i.v., tegner, c. & brooks, c.k. 2005: immiscible ironand silica-rich melts in basalt petrogenesis documented in the skaer gaard intrusion. geology 33, 885–888. mcbirney, a.r. 1989: geological map of the skaergaard intrusion, east greenland. eugene, usa: university of oregon. mcbirney, a.r. 1996: the skaergaard intrusion. in: cawthorn, r.g. (ed.): layered intrusions, 147–180. amsterdam: elsevier. mcbirney, a.r. & naslund, h.r. 1990: the differentiation of the skaer gaard intrusion. a discussion of hunter and sparks (contributions to mineralogy and petrology 95, 451–461). contributions to mineralogy and petrology 104, 235–240. naslund, h.r. 1984: petrology of the upper border series of the skaer gaard intrusion, east greenland. journal of petrology 25, 185–212. nielsen, t.f.d. 2004: the shape and volume of the skaergaard intrusion, greenland: implications for mass balance and bulk composition. journal of petrology 45, 507–530. nielsen, t.f.d., andersen, j.c.ø & brooks, c.k. 2005: the platinova reef of the skaergaard intrusion. in: mungal, j.e. (ed.): exploration for platinum group element deposits. mineralogical association of canada short course series 35, 431–455. thy, p., lesher, c.e. & tegner, c. in press: the skaergaard liquid line of descent revisited. contributions to mineralogy and petrology. toplis, m.j. & carroll, m.r. 1995: an experimental study of the influence of oxygen fugacity on fe-ti oxide stability, phase relations, and mineral–melt equilibria in ferro-basaltic systems. journal of petrology 36, 1137–1170. veksler, i.v. in press: extreme iron enrichment and liquid immiscibility in mafic intrusions: experimental evidence revisited. lithos. wager, l.r. & brown, g.m. 1968: layered igneous rocks, 588 pp. edin burgh: oliver & boyd. wager, l.r. & deer, w.a. 1939: geological investigations in east green land, part iii. the petrology of the skaergaard intrusion, kanger dlugssuaq, east greenland. meddelelser om grønland 105(4), 352 pp. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: tfn@geus.dk wo + en + fs uzp yr ox en e( s) plagioclase ab + or an oxygen units [ol, qz] mg # = 0. 05 lz mz mg # = 0. 5 mg # = 0. 25 mg # = 1 fig. 6. skaergaard liquid lines of descent and immiscible liquids in the (ab + or)–an–(wo + en + fs) projection from veksler (in press), who used the lld compositions shown in table 1. black dots: model liquids in the same sub-zones of the layered series calculated by mass balance (table 1). circles: trapped skaergaard liquids (mcbirney & naslund 1990). thick dashed curve: experimental line of liquid descent (toplis & caroll 1995). the dashed lines show the boundary between plagioclase and pyroxene crystallisation fields at different mg numbers (mg/mg + fe; see veksler in press for details). rosa_2008:rosa-2008 01/07/09 15:48 side 64 geological survey of denmark and greenland bulletin 17, 2009, 53-56 in recent years, both the petroleum industry and government research institutions have shown renewed interest in the petroleum potential of the high arctic. at the same time, a range of activities are taking place, aimed at defining national borders in the arctic ocean following ratification of article 76 of the united nations convention on the law of the sea (unclos). parallel to the general upsurge in data acquisition activities, the united states geological survey has carried out a circum-arctic resource appraisal (cara), which for north-east greenland was published in 2007. this assessment indicated that a significant petroleum exploration potential exists on the north-east greenland shelf, in particular in the danmarkshavn basin and the north danmarks havn salt province (fig. 1). the estimated potential amounts to 31 billion barrels of oil equivalents, principally in the form of natural gas. for comparison, this roughly corresponds to one third of the original reserve of the north sea basins. the geology of the danmarkshavn basin and offshore areas farther to the north is only known in broad outline, since no wells have been drilled and only reconnaissance geophysical data are available. moreover, the extensive ice cover and the overall hostile climate of the region pose significant logistical and technical challenges to data acquisition. clearly, this emphasises the importance of analogue studies based on the much better known geology of the onshore basins in east and north-east greenland. in 2007/2008, the geological survey of denmark and greenland (geus) launched a major petroleum industry-sponsored project with the objective of updating and expanding our current understanding of the petro leum geology of east and north-east greenland. the project is planned to continue for the next four to five years, and includes compilation of relevant existing data in the form of a geographic information system (gis) product, supplemented by new data obtained from shallow core drilling and new field work. below we give a brief overview of a range of field activities that took place in east and north-east green land in the summer of 2008. shallow core drilling in jameson land the objective of the drilling was to recover core material from the upper jurassic organic-rich shale of the katedralen member (hareelv formation) to obtain a reference section of shallow core drilling and petroleum geology related field work in east and north-east greenland 2008 jørgen a. bojesen-koefoed, morten bjerager and stefan piasecki © geus, 2009. geological survey of denmark and greenland bulletin 17, 53–56. available at: www.geus.dk/publications/bull c c' b' a a' 74°n 76°n 72°n 70°n lle saf pdmf df lle cretaceous jurassic triassic permian fault buried deepseated faults stauning alper fault post-devonian main fault dombjerg fault liverpool land escarpment drill site near blokelv tertiary milne land traill ø gauss halvø ymer ø geographical society ø hold with hope home forland clavering ø gael hamke bugt th.thomsen land kuhn ø daneborg rødryggen brorson halvø hochstetter forland store koldewey wollaston forland pd m f sa f d f kap dalton 100 km 26°w28°w 26°w 24°w jameson land liverpool land mestersvig schuchert dal fortet constable pynt greenland 18°w 16°w22°w 20°w bl os se vil le ky st h ud so n la nd ndsp ndsp: north danmarkshavn salt province danmarkshavn basin ugleelv kejser franz joseph fjord kong oscar fjord ca rls be rg fjo rd hall bredning scoresby sund hurry inlet fig. 1. map of east and north-east greenland, showing the distribution of permian to neogene sedimentary rocks and the location of place names mentioned in the text. ndsp: north danmarkshavn salt basin. 53 rosa_2008:rosa-2008 01/07/09 15:48 side 53 the most prolific source rock in the north atlantic region (fig. 2). the deepest and most central part of the jameson land basin at blokelv approximately 35 km west of con stable pynt was chosen as the drill site (fig. 1). the blokelv drilling (fig. 3) produced high quality cores (ggu 511101) with a diameter of 5.6 cm and 99.3% recovery to a depth of 233.8 m (fig. 4). the top part from 1.72 to 10.08 m recovered homogeneous medium to fine-grained sandstone with two thin shale intervals of the sjællandselv member (hareelv formation). the katedralen member (hare elv formation) from 10.08 to 233.8 m consists of alternating sandstone and shale units; the lower boundary of the member was not reached. studies of the new cores from the katedralen member focus on the stratigraphy and age of the hareelv formation and lateral, contemporaneous deposits (fig. 2). the lower boundary of the katedralen member is well known from the ugleelv region and the west side of hurry inlet, where few, condensed beds of mudstone and finegrained sandstone separate the fossil bjerget and hareelv formations. these beds are age equivalent to the olympen formation in central to northern jame son land (p. athleta to c. densiplicatum chronozones of late callovian to middle oxfordian age; larsen & surlyk 2003). the deposition of laminated mudstone of the katedralen member began in the late oxfordian. the continued sedimentation of the katedralen member mud reaches into the kimmeridgian and volgian especially in eastern and southern jameson land (fig. 2). during the volgian, the coarsegrained sand of the sjællandselv member and raukelv for mation was deposited in the western and central parts of the jameson land basin at the same time as the katedralen member mud was deposited in the easternmost, apparently much deeper basin (surlyk 2003). the youngest parts of the katedralen member are only known from the locality fortet near constable pynt in eastern jameson land, where the dinoflagellate assemblage indicates an age not older than latest middle volgian (fig. 2). the upper boundary of the kate dralen member is located where laminated mudstone is replaced by homo geneous sandstone of the sjæl landselv member. the sand slumped into the central basin from shelf-edge deltas prograding from north-west and west. this shift in deposition can be followed from west to east across the basin in a number of shallow core drillings and exposed 54 chronostratigraphy age (ma) stage volgian berriasian tithonian kimmeridgian oxfordian callovian jameson land c re t. ju ra ss ic lo w . u pp er m id dl e raukelv fm zeus mb no data athene mb goniomyakløft mb fossilbjerget fm condensed katedralen mb hades mb sjællandselv mb parnas mb s n u m l u l u m l u m l 160 150 shallow marine sandstones shelf transition-zone siltstones/heteroliths marine shelf/basinal mudstones deep marine sandstones hiatus/condensed mass flow sandstone source rock h ar ee lv f m fig. 2. chronoand lithostratigraphy of the middle and upper jurassic in jameson land. modified from surlyk (2003). fig 3. drilling operations near blokelv in jameson land. three-metre-long cores are drilled at a time, and each time a core is retrieved water is pouring out of the drill hole. rosa_2008:rosa-2008 01/07/09 15:48 side 54 sections. the boundary is strongly diachronous: kimmerid gian–volgian in the west to middle – upper volgian in the easternmost part of the basin. an extensive analytical programme to evaluate source and reservoir rock properties to establish a high-resolution dino flagellate cyst and macrofossil biostratigraphic zonation, and assess sedimentological, diagenetic and sequence stratigra phic aspects of the penetrated succession is in progress. field work field work took place by means of helicopter-supported field teams of 2–4 persons, operating primarily out of field camps. the activities covered a wide range of geological disciplines that are briefly described below. field teams camped at or visited locations from kap dalton on the blosseville kyst in the south to kuhn ø in the north (fig. 1). volcanology volcanic rocks in the form of plateau basalts as well as various intrusions abound in east and north-east greenland, and their histories of emplacement and mutual relationships are important elements in the understanding of the regional geology. a field team sampled and studied the youngest volcanic rocks in the region that are preserved in a small graben at kap dalton. additional studies were undertaken on hold with hope and wollaston forland and on nearby islands east and north thereof. samples collected from various outcrops will be subjected to chemical and petrological analyses as well as radiometric dating in order to establish their ages and mutual relationships. petroleum source rocks and cretaceous– palaeogene stratigraphy petroleum source rocks are known to be present in east and north-east greenland in a number of stratigraphic intervals ranging in age from middle devonian to upper jurassic, whereas source rocks in younger units still remain to be demonstrated. among these various units the upper jurassic ‘kimmeridge clay equivalents’ referred to as the hareelv, kap leslie and bernbjerg formations (surlyk 2003) must be considered the more important ones with respect to petroleum exploration. the documentation of spatial and temporal variations in petroleum potential within these units is crucial to the prediction of the distribution of the potential in the little-known offshore basins. upper jurassic shale of the bernbjerg formation was sampled on hold with hope and wollaston forland, and potential drill sites were found at rødryggen and brorson halvø on wollaston forland. in addition, cretaceous shale was sampled for both stratigraphic and geochemical purposes on wollaston forland, whereas sampling of cretaceous deposits and drill-site identification on hold with hope had to be postponed due to the presence of polar bears in the area. the stratigraphy and sedimentological development of the cretaceous–palaeogene succession of north-east green land have hitherto received relatively little attention, probably due to a general assumption that it was deposited during a period of tectonic quiescence with little change in overall basin configuration. during the field season in 2008, some effort was devoted to increasing our knowledge of the cretaceous–palaeogene development through sedimentological studies and stratigraphic sampling. among the results was the discovery of a more than 150 m thick, unmapped succession of presumably palaeogene sand with minor mud55 fig. 4. core box no. 62 with black organic rich mudstone (m), intrusive sandstone dykes (is), and laminated heterolithic sandstone-mudstone (ls-m) of the katedralen member, hareelv formation. the diameter of the core is 56 mm. top 229.66 m 0.1 m bottom 233.40 m ls-m is m rosa_2008:rosa-2008 01/07/09 15:48 side 55 56 authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: jbk@geus.dk stones and coal directly underlying the plateau basalts on eastern wollaston forland. sub-basaltic palaeogene sand is reported from several localities in the region. landscape analysis, uplift and sand provenance studies burial and uplift are geological processes, the magnitude and timing of which are of utmost importance in petroleum geology. assessment of these may be undertaken by a combination of methods, including large-scale landform analysis and apatite fission track analysis, which enable us to detect ancient erosion or peneplanisation surfaces as well as quantify palaeogeothermal gradients (bonow et al. 2007). moreover, identification of the source areas for sandy deposits through geological time is important to understand temporal dispersal patterns of sediment within the basin, and for correlation of sand units. such provenance studies can be carried out by age determinations and detailed chemical analyses of provenance-sensitive minerals such as zircon and garnet. since up lift and provenance studies to a large extent make use of the same type of sample material, two field teams collected samples for both purposes. spot and profile samples were collect ed at a large number of locations from milne land and jame son land in the south to wollaston forland in the north. seepage studies experience from central west greenland shows that when certain requirements are met petroleum seepages may be preserved in the lower parts of the palaeogene basalt succession and in carbonate veins associated with dykes (bojesenkoefoed et al. 1999). the utility of the experience gained in west greenland was tested in north-east greenland, but with little success, since essentially no traces of petroleum were found in the volcanic rocks exposed in the region. a number of locations on kuhn ø and wollaston forland were checked, but no hydrocarbons were found. the lavas are indeed very porous, but the level of thermal alteration indicated by the zeolite facies is too low, the volcanic rocks are too thin and healed carbonate-filled veins are nearly absent. similar studies of the volcanic rocks on hold with hope were severely hampered by bad weather and polar bears, but since the geological conditions appear more favourable there and seepages have been recorded previously, further attempts should be made during future field work. airborne stereo-photography systematic stereo-photography is a valuable tool for largescale stratigraphy and structural geology (dueholm & pedersen 1992). nearly 2000 stereo-photographs were taken from a partenavia aircraft during two sessions in (1) jameson land, milne land, schuchert dal, kong oscar fjord, southern traill ø region and (2) kejser franz joseph fjord, gauss halvø, hudson land, gael hamke bugt, home forland and the south-eastern hold with hope region. future activities in north-east greenland the project described here is planned to continue for the next 4–5 years, with both field work and shallow core drilling starting in the south and gradually moving northwards. in addition, an excursion to the region for sponsoring oil companies is planned for 2010. in 2008, the bureau of minerals and petroleum, greenland, published a ‘roadmap’ for a future licensing round in north-east greenland which, pending political approval, will lead to nomination and licensing rounds in 2011–2013. in order to meet the needs of the sponsors, further special studies may be undertaken in the forthcoming years. acknowledgements the staff at the sirius sledge patrol stations at daneborg and mestersvig and the staff at constable pynt airport are thanked for their practical assistance and hospitality. references bojesen-koefoed, j.a., christiansen, f.g., nytoft, h.p. & pedersen, a.k 1999: oil seepage onshore west greenland: evidence of multiple source rocks and oil mixing. in: fleet, a.j. & boldy, s.a.r. (eds): petroleum geology of northwest europe: proceedings of the 5th conference, 305–314. london: geological society. bonow, j.m., japsen, p., green, p.f., wilson, r.w., chalmers, j.a., klint, k.e.s., van gool, j.a.m., lidmar-bergström, l. & pedersen, a.k. 2007: a multi-disciplinary study of phanerozoic landscape development in west greenland. geological survey of denmark and greenland bulletin 13, 33–36. dueholm, k.s. & pedersen, a.k. (eds) 1992: geological analysis and mapping using multi-model photogrammetry. rapport grønlands geologiske undersøgelse 156, 72 pp. larsen, m. & surlyk, f. 2003: shelf-edge delta and slope deposition in the upper callovian – middle oxfordian olympen formation, east green land. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 931–948. surlyk, f. 2003: the jurassic of east greenland: a sedimentary record of thermal subsidence, onset and culmination of rifting. in: ineson, j.r. & surlyk, f. (eds): the jurassic of denmark and greenland. geological survey of denmark and greenland bulletin 1, 659–722. rosa_2008:rosa-2008 01/07/09 15:48 side 56 methods article | short koch & schneider 2022: geus bulletin 49. 8292. https://doi.org/10.34194/geusb.v49.8292 1 of 7 long short-term memory networks enhance rainfall-runoff modelling at the national scale of denmark julian koch* , raphael schneider department of hydrology, geological survey of denmark and greenland, copenhagen, denmark abstract this study explores the application of long short-term memory (lstm) networks to simulate runoff at the national scale of denmark using data from 301 catchments. this is the first lstm application on danish data. the results were benchmarked against the danish national water resources model (dk-model), a physically based hydrological model. the median kling-gupta efficiency (kge), a common metric to assess performance of runoff predictions (optimum of 1), increased from 0.7 (dk-model) to 0.8 (lstm) when trained against all catchments. overall, the lstm outperformed the dk-model in 80% of catchments. despite the compelling kge evaluation, the water balance closure was modelled less accurately by the lstm. the applicability of lstm networks for modelling ungauged catchments was assessed via a spatial split-sample experiment. a 20% spatial hold-out showed poorer performance of the lstm with respect to the dk model. however, after pre-training, that is, weight initialisation obtained from training against simulated data from the dk-model, the performance of the lstm was effectively improved. this formed a convincing argument supporting the knowledge-guided machine learning (ml) paradigm to integrate physically based models and ml to train robust models that generalise well. introduction the runoff at a given point along a river network can be defined as the outflow generated in the upstream contributing area. accurate modelling of runoff has been a prime research theme for several decades (wagener et al. 2004). a multitude of numerical modelling tools, from parsimonious conceptual rainfall-runoff models to complex fully distributed physically based models (pbms), have been developed. in recent years, machine learning (ml) models, in particular, long short-term memory (lstm) networks, have proved useful for rainfall-runoff modelling. since the first application by kratzert et  al. (2018), lstms quickly gained popularity and have typically outperformed traditional hydrological models under data-rich settings (mai et al. 2021) and in ungauged catchments (kratzert et al. 2019a). the knowledge-guided ml paradigm aims to increase robustness and generalisability by integrating scientific knowledge into ml models (nearing et al. 2020; reichstein et al. 2019). this can be achieved by building physical constraints, such as the first-principle law of mass conservation (hoedt et al. 2021), into a ml model or using a pbm to augment training data (jia et al. *correspondence: juko@geus.dk received: 17 aug 2021 accepted: 07 dec 2021 published: 13 jan 2022 keywords: rainfall-runoff modelling, long-short term memory networks, deep learning, knowledge-guided machine learning, pre-training-finetuning abbreviations: camels: catchment attributes and meteorology for large-sample studies fbal: flow balance kge: kling-gupta efficiency lstm: long short-term memory ml: machine learning mse: mean squared error pbm: physically based model geus bulletin is an open access, peerreviewed journal published by the geological survey of denmark and greenland (geus). this article is distributed under a cc-by 4.0 licence, permitting free redistribution, and reproduction for any purpose, even commercial, provided proper citation of the original work. author(s) retain copyright. edited by: hyojin kim (geus, denmark) reviewed by: two anonymous reviewers. funding: none provided competing interests: see page 6 additional files: see page 6 https://doi.org/10.34194/geusb.v49.8292 https://orcid.org/0000-0002-7732-3436 https://orcid.org/0000-0001-9628-0809 mailto:juko@geus.dk koch & schneider 2022: geus bulletin 49. 8292. https://doi.org/10.34194/geusb.v49.8292 2 of 7 w w w . g e u s b u l l e t i n . o r g 2021). in this context, the method of pre-training by weight initialisation using pbm simulation data appears to be very promising, as a pre-trained lstm attempts to emulate a pbm. the rapid advancement of ml models for runoff prediction was facilitated by the availability of multiple large-scale runoff data sets containing a long timeseries of observed runoff, dynamic meteorological forcing and static catchment attributes, referred to as catchment attributes and meteorology for large-sample studies (camels) data sets (e.g. addor et al. 2017). in this article, we highlight the value of danish hydrological big data for the advancement of ml-based runoff modelling. the danish case offers a data-rich setting with over 300 stations and high-quality auxiliary data. moreover, there exists a national water resources model (the dk-model), an advanced hydrological pbm that integrates groundwater and surface water processes (højberg et al. 2013; stisen et al. 2019). the dk-model is a perfect benchmark for ml model development and provides simulated runoff, which is valuable for augmentation, as well as auxiliary hydrological information, such as groundwater conditions. in this study, we aim to (1) highlight the value of danish hydrological big data for advancing ml research at an international level, (2) implement a state-of-the-art lstm to model runoff at the national scale of denmark and (3) test a knowledge-guided lstm based upon pre-training against simulated runoff obtained from a pbm. methods data as in existing camels data sets, we curated a data set comprising observed runoff as well as dynamic and static attributes for 301 danish catchments (fig.  1). the catchments vary in size between 10 km2 and 2574 km2 with an average of 133 km2. the dynamic variables cover a period of 21 years (1990–2011) at daily timesteps and comprise observed runoff, simulated runoff (dk-model), air temperature, potential evapotranspiration and precipitation (fig. 2). the three meteorological variables were derived from gridded data provided by the danish meteorological institute and represent daily-averaged conditions for the entire catchment (scharling 1999a, 1999b). a complete timeseries of 21 years of daily observed runoff were available for 51% of the catchments, with 77% of the catchments having at least an 80% coverage. the runoff was normalised by the catchment size to mm/ day to give equal weight to the catchments during training, independent of their size. in total, 17 static catchment attributes were compiled. eleven of which were calculated as catchment averages: precipitation, potential evapotranspiration, air temperature, slope, topographic wetness index, clay fraction, annual, summer and winter-simulated water table depth (dk-model), exceedance probability of a simulated water-table depth less than 1 m (dk-model) and the thickness of the surficial clay layer. five land-use classes were expressed as percentages: forest, wetland, lake, agriculture and urban. finally, the catchment area was included as well. all data are available at https://doi.org/10.22008/fk2/ycqxtr. long short-term memory the lstm network architecture is a special type of recurrent neural network, designed to store and regulate information over time, which makes lstms well suited to learn long-term dependencies and memory effects (hochreiter & schmidhuber 1997). the lstm is described in full elsewhere (kratzert et al. 2018; shen 2018). similar to traditional hydrological models, the lstm processes input data time step after time step. runoff on a specific day is simulated based on the timeseries of length n of the preceding n days of meteorological data. kratzert at  al. (2019b) developed the entity-aware lstm, which is an adaptation of the standard lstm capable of learning catchment similarities based on the static attributes, which are treated in a separate embedding layer. in this study, we applied the proposed entity-aware lstm, referred to simply as lstm hereafter. we used the fig. 1 map of denmark showing the 301 catchments used in this study. 60 catchments were randomly sampled for the spatio-temporal split-sample experiment. ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! 60 800 20 40 km q stations spatial split-sample catchments https://doi.org/10.34194/geusb.v49.8292 http://www.geusbulletin.org https://doi.org/10.22008/fk2/ycqxtr koch & schneider 2022: geus bulletin 49. 8292. https://doi.org/10.34194/geusb.v49.8292 3 of 7 w w w . g e u s b u l l e t i n . o r g neuralhydrology codebase (github.com/neuralhydrology/neuralhydrology/) to train and evaluate the models used in this study. experimental setup hyperparameters and general settings as the purpose of this study was to initially explore the lstm applicability, hyperparameters were not optimised. following kratzert et al. (2019b), we assigned the following hyperparameter values: a learning rate of 0.001, a batch size of 256, an input length of 270 days, 64 hidden cell states, a dropout rate of 0.4 and 20 training epochs. all models were trained with five different seeds and the average of the five models was used for the final lstm prediction. the model setup files are available at https://doi.org/10.22008/ fk2/ycqxtr. split-sample experiments we conducted both a temporal split-sample and a spatio-temporal split-sample experiment to test the capabilities of a lstm for danish runoff data. the temporal split-sample experiment used data from all 301 stations for training. the timeseries were split into a training period of 11 years (2000–2011) and a test period of 10 years (1990–1999; fig. 2). the two periods correspond to the calibration and test period of the dk-model, which permitted a fair comparison between the two models. the spatio-temporal split-sample experiment was divided into the same training and test periods. furthermore, 20% of the stations were randomly selected and removed from the training data set and retained for model evaluation of the spatio-temporal split-sample experiment (i.e. a 20% spatial hold-out; fig. 1). this experiment offers a more robust evaluation, as it tests the transferability of 80% of stations to the remaining 20%. this allows us to assess the ability to predict ungauged basins. pre-training the concept of pre-training can be used to initialise the weights of a lstm using alternative runoff data before fine-tuning the lstm using the actual runoff data from the catchments of interest. runoff data for pre-training can potentially be obtained from observational data sets from a larger or different geographical region or from a pbm. in this study, we followed the latter and employed simulation data from the dk-model to pretrain. in this way, the lstm aimed to emulate the process descriptions of the pbm before being fine-tuned against observed runoff. the training epochs were set to 15 for pre-training and 5 for fine-tuning. simulated runoff at all 301 stations for the training period of 11 years (2000–2011) was used for pre-training, and it was applied to both split-sample experiments. evaluation metrics for training the lstm network, the mean squared error (mse) between the observed and simulated runoff was selected as the loss function. two alternative metrics were calculated for the model evaluation, namely the kling-gupta efficiency (kge) and the averaged flow balance (fbal). kge is a three-component metric that considers the correlation, the standard deviation ratio and the bias between the observed and simulated runoff (gupta et al. 2009). fbal quantifies the water balance closure between the observed and simulated runoff relative to the observed flow (henriksen et al. 2003). negative fbal scores indicate an overestimation of the model with respect to the observed runoff. the optimal values for kge and fbal are 1 and 0, respectively. results and discussions the cumulative density functions for kge and fbal are presented in figure 3. the lstm was benchmarked against the dk-model (pbm), and the effect of pre-training was also investigated. superior performance could be attributed to the lstm, with and without pre-training, fig. 2 dynamic input data for a single catchment used to train the lstm. a: precipitation. b: potential evapotranspiration. c: air temperature. d: observed runoff (obs) and simulated runoff (pbm) were used as training data. the training period and test period are shown in a. b: potential evapotranspiration c: air temperature d: runoff a: precipitation test training pbm obs m 3 / s m m /d ay m m /d ay 0 10 20 19 92 19 94 19 96 19 98 20 00 20 02 20 04 20 06 20 08 20 10 19 90 40 ° c 20 20 0 0 0 2 4 https://doi.org/10.34194/geusb.v49.8292 http://www.geusbulletin.org http://github.com/neuralhydrology/neuralhydrology/ http://github.com/neuralhydrology/neuralhydrology/ https://doi.org/10.22008/fk2/ycqxtr https://doi.org/10.22008/fk2/ycqxtr koch & schneider 2022: geus bulletin 49. 8292. https://doi.org/10.34194/geusb.v49.8292 4 of 7 w w w . g e u s b u l l e t i n . o r g with respect to kge for the temporal split-sample experiment. the median kge was 0.8 for both lstm configurations and 0.7 for the pbm. the conclusion was less clear for the water balance closure (fbal); here, the pbm showed normally distributed underand over-estimates with a median close to zero. however, the lstms were skewed towards negative values, that is, overestimation of runoff, with a median of –0.08. overestimated runoff was predominately evident during the low-flow summer periods. using alternative loss functions instead of the mse in the lstm training may alleviate this problem. the spatio-temporal split-sample experiment revealed that the lstm did not generalise well to ungauged basins. the median kge was 0.69 and comparable with the pbm (kge = 0.73), despite poor kge scores for the lowest 20% of the cumulative density function. the same was evident for fbal, where the lowest 20% performed poorly with respect to the pbm. however, pre-training using pbm data resulted in better performance for ungauged basins, making them comparable with the pbm. this emphasised the merit of pre-training. for the spatio-temporal split-sample experiment, where information was evidently missing in the training data set, pre-training against pbm data helped to increase performance. however, the performance did not change for the temporal split-sample experiment, where the observations provided enough information. considering kge for the temporal split-sample experiment, the lstm outperformed the pbm in 80% of catchments. this fell to 44% for the spatio-temporal experiment but could rise to 54% through pre-training. considering the absolute fbal, 68% of the catchments were simulated more precisely by the lstm than by the pbm for the temporal split-sample experiment. for the spatio-temporal split-sample experiment, this could be raised slightly from 44% to 49% through pre-training. the simulation results for two selected catchments for the 10-year test period of the temporal and spatio-temporal split-sample experiments are presented in figure  4. in the first catchment (260080), the performance between the lstms and the pbm was very comparable with a kge score of 0.8 (pbm) and 0.78 (lstm) for the temporal split-sample experiment. the performance dropped to 0.66 in the spatio-temporal split-sample experiment but increased to 0.8 through pre-training. the second catchment (420022) showed a very poor performance for the spatio-temporal split-sample experiment (kge = –0.12). however, kge improved to 0.78 through pre-training and thus became comparable with the pbm (kge = 0.75). in other words, the spatio-temporal split-sample experiment for catchment 260 080 could be simulated accurately without pre-training, because the lstm could learn the runoff behaviour of that catchment using data from similar neighbouring or upstream catchments. however, the runoff behaviour of catchment 420022 could not be learned without data from the same catchment. nevertheless, pre-training using pbm data helped to increase the performance of the lstm. figure 4 presents results for a large (260080, 323 km2) and a small (420022, 44  km2) catchment. fig. 3 cumulative density functions for kge and fbal in the test period for runoff simulated by the dk-model (pbm), the lstm model and the pre-trained lstm model (prtrn lstm). the temporal split-sample experiment is depicted in the left panels and the spatio-temporal split-sample experiment in the right panels. the optimal value of fbal is highlighted with a dashed horizontal line. the lstm predictions are based on the mean of 5 seeds, indicated here with transparent coloured lines. spatio-temporal split-sampletemporal split-sample probability probability lstm pbm f ba l k g e prtrn lstm –0.5 0.0 0.5 –0.5 0.0 0.5 1.0 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 https://doi.org/10.34194/geusb.v49.8292 http://www.geusbulletin.org koch & schneider 2022: geus bulletin 49. 8292. https://doi.org/10.34194/geusb.v49.8292 5 of 7 w w w . g e u s b u l l e t i n . o r g smaller catchments generally perform less well due to the stronger imprint of anthropogenic activities (drainage and abstraction) and an increased uncertainty of precipitation data for smaller catchments. the superior performance of lstms over conceptual rainfall-runoff models or hydrological pbms was demonstrated for temporal split-sample experiments by kratzert et al. (2018), gauch et al. (2021), mai et al. (2021) and others; however, conclusions of the spatial transferability to ungauged basins are disputed. kratzert et  al. (2019a) reported a superior performance of lstm for a small spatial hold-out (8%), whereas mai et al. (2021) found a worse performance for a more systematic spatial hold-out. loss function plots are presented in supplementary file s1 to elucidate the training of the applied modelling experiments in more detail. the data generally support the chosen hyperparameter values and number of training epochs. to our knowledge, this is the first study that demonstrates the merits of pre-training against pbm simulation data for runoff modelling in the context of knowledge-guided ml. in a related study, pre-training using pbm data was found to be beneficial for the modelling of lake-water temperature (read et al. 2019). for rainfall-runoff modelling, pre-training has so far been found to be suitable for transferring trained lstms from one geographical region to another (ma et al. 2021). we have shown that pre-training using pbm data offers great potential to initialise the lstm with diverse runoff behaviour. here, we constrained only the pre-training to the same catchments and time; however, in theory, pbm simulations for different climate change scenarios or a larger geographical domain could inform the lstm with diverse runoff behaviour not seen in the observed runoff data. most of the published studies on lstm runoff modelling are of catchments with a low anthropogenic fig. 4 two example catchments showing the observed (obs) and simulated runoff for the test period. a: catchment 260080, 323 km2. b: catchment 420022, 44 km2. simulated data comprise the dk-model (pbm), the lstm-based model and the pre-trained lstm-based model (prtrn lstm). the runoff predictions of the lstm-based models are given for the temporal split-sample (ts) and spatio-temporal split-sample (sts) experiments. a: runoff 260080 b: runoff 420022 m 3 / s m 3 / s 15 10 20 25 5 0 1.5 1.0 2.0 0.5 0.0 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 lstm_ts lstm_sts prtrn lstm_ts prtrn lstm_sts pbm obs https://doi.org/10.34194/geusb.v49.8292 http://www.geusbulletin.org koch & schneider 2022: geus bulletin 49. 8292. https://doi.org/10.34194/geusb.v49.8292 6 of 7 w w w . g e u s b u l l e t i n . o r g impact; however, recent efforts to model highly managed catchments have documented promising results as well (ouyang et al. 2021). the 301 danish catchments selected in this study are, to a large degree, affected by groundwater abstraction and drainage, and the effect of the degree of anthropogenic impact on model performance and transferability should be investigated in future work. conclusions we draw the following main conclusions from the initial application of lstm networks for rainfall runoff modelling at the national scale of denmark: danish hydrological big data have the potential for conducting ml research at an international level. the dk-model serves as a valuable benchmark as well as a source for augmented training data and input data in the form of static catchment attributes. an lstm can outperform a state-of-the-art hydrological model; however, accuracy decreases for ungauged catchments. this can be alleviated by pre-training against physically based simulated runoff, providing crucial information to the lstm where needed. future research studies should (1) advance knowledge-guided ml to use hydrological knowledge provided by the dk-model optimally; (2) test alternative lstm architectures, hyperparameters and loss functions; (3) study the effect of anthropogenic impact (drainage and groundwater abstraction) on the lstm; (4) investigate ways of interpreting lstm models to gain new insights into the runoff process in denmark; (5) apply a broad range of hydrological signatures in the evaluation of lstms; and (6) produce a camels data set for denmark to provide high-quality hydrological and meteorological data. acknowledgements the authors acknowledge the developer team behind the neuralhydrology codebase for making lstm modelling tools so accessible. furthermore, geus colleagues h.j. henriksen and s. stisen are thanked for providing valuable feedback to this manuscript. two anonymous reviewers are thanked for providing valuable comments to this manuscript. author contributions jk: code development, writing original draft and visualisation. rs: data  preparation. both authors have  conceptualised the study and  design, read, edited and agreed to the published version of the manuscript. competing interests the authors declare no competing interests. additional files all data and model setups are available at: https://doi.org/10.22008/ fk2/ycqxtr. an additional supplementary file is available at: https:// doi.org/10.22008/fk2/wcf76i. references addor, n., newman, a.j., mizukami, n. & clark, m.p. 2017: the camels data set: catchment attributes and meteorology for large-sample studies. hydrology and earth system sciences 21, 5293–5313. https:// doi.org/10.5194/hess-21-5293-2017 gauch, m., mai, j. & lin, j. 2021: the proper care and feeding of camels: how limited training data affects streamflow prediction. environmental modelling and software 135, 104926. https://doi.org/10.1016/j. envsoft.2020.104926 gupta, h.v, kling, h., yilmaz, k.k. & martinez, g.f. 2009: decomposition of the mean squared error and nse performance criteria: implications for improving hydrological modelling. journal of hydrology 377(1–2), 80–91. https://doi.org/10.1016/j.jhydrol.2009.08.003 henriksen, h.j., troldborg, l., nyegaard, p., sonnenborg, t.o., refsgaard, j.c. & madsen, b. 2003: methodology for construction, calibration and validation of a national hydrological model for denmark. journal of hydrology 280, 52–71. https://doi.org/10.1016/s0022-1694(03)00186-0 hochreiter, s. & schmidhuber, j. 1997: long short-term memory. neural computation 9, 1735–1780. https://doi.org/10.1162/neco.1997.9.8.1735 hoedt, p.-j., kratzert, f., klotz, d., halmich, c., holzleitner, m., nearing, g., hochreiter, s. & klambauer, g. 2021: mc-lstm: mass-conserving lstm. arxiv preprint arxiv:2101.05186 (2021). højberg, a.l., troldborg, l., stisen, s., christensen, b.b.s. & henriksen, h.j. 2013: stakeholder driven update and improvement of a national water resources model. environmental modelling and software 40, 202–213. https://doi.org/10.1016/j.envsoft.2012.09.010 jia, x. et al. 2021: physics-guided recurrent graph model for predicting flow and temperature in river networks. in: demeniconi, c. & davidson, i. (eds): proceedings of the 2021 siam international conference on data mining (sdm), virtual conference, 612–620. https://doi. org/10.1137/1.9781611976700.69 kratzert, f., klotz, d., brenner, c., schulz, k. & herrnegger, m. 2018: rainfall-runoff modelling using long short-term memory (lstm) networks. hydrology and earth system sciences 22, 6005–6022. https:// doi.org/10.5194/hess-22-6005-2018 kratzert, f., klotz, d., herrnegger, m., sampson, a.k., hochreiter, s. & nearing, g.s. 2019a: toward improved predictions in ungauged basins: exploiting the power of machine learning. water resources research 55, 11344–11354. https://doi.org/10.1029/2019wr026065 kratzert, f., klotz, d., shalev, g., klambauer, g., hochreiter, s. & nearing, g. 2019b: towards learning universal, regional, and local hydrological behaviors via machine learning applied to large-sample datasets. hydrology and earth system sciences 23, 5089–5110. https://doi. org/10.5194/hess-23-5089-2019 ma, k. et al. 2021: transferring 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water temperature. water resources research 55, 9173–9190. https://doi.org/10.1029/2019wr024922 reichstein, m., camps-valls, g., stevens, b., jung, m., denzler, j., carvalhais, n. & prabhat 2019: deep learning and process understanding for data-driven earth system science. nature 566(7743), 195–204. https://doi.org/10.1038/s41586-019-0912-1 scharling, m. 1999a: klimagrid danmark: nedbør, lufttemperatur og potentiel fordampning 20*20 & 40*40 km. danish meteorological institute technical report 99-12, dmi, copenhagen, dk. https://doi.org/10.34194/geusb.v49.8292 http://www.geusbulletin.org https://doi.org/10.22008/fk2/ycqxtr https://doi.org/10.22008/fk2/ycqxtr https://doi.org/10.22008/fk2/wcf76i https://doi.org/10.22008/fk2/wcf76i https://doi.org/10.5194/hess-21-5293-2017 https://doi.org/10.5194/hess-21-5293-2017 https://doi.org/10.1016/j.envsoft.2020.104926 https://doi.org/10.1016/j.envsoft.2020.104926 https://doi.org/10.1016/j.jhydrol.2009.08.003 https://doi.org/10.1016/s0022-1694(03)00186-0 https://doi.org/10.1162/neco.1997.9.8.1735 https://doi.org/10.1016/j.envsoft.2012.09.010 https://doi.org/10.1137/1.9781611976700.69 https://doi.org/10.1137/1.9781611976700.69 https://doi.org/10.5194/hess-22-6005-2018 https://doi.org/10.5194/hess-22-6005-2018 https://doi.org/10.1029/2019wr026065 https://doi.org/10.5194/hess-23-5089-2019 https://doi.org/10.5194/hess-23-5089-2019 https://doi.org/10.1029/2020wr028600 https://doi.org/10.1061/(asce)he.1943-5584.0002097 https://doi.org/10.1061/(asce)he.1943-5584.0002097 https://doi.org/10.1029/2020wr028091 https://doi.org/10.1016/j.jhydrol.2021.126455 https://doi.org/10.1029/2019wr024922 https://doi.org/10.1038/s41586-019-0912-1 koch & schneider 2022: geus bulletin 49. 8292. https://doi.org/10.34194/geusb.v49.8292 7 of 7 w w w . g e u s b u l l e t i n . o r g scharling, m. 1999b: klimagrid danmark: nedbør 10*10 km (ver. 2). danish  meteorological institute technical report 99-15, dmi, copenhagen, dk. shen, c. 2018: a trans-disciplinary review of deep learning research and  its relevance for water resources scientists. water resources research 54, 8558–8593. https://doi. org/10.1029/2018wr022643 stisen, s., ondracek, m., troldborg, l., schneider, r.j.m. & van thil, m.j. 2019: national vandressource model. modelopstilling og kalibrering af dk-model 2019. danmarks og grønlands geologiske undersøgelse rapport 2019/31, geus, copenhagen, dk. wagener, t., wheater, h.s. & gupta, h.v. 2004: rainfall-runoff modelling in gauged and ungauged catchments, 332 pp. london: imperial college press. https://doi.org/10.1142/p335 https://doi.org/10.34194/geusb.v49.8292 http://www.geusbulletin.org https://doi.org/10.1029/2018wr022643 https://doi.org/10.1029/2018wr022643 https://doi.org/10.1142/p335 long short-term memory networks enhance rainfall-runoff modelling at the national scale of denmark abstract acknowledgements references figures fig. 1 map of denmark showing the 301 catchments used in this study. 60 catchments were randomly sam fig. 2 dynamic input data for a single catchment used to train the lstm. a: precipitation. b: potent fig. 3 cumulative density functions for kge and fbal in the test period for runoff simulated by the fig. 4 two example catchments showing the observed (obs) and simulated runoff for the test period. a geological survey of denmark and greenland bulletin 12, 57-63 57 pyritic part of the knudshoved member may correlate with the upper, tuff-poor unit b2 of the balder formation. stronsay group knox & holloway (1992) replaced the hordaland group of deegan & scull (1977) with two new groups: the stronsay group succeeded by the westray group (fig. 3). the two groups together comprise the light grey, green and brown coloured, soft, fissile, marine shales with thin limestone streaks that overlie the rogaland group and underlie the nordland group. these groups each contain two formations, one representing sandy shelf lithofacies and the other representing basinal mudstone lithofacies. in the central north sea, and in the danish sector, the stronsay group is represented by its mudstone facies, the horda formation (knox & holloway 1992). sandstone units of varying thickness occur at many levels in the stronsay and westray groups along the basin margin in the norwegian and british sectors, and many of these have been defined as formations or members (deegan & scull 1977; hardt et al. 1989; knox & holloway 1992). a sandstone unit also occurs in the horda formation on the ringkøbing–fyn high in the danish sector and is described here as a new member (hefring member). horda formation history. knox & holloway (1992) established the horda formation for the greenish grey basinal mudstone facies of their stronsay group that overlies the grey tuffaceous mudstones of the balder formation and underlies the greenish grey to brown mudstones of the lark formation (knox & holloway 1992). type well. british sector well 22/1-1a, 2379.5–1992 m mdkb. danish reference wells. mona-1, 2930.8–2363.5 m mdkb (fig. 46); siri-1, 2037.9–1916.5 m mdkb (fig. 47). distribution and thickness. the horda formation extends over the central and northern north sea and is present in 1916.5 2037.9 horda fm chalk gp lark fm balder fm sele fm lista fm våle fm 1900 2000 2100 2200 m siri-1 gr sonic rind mb idun mb tyr mb vile mb ve mb bue mb bue mb horda formation siri-1 mona-1 floki-1 100 200 300 400 500 600 700 800 900 thickness (m) 25 km fig. 47. siri-1, danish reference well for the horda formation. black bars show cored sections. fig. 48. isochore map of the horda formation in the study area. the positions of the two danish reference wells for the horda formation, mona-1 and siri-1, are indicated on the map. the position of floki-1, the type well for the hefring member, is also indicated. 58 gulnare-1 adda-2 alma-1 nnw sse 10 km horda fmhorda fmhorda fm l4l4l4 l2l2l2 0 500 1000 1500 2000 2500 3000 3500 twt (msec) tl tf uou tl2 th tb tc l3l3 lark fmlark fmlark fm 1000 1500 2000 2500 3000 3500 gert-1 sw ne mona-1 elna-1 sandra-1 horda fmhorda fmhorda fm h2h2 h3h3th2th2 h2 h3h3th2 10 km lark fmlark fmlark fm tl uou th tb tc twt (msec) th1th1th1 h1h1h1 fig. 49. nnw–sse-trending seismic section (rtd81-re94-17a) in the central graben showing southand eastward thinning of the horda formation. the location of the seismic section is shown in fig. 1. the l2, l3 and l4 subunits of the lark formation are indicated, as well as the mudstone-equivalent of the freja member. tl, top lark; tf, top freja; uou, upper oligocene unconformity; tl2, top l2; th, top horda; tb, top balder; tc, top chalk. fig. 50. sw–ne-trending seismic section (rtd81-rtd94-19a) showing the tripartite subdivision (h1–3) of the horda formation in the eastern part of the danish central graben (gert-1 and mona-1) and pronounced thinning of the horda formation east of the central graben (elna-1 and sandra-1). the location of the seismic section is shown in fig. 1. th1, top h1 marker; th2, top h2 marker; other abbreviations as in fig. 49. 59 all wells in the danish sector of the north sea. however, the lower part of the horda formation (fig. 4; equivalent to sequence 2 of michelsen et al. 1998) is lacking in the eastern wells r-1 and s-1 and in the eastern part of the ringkøbing–fyn high. the upper part of the horda formation (fig. 4; equivalent to sequence 3 of michelsen et al. 1998) is thin or absent in the same area (michelsen et al. 1998). the horda formation reaches a thickness of 906 m in the central graben well tordenskjold-1, but thins towards the east and south-east to less than 100 m, with minimum recorded thicknesses of 9 m in the ida-1 well and 4 m in the s-1 well. an isochore map of the horda formation is shown in fig. 48. the overall thinning of the horda formation towards the south-east, east and north-east is also shown on the seismic sections in figs 49 and 50 and on the log panel in fig. 51. lithology. the horda formation is characterised by greenish grey to greyish green fissile mudstone. subordinate limestone benches and thin layers of black mudstones occur at some levels in the formation. in many wells, particularly in the central graben, the lowermost 20–50 m of the horda formation consists of red-brown mudstones (fig. 52). this lithology is apparently lacking in the eastern wells of the danish sector. log characteristics. the horda formation is characterised by an overall stable gamma-ray and sonic log motif with a lower gamma-ray response than that displayed by the underlying balder formation and the overlying lark formation. in a few wells, the base of the horda formation shows relatively high gamma-ray values, which decrease to lower and more stable values over a short interval. the sonic readings decrease slightly upwards from the base to the top of the horda formation. boundaries. the base of the horda formation is placed at the change from the laminated, predominantly grey mudstones with interbedded sandy tuffs of the balder formation to the predominantly non-laminated, fissile, greenish grey or red-brown massive mudstones that form the basal part of the horda formation. the balder–horda boundary may be conformable or marked by a hiatus. the boundary is often difficult to pick on petrophysical logs. in basinal settings, knox & holloway (1992) advocated placing the lower boundary of the horda formation at the base of a marked gamma-ray peak believed to represent a glaucony-rich condensed layer in the basal part of the horda formation. however, in many sections in the danish sector there are two or more gamma-ray peaks in the balder–horda boundary interval. as the glauconyrich layer has not been identified with certainty in the few cores taken across the boundary in the danish sector, it is not possible to identify the key gamma-ray peak unambiguously. therefore, it is suggested that the lower boundary of the horda formation is placed on the basis of the sonic log where a gradual decrease in values in the upper part of the balder formation is succeeded by relatively stable, but somewhat lower readings in the horda formation (figs 46, 47). the upper boundary is at the base of the lark formation. subdivision. knox & holloway (1992) suggested a threefold subdivision of the horda formation (h1–3), based on lithology and biostratigraphy. a threefold subdivision can also be seen on seismic sections in the danish sector of the north sea (fig. 50). in some central graben wells, the subdivision may also be recognised on shifts in log patterns on both gamma-ray and sonic logs (fig. 51). in these wells, subtle peaks separate the three units on the gamma-ray log and coincide with the top h1 and top h2 seismic markers. based on analysis of cuttings samples, the subdivision apparently lacks lithological expression in the danish sector. knox & holloway (1992) noticed that the top of unit h1 is close to the ho of the dinoflagellate eatonicysta ursulae, and that the top of unit h2 is close to the ho of the foraminifer spiroplectammina spectabilis. this observation is supported by biostratigraphical data from the present study. a sandstone body within the horda formation has been encountered in the well floki-1 on the ringkøbing–fyn high) in the danish sector of the north sea. this sandstone is defined herein as the new hefring member (see below). macroand ichnofossils. the horda formation is moderately to intensely bioturbated. ichnofossils comprise chondrites ispp., phycosiphon ispp. and planolites ispp. microfossils and palynomorphs. in wells where the horda formation rests conformably on the balder formation, the dinoflagellate events ho deflandrea oebisfeldensis and ho dracodinium condylos occur in the lowermost part of the horda formation. characteristic microfossil datums from the lowermost part of the horda formation are the ho of the planktonic foraminifer subbotina ex gr. linaperta, which occurs abundantly, followed upwards by the almost coeval hos of the benthic foraminifers uvigerina batjesi, turrilina brevispira and gaudryina hiltermanni. a hiatus between the horda and balder formations is indicated in wells in the northern and eastern part of the danish sector by the absence of d. oebisfeldensis and d. condylos from the lower part of the horda formation. central 60 1700 1800 1900 1400 gr sonic gr sonic density gr sonic density gr sonic density 1500 1600 2000 2100 2200 2300 2400 2500 2600 2700 2800 2900 3000 3100 m 1000 1100 1200 700 800 900 1300 1400 1500 1600 1700 1800 1900 2100 2200 m 1700 1800 1900 1400 1500 1600 2000 2100 2200 2300 2400 2500 2600 2700 2800 2900 m 1800 2000 1500 2100 2200 2300 2400 2500 2600 2700 2800 3000 m kim-1 kim-1 mona-1 west lulu-3 siri-1 siri-1 1600 1700 1900 2900 2000 horda h1 h3 h2 lark l4 tl uou tl2 tl1 th th2 th1 tb l3 l2 l1 balder sele lista våle chalk grp sw ne 61 above the top of the lower, oxic part of the formation. the occasional influxes of radiolaria recorded throughout the upper part of the formation suggest that deeper marine conditions prevailed periodically. the palynofacies of the horda formation is characterised by a rich and dominant dinoflagellate assemblage with dispersed terrestrial matter (phytoclasts, spores and polfacing page: fig. 51. sw–ne-trending log panel showing eastward thinning of the horda formation. the figure also shows the variation in architecture and distribution of the horda units h1–h3 and lark units l1– 4 between the central graben (kim-1, mona-1 and west lulu-3) and the ringkøbing–fyn high (siri-1). seismic ties: tl1, top l1; th2, top h2; th1, top h1; other abbreviations as in fig. 49. fig. 52. core photographs showing red to reddish grey mudstones of the lowermost part of the horda formation in the sofie-1 well. depths are core depths. cm 1887 m 1888 m sofie-1 1901 m 1902 m 0 10 20 30 40 50 60 70 80 90 100 graben wells contain the downhole succession of the dinoflagellate cyst events ho areosphaeridium diktyoplokum, ho areosphaeridium michoudii, ho heteraulacacysta porosa and ho cerebrocysta bartonensis from the top of the horda formation, indicating an age as young as earliest rupelian (fig. 5b). in wells to the north and east, the top of the horda formation seems to be slightly older since a. michoudii is recorded from the top of the formation, indicating a mid-priabonian age (fig. 5b). significant dinoflagellate events from the middle to upper part of the horda formation are the succession of the hos of eatonicysta ursulae, diphyes ficosoides and phthanoperidinium clithridium in the middle part of the formation, and the hos of diphyes colligerum and c. bartonensis in the upper part of the formation. in central graben wells, significant microfossil events in the lower part of the horda formation include the ho of abundant radiolaria of the genus cenosphaera and the ho of the planktonic foraminifer cyclammina amplectens. key events in the middle and upper parts of the formation are the hos of pseudohastigerina spp. (planktonic foraminifers), lenticulina gutticostata, spiroplectammina amplectens and planulina costata (benthic foraminifers). the top of the horda formation contains the hos of cibicidoides truncanus and vaginulinopsis decorata. depositional environment. the lower part of the horda formation contains a microfauna that is significantly different from that of the underlying balder formation. the basal 5–40 m of the horda formation are characterised by a diverse fauna of both benthic and planktonic calcareous foraminifers together with agglutinated foraminifers. this indicates that the depositional setting was open marine, bathyal and with oxic bottom conditions. the upper part of the horda formation is characterised by an abundant and diverse agglutinated foraminifer fauna. calcareous foraminifers are very sparse or absent in this interval. the assemblage of rhabdammina discreta, haplophragmoides spp., recurvoides spp. and usbekistania charoides indicate that the upper part of the horda formation was deposited at upper bathyal depths with dysoxic bottom conditions. radiolaria occur commonly in several narrow intervals, the lowest of which is slightly 62 horda fm lark fm hefring mb våle fm balder fm sele fm lista fm chalk gp 1500 1600 1700 1800 m floki-1 1731.3 1793.4 gr sonic neutron/density fig. 53. floki-1, type well for the hefring member. len) as a minor component, indicating an open marine environment with only limited influx from surrounding terrestrial areas. age. in the central graben, where the horda formation is most complete, the formation spans from the middle ypresian (early eocene) at its base to earliest rupelian (earliest oligocene) at its top. in wells to the east and north, the top is as old as middle priabonian (see also biostratigraphic section above). this indicates that the top of the horda formation is diachronous, younging in a southwesterly direction. this is possibly due to increased erosion or longer intervals of non-deposition towards the north-east in the basin, or both. correlation. the horda formation can be correlated with the onshore danish succession of the røsnæs clay formation, the lillebælt clay formation and the søvind marl formation (heilmann-clausen et al. 1985), and the viborg formation (christensen & ulleberg 1973). the red-brown mudstones near the base of the horda formation in the central north sea can be correlated lithologically with the røsnæs clay formation and the lower part of the lillebælt clay formation. 63 the lower part of the overlying main body of greenish and greyish mudstones in the offshore succession can be correlated with the coeval and lithologically similar upper part of the lillebælt clay formation. the upper part of the horda formation can be correlated with the søvind marl formation, which consists of grey marls. the highest part of the horda formation, only observed in central graben wells, may be correlated with the viborg formation on biostratigraphic evidence. hefring member new member history. the hefring member consists of sandstone deposits within the horda formation. these sandstones have not previously been recognised as a separate unit in the danish sector. derivation of name. after the goddess hefring. type well. danish sector well floki-1, 1793.4–1731.3 m mdrt (fig. 53). distribution and thickness. the hefring member is only known from the floki-1 well located in the northern part of the danish sector. as the unit currently cannot be identified on seismic sections, its further distribution is unknown. in the floki-1 well, the member is 62 m thick. lithology. the hefring member consists of greenish grey, fine-grained, immature sandstones with glaucony grains. log characteristics. the hefring member is characterised by a conspicuous blocky signature on the gamma-ray, sonic and density logs (fig. 53). gamma-ray responses are lower than those of the enveloping horda formation mudstones. the hefring member can also be recognised from a combination of the density and neutron logs as the presence of pure sandstones results in a ‘cross-over’ of the two log curves (fig. 53). boundaries. the boundaries with the mudstones of the horda formation are sharp and characterised by prominent shifts on the gamma-ray and sonic logs (fig. 53). depositional environment. no cores have been taken in the hefring member, but the sandstones were probably deposited from concentrated gravity flows, based on log similarity with the other fine-grained sandstone bodies in the nearby siri canyon. age. lutetian (middle eocene) based on the age of the associated horda formation mudstones. correlation. based on biostratigraphic data, the hefring member may be contemporaneous in part with the lillebælt clay formation onshore denmark, with the lower part of the grid sandstone member (knox & holloway 1992) in the viking graben and with the upper part of the tay sandstone member (knox & holloway 1992) in the northern part of the central graben. westray group the westray group is the upper of the two groups established by knox & holloway (1992) to replace the hordaland group of deegan & scull (1977; fig. 3). in the central north sea and in the danish sector of the north sea, the westray group is represented by the lark formation. lark formation history. the lark formation was established by knox & holloway (1992) for the brownish grey mudstone-dominated lithofacies of the westray group that overlies the more variable association of red and green-grey mudstones, silty mudstones and sandstones of the horda formation and underlies the grey, sandy and shelly mudstones, siltstones and sandstones of the nordland group of deegan & scull (1977; fig. 3). the lark formation is also recognised in the danish sector although its lithology is more variable than that given in the original description. type well. british sector well 21/10-4, 1867–1217 m mdkb. danish reference wells. mona-1, 2363.5–1598.3 m mdkb (fig. 46); siri-1, 1916.5–819.3 m mdkb (fig. 54). distribution and thickness. the lark formation extends over the central and northern north sea and is probably present in the entire danish sector of the north sea. its depocentre is in the central and northern part of the danish sector, along the eastern boundary of the danish central graben, where it reaches a thickness of 1194 m in the siri-3 well. the lark formation thins west to a thickness of 389 m in the tordenskjold-1 well in the central graben, and east to a thickness of 240 m in the s-1 well on the ringkøbing–fyn high (fig. 55). geological survey of denmark and greenland bulletin 12, 73-77 73 1487.7 1623.5 freja mb lark fm 1400 1500 1600 1700 m frida-1 gr sonic ber in the inez-1 well (shown as unnamed sandstones in fig. 2); these sandstones may be contemporaneous or even contiguous with those of the freja member. however, confident correlation on the basis of log and seismic data is not possible at present. acknowledgements aage bach sørensen (geus) is thanked for help with seismic interpretations. yvonne desezar, johnny e. hansen and birthe amdrup are thanked for preparation of microfossil and palynology samples. the referees robert w.o’b. knox (british geological survey) and paul van veen (conocophilips norway) are thanked for their constructive criticism of the manuscript; the editorial contributions of adam a. garde, jon r. ineson and martin sønderholm are gratefully acknowledged. this work was made possible through grants from the danish energy authority, under the energy research project framework 2000. fig. 62. frida-1, reference well for the freja member. black bar shows cored section. references ahmadi, z.m., sawyers, m., kenyon-roberts, s., stanworth, c.w., kugler, k.a., kristensen, j. & fugelli, e.m.g. 2003: paleocene. in: evans, d. et al. 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(eds): petroleum geology of the continental shelf of north-west europe: proceedings of the 2nd conference, 3–39. london: heyden & son ltd. geological survey of denmark and greenland bulletin 11, 33-52 33 pre-nagssugtoqidian crustal evolution in west greenland: geology, geochemistry and deformation of supracrustal and granitic rocks north-east of kangaatsiaq jean-françois moyen and gordon r. watt the area north-east of kangaatsiaq features polyphase grey orthogneisses, supracrustal rocks and kangaatsiaq granite exposed within a wsw–ene-trending synform. the supracrustal rocks are comprised of garnet-bearing metapelites, layered amphibolites and layered, likewise grey biotite paragneisses. their association and geochemical compositions are consistent with a metamorphosed volcano-sedimentary basin (containing both tholeiitic and calc-alkali lavas) and is similar to other archaean greenstone belts. the kangaatsiaq granite forms a 15 × 3 km flat, subconcordant body of deformed, pink, porphyritic granite occupying the core of the supracrustal synform, and is demonstrably intrusive into the amphibolites. the granite displays a pronounced linear fabric (l or l > s). the post-granite deformation developed under lower amphibolite facies conditions (400 ± 50°c), and is characterised by a regular, ne–sw-trending subhorizontal lineation and an associated irregular foliation, whose poles define a great circle; together they are indicative of highly constrictional strain. the existence of a pre-granite event is attested by early isoclinal folds and a foliation within the amphibolites that is not present in the granite, and by the fact that the granite cuts earlier structures in the supracrustal rocks. this early event, preserved only in quartz-free lithologies, resulted in high-temperature fabrics being developed under upper amphibolite to granulite facies conditions. keywords: archaean, deformation, supracrustal rocks, granite, nagssugtoqidian _______________________________________________________________________________________________________ j.-f.m., department of geolog y, university of stellenbosch, 7602 matieland, south africa. e-mail: jfmoyen@wanadoo.fr g.r.w., marchmyres cottage, breda, alford ab33 8nq, aberdeenshire, u.k. introduction and regional geology the northern part of the nagssugtoqidian orogen (nno) is a domain of predominantly archaean rocks that have been deformed and metamorphosed during nagssugtoqidian orogenic activity at c. 1.8 ga (hollis et al. 2006, this volume; mazur et al. 2006, this volume; thrane & connelly 2006, this volume; van gool & piazolo 2006, this volume). palaeoproterozoic rocks are sparse, and apparently confined to some supracrustal belts, the most prominent one being the naternaq supracrustal belt (østergaard et al. 2002). a few small granitic-pegmatitic plugs and dykes are also related to the palaeoproterozoic evolution. therefore, while the structures probably reflect nagssugtoqidian deformation, the rocks themselves (and their protoliths) largely reflect archaean formations and evolution. among the archaean units, the ubiquitous orthogneissic basement has previously been studied (moyen et al. 2003a; steenfelt et al. 2005); it is mostly made up of classical tonalite-trondhjemite-granodiorite (ttg) gneisses, with minor components either related to ttg partial melting, or to the participation of peridotitic mantle in their petrogenesis. all these components are well known in the archaean, and are probably related to the subduc© geus, 2006. geological survey of denmark and greenland bulletin 11, 33–52. available at: www.geus.dk/publications/bull 34 tion of hot oceanic lithosphere in an arc setting (martin 1986, 1994; moyen et al. 2003b; steenfelt et al. 2005). several components of the gneissic basement have been dated (kalsbeek & nutman 1996; connelly & mengel 2000; thrane & connelly 2002, 2006, this volume), yielding ages in the range 2.9–2.6 ga. supracrustal assemblages are common, and have been mapped in many places in the kangaatsiaq, aasiaat and kangersuneq map sheet areas (marker et al. 1995; mengel et al. 1998; østergaard et al. 2002; van gool et al. 2002a; garde 2004; hollis et al. 2006, this volume). they are of two main types, either amphibolites or metasedimentary rocks, that may be either aluminous, biotite ± muscovite ± sillimanite ± garnet-bearing metapelites, or quartz-rich, psammitic rocks. the age of the supracrustal rocks is, however, poorly constrained. whilst some of them are of demonstrated palaeoproterozoic age (c. 1.95 ga, the naternaq supracrustal belt, østergaard et al. 2002; thrane & connelly 2002, 2006, this volume), others are likely to be of archaean age, for instance anatectic metapelites in saqqarput fjord in the southern part of the kangaatsiaq map sheet area (thrane & connelly 2006, this volume). lastly, small intrusions, plugs and sheets of granite and pegmatite cut across the lithologies described above. some of them have been dated (kalsbeek & nutman 1996; thrane & connelly 2002, 2006, this volume) and yielded late archaean ages (2.7–2.6 ga); it is commonly agreed that most magmatic activity in this region was related to late archaean events, palaeoproterozoic p–t conditions being such that anatexis was hardly achieved in the nno (mazur 2002; piazolo 2002). the very homogeneous and porphyritic kangaatsiaq granite north-east of kangaatsiaq, 15 by 3 km in outcrop size, is among the largest granitic bodies of presumed late archaean age in the southern disko bugt region. altogether, the three components outlined above are representative of the usual trilogy of archaean terranes (windley 1995): grey ttg gneisses; volcanic and volcano-sedimentary deposits (greenstones); and late, k-rich granites. the area east and north-east of the town of kangaatsiaq (fig. 1) is dominated by a synform of supracrustal rocks (mafic and felsic volcanic rocks associated with sediments), into which the kangaatsiaq granite was emplaced. it is, therefore, a good place to study the archaean components and local history in the nno. greenland 68°19' 53°24' kangaatsiaq granite amphibolite layered biotite gneiss of supracrustal origin and aluminous metapelite orthogneiss geological boundaries: established inferred fault c d b a a 81 82 89 92 2 km kangaatsiaq 61 73 52 85 64 58 57 80 75 fig. 1. geological map of the kangaatsiaq granite and surrounding synform, with sample localities from table 1. geology mostly from 2002 field work; some parts are drawn from 2001 data (j.a.m. van gool, g.i. alsop, s. piazolo and s. mazur). a–a, approximate position of section on fig. 2; b, loc. 89, see fig. 3; c, locs 81–82, see fig. 4; d, loc. 80, see fig. 5. 35 previous work previous studies in the kangaatsiaq area included reconnaissance mapping by noe-nygaard & ramberg (1961), 1:250 000 scale mapping by henderson (1969), and visits to key localities during the danish lithosphere centre project (marker et al. 1995; mengel et al. 1998), as a result of which most published ages were obtained (kalsbeek & nutman 1996; connelly & mengel 2000). mapping of the area was predominantly based on coastal exposures, while map information for large parts of the inland areas was based only on photogeological interpretation. therefore, the kangaatsiaq granite, which happens to crop out mostly inland and occupies the high grounds at the core of a synform, was at that time simply considered to be part of the polyphase gneissic basement. the geological survey of denmark and greenland (geus) and its partners undertook more detailed mapping of the kangaatsiaq map sheet in the summer of 2001. this included limited inland work, and the kangaatsiaq granite was recognised for the first time as belonging to the group of the late archaean intrusives. its overall shape was mapped, as well as the supracrustal rocks into which it intrudes. metasedimentary rocks in the area were also sampled, allowing for metamorphic studies (mazur 2002; piazolo 2002). finally, re-evaluation of the area in the summer of 2002 by the present authors led to the refinement of geological boundaries and the production of the map of fig. 1. sampling of the whole supracrustal series was also undertaken. thin sections were cut at université claude-bernard (lyon, france), and samples were analysed at geus using xrf as well as icp-ms (table 1). in addition, other supracrustal rocks from the same area (obtained from a.a. garde, personal communication 2003) have been used for the interpretation presented here, as they show similar geochemical features. map pattern as mentioned in the introduction, the studied area (fig. 1) is mainly made up of three main components: basement orthogneisses discussed by moyen et al. (2003a) and steenfelt et al. (2005), a succession of supracrustal rocks which comprise a sequence of amphibolite and metasedimentary rocks described below (figs 1, 2), and the kangaatsiaq granite, an intrusion of pink, coarse-grained, strongly lineated (l or l > s fabric) granite with k-feldspar phenocrysts. the foliated basement gneisses and the supracrustal rocks, together with early folds and structures, are refolded into a complex synform which is locally overturned, in particular on its north-western rim (see below). the granite occupies the core of the synform; it is intrusive within the top amphibolitic layer of the supracrustal sequence (fig. 3) and is also folded together with the supracrustal rocks. the geometry of the granite suggests that it constitutes a single sheet within the supracrustal unit, and that the original intrusion had an overall flat, laccolithlike shape (fig. 2). we consider that the mapped contact always corresponds to the bottom of the laccolith, and that the top surface has been removed by erosion (fig. 2). nw se kangaatsiaq granite amphibolite 1 km layered biotite gneiss of supracrustal origin with ultramafic layer (schematic) with gabbroic lens (schematic) aluminous metapelites basement orthogneiss amphibolite layers and enclaves in other lithologies (schematic) fig. 2. schematic nnw–sse crosssection across the kangaatsiaq granite and the surrounding synform. the laccolith shape (dashed line) is inferred, see text for details. 36 a b c d photo jfm-2002-5-22 photo jfm-2002-5-22 photo jfm-2002-5-22 photos jfm-2002-5-19–21photos jfm-2002-5-19–21photos jfm-2002-5-19–21 fig. 3. contact of the kangaatsiaq granite and the south-western limb of the synform, loc. 89. the granite clearly intrudes the supracrustal pile, and at the same time occupies the core of the (here, slightly overturned) synform with apparently conformable relationships. a: photomosaic of cliff face, facing east. b: structural interpretation (stippled: pegmatites; rectangle: location of enlargement d). c: lithological interpretation. crosses: granite; dark grey: amphibolite; light grey: layered gneiss. d: detail of a small granitic apophysis which clearly cuts across the foliation of the amphibolite. 37 the early structures are associated with syntectonic aplites and pegmatites that cut across the amphibolite but occasionally occupy shear zones or fold hinges. the supracrustal series stratigraphy the supracrustal rocks that define the synform occur as largely discontinuous layers (figs 2–4), that could either correspond to an original, discontinuous geometry (therefore suggesting lava flows), or simply be a result of tectonic stretching during the multiphase deformation witnessed by the area. indeed, some of the contacts between the lithological units appear to be tectonic (figs 4, 5), suggesting that the present-day ‘stratigraphy’ might not be original. nevertheless, our mapping suggests that three main units can be recognised, allowing the following tentative stratigraphic sequence (figs 2, 4). 1. the lowermost, c. 100 m thick part consists of an association of amphibolite interlayered with garnet-sillimanite metapelites, sometimes with augen textures. some of the amphibolites are garnet-bearing, while others contain centimetre-sized lenses of diopside-bearing gabbro and small ultrabasic layers (pyroxenite or serpentinite, observed in the south-western part of the synform). the pelitic rocks seem to be more abundant in the northern limb and north-eastern extremity of the synform, while the ultramafic rocks and gabbros were found only in its south-western part. 2. the middle part is a sequence about 100 m thick of layered biotite gneiss, i.e. quartzo-feldspathic gneiss with no discriminant minerals and a compositional layering at a scale of c. 10 cm. the layered biotite gneiss is commonly interstratified with layers and lenses of amphibolite 10–100 cm thick. the contact with the lower amphibolite is gradational. as will be discussed below, the layered biotite gneiss likely represents meta-rhyolite. the middle unit of layered biotite gneiss probably does not have a constant thickness; furthermore, in poor, inland outcrops, it is readily confused with basement orthogneisses. a detailed log of the lower and middle parts of the sequence as described in the foregoing was made in the overturned, north-eastern part of the synform, displaying its complex and composite nature (fig. 3a, locs 81–82). 3. a horizon 50–100 m thick of fine grained, dark, layered amphibolite forms the highest observed level. the southern limb (locs 86–92) northern limb (locs 81–83) layered amphibolite intrusive pink granite possible peripheric intrusion? tectonic contact ? possible leucocratic intrusion? layered biotite gneiss (metarhyolite ?) occasional amphibolite layers layered amphibolitelayered amphibolite (garnet-bearing in places)(garnet-bearing in places) layered amphibolite (garnet-bearing in places) orthogneiss basement garnet-sillimanite metapelite interlayered with amphibolite. augen texture locally unconformity or tectonic contact? unconformity or tectonic contact? unconformity or tectonic contact? 10 cm lenses of diopsidebearing gabbro ultramafic layer amphibolite and layered grey gneisses interstratified b. generalised stratigraphic columns in the kangaatsiaq syncline a. coastal section, locs 81–82 sw ne loc. 82 loc. 81 538 537 536 535 533 532 530 100 m fig. 4. stratigraphic succession of the kangaatsiaq synform. a: detailed section of the overturned northern limb of the synform in its eastern extremity (locs 81–82), with sample numbers (all with prefix ‘485’). b: inferred generalised logs in the north-eastern and south-western parts of the synform. legend: see fig. 2. 38 a b c photo jfm-2002-4-14 photo jfm-2002-4-13 photo jfm-2002-4-12 photos jfm-2002-4-06–08 photos jfm-2002-4-06–08 photos jfm-2002-4-06–08 kangaatsiaq granite amphibolite layered biotite gneiss of supracrustal origin basement orthogneiss fig. 5. photomosaic (a) and structural interpretation (b) of the cliff face at loc. 80 (photo facing east). stippled: pegmatites; grey: high-strain zones. evidence for preto syn-granite, apparently extensional deformation is preserved in the amphibolite bodies intruded by the granite. details of the cliff face display the apparently extensive deformation in the amphibolite. cross-cutting pegmatites (see photo 4-12) are occasionally affected by this deformation, suggesting that it is synchronous or nearly synchronous with granite emplacement. c: schematic relationships between the granite, the early extensional deformation, and the supracrustal pile, inspired from loc. 80. 39 a1 a2 b1 b2 c1 c3 c2 c4 c5 fig. 6. field and thin sections photographs of lithologies of the supracrustal series (xpl: crossed polarised light; ppl: plane polarised light). microphotographs are c. 5 mm across. a1: outcrop of sillimanitebearing metapelite, loc. 64 (sample 485525). hammer is 80 cm long. a2: thin section (xpl) of the same. b1: outcrop of layered biotite gneiss interstratified with amphibolite at loc. 81 (sample 485537). pen is 15 cm long. b2: thin section (xpl) of same. c1: outcrop of the top amphibolite at loc. 58 (sample 485523). pocket knife is 10 cm long. c2: thin section (ppl) of same. c3: outcrop of gabbroic inclusions in the basal amphibolite layer at loc. 92 (sample 485541). compass 5 cm wide. c4: thin section (xpl) of clinopyroxene cluster in amphibolite. c5: thin section (xpl) of sample 485540 (ultramafic layer, same locality). 40 upper boundary of this unit is not observed, since it is everywhere intruded by the granite. this ‘top amphibolite’ is continuous and can be traced all around the exposed granite contact; it is also rather homogeneous, much more so than any of the other components of the supracrustal sequence. in loc. 80 (fig. 5), it appears to be in tectonic contact with the underlying layered biotite gneiss. field description and petrology as mentioned above, three main components are observed in the supracrustal succession: aluminous metapelite, layered biotite gneiss and amphibolite. field aspects together with photographs of thin sections are presented in fig. 6. the aluminous metapelites occur as slaty, fine-grained (0.5–1 mm), grey to yellowish paragneisses (fig. 6a1). garnet or sillimanite is commonly seen in outcrop. in thin section, they display biotite, plagioclase and quartz with either sillimanite or poikiloblastic garnet (fig. 6a2) cutting across an earlier weak foliation marked by preferred orientation of biotite flakes and elongation of plagioclase crystals. the layered biotite gneisses appear as grey, relatively massive, fine grained (0.5–1 mm), finely layered rocks. they are interstratified at all scales with amphibolite (figs 3c, 6b1) and generally form discontinuous bodies on a 100 m scale. they consist of quartz, plagioclase, k-feldspar and biotite; the foliation is defined by the preferred orientation of biotite and elongation of quartz grains (fig. 6b2). the amphibolites are dark, massive rocks that also show a strong compositional banding (fig. 6c1–c2). regardless of their mode of outcrop either as a thick continuous layer, as in the ‘top amphibolite’, or as discontinuous layers interstratified with other lithologies, they are very similar in visual aspect and mineralogy. they mostly consist of a fine-grained (0.5–1 mm) hornblende-plagioclase assemblage, with preferred orientation of minerals defining the foliation. commonly, small clusters of clinopyroxene surrounded by felsic (mostly plagioclase) rims are observed (fig. 6c4). at one locality, gabbroic lenses on a scale of 5–10 cm have been observed within the amphibolite (loc. 92, fig. 6c3). they are medium grained (2–5 mm) and greenish in aspect, and composed of a clinopyroxene-plagioclase association with diffuse contacts with the neighbouring amphibolite (fig. 6c4). at the same locality, an ultramasiosio2 2 a lk al in e subalkaline/tholeiitic subalkaline/tholeiitic subalkaline/tholeiiticsubalkaline/tholeiiticsubalkaline/tholeiitic 40 50 60 70 80 0 5 10 15 ● ● paragneisses paragneisses paragneiss na2o + k2o basement supracrustal sequence kangaatsiaq granite layered biotite gneiss layered amphibolite ultramafic rocks ●‘normal’ orthogneiss high-k orthogneiss amphibolite enclaves basaltic andesite dacite rhyolite basalt basalt basalt andesite siosio2 2 sio2 fig. 7. total alkali vs. silica (tas) diagram (le maître et al. 1989) for the magmatic components of the supracrustal rocks and the surrounding orthogneisses. 41 fic layer c. 0.5 m thick has been observed. it is slightly coarser grained (2–5 mm) than the amphibolite, and solely consists of amphibole grains (fig. 6c5), which are optically similar to the hornblende in the surrounding amphibolite. geochemistry and origin figures 7–8 and table 1 summarise the major and trace element (especially ree) characteristics and relationships of the three main supracrustal components: amphibolites, metapelites and layered biotite gneisses. there is little, if any doubt of the fact that the amphibolites correspond to metamorphosed and deformed mafic igneous rocks. elsewhere, similar field characteristics in amphibolites as those observed here have been interpreted as corresponding to transposition of former pillow lavas in high strain domains (e.g. myers 2001). the metapelites obviously have a sedimentary origin and probably represent terrigeneous sediments. the origin of the layered biotite gneisses, however, is less obvious. they could represent either sedimentary or felsic volcanic rocks. therefore, they are plotted on geochemical diagrams for both magmatic and sedimentary rocks (see below), allowing comparisons. origin of the amphibolites the supracrustal amphibolites and their counterparts, enclaves in the basement orthogneisses, appear to be very similar in composition. they plot mostly as basalts in a tas diagram (fig. 7; le maître et al. 1989), and an afm diagram (fig. 9; irvine & baragar 1971) reveals that they belong to a tholeiitic series. this, together with their spectacularly flat ree pattern at about 10 times chondritic values (fig. 8), is consistent with the amphibolites corresponding to former morb basalts, possibly formed as part of an oceanic crust. many discriminant diagrams for basaltic rocks have been proposed on geochemical grounds (e.g. pearce 1982; shervais 1982; mullen 1983). however, some caution should be exercised when using such diagrams for the archaean, since the existence of modern-style tectonic settings in the archaean is not certain, and the palaeogeodynamical contexts might not be similar to those of modern settings (hamilton 1998; mccall 2003; van kranendonk 2003). nevertheless, in 100 10 1 0.1 basement orthogneiss la ce pr nd pm sm eu gd tb dy ho er tm yb lu supracrustal amphibolite amphibolite as enclaves in orthogneisses amphibolite100 10 1 0.1 la ce pr sa m pl e / r ee c ho nd ri te layered biotite gneiss100 10 1 0.1 la ce pr nd pm sm eu gd tb dy ho er tm yb lu sa m pl e / r ee c ho nd ri te kangaatsiaq granite la ce pr nd pm sm eu gd tb dy ho er tm yb lu nd pm sm eu gd tb dy ho er tm yb lu 1000 100 10 1 0.1 aluminous metapelites100 10 1 0.1 sa m pl e / r ee c ho nd ri te sa m pl e / r ee c ho nd ri te sa m pl e / r ee c ho nd ri te la ce pr nd pm sm eu gd tb dy ho er tm yb lu fig. 8. ree patterns (chondrite normalised, boynton 1984) for the lithologies in and around the kangaatsiaq synform. 42 such diagrams, the amphibolites plot either as morb or as rocks originated in oceanic arcs (arc tholeiites), leaving some ambiguity about their original setting. origin of the aluminous metapelites the geochemistry of metasedimentary rocks is commonly used to discuss their source, in terms of (1) the nature of the original sediments, (2) the nature of the weathered/ eroded source material, and (3) the degree of weathering of the source (see e.g. taylor & mclennan 1985; herron 1988; roser & korsch 1988; nesbitt & young 1989; bohlar et al. 2005). while several authors also use the geochemistry of sediments to discuss their geodynamical setting (bhatia 1983; bhatia & crook 1986; roser & korsch 1988), some caution should be exercised when dealing with archaean environments, as mentioned above. in terms of classification, the metasedimentary rocks from the kangaatsiaq area plot mostly as shales or greywackes, using either of the two schemes proposed by herron (1988). one of these is shown on fig. 10a; the ambiguity and possible (chemical) confusion between the two groups, shales and greywackes, which are poorly separated by this diagram, has been outlined by these authors. nevertheless, the conclusion points to relatively immature sediments which have undergone limited transport from their source. the nature of the source itself can be discussed using major or trace elements. roser & korsch (1988) proposed a scheme for source determination of clastic sediments on the basis of major elements. in this instance, the studied samples straddle the p2–p3 boundary (fig. 10b), suggesting a felsic to intermediate source. also trace elements can be used to refine this conclusion. as pointed out by taylor & mclennan (1985), some elements (high field strength elements, rare earth elements (ree), y, sc, th) only undergo limited fractionation during sedimentary processes; thus, their ratios reflect the signature of their source. plotting these elements against each other shows that the kangaatsiaq metasedimentary rocks (fig. 10e– h) have element ratios that are generally consistent with derivation from an orthogneissic source (amphibolites generally have too low trace element contents and incorrect ratios to be a possible source). the only exception is for heavy ree (figs 8, 10g). indeed, the relatively high yb contents of the metasedimentary rocks precludes their derivation solely from a low-yb gneissic basement, and implies that they must, at least in part, have been derived from higher-yb rocks such as the amphibolites; this is hardly a surprise, since amphibolite occurs as enclaves intercalated within the orthogneisses. modelling the ree contents of such a mixture shows that mixing of orthoa m f ● ● granite orthogneiss tholeiite series calc-alkaline series supracrustal amphibolite amphibolite enclave ultramafic rocks fig. 9. afm diagram (irvine & baragar 1971) showing the tholeiitic affinity of both the supracrustal amphibolites and the enclaves in the gneisses. a, na 2 o + k 2 o; f, feo total ; m, mgo. the fields of the basement orthogneisses and the kangaatsiaq granite are also shown for comparison. facing page: fig. 10. major and trace element geochemistry (a–d and e–h) of the metasedimentary rocks (paragneisses, and layered biotite gneisses). dotted fields show the compositions of the major regional lithologies (orthogneiss and high-k orthogneiss, moyen et al. 2003a; steenfelt et al. 2005; amphibolite; kangaatsiaq granite). a: log(sio 2 /al 2 o 3 ) vs. log(fe 2 o 3 /k 2 o), from herron (1988). b: discriminant diagrams for the metapelites, from roser and korsch (1988). the sources for each group are p1, mafic to intermediate volcanic rocks; p2, intermediate (andesitic, dacitic, occasionally rhyolitic) volcanic rocks; p3, felsic volcanic rocks; p4, evolved sediments, sandstones, etc. the discriminant functions are: f1 = –1.773 tio 2 + 0.607 al 2 o 3 + 0.760 fe 2 o 3 – 1.500 mgo + 0.616 cao + 0.509 na 2 o – 1.224 k 2 o – 9.090; f2 = 0.445 tio 2 + 0.070 al 2 o 3 – 0.250 fe 2 o 3 –1.142 mgo + 0.438 cao + 1.475 na 2 o + 1.426 k 2 o – 6.861. c, d: triangular diagrams (from nesbitt & young 1989). stars: theoretical mineral compositions; il, illite; ms, muscovite; pg, plagioclase; ksp, k-feldspar; cpx, clinopyroxene; hbl, hornblende; chl, chlorite; bt, biotite; sm, smectite. dashed arrows: trends for (1) weathering and (2) k-metasomatism, after nesbitt & young (1989) and bohlar et al. (2005). e, f: u vs. th and ti vs. zr (log scale) diagrams, showing that the metasedimentary rocks have trace elements ratios comparable to the gneisses, but mostly different from the amphibolites. g, h: la/yb vs. yb and ti/zr vs. ni (log scale) diagrams displaying the same relationships as e–f, also showing the mixing between an amphibolite-like and an orthogneiss-like source (ticks at 10% increments). 43 amphibolite yb la/yb ti/zr u ti ni zrth 0 5 10 0.0 0.5 1.0 1.5 th/u = 1 th/u = 5 th/u = 10 orthogneiss amphibolite amphibolite amphiboliteamphiboliteamphibolite granite 10 100 200 100 200 500 10 20 50 1000 2000 5000 10000 0 20 40 60 80 100 120 140 20 50 100 200 ti/z r = 10 ti/z r = 50 ti/z r = 10 0 ti/z r = 20 0 ti/z r = 20 orthogneissorthogneissorthogneissorthogneissorthogneiss amphibolite granite 0.0 0.5 1.0 1.5 2.0 2.5 3.0 orthogneisses amphibolite granite 0.1 0.5 1 5 10 50 100 500 orthogneiss amphibolite granite e f f f g h amphibolite aluminous paragneiss layered biotite gneiss standard mineral compositions for reference compositional fields of regional lithologies (see figure text) granite chl ksp, pg sm il bt cpx hbl ms pg ksp il, ms hbl cpx al2o3 k2o al2o3 cao + na2o + k2ocao + na2o feot + mgo 1 2 1 2 1 orthogneissorthogneiss c d granitegranitegranite 0.0 0.5 1.0 1.5 2.0 -0.5 0.0 0.6 1.0 1.5 fe -sh ale sh ale fe -sa nd su bli th ar en ite qu ar tz ar en ite su ba rk os e a rk os e w ac ke lit ha re nit e lo g (f e 2 o 3/ k 2o ) log(sio2/al2o3)log(siolog(sio2/al/al2o3)log(sio2/al2o3) amphiboliteamphiboliteamphibolite orthogneiss granite a p4 p3 p2 p1 8 4 0 -4 -8 8 4 0 -4 -8 f1 f2 amphiboliteamphibolite orthogneissorthogneiss amphibolite orthogneiss granite b 44 si o 2 t io 2 a l 2 o 3 fe 2o 3* m no m go c ao n a 2 o k 2o p 2 o 5 h 2o k /n a m g# a /c n k c .i. a . v c r n i c o c u z n r b sr b a y z r n b ta h f sc g a c s pb t h u t h/ u t i/z r la c e pr n d sm eu g d t b d y h o er t m y b lu la /y b eu /e u* 69 .0 0 74 .0 8 72 .9 2 72 .8 8 70 .2 1 66 .0 4 0. 37 0. 18 0. 27 0. 21 0. 43 0. 62 15 .1 6 13 .2 2 13 .4 8 13 .8 7 15 .1 4 16 .0 1 2. 46 1. 33 1. 48 1. 61 2. 50 3. 94 0. 02 0. 01 0. 01 0. 02 0. 04 0. 01 0. 79 0. 31 0. 44 0. 46 0. 89 1. 27 2. 07 1. 01 1. 17 1. 29 2. 17 5. 07 4. 18 3. 63 3. 64 4. 06 3. 93 3. 31 4. 23 4. 56 4. 74 4. 28 4. 29 1. 07 0. 16 0. 05 0. 07 0. 08 0. 17 0. 39 0. 22 0. 16 0. 17 0. 26 0. 80 0. 67 0. 83 0. 86 0. 69 0. 72 0. 21 39 32 37 36 41 39 1. 00 1. 04 1. 02 1. 02 1. 01 1. 01 28 11 10 11 33 36 7 3 3 4 14 11 8. 1 3. 5 4. 4 5. 5 bd l 22 .7 37 .0 44 .6 79 .4 68 .8 50 .7 3. 3 2. 6 2. 6 1. 7 13 .0 32 9. 1 36 .2 21 .5 20 .6 27 .9 25 .0 31 .9 11 4. 7 11 5. 5 11 8. 7 12 5. 8 56 .0 96 .0 73 5 25 2 34 2 34 0 71 2 19 13 14 76 46 3 67 2 59 3 13 84 20 95 8. 5 2. 7 5. 7 5. 5 bd l 7. 2 17 8 10 4 13 2 14 0 21 9 20 3 8. 4 3. 8 6. 0 4. 8 bd l 7. 0 4. 2 3. 1 3. 5 3. 7 4. 6 5. 4 2. 2 10 .5 2. 6 4. 7 2. 4 0. 9 1. 5 1. 5 3. 9 19 .1 17 .6 17 .8 18 .2 21 .3 1. 0 0. 4 0. 6 1. 9 6. 2 15 .6 16 .5 12 .8 17 .3 6. 9 10 .8 6. 8 9. 8 9. 2 14 .0 0. 9 1. 4 1. 0 0. 9 2. 6 12 .1 5. 0 10 .0 9. 8 5. 4 12 .6 10 .4 12 .3 9. 0 11 .8 18 .2 35 .9 19 .8 35 .2 39 .1 29 .0 15 1. 7 81 .2 39 .7 68 .9 75 .1 10 5. 0 31 3. 7 9. 7 4. 2 7. 5 8. 2 37 .7 33 .0 12 .8 23 .3 25 .4 12 6. 4 5. 3 1. 6 3. 2 3. 1 13 .4 1. 5 0. 6 0. 7 0. 7 2. 4 5. 1 1. 9 3. 0 3. 2 12 .5 0. 44 0. 15 0. 27 0. 27 0. 83 1. 96 0. 62 1. 14 1. 10 2. 81 0. 28 0. 09 0. 17 0. 17 0. 25 0. 76 0. 27 0. 50 0. 49 0. 98 0. 10 0. 03 0. 07 0. 06 0. 07 0. 57 0. 24 0. 45 0. 43 0. 47 0. 09 0. 04 0. 06 0. 06 0. 06 63 .0 83 .3 79 .0 89 .8 32 0 0. 87 0. 96 0. 70 0. 71 0. 56 62 .2 9 70 .9 7 63 .1 0 66 .0 3 0. 68 0. 26 0. 61 0. 62 15 .6 9 14 .8 8 16 .9 7 18 .9 8 5. 68 1. 85 5. 92 4. 27 0. 09 0. 02 0. 10 0. 03 3. 13 0. 48 2. 17 1. 45 4. 71 2. 13 4. 60 2. 19 3. 31 4. 23 2. 94 3. 20 2. 03 3. 38 1. 41 1. 70 0. 22 0. 08 0. 07 0. 10 0. 98 0. 18 0. 69 0. 59 0. 40 0. 53 0. 32 0. 35 52 34 42 40 0. 97 1. 03 1. 15 1. 71 60 .9 5 60 .4 4 65 .4 7 72 .8 0 1 00 12 13 3 88 68 2 13 6 61 50 .1 5. 0 79 .1 25 .1 47 .8 86 .3 10 0. 8 10 3. 0 14 .2 3. 7 10 1. 4 14 .9 67 .0 34 .7 78 .3 57 .3 46 .9 83 .2 44 .7 79 .8 8 03 82 2 23 1 21 3 8 19 14 30 31 4 26 2 16 .2 3. 8 12 .5 9. 2 1 65 14 7 98 93 8. 3 3. 5 4. 5 5. 1 3. 9 3. 8 2. 7 2. 4 3. 6 3. 5 3. 3 2. 3 14 .2 2. 3 23 .4 13 .0 18 .6 19 .6 19 .7 24 .1 4. 7 1. 2 2. 2 1. 5 8. 6 15 .4 7. 1 7. 8 4. 7 4. 8 2. 7 3. 2 0. 8 0. 6 0. 8 0. 7 5. 6 8. 2 3. 3 4. 7 24 .8 10 .5 37 .0 39 .7 35 .3 27 .3 12 .9 21 .3 74 .4 61 .0 27 .2 46 .0 9. 3 6. 9 3. 4 5. 8 33 .4 22 .2 13 .0 21 .5 4. 9 2. 8 2. 5 3. 4 1. 3 0. 9 0. 7 0. 9 5. 0 2. 8 2. 6 3. 1 0. 57 0. 22 0. 37 0. 36 2. 99 0. 86 2. 13 1. 86 0. 53 0. 13 0. 43 0. 33 1. 51 0. 35 1. 20 0. 93 0. 22 0. 05 0. 18 0. 14 1. 41 0. 30 1. 23 0. 95 0. 22 0. 04 0. 18 0. 14 25 .0 91 .8 10 .5 22 .3 0. 77 0. 93 0. 87 0. 82 70 .8 1 70 .0 3 47 .5 2 0. 29 0. 31 0. 74 15 .0 8 15 .1 5 14 .9 4 2. 47 2. 06 12 .4 6 0. 02 0. 02 0. 19 0. 90 0. 64 8. 32 2. 88 2. 39 11 .2 2 4. 42 4. 61 2. 48 2. 02 3. 13 0. 83 0. 06 0. 15 0. 04 0. 18 0. 26 0. 54 0. 30 0. 45 0. 22 42 38 57 1. 03 0. 99 0. 59 25 20 25 4 22 3 33 2 12 .9 7. 6 14 7. 8 71 .4 46 .4 72 .3 5. 4 3. 2 40 .3 43 .6 42 .7 86 .2 74 .4 92 .0 7. 7 50 4 83 9 93 55 8 10 49 39 3. 0 4. 5 17 .6 86 2 11 7 33 4 5. 4 5. 6 2. 1 2. 5 3. 2 1. 0 11 .4 7. 9 3. 1 5. 0 3. 7 43 .8 20 .8 22 .4 15 .1 1. 0 1. 3 0. 0 9. 6 15 .6 2. 6 1. 9 5. 1 0. 2 0. 5 1. 7 0. 3 3. 8 3. 0 0. 7 20 .4 15 .9 13 4 10 .2 38 .4 2. 6 21 .4 82 .7 6. 3 2. 3 8. 9 1. 0 7. 8 30 .1 4. 9 1. 3 3. 8 1. 6 0. 6 1. 0 0. 6 1. 4 3. 9 2. 3 0. 13 0. 30 0. 43 0. 69 1. 35 2. 74 0. 11 0. 16 0. 63 0. 32 0. 52 1. 68 0. 04 0. 06 0. 28 0. 27 0. 38 1. 82 0. 03 0. 05 0. 26 37 .8 10 2 1. 44 1. 34 0. 78 0. 94 47 .0 5 47 .1 4 48 .7 7 48 .7 4 48 .0 8 45 .8 7 0. 95 0. 81 0. 87 0. 77 0. 72 0. 51 14 .6 8 14 .7 2 14 .6 7 15 .8 2 14 .6 9 11 .5 4 12 .9 9 10 .9 0 12 .6 0 12 .1 4 10 .7 7 11 .7 4 0. 22 0. 26 0. 24 0. 21 0. 20 0. 21 6. 80 4. 74 6. 70 7. 18 7. 90 14 .1 9 13 .3 0 17 .8 9 11 .5 1 12 .1 8 13 .1 4 11 .7 8 2. 02 1. 40 2. 67 1. 64 2. 55 1. 39 0. 53 0. 08 0. 76 0. 31 0. 52 0. 58 0. 06 0. 06 0. 06 0. 05 0. 03 0. 04 0. 36 1. 19 0. 51 0. 45 0. 30 0. 79 0. 17 0. 04 0. 19 0. 12 0. 13 0. 27 51 46 51 54 59 71 0. 52 0. 42 0. 56 0. 63 0. 51 0. 47 27 1 23 7 27 1 24 4 22 5 17 7 20 7 30 8 28 4 24 7 42 5 17 34 15 3. 1 16 7. 6 12 1. 7 17 5. 7 19 7. 5 72 8. 1 72 .1 59 .9 57 .1 57 .5 61 .0 81 .6 78 .7 73 .7 30 .3 12 .6 24 .1 2. 2 90 .1 76 .7 10 8. 2 77 .4 74 .8 10 3. 3 9. 1 1. 7 9. 4 32 .4 6. 5 14 .8 93 11 7 11 7 92 94 78 64 22 11 8 46 37 82 21 .1 18 .8 20 .6 18 .5 17 .1 11 .6 19 16 20 32 16 24 2. 8 2. 2 2. 4 4. 1 2. 7 1. 8 0. 9 0. 6 0. 9 1. 1 0. 7 0. 8 1. 1 0. 8 0. 8 0. 7 1. 3 0. 6 41 .6 38 .2 40 .9 41 .2 38 .3 31 .3 16 .4 14 .5 16 .1 16 .5 14 .8 11 .9 0. 1 0. 1 0. 0 0. 3 0. 0 0. 3 2. 9 2. 8 3. 5 1. 7 3. 2 1. 3 0. 4 0. 2 0. 3 0. 2 0. 2 0. 2 0. 2 0. 1 0. 1 0. 3 0. 1 0. 3 1. 8 3. 5 3. 2 0. 9 1. 4 0. 5 29 6 30 3 26 6 14 2 27 0 12 5 3. 0 2. 2 3. 0 2. 2 2. 9 2. 6 7. 7 6. 2 7. 2 6. 1 7. 9 5. 2 1. 2 1. 0 1. 2 1. 0 1. 3 0. 8 6. 3 5. 4 6. 1 4. 9 6. 1 3. 7 2. 1 1. 8 2. 0 1. 8 1. 8 1. 2 0. 7 0. 6 0. 7 0. 7 0. 6 0. 4 2. 5 2. 1 2. 5 2. 3 2. 1 1. 4 0. 49 0. 43 0. 48 0. 45 0. 41 0. 28 3. 12 2. 85 3. 10 2. 89 2. 60 1. 72 0. 72 0. 64 0. 73 0. 64 0. 60 0. 40 1. 96 1. 77 1. 95 1. 72 1. 62 1. 13 0. 31 0. 28 0. 33 0. 27 0. 26 0. 18 2. 12 1. 85 2. 08 1. 82 1. 70 1. 20 0. 31 0. 29 0. 31 0. 26 0. 26 0. 17 1. 42 1. 22 1. 43 1. 20 1. 68 2. 19 0. 96 1. 01 0. 90 1. 00 0. 87 0. 99 la ye re d bi o ti te g ne is s pa le le uc o cr at ic g ne is s b io ti te -b ea ri ng g ne is s a m ph ib o lit e k an ga at si aq g ra ni te a lu m in o us m et as ed . 48 55 31 48 55 35 48 55 25 q zb tsi llg t sc hi st q zb tg t gn ei ss 81 81 81 81 52 64 48 55 37 48 55 38 48 55 23 48 55 33 48 55 36 48 55 28 48 55 40 81 58 73 92 61 73 75 85 gi a 20 01 -2 17 81 a m ph ib o lit e in lo w er la ye r as so ci at ed w it h fe ls ic r o ck s pe ri ph er ic gr an it ic d yk e m as si ve a m ph i bo lit e, t o p u lt ra m af ic la ye r in a m ph ib o lit e 48 55 29 48 55 39 48 55 24 48 55 27 47 05 29 48 55 34 81 81 57 48 55 22 48 55 30 48 55 32 b as em en t m ai n gr an it ic m as s o rt ho gn ei ss a m ph ib o lit e en cl av e sa m pl e n o . lo ca lit y ta bl e 1. c he m ic al a na ly se s o f ro ck s in a nd a ro un d th e k an ga at si aq s yn cl in e sa m pl e nu m be rs r ef er t o g eu s da ta ba se s; lo ca lit ie s ar e sh o w n o n fi gs 1 a nd 4 , e xc ep t gi a 20 01 -2 17 o ut si de t he m ap a re a (u t m 3 96 54 0, 7 57 59 84 ). m aj o r el em en ts in w t% ; t ra ce e le m en ts in p pm . a na ly ti ca l d at a o bt ai ne d at g eu s by x r f (m aj o r el em en ts a nd a pp ro xi m at e tr ac e el em en ts in 4 70 52 9) a nd ic pm s (a ll o th er t ra ce e le m en ts ). k /n a: m o le cu la r k /n a ra ti o. m g# : m o le cu la r 10 0m g/ (m g + f e) . a /c n k : m o le cu la r a l/( c a + n a + k ). c .i. a .: c o nt in en ta l i nd ex o f a lt er at io n (n es bi tt & y o un g 19 89 ); m et as ed .: m et as ed im en ta ry r o ck ; b dl : b el o w d et ec ti o n lim it . 45 gneisses with amphibolite (fig. 10g, h) can explain the yb contents of the sediments; since the amphibolites are, collectively, less enriched in trace elements than the gneisses, their involvement would only have little effect on the other incompatible elements in the metasedimentary rocks. in contrast, the latter display higher ni and cr contents than the orthogneisses, also consistent with a contribution from amphibolite or its precursor rocks in their formation (fig. 10h). finally, the degree of alteration of the source can be discussed. the metasedimentary rocks display c.i.a. values (chemical index of alteration, nesbitt & young 1989) of c. 60–70 (table 1), slightly lower than for shales or similar rocks (70–75, taylor & mclennan 1985). in the triangular diagrams proposed by nesbitt & young (1989; fig. 10c, d), they also depart only moderately from their protoliths, suggesting a relatively unweathered source. very little or no evidence for secondary kenrichment is observed. taking the above-mentioned limitations into account, the geoynamic setting inferred from the geochemistry gives consistent results regardless of the classification scheme used. both the major elements classifications of bhatia (1983) and roser & korsch (1988) and the trace element systems of bhatia & crook (1986) suggest an oceanic or continental island-arc setting. however, this only reflects the characteristics outlined above: relatively immature sediment derived from poorly weathered felsic to intermediate magmatic rocks, with a possible mafic component. origin of the layered biotite gneiss (felsic volcanic rocks?) the two samples analysed of the layered biotite gneisses give ambiguous geochemical signatures and can be interpreted either as sedimentary or igneous (figs 7–10). in general, they seem to share more similarities with the granite or the orthogneisses than with any other member of the supracrustal group. in particular, fig. 10 (c, d) shows that if these rocks are of sedimentary origin, they are indeed very similar to their source and were derived from a largely unweathered protolith. this implies that the layered biotite gneiss can be interpreted in two ways. it may represent very immature sediment derived from a mostly unweathered protolith with a very similar bulk composition, such as a conglomerate made of pebbles of unweathered orthogneiss, in which case the banding could be a trace of the transposed pebbles. alternatively the layered biotite gneiss represents calc-alkali or ttg-type felsic lavas, whose composition would of course be very similar to that of their plutonic counterparts. origin of the supracrustal sequence as a whole based on the foregoing discussion two interpretations can be proposed for the supracrustal sequence. 1. the succession could represent a dismembered ophiolite sequence intermingled with clastic sediments eroded from a nearby continent. the combined sequence could then be interpreted as an accretionary prism. the likely tectonic nature of the contact between members of the sequence (see above and figs 4, 5) supports this hypothesis. 2. the whole supracrustal pile consists of a bimodal, calcalkaline, probably subduction-related volcanic suite associated with immature terrigeneous sediments directly derived from their weathering. this is consistent with an arc situation, in which a backor fore-arc basin is being filled with both volcanic products and detrital sediments largely derived from the weathering of these lavas. at the same time, tonalitic plutons are emplaced at depth from the same magmas. the plutonic rocks are quickly uplifted and eroded, and, besides intruding into the supracrustal pile, may in some cases also represent the basement for subsequent volcano-detritic basin fill. in both cases, the rocks were formed in a convergent setting, probably above or close to an active subductions margin. in general, arcor subduction-related origins for archaean volcanic suites are preferred by most workers (e.g. card 1990; lowe 1994; windley 1995; chadwick et al. 1996), although the issue remains controversial (hamilton 1998; mccall 2003; van kranendonk 2003). nature and origin of the kangaatsiaq granite the kangaatsiaq granite is pink, porphyritic, and displays a distinct rodding (fig. 11a) showing that it has been intensely deformed (see below). while yz sections (perpendicular to the main stretching direction) display a preserved magmatic texture, sections parallel to x clearly show the gneissic texture of the rock. the mineralogical paragenesis is k-feldspar + quartz + sodic plagioclase + biotite, with accessory zircon, titanite, apatite and oxides. the granite has moderate k/na ratios (0.67–0.86), is slightly metaluminous with a/cnk ratios of 1.00–1.04, and has low mg# of 32– 41 (table 1). ni and cr contents are also low, while rb, sr and ba contents are moderate; 46 this composition corresponds to the biotite-bearing granites of moyen et al. (2003b), which are interpreted to have been derived from partial melting of ttg gneisses. this conclusion is consistent with the highly migmatitic nature of the surrounding gneissic basement (van gool et al. 2002a). structure and deformation history as mentioned above, the granite displays a strong rodding and l > s fabrics (fig. 11a). the strain pattern in the granite (fig. 11b) is consistent with highly constrictional deformation, with foliation poles plotting on a great circle, and lineations clustered near the pole of this great circle. this corresponds to subhorizontal, ene–wsw stretching, consistent with the general orientation of the structures in kangaatsiaq area (fig. 1), and more generally with the structural grain of the region (van gool et al. 2002a; piazolo et al. 2004; mazur et al. 2006, this volume). the surrounding gneissic basement and supracrustal rocks show the same strain pattern when plotted (fig. 11c), although in the field, the rocks commonly have a ls or s > l fabric. this suggests that pre-existing foliations have been reoriented during the latest constrictional deformation event, leading to their present distribution. the fact that intense constriction (rather than shortening) can produce folded structures has previously been demonstrated by e.g. leloup et al. (1995) in the red river shear zone in yunnan, china, where the ductile deformation in gneisses resulted in the development of elongate synclines and anticlines with axes parallel to the shear zone and the x-axis of deformation. the study of deformation-related textures allows the conditions of deformation to be roughly constrained. in the granite and felsic components of the supracrustal sea total data: 70 equal area, lower hemisphere b. within the granite poles to foliation lineation poles to axial planes fold axis c. outside the granite total data: 42 fig. 11. a: macroscopic view of the kangaatsiaq granite at loc. 75 (corresponding to sample 485529), showing strong rodding. hammer shaft about 4 cm wide. b, c: stereograms of poles to foliation (circles) and lineations (squares) within and outside the granitic intrusion. the strain patterns are similar in both units and define a highly constrictional, ne–sw-trending and subhorizontal deformation. 47 a b c d e fig. 12. deformation textures either related to the latest, constrictional deformation (a–c) or not compatible with low-t deformation (d, e). see comments in the main text. a: quartz ribbons in the kangaatsiaq granite (sample 485527). b: quartz subgrains in felsic supracrustal gneiss (sample 485531). c: poikiloblastic garnet in metapelite cutting across an earlier foliation (sample 485535). d, e: high-temperature recrystallisation with 120° triple junctions in amphibolite (sample 485540) and felsic rocks (sample 485530). in e, the quartz also shows low-temperature deformational features such as undulating extinction and quartz subgrains, indicating that this rock witnessed two successive deformation events. 48 ries (fig. 12a, b), the deformation led to the development of quartz subgrains and recrystallised quartz ribbons. this corresponds to deformation under lower amphibolite facies conditions (400 ± 50°c; bouchez & pécher 1976; gapais & barbarin 1986; gapais 1989; hirth & tullis 1992; vernon 2000). under these conditions, only the quartz is ductile, such that all deformation is accommodated by quartz recrystallisation or deformation. in the al-rich lithologies, deformation-related textures are mostly seen in the formation of poikiloblastic, synto post-tectonic garnets (fig. 12c). piazolo (2002) estimated that the chemistry of garnet in similar pelites nearby is compatible with a long duration of temperature conditions at around 500°c, which is in broad agreement with the above estimate. willigers et al. (2002) described the cooling history of the nno close to our study area from ar-ar dating of various minerals, and likewise concluded that the cooling history of the nno was slow, from 400°c (muscovite closure) at 1.7 ga to 200°c (k-feldspar closure) at 1.5 ga. therefore, it can be considered that a constrictional deformation event post-dating the granite emplacement occurred during cooling to lower amphibolite facies conditions. since this event is apparently responsible for the regional-scale structures (mazur 2002; van gool et al. 2002b; piazolo et al. 2004), and is of lower proterozoic age (willigers et al. 2002), we propose that it corresponds essentially to the nagssugtoqidian deformation proper. however, some textures are not compatible with the above conditions. in amphibolites, high-temperature fabrics with polygonal textures and 120° triple junctions are preserved (fig. 12d). in some of the felsic supracrustal rocks or basement gneisses (but never in the granite), evidence is preserved for a similar high-temperature fabric, overprinted by later quartz recrystallisation (fig. 12e). according to kretz (1969), gower & simpson (1992), kretz (1994) and martelat et al. (1999), such fabrics are poikiloblastic garnet cutting the d1 fabric quartz subgrains, etc. quartz subgrains, etc. high-temperature recrystallisation country rocks granite pr en ag ss ug to qi di an d 1/ d 1b (g ra nu lit ic ) n ag ss ug to qi di an d 2 (a m ph ib o lit ic ) (not formed) no quartz d2 deformation not expressed quartzo-feldspathic amphibolitic granite emplacement fig. 13. summary of the deformation history of the kangaatsiaq synform and kangaatsiaq granite. see comments in the main text. photos from fig. 12. 49 likely to develop under granulite facies conditions (600– 800°c). this points to the existence of one or more older (d1?) deformation event(s). since no evidence for this deformation is found in the granite, we suggest that it was pre-granite, and therefore likely corresponds to late archaean deformation. p–t estimates for metapelites and metabasites in the kangaatsiaq area by piazolo (2002) also indicated the existence of an early metamorphic phase with p–t conditions between 650°c, 3–5 kbar and 780°c, p unknown. this estimate is in good agreement with the textural evidence for d1 deformation under lower granulite facies conditions. the pre-granite deformation is also evidenced by the early isoclinal folds, the existence of a foliation within the supracrustal rocks that does not exist in the granite, and the fact that the granite apparently cuts earlier structures (fig. 5). at loc. 80, the granite is clearly observed cutting across the foliation and shear bands in the amphibolite; these shear bands are injected by pegmatites that might also be cut by the granite. this suggests that there were actually two pre-granite events, the first of which corresponds to the granulite facies formation of the foliation and isoclinal folds, and the second one to the pegmatite-injected shear bands. however, the floor of the granitic intrusion is also apparently offset by the shear bands (fig. 5b). furthermore, the geometry of the shear bands and the foliation suggests extensional deformation; since the cliff face studied here almost corresponds to a yz section relative to the regional constrictional deformation, this geometry is likely to correspond to the original, preserved pre-constriction geometry. finally, the fact that the granite both cuts across, and is offset by the shear bands, suggests that the granite emplacement may actually have been syn-extension as sketched in fig. 5c. altogether, the simplest possible deformation history (with the smallest number of episodes) can be summarised as follows (fig. 13). 1. a first deformation event (d1) under lower granulite facies conditions (c. 5 kb, 600–800°c), resulted in the development of granulitic (polygonal) textures in all the existing lithologies, the formation of a main foliation, and isoclinal folding. it probably corresponds to compression of the original, likely accretionaly wedge or arc sequence. 2. this may have been followed by a second event (d1b) of probably extensional deformation, maybe associated with (or shortly followed by) the emplacement of the granite sheet. this event, only witnessed by the shear zones cutting the d1 foliation, e.g. at locality 80, is poorly recorded and probably just represents the final stage of d1 deformation. assuming the granite has a late archaean age, which is very likely in the regional context, this deformation could correspond to the later stages of the evolution of an arc or active continental margin, with strain relaxation and syn-extension granite emplacement. 3. a final event of constrictional deformation under lower amphibolite conditions (d2). due to the relatively low-temperature conditions, only the quartz-bearing lithologies were affected. therefore, the granite shows strong recrystallisation, the felsic supracrustal rocks display overprinting of the d1/d1b fabric by this event, and the quartz-free amphibolites were essentially unaffected by this event. the d2 event corresponds to the purely constrictional, regional structures which have been interpreted by piazolo et al. (2004) and mazur et al. (2006, this volume) as resulting from the indentation of the nno by a solid, north-moving block immediately north of the arfersiorfik shear zone (for the latter, see e.g. sørensen et al. 2006, this volume). this palaeoproterozoic deformation gave the studied area its present synformal structure. conclusions while the present-day synclinal structure of the kangaatsiaq area essentially results from n60 constriction related to the palaeoproterozoic nagssuqtoqidian deformation, the lithologies together with early preserved structures give insight into the late archaean crustal evolution. the basement gneisses genetically belong to the ttg suite (moyen et al. 2003a; steenfelt et al. 2005), which is generally interpreted as generated by partial melting of a subducting slab (e.g. martin 1994). some components of the basement display implications of mantle wedge involvement in their genesis (steenfelt et al. 2005), which is unusual in the archaean but nevertheless consistent with an active margin setting. the supracrustal succession is composed of discontinuous layers of mafic morb-like or arc tholeiite lavas, and together with immature, terrigeneous shales or greywackes derived from erosion of the basement ttg gneisses or volcanic counterparts to them, with a likely small contribution from tholeiitic lavas. part of the succession could also have been felsic rocks derived from erosion of the basement ttg gneisses or volcanic counterparts to the latter, with a likely small contribution from tholeiitic lavas. the whole series is capped by a layer c. 100 m thick of mafic volcanic rocks likewise of tholeiitic affinity. all these lithological components are in good 50 agreement with either an arc-related setting, with a plutonic arc developing simultaneously with the filling of volcano-detritic basins with lavas of similar affinities and immature sediments; or with an accretionary wedge environment involving ocean floor juxtaposed together with similar sediments. in both cases, they correspond to an active subduction margin. intense migmatisation of the basement is probably associated with the emplacement of the anatectic, likely synkinematic kangaatsiaq granite. this was apparently synchronous with an early, lower granulite facies (d1/d1b) deformation event that may have ended with strain relaxation and exhumation of the rocks from the active margin at the end of the archaean cycle. the supracrustal association and the sequence of events in the kangaatsiaq area are comparable to the evolution of many archaean greenstone belts (e.g. card 1990; chadwick et al. 1996; hunter et al. 1998). on the other hand, classical archaean components such as orthochemical sediments and plume-related komatiites (arndt 1994) or orthochemical components (lowe 1994) are completely missing from the kangaatsiaq area. however, this apparently rather uncommon absence is known from other midto late archaean greenstones, also in west greenland (e.g. garde 1997). the setting is sometimes interpreted as being arc-related (card 1990; lowe 1994). in contrast, widespread melting and granite emplacement at the end of the archaean is a very common situation, which has been described in many studies (among others, e.g. gorman et al. 1978; card 1990; sylvester 1994; windley 1995; chadwick et al. 1996; moyen et al. 2003b). acknowledgements j.a.m. van gool, g.i. alsop, s. piazolo and s. mazur visited the area in 2001, and their work was used as a basis for the subsequent mapping. they also provided useful comments on the geology and metamorphic history of the region. a.a. garde kindly supplied analyses of the basement gneisses; his editorial help with the figures and manuscript is also gratefully acknowledged. reviews by a.g. leslie and a second reviewer greatly improved the original manuscript. linguistic corrections by r.w. belcher were also of greatest help. chemical analyses were performed at geus. references arndt, n.t. 1994: archean komatiites. in: condie, k.c. 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histories in precambrian and phanerozoic orogens. journal of geology 110, 503–517. windley, b.f. 1995: the evolving continents, 3rd ed., 526 pp. chester: john wiley and sons. _______________________________________________________________________________________________________________________________________________________________________________________________ manuscript received 7 june 2004; revision accepted 1 february 2006 geological survey of denmark and greenland bulletin 12, 1-16 1 geological survey of denmark and greenland bulletin 12 · 2007 lithostratigraphy of the palaeogene – lower neogene succession of the danish north sea poul schiøler, jan andsbjerg, ole r. clausen, gregers dam, karen dybkjær, lars hamberg, claus heilmann-clausen, erik p. johannessen, lars e. kristensen, iain prince and jan a. rasmussen geological survey of denmark and greenland danish ministry of the environment 2 geological survey of denmark and greenland bulletin 12 keywords lithostratigraphy, biostratigraphy, north sea basin, palaeogene, neogene. cover complex fabric created by multiple small-scale sand intrusions (light) into dark mudstones – such enigmatic fabrics are commonly associated with the sand-rich units of the rogaland group in the siri canyon area, offshore denmark. the illustrated section of core is about 10 cm across and is from the lower tyr member (lista formation) in the cecilie-1b well (2346.8 m). photograph: jakob lautrup. chief editor of this series: adam a. garde editorial board of this series: john a. korstgård, geological institute, university of aarhus; minik rosing, geological museum, university of copenhagen; finn surlyk, department of geography and geology, university of copenhagen scientific editors of this volume: jon r. ineson and martin sønderholm editorial secretaries: jane holst and esben w. glendal referees: paul van veen (norway) and robert o’b. knox (uk) illustrations: stefan sølberg digital photographic work: benny m. schark graphic production: knud gr@phic consult, odense, denmark printers: schultz grafisk, albertslund, denmark manuscript received: 29 august 2005 final version approved: 8 september 2006 printed: 29 june 2007 issn 1604-8156 isbn 978-87-7871-196-0 geological survey of denmark and greenland bulletin the series geological survey of denmark and greenland bulletin replaces geology of denmark survey bulletin and geology of greenland survey bulletin. citation of the name of this series it is recommended that the name of this series is cited in full, viz. geological survey of denmark and greenland bulletin. if abbreviation of this volume is necessary, the following form is suggested: geol. surv. den. green. bull. 12, 77 pp. available from geological survey of denmark and greenland (geus) øster voldgade 10, dk-1350 copenhagen k, denmark phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: geus@geus.dk and geografforlaget a/s filosofgangen 24, 1., dk-5000 odense c, denmark phone: +45 63 44 16 83, fax: +45 63 44 16 97, e-mail: go@geografforlaget.dk or at www.geus.dk/publications/bull © de nationale geologiske undersøgelser for danmark og grønland (geus), 2007 for the full text of the geus copyright clause, please refer to www.geus.dk/publications/bull 3 contents abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 geological setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 previous work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 material and methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 offshore and onshore lithostratigraphic nomenclature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 chronostratigraphy and biostratigraphy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 paleocene. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 eocene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 oligocene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 miocene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 lithostratigraphy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 rogaland group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 våle formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 bor member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 lista formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 vile member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 tyr member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 ve member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 idun member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 bue member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 rind member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 sele formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 kolga member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 fur formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 balder formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 stronsay group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 horda formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 hefring member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 westray group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 lark formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 dufa member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 freja member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 4 5 abstract schiøler, p., andsbjerg, j., clausen, o.r., dam, g., dybkjær, k., hamberg, l., heilmann-clausen, c., johannessen, e.p., kristensen, l.e., prince, i. & rasmussen, j.a. 2007: lithostratigraphy of the palaeogene – lower neogene succession of the danish north sea. geological survey of denmark and greenland bulletin 12, 77 pp. + 5 plates. as a result of a lithological, sedimentological and biostratigraphic study of well sections from the danish sector of the north sea, including some recently drilled exploration wells on the ringkøbing– fyn high, the lithostratigraphic framework for the siliciclastic palaeogene to lower neogene sediments of the danish sector of the north sea is revised. the sediment package from the top of the chalk group to the base of the nordland group is subdivided into seven formations containing eleven new members. the existing våle, lista, sele, fur, balder, horda and lark formations of previously published lithostratigraphic schemes are adequate for a subdivision of the danish sector at formation level. bor is a new sandstone member of the våle formation. the lista formation is subdivided into three new mudstone members: vile, ve and bue, and three new sandstone members: tyr, idun and rind. kolga is a new sandstone member of the sele formation. hefring is a new sandstone member of the horda formation. freja and dufa are two new sandstone members of the lark formation. danish reference sections are established for the formations, and the descriptions of their lithology, biostratigraphy, age and palaeoenvironmental setting are updated. __________________________________________________________________________________________________________ authors’ addresses p.s.*, j.a., k.d. & l.e.k., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. * present address: gns science, 1 fairway drive, avalon, p.o. box 30368, lower hutt, new zealand. e-mail: p.schioler@gns.cri.nz o.r.c. & c.h.-c., department of earth sciences, university of aarhus, høegh-guldbergsgade 2, dk-8000 århus c, denmark. g.d. & l.h., dong energy, agern allé 24–26, dk-2970 hørsholm, denmark. i.p. & e.p.j., statoil norway, forusbeen 50, n-4035 stavanger, norway. j.a.r., geological museum, university of copenhagen, øster voldgade 5–7, dk-1350 copenhagen k, denmark. 6 fig. 50 fig . 56 a f ig. 49 fig. 56b fig. 61 fig. 58 saxo-1 wessel-1 tordenskjold-1 eg-1 diamant-1 bertel-1 mona-1 karl-1 w. lulu-3,-1 cleo-1 augusta-1 amalie-1 tabita-1 gulnare-1 gwen-2 iris-1 baron-2 nora-1 elin-1w-1 ravn-1 falk-1 u-1 e-8 tove-1 john-flanke-1 alma-1 emma-1 edna-1 roxanne-1 ugle-1 frida-1 l-1 francisca-1 cecilie-1 connie-1 elna-1 siri-2 siri-3 sofie-1 floki-1 sandra-1 nolde-1 nini-1 nini-2 nini-3 d-1 vanessa-1 ibenholt-1 ida-1 r-1 c-1 k-1 f-1 inez-1 s-1 siri-1 v-1 g-1 deep-adda-1 adda-2,-1bo-1 north-jens-1 lulu-1 lulu-2 sten-1 gert-1 kim-1 lone-1 57°00' 4°00' 6°00' 56°00' 25 km 250 km c offee soil fault north sea denmark n s uk g nl p sir i c an yo n mid north sea high central graben a b norwegian–danish basin c entral g raben 100 km north polish strait east shetland platform fennoscandian shield scottish high v ik in g g ra be n rhenish massif bohemian massif jylland sjælland storebælt moray firth mid north sea high ringkøbing–fynhigh fig. 1. location maps showing the position of wells used in the study (a) and major structural elements in the greater north sea area (b) mentioned in the text. on the well map (a) are indicated the locations of the seismic sections shown in figs 49, 50, 56, 58 and 61. grey shading on this map indicates the margins of the siri canyon; grey shading inside the canyon indicates an area of positive relief within the canyon. ggggg, germany; nnnnn, norway; n ln ln ln ln l, netherlands; ppppp, poland; sssss, sweden; u ku ku ku ku k, united kingdom. 7 introduction intense drilling activity following the discovery of the siri field in 1995 has resulted in an improved understanding of the siliciclastic palaeogene sediment package in the danish sector of the north sea (fig. 1). many of the new wells were drilled in the search for oil reservoirs in sandstone bodies of paleocene–eocene age. the existing lithostratigraphy was established on the basis of data from a generation of wells that were drilled with deeper stratigraphic targets, with little or no interest in the overlying palaeogene sedimentary succession. this means that this early scheme does not include palaeogene sandstone units in the danish sector. in order to improve the understanding of the distribution, morphology and age of the palaeogene sediments, in particular the economically important sandstone bodies, a detailed study of this succession in the danish sector has been carried out. the main aim was to update the lithostratigraphic framework of the succession on the basis of new data from recently drilled wells. all of the widespread palaeogene mudstone units in the north sea were established with norwegian or united kingdom (uk) type wells. in the present work, these units have been maintained unchanged or with only slight modifications. danish reference wells have been established for the units, however, and lithological descriptions have been expanded to cover the characteristics of these units in the danish sector. many of the sandstone bodies recently discovered in the danish sector have a limited spatial distribution and are derived from sources different from those of most of the contemporaneous sandstone bodies in the norwegian and uk sectors; furthermore, the danish sandstone bodies probably neither overlap nor are in contact with the norwegian/uk sandstones. these units have therefore been established as new in the danish sector, and have been assigned danish type and reference sections. the lithostratigraphy presented herein (fig. 2) has its base at the top of the early paleocene (danian) ekofisk formation (chalk group). the top of the study section is at the unconformity between the late eocene – mid-miocene westray group and the mid-miocene to recent nordland group. oil companies operating in the north sea have collected a substantial amount of lithostratigraphic data on the palaeogene successions and a detailed lithostratigraphy has been developed for the danish and norwegian sectors (see e.g. hamberg et al. 2005). a number of informal lithostratigraphic units have been introduced that have subsequently found their way into academia and geological survey organisations. it has been the aim of the present work formally to define these new units. this has been done maintaining their original (albeit informal) names whenever feasible. it has not been the aim of this work to provide a sequence stratigraphic model for the palaeogene sediments in the central and eastern north sea; for this the reader is referred to michelsen et al. (1992, 1995, 1998), mudge & bujak (1994, 1996a, b), neal et al. (1994) and danielsen et al. (1997). the present contribution does not attempt to review the petroleum-related aspects of the palaeogene succession. information about this may be found elsewhere, for example in the annual reports from the danish energy authority. preliminary results from the present work, including a revised lithostratigraphic scheme, were previously published in a brief review paper (schiøler et al. 2005). the present contribution formally describes the new stratigraphic units suggested in the review paper and further documents the palaeogene – lower neogene lithostratigraphy in the danish sector of the north sea. 8 danian selandian thanetian sparnacian ypresian lutetian ma m id dl e eo ce ne lo w er e o ce ne u pp er p al eo ce ne c ha lk g ro up r o ga la nd g ro up st ro ns ay g ro up w es tr ay g ro up st ro ns ay g ro up lo w er p al eo ce ne priabonian rupelian chattian aquitanian burdigalian langhian serravallian 15 20 25 30 35 45 50 55 60 65 m id dl e m io ce ne lo w er m io ce ne lo w er n eo ge ne pa la eo ge ne pa la eo ge ne u pp er o lig o ce ne lo w er o lig o ce ne u pp er e o ce ne m id dl e eo ce ne lillebælt clay fm horda fm røsnæs clay fm fur fm f ølst fm stolle klint clay østerrende clay holmehus fm ve mb bue mb rindmb æbelø fm danian limestone ekofisk fm våle fm li st a fo rm at io n vile mb sele fm balder fm bartonian lutetian 40 søvind marl fm søvind marl fm viborg fm linde clay branden clay vejle fjord fm hodde fm gram fm lark fm (undivided) horda fm se ri es sy st em st ag e d en m ar k o ns ho redanish north sea kolga mb hefring mb tyr mb bor mb 49.0 55.5 54.5 57.9 60.0 41.3 37.0 33.7 28.5 23.8 20.5 16.4 14.8 dufa mb odderup fm bastrup sand ribe fm freja mb idun mb n o rd la nd g ro up arnum fm kerteminde marl lellinge greensand 9 geological setting the danish sector of the north sea is situated in the central and eastern north sea and comprises three major structural elements: the central graben, the norwegian–danish basin (the eastern part of the northern north sea basin of rhys 1974) and the ringkøbing–fyn high (fig. 1; the geographic terminology and names of structural elements in the north sea used herein are adapted from rhys 1974, rønnevik et al. 1975, deegan & scull 1977 and fyfe et al. 2003). the western boundary of the danish sector largely coincides with the eastern boundary of the mid north sea high, the southern boundary largely coincides with the southern limit of the ringkøbing–fyn high, and the northern boundary is in the norwegian– danish basin. this basin as well as the ringkøbing–fyn high are early permian structures. active rifting occurred in the central graben from the middle to late jurassic along pre-established palaeozoic fault trends. major tectonic activity around the palaeozoic and jurassic structures had largely ceased by late cretaceous time, and the sediment basin below the central north sea was largely characterised by regional subsidence (ziegler 1981). during the late cretaceous to danian sea-level high, pelagic chalk sediments draped the structural highs and the northern and southern north sea basins became one north sea basin delimited by the fennoscandian shield to the north-east, the rheinish–bohemian massif to the south and the british massifs, highs and platforms to the west (see ziegler 1981 fig. 16 for details). chalk sedimentation continued through to the end of the danian stage when it gave way to hemipelagic and siliciclastic sedimentation. this was probably caused by uplift of the basin margins to the west and east (ahmadi et al. 2003). however, most of the siliciclastic sediments were derived from the scottish high and the east shetland platform, uplifted by the iceland plume (ahmadi et al. 2003). by the time of peak uplift, in the mid-thanetian, large sand systems were building out towards the central north sea. most sediment came from the west, but the siri canyon system, a depression in the top chalk surface, was fed from the fennoscandian shield in the north-east and north (fig 1; ahmadi et al. 2003; hamberg et al. 2005). thermal subsidence centered above the central graben continued through the eocene as sea level fell and the temperature decreased. shallow-marine sediments characterised the margins of the north sea basin, especially its western margin, whereas basinal mudstone continued to accumulate in the basin centre and in the eastern part of the basin (joy 1996). inversions controlled by compression between the atlantic spreading zone to the northwest and the orogenesis of the alps to the south added to further uplift of the basin margins and submarine fans and turbidites were deposited near the centre of the basin (jones et al. 2003). during the oligocene, the north sea basin became part of a larger nw european basin. connection with the north atlantic broadened and enhanced communication with the oceanic water mass to the north-west, whereas the connection to the south through the north polish strait became closed for the deep water (fyfe et al. 2003). glacio-eustatic sea-level changes became more frequent and controlled the sedimentary cycles. the eastward progradation direction of the paleocene and eocene sediments gave way to sediment supply from the european massifs to the far south (fyfe et al. 2003). continued subsidence above the mesozoic rift structures created accommodation space for thick sediment packages of basinal mudstones, and few sandstone units reached the basin depocentre above the mesozoic rifts (fyfe et al. 2003). in the neogene epoch, sediment started to be derived from the fennoscandian shield to the north, and the progradation direction changed to the south-west and west in the danish sector of the north sea. facing page: fig. 2. lithostratigraphic column for the palaeogene and lower neogene of the danish north sea sector showing the approximate correlation with danish onshore stratigraphic units. timescale from hardenbol et al. (1998), except for the age of the paleocene–eocene boundary, which is adapted from berggren & aubry (1996) and the age of the sparnacian–ypresian boundary, which is from aubry et al. (2003). stratigraphy and ages of pre-chatian onshore lithostratigraphic units are based on heilmann-clausen (1995) and clemmensen & thomsen (2005). post-rupelian onshore stratigraphy and ages are from dybkjær & rasmussen (2000) and rasmussen (2004a). f, fur formation. 10 previous work the permian to recent lithostratigraphy of the north sea was described in two pioneering stratigraphic works. rhys (1974) provided an overview of the structural elements of the north sea and gave a brief description of the palaeogene sediments. deegan & scull (1977) compiled a detailed lithostratigraphic subdivision and lithological description for the central and northern north sea (figs 3, 4). they subdivided the siliciclastic palaeogene, neogene and quaternary sediments into five major groups: the montrose, moray, rogaland, hordaland and nordland groups. the montrose and moray groups established for the outer moray firth – forties area are proximal equivalents to the rogaland group and are not present in the danish sector, whereas the rogaland, hordaland and nordland groups have widespread distribution in the danish sector. the succession of major mudstone formations contained within the three basinwide groups has formed the backbone of all subsequent lithostratigraphic schemes for the central and northern north sea, including that of the present contribution. the post-danian cainozoic succession of the danish central graben was divided into seven informal units by kristoffersen & bang (1982). the palaeogene comprised five units: north sea marl and cen-1–4 (fig. 4). the ranks of the units were not stated. although descriptions and interpretation of the cen units were detailed, they are essentially informal and have been little used. a revised lithostratigraphy for the palaeogene and neogene of the norwegian north sea sector was published by hardt et al. (1989). their lithostratigraphic scheme includes a number of new palaeogene and neogene sandstone bodies observed in the norwegian and british sectors of the north sea (fig. 4). some of the names of the new sandstone units established by hardt et al. (1989) were subsequently used informally for comparable sandstone units discovered in the danish sector. mudge & copestake (1992a, b) presented a revised palaeogene stratigraphy for the outer moray firth and northern north sea basins. in their papers they redefined the moray and montrose groups of deegan & scull (1977) and abandoned the rogaland group. the authors also demoted the previously established sandstone formations within the two former groups to the rank of members. besides, in an innovative approach they allowed for a greater influence of biostratigraphic data on the characterisation of the various lithostratigraphic units, an approach which is also followed herein. knox & holloway (1992) updated the lithostratigraphic scheme for the palaeogene in the british and norwegian central and northern north sea (figs 3, 4). the authors followed mudge & copestake (1992a, b) in abandoning the rogaland group of deegan & scull (1977), and used mudge & copestake’s revised definition of the montrose and moray groups for the central north sea as well. furthermore, the thick and hitherto undivided hordaland group was subdivided into two new groups, the stronsay group succeeded by the westray group, each containing a distal and a proximal formation. the two distal formations of the two groups, the horda and lark formations, together constitute the bulk of the palaeogene sediments in the danish sector of the north sea and are adopted herein (figs 2–4). although sandstone units occur in both the horda and lark formations in the danish sector, the two proximal sandstone formations of the fig. 3. correlation chart showing the approximate correlation between key lithostratigraphic schemes for the central and eastern north sea at group and formation levels. fu r deegan & scull (1977) hardt et al. (1989) knox & holloway (1992) this study chalk group chalk group chalk group hordaland group lista unnamed unit/ våle sele balder balder balder lista maureen montrose group moray group lark m o us a sk ad e horda sele rogaland group rogaland group stronsay group westray group stronsay group westray group lista sele horda lark våle nordland group nordland group nordland group 11 stronsay and westray groups, the mousa and skade formations, are absent from the danish sector. following detailed analysis of new, high-resolution seismic surveys covering the succession in the eastern north sea area, efforts were focused on establishing a sequence stratigraphic subdivision of the palaeogene–neogene sediment package. the sedimentary succession was interpreted in a series of publications from a working group at the university of aarhus (e.g. michelsen et al. 1992, 1995, 1998; michelsen 1993; danielsen et al. 1997; huuse & clausen 2001). the result of that work was a subdivision of the palaeogene to mid-neogene sediment package covered by the present work into six genetic units (fig. 4). the sequence stratigraphy of the upper oligocene to miocene in the eastern north sea was dealt with by rasmussen (2004b). further sequence stratigraphic contributions covering the larger north sea basin including the british and norwegian sectors are given by armentrout et al. (1993), mudge & bujak (1994, 1996a, b) and neal et al. (1994). coastal onlap basinward 7 michelsen et al. (1998) 6 6.3 6.2 6.1 5.4 5.3 5.2 5.1 4.4 4.3 4.2 4.1 1.2 1.1 5 4 3 2 1 nordland group hordaland group balder sele lista unnamed unit ekofisk cen-5 cen-4 cen-3 cen-2 cen-1 north sea marl chalk-6 nordland group hordaland group balder sele sele lista lista våle ekofisk nordland group lark horda balder tay m o u sa s k a d e fr ej a k o lg a f u r r in d id un ty r b o r sele lista l is ta fo rt ie s c ro m ar ty m ey v a d e f o rt ie s a n d re w h e im d a l h e rm o d f is k e b a n k f is k e b a n k f ri g g r o g a la n d g ro u p maureen m a u re e n ekofisk ekofisk ekofisk nordland group lark horda balder sele bue ve vile vålevåle deegan & scull (1977) northernnorth sea central north sea kristoffersen & bang (1982) hardt et al. (1989) knox & holloway (1992) this study nordland group balder ty grid ekofisk frigg h ef ri ng d uf a skade fig. 4. correlation chart showing approximate correlation between key lithostratigraphic schemes for the central and eastern north sea and the norwegian part of the northern north sea at formation and member levels. the sequence stratigraphic subdivision of michelsen et al. (1998) is added for comparison. sandstone-dominated units indicated in yellow. 12 material and methods the present lithostratigraphic subdivision represents the combined results from studies of petrophysical logs, biostratigraphy and seismic profiles, cuttings samples and cored sections. petrophysical logs from c. 70 wells in the danish sector have been scrutinised (see fig. 1 for well locations). the wells have been correlated using petrophysical logs, predominantly gamma-ray and sonic logs. five log panels form the basis for the log correlation (plates 1–5). lithostratigraphic well correlation has been supported by biostratigraphic data: biostratigraphic reports from 29 wells have been re-assessed with the aim of identifying key micropalaeontological and palynological events that occur consistently within the study area (taxa used are planktonic and benthic foraminifers, diatoms, radiolaria, sporomorphs and dinoflagellate cysts). moreover, biostratigraphic sample suites from 11 north sea wells have been prepared at the geological survey of denmark and greenland in order to further determine the biostratigraphic event succession. the bulk of material studied for biostratigraphy is based on cuttings samples, and only few table 1. well data for the new type and reference wells in the danish sector of the north sea augusta-1 cecilie-1 cleo-1 connie-1 e-8 f-1 floki-1 francisca-1 frida-1 inez-1 k-1 mona-1 nini-3 sandra-1 siri-1 siri-2 siri-3 tabita-1 bor mb(t), bue mb(t),ve mb(t) bor mb(r), tyr mb(r) bue mb(r), lista fm(r), ve mb(r), vile mb(r) idun mb(t), rind mb(t) bue mb(r), lista fm(r), ve mb(r), vile mb(r), våle fm(r) dufa mb(r) hefring mb(t) freja mb(t) freja mb(r) dufa mb(t), fur fm(r) fur fm(r) balder fm(r), horda fm(r), lark fm(r) kolga mb(r), tyr mb(t) rind mb(r) horda fm(r), lark fm(r), sele fm(r), våle fm(r) idun mb(r) balder fm(r), kolga mb(t), vile mb(t) sele fm(r) 56°17´57.40´́ n 04°24´04.64´́ e 56°24´23.73´́ n 04°45´42.00´́ e 56°23´23.54´́ n 04°25´22.70´́ e 56°24´28.34´́ n 04°42´30.36´́ e 55°38´13.42´́ n 04°59´11.96´́ e 57°01´53.4´́ n 06°54´28.6´́ e 56°27´48.58´́ n 05°16´47.11´́ e 56°22´27.95´́ n 04°48´05.30´́ e 56°17´14.15´́ n 05°01´50.20´́ e 56°50´28.39´́ n 06°57´41.62´́ e 57°07´37.74´́ n 07°09´43.11´́ e 56°16´35.94´́ n 04°00´15.81´́ e 56°41´31.96´́ n 05°24´12.35´́ e 56°35´13.33´́ n 05°01´35.19´́ e 56°29´11.10´́ n 04°54´57.49´́ e 56°29´40.53´́ n 04°52´13.26´́ e 56°30´34.92´́ n 05°03´48.27´́ e 56°13´37.50´́ n 04°23´47.56´́ e 04.03.2001 2991.0 mdrt 37.8 rt 65 15.10.2000 2361.0 mdrt 37.8 rt 59.4 06.02.1984 4866.1 mdkb 40.5 kb 63.1 02.02.2001 2351.8 mdrt 37.8 rt 61.5 08.04.1994 2527.4 mdkb 36.6 kb 43.6 06.10.1968 2421.6 mdkb 37.19 kb 40.8 29.08.2000 1878 mdrt 35.8 rt 53.2 20.07.1998 1888.5 mdrt 36.4 kb 60 26.07.1997 2274 mdrt 39.0 rt 54.3 11.09.1977 1983.9 mdkb 35.1 kb 35.4 22.01.1970 2292.4 mdkb 37.2 kb 56.4 03.10.1982 4241.6 mdkb 36.6 kb 65.5 12.01.2001 1851.2 mdrt 37.3 rt 58.2 18.06.1998 2139 mdrt 36 kb 65 28.11.1995 2220 mdkb 23 kb 60 03.08.1996 2297.5 mdrt 36.6 rt 60.6 30.08.1996 2171.5 mdrt 36.6 rt 60.1 10.09.1983 4353 mdkb 40 kb 65 dong e&p a/s dong e&p a/s chevron petroleum co. dong e&p a/s maersk oil & gas a/s gulf oil company kerr-mcgee int. aps dansk operatørselskab i/s dansk operatørselskab i/s chevron petroleum co. california oil co. chevron petroleum co. dong e&p a/s statoil e&p a/s statoil e&p a/s statoil e&p a/s statoil e&p a/s statoil e&p a/s type (t) or reference (r) well coordinates operator spud date td (logger’s kb/rt elevation water for listed units: depth in m) (m above msl) depth (m) well fm: formation. mb: member. mdrt: measured depth below rotary table. mdkb: measured depth below kelly bushing. 13 fig. 5. chronostratigraphy and biostratigraphy of the paleocene – middle miocene. a: paleocene–eocene. b: eocene–oligocene. c: oligocene – middle miocene. calibration of chronostratigraphic units follows hardenbol et al. (1998), berggren & aubry (1996) for the paleocene–eocene boundary and aubry et al. (2003) for the sparnacian–ypresian boundary. key dinoflagellate datums are calibrated mainly using age estimates from hardenbol et al. (1998) and williams et al. (2004). key microfossil datums are calibrated via their correlation with calibrated dinoflagellate datums as suggested by mudge & bujak (1996b), using age estimates from hardenbol et al. (1998) and williams et al. (2004). the combined event succession is correlated with the north sea microfossil zonation of king (1989) and lithostratigraphic units treated herein. in the microfossil event column, the planktonic foraminifer events appear in normal font, benthic foraminifers in italics; diatoms and radiolarians are underlined. senoniasphaera inornata palynodinium grallator, dinogymnium spp. alisocysta reticulata abundant p. pyrophorum isabelidinium? viborgense p. pyrophorum, p. australinum acme a. gippingensis alisocysta margarita common cerodinium wardenense apectodinium augustum apectodinium augustum, acme apectodinium spp. acme d. oebisfeldensis, influx inaperturopollenites spp., common h. tubiferum deflandrea oebisfeldensis dracodinium condylos nsp6 (pars) nsp5b nsp5a nsp4 nsp3 nsp2 nsp1 a b c nsb4 (pars) nsb3b nsb3a nsb2 nsb1 a b c horda balder sele ekofisk tor våle bue ve vile lista planktonic foraminifers benthic foraminifers diatoms and radiolaria planktonic microfossils north sea biozones (king 1989) lithostratigraphy selected biostratigraphic events used in the present studygeochronology ma a chronostratigraphy (berggren et al. 1995) c re ta ce o us (p ar s) pa le o ce ne eo ce ne ( pa rs ) u pp er ( pa rs ) lo w er u pp er lo w er ( pa rs ) fm mbdinoflagellate cysts ypresian (pars) maastrictian (pars) thanetian sparnacian selandian danian 54.5 55.5 57.9 60.0 65.0 50 55 60 65 uvigerina batjesi turrillina brevispira gaudryina hiltermanni common subbotina ex gr. linaperta fenestrella antiqua, foraminifers very rare impoverished benthic agglutinated assemblage common globoconusa daubjergensis globanomalina cf. compressa, s. trivialis increasing diversity of calcareous foraminifers reappearance of planktonic foraminifers increasing diversity of calcareous benthic foraminifers cenodiscus spp., cenosphaera spp. cretaceous foraminifers common f. antiqua and coscinodiscus morsianus pseudotextularia elegans benthic microfossils stageseries 14 35 40 50 45 lark formation rupelian (pars) o lig o ce ne (p ar s) eo ce ne ( pa rs ) priabonian 41.3 bartonian lutetian ypresian (pars) nsb7a nsb6b nsb6a nsb5c nsb5b nsb5a nsb4 nsb3a nsb2 (pars) nsb3b planulina costata pseudohastigerina spp. abundant radiolaria (cenosphaera spp.), cyclammina amplectens lenticulina gutticostata, spiroplectammina spectabilis balder horda eatonicysta ursulae diphyes ficusoides areosphaeridium michoudii heteraulacacysta porosa diphyes colligerum areosphaeridium diktyoplokum common e. ursulae phthanoperidinium clithridium globigerinatheka index cibicidoides truncanus vaginulinopsis decorata 49.0 37.0 33.7 uvigerina batjesi turrillina brevispira gaudryina hiltermanni common subbotina patagonica dracodinium condylos deflandrea oebisfeldensis acme d. oebisfeldensis, influx inaperturopollenites spp., common h. tubiferum fenestrella antiqua, foraminifers very rare cerebrocysta bartonensis uvigerina germanica karrulina conversa corrudinium incompositum sele (pars) nsp9b nsp9a nsp8c nsp8b nsp8a nsp7 nsp6 nsp5b nsp4 (pars) nsp5a lo w er ( pa rs ) u pp er m id dl e lo w er ( pa rs ) planktonic foraminifers benthic foraminifers diatoms and radiolaria planktonic microfossils north sea biozones (king 1989) lithostratigraphy selected biostratigraphic events used in the present study chronostratigraphy (berggren et al. 1995) fm mbdinoflagellate cysts benthic microfossils stageseries geochronology ma b fig. 5b. chronostratigraphy and biostratigraphy of the eocene–oligocene. 15 lark nsp9a (pars) nsb6b (pars) uvigerina germanica karrulina conversa nsp14b nsb13a nsp14a nsb12c nsp13 nsb12b nsb12a nsp12 nsb11 nsp11 nsp10 nsb10 nsb9 nsp9c nsb8c nsb8b nsb8a nsb7b nsb7a nsp9b aulacodiscus allorgei turrillina alsatica bolboforma spiralis asterigerina staeschei, elphidium inflatum, meonis pompilioides uvigerina tenuipustulata plectofrondicularia seminuda aulacodiscus insignis quadrata (small), b. antiqua, g. girardana common elphidium subnodosum, common paragloborotalia nana rotaliatina bulimoides “turborotalia” ampliapertura common a. guerichi, paragloborotalia opima s.s. bolboforma metzmacheri pararotalia canui aulacodiscus insignis quadrata (large) spirosigmoilinella compressa cibicidoides mexicanus gyroidina mamillata wetzeliella gochtii phthanoperidinium amoenum chiropteridium spp. membranophoridium aspinatum distatodinium biffi cordosphaeridium cantharellus apteodinium spiridoides caligodinium amiculum thalassiphora pelagica hystrichokolpoma cinctum rhombodinium draco corrudinium incompositum achilleodinium biformoides enneadocysta pectiniformis burdigalian aquitanian m io ce ne ( pa rs ) lo w er chattian u pp er rupelian (pars) lo w er ( pa rs )o lig o ce ne ( pa rs ) m id dl e langhian serravallian 28.5 23.8 20.5 16.4 14.8 11.2 cousteaudinium aubryae nordland group bulimina elongata bolboforma clodiusi p. comatum 15 20 30 25 cannosphaeropsis passio tortonian (pars)u pp er (p ar s) planktonic foraminifers benthic foraminifers diatoms and radiolaria planktonic microfossils north sea biozones (king 1989) lithostratigraphy selected biostratigraphic events used in the present study chronostratigraphy (berggren et al. 1995) fm mbdinoflagellate cysts benthic microfossils stageseries geochronology ma c fig 5c. chronostratigraphy and biostratigraphy of the oligocene – middle miocene. 16 core samples have been available. as the use of stratigraphic lowest occurrences (lo) of taxa in cuttings samples may be hampered due to downhole caving, the event succession comprises almost exclusively stratigraphic highest occurrences (ho) of taxa (a single significant lo is included in the succession). the event succession is shown in fig. 5a–c; its correlation with international and north sea biozones is shown in fig. 6a–c. seismic sections from the 2-d and 3-d seismic surveys cgd85, dk-1, rtd81–re94, ucg96 and ucge97 have been used to further support the well correlation and to map the stratigraphic units in areas with only scattered well coverage. the combined results from the correlation and mapping procedures are presented as isochore maps for individual stratigraphic units. inspection of cuttings samples from 16 key wells supplemented with sedimentological studies of cored intervals from 23 wells have formed the basis for the lithological and sedimentological descriptions of the units. the well depths mentioned in the lithostratigraphy section are loggers’ depths measured either from rotary table (mdrt) or kelly bushing (mdkb). supplementary data for new type and reference wells are provided in table 1. the names assigned to the new lithostratigraphic units defined herein are derived from nordic mythology and thus follow the nomenclatural tradition previously established for the norwegian north sea (isaksen & tonstad 1989). it should be noted that the micropalaeontology-based palaeoenvironmental terminology used herein was originally developed for a passive margin situation (e.g. the terms ‘neritic’ and ‘bathyal’ to indicate the physiographic zones ‘shelf ’ and ‘shelfslope’, respectively). its application herein to the epicontinental north sea basin solely relates to depositional depth. offshore and onshore lithostratigraphic nomenclature there is a high degree of lithological similarity between the palaeogene–neogene mudstone succession in danish offshore boreholes and that in onshore exposures and boreholes. however, the status of the danish onshore units is quite varied since many units were named before a standard for description of a lithostratigraphic unit was established; some fulfil these requirements, whereas others are still informal. if a previously established onshore unit and an offshore unit can be demonstrated to be identical (e.g. the holmehus formation and the new ve member proposed herein), the name of the onshore unit theoretically has priority over the name of the offshore unit (salvador 1994). in other cases, names of offshore units can be argued to have priority over onshore units (e.g. sele and balder formations over ølst formation). however, in order to acknowledge the traditional distinction between offshore and onshore stratigraphic nomenclature, the two sets of nomenclature are kept separate herein. whenever possible, comments are given in the text to explain the relationship between offshore and onshore danish stratigraphic nomenclature. a correlation between the two sets of nomenclature is shown in fig. 2. chronostratigraphy and biostratigraphy age assessment of the lithostratigraphic units in the north sea sedimentary succession is based on correlation between key biostratigraphic events encountered in the units and the calibrated standard chronostratigraphy published by berggren et al. (1995), with modification for the paleocene–eocene boundary following ratification of its position by the international union of geological scientists (aubry et al. 2002). the key events are from biostratigraphic zonation schemes established for the north sea area. planktonic and benthic microfossils are covered by the zonation schemes of king (1983, 1989; figs 5a–c, 6a–c). dinoflagellates from the paleocene and eocene epochs are covered by the zonation scheme of mudge & bujak (1996b; fig. 6a, b); the oligocene and miocene epochs are covered by the zonation schemes of costa & manum (1988) with modifications by köthe (1990, 2003; fig. 6b, c). key events from these schemes used in this study are listed in fig. 5a–c. for the dinoflagellate events, geochronological calibration has been largely established using age estimates from hardenbol et al. (1998), munsterman & brinkhuis (2004) and williams et al. (2004). for events not mentioned in these three publications, the works of mudge & bujak geological survey of denmark and greenland bulletin 15, 2008, 93-96 computer-controlled scanning electron microscopy (ccsem) combines the advantages of energy dispersive x-ray spectrometry (edx) with those of digital image analysis of back-scattered electron (bse) micrographs. ccsem analysis of a wide range of geological or non-geological materials has been introduced at the geological survey of denmark and greenland (geus) as a fast and reliable method to determine both the chemistry of individual grains and bulk samples. the chemical analysis is combined with measurements of the two-dimensional size and morphology of every single grain. the ccsem technique was developed in the early 1980s for characterisation of coal minerals (huggins et al. 1980; lee & kelly 1980) and studies of synthetic crystals for super-conductors and catalysts (lin & barnes 1984). soon it found a broader application in the study of dust particles and fibres in lung tissue of mine workers (friedrichs 1987), in the analyses of aerosols for air quality control and source emission characterisation (e.g. heasman & watt 1989) and the degree of sintering and consolidation of coal ash deposits (e.g. huffman et al. 1994). ccsem has been used in the earth sciences for the determination of the sediment budget of a lake (yin & johnson 1984), for the characterisation of soil and dust (pirrie et al. 2004), for provenance analysis of ilmenite-bearing beach sands (knudsen et al. 2005; bernstein et al. 2008), and provenance studies on sandstones in oil-bearing basins (frei et al. 2005). other areas where ccsem has been applied range widely and include characterisation of small inclusions, e.g. impurities in metal alloys or steel (schwoeble et al. 1988), analyses of gun-shot residues (e.g. steffen et al. 2007), and analyses of bladder stones obtained from a skeleton found in a mesolithic cave-tomb (d’alessio et al. 2005). in this paper, we demonstrate the benefits of the method with examples from the cement industry and from diamond prospecting. 93 fully automated analysis of grain chemistry, size and morphology by ccsem: examples from cement produc tion and diamond exploration nynke keulen, dirk frei, stefan bernstein, mark t. hutchison, christian knudsen and lucas jensen © geus, 2008. geological survey of denmark and greenland bulletin 15, 93–96. available at: www.geus.dk/publications/bull b a b 1 mm fig. 1. a: ccsem sample of beach sediment from jylland, denmark, divided into a number of frames in a grid. part of the grid is outlined in white. grains of different chemical compositions (different grey values) are embedded in epoxy resin. b: enlargement of one of the frames of the grid (indicated in red in a). the guard region (yellow) prevents double or incomplete measurements of grains (see text). the grey-level threshold function selects the grains one by one from the matrix for analyses of chemical composition, size and shape. analysed grains are shown in red; the image represents a snapshot of the ccsem procedure. analytical technique sample preparation sample material may, for example, consist of (1) a representative part of a bulk sample, (2) carefully selected grains mounted on double-sided tape, or (3) a heavy mineral separation of a bulk sample. grains, beads, and powders of both geological and non-geological origin can be analysed. for most studies, approximately 1 g of sample material was mounted in epoxy resin, using a technique that ensures that almost every grain is completely embedded in the epoxy, without touching any neighbouring grains (frei et al. 2005). the epoxy mounts are cut to show a representative part of the mount, subsequently polished and coated with carbon to enhance their conductivity. however, it is also possible to use thin sections of sample material prepared in a similar way. ccsem analysis the ccsem analysis was undertaken using a philips xl40 sem equipped with two edx detectors: a thermo nanotrace 30 mm2 window and a pioneer voyager 2.7 10 mm2 window si(li) detector. the tungsten filament of the sem was operated with an acceleration voltage of 17 kv, a filament current of typically 50–70 µa, and the sample was placed at a distance of 10 mm from the detector. the noran system six software package was used to automatically collect x-ray spectra, grain size and morphology of all particles and to recalculate the data following the proza (ϕρz) data correction and the filtering quantification technique. the technique described here is an improvement of the method described by frei et al. (2005) and bernstein et al. (2008). the samples were studied in the bse contrast mode of the electron microscope where the individual particles appear as different shades of grey in their black epoxy matrix (fig. 1). grey-level intensity thresholding by the image analysis function integrated in the software created a binary image of the bse micrograph and allowed for the separation and selection of individual grains (fig. 1b). a grid of image frames covering the whole sample area was defined by feeding the end-coordinates of the sample to the computer and by setting the required magnification (typically 30–100×) for the analysis (fig. 1a). grids consisted of 15 to 60 frames with approximately 20–35 grains per frame. a guard region between each frame ensured that double measurements of large particles in the sample was avoided and that only grains that lay completely within the image frame were included for analysis and thus recorded the true shape of grains. a ‘hole-fill’ function enabled more precise measurement of the grain size and shape from the binary image. because the grains were mounted in epoxy resin in such a way that they do not touch each other, no grain separation techniques had to be used, as commonly applied in automatic particle analysis software. thus, the original 2-d grain shape and grain size were completely available for analysis, without the introduction of artefacts by grain erosion and dilation or median filtering. all standard grain-shape factors can be measured. the smallest grains in the sample can be excluded from the analysis to avoid the measurement of particles that are only a few pixels in size, especially if a good grain morphology resolution is required. the created binary image formed the basis for the measurements of the grain chemistry. the software forced the microscope to scan within the perimeter of each grain to obtain the chemistry of either the whole grain area or from a single point in the centre of the grain mass. a typical spectrum for one particle contained 1000–2000 counts for the highest peak. spectra with a very low number of counts can be removed to ensure good measurement statistics. commonly, 800–1200 grains were measured in approximately two hours. the noran software produces a results table that lists shape, size and chemistry for each individual grain. all spectrum files and image frames, with a typical size of 1024 × 774 pixels, are stored after analysis. spectrum files can be reprocessed to include accidentally omitted elements retrospectively, without the need to physically reanalyse the sample. the chemical data are further reduced using a software package that is connected to a mineral library database for automatic phase recognition and data storage. 94 fig. 2. grain-size distribution diagram for seven minerals from raw materials used in the cement industry. grain mineralogy and grain size were determined with ccsem. 0 20 40 60 80 100 10 100 1000 feldspar bauxite hematite illites dolomite micas quartz c um ul at iv e w ei gh t (% ) grain size (µm) application of ccsem as a practical solution quality control of raw materials in cement production for cement production, raw materials are crushed to fine grain sizes before they are mixed and reacted at high temperatures in a kiln. to optimise the performance of the grinding mill and the sintering process an investigation of the grain-size distri bution of the limestone, iron ore, clay and sand fractions of the cement was undertaken. the grain-size distribution of the individual components in particular is of great importance for further processing of the raw material into cement clinker. the raw material was sieved into different grain-size fractions and treated with hydrochloric acid to decrease the amount of calcium carbonate in the raw material. the size fraction of 10–2000 µm was analysed with ccsem to determine the grain-size distribution and grain chemistry. figure 2 shows the grain-size distribution for seven different minerals. the mica, illite, and feldspar grains show uniform grain-size distributions, whereas bauxite, hematite and particularly dolomite grains show ranges of size distributions over two orders of magnitude. the hematite grains display a bimodal-size distribution. these findings demonstrate that ccsem is a suitable option for routine quality control and improvement of the production process. ccsem: a fast and reliable tool for diamond prospecting? determinations of the elemental composition of macro-crystalline phases in kimberlitic rocks or in detrital sediment samples are an important tool in diamond exploration. the major and minor element compositions of certain minerals are diagnostic for igneous rocks of mantle origin, and in some cases also represent a defined probability that the crystallisation of these phases occurred under conditions where diamond is stable. the ratios between cr and ca concentrations of mg-rich garnets and the cr and ca concentrations of eclogitic garnets are examples where such probability fields have been defined (fig. 3; grütter et al. 2004). a standard method for analysing the composition of garnets and other macrocrystalline phases is to measure the concentration of approximately ten to fifteen oxides with an electron microprobe (emp). emp is a dependable, yet time-consuming and relatively expensive method. we therefore tested the potential of ccsem analysis as a faster and cheaper method to measure the composition of macrocrystals in kimberlitic rocks. we used indicator minerals from the ‘garnet lake’ kimberlite body in west greenland, where diamonds are common (hutchison 2005). a series of hand-picked pyrope (garnet) grains were mounted in epoxy resin. the sample was analysed using ccsem, with extended counting times to ensure good statistics: the relative error in the reproducibility of the measurements is c. 1–2% for major elements and c. 4–8% for minor elements. the accuracy of ccsem was tested by comparing the results with compositional data obtained from electron microprobe analyses for the same minerals (as reported by hut ch ison 2005). even with extended counting time, a sample consisting of 200 grains can be analysed in 1–3 hours, with less than half an hour of operator time. an excellent reproduction of the emp measurements was achieved by ccsem (fig. 3); the statistical correlation between the two methods for these elements is 70%. the few outliers reflect those garnet grains that show a compositional gradient from core to rim. the emp point ana l yses were carried out on the cores of the grains, whereas the ccsem analyses average the whole surface of the grains, therefore providing slightly different results that are closer to the bulk composition of the grains. the vast majority of the garnet grains analysed by ccsem plot in the same classi fi cation field as do the grains according to the emp measurements. ccsem is therefore a good option for reliable and more ra pid measurements of garnet minerals in diamond-bearing rocks. validity of the ccsem measurements comparison between emp and ccsem shows high accuracy of the ccsem for minor elements. figure 4 shows the precision of the ccsem method for a major element (93.71 wt%), a minor element (2.19 wt%) and a trace element (0.21 wt%), measured on the same sample. five sets of measurements at nine different maximum peak count settings (equivalent to nine different time periods) were undertaken to evaluate the reproducibility of the data. for standard single spot or single grain analyses the relative errors are high com95 2 0 0 3 6 9 12 4 6 8 10 emp ccsem c r 2 o 3 (w t% ) cao (wt%) fig. 3. comparison of electron microprobe (emp) and ccsem measurements for chromium oxide and calcium oxide in mg-rich garnets from diamondbearing rocks. note the good correlation between the results obtained with ccsem and the emp data. pared to other analytical methods: 2–3% for major elements (>20 wt%), 5–10% for minor elements (>2 wt%) and 50–100% for elements present in smaller quantities. how ever, these figures can easily be improved by slightly increasing the counting time (fig. 4). the precision of bulk sample ccsem measurements is very high: as an effect of the long counting times the relative errors are reduced to <0.2% for major elements, <2% for minor elements and <15% for trace elements. this shows that the analysis time can be usefully tailored to the sample set depending on the required precision of the measurements and the time available. applied to diamond prospecting, measurement times could be adjusted depending on how marginal the sample is in the diamond stability field. the examples discussed above indicate that ccsem provides an accurate and precise way to rapidly measure single grain and bulk compositions of minerals and of other geological and non-geological materials. coupled with measurements of the grain size and other grain parameters for the individual particles, this technique is a potent tool to solve a wide range of problems. acknowledgement hudson resources inc. is thanked for provision of garnet samples. references bernstein, s., frei, d., mclimans, r.k., knudsen, c. & vasudev, v.n. 2008: application of ccsem to heavy mineral deposits: source of high-ti ilmenite sand deposits of south kerala beaches, sw india. journal of geochemical exploration 96, 25–42. d’alessio, a., bramanti, e., piperno, m. naccarato, g. vergamini, p. & forna ciari, g. 2005: an 8500-year-old bladder stone from uzzo cave (trapani): fourier transform-infrared spectroscopy. archaeomotry 47, 127–136. frei, d., rasmussen, t., knudsen, c., larsen, m., whitham, a. & morton, a. 2005: linking the faroese area and greenland: new methods and techniques used in an innovative, integrated provenance study. fróðskaparrit 43, 96–108. friedrichs, k.h. 1987: electron microscopic analyses of dust from the lungs and the lymph nodes of talc-mine employees. american industry hygiene asso ciation journal 48, 626–633. grütter, h.s., gurney, j.j., menzies, a.h. & winter, f. 2004: an updated classification scheme for mantle-derived garnet, for use by diamond explorers. lithos 77, 841–857. heasman i. & watt, j. 1989: particulate pollution case studies which illustrate uses of individual particle analysis by scanning electron microscopy. environmental geochemistry and health 11, 157–162. huffman, g.p. et al. 1994: investigation of ash by microscopic and spectroscopic techniques. in: williamson, j. & wigley, f. (eds): the impact of ash deposition on coal fired plants. proceedings of the engineering foun dation conference (20–25 june 1993, solihull, birmingham, uk), 409–423. london: taylor & francis. huggins, f.e., kosmack, d.a., huffman, g.p. & lee, r.j. 1980: coal mineralogy by sem analysis. scanning electron microscopy 1, 531–540. hutchison, m.t. 2005: diamondiferous kimberlites from the garnet lake area, west greenland: exploration, methodologies and petrochemistry. in: secher, k. & nielsen, m.n. (eds): workshop on greenland’s diamond po tential. 7–9 november 2005 in copenhagen. extended abstracts. dan marks og grønlands geologiske undersøgelse rapport 2005/68, 33–42. knudsen, c., frei, d., rasmussen, t., rasmussen, e. s. & mclimans, r. 2005: new methods in provenance studies based on heavy minerals: an example from miocene sands in jylland, denmark. geological survey of denmark and greenland bulletin 7, 29–32. lee, r.j. & kelly, j.f. 1980: overview of sem-based automated image analysis. scanning electron microscopy 1, 303 only. lin, m.c. & barnes, r.g. 1984: mössbauer spectroscopy and scanning electron microscopy study of iron-graphimet. journal of applied physics 55, 2294– 2296. pirrie, d., butcher, a.r., power, m.r., gottlieb, p. & miller, g.l. 2004: rapid quantitative mineral and phase analysis using automated scanning electron microscopy (qemscan); potential applications in forensic geoscience. in: pye, k. & croft, d.j. (eds): forensic geoscience: principles, techniques and applications. geological society special publication (london) 232, 123–136. schwoeble, a.j., dalley, a.m., henderson, b.c. & casuccio, g.s. 1988: com putercontrolled sem and microimaging of fine particles. journal of metals 40, 11–14. steffen, s., otto, m., niewoehner, l., barth, m., brozek-mucha, z., bieg straaten, j. & horvath, r. 2007: chemometric classification of gunshot residues based on energy dispersive x-ray microanalysis and inductively coupled plasma analysis with mass-spectrometric detection. spectrochimica acta b62, 1028– 1036. yin, c. & johnson, d.l. 1984: an individual particle analysis and budget study of onondaga lake sediments. limnology & oceanography 29, 1193–1201. 96 authors’ addresses n.k., d.f., m.t.h. & c.k., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: ntk@geus.dk s.b., avannaa resources ltd., geological museum, university of copenhagen, øster voldgade 5–7, dk-1350 copenhagen k, denmark. l.j., flsmidth a/s, vigerslev allé 77, dk-2500 valby, denmark. 10 0 20 30 40 50 60 70 80 90 100 0 50 100 150 200 250 300 350 70006000 trace elements minor elements major elements time (s) r el at iv e er ro r (% ) bulk single grains fig. 4. precision of single grain and bulk sample ccsem analyses as a function of measurement times. two detectors were used for the analyses. the precision increases with counting time. data article | short tegner et al. 2023: geus bulletin 53. 8316. https://doi.org/10.34194/geusb.v53.8316 1 of 8 a whole-rock data set for the skaergaard intrusion, east greenland christian tegner*1 ,lars peter salmonsen2 , marian b. holness3 , charles e. lesher1 , madeleine c. s. humphreys3,4 , peter thy5 , troels f. d. nielsen6 1department of geoscience, aarhus university, aarhus, denmark; 2rambøll, aarhus, denmark; 3department of earth sciences, university of cambridge, cambridge, uk; 4department of earth sciences, durham university, durham, uk; 5department of earth and planetary sciences, university of california, davis, usa; 6department of mapping and mineral resources, geological survey of denmark and greenland, copenhagen, denmark abstract we report a compilation of new and published whole-rock major and trace element analyses for 646 samples of the skaergaard intrusion, east greenland. the samples were collected in 14 stratigraphic profiles either from accessible and well-exposed surface areas or from drill core, and they cover most regions of the intrusion. this includes the layered series, the upper border series, the marginal border series and the sandwich horizon. the geochemical data were obtained by a combination of x-ray fluorescence and inductively coupled plasma mass spectrometry. this data set can, for example, be used to constrain processes of igneous differentiation and ore formation. *correspondence: christian.tegner@geo.au.dk received: 05 apr 2022 revised: 01 mar 2023 accepted: 13 apr 2023 published: 15 june 2023 keywords: skaergaard intrusion, layered mafic intrusion, bulk-rock geochemical data, x-ray fluorescence (xrf), inductively coupled plasma mass spectrometry (icp-ms) abbreviations a.s.l.: above sea level f: mass fraction of melt remaining in the chamber geus: geological survey of denmark and greenland. hz: hidden zone icp-ms: inductively coupled plasma mass spectrometry loi: mass lost on ignition ls: layered series lz: lower zone mz: middle zone s.d.: standard deviation sh: sandwich horizon uz: upper zone xrf: x-ray fluorescence geus bulletin (eissn: 2597–2154) is an open access, peer-reviewed journal published by the geological survey of denmark and greenland (geus). this article is distributed under a cc-by 4.0 licence, permitting free redistribution, and reproduction for any purpose, even commercial, provided proper citation of the original work. author(s) retain copyright. edited by: kerstin saalmann (geological survey of norway) reviewed by: rais latypov (university of witwatersrand, south africa), howard naslund (binghamton university, usa) funding: see page 7 competing interests: see page 7 additional files: see page 7 tabular abstract geographical coverage the skaergaard intrusion occupies a c. 11 × 8 km outcrop area of layered gabbroic rocks at uttentals sund, kangerlussuaq area, east greenland. located at c. 68°9 ′n and 31°41′ w. temporal coverage palaeogene (c. 56.0 ma) subject(s) cosmochemistry and geochronology, economic geology, geochemistry, igneous rocks and processes data format(s) major and trace element compositions reported in an excel spreadsheet. sample collection & analysis samples (n = 646) taken from surface outcrops and drill cores were analysed by x-ray fluorescence and inductively coupled plasma mass spectrometry (icp-ms). the samples are stored and curated at: aarhus university (surface samples from the layered series and upper border series); geological survey of denmark and greenland (surface samples from the layered series); natural history museum of denmark, university of copenhagen (drill core samples) and the harker collection of the sedgwick museum, university of cambridge (cambridge 1966 drill core and surface samples of the marginal border series). parameters major and trace element whole-rock compositions. related publications: tegner 1997; tegner et al. 2009; salmonsen & tegner 2013; holness et al. 2015, 2017, 2022; thy et al. in press. potential application(s) for these data this data set can, for example, be used to constrain processes of igneous differentiation and ore formation. data collection to examine the petrology and ore bodies of the skaergaard intrusion, east greenland, we have collected hundreds of samples during six field expeditions between 1993 and 2017. in addition, we have collected samples from drill core material housed at the natural history museum of denmark https://doi.org/10.34194/geusb.v53.8316 https://orcid.org/0000-0003-1407-7298 https://orcid.org/0009-0008-8005-0150 https://orcid.org/0000-0001-9911-8292 https://orcid.org/0000-0003-4033-4809 https://orcid.org/0000-0001-9343-1237 https://orcid.org/0000-0002-9267-5798 https://orcid.org/0000-0002-4932-3869 mailto:christian.tegner@geo.au.dk tegner et al. 2023: geus bulletin 53. 8316. https://doi.org/10.34194/geusb.v53.8316 2 of 8 w w w . g e u s b u l l e t i n . o r g (university of copenhagen) and the harker collection of the sedgwick museum (university of cambridge). here, we report a compilation of 646 whole-rock analyses for these samples attached as one excel spreadsheet (supplementary data file 1). all samples were analysed by x-ray fluorescence (xrf); most of these data (n = 409) were published in tegner (1997), tegner et al. (2009), salmonsen & tegner (2013), holness et al. (2015, 2022) and thy et al. (in press). the remaining analyses (n = 237) are reported here for the first time apart from p2o5 data (n = 167), which were reported in holness et al. (2017). a subset of 271 samples were analysed by inductively coupled plasma mass spectrometry (icp-ms). about half of these (n = 130) were published in tegner et al. (2009) and thy et al. (in press); the remaining analyses (n = 141) are reported here for the first time. the analysed samples mainly represent mafic cumulate rocks (n = 623) but also include gabbropegmatite and granophyric pods and layers (n = 23). details of subsets of the present bulkrock data set have been described and discussed in a number of publications (e.g. tegner 1997; tegner et al. 2009; thy et al. 2009, in press; tegner & cawthorn 2010; mckenzie 2011; salmonsen & tegner 2013; namur et al. 2013, 2014; holness et al. 2015, 2017, 2022; nielsen et al. 2015; keays & tegner 2016; pedersen et al. 2021). the samples were collected in 14 stratigraphic profiles as shown on the geological map (fig. 1), in a schematic cross-section (fig. 2), listed in table 1 and described in detail in supplementary data file 2. the sample sections thus cover the known stratigraphy and rock units reported in the layered series (ls: including hidden zone, hz; lower zone a, lza; lower zone b, lzb; lower zone c, lzc; middle zone, mz; upper zone a; uza; upper zone b, uzb; upper zone c, uzc), the marginal border series (mbs: including lower zone a*, lza*; lower zone b*, lzb*; lower zone c*, lzc*; middle zone*, mz*; upper zone a*; uza*; upper zone b*, uzb*; upper zone c*, uzc*), the upper border series (ubs: including lower zone a´, lza´; lower zone b´, lzb´; lower zone c´, lzc´; middle zone´, mz´; upper zone a´; uza´; upper zone b´, uzb´; upper zone c´, uzc´), and the sandwich horizon (sh). this zonal subdivision is outlined in figs  1 and 2. a field photograph (fig. 3) shows an example of layered rocks (layered series). further selected outcrops are shown in fig. s1 (supplementary data file 2). previous work has shown that the intrusion represents the result of prolonged, uninterrupted differentiation of a tholeiitic magma (wager & deer 1939; wager & brown 1968; naslund 1984; hoover 1989; mcbirney 1996; irvine et al. 1998). palladium and gold mineralisations have been identified in the ls (andersen et al. 1998; nielsen et al. 2015). a key point is that the ls, mbs and ubs appear to represent continuous and synchronous crystallisation on the floor, margins and roof and sh the products of the most evolved, last drops of magma in the interior of the intrusion. these rocks, therefore, allow evaluation of the processes resulting in igneous differentiation and ore formation in opposite positions relative to gravity (e.g. mcbirney 1995). sample profiles the stratigraphic profiles (n = 14) are summarised in table 1 and illustrated in figs 1 and 2. the profiles cover most regions of the intrusion and were collected either from accessible and well exposed surface areas or from drill core. the details of the sample profiles are described in supplementary data file 2. sampling strategy the sampling was directed to obtain mainly average rock compositions in systematic stratigraphic sections. additional samples of outcrop features such as gabbropegmatites, subzone boundaries and layered structures were also included, for example, the ‘wavy pyroxene rocks’ and colloform banding of the mbs (humphreys & holness 2010; namur et al. 2013). the sample positions were recorded by gps and altimeter readings (supplementary data file 1). for ls and ubs, the stratigraphic thicknesses were calculated relative to the local strike and dip of layering as described previously (tegner et al. 2009; salmonsen & tegner 2013) and are listed in supplementary data file 1. within the limitations of outcrops, we aimed to sample at regular stratigraphic intervals. for ls and ubs, the average stratigraphic interval was 12 ± 13 m (1 s.d.). for mbs, the lateral distance from the contact is recorded and the average spacing between samples was 18 ± 6 m (1 s.d.; holness et al. 2022). calculation of fraction of melt remaining (f) the box-like appearance of the intrusion with onionring distribution of zones and subzones (fig. 2) implies that stratigraphic thickness, and mass proportions are not proportional (nielsen 2004). based on mass proportions estimated for each subzone in the floor, wall and roof series (nielsen 2004), the mass fraction of melt remaining in the chamber, f, can be estimated for subzone boundaries. for the ‘reference profile’ of ls, a second-order polynomial was fitted to subzone boundaries to relate f to stratigraphic height (h) and given below as equation 1 (tegner et al. 2009): f = 1.091 × 10-7h2 – 5.9064 × 10-4h + 0.7678 (1) the f values for the 90-10 and 90-23 drill core samples were also estimated using equation 1 and tied to the ‘reference profile’ at the h of the uza/b boundary https://doi.org/10.34194/geusb.v53.8316 http://www.geusbulletin.org tegner et al. 2023: geus bulletin 53. 8316. https://doi.org/10.34194/geusb.v53.8316 3 of 8 w w w . g e u s b u l l e t i n . o r g fig. 1 geological map of the skaergaard intrusion and adjacent host rocks. the rocks that solidified at the floor (layered series composed of lower zone, lz, middle zone, mz, and upper zone, uz), walls (marginal border series, mbs) and roof (upper border series, ubs) are shown. also shown are the approximate locations of 14 sample profiles (surface samples and drill cores) that are studied here. the sample profiles are numbered 1 to 14 and listed in table 1. further subzone abbreviations are in the text. modified from mcbirney (1989). uttental sund forbindelsesgletscher lzb lzc lzc lza mb s uza 2 km uza uzc uzb uzb mz mz uttental plateau kraemer ø figure 1 dobbelt gletscher skaergaard bay hammer gletscher basistoppen lz mz uz mbs ubs basalt contact of the skaergaard intrusion la ye re d s er ie s gneiss sea ice later mafic intrusion drill core sample profile [1] [1] [2] [1] [1] [4] [1] [3] [5][6] [7] [8] [9] [14] [13] [12] [11] [10] 68 °0 8ʹ n 68 °1 3ʹ n 31°45ʹw 31°35ʹw https://doi.org/10.34194/geusb.v53.8316 http://www.geusbulletin.org tegner et al. 2023: geus bulletin 53. 8316. https://doi.org/10.34194/geusb.v53.8316 4 of 8 w w w . g e u s b u l l e t i n . o r g (1615 m). similarly, the f values for the samples of the cambridge core were estimated with equation 1, setting h to zero at the lza/hz boundary (holness et al. 2015). for ubs, f values of subzone boundaries were fixed to the same values as for ls, and f values of samples were related to stratigraphic height by linear interpolation (salmonsen & tegner 2013). similarly for mbs, the f values at subzone boundaries were assumed equal to those of ls, and the f values of the samples were related to the distance between subzone boundaries by linear interpolation. finally, in the sections crossing the sh, we assigned an f value of zero to the sample with the lowest mgo content (≤0.02 wt%). the estimated f values are reported in supplementary data file 1. analytical methods all samples were collected, prepared and analysed in the same way. from surface outcrops, we collected samples weighing 1–4 kg and avoiding alteration veins. the samples were trimmed for surface weathering by sawing, and an aliquot (100–400 g) was crushed to small aggregates (<2  cm) in a hydraulic steel press. this was followed by splitting, pre-contamination of a corundum shatterbox, cleaning and finally powdering of c. 30 g. the drill core material was prepared in the same way with one exception. the powders of drill core 90-22 (n = 51) were prepared using a steel jaw crusher and a tungsten-carbide shatterbox. all samples were prepared at aarhus university as described in tegner et al. (2009). fig. 2 schematic cross-section of the skaergaard intrusion showing the distribution of rocks that solidified at the floor (layered series), the walls (marginal border series, mbs) and the roof (upper border series, ubs). also shown are the approximate locations of 14 sample profiles (surface samples: blue lines, drill cores: orange lines) that are studied here. the sample profiles are also shown on the map in fig. 1 and numbered 1 to 14 as listed in table 1. the floor, wall and roof sequences are divided into subzones (hz–uzc) depending on the appearance and disappearance of primary (cumulus) crystal phases as marked on the subzone boundaries. abbreviations: hz: hidden zone. lz: lower zone. mz: middle zone. uz: upper zone. sh: sandwich horizon. further subzone abbreviations and nomenclature are in the text. modified from mcbirney (2002) and nielsen (2004). 2.5 2.0 1.5 1.0 0.5 0 lza lzb lzc mz uza uzb uzc lza’ lzb’ lzc’ mz’ uza’ uzb’ uzc’ hz lza* lzb* lzc* m z* u za* u zb* s tra tig ra ph ic th ic kn es s (k m ) sandwich horizon platinova reefs 3.0 east west c. 8 km aug+ mt+ ap+ olol+ granophyre uzb’+c’ [1] [6] [1] [1] [1] [1] [11] [10] [8] [7] [9] [5] [4] [3] [2] [14] [13] [12] mbs mbs ubs layered series basistoppen sill melanogranophyre https://doi.org/10.34194/geusb.v53.8316 http://www.geusbulletin.org tegner et al. 2023: geus bulletin 53. 8316. https://doi.org/10.34194/geusb.v53.8316 5 of 8 w w w . g e u s b u l l e t i n . o r g ta b le 1  o ve rv ie w o f sa m p le s an d s am p le p ro fil es sa m p le p ro fil e r o ck s er ie s su b zo n es n o . o f sa m p le s n o . o f sa m p le s n o . o f sa m p le s n o . o f sa m p le s r ef er en ce n am e n o . b     to ta l c u m u la te m el an o gr an o p h yr e g ab b ro p eg m at it e r ef er en ce p ro fil e a [1 ] la ye re d s er ie s lz a, l zb , l zc , m z, u za , u zb , u zc 13 8 13 5 2 1 te gn er (1 99 7) ; t eg n er e t a l. (2 00 9) ; t h y et a l. (in p re ss ) c am b ri d ge d ri ll co re [2 ] la ye re d s er ie s h z, l za 12 1 12 1 h o ln es s et a l. (2 01 5) d o b b el t g le ts ch er [3 ] la ye re d s er ie s h z, l za 8 8 th is s tu d y 90 -1 0 d ri ll co re [4 ] la ye re d s er ie s m z, u za , u zb 81 81 th is s tu d y 90 -2 3 d ri ll co re [5 ] la ye re d s er ie s u za , u zb , u zc 87 87 th is s tu d y n w b as is to p p en [6 ] la ye re d s er ie s/ u p p er b o rd er s er ie s u zc , s h , u zc ´ 21 12 9 th is s tu d y k ile n [7 ] u p p er b o rd er s er ie s/ la ye re d s er ie s h z´ , l za ´, l zb ´, l zc ´, m z´ , u za ´, u zb ´, u zc ´, s h ; u zc 33 26 6 1 sa lm o n se n & t eg n er (2 01 3) h am m er p as s [8 ] u p p er b o rd er s er ie s h z´ , l za ´, l zb ´, l zc ´, m z´ , u za ´ 25 25 sa lm o n se n & t eg n er (2 01 3) b rø d re to p p en [9 ] u p p er b o rd er s er ie s h z´ , l za ´, l zb ´, l zc ´, m z´ , u za ´, u zb ´, u zc ´, s h 37 34 3 sa lm o n se n & t eg n er (2 01 3) sy d to p p en [1 0] u p p er b o rd er s er ie s h z´ 11 11 sa lm o n se n & t eg n er (2 01 3) sk ae rg aa rd b ay [1 1] u p p er b o rd er s er ie s h z´ , l za ´, l zb ´ 15 15 th is s tu d y sk ae rg aa rd p en in su la [1 2] m ar gi n al b o rd er s er ie s lz a* , l zb *, l zc *, m z* , u za *, u zb * 33 33 h o ln es s et a l. (2 02 2) iv n ar m iu t is la n d [1 3] m ar gi n al b o rd er s er ie s lz a* , l zb *, m z* 17 17 h o ln es s et a l. (2 02 2) k ra em er ø [1 4] m ar gi n al b o rd er s er ie s lz a* , l zb * 19 19 h o ln es s et a l. (2 02 2) to ta l n o . o f sa m p le s 64 6 62 4 20 2   a r ef er en ce p ro fil e co n si st s o f su rf ac e sa m p le s fr o m u tt en ta l p la te au , k ra em er ø , p u ku ga gr yg ge n /f o rb in d el se sg le ts ch er , w es t b as is to p p en , a n d d ri ll co re 9 022 . b n u m b er s la b el le d in f ig . 1 . lz : l o w er z o n e. m z: m id d le z o n e. u z: u p p er z o n e. h z: h id d en z o n e. s h : s an d w ic h h o ri zo n . https://doi.org/10.34194/geusb.v53.8316 http://www.geusbulletin.org tegner et al. 2023: geus bulletin 53. 8316. https://doi.org/10.34194/geusb.v53.8316 6 of 8 w w w . g e u s b u l l e t i n . o r g the major and trace element data were obtained by a combination of xrf at aarhus university and icp-ms at the university of california, davis and acmelabs as described in tegner et al. (2009), thy et al. (in press) and tegner et al. (2019), respectively. concentrations of feo were determined by titration with potassium dichromate. the mass lost on ignition (loi) was determined by heating the powder in air in a muffle furnace at 950°c for 3 h. the values obtained for certified reference materials, bhvo-1 and bir-1, are reported in supplementary data file 3. xrf analyses of bhvo-1 and bir-1 (n = 53–63) demonstrate that the relative variation of repeated analyses is less than 4.5% (1 s.d./average value) for most major element oxides. however, in bir-1, the relative variation is higher (14%) for k2o, which has a relatively low concentration (0.027 wt%; jochum et al. 2016). for the trace elements measured by xrf, the relative variation of the transition metals (v, cr, ni, cu, zn) and sr are within 5%. in bhvo-1, the relative variation is moderate for rb, y, zr, nb and ba (4–12%) and higher for ce (20%). in bir-1, which is depleted in these elements relative to bhvo-1 (jochum et al. 2016), the relative variation of repeat analyses is somewhat higher for rb, y, zr and nb and pb (7–28%) and much higher for ba and ce. the accuracy or relative deviation from the preferred values for bhvo-1 is within 11% for all oxides and trace elements. similar values were obtained for the accuracy of bir-1, except for rb, nb and ce, which have sub-ppm preferred values. in conclusion, the xrf data can generally be viewed as accurate down to a few ppm. repeat icp-ms analyses of standards at acmelab (n = 14) and university of california (n = 6) deviate less than 7 and 18%, respectively, from the preferred values for all trace elements reported in this study (supplementary data file 3). data description and main features the bulk compositions of cumulate rocks, such as those reported here, represent a mix of accumulated liquidus crystals (cumulus) and interstitial material (intercumulus) derived from crystallisation of interstitial melt (wager et al. 1960; irvine 1982). the present data set thus tracks changes in the compositions fig. 3 field photo showing the northwards view from kraemer ø. metre-scale modal layering occurs in the middle zone (mz) (foreground, lower two-thirds) and in the background where the triple group can be seen on wager peak (c. 1200 m a.s.l.). wager peak triple group senw mz mz fig. 4 example compositional data available in the data set. a: whole-rock feototal versus sio2 (wt%) for the skaergaard intrusion. one outlier at 17 wt% sio2 and 50 wt% feo is not shown. b, c: stratigraphic variations in whole-rock feototal and rb contents. data from supplementary data file 1. 0 5 10 15 20 25 30 35 40 20 30 40 50 60 70 80 fe o (w t% ) sio2 (wt%) hz+lz mzls ubs mbs uz lz* mz* uz* hz´+lz´ mz´ uz´ gabbropegmatite melanogranophyre 0 5 10 15 20 25 30 35 40 fe o (w t% ) 10 20 30 40 50 0.00.20.40.60.81.0 r b (p pm ) fraction of magma remaining (f) 60 hz lza lzb lzc mz uza uzb uzc (b) (a) (c) https://doi.org/10.34194/geusb.v53.8316 http://www.geusbulletin.org tegner et al. 2023: geus bulletin 53. 8316. https://doi.org/10.34194/geusb.v53.8316 7 of 8 w w w . g e u s b u l l e t i n . o r g and proportions of minerals and trapped melt during solidification of the skaergaard magma chamber. importantly, the bulk-rock compositions do not directly represent liquid compositions. the data set can therefore be used to evaluate igneous processes during crystallisation and ore formation. figure 4a, for example, shows that bulk-rock feototal and sio2 vary considerably and display a negative correlation. these two oxides also show systematic variations between zones (hz, lz, mz, uz). the compositions generally overlap between ls, mbs and ubs rocks although the most feo-rich rocks occur in ls. in the uz equivalents, the ubs rocks are enriched in sio2 relative to ls and mbs rocks. not surprisingly, the highest sio2 and the lowest feo values are seen for granophyres sensu lato. figure 4 also shows two examples of stratigraphic variations plotted against the calculated fraction of melt remaining (f). in fig. 4b, feo generally increases from lz to uz equivalents and displays a marked increase across the lzb/lzc boundary, reflecting accumulation of magnetite and ilmenite. in the lower and middle part of the stratigraphy (hz–uza), the feo contents are comparable in the floor, wall and roof rocks. however, in uzb’ and uzc’ of the roof (ubs), feo is markedly lower compared to ls and mbs rocks. figure 4c shows the stratigraphic trends of the incompatible element rb. in the lower and middle parts (hz–uza), the trends are relatively flat and display comparable values in rocks from ls and mbs, while higher values are found in ubs rocks. closer to sh (uzb and uzc equivalents), rb increases exponentially in the cumulate rocks and shows the highest values in the melanogranophyres. the compiled whole-rock data set can, for example, be used to constrain processes of igneous differentiation and ore formation. acknowledgements we are grateful to the danish lithosphere centre for supporting field work in 2000. platina resources were accommodating during the 2008 and 2011 field seasons. the geological survey of denmark and greenland (geus) helped with field logistics in 2017. platinova resources ltd. are thanked for access to drill core material. we thank c. kent brooks for inspiring this project. we are indebted to jakob k. keiding for help with field work, sample preparation and discussion. we also enjoyed assistance and company in the field from jens c.ø. andersen, olivier namur, anja k.m. fonseca and joel a. simpson. sidsel grundvig, ingrid aaes and jette villesen, aarhus university, are thanked for help with sample preparation and x-ray fluorescence analyses. we thank two reviewers, rais latypov and howard naslund, as well as kerstin saalmann for careful editorial handling. additional information funding statement this work was supported by funding from danish national science research council (ct, tfdn), the danish national research foundation (tfdn, cel, ct), the carlsberg foundation (ct), aarhus university (ct, lps), the uk natural environment research council (mbh, mcsh), the us national science foundation under grant number nsf-ear-0208075 (cel), the uk royal society international joint project (mbh, ct). author contributions ct: conceptualisation, data curation, funding acquisition, investigation, methodology, supervision, visualisation, writing – original draft. lps: investigation, methodology, writing – review and editing. mbh: conceptualisation, data curation, funding acquisition, investigation, methodology, writing – review and editing. cel: investigation, conceptualisation, funding acquisition, methodology, writing – review and editing. mcsh: investigation, methodology, writing – review and editing. pt: investigation, methodology, writing – review and editing. tfdn: investigation, conceptualisation, funding acquisition, methodology, writing – review and editing. competing interests the authors declare no competing interests. additional files three additional files, including the data set, a description of sample profiles and analytical precision and uncertainty are available at https://doi.org/10.22008/fk2/howw6f. references andersen, j.c.ø., rasmussen, h., nielsen, t.f.d. & rønsbo, j.c. 1998: the triple group and the platinova gold and palladium reefs in the skaergaard intrusion: stratigraphic and petrographic relations. economic geology 93, 488–509. https://doi.org/10.2113/ gsecongeo.93.4.488 holness, m.b., humphreys, m.c.s., namur, o., andersen, j.c.ø., tegner, c. & nielsen, t.f.d. 2022: crystal mush growth and collapse on a steep wall: the marginal border series of the skaergaard intrusion, east greenland. journal of petrology 63, 1–21. https://doi.org/10.1093/ petrology/egab100 holness, m.b., tegner, c., namur, o. & pilbeam, l. 2015: the earliest history of the skaergaard magma chamber: a textural and geochemical study of the cambridge drill core. journal of petrology 56, 1199–1227. 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petrology of the skaergaard intrusion. kangerdlussuaq, east greenland. meddelelser om grønland 105, 352 pp. https://doi.org/10.34194/geusb.v53.8316 http://www.geusbulletin.org https://doi.org/10.1144/gsjgs.152.3.0421 https://doi.org/10.1016/s0167-2894(96)80007-8 https://doi.org/10.1016/s0167-2894(96)80007-8 https://doi.org/10.1093/petrology/43.3.535 https://doi.org/10.1093/petrology/43.3.535 https://doi.org/10.1093/petrology/egr009 https://doi.org/10.1093/petrology/egt003 https://doi.org/10.1093/petrology/egt003 https://doi.org/10.1093/petrology/egu028 https://doi.org/10.1093/petrology/25.1.185 https://doi.org/10.1093/petrology/25.1.185 https://doi.org/10.1093/petrology/egg092 https://doi.org/10.1093/petrology/egv049 https://doi.org/10.1007/s00410-021-01861-x https://doi.org/10.1007/s00410-013-0852-y https://doi.org/10.1007/s00410-013-0852-y https://doi.org/10.1007/s004100050292 https://doi.org/10.1029/2018gc007941 https://doi.org/10.1007/s00410-009-0450-1 https://doi.org/10.1093/petrology/egp020 https://doi.org/10.1093/petrology/egp020 https://doi.org/10.1007/s00410-008-0361-6 https://doi.org/10.34196.v53.8327 https://doi.org/10.34196.v53.8327 https://doi.org/10.1093/petrology/1.1.73 https://doi.org/10.1093/petrology/1.1.73 geological survey of denmark and greenland bulletin 6, 29-39 29 the neoproterozoic rivieradal group of kronprins christian land, eastern north greenland m. paul smith, a.k. higgins, n.j. soper and martin sønderholm the rivieradal group, formally defined here, is confined to the vandredalen thrust sheet of the caledonian orogen in kronprins christian land, eastern north greenland. it comprises a succession of neoproterozoic siliciclastic sediments that represent the fill of a half-graben basin. the syn-rift rivieradal group is overlain by post-rift sediments of the hagen fjord group. the latter succession is present in both the thrust sheet and the caledonian foreland to the west. in the foreland, where the rivieradal group is not represented, the hagen fjord group disconformably overlies palaeoproterozoic–mesoproterozoic sandstones of the independence fjord group. keywords: caledonian, north greenland, precambrian, proterozoic, stratigraphy m.p.s., lapworth museum, school of geography, earth and environmental sciences, university of birmingham, edgbaston, birmingham b15 2tt, uk. e-mail: m.p.smith@bham.ac.uk a.k.h. & m.s., geological survey of denmark and greenland, øster voldgade 10, dk-1350, copenhagen k, denmark. n.j.s., gams bank, threshfield, skipton bd23 5np, uk. also affiliated with: department of geology, university college, galway, ireland. kronprins christian land lies at the northern termination of the east greenland caledonides, and constitutes a key area for studies of the western border zone of the orogen (fig. 1). this region exposes continuous sections from the undisturbed foreland in the west, across parautochthonous foreland affected by folding and thin-skinned thrusting to allochthonous thrust sheets in the east (higgins et al. 2001a, b). the foreland comprises three principal lithostratigraphical divisions: (1) palaeoproterozoic–mesoproterozoic sandstones of the independence fjord group, the mesoproterozoic zig-zag dal basalt formation and associated dolerites (midsommersø dolerite formation); (2) neoproterozoic shallow marine sediments of the hagen fjord group (sønderholm & jepsen 1991); (3) cambrian–silurian shelf sediments of the franklinian basin (higgins et al. 1991). the hagen fjord group is also represented within the allochthon, in the vandredalen thrust sheet, where it overlies the clastic sediments of the rivieradal group, which are the subject of this paper. in kronprins christian land the parautochthonous lower palaeozoic sediments lie in the foot wall of the vandredalen thrust sheet, and are deformed by a series of thin-skinned thrusts that constitute a duplex below the vandredalen thrust (figs 1, 2). this parautochthonous area extends as a 30–50 km wide belt to the west of the 200 km long, n–s-trending vandredalen thrust front. the vandredalen thrust displays a classical staircase trajectory with very long (20+ km) flats developed in dolomitic horizons, and ramps developed in the more resistant subtidal carbonate units of the franklinian basin succession (cf. smith et al. 2004, this volume). the thrust roots to the east along the spærregletscher – hekla sund lineament and has a total westward displacement estimated at c. 40 km, of which c. 18 km are taken up in the thin-skinned parautochthonous belt (higgins et al. 2001b, 2004). the geological survey of denmark and greenland bulletin 6, 29–39 © geus, 2004 geus bulletin 6.pmd 10-02-2005, 09:5329 30 ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲▲ ▲ ▲ ▲ ro m er sø i n go lf fjor d amdrup land holm land hovgaard ø kap bernhoft dijmphna sund h ek la sund cen tru ms ø s k a l l in g e n sy dv ejd al sp t sp t r ivie r a d a l 20°w 80°n 81°n blåsø sk jo ld un ge el v nio gha lvfje rdsf jord en gr æs elv sæ faxi elv d an m ar k fj or d va nd re d al en th ru st v an dr ed al en kap holbæk p c m a hj h bs fl d v lambert land mfig. 3 wandel sea basin sequence (post-caledonian) samuelsen høj formation lauge koch land formation odins fjord formation turesø formation wandel valley formation kap holbæk formation crystalline basement thrust fault, shear zone børglum river and sjælland fjelde formations fyns sø, kap bernhard, campanuladal fms hagen fjord gp rivieradal group independence fjord gp and basaltic formations vandredalen thrust hagen fjord group ▲ ▲ ▲ ▲ vandredalen thrust sheet ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲▲ ▲ ▲ c a le d o n id es greenland i 25 km geus bulletin 6.pmd 10-02-2005, 09:5330 31 vandredalen thrust sheet, in turn, is structurally overlain by a thrust sheet that transported palaeoproterozoic to mesoproterozoic clastic and volcanic rocks westwards. the allochthonous quartzites have traditionally been viewed as equivalents of the independence fjord group on the foreland (see figs 1, 2), but shrimp isotopic studies on rhyolites interbedded with the quartzites that yielded an age of 1740 ma (kalsbeek et al. 1999) have cast some doubt on this interpretation (see also pedersen et al. 2002). still farther to the east, higher thick-skinned thrust sheets incorporate crystalline basement gneisses. this paper provides a formal stratigraphic basis, at group level, for the rocks that underlie the hagen fjord group within the vandredalen thrust sheet, and collates available field data regarding this succession. as noted below, formal definition of the constituent formations awaits more detailed field analysis of the rivieradal group. the informal units of fränkl (1954, 1955) were found to be generally usable as field divisions, although there is uncertainty in places about their correlation. stratigraphy of the vandredalen thrust sheet restoration of the displacement associated with the vandredalen thrust sheet demonstrates that much of the sediment within the thrust sheet was deposited in an east-facing extensional half-graben (hekla sund basin) that originally lay immediately to the east of the spærregletscher – hekla sund lineament (higgins et al. 2001b). this basin fill was thrust out of the halfgraben and transported westwards on the vandredalen thrust (fig. 2). these syn-rift sediments are assigned to the rivieradal group, which is formally erected below. they are overlain by sediments of the hagen fjord group, which were deposited during postrift thermal subsidence and extended westwards beyond the confines of the hekla sund basin. the hagen fjord group, in consequence, is present both in the foreland and the hanging wall of the vandredalen thrust whereas the rivieradal group is restricted to the hanging wall (higgins et al. 2001b). the hagen fjord group within the vandredalen thrust sheet is represented by the campanuladal, kap bernhard and fyns sø formations. the campanuladal formation comprises 200 m of variegated sandstones, siltstones and mudstones of generally similar appearance to successions of the same unit in the foreland around danmark fjord. a lower, greenish weathering unit containing parallel and trough cross-laminated sandstones, and mudstones with desiccation cracks, is overlain by an upper, dark red weathering unit dominated by calcareous mudstones with some trough cross-bedded sandstones (jepsen & sønderholm 1994). the kap bernhard formation comprises brownish red weathering, finely laminated algal limestones and the fyns sø formation contains pale stromatolitic dolostones; both correspond very closely to their counterparts in the foreland. in the northernmost part of the outcrop area of the vandredalen thrust sheet, in finderup land (fig. 1), the fyns sø formation is unconformably overlain by sandstones of the kap holbæk formation. this latter unit was included within the redefined hagen fjord group of clemmensen & jepsen (1992), but stratigraphic data obtained during the 1994–1995 field seasons demonstrated that a significant hiatus occurs between the two units. in particular, a well-developed palaeokarst horizon developed at the top of the fyns sø formation is infilled by the kap holbæk formation (smith et al. 1999). it is probable that the carbonates of the fyns sø formation are correlatives of similar late riphean to sturtian units, which are widely developed in the north atlantic region, while the presence of deep skolithos burrows in the kap holbæk formation indicates a lower cambrian age (smith et al. 2004, this volume). since the hiatus between the two units probably spans the entire vendian, smith et al. (2004) proposed that the kap holbæk formation be removed from the hagen fjord group. facing page: fig. 1. geological map of kronprins christian land, eastern north greenland, and lambert land, north-east greenland. black oval symbols in the rivieradal group, in legend and on map, indicate conglomerates. bs, brede spærregletscher; d, ‘dunkeldal’; fl, finderup land; h, harefjeld; hj, hjørnegletscher; m, marmorvigen; pcma, prinsesse caroline mathilde alper; spt, spærregletscher thrust; v, vardedalen. on index map: i, independence fjord. see figs 2 and 3 for cross-sections along rivieradal. modified from rasmussen & smith (2001). note that the traditional interpretation of the allochthonous quartzites as equivalents of the foreland independence fjord group (as depicted here and on fig. 2), has been brought into doubt by the 1740 ma age on interbedded rhyolites (see discussion in kalsbeek et al. 1999 and pedersen et al. 2002). geus bulletin 6.pmd 10-02-2005, 09:5331 32 rivieradal group new group history. the proterozoic rocks of kronprins christian land were first examined systematically by geologists of lauge koch’s 1926–1958 expeditions. the region around danmark fjord was documented by adams & cowie (1953), and that around centrumsø by fränkl (1954, 1955). fränkl recognised that the neoproterozoic succession could be divided into autochthonous and allochthonous parts, the two separated by a major thrust upon which his ‘main nappe’ was transported. the metasediments of the nappe were divided into a lower, more metamorphosed part, comprising the stenørkenen phyllites (> 1000 m) and the sydvejdal marbles (100–400 m), and an upper less metamorphic part. the latter included, from base to top, the taagefjeldene greywackes (> 700 m) with a layer of alum shales at the base (c. 150 m), the rivieradal sandstones (1000–2000 m), the ulvebjerg sandstones & tillites (20–35 m), the red, shaly campanuladal limestone and the fyns sø formation. the two last-named units were also identified as lying in the foot wall of the nappe (fränkl 1954, 1955). the succession present in the ‘main nappe’ was recognised as having been deposited in a basin located to the east, which fränkl (1955) termed the ‘hekla sund basin’; the latter term is retained here for the depositional basin in which the rivieradal group accumulated. fig. 2. schematic nw–se cross-sections of the vandredalen rift system, approximately along the section line of fig. 3 shown on fig. 1, but with extensions to both south-east and north-west. a: present-day section, with overburden calculated from conodont alteration temperatures (after rasmussen & smith 2001). b: with displacements on the thrusts restored, illustrating the fault-bounded control of the west margin of the hekla sund basin. modified from higgins et al. (2001b). spærregletscher thrust if rg 22 km 18 km spt 50 ? km 100 ? km st hf if o–s o–s o– s hf vt vt o–s upper allochthon– higher thrust sheets comprising ordovician–silurian, hagen fjord group, rivieradal group (distal part of hekla sund basin), independence fjord group and associated volcanic rocks and crystalline basement. estima ted o verbur den st vt spt spærregletscher thrust vandredalen thrust sole thrust rg if cb hf o–s ordovician–silurian hagen fjord group rivieradal group crystalline basement independence fjord group and associated volcanic rocks 5 km 0 10 20 km hf present day rg cb cb if if if if cb cb hekla sund basin rivieradal group succession) a b wnw ese conglomerate hekla sund basin (rivieradal group) sandstone mudstone and calcareous mudstone geus bulletin 6.pmd 10-02-2005, 09:5432 33 haller (1961, 1971) erected the hagen fjord group for proterozoic sediments of the autochthon and allochthon in kronprins christian land, including volcanic rocks now referred to the zig-zag dal basalt formation, hekla sund formation and aage berthelsen gletscher formation, and lower cambrian carbonates now referred to the portfjeld formation. clemmensen & jepsen (1992) restricted the group, following work by the geological survey of greenland in 1978–1980, to include only the neoproterozoic shallow water carbonate and siliciclastic succession present in the area between lambert land and independence fjord. additional formations were also erected by clemmensen & jepsen, to improve the stratigraphical framework of the group. hurst & mckerrow (1981a, b), on the basis of reconnaissance field work in kronprins christian land in 1980 by the former geological survey of greenland (ggu), concluded that all of the units beneath the campanuladal formation within the main thrust sheet were representative of a single unit of deepwater turbidites, mud and resedimented conglomerates; they collectively referred to this succession as the ‘rivieradal sandstones’. although sedimentological interpretations of the succession have been refined (see below), this is the concept that we here formalise as the rivieradal group. hurst & mckerrow (1981a, b) and hurst et al. (1985) recognised a number of thrust sheets in the kronprins christian land sector of the east greenland caledonides. these included the vandredalen nappe (which corresponds to fränkl’s ‘main nappe’), the finderup land nappe and the sæfaxi elv nappe. the finderup land nappe was a geographically isolated structure rimming the western edge of the main ice sheet, and a succession that incorporated the campanuladal, fyns sø and kap holbæk formations was recognised. subsequent regional mapping by ggu in 1994–1995 has demonstrated that the finderup land nappe is a northward continuation of the vandredalen nappe (now the vandredalen thrust sheet) in which only the higher stratigraphic levels are preserved. the sæfaxi elv nappe was considered by hurst & mckerrow to be a thrust sheet containing allochthonous early palaeozoic sediments that were deep-water equivalents of the platform succession, and these were assigned to the harefjeld formation by hurst (1984). however, rasmussen & smith (1996) demonstrated that these sediments were highly strained equivalents of the platform succession, and that the lower contact with the underlying fyns sø formation was an unconformity and not a thrust. the ‘sæfaxi elv nappe’ is thus a succession of parautochthonous foreland carbonates deformed in the foot wall of the vandredalen thrust, and the concept of an independent thrust sheet (and of the harefjeld formation) has been abandoned (rasmussen & smith 1996). name. the group takes its name from rivieradal, the e–w-trending valley south-east of centrumsø that contains the most complete section through the unit (higgins & soper 1994, 1995). type area and reference sections. the type area for the group is rivieradal itself, where an excellent reference section through the upper part of the group occurs and the lower part, although highly deformed, is also present. additional reference sections through parts of the group are available through ‘dunkeldal’ (between northern vandredalen and inner ingolf fjord; fig. 1), and along much of the western side of vandredalen between the western end of ingolf fjord and romer sø. thickness. hurst et al. (1985) estimated a thickness of 2.5 km for the ‘rivieradal sandstones’. structural studies in rivieradal and ‘dunkeldal’, carried out during the 1994 and 1995 field seasons, suggest that the combined thickness of the highly deformed lower part of the rivieradal group and the less deformed upper part is substantially higher, in the order of 7.5–10 km (higgins et al. 2001b). lithology, facies associations and depositional environments. the sedimentological and stratigraphical variations within the rivieradal group should be viewed in the context of the internal structure of the vandredalen thrust sheet, which is best exposed in the 35 km long section along rivieradal between the thrust sheet front at the east end of centrumsø and its trailing edge near marmorvigen (fig. 3). the western frontal region of the thrust sheet is characterised by simple, large-scale folds developed in the fyns sø and kap bernhard formations; these overlie the rivieradal group sediments, which are well exposed throughout the valley of rivieradal. steep to vertical dips characterise much of the western third of the section, with occasional west-facing fold pairs showing flat common limbs. the central third of the section begins with an abrupt change to tightly developed folds, which become progressively more intense eastwards with the inclination of the axial surfaces decreasing geus bulletin 6.pmd 10-02-2005, 09:5433 34 from moderate eastward dips to almost horizontal. in the eastern third of the section deformation is intense with complete erasure of sedimentary way-up indicators in long-limbed isoclinal folds; the units exposed here correspond to the most distal parts of the rivieradal group. the fold style and orientation of strata in the rivieradal section suggest that the vandredalen thrust follows a series of ramps and flats, and can be viewed as sampling an oblique segment of the half-graben hekla sund basin in which the rivieradal group accumulated. the oldest and most distal parts of the succession are therefore preserved in the eastern part of the thrust sheet, and the younger and more proximal lithofacies are present in the west. the present-day distribution of remnants of the rivieradal group succession indicates that the original hekla sund basin must have been at least 200 km long from north to south and 50 km wide from east to west. the rivieradal group is lithologically variable and possesses a strong proximal to distal polarity. one of the most distinctive lithologies present is a coarse conglomerate, which occurs repeatedly along the leading edge of the vandredalen thrust sheet. substantial conglomerate units are present in three discrete areas (fig. 1). the northernmost is along a 15–20 km strike section on the west side of romer sø, the second is a 20 km long strike section on the west side of central vandredalen, and the southernmost is found in southern skallingen near blåsø. the best known of the conglomeratic successions is that in central vandredalen where several thick sections have been measured. quartzite clasts (90–95%) dominate everywhere over dolerite clasts (5–10%), and are probably derived from the independence fjord group and the midsommersø dolerite formation; these units are presumed to have been exposed to active erosion to the west of the basin. clasts vary in size from a few decimetres to well over a metre in the thicker beds, with occasional outsize clasts as much as 3–4 m across; these large clasts are indisputably proximal. viewed from a distance, the thick conglomerate units appear to have a lensoid form, suggesting deposition in a series of nested channels. in e–w valley sections to the west of romer sø, rapid lateral facies changes are well exposed. thick conglomerate-dominated units pass eastwards, over as an ds to ne m ud st o ne m ud st o ne , s ilt st o ne an d sa nd st o ne c ar bo na te a nd ca lc ar eo us m ud st o ne lo w er p al ae o zo ic p la tf o rm t u , t ur es ø f o rm at io n; b r , b ø rg lu m r iv er f o rm at io n; s f, sj æ lla nd f je ld e fo rm at io n; w v, w an de l v al le y fo rm at io n r iv ie ra da l g ro up ( pr o te ro zo ic ) o th er p ro te ro zo ic a nd l o w er p al ae o zo ic u ni ts : fs , f yn s sø f o rm at io n; k b , k ap b er nh ar d fo rm at io n; c d , c am pa nu la da l f o rm at io n; i f, in de pe nd en ce f jo rd g ro up 0 5 10 k m 1 km if if k b f s sf fs w v k b b r pa ra ut o ch th o no us th ru st b el t v an dr ed al en th ru st f ro nt h ag en f jo rd g ro up r iv ie ra da l g ro up m ar m o rv ig en e se w n w b r c d t u w v ? v a n d r e d a l e n t h r u st fig. 3. cross-section through the vandredalen thrust sheet along rivieradal. see fig. 1 for section line. modified from higgins et al. (2001b). geus bulletin 6.pmd 10-02-2005, 09:5434 35 distance of 1–2 km, into upward-thickening packets of sandstone in which the individual beds coarsen upwards, sometimes into conglomerate. these in turn pass farther eastwards, over a similar distance, into upward-thickening and coarsening mudstone-siltstonesandstone packets. in the southern area of conglomerates near blåsø, rounded granite and quartz pebbles (up to 20%) make an appearance, although most clasts are again quartzite and dolerite; a deeper erosion level was evidently reached in the southern source region. the geometry of the conglomerate deposits, together with their discrete occurrences, suggests the presence of three discrete fan delta systems that acted as major feeder distributary systems on the western side of the original basin. while the three main conglomerate developments are all in the upper part of the rivieradal group succession, they may not be at exactly the same stratigraphical level. input might have been via a single major fluvial system, which varied in position with time, and if so the blåsø fan delta with its crystalline clasts may be the youngest of these. the repeated cycles of conglomeratic deposition, and the upward-coarsening sandstone cycles in other areas at the frontal part of the thrust sheet, may have been controlled by displacements on the basin-margin fault system. in ‘dunkeldal’, a valley on the east side of vandredalen, a total thickness of 3000 m has been measured in a continuously exposed section (lower part of measured section in fig. 4). the basal 200 m of this section lie above a thrust contact with ordovician carbonates, and comprise strongly sheared conglomerates. the conglomerates are overlain by a 500 m thick phyllite-dominated unit (‘stenørkenen phyllites’ of fränkl 1955), and then by over 2200 m of sandstone turbidites interbedded with dark pyritic mudstones (‘taagefjeldene greywackes’ of fränkl). laterally and vertically, this sandstone-dominated succession grades into homogeneous black mudstones, and equivalent phyllitic rocks, which are widely exposed around the innermost branch of ingolf fjord. the lack of marker horizons and non-exposure in the flat valley bottom of vandredalen makes thickness estimates in these areas difficult; thus the notional gap of 350 m in the measured section of fig. 4 may in fact correspond to several kilometres of section. on the west side of vandredalen, to the north-west of innermost ingolf fjord, a 900 m thick succession comprises coarsening-upwards sequences of parallel laminated mudstone, lenticular and wavy-bedded mudstones, sandstone-dominated heterolithic sediments with parallel lamination, trough cross-lamination and hummocky cross-stratification, overlain by trough and planar cross-bedded sandstones with occasional herringbone cross-bedding (upper part of section in fig. 4). these correspond to the original ‘rivieradal sandstones’ of fränkl (1955). current directions are predominantly towards the north-east and are interpreted as the products of stormand tidedominated shallow marine deposition. this facies association in the upper part of the rivieradal group can be recognised throughout the outcrop area, from romer sø in the north to blåsø in the south. on the west side of vandredalen, the succession of fig. 4 continues with about 300 m of interfingering conglomerates and sandstones (the ‘ulvebjerg sandstones and tillites’ of fränkl – equivalent to the conglomeratic developments described above), which are overlain by sediments referred to the hagen fjord group. the latter shallow marine succession constitutes the postrift fill of the basin. the most distal representatives of the rivieradal group are seen in the valley of rivieradal itself. at the eastern end of the valley, pelitic slates with sandstones form the coastal mountains south of the mouth of rivieradal. these are overlain farther to the west by pelitic and calcareous slates and siltstones with prominent yellow-weathering carbonate units, which correspond to the ‘sydvejdal marbles with chloritic shales’ of fränkl (1955). this unit is overlain, in turn, by phyllites and turbidites corresponding to those seen in the ‘dunkeldal’ section (fig. 4). overall, the rivieradal group is characterised by point sources of sediment input which generated substantial conglomerate fan deltas, and which are associated with sandy, proximal turbidites. between the fans and in the eastern (distal) part of the basin, sedimentation was dominated by mud and calcareous mud. as the basin filled, the depositional style switched from deep to shallow marine, and less localised, more laterally persistent, tidal and storm-dominated deposition began to predominate. boundaries. since the group is restricted to the vandredalen thrust sheet, the rivieradal group is everywhere bounded on its lower surface by the vandredalen thrust; a stratigraphic base to the group has not been identified within the thrust sheet. the upper boundary of the group is placed where sandstones and laterally equivalent conglomerates are overlain by a characteristic 200 m variegated unit comprising a geus bulletin 6.pmd 10-02-2005, 09:5435 3 6 1200 2500 3700 3600 3500 3400 3300 3200 3100 3000 2900 2800 2700 2600 2500 3800 3900 4000 4100 4200 4300 4400 4500 4600 4700 4800 4900 5000 2400 2300 2200 2100 2000 1900 1800 1700 1600 1500 1400 1300 1100 1000 900 800 700 600 500 400 300 200 1000 ? ? 'taagefjeldene greywackes' massive ta,b sandstone turbidites and black pyritic mudstones 'stenørkenen phyllites' ? black phyllites, pyritic 'taagefjeldene greywackes' not exposed black mudstones with thin sandstones sandstone dominated coarsening-upward sequences fyns sø fm pale dolostone kap bernhard fm red limestone campanuladal fm. variegated sandstones and mudstones 'ulvebjerg sandstones' laterally interfingering conglomerates and sandstones 'rivieradal sandstones' mudstone dominated coarsening-upward sequences basal conglomerate b asal thrust m ud cracks c ro ssbedding parallel lam inatio n 'rivieradal sandstones' 'taagefjeldene greywackes' g e u s b u lle tin 6 .p m d 1 0 -0 2 -2 0 0 5 , 0 9 :5 4 3 6 37 lower greenish sandstone and mudstone interval overlain by a dark red calcareous mudstone-dominated interval. the greenish sandstone and mudstone interval contains parallel and trough cross-laminated sandstones and abundant desiccation cracks. the variegated unit is identified as the campanuladal formation of the foreland and, as in the foreland, is overlain by brownish red weathering microbially laminated limestones of the kap bernhard formation (fig. 4). distribution. the rivieradal group is restricted to the vandredalen thrust sheet, and crops out in a broad zone extending from romer sø southwards along vandredalen; a further broad zone extends from the eastern end of centrumsø southwards through rivieradal and skallingen to blåsø (fig. 1). a narrow strip of outcrops, in the hanging wall of the main thrust ramp, extends from vardedalen (on the north side of central ingolf fjord) southwards to brede spærregletscher and along the west side of hekla sund to marmorvigen. the southernmost outcrops of the rivieradal group are present in nunataks at the westernmost extremity of lambert land (fig. 1). geological age. the group is older than the hagen fjord group, specifically the kap bernhard and fyns sø formations, thought to be of probable riphean age (smith et al. 1999). however, frederiksen (2000) has suggested the hagen fjord group is sturtian, and equivalent to the andrée land group of the eleonore bay supergroup. the rivieradal group post-dates the independence fjord group, midsommersø dolerite formation and zig-zag dal basalt formation, all of which are represented by clasts within the conglomeratic units. the dolerites of the midsommersø dolerite formation were originally dated at c. 1230 ma by kalsbeek & jepsen (1984), but a recent baddeleyite age on a dolerite of 1380 ma has been obtained by upton et al. (in press); this provides a maximum age limit for deposition. the rivieradal group was thus deposited in the interval between 1380 ma and ~ 700 ma. g. vidal (in hurst et al. 1985) recorded ‘several comparatively well-preserved specimens’ of acritarchs from the upper part of the rivieradal group which were thought indicative of an upper proterozoic age. in particular, a single specimen of chuaria circularis was considered to be indicative of an upper riphean age since, elsewhere in scandinavia and north america, the species occurs at around 800 ma. taken together with the evidence for a conformable upper boundary, this suggests that the rivieradal group was deposited in the younger part of the broad age range outlined above. subdivision. fränkl (1954, 1955) recognised five units within the succession now assigned to the rivieradal group: ‘stenørkenen phyllites’, ‘sydvejdal marbles with chloritic shales’, ‘taagefjeldene greywackes’ with a layer of alum shales at the base, ‘rivieradal sandstones’, and the ‘ulvebjerg sandstones and tillites’. these units were used as field terms during the 1994–1995 field seasons and proved to be recognisable throughout the area, although this is at least partly because they represent lithological types rather than coherent and homologous stratigraphic units. the ‘stenørkenen phyllites’ are present in rivieradal and similar phyllites are present throughout the region, although thickness estimates and correlation is hampered by the paucity of marker horizons. fränkl (1955) estimated a thickness of > 1000 m. the ‘sydvejdal marbles with chloritic shales’ are also present in eastern rivieradal, and include pelitic and calcareous slates and siltstones with prominent yellow-weathering carbonate units. fränkl (1955) estimated a thickness of 100–400 m. the ‘taagefjeldene greywackes’ are best seen in the section through ‘dunkeldal’ (fig. 4), where jepsen & sønderholm (1994) recorded a thickness of over 2200 m. this compares with fränkl’s (1954, 1955) estimate of > 700 m, of which 150–200 m were alum shales; multicoloured friable shales cover large areas around the head of ingolf fjord, and pass laterally (northwards) along vandredalen into a sandstonesiltstone-mudstone succession. the ‘rivieradal sandstones’ sensu fränkl have a thickness of 1400 m, measured in a section across skallingen for which no base was present (leslie & jepsen 1995), and jepsen & sønderholm (1994) measured a thickness of 900 m on the western side of vandredalen (fig. 4). fränkl (1954) estimated a range of 1000–2000 m, which appears to be the right order of magnitude. the ‘tillites’ of fränkl’s (1954, 1955) ‘ulvebjerg sandstones and tillites’ unit were relatively soon re-interpreted as non-glacial facing page: fig. 4. simplified measured section through part of the synrift rivieradal group succession, the lower part in ‘dunkeldal’, and the upper part from the west side of vandredalen. the corresponding lithostratigraphical terms of fränkl (1955) are indicated. the designation ‘t a,b ’ refers to bouma cycle intervals in the sandstone turbidites. the campanuladal, kap bernhard and fyns sø formations form part of the post-rift hagen fjord group. slightly modified from jepsen & sønderholm (1994). geus bulletin 6.pmd 10-02-2005, 09:5437 38 conglomerate horizons (haller 1971; hurst & mckerrow 1981a), and they are one of the most spectacular stratigraphic developments within the group. on the western side of vandredalen, a sandstonedominated unit at least 300 m thick can be seen to pass laterally into thick conglomerates up to 500 m thick (jepsen & sønderholm 1994). as noted above, three of these major conglomerate developments are present within the region and represent fan deltas that supplied sediment to the basin. although these observations indicate that fränkl’s units may in time form the basis for a stratigraphic framework, any formal definition must await more detailed investigation of the rivieradal group. acknowledgements we are grateful to the referees, l. clemmensen and j.s. peel, for their helpful comments. references adams, p.j. & cowie, j.f. 1953: a geological reconnaissance of the region round the inner part of danmarks fjord, northeast greenland. meddelelser om grønland 111(7), 24 pp. clemmensen, l.b. & jepsen, h.f. 1992: lithostratigraphy and geological setting of upper proterozoic shelf deposits, hagen fjord group, eastern north greenland. rapport grønlands geologiske undersøgelse 157, 27 pp. fränkl, e. 1954: vorläufige mitteilung über die geologie von kronprins christian land (ne-grönland). meddelelser om grønland 116(2), 85 pp. fränkl, e. 1955: weitere beiträge zur geologie von kronprins christian land (ne-grönland, zwischen 80° und 80°30′n). meddelelser om grønland 103(7), 35 pp. frederiksen, k.s. 2000: a neoproterozoic carbonate ramp and base-of-slope succession, the andrée land group, eleonore bay supergroup, north-east greenland: sedimentary facies, stratigraphy and basin evolution, 242 pp. unpublished ph.d. thesis, university of copenhagen, denmark. haller, j. 1961: the carolinides: an orogenic belt of upper precambrian age in northeast greenland. in: raasch, g.o. 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(ed.): express report: eastern north greenland and north-east greenland 1995, 93– 103. unpublished report, geological survey of greenland, copenhagen. pedersen, s.a.s., craig, l.e., upton, b.g.j., rämö, o.t., jepsen, h.f. & kalsbeek, f. 2002: palaeoproterozoic (1740 ma) riftrelated volcanism in the hekla sund region, eastern north greenland: field occurrence, geochemistry and tectonic setting. precambrian research 114, 327–346. rasmussen, j.a. & smith, m.p. 1996: lower palaeozoic carbonates in eastern north greenland, and the demise of the ‘sæfaxi elv nappe’. bulletin grønlands geologiske undersøgelse 172, 49–54. rasmussen, j.a. & smith, m.p. 2001: conodont geothermometry and tectonic overburden in the northernmost east greenland caledonides. geological magazine 138(6), 687–698. smith, m.p., soper, n.j., higgins, a.k., rasmussen, j.a. & craig, l.e. 1999: palaeokarst systems in the neoproterozoic of eastern north greenland in relation to extensional tectonics on the laurentian margin. journal of the geological society (london) 156, 113–124. smith, m.p., rasmussen, j.a., robertson, s., higgins, a.k. & leslie, a.g. 2004: lower palaeozoic stratigraphy of the east greenland caledonides. in: higgins, a.k. & kalsbeek, f. (eds): east greenland caledonides: stratigraphy, structure and geochronology. geological survey of denmark and greenland bulletin 6, 5–28 (this volume). sønderholm, m. & jepsen, h.f. 1991: proterozoic basins of north greenland. in: peel, j.s. & sønderholm, m. (eds): sedimentary basins of north greenland. bulletin grønlands geologiske undersøgelse 160, 49–69. upton, b.g.j., rämö, o.t., heaman, l.m., blichert-toft, j., barry, t.l., kalsbeek, f. & jepsen, h.f. in press: the zig-zag dal basalts and associated intrusions of eastern north greenland: progressive mantle plume – lithosphere interaction. contributions to mineralogy and petrology. geus bulletin 6.pmd 10-02-2005, 09:5439 geological survey of denmark and greenland bulletin 35, 2016, 43-46 43 injection of chemically tuned, ‘smart’ water in oil reservoirs may increase both oil recovery rates and the total recovery (e.g. morrow & buckley 2011; austad 2013; zeinijahromi et al. 2015). this kind of water management has gained increased importance in the danish north sea reservoirs due to decreasing sweep efficiency in maturing oilfields. knowledge about the compatibility of the injected water with local formation waters is, however, a prerequisite for successful implementation. here, we present a regional overview of formation waters from oil reservoirs in the danish north sea, which comprise three main types of formation brine, and one type of modified seawater related to extensive water flooding. the water types show a distinct geographical distribution, which reflects original connate waters that are modified by saline brine being either depleted or enriched in so 4 2–. formation water and produced water database in order to characterise the water types we have selected a total of 33 water analyses, 25 of produced water and six of formation water from north sea wells (three core samples from the francisca-1 well and production tests from the boje-1, elna-1 and m-9x, wells) and finally two analyses of seawater (north sea mean water composition and a treated low-sulphate seawater), see fig. 1. for characterisation, samples analysed for na, k, ca2, mg2, sr2, ba2, cl–, and so 4 2– were used. water density had been measured for most of the samples, however, it was estimated for four samples. the data were collected from samuelsen et al. (2009), mackay et al. (2012), and undall-behrend (2012) and from final well reports for the boje-1, elna-1, francisca-1 and m-9x wells. water type classification to classify the water types in our database, principal component analysis (pca) was applied, whereby a matrix x of measured data (n samples, p variables) is transformed into sets of projection subspaces delineated by principal components (each a linear combination of all p variables), which display variance-maximised interrelationships between variables (esbensen 2010, esbensen et al. 2015). pca score plots display groupings, or clusters, of samples based on compositional similarities, as described by the variable correlations (shown in accompanying loading plots). they also quantify the proportion of total dataset variance that can be modelled by each component, see fig. 2. all data analyses in this work are based on auto-scaled data. the data analysis was performed in two steps. step one is a pca analysis of all 33 samples to investigate relationships between seawater and reservoir water (fig. 2a, b). based hereon, pure seawater and the samples produced from skjold, dan b, dan f and halfdan, which represent extensively seawater-flooded reservoirs, were removed types of formation water and produced water in danish oiland gasfields: i mplications for enhanced oil recovery by injection of ‘smart’ water niels h. schovsbo, hanne d. holmslykke, claus kjøller, kathrine hedegaard, lars kristensen erik thomsen and kim h. esbensen valdemar a kraka regnar dan fdan b cecilie lulita gorm roar rolf m-9 x svend skjold boje-1 siri nini dagmar halfdan tyra se s. arne tyra w tyra e valdemar b fransisca-1 harald e harald w valdemar a kraka regnar dan fdan b cecilie lulita gorm roar rolf m-9 x svend skjold boje-1 siri nini elna-1 dagmar halfdan tyra se s. arne tyra w tyra e valdemar b fransisca-1 harald e harald w uk germany norway denmark the netherlands 500 km 0 50 km well-head well field deliniation fig. 1. location of the wells used for water-type characterisation in the danish part of the north sea. © 2016 geus. geological survey of denmark and greenland bulletin 35, 43–46. open access: www.geus.dk/publications/bull 4444 to examine the relationships between the primary water types, which is done in step 2 of the analysis (fig. 2c, d). in both pca models the first two principal component axes resolve 80% of the total data variance, with the main trend expressed on the pca-1 axis being salinity variation (seen as high positive pca-1 loadings for cl, na and k). the pca-2 axis displays high positive loadings of so 4 2– and high negative loadings of elements such as ba, sr, mg and ca.this could indicate that so 4 2– concentrations control the concentration of ba2+, sr2+, mg2+ and ca2+ due to the low solubility of e.g. barite (baso 4 ) and anhydrite (caso 4 ). however, chemical speciation calculations using the numerical code phreeqc suggest sub-saturation of so 4 2–-bearing minerals except for barite in all water types. composition and occurrence of water types from the pca analysis, four water types can be identified based on natural groupings in the pca-2 versus pca-1 plot (fig. 2). the most likely cause of the salinity variation is a variable mixing of primary connate waters with brine originating from permian zechstein salt, which may or may not be so 4 2–-rich (warren et al. 1994). the characteristics and occurrence of each of the water types are presented below. water types 1–3 have compositional characteristics similar to types presented in the comprehensive overview paper by warren et al. (1994). water type 1 plots within a very narrow group in the third quadrant of the pca-2– pca-1 plot (fig. 2c), characterised by low salinity water with an overall low abundance of all elements (fig. 3). this water type is found in the boje1, francisca-1, roar, tyra e, tyra se and valdemar fields and thus occurs in a broad range of reservoirs from lower to upper cretaceous – paleocene chalk to oligocene sandstone. the location borders the greater tyra–valdemar area, in geographical areas separated from saline permian brines (fig. 4). the water is interpreted to reflect unmodified so 4 2–-depleted formation water. fig. 2. principal component analysis, pca. a: score. b: loading plot of pca on all data. c: score. d: loading plot of pca from which seawater from the dan b, dan f, skjold and halfdan installations and produced waters were excluded. the plot models 79% (a, b) and 83% (c, d) of the total data variance, respectively; variance proportions are shown along each component axis. water types are classified according to their groupings in a (water type 4) and c (water type 1, 2, 3). f-1: francisca-1. vald: valdemar. sw: seawater. lssw: low so 4 2–-treated seawater. p c a 2 ( 1 6 % ) -0.4 0.0 0.4 0.8 -4 0 4 8 pca 1 (63 %) 0.0 0.2 0.4 p c a 2 ( 1 6 % ) -2 0 2 4 p c a 2 ( 1 6 % ) -2 0 2 4 pca 1 (63 %) pca 1 (67%) -4 0 4 8 0.0 0.2 0.4 pca 1 (67%) -0.4 0.0 0.4 0.8 p c a 2 ( 1 6 % ) boje-1 f-1roar tyra e tyra se tyra w valda&b dagmar harald w kraka lulita m-9x regnar rolf elna-1 harald east s. arne siri a siri c siri d gorm na k ca mg sr ba cl so4 density siri b svend na ca mg sr ba cl so4 density lssw dan b dan f halfdan skjold kdagmar harald wkraka lulita m-9x regnar rolf elna-1 harald e s. arnesiri asiri c siri b siri d svend tyra se vald a vald b gorm f-1 b d chalk field sandstone field produced water formation water sea water c a 45 water type 2 is characterised by positive pca-1 and negative pca-2 scores (fig. 2c) and can compositionally be characterised by medium to high salinities, no so 4 2–, and high to very high ca and ba concentrations (fig. 3). this water type occurs in the harald e and w, lulita, s. arne, siri, nini, stine and cecilie fields, all of which are located in the northern part of the danish north sea and in the siri canyon – i.e. in reservoirs that range in age from jurassic to paleocene and both in chalk and sand lithologies. water type 2 is interpreted to reflect formation water modified by so 4 2– depletion. water type 3 plots with generally positive pca-1 and pca-2 scores in fig. 2c, reflecting medium to high salinities and variable, low to high so 4 2– concentrations (fig. 3). this water type is found in the dagmar, elna-1, gorm, kraka, m-9x, regnar, rolf and svend fields, most clearly expressed in the intensely fractured dagmar field sample. this field is situated on top of a salt dome that has reservoir oil in chalk and zechstein carbonates. type 3 waters are restricted to chalk reservoirs overlying salt domes in the southern salt dome province, and are interpreted as formation water enriched in so 4 2–. water type 4 plots close to, or together with seawater with negative pca-1 and positive pca-2 scores in fig. 2a, corresponding to low to medium salinity with high so 4 2– concentrations (fig. 3). this water type occurs in the dan, halfdan and skjold fields and is interpreted to be the result of decades of extensive water flooding performed by the operator (energistyrelsen 2013). analyses of water from the dan field (the m-9x well; fig. 2c) prior to flooding suggest that it was originally filled with water type 3. implications for enhanced oil recovery by injection of ‘smart’ water water injection is currently applied in several of the danish oil fields, mainly in order to provide pressure support. however, such injection may also have secondary effects such as increased imbibition, alteration of the reservoir rock wettability or mobilisation of fines with a resulting increase in reservoir sweep. in some cases, the specific chemical composition of the injection water may be important. thus, it has been suggested that carbonate rocks become more water wet if the injection water contains so 4 2– in combination with excess ca2+ or mg2+ (e.g. austad 2013). the result is enhanced oil recovery, which is even more pronounced both for chalk and sandstone if the salinity of the injection water is significantly lower than that of the formation water (morrow & buckley 2011; austad 2013). na k cl ca mg sr ba s e a w at e r n o rm al is e d , p p m /p p m 0.01 1 100 10 000 na k cl ca mg sr ba so4so4 water type 1 water type 2 water type 3 water type 4 a b fig. 3. a: water concentration normalised to seawater composition. b: calculated average compositions of the four water types observed in this study. for display purposes, ba2+ and sr2+ concentrations of 0 ppm in seawater have been increased to 1 ppm. water types: 1: low salinity 2: high salinity so4 3: high salinity + so4 4: sea water-modified type 2-dominated type 3-dominated type 1-dominated type 2-dominated type 3-dominated type 1-dominated type 2-dominated type 3-dominated type 1-dominated 0 50 km fig. 4. occurrence of resolved water types in the danish oiland gasfields. for location names see fig. 1. the water types are geographically restricted and ref lect both structural basin development and reservoir conditions. the seawater modified water type 4 is assumed to have originated as water type 3 based on pre-waterf looding formation water analysis and its structural position within the salt dome province. 4646 although several different mechanistic explanations have been suggested, a supposed change in carbonate rock wettability would involve surface chemical reactions such as ion exchange between so 4 2– and oil molecules (e.g. austad 2013). following this argumentation, it is likely that injection of ‘smart’ so 4 2–-bearing water in chalk reservoirs would have the largest effect in reservoirs with saline formation water depleted in so 4 2– (water type 2). however, the application of so 4 2–-rich water in reservoirs with this type of connate water is not straightforward, as there is a risk of scaling and subsequent clogging of the reservoir if the injected water is mixed with the connate water, due to its high concentrations of ca2+, ba2+, and sr2+ (samuelson et al. 2009; mackay et al. 2012). another risk related to injection of so 4 2–-bearing water in so 4 2–-depleted reservoirs is the possibility of hydrogen sulphide formation due to so 4 2– reducing microbial activity. for reservoirs already enriched in so 4 2– (water type 3) or with water of relatively low salinity (water type 1), other types of injection water may have greater effects on oil recovery. in shaly sand reservoirs, injection of low-salinity ‘smart’ water can also mobilise clay fines, in order to intentionally clog current flow paths and redirect the flow in the reservoir (e.g. morrow & buckley 2011; zeinijahromi et al. 2015). in this case, the mobilisation of non-swelling clays is provoked solely by the change in salinity. therefore, application of this type of water technology seems to be most relevant in reservoirs with connate water of relatively high salinity, such as most of the reservoirs in the siri canyon (water type 2). conclusions four water types are present in the danish north sea: so 4 2–-bearing, mediumto highly saline water (type 3), so 4 2–-depleted medium to high saline water (type 2), so 4 2–-depleted low saline (type 1), and a seawater-modified manifestation (type 4 water). these water types reflect variable mixing of connate water with deeper brines and are tied in with the known hydrocarbon provinces. type 2 represents the siri canyon and the south arne – svend areas. water type 3 is characteristic of salt dome reservoirs, while water type 1 represents the greater tyra–valdemar area. the variable chemistry of the formation water in the danish north sea imposes regional differences in production strategies and hence in the designing of ‘smart’ water for enhanced oil recovery. the classification of water types presented here shows that their composition is predictable and related to geographical domains in the north sea. this may be useful when designing procedures for optimal water management in the danish north sea, e.g. application of low salinity water flooding on mature fields, or in some cases even during the exploration stage. references austad, t. 2013: water-based eor in carbonates and sandstones: new chemical understanding of the eor potential using ‘smartwater’. in: sheng, j.j. (ed.): enchanced oil recovery field case studies, 301–335. waltham, ma, usa: elsevier. energistyrelsen, 2013: danmarks olieog gasproduktion 2013, 105 pp. københavn: energistyrelsen. esbensen, k.h. 2010: multivariate data analysis – in practice. an introduction to multivariate data analysis and experimental design, 5th edition, 598 pp. oslo: camo software as. esbensen, k., schovsbo, n.h. & kristiansen, l. 2015: down-hole permeability prediction – a chemometric wire-line log feasibility study from a north sea chalk well. geological survey of denmark and greenland bulletin 33, 13–16. mackay, e., ginty, w.r. & jones, t.j. 2012: oilfield scale management in the siri asset – paradigm shift due to the use of mixed pwri / seawater injection. 74th eage conference and exhibition incorporating europec 2012. copenhagen, denmark, 4–7 june 2012. spe 154534, 1–12. morrow, n. & buckley, j. 2011: improved oil recovery by low-salinity waterf looding. journal of petroleum technology 63, 106–112. samuelsen, e.h., frederiksen, r.a., heath, s.m., thornton, a., sim, m., arefjord, a. & mcara, e.k. 2009: downhole scale control through continuous injection of scale inhibitor in the water injection – a field case. conference tekna geilo paper 240309, 23 pp. undall-behrend, g. 2012: produceret vand på tyra øst f. bachelorprojekt århus maskinmesterskole, 75 pp. warren, e.a., smalley, c.p. & howarth, r.j. 1994: compositional variations of north sea formation waters, part 4. geological society, london. memoirs 15, 119–208. zeinijahromi, a., ahmetgareev, v., badalyan, a., khisamov, r. & bedrikovetsky, p. 2015: case study of low salinity water injection in zichebashskoe field. journal of petroleum science research 4, 16–31. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark; e-mail: nsc@geus.dk geological survey of denmark and greenland bulletin 10 g e o l o g i c a l s u r v e y o f d e n m a r k a n d g r e e n l a n d b u l l e t i n 1 0 • 2 0 0 6 review of survey activities 2005 edited by martin sønderholm and a.k. higgins geological survey of denmark and greenland danish ministry of the environment geological survey of denmark and greenland bulletin 10 keywords geological survey of denmark and greenland, survey organisations, current research, denmark, greenland. cover photographs from left to right 1. the barrier reef complex fringing most of the kenya coastline is also one of the most vulnerable environments to pollution. a new oil spill sensitivity atlas for kenya helps to prioritise the emergency response on the most susceptible areas (see article, page 65). photograph: john tychsen, geus. 2. vibro-seismic data were acquired on stevns, denmark to be able to correlate the danian–campanian cores drilled along the east coast of stevns (see article, page 13). photograph: lars stemmerik, geus. 3. farming on the rooftops. experiment carried out at geus to investigate concentrations of pathogens leached to drainage water as a result of different slurry manure application methods. photograph: peter k. warna-moors, geus. 4. refuelling of helicopter on the arctic sea ice during seismic acquisition programme related to data collection for the continental shelf project around greenland. photograph: trine dahl-jensen, geus. frontispiece: facing page thrust sheet pair exposed in the rubjerg knude glaciotectonic complex, vendsyssel, denmark. photograph: stig a. schack pedersen, geus. chief editor of this series: adam a. garde scientific editors: martin sønderholm and a.k. higgins editorial secretaries: birgit eriksen and esben w. glendal external referees (numbers refer to first page of reviewed article): lars ole boldreel (29), michael houmark-nielsen (21, 61) and kristine thrane (25, 49, 53); geological institute, university of copenhagen, denmark. asger ken pedersen (37, 41, 45); geological museum, copenhagen, denmark. gregers dam (9, 13, 33) and michael larsen (17); dong energy, agern alle 24–26, hørsholm, denmark illustrations: : stefan sølberg with contributions from jette halskov lay-out and graphic production: annabeth andersen, carsten e. thuesen printers: schultz grafisk, albertslund, denmark manuscripts submitted: 15 january – 27 february 2006 final versions approved: 26 october 2006 printed: 29 november 2006 issn 1603-9769, 1604-8156 isbn-10: 87-7871-189-4 isbn-13: 978-87-7871-189-2 geological survey of denmark and greenland bulletin the series geological survey of denmark and greenland bulletin replaces geology of denmark survey bulletin and geology of greenland survey bulletin. citation of the name of this series it is recommended that the name of this series is cited in full, viz. geological survey of denmark and greenland bulletin. if abbreviation of this volume is necessary, the following form is suggested: geol. surv. den. green. bull. 10, 68 pp. available from geological survey of denmark and greenland (geus) • øster voldgade 10 • dk-1350 copenhagen k • denmark phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: geus@geus.dk or geografforlaget aps • rugårdsvej 55 • dk-5000 odense c • denmark phone: +45 63 44 16 83, fax: +45 63 44 16 97, e-mail: go@geografforlaget.dk © danmarks og grønlands geologiske undersøgelse (geus), 2006 4 7. review of survey activities 2005 a.a. garde 9. stratigraphy and palaeoceanography of upper maastrichtian chalks, southern danish central graben j.r. ineson, b. buchardt, s. lassen, j.a. rasmussen, p. schiøler, n.h. schovsbo, e. sheldon and f. surlyk 13. shallow core drilling of the upper cretaceous chalk at stevns klint, denmark l. stemmerik, f. surlyk, k. klitten, s.l. rasmussen and n. schovsbo 17. spit-systems – an overlooked target in hydrocarbon exploration: the holocene to recent skagen odde, denmark p.n. johannessen and l.h. nielsen 21. construction of 3d geological models in glacial deposits to characterise migration of pollution k.e.s. klint, f. von platen-hallermund and m. christophersen 25. advanced in situ geochronological and trace element microanalysis by laser ablation techniques d. frei, j.a. hollis, a. gerdes, d. harlov, c. karlsson, p. vasquez, g. franz, l. johansson and c. knudsen 29. east greenland and faroe–shetland sediment provenance and palaeogene sand dispersal systems m. larsen, c. knudsen, d. frei, m. frei, t. rasmussen and a.g. whitham denmark greece turkey albania ghana cameroon west indies uganda sudan tanzania mozambique latvia greenland madagascar canada united kingdom norway faroe islands kenya sweden rusland (novaya zemlya) geus working areas 2005. orange areas are covered in this volume. for further information on other working areas please refer to our website: www.geus.dk/international 5 33. continental crust in the davis strait: new evidence from seabed sampling f. dalhoff, l.m. larsen, j.r. ineson, s. stouge, j.a. bojesen-koefoed, s. lassen, a. kuijpers, j.a. rasmussen and h. nøhr-hansen 37. an integrative and quantitative assessment of the gold potential of the nuuk region, west greenland b. møller stensgaard, t.m. rasmussen and a. steenfelt 41. the tikiusaaq carbonatite: a new mesozoic intrusive complex in southern west greenland a. steenfelt, j.a. hollis and k. secher 45. archetypal kimberlite from the maniitsoq region, southern west greenland and analogy to south africa t.f.d. nielsen, m. jebens, s.m. jensen and k. secher 49. using zircon geochronology to resolve the archaean geology of southern west greenland j.a. hollis, d. frei, j.a.m. van gool, a.a. garde and m. persson 53. five slices through the nuussuaq basin, west greenland a.k. pedersen, l.m. larsen, g. krarup pedersen and k.s. dueholm 57. earthquake seismology in greenland – improved data with multiple applications t.b. larsen, t. dahl-jensen, p. voss, t. møller jørgensen, s. gregersen and h.p. rasmussen 61. radical past climatic changes in the arctic ocean and a geophysical signature of the lomonosov ridge north of greenland n. mikkelsen, n. nørgaard-pedersen, y. kristoffersen, s. juul lassen and e. sheldon 65. kensea – development of an environmental sensitivity atlas for coastal areas of kenya j. tychsen, o. geertz-hansen and j. kofoed india thailand lao pdr vietnam sri lanka mongolia 7 the present volume is the third issue of review of survey activities (rosa). it contains 15 four-page contributions that cover a wide range of the current activities at the geological survey of denmark and greenland (geus). thirteen of these are short scientific papers dealing with ongoing research by the survey and its external partners. for the first time the research-based papers in the review are now externally peer reviewed. a new standing panel of reviewers for rosa has been established to ensure that the contributions are of general interest to a wide readership and that, within the limitations of space, they maintain the normal scientific standards of the survey’s publications. all articles are planned to be easily readable by non-specialists, and since this is a review of survey activities, it should be borne in mind that many papers are first accounts of ongoing research. the fact that almost all contributions in the current volume are scientific in nature implies that while providing a timely panorama of current research at the survey, they are far from embracing all projects undertaken by the survey in denmark, greenland and other countries in 2005. a factual overview of the activities of geus as a whole can be obtained at geus’ website. in the present volume three papers deal with cretaceous–holocene onshore and offshore stratigraphy, sedimentology and palaeoceanography in denmark, in part related to hydrocarbon exploration. a fourth paper from denmark, that illustrates just one of the broad spectrum of the survey’s routine responsibilities undertaken on behalf of the state, addresses construction of 3d geological models to characterise the migration of point-source pollution in groundwater reservoirs. projects related to greenland and the arctic in general are represented in this volume by a group of nine papers. the first is a methodology paper describing advanced in situ geochronological and trace element microanalysis by laser ablation techniques, a now routine analytical tool at the survey that has provided data for several of the subsequent articles, including a study of sediment provenance in the east greenland – faroe islands – shetland region, and an account of zircon geochronology applied to archaean geological studies in southern west greenland. within the same region, a new method of integrative and quantitative assessment of the gold potential is presented, and two papers deal with newly discovered kimberlites and carbonatites and their potential economic significance. one paper describes five profiles through basalts and sedimentary rocks in the nuussuaq basin in west greenland, constructed using geological photogrammetrical techniques along coastal cliffs and steep valley sides. another paper presents new evidence for the presence of continental crust in the davis strait obtained from seabed sampling; this is an important new contribution to the long-standing debate of the nature of the crust under the labrador sea and davis strait and its stratigraphy. a report on ongoing studies of the deep crustal structure of greenland using earthquake seismology is presented, and a last paper concerning the arctic region describes radical former climatic changes in the arctic ocean and the geophysical signature of the lomonosov ridge north of greenland, and discusses the sensitivity of the sea-ice cover to global warming. the final paper in the present volume describes the development of an environmental sensitivity atlas for coastal areas of kenya. this project is just one of several current geus projects where the survey's broad technical and managing expertise is put to use in developing countries. review of survey activities 2005 adam a. garde chief editor © geus, 2006. geological survey of denmark and greenland bulletin 10, 7 only. available at: www.geus.dk/publications/bull geological survey of denmark and greenland bulletin 31, 2014, 31-34 31 calcareous nannofossil and foraminifer biostratigraphy of the campanian–maastrichtian chalk of the femern bælt (denmark–germany) emma sheldon, caterina morigi and sarah d. møller a new study based on calcareous nannofossil and benthic and planktonic foraminifer biostratigraphy is presented for the upper campanian – maastrichtian chalk of the femern bælt (denmark and germany; fig.1). the results are consistent with recent studies of the danish chalk for this interval, allowing correlation across the danish basin and forming the basis for correlation further afield within the boreal realm. numerous studies have been carried out recently on the upper campanian – maastrichtian chalk of the danish basin, covering aspects such as sedimentology, depositional environment, macrofossil biostratigraphy, carbon isotope stratigraphy as well as nannofossil and dinoflagellate biostratigraphy. however, very few published studies on foraminifers exist across this interval in this area. the 09.a.006, 09.a.007 and 09.a.008 boreholes (fig. 2) were drilled in 2009 in preparation for construction of a fixed link across the femern bælt, which will connect denmark to germany (rambøll arup jv 2011). the boreholes penetrated glacial till, paleocene–eocene clay and chalk (sheldon et al. 2012). here, for the first time, the boreal foraminifer biostratigraphy of the late campanian – maastrichtian interval is investigated and presented alongside nannofossil biostratigraphy. geological setting and palaeogeography the femern bælt area is located to the south of the ringkøbing–fyn high and is part of the german basin (fig. 1). during the late cretaceous the danish area was part of the extensive epicontinental sea where cool-water carbonate deposition dominated. the maastrichtian chalk was deposited at depths of 100–250 m (surlyk 1997). chalk distribution patterns are affected in the danish area by folding, salt diapirism, non-deposition and erosion, especially in the southern region (lieberkind et al. 1982). in the maastrichtian to danian, the area was situated at 44°–46°n (smith et al. 1994). in the upper maastrichtian of this part of the danish area, two main facies types dominate: (1) relatively deep water basinal sediments comprising coccolith and foraminferarich pelagic chalk, and (2) shallow marine chalk with high diversity faunas dominated by bryozoans, echinoids, bivalves and brachiopods (surlyk 1997; hart et al. 2004). the upper campanian – maastrichtian chalk of onshore denmark was until recently referred to the tor formation equivalent. the tor formation was established by deegan & scull (1977) as a maastrichtian (locally upper campanian) chalk unit in the norwegian and danish sectors of the north sea. a new holostratigraphic analysis of the upper cretaceous chalk of eastern denmark resulted in a lithostratigraphic subdivision of the onshore chalk (surlyk et al. 2013). however due to local facies variations this new subdivision cannot be applied to the chalk of the femern belt area with© 2014 geus. geological survey of denmark and greenland bulletin 31, 31–34. open access: www.geus.dk/publications/bull fehmarn south north lolland09.a.006 09.a.00809.a.007 3 km 0 m 50 100 150 quaternary deposits folded and faulted palaeogene clay palaeogene cretaceous fig.1. map of denmark and northern germany showing the location of the planned fixed road and rail link across femern bælt. l: lolland, f: fehmarn, fb: femern bælt. fig. 2. sketch south–north cross-section of the femern bælt area and the location of the boreholes (from sheldon et al. 2012). 55° 10°e 100 km 14°e 57° sweden denmark germany german basin danish basin norway l f fb 54° 56°n 58° poland ringkøbing–fyn high 3232 out sedimentological analysis and the term ‘tor formation equivalent’ is retained here. biostratigraphy from the 09.a.008 and 09.a.006 boreholes nannofossils and foraminifers from the campanian–maastrichtian were analysed; from the 09.a.007 borehole nannofossils from the upper maastrichtian were examined. the southern north sea foraminifer zonation of king et al. (1989) and the boreal nannofossil scheme of burnett (1998) were applied (fig. 3). marker species are shown in fig. 4 and biostratigraphic results on fig. 5. nannofossil zones – the co-occurrence of orastrum campanensis and eiffelithus eximius indicates the presence of uc15dbp at the base of core 09.a.008. subzone uc15ebp is absent. uc16bp was defined by burnett (1998) but recent studies of danish campanian–maastrichtian chalks (sheldon 2008; thibault et al. 2012) question the reliability of the uc16bp marker species in the danish area. the top of uc16abp is defined by the last occurrence (lo) of heteromarginatus bugensis. in the present study and in the stevns-1 borehole, eastern denmark, the lo of h. bugensis is below the lo of tortolithus caistorensis (marker for top uc16bbp). other studies (e.g. fritsen et al. 1999) assign the lo of h. bugensis to the top of uc16cbp. the top of uc16bbp is defined by the lo of t. caistorensis, which is very rare in the danish area. uc16abp and b are not easily subdivided in the danish area and alternative markers are suggested for the top of uc16bbp: the lo’s of tortolithus hallii and tortolithus pagei were successfully applied in the present study, positioned prior to the los of broinsonia parca parca and zeugrhabdotus praesigmoides (markers for the overlying uc16cbp). the top of uc16cbp is defined by the lo of monomarginatus quaternarius. the lo of b. parca parca as a top uc16cbp marker is a more reliable marker in this study. the lo of z. praesigmoides as an additional top uc16cbp marker is confirmed in this study. the top of subzone uc16d bp is defined by the lo of broinsonia parca constricta. the first occurrence (fo) of prediscosphaera mgayae as an additional marker c am pa ni an m aa st ri ch tia n southern north sea foraminifer zonation boreal calcareous nannofossils fc s2 3 fc s2 2 la te c re ta ce ou s fc s2 1b a a b c a b c u c 16 u c 20 u c 15 d d b. draco b. miliaris n. frequens a. maastrichtiana c. daniae cretaceous taxa l. quadratus r. levis t. orionatus b. parca constricta m. quaternarius t. caistorensis h. bugensis e. eximius a. bettenstaedti b. decoratus g. monterelensis b palaeogene epoch/ageage (ma) uc19 uc18 uc17 70 75 65 72.1 e m lt lt lt 66.0 a b c d e f g h i j k l m n o p q r s t u v w fig. 3. nannofossil and foraminifer zonations. the timescale is according to gradstein et al. (2012). ucbp: upper cretaceous boreal province nannofossil zones of burnett (1998), fcs: cretaceous southern north sea foraminfers, shelf facies, including chalk, zones of king et al. (1989). nannofossil and foraminifer zonations correlated using fritsen (1999). fig. 4. sselected nannofossils and foraminifers from the femern bælt. a: arkhangelskiella maastrichtiana. b: prediscosphaera  stoveri. c: nephrolithus  frequens. d: reinhardtites levis. e: tranolithus orionatus. f: prediscosphaera mgayae. g: broinsonia  parca constricta. h: monomarginatus  quaternarius. i: zeugrhabdotus praesigmoides. j: tortolithus caistorensis. k: heteromarginatus bugensis. l: orastrum campanensis. m: bolivinoides draco. n: pseudouvigerina cristata. o: brizalina incrassata. p: hagenowella paleocenica. q: bolivinoides draco giganteus. r: bolivinoides  decoratus.  s: stensioeina pommerana. t: angulogavelinella bettenstaedti. u: globotruncana arca. v: gavelinella monterelensis. w: globorotalites micheliana. scale bars, nannofossils: 5 µm, foraminifers: 0.1 mm. 33 in the middle of uc16d bp (thibaut et al. 2012) is confirmed in this study. the lo of tranolithus orionatus marks the top of uc17 bp. in the present study, the lo of this species occurred after the lo of reinhardtites levis (the lo of which marks the top of the overlying uc18 bp). in stevns-1 these species also occur in the ‘reverse’ order. the lo of r. levis marks the top of uc18bp, but in this study its lo is before that of t. orionatus. it is suggested that in the danish area, uc17bp and uc18bp should be combined, using either the lo of t. orionatus or the lo of r. levis to mark the zone top. the lo of p. mgayae has been suggested as an additional marker for the top of this zone (thibaut et al. 2012); this is confirmed in this study. uc19bp comprises the interval from the lo of reinhardtites levis to the fo of lithraphidites quadratus. the fo of l. quadratus defines the base of uc20abp. the base of uc20bbp is defined by the fo of nephrolithus frequens. the base of uc20cbp is defined by the fo of arkhangelskiella maastrichtiana. the uncertainties surrounding the use of the fo of a. maastrichtiana as a marker are well-documented (e.g. thibault 2010) and the two subzones are merged here. the first common occurrence of a. maastrichtiana is used to mark the base of uc20b-cbp in this study. the base of the prediscosphaera stoveri acme within this combined subzone is also applied successfully in this study. the lo of helicolithus trabeculatus was suggested as a supplementary marker for this level (sheldon 2008) and is confirmed here. the fo of cribrosphaerella daniae marks the base of uc20dbp, the uppermost subzone of the maastrichtian. the co-occurrence of chiasmolithus edentulus, coccolithus pelagicus, cyclagelosphaera alta and neochiastozygus saepes assigns the base of the overlying danian in borehole 09.a.008 to the upper danian subzone nntp4f (varol 1998). lower – upper danian subzones nntp1a-4f are missing or were not sampled. danian chalk in the femern area was documented for the first time recently (sheldon et al. 2012). previously the southern limits of danian deposits were thought to be farther to the north (håkansson & pedersen 1992). foraminifer zones – the top of fcs23 is defined by the lo of pseudotextularia elegans. bolivinoides draco (s.s.) is an index species. the top of subzone fcs23a is defined by the fo of p. elegans. p. elegans is not seen in the present study, but rare occurrences of bolivinoides draco were noted, indicating the fig. 5. nannofossil and foraminifer biostratigraphic correlations of the three boreholes at the femern bælt. 20 25 30 35 40 45 50 55 60 65 70 75 80 85 22 ac 21 b 23 90 95 100 20 bc 20 a present 09.a.006 09.a.007 09.a.008 fo lo foraminifersf n common a. maastrichtiana common a. maastrichtiana c. daniae and danian flora l. quadratus t. orionatus, r. levis p. mgayae p. mgayae b. parca constricta z. praesigmoides tortolithus spp. h. bugensis o. campanensis, e. eximius n. frequens, common a. maastrichtiana p. cristata total depth 100.6 m total depth 50.1 m total depth 99.9 m b. draco giganteus b. draco, spirillina spp. a. bettenstaedti g. arca barren p. cristata s. pommerana h. paleocenica (black) h. paleocenica (black) n. frequens n. frequens l. quadratus l. quadratus t. orionatus, p. mgayae b. parca constricta r. levis p. mgayae m. quaternarius tortolithus spp. z. praesigmoides h. bugensis 20 bc 20 a 19 17/18 16 d 16 c 16 b 23 fc s 22 ab 21 -b 20 bc 20 d 20 a 19 17 -1 8 16 c 16 b 16 a 15 d 16 d ucfcs f n f nn uc ucfcs depth (m) b. draco, h. paleocenica (black) h. paleocenica (black) p. cristata spirillina spp. b. draco giganteus,s. pommerana p. cristata barren g. arca, ? r. szajnochae g. monterelensis g. arca globotruncana spp., a. bettenstaedti b. miliaris, a. bettenstaedti b. draco giganteus nannofossils (first occurrence) (last occurrence) 3434 presence of fcs23. in upper fcs23 the range of hagenowella paleocenica and the fo of spirillina spp. are additional markers in the present study. the lo of stensioeina pommerana occurring towards the bottom of fcs23 (corresponding to the base of nannofossil subzone uc20abp) in this study may also prove useful. the range of pseudouvigernina cristata within fcs23 may prove to be another useful marker. the absence of p. elegans means that it is not possible to subdivide fcs23 in this study. the top of fcs22 is defined by the lo of bolivinoides miliaris. fcs22 is divided into fcs22b, the top of which is defined by the lo of b. miliaris, and fcs22a, the top of which is defined by the lo of angulogavelinella bettenstaedti. the los of a. bettenstaedti and b. miliaris occurred in the same sample suggesting the presence of only fcs22a, but the range of a. bettenstaedti within fcs22 could be useful. the top of fcs21 is defined by the lo (often a flood occurrence) of reussella szajnochae. fcs21 is divided into fcs21b, the top of which is defined by the lo of r. szajnochae, and fcs21a, the top of which is defined by the lo of gavelinella usakensis. g. usakensis was not found in the present study, indicating the presence only of fcs21b. the lo of globotruncana arca at the top of fcs21 is an additional marker, as are the los of gavelinella monterelensis and globorotalites micheliana and fo of brizalina incrassata at a slightly lower stratigraphic level. conclusions the campanian–maastrichtian chalk of the danish area has recently been studied intensively using calcareous nannofossils, applying the ucbp scheme. the studies underline the need for an amendment of the uc scheme for the danish area. the present study highlights the need to reconsider the subdivision of uc20bbp and uc20cbp based on the fo of arkhangelskiella maastrichtiana. it is recommended for the danish area to use the fo of common a. maastrichtiana to mark the base of uc20cbp. it may also be practical to merge uc17bp and uc18bp. additionally the subdivision of uc16bp cannot be reliably applied in the danish area. the danian nannofossil assemblage in borehole 09.a.008 provides further evidence for the southerly encroachment of the danian sea. the foraminifer zonation of the late campanian – maastrichtian is for the first time correlated with the nannofossil zonation based on the 09.a.006 and 09.a.008 cores (fig. 5). in the absence of certain established fcs marker foraminifera for the north sea chalk, new zonal markers, e.g. hagenowella paleocenica, pseudouvigerina cristata, globotruncana arca, gavelinella monterelensis and globorotalites micheliana are used here in addition to conventional taxa for the campanian–maastrichtian chalk of denmark, perhaps allowing correlation with the north sea area, and further afield. references burnett, j.a. 1998: upper cretaceous. in: bown, p.r. (ed.): calcareous nannofossil biostratigraphy. british micropalaeontological society series 5, 132–199. deegan, c.e. & scull, b.j. 1977: a standard lithostratigraphical nomenclature for the central and northern north sea. the institute of geological sciences report 77/25, 36 pp. fritsen, a. (ed.) 1999: a joint chalk stratigraphic framework. in: joint chalk research program topic v 1. norwegian petroleum directorate. 206 pp. gradstein, f.m., ogg, j.g., schmitz, m.d. & ogg, g.m. 2012: the geologic time scale 2012, 1176 pp. amsterdam: elsevier. hart, m.b., feist, s.e., price, g.d. & leng, m.j. 2004: reappraisal of the k–t boundary succession at stevns klint, denmark. journal of the geological society (london) 161, 885–892. håkansson, e., & pedersen, s.a.s. 1992: geologisk kort over den danske undergrund. map sheet. københavn: varv. king, c., bailey, h.w., burton, c.a. & king, a.d. 1989: cretaceous of the north sea. in: jenkins, d.g. & murray, j.w. (eds): stratigraphic atlas of fossil foraminifera, 372–417. chichester: ellis horwood. lieberkind, k., bang, i., mikkelsen, n. & nygaard, e. 1982: late cretaceous and danian limestone. danmarks geologiske undersøgelse serie b 8, 49–62. rambøll arup jv 2011: summary of geological conditions. geotechnical data report 01.3-002, 53 pp. virum: femern a/s. sheldon, e. 2008: upper campanian–maastrichtian calcareous nannofossil biostratigraphy of the stevns-1 borehole, denmark. journal of nannoplankton research 30, 39–49. sheldon, e., gravesen, p. & nøhr-hansen, h. 2012: geolog y of the femern bælt area between denmark and germany. geological survey of denmark and greenland bulletin 26, 13–16. smith a.g., smith, d.g. & funnel, b.m. 1994: atlas of mesozoic and cenozoic coastlines, 99 pp. cambridge: cambridge university press. surlyk, f. 1997: a cool-water carbonate ramp with bryozoan mounds: late cretaceous – danian of the danish basin. sepm special publication 56, 293–307. surlyk, f., rasmussen, s.l., boussaha, m., schiøler, p., schovsbo, n.h., sheldon, e., stemmerik, l. & thibault, n. 2013: upper campanian − maastrichtian holostratigraphy of the eastern danish basin. cretaceous research 46, 232–256. thibault, n. 2010: biometric analysis of the arkhangelskiella group in the upper campanian–maastrichtian of the stevns-1 borehole, denmark: taxonomic implications and evolutionary trends. geobios 43, 639–652. thibault, n., harlou, r., schovsbo, n., schiøler, p., minoletti, f., galbrun, b., lauridsen, b.w., sheldon, e., stemmerik, l. & surlyk, f. 2012: upper campanian – maastrichtian nannofossil biostratigraphy and high resolution carbon isotope stratigraphy of the danish basin: towards a standard δ13c curve for the boreal realm. cretaceous research 33, 72–90. varol, o. 1998: palaeogene. in: bown, p.r. (ed.): calcareous nannofossil biostratigraphy. british micropalaeontological society publication series, 200–224. authors’ address geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: es@geus.dk http://store.elsevier.com/the-geologic-time-scale-2012-2-volume-set/isbn-9780444594259/ http://store.elsevier.com/the-geologic-time-scale-2012-2-volume-set/isbn-9780444594259/ mailto:obe@geus.dk geological survey of denmark and greenland bulletin 12, 24-46 24 0 10 20 30 40 50 60 70 80 90 100 cm 2239 m 2240 m 2245 m 2246 m cecilie-1 fig. 10. core photographs showing dark grey, largely structureless, discordant, intrusive sandstones within the lighter grey mudstones of the upper tyr member in the cecilie-1 well. depths are core depths. stratigraphic positions of the figured intervals are shown on fig. 8. lithostratigraphy rogaland group the rogaland group was established by deegan & scull (1977) and comprises the paleocene to lower eocene marlstone and mudstone succession between the top of the ekofisk formation of the chalk group (deegan & scull 1977) and the glaucony-rich mudstones of the hordaland group (now stronsay and westray groups) in the central north sea. in most of the danish sector, the rogaland group has a relatively uniform thickness and comprises the våle, lista, sele and balder formations (fig. 7). the fur formation is a part of the rogaland group and is present in a limited area in the north-eastern part of the danish sector of the north sea stretching into the norwegian sector. hardt et al. (1989) added three new sandstone units to the rogaland group in the southern viking graben (norwegian sector): ty formation, heimdal formation and hermod formation (fig. 4). although these sandstone units are broadly comparable to coeval sandstone units encountered in the siri canyon system (figs 1, 4) in the danish sector, the norwegian units and the siri canyon sandstones have different provenances and are not contiguous with each other. therefore, the sandstone units in the danish sector are described herein as new members. in the siri canyon (fig. 1), the mudstones of the rogaland group contain concordant or discordant postdepositional sandstone intrusions (hamberg et al. 2005). in some wells (e.g. cecilie-1 and nini-3) sandstone intrusions are very common (figs 8–11). the sands have intruded most levels in the rogaland group, but the ve member (new member of the lista formation, see below) in the middle part of the group is particularly rich in intrusions. most of the intrusive sandstones are only a few millimetres thick, but they may reach a thickness of 5 m. in some wells they constitute up to 30% of the total sandstone thickness. the intrusions are usually massive, but faint lamination is locally present, especially at the top of the beds. most of the intrusive sandstone bodies are separated by in situ mudstones, but they may also occur in intervals showing multiple intrusions. the boundaries with the host rock are slightly to very irregular or wavy, and in places discordant. minor intrusive offshoots (apophyses) into the host rock are common. the petrography of the intrusive sandstones is similar to that of the in situ sandstones and they are therefore most likely sourced from the 25 latter. the intrusion of sand was mainly subhorizontal, parallel to the bedding, and most of the intrusions can thus be classified as sills. the sandstone intrusions are either unconsolidated or cemented by calcite or other carbonate minerals. in some wells the intrusive sandstones are chlorite-cemented. in the nini-3 cores, the vile and ve members of the lista formation (new members, see below) are particularly rich in intrusive sandstones (figs 11, 12); the intrusions increase in number and thickness upward through the vile member to terminate in a large intrusion complex in the ve member. commonly, mudstone clasts are abundant in the sandstones and in the intrusion complex in the nini-3 well. where present, they constitute from a few percent up to 90% of the volume of the host sandstones. they are most abundant in the upper parts of the beds. the clasts range in size from a few millimetres to wider than the core diameter. most of the clasts are angular, often with delicate protrusions, and aligned parallel to the bounding planes of the intrusive sandstone body. in thick intrusions, flow banding and dewatering structures are occasionally present. top-bed rip-down mudstone clasts (stow & johansson 2000) are common (fig. 12). fossil wood fragments are present, but rare. as the distribution of intrusive sandstones is the result of postdepositional rather than synsedimentary processes, they may cross lithostratigraphic boundaries. when an injected sandstone body occurs in direct contact with an in situ sandstone unit (e.g. as seen in the higher parts of the new tyr member in fig. 8), it is impossible to distinguish between the two genetically different units on the basis of petrophysical logs and cuttings samples alone; only a sedimentological study of core material may reveal the different nature of the two sandstones. våle formation history. the våle formation was established by hardt et al. (1989) for the marls with interbedded claystones, limestones and siltand sandstone stringers that overlie the chalk group in the central and northern north sea. the lista fm vile mb tyr mb idun mb nini-3 clay si. vf. f. m. sand c. vc. p c c log depth core depthgr sonic 1760 1750 1740 1730 1760 1750 1740 1730 fig. 11. core log showing intrusive sandstones in the vile and idun members in the nini-3 well. for legend, see fig. 9. the two intervals marked by grey bars in the core depth column are shown as core photographs in fig. 12. 26 fig. 12. core photographs of the vile and idun members in the nini3 well showing sandstone intrusions, weak flow banding (1), injection breccia with abundant irregular and angular clasts (2), mudstone clasts in injected sand (3) and top bed rip-down clasts (4). depths are core depths. stratigraphic positions of the figured intervals are shown on fig. 11. fig. 13. e-8, danish reference well for the våle and lista formations, and reference well for the vile, ve and bue members. black bar shows cored section. 1726 m 1727 m nini-3 1739 m 0 10 20 30 40 50 60 70 80 90 100 cm 4 3 1 2 2060.3 2044.0 2030.3 2027.6 2057.0 horda fm balder fm sele fm lista fm bue mb ve mb vile mb våle fm chalk gp 2100 2000 m e-8 gr sonic presence of a marly succession on top of the chalk group was previously noted by deegan & scull (1977) and treated informally as an equivalent to the more coarse-grained maureen formation in the uk sector of the north sea. kristoffersen & bang (1982) established the north sea marl for an exclusively marly and calcareous unit corresponding to the maureen formation-equivalent unit of deegan & scull (1977). although the description of the north sea marl fulfils the requirements for a formal description of a lithostratigraphic unit (with the exception of lacking indication of the rank of the unit), they specifically stated that their unit was only informally established. the name north sea marl has only rarely been used outside the danish sector of the north sea; the sediments are instead referred to the våle formation, which covers most national sectors of the north sea basin. as doubt may be raised about the formal status of the north sea marl unit, and in order to promote communication between north sea stratigraphers, it is considered by the present authors that the våle formation of hardt et al. (1989) serves as the better name for the marlstone unit. type well. norwegian sector well 1/3-1, 3258–3209 m mdkb. danish reference wells. e-8, 2060.3–2057.0 m mdkb (fig. 13); siri-1, 2186.5–2156.3 m mdkb (fig. 14; plates 1, 4). distribution and thickness. the våle formation and its equivalents are present throughout the north sea basin, except in a few areas where their absence is due to nondeposition or erosion. the våle formation is absent on 27 pyrite-bearing marlstones dominate the formation (fig. 16). thin sandstone intrusions are present locally. in the siri canyon, the marls are interbedded with turbidite sandstones; where sandstone-dominated, the succession is referred to a new member (bor member, defined below). log characteristics. from its base to its top, the våle formation is characterised by an overall steady increase in gamma-ray response, combined with an overall steady decrease in sonic readings. when the bor member sandstones are present, blocky log signatures with higher gamma-ray values and lower sonic readings interrupt this general trend (fig. 17). boundaries. in most wells in the danish sector, the change from the chalks of the chalk group to the marlstones of the våle formation is gradational and the boundary can be difficult to position (fig. 16). in the siri canyon, however, most wells show an erosional contact between the chalk group and the våle formation and the formation boundary is sharp. on the petrophysical logs, the boundary is placed where the stable, low gamma-ray response characteristic of the ekofisk formation starts to increase upwards and the high sonic readings (also characteristic of the latter formation) start to decrease upwards. the change in the log pattern may be stepwise with each step represented by a small increase in gamma-ray values and an accompanying decrease in sonic readings. the våle formation is overlain by the lista formation. intrabasinal highs (hardt et al. 1989) and in parts of the siri canyon where the rogaland group overlies the chalk group with an erosional unconformity. its thickness varies from 0 to 48 m in the danish sector of the north sea (fig. 15). lithology. light grey to greenish grey, heavily bioturbated fig. 15. isochore map of the våle formation in the study area. the positions of the two danish reference wells, e-8 and siri-1, are indicated on the figure. 2047.5 2072.6 2186.5 2156.3 horda fm balder fm sele fm lista fm rind mb idun mb tyr mb vile mb ve mb bue mb bue mb våle fm chalk gp 2000 2100 2200 m siri-1 gr sonic neutron/densityfig. 14. siri-1, danish reference well for the våle and sele formations. black bars show cored sections. e-8 siri-1 0 10 20 30 40 thickness (m) våle formation 25 km 28 cm 2398 m 2399 m 2400 m cecilie-1b 2401 m 2402 m 0 10 20 30 40 50 60 70 80 90 100 cm underlying ekofisk formation is characterised by the ho of the dinoflagellate senoniasphaera inornata followed uphole by the ho of the planktonic foraminifer globoconusa daubjergensis. there is a hiatus at the contact between the ekofisk and våle formation in many sections and wells (clemmensen & thomsen 2005). the basal part of the våle formation, just above the top of the ekofisk formation, is marked by the downhole increase in calcareous foraminifer diversity and the ho of the planktonic foraminifers globanomalina cf. compressa and subbotina subdivision. the våle formation includes a sandstone unit (bor member, new) in the danish north sea sector. macroand ichnofossils. fragments of shelly macrofossils are present, but rare. the våle formation is heavily bioturbated. trace fossils in the formation include chondrites ispp., phycosiphon ispp., planolites ispp. and zoophycos ispp. thalassinoides ispp. burrows are only present locally. microfossils and palynomorphs. the uppermost part of the fig. 16. core photographs of the ekofisk–våle formation boundary in the cecilie-1b well. the shift from chalk to marlstones is gradational and placing the boundary can be difficult; it is positioned in the middle part of the core interval 2400.00–2401 m, at 2400.35 m (arrow), where light grey marls become dominant. depths are core depths. 29 trivialis. thus, the boundary between the two formations may in practice be located by reference to these three events (fig. 5a). the ho of the dinoflagellate alisocysta reticulata marks a level in the lower part of the våle formation. calcareous microfossil events near the top of the våle formation in the danish sector include the provisional ho of planktonic foraminifers. depositional environment. over most of the danish sector, the marlstones of the våle formation comprise hemipelagic deposits and deposits from dilute turbidity currents. the marlstones are probably largely of turbiditic origin. the foraminifer fauna of the våle formation is characterised by common calcareous taxa. taxa belonging to the neritic ‘midway-type’ fauna (berggren & aubert 1975) are especially common. the plankton/benthos ratio varies from approximately 1:1 in some areas to a total dominance of calcareous benthic foraminifers in other areas. the microfaunal composition indicates that the våle formation was deposited in an open marine, outer neritic environment that periodically reached upper bathyal depths. the bottom conditions were predominantly oxic with periods of dysoxia. the indications from the microfauna are supported by the trace fossil assemblage, which indicates water depths of at least 200 m combined with oxic to dysoxic bottom conditions. in the siri canyon, where thin turbidites are common in the våle formation, gravity flows played a major role during the deposition of the formation. age. selandian. correlation. the våle formation is equivalent to the lellinge greensand and the kerteminde marl onshore denmark and lithologically most closely resembles the latter. the oldest part of the kerteminde marl and the lellinge greensand are coeval, but the latter has a more restricted distribution (sjælland and storebælt regions only, fig. 1; thomsen 1994; clemmensen & thomsen 2005). alisocysta reticulata is consistently present in the lowest part of the kerteminde marl (clemmensen & thomsen 2005). the ho of a. reticulata is therefore an important intravåle as well as intra-kerteminde marl marker that may be used to correlate the two formations. the våle formation correlates with the marly facies of the maureen formation in the uk and norwegian sectors of the central and viking grabens (knox & holloway 1992). 2900 2800 2940.5 2903.0 2894.4 2913.3 2963.2 horda fm balder fm sele fm lista fm våle fm bor mb vile mb ve mb bue mb chalk gp m augusta-1 gr sonic neutron/densityfig. 17. augusta-1, type well for the bor, ve and bue members. black bars show cored sections. 30 våle fm chalk group vile mb bor mb lista fm augusta-1 clay si. vf. f. m. sand c. vc. c c c 45° 27° 2920 2930 2940 2950 2960 2920 2930 2940 2950 2960 log depth core depthgr sonic bor member new member history. the bor member encompasses sandstone bodies enveloped in the marlstones of the våle formation in the danish north sea sector. hardt et al. (1989) recognised a pure sandstone unit, the ty formation, located between the ekofisk and lista formations in the southern viking graben. the ty formation replaces the våle formation in its occurrence area and may be contemporaneous with the bor member, but it is not contiguous with it and it has a different source area. the presence of sandstone bodies in the våle formation in the danish sector was recognised by a stratigraphic working group at statoil norway in the mid-1990s and the sandstones were informally named the ‘borr member’. derivation of name. after bor (danish spelling), the father of odin. type well. danish sector well augusta-1, 2963.2–2940.5 m mdrt (figs 17, 18). reference well. danish sector well cecilie-1, 2319.6–2284.6 m mdrt (fig. 19). distribution and thickness. the bor member has been encountered at the mouth of the siri canyon as well as in fig. 18. core log of bor member sandstones in the augusta-1 well. legend in fig. 9. the interval around the våle–lista formation boundary marked by a grey bar in the core depth column is shown as core photographs in fig. 23. 31 the nearby wells tabita-1, augusta-1 and cleo-1 (fig. 20a; plate 1). it reaches a thickness of up to 23 m. lithology. the bor member consists of olive-green, partly calcite-cemented sandstones. the sandstones are very fine grained to fine grained and well sorted (fig. 18). rounded and translucent quartz grains dominate, but the content of glaucony grains is high (20–25%). mica and pyrite concretions are present in small amounts. angular chalk and claystone clasts occur locally. although composed exclusively of sandstone in the type well (fig. 18), the member may also include subordinate interbedded marlstones (e.g. cecilie-1, fig. 19). log characteristics. the bor member sandstones are best identified on the density log where they produce a blocky pattern with density values significantly lower than those of the marlstones beneath and above. the sandstones may also be identified from a combination of the density and neutron logs, as the presence of pure sandstone results in a ‘cross-over’ of the two log curves (figs 17, 19). on the gamma-ray log, the bor member is characterised by a blocky log signature with only small-scale increasing or decreasing trends and with values clearly higher than those of the subjacent, suprajacent and locally interbedded marlstones. boundaries. the boundaries with the marlstones of the våle formation, the chalks of the ekofisk formation and the mudstones of the lista formation are sharp and characterised by prominent shifts on the gamma-ray, sonic and density logs (figs 17–19, 21). depositional environment. the sandstones of the bor member were deposited from highly concentrated gravity flows at bathyal depths. age. selandian. correlation. the bor member is contemporaneous with parts of the kerteminde marl onshore denmark. the lellinge greensand, which appears between the top chalk surface and the kerteminde marl in some areas in eastern denmark, may also be broadly contemporaneous with the bor member, but differs from it lithologically in being predominantly a glaucony-rich calcilutite, rich in bryozoan fragments. the bor member may be compared with the ty formation (hardt et al. 1989) and with sandstones in the maureen formation (deegan & scull 1977) in the norwegian and uk sectors of the southern viking graben and the central graben. however, it is not contiguous with these units and it has a different source area. 2100 2200 2300 bue mb ve mb vile mb tyr mb bor mb horda fm balder fm sele fm lista fm våle fm chalk gp m cecilie-1 gr sonic neutron/density 2241.7 2276.6 2284.6 2319.6 fig. 19. cecilie-1, reference well for the bor and tyr members. black bar shows cored section. 32 fig. 20. location map showing the distribution of the rogaland group sandstones in the siri canyon (the outline of the canyon is indicated by grey shading, the grey shading inside the canyon indicates an area of positive relief within the canyon). a: bor and tyr members. b: idun member. c: rind and kolga members. cleo-1 francisca-1 frida-1 d-1 nolde-1 siri-3siri-2 connie-1 siri-1 augusta-1 elna-1 tabita-1 amalie-1 cecilie-1 10 km augusta-1 tabita-1 nini-3 amalie-1 cleo-1 elna-1 frida-1 d-1 nolde-1 cecilie-1 siri-3 sandra-1 sandra-1 siri-2 siri-1 connie-1 10 km augusta-1 tabita-1 amalie-1 cleo-1 elna-1 frida-1 d-1 nolde-1 cecilie-1 siri-3 sandra-1 siri-2 siri-1 connie-1 10 km tyr mb bor mb both mbs idun mb rind mb kolga mb both mbs sir i c an yo n sir i c an yo n sir i c an yo n a b c nini-3 francisca-1 francisca-1 nini-3 lista formation history. deegan & scull (1977) established the lista formation for the widespread, non-laminated mudstones that overlie the marls of the unit equivalent to the maureen formation (våle formation). kristoffersen & bang (1982) established the non-calcareous clay and shale unit cen-1 between the top of their north sea marl (våle formation) and the base of the beds with volcanic tuff. they noted that the cen-1 unit corresponds to the lista formation. for reasons of seniority and the informal nature of the cen units, we maintain the name lista formation for this stratigraphic unit. type well. norwegian sector well 2/7–1, 2917.5–2872.5 m mdkb. danish reference wells. e-8, 2057.0–2027.6 m mdkb (fig. 13); cleo-1, 2812.0–2765.5 m mdkb (fig. 21; plate 1). distribution and thickness. the lista formation is present throughout the north sea basin, except in a few areas where it has been removed by erosion. in the danish sector, its thickness varies from 0 to 108 m (fig. 22). lithology. the formation is characterised by dark coloured, predominantly greyish, greenish or brownish, non-laminated to faintly laminated, non-calcareous mudstones. the lista formation is predominantly non-tuffaceous but becomes tuffaceous towards its top. in the siri canyon, glaucony-rich, massive sandstone layers and injected sandstone bodies occur in the lista formation. log characteristics. although fluctuating, both the gamma-ray and sonic log readings in the lista formation have higher mean values than those of the underlying våle formation and lower mean values than those of the overlying sele formation. in wells where mudstone facies dominate in the lista formation, the gamma-ray and sonic log patterns can be subdivided into three. the tripartite log pattern reflects the succession of three different mudstone units, established as new members herein (see below). boundaries. in most wells where the transition has been cored, the boundary is sharp between the light-coloured marlstones of the våle formation and the dark-coloured, non-calcareous mudstones of the lower lista formation (vile member, see below; fig. 23). on the gamma-ray log, the boundary is picked at an abrupt upward shift to higher values than in the underlying våle formation. this level can typically be identified on the sonic log at a velocity 33 minimum. above this minimum, the sonic readings increase slightly upwards. the lista formation is overlain by the sele formation. the base of the sele formation was defined by deegan & scull (1977 p. 34) at the contact between “non-laminated, non-tuffaceous shales” (lista formation) and “laminated tuffaceous shales” (sele formation). this boundary definition was followed by mudge & copestake (1992a, b). on the other hand, knox & holloway (1992 p. 46) followed o’connor &walker (1993) and placed the boundary somewhat lower, at the contact between “grey-green and green-grey, blocky, bioturbated claystones” of the lista formation and “dark grey fissile mudstones” of the sele formation. the boundary concept of knox & holloway implies that the “non-laminated, non-tuffaceous shales” of deegan & scull are incorporated in the sele formation where these, together with overlying laminated indisputable sele mudstones, constitute the basal sele unit s1a (knox & holloway 1992). in the present paper, the boundary concept of deegan & scull (1977) is followed, and the lower part of the unit of “non-laminated, nontuffaceous shales” (the “dark grey, fissile mudstones” of knox & holloway) that overlies the grey-green mudstones is retained in the lista formation as its topmost unit. this unit is formalised as a new member of lista formation herein (bue member, see below). subdivision. the lista formation is subdivided into six new members. three of these, the vile, ve and bue members, are mudstone units that have widespread distribution in the north sea basin and can be correlated with danish onshore units. in the siri canyon, fine-grained fig. 22. isochore map of the lista formation in the study area. the positions of the two danish reference wells, cleo-1 and e-8, are indicated. 2700 2800 bue mb ve mb vile mb bor mb horda fm balder fm sele fm lista fm våle fm chalk gp m cleo-1 2765.5 2812.0 2792.4 2777.6 gr sonic densityfig. 21. cleo-1, danish reference well for the lista formation and the vile, ve and bue members. lista formation cleo-1 e-8 20 40 60 80 100 thickness (m) 25 km 34 2918 m 2919 m augusta-1 2920 m 2921 m 0 10 20 30 40 50 60 70 80 90 100 cm sandstone bodies occur within each of the three mudstone units. these sandstone-dominated units are proposed here as three new members: the tyr member for the sandstones in the vile member, the idun member for the sandstones in the ve member, and the rind member for the sandstones in the bue member. knox & holloway (1992) recognised a threefold subdivision of the lista formation exclusively based on biostratigraphy. their l1 and l2 units are separated by the ho of the dinoflagellate palaeoperidinium pyrophorum, and the l2 and l3 units are separated by the ho of areoligera gippingense. it is noticeable that these two bioevents occur close to the boundaries between the three mudstone members of the lista formation proposed herein on the basis of lithology. macroand ichnofossils. macrofossils have not been reported fromthelistaformation;theformationismoderatelytoheavily bioturbated (for ichnotaxa, see individual members below). microfossils and palynomorphs. the lista formation differs from the underlying våle formation by lacking common planktonic foraminifers and from the overlying sele formation by having an impoverished agglutinated benthic foraminifer assemblage. the lista formation contains a characteristic sequence of palynomorph datums that can aid separation of its members. these datums are treated under the individual lista members below. depositional environment. the lista formation consists predominantly of hemipelagic mudstones and was probably deposited from very dilute turbidity currents and from suspension. the composition of the microfaunal assemblage indicates a relatively open marine depositional setting in upper to possibly middle bathyal depths with oxic to dysoxic bottom conditions. this is based on the presence of an impoverished agglutinated foraminifer assemblage dominated by tubular suspension feeders (especially rhabdammina spp.) together with epifaunal and infaunal detritivores (e.g. haplophragmoides spp. and spiroplectammina spectabilis). the relative abundance of tubular suspension feeders is higher in wells in the siri canyon than in wells outside the canyon. this probably indicates slightly deeper water within the canyon area during deposition of the lista formation. age. selandian–thanetian (upper paleocene). the selandian–thanetian boundary may be placed in the middle part of the lista formation (in the lower part of the ve member, see below), at the ho of the dinoflagellate palaeoperidinium pyrophorum. correlation. the lista formation corresponds to the following succession of upper paleocene units from onshore fig. 23. core photographs of the våle–lista formation boundary interval in the augusta-1 well. the boundary is at 2919.46 m where dark grey non-calcareous mudstones of the vile member overlie greenish grey marls of the våle formation. in most cores the boundary is sharp, as illustrated here. depths are core depths. stratigraphic position of the figured interval is shown in fig. 18. 35 fig. 25. correlation diagram showing possible diachronism of the våle–vile boundary in an east–west transect extending into the norwegian sector of the north sea (1/3-1 and 2/7-1 are norwegian sector wells). the distribution of biostratigraphic events shows that the våle–vile boundary youngs in a westerly direction (ho, highest occurrence). alternatively, the event distribution could be explained as a result of reworking of older strata into the lista formation in the danish sector. the figure also shows an example of a well (2/7-1) with a relatively large separation between the base of the sele formation and the lowest and most conspicuous gamma-ray peak in the formation (see text for further explanation). æbelø fm holmehus fm østerrende clay ølst fm kerteminde marl danian limestone 1/3-1 gr sonic gr sonic gr sonic gr sonic 1/3-1 2/7-1 mona-1 e-8 viborg-1 viborg-1 sele fm lista fm bue mb ve mb vile mb våle fm chalk group ho abundant palaeoperidinium pyrophorum ho isabelidinium? viborgense ho diverse calcareous benthic foraminifers ho (provisional) planktonic foraminifers 2050 2075 450 400 3050 3000 2900 2950 3150 3200 3250 kolga mb s3 s2b s2a s1b bue mb ve mb vile mb horda fm balder fm sele fm lista fm våle fm chalk gp 2000 2100 m siri-3 1998.8 2016.8 2036.1 2066.4 2072.8 2102.6 gr sonic densityfig. 24. siri-3, type well for the vile and kolga members, and danish reference well for the balder formation. the figure also shows the subdivision of the sele formation used by knox & holloway (1992); in this well, the bue member is equivalent to the s1a subunit of these authors. black bar shows cored section. 36 denmark: æbelø formation (informal mudstone unit described by bøggild 1918 and heilmann-clausen 1995), holmehus formation (heilmann-clausen et al. 1985) and østerrende clay (informal mudstone unit described by nielsen et al. 1986 and heilmann-clausen 1995). vile member new member history. the vile member comprises the widespread, dark olive-grey to dark grey, non-calcareous, fissile mudstones that constitute the lower part of the lista formation. the unit was recognised by a stratigraphic working group at statoil norway in the mid-1990s and informally named the ‘vile formation’. derivation of name. after vile, the brother of odin. type well. danish sector well siri-3, 2102.6–2072.8 m mbrt (fig. 24; plate 4). reference wells. danish sector wells e-8, 2057.0–2044.0 m mdkb (fig. 13); cleo-1, 2812.0–2792.4 m mdkb (fig. 21; plate 1). distribution and thickness. the vile member has been recognised in a large number of north sea wells, and the unit probably has a basinwide distribution. however, it is apparently lacking in the siri canyon wells connie-1 and siri-2 (figs 29, 31), probably due to erosion. its thickness varies between 0 and 30 m over most of the danish sector. it greatest thickness is reached in the siri canyon. lithology. the member consists of dark olive-grey to dark grey, non-calcareous, swelling, smectitic, fissile mudstones (fig. 23). thin silicified layers occur in the member. calcite is common and occurs as small nodules and larger concretions. in the siri canyon, small pyrite concretions and less than 1 cm thick, silty, very fine-grained glaucony-rich sandor siltstone laminae are locally present in the vile member. the laminae are parallel to the bedding of the mudstones; they have sharp bases and are normally grad1803.7 1763.9 1700.4 1717.2 horda fm lark fm balder fm sele fm kolga mb bue mb vile mb idun mb tyr mb lista fm chalk gp 1600 1700 1800 m nini-3 gr sonic neutron/density s3 s2b s2a s1b fig. 26. nini-3, type well for the tyr member and reference well for the kolga member. the figure shows the subdivision of the sele formation used by knox & holloway (1992); in this well, the bue member is equivalent to the s1a subunit of these authors. black bar shows cored section. 37 ed. thin concordant or discordant, postdepositional sandstone intrusions are locally present. in the lower part of the vile member, the intrusions are only a few millimetres thick, but they often increase in number and thickness towards the top of the member (fig. 11). log characteristics. in most wells there is a gradual increase in gamma-ray response up through the vile member, accompanied by a slight decrease in sonic readings. boundaries. the lower boundary of the vile member is that of the lista formation. the upper boundary is defined by the base of the ve member; boundaries with the sandstone-dominated tyr member are described under that member. macroand ichnofossils. the vile member is moderately to intensely bioturbated. ichnogenera in the member include chondrites ispp., phycosiphon ispp., planolites ispp. and zoophycos ispp. microfossils and palynomorphs. the vile member is characterised by a general decrease in the diversity of benthic foraminifers and radiolaria from its base to its top. in the danish sector, the transition from the underlying våle formation to the vile member is marked by the provisional ho of planktonic foraminifers. a conspicuous drop in diversity of benthic foraminifers takes place in the middle of the vile member. the ho of the dinoflagellate isabelidinium? viborgense is an important intra-vile marker located in the upper part of the member. above it, a sudden decrease in the abundance of radiolaria further charlista fm chalk group nini-3 clay si. vf. f. m. sand c. vc. p p p 1800 1790 1780 1770 1760 1800 1790 1780 1770 1760 log depth core depthgr sonic vile mb tyr mb fig. 27. core log of the tyr member in the nini-3 well. for legend, see fig. 9. 38 2908 m2907 m 2909 m augusta-1 2910 m 2911 m 2912 m 0 10 20 30 40 50 60 70 80 90 100 cm acterises a level within the uppermost part of the vile member. the transition from the vile member to the overlying ve member is marked by a conspicuous drop in the abundance of the dinoflagellate palaeoperidinium pyrophorum (which has its ho at a slightly higher stratigraphic level, within the lower part of the ve member, see below). depositional environment. the mudstones of the vile member are hemipelagic deposits, whereas the thin sandstone and siltstone laminae are interpreted as the deposits of low-density turbidity currents. the presence of zoophycos ispp. suggests depositional water depths of at least 200 m (bottjer & droser 1992). age. selandian. correlation. the vile member corresponds to the æbelø formation, onshore denmark (informal mudstone unit described by bøggild 1918 and heilmann-clausen 1995). it corresponds to the lista l1 subunit of knox & holloway (1992). fig. 28. core photographs of mudstones of the vile and ve members in the augusta-1 well. depths are core depths. the boundary between the two members is placed where greenish and reddish grey mudstones become dominant, at 2910.4 m (arrow). this depth corresponds to log depth 2913.3 m on fig. 17. 39 biostratigraphic correlation with well sections in the norwegian north sea sector may indicate that the lower boundary of the vile member is diachronous (fig. 25). in the type well for the lista formation (norwegian well 2/7-1; fig. 25), its base (i.e. its contact with the marlstones of the underlying våle formation) is above the ho of a diverse calcareous benthic foraminifer assemblage. in wells in the danish sector, this event occurs within the vile member. similarly, the provisional ho of planktonic foraminifers, an event that is close to the boundary between the våle and lista formations in denmark, is found well within the våle formation in well 2/7-1. in the type well for the våle formation (norwegian well 1/3-1; fig. 25), the ho of i.? viborgense coincides with the våle–lista boundary (i. prince, unpublished biostratigraphic data). this event occurs above the våle formation in the danish sector, in the middle to upper part of the vile member. in the danish onshore well viborg-1, the latter event and the ho of the diverse calcareous benthic foraminifer assemblage occur above the kerteminde marl in the upper part of the æbelø formation, a correlative of the vile member (fig. 25; heilmann-clausen 1985). the distribution pattern of the biostratigraphic events indicates that sedimentation of marls continued in the norwegian sector some time after marl sedimentation was replaced by sedimentation of non-calcareous mudstones in the danish sector. alternatively, calcareous foraminifer assemblages and associated lithologies have been reworked into higher levels of the våle formation or even into the lista formation in the danish sector. tyr member new member history. the tyr member consists of glaucony-rich, sandstone-dominated deposits that are laterally equivalent to, and commonly underlain and overlain by, mudstones of the vile member. these sandstones were previously recognised by a stratigraphic working group at statoil norway in the mid-1990s and informally referred to the ty formation of hardt et al. (1989). derivation of name. after tyr, the son of odin. type well. danish sector well nini-3, 1803.7–1763.9 m mdrt (figs 26, 27; plate 4). reference well. danish sector well cecilie-1, 2276.6–2241.7 m mdrt (figs 8, 19). distribution and thickness. the tyr member has only been encountered in the siri canyon and it may be restricted to that area. it reaches a thickness of up to 40 m (fig. 20a). lithology. the tyr member is characterised by thick beds of olive-green to greenish grey, very fine-grained to finegrained and well-sorted sandstone (fig. 27). rounded and translucent quartz grains dominate, but the content of glaucony grains is high (15–20%), hence the greenish colour of the sandstones. mica and small pyrite concretions are present in small amounts throughout the member. angular chalk and claystone clasts occur locally in the sandstones. the sandstones are partly calcite-cemented. intrusive sandstones are common, particularly towards the top of the member where they may be several metres thick (fig. 8). subordinate interbedded dark grey noncalcareous mudstones resemble those of the laterally equivalent vile member. log characteristics. the tyr member is best identified on the density log where the sandstones are characterised by a conspicuously lower density than the associated mudstones. the sandstones may also be identified from a combination of the density and neutron logs, as the presence of pure sandstone results in a ‘cross-over’ of the two log curves (figs 19, 26). the gamma-ray response resembles that of the underlying våle formation, but is slightly lower than the response of the vile member (figs 8, 26). this log pattern makes it feasible to differentiate even minor sand units from mudstone beds in the tyr member. thicker sand units may show decreasingor increasingupwards gamma-ray values. these trends do not seem to be related to grain-size variations, judging from core studies. boundaries. the boundaries to the mudstones of the vile member, the marlstones of the våle formation and the chalks of the ekofisk formation are sharp and characterised by prominent shifts in gamma, sonic and density log readings (figs 19, 26, 27). in some wells, the tyr member overlies the våle formation or the ekofisk formation with an erosional contact (e.g. nini-3; figs 26, 27). depositional environment. although the sandstones of the tyr member were deposited from highly concentrated gravity flows, their present appearance is dominated by the effects of postdepositional liquefaction and fluidisation. age. selandian. correlation. the tyr member is contemporaneous with parts of the lithologically dissimilar æbelø formation in 40 onshore denmark and with the lower part of the heimdal formation of deegan & scull (1977) as well as the andrew sandstone and the mey sandstone member of knox & holloway (1992) in the norwegian and uk sectors of the southern viking graben. however, it is not contiguous with the latter three sandstone units and has a different source area. ve member new member history. the ve member consists of variegated mudstones that have previously been recognised from north sea wells as the holmehus formation by heilmann-clausen et al. (1985), who gave no further details, and by danielsen & thomsen (1997), who indicated its presence in several wells. the unit was also recognised by a stratigraphic working group at statoil norway in the mid-1990s and informally named the ‘ve formation’. derivation of name. after ve, the brother of odin. type well. danish sector well augusta-1, 2913.3–2903.0 m mdrt (fig. 17). reference wells. danish sector wells e-8, 2044.0–2030.3 m mdkb (fig. 13); cleo-1, 2792.4–2777.6 m mdkb (fig. 21; plate 1). distribution and thickness. the sediments of the ve member have been recognised from a large number of north sea wells, and the unit probably has an almost basinwide distribution. its thickness varies from 0 to 21 m in the danish sector. lithology. the ve member consists of mottled green, bluish green, reddish brown and brown mudstones (fig. 28). mottled, purple coloured intervals are also present locally. the middle part of the member is often characterised by a thick dark reddish brown to chocolate brown interval. the ve member mudstones are non-calcareous and rich in smectite. pyrite and carbonate concretions occur throughout the member. a weak biogenic lamination is sometimes observed in cores. only very little organic material is present in the member. in the siri canyon, thin intrusive sandstones are common in the ve member. log characteristics. in general, the gamma-ray log shows a decreasing-upwards trend through the ve member, as opposed to the increasing trend through the underlying vile member. in the uppermost part of the ve member, the gamma-ray response increases over a short interval before reaching the base of the overlying bue member. the sonic log pattern throughout the ve member is smooth and relatively stable compared with the sonic pattern of the vile member. it also differs from the latter in having an increasing-upwards trend. the log pattern of the ve member differs from that of the overlying bue member in having a lower gamma-ray response level. boundaries. the lower boundary, with the vile member, is placed at the first appearance of greenish, bluish or reddish brown mudstones above the dark olive-grey to dark grey mudstones of the vile member. the colour change from vile to ve mudstones is often gradational and the boundary may be difficult to define precisely (fig. 28), especially when only cuttings samples are available. however, in the colour transition interval, a gamma-ray spike separates an interval with an increasing-upwards gammaray trend below from an interval with a decreasing gamma-ray trend above (compare figs 17 and 28). in the absence of a clear indication of the boundary level from sediment colour change, the gamma spike at the shift from increasing to decreasing gamma-ray values may be used as a marker for the boundary. the vile member is absent from the connie-1 well, and in this well the lower contact of the ve member is with the marlstones of the våle formation (fig. 31). the upper boundary is at the base of the bue member (see below). boundaries with the idun member are described under that member. macroand ichnofossils. the mudstones of the ve member are normally heavily bioturbated. the most common trace fossils are phycosiphon ispp. and zoophycos ispp. chondrites ispp. and planolites ispp. are present, but rare. microfossils and palynomorphs. in the danish sector of the north sea, the ho of abundant palaeoperidinium pyrophorum is located at or close to the vile–ve boundary. the hos of p. pyrophorum and palaeocystodinium australinum are in the lower part of the ve member. in general, the dinoflagellate assemblage from the upper part of the ve member is sparse and is characterised by specimens of areoligera gippingensis. an acme of the latter species marks a level in the upper part of the ve member. the highest in situ occurrence of the dinoflagellate alisocysta margarita is located close to the top of the ve member. depositional environment. deposition of the mudstones of the ve member was controlled by hemipelagic sedimentation and sedimentation from dilute turbidites. the 41 idun member new member history. the idun member consists of sandstone-dominated deposits that are laterally equivalent to, and commonly underlain by, mudstones of the ve member. this sandstone unit was previously recognised by a stratigraphic working group at statoil norway in the mid-1990s and was informally referred to the heimdal formation of deegan & scull (1977). derivation of name. after idun, the goddess of youth. type well. danish sector well connie-1, 2368.3–2332.0 m mdrt (figs 29, 30). 2200 2300 2368.3 2332.0 2329.6 2292.2 idun mb rind mb bue mb bue mb ve mb horda fm balder fm sele fm lista fm våle fm chalk gp m connie-1 gr sonic neutron/densityfig. 29. connie-1, type well for the idun and rind members. in this well, the rind member may be divided into three major sandstone intervals. the idun member consists of two thick sandstone intervals, separated by a thick mudstone unit. black bars show cored sections. occurrence of the trace fossil zoophycos ispp. indicates a water depth of at least 200 m (bottjer & droser 1992). the overall high degree of bioturbation, the lack of organic material and the greenish, bluish and reddish brown colours together suggest oxygenated bottom conditions. age. selandian–thanetian. the selandian–thanetian boundary is placed atthe ho of the dinoflagellatepalaeoperidinium pyrophorum, in the lower part of the ve member. correlation. the ve member correlates with the holmehus formation (heilmann-clausen et al. 1985) onshore denmark and is lithologically indistinguishable from that formation. 42 lista fm våle fm connie-1 clay si. vf. f. m. sand c. vc. 45o s v g g g pp ppp 45o 2290 2300 2310 2320 2340 2350 2360 2300 2290 2310 2320 2330 2340 2350 2360 2370 log depth core depthgr sonic p p p p p p p p p p p p change of core depth scale bue mb idun mb bue mb rind mb ve mb fig. 30. core log of the idun and rind members in the connie-1 well. for legend, see fig. 9. minor mudstone beds separate the three major sandstone intervals of the rind member. minor mudstone layers are also intercalated with the idun member sandstone intervals. the core depth scale of the lower core is offset by c. 1.6 m relative to the scale of the upper core in the figure. for reasons of consistency with core data from this well, the original (albeit erroneous) core depths of the lower core are maintained in the figure. this does not affect the depths of the top and base of the idun member given in the text, as these are based on log depths. 43 reference well. danish sector well siri-2, 2205.5–2127.0 m mdrt (fig. 31). distribution and thickness. the idun member is only known from the siri canyon, and it may be restricted to that area (fig. 20b). it reaches a thickness of up to 179 m in the siri-2 well. lithology. the idun member is dominated by very finegrained to fine-grained, well-sorted sandstones (fig. 30). rounded and translucent quartz grains dominate, but the content of glaucony grains is high (15–25%). the sandstones are olive green to greenish grey due to the high content of glaucony. mica and small pyrite concretions are present in small amounts. angular chalk and claystone clasts occur locally. intrusive sandstones are also represented (figs 11, 12, 30). the sandstones and adjacent mudstones are partly calcite-cemented. in the nini and siri wells, the sandstones occur in thick amalgamated successions with only rare, thin mudstone interbeds; the latter are lithologically comparable to the laterally equivalent ve member mudstones (see above). in the connie-1 well, however, the sand-rich succession is interrupted by a discrete 6 m thick mudstone unit (fig. 30). log characteristics. the sandstone-dominated idun member is best identified on the density log where it is characterised by a conspicuously lower density than the underlying and overlying mudstones (figs 29, 31). the sandstone component may also be identified from a combination of the density and neutron logs, as the presence of pure sandstones results in a ‘cross-over’ of the two log curves (figs 29, 31). the idun member is characterised by a blocky, decreasing-upwards gamma-ray and density log pattern. intervals with an overall constant gamma-ray pattern may be characterised by many small-scale increasingor decreasing-upwards gamma-ray cycles. boundaries. in sections where the sandstones of the idun member are enveloped by mudstones of the ve member, the boundaries are sharp and characterised by prominent shifts on the gamma-ray, sonic and density logs (figs 29, 30). where the ve member is absent, comparable, sharp boundaries are observed with the mudstones of the vile member beneath and the bue member above (figs 11, 26, 30). in the siri-2 well, the lower lista formation is absent and an erosive unconformity separates the idun member sandstones from the marlstones of the våle formation (fig. 31). depositional environment. although the sandstones of the idun member were deposited from highly concentrated gravity flows, their present appearance largely records postdepositional liquefaction and fluidisation processes. age. selandian–thanetian. bue mb bue mb rind mb idun mb balder fm horda fm sele fm lista fm chalk gp våle fm 2100 2200 m siri-2 gr sonic neutron/density 2127.0 2205.5 fig. 31. siri-2, reference well for the idun member. black bar shows cored section. 44 with these sandstone units, however, and has a different source area. bue member new member history. the bue member encompasses the light to dark grey and greyish black mudstones that occur between the top of the ve member and the base of the sele formation. these mudstones have not previously been recognised as a separate unit in the danish sector. derivation of name. after bue, the son of odin and rind. type well. danish sector well augusta-1, 2903.0–2894.4 m mdrt (fig. 17). reference wells. danish sector wells e-8, 2030.3–2027.6 m below mdkb (fig. 13); cleo-1, 2777.6–2765.5 m mdkb (fig. 21; plate 1). distribution and thickness. the sediments of the bue member have been recognised from a large number of north sea wells, and the unit probably has a basinwide distribution. its thickness varies from 0 to 18 m in the danish sector. lithology. the bue member consists of light to dark grey and greyish black mudstones. the mudstones are generally rich in smectite. in the siri canyon, the upper part of the member sometimes contains laminae of very finegrained to fine-grained sandstones or siltstones, mimicking the laminated mudstones of the overlying sele formation (figs 32, 39). the laminae are less than 2 cm thick, have sharp bases, are normally graded and show parallel lamination. concordant or discordant sandstone intrusions are locally present in the member (fig. 8). small calcite and siderite concretions are occasionally present. moderately to intensely bioturbated intervals are interbedded with non-bioturbated intervals. tuff layers may be present in the member. log characteristics. the gamma-ray response of the bue member is generally higher than that of the underlying ve member, but lower than that of the overlying sele formation. in some siri canyon wells, minor coarseningupwards cycles are indicated by the gamma-ray log of the bue member. boundaries. the transition from typical lithologies of the ve member to those of the bue member is often gradafig. 32. core photographs showing the bue member mudstones with numerous sandstone laminae in the augusta-1 well. depths are core depths. 0 10 20 30 40 50 60 70 80 90 100 cm 2891 m 2892 m augusta-1 2893 m correlation. the idun member is contemporaneous with parts of the lithologically dissimilar holmehus formation onshore denmark and with parts of the heimdal formation of hardt et al. (1989) and the lower balmoral sandstone and tuffite of the mey sandstone member of knox & holloway (1992). the idun member is not contiguous 45 rind member new member history. the rind member consists of sandstone-dominated deposits that are laterally equivalent to, and commonly underlain and overlain by, mudstones of the bue member. sandstone bodies at this stratigraphic level were previously recognised by a stratigraphic working group at statoil norway in the mid-1990s and were informally referred to the heimdal formation of deegan & scull (1977). derivation of name. after the giantess rind. type well. danish sector well connie-1, 2329.6–2292.2 m mdrt (figs 29, 30). reference well. danish sector well sandra-1, 2066.3– 2004.8 m mdrt (fig. 33). distribution and thickness. the rind member has only been encountered in the siri canyon, and it may be restricted to that area where it reaches a thickness of 62 m (fig. 20c). lithology. the rind member consists of very fine-grained, well-sorted sandstones interbedded with thin mudstone beds that typically form less than 15% of the member (fig. 30). rounded and translucent quartz grains dominate in the sandstones, but the content of glaucony grains in the very fine-grained to fine-grained size fraction is high (15–25%). the sandstones are olive green to greenish grey due to the high content of glaucony. mica and small pyrite concretions are present in small amounts. angular chalk and claystone clasts occur locally in the sandstones, which are partly calcite-cemented. the interbedded mudstones are lithologically comparable to the bue member mudstones (see above). log characteristics. the rind member is best recognised on the density log where it shows either a blocky or a serrate pattern created by the alternation of sandstone beds or amalgamated units (low density) with thin mudstone beds (high density; figs 29, 33). the sandstones may also be identified from a combination of the density and neutron logs, since the presence of pure sandstones results in a ‘cross-over’ of the two log curves (figs 29, 33). the gamma-ray log shows a low-amplitude serrate pattern. this pattern does not reflect alternating sand or mudstones, judging from core inspection. boundaries. the boundary between the sandstones of the rind member and the mudstones of the bue member is tional and the boundary may therefore be difficult to position precisely. it is placed where mottled green, bluish green, reddish brown and brown mudstones pass upwards into grey mudstones with sandstone and siltstone laminae. on the petrophysical logs, this transition is reflected by a shift from decreasingto increasing-upwards gamma-ray values or at an abrupt increase in the gamma-ray response. the upper boundary of the bue member is at the base of the sele formation. macroand ichnofossils. trace fossils recognised in the bue member are phycosiphon ispp., planolites ispp., thalassinoides ispp. and rare zoophycos ispp. microfossils and palynomorphs. the ve–bue boundary is bracketed by the stratigraphic succession of the ho of in situ alisocysta margarita (occurring in the upper ve member) followed by the ho of an impoverished assemblage of benthic agglutinated foraminifers (in the lower part of the bue member). the upper part of the bue member is characterised by common spores and pollen, in particular bisaccate pollen and inaperturopollenites spp. the bue– sele boundary is marked by the base of an acme of the dinoflagellate genus apectodinium and the lo of apectodinium augustum. depositional environment. the normally graded sandstone to siltstone laminae in the upper part of the member indicate that deposition of the bue member took place from dilute, low-density, turbidity currents in a generally sediment-starved environment at this level. the minor coarsening-upwards cycles observed on petrophysical logs from some siri canyon wells probably indicate either small distal lobes of deep-water channel-sandstones or levee deposits. age. thanetian. correlation. the bue member corresponds to the østerrende clay (informal mudstone unit described by nielsen et al. 1986 and heilmann-clausen 1995) onshore denmark. the level here defined as the boundary between the ve and the bue members was correlated by knox (1997 fig. 3; the lista–sele boundary of this worker) with the boundary between the holmehus formation and the østerrende clay (as ‘grey clay’) onshore denmark. the bue member further correlates with the lower part of the s1a subunit of the sele formation established by knox & holloway (1992; see correlation section under the lista formation for further details). 46 sharp and characterised by prominent shifts on both the sonic and density logs (figs 29, 33). it is often difficult to identify the boundaries on the gamma-ray log alone. depositional environment. although the sandstones of the rind member were deposited from highly concentrated gravity flows, their present appearance largely records postdepositional liquefaction and fluidisation processes. age. thanetian. correlation. the rind member may be contemporaneous with parts of the lithologically dissimilar østerrende clay encountered in the storebælt region (fig. 1), with sandstones in the higher parts of the heimdal formation (hardt et al. 1989) and with the upper balmoral sandstone of the mey sandstone member of knox & holloway (1992). however, the rind member is not contiguous with those sandstone units and has a different source area. sele formation history. the sele formation was established by deegan & scull (1977) for the dark grey to greenish grey, laminated and carbonaceous, tuffaceous, montmorillonite-rich shales and siltstones that overlie the non-laminated and nontuffaceous shales of the lista formation in some areas, or arenaceous sediments belonging to a variety of different units in other areas. the original definition of the sele boundary is followed herein. this implies that the base of the sele formation is located at the base of the “laminated tuffaceous shales” that overlie the “non-laminated, nontuffaceous shales” of the lista formation (deegan & scull 1977; see boundaries section under the lista formation for further details). sandstones occur in the sele formation in the danish sector; these are established as a new member, the kolga member. type well. british sector well 21/10-1, 2131–2100 m mdkb. bue mb rind mb vile mb ve mb balder fm horda fm lark fm sele fm lista fm våle fm 1800 1900 2000 2004.8 2066.3 2100 m sandra-1 gr sonic neutron/density fig. 33. sandra-1, reference well for the rind member. black bar shows cored section. geological survey of denmark and greenland bulletin 11, 115-123 115 new hornblende and muscovite 40ar/39ar cooling ages in the central rinkian fold belt, west greenland ann-sofie sidgren, laurence page and adam a. garde the palaeoproterozoic rinkian fold belt in west greenland consists of reworked archaean basement, mainly orthogneiss, and the unconformably overlying palaeoproterozoic karrat group. both parts were intensely deformed and metamorphosed at around 1.87 ga, at which time the crustal anatectic prøven igneous complex was emplaced into the northern part of the belt. seven new hornblende and muscovite 40ar/39ar cooling ages are presented from the central–northern parts of the rinkian fold belt. four 40ar/39ar hornblende ages ranging from 1795 ± 3 to 1782 ± 3 ma were obtained from amphibolite and hornblendite enclaves in the archaean orthogneiss, and two from relict dyke fragments in the latter that may be of palaeoproterozoic age. three 40ar/39ar muscovite ages of 1681 ± 6 ma, 1686 ± 3 ma and 1676 ± 3 ma were obtained from samples of karrat group metagreywacke, andalusite schist and metasiltstone. the new 40ar/39ar ages, from hornblende and muscovite respectively, are very uniform and probably unrelated to local metamorphic grade and structural history, and are interpreted as regional late orogenic cooling ages. the new hornblende ages are significantly older than those previously obtained from the central and northern parts of the adjacent nagssugtoqidian orogen to the south, and point to different uplift histories, which may suggest that the orogeny was not synchronous in the two regions. keywords: ar-ar, geochronology, rinkian, palaeoproterozoic, west greenland ____________________________________________________________________________________________________________________________________________________________________ a.-s.s. & l.p., department of geolog y, geobiosphere science center, lund university, sölvegatan 12, s-223 62 lund, sweden. e-mail: ann-sofie.sidgren@bd.lst.se a.a.g., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. this paper presents seven new hornblende and muscovite 40ar/39ar cooling ages from the central part of the palaeoproterozoic rinkian fold belt in west greenland. the new data set provides insight into the cooling history of the rinkian fold belt and can also be used to address its temporal relationship with the adjacent nagssugtoqidian orogen to the south, from which other 40ar/39ar cooling ages have previously been published. most of central and northern west greenland consists of archaean continental crust which was intensively reworked during the palaeoproterozoic. this reworking was first recognised in central west greenland between 66° and 69°n by ramberg (1949), who established the nagssugtoqidian mobile belt (now called the nagssugtoqidian orogen) in this area. escher & pulvertaft (1976) subsequently proposed that a separate palaeoproterozoic mobile belt, the rinkian fold belt, existed in central and northern west greenland between 69° and 75°n (see inset map of fig. 1). they noted that the latter region was dominated by an overall flat-lying tectonic foliation with superimposed large domes, and considered that these structures were of a different nature from the generally steep foliations and tight folds that had previously been identified in the nagssugtoqidian belt. in contrast to the collisional structures recognised within the nagssugtoqidian orogen, it was thought that the rinkian deformation had taken place without significant crustal shortening. furthermore, whereas the collisional nagssugtoqidian © geus, 2006. geological survey of denmark and greenland bulletin 11, 115–123. available at: www.geus.dk/publications/bull 116 orogen was originally believed only to comprise archaean supracrustal and infracrustal rocks, the rinkian fold belt contains a widespread, metamorphosed and deformed cover sequence, the c. 2 ga old karrat group, which was unconformably deposited on the archaean basement gneisses (garde & pulvertaft 1976; henderson & pulvertaft 1987; kalsbeek et al. 1998). the lowest parts of the karrat group consist of quartzite, marble and minor amphibolite (the qeqertarsuaq and marmorilik formations), which are overlain by a very uniform sequence of metagreywacke, the nukavsak formation, which is several kilometres thick and occurs throughout most of the rinkian belt (fig. 1; henderson & pulvertaft 1987). the geochemistry of the karrat group and studies of its detrital zircons indicate that the karrat group was derived from a mixed source including palaeoproterozoic magmatic arc 483667 hbl 1782 ± 2 ma 483696 hbl 1785 ± 3 ma 483708 hbl 1784 ± 3 ma 483657 hbl 1795 ± 3 ma 483671 mu 1676 ± 3 ma 483654 mu 1686 ± 3 ma 483653 mu 1681 ± 6 ma 500 km rinkian nagssugtoqidian disko bugt 72°n 51°w 55°w 71°n upernavik kang illeq 50 km ukkusissat fjord qeqertarsuaq qinngusaaq inland ice surficial deposits quaternary basalt paleocene sandstone karrat group palaeoproterozoic prøven igneous complex archaean, variably reworked orthogneiss and minor supracrustal rocks ar-ar sample hbl: hornblende mu: muscovite kang erlus suaq uummannaq appat svartenhuk nuussuaq fig. 1. map of the central rinkian fold belt showing the locations of samples collected for 40ar/39ar age determination. the index map shows the position of fig. 1 and the approximate extent of nagssugtoqidian and rinkian reworking in west greenland. modified from garde et al. (2004). 117 rocks and archaean basement rocks, and that it was deposited at around 2.0–1.9 ga ago (kalsbeek et al. 1998; thrane et al. 2003). the rinkian fold belt also incorporates the prøven igneous complex, a very large plutonic complex of granitic and microdioritic crustal melts that were emplaced under granulite facies conditions into the middle to upper crust in the upernavik region of the rinkian belt and is also found as the cumberland batholith on adjacent baffin island, canada. the pluton has previously yielded a rbsr whole rock isochron age of 1860 ± 25 ma with a high initial 87sr/86sr ratio (kalsbeek 1981) and has recently also been studied by thrane et al. (2005). the latter produced a more precise zircon u-pb ion probe age of 1869 ± 9 ma and obtained negative εnd values from the pluton (calculated at 1870 ma) ranging between –5.2 and –4.3. in agreement with the previous rb/sr data this shows that the plutonic complex contains a large archaean continental crustal component. it is therefore questionable whether the prøven igneous complex – cumberland batholith is subduction-related as has been proposed by canadian workers. thrane et al. (2005) suggest it represents a crustal melt, induced by upwelling hot asthenospheric mantle. pulvertaft (1986), henderson & pulvertaft (1987), grocott & pulvertaft (1990) and garde & steenfelt (1999b) have described the structural evolution in various parts of the rinkian fold belt, and recognised largescale thrusts in its southern part. following new field work in 2002–2003, the structural evolution in the uummannaq region is at present regarded as consisting of four main phases (briefly outlined by garde et al. 2003, 2004). deformation began with tight folding and possibly thrusting (d1), which developed prior to cleavage formation. this was followed by neto e-directed thrusting and ductile tectonic transport (d2) accompanied by formation of a penetrative schistosity, and then by nwto w-directed tectonic transport (d3) and intensification of the pre-existing schistosity. lastly, very large, upright to overturned, dome-shaped anticlines and tight synclinal cusps were developed during continued shortening of the now strongly tectonically layered crust; these large structures are only locally accompanied by a new tectonic fabric. the prøven igneous complex was emplaced at a late stage of the main fabric-forming events and gave rise to a wide metamorphic aureole that was overprinted on rocks that were already regionally metamorphosed at high grade. 1900 1700 0 4020 60 80 100 1750 1850 1800 1795 ± 3 ma integrated age = 1797 ± 3 ma hornblende483657 1800 1600 1650 1750 1700 1681 ± 6 ma* integrated age = 1703 ± 3 ma muscovite483653 1600 1650 1750 1700 1686 ± 3 ma* integrated age = 1716 ± 2 ma muscovite483654 1600 1650 1750 1700 1676 ± 3 ma integrated age = 1684 ± 3 ma muscovite483671 1700 0 4020 60 80 100 1750 1850 1800 1782 ± 2 ma integrated age = 1801 ± 2 ma hornblende483667 1900 1700 1750 1850 1800 1785 ± 3 ma integrated age = 1864 ± 2 ma hornblende483696 1700 0 4020 60 80 100 1750 1850 1800 1784 ± 3 ma integrated age = 1798 ± 3 ma hornblende483708 cumulative % 39ar released a pp ar en t ag e (m a) ukkusissat area north-eastern uummannaq area south-eastern uummannaq area fig. 2. 40ar/39ar plateau age spectra from the rinkian fold belt. ages with an asterisk (*): 40ar/39ar plateau age representing less than 50% of total 39ar release. ages without an asterisk: 40ar/39ar plateau age. 118 483653 muscovite (j = 0.01071 ± 0.00001): c 1.4 0.00001 0.001 0.00011 0 147.485 0.093 10.9 10.9 100 1709.6 4.4 d 1.4 0.1461 0.004 0.00008 26.5 147.544 0.306 35.6 46.4 100 1710 1.7 •e 1.5 1.9453 0.021 0.00097 27.6 143.552 0.011 1.2 47.7 99.9 1679.9 13.4 •f 1.6 2.875 0.004 0.00041 96.1 143.488 0.009 1 48.7 100 1679.4 17.2 •g 1.9 0.4853 0.003 0.00010 68.7 143.739 0.187 21.7 70.3 100 1681.3 2.7 h 4 0.3402 0.004 0.00019 24.8 147.664 0.256 29.7 100 100 1710.9 1.6 integrated (total fusion) age: 1703 3 (•) plateau age: 23.9 1681 6 483654 muscovite (j = 0.01071 ± 0.00001): a 1.4 0.005 0.003 0.00106 0.1 150.444 0.767 26.9 26.9 99.8 1731.6 1.0 b 1.5 0.006 0.005 0.00033 0.2 149.670 0.692 24.3 51.2 99.9 1725.9 1.2 •c 1.6 0.0499 0.009 0.00063 1.1 144.382 0.265 9.3 60.5 99.9 1686.2 1.5 •d 1.7 0.9006 0.020 0.00077 16.1 143.337 0.075 2.6 63.1 99.9 1678.2 3.3 •e 1.8 0.1521 0.007 0.00147 1.4 144.323 0.153 5.4 68.5 99.7 1685.7 2.2 •f 1.9 0.357 0.009 0.00015 32.9 144.706 0.251 8.8 77.3 100 1688.6 3.1 g 2.3 0.0741 0.003 0.00003 35.7 148.939 0.648 22.7 100 100 1720.4 2.1 integrated (total fusion) age: 1716 2 (•) plateau age: 26.1 1686 3 483657 hornblende (j = 0.01071 ± 0.00001): a 1.8 11.847 0.123 0.04105 4 184.220 0.019 1 1 94 1965.7 11.4 b 1.9 11.642 0.027 0.00559 28.7 163.894 0.059 3.1 4.1 99.3 1828.5 3.3 •c 2 10.312 0.013 0.00193 73.5 159.127 1.198 63.2 67.3 99.9 1794.7 1.1 •d 2 10.03 0.014 0.00155 89 159.084 0.463 24.4 91.7 100 1794.4 1.3 •e 2.1 11.862 0.043 0.00182 90 158.317 0.028 1.5 93.2 100 1788.9 8.0 •f 2.6 11.62 0.018 0.00223 71.9 159.178 0.130 6.8 100 99.9 1795.1 2.3 integrated (total fusion) age: 1797 3 (•) plateau age: 95.9 1795 3 483667 hornblende (j = 0.01071 ± 0.00001): a 1.8 14 0.277 0.08890 2.2 501.205 0.011 0.5 0.5 95.1 3339.8 25.5 b 1.9 8.88 -0.010 0.01236 9.9 166.723 0.006 0.2 0.7 98.1 1848.2 27.0 c 2 8.133 0.066 0.00845 13.3 196.061 0.068 3 3.7 98.9 2041 3.3 d 2 8.823 0.082 0.01454 8.4 148.220 0.042 1.8 5.5 97.4 1715.1 6.7 e 2.1 5.161 0.073 0.01482 4.8 146.685 0.009 0.4 5.9 97.2 1703.6 17.3 •f 2.2 8.525 0.054 0.00482 24.4 157.760 0.118 5.2 11 99.3 1784.9 2.3 •g 2.2 9.17 0.048 0.00241 52.4 157.782 0.188 8.2 19.2 99.8 1785.1 1.7 •h 2.3 8.683 0.050 0.00316 37.8 157.288 0.206 9 28.2 99.6 1781.6 1.6 •i 2.3 8.979 0.056 0.00234 53 157.382 0.328 14.3 42.5 99.8 1782.2 1.4 •j 2.4 8.623 0.055 0.00105 113.4 157.274 0.432 18.8 61.3 100 1781.5 1.9 •k 2.6 8.346 0.056 0.00150 77 157.395 0.561 24.4 85.8 99.9 1782.3 1.1 •l 2.8 9.598 0.067 0.00374 35.4 156.861 0.081 3.5 89.3 99.5 1778.5 3.0 •m 4 10.4 0.062 0.00273 52.5 157.231 0.246 10.7 100 99.8 1781.1 1.9 integrated (total fusion) age: 1801 2 (•) plateau age: 94.1 1782 2 483671 muscovite (j = 0.01071 ± 0.00001): a 1.4 0.2482 0.005 0.00153 2.2 145.263 0.449 27.4 27.4 99.7 1692.9 1.2 b 1.5 0.7642 0.007 0.00189 5.6 145.703 0.168 10.3 37.6 99.6 1696.2 1.9 •c 1.5 0.3775 0.007 0.00197 2.6 143.327 0.168 10.2 47.8 99.6 1678.2 1.6 •d 1.6 0.4299 0.017 0.00377 1.6 142.856 0.089 5.4 53.3 99.2 1674.6 2.8 •e 1.6 1.5215 0.010 0.00180 11.7 142.234 0.057 3.5 56.7 99.7 1669.8 3.7 •f 1.7 0.9017 0.017 0.00144 8.7 142.377 0.093 5.7 62.4 99.7 1670.9 3.0 •g 1.7 0.2113 0.005 0.00004 79.6 143.047 0.230 14 76.4 100 1676 1.7 •h 1.8 1.123 0.015 0.00144 10.7 142.970 0.065 4 80.4 99.7 1675.4 23.0 •i 2 0.4492 0.005 0.00121 5.1 143.638 0.152 9.3 89.7 99.8 1680.5 4.2 j 2.3 0.2898 0.004 0.00172 2.3 144.357 0.169 10.3 100 99.7 1686 3.2 integrated (total fusion) age: 1684 3 (•) plateau age: 52.1 1676 3 table 1. 40ar-39ar analytical data for step heating experiments on amphiboles and muscovites from the rinkian fold belt step pwr/t°c ca/k cl/k 36ar/39ar %36ar(ca) 40*ar/39ar mol 39ar % step %39ar %40*ar age (ma) ± age cumulated (2σ) j: irradiation parameter. 40*ar: radiogenic 40ar. steps marked with dot (•) are included in the plateau age for each sample. 119 whereas the tectonic model of grocott & pulvertaft (1990) operated with four contractional and three extensional events in an epicontinental marginal basin, four main phases of deformation that developed during progressive crustal shortening are now recognised. it has been debated in recent years whether the previous distinction between the rinkian and nagssugtoqidian belts in west greenland is meaningful in tectonic terms (e.g. garde & steenfelt 1999a; van gool et al. 2002), and it has now been proposed that the two belts represent the northern and southern parts of a common, more than 1100 km wide collisional orogen, separated by a suture located in the disko bugt region (fig. 1; connelly et al. 2005). the continuous crustal shortening in the rinkian fold belt throughout its tectonic evolution is in agreement with a setting within the northern of two colliding plates at some distance from the suture, and thus in accordance with the proposed tectonic linkage to the nagssugtoqidian orogen. however, the 40ar/39ar data presented in the following section may be interpreted to indicate that the tectonometamorphic events in the rinkian and nagssugtoqidian belts were not contemporaneous. descriptions of samples and results of 40ar/39ar age determinations four hornblende samples and three muscovite samples were collected at the head of ukkusissat fjord close to the prøven igneous complex, between svartenhuk and uummannaq, and close to the north coast of nuussuaq (fig. 1). sample numbers refer to the data base of the geological survey of denmark and greenland. ukkusissat fjord near the prøven igneous complex a sample with hornblende was collected south of the prøven igneous complex, within the high-grade contact metamorphic aureole where extensive partial melting has been observed, particularly within the karrat group (grocott & pulvertaft 1990). the sample (483657, fig. 1) comes from a homogeneous, medium-grained, amphibolitic relict dyke within the regional flat-lying tonalitic orthogneiss basement. the amphibolite dyke is approximately one metre thick, a few metres long, and has been isoclinally folded. the sample is mostly composed of light to dark green hornblende between 0.5 and 1 mm in diameter, together with some plagioclase and minor phases step pwr/t°c ca/k cl/k 36ar/39ar %36ar(ca) 40*ar/39ar mol 39ar % step %39ar %40*ar age (ma) ± age cumulated (2σ) 483696 hornblende (j = 0.01071 ± 0.00001): a 1.9 4.9568 0.167 0.02251 3 557.080 0.091 1.9 1.9 98.9 3501.9 4.4 b 2 5.6395 0.198 0.00248 31.3 176.447 0.447 9.5 11.5 99.7 1914.4 1.3 c 2.1 5.7159 0.202 0.00177 44.4 164.542 0.370 7.9 19.4 99.8 1833 1.7 d 2.2 5.9588 0.197 0.00468 17.5 161.233 0.042 0.9 20.3 99.3 1809.7 6.6 e 2.2 5.7368 0.198 0.00147 53.9 161.903 0.098 2.1 22.3 99.9 1814.5 2.5 f 2.3 5.3872 0.190 0.00107 69.3 162.278 1.212 26.4 48.8 99.9 1817.1 1.0 •g 2.3 5.3337 0.184 0.00097 75.5 157.503 1.620 34.6 83.4 100 1783.1 1.3 •h 2.4 5.3052 0.209 0.00097 75.2 157.732 0.242 5.2 88.5 100 1784.7 1.6 •i 2.6 6.2547 0.255 0.00436 19.8 161.354 0.017 0.4 88.9 99.4 1810.6 13.4 •j 2.9 7.1602 0.246 0.00815 12.1 156.396 0.009 0.2 89.1 98.7 1775.1 13.0 •k 4 5.4765 0.189 0.00181 41.7 158.216 0.511 10.9 100 99.8 1788.2 1.6 integrated (total fusion) age: 1864 2 (•) plateau age: 51.2 1785 3 483708 hornblende (j = 0.01071 ± 0.00001): a 1.9 7.672 0.051 0.00834 12.7 181.053 0.134 8.2 8.2 98.8 1945 2.2 •b 2 9.5527 0.062 0.00197 66.7 157.766 0.855 52.6 60.8 99.9 1785 1.0 •c 2.1 9.6506 0.062 0.00317 42 157.637 0.376 23.2 84 99.7 1784.1 1.5 •d 2.2 8.7213 0.062 0.00050 241.2 157.711 0.054 3.3 87.3 100.1 1784.6 3.8 •e 2.3 10.597 0.109 0.00836 17.5 157.274 0.024 1.5 88.7 98.7 1781.5 8.4 •f 2.4 13.824 0.144 0.00502 38 156.401 0.012 0.7 89.5 99.4 1775.2 12.1 •g 2.7 10.368 0.067 0.00298 47.9 157.265 0.171 10.5 100 99.7 1781.4 3.3 integrated (total fusion) age: 1798 3 (•) plateau age: 91.8 1784 3 table 1 (continued) 120 such as biotite, titanite and zoizite. the biotite is intergrown with hornblende, and the plagioclase is partly altered to sericite. the obtained plateau age is 1795 ± 3 ma (fig 2; table 1). north-eastern uummannaq four samples were collected in the kangilleq–kangerlussuaq area, 75–100 km north of uummannaq (fig. 1). this area was less intensely affected by rinkian metamorphism than other areas investigated in this study, with chlorite schist locally preserved on the north coast of qeqertarsuaq. samples 483653 and 483654, both from the nukavsak formation, were collected at two localities close to each other near the southern end of qeqertarsuaq (fig. 1). sample 483653 (fig. 1) is a greywacke consisting of biotite, sillimanite, quartz, muscovite and small amounts of tourmaline and zircon. it is a fine-grained rock, where biotite and muscovite together define the main tectonic foliation. fibrolitic sillimanite occurs in broom-shaped clusters close to muscovite. it was difficult to obtain a good separate from this sample because the muscovite is very fine grained, intergrown with biotite, and sometimes has altered rims. this sample yielded a u-shaped spectrum, with a minimum which yields an age of 1681 ± 6 ma and represents 24% of the total 39ar-release (fig. 2; table 1). sample 483654 (fig. 1) is a fine-grained andalusite schist with centimetre-sized andalusite poikiloblasts in a matrix of biotite and quartz, minor tourmaline and muscovite. partial recrystallisation of andalusite to fibrolite was observed. the biotite shows two different orientations implying growth both during d2 and d3 deformation. the muscovite crystals are very small and often occur close to biotite, but sometimes also in small separate clusters. this sample gave a u-shaped spectrum, with a minimum representing 26% of the total 39ar-release and yielding an age of 1686 ± 3 ma (fig. 2; table 1). sample 483667 (fig. 1) was collected from a decimetre-thick, boudinaged, homogeneous amphibolite band in tonalitic reworked orthogneiss on qinngusaaq (fig. 1). folds, lineations, δand σ-shaped porphyroclasts and foliations representing both d2–d3 and d4 occur at the sampling locality. the light to dark brownish-green hornblende forms well-crystallised medium-grained aggregates with interstitial plagioclase partly altered to sericite. small grains of pale green pyroxene, probably diopside, occur together with the hornblende. a hornblende plateau age of 1782 ± 2 ma was obtained (fig. 2; table 1). sample 483671 (fig. 1) consists of fine-grained metasandstone to metasiltstone from the nukavsak formation with quartz, biotite, muscovite and sillimanite as main minerals. biotite, muscovite and sillimanite define the main tectonic foliation, where sillimanite often occurs in clusters containing small muscovite and biotite grains. at this locality, quartz pods display distinct asymmetries in two different directions. the asymmetric pods on rock faces with sw–ne orientations suggest top-to-ne tectonic transport (during d2), whereas rock faces with se– nw orientations suggest transport to the nw (during d3) and contain biotite lineations with that trend. muscovite from this rock, presumably grown during d3, gave a plateau age of 1676 ± 3 ma (fig. 2; table 1). south-east of uummannaq two samples with hornblende were collected from the archaean basement south-east of the uummannaq area, close to the north coast of nuussuaq (fig. 1). sample 483696 (fig. 1) comes from a hornblenditic layer in a leucogabbro that occurs as enclaves in quartzo-feldspathic orthogneiss. the sample consists almost exclusively of light to dark green, mediumto coarse-grained hornblende. the hornblende plateau age is 1785 ± 3 ma (fig. 2; table 1). sample 483708 (fig. 2) comes from an amphibolite dyke that cuts the fabric of the surrounding augen gneiss and is probably palaeoproterozoic in age. both the amphibolite and the host gneiss are intensely deformed. this sample has biotite and hornblende growing together, feldspars partly altered to sericite, and minor amounts of quartz. the hornblende plateau age is 1784 ± 3 ma (fig. 2; table 1). discussion and conclusions the results from this study provide the first published constraints on cooling ages of hornblende and muscovite in the central rinkian belt. hornblende 40ar/39ar plateau age spectra from samples 483657, 483667 and 483708 yield ages between 1795 and 1782 ma. these ages all form well-defined plateaus, and the plateaus represent more than 90% of total 39ar release. sample 483696 yielded a plateau age of 1785 ma for 51% of the total 39ar release, and is consistent with the other hornblende ages. muscovite samples 483653 and 483654 both yield u-shaped age spectra with minima representing less than 50% of the total 39ar release, at 1681 and 1686 ma respectively. sample 483671 provides a plateau age of 1676 ma defined by 121 52% of the total 39ar release. the muscovite plateau age spectrum for sample 483671 is consistent with the minima provided by samples 483653 and 483654. these taken together suggest a relatively consistent muscovite cooling age below 350°c of c. 1680 ma in the central rinkian belt. the obtained hornblende and muscovite ages at 1795– 1782 and 1686–1676 ma, respectively, are remarkably uniform, although they cover a distance of c. 200 km in chlorite to sillimanite grade amphibolite facies terrain across the entire central part of the rinkian fold belt. this 40ar/39ar age study shows that the temperatures reached during the palaeoproterozoic tectonothermal reworking were everywhere sufficiently high to reset the 40ar/39ar hornblende and muscovite systems in the rocks examined. the ages date the cooling below the closure temperature of ar diffusion in hornblende and muscovite after the palaeoproterozoic metamorphic event, and the data suggest a slow cooling rate of c. 1.5°c/ma between c. 1780 and 1680 ma, using closure temperatures of 500°c for hornblende and 350°c for muscovite (mcdougall & harrison 1999). due to recent recalculation of the primary and secondary standards used in 40ar/39ar geochronological experiments (renne et al. 1998), the previously published 40ar/ 39ar ages from the nagssugtoqidian belt (rasmussen & holm 1999; willigers et al. 2001, 2002), which use the older standard age, have to be multiplied by 1.009 in order to compare directly with the new 40ar/39ar ages presented here from the rinkian belt. in the northern part of the nagssugtoqidian orogen, willigers et al. (2001, 2002) obtained 40ar/39ar hornblende ages of 1756–1733 ma (recalculated from 1740–1717 ma) and muscovite ages of c. 1715 ma (recalculated from 1700 ma). in the central part of the orogen still farther south, their hornblende ages range between c. 1750–1700 ma and muscovite ages between c. 1765–1715 ma (recalculated from 1750–1700 ma). in the disko bugt area (fig. 1), where connelly et al. (2005) proposed a suture between the two belts, a set of 40ar/39ar and k-ar hornblende age data reported by rasmussen & holm (1999) scatter between archaean ages and a k-ar age of c. 1765 ma, revealing that temperatures during the palaeoproterozoic thermal event were not sufficiently high in all parts of this area to reset the k-ar isotope system (rasmussen & holm 1999). the uniformity of the new 40ar/39ar ages from the central and northern rinkian fold belt suggests that the ages are largely unrelated to the metamorphic grade and to the structural history of the geographical locations of the samples, with the possible exception of sample 483657 from ukkusissat fjord (see below). accordingly, the 40ar/39ar data are interpreted as regional, late orogenic cooling ages which are not directly related to the tectono-metamorphic history of the individual samples. this conclusion is supported by (in part unpublished) u-pb zircon ages of synto late-kinematic palaeoproterozoic pegmatites from the same region, which are older than 1800 ma (thrane et al. 2003; k. thrane, personal communication 2004). willigers et al. (2002) reached the same conclusion from their 40ar/39ar studies of the central and northern nagssugtoqidian orogen reported above, pointing out that their study area represents a section of middle to lower crust that was only slowly exhumed by erosion. in preserved upper crustal levels of younger orogens it is commonly possible to date specific tectonic events using the 40ar/39ar method, because the dated units were either transported rapidly to these crustal levels and are not yet eroded away, or the minerals grew at temperatures near or below their closing temperature and thus constrain the age of the prograde tectonothermal event itself. the 1795 ± 3 ma age of the hornblende from ukkusissat fjord (sample 483657, about 12 ma older than the other hornblende ages) may point to early uplift of this particular area, which is a domain of early ne-directed d2 thrusting that was not affected by the subsequent nw-directed tectonic transport during d3. the cooling rate of c. 1.5°c/ma documented by this study (using hornblende and muscovite closure temperatures of 500°c and 350°c) is only slightly slower than the 2–3°c/ma reported by willigers et al. (2001, 2002) from the central nagssugtoqidian orogen, but considerably slower than rates between 5° and 7°c/ma reported by the latter authors from the northern nagssugtoqidian orogen. willigers et al. (2001, 2002) used less accepted closure temperatures of 580°c and 410°c for hornblende and muscovite, respectively, implying a difference of 170°c between hornblende and muscovite closure temperatures. the latter temperature gap is larger than the 150°c used in this study, but this makes little difference to the calculation of cooling rates. the uniform 40ar/39ar hornblende ages resulting from the present investigation are significantly older than those in both the northern and central parts of the nagssugtoqidian orogen (willigers et al. 2001, 2002). as regards muscovite, the rinkian muscovite ages are younger than muscovite ages in the northern nagssugtoqidian belt, but older than those in the central nagssugtoqidian orogen (willigers et al. 2001, 2002). the fact that rinkian hornblende ages are older than those in the nagssugtoqidian orogen shows that cooling below 500°c took place earlier in the rinkian fold belt than in both the central and northern parts of the nagssugtoqidian orogen. it is therefore 122 plausible that uplift began significantly earlier in the rinkian belt but was slower than in the nagssugtoqidian orogen, which may in turn suggest that the main phases of compression and peak metamorphism in the two belts were not synchronous. these interpretations are consistent with the observation by taylor & kalsbeek (1990) that pb-pb whole-rock isochron ages of marbles in the two belts (interpreted as representing recrystallisation of the marbles during peak metamorphism) differ significantly from each other. marbles collected on appat island in the central rinkian belt (fig. 1) yielded a pb-pb isochron of 1881 ± 20 ma, whereas an age of 1845 ± 23 ma was obtained from marbles in the central part of the nagssugtoqidian orogen. our interpretations are also consistent with the fact that the 40ar/ 39ar data reported here show no signs of having been affected by a contact metamorphic aureole around the prøven igneous complex. the intrusion age of the latter at 1869 ± 9 ma is coeval with the youngest members of the arfersiorfik complex and sisimiut charnockite in the central nagssugtoqidian orogen (connelly et al. 2000; van gool et al. 2002). the prøven igneous complex has intruded rocks belonging to the karrat group that were already intensely deformed and metamorphosed prior to the intrusion, but before the last major deformation and peak metamorphism (thrane et al. 2005); the prøven igneous complex represents a crustal melt that was apparently not related to subduction processes. in contrast, the arfersiorfik complex and sisimiut charnockite in the south represent i-type magmas that were related to precollision subduction. notwithstanding the overall structural and geochronological evidence for a direct linkage between the rinkian fold belt and the nagssugtoqidian orogen, the age relationships outlined above may imply that collision-related deformation, metamorphism and magmatic activity took place in the northern rinkian belt while subduction was still going on south of the recently proposed suture in the disko bugt region. it may be speculated that such diachronism is also reflected in the dissimilar 40ar/39ar cooling ages from the rinkian and nagssugtoqidian parts of the entire palaeoproterozoic orogenic complex in west greenland. alternatively, the different rinkian and nagssugtoqidian cooling ages might relate to different depths of burial. however, this is not supported by the uniform hornblende 40ar/39ar cooling ages found within the rinkian belt itself, regardless of geographical distance and metamorphic facies; further discussion of large-scale platetectonic implications is beyond the scope of the present paper. analytical procedure four hornblende and three muscovite separates from the central rinkian belt have been dated with the 40ar/39armethod. the hornblende separates were obtained from amphibolite and diorite, and muscovite from metasedimentary rocks, by crushing, sieving and handpicking. the hornblende and muscovite samples selected for 40ar/39ar geochronology were irradiated together with the dra-2 sanidine standard (25.26 ma; wijbrans et al. 1995, recalculated following renne et al. 1998), for 35 hours at the nrg-petten hfr rodeo facility in petten, the netherlands. j-values (the irradiation parameter) were calculated with a precision of 0.5%. the 40ar/39ar geochronology laboratory at the university of lund employs a micromass 5400 mass spectrometer with a faraday cup and an electron multiplier. a metal extraction line, which contains two saes c50-st101 zr-al getters and a cold finger cooled to c. –155°c by a polycold p100 cryogenic refrigeration unit, is also present. one or two grains of hornblende or muscovite were loaded into a copper planchette that consists of several 3 mm holes. samples were step-heated using a defocused 50w co2 laser. sample clean-up time was 5 minutes, using the two hot zr-al saes getters and the cold finger. the laser was rastered over the samples to provide even heating of all grains. the entire analytical process is automated and runs on a macintosh computer with software developed at the berkeley geochronology center by al deino and modified for the laboratory at the university of lund. time zero regressions were fitted to data collected from 10 scans over the mass range of 40 to 36. peak heights and backgrounds were corrected for mass discrimination, isotopic decay and interfering nucleogenic ca-, k-, and cl-derived isotopes. isotopic production values for the cadmium lined position in the petten reactor are 36ar/ 37ar(ca) = 0.000270, 39ar/37ar(ca) = 0.000699, and 40ar/ 39ar(k) = 0.00183. 40ar blanks were calculated before every new sample and after every three sample steps. 40ar blanks were between 5.0 and 3 × 10–16. blank values for masses 39 to 36 were all less than 7 × 10–18. blank values were subtracted for all incremental steps from the sample signal. the laboratory was able to produce very good incremental gas splits, using a combination of increasing time at the same laser output, followed by increasing laser output. age plateaus were determined using the criteria of dalrymple & lanphere (1971), which specify the presence of at least three contiguous incremental heating steps with statistically indistinguishable ages and constituting greater than 50% of the total 39ar released during the experiment. inverse isochrons yield ages statistically indis123 tinguishable from those given by the plateaus and are not presented here. 40ar/39ar plateau age spectra are presented in fig. 2 and the analytical data in table 1. acknowledgements the authors thank j.n. connelly, j. grocott, m. hand, k.j.w. mccaffrey and k. thrane for discussions leading to the preparation of this manuscript, which also draws on their collective field observations in 2002–2003. we are grateful to j. grocott and å. johansson for critical reviews. references connelly, j.n., van gool, j.a.m. & mengel, f.c. 2000: temporal evolution of a deeply eroded orogen: the nagssugtoqidian orogen, west greenland. canadian journal of earth sciences 37, 1121–1142. connelly, j.n., thrane k., krawiec, a. & garde a.a. 2005: linking the palaeoproterozoic nagssugtoqidian and rinkian orogens through the disko bugt region of west greenland. journal of the geological society (london) 162, 1–17. dalrymple, g.b & lanphere, m.a. 1971: 40ar/39ar technique of k-ar dating: a comparison with the conventional technique. earth and planetary science letters 12, 300–308. escher, a. & pulvertaft, t.c.r. 1976: rinkian mobile belt of west greenland. in: escher, a. & watt, w.s. (eds): geology of greenland, 105–119. copenhagen: geological survey of greenland. garde, a.a. & pulvertaft, t.c.r. 1976: age relations of the precambrian mârmorilik marble formation, central west greenland. rapport grønlands geologiske undersøgelse 80, 49–53. garde, a.a. & steenfelt, a. 1999a: precambrian geology of nuussuaq and the area north-east of disko bugt, west greenland. geology of greenland survey bulletin 181, 6–40. garde, a.a. & steenfelt, a. 1999b: proterozoic tectonic overprinting of archaean gneisses in nuussuaq, west greenland. geology of greenland survey bulletin 181, 141–154. garde, a.a., grocott, j., thrane, k. & connelly, j.n. 2003: reappraisal of the rinkian fold belt in central west greenland: tectonic evolution during crustal shortening and linkage with the nagssugtoqidian orogen. geophysical research abstracts 5 (egs-agu-eug joint assembly), 09411. garde, a.a., connelly, j.n., grocott, j., hand, m., mccaffrey, k.j.w. & thrane, k. 2004: crustal shortening and granite emplacement in the rinkian fold belt, west greenland, and implications for palaeoproterozoic laurentian evolution. danmarks og grønlands geologiske undersøgelse rapport 2004/17, 16–18. grocott, j. & pulvertaft, t.c.r. 1990: the early proterozoic rinkian belt of central west greenland. in: lewry, j.f. & stauffer, m.r. (eds): the early proterozoic trans-hudson orogen of north america. geological association of canada special paper 37, 443–463. henderson, g. & pulvertaft, t.c.r. 1987: geological map of greenland, 1:100 000, mârmorilik 71 v.2 syd, nûgâtsiaq 71 v.2 nord, pangnertôq 72 v.2 syd. descriptive text, 72 pp., 8 plates. copenhagen: geological survey of greenland. kalsbeek, f. 1981: the northward extent of the archaean basement of greenland – a review of rb-sr whole-rock ages. precambrian research 14, 203–219. kalsbeek, f., pulvertaft, t.c.r. & nutman, a.p. 1998: geochemistry, age and origin of metagreywackes from the palaeoproterozoic karrat group, rinkian belt, west greenland. precambrian research 91, 383–399. mcdougall, i. & harrison, t.m. 1999: geochronology and thermochronology by the 40ar/39ar method. oxford: oxford university press. pulvertaft, t.c.r. 1986: the development of thin thrust sheets and basement-cover sandwiches in the southern part of the rinkian belt, umanak district, west greenland. rapport grønlands geologiske undersøgelse 128, 75–87. ramberg, h. 1949: on the petrogenesis of the gneiss complexes between sukkertoppen and christianshaab, west greenland. meddelelser dansk geologisk forening 11, 312–327. rasmussen, h. & holm, p.m. 1999: proterozoic thermal activity in the archaean basement of disko bugt region and eastern nuussuaq, west greenland: evidence from 40ar–39ar mineral age investigations. geology of greenland survey bulletin 181, 55–64. renne, p.r., swisher, c.c., deino, a.l., karner, d.b., owens, t.l. & depaolo, d.j. 1998: intercalibration of standards, absolute ages and uncertainties in 40ar/39ar dating. chemical geology 145, 117–152. taylor, p.n. & kalsbeek, f. 1990: dating the metamorphism of precambrian marbles: examples from proterozoic mobile belts in greenland. chemical geology (isotope geoscience section) 86, 21–28. thrane, k., connelly, j.n., garde, a.a., grocott, j. & krawiec, a.w. 2003: linking the palaeoproterozoic rinkian and nagssugtoqidian belts of central west greenland: implications of new u-pb and pbpb zircon ages. geophysical research abstracts 5 (egs-agu-eug joint assembly), 09275 only. thrane, k., baker, j., connelly, j.[n.] & nutman, a.p. 2005: age, petrogenesis and metamorphism of the syn-collisional prøven igneous complex, west greenland. contributions to mineralogy and petrology 149, 541–555. van gool, j.a.m., connelly, j.n., marker, m. & mengel, f.c. 2002: the nagssugtoqidian orogen of west greenland: tectonic evolution and regional correlation from a west greenland perspective. canadian journal of earth sciences 39, 665–686. wijbrans, j.r., pringle, m.s., koppers, a.a.p & scheveers, r. 1995: argon geochronology of small samples using the vulkaan argon laserprobe. proceedings of the koninklijke nederlandse akademie van wetenschappen 98, 185–218. willigers, b.j.a., krogstad, e.j. & wijbrans, j.r. 2001: comparison of thermochronometers in a slowly cooled granulite terrain: nagssugtoqidian orogen, west greenland. journal of petrology 42, 1729– 1749. willigers, b.j.a., van gool, j.a.m., wijbrans, j.r., krogstad, e.j. & mezger, k. 2002: posttectonic cooling of the nagssugtoqidian orogen and a comparison of contrasting cooling histories in precambrian and phanerozoic orogens. journal of geology 110(5), 503–517. _________________________________________________________________________________________________________________________________________________________________________________ manuscript received 21 june 2004; revision accepted 15 march 2005 124 geological survey of denmark and greenland bulletin 1, 931-948 931 shelf-edge delta and slope deposition in the upper callovian – middle oxfordian olympen formation, east greenland michael larsen and finn surlyk the upper bajocian – upper volgian succession of the jameson land basin in east greenland forms an overall transgressive–regressive cycle. the upper callovian – middle oxfordian olympen formation represents the first regressive deposits after maximum flooding in the middle to early late callovian. the formation was deposited during two southwards progradational phases separated by a major drowning event in the early oxfordian. the first phase was marked by incoming of massive slope and base-of-slope sand (athene member), but the delta front and top did not reach the area of present-day exposure. the second phase was initiated by deposition of a thick mud succession (hades member) indicating that the delta had shifted far to the north during the drowning event. southwards progradation of the delta was heralded by gully erosion and the deposition of lenticular bodies of massive slope sand; on this occasion, mediumand largescale cross-bedded sand of the delta front and top (zeus member) reached the area. the boundary between middle–upper callovian mudstones in the upper part of the underlying fossilbjerget formation and the upper callovian athene member sandstones formed at the turn-around point between sea-level rise and fall. the athene member sandstones are interpreted as an undifferentiated falling stage – lowstand systems tract and span a sequence boundary. the top of the athene member is the basinal correlative of the transgressive surface. the basal few metres of the overlying hades member mudstones represent the transgressive systems tract and a level with organic-rich mudstones is interpreted to represent the maximum flooding zone. the remainder of the hades member and the slope sandstones are assigned to the highstand systems tract. the succeeding cross-bedded delta front sandstones of the zeus member are placed in the falling stage systems tract and their sharp base is interpreted as a marine regressive surface of erosion. comparison of this history with published sea-level curves suggests that the short term changes may be eustatic in origin including the middle callovian maximum flooding (k. jason – lower p. athleta chronozones), late callovian regression (p. athleta – q. lamberti chronozones), latest callovian – early oxfordian flooding (q. mariae – c. cordatum chronozones) and late early – middle oxfordian regression (c. densiplicatum chronozone). keywords: east greenland, jameson land basin, middle–upper jurassic, sedimentology, lithostratigraphy, sequence stratigraphy, shelf-edge delta, slope gullies, massive sandstones, sediment gravity flow, sea-level curve m.l., geological survey of denmark and greenland, geocenter copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: mil@geus.dk f.s., geological institute, university of copenhagen, geocenter copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. geological survey of denmark and greenland bulletin 1, 931–948 (2003) © geus, 2003 shelf-edge deltas and their associated slope/base-of-slope deposits are becoming increasingly well-known, especially from the passive margins of the gulf of mexico and the western mediterranean (suter & berryhill 1985; suter et al. 1987; tesson et al. 1990, 1993; sydow & roberts 1994; gensous & tesson 1996; henriksen & weimer 1996). in this study we describe upper callovian – middle oxfordian sandy shelf-edge deltas and slope gravity flow deposits formed during the early stages of jurassic rifting in the east greenland basin. in the jameson land basin, rifting was initiated in the early bajocian, reached a climax in the volgian and waned in the earliest cretaceous. the resulting marine middle – lower upper jurassic rift succession forms an overall transgressive–regressive cycle with a duration of c. 30 ma. the basin axis was oriented north– south, deepening southwards. middle jurassic sediment influx was from the north and transport was mainly axial towards the south resulting in a marked north–south grain-size gradient with a thick succession of shallow marine sandstones in the northern part of the basin passing into thinner offshore mudstones towards the south. the aim of the study is to describe the development of the forestepping late callovian – middle oxfordian shelfedge delta and slope system constituting the olympen formation of the jameson land basin (surlyk et al. 1973; surlyk 2003, this volume, fig. 5). it marks the initiation of the stepwise late jurassic regression after middle to early late callovian maximum flooding of the basin. 932 3 km 71°27'n 23°40'w 23°20´ ice quaternary olympen formation olympen formation fossilbjerget formation lower and middle jurassic undifferentiated olympen 71°24'n sections 1–9 25 km 22°w24°w 71°n jameson land olympen antarctic havn parnas fossilbjerget mikael bjerg 23°30'w parnas o ly m pe lv en greenland fig. 1. map showing the distribution of the upper callovian – middle oxfordian olympen formation in jameson land and place names mentioned in the text. geological setting the onshore part of the late paleozoic – mesozoic rift basin of east greenland is about 600 km long and about 200 km wide at the southern end where the jameson land basin is located (fig. 1). the basin was uplifted in tertiary times and the mesozoic succession is excellently exposed. in east greenland, the early jurassic period was tectonically quiescent and deposition was restricted to the jameson land basin, whilst the northern parts of the rift basin were emergent. marine communication between the boreal sea and the tethys ocean was effectively obstructed at the end of the early jurassic by uplift of the north sea dome (surlyk et al. 1973; underhill & partington 1994). distinct faunal provinces rapidly developed and a separate ammonite-based biostratigraphic scheme is used for the bajocian – lower callovian interval in the boreal realm (callomon 1993; 2003, this volume). a combination of bathonian–callovian eustatic sealevel rise, domal deflation and erosion, and onset of the important middle–late jurassic rift phase led to gradual resumption of the north–south marine connection from mid-callovian times. although there was still a marked faunal provincialism in the oxfordian–kimmeridgian, the degree of faunal overlap allows good correlation between east greenland and europe. maximum flooding of the jameson land basin took place in the middle to early late callovian when the middle jurassic sand-dominated system was completely drowned and offshore muds were deposited throughout the basin. rifting increased in the oxfordian– kimmeridgian and reached a climax in the volgian, contemporaneous with the onset of a late jurassic eustatic sea-level fall. this led to a punctuated late jurassic regression and by late volgian times, deltaic deposits had prograded to the southernmost end of jameson land. during the early part of the rift phase, in bajocian– bathonian times, the sea floor was essentially flat and differentiation into shelf, slope and basin was not developed. however, continued southwards axial sediment transport resulted in higher sedimentation rates and preferential sand deposition in the northern part of the basin, whereas the southern part mainly received mud. this led to the gradual development of a northern shallow marine shelf passing southwards into an east–west striking ramp with an incipient slope grading into a deeper-water basin towards the south. two important regressive phases separated by a major drowning event took place in the late callovian and middle oxfordian, respectively, and southwards axial progradation of shallow marine and deltaic sands reached central jameson land. a marked slope was formed in front of the two forestepping successions, and well-developed slope and shelf-edge delta deposits are preserved on several mountain tops in central jameson land (fig. 1). the slope facies are composed of dark grey mudstones and massive, sediment gravity flow sandstones. similar facies types are known from the slightly younger upper oxfordian – volgian hareelv formation in southern jameson land (surlyk 1987) but this latter unit has experienced major post-depositional modification characterised by syndepositional loading structures and evidence of post-burial liquefaction and intrusion of sands into the adjacent and overlying mud (surlyk & noenygaard 2001). post-middle oxfordian shelf-edge deltas are only preserved in the middle–upper volgian part of the succession in southernmost jameson land, due to present-day erosion levels. the shelf-edge delta and slope deposits of the late callovian and middle oxfordian progradational phases constitute the olympen formation of surlyk et al. (1973; fig. 2). the olympen formation stratigraphy the olympen formation was defined by surlyk et al. (1973) for an upper callovian – middle oxfordian tripartite sandstone–mudstone–sandstone succession forming the youngest pre-quaternary sedimentary unit in central jameson land (fig. 1). the formation is divided into three members following the revised lithostratigraphic scheme for the jurassic of east greenland, provisionally introduced by surlyk (2003, this volume, fig. 5). it consists of: (1) a lower unit of massive, fineto medium-grained sandstones intercalated with subordinate, laminated, dark silty mudstones and finegrained laminated sandstones termed the athene member, (2) a middle unit, termed the hades member, of dark silty mudstones which passes upwards into sandy mudstones intercalated with lenticular bodies of massive sandstones and (3) an upper unit of massive or large-scale cross-bedded, mediumto coarse-grained sandstones with subordinate intercalations of silty mudstones termed the zeus member (figs 2, 3; surlyk 2003, this volume, fig. 5). the complete thickness is not known as the formation forms the top of the succession in central jameson 933 934 mud f m c gr 80 70 60 50 40 30 20 10 0 poor exposure poor exposure q. mariae chronozone (early oxfordian) lower–middle p. athleta chronozone (late callovian) p. athleta chronozone (late callovian) k. jason chronozone (middle callovian) c. densiplicatum chronozone (middle oxfordian) ba si n flo o r o ly m pe n fo rm at io n fo ss ilb je rg et fo rm at io n sl o pe a pr o n a th en e m em be r h ad es m em be r z eu s m em be r ba si n flo o r/ sl o pe ba si n flo o r/ sl o pe sl o pe g ul ly de lt a to p de lt a to p de lt a fr o nt lo w er c yc le u pp er c yc le c. 900 m massive sandstone planar cross-bedded sandstone trough cross-bedded sandstone laminated silty mudstone parallel-laminated sandstone carbonate concretion pebbles carbonaceous material ripple formset ripple cross-lamination climbing ripple lamination wave ripple lamination antidunes load structures ripple lamination planar cross-bedding gully axis ammonite belemnite bivalve leaf imprints helminthoida isp. planolites isp. diplocraterion habichi skolithos isp. piscichnus ?kulindrichnus mm 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 fossils facies directional features trace fossils sand mud f m c gr sand 3 7 fig. 2. vertical sections including the type section (left) of the olympen formation at the head of the river olympelven. the olympen formation overlies mudstones of the fossilbjerget formation. note the tripartite lithostratigraphic subdivision of the olympen formation into lower and upper sandstone-dominated units of the athene and zeus members, respectively, separated by the middle mudstone-dominated hades member. the upper boundary is not exposed as the formation forms the summit of the mountains in central jameson land. 935 land. the type section (figs 2–4, section 3) at the top of the olympen mountain measures 150 m, but the thickness in this area may reach 250 m, the upper part being poorly exposed below scree, till and ice. at the parnas, fossilbjerget and mikael bjerg mountains, the formation is 300 m, 250 m and 200 m thick, respectively; further south, in the hurry inlet region, it wedges out completely or is only represented by a few metres of mudstones (surlyk 1991). the olympen formation conformably overlies fossiliferous middle and lower upper callovian mudstones of the fossilbjerget formation of surlyk (2003, this volume, fig. 5; equivalent to the fossilbjerget member of surlyk et al. 1973). the base of the olympen formation is defined by the base of the first thick massive sandstone in the succession (fig. 2). the age of the lower boundary of the formation generally becomes younger from north to south. at the type section, ammonites of the middle callovian k. jason chronozone occur 20 m below the base of the olympen formation and the lower upper callovian p. athleta chronozone is represented 13 m below the base (fig. 2). ammonites from the lower–middle p. athleta chronozone (kosmoceras (zugokosmokeras) cf. proniae teisseyre) occur 3 m below the base, close to the type section, and have also been found 15 m above the base north of olympen (figs 1, 2; birkelund et al. 1971). at mikael bjerg, the upper part of the fossilbjerget formation yields ammonites of the lower p. athleta chronozone (longaeviceras keyserlingi sokolov) in contrast to the northernmost outcrops at antarctic havn where the same ammonite fauna occurs in the lowermost member (athene member) of the olympen formation (callomon 1993). the middle mudstone-dominated hades member has yielded ammonites of the lower oxfordian q. mariae chronozone, c. scarburgense subzone (surlyk et al. 1973; callomon 1993). scattered finds of ammonites from the upper sandstone-dominated zeus member indicate the presence of the middle oxfordian c. densiplicatum chronozone, c. vertebrale subzone (birkelund et al. 1971; callomon 1993). the base of the olympen formation is located just above a regional drowning surface at the turn-around point between the backstepping upper bajocian – upper callovian pelion–fossilbjerget formation couplet and the forestepping upper callovian – middle oxfordian olympen formation (surlyk 1991; 2003, this volume). the olympen formation records two marked progradational phases, one in the late callovian (p. athleta chronozone) and one in the early middle oxfordian (c. densiplicatum chronozone), separated by a drowning event in the early oxfordian (q. mariae chronozone). sedimentary facies recent field work has demonstrated that the upper bajocian – upper volgian package of the jameson land basin forms an overall transgressive–regressive cycle and that massive base-of-slope sandstones are developed in front of stacked, forestepping shelf-edge deltas from the late callovian and through the rest of the jurassic period (surlyk 2003, this volume). the facies of the olympen formation clearly fall within this spectrum of shelf-edge delta and slope deposits and are described below. 1 2 fossilbjerget fm olympen fm athene member olympen fm hades member olympen fm zeus member 3 4 5 6 7 8 9 nesw 50 m fig. 3. photomosaic of the type locality at olympelven on the south side of the glacier-covered mountain olympen. the positions of the measured vertical sections (1–9) are shown (see also fig. 4). 936 mud f m c gr mud f m c gr mud f m c gr mud f m c gr 1 2 3 4 10 20% n = 43 v = 191° 100 m 150 m300 m 500 m south delta top, zeus member planar cross-bedding t st h st hst fs st fs st –l st poor exposures sand sand sand sand fig. 4. north–south correlation panel of the olympen formation at the type locality. sheet-like beds of massive sandstone deposited from sediment gravity flows dominate the athene member. the hades member consists of silty mudstones with lenticular bodies of gravity flow sandstones (sections 7–9) and is overlain by cross-bedded, coarse-grained sandstones of the zeus member. the succession represents two cycles of slope and shelf-edge delta progradation. for legend, see fig. 2; n = number of measurements, -v = vector mean. 937 mud f m c gr mud f m c gr mud f m c gr mud f m c gr mud f m c gr 5 6 7 8 9 1020% n = 26 v = 151° 50 m 400 m 500 m 50 m north turbidites, athene member cross-lamination 10 m rse mfz tlst mfz sand sand sand sand sand hst highstand systems tract fsst falling stage systems tract lst lowstand systems tract tst transgressive systems tract mfz maximum flooding zone tlst top of lowstand surface rse regressive surface of erosion 938 facies 1. laminated mudstones the facies consists of dark brown or dark grey to black, micaceous, silty and sandy mudstones. they are generally well-laminated although the lamination is commonly disrupted by bioturbation. at some levels, the facies is heterolithic with alternating very fine-grained sandstone and mudstone laminae giving the facies a striped appearance (fig. 5a). locally the sandstone laminae pinch and swell with incipient ripple formsets some of which show cross-lamination. helminthoida isp. grazing or crawling traces occur in high densities on bedding planes. the mudstones have a total organic carbon (toc) content of 1–9% and a total sulphur (ts) content of 0.1–1.3%. the highest toc value is shown by a black finely laminated mudstone 2 m above the base of the hades member (fig. 2, section 3, 78 m). carbonate concretions are common and form isolated lenses or lensoid layers. they have nuclei of fossil wood and, in a few cases, ammonites. the mudstones contain rare belemnites, bivalves and ammonites. a marine, low diversity dinoflagellate cyst assemblage was described by fensome (1979). facies 1 is dominated by fine-grained sediment deposited from suspension. intervals of ripple cross-laminated siltstones and fine sandstones, however, indicate traction current action representing low-energy turbidity currents or weak bottom currents. facies 2. cross-laminated sandstones the facies consists of well-sorted, very fineor finegrained current ripple cross-laminated sandstone. set fig. 5. a: heterolithic mudstones and fine-grained sandstones (facies 1) intercalated with thin-bedded, massive sandstones (facies 4). the upper massive sandstone is strongly erosional and probably represents a local cut-and-fill. athene member, section 4. pencil is 14 cm long. b: fine-grained sandstones showing climbing ripple cross-lamination (facies 2). the sandstones are closely associated with laminated mudstones and parallel-laminated sandstones and represent low-density turbidites. scale is 10 cm long. a b 939 thickness normally varies from 0.5–2 cm, but may reach 4 cm. asymmetric ripple-formsets and climbing-ripple cross-lamination occur locally (fig. 5b). ripple asymmetry and orientations of foresets indicate a south to south-easterly palaeocurrent direction (fig. 4). the facies forms sandstone-dominated packages with gradational boundaries to facies 1. the rippled sandstones were deposited from low-density turbidity currents (bouma 1962) or weak bottom currents. the close association with mudstones of facies 1 suggests that the cross-laminated sandstones were deposited in a deep-water environment with only episodic sand deposition. facies 3. parallel-laminated sandstones the facies is composed of well-sorted, very fine-grained or fine-grained sandstones forming beds up to 60 cm thick. these beds show marked lateral changes in thickness from a few centimetres to 60 cm over a few tens of metres, and pinch-and-swell morphology is common. the thicker beds show parallel and low angle hummocky-like stratification associated with soft-sediment deformation structures including overturned folds. antidune lamination showing aggradation on the upslope side of low-angle bedforms and draping of previous topography by parallel-laminated sandstones is also represented. the parallel-laminated sandstones mainly have flat bases, but scouring occurs locally. the erosional topography is filled by laminated sandstones with divergent laminae thickening over the deepest part of the scour depressions. facies 3 is interpreted as having been deposited from low density turbidity currents (tb division; bouma 1962). some of the structures show a superficial resemblance to hummocky cross-stratification, but are interpreted as having been formed in the upper flow regime with plane bed deposition transitional to antidune bedding (skipper 1971; hand et al. 1972; prave & duke 1990). facies 4. massive sandstones the facies consists of white to light grey, micaceous, fineto medium-grained well sorted, massive sandstone beds commonly with a slightly graded, parallel-laminated top rich in disseminated plant material. two subfacies are recognised. subfacies 4a. sheet-like massive sandstones the subfacies includes sheet-like units of massive sandstones, up to 8 m thick, built up of amalgamated beds 0.5–2 m thick, or occasionally comprising single beds. the lower boundaries of the sandstone sheets are sharp, but typically flat and apparently non-erosional (fig. 6). the sandstone beds in general show parallel boundaries, but emplacement folds and local scouring sometimes occur at amalgamation surfaces (fig. 7a; heller & dickinson 1985). the individual sandstone beds are massive with grading in the uppermost few centimetres. the graded tops are rich in disseminated, carbonaceous plant material and commonly show deformation by water-escape and loading (fig. 7b). amalgamated beds may split into separate beds over a distance of a fig. 6. sheet-like units of amalgamated, massive, fine-grained sandstone beds (facies 4a) interbedded with mudstonedominated intervals (facies 1–3) in the athene member. note the sharp but apparently non-erosional lower boundary of the sandstones (arrows). the white sandstone bed in the centre of the photo is 8 m thick. section 1, 15–40 m above base of athene member (fig. 4). 940 2 cm fig. 7. a: amalgamated, massive, finegrained sandstone beds separated by thin carbonaceous levels in the lower part of the athene member (facies 4a). note the truncation of the lower beds in the centre of the photograph (arrows). person for scale. b: top of a massive sandstone bed (facies 4). note the horizon of carbonaceous plant material showing flow structures (arrow) overlain by parallel-laminated fine-grained sandstones. the top part shows a concentration of low-density organic material and the upwards change in structures suggest deposition from the waning phase of a turbidity current. the sharp base of the overlying bed is indicated by a dashed line. section 3. fig. 8. massive sandstone bed (facies 4), 12 m thick, forming the top of the athene member. the massive nature of the sandstone suggests deposition from either a sandy debris flow or a sustained high-density turbidity current. section 5; person (encircled) for scale. a b 941 few hundred metres. pyrite concretions, up to 3 cm in diameter, are common along the lower bed boundaries. in the upper part of the sandstone-dominated athene member, an up to 17 m thick massive sandstone bed is referred to facies 4a (fig. 8). the base of the bed shows evidence of loading, but only minor erosion. the massive sandstones are interpreted as the deposits of sediment gravity flows, either turbidity currents or sandy debris flows (lowe 1982; surlyk 1987; kneller & branney 1995). the graded tops with abundant carbonaceous plant material, however, suggest deposition from turbidity currents. this implies that the thick, ungraded part of each bed was probably formed by gradual aggradation of sand beneath a sustained steady or quasi-steady current (kneller & branney 1995). the largely planar and parallel lower and upper bed boundaries indicate that the flows were in a largely non-erosive stage and deposition probably occurred in a base-of-slope and basin floor setting (heller & dickinson 1985). the thicker beds commonly consist of amalgamated units, as indicated by horizons of carbonaceous plant material. emplacement folds between amalgamated sandstones suggest that the sands of the upper bed were emplaced upon the still largely unconsolidated substratum of the underlying bed (heller & dickinson 1985). the common occurrence of packets of amalgamated sandstones separated by thick mudstone units suggests that sandstone deposition occurred in discrete pulses separated by longer periods of background sedimentation of fines. fig. 9. gully fill (facies 4b) at the top of the middle unit (sections 7–9). a: large slab of mudstone lifted by intrusive sand at the base of the gully. the left side of the slab is partly in situ, whereas the right side is lifted and truncated. b: mudstone rip-up clast in the lower part of the gully fill sandstone. note the sharp lower boundary of the sandstone (arrows); hammer for scale. a b 942 subfacies 4b. lenticular massive sandstones the subfacies consists of lenticular sandstone bodies, up to 16 m thick, that fill deep erosional scours or gullies several tens of metres wide in cross-section. the most spectacular example occurs in the upper part of the hades member (fig. 4, section 7). at this locality, a large slab of mudstone is partially detached, and truncated by massive sands at the base of the gully fill (fig. 9a). the sandstone fill is massive, fineto medium-, or locally coarse-grained, and shows normal grading in the lower levels and at the top. floating well-rounded, oblate quartzite pebbles occur in the lower levels of one thick gully fill (fig. 2, section 7, 30 m). mudstone clasts ranging from a few millimetres to several metres in largest dimension occur scattered or in distinct horizons (fig. 9b). the larger clasts are found relatively close to the base of the sandstone beds. the mudstone clasts are commonly undeformed except for torn-up ends (fig. 10a), but sheared clasts occur along the lower margins of some beds. the axis of the gully exposed in section 7 strikes nw–se (137°). the massive sandstones grade upwards into parallel-laminated sandstones from a few centimetres to several metres thick, capped by cross-laminated sandstones (fig. 10b). the massive sandstone bodies were emplaced by sediment gravity flows (lowe 1982; kneller & branney 1995). the basal grading and the upwards change into parallel-laminated sandstones suggest deposition from sustained high-density turbidity currents (kneller & branney 1995) although a sandy debris flow origin is also possible. horizons of mudstone intraclasts may mark the forfig. 10. a: zones with aligned mudstone clasts in the lower part of the gully fill indicate that deposition occurred in pulses or as separate flows that followed shortly after one another. b: several metres thick unit of parallel-laminated fine-grained sandstones forming the top part of the gully fill, section 7. hammer (centre right) for scale. a b 943 mer position of the rising depositional flow boundary or may, in some cases, show the presence of thinner depositional units separated by subhorizontal amalgamation surfaces. the shape of the clasts shows that the adjacent mudstones were cohesive or partly consolidated at the time of gully erosion and sandstone deposition. facies 5.trough cross-bedded sandstones the facies consists of trough cross-bedded, mediumto coarse-grained sandstones with sets 10–15 cm thick, forming cosets up to 1.5 m thick. trough axes indicate palaeocurrent directions towards the south-east. bioturbation is common and includes diplocraterion habichi and skolithos isp. the facies is confined to the zeus member (fig. 2). the trough cross-sets are commonly located at the down-current termination of lenticular bodies of large-scale cross-bedded sandstones of facies 6. the facies was deposited by traction currents in the upper part of the lower flow regime. the trace fossil assemblage suggests a shallow marine environment. facies 6. large-scale cross-bedded sandstones the facies consists of coarse-grained sandstones showing large-scale cross-bedding with tangential, locally sigmoidal foresets (fig. 11). the thickness of the crossbeds varies from 0.4–6 m, but is mainly 2–4 m. the crosssets are composed of graded avalanche foresets that reach maximum dips of 26°. they pass downwards into carbonaceous, strongly bioturbated toesets. double mud drapes are found locally in the sandstones, but no systematic changes were recorded in foreset thicknesses. the cross-sets are commonly truncated at the top and are overlain by trough cross-bedded sandstones. in the upper part of the zeus member, wave-rippled topsets occur. dip azimuths of foresets indicate unimodal palaeocurrent directions towards the south with a vector mean of 191° (fig. 4). bioturbation is concentrated along set boundaries and shows high density and diversity. the trace fossil assemblage includes horizontal burrows of planolites isp., taenidium serpentinum, gyrochorte comosa, vertical burrows of diplocraterion habichi, skolithos isp. and the resting trace piscichnus ?kulindrichnus. the facies is only present in the zeus member (fig. 2). the large-scale cross-sets may pass downcurrent into trough cross-bedded sandstones of facies 5. the cross-beds were formed by southwards progradation of subtidal sand bodies, the top of which were periodically exposed to wave reworking indicating a water depth around wave base. comparison with similar facies in the volgian raukelv formation of southern jameson land (surlyk & noe-nygaard 1991) suggests that the cross-beds may form intrasets in large-scale compound foreset beds. facies successions the facies of the olympen formation form an overall progradational megacycle that is made up of two shallowing-upwards cycles: (1) the uppermost fossilbjerget formation together with the athene member and (2) fig. 11. cross-bedded, coarse-grained sandstones (facies 6) of the zeus member. individual sets are up to 3 m thick (locally up to 6 m), and are separated by heterolithic mudstones and fine-grained sandstones. foresets are commonly tangential with strongly bioturbated toesets and truncated topsets. section 3. 2 m the hades and zeus members of the olympen formation (fig. 2). they are described in turn and interpreted within the framework of the delta-fed turbidite ramp model of heller & dickinson (1985) and surlyk (1987). lower cycle the lower shallowing-upwards cycle is formed by the silty mudstones of the uppermost part of the fossilbjerget formation and the sharp-based, mainly massive sandstones (facies 4) intercalated with mudstones (facies 1) and fine-grained sandstones (facies 2 and 3) forming the athene member (fig. 2). the first sandstone bed is 4 m thick and abruptly overlies a uniform succession of silty mudstones, several tens of metres thick. above this level, massive sandstones of facies 4 dominate volumetrically. they are commonly amalgamated and may form units up to 17 m thick, whereas single beds may reach 8 m in thickness. the laterally persistent sheetlike beds of massive sandstone (facies 4a) dominate the lower part of the cycle, whereas the upper part of the cycle is characterised by thick, lenticular sandstones (facies 4b). a few beds of ripple cross-laminated sandstones (facies 2) and parallel-laminated sandstones (facies 3) are intercalated with mudstone units in the middle part of the cycle. the mudstones change from non-bioturbated to bioturbated c. 20 m above the base of the first sandstone bed. a marked change in facies occurs at the transition to the overlying mudstone-dominated association of the hades member and the top of the uppermost massive sandstone bed has been reworked into low-angle inclined sets. at locality 4 (fig. 4), an isolated cross-bedded coarse-grained sandstone bed is intercalated in mudstones, c. 2 m above the base of the upper cycle. the sandstones at the top of the lower cycle are intensively bioturbated and show a diverse trace fossil assemblage compared to the underlying sandstones. upper cycle the base of the upper cycle is marked by a sharp boundary between sandstones at the top of the athene member and dark silty mudstones of the hades member (facies 1; figs 2, 4). the mudstone-dominated lower portion is about 50 m thick and shows a slight coarsening-upwards trend in the upper 15 m. the most finegrained mudstones occur at 1.5 m and 6 m above the base of the cycle and are black, organic-rich (9% toc) and finely laminated. with these exceptions, the micarich mudstones are typically silty, locally sandy and intensely bioturbated. at locality 7 (fig. 4), the mudstones are succeeded by about 16 m of massive, fineto mediumgrained sandstones (facies 4b), which fill a deep erosional scour or gully cut into the mudstones (figs 4, 9). elsewhere, the mudstone succession is sharply overlain by a coarse-grained sandstone succession composed of stacked sets of large-scale cross-bedded sandstones (facies 6), trough cross-bedded sandstones (facies 5) and intercalated mudstones (facies 1; figs 2, 4). channelling and scouring are common. the coarse-grained sandstones are strongly bioturbated and show a diverse trace fossil assemblage. in the uppermost part of section 3 (fig. 4), wave-ripple formsets are common on the upper bedding planes of large-scale cross-sets. the uppermost part of the upper cycle is poorly exposed. isolated outcrops suggest, however, that the coarsegrained cross-bedded sandstone facies continues to the top of the formation. depositional model for the olympen formation the lower cycle represents late callovian progradation of a proximal basin and base-of-slope setting. the dominance of laterally continuous, massive, non-erosional gravity flow sandstones (facies 4a), and the lack of obvious vertical organisation of the sandstones suggest that they represent a proximal ramp facies of a deltafed turbidite system (heller & dickinson 1985; surlyk 1987). the shallow marine part of the delta front did not reach the present outcrop area and the interpretation is thus based on comparison with the upper cycle and with shelf-edge deltas and redeposited mass-flow sandstones of the volgian raukelv formation (surlyk & noe-nygaard 1995). the abrupt incoming of sandstones in the basin plain facies contrasts with the model of heller & dickinson (1985), which predicts a gradual increase in bed thickness and grain size from the basin plain – distal ramp facies to the proximal ramp. the concentration of pyrite concretions in the lower part of the cycle and the upwards change towards more bioturbated sediments suggests a change from a poorly oxygenated deeper-water setting into a more well-aerated, relatively shallow-water environment. a major drowning event occurred in latest callovian – early oxfordian times before the inferred shelf-edge delta of the lower cycle had reached the area of present-day outcrop. this was followed by renewed progra944 945 dation in the early–middle oxfordian. the relatively great thickness of the lower oxfordian basinal mudstones, which form the lower 50 m of the upper progradational cycle, suggests that the drowning event had translated the shelf edge far northwards. at olympen, shelf-edge delta progradation was heralded by the incoming of thick amalgamated slope sandstones with a strongly scoured base. they were probably deposited in a slope gully of the same type as described from the upper oxfordian part of the hareelv formation further south in jameson land (surlyk 1987; surlyk & noenygaard 2001). finally the shelf-edge delta reached the outcrop area as marked by the incoming of coarsegrained high-angle cross-beds. such beds are characteristic of lowstand deltas that prograded to the edge of the shelf in the middle jurassic (pelion formation; engkilde & surlyk 2003, this volume) and especially in the volgian (raukelv formation; surlyk & noe-nygaard 1991, 1995; surlyk et al. 1993; surlyk 2003, this volume). sequence stratigraphy a sequence stratigraphic interpretation of the olympen formation is not straightforward due to the relatively deep-water nature of most of the succession. the mudstones at the base of the lower cycle represent late callovian maximum flooding of the whole jameson land basin. the delta top of the lower unit is not preserved in jameson land. the slope and base-of-slope mass-flow sandstones were most likely deposited during late fall, maximum lowstand or early rise. thus, the base of the lower sandstone package may not necessarily represent the time of maximum sea-level lowstand and the correlative surface to the subaerial sequence boundary could be found within the sandstone package (hunt & tucker 1993, 1995). however, it has not been possible to define this deep-water correlative surface in the succession and present-day exposures do not allow tracing of the surface from the basin margin into the slope system. in our view, the sandstone succession is thus best interpreted as an undifferentiated falling stage and lowstand systems tract (fig. 4). the drowning surface at the top of the lower cycle is interpreted to represent the slope correlative of the transgressive surface defining the top of the lowstand systems tract. it probably passes up-dip into a ravinement surface, which extended across the inner shelf to the north. the thin organic-rich mudstone unit in the basal part of the second cycle represents the maximum flooding zone overlying a transgressive systems tract which is only a few metres thick (fig. 4). it is overlain by a thick coarsening-upwards mudstone-dominated highstand systems tract. the incoming of massive sandstones indicates that the delta had prograded to the shelf edge, and massive sands were shed down the slope from the delta front. the sharp base of the overlying cross-bedded delta front sandstones was possibly formed by marine erosion in front of the prograding delta and may represent a marine regressive surface of erosion (posamentier et al. 1992). the cross-bedded delta front sandstones (fig. 4) are thus tentatively placed in the falling stage systems tract (hunt & tucker 1993, 1995; nummedal et al. 1993). comparison with eustatic sea-level curves since the seminal work of vail et al. (1977; see miall 1997 for an overview), the validity of global sea-level curves has been extensively debated. however, as data from different regions are added and the dating of observed sea-level changes is refined, portions of the curve may prove to be eustatic. a regional sea-level curve for the jurassic of east greenland was presented by surlyk (1990) and compared with the eustatic curves of haq et al. (1988) and hallam (1988). sea-level changes based on the sequence stratigraphic interpretation of the olympen formation can be tied to ammonite chronozones and allow refinement of the regional sea-level curve for the late middle and early late jurassic of the jameson land basin of east greenland (fig. 12). the late jurassic part of the curve is supplemented with data from the charcot bugt formation in milne land situated at the western margin of the east greenland basin (larsen 1995; larsen et al. 2003, this volume). the sea-level changes recorded in the olympen formation include a sea-level rise in the middle callovian (k. jason chron), a late callovian fall (early–middle p. athleta and possibly q. lamberti chrons), an end callovian – early oxfordian rise (q. mariae chron) and a late early – middle oxfordian fall (c. densiplicatum chron) (fig. 12). these changes can be matched closely with a proposed eustatic sea-level curve for the central part of the russian platform (sahagian et al. 1996). the callovian part of the curve does not match the sealevel curve of haq et al. (1988), whereas the early oxfordian rise followed by middle oxfordian fall is recorded in all three curves (fig. 12). conclusions the upper bajocian – upper volgian succession in the jameson land basin, east greenland forms a long-term transgressive–regressive cycle with maximum flooding in the middle callovian and early kimmeridgian and regressive pulses in the late callovian, and the middle and late oxfordian. the upper callovian – middle oxfordian olympen formation represents the initial regression following middle callovian flooding. the formation consists of a tripartite sandstone–mudstone–sandstone package overlying upper callovian mudstones of the fossilbjerget formation. the top of the fossilbjerget formation and the lower sandstone-dominated athene member of the olympen formation together record late callovian progradation of the shelf-edge delta and slope towards the south. the delta top did not reach the area of present-day exposure, however, and the sandstone unit consists solely of massive gravity flow sandstones deposited on the slope and base-of-slope. progradation was terminated by a major early oxfordian drowning event. renewed progradation took place in the early–middle oxfordian heralded by slight coarsening-upwards of the hades member mudstones and the formation of erosional slope gullies filled with massive gravity flow sandstones, tens of metres thick. they are directly overlain by delta front and coarse-grained, cross-bedded delta top sandstones of the zeus member indicating that the delta finally reached the area. the athene member of the olympen formation represents an undifferentiated falling stage – lowstand systems tract. the drowning surface at the top of the athene member is interpreted as the top lowstand surface forming the distal correlative of the transgressive surface. a maximum flooding zone is recognised in the basal part of the mudstones of the hades member, followed by a thick, coarsening-upwards mudstone succession with lenticular bodies of massive sandstones representing the highstand systems tract. the sharp base of the overlying cross-bedded delta front sandstones of the zeus member is interpreted to represent a marine regressive surface of erosion, and the sandstones are tentatively placed in a falling stage systems tract. comparison of this history of middle callovian maximum flooding (k. jason chron), late callovian fall (early–middle p. athleta and possibly q. lamberti chrons), latest callovian – early oxfordian flooding (q. mariae chron) and late early – middle oxfordian (c. densiplicatum chron) regression with published eustatic sea-level curves suggests that the short-term changes can be matched within the resolution of ammonite zones. 946 geochronology haq et al. 1988 sahagian et al. 1996 this study chronozones g. transversarium c. tenuiserratum c. densiplicatum c. cordatumc. cordatum p. plicatilis q. mariaeq. mariae q. lambertiq. lamberti p. athleta short-term long-term p. athleta e. coronatume. coronatum k. jason s. calloviense k. jason s. calloviense chronozones low high low high low highageperiod submediterranean province boreal–subboreal province o xf o rd ia n la te ju ra ss ic m id dl e m id dl e m id dl e la te ea rl y ea rl y c al lo vi an ammonite dating fig. 12. comparison of sea-level curves for the callovian–oxfordian time interval based on the data in this study (east greenland), haq et al. (1988) (global) and sahagian et al. (1996) (russian platform). note the close correlation between short-term changes in the east greenland and russian platform curves. amplitudes of the curves have been rescaled for illustration purposes. ammonite zonation based on sykes & callomon (1979) and callomon (2003, this volume). 947 acknowledgements m.l. gratefully acknowledges a three-year ph.d. stipend from the carlsberg foundation (91-0683/20, 92-0505/20 and 93-0735/20). the danish natural science research council supported subsequent work. we wish to thank michael engkilde and john h. callomon for sedimentological and stratigraphic discussions and the referees, stephen p. hesselbo, kevin t. pickering and duncan pirrie, for their thorough reviews and suggestions to improve the manuscript. references birkelund, t., håkansson, e. & surlyk, f. 1971: new finds of bathonian, callovian and oxfordian ammonites in northern jameson land, east greenland. bulletin of the geological society of denmark 20, 240–259. bouma, a.h. 1962: sedimentology of some flysch deposits: a graphic approach to facies interpretation, 168 pp. amsterdam: elsevier. callomon, j.h. 1993: the ammonite succession in the middle jurassic of east greenland. bulletin of the geological society of denmark 40, 83–113. callomon, j.h. 2003: the middle jurassic of western and northern europe: its subdivisions, geochronology and correlations. in: ineson, j.r. & surlyk, f. 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(eds): siliciclastic sequence stratigraphy: recent developments and applications. american association of petroleum geologists memoir 58, 449–484. vail, p.r., mitchum, r.m., todd, r.g., widmier, j.m., thompson, s., sangree, j.b., bubb, j.n. & hatlelid, w.g. 1977: seismic stratigraphy and global changes of sea level. american association of petroleum geologists memoir 26, 49–212. 948 manuscript received 8 january 1998; revision accepted 23 february 1999. danmarks og grønlands geologiske undersøgelse (geus) geological survey of denmark and greenland øster voldgade 10, dk-1350 copenhagen k denmark geological survey of denmark and greenland bulletin is a new series started in 2003 to replace the two former bulletin series of the survey, viz. geology of greenland survey bulletin and geology of denmark survey bulletin. the twenty-one volumes published since 1997 in those two series are listed below, followed by titles in the new bulletin series. the new series, together with geological 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short dahl-jensen et al. 2021: geus bulletin 47. 5552. https://doi.org/10.34194/geusb.v47.5552 1 of 8 monitoring for seismological and geochemical groundwater effects of high-volume pumping of natural gas at the stenlille underground gas storage facility, denmark trine dahl-jensen1* , rasmus jakobsen1 , tina bundgaard bech1 , carsten møller nielsen1 , christian nyrop albers1 , peter h. voss1 , tine b. larsen1 1geological survey of denmark and greenland (geus), copenhagen, denmark abstract the large natural gas storage facility at stenlille, denmark, has been monitored to investigate the effect of pumping large amounts of gas into the subsurface. here, we present a new dataset of microseismicity at stenlille since 2018. we compare these data with methane in groundwater, which has been monitored since gas storage was established in 1989. further, we conducted a controlled 172 day microcosm experiment of methane oxidation on an isolated microbial community under both aerobic and anaerobic conditions. for this experiment, water was filtered from a well at stenlille with elevated levels of thermogenic methane and ethane. no microseismic activity was detected in the gas storage area above an estimated detection level of ml 0.0 for the established network. the long-term monitoring for methane in groundwater has still only detected one leak, in 1995, related to a technical problem during injection. the microcosm experiment revealed that oxidation of methane occurred only under aerobic conditions during the experiment, as compared to anaerobic conditions, even though the filtered water was anoxic. introduction storage of co2 in the subsurface as a means of reducing co2 in the atmosphere receives great international interest. therefore, there is a need for knowledge about how the subsurface behaves when large volumes of gas are pumped into reservoirs accompanied by potential contamination of groundwater aquifers. in denmark, the primary onshore interest focusses on sandstone reservoirs, with the gassum formation as a prime candidate (hamberg & nielsen 2000). the stenlille underground gas storage facility (fig. 1a) provides an opportunity to monitor the effects of large-volume pumping; while the gas pumped is natural gas and not co2, the volume pumped is large and can provide information about the effects of pumping activity on both groundwater geochemistry and microseismic activity. leakage is also important to monitor because groundwater aquifers are sensitive to changes (datry et al. 2004), and therefore increases in methane as well as trace concentrations of other alkanes may alter the groundwater ecosystem. groundwater aquifers are complex ecosystems that are of critical importance for geochemical cycles (griebler & lueders 2009). therefore, it has been important to monitor for hydrocarbons in the shallow groundwater *correspondence: tdj@geus.dk received: 08 sep 2020 accepted: 16 feb 2021 published: 22 mar 2021 keywords: co2 storage, carbon capture, geochemical monitoring, induced earthquakes, natural gas storage abbreviations: gc-fid: gas chromatography flame ionization detector ml: local magnitude mb: body wave magnitude geus bulletin is an open access, peerreviewed journal published by the geological survey of denmark and greenland (geus). this article is distributed under a cc-by 4.0 licence, permitting free redistribution, and reproduction for any purpose, even commercial, provided proper citation of the original work. author(s) retain copyright. edited by: stefanie lode (geus) reviewed by: aaron cahill (heriot-watt university, uk) and one anonymous reviewer funding: see page 7 competing interests: none declared additional files: see page 7 https://doi.org/10.34194/geusb.v47.5552 https://orcid.org/000-002-0800-3105 https://orcid.org/0000-0003-1882-2961 https://orcid.org/0000-0001-8031-9326 https://orcid.org/0000-0002-1525-1385 https://orcid.org/0000-0001-7253-3509 https://orcid.org/0000-0002-6689-564x https://orcid.org/0000-0001-8240-337x mailto:tdj@geus.dk dahl-jensen et al. 2021: geus bulletin 47. 5552. https://doi.org/10.34194/geusb.v47.5552 2 of 8 w w w . g e u s b u l l e t i n . o r g because of the underground gas storage, and thereby detect possible impacts on this environment. here, we present a new dataset of microseismicity at stenlille since 2018 and compare these data with methane in groundwater, which has been monitored since gas storage was established in 1989. further, we report on a controlled 172 day microcosm experiment of methane oxidation on an isolated microbial community under both aerobic and anaerobic conditions. stenlille underground gas storage facility the stenlille underground gas storage facility is located 70 km south-west of copenhagen, operated by gas storage denmark a/s (fig. 1a). it was established in 1989 to buffer the supply of gas from the north sea and has since been re-developed to increase storage capacity. today, a total of 20 deep wells operate at the facility. fourteen wells are deployed for injection and withdrawal of gas and six wells are used for observational purposes. most observation wells are located in the periphery of the site (fig. 1b; laier & øbro 2009). the storage at stenlille is an anticlinal structure shaped by salt tectonics. a vertical closure of c. 35 m covers an area of 14 km2 (fig. 1c). the reservoir is formed in the upper triassic – lower jurassic gassum sandstone formation, where gas is stored by displacing formation water. the top gassum surface is located 1500–1600 m below ground level. the gassum formation consists of cyclically interbedded sandstone and marine mudstone deposited in a changing depositional environment (hamberg & nielsen 2000). the formation has excellent reservoir properties due to the overlying 300 m thick lower jurassic fjerritslev formation. it consists of claystone and hence serves as a caprock for the sandstone reservoir. the total estimated storage capacity of the stenlille structure equals three billion normal cubic metres (nm3), and due to reservoir heterogeneities, gas is stored in several separate zones. for safety and environmental reasons, the storage operation is monitored carefully. no sign of gas leakage has been observed in a monitoring well located in a sand stringer 15 m above the gas reservoir (laier & øbro 2009). other wells are monitored for possible lateral escape of natural gas. a baseline study of naturally occurring hydrocarbons (laier & øbro 2009) performed before the stenlille facility came into operation indicated the presence of only trace amounts hydrocarbon gases (in the form of biogenic methane) in the subsurface of the stenlille facility. the current amount of gas stored is just under 1600 mnm3, with an annual injection and extraction of close to 500 mnm3. the pumping rates typically vary between 100 and 250 knm3/h but with extraction rates occasionally going up to 400 knm3/h (fig. 1d). the detailed pumping activity for the individual wells for the period summer 2018 to summer 2019 can be seen in supplementary file s1. methods seismological monitoring during august and september 2018, we established a seismic network for monitoring microseismicity around the stenlille underground gas storage facility. the network consists of six seismographs placed within 5 km of the main pumping facility (fig. 1b). data for the period 1 october 2018 to 31 march 2020 have been screened for events, using the condet code (havskov et al. 2020). the screening triggers several hundred times on the data. the triggers are very unevenly spaced in time, depending not only on actual seismic events, but also on thunderstorms and noise. a manual screening of the triggered events resulted in 32 locatable seismic events and a large number of acoustic events related to thunderstorms. geochemical monitoring monitoring for hydrocarbons has been carried out monthly from 1989 to 1994, followed by quarterly measurements thereafter by the geological survey of denmark and greenland (geus). shallow groundwater is monitored from private drinking water wells, groundwater wells supplying waterworks in the vicinity of the gas storage and observation wells at stenlille. the two observation wells, k1 and k2, were established where the risk of leakage was considered highest. observation well k1 allows water samples to be taken from melt-water sand at 36 m depth and at 98 m in paleocene calcareous sand (fig. 2). observation well k2 was established in 1993 with a screen in the melt-water sand at a depth of 25–39 m (fig. 2). groundwater was sampled quarterly in 15 ml serum bottles with rubber septa and stored at 5°c until analysis within two days of sampling. analysis of c1–c4 hydrocarbons was done by gas chromatography flame ionization detection (gc-fid) on a shimadzu gc2010 equipped with a capillary column (gs-gaspro, 60 m, 0.32 mm) with a detection limit of 2 µg/l for both methane and larger hydrocarbons. microcosm experiment a total of 2400 l of groundwater was pumped and filtered over a glass fibre filter with a pore size of 0.3 µm and 293 mm in diameter (sterlitech, kent, washington, usa) using a submersible pump (grundfos mp1, grundfos, bjerrringbro, denmark). the pump rate was 8–10 l  min-1 (september 2019). the filter was stored https://doi.org/10.34194/geusb.v47.5552 http://www.geusbulletin.org dahl-jensen et al. 2021: geus bulletin 47. 5552. https://doi.org/10.34194/geusb.v47.5552 3 of 8 w w w . g e u s b u l l e t i n . o r g fig. 1 location, site details and pumping activity at the stenlille underground gas storage facility. a: the stenlille facility is located on sjælland, denmark (red hexagon) b: well locations and extension of the different gas zones at the stenlille underground gas storage facility. contour lines indicate depth in metres to the top gassum formation. red triangles indicate the stenlille seismic network seismographs deployed as part of the secure project. seismographs are within 5 km of the main pumping station (ste00). st-01 to -20 are wells and ste01–06 are seismic stations. modified from gas storage denmark a/s 2018 (fig. 2.2). c: the cross-section of the stenlille underground gas storage facility. prod.: production well. obs.: observation well. modified from gas storage denmark a/s 2018 (fig. 2.1). d: history of pumping activity at stenlille. modified from gas storage denmark a/s 2018 (fig. 3.1). 0 1 km n legend zone 1–3 gas wells zone 5 gas wells observation well (reservoir) observation well (cap rock) fault gas zone 1–3 (estimated nov. 2011) gas zone 5 (estimated nov. 2011) 15 00 15 00 14 90 149 0 148 0 14 70 14 60 1470 1460 1450 148 0 14 60 ste05 b ste00 ste01 ste02 ste06 ste03 st-06 st-01 st-05st-02 st-03 st-09 st-16 st-17 st-19 st-12 st-10 st-13 st-14 st-11 st-18 st-20 st-04 st-15 st-08 st-07 d 800 0 1600 t o ta l g a s [ m io n m 3 ] gas extraction 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015 2017 1570 clay, sealing d e p th ( m b e lo w s e a l l e ve l) d e p th (m b e lo w se a l le ve l) 0 1550 1530 1510 1490 1470 1450 nw c se 1570 1550 1530 1510 1490 1470 1450 1 2 3 4 5 6 7 8 9 gas sand clay/silt, partly sealing obs. st-15 obs. st-4 prod. st-17 prod. st-11 prod. st-7 prod. st-1 storage zone 1 2b 3 4 5 6 obs. st-6 prod. st-19 7˚e 15˚e 54˚n 58˚n stenlille a https://doi.org/10.34194/geusb.v47.5552 http://www.geusbulletin.org dahl-jensen et al. 2021: geus bulletin 47. 5552. https://doi.org/10.34194/geusb.v47.5552 4 of 8 w w w . g e u s b u l l e t i n . o r g paleocene calcareous sand paleocene marine clay glacial till meltwater sand 500 m level (m) 60 40 20 0 –20 –40 –60 –80 k2 k1 wsw ene fig. 2 geological cross-section of the upper layers of the stenlille underground gas storage facility. approximate location and depth of monitoring screens in k1 and k2 are shown. the red shading indicates the probable distribution of gas after a leakage event at st-14 in august 1995. modified from the work of laier (2012). cold after sampling and microcosms were setup within 24 hours. the filter was divided into 24 fragments, and each part was placed in a 583 ml flask containing 90 ml of groundwater and 10 ml of salt solution. the concentrations in each microcosm were 0.62 mm mgso4•7h2o, 0.99 mm kno3, 0.88 mm nh4cl, 0.18 mm nahco3, 0.51 mm nacl, 0.52 mm cacl2•2h2o, 5.00 mm caco3 and 0.50 mm fe(iii)ooh. flasks were crimp sealed with butyl rubber stoppers and flushed with he before a controlled headspace was created comparing (1) untreated control, (2) ch4 and (3) ch4 and c2h6 under both aerobic and anaerobic conditions. flasks were incubated in the dark at 10°c on a rotational shaker at 75 rpm. during incubation, the concentrations of ch4, c2h6, o2 and co2 was quantified by gc-fid. results and discussion seismological events of the 32 located events, 20 were previously known (both earthquakes and explosions) and occurred close to stenlille (fig. 3) or were large enough and had a frequency content within the range used to trigger on the stenlille stations alone. twelve previously unknown and ‘spurious events’ (events of unknown origin) were found. these were only observed on the stenlille network along with many similar events, which could not be located. none of the events found are within the stenlille underground gas storage facility (fig. 3). the events identified are of a local magnitude (ml) of –0.2 to 2.5. a distant event with body wave magnitude (mb) 6.7 is observed and two regional events of ml 3.5 and ml 2.8 were also observed. the newly identified spurious events are all smaller than ml 1.0. a full list is provided in supplementary file s2. earthquakes and explosions these events, detected by screening the stenlille network, were all previously located by the routine monitoring of the danish seismic service. the fact that these events were also detected by independent screening of the stenlille seismic network confirms the fact that the network is capable of detecting such events (fig. 3). spurious events these events all have magnitudes smaller than ml 1 (fig. 3) – most are much smaller and all have similar signals, with strangely low frequencies in the range of 10 hz. this is much lower than expected for such small events. we do not know the cause of these events and their locations have an uncertainty of up to tens of kilometres. nonetheless, due to the difference in p and s wave arrival times (which relates to the distance from the station to the event; data not shown) we are convinced that they do not originate within the area of the stenlille underground gas storage facility. correlation with pumping we have detailed information on the pumping activity at the stenlille underground gas storage facility (see supplementary file s1). however, we observe no seismic events in the immediate vicinity of the stenlille facility, and so it is not possible to correlate events at stenlille with pumping activity. detection level in order to determine the detection level within the area covered by the stenlille facility we have used 10 natural earthquakes detected by the stenlille network. https://doi.org/10.34194/geusb.v47.5552 http://www.geusbulletin.org dahl-jensen et al. 2021: geus bulletin 47. 5552. https://doi.org/10.34194/geusb.v47.5552 5 of 8 w w w . g e u s b u l l e t i n . o r g the equation for calculating the ml for earthquakes in denmark is: ml = 0.925 × log10(a) + 1.61 log10(δ) – 2.38 (1) where a is the maximum amplitude of the s and surface wave arrival train in nm and δ is the distance in km (gregersen 1999). using the amplitude actually observed at each of the stenlillle stations for each of the 10 natural earthquakes and calculating what ml would be at distances covering the stenlille gas storage area, we obtain a series of estimates at which magnitudes it would be possible to see if the events occurred within the stenlille gas storage facility. the complete set of calculations are provided in supplementary file s3. average values for all earthquakes and stations are shown in table 1. we estimate the detection level of the stenlille seismic network to be at least ml 0.0. examples of noise analysis can be found in supplementary file s4. 8˚e 8˚e 9˚e 9˚e 10˚e 10˚e 11˚e 11˚e 12 e̊ 12˚e 13 e̊ 13˚e 14˚e 54˚n 54˚n 55˚n 55 n̊ 56˚n 56 n̊ 57˚n 57˚n 0 50 kmmagnitude 4 magnitude 3 magnitude 2 magnitude 1 fig. 3 seismological events detected by screening data from the stenlille seismic network. blue: earthquakes. light blue: explosions or presumed explosions. lilac: spurious events. red: earthquakes and explosions found by the danish seismological service in the period october 2018 to march 2020. triangles are seismological stations. dark green: the stenlille network. yellow: raspberry shake stations. light green: permanent stations in national networks. table 1 observed local magnitude (ml) around stenlille natural gas storage facility distance (km) 1 2 3 4 5 6 7 8 9 10 average observed ml (no units) –1.2 –0.7 –0.4 –0.2 0.0 0.1 0.2 0.3 0.4 0.4 https://doi.org/10.34194/geusb.v47.5552 http://www.geusbulletin.org dahl-jensen et al. 2021: geus bulletin 47. 5552. https://doi.org/10.34194/geusb.v47.5552 6 of 8 w w w . g e u s b u l l e t i n . o r g why are no events observed at stenlille? the stenlille network has, through 18 months of monitoring, not registered any seismic events within the stenlille underground gas storage facility. the detection level is estimated to be at or below ml 0.0, meaning that any missed events are very small. geus has monitored for earthquakes in denmark for many years, and no earthquake has ever been located at stenlille, bearing in mind that the detection level for the national monitoring network is higher at ml 2.0 (dahl-jensen et al. 2013; voss et al. 2015). the stenlille facility has been operational since 1989, pumping up to 500 mnm3 of gas in and out (fig. 1d) and has to our knowledge never received a complaint about shaking. we do not know the reason for the lack of events, but we can speculate. of course, events below our detection level could be occurring. it is possible that during the operation of the monitoring network, after almost 30 years of pumping, all stresses have long since been relieved. possibly events did occur early in the storage facility’s life. the stresses in the subsurface, both natural and established by the pumping itself, are too small to trigger earthquakes. geochemistry: preliminary results and longterm monitoring prior to operational onset the background concentration in the groundwater aquifers at stenlille contained only biogenic methane with concentrations <0.5 mg/l (laier & øbro 2009). hence, leaks from the gas storage site are simple to monitor due to low methane background concentrations and the lack of higher hydrocarbons. the injected gas consists of methane (89.5%), ethane (6.9%) and propane (2.6%; laier & øbro 2009); therefore, traces of ethane in groundwater would be a sensitive indicator of gas leakage. the analytical detection limit is c. 2 µg/l. during the 30 years of operation, there has only been one known leakage. in september 1995 there was a leak due to technical problems during gas injection, and even though it was quickly stopped, an estimated 5000 nm3 were lost to geological formations above the k1 m g c h 4 /l 0 2 4 6 8 10 98–128 m 36–46 m k2 1 9 9 0 1 9 9 1 1 9 9 2 1 9 9 3 1 9 9 4 1 9 9 5 1 9 9 6 1 9 9 7 1 9 9 8 1 9 9 9 2 0 0 0 2 0 0 1 2 0 0 2 2 0 0 3 2 0 0 4 2 0 0 5 2 0 0 6 2 0 0 7 2 0 0 8 2 0 0 9 2 0 1 0 2 0 1 1 2 0 1 2 2 0 1 3 2 0 1 4 2 0 1 5 2 0 1 6 2 0 1 7 2 0 1 8 2 0 1 9 2 0 2 0 m g c h 4 /l 0.0 0.1 0.2 0.3 0.4 0.5 25–39 m fig. 4 methane concentration in groundwater from monitoring wells k1 (91–128 m and 36–46 m depth) and k2 (25–39 m depth). in 1995, methane concentrations reached 27 mg/l in the deep k1 screen. https://doi.org/10.34194/geusb.v47.5552 http://www.geusbulletin.org dahl-jensen et al. 2021: geus bulletin 47. 5552. https://doi.org/10.34194/geusb.v47.5552 7 of 8 w w w . g e u s b u l l e t i n . o r g reservoir cap rock. for further details see the work of laier & øbro (2009). this leak has resulted in elevated thermogenic methane and ethane concentrations in the deep k1 monitoring with a decreasing trend since 1995 as shown in fig. 4. methane in groundwater aquifers can have different origins. thermogenic methane can rise from deeper or shallower hydrocarbon reservoirs into shallow sediment layers and aquifers due to natural gas migration, as observed from contamination in the deep k1 well. biogenic methane originates from methanogens that produce methane from acetate or hydrogen and co2 released when other microorganisms ferment organic matter in anoxic subsurface systems (beeman & suflita 1990; kleikemper et al. 2005). biogenic methane is detected in the k2 screen. during migration, methane can be oxidized by methanothrophic bacteria or archaea. this oxidation may occur aerobically in the presence of oxygen or anaerobically with nitrate, sulphate, and oxidized forms of iron and manganese. because the energetics of the anaerobic process are severely constrained, the process can take place only through syntrophic cooperation, involving interspecies electron transfer or other interdependencies. accordingly, anaerobic methane-oxidizing archaea organisms have never been obtained in pure cultures (knittel & boetius 2009). even though methane is often detected in groundwater with reducing redox conditions there is limited literature on methane oxidation in groundwater compared to marine and freshwater sediments. hence, from the thermogenic impacted k1 well, isolated microbial communities were established in controlled microcosms under both aerobic and anaerobic conditions to compare methane and ethane oxidation at stenlille. the concentration of methane and ethane were monitored for 172 days. during the incubation study the average methane oxidation rate was 35.97 µmol l-1 day-1 and 27.99 µmol l-1 day-1 in a headspace of methane or methane and ethane, respectively. the average ethane oxidation rate was 11.07 µmol l-1 day-1. oxidation of ch4 occurred only under aerobic conditions even though the isolated microbial community was adapted to anaerobic conditions from the k1 well. further, the added salt solution contained no3, so4 and fe(iii) that have been shown to work as an electron acceptor during anaerobic methane oxidation. lack of methane oxidation under anaerobic conditions has been observed elsewhere (cahill et al. 2017; kuloyo et al. 2020). implications for future co2 gas storage sites in denmark we report no seismic events at the stenlille facility during the monitoring period (october 2018 to may 2020) and no sign of elevated methane concentrations in the shallow groundwater that could be linked to operational activities. further, if small leaks are occurring from the underground storage there is a natural capacity in the microbial subsurface community to oxidize methane as observed in our microcosm experiments. based on our results, this oxidation will most likely take place in the transition zone between aerobic and anaerobic conditions, or potentially by an anaerobic community not captured in our experimental setup. it is important to detect leakage immediately. the seismic method described facilitates an online continuous detection and could be combined with additional geochemical sampling. this could supplement the quarterly monitoring, triggered by registered seismic events of a certain magnitude and location. this does not imply that seismic events necessarily lead to leakage, but it could be an additional tool to increase the likelihood of rapidly detecting a leak. acknowledgements the authors thank gas storage denmark a/s for hosting a seismic station and providing them with pumping data and methane samples. they are also thankful to the residents in the vicinity of the stenlille underground gas storage facility who kindly allowed them to place seismic monitoring stations on their properties. funding this work was carried out as part of the eu project secure, funded by the european union’s horizon 2020 research and innovation program under grant agreement number 764531. author contributions tdj: conceptualization, formal analysis, investigation, methodology, resources, visualization, writing – original draft, writing – review & editing. rj: resources, supervision, writing – review & editing. tib: data curation, methodology, visualization, writing – original draft, writing  – review & editing. cmn: conceptualization, project administration, writing – original draft, writing – review & editing. cal: data curation, investigation, writing – original draft. pv: conceptualization, data curation, formal analysis, investigation, software, writing – review & editing. tbl: data curation, formal analysis, investigation, writing – review & editing additional files four additional files are available at https://doi.org/10.22008/fk2/t2251f references beeman, r.e. & suflita, j.m. 1990: environmental factors influencing methanogenesis in a shallow anoxic aquifer: a field and laboratory study. journal of industrial microbiology 5(1), 45–57. https://doi. org/10.1007/bf01569605 cahill, a.g., steelman, c.m., forde, o., kuloyo, o., ruff, s.e., mayer, b., mayer, k.u., strous, m., ryan, m.c. & cherry, j.a.j.n.g. 2017: mobility and persistence of methane in groundwater in a controlled-release field experiment. nature geoscience 10(4), 289–294. https://doi. org/10.1038/ngeo2919 dahl-jensen, t., voss, p.h., larsen, t.b. & gregersen, s. 2013: seismic activity in denmark: detection level and recent felt earthquakes. geological survey of denmark and greenland bulletin 28, 41–44. https:// doi.org/10.34194/geusb.v28.4717 datry, t., malard, f. & gibert, j. 2004: dynamics of solutes and dissolved oxygen in shallow urban groundwater below a stormwater https://doi.org/10.34194/geusb.v47.5552 http://www.geusbulletin.org https://doi.org/10.22008/fk2/t2251f https://doi.org/10.1007/bf01569605 https://doi.org/10.1007/bf01569605 https://doi.org/10.1038/ngeo2919 https://doi.org/10.1038/ngeo2919 https://doi.org/10.34194/geusb.v28.4717 https://doi.org/10.34194/geusb.v28.4717 dahl-jensen et al. 2021: geus bulletin 47. 5552. https://doi.org/10.34194/geusb.v47.5552 8 of 8 w w w . g e u s b u l l e t i n . o r g infiltration basin. science of the total environment 329(1–3), 215– 229. https://doi.org/10.1016/j.scitotenv.2004.02.022 gas storage denmark a/s. 2018: stenlille gaslager – undergrunden årsrapport 2017 rep. unpublished company report for gas storage denmark (in danish only). gregersen, s. 1999: national survey and cadastre (kms), copenhagen, denmark. in: emsc-csem newsletter no 15. european-mediterranean seismological centre. griebler, c. & lueders, t. 2009: microbial biodiversity in groundwater ecosystems. freshwater biology 54(4), 649–677. https://doi. org/10.1111/j.1365-2427.2008.02013.x hamberg, l. & nielsen, l.h. 2000: shingled, sharp-based shoreface sandstones: depositional response to stepwise forced regression in a shallow basin, upper triassic gassum formation, denmark. geological society, london, special publications 172, 69–89. https://doi. org/10.1144/gsl.sp.2000.172.01.04 havskov, j., voss, p.h. & ottemöller, l. 2020: seismological observatory software: 30 yr of seisan. seismological research letters 91(3), 1846–1852. https://doi.org/10.1785/0220190313 kleikemper, j., pombo, s.a., schroth, m.h., sigler, w.v., pesaro, m. & zeyer, j. 2005: activity and diversity of methanogens in a petroleum hydrocarbon-contaminated aquifer. applied and environmental microbiology 71(1), 149–158. https://doi.org/10.1128/ aem.71.1.149-158.2005 knittel, k. & boetius, a. 2009: anaerobic oxidation of methane: progress with an unknown process. annual review of microbiology 63(1), 311–334, https://doi.org/10.1146/annurev.micro.61.080706. 093130 kuloyo, o., ruff, s.e., cahill, a., connors, l., zorz, j.k., hrabe de angelis, i., nightingale, m., mayer, b. & strous, m. 2020: methane oxidation and methylotroph population dynamics in groundwater mesocosms. environmental microbiology 22(4), 1222–1237. https:// doi.org/10.1111/1462-2920.14929 laier, t. 2012: results of monitoring groundwater above the natural gas underground storage at stenlille, denmark. geological survey of denmark and greenland bulletin 26, 45–48. https://doi.org/10.34194/ geusb.v26.4748 laier, t. & øbro, h. 2009: environmental and safety monitoring of the natural gas underground storage at stenlille, denmark. geological society, london, special publications 313(1), 81–92. https://doi. org/10.1144/sp313.6 voss, p., dahl-jensen, t. & larsen, t.b. 2015: earthquake hazard in denmark. unpublished geological survey of denmark and greenland report, 2015/24, p. 53. copenhagen: geological survey of denmark and greenland. https://doi.org/10.34194/geusb.v47.5552 http://www.geusbulletin.org https://doi.org/10.1016/j.scitotenv.2004.02.022 https://doi.org/10.1111/j.1365-2427.2008.02013.x https://doi.org/10.1111/j.1365-2427.2008.02013.x https://doi.org/10.1144/gsl.sp.2000.172.01.04 https://doi.org/10.1144/gsl.sp.2000.172.01.04 https://doi.org/10.1785/0220190313 https://doi.org/10.1128/aem.71.1.149-158.2005 https://doi.org/10.1128/aem.71.1.149-158.2005 https://doi.org/10.1146/annurev.micro.61.080706.093130 https://doi.org/10.1111/1462-2920.14929 https://doi.org/10.1111/1462-2920.14929 https://doi.org/10.34194/geusb.v26.4748 https://doi.org/10.34194/geusb.v26.4748 https://doi.org/10.1144/sp313.6 https://doi.org/10.1144/sp313.6 monitoring for seismological and geochemical groundwater effects of high-volume pumping of natural g abstract introduction stenlille underground gas storage facility methods seismological monitoring geochemical monitoring microcosm experiment results and discussion seismological events earthquakes and explosions spurious events correlation with pumping detection level why are no events observed at stenlille? geochemistry: preliminary results and long-term monitoring implications for future co2 gas storage sites in denmark acknowledgements funding author contributions additional files references figures fig. 1 location, site details and pumping activity at the stenlille underground gas storage facility fig. 2 geological cross-section of the upper layers of the stenlille underground gas storage facilit fig. 3 seismological events detected by screening data from the stenlille seismic network. blue: ear fig. 4 methane concentration in groundwater from monitoring wells k1 (91-128 m and 36-46 m depth) an table table 1 observed local magnitude (ml) around stenlille natural gas storage facility geological survey of denmark and greenland bulletin 1, 611-630 611 maturation of organic matter with increasing temperature is one of the most important parameters when evaluating the thermal history and hydrocarbon potential of a basin. a common way to assess the maturation depthtrend is to construct coalification curves by plotting measured huminite/vitrinite reflectances against depth. various attempts have been made to construct such curves for the danish basin and the fennoscandian border zone (thomsen 1980; thomsen et al. 1983, 1987; schmidt 1985). however, these attempts have to some extent overlooked the significant amounts of post-early cretaceous differential uplift that have influenced the danish basin and the fennoscandian border zone. forchhammer (1835) recognised the pronounced erosional unconformity at the base of the quaternary. the hiatus at this surface increases significantly towards the northern and eastern margin of the danish basin. it is now widely accepted that significant regional uplift occurred in neogene and pleistocene times in the north atlantic area and along the norwegian west coast into the burial depth and post-early cretaceous uplift of lower–middle jurassic strata in the fennoscandian border zone based on organic maturity henrik i. petersen, lars h. nielsen,torben bidstrup and erik thomsen the burial depth and the magnitude of late cretaceous – early cenozoic and neogene–pleistocene uplift of lower–middle jurassic strata in the fennoscandian border zone are estimated from measurements of huminite reflectance and comparison with a regional coalification gradient. the regional coalification curve is constructed by plotting uplift-corrected sample depths against more than 300 huminite/vitrinite reflectance values from upper triassic – lower cretaceous deposits in the danish basin and the fennoscandian border zone. the present sample depths are corrected for late cretaceous inversion in the sorgenfrei–tornquist zone and for neogene–pleistocene regional uplift. a coalification curve is erected; it cuts the abscissa at 0.2 %ro corresponding to the reflectance of peat. this curve is considered to approximate to a reliable coalification profile over much of the study area. the jurassic coals from the fennoscandian border zone are of low rank and, based on the regional coalification curve, they have been buried to c. 625–2450 m. in the eastern part of the rønne graben, in the kolobrzeg graben and in the arnager–sose fault block, the jurassic strata were subsequently uplifted c. 290–1400 m, corresponding to the amount of late cretaceous – early cenozoic inversion observed on seismic sections. thus, it appears that neogene–pleistocene uplift did not influence the bornholm area significantly. the data from the höganäs basin and fyledal indicate a total uplift of c. 1450–2450 m, corresponding to estimates from the inversion zone in the kattegat. the data from anholt, on the eastern margin of the inversion zone, indicate c. 975 m of uplift. keywords: danish basin, fennoscandian border zone, lower–middle jurassic, organic maturity, coalification curve, burial depth, late cretaceous – early tertiary inversion, neogene–pleistocene uplift geological survey of denmark and greenland, geocenter copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: hip@geus.dk geological survey of denmark and greenland bulletin 1, 611–630 (2003) © geus, 2003 612 skagerrak and the kattegat to the swedish coast (manum & throndsen 1978; jensen & michelsen 1992; jensen & schmidt 1992, 1993; nyland et al. 1992; japsen 1993, 1998; michelsen & nielsen 1993). in addition to the regional neogene–pleistocene uplift, significant inversion occurred in the sorgenfrei–tornquist zone in late cretaceous – early cenozoic times due to right-lateral transpression (liboriussen et al. 1987; norling & bergström 1987; eugeno-s working group 1988; michelsen & nielsen 1991, 1993; mogensen 1994). the amount and distribution of the two types of uplift of the danish basin and sorgenfrei–tornquist zone have been estimated by comparing the lateral variation of the sonic velocities of a uniform unit of lower jurassic marine mudstones with the structural and stratigraphic development of the area (jensen & michelsen 1992; japsen 1993; michelsen & nielsen 1993). these estimates indicate uplift of 100–2000 m, emphasising that variable amounts of uplift have to be considered when huminite/vitrinite reflectances are used to interpret the thermal history and predict maturity of undrilled sections. we have used 311 reflectance measurements (corrected for uplift) from 20 well-sections (fig. 1) in order to construct a reliable coalification curve which can be used to evaluate the thermal history and maturation of organic matter in the danish basin and the fennoscandian border zone. the amount of uplift was primarily estimated from seismic interval velocities (japsen 1993). the aims of the paper are: (1) to construct a regional coalification curve for the danish basin and the fennoscandian border zone and (2) to use the curve to estimate the burial depth and later uplift of lower–middle jurassic strata exposed or cored in shallow wells in the fennoscandian border zone by comparing huminite reflectances with the curve. the maturation of organic matter provides the best estimate of the burial and uplift history, as measurements of sonic velocities in general are not available from these localities. geological setting the fennoscandian border zone is divided into the skagerrak–kattegat platform and the sorgenfrei–tornquist zone (fig. 1; sorgenfrei & buch 1964; eugeno-s børglum fault ullerslev-1 horsens-1 rønde-1 voldum-1 terne-1 gassum-1 hobro-1 farsø-1 års-1hyllebjerg-1 vedsted-1 vinding-1 mors-1 kvols-1 børglum-1 haldager-1 frederikshavn-1 skagen-2 sæby-1 lavø-1 stenlille-1 hans-1 ramlösa-1b pernille-1 stina-1 fjerritslev-2 anholt-3/4 fyledal 100 km bornholm skåne fjerritslev fault fjerritslev trough well normal fault erosion limit of triassic–jurassic areas of late cretaceous and early tertiary inversion basement high outcrop locality r øn ne g ra be n skagerrak kattegat ringkøbing–fyn high danish basin skagerrak–kattegat platform sorgenfrei–tornquist zone 56°n 57°n 55°n east north sea high 5 15 7 18øresund wells øresund 13 8°e 10°e 12°e 13°e fig. 1. structural map showing the danish basin and the fennoscandian border zone, and locations of the study wells and the outcrop at fyleverken sand pit, fyledal, skåne (see also fig. 9). inset map shows the location of the wells in the helsingør–helsingborg area. studied wells and outcrops on bornholm are shown in fig. 6. modified from liboriussen et al. (1987) and eugeno-s working group (1988). 613 working group 1988; michelsen & nielsen 1991, 1993). the skagerrak–kattegat platform is a large stable platform area to the north-east where the mesozoic succession onlaps palaeozoic and crystalline basement rocks and thins towards the north-east. the sorgenfrei–tornquist zone is 20–50 km wide and strongly block-faulted. the zone demarcates the stable baltic shield and forms the north-western extension of one of europes most prominent tectonic structures, the tornquist zone. the sorgenfrei–tornquist zone converges at the rønne graben, offshore bornholm, with the teisseyre–tornquist zone which constitutes a tectonic lineament extending to the black sea (ziegler 1982). the rønne graben is a pull-apart basin that formed by dextral wrench-faulting in late carboniferous – early permian times (vejbæk 1985; liboriussen et al. 1987). during the late palaeozoic – mesozoic breakup of the supercontinent pangaea, the tornquist zone was dominated by transtensional stress resulting in subsidence and tilting of fault blocks, and deposition of mesozoic sedimentary successions up to 8 km thick. the sorgenfrei–tornquist zone demarcates the transition from the baltic shield to the wnw–ese-trending intracratonic danish basin that was formed during a late carboniferous – early permian rift phase accompanied by formation of both extrusive and intrusive volcanic rocks. after rifting, the basin subsided due to thermal cooling (sørensen 1986; vejbæk 1989, 1990). the postrift basin-fill consists of a relatively complete section of zechstein, mesozoic and cenozoic deposits which are 6–7 km thick along the axis of the basin. a gradual shallowing of the basin towards the high-lying basement blocks of the ringkøbing–fyn high to the south-west is indicated by thinning of the section. this is most pronounced for the upper permian (zechstein) strata. the ringkøbing–fyn high was periodically subjected to erosion. in the fjerritslev trough, within the sorgenfrei–tornquist zone, an important thickness anomaly was formed due to transtensional strike-slip movements possibly accompanied by salt withdrawal causing relatively fast subsidence and deposition (bertelsen 1980; liboriussen et al. 1987; vejbæk 1990; christensen & korstgård 1994). late early jurassic – early middle jurassic uplift of the ringkøbing–fyn high, presumably connected to the updoming of the central north sea, caused north-eastwards tilting of the basin and erosion both on the high and in the southern part of the basin (michelsen 1978; koch 1983; nielsen 1993, 1995, 2003, this volume). extensive volcanism and uplift occurred in skåne, possibly connected to general updoming (klingspor 1976; norling & bergström 1987; f. surlyk, personal communication 1996). in late middle u m l u l u l u m l u l u l annero fm a nn er o f m m ar ie da l f m vilhelmsfält fm fyledal clay fortuna marl glass sand mb fuglunda mb r ya f m h ö ga nä s fm helsingborg mb döshult mb pankarp mb katslösa mb rydebäck mb röddinge fm ? sorthat fm bagå fm hasle fm galgeløkke mb sose bugt mb munkerup mb r ø nn e fm gassum fm fjerritslev fm haldager sand fm hettangian sinemurian pliensbachian toarcian aalenian bajocian bathonian callovian oxfordian m id dl e u pp er lo w er ju ra ss ic system stage sw ne nw se danish basin bornholm onshore skåne flyvbjerg fm ? ?? ? fig. 2. stratigraphic scheme of the lower–middle jurassic of the danish basin, bornholm and skåne. compiled from nielsen (1995; 2003, this volume), ahlberg et al. (2003, this volume) and michelsen et al. (2003, this volume). – late jurassic times, the ringkøbing–fyn high began to subside again and gradually the basin expanded towards the south-west, attaining its previous size towards the end of the early cretaceous (nielsen 1995). during late cretaceous – early cenozoic times, transpressional tectonism in the sorgenfrei–tornquist zone and the rønne graben, caused by the alpine orogenesis, led to reactivation and pronounced inversion of fault blocks in the zone, which together with neogene– pleistocene regional uplift resulted in erosion of the mesozoic deposits (gry 1969; gravesen et al. 1982; liboriussen et al. 1987; norling & bergström 1987; japsen 1993, 1998; michelsen & nielsen 1991, 1993). the lower–middle jurassic stratigraphy of the danish basin, bornholm and skåne is shown in figure 2. note that the upper pliensbachian – lower aalenian section on bornholm has previously been referred to the lower bagå formation (koppelhus & nielsen 1994), but is now assigned to the sorthat formation (michelsen et al. 2003, this volume). prerequisites for construction of a regional coalification curve construction of a regional coalification curve requires that the following conditions are fulfilled: (1) many geographically widespread data, (2) exclusion of data from well-sections with an abnormal thermal history, (3) reliable corrections for uplift and (4) a relatively constant temperature gradient both in time and space. although totalling more than 300, the reflectance measurements from the triassic – lower cretaceous deposits in the danish basin and the fennoscandian border zone only partly fulfil the first condition (fig. 1). close to half of the data points come from the central part of the basin from wells such as mors-1, hyllebjerg-1, års-1 and farsø-1. however, this is not a serious problem because in this area there is good agreement between uplift values determined from shale velocities and results from modelling of the maturation history. for example, in the hyllebjerg-1 well (fig. 3), the uplift determined by basin modelling is 600 m compared with 575 m obtained from shale velocities. reflectance values from deposits directly overlying salt diapirs clearly indicate a locally increased heat flow (uglev-1; schmidt 1985), and have been omitted in the construction of the regional curve. the corrections for uplift of the selected well-sections have been mainly calculated from seismic velocity data (japsen 1993). the amount of correction is further controlled by the well-known stratigraphy and structures of the area as shown by interpreted seismic sections and preserved thicknesses of lithostratigraphic units in wellsections. the basin subsided due to thermal contraction after the permian rift phase with raised heat flow (vejbæk 1989). the initial phase of the basin development was probably characterised by lateral variations in heat flow, but after the deposition of a thick sedimentary cover of zechstein and lower–middle triassic deposits, the lateral variations in heat flow probably ceased due to the effect of sediment blanketing (nielsen & balling 1990). recent mapping and modelling of the subsurface temperature at various depths demonstrate a uniform regional temperature distribution in the study area (j.j. møller, personal communication 1997). furthermore, regional corrected measurements of heat flow at the sur614 0 1600 3200 d ep th ( m ) 1.200.600.00 %r : measured %ro : modelled %r fig. 3. modelled reflectance values and selected measured reflectance values from the hyllebjerg-1 well. the uplift determined by basin modelling is 600 m compared to 575 m obtained from shale velocities. this confirms that the area around hyllebjerg-1 is a good reference area. face are uniform, in the range 60–70 mw/m2 (balling 1995). based on the structural and thermal evolution of the basin, therefore, we assume that the lateral variation in heat flow from late triassic to recent times in general was relatively small, and that lateral heat flow variations did not influence the maturation of the organic matter significantly. the necessary prerequisites for the construction of a regional coalification curve are thus fulfilled to a large extent. in order to avoid complications due to the late early jurassic – middle jurassic uplift of the ringkøbing–fyn high and the southern parts of the basin, the majority of the data used for construction of the curve comes from well-sections that experienced continued subsidence or only limited uplift and erosion during this phase (nielsen 1995). influence of temperature on maturation the increase in rank with depth in a well-section is mainly caused by rising temperature with depth, and the rate of rank increase is strongly dependent on the geothermal gradient. in a sandstone succession, for instance, the rank gradient is much lower than in a mudstone succession due to the higher thermal conductivity of sandstones (damberger 1968). raised heat flow and thus a higher geothermal gradient also raises the rank gradient (teichmüller 1979; suggate 1998). however, in a basin with a relatively constant heat flow and a laterally uniform lithology, the rank of coals is primarily dependent on the maximum temperature to which the organic matter was subjected, which corresponds to the maximum burial depth. since coalification of organic matter is irreversible, later uplift does not influence the measured reflectance values. as demonstrated below, the majority of the reflectance values from the danish basin and the fennoscandian border zone are interpreted to show a normal coalification trend. the rank of the coals thus reflects the maximum burial depth of the strata. construction of the coalification curve a total of 311 reflectance measurements from the upper triassic, jurassic and lower cretaceous successions in twenty wells from the fennoscandian border zone and the danish basin are used in the construction of the coalification curve (fig. 1). all the reflectance values are random measurements. samples from drill cores were available from the frederikshavn-1, fjerritslev-2, gassum-1, haldager-1, horsens-1, lavø-1, skagen-2, ullerslev-1, vedsted-1 and vinding-1 wells. where possible, samples with coal, coaly inclusions, or dark-coloured shales or siltstones were selected for reflectance measurements as these rocks contain the best organic matter for rank determination (thomsen 1980). untreated rock samples were studied as they more easily allow identification of oxidised and bituminous organic matter (unsuitable for reflectance measurements) than is the case for kerogen concentrates. in coal or coaly samples, approximately 50–100 measurements were carried out in each sample; in samples with disseminated organic matter, as many particles as possible were measured, usually 20–50. core samples from the børglum-1 well were analysed in the same fashion (schmidt 1985), whereas coaly or dark-coloured shaly intervals were selected from sidewall cores and core samples in the farsø-1 well (thomsen 1983). cuttings and a limited number of core samples were available from the års-1 well, whereas only cuttings were available from the rest 615 års-1 børglum-1 farsø-1 fjerritslev-2 frederikshavn-1 gassum-1 haldager-1 hans-1 hobro-1 horsens-1 hyllebjerg-1 kvols-1 lavø-1 mors-1 rønde-1 skagen-2 terne-1 ullerslev-1 vedsted-1 vinding-1 558 m 1273 m 481 m 1531 m 1000 m 1190 m 1400 m 1733 m 550 m 200 m 575 m 448 m 1000 m 785 m 513 m 1100 m 1405 m 500 m 1400 m 250 m total post-early cretaceous uplift (amount of correction) comments on the estimated amounts of uplift well table 1. correction for post-early cretaceous uplift after japsen (1993) after japsen (1993) after japsen (1993) after japsen (1993) by comparison to sæby-1, 997 m (japsen 1993) by comparison to voldum-1, 942 m (japsen 1993) and 248 m deeper truncation of chalk by comparison to børglum-1 and fjerritslev-2 after japsen (1993) by comparison to års-1 by using fig. 1c in japsen (1993) after japsen (1993) after japsen (1993) by using fig. 1c in japsen (1993) and stenlille-1, 850 m after japsen (1993) after japsen (1993) by comparison to sæby-1, 997 m after japsen (1993) by using fig. 1c in japsen (1993) by comparison to børglum-1 and fjerritslev-2 by comparison to mejrup-1, 327 m, and vemb-1, 309 m (japsen 1993) of the wells (rønde-1: thomsen 1980; hyllebjerg-1: schmidt 1988; hans-1, hobro-1, kvols-1, mors-1, terne-1: geus, unpublished data). all sample depths were corrected for post-early cretaceous net uplift before being plotted against reflectance (table 1). the correction for the well-sections was based on the analysis of sonic velocities of shales by japsen (1993). the main uncertainties related to this method are the requirement 616 0.0 0.2 0.4 0.6 0.8 0 500 1000 1500 2000 2500 3000 3500 4000 %ro d ep th ( m ) års-1 børglum-1 farsø-1 fjerritslev-2 frederikshavn-1 gassum-1 haldager-1 hans-1 hobro-1 horsens-1 hyllebjerg-1 kvols-1 lavø-1 mors-1 rønde-1 skagen-2 terne-1 ullerslev-1 vedsted-1 vinding-1 0.0 0.2 0.4 0.6 0.8 %ro års-1 farsø-1 frederikshavn-1 gassum-1 hans-1 hobro-1 horsens-1 hyllebjerg-1 kvols-1 lavø-1 mors-1 rønde-1 skagen-2 ullerslev-1 vinding-1 a b fig. 4. a: coalification profile for the 20 investigated wells (n = 311); the depths are corrected for post-cretaceous uplift. data from thomsen (1980, 1983, 1984), schmidt (1985, 1988) and unpublished geus data. b: coalification profile (uplift-corrected depths) for 15 wells in the danish basin, the fennoscandian border zone and the skagerrak–kattegat platform (n = 249). the regression line has a correlation coefficient of 0.88, and intercepts the reflectance axis at 0.21 %ro. of a uniform shale unit covering the entire study area and a valid reference curve (discussed in japsen 1993). the analyses of the velocity data provide an uplift pattern that is compatible with structural interpretations of seismic sections and stratigraphic well data. the present sample depths are thus corrected by adding the amount of uplift proposed by japsen (1993). the uplift of wells not included by japsen (1993) is estimated by comparison to nearby wells and interpolation (table 1). the gassum-1 well, for example, is situated on a salt structure, in a setting comparable to the nearby voldum-1 well, which was uplifted 942 m (japsen 1993). the chalk section in gassum-1 seems to be more deeply truncated than that in voldum-1 (c. 250 m), and an uplift of c. 1190 m is thus estimated for the gassum-1 section. the uplift of the horsens-1 and ullerslev-1 wells is estimated to be 200 m and 500 m, respectively, by using the general uplift map of japsen (1993). the uplift of the lavø-1 well is estimated to be 1000 m based on the same map and comparison with the stenlille-1 well (850 m). two coalification trends are recognised when the reflectance measurements are plotted against uplift-corrected depths: a well-defined main trend to the right and a less pronounced trend to the left (fig. 4a). the main coalification trend is based on well data from the danish basin and the skagerrak–kattegat platform (fig. 4b), whereas well data from the fjerritslev trough (børglum-1, fjerritslev-2, haldager-1, vedsted-1) and the terne-1 well define the other coalification trend. huminite/vitrinite reflectance is largely unaffected by the formation of mainly isolated aromatic rings up to a reflectance of c. 0.7 %ro, resulting in a slow and more or less linear increase in reflectance (carr & williamson 1990; suggate 1998). however, as maturation proceeds past this point the formation of polycyclic aromatic units significantly increases the reflectance. as the level of coalification in the studied sections is in the low rank range (< 0.7 %ro), it is possible to approximate this ‘straight’ section of the curve with a linear regression line. the linear regression line for the danish basin/skagerrak–kattegat platform intersects the %ro-axis at 0.2 %ro, which is the expected reflectance at the surface (fig. 4b; dow 1977; suggate 1998). the rank gradient is 0.12 %ro/km. the absence of significant anomalies indicates that the assumption of a relatively uniform geothermal gradient in the study area is justified, and that the corrections for uplift are reasonable. the regression line of the coalification curve is based on 249 samples; it has a correlation coefficient of 0.88, and is considered to be a good approximation of the coalification profile. this relationship can then be used to estimate the maximum burial depths and later uplift of jurassic coal seams in the fennoscandian border zone. the reasonable and stratigraphically consistent estimates are taken as indirect evidence of the reliability of the coalification curve, and the coalification curve is considered as a valid approximation of the maturation trend over most of the study area. the data from børglum-1, fjerritslev-2, haldager-1, vedsted-1 and terne-1 form an atypically steep coalification trend which was investigated by modelling of the basin development. modelled vitrinite reflectances for the børglum-1 well are shown in figure 5, together with the measured values. the basin modelling indicates uplift of only 800 m, compared with 1300 m derived from shale velocities. interval velocities for the 617 0 1600 3200 d ep th ( m ) 1.200.600.00 %r : measured %ro : modelled %r fig. 5. modelled reflectance values and measured reflectance values from the børglum-1 well. the amount of uplift determined by basin modelling is 800 m compared to the 1300 m obtained from shale velocities. it is suggested that the uplift of the wells in the fjerritslev trough (and the terne-1 well) determined from the shale velocities is overestimated due to the sand-rich nature of the succession in these wells. chalk section in the fjerritslev trough are low, and new data based on chalk group velocities yield significantly lower uplift values (japsen 1998). the data suggest correction for uplift of only 817 m for børglum-1, 1012 m for fjerritslev-2, and 644 m for haldager-1. if the present depths of these wells are uplift-corrected according to the new chalk group data, the huminite reflectance values would fit the coalification curve shown in figure 4b. this suggests that uplift values determined from shale velocities are probably overestimates. the relatively high shale velocities in this area (japsen 1993) may be the result of an increased coarse-grained component within the lowermost fjerritslev formation than is typical of the rest of the basin. estimation of burial depth and later uplift of lower–middle jurassic coal seams in the fennoscandian border zone determination of coal rank the rank, or the level of thermal maturity, of the coals was determined by random reflectance measurements on eu-ulminite, the brown coal equivalent of collotelinite, following the standard procedure outlined in taylor et al. (1998). up to 100 measurements were made on each sample and a mean reflectance (%ro) was calculated. parameters obtained by organic geochemical methods, when available, were used to support the estimation of the maturity. rock-eval pyrolysis was used to determine the tmax value which is the temperature at which maximum pyrolysis occurs (peters 1986). the value of tmax increases with increasing maturity of the organic matter, but is also influenced by the composition of the organic matter, as a high content of inert components may result in an elevated tmax value. biomarker data were obtained from the saturated fraction of solvent extracts from the coal samples using gas chromatography/mass spectrometry. pentacyclic hopanes were identified by detecting the most characteristic fragmentation ion, the m/z 191. the occurrence of the thermally unstable hopenes and 17ß(h),21ß(h) forms in the coals is indicative of immaturity, and the c31-homohopane 22s/(22r+22s) epimerisation ratio approaches an equilibrium value of approximately 0.6 with increasing maturity. the sensitivity of the hopanes to thermal influence at low maturity levels may be a valuable criterion when evaluating the validity of maturity differences obtained by reflectance measurements. the carbon preference index (cpi) was calculated from traces obtained from gas chromatography. the cpi is a measure of the predominance of odd carbon numbered n-alkanes calculated over a specified range (bray & evans 1961; cooper & bray 1963). in the present study, the range was from nc22 to nc32. the dominance of odd carbon numbered n-alkanes together with a prominent heavy-end fraction are characteristic features of terrestrially derived organic matter (isaksen 1995). however, increasing maturity seems to minimise the cpi due to alkane cleavage reactions and dilution of the odd carbon numbered n-alkanes (radke et al. 1980). hence, the cpi tends to reach an equilibrium of 1 with increasing maturity. huminite reflectances of the coals the following section focuses on the degree of coalification of lower and middle jurassic coal seams and strata from the island of bornholm, the rønne and kolobrzeg grabens (offshore bornholm), skåne, the øresund area, and kattegat in order to present the rank distribution. hettangian–sinemurian rønne formation, bornholm two coal seams in the hettangian munkerup member of the rønne formation in the arnager–sose fault block have reflectances of 0.40 %ro and 0.41 %ro (figs 2, 6; table 2). however, samples from carbonaceous seams in the overlying hettangian–sinemurian sose bugt member display significantly lower reflectance values (0.28 %ro and 0.30 %ro) (figs 2, 6; table 2). the coal seam in the sinemurian galgeløkke member of the rønne formation at the galgeløkke coastal cliff (rønne–hasle fault block) has a reflectance of 0.38 %ro (figs 2, 6; table 2). the galgeløkke-2 well was drilled close to the galgeløkke cliff and cored c. 400 m of hettangian–sinemurian strata (nielsen 1995). a hettangian coal seam situated at a depth of 383 m has a reflectance value of 0.42 %ro. this is compatible with a tmax value of 427°c and a c31-homohopane 22s/(22s+22r) epimerisation ratio of only 0.06. the coal seam is estimated to lie 50–75 m above the base of the jurassic, as suggested by log correlations between the galgeløkke-2, pernille-1 and stina-1 wells (nielsen 1995). 618 619 rønne– hasle fault block nyker block rønne graben arnager–sose fault block gudhjem trough bornholm high 5 6 3 4 2 1 10 km c t n fig. 6. geological map of bornholm showing the investigated localities: 1, exposed munkerup member (rønne formation); 2, type section of the sose bugt member (rønne formation); 3, type section of the galgeløkke member (rønne formation) at the galgeløkke coastal exposures and the galgeløkke-2 well; 4, korsodde coastal cliff, sorthat formation; 5, levka-1 well, sorthat formation; 6, hasle klinkerfabrik clay pit, upper bagå formation. modified from gravesen et al. (1982). sose bugt section hettangian–sinemurian 0.29 2 625 anholt well* lower jurassic 0.33 12 975 975 levka-1 well / upper pliensbachian – 0.36 13 420(60) 0.06–0.1 1210 1210 korsodde section** lower toarcian øresund-15 well+ sinemurian 0.36 1 419(1) 1210 1210 galgeløkke section sinemurian 0.38 2 1400 1400 øresund-5 well+ bajocian 0.39 1 421(2) 1450 1450 fyleverken sand pit bajocian 0.39 2 430(2) 1450 1450 munkerup section hettangian 0.41 2 1660 1660 galgeløkke-2 well hettangian 0.42 1 427(1) 0.06 1700 1320 hasle kl. clay pit bathonian 0.42 6 1700 1700 øresund-7 well+ bajocian–bathonian 0.43 5 418(9) 0.05–0.09 1875 1875 øresund-13 well+ hettangian–sinemurian 0.46 1 426(1) 0.23 2100 2010 øresund-18 well+ hettangian–sinemurian 0.51 2 426(7) 0.37–0.42 2440 2440 # the average reflectance is calculated from mean random reflectance (nos of analyses). a mean random reflectance value is based on c. 100 measurements in each sample. * data from nielsen et al. (2003, this volume). ** data from petersen & nielsen (1995). + data from petersen (1994). ++ post-early cretaceous uplift: 290 m (petersen et al. 1996) locallity table 2. maturity data, estimated burial depth/magnitude of later uplift age average reflectance %ro # average tmax (c°) (n) net uplift (m) maximum burial depth (m) c31-homohopane 22s/(22s+22r) number of mean random reflectances 625++ cretaceous lower–middle jurassic sorthat formation and middle jurassic bagå formation lower jurassic hasle formation lower jurassic rønne formation upper triassic kågeröd formation lower palaeozoic precambrian crystalline basement fault 620 upper pliensbachian – lower toarcian part of the sorthat formation, bornholm reflectance values of coal seams from the upper pliensbachian – lower toarcian part of the sorthat formation in cores from the levka-1 well and in the korsodde coastal cliff (rønne–hasle fault block) average 0.36 %ro (figs 2, 6; table 2). tmax values average 421°c, and c31-homohopane 22s/(22s+22r) epimerisation ratios for eight samples from the levka-1 well are in the range 0.06–0.1, which conforms with low rank coals. thermally sensitive hopenes and ßß-forms occur, and cpi values greater than 3 are compatible with immature low rank coals (petersen & nielsen 1995). bathonian part of the bagå formation, bornholm the coal-bearing aalenian–bathonian bagå formation is exposed in the hasle klinkerfabrik clay pit (figs 2, 6). the clay pit is situated in the rønne–hasle fault block, close to the faulted margin of the rønne graben. reflectance values from eight coal seams in the uppermost part of the bagå formation (bathonian) are in the range 0.36–0.46 %ro, averaging 0.42 %ro (table 2). lower jurassic in the rønne and kolobrzeg grabens the lower jurassic from the western part of the rønne graben is represented by the pernille-1 well, and from the kolobrzeg graben by the stina-1 well (fig. 7). in pernille-1, the lower jurassic from 980–1470 m is referred to the hettangian–sinemurian rønne formation (nielsen 1995). the reflectance values show a well-defined coalification trend with increasing depth (fig. 8). in stina-1, the lower jurassic from 180–560 m possibly includes the hettangian to upper pliensbachian (nielsen 1995). the reflectance values vary between 0.31 %ro and 0.40 %ro (fig. 8). hanö bay half-graben christiansø ridge ustka block darlowo block kolobrzeg graben gryfice graben rønne graben colonus trough romele ridge vomb trough skurup block bornholm gat block a rn ag er –s os e bl oc k ri se bæ k tr ou gh arkona block w iek–trent block wolin block bornholm high gudhjem trough r ø nn e fa ul t g at fa ul t trzebiatow fault adler fault koszalin–chojnice fault ustki fault h am m er fault ringsjö–andraru m fault fyledal fault hälsingborg–rom ele fault 25 km 55°n 14°e 15°e 16°e pernille-1 stina-1 fig. 7. structural map showing the block mosaic of the bornholm region and the position of the pernille-1 and stina-1 wells. the relative significance of the faults is indicated by varying line thickness. slightly modified from hamann (1994). 621 bajocian fuglunda member of skåne bajocian coal-bearing sediments of the fuglunda member (mariedal formation) are exposed in the fyleverken sand pit, fyledal at eriksdal (figs 1, 2). the sediments are part of a 400–600 m thick succession that was deposited close to the boundary between the vomb trough and the palaeozoic colonus trough (fig. 9). two coal samples from the lower part of the fuglunda member show reflectance values of 0.38 %ro and 0.39 %ro (table 2), and tmax values of 427°c and 433°c. jurassic of the northern øresund knowledge of the jurassic in the helsingør–helsingborg area is derived from sea cliff and quarry exposures, from tunnel excavations, and from cored shallow wells in the øresund and skåne (fig. 1). the deposits belong to the faultand flexure-bounded höganäs basin within the sorgenfrei–tornquist zone (fig. 9). hettangian–sinemurian sediments occur in the øresund-13 and -18 wells. a coal seam in the former well yielded a reflectance of 0.46 %ro, whereas a coal seam in the latter well yielded a reflectance of 0.51 %ro (table 2). a sinemurian coal seam in the øresund-15 well has a reflectance of 0.36 %ro (table 2). the relatively low reflectance value of the seam from the øresund-15 well may be suppressed, as the pronounced content of huminite and the presence of pyrite indicate 0 500 1000 1500 2000 d ep th ( m ) 0.60.4 %ro 0.20.0 pernille-1 stina-1 stina-1 corrected vomb trough colonus trough n fyledal fault fyleverken sand pit rom ele ridge ▲ ▲ ■■ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ■■ ■ ■ ▲ ▲ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ 25 km höganäs basin skurup block rhaetian and jurassic present distribution reverse fault normal fault fault of unknown type fig. 8. coalification profiles for the lower jurassic in the pernille-1 well in the rønne graben and the stina-1 well in the kolobrzeg graben. the regional coalification profile for the danish basin/ skagerrak–kattegat platform is also shown. the profile from pernille-1 falls on the regional trend indicating that the section has not been uplifted. the stina-1 section has been uplifted c. 900 m. fig. 9. structural map of skåne showing the present distribution of rhaetian and jurassic deposits. modified from norling & bergström (1987). that anoxic and possibly occasional saline conditions were present in the precursor mire. this may have resulted in the formation of hydrogen-enriched huminite, which matures at a lower rate (petersen & rosenberg 1998). the tmax is also low (419°c). the tmax value of the coal from the øresund-13 well is 426°c and the values from the øresund-18 well are 424–428°c. the c31-homohopane 22s/(22s+22r) epimerisation ratio is 0.23 for the øresund-13 well, whereas the ratio is in the range 0.37–0.42 for the øresund-18 well. together with the reflectance values, these data are consistent with a higher rank of the coals from the øresund-18 well compared to the coal from the øresund-13 well. the bajocian–bathonian coal from the øresund-5 well has a reflectance of 0.39 %ro, and the coals from the øresund-7 well have reflectances in the range 0.41–0.46 %ro, averaging 0.43 %ro (table 2). relative proportions of the thermally unstable hopenes and ßßforms are high in the øresund-7 coals, and the c31homohopane 22s/(22s+22r) epimerisation ratios are low (0.05–0.09). the average tmax value and the hopane ratios are similar to the values obtained from the upper pliensbachian – lower toarcian (sorthat formation) coal seams in the levka-1 well on bornholm. however, the reflectance values of the coal seams from the øresund-7 well are higher, possibly due to increased oxidation during the humification process in the early stages of biochemical gelification (diessel 1992; hao & chen 1992). lower–middle jurassic fjerritslev and haldager sand formations, kattegat approximately 200 m of lower and middle jurassic deposits of the fjerritslev and haldager sand formations overlain by c. 100 m of quaternary deposits were cored by a shallow well on the island of anholt located in the kattegat (figs 1, 2). reflectance measurements by nielsen et al. (2003, this volume) give an average value of 0.33 %ro (table 2). estimation of burial depths and later uplift the average reflectance values of the coals and the constructed regional coalification curve are used to estimate the maximum burial depth of the coal-bearing lower and middle jurassic strata in the fennoscandian border zone. the amount of later uplift equals the maximum burial depth in most cases as the majority of the samples were collected close to present sea level. bornholm a burial depth of c. 1660 m is suggested for the outcropping coals of the hettangian munkerup member, whereas the data from the overlying hettangian to sinemurian sose bugt member (both of the rønne formation) indicate only c. 625 m of burial (fig. 10; table 2). the thickness of the non-exposed section between the seams in the munkerup member and those in the sose bugt member is less than a few tens of metres (gry 1969; gravesen et al. 1982); a difference of approximately 1000 m in estimated burial depth between the seams is therefore impossible. the reflectance values from the munkerup member are considered to be too high, possibly due to hydrothermal influence; this aspect is discussed further below. the sose bugt member in the arnager–sose fault block is overlain by at least 60 m of sediments assigned to the hasle formation (gravesen et al. 1982; surlyk et al. 1995), which in turn are unconformably overlain by lower cretaceous sediments. the base of the lower cretaceous was buried to c. 290 m followed by a similar amount of uplift (petersen et al. 1996). this suggests that part of the uplift experienced by the sose bugt member was related to the middle jurassic uplift event, which influenced the areas outside the sorgenfrei–tornquist zone (andsbjerg et al. 2001; nielsen 2003, this volume), and only c. 290 m of the total uplift was caused by post-early cretaceous uplift. the coal seams of the sinemurian galgeløkke member exposed at the galgeløkke coastal cliff have been buried to c. 1400 m with a later uplift of the same magnitude (fig. 10; table 2). the hettangian coal seam at a depth of 383 m in the nearby galgeløkke-2 well was buried to c. 1700 m, corresponding to a burial depth for the base of the jurassic of c. 1750–1775 m with a later uplift of c. 1320 m. the difference in estimated burial depths of the two seams is thus c. 300 m which corresponds reasonably well with the estimated thickness of c. 400 m of the intervening strata. the coal seams in the upper pliensbachian – lower toarcian part of the sorthat formation have been buried to c. 1210 m (fig. 10; table 2). the difference between the estimated burial depths of the seam from the galgeløkke coastal cliff and the seams from the levka-1 and korsodde sections is c. 200 m which conforms well with an estimated thickness of 225–290 m of intervening strata. however, it should be noted that the estimated burial depth of the levka-1 and korsodde coals may be an under-estimate as the reflectance values of the coals may be slightly suppressed (petersen et al. 2003, this volume). 622 623 the data from the bathonian coal seams in the uppermost bagå formation indicate a burial depth of c. 1700 m (fig. 10; table 2). this corresponds to c. 800 m deeper burial than the levka-1 and korsodde sections, and is unrealistic considering the structural and stratigraphic development of the two localities (gry 1969; gravesen et al. 1982; jensen & hamann 1989). hence, it is likely that the high reflectance values of the coals in the upper part of the bagå formation were caused by an additional factor linked to the proximity of the major rønne–hasle fault as discussed below. these estimates suggest that the base of the jurassic in the rønne–hasle block at galgeløkke-2 was buried to c. 1750–1775 m and later uplifted c. 1320 m. this is consistent with the seismic interpretation by hamann (1994) indicating up to 1400 m of inversion along the rønne–hasle fault. the maximum burial depth of 1750–1775 m is compatible with the likely cumulative thicknesses of the jurassic–cretaceous section in the rønne–hasle block. in pernille-1, for instance, the jurassic–cretaceous section has a minimum thickness of c. 1450 m, comprising c. 600 m of lower jurassic deposits overlain by c. 850 m of probable lower to upper cretaceous deposits. in the rønne–hasle block, the cumulative thickness may have been up to 2000 m, as c. 1000 m of jurassic deposits are preserved, and the original thickness of the cretaceous succession may have been up to c. 1000 m, as suggested by reference to the adjacent nyker block and pernille-1. rønne and kolobrzeg grabens the reflectance values of the rønne formation in pernille-1 plot on the trend of the coalification curve (fig. 8). thus the present depth of the jurassic deposits corresponds to the maximum burial depth. this contrasts with the interpretation of a seismic section through the pernille-1 well indicating c. 270 msec (c. 400 m) of inversion relative to the stable skurup block (fig. 11). the data from the stina-1 section situated in the kolobrzeg graben suggest a burial depth of c. 1500 m for the base of the jurassic and c. 900 m of later uplift (figs 7, 8). seismic interpretation suggests a similar sose bugt section (0.29 %ro; hettangian–sinemurian) anholt well (0.33 %ro; lower jurassic) levka-1 well and korsodde section (0.36 %ro; u. pliensbachian – l. toarcian)/ øresund-5 well and fyleverken sand pit (0.39 %ro; bajocian) galgeløkke section (0.38 %ro; sinemurian) munkerup section (0.41 %ro; hettangian) galgeløkke-2 well (0.42 %ro; hettangian)/ øresund-7 well (0.43 %ro; bajocian–bathonian) øresund-13 well (0.46 %ro; hettangian–sinemurian) øresund-18 well (0.51 %ro; hettangian–sinemurian) hasle klinkerfabrik clay pit (0.42 %ro; bathonian) øresund-15 well (0.36 %ro; sinemurian) 0.80.60.40.20.0 %ro 0 500 1000 1500 2000 2500 3000 d ep th ( m ) fig. 10. the standard coalification curve for the danish basin/skagerrak–kattegat platform used to estimate the burial depth of lower and middle jurassic coalbearing strata from the islands of anholt and bornholm, the øresund area and skåne by means of huminite reflectance values. 624 amount of uplift during the inversion phase (hamann 1994; vejbæk et al. 1994). stina-1 is located close to the section shown in figure 12b, which indicates inversion of 1000–1100 m within the kolobrzeg graben. evidence of inversion is also prominent on a sw–ne section east of bornholm (fig. 12c). the lower jurassic strata in the pernille-1 and stina-1 wells were buried to the same depth in the two areas prior to uplift at stina-1. the lower jurassic is unconformably overlain by quaternary deposits in stina-1, whereas the lower jurassic is overlain by c. 850 m of upper cretaceous deposits in pernille-1; this is consistent with the estimate of c. 900 m of uplift at stina-1. fyleverken sand pit, fyledal, skåne the reflectance values of the bajocian coals from fyledal suggest a burial depth of c. 1450 m in the eriksdal area and a similar amount of later uplift (fig. 10; table 2). in the vomb trough, crystalline basement is overlain by up to 200 m of jurassic – lower cretaceous strata and c. 1000 m of upper cretaceous deposits, but much of the santonian–campanian succession accumulated contemporaneously with the inversion of the sorgenfrei– tornquist zone (erlström & guy-ohlson 1994). the thickness of the santonian–campanian succession thus reflects the relative fault movements and not directly the uplift. in the fyleverken sand pit section in fyledal, the post-bajocian jurassic section is c. 400 m thick, and the lower cretaceous – turonian section was probably c. 200 m thick before tilting during santonian–campanian inversion (norling & bergström 1987). erlström (1994) suggested that c. 300 m of maastrichtian deposits were eroded during neogene uplift. the jurassic–cretaceous succession may thus have been c. 900 m thick. paleocene and eocene deposits seem to be confined to the basin south-west of the helsingborg–romele fault. however, cenozoic deposits may have covered eastern skåne and are thought to be present in the hanö bay area (lidmar-bergström 1982; norling & bergström 1987). it is thus very difficult to evaluate in detail the thickness of strata that has been removed on the basis of the preserved stratigraphy, and to support the burial estimate of c. 1450 m. in addition, hydrothermal influence on the rank cannot be precluded (see below). the amount of inversion in the north-western part of the sorgenfrei– tornquist zone is typically suggested to 0 1 2 3 4 t w t ( se c) pernille-1w e basement basement triassic triassic cretaceous jurassic permian l. palaeozoic fig. 11. interpreted seismic section through the pernille-1 well showing c. 270 msec of inversion corresponding to c. 400 m (interval velocity = 2942 m/sec; nielsen & japsen 1992). slightly modified from vejbæk et al. (1994). 625 be up to 1000 m (jensen & michelsen 1992; japsen 1993; michelsen & nielsen 1993). extension of the regional trend of neogene uplift shown by jensen & michelsen (1992) and japsen (1993) into skåne may suggest 1000–1500 m of uplift in this area. however, this trend is mainly based on data to the north-west of skåne and thus may not be directly applicable. northern øresund in the höganäs basin, the data from the hettangian– sinemurian coal seams in the øresund-13 and -18 wells indicate burial depths of c. 2100 m and 2440 m respectively (figs 1, 9, 10; table 2). uplift in the øresund area was evaluated by modelling of a pseudo-well, based on a stratigraphic reconstruction from the shallow wells (fig. 13) and the stratigraphic information given in plate 21 of larsen et al. (1968). the modelling shows that the differences in reflectance (%ro) can be explained by the thickness of the intervening strata with the exception of the øresund-15 well. the low value obtained from this well may be due to suppression, as mentioned earlier. the basin modelling indicates an uplift of 1200 m for the øresund-1 well location, corresponding to uplift of 2100 m at the øresund-13 well location and 2550 m at the øresund-18 well location. this is in close agreement with the values determined from the coalification curve and is compatible with the stratigraphy (fig. 13; larsen et al. 1968, plate 21). reflectance values of three hettangian coal samples from the nearby helsingborg railway tunnel range from 0.48 %ro to 0.57 %ro, and dispersed huminite from hettangian deposits in the nearby ramlösa-1b well gives 0 1 2 3 4 5 0 1 2 3 4 5 skurup block rønne graben arnager block risebæk graben darlowo block hanö bay basin baltic syneclise christiansø high rønne graben k o sz al in f au lt k o sz al in f au lt kolobrzeg graben kolobrzeg graben darlowo block ustka block bornholm block svaneke trough christiansø high se ne u. cretaceous jurassic–triassic permian pre-permian fault basement t w t (sec) t w t (sec) t w t (sec) a c c b a nw sw sw ne 20 km b 0 1 2 3 4 5 6 ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ■■ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ■■ ■ ■ ■ ■ ▲ ▲ ▲ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■ ■ ■■ fig. 12. geosections around bornholm (see inset map) with depths in two-way travel time (twt), based on interpreted seismic sections. a: note the lack of significant inversion relative to the skurup platform at the western margin of the rønne graben in contrast to the marked inversion relative to the arnager block in the south-eastern part of the graben. b: note the very significant inversion of the kolobrzeg graben relative to the hanö bay basin. stina-1 is located in the kolobrzeg graben close to the koszalin fault. c: inversion of the kolobrzeg graben is also evident on the sw–ne section, east of bornholm. slightly modified from vejbæk et al. (1994). 626 a value of 0.48 %ro (ahlberg 1994). these data suggest burial depths between 2250 m and 3050 m. the bajocian–bathonian coal seams in the øresund-5 and øresund-7 wells situated immediately west of the inversion zone, were buried and later uplifted c. 1450 m and c. 1875 m, respectively, corresponding to modelled values of c. 1400 m for the øresund-5 well and c. 1500 m for the øresund-7 well (figs 10, 13; table 2). anholt well, kattegat the lower–middle jurassic strata encountered in the anholt well were buried and uplifted c. 975 m (fig. 10; table 2). the island of anholt is located on the boundary between the skagerrak–kattegat platform and the inversion zone. the uplift is mainly interpreted as being of neogene–pleistocene age, and the degree of uplift is slightly less than that inferred for the sæby-1 well (japsen 1993; michelsen & nielsen 1993). approximately 1000 m of uplift was estimated by nielsen et al. (2003, this volume) based on the same reflectance data but utilising a general north sea coalification curve. hydrothermal influence on the maturation of organic matter the vast majority of the reflectance values provide reasonable estimates of burial depths that are consistent i ii (a) top kimmeridgian 0.43 %ro 0.39 %ro 0.36 %ro 0.46 %ro 0.51 %ro katslösa mb döshult mb øresund-1 øresund-7 øresund-2 øresund-3 øresund-12 øresund-11 øresund-10 øresund-9 øresund-8 øresund-18 øresund-13 øresund-14 øresund-15 øresund-4 øresund-5 well section (b) 0 0.60 1.20 %r m et re s d ep th ( m ) 0 500 1000 1500 0 1600 3200 : measured %ro : modelled %r fig. 13. a: reconstructed stratigraphic columns at the location of the øresund-1 well. the reconstructions are based on the geological profiles along the tunnel transect (column i) and the bridge transect (column ii) shown on plate 21 in larsen et al. (1968). b: modelled reflectance values from the constructed pseudo-well compared to measured values. with stratigraphic thicknesses and other evidence of burial depths. however, the rank of the coals from the munkerup member, the uppermost bagå formation, and possibly the fuglunda member appear anomalously high. a mechanism other than thermal influence with burial depth is needed to explain these anomalies. the precursor peats of the uppermost bagå formation coals were formed in a relatively well-aerated environment, which may have produced hydrogen-poor and oxygen-rich huminite precursor material that matured at an enhanced rate (hao & chen 1992). however, this explanation cannot be applied to the coals of the munkerup member, and may not be sufficient to explain the large difference in reflectance between the coals from the sorthat and bagå formations on bornholm. therefore, it is proposed that the elevated maturity was the result of a local rise in temperature due to hydrothermal activity. hydrothermal processes associated with fault movements have been proposed to explain the occurrence of sideritic iron ores and copper mineralisation along the fyledal fault zone and zeolites in campanian deposits in the vomb trough (norling & bergström 1987; erlström 1994). middle jurassic volcanic activity occurred in skåne along fault and fracture zones, and hot brines influenced the diagenesis of rhaetian and lower jurassic sandstones and caused anomalously high vitrinite reflectances (klingspor 1976; norling & bergström 1987; ahlberg 1994; ahlberg & goldstein 1994). the silica-cemented höör sandstone (a lateral equivalent of the höganäs formation, fig. 2), which has not been buried more than a few hundred metres, was indurated at temperatures from 100–200°c, and the organic matter shows reflectance values that locally reach 0.9 %ro corresponding to a burial depth of c. 5700 m. bottomhole temperatures in the hans-1 well in the kattegat were high in lower jurassic strata at very shallow depths (45°c at 316 m) whereas normal temperatures were recorded at deeper levels. the real temperature of the jurassic deposits is even higher than indicated by the borehole measurement, because of the cooling effect of the drilling mud. the occurrence of hydrothermal activity along faults and the effect on the diagenesis of organic as well as siliciclastic deposits is thus well-documented. some of the observed anomalies in the jurassic coals may therefore be related to the middle jurassic volcanic activity in skåne. the uppermost bagå formation coals are situated close to the fault that separates the rønne graben from the crystalline basement of the bornholm high, and it is possible that hot formation waters expelled from deeply buried deposits percolated upwards along the fault and into the coal-bearing strata. the occurrence of abundant epigenetic pyrite in the coals and large pyrite nodules in sand interbeds lend support to this interpretation, as the most likely source of the sulphur is saline formation water from older sediments containing salt and gypsum (petersen et al. 2003, this volume). a similar situation has been reported from the carboniferous st. rose and chimney corner coalfields in nova scotia, canada (beaton et al. 1993). the munkerup member coals occur close to the northern and eastern bounding faults of the arnager– sose fault block, and these faults may also have functioned as conduits for hot formation waters, thus explaining the high rank of the coals. discussion and conclusions a well-constrained, uplift-corrected coalification curve has been constructed from reflectance data representing a wide range of burial depths of the upper triassic – lower cretaceous succession in the danish basin and the fennoscandian border zone. we suggest that this curve may be used as a standard with which new data can be compared. the reflectance values from wells in the fjerritslev trough and the terne-1 well deviate from the main coalification trend. basin modelling and velocity data from the chalk group (japsen 1998) suggest that the uplift correction may be erroneous due to overestimation of the burial depth based on fjerritslev formation sonic velocities in these wells. these data have thus not been incorporated in the standard curve. average reflectance values from the lower–middle jurassic coals in the fennoscandian border zone range from 0.29 %ro to 0.51 %ro (table 2), which are compatible with low rank coals, and directly indicate relatively shallow burial depths. the use of the regional curve to assess the burial depths and later uplift of coalbearing lower–middle jurassic strata in the fennoscandian border zone has provided reliable and consistent results (table 2). hydrothermal activity related to the middle jurassic volcanic event may locally have influenced the maturation of the coals in the hettangian–sinemurian of the höganäs basin, and possibly the coals in the fuglunda member at fyledal. the rank of the coals in the munkerup member (rønne formation) and uppermost bagå formation on bornholm was probably raised by hot formation waters expelled from deeply buried layers. 627 628 the reflectance data indicate c. 900–1400 m of postearly cretaceous uplift of the jurassic succession in the rønne–hasle fault block and the kolobrzeg graben (table 2). this degree of uplift is compatible with the amount of late cretaceous – early cenozoic inversion based on seismic interpretation (hamann 1994; vejbæk et al. 1994), and is similar to the 550–1000 m of inversion that has been interpreted from the sorgenfrei– tornquist zone further to the north-west (japsen 1993; michelsen & nielsen 1993). thus the total post-early cretaceous uplift in the bornholm area determined from reflectance values can be explained by inversion alone, without the need for significant neogene–pleistocene uplift. the data from the arnager–sose fault block indicate early jurassic burial of 625 m followed by a similar magnitude of middle–late jurassic uplift and erosion. post-early cretaceous uplift only amounts to 290 m. the estimated uplift of the jurassic section in the höganäs basin, reflecting both inversion and neogene– pleistocene uplift, is a minimum of 2010 m (table 2). this is similar to the total uplift of 1730–2000 m of the hans-1 well-section in the kattegat (japsen 1993; michelsen & nielsen 1993). the c. 1450–1875 m of uplift indicated by the øresund-5 and -7 data is a function of both neogene uplift and drag along the inversion zone. the rank of the bajocian fuglunda member coal bed suggests c. 1450 m of total uplift, which appears to be a reasonable estimate based on the likely overburden and regional evidence, but it cannot be precluded that the rank has been increased due to hydrothermal influence. the total uplift of the anholt well-section is estimated to be c. 975 m, rather than the > 1200 m suggested by jensen & michelsen (1992) but in agreement with the c. 1000 m of nielsen et al. (2003, this volume). the data from anholt and bornholm may suggest that the amount of neogene–pleistocene uplift in skåne was relatively small compared to the northern part of the danish basin and the fennoscandian border zone, but further data are needed for confirmation. acknowledgements ole v. vejbæk and peter japsen are thanked for discussions, jørgen a. bojesen-koefoed kindly assisted with data plotting, and niels-erik hamann generously allowed us to include an unpublished figure (fig. 7). the referees, lars n. jensen and john e.a. marshall, are thanked for their constructive comments. references ahlberg, a. 1994: diagenesis of rhaetian–hettangian coal-bearing siliciclastic strata in nw skåne, southern sweden. in: ahlberg, a.: deposition and diagenesis of the rhaetian– hettangian succession (triassic–jurassic) in southern sweden, 53 pp. unpublished ph.d. thesis, lund university, sweden. ahlberg, a. & goldstein, r.h. 1994: fluid inclusions in quartz overgrowths: evidence of mid-jurassic volcanic hot brine flushing at shallow burial depth in the lower jurassic höör sandstone, southern sweden. in: ahlberg, a.: deposition and diagenesis of the rhaetian–hettangian succession (triassic–jurassic) in southern sweden, 53 pp. unpublished ph.d. thesis, lund university, sweden. ahlberg, a., sivhed, u. & erlström, m. 2003: the jurassic of skåne, southern sweden. in: ineson, j.r. & surlyk, f. 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(ed.): rift zones in the continental crust of europe – geophysical, geological and geochemical evidence: oslo – horn graben. tectonophysics 178, 29–49. vejbæk, o.v., stouge, s. & poulsen, k.d. 1994: palaeozoic tectonic and sedimentary evolution and hydrocarbon prospectivity in the bornholm area. danmarks geologiske undersøgelse serie a 34, 23 pp. ziegler, p.a. 1982: geological atlas of western and central europe, 130 pp. the hague: elsevier for shell internationale petroleum maatschappij. 630 manuscript received 12 january 1996; revision accepted 5 march 1997. geological survey of denmark and greenland bulletin 11, 61-86 61 origin and evolution of the kangâmiut mafic dyke swarm, west greenland kyle r. mayborn and charles e. lesher the kangâmiut dyke swarm in west greenland intruded archaean terrains at 2.04 ga, and its northern portion was subsequently metamorphosed to granulite facies during the nagssugtoqidian orogeny (c. 1.8 ga). mineral and whole-rock major and trace element compositions show that the parental magmas for the dyke swarm differentiated by the fractionation of olivine, clinopyroxene, plagioclase and late stage fe-ti oxides. petrographical observations and the enrichment of k 2 o during differentiation argue that hornblende was not an important fractionating phase. field observations suggest emplacement at crustal levels above the brittle–ductile transition, and clinopyroxene geothermobarometry constrains dyke emplacement depths to less than 10 km. granulite facies metamorphism of the kangâmiut dykes and their host rocks in the northern portion of the swarm requires subsequent burial to c. 30 km, related to roughly 20 km of crustal thickening between the time of dyke emplacement and peak metamorphism during the nagssugtoqidian orogeny. kangâmiut dykes are characterised by low ba/la ratios (12 ± 5), and high nb/la ratios (0.8 ± 0.2), compared to subduction related basalts (ba/la c. 25; nb/la c. 0.35). these geochemical characteristics argue that the kangâmiut dykes are not related to subduction processes. forward modelling of rare-earth element data requires that primitive magmas for the kangâmiut dykes originated from a moderately depleted mantle source with a mantle potential temperature of c. 1420°c. the inferred potential temperature is consistent with potential temperature estimates for ambient mantle at 2.0 ga derived from secular cooling models and continental freeboard constraints. the geochemistry and petrology of the kangâmiut dykes support a model that relates the dyke activity to passive rifting of the proposed kenorland supercontinent rather than to mantle plume activity or subduction. keywords: dyke swarm, laurentia, palaeoproterozoic, rifting _______________________________________________________________________________________________________________________________________________________________________ k.r.m., department of geology, western illinois university, macomb, il 61455, usa. e-mail: kr-mayborn@wiu.edu c.e.l., department of geolog y, university of california-davis, davis, ca 95616, usa. the 2.04 ga kangâmiut dyke swarm of west greenland has been the subject of numerous investigations over the past 35 years (windley 1970; escher et al. 1976; bridgwater et al. 1995; cadman et al. 1999), yet there is still considerable disagreement over many aspects of the swarm’s history. since the work of escher et al. (1976), who associated the dykes with synkinematic shearing during n–s compression, the swarm has often been cited as a type example of dykes that are emplaced into crustal regions undergoing shear deformation (cadman et al. 1999). the proposed compressional setting led cadman et al. (2001) to speculate that the swarm formed in a subduction-related environment. nevertheless, recent geochronology has shown that many of the shear zones originally thought to be consanguineous with the dykes are actually significantly older or younger than the dykes themselves (connelly & mengel 2000). the field area for escher et al.’s (1976) investigations is now known to contain archaean shear © geus, 2006. geological survey of denmark and greenland bulletin 11, 61–86. available at: www.geus.dk/publications/bull 62 zones and post-kangâmiut dyke shearing associated with the nagssugtoqidian orogeny. despite these complications, the kangâmiut dyke swarm offers a unique opportunity to constrain the magmatic and tectonic evolution of the province spanning the period from dyke emplacement to the nagssugtoqidian orogeny (2.04 to c. 1.8 ga). the present work discusses the constraints on the magmatic and metamorphic history of the kangâmiut dykes provided by field observations, petrology, geochemistry, and geochronology and critically evaluates previous and newly proposed models for their origin and subsequent metamorphism during the nagssugtoqidian orogeny. regional geology figure 1 is a geological map of central west greenland showing the nagssugtoqidian orogen and the kangâmiut dykes. the nagssugtoqidian orogen is bounded to the north by the palaeoproterozoic rinkian orogen (escher & pulvertaft 1976) and to the south by the archaean nain craton (nutman & bridgwater 1986; nutman & collerson 1991; friend & nutman 1994). the orogen is divided into four parts based on lithology, structure, stream sediment geochemistry, and aeromagnetic data. from north to south, these are the northern nagssugtoqidian orogen (nno), the central nagssugtoqidian orogen (cno), the southern nagssugtoqidian orogen (sno), and the southern nagssugtoqidian foreland (snf). these terrains are separated by three shear zones. the nordre strømfjord shear zone separates the nno from the cno, the ikertôq shear zone separates the cno from the sno, and the nagssugtoqidian front separates the sno from the snf. the nno contains archaean granitic gneisses and supracrustal rocks (van gool et al. 2002), whereas the cno is characterised by reworked archaean granitic and tonalitic gneisses, the 1.92 ga arfersiorfik quartz diorite, the 1.92 ga sisimiut charnockite, and supracrustal rocks (bak et al. 1975; kalsbeek et al. 1987; manatschal et al. 1998; kalsbeek & manatschal 1999; nutman et al. 1999; van gool et al. 1999). the sno and snf are composed of archaean granitic and tonalitic gneisses and the kangâmiut dykes. in the sno the dykes are metamorphosed to amphibolite facies in the south and granulite facies in the extreme north. the transition from amphibolite facies to granulite facies occurs within the ikertôq shear zone (korstgård 1979). in the snf, most of the kangâmiut dykes retain igneous textures and mineralogies. figure 1 shows that the ikertôq shear zone is the most continuous structure within the nagssugtoqidian orogenic belt and represents an important lithological boundary between the sno and the cno. it is traceable from the western shoreline, just south of the village of sisimiut, to the inland icecap. the shear zone contains panels of kangâmiut dyke-bearing tonalitic gneiss alternating with layers of garnet-sillimanite-kyanite-bearing metapelites, marbles, and quartzites that dip steeply nnw. the repetition of lithological units, the presence of down-dip lineations and s-vergent kinematic indicators show that this structure is a reverse fault (grocott 1979). deformed kangâmiut dykes are restricted to the southern footwall, while palaeoproterozoic felsic igneous rocks, including the 1.92 ga sisimiut charnockite and the 1.92 ga arfersiorfik quartz diorite, are found only north of the shear zone. u/pb dates for detrital zircons from the supracrustal rocks of the region require that these units were deposited after 2.10 ga (nutman et al. 1999), while 40ar/39ar dating of hornblende from metamorphosed kangâmiut dykes and orthogneisses from within the shear zone gives cooling ages of c. 1.73 ga (willigers et al. 1999). the itivdleq shear zone is located to the south of the ikertôq shear zone within the sno and is c. 6 km wide with e–w-trending lineations (hanmer et al. 1997). it contains multiple bands of sheared kangâmiut dykes and archaean orthogneisses that connelly & mengel (2000) used to document shearing during the archaean and the palaeoproterozoic nagssugtoqidian orogeny. for example, some of the shear bands are cut by weakly deformed tonalites that yield a magmatic age of 2498 ± 4 ma with a metamorphic overprint at 1782 ± 12 ma (connelly & mengel 2000). this shows that some of the shear bands near itilleq fjord developed prior to c. 2.5 ga and were subsequently intruded by tonalite. the metamorphic overprint age of 1782 ma and the presence of shear bands that cut the kangâmiut dykes indicate reactivation during the nagssugtoqidian orogeny. metamorphic hornblende from a recrystallised kangâmiut dyke within the itivdleq shear zone gives an 40ar/39ar age of 1873 ± 13 ma, consistent with the age of nagssugtoqidian metamorphism (willigers et al. 1999). the nagssugtoqidian front is the southernmost structural expression of the nagssugtoqidian orogenic event (fig. 1). hageskov (1995) showed that it is a discontinuous, en échelon array of nw-dipping, low-angle thrust facing page: fig. 1. geological map of the nagssugtoqidian orogen and its southern foreland in west greenland. nno, northern nagssugtoqidian orogen; cno, central nagssugtoqidian orogen; sno, southern nagssugtoqidian orogen; snf, southern nagssugtoqidian foreland. modified from van gool et al. (2002). 63 kangerlussuaq ikertooq northern cno ‘flat belt’ sisimiut nordre isortoqc n o sø nd re str øm fjo rd sø nd re str øm fjo rd sø nd re str øm fjo rd sukkertoppen iskappe inland ice attu n n o disko bugt qasigiannguit aasiaat itilleq kangaamiut maniitsoq sn o nordre strømfjord nord re str ømfjo rd shear zone no rdre iso rtoq she ar z one ikertôq shear zone sn f nagssugtoqidian front kangerluarsussuaq 68° 67° 52° 50° 66° 50 km archaean palaeoproterozoic undifferentiated archaean gneisses aasivik terrane kangâmiut mafic dyke swarm supracrustal rocks sisimiut charnockite syntectonic granite suite arfersiorfik quartz diorite aasivik 64 faults that deformed the kangâmiut dykes in this region. the nagssugtoqidian front is well defined in the eastern portion of the orogen but is difficult to trace to the west approaching the sukkertoppen iskappe. it is not known whether the nagssugtoqidian front dies out beneath the icecap or swings to the nnw merging with the itivdleq shear zone (hageskov 1995). geological history the precambrian history of central west greenland involves five major events: (1) genesis and metamorphism of archaean crust; (2) emplacement of the kangâmiut dykes (2.04 ga); (3) deposition of sediments (c. 2.00–1.92 ga); (4) emplacement of the sisimiut and arfersiorfik intrusions (c. 1.92–1.87 ga); and (5) metamorphism and deformation accompanying the nagssugtoqidian orogeny (c. 1.82– 1.77 ga). genesis and metamorphism of archaean crust connelly & mengel (2000) and kalsbeek & nutman (1996) present u/pb dates and field observations that document the genesis and metamorphism of a large portion of the central west greenland crust during the late archaean. igneous zircons from foliated granulite facies gneisses give ages between 2.87 and 2.81 ga. granitoids that cut the foliation in these gneisses give ages between 2.81 and 2.72 ga. these cross-cutting relationships and dates indicate widespread genesis of granitic crust between 2.87 and 2.81 ga, immediately followed by metamorphism at 2.81–2.72 ga. emplacement of the kangâmiut dykes the emplacement of the kangâmiut dykes occurred after the formation of the archaean host rocks and before the nagssugtoqidian orogeny. u/pb geochronology on igneous zircons from three dykes gives ages of 2036 ± 5 ma, 2046 ± 8 ma (nutman et al. 1999), and 2048 ± 4 ma (connelly et al. 2000). the analysed zircons come from dioritic centres in wide composite dykes and cover most of the n–s extent of the dyke swarm. 40ar/39ar dating of hornblende from the kangâmiut dykes from the snf by willigers et al. (1999) gives emplacement related ages of 2.05–2.02 ga. deposition of sediments dating of detrital zircons from metasedimentary units just south of the nordre strømfjord shear zone and within the ikertôq shear zone (fig. 1) yields ages between 3.4 and 1.95 ga (nutman et al. 1999). some metasediments containing 1.95 ga zircons are cut by 1.92 ga quartzdiorites, requiring that deposition of the sediments occurred between 1.95 and 1.92 ga. metasediments found within thrust-bounded panels in the ikertôq shear zone contain zircons that yield ages between 2.1 and 2.0 ga. there are no known granitic intrusive rocks with ages between 2.5 and 1.92 ga within the central west greenland field area, suggesting that the sediments originated from a distal source. nutman et al. (1999) propose that the archaean and palaeoproterozoic terranes of eastern canada are possible source regions. sediments derived from these terranes would support the existence of the supercontinent kenorland (williams et al. 1991; aspler & chiarenzelli 1998). additionally, the deposition of sediments suggests the presence of basins that may have developed during the rifting and break-up of kenorland (van gool et al. 2002). the nagssugtoqidian orogeny and emplacement of sisimiut and arfersiorfik intrusions ramberg (1949) and noe-nygaard (1952) first recognised the nagssugtoqidian orogen based on the deformation and metamorphism of the kangâmiut dykes and the occurrence of shear zones with steeply dipping foliations. geochronological data show that the nagssugtoqidian orogenic event occurred between 1.91 and 1.77 ga (connelly et al. 2000) and resulted in granulite to amphibolite grade metamorphism and the development of discrete shear zones. pre-orogenic magmatism includes the emplacement of the 1.92 ga arfersiorfik quartz diorite (kalsbeek et al. 1987) and the 1.92 ga sisimiut charnockite. the orogenic event is proposed to be the result of continental collision that produced thrust stacking, folding and associated metamorphism (van gool et al. 2002). the suture between the two continents is not easily identifiable, but kalsbeek et al. (1987) proposed that the suture is located in what is now the boundary between the nno and the cno. 65 previous work on the origin of the kangâmiut dykes many early workers suggested that the emplacement of the kangâmiut dykes was directly related to the nagssugtoqidian orogeny. escher et al. (1976) stated that the dykes were emplaced into conjugate sets of active shear zones during nnw–sse compression. they based this hypothesis on their observations of conjugate sets of dykes that show a variety of cross-cutting relationships. they, and hanmer et al. (1997), proposed that the emplacement of both dyke sets occurred during shearing. bridgwater et al. (1995) expanded on the escher et al. (1976) hypothesis by proposing that the dykes formed during thrusting of amphibolite facies crust from the north under the granulite facies terrain in the southern nagssugtoqidian orogen. they invoked this hypothesis because the kangâmiut dykes contain hornblende suggesting they crystallised from a hydrous magma. bridgwater et al.’s (1995) hypothesis seeks to explain the hydrous nature of the kangâmiut dyke magmas by placing a hydrous source beneath the granulite facies host rocks. a potential problem with the escher et al. (1976) and bridgwater et al. (1995) hypotheses is that neither easily explains how partial melting of hydrous lower crust would directly produce melt of basaltic composition. if the escher et al. (1976) and bridgwater et al. (1995) hypotheses of dyke emplacement during compression are correct, then subduction related magmatism becomes a possibility. cadman et al. (2001) explicitly consider this possibility and proposed that the kangâmiut dyke swarm formed by adiabatic decompression of metasomatised mantle during passage of a slab window. the recent work of kalsbeek & manatschal (1999), connelly & mengel (2000) and van gool et al. (2002), offer alternatives to the subduction hypothesis and suggest that the swarm was emplaced during continental rifting. van gool et al. (2002) cite evidence of 2.0 ga rift related sediments in support for the rifting hypothesis. kalsbeek & manatschal (1999) speculate that the kangâmiut dykes are the product of mantle plume-related rifting based on the presence of ultramafic rocks found within the nagssugtoqidian orogeny. although these authors discuss the origin of the kangâmiut dykes, they do so only briefly, because their primary focus is on the nagssugtoqidian orogeny. field setting the kangâmiut dyke swarm intruded granulite facies archaean orthogneisses and is exposed over an 18 000 km2 area. figure 1 shows that the swarm extends for 150 km from just south of the village of maniitsoq towards sisimiut in the north and from the coast eastward to the ice cap. the dykes are most abundant near the coast and less so towards the ice cap. dyke widths range from a few centimetres to greater than 140 m. escher et al. (1975) estimated that dyke emplacement was accommodated by 2–3% crustal extension. appendix a provides locality and field characteristics of all the dykes examined in this study. field observations show that there are three dyke suites (mengel et al. 1996). two of these trend east–west, while the third has a ne trend. the ne-trending suite of dykes represents the vast majority of the dykes in the area and is the only suite that contains dykes with dioritic centres. the three sets of zircon populations used to date three separate dykes all come from these dioritic centres (nutman et al. 1999; connelly et al. 2000). thus, the netrending suite is dated at 2.04 ga and will be referred to as the ‘kangâmiut dykes’ proper as suggested by mengel et al. (1996). although the kangâmiut dykes have an overall ne trend, there are some systematic deviations. figure 1 shows that the southern portion of the swarm trends nne. moving northward, the orientation gradually changes to ene. changes in the orientation of the swarm correlate with increased dyke deformation and recrystallisation. escher et al. (1975) suggested that the bend in the swarm resulted from deformation during the nagssugtoqidian. hanmer et al. (1997) argue that this change in orientation is a primary feature related to the regional stress field during dyke emplacement. the majority of dykes south of the nagssugtoqidian front retain igneous mineralogies and textures with the exception of a small number of composite dykes with sheared dioritic centres. shearing was parallel to the dyke contacts, and mostly affected the large composite dykes. windley (1970) worked in an area just north of maniitsoq village where he observed cross-cutting dykes. he described a set of cross-cutting dykes where a younger dyke cuts the internal foliation of an older dyke. not all of the composite dykes show internal deformation. some dykes show irregular intrusive contacts between the dioritic centre and mafic host dyke showing that they formed by successive injections, closely spaced in time. large composite dykes show structural and petrological features not seen in the smaller non-composite dykes. for example, a 140 m wide dyke in kangerluarsussuaq fjord has fine-grained (c. 0.1–0.5 mm) equigranular mafic contacts. twelve metres from the contact the grain size is c. 1 mm with some contact-parallel primary layering. halfway towards the dyke centre the grain size increases 66 to c. 3 mm with primary clinopyroxene mostly replaced by hornblende. near its centre the dyke is slightly foliated and recrystallised to a garnet amphibolite. the centre of the dyke is a strongly foliated garnet-plagioclase-hornblende schist with a dioritic composition. a 10 cm wide epidote-calcite-quartz vein originates from the sheared centre and cuts the non-sheared mafic portion of the dyke. there are a variety of intrusive relationships between dykes and host rocks including en échelon steps, bridges, and forks. figure 2 shows bridges with sharp, angular edges contained within the chilled margin of a kangâmiut dyke. some dykes have chilled margins up to 40 cm thick, while others have no chilled margins. chilled margins contain fine-grained plagioclase and clinopyroxene phenocrysts in a microcrystalline groundmass. some chilled margins contain dismembered bridges of host rock, whereas dyke interiors contain no bridges or xenoliths. in the northern portion of the dyke swarm, metamorphic minerals and deformation features replace igneous minerals and primary intrusive features. in the itilleq fjord region, most of the dykes are partly to completely altered during static or shear-related recrystallisation. some dykes show penetrative foliation, whereas other dykes are deformed only at the contacts and form boudins within the deformed country rock. the central portions of these boudins are partially recrystallised. on the south shore of itilleq fjord, away from most of the nagssugtoqidian deformation, the dykes preserve primary emplacement structures, but are statically recrystallised to garnet amphibolites. dykes at the northern extent of the swarm within ikertooq fjord are completely recrystallised to granulite facies. petrography the chilled margins of the kangâmiut dykes contain 0.2– 0.8 mm phenocrysts of clinopyroxene and plagioclase in a microcrystalline groundmass of plagioclase, clinopyroxene, hornblende, quartz, and fe-ti oxides. plagioclase phenocrysts are euhedral to subhedral and weakly zoned, whereas the clinopyroxene phenocrysts are subhedral to anhedral. some chilled margins contain 0.2–1.5 mm hornblende crystals. figure 3a shows that these hornblende crystals contain abundant inclusions of fe-ti oxides, which are absent from the clinopyroxene and plagioclase phenocrysts. these hornblende crystals also enclose plagioclase and clinopyroxene phenocrysts suggesting they are a later phase that crystallised in situ. the interiors of most kangâmiut dykes are fineto medium-grained with subophitic textures. subhedral to anhedral clinopyroxene, plagioclase, and fe-ti oxides are the primary constituents along with interstitial quartz, hornblende, and trace amounts of apatite. in some of the dykes, anhedral clinopyroxene fills interstitial areas between subhedral to euhedral plagioclase. clinopyroxene displays two types of exsolution. the first type is laminar exsolution of low-ca pyroxene. the second type appears to be granular exsolution of low-ca pyroxene around the outer parts of the original clinopyroxene crystal. additionally, most clinopyroxene grains have rims of hornblende (fig. 3b). kangâmiut dyke samples from itilleq fjord are variably metamorphosed to fine-grained (0.2–1.0 mm) amphibolites with well-developed foliations. metamorphic assemblages include hornblende, plagioclase, quartz, garnet, titanite, and biotite. hornblende replaces clinopyroxene, whereas plagioclase and garnet form at contacts between hornblende and plagioclase (see also mengel et al. 1996). titanite replaces fe-ti oxides. metamorphic orthopyroxene occurs within kangâmiut dykes in ikertooq fjord near the northern extent of the swarm (fig. 1), marking the transition from amphibolite to granulite facies. the typical assemblage in these granulite facies dykes is plagioclase + hornblende + orthopyroxene + clinopyroxene ± garnet ± titanite (see also korstgård fig. 2. kangâmiut dyke with angular bridges within the chilled margin (photo: david bridgwater). 67 1979). these dykes are weakly foliated and fine-grained (0.1–1.0 mm). petrology and geochemistry whole-rock major and trace elements a total of 122 dyke samples were analysed for most major and minor elements on fused glass discs using a wavelength dispersive x-ray fluorescence (xrf) spectrometer at the geological survey of denmark and greenland (geus) in copenhagen. na 2 o was determined by atomic absorption spectrometry. kystol & larsen (1999) describe the analytical methods, precision, and accuracy of the geus lab and report that the standard error for all major and minor elements is less than 0.25 wt%, based on multiple analyses of international standards. trace element concentrations for 73 dyke samples were measured at the university of california-davis using a 1.0 mm plag hbl cpx a hbl plag cpx 0,5 mm b fig. 3. a: photomicrograph of a chilled margin of a kangâmiut dyke with clinopyroxene (cpx) and plagioclase (plag) phenocrysts in a groundmass of the same plus fe-ti oxides. the large crystal in the centre is hornblende (hbl) with inclusions of a plagioclase phenocryst and groundmass plagioclase and fe-ti oxides. sample ggu 430267, plane polarised light. b: photomicrograph of a sample from the interior of a kangâmiut dyke showing hornblende (hbl) rims on clinopyroxene (cpx). sample ggu 430999, plane polarised light. 68 perkin-elmer elan 500 inductively coupled plasma mass spectrometer (icp-ms). samples were prepared for analyses using the method described by jenner et al. (1990) with the exception that we utilised microwave digestion bombs to insure total dissolution. table 1 presents representative major and trace element data for the kangâmiut dykes, and figs 4 and 5 show these data in covariation diagrams. the full data set is available upon request from the first author. the kangâmiut dykes cover a range from 9.0–0.9 wt% mgo and the majority of the dykes would be classified as medium-k basalts or low-k basalts based on their k 2 o and sio 2 contents (le maitre 2002). first order observations of the major and compatible trace element data, as described below, indicate that the differentiation of the parental magma(s) of the kangâmiut dykes was influenced by the fractionation of plagioclase, clinopyroxene, late stage feti oxides and possibly olivine. first order observations based on covariation diagrams neither support nor refute the involvement of hornblende as a fractionating phase. figure 4c shows al 2 o 3 concentrations that range between 11.4 and 15.8 wt%. the highest mgo sample has a low al 2 o 3 concentration, whereas the next group of dykes at c. 7.0–7.5 wt% mgo have higher concentrations of al 2 o 3 . this increase of al 2 o 3 between c. 9 and 7 wt% mgo likely reflects olivine and/or clinopyroxene fractionation. clustering of data between 7.5 and 4.5 wt% mgo defines a trend of decreasing al 2 o 3 with decreasing mgo, indicative of plagioclase fractionation. the initial increase in total feo (feo + 0.9 × fe 2 o 3 ) between c. 8.0 and 4.5 sample 430904 430923 430926 430931 430952 430970 430981 430988 430997 dyke 5 13 14 16 27 37 42 45 54 sio2 50.87 52.78 50.64 50.73 52.19 48.90 50.71 49.30 56.06 tio2 2.47 2.31 1.94 0.88 1.62 1.66 1.02 1.45 0.79 al2o3 12.62 13.65 13.29 12.57 13.19 13.14 14.09 13.34 21.46 fe2o3 4.27 3.53 4.26 1.74 4.14 2.52 1.55 1.91 1.24 feo 11.67 11.34 9.99 9.10 11.05 11.98 9.89 11.40 4.34 mno 0.24 0.20 0.22 0.21 0.24 0.24 0.21 0.22 0.08 mgo 4.27 3.51 5.55 8.90 4.57 6.40 7.43 6.60 0.92 cao 8.93 8.24 9.86 12.31 8.48 10.85 11.27 11.39 9.07 na2o 2.47 2.91 2.55 2.27 2.80 2.28 2.15 2.25 4.19 k2o 0.69 1.13 0.58 0.18 0.87 0.28 0.18 0.30 0.51 p2o5 0.26 0.29 0.19 0.07 0.19 0.13 0.09 0.13 0.16 loi 0.84 0.63 0.94 0.91 1.07 1.34 0.79 1.31 0.79 sum 99.60 100.52 100.03 99.88 100.40 99.72 99.39 99.58 99.61 sc 38 30 36 58 44 46 47 45 14 v 368 355 333 389 318 381 296 362 29 cr 47 14 63 145 43 63 153 98 5 ni 40 28 65 113 40 74 88 60 1 co 46 44 47 52 44 61 51 56 14 rb 22 33 16 3.9 25 5.6 4.3 6.1 10 sr 171 201 241 117 207 160 136 160 290 y 47 34 29 19 35 27 18 27 34 zr 182 168 139 47 133 99 46 92 157 nb 14.7 10.9 11.8 3.3 9.2 9.2 3.2 8.2 11.3 ba 204 321 156 50 306 90 50 95 192 la 17.5 20.5 17.1 4.4 12.7 9.2 4.4 8.4 12.3 ce 43.8 46.0 40.2 10.6 31.9 21.8 10.7 20.7 32.0 pr 6.07 6.13 5.41 1.49 4.43 3.10 1.70 3.00 4.54 nd 27.8 27.1 22.7 7.37 18.8 14.2 7.31 13.9 20.6 sm 7.14 6.11 5.44 2.45 4.58 3.93 2.32 3.71 5.09 eu 2.08 1.84 1.66 0.82 1.56 1.33 0.89 1.22 1.88 gd 7.52 6.84 5.55 3.01 5.42 4.51 2.76 4.16 5.41 tb 1.33 1.12 0.87 0.51 0.95 0.79 0.50 0.73 0.90 dy 8.17 6.80 5.22 3.12 5.63 4.61 3.10 4.37 5.44 ho 1.62 1.28 1.06 0.68 1.22 0.99 0.69 0.93 1.15 er 4.76 3.73 2.96 1.90 3.39 2.75 2.12 2.56 3.23 tm 0.70 0.52 0.42 0.30 0.52 0.42 0.29 0.38 0.48 yb 4.52 3.34 2.67 1.97 3.53 2.61 1.96 2.54 3.11 lu 0.63 0.49 0.39 0.29 0.54 0.42 0.29 0.37 0.45 hf 4.78 4.60 3.68 1.27 3.54 2.77 1.44 2.47 4.13 ta 1.03 0.76 0.82 0.26 0.64 0.54 0.24 0.52 0.72 pb 4.04 5.81 3.26 1.49 6.50 1.84 1.08 3.35 3.78 th 2.83 3.80 2.12 0.50 3.47 0.90 0.42 0.90 1.88 u 0.71 0.93 0.54 0.14 0.79 0.24 0.11 0.24 0.49 table 1. major and trace element data for representative kangâmiut dykes major element oxides in wt%; trace elements in ppm. sample numbers refer to geus databases. dyke localities shown in fig. a1 (appendix). 432102 432108 432115 432118 432122 432133 432138 432143 432158 86 60 64 64 64 71 70 76 75 57.18 48.97 51.01 56.84 50.25 51.00 49.46 50.57 50.48 1.65 1.69 1.92 2.12 1.82 1.64 2.70 1.33 1.34 14.37 13.75 12.97 13.07 13.67 13.96 15.57 13.14 13.59 2.15 4.73 2.21 1.98 2.17 2.06 2.54 1.26 1.75 8.94 9.48 12.73 10.99 12.22 11.59 11.51 11.99 11.84 0.16 0.23 0.24 0.19 0.23 0.21 0.20 0.23 0.23 2.34 6.12 5.08 2.14 5.81 4.78 3.44 6.98 6.12 6.11 10.72 9.46 6.17 10.12 9.53 8.61 11.40 10.59 3.69 2.44 2.57 3.37 2.45 2.46 2.99 2.11 2.07 1.14 0.39 0.52 1.43 0.33 0.47 1.02 0.22 0.35 0.35 0.15 0.19 0.39 0.10 0.18 0.44 0.10 0.13 1.43 1.41 1.01 1.17 0.91 1.64 1.35 1.11 1.06 99.50 100.08 99.90 99.86 100.07 99.53 99.83 100.44 99.55 20 38 41 22 41 36 29 49 45 155 348 393 207 558 303 259 390 336 33 134 83 22 94 61 33 174 103 17 82 54 15 66 49 23 78 74 28 53 46 32 54 49 32 53 52 31 7.4 13 45 8.0 12 28 4.6 8.5 306 235 164 247 164 200 213 138 142 35 26.2 37 48 23 30 53 24 28 194 106 133 326 78 110 200 58 84 18.1 9.3 10.0 23.9 6.2 7.3 15.8 4.6 5.2 392 104 145 454 98 156 366 69 106 27.8 10.86 12.9 42.0 7.4 11.4 18.2 5.8 7.6 63.9 26.28 30.6 94.4 18.1 26.7 40.4 14.1 18.0 8.66 3.73 4.36 11.96 2.58 3.83 5.58 2.07 2.67 36.2 16.93 19.1 49.7 11.6 17.3 25.7 9.90 12.2 8.12 4.35 5.05 10.85 3.02 4.71 6.91 2.72 3.24 2.49 1.45 1.68 2.93 1.10 1.47 2.20 1.02 1.20 6.98 4.46 5.27 10.02 3.51 4.86 7.39 3.27 3.99 1.11 0.75 0.99 1.47 0.60 0.82 1.32 0.57 0.68 6.31 4.47 6.23 8.26 3.75 5.01 8.56 3.68 4.51 1.20 0.98 1.24 1.60 0.81 1.08 1.88 0.82 1.04 3.19 2.44 3.71 4.22 2.28 2.92 5.03 2.36 2.89 0.45 0.34 0.57 0.61 0.34 0.41 0.70 0.36 0.41 2.89 2.31 3.45 3.90 2.20 2.67 4.97 2.31 2.81 0.44 0.35 0.55 0.55 0.32 0.43 0.74 0.35 0.41 4.68 2.83 3.49 7.64 2.10 2.78 5.19 1.59 2.36 1.27 0.64 0.66 1.55 0.41 0.50 0.98 0.30 0.34 3.65 1.92 2.63 4.89 1.73 3.07 6.66 1.03 1.88 4.52 1.19 1.73 7.92 1.00 1.61 3.88 0.60 1.04 1.10 0.29 0.46 1.92 0.28 0.40 0.87 0.16 0.29 69 wt% mgo is also indicative of plagioclase fractionation (fig. 4d). figure 4e shows that cao ranges from 12.4 to 6.0 wt% and correlates positively with mgo, indicating that clinopyroxene and/or plagioclase was part of the fractionating assemblage. figure 6 shows the cao/al 2 o 3 ratio for the kangâmiut dykes decreases with decreasing mgo, and fig. 5a shows decreasing sc with increasing zr. both of these observations further indicate that clinopyroxene was a fractionating phase. the decrease in nickel with increasing zirconium, shown in fig. 5c, is related to clinopyroxene and/or olivine fractionation. figure 4b shows tio 2 concentrations that range from 0.9–3.5 wt% with trends that show increasing tio 2 from 9–4.5 wt% mgo that changes to decreasing tio 2 below c. 4.5 wt% mgo. figure 4d shows that a similar trend is a b c d e f g h 5 0 5 5 6 0 sio2 4 5 4 6 8 10 12 14 cao 0.5 1.5 2.5 3.5 tio2 10 12 14 16 18 al2o3 4 8 12 16 20 feo* 1.5 2.5 3.5 4.5 na2o 0 0.0 0.4 0.8 1.2 1.6 2.0 mgo k2o 2 4 6 8 10 0.0 0.2 0.4 0.6 mgo p2o5 0 2 4 6 8 10 fig. 4. variations of sio 2 , tio 2 , al 2 o 3 , feo, cao, na 2 o, k 2 o, p 2 o 5 with mgo (in wt%) for the kangâmiut dykes. all analyses are recalculated on an anhydrous basis with all iron as feo. 70 observed for total feo. additionally, vanadium (fig. 5d) shows an initial increase, then decrease with increasing zirconium. these changes from increasing to decreasing tio 2 , feo and vanadium concentrations suggest fe-ti oxides fractionated when the magmas reached c. 4.5 wt% mgo. mineral chemistry major element compositions of pyroxenes, plagioclase, and hornblende were acquired using a cameca sx-50 microprobe at the university of california-davis. analyses were made using a 15 kv accelerating voltage, a 10 na beam current, and a 1 µm beam. elements were calibrated using mineral standards. the data in tables 2–4 give the compositions of clinopyroxene, plagioclase, and hornblende phenocrysts from chilled margins. table 2 presents major and minor element compositions of clinopyroxene phenocrysts from chilled margins based on the average of 2–4 spot analyses of 4–7 grains per sample. the proportions of enstatite, ferrosilite, and wollastonite components are 0.48–0.52, 0.13–0.23, and 0.28–0.35, respectively. al 2 o 3 concentrations range from 3.93–2.75 wt%, while na 2 o varies from 0.36–0.26 wt%. table 3 presents plagioclase phenocryst compositions from chilled margins. plagioclase phenocryst cores have an anorthite (an) component range of an 69 –an 55 . table 4 presents compositions of the hornblendes found in the chilled margins of some kangâmiut dykes. they would be classified as ferrohornblende and ferrotschermakite based on the classification of leake et al. (1997). whole-rock and mineral compositions in projection space figure 7 shows pseudo-ternary projections of whole-rock and mineral data for the kangâmiut dykes. the components cpx, plag, ol, and qtz were calculated using major and minor elements and the scheme of tormey et al. (1987). in the projection from qtz (fig. 7a), the dyke data form a cluster that is displaced from the centre 1 0 2 0 3 0 4 0 5 0 6 0 a b c d sc sr ni v zr zr 5 0 1 5 0 2 5 0 3 5 0 4 5 0 0 4 0 8 0 1 2 0 0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 fig. 5. variation of sc, sr, ni, and v with zr (in ppm) for the kangâmiut dykes. 0 2 4 6 8 1 0 mgo 0.2 0.4 0.6 0.8 1.0 1.2 cao/al2o3 pl cpx ol fig. 6. variation of cao/al 2 o 3 with mgo. arrows show path caused by fractionation of olivine, clinopyroxene, or plagioclase from a starting composition with 9 wt% mgo and ca/al 2 o 3 = 1.0. 71 of the ternary plot towards the plag apex. in this projection all the dykes lie within the phase volumes defined by the joins between olivine, clinopyroxene and plagioclase (ol:cpx:pl) or hornblende, clinopyroxene and plagioclase (hbl:cpx:pl). in the projection from the cpx component (fig. 7b), the dykes define an array that projects away from both the pl:ol and the pl:hbl joins. similarly, in the projection from the plag component (fig. 7c), the dykes form an array that intersects both the cpx:ol and cpx:hbl joins. these observations show that plagioclase, clinopyroxene and either olivine or hornblende were cofractionating phases. a and c in fig. 7 also show experimentally determined 1 atm and 0.8 gpa ol:cpx:pl cotectics derived from melting experiments using a primitive kangâmiut dyke (dyke #45) as the starting material (mayborn 2000). the wholerock data form a cluster near the low pressure ol:cpx:pl cotectic in the projection from the qtz component. similarly, in the projection from the plag component the whole-rock data also plot close to the low-pressure cotectic. incompatible trace element behaviour figure 8 shows representative chondrite normalised rareearth element (ree) patterns for the kangâmiut dykes. the dykes are slightly light rare-earth element (lree) enriched with a la/sm n ratio ranging from 1.16 to 2.50, with an average of 1.50. the heavy rare-earth (hree) patterns have shallow slopes with a dy/yb n range of 1.05 sio2 52.34 50.68 51.88 51.17 52.01 51.36 51.85 51.59 tio2 0.47 0.65 0.44 0.61 0.45 0.34 0.44 0.60 al2o3 3.17 3.93 3.14 3.21 3.34 2.75 3.63 2.68 cr2o3 0.11 0.19 0.18 0.21 0.22 0.08 0.18 0.07 feo 8.29 9.83 8.76 12.45 9.43 13.79 9.72 12.94 mgo 16.46 15.18 15.70 15.62 15.54 16.94 15.62 15.37 cao 19.59 19.18 18.96 16.16 19.01 14.32 18.01 16.52 na2o 0.29 0.32 0.26 0.29 0.28 0.36 0.31 0.26 sum 100.72 99.96 99.31 99.72 100.28 99.94 99.76 100.03 si 1.917 1.886 1.927 1.913 1.920 1.922 1.920 1.928 al(iv) 0.083 0.114 0.073 0.087 0.080 0.078 0.080 0.072 al(vi) 0.053 0.058 0.065 0.055 0.065 0.074 0.079 0.046 ti 0.013 0.018 0.012 0.017 0.012 0.011 0.012 0.017 cr 0.003 0.006 0.005 0.006 0.007 0.001 0.005 0.002 fe3+* 0.022 0.039 0.000 0.013 0.004 0.016 0.000 0.010 fe2+ 0.232 0.266 0.274 0.377 0.287 0.401 0.308 0.395 mn 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 mg 0.899 0.842 0.870 0.871 0.855 0.858 0.862 0.856 ca 0.768 0.765 0.755 0.647 0.752 0.611 0.715 0.661 na 0.021 0.025 0.020 0.021 0.020 0.036 0.022 0.019 k 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 total 4.011 4.020 4.001 4.006 4.002 4.008 3.996 4.005 mg# 0.78 0.73 0.76 0.69 0.75 0.67 0.74 0.68 wo 0.35 0.34 0.35 0.29 0.34 0.28 0.33 0.30 en 0.52 0.51 0.50 0.50 0.49 0.49 0.50 0.48 fs 0.13 0.16 0.16 0.22 0.17 0.23 0.18 0.22 sample 430988 432108 432145 432148 432158 430211 430267 430283 dyke 45 60 76 77 75 82 84 85 n = 7 n = 8 n = 6 n = 8 n = 8 n = 8 n = 10 n = 10 table 2. microprobe analyses of clinopyroxene phenocrysts from chilled margins oxides in wt%; n = number of grains. fe3+* calculated using the method of papike et al. (1974). dyke localities shown in fig. a1 (appendix). sample 430988 432108 432145 432148 432158 430211 dyke 45 60 76 77 75 82 n = 8 n = 8 n = 8 n = 8 n = 7 n = 8 sio2 52.18 49.74 53.36 53.79 51.23 54.13 al2o3 30.45 31.49 29.65 29.65 30.91 29.03 feo 0.65 0.57 0.59 0.74 0.96 0.92 cao 13.11 14.13 12.43 12.23 13.34 11.24 na2o 4.02 3.36 4.33 4.64 3.89 4.84 k2o 0.05 0.05 0.09 0.07 0.09 0.17 sum 100.46 99.34 100.45 101.12 100.41 100.34 ab 35 30 38 40 34 43 an 64 69 61 59 65 55 or 0.3 0.3 0.5 0.4 0.5 1.0 table 3. microprobe analyses of plagioclase phenocrysts from chilled margins oxides in wt%; n = number of grains. dyke localities shown in fig. a1 (appendix). sample 432158 430267 430283 dyke 75 84 85 n = 12 n = 14 n = 6 sio2 43.90 42.63 40.88 tio2 1.04 1.92 1.64 al2o3 10.69 10.05 9.98 feo 21.09 21.73 24.02 mno 0.22 0.19 0.21 mgo 8.09 8.05 6.44 cao 10.93 10.78 10.58 na2o 1.18 1.63 1.58 k2o 0.99 0.90 0.90 cl 0.57 0.67 0.65 f 0.09 0.05 0.14 sum 98.79 98.60 97.02 si 6.549 6.425 6.346 ti 0.117 0.218 0.192 al(iv) 1.451 1.575 1.654 al(vi) 0.427 0.209 0.172 fe3+ 0.767 0.799 0.922 fe2+ 1.864 1.940 2.196 mn 0.027 0.025 0.027 mg 1.798 1.809 1.491 ca 1.747 1.741 1.760 na(m4) 0.253 0.259 0.240 na(a) 0.089 0.217 0.237 k(a) 0.189 0.172 0.178 total 15.28 15.39 15.41 table 4. microprobe analyses of amphiboles from chilled margins oxides, cl and f in wt%. dyke localities shown in fig. a1 (appendix). 72 plag cpx ol proj. from qtz 0.8 gpa 1 atm 0.8 gpa 1 atm proj. from cpx ol plag 0.5 qtz 0.5 qtz cpx plag 0.5 qtz proj. from ol 0.5 qtz proj. from plag cpx ol 0.5 qtz 0.5 qtz ol:pl 17:83 hbl:pl 55:45 hbl:cpx:pl 40:20:40 ol:cpx:pl 10:40:50 kangâmiut dykes clinopyroxene hornblende plagioclase a b d c ol qtzplag +cpx ol qtz +plag cpx +ol qtzplag cpx fig. 7. pseudo-ternary projections of whole-rock and mineral compositions from the kangâmiut dykes using the projection scheme of tormey et al. (1987). dashed lines connect possible crystallisation assemblages. solid lines through data show the trend of kangâmiut dykes where this is well defined, and the locations of the olivine:clinopyroxene:plagioclase cotectics at 0.8 gpa and 1 atm. a: projection from the qtz component. b: projection from the cpx component. c: projection from the plag component. d: projection from the ol component. to 1.46 and an average of 1.15. the two most lreeenriched samples come from sheared dioritic centres and have dy/yb n ratios of 1.46 and 1.42, respectively. the patterns for the sheared dioritic centres cross-cut the patterns for non-sheared dykes. figure 9a shows incompatible trace elements for the kangâmiut dykes on primitive mantle normalised compatibility diagrams (thompson 1982). the elements on the right hand side of fig. 9a are moderately incompatible, with incompatibility increasing towards the left using the element order from sun & mcdonough (1989). the most primitive kangâmiut dykes have the lowest concentration of incompatible elements and have flat patterns with small negative nb and zr anomalies. the negative sr anomaly seen in the more evolved samples reflects plagioclase fractionation. the two most evolved samples 73 of peridotite is the mantle, then the basaltic nature of the kangâmiut dykes indicates that they resulted from partial melting of mantle peridotite followed by intracrustal differentiation. three settings where mantle melting occurs beneath continental crust are (1) subduction zones, (2) active rifts associated with mantle plumes, and (3) passive rift settings. each of these settings can have distinctive mantle compositions and conditions for melting 5 1 0 1 0 0 5 0 0 la ce pr nd sm eu gd tb dy ho er tm yb lu 430931 432143 430988 432115 432138 432102 432118 sample/chondrite 3 1 0 1 0 0 430931 432143 430988 432115 432138 432102 432118 rb ba th u nb la ce sr nd zr sm eu ti dy y yb lu sample/primitive mantle sample/primitive mantle 0 . 5 1 1 0 1 0 0 rb ba th u nb la ce sr nd zr sm eu ti dy y yb lu n-morb oib cfb island arcs primitive k-dykes continental arcs a b fig. 8. rare-earth element compositions of representative kangâmiut dykes normalised to c1 chondrite. chondrite normalising values from sun & mcdonough (1989). fig. 9. a: normalised incompatible trace element compositions of representative kangâmiut dykes. b: comparison of the kangâmiut dykes with normal mid-ocean ridge basalts (n-morb), ocean-island basalts (oib), island arc basalts, continental flood basalts (cfb), and continental arcs. representative ‘primitive kangâmiut dykes’ is the average composition of 18 kangâmiut dykes with a mgo range of 8.9–6.1 wt%. data for n-morb and oib are from sun & mcdonough (1989). island arc data compiled from bailey et al. (1989), pearce et al. (1995), and gust et al. (1997). cfb data compiled from hooper & hawkesworth (1993), lightfoot et al. (1993), wooden et al. (1993), peate & hawkesworth (1996) and storey et al. (1997). continental arc data compiled from tormey et al. (1991) and bacon et al. (1997). (432102 and 432118) are sheared dioritic centres and display negative ti anomalies. they also show a depletion of hree, as noted in fig. 8. figure 9b shows representative patterns for basalts from a variety of tectonic settings and a pattern representing the average of kangâmiut dykes with mgo > 6 wt%. notable features in the kangâmiut pattern are a smooth, slightly increasing trend from right to left through the moderately incompatible elements (lu to sm), small negative anomalies of nb, sr, and zr, and a relatively flat trend for th, ba and rb. the kangâmiut dyke pattern is distinct relative to the ocean island basalt (oib), midocean ridge basalt (morb), island arc basalt (iab), and continental arc basalt (cab) patterns. for example, the kangâmiut dykes do not display the enrichment of highly incompatible elements, or the positive nb anomaly seen in the oib pattern, or depletions seen in the morb pattern. relative to iab and cab, the kangâmiut dyke patterns do not exhibit the large negative nb anomaly or the positive sr anomaly. overall, the kangâmiut dyke pattern most closely resembles the pattern for continental flood basalts (cfb), including the shallow slope of the pattern, and the small negative nb and sr anomalies. discussion tectonic setting one of the primary goals of this study is to constrain the tectonic environment during emplacement of the kangâmiut dykes. experimental melting studies over the past 40 years have shown that basalts are products of partial melting of peridotite (reay & harris 1964; takahashi 1986; baker & stolper 1994). since the dominant source 74 that are reflected in the trace element compositions of the associated basalts. the kangâmiut dykes have evolved compositions with a mg-number (defined as 100mg/(mg + fe) on a molecular basis) range of 0.60–0.21. magmas in equilibrium with mantle peridotite will have a mg-number close to 0.71 (roeder & emslie 1970; langmuir et al. 1992) showing that even the most primitive kangâmiut dykes represent somewhat evolved magmas. thus, the major elements reflect both the fractionation and mantle melting histories. however, most incompatible trace element ratios remain relatively constant during crystallisation and can be used to constrain primary source characteristics. the following discussion examines some characteristics of the mantle source and the conditions of mantle melting revealed by examining incompatible trace elements from the more primitive dyke samples (with mgo > 4.5 wt%). subduction hypothesis for generation of kangâmiut dykes subduction environments generate basaltic melts by two different mechanisms of partial melting. the first is melting induced by lowering the solidus temperature of the peridotite by the introduction of volatiles from the subducting slab and subsequent decompression melting within the mantle wedge (jakes & gill 1970; tatsumi 1989; arculus 1994). the second is decompression melting associated with back-arc spreading (tatsumi et al. 1989; gribble et al. 1998). although the mechanisms of melting in these settings are different from each other, they both produce magmas with a compositional ‘subduction component’ that is indicative of a hydrated and metasomatised mantle. some important characteristics of subduction zone basalts are hfse depletions, lile enrichment, and high al 2 o 3 . the available data can be used to evaluate the subduction hypothesis for the kangâmiut dyke swarm implied by escher et al. (1976) and bridgwater et al. (1995), and explicitly proposed by cadman et al. (2001). as shown in fig. 9b, arc basalts have distinctive depletions in hfse. these hfse depletions occur in palaeozoic, proterozoic, and archaean arc-related basalts, suggesting that modern style subduction occurred in the archaean (stern et al. 1994; blichert-toft et al. 1995). in addition to hfse depletions, arc basalts are enriched in lile (e.g. pb, k, ba, rb, and cs) relative to basalts from other tectonic settings. this enrichment is proposed to 0 1 0 2 0 3 0 4 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 nb/la ba/la continental and island arc basalts kangâmiut dykes clear lake basalts continental flood basalts fig. 10. ba/la versus nb/la showing the differences between arc basalts, the kangâmiut dykes, and basalts from the clear lake volcanic field. data for the arc field are from bailey et al. (1989), tormey et al. (1991), francalanci et al. (1993), pearce et al. (1995), bacon et al. 1997), gust et al. (1997), and kelemen et al. (2003). data for the continental flood basalt field are from hooper & hawkesworth (1993), lightfoot et al. (1993), wooden et al. (1993), peate & hawkesworth (1996), and storey et al. (1997). data for the clear lake volcanic field are from charles lesher (unpublished data). 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 1.0 1.5 2.0 2.5 3.0 3.5 la/smn dy/ybn 3.0 2.9 2.8 2.7 2.6 2.5 2.42.22.01.81.61.4 2% 4% 6% de gr ee o f m elt ing s o lid u s p re ss u re ( g p a ) segregation pressure (gpa) fig. 11. chondrite-normalised dyyb versus la/sm ratios for the kangâmiut dykes and mantle melting models using the algorithm of fram & lesher (1993) based on a 0.5% depleted pm source composition, where f is the melt proportion. the model assumes partial melting proceeds by incremental non-modal batch melting at 1% per kbar of decompression in a corner flow melting regime. melts are pooled after each kbar of decompression. ree distribution coefficients are taken from green (1994). the garnet-spinel transition is modelled as a gradual change between 30 and 25 kbar. the spinel–plagioclase transition is modelled as a gradual change between 14 and 10 kbar. residues are recalculated after each melting increment and adjusted for pressure dependent phase transitions using melting reactions as given by fram & lesher (1993). model curves, for melting starting at 3.0, 2.9, 2.8, 2.7, 2.6 and 2.5 gpa and ending at 0.5 gpa, define a melting grid, where solid subvertical lines contour constant mean melt fraction, whereas the dashed subvertical lines contour final pooled melt segregation pressure (i.e. the top of the melting column). slightly modified from mayborn & lesher (2004). 75 occur during the flux of fluids from the slab into the mantle wedge (miller et al. 1994; pearce et al. 1995; becker et al. 1999). mafic rock suites in volcanic arc settings also typically contain a large proportion of high-alumina basalts (perfit et al. 1980; brophy & marsh 1986; kelemen et al. 2003). if the kangâmiut dykes are arc-related, they should show lile enrichment, hfse depletions, and high al 2 o 3 . figure 10 shows a comparison of the nb/la and ba/la ratios for the kangâmiut dykes, island arcs, continental arcs, and continental flood basalts. relative to arc basalts, the kangâmiut dykes have lower ba/la and nb/la ratios – unlike arc-related basalts. additionally, subduction zone basalts typically have al 2 o 3 contents of 19–15 wt% (plank & langmuir 1988, 1992; kelemen et al. 2003), whereas all of the kangâmiut dykes have lower al 2 o 3 concentrations (16–12 wt%). thus, the kangâmiut dykes have none of the geochemical characteristics of subduction related basalts, contrary to previous conjecture (cadman et al. 2001). a more detailed analysis of the cadman et al. (2001) hypothesis also raises significant questions about its viability. cadman et al. (2001) propose that the kangâmiut dykes formed after ridge subduction resulting in a ‘slab window’ passing beneath metasomatised mantle. the resulting mantle upwelling lead to melting within hydrated mantle wedge material. although cadman et al.’s hypothesis would explain elevated water contents postulated for kangâmiut dyke magmas, such an origin would also be expected to impart an arc geochemical signature to the magmas. it is instructive to directly compare the composition of the kangâmiut dykes with those from the clear lake volcanic field located in the coastal region of northern california and associated with the development of a slab window after passage of the mendocino triple junction (furlong & schwartz 2004). figure 10 compares the ba/la and nb/la ratios for clear lake basalts, with typical arc basalts, the kangâmiut dykes and continental flood basalts. it is evident from these, among other, geochemical indices that the kangâmiut dykes lack the expected arc signature postulated by cadman et al. (2001). rather the kangâmiut dykes have compositions consistent with their derivation from asthenospheric mantle supplying normal continental flood basalts. active rifting, plume and passive rifting hypotheses the temperature of the mantle is an important difference between plume associated rifting and passive rifting. mayborn & lesher (2004) presented a detailed analysis of the temperature of the mantle during kangâmiut dyke magma genesis as constrained by ree systematics. they used the algorithm of fram & lesher (1993), as shown in fig. 11, to propose that the kangâmiut dykes are the results of mantle melting with a mean solidus pressure of c. 2.75 gpa and a mean extent of melting of 5%. when compared to the solidus for nominally anhydrous mantle (fig. 12), this mean solidus temperature would correspond with a potential mantle temperature of 1420°c. this temperature estimate falls at the lower end of potential temperatures estimated for c. 2.0 ga mantle by richter (1984, 1420–1600°c) and abbott et al. (1994, 1380–1680°c) based on secular cooling models and geochemical data for precambrian morb-type basalts, respectively. addition1200 1400 1600 1800 0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 pressure (gpa) temperature (°c) modern adiabat (tp = 13 00°c) 2.0 ga adiabat (tp = 1 420°c) 2.0 ga plume adiabats ma ntl e s oli du s fig. 12. plot showing the fertile peridotite solidus and adiabats for modern mantle, 2.0 ga mantle, and plume mantle associated with potential temperatures of 100 to 300°c greater than 2.0 ga mantle. pressures and temperatures for the fertile peridotite from hirschmann (2000). slightly modified from mayborn & lesher (2004). fig. 13. variation of k 2 o (in wt%) with zr (in ppm) for the kangâmiut dykes. solid lines show results of fractional crystallisation models using mineral proportions of 10:50:40 ol:pl:cpx and 40:40:20 hbl:pl:cpx. the model starting composition is the sample with lowest k 2 o and zr, which are 0.19 wt% k 2 o and 47 ppm zr. based on cadman et al. (2001). 0.0 0.4 0.8 1.2 1.6 0 100 200 300 400 zr k2o 10:50:40 ol:pl:cpx 40:40:20 hbl:pl:cpx 76 ally, an ambient mantle potential temperature of 1420°c at 2.0 ga. is consistent with constraints from continental freeboard that suggests that mantle temperatures were below 1430°c by the mid-archaean (galer 1991). thus, the 1420°c mantle temperature for the kangâmiut dykes is consistent with ambient mantle temperatures for that time, reducing the need for anomalously high potential temperatures commonly associated with plume magmatism. the explanation that best fits both the geochemical and field data is that the kangâmiut dykes formed by decompression melting in a rift environment under ambient mantle conditions. this conclusion implies that the dykes are the products of rifting of kenorland supercontinent between 2.1 and 2.0 ga (williams et al. 1991). the implications of these findings for the temperature of the palaeoproterozoic mantle, the occurrence of palaeoproterozoic mantle plumes, and for palaeoproterozoic continental crustal growth are discussed in mayborn & lesher (2004). fractionation of the kangâmiut dykes as noted previously, the range in mg-number (0.60–0.21) of the kangâmiut dykes shows that they are not in equilibrium with mantle peridotite and do not represent direct mantle melts. thus, even the most primitive sampled kangâmiut dyke represents an evolved magma. first order observations of the whole-rock and mineral data show that the dykes evolved by ol:cpx:pl or hbl:cpx:pl fractionation with the late-stage introduction of fe-ti oxides into the fractionating assemblage. windley (1970) and bridgwater et al. (1995) proposed that hornblende was a primary crystallising phase from the kangâmiut dyke magmas partly based on the occurrence of large hornblende crystals in chilled margins. however, our petrographical studies of the chilled margins show that these amphiboles grew in situ during the final stage of solidification (see fig. 3). this does not preclude the possibility that hornblende was a stable and fractionating phase at depth and thus influenced the composition of evolved kangâmiut dyke magmas prior to their emplacement. the main difference between hbl:cpx:pl and ol:cpx:pl crystallisation to explain the magmatic evolution of the dykes is the relative cotectic proportions of hornblende and olivine. in the projection from qtz (fig. 6a) the dyke compositions lie within both the hbl:cpx:pl and ol:cpx:pl phase volumes. if hornblende is a fractionating phase its cotectic proportion would be c. 0.40 (based on the projections from qtz, cpx, and plag), with plagioclase and clinopyroxene at 0.40 and 0.20, respectively. if olivine, and not hornblende, is a fractionating phase, the cotectic proportions would be c. 0.10 olivine, 0.50 plagioclase, and 0.40 clinopyroxene. these different cotectic proportions can be used to determine if hornblende or olivine was a fractionating phase by examining the partitioning behaviour of potassium. experimentally determined amphibole-basaltic melt kds for potassium range between 1 and 2 (green 1994). in contrast, the olivine-basaltic melt kd is c. 0.0005 (green 1994) for potassium between olivine and basaltic liquid. figure 13 shows the results of fractional crystallisation modelling for k 2 o and zr. the cotectic assemblage 40:40:20 hbl:cpx:pl gives a bulk distribution coefficient (d) of 0.52 for k and 0.094 for zr. the olivine-bearing assemblage, 10:50:40 ol:cpx:pl, gives a bulk d of 0.16 for k and 0.026 for zr. as shown in fig. 13, the hornblende-bearing assemblage underestimates the concentration of k 2 o and is not consistent with the trend defined by the dyke data, whereas the olivine-bearing assemblage provides a better fit to the data. thus, these relationships show that the kangâmiut dykes evolved by the fractionation of olivine, clinopyroxene, plagioclase and late stage fe-ti oxides, and that hornblende was not a significant fractionating phase at any stage of their evolution. support for this conclusion comes from the 0.8 gpa melting experiments of mayborn (2000) showing that the cotectic assemblage for a water-bearing kangâmiut dyke starting material is olivine, clinopyroxene, and plagioclase, but no hornblende. 0 100 200 300 400 500 zr ce 0 20 40 60 80 100 0.1 0.2 0.3 0.4 0.5 f = 1.0 fig. 14. variation of ce with zr (in ppm) showing the results of a fractional crystallisation model where f is the melt proportion. tic marks on model curve are drawn at 0.1 intervals of f. 77 origin of water in the kangâmiut dykes based on the presence of hornblende in the kangâmiut dykes, bridgwater et al. (1995) speculated that the parental magmas for the dykes were derived from a hydrous protolith during thrusting of an amphibolite facies terrain beneath the granulite facies terrain in the southern nagssugtoqidian orogen. although this model does offer an explanation for the proposed high water contents of the dykes, the presence of hornblende itself, often as reaction rims on clinopyroxene or poikilitic grains enclosing plagioclase and clinopyroxene, only argues for elevated water contents during final stages of crystallisation of the dykes. it is, therefore, possible that the high water contents sufficient to stabilise hornblende resulted solely from its enrichment during crystal fractionation. the modal abundance of hornblende in dykes not affected by nagssugtoqidian deformation is c. 5–20% for dolerites and 10–35% for dioritic centres. since amphiboles contain c. 2 wt% water, these modes would indicate a whole-rock water concentration of 0.1 wt% in the primitive dolerites and 0.7 wt% in the more evolved dioritic centres. whether these differences in concentrations between the primitive and evolved samples are related to enrichment during crystal-liquid fractionation can be evaluated using the following equation for fractional crystallisation: c l = c 0 × f (d–1) (1) where c 0 is the initial concentration, c l is the liquid concentration, f is the proportion of liquid, and d is the bulk distribution coefficient. danyuschevsky et al. (2000) showed that in mafic systems water will have a bulk distribution coefficient of c. 0.01. starting with a magma with 0.1 wt% (c 0 ) h 2 o, representing the primitive dolerites, and ending with 0.7 wt% (c l ) h 2 o, representing the evolved dioritic centres, requires 86% crystallisation (f = 0.14) of the primitive magma. figure 14 shows the relative enrichment of highly incompatible elements zr and ce during fractional crystallisation, where ce is used as a proxy for water given their similar incompatibilities (danyuschevsky et al. 2000). the amount of fractionation required to relate the primitive samples to dioritic centres is 0.3–0.13, corresponding to 70–87% crystallisation. thus, the evolved dykes reflect sufficient fractionation to explain the difference in water concentrations between the primitive dykes and dioritic centres. the origin of the water in the primitive dykes can also be addressed using equation 1. the most primitive kangâmiut dykes (mgo > 6 wt%) have a modal hornblende content of 5–10% indicating a maximum of 0.1–0.2 wt% water content in the rocks. this suggests that the amount of water in the parental magma derived from the mantle is less than 0.2 wt%. equation 1 can also approximate fractional mantle melting and can help constrain the amount of water in the mantle source needed to produce a primitive magma containing 0.2 wt% h 2 o. in this case, the unknown variable is c 0 , the initial concentration in the mantle. the concentration in the liquid (c l ) is 0.2 wt%, and d is equal to 0.01. the evaluation of ree systematics, presented by mayborn & lesher (2004) and illustrated in fig. 11, shows that the average f value for mantle melting leading to the kangâmiut dykes was 0.05. thus, using these values in equation 1 results in a concentration in the mantle source (c 0 ) of 0.01 wt% (100 ppm). this is well within the range of 28–300 ppm h 2 o given by bell & rossman (1992) for the upper mantle containing nominally anhydrous phases. as such, the water present in the hornblende within the kangâmiut dykes can be reasonably accounted for given estimates of its original concentration in primary melts and enrichment through subsequent differentiation. although these considerations do not rule out bridgwater et al.’s (1995) model for the kangâmiut dykes derived from an amphibolite facies protolith, we show that differentiation of partial melts derived from depleted upper mantle can readily explain the occurrence of late crystallising hornblende in the evolved kangâmiut magmas. the kangâmiut dykes and the nagssugtoqidian orogeny the preservation of both igneous and metamorphic features in the kangâmiut dyke swarm provides an excellent opportunity to evaluate the amount of crustal thickening that likely occurred during the nagssugtoqidian orogeny. determining the amount of thickening requires knowledge of the depths associated with emplacement and peak metamorphism for currently exposed dykes. field relationships show brittle deformation of host rocks and segmentation of the kangâmiut dykes into en échelon arrays during emplacement. reches & fink (1988) proposed that the segmentation of dykes into en échelon arrays occurs when they cross from the ductile into the brittle regime. in modern continental crust the brittle– ductile transition is observed as the seismic to aseismic transition at depths of 10–15 km (chen & molnar 1983). chen & molnar (1983) and williams (1996) give temperature estimates for the brittle–ductile transition between 450 and 250°c. 78 fahrig & bridgwater (1976) presented palaeomagnetic data from dykes and host rocks unaffected by nagssugtoqidian metamorphism, and showed that the host rocks and dykes record different declinations. these differences in declination show that the host rocks were below their curie temperature during dyke emplacement. fahrig & bridgwater (1976) do not discuss the magnetic carrier in the host rocks, but an examination of host rock samples suggests that the magnetic carrier(s) are magnetite and/or ilmenite. the curie temperatures of these minerals vary due to solid solutions amongst magnetite-ulvöspinel and hematite-ilmenite, but the upper limit is 580°c if the magnetic carrier is pure magnetite. additional support for dyke emplacement into host rocks with temperatures below 580°c comes from 40ar/ 39ar dating of dykes and host rocks. willigers et al. (1999) presented 40ar/39ar cooling ages from dykes in the southern foreland that gave a mean age of 2.02 ga. this age is within error of the 2.04 ga emplacement age determined by dating of igneous zircons (nutman et al. 1999). the 40ar/39ar cooling age of a regional granitic host rock is 2.5 ga (willigers et al. 1999). this older age indicates that the host rocks have remained below 480°c, the closure temperature of argon in hornblende (harrison 1981), since 2.5 ga. field evidence of brittle deformation, palaeomagnetic data, and 40ar/39ar cooling ages all indicates that the peak crustal temperatures of exposed basement hosting the kangâmiut dykes were less than c. 450°c at the time of dyke emplacement. estimates of the geothermal gradient appropriate for continental crust at 2.0 ga can help to constrain the depth of the 450°c isotherm and thus the depth of dyke emplacement. the geotherm is computed from the heat flow equation assuming an exponential distribution of heat producing elements that includes contributions from heat conduction, advection, and production (carslaw & jaeger 1959): where t is temperature in °c, q* is the reduced heat flow at the crust-mantle boundary in mwm–2, z is the depth in km, k is the thermal conductivity of the crust in wm–1k– 1, ao is the concentration of heat producing elements at the earth’s surface in µwm–3, d is crustal thickness in km, and hr is the length scale for the decrease in heat producing elements with depth in km. current average values are q = 30 mwm–2, k = 2.25 wm–1k–1, ao = 0.75 µwm– 3, d = 35 km, and hr = 15 km. the model geotherm shown in fig. 15 uses these values with the exception of ao = 1.2 to account for higher heat production during the palaeoproterozoic and archaean (stein 1995). using the geotherm in fig. 15 and a maximum host rock tempera(2)0 0.3 0.6 0 2 0 0 4 0 0 6 0 0 8 0 0 10 20 d ep th ( km ) t (°c) 0 geotherm p (g pa ) fig. 15. model continental geotherm constructed using the heat flow equation shown in text (equation 2). solid vertical line represents the 450°c isotherm that intersects the geotherm at c. 0.3 gpa (10 km) as shown by dashed horizontal line. 0 0.2 0.4 0.6 0.8 1.0 1.2 200 400 600 800 ky and sil kangâmiut dyke peak metamorphism p (gpa) t (°c) g ra nu lit e a m ph ib o lit e fig. 16. pressure versus temperature diagram showing the intersection of the amphibolite/granulite facies transition with the kyanite– sillimanite transition. the black rectangle around the intersection shows possible temperature and pressure ranges of peak metamorphism of the kangâmiut dykes and metasediments in ikertooq fjord. the al 2 sio 5 phase diagram is from holdaway (1971) and the amphibolite to granulite transition is based on the first occurrence of orthopyroxene in experiments on mafic rocks by spear (1981). t = q* z k + a o d 2 k 1 − e − z / hr( ) 79 ture of 450°c require that the dykes intruded to a minimum depth of 10 km corresponding to a lithostatic pressure of c. 0.3 gpa. this estimate of a shallow emplacement level for the dykes is also supported by the clustering of whole-rock data near the low-pressure ol:cpx:pl cotectics as previously shown in fig. 7. application of the clinopyroxene geothermobarometry developed by putirka et al. (1996) provides another independent estimate of the depth of dyke emplacement. this geothermobarometer uses compositions of clinopyroxenes and their host rocks to estimate the pressure and temperature of clinopyroxene crystallisation. there are two important assumptions when applying this geothermobarometer to chilled margins in the kangâmiut dykes. first, we assume that the whole-rock composition is a close approximation of the original liquid composition. second, we assume that the cores of the clinopyroxene phenocrysts were once in equilibrium with this liquid. one test of equilibrium between the whole-rock and clinopyroxene phenocrysts is given by the feo/mgo ratios in the whole rocks and pyroxenes. the feo/mgo ratios in the clinopyroxenes from eight chilled margins and the feo/mgo ratio in their host rocks yield an average k d fe-mg for clinopyroxene and liquid of 0.32 ± 4. based on experimental work, k d fe-mg for basaltic systems between 1 atm and 1.5 gpa ranges from 0.22–0.36 (baker & eggler 1987; putirka et al. 1996). our estimates for the kangâmiut dykes fall within this range. applying the putirka et al. (1996) geothermobarometer to clinopyroxene phenocrysts cores and whole-rock compositions from chilled margins of eight kangâmiut dykes gives temperatures of 1199–1170°c and pressures of 0.75– 0.35 gpa. the upper pressure limit of 0.75 gpa indicates a maximum recorded depth of fractionation recorded by clinopyroxene phenocrysts of c. 25 km. the lower pressure estimate of 0.35 gpa constrains a maximum emplacement depth of c. 12 km, since the clinopyroxene phenocrysts in the chilled margins must have formed at a depth greater or equal to the final depth of dyke emplacement. this is consistent with the preceding results from temperature estimates of the host rocks during emplacement that indicate a maximum of c. 0.3 gpa or a depth of c. 10 km. if these independent estimates of the kangâmiut dyke emplacement depths are taken as representative of the dyke swarm in general, then a consideration of peak metamorphic conditions during the nagssugtoqidian orogeny can be used to constrain the amount of crustal thickening during orogenesis. the majority of the metamorphism of the northern portion of the swarm during the nagssugtoqidian orogeny occurred at amphibolite facies, with the exception of the northernmost portion within ikertooq fjord where the transition to granulite facies metamorphism occurs. the amphibolite to granulite facies transition is marked by the first appearance of orthopyroxene in mafic rocks and is known to occur at c. 800°c (spear 1981). the constraint on the pressure of the granulite facies metamorphism comes from the presence of kyanite-sillimanite paragneisses that are interleaved with sheets of dyke-bearing orthogneisses. the presence of granulite facies metamorphosed kangâmiut dykes and the alumina-silicate-bearing gneisses indicates that peak metamorphism occurred at conditions corresponding to both the amphibolite to granulite and kyanite to sillimanite transitions. figure 16 shows that these transitions indicate a peak metamorphic pressure of c. 0.9 gpa. this pressure is consistent with the results of mengel et al. (1995) who determined metamorphic pressures on the kangâmiut dykes in the ikertooq region using tweequ geothermobarometry (berman 1991). knowing the approximate depth of emplacement and the pressure of peak metamorphism provides constraints on the amount and style of burial during the nagssugtoqidian orogeny. emplacement at 0.3 gpa of pressure followed by peak metamorphism at 0.9 gpa requires an increase of 0.6 gpa. this indicates a minimum of 20 km of crustal thickening between dyke emplacement and peak metamorphism. a probable mechanism of crustal thickening in this case is thrust imbrication and crustal loading of material from north to south. the structural feature associated with this imbrication is most likely the ikertôq shear zone (fig. 1). the imbrication of rock types, the lithostratigraphic changes, including the disappearance of the kangâmiut dykes, and the lateral continuity of the ikertôq shear zone suggest that it is a major structure capable of accommodating displacement of material that buried the northern portion of the dyke swarm with 20 km of overburden. crustal thickening must have occurred over a minimum map distance of 50 km extending from the ikertôq shear zone to at least the itivdleq shear zone (fig. 1) and farther to the south approaching the nagssugtoqidian front where the last significant metamorphism occurs. summary and conclusions the 2.04 ga kangâmiut dyke swarm in west greenland is composed of tholeiitic dykes that intruded during passive rifting of archaean continental crust. the current level of exposure corresponds to emplacement depths less than 10 km based on estimated host rock temperatures less than 450°c during emplacement and geothermobarometry for 80 kangâmiut dyke clinopyroxenes. major and trace element systematics show that the parental magmas for the kangâmiut dykes differentiated by fractionation of plagioclase, clinopyroxene, olivine, and late state fe-ti oxides. the rare-earth element systematics of the dykes indicate initiation of mantle melting at c. 2.75 gpa, corresponding to a potential mantle temperature of c. 1420°c. this temperature is consistent with ambient mantle temperature estimates for 2.0 ga and shows that the kangâmiut dyke swarm formed during passive rifting of the kenorland supercontinent. anomalously hot plume mantle is not required for their generation. subsequent metamorphism of the northern portion of the swarm reached granulite facies, with an estimated temperature of 800°c and pressure of 0.9 gpa. the emplacement pressure of less than 0.3 gpa and peak metamorphism at 0.9 gpa indicate a minimum of 20 km of crustal thickening associated with the nagssugtoqidian orogeny. crustal thickening likely occurred during thrusting of material from the central nagssugtoqidian orogen southward over the southern nagssugtoqidian orogen along the ikertôq shear zone. acknowledgements we are especially grateful to the late david bridgwater, whose boundless energy and enthusiasm for the kangâmiut dykes inspired this work from beginning to end. we also thank flemming mengel, jim connelly, and minik rosing for their support of this project at various stages, and andy saunders and karen hanghøj for their constructive reviews of the final manuscript. this work was partially supported by the danish lithosphere centre and grants from the us national science foundation (ear 97-06677 and oce 98-11453). references abbott, d., burgess, l., longhi, j. & smith, w.h.f. 1994: an empirical thermal history of the earth’s upper mantle. journal of geophysical research 99(7), 13835–13850. arculus, r.j. 1994: aspects of magma genesis in arcs. lithos 33(1–3), 189–208. aspler, l.b. & chiarenzelli, j.r. 1998: two neoarchean supercontinents? 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(eds): mechanism of igneous intrusion, 79–92. liverpool: seel house press. wooden, j.l., czamanske, g.k., fedorenko, v.a., arndt, n.t., chauvel, c., bouse, r.m., king, b.w., knight, r.j. & siems, d.f. 1993: isotopic and trace-element constraints on mantle and crustal contributions to siberian continental flood basalts, noril’sk area, siberia. geochimica et cosmochimica acta 57(15), 3677–3704. 84 appendix dyke location latitude longitude trend thickness (m) samples 1 søndre strømfjord 66°05.266'n 053°33.211'w 010 2 430901 middle of dyke, 430902 near contact 2 søndre strømfjord 66°05.26'n 053°33.5'w 080 20 430903 ~7 m from dyke contact 3 søndre strømfjord 66°05.26'n 053°33.5'w 010 0.4 none 4 søndre strømfjord 66°05.26'n 053°33.7'w 020 ? none 5 itilleq 66°33.3'n 053°02.5'w 086 6 430904 ~2 m from contact 6 itilleq 66°33.3'n 053°02.5'w ? 1.5 430905 middle of dyke 7 ikertooq 66°58.1'n 052°28.9'w 079 0.3 none 8 ikertooq 66°58.1'n 052°28.9'w 123 0.15 none 9 ikertooq 66°57.55'n 052°31.7'w 010 2 430910 0.5 m from dyke margin 10 ikertooq 66°58.95'n 052°26.8'w 080 2 430915 middle of dyke 11 ikertooq 66°49.7'n 052°16.7'w 054 0.3 430917 middle of dyke 12 ikertooq 66°50.1'n 052°19.2'w ? ? 430919 middle of dyke 13 itilleq 66°32.25'n 052°45.0'w 080 8 430923 middle of dyke 14 itilleq 66°32.85'n 052°47.15'w ? 0.1 430926 whole width of dyke 15 itilleq 66°33.3'n 052°51.3'w 095 1 430929 middle of dyke 16 itilleq 66°33.03'n 052°53.54'w 035 8 430930 ~2.5 m from contact, 430931 dyke contact 17 itilleq 66°33.5'n 052°56.0'w 080 2 430933 0.3 m from contact 18 itilleq 66°34.7'n 052°56.0'w 062 10 430935 middle of dyke 19 itilleq 66°34.7'n 052°56.0'w 090 14 430936 middle of dyke 20 itilleq 66°35.1'n 052°49.0'w 090 8 430939 middle of dyke 21 itilleq 66°35.1'n 052°47.5'w 079 8 430940 middle of dyke 22 itilleq 66°34.75'n 052°48.5'w ? ? 430942 middle of dyke 23 itilleq 66°34.75'n 052°48.5'w ? ? 430943 middle of dyke 24 itilleq 66°33.1'n 053°04.0'w ? 25 430946 middle of dyke 25 itilleq 66°33.7'n 052°55.1'w 087 16 430948 middle of dyke, 430950 dyke contact 26 itilleq 66°33.25'n 052°38.5'w 100 1 430951 middle of dyke 27 itilleq 66°33.25'n 052°33.0'w 096 20 430952 middle of dyke 28 itilleq 66°32.6'n 052°27.0'w 057 30 430953 middle of dyke 29 itilleq 66°31.8'n 052°41.0'w 061 5 430955 ~1.5 m from contact, 430956 ~5 m from contact 30 itilleq 66°31.9'n 052°38.5'w 085 15 430957 dyke contact, 430959 ~5 m from contact 31 itilleq 66°31.8'n 052°36.2'w 065 18 430960 middle of dyke 32 itilleq 66°31.7'n 052°34.0'w 078 22 430961 middle of dyke 33 mouth of itilleq 66°29.9'n 053°33.5'w 022 20 430965 middle of dyke 34 mouth of itilleq 66°30'n 053°34.8'w 065 25 430966 ~7 m from contact 35 mouth of itilleq 66°30.05'n 053°35.8'w 117 40 430967 ~7 m from contact 36 mouth of itilleq 66°30.5'n 053°36.4'w 006 10 430969 middle of dyke 37 south of maniitsoq 65°22.7'n 052°47.3'w 345 4.5 430970 middle of dyke 38 east of maniitsoq 65°25.5'n 052°24.0'w ? 15 430972 middle of dyke 39 east of maniitsoq 65°25.4'n 052°23.0'w 054 0.4 430973 middle of dyke 40 east of maniitsoq 65°25.5'n 052°18.0'w 117 12 430974 middle of dyke 41 east of maniitsoq 65°26.0'n 052°14.8'w 354 7 430975 middle of dyke 42 east of maniitsoq 65°35.15'n 052°46.0'w 002 49 430977 dyke contact, 430979 1 m from contact, 430981 5 m from contact, 430982 17 m from contact 43 north of maniitsoq 65°39.85'n 052°37.0'w 003 25 430983 middle of dyke, 430984 dyke contact 44 north of maniitsoq 65°44.4'n 052°38.5'w 344 0.5 430986 middle of dyke 45 north of maniitsoq 65°38.75'n 052°37.5'w 002 16 430987 middle of dyke, 430988 ~6 cm from contact 46 north of maniitsoq 65°36.9'n 052°43.5'w 005 10 430990 ~4 m from contact, 430991 ~0.5 m from contact table a1. field data for kangâmiut dykes examined for this study 85 dyke location latitude longitude trend thickness (m) samples 47 north of maniitsoq 65°40.1'n 052°49.0'w 010 17 430992 middle of dyke 48 north-east of kangaamiut 65°54.9'n 053°14.5'w 050 12 430993 ~2 m from contact 49 north-east of kangaamiut 65°53.95'n 053°16.0'w 045 27 430994 middle of dyke 50 north-east of kangaamiut 65°53.4'n 053°14.95'w 033 1 none 51 north-east of kangaamiut 65°53.4'n 053°14.95'w 110 0.2 none 52 north-east of kangaamiut 65°53.4'n 053°14.95'w 030 1.5 430995 middle of dyke 53 north-east of kangaamiut 65°53.4'n 053°14.95'w 110 2 430996 middle of dyke 54 north-east of kangaamiut 65°52.6'n 053°14.0'w 063 60 430997 andesitic portion of dyke, 430998 mafic portion of dyke 55 north-east of kangaamiut 65°50.8'n 053°13.0'w 064 1.5 432101 middle of dyke 56 north-east of kangaamiut 65°50.8'n 053°13.0'w 015 15 430999 middle of dyke 57 søndre strømfjord 66°01.4'n 053°28.65'w 028 60 432103 middle of dyke 58 kangerluarsussuaq 66°17.5'n 053°05.65'w 065 40 432104 dyke contact, 432105 middle of dyke 59 kangerluarsussuaq 66°17.5'n 053°05.8'w 057 40 432107 middle of dyke 60 kangerluarsussuaq 66°17.25'n 053°07.5'w 022 1 432108 middle of dyke 61 kangerluarsussuaq 66°17.25'n 053°07.5'w 145 45 432106 1 m from contact, 432108 middle of dyke 62 kangerluarsussuaq 66°17.15'n 053°08.5'w 045 21 432111 middle of dyke 63 kangerluarsussuaq 66°17.05'n 053°11.25'w 028 40 432112 ~7 m from contact 64 kangerluarsussuaq 66°16.9'n 053°09.7'w 031 140 432115 dyke contact, 432116 ~2.5 m from w contact, 432118 ~45 m from w contact, 432119 ~70 m from w contact, 432120 ~95 m from w contact, 432121 ~19 m from e contact, 432122 ~18 m from w contact, 432136 ~40 m from w contact, 432137 middle of dyke 65 kangerluarsussuaq 66°39.5'n 053°03.0'w 065 50 432123 middle of dyke 66 east of itilleq 66°29.3'n 052°25.0'w 065 15 432125 middle of dyke 67 east of itilleq 66°29.1'n 052°24.0'w 050 8 432128 middle of dyke 68 east of itilleq 66°33.1'n 052°07.5'w 072 1 432129 middle of dyke 69 east of itilleq 66°31.75'n 052°18.0'w 050 4 432130 middle of dyke 70 east of itilleq 66°30.5'n 052°27.5'w 090 25 432138 middle of dyke 71 east of itilleq 66°27.9'n 052°27.0'w 022 70 432133 middle of dyke 72 east of itilleq 66°26.0'n 052°40.5'w 080 5 432134 middle of dyke 73 east of itilleq 66°27.45'n 052°45.5'w 055 4 432135 middle of dyke 74 kangerluarsussuaq 66°16.6'n 053°17.0'w 032 17 432139 middle of dyke 75 kangerluarsussuaq 66°15.3'n 053°22.5'w 036 18 432140 middle of dyke, 432151 9 m from n contact, 432152 6 m from n contact, 432153 4 m from n contact, 432154 2 m from n contact, 432155 1 m from n contact, 432156 0.5 m from n contact, 432157 0.25 m from n contact, 432158 dyke contact, highly jointed 76 kangerluarsussuaq 66°14.6'n 053°33.0'w 020 25 432143 middle of dyke, 432144 5 m from e contact, 432145 e contact 77 kangerluarsussuaq 66°14.7'n 053°31.7'w 044 0.4 432147 nw contact, 432148 middle of dyke 432149 se contact 78 kangerluarsussuaq 66°15.15'n 053°29.0'w 086 2 432150 middle of dyke 79 mouth of itilleq 66°30.05'n 053°35.8'w 090 50 430206 and 430207 middle of dyke 80 mouth of itilleq 66°30.05'n 053°35.8'w 090 15 430208 and 430209 middle of dyke 81 mouth of itilleq 66°30.05'n 053°35.8'w 090 ? 430210 middle of dyke 82 mouth of itilleq 66°30.05'n 053°35.8'w 090 0.1 430211 whole width of dyke 83 søndre strømfjord 66°01.4'n 053°28.65'w ? ? 430258 dyke contact 84 north-east of kangaamiut 65°52.6'n 053°14.9'w 022 30 430267 dyke contact, 430265 middle of dyke 85 north-east of kangaamiut 65°53.6'n 053°14.9'w 045 30 430283 dyke contact, 430284 middle of dyke 86 north-west of kangaamiut 65°56.6'n 053°28.0'w 25 60 158074 and 430288 dyke contact, 432102 and 158077 middle of dyke table a1 (continued) 86 maniitsoq 25 km hamborgerland kangaamiut s øn dr e st rø m fjo rd sukkertoppen iskappe itilleq itilleq sisimiut ikertooq ta sersuaq sarfartoq maligiaq avalleq evi ghe dsf jor d søn dre iso rto q 65°30' 66° 66°30' 51° 53° 52° 137013 5 6 12 34 7 8 9 10 11 12 1417 24 19 16 15 20 26 21 18 22 28 23 27 25 30 3129 35 323436 37 33 38 39 40 41 56 46 45 44 43 42 47 4849 51 54 55 50 5352 1357 13581359 1360136113621364 1363 1365 1366 1367 1368 1369 1371 1372 1373 137413751376 1377 1378 79 80 81 82 86 85 84 83 fig. a1. map showing the locations of dykes examined in this study. geological survey of denmark and greenland bulletin 11, 53-60 53© geus, 2006. geological survey of denmark and greenland bulletin 11, 53–60. available at: www.geus.dk/publications/bull a lead isotope study of an archaean gold prospect in the attu region, nagssugtoqidian orogen, west greenland henrik stendal, robert frei and bo møller stensgaard this paper presents a lead isotope investigation of a gold prospect south of the village attu in the northern part of the nagssugtoqidian orogen in central west greenland. the attu gold prospect is a replacement gold occurrence, related to a shear/mylonite zone along a contact between orthogneiss and amphibolite within the nagssugtoqidian orogenic belt. the mineral occurrence is small, less than 0.5 m wide, and can be followed along strike for several hundred metres. the mineral assemblage is pyrite, chalcopyrite, magnetite and gold. the host rocks to the gold prospect are granulite facies ‘brown gneisses’ and amphibolites. pb-isotopic data on magnetite from the host rocks yield an isochron in a 207pb/204pb vs. 206pb/204pb diagram, giving a date of 3162 ± 43 ma (mswd = 0.5). this date is interpreted to represent the age of the rocks in question, and is older than dates obtained from rocks elsewhere within the nagssugtoqidian orogen. pb-isotopic data on cataclastic magnetite from the shear zone lie close to this isochron, indicating a similar origin. the pb-isotopic compositions of the ore minerals are similar to those previously obtained from the close-by ~2650 ma rifkol granite, and suggest a genetic link between the emplacement of this granite and the formation of the ore minerals in the shear/mylonite zone. consequently, the age of the gold mineralisation is interpreted to be late archaean. keywords: archaean, gold, magnetite, pb isotopes, geochronology, west greenland ________________________________________________________________________________________________________________________________________________________________________________________ h.s. & b.m.s., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: hst@geus.dk r.f., geological institute, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. discovery of the gold prospect described in this study was due to the find of a mineralised sample, which karl markussen from attu submitted to the bureau of minerals and petroleum in greenland. the geological survey of denmark and greenland (geus) visited the locality in 2001 and in 2002 (stendal et al. 2002, 2004), and the present paper reports pb-isotopic data for minerals from the prospect and its surroundings. the attu gold prospect lies within the nagssugtoqidian orogen of west greenland (fig. 1), where geological mapping and exploration has been carried out for decades by the geological survey, the danish lithosphere centre, university research groups and exploration companies (e.g. kalsbeek et al. 1987; connelly et al. 2000; van gool et al. 2002). in addition to the general investigations, steenfelt (2001) has summarised geochemical signatures from stream sediments, rasmussen & van gool (2000) have described geophysical aspects, and steenfelt et al. (2002), stendal & schønwandt (2003) and stendal et al. (2004) have described mineral occurrences and their economic potential. an overview of the mineral occurrences in the entire region has been presented by stendal et al. (2004). detailed, mainly zircon u-pb geochronological data from the nagssugtoqidian orogen have been presented by kalsbeek & nutman (1996), connelly & mengel (2000) and connelly et al. (2000), and pb-pb, rb-sr and sm54 nd whole-rock isotope data from the region have been reported by kalsbeek et al. (1984, 1987), taylor & kalsbeek (1990) and whitehouse et al. (1998). in addition, some pb-isotopic work has been carried out on sulphide separates, mainly pyrite, from mineral occurrences in the disko bugt region (stendal 1998). geological setting the palaeoproterozoic nagssugtoqidian orogen of west greenland (van gool et al. 2002) is located between the archaean north atlantic craton to the south and a lesserknown continental mass to the north that includes the palaeoproterozoic rinkian fold belt. most of the orogen consists of variably reworked archaean orthogneisses. several thin belts of supracrustal and intrusive igneous rocks occur within this gneiss terrain. granitoid rocks and numerous pegmatites intrude the gneisses. formations of palaeoproterozoic age are limited to the arfersiorfik and sisimiut igneous suites and minor supracrustal sequences (connelly et al. 2000). the attu area itself is located in the southern part of the northern nagssugtoqidian orogen (nno; fig. 1). the metamorphic grade is granulite facies; metamorphism and deformation of the archaean granitoid rocks in the nno gradually decrease northwards, from granulite to amphibolite facies, and from high strain to lower strain with more open structures. steeply and shallowly dipping shear and fault zones are common in contact zones between 68° inland ice 54°54°54° 67°30' attuattu gold prospect ar nssz nno cno rifkol undifferentiated orthogneiss attu gold prospect amphibolite and metasedimentary rocks archaean mainly metasedimentary rocks palaeoproterozoic a 18 60 74 18 64 74 55 58 60 60 56 70 62 70 48 70 63 70 62 70 62 82 50 60 15 40 75 1 km attu gold prospect 53 °3 0' 67°51' 67°48' 53 °2 1' biotite gneiss, mainly granodioritic-tonalitic orthopyroxene gneiss, mainly tonalitic granite/charnockite amphibolite metasedimentary and metavolcanic rocks strike and dip of dominant lithological layering and foliation direction and plunge of fold axis, measured, constructed rock samples with elevated gold values fault, shear zone, mylonite zone quaternary deposits kangiussaq tateraat 50 km50 km50 km 50°52° b 500 km inland ice greenland inland ice greenland iceland ketilidian orogen north atlantic craton nagssugtoqidian orogen rinkian fold belt canada fig. 1. a: geological map of the attu region with index map of greenland. cno, central nagssugtoqidian orogen; nno, northern nagssugtoqidian orogen; nssz, nordre strømfjord shear zone. b: geological map of the attu gold prospect area (modified from olesen 1984). 55 different lithologies. major fault zones generally strike nne to ne. the major nordre strømfjord shear zone (van gool 2002) is located c. 20 km south of the study area. the shear zone is traceable from the coast to the inland ice and forms the southern boundary of the nno. the gneisses of the nno are late archaean, with ages between 2870 and 2700 ma (kalsbeek & nutman 1996; connelly & mengel 2000; hollis et al. 2006, this volume; thrane & connelly 2006, this volume). discordant sheets of granitoid rocks of archaean age occur in the centre of the nno and large charnockite/granite bodies including the rifkol granite are situated 20 km to the northwest and just south of the study area (fig. 1; hansen 1979; kalsbeek et al. 1984). only a few younger palaeoproterozoic ages have been obtained from the nno: thrane & connelly (2006, this volume) have obtained an approximate depositional age of the naternaq supracrustal belt some 80 km north-east of attu of c. 1950–1900 ma, and an undeformed pegmatite between attu and aasiaat has yielded an age of c. 1790 ma (connelly & mengel 2000). the attu gold prospect the attu gold prospect is located south of the village attu within a 100–330 m wide, complex tract hosting several parallel shear/mylonite zones and faults that strike nne to ne and dip 60–70°w (figs 1, 2). the fault zone can be followed along strike in a north-easterly direction for several kilometres. the host rocks are layered, brown 2.24 ppm au 0.34% cu 124 ppb au 0.11% cu 12 ppb au 17 ppb au 2–6 ppm au < 0.5% cu fig. 2. the site of the attu gold prospect. gold values are given for rock samples. red circles are sample sites with gold values obtained from fine-grained stream sediments (see fig. 1 for geographical location). the red line shows the approximate position of the gold-bearing zone in the shear/mylonite zone. the black line shows the approximate position of a stream. fig. 3. layered brown gneiss with black bands of amphibolite. the hammer shaft is 50 cm long. 56 weathering gneiss and amphibolite (fig. 3). at the western border of the tract a gold-bearing shear/mylonite zone follows the contact between brown gneisses and amphibolites. the gold-bearing shear/mylonite zone (fig. 4) is invaded by pegmatite sheets as well as centimetre-wide veins consisting of red alkali-feldspar and quartz with occasional pyrite and magnetite. the estimated relative volume of pegmatite in the tract varies from 1 to 10% (stendal et al. 2002, 2004). the most promising gold showings are found in a coastal profile along the shear/mylonite zone, which can be followed along strike for several hundreds of metres (figs 1, 2). the studied site is a cliff exposure consisting of mylonite (fig. 4) and a rusty weathered band (10–20 cm in width) mineralised with pyrite, magnetite and some chalcopyrite (fig. 5). pyrite and chalcopyrite replace magnetite. the magnetite is predominantly cataclastic in nature, but recrystallised ore also occurs. the gold is found within pyrite and chalcopyrite. the gangue mineralogy comprises quartz, k-feldspar, muscovite, biotite and carbonates (calcite, dolomite and/or ankerite). the mylonite zone is silicified at the contact with the mineralised zone, and sulphide-rich parts are weathered. secondary goethite and malachite are common (fig. 5). the ore is structurally controlled by and confined to favourable sites (sulphide-bearing zones) within the mylonite/ shear/fault zone. the attu gold prospect has returned reproducable gold fig. 4. the gold bearing mylonite zone. kfeldspar occurs on the right side of the yellow magnet pen (10 cm long). the zone also contains pyrite, chalcopyrite and magnetite. amphibolite and orthogneiss (host rocks) 446601 magnetite 14.631 0.007 14.642 0.009 44.688 0.033 0.961 0.939 446602 magnetite 15.051 0.014 14.752 0.015 36.702 0.040 0.969 0.942 446610 magnetite 17.540 0.051 15.361 0.046 37.613 0.112 0.977 0.988 446614 magnetite 17.002 0.025 15.225 0.024 38.086 0.061 0.976 0.967 shear zone and mineralised rock 446616 magnetite 15.423 0.023 14.844 0.023 41.598 0.068 0.979 0.957 2000368 magnetite 15.286 0.009 14.832 0.010 41.201 0.034 0.962 0.936 481093 magnetite 14.247 0.042 14.625 0.044 41.821 0.130 0.982 0.960 446615 pyrite 14.241 0.009 14.587 0.010 42.001 0.035 0.963 0.934 481078 pyrite 14.447 0.011 14.633 0.012 40.805 0.039 0.967 0.925 446616 k-feldspar 15.123 0.008 14.893 0.010 36.451 0.029 0.958 0.932 table 1. pb-isotopic ratios of magnetite, pyrite and k-feldspar from the attu gold prospect and its host rocks sample number mineral 206pb/204pb ± 2σ* 207pb/204pb ± 2σ 208pb/204pb ± 2σ r1** r2† * errors are two standard deviations absolute (ludwig 1990). ** r1 = 206pb/204pb versus 207pb/204pb error correlation (ludwig 1990). † r2 = 206pb/204pb versus 208pb/204pb error correlation (ludwig 1990). 57 concentrations in the range 2.3–5.8 ppm. other localities in the same fault structure yielded 2.24 ppm and 124 ppb au (fig. 2). the gold concentrations are positively correlated with concentrations of copper, and gold-bearing samples often contain magnetite. two stream sediment samples yielded anomalous gold concentrations of 12 ppb and 17 ppb au, respectively (fig. 2). the host gneisses are brownish in colour and comprise orthopyroxene, amphibole, biotite and feldspar, but little quartz. magnetite is in equilibrium with the rock forming minerals and has the same granular texture. in the amphibolites magnetite forms up to millimetre-thick layers, and also occurs in disseminated form. within the mylonite zone, magnetite occurs as a primary phase in the host gneiss as cataclastic grains with cracks filled with pyrite and chalcopyrite, and as a residual phase resulting from sulphide replacement. ten samples were analysed for pb-isotopic compositions. fig. 5. the gold bearing zone (10 cm wide) within the mylonite zone, with malachite and rusty weathered sulphides. 14 15 16 17 1918 14.4 14.6 14.8 15.0 15.2 15.4 15.6 15.8 206pb/204pb 20 7 p b/ 20 4 p b 2400 2000 1600 1200 800 400 0 kfsp mt mt mt mt brown gneiss py py mt amphibolite mt amphibolite mt amphibolite rifkol granite trend line c. 2650 ma 60 ma lower intercept 3143 ma age = 3162 ± 43 ma mswd = 0.50 fig. 6. 206pb/204pb–207pb/204pb diagram for minerals from the attu area listed in table 1. open squares, mineral separates from the gold-bearing mylonite zone. red squares, host rock data. black diamonds, whole-rock samples from the rifkol granite for comparison (data from kalsbeek et al. 1984). mt, magnetite; py, pyrite; kfsp, k-feldspar. blue curve, the pb-isotopic growth curve from stacey & kramers (1975). 58 analytical methods the pb-isotopic study was carried out on magnetite from host gneisses and amphibolites, and on k-feldspar, magnetite and pyrite from the shear zone-hosted mineralised zone (table 1). the isotope analyses were carried out at the danish centre for isotope geology, geological institute, university of copenhagen. near-pure mineral fractions were separated from dry split aliquots of crushed and sieved (100–200 µm) rock powders using a hand magnet, a frantz isodynamic separator and heavy liquid techniques. ore minerals were dissolved in concentrated aqua regia. total procedural blanks for pb amounted to < 120 pg which is considered insignificant for the measured pb-isotopic results, relative to the amount of sample pb estimated from the mass spectrometer signal intensities. isotope analyses were carried out on a vg sector 54-it instrument in static collection mode. fractionation for pb was controlled by repetitive analysis of the nbs 981 standard (values of todt et al. 1993) and amounted to 0.103 ± 0.007% / amu (2 σ; n = 11). all results are quoted with 2 σ precisions. results the pb-isotopic compositions of mineral separates from the gold-bearing mylonite zone and its host rocks are listed in table 1. in the 207pb/204pb vs. 206pb/204pb diagram shown in fig. 6, the pb-isotopic compositions of magnetite from the four host rock samples of brown gneiss and amphibolite (red squares) define a straight line with a slope corresponding to 3162 ± 43 ma (mswd = 0.50). this line has intercepts with the stacey & kramers (1975) pb-isotopic growth curve at 3143 and 60 ma. based on the good fit of the data points on the isochron, and the agreement of the isochron age with the intercepts of the growth curve, we interpret the 3162 ma date as the age of the rocks in question. however, farther south, in the central part of the nagssugtoqidian orogen, palaeoproterozoic granulite facies metamorphism has led to u loss in archaean rocks, resulting in pb-isotopic compositions plotting above and to the left of an 2800 ma reference isochron (whitehouse et. al. 1998). if this process had also taken place in the area of the present study, the 3162 ma date might give a false impression of the age of the rocks. however, the good fit of the data points on the isochron and the agreement of the intercepts with the stacey & kramers (1975) growth curve with the isochron age would then be accidental, a coincidence which we regard as very unlikely. six mineral separates from the gold-bearing mylonite zone (fig. 6, open squares) lie close to or slightly above the isochron obtained for magnetite from the host rocks. the most primitive 206pb/204pb and 207pb/204pb ratios have been measured in pyrite and magnetite from the ore-bearing zone, whereas the two primary magnetites with cataclastic texture from within the shear zone plot very close to the host rock magnetite isochron. this suggests that their crystallisation took place at about the same time as the magnetites from outside the shear zone. whole-rock pb-isotopic ratios from the rifkol granite (kalsbeek et al. 1984) are also plotted on fig. 6 for comparison, and the isotopic values are listed in table 1. the errorchron defined by these samples has a slope corresponding to an age of 2653 ± 110 ma, which has been interpreted as emplacement age of the granite (kalsbeek et al. 1984). this errorchron is oblique and discordant to the isochron obtained for magnetite from the host rocks, but the three least radiogenic data points from ore minerals associated with native gold from within the shear zone are conformable with this younger trend. this suggests that the fluids in the shear zone from which the gold mineralisation was deposited were somehow genetically linked to the intrusion of the rifkol granite. alkali feldspar from the shear zone has its own pb-isotopic signature, which is neither compatible with a ‘rifkol’ source nor with a source typical of the immediate host rocks. the uranogenic vs. thorogenic isotopic pattern (not shown in a figure) is more disperse than the uranogenic pattern and does not add to the understanding of the uranogenic pb-isotopic data; as expected, it mostly reflects the differences in u and th concentrations in the different analysed minerals. summary, discussion and conclusions the attu gold prospect is small. the gold mineralised zone does not exceed 0.5 m in width, and its length is now known to be only a few hundred metres. gold has also been detected along strike several kilometres away, but the mineralisation does not show a continuous outcrop pattern. however, the fact that gold is present indicates that the ne-striking shear/mylonite zone is mineralised and that hydrothermal activity seems to have occurred in most of the prominent lineaments in the region. the goldbearing sulphide deposit is of replacement type, where pyrite and chalcopyrite grew at the expense of e.g. magnetite. it is envisaged that gold was introduced contemporaneously with the replacement processes. reworked archaean orthogneisses dominate all segments of the nagssugtoqidian orogen. published age deter59 minations range from 2870–2700 ma (e.g. kalsbeek & nutman 1996; connelly & mengel 2000), but no chronological information has yet been available from the attu region. the 3162 ± 43 ma magnetite age obtained from the attu host rocks suggests that the rocks in this part of the nagssugtoqidian orogen may be significantly older than similar rocks elsewhere in the orogen. however, smnd isotope data from archaean gneisses in the central part of the orogen suggest the involvement of pre-2800 ma crustal material (possibly 3100 ma or older) in their source (whitehouse et al. 1998). large parts of the nagssugtoqidian orogen underwent palaeoproterozoic granulite facies metamorphism around 1850 ma (e.g. willigers et al. 2001), which resulted in severe disturbance of the pbisotopic evolution of the rocks (whitehouse et al. 1998). in view of the well-preserved 3162 ma isochron relationships for the attu gneisses it appears possible that these rocks escaped high-grade nagssugtoqidian metamorphism and that granulite facies metamorphism here is of archaean age, in agreement with the conclusions of mazur et al. (2006, this volume) and thrane & connelly (2006, this volume). the pb-isotopic data of the gold bearing samples (fig. 6) suggest a genetic link between the rifkol granite intrusion and the fluids percolating through the shear zone, implying an archaean age of the mineralisation. without further analytical work we are unable to elaborate and comment on a possible source of the pb that has been incorporated into the k-feldspar in the shear zone. acknowledgements the authors acknowledge f. kalsbeek, p.m. holm and an anonymous reviewer for thorough criticism and constructive suggestions, which greatly improved the manuscript. the authors would also like to thank the participants in the resource assessment programme mineral resources of the precambrian shield of central west greenland (66°– 70°15′n) for valuable discussions concerning mineralising events in the region. input from other scientists in the region is also gratefully acknowledged. special thanks go to karl markussen, attu, who submitted the first gold bearing sample, for showing us the exact sample locality. references connelly, j.n. & mengel, f.c. 2000: evolution of archean components in the paleoproterozoic nagssugtoqidian orogen, west greenland. geological society of america bulletin 112, 747–763. connelly, j.n., van gool, j.a.m. & mengel, f.c. 2000: temporal evolution of a deeply eroded orogen: the nagssugtoqidian orogen, west greenland. canadian journal of earth sciences 37, 1121–1142. hansen, b.f. 1979: some charnockitic rocks in the nagssugtoqidian of west greenland. rapport grønlands geologiske undersøgelse 89, 85–96. hollis, j.a., keiding, m., stensgaard, b.m., van gool, j.a.m. & garde, a.a. 2006: evolution of neoarchaean supracrustal belts at the northern margin of the north atlantic craton, west greenland. in: garde, a.a. & kalsbeek, f. (eds): precambrian crustal evolution and cretaceous–palaeogene faulting in west greenland. geological survey of denmark and greenland bulletin 11, 9–31 (this volume). kalsbeek, f. & nutman, a.p. 1996: anatomy of the early proterozoic nagssugtoqidian orogen, west greenland, explored by reconnaissance shrimp u-pb zircon dating. geology 24, 515–518. kalsbeek, f., taylor, p.n. & henriksen, n. 1984: age of rocks, structures, and metamorphism in the nagssugtoqidian mobile belt, west greenland – field and pb-isotope evidence. canadian journal of earth sciences 21, 1126–1131. kalsbeek, f., pidgeon, r.t. & taylor, p.n. 1987: nagssugtoqidian mobile belt of west greenland: a cryptic 1850 ma suture between two archaean continents – chemical and isotopic evidence. earth and planetary science letters 85, 365–385. mazur, s., piazolo, s. & alsop, g.i. 2006: structural analysis of the northern nagssugtoqidian orogen, west greenland: an example of complex tectonic patterns in reworked high-grade metamorphic terrains. in: garde, a.a. & kalsbeek, f. (eds): precambrian crustal evolution and cretaceous–palaeogene faulting in west greenland. geological survey of denmark and greenland bulletin 11, 163–178 (this volume). olesen, n.ø. 1984: geological map of greenland, 1:100 000, agto 67 v.1 nord. copenhagen: geological survey of greenland. rasmussen, t.m. & van gool, j.a.m. 2000: aeromagnetic survey in southern west greenland: project aeromag 1999. geology of greenland survey bulletin 186, 73–77. stacey, j.s. & kramers, j.d. 1975: approximation of terrestrial lead isotope evolution by a two-stage model. earth and planetary science letters 26, 207–221. steenfelt, a. 2001: geochemical atlas of greenland – west and south greenland. danmarks og grønlands geologiske undersøgelse rapport 2001/46, 39 pp., 1 cd-rom. steenfelt, a., stendal, h., nielsen, b.m. & rasmussen, t.m. 2004: gold in central west greenland – known and prospective occurrences. geological survey of denmark and greenland bulletin 4, 65–68. stendal, h. 1998: contrasting pb isotopes of archaean and palaeoproterozoic sulphide mineralisation, disko bugt, central west greenland. mineralium deposita 33, 255–265. stendal, h. & schønwandt, h.k. 2003: precambrian supracrustal rocks 60 and mineral occurrences, northeast disko bugt. danmarks og grønlands geologiske undersøgelse rapport 2003/24, 57 pp. stendal, h., blomsterberg, j., jensen, s.m., lind, m., madsen, h.b., nielsen, b.m., thorning, l. & østergaard, c. 2002: the mineral resource potential of the nordre strømfjord – qasigiannguit region, southern central west greenland. geology of greenland survey bulletin 191, 39–47. stendal, h., nielsen, b.m., secher, k. & steenfelt, a. 2004: mineral resources of the precambrian shield of central west greenland (66° to 70°15′). part 2. mineral occurrences. danmarks og grønlands geologiske undersøgelse rapport 2004/20, 212 pp. taylor, p.n. & kalsbeek, f. 1990: dating the metamorphism of precambrian marbles: examples from proterozoic mobile belts in greenland. chemical geology 86, 21–28. thrane, k. & connelly, j.n. 2006: zircon geochronology from the kangaatsiaq–qasigiannguit region, the northern part of the 1.9– 1.8 ga nagssugtoqidian orogen, west greenland. in: garde, a.a. & kalsbeek, f. (eds): precambrian crustal evolution and cretaceous– palaeogene faulting in west greenland. geological survey of denmark and greenland bulletin 11, 87–99 (this volume). todt, w., cliff, r.a., hanser, a. & hofmann, a.w. 1993: re-calibration of nbs lead standards using a 202pb + 205pb double spike. terra abstracts 5, supplement 1, 396 only. van gool, j.a.m., connelly, j.n., marker, m. & mengel, f. 2002: the nagssugtoqidian orogen of west greenland: tectonic evolution and regional correlations from a west greenland perspective. canadian journal of earth sciences 39, 665–686. whitehouse, m.j., kalsbeek, f. & nutman, a.p. 1998: crustal growth and crustal recycling in the nagssugtoqidian orogen of west greenland: constraints from radiogenic isotope systematics and u-pb zircon geochronology. precambrian research 91, 365–381. willigers, b.j.a., krogstad, e.j. & wijbrans, j.r. 2002: comparison of thermochronometers in a slowly cooled granulite terrain: nagssugtoqidian orogen, west greenland. journal of petrology 42, 1729– 1749. __________________________________________________________________________________________________________________________________________________________________________________ manuscript received 4 october 2004; revision accepted 19 december 2005 data article | short bennike & wiberg-larsen 2022: geus bulletin 49. 8294. https://doi.org/10.34194/geusb.v49.8294 1 of 5 a new middle pleistocene interglacial occurrence from ejby, sjælland, denmark ole bennike*1 , peter wiberg-larsen2 1geological survey of denmark and greenland (geus), aarhus, denmark; 2institute for ecoscience, aarhus university, silkeborg, denmark. abstract despite more than a century of investigations, parts of the quaternary stratigraphy of denmark with their fragmented record of deposits remain ambiguous. here we describe a newly found interglacial clay deposit from ejby on sjælland, denmark, from a borehole at 55.695°n, 11.839°e (terrain elevation 5.7 m above sea level). we place the new occurrence on record and provide details of the macrofossil analysis of the sample. the clay contains remains of the present-day temperate bivalve corbicula fluminalis and the caddis fly hydropsyche contubernalis – both inhabiting rivers. the presence of c. fluminalis indicates that the deposit most probably is of middle pleistocene age, older than the last interglacial, the eemian. introduction during the quaternary period that began 2.58 million years, the climate has alternated between glacial and interglacial conditions. interglacial deposits are characterised by remains of plants and animals such as oak and red deer that indicate climatic conditions similar to or warmer than at present, whereas interstadial deposits from glacial stages contain remains of relatively cold-adapted, arctic or subarctic species such as polar willow and reindeer. despite more than a century of investigations, parts of the quaternary stratigraphy of denmark with their fragmented record of deposits remain ambiguous. known interglacial occurrences include the cromerian complex (the harreskovian, marine isotope stage [mis] 19), the holsteinian (mis 11c), the trelde klint interglacial (mis 11), the trianglen interglacial (mis 7), the eemian (mis 5e) and the current interglacial, the holocene (kuneš et al. 2013; odgaard et al. 2016; bennike et al. 2019; candy et al. 2021). moreover, several deposits of unknown age have been described (andersen 1967). in 2018, the geological survey of denmark and greenland (geus) received samples collected at 3-m intervals from a borehole at 55.695°n, 11.839°e (terrain elevation 5.7 m a.s.l.), at the address ejby havnevej 101 on sjælland (fig. 1). shells of the bivalve corbicula were noted in one of the samples; this species indicates a middle pleistocene interglacial age (meijer & preece 2000; bennike et al. 2019), and since such occurrences are rare in denmark, we decided to conduct analyses of macrofossils. this data article puts the new occurrence on record and provides details of the macrofossil analysis of the sample. the identification of fossils from a deposit can help us determine *correspondence: obe@geus.dk received: 08 sept 2021 accepted: 03 jan 2022 published: 02 mar 2022 keywords: middle pleistocene, quaternary, interglacial, river macroinvertebrates, denmark abbreviations: geus: geological survey of denmark and greenland mis: marine isotope stage cal. years bp: calendar years before present a.s.l.: above sea level b.s.l.: below sea level geus bulletin is an open access, peer-reviewed journal published by the geological survey of denmark and greenland (geus). this article is distributed under a cc-by 4.0 licence, permitting free redistribution, and reproduction for any purpose, even commercial, provided proper citation of the original work. author(s) retain copyright. edited by: sofie lindström, geus, denmark reviewed by: anne elisabeth bjune (university of bergen, norway), matthew pound (northumbria university, uk). funding: none provided competing interests: see page 4 additional files: see page 4 https://doi.org/10.34194/geusb.v49.8294 https://orcid.org/0000-0002-5486-9946 https://orcid.org/0000-0003-2441-4286 mailto:obe@geus.dk bennike & wiberg-larsen 2022: geus bulletin 49. 8294. https://doi.org/10.34194/geusb.v49.8294 2 of 5 w w w . g e u s b u l l e t i n . o r g the age and palaeoenvironment of the deposit. we also briefly review other interglacial and interstadial occurrences from eastern denmark. lithostratigraphy the drilling penetrated clayey till, glaciofluvial gravel, clay with bivalve shells, glaciofluvial gravel and danian limestone (fig. 2). drilling stopped at a depth of 147.5 m below the terrain surface. materials and methods only a single sediment sample was available for analysis of macrofossils from the clay unit with bivalve shells. the sample weighed c. 200 g. it was soaked in a naoh solution at room temperature for 2 days and wet sieved on 0.4-, 0.2and 0.1-mm sieves. the residue left on the sieves was analysed using a dissecting microscope. results and discussion the results of the macrofossil analyses are presented in table 1. the sample was small, and we only found the remains of five taxa. however, some of them are of interest, providing insights into the age and palaeoenvironmental conditions. vascular plants are represented by two taxa. betula sect. albae sp. (tree birch) is common in interglacial assemblages. the small birch nutlets are produced in vast quantities and easily dispersed by wind or rivers. the presence of tree birch indicates a forested environment. zannichellia palustris (horned pondweed) is a small, submerged, perennial water plant that grows in shallow, fresh or brackish waters, in lakes and rivers. it has a wide geographical range, but it does not grow in arctic regions. achenes of z. palustris have previously been reported from interglacial deposits in denmark by hartz (1909) and bennike et al. (2019). invertebrates are represented by shells of the bivalve corbicula fluminalis (fig. 3). the pleistocene occurrence of this species was discussed by meijer & preece (2000), who concluded that the species was present only in temperate stages. although mainly a fresh-water species that lives in rivers, it may have been able to tolerate slightly brackish conditions. it occurred in north-western europe during the early and middle pleistocene, whereas it was absent during the last interglacial. in denmark, it has been found in interglacial deposits from the former free port in copenhagen (johansen 1904), a deposit nowadays referred to mis 7 (bennike et al. 2019). the species has also been reported from an interglacial deposit at førslevgaard in southern sjælland (johansen 1904; location in fig. 1). the age of the deposit at førslevgaard is unknown, but its fauna indicates a middle pleistocene age. fig. 1 map of denmark showing the location of ejby and other middle pleistocene interglacial deposits on sjælland discussed in the text. 10°e 14°e 56°n 57°nsweden denmark germany50 km jylland måløv sjælland fyn førslevgaard trianglen ejby fig. 2 lithological log of the well from ejby (dgu no. 198.964). samples were collected at an interval of 3 m, and the exact thicknesses of the units are unknown. drilling stopped at a depth of 147.5 m below the terrain surface. the star shows the position of the analysed sample. more details on the sediments can be found at https://data.geus.dk/jupiterwww/borerapport. jsp?borid=599264. d ep th b el ow te rr ai n su rfa ce (m ) clayey till glaciofluvial gravel glaciofluvial gravel clay with shells danian limestone 0 10 20 30 40 50 table 1 macrofossils from the interglacial deposit at ejby, sjælland. plants betula sect. albae (nutlet) 1 zannichellia palustris (achene) 1 invertebrates daphnia cf. pulex (ephippium) 1 hydropsyche contubernalis (frontoclypeal apotomes) 2 corbicula fluminalis (shells) 10 https://doi.org/10.34194/geusb.v49.8294 http://www.geusbulletin.org https://data.geus.dk/jupiterwww/borerapport.jsp?borid=599264 https://data.geus.dk/jupiterwww/borerapport.jsp?borid=599264 bennike & wiberg-larsen 2022: geus bulletin 49. 8294. https://doi.org/10.34194/geusb.v49.8294 3 of 5 w w w . g e u s b u l l e t i n . o r g in addition to bivalve shells, two frontoclypeal apotomes of larvae of the caddisfly (trichoptera) hydropsyche contubernalis were found. like c. fluminalis, h. contubernalis is mainly a fluvial species, nowadays living primarily on the stony or coarse gravel bottom of rivers. however, it is also found in stony, wind-exposed, littoral zones of large lakes, especially in the northern parts of europe (rinne & wiberg-larsen 2017). h. contubernalis nowadays occurs in arresø, the largest lake in denmark (wiberg-larsen 2010). on the undersurface of the substrates mentioned above, larvae build retreats of mineral and organic coarse particles, and in association with these, they spin silky capture nets. the nets function as traps for microand macroinvertebrate prey, transported downstream by the flowing water (or by turbulent currents in lakes). h. contubernalis is nowadays widely distributed throughout europe, from northern scandinavia to spain and the balkans, extending to the british isles in the west and in the east to the urals (neu et al. 2018). there are quaternary danish records from c. 13 300 cal. years bp (coope & böcher 2000) and 10 400 cal. years bp (wiberg-larsen et al. 2001), respectively. in the united kingdom, remains of the species are recorded from late pleistocene deposits (age 35 000−60 000 years bp); langford et al. 2014), and horton et al. (1992) found remains of this and two other hydropsychids in fluvial deposits suggested to be of hoxnian stage ii age. according to ashton et al. (2008), this may correspond to the middle pleistocene, mis 11, corresponding to c. 420 000−370 000 years bp. finally, a single ephippium of daphnia was found. the ephippium is similar to ephippia produced by d. pulex, but it could also represent other species in the daphnia genus. daphnia is a small planktonic crustacean that is often abundant in lakes and ponds, but it can also live in slow-flowing or stagnant parts of rivers. analyses of mitochondrial sequence data (e.g. coi and 16s genes) of aquatic and terrestrial organisms have revealed that the pleistocene was an important period for generating biodiversity, also of species that still exist (e.g. hungerer & kadereit 1998; ribera & vogler 2004; previšic et al. 2009). both c. fluminalis and h. contubernalis are examples of such species. the investigated interglacial clay is a low-energy deposit that likely accumulated in a lake – probably near the mouth of a river as indicated by the two fluvial species. other interglacial and interstadial deposits on sjælland and møn the new investigated site is located c. 500 m south of an overgrown coastal cliff with a layer of stones with an eemian marine fauna that includes paphia senescens (madsen 1968). this last-mentioned deposit is located 10.5 m a.s.l., whereas the new interglacial deposit is located c. 35 m b.s.l., below a succession of clayey till and glaciofluvial gravel. although located in the same area, these deposits appear to belong to two different interglacial stages. other marine faunas referred to the eemian have been reported from nebbegaard in ne sjælland, the former free port in copenhagen, strandegaards dyrehave in se sjælland, stubberup have in eastern møn and hjelm nakke in se møn as well as other sites on møn (fig.  4; madsen et al. 1908; ødum 1933; petersen & konradi 1974; berthelsen et al. 1977; miller & mangerud 1985; pedersen & gravesen 2021). non-marine eemian deposits have also been found on møn (n. hartz in hinze 1937). from slettenshage on røsnæs, nw sjælland, a marine fauna dominated by the marine gastropod turritella communis was described by petersen (1973). based on amino acid analyses, the occurrence was correlated with  holsteinian deposits in nw germany fig. 3 five shells of corbicula fluminalis from ejby. 10 mm https://doi.org/10.34194/geusb.v49.8294 http://www.geusbulletin.org bennike & wiberg-larsen 2022: geus bulletin 49. 8294. https://doi.org/10.34194/geusb.v49.8294 4 of 5 w w w . g e u s b u l l e t i n . o r g (miller & mangerud 1985). another interglacial deposit from røsnæs, near skambæks mølle (madsen et al. 1908), may be of the same age. as mentioned earlier, interglacial non-marine deposits referred to mis 7 are known from the former free port in copenhagen and nearby trianglen (bennike et al. 2019; location in fig. 1). other middle pleistocene occurrences have been reported from måløv (bennike et al. 2011; location in fig. 1) and førslevgaard (johansen 1904; hartz 1909). interstadial weichselian non-marine deposits have been reported from kobbelgård and klintholm, se møn (bennike et al. 1994; houmark-nielsen et al. 2016) and sejerø (bennike et al. 2007). marine interstadial deposits with boreoarctic or arctic faunas have been reported from høve (milthers 1900; ødum 1933), holbæk, høng (ødum 1933), nordruplund, bjernede and fjenneslev (ødum 1933; lykke-andersen 1990), gyrstinge (sorgenfrei 1945) and holmstrup (petersen & buch 1974). lists of macrofossils reported from the sites are shown in table s1. conclusions we conclude that the clayey deposit found at ejby was deposited in a low-energy fluvial environment. the mean july temperature was likely higher than in denmark today, and the deposit is clearly interglacial rather than interstadial. the occurrence of the bivalve corbicula fluminalis indicates that the deposit is probably of pre-eemian, middle pleistocene age, at least 200 000 years bp. acknowledgements we thank the reviewers for their valuable corrections to the manuscript. additional information funding statement this study did not receive any funding. author contributions ob: macrofossil analyses, manuscript writing. pwl: identification and interpretation of trichoptera remains as well as supplementary writing/ editing of the manuscript. competing interests none declared. additional files one additional file is available at https://doi.org/10.22008/fk2/qeuaxo references andersen, s.t. 1967: kvartærtiden. istider og mellemistider i danmark. in: nørrevang, a. & meyer, t.j. (eds): danmarks natur 1, landskabernes opståen, 199–250. copenhagen: politikens forlag. ashton, n., lewis, s.g., parfitt, s.a., penkman, k.e.h. & coope, g.r. 2008: new evidence for complex climate change in mis 11 from hoxne, suffolk, uk. quaternary science reviews 27, 652–668. https://doi. org/10.1016/j.quascirev.2008.01.003 bennike, o., hedenäs, l., high, k., korshøj, j.s., lemdahl, g., penkman, k., preece, r.c., rosenlund, k. & viehberg, f.a. 2019: new interglacial deposits from copenhagen, denmark: marine isotope stage 7. boreas 48, 107–118. https://doi.org/10.1111/bor.12342 bennike, o., houmark-nielsen, m., böcher, j. & heiberg, e.o. 1994: a multi-disciplinary macrofossil study of middle weichselian sediments at kobbelgård, møn, denmark. palaeogeography, palaeoclimatology, palaeoecology 111, 1–15. https://doi.org/10.1016/0031-0182(94)90344-1 bennike, o., houmark-nielsen, m. & wiberg-larsen, p. 2007: a middle weichselian interstadial lake deposit on sejerø, denmark: macrofossil studies and dating. journal of quaternary science 22, 647–651. https://doi.org/10.1002/jqs.1084 bennike, o., lindgård, e., granat, h.j., preece, r.c. & viehberg, f. 2011: a new middle pleistocene interglacial sequence from måløv, sjælland, denmark. geological survey of denmark and greenland bulletin 23, 29–32. https://doi.org/10.34194/geusb.v23.4805 berthelsen, a., konradi, p. & petersen, k.s. 1977: kvartære lagfølger og strukturer i vestmøns klinter. dansk geologisk forenings årsskrift for 1976, 93–99. candy, i., tye, g., coxon, p., hardiman, m., matthews, i. & palmer, a. 2021: a tephra-based correlation of marine and terrestrial records of mis 11c from britain and the north atlantic. journal of quaternary science 36, 1149–1161. https://doi.org/10.1002/jqs.3367 coope, g.r. & böcher, j. 2000: coleoptera from the late weichselian deposits at nørre lyngby, denmark and their bearing on palaeoecology, biogeography and palaeoclimate. boreas 29, 26–34. https://doi. org/10.1111/j.1502-3885.2000.tb01198.x hartz, n. 1909: bidrag til danmarks tertiære og diluviale flora. danmarks geologiske undersøgelse ii. række 20, 292 pp. https://doi. org/10.34194/raekke2.v20.6804 hintze, v. 1937: møens klints geologi, 410 pp. copenhagen: reitzels forlag. horton, a., keen, d.h., field, m.h., robinson, j.e., coope, g.r., currant, a.p., graham, d.k., green, c.p. & phillips, l.m. 1992: the hoxnian interglacial fig. 4 google earth image of sjælland and møn showing localities mentioned in the text. 1: slettenshage. 2: skambæks mølle. 3: sejerø. 4: høve. 5: holbæk. 6: ejby. 7: nebbegaard. 8: måløv. 9: trianglen. 10: the former free port in copenhagen. 11: holmstrup. 12: høng. 13: nordrup. 14: gyrstinge. 15: bjernede. 16: fjenneslev. 17: førslevgaard. 18: strandegaards dyrehave. 19: stubberup have. 20: kobbelgård/klintholm. 21: hjelm nakke. sjælland møn 1 14 15 12 18 19 20 17 109 11 8 7 6 5 4 3 2 13 16 2125 km https://doi.org/10.34194/geusb.v49.8294 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collided at c. 1.9 ga with a lesser-known archaean craton to the north, to form the nagssugtoqidian orogen. the palaeoproterozoic metamorphic grade and strain intensity decrease northward through the orogen, allowing investigation of the reworked archaean components in its northern part. two archaean supracrustal belts in this region – the ikamiut and kangilinaaq belts – are investigated here using field mapping, aeromagnetic data, zircon geochronology, and geochemistry. both belts comprise quartzo-feldspathic and pelitic metasedimentary rocks, amphibolite, and minor calc-silicate rocks, anorthosite and ultramafic rocks. pbpb and u-pb dating of detrital zircons and host orthogneisses suggest deposition at c. 2800 ma (kangilinaaq belt) and after 2740 ma (ikamiut belt); both belts have zircons with neoarchaean metamorphic rims. metasedimentary rocks and orthogneisses at ikamiut share similar steep ree signatures with strong lree enrichment, consistent with local derivation of the sediment and deposition directly onto or proximal to the regional orthogneiss precursors. zircon age data from kangilinaaq indicate both local and distal sources for the sediment there. geochemical data for kangilinaaq amphibolites indicate bimodal, mixed felsic–mafic source rocks with island-arc basaltic affinities, consistent with a shelf or arc setting. both belts experienced a similar tectono-metamorphic history involving neoarchaean amphibolite facies peak metamorphism at c. 2740–2700 ma, possibly due to continued emplacement of tonalitic and granodioritic magmas. nagssugtoqidian lower amphibolite facies metamorphism at c. 1850 ma was associated with development of the large-scale f 2 folds and shear zones that control the present outcrop pattern. the observed differences in the sources of the kangilinaaq and ikamiut belts and their shared post-archaean history suggest they were formed in different neoarchaean environments proximal to and on a continental plate, and were amalgamated in a convergent margin setting shortly after their deposition. keywords: north atlantic craton, northern nagssugtoqidian orogen, la-icp-ms, sims, zircon ________________________________________________________________________________________________________________________________________________________________ j.a.h., b.m.s., j.a.m.v.g. & a.a.g., geological survey of denmark and greenland, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: jho@geus.dk m.k., geological museum, university of copenhagen, øster voldgade 5–7, dk-1350 copenhagen k, denmark. © geus, 2006. geological survey of denmark and greenland bulletin 11, 9–31. available at: www.geus.dk/publications/bull 10 greenland inland ice greenland canada archaean, variably reworked metasedimentary rocks surficial deposits basalt quaternary cretaceous–palaeogene proterozoic sandstone sarfartoq carbonatite complex sisimiut charnockite arfersiorfik quartz diorite granodioritic and granitic gneiss granodioritic and granitic gneiss orthogneiss dioritic gneiss orthogneiss metasedimentary rocks amphibolite (including proterozoic components) intermediate to basic intrusions boye sø anorthosite complex archaean, unreworked thrustt t jakobshavn isfjord us sui tnordre strømfjord arfersiorfik aasiaat qeqertarsuaq ilulissat qasigiannguit kangaatsiaq attu sisimiut sø nd re st røm fjor d kangerlussuaq naternaq nuussuaq vaigat 51° disko n ag ss u gt o q id ia n o ro ge n r in ki an f o ld b el t n o rt h a tl an ti c cr at o n sn o c n o nssb itz n n o inland ice fig. 2a ikamiut region fig. 2b kangilinaaq peninsula sydostbugten 0 50 km t t t t t t t t t t t t ttt t disk o bu gt sukkertoppen iskappe 68° 66° 70° fig. 1. geological map of the nagssugtoqidian orogen, west greenland, from van gool et al. (2002b). frames show locations of figs 2 and 3. 11 the palaeoproterozoic nagssugtoqidian orogen, central west greenland, comprises archaean and less abundant proterozoic orthogneiss and metasedimentary rocks deformed and metamorphosed at c. 1850 ma during collision of the north atlantic craton with a lesser-known, likewise archaean craton to the north (kalsbeek et al. 1987; taylor & kalsbeek 1990; kalsbeek & nutman 1996; connelly et al. 2000; van gool et al. 2002a). the orogen extends from søndre strømfjord in the south, northward to disko bugt and possibly farther into the largely contemporaneous rinkian fold belt (fig. 1). the metamorphic grade associated with orogenesis decreases from granulite facies in the collisional core (the central nagssugtoqidian orogen) to amphibolite facies in the southern foreland and the northern part of the orogen. also the penetrative palaeoproterozoic deformation diminishes toward the north in the northern nagssugtoqidian orogen (nno), and heterogeneous strain distribution may have been important in the preservation of pre-nagssugtoqidian, i.e. archaean structural fabrics and metamorphic assemblages and textures (van gool et al. 2002a; garde et al. 2004; hollis et al. 2004; piazolo et al. 2004; mazur et al. 2006, this volume). as a consequence of the northward decrease in the palaeoproterozoic thermal overprint and deformation, the nno provides an opportunity for investigation of the pre-nagssugtoqidian history of its archaean components. in particular, its supracrustal belts can pro vide valuable information o n t h e tectonic environment(s) of their formation, their relationship to the plate-tectonic configuration, and whether different parts of the craton experienced the same or different archaean histories. here we investigate two supracrustal belts within the nno – the kilometre-wide ikamiut and kangilinaaq belts – that crop out on the western and eastern sides of sydostbugten in southern disko bugt (fig. 1). parts of the nno were mapped by the geological survey of greenland in the 1960s for its 1:500 000 scale geological map series (noe-nygaard & ramberg 1961; henderson 1969) and also by the geological survey of denmark and greenland (geus) in 2000–2003 for the 1:100 000 scale geological map series (see below). henderson (1969) identified a complex map-scale fold structure that dominates the ikamiut peninsula and adjacent inland areas in the western sydostbugten region, and also outlined many of the dominant lithologies and large structural elements in the kangilinaaq region. in this paper we present geological, geochemical, geochronological and geophysical data from work carried out in the period 2000–2003 by geus mapping teams for the kangersuneq and ikamiut 1:100 000 scale geological map sheets (van gool 2005; garde in press); part of this work is reported in more detail in keiding (2004). aeromagnetic data for the sydostbugten region are correlated with major lithological and structural elements. geochemical data from amphibolites in the kangilinaaq region interpreted as deformed and metamorphosed basaltic volcanic rocks, and interlayered pelitic rocks, are used to determine the likely depositional environment. zircon pb-pb and u-pb geochronology on granodioritic orthogneisses and a metasedimentary rock from the ikamiut region is compared with existing data from the ikamiut and kangilinaaq regions. finally, the implications for regional neoarchaean tectonics are discussed. ikamiut belt and host rocks west of sydostbugten the ikamiut belt is a deformed, kilometre-thick sequence of biotite schists, with less abundant siliceous and pelitic rocks, amphibolite and minor ultramafic rocks. the belt forms a ten kilometre-scale antiform in the north-western part of sydostbugten (fig. 2a). it is everywhere in contact with c. 2830–2760 ma old, tonalitic to granodioritic orthogneiss (pb-pb whole rock, kalsbeek et al. 1987; u-pb zircon, connelly & mengel 2000 and this study), which dominates the region. the original nature of the contacts between the supracrustal belt and the regional orthogneiss is obscured by later ductile deformation (see also østergaard et al. 2002). rb-sr data for 12 metasedimentary samples from this belt, near ikamiut, gave an age of c. 1880 ma for closure of the rb-sr system and a very high initial 87sr-86sr ratio of c. 0.712, suggesting that these rocks were deposited at around 2.8 ga and isotopically strongly reset during nagssugtoqidian metamorphism (kalsbeek & taylor 1999). structure the structural pattern is dominated by kilometre-scale, closed, upright f 2 folds folding an s 1 foliation and associated with a moderate to intense, ene-striking s 2 foliation (fig. 2a). preservation of s 1 fabrics is found in areas of low d 2 strain, typically within the cores of large f 2 folds. outcrop-scale, parasitic f 2 folds associated with weak to moderately developed mineral lineations (l 2 ) plunge at shallow angles to the wsw. in the eastern ikamiut region, l 2 lineations are shallow and, in some cases, plunge to the east. some f 2 folds may be doubly plunging and/or refolded, consistent with localised outcrop-scale refolded 12 b 467433 467436 467401 467403 467404 467405 467408 467444 467445 467446 467413 467426 467440 467420 467423 qasigiannguit 30 10 44 35 40 78 10 14 20 20 8 6 10 10 22 25 30 35 32 38 44 48 35 44 63 63 50 52 40 35 73 68 45 13 60 60 15 55 45 15 28 55 20 50 70 14 62 48 44 38 41 28 30 2631 1035 3513 39 22 2886 32 68°45' 68°55' 51°15' 51° 50°45' la ks eb ug t ka ng erl ulu k f1 f2 f2 f2 ka ng ilin aa q 68°35' 68°40' a467526 440938 44 15 40 2 3751 9 62 55 10 48 75 14 16 38 21 22 20 2 79 5 72 87 85 3212 8 34 23 8 8 14 5 5 35 2 4 22 5 nivaap paa ka ng ers un eq 440910 ikamiut 52° 51°45'langesund f1 f2 f2 f2 f1 amphibolite, unspecified quartzo-feldspathic paragneiss, locally garnet bearing pelitic gneiss, garnet-biotitesillimanite bearing biotite schist, dark, well foliated, with small garnets marble and calc-silicate rock quaternary cover anorthosite mafic dyke trace of axial surface, antiformal/synformal fold 5 km homogeneous amphibolite – mafic intrusive rock complex layered amphibolite – mafic supracrustal rocks two-mica granite pegmatite porphyritic granite porphyritic orthogneiss to foliated granite porphyritic quartz diorite n 5 km n biotite-bearing, grey orthogneiss fig. 2. preliminary geological interpretation maps on (a) the ikamiut region and (b) the kangilinaaq peninsula, showing representative structural data, sample numbers and localities. for regional location see frames in fig. 1. 13 folds. the kilometre-scale, upright f 2 folds are probably parasitic on the major antiformal structure that dominates the outcrop pattern. ten to hundred metre-scale, shallowly w-plunging f 2 folds of flat-lying s 1 foliation are abundant in the tonalitic to granodioritic orthogneiss inland at the head of nivaap paa (fig. 2a). these folds are difficult to trace for long distances along strike. the inland outcrop is relatively poor, and available outcrop suggests that some of the folds die out towards the west, apparently because of homogeneity and lack of ductility contrast within the orthogneiss. lithologies, mineral assemblages and fabrics the tonalitic to granodioritic orthogneiss is a compositionally layered, medium-grained, pale pink and grey rock dominantly comprising plagioclase and quartz, with lesser k-feldspar and disseminated biotite. a mediumto coarse-grained gneissic layering (s 1 ) is discontinuous on a scale of metres to tens of metres and commonly displays intrafolial isoclinal folds. the orthogneiss typically also holds a moderate, ene-striking s 2 foliation that is a partially to completely transposed s 1 fabric, and a weakly to moderately developed, shallow w-plunging l 2 mineral lineation. mediumto coarse-grained, centimetre-scale granitic veins indicate variable d 2 strain: they form a layering that is typically transposed into s 2 , but in some cases they are slightly discordant. the supracrustal sequence is dominated by biotite schists to gneissic rocks that typically comprise plagioclase, quartz, biotite, and rarely garnet. interlayered with these rocks occur local, more mica-rich and aluminous layers up to 20 m thick, which commonly display a schistose s 1 fabric. these rocks typically comprise biotite, plagioclase, quartz, muscovite, sillimanite, and garnet, with accessory tourmaline. locally, in the most micaceous parts, a d 2 crenulation of s 1 biotite, plagioclase and quartz ± sillimanite is developed, with axial planes parallel to the dominant regional s 2 gneissosity of the tonalitic–granodioritic orthogneiss host, and fine-grained biotite and muscovite along the crenulations. aggregates of fine-grained sillimanite and biotite in biotite-rich schists form blocky, centimetre-scale patches interpreted as pseudomorphs after andalusite. this suggests that the s 1 fabrics and assemblages were formed at low-pressure (< 3.85 kbar), lower amphibolite facies metamorphic conditions, followed by increasing temperature (and possibly also pressure) into sillimanite-grade conditions. a distinct unit of siliceous paragneiss, locally garnetbearing, is also volumetrically important. it is distinguished from the biotite schist/gneiss by its more quartz-rich and mica-poor composition. it is often difficult to distinguish this lithology from the tonalitic to granodioritic orthogneiss, particularly in inland areas where outcrop is poor. amphibolite layers, which are 10–50 m thick and laterally discontinuous on a kilometre-scale, are associated with the metasedimentary sequence. they commonly occur at or near boundaries between the metasedimentary rocks and orthogneiss. the amphibolites are medium grained and comprise hornblende with lesser plagioclase and quartz, and locally clinopyroxene ± garnet. in some cases they show distinct mafic–felsic layering, and they commonly contain thin (0.5–5 cm), discontinuous felsic layers. a few isolated occurrences of intensely deformed anorthosite occur at tectonised boundaries between the tonalitic to granodioritic orthogneiss and metasedimentary rocks. the largest occurrence is in the northern island group of nivaap paa (fig. 2a). the anorthositic rock is coarse grained and ‘zebra-striped’, and consists of hornblende and calcic plagioclase with a variably developed foliation and an intense linear fabric. the mafic parts are commonly boudinaged within the more felsic component. an extensive body of mediumto coarse-grained granite is located within the hinge zone of the large antiformal structure along the southern coast of nivaap paa. the granite is porphyritic and white to red in colour, and holds a weak gneissose fabric. its northern contact with the regional orthogneiss is tectonised and possibly tectonically repeated. the relatively undeformed nature of the granite suggests it intruded into the orthogneiss after formation of the regional gneissose fabric (s 2 ). the granite contains thin lenses and layers of medium-grained amphibolite, and is bounded to the south by a layer of amphibolite 50–400 m thick, the outcrop of which defines a tight synformal fold closure (fig. 2a). kangilinaaq belt and host orthogneiss east of sydostbugten the kangilinaaq peninsula (fig. 2b) is dominated by a kilometre-scale synformal structure comprising a series of ne-trending, upright, isoclinal f 1 and f 2 folds that repeat a thick supracrustal sequence. the most common lithologies are quartzo-feldspathic and pelitic metasedimentary rocks, with lesser amphibolite and subordinate marble and calc-silicate rocks. an equivalent supracrustal sequence is found south of kangersuneq fjord, on the southern limb of an antiformal fold running through the fjord. a lithologically distinct unit of amphibolite and associated metasedimentary rocks runs through the town 14 of qasigiannguit in the west of the peninsula. for ease of reference this unit is named the qasigiannguit amphibolite in the following. it is separated from the main supracrustal sequence by 200–500 m of high-strain archaean orthogneiss. the significance of this high-strain zone in terms of the original supracrustal stratigraphy is uncertain, and thus the qasigiannguit amphibolite may or may not be part of an originally continuous supracrustal series on the kangilinaaq peninsula. for descriptive reasons the two supracrustal sequences are collectively termed the kangilinaaq belt in the following. pelitic rocks from the main supracrustal sequence contain archaean detrital zircon populations in the range 2820–2760 ma, with a minimum depositional age constrained by an intrusive two-mica granite at 2723 ± 15 ma (thrane & connelly 2006, this volume). metamorphic zircon growth occurred at 1920–1820 ma in various rocks (keiding 2004; thrane & connelly 2006, this volume). age data are addressed in more detail in the discussion. structure the structural pattern is dominated by large, tight to isoclinal folds. especially along the south-eastern side of the peninsula, the quartzo-feldspathic and pelitic rocks are intensely folded into upright folds on scales from decimetres to tens of metres with shallowly ne-plunging fold axes. older, isoclinal, often intrafolial folds indicate that the upright folds are at least second-generation (f 2 ). a shear zone containing mylonitic orthogneiss bounds the supracrustal rocks to the south-east. it can be traced from the south-western part of the peninsula to half-way up kangersuneq fjord, where it meets the water (fig. 2b). kinematic indicators and a lineation suggesting sinistral/ top to the west movement are poorly developed in the shear zone. the continuation of the shear zone may be found in a poorly developed, but continuous se-trending shear zone south of kangersuneq fjord, marked by a sliver of metasedimentary rocks. north-west of the supracrustal sequence, no similar shear zone was found, although some smaller zones of high strain were recognised. lithologies, mineral assemblages and fabrics the predominant regional lithologies are layered, grey tonalitic to granodioritic orthogneisses interleaved with supracrustal rocks. the orthogneisses contain variable proportions of plagioclase, quartz and biotite, with minor kfeldspar and hornblende. compositional layering of orthogneiss with thin amphibolite layers interpreted as highly attenuated enclaves, give the rocks a layered appearance. the orthogneisses are intersected by concordant to slightly discordant, mediumto coarse-grained, centimetreto half metre-scale granitic veins interpreted as derived from local melts. the orthogneisses show intrusive contacts into part of the supracrustal sequence (see below), although it is not certain that this relationship applies to all of the supracrustal rocks on the peninsula. the gneissic fabric of orthogneiss in the core of the peninsula is locally disturbed by pods and sweats of partial melt, which can contain millimetre-sized garnets. garnet formation in the orthogneiss is restricted to the core of the peninsula, a region of abundant metasedimentary rocks. the garnet formation may be the product of contamination during partial melting of the metasedimentary rocks, either during intrusion of the precursors to the orthogneiss, or during metamorphism. variably deformed quartz diorite occurs in two localities. typically it has tectonised contacts with the supracrustal rocks, but east of qasigiannguit it has intrusive contacts to the latter and has yielded a u-pb zircon emplacement age of 2801 ± 34 ma (thrane & connelly 2006, this volume). the main supracrustal sequence is dominated by medium-grained, quartzo-feldspathic metasedimentary rocks that commonly contain garnet. where garnet is absent in these rocks, they are difficult to distinguish from the orthogneisses. the quartzo-feldspathic paragneiss alternates on metreto 100 metre-scale with pelitic rocks, amphibolite and rare calc-silicate rocks. the pelitic rock comprises quartz, plagioclase, biotite, garnet, and sillimanite. locally, it has a large component of granitic partial melt, commonly occurring in boudinaged lenses, indicative of upper amphibolite facies metamorphic conditions. amphibolites are commonly dark and subtly layered, fine to medium grained and few metres to 50 m wide. remnants of deformed pillows are locally present. in the eastern part of the sequence isolated lenses of metamorphosed ultramafic rocks occur in a few locations, commonly within amphibolites. they comprise predominantly amphibole and orthopyroxene, with or without clinopyroxene, olivine, phlogopite, and serpentinite. minor calc-silicate rocks are layered, with variable grain size, and comprise calcite, phlogopite, quartz, tremolite and locally actinolite. pelitic rocks in this sequence are commonly coarse grained and comprise quartz, biotite, garnet, plagioclase, and sillimanite. large lumps of fibrous sillimanite (up to 3 cm in diameter) are likely pseudomorphs after andalusite. rare pseudomorphs of sillimanite after kyanite were also found. 15 this may indicate variability in pressure conditions in the kangilinaaq belt or prograde barrovian-style metamorphism. quartzo-feldspathic metasedimentary rocks in the central/northern part of the synform are coarse grained, heterogeneous, and rarely garnet-bearing. the qasigiannguit sequence comprises mafic and felsic metavolcanic rocks intercalated with clastic sequences and isolated layers and lenses of strongly deformed, zebrastriped anorthosite. the sequence is c. 700 m wide, trends sw–ne, and is well exposed on the islands south-west of qasigiannguit. the rocks are isoclinally folded with an intrafolially folded gneissic fabric. as mentioned above it is separated from the predominantly clastic sequence of kangilinaaq by 200–500 m of high-strain archaean orthogneiss (fig. 2b; see also below). in contrast with the main supracrustal belt, the metamorphic grade is lower amphibolite facies. the fineto medium-grained, layered amphibolite contains hornblende and plagioclase, and minor clinopyroxene, epidote, biotite, quartz, and possibly also chlorite. only along laksebugt is the amphibolite locally garnet-bearing. felsic layers can be up to several metres wide and contain predominantly plagioclase and quartz, with minor amphibole, white mica and titanite. pelitic and semipelitic layers up to 50 m wide occur mainly on the islands south-west of qasigiannguit. these layers are generally schistose and contain predominantly quartz, plagioclase, biotite and minor garnet, while sillimanite and muscovite are rare. in exposures 25 km north-east of qasigiannguit, an outcrop of kyanite-bearing pelite shows no indications of replacement by sillimanite. this is the only known occurrence in the north-eastern part of the nagssugtoqidian orogen of stable kyanite, although this mineral has also been described from archaean supracrustal rocks within the southern part of the rinkian fold belt (garde & steenfelt 1999). fine-grained, dark grey biotiterich schist/gneiss forms layers 50–80 m wide that grade locally into layered amphibolites. homogeneous, mediumgrained, greyish green, quartzo-feldspathic gneisses form layers up to 30 m wide that are generally platy and contain quartz, plagioclase, white mica, and amphibole. their origin is uncertain. their occurrence in a layered supracrustal sequence, without obvious intrusive contacts, could indicate that these rocks are also of supracrustal origin, but similar rocks in the main kangilinaaq sequence grade into low-strain megacrystic granodiorite to quartz diorite. the contacts between the qasigiannguit amphibolite and the regional archaean orthogneiss are always tectonised, and their original contact relationships are uncertain. however, lenses of amphibolite, and locally also anorthosite, occur abundantly as inclusions in the regional archaean orthogneiss close to its contacts with the supracrustal sequence. these lenses are unlikely to be tectonic because they occur in an irregular pattern, not along zones of high strain. it is more likely that they are xenoliths, suggesting that the orthogneiss precursors intruded into the supracrustal sequence. aeromagnetic characteristics aeromagnetic data covering the ikamiut and kangilinaaq regions (thorning 1993) allow us to image geological features in terms of magnetic responses, also in areas covered by lakes, sea and overburden. a spacing of flight lines of 1 km and a survey altitude of 500 m control the resolution of the aeromagnetic data. in order to enhance the anomaly patterns from shallow-seated geological features, a separation filter has been applied (jacobsen 1987). the filter enhances magnetic anomalies caused by geological features within a specific depth interval in the crust. the rationale of the filter is that the upward continuation of a potential field to a selected height represents the field from sources in the crust below half the selected height. the difference, or residual, between fields at two different heights can then be viewed as representing the field from sources within the corresponding depth interval in the crust. thus, a total magnetic field that has been continued upward to a height of 2 km represents sources in the crust below 1 km. likewise, the field observed at 500 m represents sources below 250 m. consequently, the residual obtained from these two fields by subtraction represents an enhanced image of the anomaly pattern of geological features in the depth interval 250 m – 1 km. the resulting ‘subsurface’ total magnetic field for the ikamiut– kangilinaaq region is shown in figs 3–5. in view of the fundamental ambiguity and complexity of the magnetic field separation, the filtering should only be used as a tool for detection of anomalies and discrimination of patterns, and qualitative interpretations should be supported by other types of geological data. aeromagnetic patterns in the ikamiut region the supracrustal rocks in the ikamiut region appear as intermediate to low magnetic anomalies in the separationfiltered total magnetic field intensity map (–1 to –30 nt, a’s in fig. 4). the orthogneisses are expressed as slightly higher magnetic anomalies (5–20 nt, b and c in fig. 4), although these show considerable variability that may be a consequence of differing contributions from other subsurface lithologies. from the aeromagnetic anomalies it is 16 52° 10 km sydostbugten qasigiannguit ka ng ilin aa q figs 2b, 5 figs 2a, 4 ikamiut nivaap paa 51° 68°45' 68°30' p p p q o o o h h h o 779 193 139 107 78 55 35 19 4 –10 –22 –32 –42 –51 –59 –67 –74 –81 –87 –93 –98 –104 –109 –114 –118 –122 –127 –131 –136 –140 –145 –151 –157 –163 –170 –179 –189 –204 –226 –359 nt fig. 3. total magnetic field intensity for the ikamiut and kangilinaaq regions. the labels h, o, p and q are referred to in the main text. a shadowing effect from nw (315°n) with an inclination of 45° has been applied. the areas of figs 4 and 5 are outlined by white frames. 68°42' 68°39' 68°36' 52°15' 51°45'52° 2.5 km nt ikamiut nivaap paa a a b g a a d c e f i –36 –27 –20 –16 –13 –10 14 17 20 25 33 60 6 4 2 –1 –3 –7 11 8 fig. 4. the separation-filtered total magnetic field intensity in the interval from 0.250 m – 1 km for the ikamiut area. shadowing effect as in fig. 3. the labels a–i are referred to in the main text. 17 possible to recognise folding of the orthogneiss (e.g. east of c, fig. 4), which correlates closely with the geological mapping (fig. 2a). similarly, a strong magnetic low visible between b and d (fig. 4) defines a refolded fold structure in pelitic gneiss identified during mapping. exposed granitic rocks are visible as high positive anomalies (d, fig. 4). similar anomalies are visible beneath the sea north and east of ikamiut and beneath the bay of nivaap paa (e, f and g, fig. 4). the orthogneiss north of nivaap paa (i, fig. 4) shows slightly lower magnetic anomalies than the orthogneisses to the south. aeromagnetic patterns in the kangilinaaq region the supracrustal belt on the kangilinaaq peninsula appears as a distinct, rather homogeneous, low negative magnetic anomaly (–35 to –300 nt, fig. 5), possibly reflecting the dominance of quartzo-feldspathic rocks with low magnetite contents. small positive, short-wavelength, ovoid anomalies within the supracrustal rocks reflect small ultramafic bodies (j’s, fig. 5, too small to appear on the map of fig. 2b). the biotite-bearing orthogneiss south of the supracrustal belt shows a positive magnetic anomaly (0–55 nt, k in fig. 5). the change is rather abrupt and correlates with the ene-trending mylonitic shear zone along the south-eastern margin of the supracrustal rocks close to the coast of the peninsula (see also fig. 2b). the north-western boundary of the supracrustal belt on the opposite side of the peninsula, where supracrustal rocks and orthogneiss are interleaved, is less well defined. farther north in the vicinity of qasigiannguit, an abrupt change to a high positive magnetic anomaly field to the north-west corresponds with the northern contact of the amphibolite sequence against the orthogneiss (l in fig. n l j j k m 68°55' 51°15' 51° 50°45' 68°50' 68°45' 5 km nt qasigiannguit ka ng ers un eq ka ng ilin aaq –307 –79 –67 –56 –49 –44 –40 –37 –33 –30 –27 –23 –20 –17 –15 –12 –10 –7 –4 –1 2 6 10 14 17 21 24 26 29 32 36 40 44 48 53 58 65 75 94 162 fig. 5. the separation-filtered total magnetic field intensity in the interval from 0.250 m – 1 km for the kangilinaaq area. shadowing effect as in fig. 3. the labels j–n are referred to in the main text. 18 5). the positive magnetic anomalies within the orthogneiss domains immediately north and south of the kangilinaaq peninsula (m and n in fig. 5) are much stronger than found within the orthogneiss in the north-eastern region of fig. 5 (e.g. at 68°55′n, 50°45′w). based on similar strong positive anomalies associated with granitic rocks in the ikamiut area (fig. 4) and the porphyritic granite on the south-western tip of the kangilinaaq peninsula (fig. 5), the former anomalies may correspond to large deepseated granitic intrusives. likewise, the large magnetic high at eastern sydostbugten may represent granitic intrusive rocks hidden 1–2 km below the present surface (h’s, fig. 3; thorning 1993; nielsen & rasmussen 2004). geochronology zircon separates from three samples from the ikamiut region were analysed to determine (1) the age of emplacement of the regional tonalitic to granodioritic orthogneiss, (2) the age distribution, provenance and minimum age of deposition of the sedimentary precursor to the ikamiut metasedimentary rocks, and (3) the timing of metamorphism. samples of two granodioritic orthogneisses and a quartzo-feldspathic metasedimentary rock were analysed, see below. sample descriptions of these and other rocks are given in table 1, and the age data are presented in tables 2–3 and figs 6–7. all age data in the text are quoted with 2σ absolute uncertainty. methodology samples were crushed and sieved to < 400 µm. the fraction < 45 µm was removed via washing and sieving and the remaining sample panned in water to concentrate the heavy fraction. the heavy, nonmagnetic fraction was separated using heavy liquids (3.30 gcm–3) and a frantz magnetic separator. zircons were hand-picked and mounted in epoxy resin. for secondary ion mass spectrometry (sims) analysis, grains were mounted together with 1065 ma zircons from reference sample 91500, ontario, canada (wiedenbeck et al. 1995). for laser inductively-coupled plasma mass spectrometry (la-icp-ms) analysis no zircon standard was used. the mounted samples were ground to expose the mid-sections of the zircons and polished. the polished samples were examined using backscattered electron (bse) imaging on a philips xl 40 scanning electron microscope at geus, operating at 20kv and a working distance of 10 mm. backscattered electron sample region rock type paragenesis amphibolite 467403 kangilinaaq fine-grained, layered amphibolite 467405 kangilinaaq fine-grained, layered amphibolite 467413 kangilinaaq fine-grained, layered amphibolite 467426 kangilinaaq fine-grained, layered amphibolite 467436 kangilinaaq fine-grained, layered amphibolite hbl-pl ± cpx ± grt, accessory fe-ti oxides 467440 kangilinaaq fine-grained, layered amphibolite 467444 kangilinaaq fine-grained, layered amphibolite 467445 kangilinaaq fine-grained, layered amphibolite 467446 kangilinaaq fine-grained, layered amphibolite orthogneiss 440938 ikamiut medium-grained granodioritic orthogneiss pl-qtz-ksp-bi 467526 ikamiut medium-grained granodioritic orthogneiss pl-qtz-ksp-bi 467401 kangilinaaq medium-grained tonalitic orthogneiss pl-qtz-bi metasedimentary rocks 440910 ikamiut quartzo-feldspathic gneiss pl-qtz-grt-bi, minor sill-ksp 440931 ikamiut quartzo-feldspathic gneiss pl-qtz-bi, minor ksp-mag. bi partly replaced by chl 467503 ikamiut quartzo-feldspathic gneiss pl-qtz-bi, minor ksp-mag-mu 467404 kangilinaaq garnet-bearing schist qtz-pl-bi-sill-grt. bi partly replaced by sill 467408 kangilinaaq cummingtonite gneiss qtz-pl-bi-cu, minor hbl 467417 kangilinaaq biotite-hornblende gneiss qtz-pl-bi-hbl 467420 kangilinaaq fine-grained schist qtz-pl-bi-ep, accessory al & zn 467423 kangilinaaq hornblende gneiss hbl-pl, minor qtz, bi 467433 kangilinaaq hornblende gneiss hbl-pl, minor qtz, bi mineral abbreviations: al: allanite, bi: biotite, cpx: clinopyroxene, cu: cummingtonite, ep: epidote, grt: garnet, hbl: hornblende, ksp: k-feldspar, mag: magnetite, mu: muscovite, pl: plagioclase, qtz: quartz, sill: sillimanite, ti: titanite, zn: zircon. table 1. sample descriptions 19 440938 granodioritic orthogneiss 1 44913 0.207628 2847 4.8 2 54464 0.206401 2843 6.1 3 51744 0.211202 2865 10.9 5 66847 0.205833 2818 12.1 6 45663 0.239096 3072 7.3 7 114515 0.203027 2811 4.9 10 29662 0.206933 2835 8.2 12 81235 0.200267 2785 5.6 15 63304 0.204663 2825 8.7 16 58962 0.203500 2813 7.4 17 32961 0.211432 2888 7.4 20 86073 0.205326 2830 9.7 21 125993 0.199600 2796 4.5 25 60136 0.185466 2664 6.1 26 48587 0.207014 2855 5.6 27 98098 0.202412 2838 8.0 28 46100 0.198084 2836 11.7 29 44476 0.209520 2878 6.4 30 55984 0.205825 2836 9.9 31 52515 0.204633 2835 7.3 33 60481 0.205708 2838 7.2 34 41693 0.217275 2967 29.6 40 16473 0.210866 2905 33.5 41 63641 0.205836 2847 6.9 42 26576 0.199429 2802 10.4 43 34970 0.210589 2882 6.9 44 66299 0.200725 2807 4.9 47 76450 0.185001 2778 5.5 48 344404 0.196981 2819 6.9 50 94026 0.206532 2859 4.6 54 32535 0.206805 2838 17.7 55 18887 0.185070 2753 19.3 57 45001 0.201119 2811 5.3 59 63523 0.203583 2830 8.1 60 35435 0.205041 2842 6.2 61 23531 0.190093 2715 6.2 63 112296 0.208790 2878 4.6 64 39902 0.195071 2763 6.6 74 19592 0.202403 2820 6.2 75 30652 0.204612 2837 11.0 77 41961 0.195999 2774 6.8 78 64028 0.206406 2860 6.1 80 30243 0.209704 2877 6.2 81 106313 0.203552 2844 6.4 82 47863 0.206121 2857 7.4 83 58886 0.201354 2817 6.6 84 119357 0.209519 2882 4.0 86 93017 0.206130 2857 4.8 87 59542 0.208843 2878 4.8 88 80384 0.190889 2738 6.0 89 56425 0.198658 2797 6.6 90 52868 0.194667 2773 5.8 36 30037 0.201451 2808 6.6 37 31254 0.193787 2730 7.6 38 22041 0.205579 2827 10.1 39 52491 0.162084 2504 10.1 40 40780 0.194811 2741 5.7 42 61409 0.195555 2747 4.9 43 103057 0.171459 2534 10.0 44 40828 0.200096 2744 7.8 45 58477 0.197715 2764 5.3 46 20270 0.206049 2843 8.7 47 33049 0.196133 2748 6.5 48 28126 0.193760 2738 6.3 50 19721 0.207732 2845 6.6 51 86891 0.232092 2997 11.6 52 58228 0.201806 2799 5.0 53 50522 0.190800 2710 5.8 54 60856 0.195334 2736 5.6 55 35515 0.198275 2772 5.4 56 51577 0.196653 2758 5.9 58 27007 0.203361 2811 5.7 59 49414 0.202192 2798 5.8 62 10375 0.207836 2855 9.5 63 120563 0.189864 2717 4.2 64 23252 0.187771 2722 7.0 65 26567 0.202492 2801 6.5 69 89976 0.191213 2728 4.7 70 25130 0.199809 2796 6.1 71 68881 0.206577 2861 4.6 72 53407 0.199076 2805 5.1 73 51707 0.194570 2755 4.9 74 67393 0.179579 2625 5.3 75 30132 0.198104 2773 6.6 76 36875 0.197163 2802 7.8 77 28362 0.198893 2790 5.4 78 27133 0.201214 2812 5.7 79 133087 0.188329 2702 4.7 80 45162 0.206677 2856 4.4 81 51961 0.194173 2749 4.6 83 27444 0.201457 2807 5.6 84 26057 0.208900 2868 5.4 85 31842 0.198490 2789 7.0 86 114220 0.180764 2635 5.5 87 62748 0.189371 2717 5.5 88 42113 0.198204 2782 5.2 89 24400 0.199600 2793 6.6 90 29322 0.208314 2861 5.3 91 75430 0.205029 2835 6.0 93 24848 0.198066 2773 6.3 95 60703 0.191617 2717 6.7 96 40762 0.207364 2850 4.1 97 131809 0.193200 2737 6.3 98 43657 0.197222 2778 5.6 99 17404 0.199360 2767 19.2 91 54794 0.203058 2825 6.2 92 86828 0.211233 2895 4.7 93 86433 0.207258 2863 4.4 94 41347 0.203007 2830 5.5 467526 granodioritic orthogneiss 5 56698 0.200720 2804 5.3 6 33787 0.193076 2748 6.6 7 55326 0.195289 2762 4.8 8 76699 0.182851 2652 4.9 10 31196 0.183045 2654 6.6 11 4904 0.204104 2807 12.9 13 39648 0.191787 2718 5.5 15 40707 0.202256 2816 5.0 17 29635 0.217163 2844 19.1 18 6853 0.206028 2827 14.9 19 9339 0.206467 2995 5.7 440910 metasedimentary rock 1 35535 0.200401 2828 6.5 2 31197 0.211066 2824 10.1 3 41461 0.193703 2741 6.1 4 30241 0.204419 2821 6.0 5 25534 0.191383 2718 5.6 6 46366 0.198531 2774 6.1 7 86549 0.207000 2846 5.7 8 48635 0.201767 2807 5.3 9 36751 0.209132 2858 7.0 10 27744 0.183921 2654 9.9 11 43029 0.194263 2742 6.7 12 29314 0.172110 2520 8.6 13 47160 0.206249 2841 5.9 14 49306 0.201659 2804 7.0 15 29978 0.198089 2779 6.0 17 53134 0.194413 2748 5.4 18 27856 0.201215 2810 6.9 19 30082 0.205162 2842 5.9 20 55684 0.198413 2780 5.1 21 147594 0.191303 2722 5.3 22 25436 0.210142 2870 7.0 23 29257 0.196016 2766 7.0 24 20655 0.203877 2826 6.4 25 26159 0.201727 2796 6.6 26 82319 0.215426 2917 4.5 27 112103 0.194672 2751 5.1 30 15491 0.200465 2794 7.1 31 21709 0.204749 2831 8.0 32 14364 0.206770 2843 11.0 33 41967 0.201274 2800 6.8 34 56320 0.189864 2710 5.6 35 23757 0.202176 2801 9.1 table 2. zircon la-icp-ms 207pb-206pb data spot 206pb (cps) 207pb/206pb age (ma) 2σ %spot 206pb (cps) 207pb/206pb age (ma) 2σ % spot 206pb (cps) 207pb/206pb age (ma) 2σ % 20 (bse) images of some of the analysed grains showing sites of analysis and ages obtained are presented in fig. 6. all three samples were analysed at geus using a perkinelmer 6100 drc quadrupole inductively-coupled plasma mass spectrometer combined with a cetac lsx 200 laser ablation unit based on a solid-state nd-yag laser, emitting at a wavelength of 266 nm. the laser was operated at 20 hz with a spot size of 30 µm, producing pits of c. 50 µm depth. the masses 208pb, 207pb, 206pb, and 204pb were analysed in line scans run at 1 µm per second. each analysis comprised 150 time-resolved replicates (duration of total analysis 150 s). in the case of small grains with diameters < 100 µm, only 100 replicates over 100 s were collected. if inconsistencies in the measured ratios were identified within the time span of each analysis, such as spikes relating to inclusions, or significant changes in pbpb ratios indicative of sampling of different age zones, then the whole analysis was discarded. the analyses were standardised against nist 610 glass (pearce et al. 1997) to account for instrument drift. the influence of common pb cannot be assessed using this method, since 204pb was generally below the detection limit. also, because u isotopes could not be measured, the significance of pb loss cannot be assessed, and therefore the ages determined should be regarded as minimum ages. in addition, the age resolution on any individual analysis was restricted owing to relatively low count rates obtained. however, it is a great advantage of the la-icp-ms method that a large number of analyses can be made within a short time period, allowing analysis of large numbers of grains in samples with isotopically simple zircon. the la-icp-ms age data are presented in table 2 and as histograms coupled with relative probability curves (fig. 7). sims analysis of zircon from two samples (440938, 440910) was carried out using a cameca ims 1270 secondary ion mass spectrometer at the nordsim laboratory, swedish museum of natural history, stockholm. the polished zircon mounts were coated with a c. 30 nm layer of gold. analytical procedures and common lead corrections are similar to those described by whitehouse et al. (1997). a primary o2– ion beam is focussed into a spot with a diameter of 20 µm that sputters material from the sample to leave a flat-bottomed crater. positive ions sputtered from the crater are extracted and mass-separated into the peaks of interest: 90zr 2 16o, 204pb, 206pb, 207pb, 208pb, 238u, 232th16o, and 238u16o. calibrations of pb/u ratios are based on the observed relationship between pb/u and uo 2 /u. weighted average 207pb/206pb ages were calculated using isoplot (ludwig 2000). sims age data are presented in table 3 and on tera-wasserburg diagrams in fig. 7. 440938 granodioritic orthogneiss 3 155 94 113 0.607 0.04 0.19819 0.28 14.5789 1.06 0.53352 1.03 –2.4 2811.3 4.6 4 575 274 417 0.502 0.07 0.19781 0.18 14.8262 1.04 0.54361 1.03 –0.4 2808.2 2.9 8 192 24 127 0.117 0.05 0.19575 0.28 14.5329 1.07 0.53845 1.03 –0.6 2791.1 4.6 14 164 23 109 0.140 0.02 0.19767 0.38 14.7352 1.09 0.54065 1.03 –0.9 2807.1 6.1 20a 206 56 134 0.222 0.09 0.19216 0.30 13.6935 1.07 0.51684 1.03 –3.3 2760.7 5.0 24 175 37 117 0.170 0.05 0.19891 0.31 14.7222 1.07 0.53682 1.03 –2.1 2817.2 5.0 29 578 153 384 0.217 0.23 0.19498 0.17 14.2171 1.04 0.52885 1.03 –2.1 2784.6 2.8 41 632 35 391 0.054 0.01 0.19138 0.14 13.5355 1.04 0.51295 1.03 –3.8 2754.1 2.4 54 273 155 199 0.555 0.09 0.19767 0.29 14.6540 1.07 0.53768 1.03 –1.5 2807.0 4.8 66 251 227 191 0.878 0.07 0.19836 0.23 14.3381 1.05 0.52425 1.03 –4.2 2812.7 3.7 72 203 158 150 0.762 0.09 0.19789 0.29 14.2560 1.07 0.52248 1.03 –4.3 2808.9 4.7 76 157 49 107 0.307 0.02 0.20014 0.33 14.6609 1.09 0.53127 1.04 –3.5 2827.4 5.4 440910 metasedimentary rock 22 850 51 526 0.057 0.01 0.18523 0.20 13.1609 1.78 0.51532 1.77 –0.9 2700.3 3.4 29 480 2 308 0.002 0.03 0.18986 0.27 14.0987 1.79 0.53857 1.77 1.6 2740.9 4.4 42 609 3 390 0.003 0.05 0.18800 0.22 13.9521 1.78 0.53823 1.77 2.3 2724.8 3.6 54 554 2 344 0.004 0.01 0.18507 0.22 13.3561 1.78 0.52342 1.77 0.7 2698.8 3.6 58c 106 32 71 0.275 0.23 0.19043 0.43 14.0439 1.82 0.53488 1.77 0.7 2745.9 7.1 58r 610 2 378 0.003 0.04 0.18916 0.21 13.6001 1.79 0.52146 1.77 –1.3 2734.8 3.5 82 1178 7 730 0.004 0.07 0.18473 0.17 13.3129 1.78 0.52267 1.77 0.7 2695.8 2.9 table 3. zircon ion probe (sims) u-th-pb data spot u th pb th/u f 206 % 207pb σ % 207pb σ % 206pb σ % discordance % 207pb σ ppm ppm ppm measured 206pb 235u 238u (conventional) 206pb ages (ma) errors on ratios and ages are quoted at the 1σ level. c: core; r: rim; f 206 %: the fraction of common 206pb, estimated from the measured 204pb. discordance %: degree of discordance of the zircon analysis (at the centre of the error ellipse). 21 orthogneiss the two samples of granodioritic orthogneiss selected for geochronology (440938 and 467526) were collected at the south coast of langesund (fig. 2a). sample descriptions and chemical composition are presented in tables 1 and 4. sample 440938 yielded abundant zircon and contains common thin, transposed granitic layers, whereas sample 467526 does not contain such granitic leucosome. the zircons from both samples are 100–600 µm (mostly c. 200–300 µm) in length and translucent with a heterogeneous orange colour. the crystals are euhedral with slightly rounded terminations and aspect ratios from 1:2.5–1:4, typically c. 1:3. broad oscillatory zones c. 10– 30 µm wide are very common, with rare development of bright, presumably metamorphic rims (see below). the zircons are commonly weakly to moderately fractured, both concentrically and radially, and often show partial fracture healing within bright oscillatory zones (fig. 6). la-icp-ms analyses of 57 oscillatory zoned grains from sample 440938 give a weighted mean age of 2831 ± 23 ma (2σ, mswd = 0.36; table 2; fig. 7a). ten sims analyses of cores of oscillatory zoned grains and two of bright rims reveal more age complexity, with seven of the cores yielding an important 2820–2810 ma age component (table 3; fig. 7b, black data ellipses). four of these seven analyses lie slightly off concordia. another, slightly older and likewise discordant grain (2827 ma, blue in fig. 7b) belongs to the 2831 ± 23 ma la-icp-ms age group. many of the analysed grains show slight discordance indicating partial pb loss, the timing of which is unclear from the data available. two bright rims with significantly younger ages of 2761 ± 10 ma and 2754 ± 5 ma are interpreted as metamorphic. this is supported by the very low th/u of the latter (0.054), though the former is not anomalous in this respect (th/u = 0.22). the sims data are slightly but significantly younger than the la-icp-ms data for the same sample (but from different analysed grains), although the 2σ error on the la-icp-ms age spectrum encompasses most of the sims data. it is difficult to establish the reason for this, particularly given the apparent complexity of the zircons (fig. 7b). it is possible that a larger proportion of older material has been sampled in the la-icp-ms work. it may also be that matrix effects had some influence in standardising zircon data against nist610 glass, though such effects are not generally regarded as significant. the few zircons separated from sample 467526 were analysed via la-icp-ms. eleven analyses of cores displaying oscillatory zonation yield a poorly constrained weighted mean age of 2741 ± 53 ma (2σ, mswd = 0.55; fig. 7c). it might be considered that the large analytical error for this sample leaves room for age complexity, possibly involving analysis of both inherited grains and pb loss (similar to sample 440938). however, all analyses statistically belong to the same population, and there are no significant differences in internal zircon morphology that might account for different age groups. metasedimentary rocks sample 440910 from the ikamiut belt (fig. 2a) is a medium-grained, garnet-bearing quartzo-feldspathic, gneissic rock. colourless, pale yellow and pale pink zircon grains are abundant. they are elongate and generally 100–200 2817 ± 10 200 µm 200 µm b 440938 440910 2700 ± 7 2699 ± 7 2696 ± 6 2746 ± 14 2811 ± 10 2807 ± 10 a fig. 6. backscattered electron images of zircons in samples 440938 (orthogneiss) and 440910 (metasediment) analysed via sims, showing analysed areas and ages obtained. 22 µm in length, with rounded terminations and aspect ratios of 1:1–1:3, typically c. 1:2. bse imaging reveals relatively wide (c. 10–30 µm) oscillatory zoned cores with moderate to well-developed bright rims c. 10–60 µm wide, which in many cases have annealed former fractures (fig. 6). 207pb-206pb ages from 87 la-icp-ms analyses of oscillatory zoned zircon cores are shown in fig. 7d. the vast majority (79) define a tightly clustered peak at c. 2800 ma. the complete age range spans 2997–2520 ma. the youngest ages (< 2700 ma) may reflect mixed core–rim data, although most of them are statistically within the main age population. if a few anomalous old and young ages are disregarded, a weighted mean age of 2779 ± 18 ma is obtained (2σ, mswd = 0.32, n = 79). this group is interpreted as comprising a homogeneous population of detrital zircons, consistent with local derivation from orthogneiss of this age (see above). seven sims analyses, of one core with oscillatory zonation and six bright rims, all fall on concordia (fig. 7e). the core gives the oldest age of 2746 ± 14 ma (th/u = 0.275). the six analyses of bright rims give ages between 2741 ± 9 and 2696 ± 6 ma. all have very low th/u (0.004–0.06), consistent with a metamorphic origin. these metamorphic ages are comparable to the few young ages also identified in the laicp-ms analyses, and suggest that this sample underwent metamorphism at c. 2740–2700 ma, shortly after its deposition. an alternative, and in our view less likely interpretation is that the metamorphic rims were developed during metamorphism of the source rock prior to erosion and deposition of the sediment. age (ma) 2779 ± 18 ma (2σ) mswd = 0.32 n = 79 440910 467526 2741 ± 53 ma (2σ) mswd = 0.55 n = 11 age (ma) 440938 orthogneiss d c a 2831 ± 23 ma (2σ) mswd = 0.36 n = 57 age (ma) 16 14 12 10 8 6 4 2 0 16 14 12 10 8 6 4 2 0 6 4 2 3 0 5 1 n um be r o f an al ys es n um be r o f an al ys es n um be r o f an al ys es 1500 2000 2500 3000 3500 1500 2000 2500 3000 3500 1500 2000 2500 3000 3500 orthogneiss metasedimentary rock 20 7 p b/ 20 6 p b 20 7 p b/ 20 6 p b 238u/206pb 238u/206pb 2770 2750 2730 2710 2690 0.182 0.184 0.186 0.188 0.190 0.192 0.194 1.7 1.8 1.9 2.0 2.1 440910e 0.188 0.192 0.196 0.200 0.204 440938b 2840 2820 2800 2780 2760 2740 1.80 1.9 2.0 fig. 7. la-icp-ms 207pb/206pb histograms and sims u-pb tera-wasserburg concordia plots of zircon age data from the ikamiut region. a: histogram of 207pb/206pb ages from orthogneiss sample 440938. b: terawasserburg plot for orthogneiss sample 440938 showing nine cores of oscillatoryzoned grains (black), an older core (blue), and two bright rims (red). c, d: histograms of 207pb/206pb ages from orthogneiss 467526 and metasedimentary sample 440910. e: tera-wasserburg plot for metasedimentary sample 440910 showing one core (black) and six metamorphic rims (red). the histogram bin size is 25 ma (a, d) or 50 ma (c). error ellipses on concordia diagrams are drawn at 68.3% confidence (1σ). 23 geochemistry whole-rock geochemical analysis of amphibolites, felsic orthogneiss and metasedimentary rocks from the ikamiut and kangilinaaq regions was undertaken to (a) geochemically characterise these rock types, (b) investigate the likely tectonic environment of formation and provenance of the amphibolites and metasedimentary rocks, and (c) investigate likely regional correlations. sample descriptions are presented in table 1, and major and trace element compositions in table 4. analytical procedure major and trace element analyses (table 4) were performed by geus. the samples were ground in tungsten (ikamiut samples) or agate (kangilinaaq samples) mills, and dried. for major elements the rock powders were fluxed with sodium tetraborate and fused to glass discs and analysed with a philips pw1606 x-ray fluorescence (xrf) mass spectrometer. na and cu were determined by atomic absorption spectrometry, and volatiles were analysed by gravimetry. refer to kystol & larsen (1999) for the complete analytical procedure. for trace element analyses, powdered samples were brought into solution and analysed using a perkinelmer 6100 drc quadrupole icpms instrument. for the ikamiut samples zr, cr, rees and hf were determined by dissolving a piece of the borate glass used in the major element xrf analyses, in order to obtain complete contributions of these elements from chromite and zircon. the icp-ms results were corrected for the relevant oxide interferences using bhvo-1 and gh as standards. for the kangilinaaq samples some trace elements were also analysed by xrf performed directly on pressed powder tablets at the geological institute, university of copenhagen, using a phillips pw 1400 xrf spectrometer. the data were corrected for matrix variations using the major element compositions, and agv-1 was run as standard. orthogneisses two orthogneiss samples from the ikamiut region were analysed (440938 and 467526), and one from kangilinaaq (467401; table 4a; fig. 2). the two ikamiut samples show very similar granodioritic major element chemistry, while the kangilinaaq sample is more tonalitic. the kangilinaaq sample has low ree concentrations and a fairly steep ree curve with la n /lu n ~ 16 (fig. 8b). in contrast, the two ikamiut samples have higher ree concentrations and significant negative eu anomalies, consistent with the more evolved composition of these rocks. amphibolites from the kangilinaaq belt nine amphibolites s.s. from the kangilinaaq belt were analysed for major and trace elements (table 4a); no amphibolite samples have been analysed from the ikamiut region, where amphibolites only constitute a minor component of the supracrustal rocks. the nine samples from kangilinaaq show only a small range in chemical composition. they have relatively primitive signatures with low sio 2 (46–49 wt%) and high mgo (7–11 wt%), and flat ree patterns that group tightly around ten times chondrite values (fig. 8a). their ti/v ratios display a narrow range of 16–19, and in a ti-v diagram (shervais 1982) they plot just within the island arc field (fig. 9). the positive correlation between ti and v could reflect fractionation of olivine and plagioclase. the geochemical resemblance between all nine samples and their well-defined ti/v trend are consistent with formation within a single volcanic suite. metasedimentary rocks and hornblendebearing gneisses from the kangilinaaq belt metasedimentary sample 467404 is characterised by high alumina (19 wt%) coupled to low cao (0.7 wt%) and high concentrations of ree and ba (605 ppm), consistent with a clay-rich precursor. the ree curve is steep (la n /lu n = 30, la = 140 times chondrite), and has a significantly negative eu anomaly. sample 467420 is siliceous (75 wt% sio 2 ), consistent with a relatively mature sedimentary precursor. its ree concentrations lie just below those of sample 467404, with a similar steep ree pattern. for sample 467417, both major and trace elements agree well with the average composition of archaean mudstone from taylor & mclennan (1985, table 7.8). the ree curve resembles that of sample 467408 (see below), although it has slightly lower concentrations of the hree. the hornblende-bearing gneisses 467423 and 467433 were collected from thin (< 1 m) amphibolite units within metasedimentary sequences. the geochemical compositions of these two samples are close to those of the nine amphibolite samples described above, and they can only be distinguished from the latter by their higher concentrations of lree, ba, and sr, and higher k 2 o and rb in 24 467403 467405 467413 467426 467436 467440 467444 467445 467446 440938 467526 467401 sio2 48.73 48.72 49.3 46.86 48.39 47.37 48.01 48.25 46.00 71.93 71.70 68.86 tio2 1.03 0.87 0.83 0.60 0.64 0.66 0.90 0.88 0.75 0.24 0.39 0.22 al2o3 13.16 15.81 14.61 16.21 15.68 16.36 13.29 12.18 16.25 14.58 14.64 16.93 fe2o3 1.67 2.54 2.7 1.88 2.13 2.79 1.90 1.88 2.83 1.99 2.09 0.09 feo 10.64 8.89 9.11 7.48 7.85 8.14 8.04 8.82 7.94 0.00 0.00 1.68 feo* 12.14 11.17 11.53 9.17 9.77 10.65 9.75 10.51 10.49 1.79 1.88 1.76 mno 0.22 0.21 0.20 0.18 0.17 0.16 0.13 0.19 0.17 0.01 0.02 0.02 mgo 8.82 6.90 7.73 8.30 8.34 9.37 10.74 11.15 10.04 0.57 0.57 0.98 cao 11.46 12.72 11.51 14.17 12.78 10.91 12.31 12.43 10.42 2.02 2.12 4.02 na2o 2.25 1.28 1.58 1.60 1.36 2.00 1.97 1.56 2.38 4.47 4.70 5.17 k2o 0.11 0.23 0.25 0.31 0.25 0.08 0.52 0.10 0.48 3.08 2.31 1.05 p2o5 0.06 0.06 0.05 0.04 0.04 0.04 0.06 0.06 0.05 0.07 0.08 0.07 volatiles 1.58 1.5 1.57 1.48 1.57 1.6 1.43 1.53 2.06 0.27 0.10 0.53 sum 99.74 99.72 99.43 99.11 99.21 99.47 99.29 99.02 99.36 99.23 98.71 99.62 sc 53.6 49.0 54.8 44.1 44.2 38.7 49.6 52.3 49.7 5.5 8.1 4.6 v 347 283 308 214 237 220 301 297 256 16 13.8 24.1 cr 106 301 380 444 450 207 521 485 411 5.0 2.6 35.9 co 53.5 55.1 51.6 51.2 56.1 58.0 70.3 56.6 54.0 17.2 14.7 6.0 ni 117 150 160 221 222 254 214 221 159 3.6 3.4 12.9 cu 64.2 89.0 82.7 39.1 90.3 89.5 4.8 82.8 80.8 2.4 8.1 7.3 zn 91.9 86.0 92.2 74.3 74.8 80.1 40.0 77.3 74.6 40.9 39.8 45.2 ga 15.7 16.3 15.7 14.2 14.2 14.8 14.8 14.1 15.4 18.2 20.8 23.2 rb 1.1 7.6 9.1 12.4 10.9 1.2 9.5 2 10.6 82.1 91.4 92.9 sr 124 111 91 118 150 100 94 109 155 385 303 375 y 19.6 19.5 19.6 13.6 14.3 14.2 18.1 17.4 17 3 7.8 2.8 zr 29.7 11.8 12.5 9.4 9.4 15.8 18.4 11.6 16.2 143 117 57.9 nb 3.1 2 1.9 1.5 1.4 1.1 2.4 2.2 1.7 2.5 4.9 15.4 cs 0.0 0.3 0.2 0.7 0.8 0.0 0.1 0.0 0.2 1.2 2.6 5.6 ba 18 56 43 47 25 6 31 20 60 748 446 210 la 3.2 2.2 2.4 1.7 1.6 1.6 3.5 2.5 2.2 34.1 18.9 4.0 ce 8.4 6.0 6.3 4.5 4.3 4.3 8.0 6.5 6.0 65.0 37.8 8.3 pr 1.3 1.0 1.0 0.7 0.7 0.7 1.2 1.0 0.9 7.2 4.2 1.0 nd 6.7 5.3 5.3 3.7 3.7 3.7 6.0 5.6 5.1 24.2 14.9 3.7 sm 2.2 1.8 1.8 1.4 1.4 1.3 1.9 1.9 1.7 3.3 2.5 0.8 eu 0.7 0.7 0.7 0.5 0.5 0.6 0.7 0.7 0.6 0.6 0.6 0.3 gd 3.0 2.7 2.6 1.6 1.7 1.6 2.4 2.3 2.2 3.4 2.6 1.0 tb 0.5 0.5 0.5 0.3 0.3 0.3 0.5 0.4 0.4 0.2 0.3 0.1 dy 3.3 3.2 3.1 2.3 2.3 2.3 3.1 2.9 2.8 0.9 1.5 0.6 ho 0.7 0.7 0.7 0.5 0.5 0.5 0.6 0.6 0.6 0.1 0.3 0.1 er 1.9 1.9 2.0 1.3 1.4 1.4 1.8 1.7 1.6 0.3 0.7 0.2 tm 0.3 0.3 0.3 0.2 0.2 0.2 0.3 0.2 0.2 0.0 0.1 0.0 yb 1.8 1.9 2.0 1.3 1.5 1.4 1.7 1.6 1.6 0.2 0.7 0.2 lu 0.3 0.3 0.3 0.2 0.2 0.2 0.3 0.3 0.3 0.0 0.1 0.0 hf 1.0 0.6 0.6 0.4 0.5 0.6 0.7 0.6 0.6 3.8 3.3 1.5 ta 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.5 1.1 1.9 pb 1.4 1.5 1.1 1.3 0.8 0.5 0.6 1.3 1.2 9.5 7.6 7.4 th 0.4 0.2 0.2 0.2 0.2 0.1 0.3 0.3 0.2 10.1 4.2 0.9 u 0.1 0.1 0.1 0.1 0.1 0.0 0.2 0.1 0.0 0.5 0.9 0.4 total ree 34 28 29 20 20 20 32 28 26 140 85 20 amphibolite, kangilinaaq belt table 4a. chemical analyses of amphibolite and orthogneiss orthogneiss major elements (in wt%) by xrf at geus. trace elements (in ppm) by icp-ms at geus. feo* = total fe calculated as feo. volatiles = loss on ignition corrected for oxygen uptake due to oxidation of iron. 25 440910 440931 467503 467404 467408 467417 467420 467423 467433 sio2 63.27 69.36 74.26 62.76 61.37 59.87 75.29 49.25 49.94 tio2 0.59 0.49 0.03 0.61 0.67 0.64 0.34 0.61 0.78 al2o3 17.61 16.08 14.81 19.09 13.90 16.78 13.01 16.21 15.53 fe2o3 5.19 2.38 0.01 1.17 1.32 1.25 0.51 3.63 1.80 feo 0.00 0.00 0.37 5.82 6.73 5.38 1.26 6.97 8.34 feo* 4.67 2.14 0.38 6.87 7.92 6.50 1.72 10.24 9.96 mno 0.05 0.01 0.00 0.05 0.11 0.15 0.01 0.19 0.16 mgo 2.31 1.03 0.10 2.80 6.41 3.97 0.57 7.70 7.78 cao 2.26 3.17 2.02 0.75 4.60 3.68 5.62 9.21 10.73 na2o 3.84 3.85 4.89 1.60 1.82 2.73 1.05 2.63 1.88 k2o 3.02 1.79 2.81 3.20 1.46 3.21 0.62 1.63 0.50 p2o5 0.13 0.11 0.02 0.03 0.07 0.08 0.05 0.13 0.16 volatiles 1.00 0.75 0.29 1.64 1.26 1.28 0.90 1.39 1.48 sum 99.27 99.02 99.62 99.52 99.71 99.01 99.23 99.55 99.06 sc 18.0 10.2 0.8 17.6 39.3 26.6 7.7 43.8 39.7 v 98.5 38.2 1.7 56.7 208 149 43.5 204 209 cr 89.1 25.0 0.4 120.0 667 312 66.1 268 318 co 22.3 17.2 26.9 16.3 44.8 28.4 14.0 51.2 50.7 ni 32.3 5.2 1.3 54.7 194.0 106.0 34.0 148.0 145.0 cu 21.9 8.8 5.2 4.8 20.0 26.3 26.9 25.1 34.8 zn 71.4 38.9 4.4 37.8 89.5 104.5 41.4 81.8 87.4 ga 20.8 19.6 16.0 25.7 17.5 23.1 15.5 16.3 15.9 rb 82.7 48.2 58.5 96.9 51.1 197.0 41.6 59.1 8.0 sr 210 314 402 47 117 177 137 270 288 y 16.0 6.4 2.4 11.1 15.4 16.7 11.1 17.4 17.0 zr 134 151 70.8 57.7 82.4 83.1 73.9 38.4 24.0 nb 5.6 5.6 0.8 8.7 3.3 6.9 2.9 2.3 2.0 cs 4.1 4.7 0.5 2.0 2.5 8.1 2.7 2.4 0.0 ba 417 286 591 581 386 377 310 153 97 la 28.2 20.0 7.9 34.5 11.0 9.6 28.3 11.9 13.4 ce 58.3 40.6 16.1 64.7 29.1 28.5 56.0 29.5 37.5 pr 6.9 4.4 2.1 7.4 2.9 2.6 6.5 3.8 4.5 nd 25.3 15.7 7.7 26.4 11.8 10.5 24.5 16.8 19.7 sm 4.3 2.6 1.8 4.4 2.7 2.5 4.0 3.9 4.4 eu 1.2 0.7 0.4 0.7 0.7 0.7 1.0 1.2 1.1 gd 4.5 2.6 1.5 5.0 3.6 2.3 3.9 3.5 3.8 tb 0.6 0.3 0.2 0.5 0.5 0.4 0.4 0.5 0.5 dy 3.0 1.4 0.6 2.4 2.8 2.4 2.3 2.9 3.0 ho 0.6 0.2 0.1 0.4 0.6 0.6 0.4 0.6 0.6 er 1.6 0.6 0.2 1.1 1.6 1.9 1.1 1.7 1.7 tm 0.2 0.1 0.0 0.1 0.2 0.3 0.1 0.3 0.3 yb 1.5 0.5 0.2 0.9 1.5 2.1 0.8 1.6 1.6 lu 0.2 0.1 0.0 0.1 0.2 0.3 0.1 0.2 0.2 hf 3.7 3.9 2.8 1.5 2.2 2.2 1.8 1.0 0.8 ta 0.9 2.6 1.9 0.6 0.3 0.6 0.2 0.1 0.1 pb 12.7 5.2 11.8 3.7 4.7 9.5 6.1 6.6 4.2 th 6.2 3.3 4.8 8.5 3.5 6.0 4.2 2.0 2.0 u 1.5 0.9 1.3 0.8 0.9 3.1 0.9 0.7 0.6 total ree 137 90 39 149 69 65 129 79 92 major elements (in wt%) by xrf at geus. trace elements (in ppm) by icp-ms at geus. volatiles: loss on ignition corrected for oxygen uptake due to oxidation of iron. feo*: total fe calculated as feo. table 4b. chemical analyses of various supracrustal rocks 26 sample 467423. sample 467408 has an intermediate silica content (61.37 wt% sio 2 ), is cummingtonite-bearing, and has high concentrations of mgo (6.41 wt%) and feo* (7.92 wt%) as well as cr and n (627 and 186 ppm, respectively). it also has high ba (405 ppm). the ree curve is almost flat, with ten times chondritic hree and a weak lree enrichment (la n /lu n = 5). there is a small positive ce anomaly in addition to a negative eu anomaly. metasedimentary rocks from the ikamiut belt sample 440910 is the most aluminous (18 wt% al 2 o 3 , table 4), has high ree concentrations, and a fairly steep ree curve with la n /lu n = 15 (fig. 8c). samples 440931 and 467503 are more siliceous (69 and 74 wt% sio 2 , respectively) with lower al, fe and mg. both have lower ree concentrations and slightly steeper ree curves than sample 440910. interpretation the metasedimentary rocks and amphibole-bearing gneisses of supracrustal origin described above from the ikamiut and kangilinaaq belts can be divided into two groups based on their geochemical compositions and ree patterns. five of them, namely all three ikamiut samples and samples 467404 and 467420 from kangilinaaq, are typical metasedimentary lithologies with steep ree curves (fig. 8c). although they have varying ree concentrations, all five samples have fairly steep ree curves that are comparable to the ree patterns seen in the kangilinaaq and ikamiut orthogneisses. the group shows a trend of increasing ree concentrations with decreasing sio 2 and increasing al 2 o 3 , consistent with the general presumption that the ree are preferentially concentrated in the clay fraction of sediments. one exception from this is the siliceous sample 467420 that has ree concentrations comparable to the most aluminous metasediments. its unusual ree enrichment may be due to high contents of detrital allanite and zircon, as these minerals incorporate high ree concentrations. the ree curves for the four amphibole-bearing gneisses (467408, 467417, 467423, and 467433; fig. 8d) have la n /lu n ~ 5, showing significantly flatter patterns. these four samples all have high concentrations of mafic minerals and may represent intermediate tuffaceous rocks or mildly chemically altered mafic volcanic rocks. the rather peculiar composition of sample 467408, with high ni and cr, suggests that it is a metamorphosed, hydrothermally 100 10 1 ree sample / chondrite la ce pr nd pm sm eu gd tb dy ho er tm yb lu la ce pr nd pm sm eu gd tb dy ho er tm yb lu 100 10 1 100 10 1 la ce pr nd pm sm eu gd tb dy ho er tm yb lu 100 10 1 la ce pr nd pm sm eu gd tb dy clastic metasedimentary rocks amphibolites amphibole-bearing paragneisses felsic orthogneisses 467503 440931 440910 467404 467420 440938 467526 467401 c b d a 467408 467433 467423 467417 fig. 8. chondrite-normalised ree plots. a: amphibolites. b: felsic orthogneiss. c: quartzo-feldspathic metasedimentary rocks. d: mafic metasedimentary rocks. blue: samples from the kangilinaaq region. red: samples from the ikamiut region. 27 altered mafic volcanic rock. alternatively, such high ni and cr in a clastic sedimentary precursor would require an abundance of heavy minerals such as garnet and spinel. discussion regional structures both the ikamiut and kangilinaaq regions preserve complex tectono-metamorphic histories, and although they show similarities in lithologies and metamorphic grade (amphibolite facies mineral assemblages defining d 1 and d 2 structures) and lie roughly along strike, the large structures are sufficiently different to make a direct correlation between the two regions and their supracrustal belts difficult and dubious. both regions show evidence for at least two generations of fold structures, with kilometreto ten kilometre-scale f 2 folds dominating the outcrop pattern. however, there is considerable variation in the typical strike of foliation and plunge of large-scale folds and lineations between the two regions. furthermore, the aeromagnetic data do not suggest a strong link between the two regions. on the basis of geological mapping and the aeromagnetic data it seems likely that the kangilinaaq belt forms a synformal fold closure at the south-western tip of the kangilinaaq peninsula, with little or no westward continuation. we cannot rule out the possibility that there is continuation of this belt across sydostbugten into the ikamiut region along an abrupt change in the aeromagnetic response across northern sydostbugten (boundary o in fig. 3). this could be interpreted as an extension of the linear aeromagnetic anomaly marking the northern contact of the qasigiannguit amphibolite sequence with the surrounding orthogneiss, which appears to extend westward to several kilometres north of the nivaap paa bay (boundary p in fig. 3). however, there is no strong field evidence to support this, since no comparable amphibolite sequence occurs on land at q (fig. 3). it is possible that this linear aeromagnetic anomaly relates instead to an interpreted granitic body beneath sydostbugten, represented by outcrop on the south-eastern tip of the kangilinaaq peninsula, and on the south-west coast of nivaap paa. magmatism geochronological data show that the magmatic precursors to granodioritic orthogneiss from the ikamiut region were emplaced in the late archaean. sample 440938, with a la-icp-ms pb-pb zircon age of 2831 ± 23 ma u-pb zircon ages of 2820–2810 ma, is significantly older than sample 467526, which was collected from a nearby locality (la-icp-ms pb-pb zircon age = 2741 ± 53 ma). the latter compares well with a homogeneous undeformed granite collected a few kilometres west of the head of nivaap paa, which yielded an upper intercept u-pb zircon age of 2778 +7/–3 ma (connelly & mengel 2000). similarly, a grey tonalitic orthogneiss sampled close to aasiaat yielded a u-pb concordia age of 2727 +36/–22 ma and consistent pb-pb and rb-sr whole-rock ages of 2759 +87/–92 ma and 2752 ± 656 ma respectively (kalsbeek et al. 1987). available data on emplacement ages of the precursors to the tonalitic orthogneiss in the kangilinaaq region suggest these may be slightly older than those in the ikamiut region. kalsbeek & nutman (1996) reported ion probe data for a few zircon grains from a granodioritic to granitic orthogneiss in the kangilinaaq area, which gave an emplacement age between 2900 and 2750 ma. keiding (2004) presented la-icp-ms 207pb/206pb zircon age data for a tonalitic orthogneiss of 2818 ± 1 ma, interpreted as an igneous crystallisation age. 700 600 500 400 300 200 100 0 20 ti/v = 10 20 50 100 ti (ppm) /100 v arc tholeiite morb oib 0 2 4 6 8 10 12 14 16 18 fig. 9. ti/v discrimination diagram (shervais 1982) for nine amphibolite samples from the kangilinaaq peninsula (fig. 2b), illustrating their island arc affinities. note that ti and v are both immobile elements, considered to be stable during hydrothermal alteration and regional metamorphism (e.g. nicollet & andriambololona 1980; mottl 1983). the partition coefficient of v varies with the oxygen fugacity of the magma, whereas the partition coefficient of ti remains unchanged. 28 sedimentation deposition of the sedimentary precursors to the ikamiut and kangilinaaq belts likely occurred in the neoarchaean, as indicated by the metamorphic ages of c. 2800–2700 ma of zircon from both belts. the age of the kangilinaaq belt is further constrained by the 2723 ± 15 ma emplacement age of a two-mica granite, which cross-cuts pelitic metasedimentary rocks of this belt on the south shore of kangersuneq fjord (thrane & connelly 2006, this volume). as regards the ikamiut belt, its detrital zircon ages do not preclude deposition after the archaean. neoarchaean metamorphic rims have been observed on some detrital grains, but these might have formed already during metamorphism of the source and survived during erosion and deposition. however, we consider this possibility unlikely. a neoarchaean depositional age is furthermore in agreement with the rb-sr isotopic data for 12 metasedimentary samples from ikamiut reported by kalsbeek & taylor (1999), which likewise show that their source was archaean. finally, the ikamiut belt has experienced a more complex structural history than the naternaq supracrustal belt of palaeoproterozoic age to its south (østergaard et al. 2002; garde 2004; thrane & connelly 2006, this volume). this likewise points to an archaean age of the ikamiut belt. the depositional sources themselves are constrained by detrital zircon populations. the detrital age spectrum for zircon grains (with igneous zonation) from metasedimentary sample 440910 from the ikamiut region forms a tightly clustered peak at c. 2800 ma, consistent with the age of the older tonalitic orthogneiss in this area. furthermore, the steep ree pattern of this sample mimics that of the granodioritic to tonalitic orthogneiss that dominates the region. thus the sedimentary precursor to this rock was probably derived locally from (and possibly deposited onto) the igneous precursor to the neoarchaean orthogneiss basement. this requires a tectonic environment conducive to rapid erosion of the precursor to the source orthogneiss shortly after its emplacement at c. 2800 ma. similarly, a metasedimentary rock from the kangilinaaq region contains archaean detrital zircon, with a strong peak at c. 2800 ma (thrane & connelly 2006, this volume, 207pb/206pb zircon). however, there is also evidence for a significant older component, not recognised in metasedimentary rocks from the ikamiut region: keiding (2004) reported detrital zircon ages for two metasedimentary samples from the kangilinaaq region with grains as old as 3600 ma, and down to 2500 ma, although the youngest grains (< 2800 ma) were suspected of having suffered lead loss. both samples show a large spread of ages, but neither has a significant neoarchaean component at c. 2800 ma. these data contrast with those of sample 440910 from the ikamiut region, which has a tightly clustered detrital zircon population at c. 2800 ma. this suggests that at least some of the kangilinaaq metasedimentary rocks were derived from different, older, and distal source rocks: the older (> 2900 ma) component may be derived from a presently unexposed region within the nagssugtoqidian orogen or possibly from the lesser-known craton to the north (keiding 2004). a difference in the depositional sources of the ikamiut and kangilinaaq belts is also apparent from the geochemical data. the metasedimentary rocks form two groups based on their ree patterns. the first group (three ikamiut and two kangilinaaq samples) shows steep ree curves (fig. 8c), interpreted as indicative of derivation from a felsic source, based on their similarity with ree patterns seen in the kangilinaaq and ikamiut orthogneisses. the second group (four kangilinaaq samples, fig. 8d) shows flatter patterns, consistent with derivation from a bimodal source, i.e. detritus of both felsic (steep ree patterns) and mafic (flat ree patterns) igneous rocks. the precursors to the amphibole-bearing gneisses are interpreted as volcaniclastic material that may have been mixed with clastic material during deposition or by tectonic interleaving. given the intensity of deformation and paucity of information on the depositional environment(s) we consider it imprudent to establish a single stratigraphicstructural interpretation. in view of the different dominant lithologies of the qasigiannguit amphibolite and the remainder of the kangilinaaq belt, it would be interesting to investigate further whether they represent the same or different settings. the geochemistry of their amphibolite samples fall within the same range, but no metasedimentary rocks associated with the qasigiannguit amphibolite have been analysed, and these may be important for identifying links between the latter unit and the kangilinaaq belt. metamorphism age data for metamorphic zircon from orthogneiss and metasedimentary samples from the ikamiut region indicate an important neoarchaean thermal event. two analyses of metamorphic rims from the 2831 ± 23 ma orthogneiss 440938 yield ages of 2761 ± 10 ma and 2754 ± 5 ma, within error the same as the 2741 ± 53 ma emplacement age of sample 467526 (fig. 7). this may suggest that continued synkinematic emplacement of neoarchaean granitoids at c. 2760–2700 ma resulted in metamorphism 29 of slightly older (c. 2800 ma) crust. this is also supported by u-pb zircon data from the metasedimentary sample 440910. the six sims ages of metamorphic rims fall in two ranges, 2741 ± 9 ma and 2696 ± 6 ma, and similar young ages were identified in the la-icp-ms data (fig. 7). these ages probably relate to the growth of s 1 garnet, biotite, plagioclase, quartz, minor sillimanite and k-feldspar in this and other metasedimentary rocks, indicative of amphibolite facies conditions only shortly after deposition, and predating regional f 2 folding. neoarchaean metamorphism has also been recognised from zircon age data in the kangilinaaq region. keiding (2004) reported c. 2800 and 2760 ma la-icp-ms ages of zircon rims and discrete grains, interpreted as metamorphic in origin, in a 2818 ± 1 ma tonalitic orthogneiss. these ages correlate reasonably well with 2810–2720 ma metamorphic u-pb zircon and monazite ages in 2870–2810 ma orthogneisses from throughout the nagssugtoqidian orogen (connelly & mengel 2000). it is likely that neoarchaean amphibolite facies metamorphism in the ikamiut and kangilinaaq regions was the product of tectonism along a convergent margin (see also connelly & mengel 2000) on the basis of (1) the tonalitic to granodioritic composition of the neoarchaean regional orthogneisses, (2) the apparent island arc geochemical character of amphibolites of the kangilinaaq belt, (3) differences in the ages of sediment sources in the two supracrustal belts, and (4) the rapidity of the cycle of magmatism, erosion, sedimentation, and metamorphism. proterozoic zircon ages are known from the kangilinaaq region. keiding (2004) reported 1920–1820 ma laicp-ms ages of zircon rims and discrete grains in archaean tonalitic orthogneisses, and also reported weighted mean age of 1919 ± 11 ma from three rims of detrital grains in a metasedimentary rock from the kangilinaaq belt. thrane & connelly (2006, this volume) report metamorphic ages of c. 1850 ma for a metasedimentary rock collected on the south shore of kangersuneq fjord, attributed to the peak of regional nagssugtoqidian metamorphism. given the consistency of ene-trending d 2 structures in the kangilinaaq and ikamiut regions with enetrending palaeoproterozoic structures throughout the orogen, these are interpreted as the product of the c. 1850 ma nagssugtoqidian orogenesis. the significance of the slightly older, c. 1920 ma metamorphic age is not clear, but may indicate that part of this region experienced a thermal event prior to the main regional nagssugtoqidian orogenesis. by contrast, no significant indications of palaeoproterozoic resetting are found in our ikamiut data. the slightly discordant zircon data in sample 440938 suggest some pb loss in this sample, although the timing is not clear. similarly, three titanite u-pb analyses of 2778 +7/–3 ma reported by connelly & mengel (2000) from a homogeneous, undeformed granite plot on a discordia line between 2789 ± 100 and 1775 ± 10 ma. this indicates that palaeoproterozoic metamorphic temperatures were too low to completely reset titanite in this region. likewise, no indication of u-pb resetting in zircon was found in the 2727 +36/–22 ma age from a tonalitic gneiss reported by kalsbeek et al. (1987). this contrasts with zircon u-pb analyses of samples from the nordre strømfjord region in the core of the nagssugtoqidian orogen, which experienced significant pb-loss at c. 1850 ma (kalsbeek et al. 1987). conclusions new mapping, geochemical, geochronological and geophysical studies of two supracrustal belts from sydostbugten, southern disko bugt region, west greenland, shed light on the neoarchaean tectonic evolution of the northern nagssugtoqidian basement. the kangilinaaq belt was deposited at c. 2800 ma, whereas the deposition of the ikamiut belt may postdate c. 2740 ma. the geochemical signatures of the majority of metasedimentary samples from the kangilinaaq region show ree patterns indicative of mixed felsic and mafic sources with distal mesoand palaeoarchaean components that are not currently known in situ in this part of west greenland. island-arc geochemical affinities of intercalated amphibolites are consistent with deposition in an arc setting. in contrast, the ikamiut belt was sourced locally from, and deposited onto or proximal to the igneous precursors of neoarchaean granodioritic to tonalitic orthogneisses. this is constrained by (1) the similarity in ree signatures of metasedimentary rocks and local orthogneisses and (2) the zircon emplacement ages of orthogneisses (c. 2820–2810 ma; 2831 ± 23 ma; 2741 ± 53 ma) and detrital zircons in metasediment (2779 ± 18 ma). zircon u-pb data and s 1–2 sillimanite-bearing mineral assemblages (this study and existing data) indicate that c. 2800–2700 ma amphibolite facies metamorphism affected both regions, shortly after the emplacement of the regional orthogneiss precursors and deposition of the supracrustal rocks. the rather rapid cycle of magmatic emplacement, island arc volcanism, erosion and sedimentation, and subsequent amphibolite facies metamorphism is consistent with neoarchaean convergent tectonism at the northern margin of the present nagssugtoqidian orogen. subsequently, both regions underwent palaeoproterozoic regional deformation and lower amphibolite facies 30 metamorphism at c. 1850 ma during the nagssugtoqidian orogenesis, the effects of which control outcrop patterns in both areas. in the ikamiut region, the supracrustal belt defines a broad, shallowly w-plunging antiformal structure with associated kilometre-scale parasitic f 2 folds. s 1 fabrics are folded into metreto kilometre-scale f 2 folds and variably transposed into ene-striking, steeply dipping s 2 fabrics and shallow w-plunging mineral lineations defined by biotite and muscovite. in the kangilinaaq region, the supracrustal belt defines a broad, ne-plunging f 2 fold structure. a pervasive, nestriking, moderately dipping s 2 fabric, defined by mediumto coarse-grained garnet-hornblende-biotite-sillimanitebearing assemblages in pelitic rocks, is folded into f 3 folds, and attests to amphibolite facies metamorphic conditions during deformation. lack of palaeoproterozoic resetting of the zircon u-pb isotopic system in the ikamiut region, cf. the kangilinaaq region, suggests that temperatures were relatively lower in the former region during the nagssugtoqidian orogenesis. acknowledgements mads sylvest christensen, jane gilotti, christian knudsen, stanislaw mazur, mac persson, sandra piazolo and thomas v. rasmussen contributed to field work in 2002– 2003 reported here and part of the geus project archaean and proterozoic crustal evolution in the aasiaat region, central west greenland. dirk frei, mark t. hutchison, lev ilyinsky, jørgen kystol, ingerlise nørgaard, thomas v. rasmussen, mikkel vognsen, and martin whitehouse provided support and assistance in sample preparation and collection of analytical data. the nordsim laboratory is funded and operated under agreement between the research funding agencies of denmark, norway, and sweden, gtk, finland, and naturhistoriska riksmuseet, sweden; this is nordsim contribution no. 164. clark friend, lotte melchoir larsen and an anonymous reviewer are thanked for critical reviews. references connelly, j.n. & mengel, f.c. 2000: evolution of archean components in the paleoproterozoic nagssugtoqidian orogen, west greenland. geological society of america bulletin 112, 747–763. connelly, j.n., van gool, j.a.m. & mengel, f.c. 2000: temporal evolution of a deeply eroded orogen: the nagssugtoqidian orogen, west greenland. canadian journal of earth sciences 37, 1121–1142. garde, a.a. 2004: geological map of greenland, 1:100 000, kangaatsiaq, 68 v.1 syd. copenhagen: geological survey of denmark and greenland. garde, a.a. in press: geological map of greenland, 1:100 000, ikamiut, 68 v.1 nord. copenhagen: geological survey of denmark and greenland. garde, a.a. & steenfelt, a. 1999: precambrian geology of nuussuaq and the area north-east of disko bugt, west greenland. geology of greenland survey bulletin 181, 6–40. garde, a.a., christiansen, m.s., hollis, j.a., mazur, s. & van gool, j.a.m. 2004: low-pressure metamorphism during archaean crustal growth: a low-strain zone in the northern nagssugtoqidian orogen, west greenland. geological survey of denmark and greenland bulletin 4, 73–76. henderson, g. 1969: the precambrian rocks of the egedesminde–christianshåb area (sheets 68v.1 and 68v.2). rapport grønlands geologiske undersøgelse 23, 1–37. hollis, j.a., garde, a.a., van gool, j.a.m. & thrane k. 2004: polymetamorphism in the northern nagssugtoqidian orogen: a review and presentation of recent data. danmarks og grønlands geologiske undersøgelse rapport 2004/17, 25–27. jacobsen, b.h. 1987: a case for upward continuation as a standard separation filter for potential-field maps. geophysics 52, 1138–1148. kalsbeek, f. & nutman a.p. 1996: anatomy of the early proterozoic nagssugtoqidian orogen, west greenland, explored by reconnaissance shrimp u-pb zircon dating. geology 24, 515–518. kalsbeek, f. & taylor, p.n. 1999: review of isotope data for precambrian rocks from the disko bugt region, west greenland. geology of greenland survey bulletin 181, 41–47. kalsbeek, f., pidgeon, r.t. & taylor, p.n. 1987: nagssugtoqidian mobile belt of west greenland: a cryptic 1850 ma suture between two archaean continents – chemical and isotopic evidence. earth and planetary science letters 85, 365–385. keiding, m. 2004: petrologiske og geokronologiske unders¿gelser af prækambriske bjergarter fra kangilinaaq, vestgrønland, 70 pp. unpublished master thesis, københavns universitet, danmark. kystol, j. & larsen, l.m. 1999: analytical procedures in the rock geochemical laboratory of the geological survey of denmark and greenland. geology of greenland survey bulletin 184, 59–62. ludwig, k.r. 2000: isoplot/ex version 2.2: a geochronological toolkit for microsoft excel. berkeley: berkeley geochronology center. mazur, s., piazolo, s. & alsop, g.i. 2006: structural analysis of the northern nagssugtoqidian orogen, west greenland: an example of complex tectonic patterns in reworked high-grade metamorphic terrains. in: garde, a.a. & kalsbeek, f. 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revision accepted 15 february 2006 32 research article | short larsen et al. 2023: geus bulletin 53. 8330. https://doi.org/10.34194/geusb.v53.8330 1 of 7 x-ray fluorescence (xrf) fingerprinting of palaeogene deposits in denmark nicolaj k. larsen*1 , kristian b.r. kristensen1 , marie-louise siggaard-andersen1 , claus heilmann-clausen2  , kurt h. kjær1 1globe institute, university of copenhagen, denmark. 2department of geoscience, aarhus university, denmark *correspondence: nicl@sund.ku.dk received: 07 oct 2022 accepted: 06 feb 2023 published: 10 mar 2023 keywords: denmark, geochemical fingerprinting, palaeogene, xrf analysis abbreviations: edxrf: energy-dispersive x-ray fluorescence geus: geological survey of denmark and greenland nr.: nørre pc: principal component pca: principal component analysis petm: paleocene–eocene thermal maximum xrf: x-ray fluorescence geus bulletin (eissn: 2597-2154) is an open access, peer-reviewed journal published by the geological survey of denmark and greenland (geus). this article is distributed under a cc-by 4.0 licence, permitting free redistribution, and reproduction for any purpose, even commercial, provided proper citation of the original work. author(s) retain copyright. edited by: karen dybkjær (geus, denmark) reviewed by: noël vandenberghe (ku leuven, netherlands), nicolas thibault (university of copenhagen, denmark) funding: see page 6 competing interests: see page 6 additional files: see page 6 abstract in this study, we test if cost-efficient x-ray fluorescence (xrf) analyses can be used to fingerprint palaeogene clay and marl deposits in denmark. a total of 67 samples from key sites in denmark have been analysed. our preliminary results indicate that it is possible locally within 10–30 km to distinguish between most of the palaeogene units, but on a regional scale across denmark, the units are not unique, and this probably reflects variations in clay mineralogy, grain size and calcareous content. accordingly, we suggest that a comprehensive reference database is now needed if the full potential of the method is to be utilised, and this will ultimately result in more reliable geological models. introduction in denmark, the surficial deposits (<100 m) are of a large societal interest (farming, forestry, natural resources and geotechnical properties), and they also comprise a vital groundwater reservoir. the surficial deposits consist of quaternary sediments (c. 10–30 m) above palaeogene sediments in northern and eastern denmark and neogene sediments in south-western denmark (binzer & stockmarr 1994; fig. 1). accordingly, pre-quaternary deposits are often encountered in boreholes during large infrastructure projects and in connection with groundwater projects. knowledge about the surface deposits mainly derives from more than 260 000 boreholes drilled in denmark in the last c. 125 years, and the data are available in the open-access jupiter database hosted by the geological survey of denmark and greenland (geus; hansen & pjetursson 2011). the jupiter database records the lithology and inferred age, whereas additional information that can be used to further discriminate sedimentary units (e.g. biostratigraphy) is only available for a very limited number of the boreholes. another complicating matter when making geological models is that the surface deposits have often been disturbed by glaciotectonics (jakobsen 2003). the heterogeneous surface geology in denmark thus presents a serious challenge when trying to make a geological model based on borehole data. one way to produce more reliable geological models is to make additional analyses (e.g. biostratigraphy and clay mineralogy) to characterise and discriminate the deposits (heilmann-clausen et al. 1985; nielsen et al. 2015). these procedures have, however, never been implemented routinely for geological investigations in denmark because the analyses are very time-consuming. in this study, we test a new cost-effective method to characterise and fingerprint palaeogene deposits in denmark using an x-ray fluorescence (xrf) analyser for discrete samples. we have analysed palaeogene units (mainly https://doi.org/10.34194/geusb.v53.8330 http://creativecommons.org/licenses/by-nc/4.0/ https://orcid.org/0000-0003-4171-9882 https://orcid.org/0000-0001-8986-1920 https://orcid.org/0000-0002-5894-7139 mailto:nicl@sund.ku.dk https://creativecommons.org/licenses/by/4.0/ larsen et al. 2023: geus bulletin 53. 8330. https://doi.org/10.34194/geusb.v53.8330 2 of 7 w w w . g e u s b u l l e t i n . o r g marls and clays) from key localities (fig. 1). our results show that the method can be used to discriminate most palaeogene units on a local scale (10–30 km) but lack the ability to differentiate the units on a regional scale across denmark. palaeogene deposits in denmark denmark is situated in the eastern part of the intracratonic cenozoic north sea basin (ziegler 1990). in most of paleocene and eocene times, the basin was inundated by relatively deep marine water that gradually became shallower and even subaerially exposed several times during the early oligocene (śliwińska et al. 2012; king et  al. 2016). overall, the palaeogene succession comprises a series of lithologically distinct units composed of early paleocene chalk, middle and late paleocene and eocene fine-grained clays and marls as well as oligocene silty clays (fig. 2). pre-cambrian crystalline rocks illite & chlorite cambrian sandstones palaeozoic limestone, shales & sandstones triassic–lower cretaceous sediments & sedimentary rocks upper cretaceous chalk paleocene–oligocene clay, silt & sand smectite miocene–pliocene sand & clay kaolinite danian limestone & chert 15° 58° 56° 54° 10° norway sweden denmark germany poland fur hinge kysing lundsgård klint tåsinge æbelø hesselbjerg mogenstrup nørre vissing juelsminde treldenæs albæk hoved ølst fig. 1 map of pre-quaternary deposits in denmark (based on sorgenfrei & berthelsen 1954). sample sites are divided into four local areas: limfjorden (purple), east jylland (yellow), lillebælt (red) and fyn (blue). https://doi.org/10.34194/geusb.v53.8330 http://www.geusbulletin.org larsen et al. 2023: geus bulletin 53. 8330. https://doi.org/10.34194/geusb.v53.8330 3 of 7 w w w . g e u s b u l l e t i n . o r g during the late cretaceous and early paleocene (danian), a chalk regime with the deposition of thick coccolithic chalk, bryozoan limestone and calcisiltite prevailed (thomsen 1995). the oldest siliciclastic deposits in denmark are the middle paleocene (selandian) lellinge greensand (up to 30 m) and the light grey kerteminde marl (c. 12–136 m), which in its upper part holds up to 50% reworked cretaceous chalk (thomsen 1995). above this follows two units deposited under increasing water depth: the grey, partly silicified æbelø formation (c. 16–57 m) and the late paleocene non-calcareous, varicoloured, very fine-grained holmehus formation (c. 12–40 m; nielsen et al. 1986; heilmann-clausen 1995). in the latest paleocene, the grey østerrende clay (up to 6 m) was deposited (nielsen et al. 1986). the paleocene–eocene transition coincided with a phase of intense activity in the iceland mantle plume leading to major basaltic volcanism centred on the rift zone in the norwegian–greenland sea (e.g. king et  al. 2016; ziegler 1990). during the paleocene–eocene thermal maximum (petm), the laminated and in part organic-rich stolleklint clay (c. 15–24 m) was deposited søvind marl fm viborg fm linde clay branden clay vejle fjord fm lillebælt clay fm røsnæs clay fm ølst fm fur fm stolleklint clay østerrende clay holmehus fm æbelø fm kerteminde marl danien limestone lo w er p al eo ce ne u pp er p al eo ce ne lo w er e oc en e m id dl e e oc en e u pp er e oc en e lo w er o lig oc en e u pp er o lig oc en e 23.8 28.5 33.7 37.0 49.0 55.5 60.0 65.6 lellinge greensand brejning fm east jyllandlimfjorden (n) (ø) værum mb 20 cm below 0 (h) værum mb 20 cm below +19 (h) værum mb 100 cm below top (h) (ø) r1 ± glauconite (h) r3 (h) r2 (h) r5 ± tephra (h) r4 (h) r6 upper/lower white bed + sapropel (h) l1 (h) l2 upper/lower white bed + sapropel (h) l3 (h,ø) l4 (h,ø) l5 + concretion (h,ø) l6 dark/light bed (h) pyt mb (h) kysing mb (k) viborg clay (k,ø) grundfør mb (h,ø) lower viborg clay (h) upper viborg clay (h) (f) knudeklint mb 10 cm below –33 (f) knudeklint mb -33 (f) knudeklint mb, concretion –24 to –29 (f) silstrup mb +19 (f) silstrup mb 10 cm below +19 (f) knudeklint mb 10 cm below –17 (f) skive clay (he) (m) ± glauconite (m) a: albæk hoved f: fur h: hinge he: hesselbjerg j: juelsminde k: kysing strand l: lundsgård klint m: mogenstrup n: nr vissing t: treldenæs tå: tåsinge æ: æbelø ø: ølst lillebælt fyn pyt mb (j) l4 (t) l3 (a) l2 (a,t) r5 (a) r4 (a) (a) ± silicified (æ) (j) (l) (tå) (tå) (tå) haslund mb 1-3 (tå) værum mb (tå) fig. 2 lithostratigraphy of the palaeogene deposits in denmark (after schiøler et al. 2007) and distribution of the 67 analysed samples. stratigraphy and ages of the lithostratigraphic units are based on heilmann-clausen (1995), clemmensen & thomsen (2005) and rasmussen et al. (2010). note that knudeklint and silstrup members are part of the fur formation. værum and haslund members are part of the ølst formation. stolleklint clay is a subunit of the haslund member. skive clay is a local facies of the branden clay. https://doi.org/10.34194/geusb.v53.8330 http://www.geusbulletin.org larsen et al. 2023: geus bulletin 53. 8330. https://doi.org/10.34194/geusb.v53.8330 4 of 7 w w w . g e u s b u l l e t i n . o r g (heilmann-clausen 1995). sometime after the petm, the character of the volcanism in the rift zone changed from effusive, forming huge flood basalts in east greenland and the faroe islands, to highly explosive, phreatomagmatic eruptions, spreading basaltic ash as far as 2000 km away in the northern tethys (e.g. stokke et al. 2020). in denmark, more than 180 ash layers were deposited in probably outer neritic waters. the ash layers are a few mm to 20 cm thick and occur in the clayey ølst formation, all over the north sea and most of denmark. a remarkable exception is nw jylland where the ashes occur in the diatomaceous fur formation (pedersen et al. 2011). after the deposition of the ølst and fur formations, sea-level rise led to a high eustatic sea level and the opening of the english channel and a marine connection across eastern europe to the peri-tethys in western asia (king et al. 2013). the hemipelagic, bathyal early eocene, mainly red and calcareous røsnæs clay formation (c. 3–28 m), and the early to middle eocene, mainly non-calcareous lillebælt clay formation (c. 40–100 m), were deposited in the present danish land area. the two formations are each subdivided into 6 members based mainly on differences in calcareous content and colour (heilmann-clausen et al. 1985). the røsnæs clay formation and lower members l1–l4 of the lillebælt clay formation resemble the holmehus formation in being varicoloured, very fine-grained and condensed. above these members follows the slightly siltier grey-green upper members l5 and l6 and the light grey middle to late eocene søvind marl formation (up to 90 m; heilmann-clausen et al. 1985). the søvind marl formation represents the last hemipelagic eocene sedimentary unit (thomsen et al. 2012) and is unconformably overlain by oligocene deposits of variable age. in the central part of the danish basin, sedimentation of marl continued locally to the eocene–oligocene boundary, and here, the søvind marl formation is usually overlain by the earliest oligocene viborg formation composed of up to 85 m thick dark grey finely micaceous silty clay, coarsening upwards to sandy silt (śliwińska et al. 2012; thomsen et al. 2012). above this formation usually follows the grey-green, silty, finely micaceous skive clay (80–90 m). the dark brown to nearly black, glauconitic and micaceous brejning formation was deposited in a marine, sediment-starved environment following a major fall in relative sea level during latest oligocene (rasmussen et al. 2010). on and south of the ringkøbing–fyn high, there is a major hiatus with only the oldest part of the søvind marl present, overlain by the brejning formation or younger units (rasmussen et al. 2010). materials and methods samples have been collected in type and reference sections (heilmann-clausen et al. 1985; heilmann-clausen 1995) and other biostratigraphically controlled sections (figs 1, 2). four samples from mogenstrup and nørre (nr.) vissing (supplementary file, table s1) are tentatively assigned to brejning and vejle fjord formations. the samples are not equally distributed across denmark or within the units but are the only samples available for this preliminary test of the method. from some units, we collected several samples if they were heterogeneous or contained, for example, concretions or ash layers. a total of 67 samples were analysed. each analysis was repeated five times to estimate the analytical uncertainty. after retrieval, the samples were dried in an oven at 90ºc for 24 h. the dry samples were loosened in a mortar and sieved to 0–500 μm before they were poured into 40 mm xrf sample cups. the samples were analysed using a bruker s2 puma energy-dispersive x-ray fluorescence (edxrf) spectrometer. the spectrometer was equipped with a 50 w x-ray tube with an ag anode. for each analysis, three different tube settings were used: no filter, a 250 µm cu filter and a 500 µm al filter in front of the x-ray tube for a total time of 400 sec. before each repeated analysis, the samples were gently stirred in the cup and lightly compacted. the analyses and data evaluation were performed using the bruker spectra. elements software for standardless xrf analysis. the spectrometer was calibrated using a glass disc (flx-k04 from fluxana) that was also used for drift monitoring. elements with insufficient counts, including some of the trace elements, have been excluded from the data set. results the xrf results show that the analytical uncertainty is minimal, and that there are variations in the abundance of elements between the palaeogene units (fig. s1 and table s1). elements like silicon (si), potassium (k), aluminium (al) and iron (fe) are abundant in all units but because they vary little, and they cannot be used to discriminate the units. in contrast, some units are rather unique as they have a high content of sulphur (s), such as the ash-bearing ølst, fur and stolleklint formations. other units contain higher amounts of calcium (ca), such as the kerteminde and søvind marl formations as well as the calcareous parts of the røsnæs clay formation (samples r3, r5 and r6 in fig. s1). barium (ba) and manganese (mn) are unique for the lillebælt clay and røsnæs clay formations and less abundant in the other units. however, none of the elements is unique and cannot be used to fingerprint a unit alone. principal component analysis (pca) of the data set groups the samples according to the formations that the samples come from (fig. s2). the first principal component (pc) represents varying proportions of lime and clay having positive loading from elements associated with lime (ca and sr) and negative loading from elements associated with clay (al, k, rb and si), whilst the second pc represents some diagnostic elements with positive https://doi.org/10.34194/geusb.v53.8330 http://www.geusbulletin.org larsen et al. 2023: geus bulletin 53. 8330. https://doi.org/10.34194/geusb.v53.8330 5 of 7 w w w . g e u s b u l l e t i n . o r g loading from ba and ni that are diagnostic for the lower lillebælt and upper røsnæs divisions and negative loadings from s and si that in high concentrations are diagnostic for ash layers and the fur formation, respectively. however, we do not consider pca further as a tool for fingerprinting because the groups are not sufficiently distinct and because some very different units are grouped together by pca. thus, results from a pca are not very useful to classify a new sample. instead, we have plotted the ratios between element concentrations for some of the most diagnostic elements in a 2d scatter plot, which makes it possible to differentiate most of the units (fig. 3 and fig. s3). we found that the ratios of k/fe and al/si plotted against 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 al/si 0.22 0.24 0.26 0.28 0.3 0.32 0.34 0.36 0.38 0.4 k /f e 0.32 0.34 0.36 0.38 0.4 0.42 0.44 0.46 al/si 0.2 0.25 0.3 0.35 0.4 0.45 k /f e æbelø fm (f) stolleklint (ej) stolleklint (l) holmehus fm (f) holmehus fm (ej) holmehus fm (li) østerrende clay (f) l1 (ej) l2 (ej) l4 (ej) l5 (ej) l6 (ej) l4 (li) l2 (li) l5 (ej) l3 (ej) l3 (li) al/si 0.1 0.15 0.2 0.25 0.3 0.35 0.2 0.4 0.6 0.8 1 1.2 k /f e fur fm diatomite (l) fur fm ash (l) ølst fm ash (f) ølst fm clay (ej) fur fm concretion (l) c b 0.25 0.3 0.35 0.4 0.45 al/si 0.15 0.2 0.25 0.3 0.35 k /f e kerteminde marl (f) pyt mb (ej) pyt mb (li) kysing mb (ej) søvind marl fm a 0.25 0.3 0.35 0.4 0.45 al/si 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 k /f e vejle fjord fm (ej) vejle fjord fm (l) skive clay (l) viborg fm (ej) brejning fm (l) brejning fm (li) f e 0.25 0.3 0.35 0.4 0.45 al/si 0.15 0.2 0.25 0.3 0.35 k /f e r2 (ej) r4 (ej)r3 (ej) r6 (ej) r5 (ej)r1 (ej) r4 (li) r5 (li) r5 ash layer (ej) d fig. 3 xrf plot (ratios of al/si and k/fe) from various palaeogene deposits. a: kerteminde marl and søvind marl fm. b: æbelø fm, holmehus fm, østerrende clay and stolleklint clay. c: fur fm and ølst fm. d: røsnæs clay fm divided into members r1–r6. e: lillebælt clay fm divided into members l1–l6. f: viborg fm, skive clay, brejning fm and vejle fjord fm. ej: east jylland, li: lillebælt, l: limfjorden and f: fyn. https://doi.org/10.34194/geusb.v53.8330 http://www.geusbulletin.org larsen et al. 2023: geus bulletin 53. 8330. https://doi.org/10.34194/geusb.v53.8330 6 of 7 w w w . g e u s b u l l e t i n . o r g each other resulted in the best differentiation for palaeogene units overall. in the palaeogene, there are two marl units: the paleocene kerteminde marl formation and the eocene søvind marl formation (fig. 3a). it is possible to differentiate the two formations, and it is even possible to distinguish between the two members, pyt and kysing, in the søvind marl formation. the next units comprise æbelø and holmehus formations, and østerrende and stolleklint clays from the upper paleocene and lower eocene, and it is also possible to distinguish between these (fig.  3b). in the æbelø formation, the xrf data are scattered, and this probably reflects the heterogenous nature of the unit, which is composed of silicified and nonsilicified clay. the more homogenous stolleklint clay and holmehus formation also have a scattered distribution, but this is probably because the samples were collected in different regions of denmark. the xrf data from the contemporaneous eocene ash-bearing diatomite (fur fm) and clay (ølst fm) are scattered, but the two formations can be clearly differentiated (fig. 3c). the large scatter within the formations is probably due to the heterogenous nature of the units, which contain c. 180 ash layers as well as numerous barium carbonate and calcium carbonate concretions. the xrf data show that it is possible to distinguish between all members in the overlying røsnæs clay and lillebælt clay formations within the same area, both in east jylland and in the lillebælt area (fig. 3d–e). however, there are changes in the composition within the same member between the different regions. the youngest palaeogene formations comprise the viborg, vejle fjord and brejning formations and the informal skive clay. within the different regions, the formations can be differentiated although there are significant inter-formational variations (fig. 3f). discussion overall, our preliminary results suggest that it is possible to differentiate most of the palaeogene units in the danish area using xrf fingerprinting on a local scale (e.g. limfjorden area) in combination with traditional facies analysis, whereas it is more difficult on a regional scale across denmark. in the lithologically homogenous units (e.g. holmehus, røsnæs clay, lillebælt clay and søvind marl formations), there is very little variation in the xrf results locally, and the fingerprinting method is very promising. in contrast, there is more variability locally in some of the more heterogenous units (e.g. fur, ølst and æbelø formations), which contain ash layers and silicified or calcareous intervals that are in part modified by diagenetic processes (fig. 3). on a regional scale across denmark, we observe a variability within both the homogenous and less-homogenous units, which is greater than the differences between units. accordingly, none of the palaeogene units has a unique xrf signature across denmark. the regional xrf variability across denmark probably reflects lateral facies variations in clay mineralogy, grain-size composition and calcareous content. in the norwegian–danish basin, the clay mineralogy reflects the different composition of the source rock (nielsen et al. 2015). for example, the high smectite content in paleocene and early eocene units reflects weathering of volcanic material, whereas abundant amounts of illite indicate a source area composed of metamorphic rocks. sorting of the clay minerals also influences the composition where larger particles of kaolinite are more abundant close to the shore, whereas smectite often dominates the central part of the basin (nielsen et al. 2015). conclusions in this preliminary study, we have used xrf to analyse 67 samples of palaeogene clayey and marly lithostratigraphic units from key sites in denmark for their content of selected elements. we find that it is possible locally, within 10–30 km, to distinguish between most of the palaeogene units, although some of them show large variability because of their content of ash, concretions and silicified intervals. on a regional scale across denmark, the units are not unique, and this probably reflects basin-wide variations in grain size, clay mineralogy and calcareous content. by establishing a comprehensive reference database, the full potential of this cost-effective method could be realised, and this can ultimately be used to make better geological models. this is now planned by analysing more samples from repositories and future geotechnical boreholes. acknowledgements we thank rené lyng sylvestersen from museum salling for providing samples from the fur formation. we also thank the two reviewers, nicolas rudolph thibault and noël vandenberghe, and the journal editor karen dybkjær for constructive comments and feedback. funding statement none declared. author contributions nkl and khk conceptualised the study. nkl, kbrk, mlsa and chc collected or supplied the material. kbrk and mlsa analysed the samples. all authors contributed to the interpretation of the data and in writing the manuscript. competing interests the authors declare no competing interests. additional files one supplementary file is available at 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(ed.): danmarks geologi fra kridt og til i dag. aarhus geokompendier 1, 32–67. thomsen, e., abrahamsen, n., heilmann-clausen, c., king, c. & nielsen, o.b. 2012: middle eocene to earliest oligocene development in the eastern north sea basin: biostratigraphy, magnetostratigraphy and palaeoenvironment of the kysing-4 borehole, denmark. palaeogeography, palaeoclimatology, palaeoecology 350–352, 212–235. https:// doi.org/10.1016/j.palaeo.2012.06.034 ziegler, p.a. 1990: geological atlas of western and central europe, 1990. shell internationale petroleum maatschappij b.v. 239 pp + 56 maps. https://doi.org/10.34194/geusb.v53.8330 http://www.geusbulletin.org https://doi.org/10.1016/j.palaeo.2005.01.005 https://doi.org/10.1016/j.palaeo.2005.01.005 https://doi.org/10.34194/geusb.v23.4842 https://doi.org/10.37570/bgsd-1984-33-26 https://doi.org/10.1144/sr27 https://doi.org/10.2110/jsr.2015.40 https://doi.org/10.2110/jsr.2015.40 https://doi.org/10.34194/geusb.v22.4733 https://doi.org/10.34194/geusb.v22.4733 https://doi.org/10.34194/geusb.v12.5249 https://doi.org/10.34194/geusb.v12.5249 https://doi.org/10.1016/j.revpalbo.2012.01.008 https://doi.org/10.1016/j.revpalbo.2012.01.008 https://doi.org/10.34194/raekke3.v31.6936 https://doi.org/10.34194/raekke3.v31.6936 https://doi.org/10.30909/vol.03.02.227250 https://doi.org/10.30909/vol.03.02.227250 https://doi.org/10.1016/j.palaeo.2012.06.034 https://doi.org/10.1016/j.palaeo.2012.06.034 geological survey of denmark and greenland bulletin 1, 403-436 403 one of the most important factors in the success of the north sea basin as a major oil province is the presence of the thick succession of marine mudstones of late jurassic to earliest cretaceous age. this succession, which comes under various stratigraphic guises (figs 1, 2), is generally accepted to have been the source of much volgian–ryazanian ‘hot shales’ of the bo member (farsund formation) in the danish central graben, north sea: stratigraphy, facies and geochemistry jon r. ineson, jørgen a. bojesen-koefoed, karen dybkjær and lars h. nielsen upper jurassic – lowermost cretaceous marine mudstones represent the most significant source of hydrocarbons in the central and northern north sea. of particular importance in the danish sector of the central graben is a succession of radioactive ‘hot shales’ referred to the bo member, in the upper levels of the farsund formation (kimmeridge clay formation equivalent). this mudstone-dominated succession is typically 15–30 m thick and has a total organic carbon (toc) content of 3–8%, though locally exceeding 15%. although truncated on some structural highs, the bo member is a persistent feature of the danish central graben. lateral variation in both thickness and organic richness is attributed to intrabasinal structural topography and to the location of sediment input centres. detailed study of the dinoflagellate cyst biostratigraphy of 10 wells indicates that the onset of enhanced organic carbon burial began in the middle–late middle volgian in this portion of the central graben. the bo member, representing the peak of organic carbon enrichment, is largely of early ryazanian age. core data (jeppe-1, e-1 wells) indicate that the organic-rich shales of the bo member are not wholly of hemipelagic origin, as commonly assumed, but may locally be dominated by fine-grained turbidites. absence of bioturbation, well-preserved lamination and high toc values suggest that bottom waters were predominantly anoxic although the presence of in-situ benthic bivalves at discrete horizons in the e-1 well suggests that suboxic conditions prevailed on occasion. the bo member is a good to very good source rock, showing very high pyrolysis yields (10–100 kg hc/ton rock) and hydrogen index (hi) values in the range 200–600. in particular, the bo member is characterised by an abundance of 28,30 bisnorhopane (h28), a compound that is indicative of anoxic environments. these new data from the danish sector of the central graben are compatible with the model of tyson et al. (1979) in which the accumulation of organic-rich mudstones was controlled primarily by bottom-water anoxia beneath a stratified watermass. a number of factors probably contributed to the development of watermass stratification, both intrinsic such as the tectonic morphology of the graben system and extrinsic including climate and sea-level stand. keywords: danish central graben, north sea, volgian–ryazanian, organic-rich mudstones, marine source rock, depositional processes, geochemistry, anoxia geological survey of denmark and greenland, geocenter copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: ji@geus.dk geological survey of denmark and greenland bulletin 1, 403–436 (2003) © geus, 2003 404 of the hydrocarbons in the central and northern north sea (barnard & cooper 1981; cornford 1994, 1998; kubala et al. 2003) and also forms the seal in many of the jurassic oilfields in this area (e.g. south brae, turner et al. 1987). in well sections, this basinal mud-dominated succession is characterised by alternations of ‘hot’ and ‘cold’ mudstone intervals (price et al. 1993). this refers to relative levels of radioactivity emitted by the mudstones, as recorded by the gamma-ray log. in general, such variation in the levels of gamma radioactivity in marine mudstones is assumed to reflect the organic richness of the sediment. of particular note in the central graben of the north sea are the ‘hot shales’ of volgian to ryazanian age which have been formalised as the clay deep member (kimmeridge clay formation) in the dutch sector and the mandal formation in the norwegian sector (fig. 2; vollset & doré 1984; van adrichem boogaert & kouwe 1993). in the danish sector, partially equivalent organic-rich mudstones have been described as the ‘hot unit’, an informal member of the farsund formation (jensen et al. 1986); this unit is formally defined as the bo member of the farsund formation in this volume (michelsen et al. 2003, this volume). in the uk sector of the central north sea, equivalent organic-rich mudstones are not given formal lithostratigraphic status within the kimmeridge clay formation (see the ‘hot shales’ of donovan et al. 1993). the aim of this paper is to integrate data from various ■■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■■ ■■ ■ ■ ■■ ■■ ■■ ■■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■■ ■■ 0° 55°n 100 km outer moray firth v ik in g g ra be n sørvestlandet high central graben ringkøbing– fyn high n g nl uk dk danish basin basement or intrabasinal high english kimmeridge clay outcrop english kimmeridge clay subcrop international sector boundary normal fault■■ mid-north sea high east shetland platform fennoscandian shield 60°n 50°n 10°e fig. 1. generalised jurassic tectonic setting of the north sea region (based on doré et al. 1985). dk, denmark; g, germany; n, norway; nl, the netherlands; uk, united kingdom. disciplines and thus to provide an up-to-date assessment of the nature, distribution and origin of the ‘hot shales’ of the bo member in the danish central graben. geological setting the danish offshore area extends westwards to include a segment of the north sea central graben, a complex mesozoic rift system that trends roughly nnw–sse (fig. 1). although probably following palaeozoic lineaments (glennie 1990), a discrete rift system is thought to have first developed in the earliest triassic, trending north–south (ziegler 1988, 1990; sundsbø & megson 1993). the dominant nw–se structural trends in the danish central graben developed during the late jurassic when the rift was at its most active, with the accumulation of up to 4 km of (compacted) sediment in the most rapidly subsiding sub-basins of the danish central graben (møller 1986; sundsbø & megson 1993; japsen et al. 2003, this volume). the early cretaceous saw the transition from this phase of active extension and rapid fault-controlled subsidence in the late jurassic to the regional subsidence pattern, centred on the axial graben system, that characterised the late cretaceous and cenozoic. late jurassic – earliest cretaceous structural evolution the late jurassic was characterised by the development and pronounced differential subsidence of successive half-grabens within the complex rift basin of the central graben. subsidence and sedimentation was focussed on the eastern and southern area (søgne basin, tail end graben and salt dome province; fig. 3) during the latter part of the middle jurassic but extended north-westwards in the late jurassic due to both the overall sea-level rise and the development of secondary depocentres in successive half-grabens (møller 1986; damtoft et al. 1992; andsbjerg & dybkjær 2003, this volume; møller & rasmussen 2003, this volume). the feda graben in the danish sector was probably initiated in the early late jurassic (?oxfordian) and formed the dominant sediment depocentre in the area during the 405 northern dutch central graben danish central graben norwegian central graben uk central graben outer moray firth south viking graben (uk) age valanginian ryazanian volgian kimmeridgian oxfordian la te ju ra ss ic c re ta ce o us vlieland claystone fm scruff greensand fm kimmeridge clay fm upper graben fm middle graben fm lola fm heno fm farsund fm bo member poul fm mandal fm ula fm farsund fm haugesund fm fulmar fm heather fm heather fm heather fm kimmeridge clay fm kimmeridge clay fm kimmeridge clay fm brae fm piper fm cromer knoll group cromer knoll group cromer knoll group cromer knoll group cromer knoll group clay deep mb fig. 2. generalised upper jurassic lithostratigraphy in the north sea rift system from the dutch sector of the central graben in the south to the moray firth and southern viking graben in the north (vollset & doré 1984; van adrichem boogaert & kouwe 1993; richards et al. 1993; lott & knox 1994; michelsen et al. 2003, this volume). sand-rich formations are indicated by a stipple ornament, lithostratigraphically defined ‘hot shales’ by oblique shading. 406 b a 56°00´n 4°00´e ? ? ? b-1 5 10 15 6 85 10 15 13 25 39 14 114 76 7 20 27 18 34 101 deep adda-1 elin-1 lone-1 kim-1 bo-1 edna-1 e-1 anne-3 56°00´n 4°00´e n. jens-1ravn-2 i-1 iris-1 v-1 ugle-1 20 km 20 km adda-1 jens-1 g-1 alma-1 s.e. igor-1 gwen-2 mid north sea high inge h igh c offee soil fault tail end g raben gulnare-1 salt d om e province g ertrud g raben feda graben eg-1 jeppe-1 deep gorm-1 gert-2 emma-1 ål basin gert ridge o uter rough basin søgne basin mandal high ringkøbing–fyn high wells in which the bo member is present wells in which the bo member is not developed inferred distribution of the bo member marginal zone in which the bo member is probably not developed salt diapirs normal fault reverse fault kimmeridgian (söderström et al. 1991; johannessen & andsbjerg 1993; rasmussen 1995). the gertrud graben developed as a discrete depocentre during the late kimmeridgian whereas onlap onto the mid north sea high to the west began in the volgian (møller 1986; damtoft et al. 1992). in this western area, two discrete depocentres (the ål and outer rough basins) were initiated in the latest jurassic and formed important sediment sinks in the early cretaceous (japsen et al. 2003, this volume). during the latter part of the late jurassic, therefore, the danish central graben was segmented into a number of nw–se-trending depocentres, separated by elongate highs or broad plateaus (johannessen & andsbjerg 1993; andsbjerg & dybkjær 2003, this volume; johannessen 2003, this volume). this history of protracted extension during the middle and late jurassic was interrupted in the latest jurassic – earliest cretaceous by a complex tectonic phase that was essentially extensional in character but involved block rotation associated with localised compression, reverse faulting and uplift (rasmussen 1995; møller & rasmussen 2003, this volume). this end-jurassic tectonic phase coincided broadly with deposition of the organic-rich bo member and thus is of direct relevance to this study. stratigraphy history and stratigraphic status the organic-rich ‘hot shales’ of the bo member occur within the uppermost levels of the farsund formation (fig. 2). originally described informally by jensen et al. (1986) as the ‘hot unit’, the stratigraphy of this unit was subsequently discussed briefly by michelsen & wong (1991) and the hydrocarbon source rock characteristics were reported by østfeldt (1987) and damtoft et al. (1987, 1992). a detailed study of these deposits was undertaken by bojesen-koefoed (1988). as noted earlier, michelsen et al. (2003, this volume) formally define the ‘hot unit’ of jensen et al. (1986) as the bo member in an accompanying paper. log character the bo member is recognised primarily on the basis of log character since the gross lithological contrast between this member and the remainder of the farsund formation is often slight and rarely detectable in ditch cuttings. jensen et al. (1986) described the unit from the bo-1 well at the southern end of the tail end graben (figs 3, 4). this description relied heavily on the gamma-ray log which thus forms the essential criterion for its recognition. in bo-1, the background gamma-ray values of the farsund formation mudstones are in the range 75–100 api (fig. 4); the bo member shows values ranging from 120 to 160 api with marked upward shifts to higher and lower values defining the lower and upper boundaries of the member respectively. although generally high, gamma-ray values may vary significantly within the bo member; in bo-1 and many other wells, upward-decreasing gamma trends are evident, typically 3–5 m thick and separated by intervals showing more consistently high gamma-ray values. a marked feature of the bo-1 section is the upward increase in gamma-ray values beneath the bo member over an interval of about 50 m (8724–8561 ft). this ‘warming-upwards’ interval (henceforth referred to as the w-u interval) is also a feature of many other wells (see below). variation in the degree of development of this w-u interval in relation to the ‘hottest’ interval can result in ambiguity in locating the base of the bo member. in recognising the bo member throughout the danish central graben, the bo-1 gamma log pattern was used as the basic reference. it is important to note that the bo member of the danish sector of the central graben is more restricted in its definition than the partially equivalent mandal formation in the norwegian sector and the clay deep member of the dutch sector (fig. 2; dybkjær 1998). the bases of these units are defined at the point at which the overall gamma values begin to increase (i.e. at the base of 407 facing page: fig. 3. a: late jurassic tectonic framework of the danish central graben (modified from damtoft et al. 1992) showing the location of released wells in which the bo member is recognised. the bo member is not recognised in the wells indicated by open circles in the east of the area, although the same stratigraphic interval is represented in these wells. note that the ål and outer rough basins, although depicted on this map, were areas of active subsidence primarily in the early cretaceous (japsen et al. 2003, this volume). b: map showing the thickness (in metres) of the bo member in well sections and the lateral distribution of this member (blue) as deduced from well and seismic data. stipple indicates the inferred area in which the bo member is not developed due to siliciclastic dilution of the organic matter proximal to the ringkøbing–fyn high. the distribution of the bo member is not inferred for the southern area (salt dome province) due to sparse data points and the thin, irregular development of the ‘hot shales’ in this region. the w-u interval) and they are succeeded by cretaceous strata of the cromer knoll and rijnland groups (vollset & doré 1984; michelsen & wong 1991); the mandal formation and the clay deep member clearly span a greater stratigraphic interval than the bo member as defined by michelsen et al. (2003, this volume). spectral gamma-ray logs are not available for the bo-1 well but the example illustrated from the lone-1 well (fig. 5) shows an overall gamma log pattern that is comparable with the bo-1 section. it is clear from the spectral log that the increase in the overall gamma-ray values both beneath and within the bo member is the result of an increased content of uranium (jensen et al. 1986); the thorium and potassium values show little variation. as demonstrated by swanson (1961), uranium in sedimentary rocks is typically bound to organic matter and the positive correlation between gamma radioactivity and total organic carbon (toc) in the bo member is marked in most wells (see fig. 14; damtoft et al. 1992, fig. 5). uranium may also be concentrated in biogenic phosphate material, however, and since such debris is common in the organic-rich mudstones of the bo member, this may provide an additional contribution to the total gamma response. 408 gert-2 kim-1 gr (api) dt (µsec/ft) ild (ohms m2/m) dt (µsec/ft) ild (ohms m2/m) 132 0 150 13400 13600 13800 13200 14000 14200 13800 13600 0 8400 ft b.kb ft b.kb ft b.kb 8600 8800 bo-1 density (g/cm3) gr (api) gr (api) 1 10010150 120 600 150 ild (ohms m2/m) 10010 1 10 100120 60 fig. 4. the bo member (blue) in the bo-1 (the type well), gert-2 and kim-1 wells; for well locations, see fig. 3. the bo member is succeeded by the uppermost farsund formation in the bo-1 well, but is overlain directly by the cromer knoll group (åsgaard formation) in the gert-2 and kim-1 wells; the contact is probably a fault in the kim-1 well. the variation in log expression and stratigraphic development is discussed in the text. depth in feet below kelly bushing (kb); note that imperial units are retained for original well data measured in feet although metric units are preferred elsewhere. gr, gamma ray; dt, sonic velocity; ild, deep induction (resistivity). resistivity logs through this stratigraphic interval often show anomalously high readings which correspond, at least in part, to the bo member as defined on the gamma log. this gross correspondence is not surprising since resistivity logs are often used to recognise zones of organic richness (meyer & nederlof 1984; passey et al. 1990). in bo-1, the base of the bo member is marked by an abrupt increase in resistivity readings which remain relatively high throughout the unit (fig. 4). it is noteworthy, however, that these high resistivities continue upwards to the top of the farsund formation, above the upper boundary of the bo member as defined by the gamma log. in a number of wells, the resistivity logs display a stepped increase, corresponding roughly to the w-u interval on the gamma log beneath the bo member. it should be acknowledged, however, that the marked log shifts on the gamma and resistivity logs often do not coincide in detail, despite the broad correspondence, and the boundaries defined on the gamma log are considered to take priority, following jensen et al. (1986). in bo-1, the sonic and density–neutron logs do not vary substantially through this stratigraphic interval, indicating that gross lithological variation between the bo member and the host farsund formation is small; bulk densities and sonic velocities are slightly lower and neutron log values slightly higher in the ‘hottest’ zones of the bo member compared with the farsund formation in general. distribution and regional development the bo member is recognised widely in the danish central graben in wells where this portion of the upper farsund formation is preserved (fig. 3). the uppermost farsund formation is often truncated on structural highs (e.g. the inverted søgne basin, fig. 3) such that the original extent and variation in development of the bo member in the various subbasins is difficult to evaluate. furthermore, although forming part of the uppermost seismic sequence of the farsund formation mapped by møller (1986), the bo member alone cannot be differentiated on seismic data. knowledge of the lateral extent and variation in development of the member is thus fragmentary. it is possible, however, to make certain broad observations concerning both the distribution and lateral variation in the stratigraphic development of the bo member. firstly, it is absent in a number of wells flanking the eastern margin of the danish central graben, from gulnare-1 in the north to alma-1 in the south (fig. 3). in these wells, biostratigraphic data indicate the presence of the stratigraphic interval occupied by the bo member elsewhere yet the anomalously high gamma values characteristic of this member are not observed. it is likely that the lack of development of organic-rich mudstones in these marginal wells is largely the result of increased siliciclastic input and consequent dilution of the organic matter. it is noteworthy that discrete sand-rich intervals are characteristic of the uppermost jurassic – lowermost cretaceous in a number of these wells and indeed are recognised at formation 409 th k u 11600 11700 11800 11900 11500 ft.b.kb 0 150 -10 300 10 20 sgr (api) uranium (ppm) potassium (%) thorium (ppm) 0 0.05 0.1 0 20 40 c ro m er k no ll g p fa rs un d fo rm at io n b o m em be r fig. 5. spectral gamma log through the bo member in the lone-1 well. note that the increased gamma radioactivity exhibited by this interval is attributable solely to the contribution from uranium. sgr, total gamma-ray log; th, thorium; k, potassium; u, uranium. 410 kim-1 gert-2 jeppe-1 elin-1 no data gr 0 150 gr 0 150 gr 0 150 gr 0 180 6 5 2 6 5 4 1 2,3 4 5 4 3 1 1 5 6 1 nw core 100 m elin-1 kim-1 bo-1 edna-1 e-1 anne-3 20 km jeppe-1 gert-2 last occurrence datum, dinoflagellate cyst species: 6 dichadogonyaulax culmula/dingodinium? spinosum 5 rotosphaeropsis thula 4 amphorula expirata 3 egmontodinium polyplacophorum 2 dichadogonyaulax pannea/glossodinium dimorphum 1 senoniasphaera jurassica base cromer knoll group bo member base ryaz-1 sequence boundary base volg-4 sequence boundary fig. 6. variation in the development of the bo member in the danish central graben, illustrated by gamma logs (datum: top bo member). sequence boundaries ‘base volg-4’ and ‘base ryaz-1’ are from andsbjerg & dybkjær (2003, this volume). 411 level (poul and vyl formations; michelsen et al. 2003, this volume) in the deep adda-1, v-1 and ugle-1 wells. furthermore, the bo member is poorly defined, and only tentatively recognised, in several wells that lie adjacent to this marginal belt. in the elin-1 well in the tail end graben (fig. 3), for example, biostratigraphic data indicate that the upper volgian to ryazanian succession is highly expanded relative to other wells (fig. 6). the bo member in this well is thick (114 m compared with 39 m in bo-1) but shows only slightly higher gamma values than the background farsund formation. the thickness of the bo member varies greatly in the danish central graben, from less than 10 m in the southern salt dome province to over 100 m in the western part of the danish central graben (fig. 3). although this overall trend appears significant, thickness variation over much of the danish central graben does not show any systematic regional trend. it was probably controlled by local factors such as structural position within individual subbasins and local variations in the rate of sediment supply. the complexity is exemplified in the central portion of the danish central graben where the bo member is 39 m and 25 m thick, respectively, in the bo-1 and e-1 wells but under 15 m in nearby wells such as north jens-1 and jens-1 (fig. 3). the influence of structural position (and hence proximity to depocentres) is illustrated by comparing the gert-2 well on the gert ridge (18 m) with the jeppe-1 well within the gertrud graben (27 m) and the i-1 well in the major depocentre of the tail end graben (76 m). it should be emphasised again, however, that the bo member, although potentially thick, is only weakly developed in the major depocentre of the tail end graben. the log character of the bo member also varies through the danish central graben (figs 4, 6), often in association with variation in thickness. on structural bo-1 edna-1 e-1 anne-3 gr 0 180 gr 0 180 gr 0 180 gr 0 180 6 6 6 5 4 2 1 5 4 1 ? 5 4 2 1 5 4 3 2 1 se core 412 egmontodinium polyplacophorum dingodinium? spinosum daveya boresphaera, stiphosphaeridium arbustum amphorula expirata glossodinium dimorphum senoniasphaera jurassica scriniodinium inritibile, leptodinium subtile occisucysta balia rotosphaeropsis thula, systemaphora? daveyi albidum stenomphalus icenii kochi runctoni paratollia preplicomphalus lamplughi primitivus oppressus anguiformis kerberus okusensis glaucolithus albani fittoni rotunda boreal ammonite zonation u pp er ju ra ss ic lo w er v al an g. u pp er r ya za ni an lo w er r ya z. u pp er vo lg ia n up pe r m id dl e vo lg ia n m id dl e m id dl e vo lg ia n lo w er m id dl e vo lg ia n lo w er c re ta ce o us chronostratigraphy lo w er m id dl e vo lg ia n v al an gi ni an to l. h au te ri vi an u pp er r ya za ni an lo w er r ya z. b o m em be r fa rs un d fm v al ha ll fo rm at io n d.? spinosum daveya boresphaera s. arbustum r. thula s.? daveyi a. expirata g. dimorphum s. jurassica s. inritibile l. subtile o. balia e. polyplacophorum lo w er c re ta ce o us u pp er ju ra ss ic fa rs un d fo rm at io n 8600 8200 8400 8800 0 50 100 150 chronostratigraphy lithostratigraphy depth (ft.b. kb) last occurrence datum (lod), dinocysts gamma-ray (api) a b last occurrence datum (lod), dinocysts u pp er vo lg ia n m id dl e m id dl e vo lg ia n up pe r m id dl e vo lg ia n fig. 7. a: biostratigraphy of the bo-1 well, the type well of the bo member, based on analysis of ditch cuttings. the stippled chronostratigraphic boundaries cannot be accurately positioned in the succession on the basis of the palynology (fig. 7b). b: correlation of dinocyst ‘tops’ to the standard boreal ammonite zonation compiled from costa & davey (1992) and riding & thomas (1992). highs, such as the gert ridge (gert-2, fig. 4), both the bo member and the underlying w-u interval may be thin in comparison to the type bo-1 well, although still well-defined on petrophysical logs. in a number of wells (e.g. jeppe-1, fig. 6), an important erosional surface has been recognised beneath the bo member, truncating the w-u interval and in places succeeded by deep-water sandstones. this surface has been interpreted as a sequence boundary of regional significance by andsbjerg & dybkjær (2003, this volume; see also below). biostratigraphy the farsund formation in the danish central graben has a maximum age range of kimmeridgian to ryazanian. the bo member (michelsen et al. 2003, this volume) occurs in the uppermost farsund formation, in the interval broadly dated as latest middle volgian to early ryazanian (poulsen 1991). previous work on both ammonites and dinoflagellate cysts (hereafter referred to as dinocysts) from the cored portion of the bo member in the e-1 well (fig. 6) indicated an early ryazanian age (kochi chronozone) for at least the uppermost bo member (birkelund et al. 1983). in the present study, the biostratigraphy of the bo member and the immediately underlying and overlying farsund formation was investigated by means of palynological analysis of core where available (e-1, jeppe-1), sidewall cores and ditch cuttings from a total of 10 wells. the results of this study are summarised in figures 6–8; detailed biostratigraphic data from bo-1 in comparison with the type well of the mandal formation (7/12-3a) have been presented by dybkjær (1998). a number of key dinocysts (fig. 8c–h) can be used to bracket the bo member over much of the danish central graben; these dinocysts are well-known as stratigraphically useful species in the north sea region (davey 1979, 1982; riding 1984; riding & thomas 1992). as illustrated for bo-1 (fig. 7), the top of the bo member typically occurs immediately above the last occurrence datum (lod) of rotosphaeropsis thula whereas the base falls between the lod of amphorula expirata and the lod of egmontodinium polyplacophorum. the interval showing the highest gamma values is bracketed by the lod’s of r. thula and a. expirata, corresponding to the kochi chronozone of the early ryazanian (fig. 7). the results from the bo-1 well, supported in general by the regional data (fig. 6), indicate a maximum age range for the bo member of late volgian (preplicomphalus chronozone) to middle late ryazanian (stenomphalus chronozone). the point at which the gamma values begin to increase, i.e. the base of the w-u interval underlying the bo member (equivalent to the base of the mandal formation in the norwegian sector), corresponds roughly to the lod of senoniasphaera jurassica in bo-1 and many other wells (figs 6, 7), giving a middle–late middle volgian age for the onset of increased preservation of organic carbon in the succession. over much of the danish central graben, the biostratigraphy of the bo member is closely comparable to that in bo-1 (fig. 6), despite the variation in thickness and local problems of definition (see discussion above). in most wells, the top of the bo member lies between the lod of dichadogonyaulax culmula/dingodinium? spinosum and that of r. thula as observed in the type well (figs 6, 7), although deviations from this pattern were recorded (compare gert-2 with e-1). over most of the transect in figure 6, from gert-2 in the north to anne-3 in the south, the base of the bo member coincides roughly with the lod of a. expirata. key volgian dinocysts are absent from the underlying farsund formation in the edna-1 and e-1 wells; in the latter case this may be attributable to an erosional hiatus near the base of the bo member (fig. 6; andsbjerg & dybkjær 2003, this volume). in the jeppe-1 well, the ranges of dichadogonyaulax? pannea/glossodinium dimorphum and e. polyplacophorum extend into the bo member and share a common lod (fig. 6). it is thought likely that this anomaly can be attributed to reworking of these species, extending their ranges upwards. as described in detail below, the strata underlying the bo member in jeppe-1 are characterised by abundant evidence of slumping and sediment gravity flow and the potential for redeposition of older sediments must be considered high. in the gert-2 well on the gert ridge, in contrast, these dinocysts are not recorded and uppermost middle to upper volgian strata may be absent in this well; a sequence boundary is recognised at this level in gert-2 by andsbjerg & dybkjær (2003, this volume; fig. 6). thus, the anomalous biostratigraphic results from this northern portion of the danish central graben are perhaps best explained by local erosion of structurally positive regions during the latest volgian with concomitant redeposition in adjacent lows; this subject is discussed further below. as noted earlier, the bo member is well-developed and anomalously thick in the kim-1 and b-1 wells in the westernmost part of the danish central graben (the incipient ål and outer rough basins). in addition, the 413 414 a c d e f g h b p d a a w w p p 100 µm 20 µm 20 µm 20 µm 50 µm 20 µm 20 µm 20 µm fig. 8. palynofacies assemblages (a, b) and stratigraphically important dinocysts (c–f) from the bo member and the upper farsund formation in general. the figured specimens are stored at the geological survey of denmark and greenland, copenhagen, under the catalogue numbers provided. a: a typical palynofacies assemblage from the organic-rich mudstones (facies 1, 2) of the bo member showing a dominance of aom (a), dinocysts (d) and prasinophyte algae (p). jeppe-1, core 1, 4402.71 m (drill depth). b: palynofacies assemblage from a muddy sandstone bed (facies 3b; fig. 13, sample 2). note the heterogeneous nature of the assemblage, comprising wood particles (w), aom (a) and palynomorph fragments, including prasinophyte algae (p). jeppe-1, core 1, 4418.73 m (drill depth). c: rotosphaeropsis thula. bo-1, cuttings sample 8670–8680 ft, geological survey of denmark and greenland (geus) catalogue no. 2000-kd-001. d: dingodinium? spinosum. bo-1, cuttings sample 8370–8380 ft, geus catalogue no. 2000-kd-002. e: systematophora? daveyi. bo-1, cuttings sample 8790–8800 ft, geus catalogue no. 2000-kd-003. f: amphorula expirata. bo-1, cuttings sample 8640–8650 ft, geus catalogue no. 2000-kd-004. g: egmontodinium polyplacophorum. bo-1, cuttings sample 8580– 8590 ft, geus catalogue no. 2000-kd-005. h: senoniasphaera jurassica. bo-1, cuttings sample 8760–8770 ft, geus catalogue no. 2000-kd-006. w-u interval that is characteristic of the strata underlying the bo member over much of the danish central graben is absent or very thin in this western area. the biostratigraphic data are poor but the results from kim-1 suggest that the lower portion of the bo member in this well may be time-equivalent to at least part of the w-u interval in the remainder of the danish central graben (fig. 6). sequence stratigraphic framework the sequence stratigraphy of the jurassic in the central graben presented by andsbjerg & dybkjær (2003, this volume) is adopted here. based primarily on new biostratigraphic data integrated with detailed log analysis, these workers subdivided the upper jurassic mudstonedominated farsund formation into 11 sequences. in their study, sequence boundaries are recognised in well sections on the basis of parasequence stacking patterns (derived from log analysis), abrupt facies shifts and biostratigraphic evidence for hiatuses. in most wells, the uppermost sequence boundary (base ryaz-1) lies beneath or at the base of the bo member (fig. 6). in wells exhibiting an expanded section (e.g. bo-1, fig. 6) this surface lies within the upper levels of the w-u interval and there is no evidence of a significant stratigraphic gap. in such apparently conformable sections, the sequence boundary is of late volgian or early ryazanian age. in other wells, particularly on late jurassic structural highs (e.g. the gert ridge), this sequence boundary lies close to, or is coincident with, the base of the bo member and is marked by a significant stratigraphic gap (e.g. gert-2, fig. 6). andsbjerg & dybkjær (2003, this volume) did not present a sequence stratigraphic interpretation of the succession overlying this sequence boundary up to the base of the cromer knoll group, acknowledging the probable complexity of the bo member itself and the unresolved debate concerning the sequence stratigraphic identity of the ‘base cretaceous unconformity’ (rawson & riley 1982; donovan et al. 1993). donovan et al. (1993) presented the results of an integrated sequence stratigraphic study of the middle–upper jurassic in a portion of the uk central graben, some 200 km north-west of the danish sector. they recognised eight depositional sequences, the uppermost of which includes volgian–ryazanian ‘hot shales’ that are equivalent in part to the bo member of the danish central graben. the lower boundary of this sequence (the ‘purple’ sequence boundary of donovan et al. 1993) occurs beneath the ‘hot shales’; in some wells, this is a major truncation surface at which the volgian and uppermost kimmeridgian are absent. at its correlative conformity, this surface is suggested to be of medial middle volgian age (base portlandian, sensu anglico). donovan et al. (1993) suggested further that the maximum gamma peak within the ‘hot shales’ represents a maximum flooding surface; the succeeding sequence boundary was placed at the base of the cromer knoll group although donovan et al. (1993) acknowledged that evidence for truncation at this surface is scarce. there is a striking similarity between the log character of the bo member in the danish sector and the equivalent succession in the uk sector of the central graben, particularly with respect to the relationship of these ‘hot shales’ to the regional sequence stratigraphic framework. however, the ages referred to the sequence boundaries underlying the ‘hot shales’ do not match and there is clearly a problem in integrating these two sequence stratigraphic frameworks. facies, processes and depositional environment the uppermost jurassic – lowermost cretaceous ‘hot shales’ in the north sea central graben occur within a thick upper jurassic – lower cretaceous mudstonedominated marine succession (farsund formation and cromer knoll group; fig. 2), an unattractive stratigraphic position with respect to exploration for hydrocarbon reservoirs. as a result, this interval is rarely cored (pegrum & spencer 1990) and lithological, biostratigraphic and geochemical studies are generally based on ditch cuttings and sidewall cores. the bo member of the danish central graben has, however, been partially cored in two wells, e-1 and jeppe-1 (figs 3, 6). the following discussion of facies, processes and depositional environment is based on these cores. it is wellestablished that the farsund formation was deposited in a fully marine environment (michelsen et al. 1987); the bo member yields ammonites, inoceramid bivalves and dinocysts confirming its overall marine character (birkelund et al. 1983 and this study). jeppe-1 well core 1 in jeppe-1 spans the lower boundary of the bo member (fig. 6), exhibiting 11.97 m of the underlying strata and 6.21 m of the bo member itself (figs 9–11). 415 416 c sl vf m sand f c vcc sl vf m sand f c vc c sl vf m sand f c vc 4407.5 4408.04405 depth in metres below kb 4410 4415 4416.0 4415.0 facies 1, 2: interbedded laminated mudstones and thin graded sandstone–mudstone couplets facies 3: structureless/graded sandstones facies 4: contorted sandstone–mudstone mudstone sandstone mudstone clasts contorted, slump-folded strata cross-lamination fig. 11a fig. 11b e d c b a 12 11 10 9 8 7 6 5 4 3 2 1 fig. 9. log of core 1 from the jeppe-1 well, spanning the base of the bo member (large arrow). note the clear subdivision into a heterogeneous, sandrich lower portion (up to base bo member) and an upper mud-dominated portion showing a fining-upwards trend. detailed logs illustrate the lithofacies described in the text; inferred sandstone injection structures occur at 4408 m and at 4415 m in these detailed sections. small arrows 1–12 indicate locations of palynofacies analyses exhibited in figure 13. the results of detailed lamina-bylamina logs (a–e) through the finegrained fraction are presented on table 1 and figure 10. the intervals illustrated in figure 11 are indicated. the core is well-preserved, in contrast to the e-1 core, and thus forms the dominant data source for detailed facies analysis, including palynofacies analysis. facies and depositional processes facies 1. black claystones this facies occurs intimately interbedded with thin-bedded sandstone–mudstone couplets (facies 2) where it ranges from laminae less than a millimetre thick to beds several centimetres thick. in representative detailed lamina-by-lamina sections (fig. 10), the black claystone laminae are typically 1–3 mm thick, increasing both in thickness and overall proportion of the section upwards from the sub-bo member strata into the bo member itself (fig. 12; table 1). laminae and beds are typically parallel-sided with sharp, flat boundaries, except where scoured and/or loaded at the contact with an overlying sandstone bed (facies 2). the claystones are black or very dark grey, locally with a faint brownish cast, and show a weak, yet pervasive planar structure defined by discontinuous organic wisps, an overall platy fabric and, in places, by concentrations of calcareous microfossils (largely rhaxella perforata, sponge reproductive cysts). bioturbation is absent. a characteristic feature of this facies is the occurrence of phosphatic fragments, typically concentrated along specific horizons; on bedding plane surfaces these are often identifiable as fish scales. larger vertebrate remains occur in this facies within the bo member at 4402.45 m (figs 9, 10); these have been preliminarily identified as vertebrae, ribs and other bones of a marine reptile, most likely of plesiosaur or ichthyosaur type (s.e. bendix-almgreen, personal communication 1994). due to the finely interstratified nature of facies 1 and 2, analysis of palynofacies and source rock potential was largely undertaken on mudstone plug samples that included both facies. as shown on figure 13 (see also fig. 8a), the composition of the organic matter in these composite samples is very uniform. amorphous organic matter (aom) and dinocysts together form over 75% of the organic matter, dominating over the terrestrial component (wood fragments, spores and pollen). the total organic carbon (toc) content of the mudstones (facies 1 and 2) in the bo member itself has a range of 5.2–7.1 wt% with an average of 6.0 wt% (table 2). in the succession beneath the bo member, the mudstones show toc values in the range 3.8–7.1 wt% (average of 5.0 wt%). supplementary analyses were undertaken on two samples of facies 1 and one sample of facies 2 from the bo member. these few analyses (table 2) suggest that the facies 1 mudstones show slightly higher toc values (7.3, 8.4 wt%) than the facies 2 mudstones (6.8 wt%), the slight difference being attributable largely to the higher silt content of the latter facies. interpretation. this facies is characterised by its finegrained nature, the high organic carbon content, the dominance of aom and dinocysts over terrestrial components, the lack of bioturbation and the weak yet pervasive planar fabric. all these features indicate deposition in a low-energy, oxygen-deficient marine environment, distant from terrestrial influence. the facies is interpreted to represent hemipelagic/pelagic fines, deposited by settling through the water column. the preservation of very thin (millimetric) sedimentation units in this succession, as a result of the suboxic–anoxic bottom conditions (terminology from tyson & pearson 1991) and consequent absence of bioturbation, permits the identification and differentiation of hemipelagic deposits from fine-grained sediment gravity flow deposits (see facies 2); in many deep-water fine-grained deposits, such differentiation is impossible (e.g. ineson 1989). this facies is equivalent to the ‘fissile-laminated non-bioturbated mudrock’ facies of stow & atkin (1987), in their study of upper jurassic mudrocks from the uk sector of the north sea, and to facies e2.2 of the deepwater facies scheme of pickering et al. (1986). facies 2. sandstone–mudstone couplets this facies is an important component of the sub-bo member succession and forms over 70% of the cored portion of the bo member itself (table 1). where fully developed (figs 9–11), it comprises two well-differentiated components: a lower parallelto cross-laminated, fineto very fine-grained sandstone succeeded by a structureless or coarse-tail graded, weakly laminated silty mudstone. such couplets may be up to 5 cm thick, but are typically 0.5–2 cm thick; the sandstone portion is typically in the range 1–5 mm whereas the mudstone portion is typically 5–10 mm thick. this facies, together with facies 1, is a common component of the slump sheets assigned to facies 4. syndepositional extensional microfaults and boudinage are observed locally. the organic composition of facies 2 is discussed under facies 1 (see above). the basal sand–silt layer has a sharp base, often erosional and loaded. some of these sandstones are normally graded but most are ungraded and show parallel417 418 section d section b 2 cm hemipelagic mudstone claystone cap structureless silty mudstone, weak coarse-tail grading laminated silty/ sandy mudstone cross-laminated sandstone fig. 10. logs of the fine-grained fraction (facies 1, 2) from the lower levels of the bo member (section b) and from the upper part of the cored portion of the bo member (section d) in jeppe-1 (for precise locations, see fig. 9). core photograph shows the thinly-bedded mud-dominated nature of the bo member (section d); arrows indicate the basal contacts of four typical sandstone–mudstone couplets (facies 2), interbedded with thin (1–3 mm) laminae of hemipelagic mudstone (facies 1). note the vertebrate remains (?plesiosaur/ichthyosaur) in the upper part of section d. inset shows an idealised fine-grained turbidite in the jeppe-1 core. or cross-lamination. such cross-lamination is low-angle, sometimes with muddy toesets, and the sandstones are often lenticular, resembling the ‘fading ripples’ of stow & shanmugam (1980). such well-developed sand–mud couplets (sand component > 2 mm thick) are subordinate in the facies (under 20% of facies 2 beds in the detailed sections) and many beds (about 30% in the detailed sections; fig. 10; table 1) possess only a discontinuous sand or silt lamina, less than 2 mm thick. in the bo member itself, nearly 70% of facies 2 beds lack the sand portion (i.e. ‘base cut-off’). the mudstone portion of these couplets typically abruptly overlies the sand component, if present, although graded transitions were observed in a few beds. the silty mudstones are commonly structureless but may show weakly defined coarse-tail grading, particularly in the lower levels in association with diffuse lamination. on polished slabs, the grading is picked out by an upward decrease in the proportion of dispersed very fine sand and coarse silt grains, or rhaxella cysts at some levels in the core. an interesting feature of this facies is the presence of a very thin (0.1–0.2 mm) but persistent cap of midbrown claystone (fig. 10). in detailed lamina-by-lamina sections, over 75% of beds with non-erosional upper contacts possess this ultra-thin claystone cap. the base of this layer is sharp although rapid grading from dark grey silty mudstone to paler-coloured claystone is observed; the upper contact with succeeding hemipelagic deposits (facies 1) is sharp and planar. interpretation. although the two components of these sandstone–mudstone couplets are often well-differentiated, their close association and the occurrence, in places, of a graded transition from sand to mud indicates that they are the result of a common process. the scoured basal contacts and the presence of grading indicates deposition from a waning turbulent bottom current. in the absence of evidence of wave or storm activity, and in view of the close similarity to descrip419 facies 1 hemipelagic mud facies 2 sand–mud couplets (fine-grained turbidites) e 27.3 2.4 (n = 33) 28.9 3.8 (n = 50) 60.4 10.7 d 26.5 2.7 (n = 31) 31.9 4.6 (n = 39) 64.6 3.5 c 25.4 3.1 (n = 16) 16.8 7.9 (n = 26) 76.5 6.7 b 35.9 1.5 (n = 18) 7.6 12.3 (n = 27) 73.4 19.0 a 53.0 1.1 (n = 12) 2.4 16.2 (n = 32) 81.9 15.7 proportion of section (%) average thickness (mm) average thickness (mm) proportion of mud component in section (%) proportion of sand component in section (%) section thickness (cm) table 1. jeppe-1 well, core 1: sedimentological data from the bo member (sections b–e), and underlying strata (section a) depth (m) facies toc (wt%) tmax (°c) s1 (mg/g) s2 (mg/g) hi 4401.36 1, 2 5.5 445 4.5 28.0 508 4401.37 1 7.3 446 3.6 33.0 454 4402.67 1 8.4 445 4.5 39.5 473 4402.69 2 6.8 444 4.0 31.2 458 4402.71 1, 2 7.1 444 5.2 37.7 533 4404.18 1, 2 5.2 443 4.1 24.7 477 4404.97 1, 2 6.6 441 5.5 35.7 543 12 4406.98 1, 2 5.9 443 3.6 28.7 488 11 4407.19 1, 2 5.6 444 3.0 27.9 497 10 4408.09 1, 2 4.7 441 2.5 20.8 443 9 4409.35 1, 2 3.8 441 2.6 14.5 378 4410.86 1, 2 5.3 443 2.6 22.4 425 4411.12 3a 0.5 434 2.0 0.8 169 8 4411.36 3a n.d. n.d. n.d. n.d. n.d. 7 4412.94 1, 2 7.1 433 5.4 36.9 518 4414.72 1, 2 5.3 445 3.1 22.6 431 4414.97 3b 0.2 n.d. n.d. n.d. n.d. 6 4415.49 1, 2 4.7 445 2.6 19.3 412 5 4417.33 1, 2 4.5 442 2.9 18.3 405 4 4417.47 4 2.3 443 2.3 6.3 276 3 4418.73 3b 1.2 442 1.7 3.5 281 2 4419.36 4 4.7 445 2.7 22.0 466 1 n.d., not detected palynofacies sample no. table 2. jeppe-1 well: geochemical data from core 1 spanning the base of the bo member (dashed line) 420 tions of fine-grained sediment gravity flow deposits in the literature (piper 1972; stow 1979; stow & shanmugan 1980; pickering et al. 1986), these beds are attributed to deposition from sediment-starved, dilute turbidity currents. the basal laminated and ripple cross-laminated sandstone portion, where present, is indicative of tractional processes whereas the succeeding structureless or graded mudstone portion was deposited prifig. 11. selected intervals of core 1, jeppe-1 (fig. 9); the section youngs from bottom left to top right. depths (drill) in metres below well reference point. a: the lowermost beds (4419.4–4416.9 m) typify the cored interval beneath the bo member. massive sandstones (s; facies 3) and slump sheets (ss; facies 4) are interbedded with fine-grained turbidites and hemipelagic mudstones (facies 1, 2). b: this core section (4408.9–4406.1 m) spans the lower boundary of the bo member (arrow; see also fig. 9) and illustrates the thinbedded, mud-dominated nature of this member. s a b ss 20 cm 0 421 marily from suspension. the silty lamination observed locally within the mudstones may be the result of shear sorting within the bottom boundary layer (stow & bowen 1978). these couplets are comparable to facies c2.3/d2.1 of pickering et al. (1986) and closely resemble the ‘mudstone facies’ described from the upper jurassic brae oilfield of the uk sector of the north sea (stow et al. 1982). these beds can be described as tc(d)e turbidites on the classical bouma (1962) scheme; within the mudstone portion, the divisions e1, e2, e3 of piper (1972) and t3/t4, t6, t7 of stow & shanmugan (1980) are represented. interestingly, the discrete, ultra-thin (0.1–0.2 mm) claystone cap observed in this study is not evident in these facies schemes for fine-grained turbidites. this cap is clearly differentiated from the graded or structureless mudstone division and from overlying hemipelagic deposits; it probably represents the fall-out of the finest sediment fraction following the passage of the muddy turbulent cloud. preservation of this thin lamina requires the total absence of burrowing infauna, perhaps explaining its lack of recognition in other finegrained successions. as noted under facies 1, the absence of bioturbation in association with the high toc content and the nature of the palynofacies indicates deposition in an oxygen-deficient marine environment. facies 3. sandstones this facies is absent from the cored portion of the bo member but forms about 17% of the underlying farsund formation (fig. 9). the sandstones are typically mediumto fine-grained, although locally coarseor very coarsegrained, and commonly contain up to 20% abraded shell fragments (bivalves, echinoderms, sponge spicules, bryozoans). the sandstones are mineralogically submature, containing up to 30% feldspar grains, mica flakes and rock fragments. the lithics include basement lithologies, such as meta-quartzite, acid plutonics and foliated mica-quartz aggregates, in addition to volcanic and dolomite fragments probably derived from the permian section. coalified wood fragments, locally up to 1 cm across, are present in some beds. glaucony is a characteristic although minor component. the toc content of this facies varies considerably, dependent on the proportion of mud either as matrix or as discrete clasts (table 2). two subfacies are recognised, based on the presence or absence of mud matrix. subfacies 3a. these mud-free, calcite-cemented sandstones are rare, being represented by just three beds ranging in thickness from 5 cm to 20 cm. they are of medium or medium–coarse sand grade and are structureless or show diffuse parallel to low-angle (deformed?) lamination. bed boundaries are typically sharp and planar but one bed has an erosional, scoured base and a normally graded, pebbly basal few centimetres (fig. 9). this facies occurs in association with muddy sandstones (facies 3b) and slumped sediment (facies 4). interpretation. the sharp, locally erosive basal contacts, the presence of normal grading, the massive to parallel-stratified structure and the lack of mud matrix suggests deposition from energetic, waning currents that were capable of sorting sand from mud-grade sediment. these beds are interpreted as the deposits of sandy turbidity currents and can be broadly classified as bouma tab turbidites. the implications of their close association with facies 3b and 4 is discussed below. the 40 15 10 5 0 30 20 10 0 e d c b a e d c b a average turbidite thickness (mm) proportion of hemipelagic mud (%) d et ai le d s ec ti o ns d et ai le d s ec ti o ns fig. 12. histograms showing the stratigraphic variation in the average thickness of the fine-grained turbidites (facies 2) and in the relative importance of the hemipelagic deposits (facies 1), based on the detailed sections a–e (fig. 9). 422 organic content of this subfacies shows a typically marine signature, aom and dinocysts together dominating the assemblage (fig. 13). subfacies 3b. mud-rich, mediumto coarse-grained sandstones dominate facies 3 and occur in close association with slumped sediments (facies 4). indeed, there is a complete gradation between muddy sandstones containing discrete intraformational sandstone or mudstone clasts and intervals of contorted sandstone and mudstone (cf. in situ facies 1/2) in which semi-coherent, slump-folded sediment rafts are separated by zones of muddy sandstone (cf. facies 3b). sandstone beds referred to this subfacies are 5–25 cm in thickness (typically about 10 cm thick) and generally show sharp, flat bed boundaries; loading and water escape structures are observed in places. they are typically structureless but a few beds show faint parallel stratification. elongate intrabasinal clasts ranging in length from a few centimetres to the width of the core (10 cm) are oriented parallel to bedding and in several cases are concentrated in the upper levels of the bed. two muddy sandstone beds assigned to this facies were subjected to palynofacies analysis (fig. 13, samples 2, 6); the results contrast with the fine-grained fraction (see discussion under facies 1) but also differ from each other. both samples show a decrease in the relative importance of aom compared with the mudstone 12 11 10 9 8 7 6 5 4 3 2 1 1, 2 1, 2 1, 2 1, 2 3a 3a 3b 1, 2 1, 2 4 3b 4 100% aom (amorphous organic matter) wood dinoflagellate cysts prasinophyte algae spores and pollen palynofacies category faciessample no. fig. 13. selected results of the palynofacies study of the jeppe-1 core (for sample locations, see fig. 9); a total of 20 samples were subjected to palynofacies analysis and a minimum of 500 kerogen particles were counted in each sample. note the consistent results obtained from the fine-grained fraction (facies 1, 2), and the atypical composition of the organic matter from the muddy sandstones (facies 3b). dashed line indicates the base of the bo member; note that the organic composition of the bo member mudstones is closely comparable to that of the mudstones in the underlying strata. facies, but the lower sample (fig. 8b) shows a relative increase in the wood component whereas the upper sample shows an increase in the proportion of dinocysts and prasinophyte algae. interpretation. the poor sorting, mud matrix, structureless ungraded character, flat non-erosional boundaries and gradation to slumped strata indicate deposition from viscous sediment gravity flows of debris flow type. this facies is equivalent to facies c1.1 of pickering et al. (1986). a few thin beds (max. 10 cm thick) assigned broadly to this facies show some features that are not wholly compatible with the interpretation given above (fig. 9). they show sharp, subparallel boundaries that are locally slightly oblique to the general bedding and display elongate, tapering offshoots up to a few centimetres long and a centimetre across, both on the upper and lower bed boundaries. although largely structureless, weak lamination may be present in the middle zone of the bed. these sandstones are interpreted to be of intrusive origin (i.e. sandstone sills) rather than representing primary sediment gravity flow deposits, although confirmation is impossible in core. facies 4. contorted sandstone–mudstone units of contorted intraformational sediment form an important and striking part of the sub-bo member succession in the jeppe-1 core (figs 9, 11). they are 10–50 cm thick and typically show flat, non-erosional bases and flat or slightly irregular tops. a complete gradation is represented from sheets composed entirely of slumpfolded but essentially coherent thinly interbedded sandstones and mudstones (cf. facies 1, 2) to sheets composed of lenses (phacoids sensu voigt 1962) of internally deformed bedded sandstone and mudstone floating in a muddy sandstone matrix. with increasing disintegration of intraformational slabs, this facies grades into the muddy sandstones assigned to facies 3b. the organic composition and toc content of this facies are very variable, most likely due to the variable proportion of mud in these heterogeneous deposits. interpretation. this facies records remobilisation and partial disaggregation of thin-bedded sandstone and mudstone and is thought to have originated largely by surficial downslope transport by processes ranging between sliding or slumping and viscous debris flow. it is thus equivalent to facies f2.1 transitional to c1.1 of pickering et al. 1986. it is possible, however, that subsurface injection processes may have created some of the fabrics illustrated by this facies (cf. anderton 1997). stratigraphic distribution of facies as shown on figure 9, the cored section in the jeppe-1 well is readily subdivided into a lower heterogeneous, relatively sand-rich interval capped by a fining-upwards, mud-dominated unit, representing the basal beds of the bo member. the base of the sand-rich interval beneath the bo member occurs at a log depth of 4431 m, at an inferred sequence boundary (fig. 6; andsbjerg & dybkjær 2003, this volume). in the cored sub-bo member interval, packets of thinbedded sandstone–mudstone turbidites (facies 2) with intervening hemipelagic laminae and beds (facies 1) make up around half (47%) of the succession, interbedded with sandstone turbidites and debris flows (facies 3; 17%) and sandstone–mudstone slump sheets (36%). in a representative detailed section (section a) through the fine-grained fraction (figs 9, 12; table 1), hemipelagic mud (facies 1) forms less than 5% of the fine-grained fraction at this level, typically occurring as thin laminae (about 1 mm thick) sandwiched between sand–mud turbidites (facies 2; average thickness 16 mm). the cored section of the bo member is composed solely of facies 1 and 2. the abundance and thickness of the sand component in facies 2 decreases upwards from the sub-bo member succession into the bo member itself, in parallel with an upward decrease in turbidite thickness and a relative increase in the proportion of hemipelagic mud (figs 10, 12; table 1). in the uppermost detailed sections (fig. 9, sections d, e), hemipelagic mudstone forms about 30% of the succession in laminae up to 10 mm thick. depositional setting the cored section from the jeppe-1 well records deposition in a low-energy marine environment characterised by background sedimentation of muds and subordinate thin sands from dilute, muddy turbidity currents and by suspension settling through the water column. the absence of bioturbation and the preservation of high levels of organic carbon indicate very low levels of free oxygen (suboxic–anoxic) within the bottom waters. in contrast, coarse poorly-sorted shelly sandstone turbidites, debris flow deposits and slump sheets record a more dynamic depositional environment. firstly, the 423 shelly sands testify to a source of immature sediment, including basement rock fragments; the presence of a varied assemblage of coarse shell fragments and glaucony suggest relatively high-energy, shallow marine conditions in the source area. secondly, the slump sheets of turbiditic sandstone and mudstone and associated debris flow deposits provide evidence of intrabasinal slopes in the vicinity of the jeppe-1 well. indeed, the sandstone injection structures, the evidence of minor slope creep and the close similarity between the in situ sediments (facies 1, 2) and the slump sheet components indicate that this succession accumulated very close to the base-of-slope. the jeppe-1 well is located near the western margin of the gertrud graben, a half-graben that was most active in volgian times when it was bounded by the gert ridge to the west and the mandal high to the east (fig. 3). as noted earlier, block rotation in association with subsidence of the feda and gertrud grabens resulted in local compression and uplift of the gert ridge during the latest jurassic (rasmussen 1995), yielding a potential sediment source just west of the jeppe-1 location. in the gert field at the northern end of the gert ridge, permian, carboniferous and metamorphic basement were encountered beneath the jurassic succession (rasmussen 1995). in the immediate area of the field, such potential sediment sources were draped by upper jurassic sediment during deposition of the bo member, but it is possible that these strata were locally exposed in uplifted fault slices at the southern end of the gert ridge. it is likely, however, that the gert ridge was most important as a source of intraformational sediment in the latest jurassic and earliest cretaceous. both the sedimentological and palynological data from jeppe-1 testify to significant reworking of middle to upper volgian sediments in the form of slumps, slides and debris flows. the well data from the gert field atop the gert ridge also suggest that the ridge experienced significant erosion in the latest jurassic. the uppermost farsund formation, including the bo member, is absent from the gert-1 and gert-3 wells and a significant stratigraphic gap spanning the late middle and late volgian is recognised immediately beneath the bo member in gert-2 (fig. 6 and previous discussion). the data suggest, therefore, that the cored succession in jeppe-1 was derived from two sources. the thin muddy turbidites that form the bulk of the succession were probably derived from regional sediment sources; transport paths are difficult to infer, especially given the complex nature of the danish central graben in the late jurassic, but were most likely axial in the various elongate subbasins. in this context, it should be noted that rasmussen et al. (1999) have proposed, on the basis of seismic data, the existence of a channelised sandy fan system in the axis of the gertrud graben that was broadly coeval with the cored section beneath the bo member in jeppe-1. these workers suggested that the thin-bedded turbidites observed in the jeppe-1 core represent ‘fan-fringe’ or levee/overbank deposits related to the axial channel system. rasmussen et al. (1999) postulated that the siliciclastic source for this fan system was the sørvestlandet high (fig. 1), although the mandal high and the inverted søgne basin area are also possible candidates (fig. 3). it is notable, however, that the mudstone component of the thin turbidites is palynologically and geochemically closely comparable to the hemipelagic mudstones. this suggests that the clay fraction was mainly of intrabasinal origin, cannibalised by erosive, turbulent flows entering the central graben. in contrast, the coarse shelly sands and the slumps, slides and debris flow deposits of intraformational sediment may have been of local origin, perhaps shed from the gert ridge immediately to the east of the gertrud graben. dispersal of this intrabasinal sediment from the flanks of the gert ridge may have occurred during storms; the close association of shelly sands with slump sheets or debris flow deposits suggests a common triggering mechanism. although acknowledging the possibility of local derivation, rasmussen et al. (1999) suggested that the shelly sands and slump–debris flow deposits may alternatively be related to the axial fan system, perhaps recording periodic levee collapse or breach. a number of the facies displayed by the jeppe-1 well are closely comparable to those described from the brae and miller oilfields in the viking graben of the north sea (stow et al. 1982; turner et al. 1987; mcclure & brown 1992). in particular, the sandstone–mudstone couplets (facies 2) are closely comparable to the ‘tiger stripe’ facies described by stow et al. (1982). such facies are commonly termed ‘interchannel’ or ‘levee’ deposits when observed in close association with coarse-grained channelised turbidites (mutti 1977; walker 1985). the inferred existence of a channelised fan system in the axis of the gertrud graben (rasmussen et al. 1999) is interesting in this respect. the large-scale fining-upwards trends observed in the core and in the overlying uncored portion of the bo member (fig. 6), record pulses of erosion and sediment dispersal both from regional and intrabasinal sediment sources. as discussed above, the mud-rich turbidites in the cored section become thinner, and in general finer-grained, upwards whereas the 424 interbedded hemipelagic muds form an increasing proportion of the succession (fig. 12; table 1). although the biostratigraphic resolution does not permit direct measurement of sedimentation rates at this scale, this pattern is suggestive of a waning supply of turbiditic mud relative to the background hemipelagic rain, perhaps related to rising sea level. e-1 well the cored section in the e-1 well is from the uppermost portion of the bo member, where the gamma-ray values are consistently high (fig. 6). although originally totalling some 2 m of core (9783–9792 ft, 77% recovery), this core dates from 1968 and has been intensively sampled. representative slabs remain, totalling about 1 m of core. this core and the boundary between the farsund formation and the overlying cromer knoll group in this well were subjected to a detailed biostratigraphic study by birkelund et al. (1983). the core fragments that remain are composed solely of parallellaminated black or very dark grey claystone, comparable to facies 1 of the jeppe-1 core. facies and depositional processes facies 1. black claystones the lamination in this dark organic-rich claystone is defined by slight colour variation, concentrations of silt-sized calcite grains (?rhaxella sp.) and phosphatic fish fragments. birkelund et al. (1983; fig. 3) illustrated the well-laminated nature of this facies by means of an x-radiograph, and suggested that two orders of lamination are present. the sub-millimetric parallel lamination is interrupted at regular intervals (5–20 mm) by discrete paler homogeneous claystone laminae (0.1–0.3 mm thick); these laminae define the second order lamination of birkelund et al. (1983). ammonites and inoceramid bivalves are present in this core; the latter occur at discrete horizons and in places appear to extend across the full width of the core. birkelund et al. (1983) figured complete inoceramid valves (assigned to inoceramus aff. vereshagini) and cross-sections indicate the presence of compacted yet entire valves; no evidence of transport is observed. the organic composition of the bo member in the e-1 core is very uniform (table 3); toc values range from 6.7 to 8.5 wt% (average of 7.3 wt%), comparable to the individual analyses of the hemipelagic facies (facies 1) in jeppe-1. the content of organic matter is also very homogeneous, being strongly dominated by amorphous organic matter (aom), dinocysts and prasinophyte algae. interpretation. in common with facies 1 of the jeppe-1 core, this well-laminated organic-rich mudstone facies is attributed to hemipelagic settling of fines through the water column. the discrete light-coloured claystone laminae are reminiscent of those that cap the mudstone turbidites (facies 2) in the jeppe-1 core and may have a similar origin i.e. they may represent the fine-grained tail of individual turbidite events. sandstone–mudstone couplets of the type seen in jeppe-1 (facies 2) are, however, not recognised in e-1. the well-preserved parallel lamination with no sign of bioturbation (even in radiographs), and the high content of organic matter (toc), particularly aom, suggest that anoxic conditions prevailed for much of the time in the bottom waters. the occurrence of in-situ inoceramid bivalves at certain horizons, however, indicates at least periodic suboxic conditions on the sea floor (birkelund et al. 1983). bioturbation is not evident in association with these faunas suggesting that conditions on the sea floor were close to the boundary between anoxic and dysoxic (i.e. suboxic in the terminology of tyson & pearson 1991). comparable apparently anomalous sediment–faunal associations have been described and similarly interpreted by savrda & bottjer (1987) from the miocene of california and by doyle & whitham (1991) from the upper jurassic – lower cretaceous of the antarctic peninsula. savrda & bottjer (1987) suggested that the development of such associations (their exaerobic biofacies) is favoured by the development of bacterial mats on the sediment surface (see also tyson & pearson 1991). the association of benthic inoceramid faunas, in particular, with laminated ‘black shales’ has been noted by many workers (see discussion by macleod & hoppe 1992). on the basis of facies criteria (kauffman & 425 depth (ft) facies toc (wt%) tmax (°c) s1 (mg/g) s2 (mg/g) hi 9784 1 7.0 431 2.7 40.6 582 9786 1 6.8 424 4.0 40.6 601 9787 1 7.0 426 3.5 42.9 614 9788 1 7.8 426 4.4 45.5 587 9789 1 6.7 433 3.6 40.2 599 9790 1 8.5 430 4.8 56.3 660 table 3. e-1 well: geochemical data from the bo member in core 8 sageman 1990) and isotope data (macleod & hoppe 1992), it has been suggested that inoceramids may have benefited from bacterial chemosymbiosis, thus extending their potential environmental range. although the isotopic evidence has been disputed (grossman 1993), there is well-documented evidence that inoceramid bivalves were tolerant of conditions that excluded most other forms (macleod & hoppe 1992), whether this was the result of a highly efficient metabolism, chemosymbiosis or a combination of these factors. in any event, inoceramids are not observed in the jeppe-1 core and only occur at specific levels in the e-1 core, indicating that even the most tolerant benthic invertebrates were largely excluded from the floor of the danish central graben during the deposition of the bo member. depositional setting the e-1 core consists solely of laminated organic-rich hemipelagic mudstones that accumulated under suboxic–anoxic bottom conditions. in contrast to the jeppe-1 core, turbidite processes were apparently unimportant in this setting. as shown on figure 6, however, the e-1 and jeppe-1 cored sections are not time-equivalent so that it is not clear whether this contrast in sedimentation style reflects a geographical or a temporal shift in the dominant depositional processes. organic geochemistry and source rock potential a number of studies have documented the good to very good source potential of the farsund formation in the danish sector (damtoft et al. 1987, 1992) and a positive correlation between source characteristics and the produced hydrocarbons in danish fields has been achieved in a number of cases (østfeldt 1987; unpublished geus data). in this section, the source characteristics and geochemistry of the farsund formation are described with particular emphasis on the bo member. farsund formation the total organic content (toc) of the farsund formation is very variable, being dependent on lithology, stratigraphic position, geographical setting and level of thermal maturity. it ranges from less than 1 wt%, typically in sandstone or dolomite/limestone stringers and in mudstones in the lower levels of the formation, to more than 15 wt% in the mudstones of the bo member. pyrolysis yields (rock-eval s2) vary from less than 1 kg hc/ton rock to more than 90 kg hc/ton rock. corresponding values of the hydrogen index range from less than 100 to approximately 600. however, in general, the farsund formation can be considered a good or even very good hydrocarbon source rock. the source rock potential varies with depth through the formation, as well as geographically within the central graben. in general terms, the lower farsund formation is poorer in organic carbon and the proportion of terrigenous organic matter is significant, leading to a mixed gas-/oil-prone kerogen type (damtoft et al. 1987, 1992). upwards, the terrigenous component of the organic matter decreases in abundance, leading to highly oil-prone kerogen of predominantly marine/bacterial origin. in the south-eastern part of the central graben, and along the eastern border fault (coffee soil fault), the source rock potential deteriorates, probably due to dilution with mineral matter (siliciclastic detritus) and incorporation of larger proportions of inert terrigenous organic matter. in the upper farsund formation, n-alkane distributions are unimodal, with low to moderate proportions of ‘unresolved complex mixture’ (ucm), centred in the range c15–19. with a few exceptions, the n-alkane distributions are smooth, with little or no preference for odd or even numbered compounds. the abundance of linear isoprenoids is generally low to moderate. pristane/phytane ratios are mainly in the range 0.9–1.6. occasionally, an increased contribution of terrigenous organic matter to the kerogen is manifest in slightly increased abundance of waxy components (nc22+), slight predominance of odd-numbered n-alkanes in the range nc23–31, and a bimodal distribution of ucm. in the lower farsund formation these features are pronounced, testifying to a general increase in the proportion of the kerogen component derived from terrigenous organic matter. the terpane distributions show very variable, but mostly modest amounts of tricyclic triterpanes, which may form a homologous series ranging from c20 to c30 (see below). the pentacyclic terpanes of the hopane series are dominated by hopane and norhopane. in low maturity samples, moretanes and ßß-hopanes, in particular 17ß(h)-trisnorhopane, may be rather abundant, whereas 28,30-bisnorhopane, where present, forms only a minor proportion. the proportions of ts and tm, 426 427 and 29ts vary with the level of thermal maturity. c30 diahopane (compound ‘x’ of philp & gilbert 1986; moldowan et al. 1991), is generally present in very low proportions, but tends to become increasingly prominent with maturation. extended hopanes are abundant, displaying a regular decrease in abundance with increasing carbon number from c31 to c35. the distribution of regular steranes is very homogenous, featuring a slight predominance of c27 steranes over c28 and c29 steranes, which are roughly equal in abundance. diasteranes are rather abundant, generally increasing with level of thermal maturity. c30 steranes are present in all samples. bo member at ‘bulk level’, the mudstones of the bo member are characterised by high or even very high organic carbon contents, generally in the range 4–8 wt% toc, occasionally exceeding 15 wt% toc. pyrolysis yields are very high, 10–100 kg hc/ton rock (rock-eval s2), with corresponding values of the hydrogen index occasionally exceeding 500, somewhat dependent on the level of thermal maturity (figs 14, 15; tables 2, 3). interestingly, organic matter enrichment may extend above the upper boundary of the bo member as defined by the gamma log (ravn-2, g-1). as discussed earlier, the high gamma radiation exhibited by the bo member mudstones is attributed primarily to uranium bound to organic matter. the occurrence of organic-rich shales with relatively low gamma values above the bo member may, therefore, be either the result of exhaustion of available uranium in the geochemical system or a decrease in the ability of the sediments to incorporate uranium. factors that may conceivably influence the incorporation of uranium into sediments are organic matter type, redox conditions and sedimentation rate. the data show no marked changes in organic matter type and, in any event, complexation and subsequent reduction of u6+ 10000 10050 10100 10150 10200 10250 10300 10350 10400 0 50 100 150 0.0 2.0 4.0 6.0 8.0 0 200 400 600 0.1 0.2 0.3 0.4 0.0 0.5 1.0 1.5 0.0 0.3 0.6 0.9 1.2 0.75 1.00 1.25 1.50 gamma ray (api) toc (%) hi t23/h30 h28/h29 h35/h34 cpidepth (ft.b.kb) fig. 14. geochemical profile of the upper farsund formation, including the bo member (blue), in the edna-1 well. toc, total organic carbon; hi, hydrogen index; t23/h30, ratio of c23-tricyclic terpane to c30 hopane; h28/h29, ratio of 28,30-bisnorhopane to norhopane; h35/h34, ratio of pentakishomohopane to tetrakishomohopane; cpi, carbon preference index. takes place in deposits containing both type ii and type iii kerogen, apparently with no significant differences in enrichment factors (disnar & sureau 1990). cuttings samples from this interval indicate the persistence of black laminated mudstones, suggesting that there were no significant changes in redox conditions in the sedimentary environment. the third possible factor, sedimentation rate, cannot be evaluated meaningfully on the basis of the available data. in general terms, the geochemical characteristics of the bo member conform to those of the remainder of the farsund formation as outlined above. however, a number of specific characteristics serve to geochemically differentiate the bo member from the remainder of the farsund formation (figs 14–16). firstly, n-alkane distributions may display a slightly increased abundance of nc15 and/or nc17, and in the c20–28 range, a slight predominance of even carbon numbered components is sometimes noted, for example in the edna-1 well. in the m/z 191 ion fragmentogram, the proportion of tricyclic triterpanes relative to pentacyclic triterpanes, shown by the ratio of c23 tricyclic triterpane (t23) to c30 hopane (h30), may be increased (fig. 14). the abundance of 28,30-bisnorhopane (h28) is often very high (fig. 16), and in samples of low to moderate thermal maturity, this compound may even dominate the m/z 191 fragmentogram. extended hopanes may be abundant. the c35 and, in some cases, the c33 homologues are slightly enriched, leading to c35/c34 homologue ratios close to unity or above. geochemical interpretation of the bo member a predominance of nc15 and nc17 is generally assumed to indicate algal organic matter (gelpi et al. 1970; tissot & welte 1984). an abundance of tricyclic triterpanes has been linked to the occurrence of tasmanites-type alginite (azevedo et al. 1992; revill et al. 1994), which is present in large proportions in the bo member (bojesenkoefoed 1988). the presence of 28,30-bisnorhopane is 428 400 425 450 475 500 525 550 0 200 800 400 1000 600 tmax (°c) h yd ro ge n i nd ex (h i) total organic carbon (%) poor .2 .3 .7 .8.9.4 .6.5 0.1 1 2 3 7 8 94 65 20 30 40 50 10 2 0.1 4 6 8 2 2 4 6 8 4 6 8 2 1 10 100 excellent ex ce lle nt good g o o d fa ir po o rs2 (k g h yd ro ca rb o ns /t o n r o ck ) type i type ii type iii a b fig. 15. rock-eval/toc data for samples of the bo member in various sub-basins of the danish central graben. a: tmax vs. hydrogen index (hi); dashed lines indicate maturity evolution paths for kerogen types i, ii and iii. note the elongate distribution of data points, mainly reflecting variation in thermal maturity of the bo member in the different sub-basins. b: total organic carbon (toc) vs. s2 pyrolysis yield; note the overall organic richness and high pyrolysis yields. generally assumed to indicate highly anoxic environments, and its occurrence has also been linked to bacterial activity (katz & elrod 1983; williams 1984; moldowan et al. 1985; peters & moldowan 1993). a predominance of even-numbered n-alkanes in the c20–28 range is often observed in mildly hypersaline depositional environments (welte & waples 1973; nishimura & baker 1986; grimalt & albaiges 1987; bojesen-koefoed et al. 1997) but has also been recorded from a marine setting with little terrigenous input (kennicutt & brooks 1990). a high proportion of homohopanes is generally favoured by strongly reducing environments (peters & moldowan 1993), and enrichment in c33 and c35 homologues is often observed in carbonate and hypersaline environments (mello et al. 1988). hence, the biomarker distribution is indicative of anoxia, a minimal input of organic matter derived from higher land plants and perhaps of conditions of mild hypersalinity. as noted earlier, the vast majority of commercial as well as non-commercial petroleum accumulations in the danish north sea can, with a high degree of certainty, be genetically related to the farsund formation (and its stratigraphic equivalents). a common feature of almost all crude oils from the danish north sea is 429 10 20 30 40 50 60 7010 20 30 40 50 60 70 36 38 40 42 44 46 48 50 30 40 50 60 abundance abundance abundance abundance m/z 191 m/z 217 36 38 40 42 44 46 48 50 60504030 abundance abundance m/z 191 m/z 217 time (min.) time (min.)time (min.) time (min.) (a) (b) bo member farsund formation 17 ph pr 17 { { { { 14 15 {16 17 18 19 20 21 22 23 24 14 15 {16 17 18 19 20 21 22 23 24 4 1 2 3 5 6 7 8 9 10 { 11 12 13 1 2 3 5 6 7 8 9 10 { 12 13 { { 11{ { pr ph time (min.)time (min.) fig. 16. comparison of the geochemical characteristics of the bo member (a) and ‘background’ farsund formation mudstones (b). the uppermost pair of traces are gas chromatograms; the solid line connects n-alkanes with even numbers of carbon atoms, the dashed line connects n-alkanes with odd numbers of carbon atoms. note the dominance of even-numbered n-alkanes in the bo member. the two pairs of traces beneath illustrate biomarker data, ion fragmentograms m/z 191 and m/z 217. note the relative abundance of c23 tricyclic triterpanes (peak number 1) and 28,30-bisnorhopane (4) in the bo member mudstones. additional peaks: 2, ts; 3, tm; 5, norhopane; 6, c29-moretane; 7, hopane; 8, c30-moretane; 9–13, homohopanes; 14–17, c27-diasteranes; 18–21, c27 regular steranes; 22–24, c29 regular steranes. the presence of varying proportions of 28,30-bisnorhopane. this compound is thermally labile and its presence will to some extent be governed by maturity; indeed, the variation observed roughly parallels the maturity of the oils (unpublished geus data). since 28,30-bisnorhopane is only found in appreciable proportions in the sediments of the bo member, it may be assumed that this member has contributed to most of the hydrocarbon occurrences in the danish north sea. this further supports the idea that the bo member is a persistent feature in the danish central graben, and probably retains its identity in areas outside present well control, such as in the central portions of the feda and gertrud grabens and along the western flank of the central graben. furthermore, the occurrence of a large number of ‘immature’ oils, particularly in the southern part of the danish central graben, all carrying notable proportions of 28,30-bisnorhopane, suggests that the kerogen of the bo member and the upper farsund formation in general is able to generate and expel petroleum at low levels of thermal maturity. discussion upper jurassic organic-rich shales: current models the importance of upper jurassic source rocks in northwest europe has resulted in numerous studies focussing on the mode of accumulation and preservation of organic matter in this intra-cratonic setting (e.g. tyson et al. 1979; oschmann 1988; miller 1990; wignall 1991a). there is general agreement that a stratified water column with anoxic or dysoxic bottom waters, at least periodically, is indicated by the lithofacies, biofacies, palynofacies and geochemistry. rather less agreement has been reached, however, concerning the dominant mechanism(s) controlling such stratification and anoxia. tyson et al. (1979) suggested that stagnation and stratification in the kimmeridgian sea was influenced both by the regional palaeogeography and the overall high sea level; the complexity of the former inhibited circulation and open ocean transfer while the increased water depths over the shelf favoured stratification of bottom waters beneath wave-base. in some respects, this resembles the ‘silled basin model’ of demaison & moore (1980), using the quaternary of the black sea as a broad analogy; the onset of stratification on the late jurassic shelf was envisaged as a response to thermocline development, however, rather than to salinity stratification. the role of sea-level variation in controlling the regional extent of bottom-water anoxia has been emphasised (wignall 1991a; wignall & hallam 1991) while the link between cyclical variations in source rock development and climatic fluctuations has been discussed by a number of workers (e.g. oschmann 1988). alternative models have been presented to explain the regional development of a stratified water mass in northwest europe during the late jurassic – earliest cretaceous. oschmann (1988) suggested that the ‘silled basin’ model was inappropriate, given the regional extent of the organic-rich facies and the well-established connections to the tethyan and boreal seas. he argued for the seasonal development of extensive anoxia due to the southward migration of cold, oxygen-poor boreal waters during the summer in response to a northerly, wind-driven surface current. turnover of this stratified system probably occurred during the winter in all but the deepest submarine grabens. miller (1990) proposed a simple two-layer oceanographic model that is grossly the reverse of oschmann (1988): cold oxygenated boreal waters formed the surface layer flowing southward above warm saline bottom waters that originated in hypothetical shallow evaporative bays and flowed sluggishly northwards collecting in local depocentres and major rift axes. this model requires a sensitive balance between temperature and salinity of the two water masses since slight cooling of the boreal waters or decrease in the elevated salinities of the warmer southern waters would result in complete overturn. such a scenario, initiated by climatic or oceanographic shifts, was envisaged by miller (1990) for the regional destabilisation of the stratified system in the latest ryazanian (the basin ‘flushing’ of rawson & riley 1982). volgian–ryazanian ‘hot shales’ in discussion of the models proposed for the development of the ‘kimmeridge clay formation’ sea, it should be noted that such models are based largely on onshore data, particularly from the type area (see discussion by miller 1990). the facies are thus not directly comparable to those of the central graben, and indeed the depositional models are only strictly applicable to the period represented by the onshore section (i.e. kimmeridgian – middle volgian). furthermore, such models are designed to explain the long-term controls on the deposition and preservation of organic-rich shales that characterise the ‘kimmeridge clay formation’ in all 430 its stratigraphic guises throughout northwest europe. the ‘hot shales’ of the uppermost jurassic – lowermost cretaceous in the central graben of the north sea record a distinctive event within the background of organic-rich shale sedimentation, perhaps precipitated by the enhancement of one controlling factor or a coincidental combination of factors. the data presented here from the danish central graben are assessed below in the light of the current models summarised above. stratigraphic continuity in attempting to understand the origin of these organicrich shales, it is clearly important to establish the regional extent and degree of synchroneity of these deposits. black, organic-rich shales are a characteristic feature of the kimmeridgian–ryazanian of northwest europe and indeed farther afield (ager 1975; doré et al. 1985; klemme 1994). clearly, this represents a time during which burial and preservation of organic carbon was favoured on a global scale. it is also clear, however, that local factors such as structural configuration and sediment influx in addition to short-term global variables (e.g. sea level, climate) controlled the degree of development in any one location. in the north sea basin, the regional development of organic-rich shales in the kimmeridge clay formation (and stratigraphic equivalents) shows marked diachronism, although peak developments may be more widespread and biostratigraphically correlatable. doré et al. (1985), discussed at length the temporal and geographic distribution of ‘hot shales’ in the north sea region. these workers proposed that deposition of organic-rich ‘hot shales’ was most extensive, temporally, in the viking graben of the northern north sea where much of the kimmeridgian and volgian stages are represented by anaerobic, organicrich claystones in distal basin-centre locations. according to doré et al. (1985), such facies are not well-developed in the ryazanian succession of the viking graben, however, in contrast to the central graben farther south. as noted earlier, ‘hot shales’ occur at a number of levels in the upper jurassic of the north sea basin, the middle volgian – ryazanian succession under focus here forming the uppermost and best-developed example (price et al. 1993). in the norwegian sector of the danish basin, hot shales of kimmeridgian – early volgian age form a mappable unit defined as the tau formation (hamar et al. 1983; doré et al. 1985). as observed by rawson & riley (1982), the onset of anoxia in the kimmeridgian marked by the appearance of the tau formation organic-rich shales corresponds to the base of the oil shale facies in the eudoxus chronozone in the type kimmeridge clay formation of the wessex basin (tyson 1996). this event is marked by thin ‘hot’ log spikes within the farsund formation of the southern norwegian (doré et al. 1985) and danish sectors of the central graben (johannessen et al. 1996). according to wignall (1991b), this is one of the most important flooding events recorded in the onshore kimmeridge clay formation. from the outer moray firth through the central graben to the netherlands sector (fig. 1), the volgian– ryazanian succession is characterised, to a greater or lesser extent, by ‘hot’ organic-rich shales. on the basis of available published data, it appears that the onset of the development of this organic-rich facies may not have been wholly synchronous. in the uk sector of the central graben, donovan et al. (1993) ascribed an early volgian age to this event whereas a middle–late middle volgian age is likely in the norwegian and danish sectors (doré et al. 1985; dybkjær 1998). the same event has been referred to the late middle – late volgian in the northern part of the netherlands sector (g.f.w. herngreen, personal communication 1995). although these sources suggest a crude north-to-south younging of the initiation of ‘hot shale’ sedimentation, caution should be exercised. firstly, there is a scarcity of well-documented biostratigraphic information and secondly, watermass stratification may well have been regionally synchronous throughout the central graben, yet local factors (organic productivity, siliciclastic dilution, basin morphology etc) may have dictated when organic-rich mudstones began to be preserved at any one location. in any event, existing data suggest that there is considerable overlap in the age of the most organic-rich facies; true ‘hot shales’ accumulated from the latest volgian to the mid-ryazanian in most parts of the central graben and the moray firth. depositional and structural setting the data from the danish sector reinforce the regional interpretations of the upper jurassic mudstones in the central graben and onshore (tyson et al. 1979; miller 1990; tyson 1996). sedimentological core data, combined with palynological and geochemical data, attest to predominantly anoxic conditions on the sea floor; suboxic conditions may have prevailed periodically in certain locations. regional stratigraphic data from the danish central graben indicate that the mid-volgian – 431 ryazanian succession is sediment-starved relative to the kimmeridgian – mid-volgian (andsbjerg & dybkjær 2003, this volume). this period of reduced sediment supply to basinal settings has been correlated with an arid climatic episode between the early volgian and the late ryazanian (hallam 1985; wignall & ruffell 1990; hallam et al. 1991; ruffell & rawson 1994), an event which is also reflected in the upwards decrease in the terrigenous component of the kerogen of the farsund formation in the danish central graben (see above). with the exception of the easternmost portion of the danish central graben, where increased siliciclastic supply is thought to have suppressed the organic signal, the bo member is recognised throughout the danish central graben, even on late jurassic intrabasinal highs. position within the complex segmented central graben clearly influenced the degree of development of the ‘hot shales’ (i.e. thickness, organic richness, timing of initiation etc. – see earlier discussion and figs 4, 6). at its peak, however, watermass stratification and resultant bottom-water anoxia was sufficiently pervasive as to extend over most structural highs within the danish central graben. role of sea-level variation in assessing the possible contribution of sea-level variation to the development of a stratified watermass and bottom-water anoxia, it is important to recognise that the volgian–ryazanian succession records organic carbon burial and preservation at two different temporal scales. enhanced preservation of organic carbon began in the middle–late middle volgian in the danish sector and persisted until the early late ryazanian. the organicrich shales of the bo member, however, record a discrete short-term pulse, essentially restricted to the early ryazanian, that was superimposed on the long-term trend. referring, then, to published sea-level curves (hallam 1988; haq et al. 1988), it is apparent that the middle volgian – late ryazanian period was characterised, in broad terms, by a downward trend in sea level following the long-term sea-level rise that dominated most of the late jurassic and peaked in the early volgian. superimposed on this ‘second order’ fall in sea level, however, were a number of short-term sea-level events, as indicated by rawson & riley (1982, p. 2630) who referred to the middle – late volgian period as a “strongly regressive phase with occasional transgression”. one such minor transgressive event is recorded, for example, by the quasi-marine cinder bed which records a base kochi chronozone (early ryazanian) marine incursion into the largely non-marine wessex basin (rawson & riley 1982). an early ryazanian transgressive trend is also reflected in the regional onlap of ryazanian ‘hot shales’ onto the flanks of the central graben in the uk sector (gatliff et al. 1994), culminating in the deposition of upper ryazanian black laminated mudstones on kimmeridgian strata in eastern england (lott et al. 1986, 1989). it is apparent, therefore, that conditions favourable for the deposition and preservation of organic-rich sediments in the central graben from the middle–late middle volgian to the early late ryazanian coincided broadly with a long-term fall in sea level. in contrast, the pulse of highly efficient burial of organic carbon in the early ryazanian, represented by the bo member, may correlate with a short-term sea-level rise; this is compatible with the evidence presented here from the lower boundary of the bo member of a marked decrease in sediment supply to the deep basin at this time. conclusions it seems likely that the enhanced anoxia that developed in the central graben of the north sea in the latest jurassic and earliest cretaceous was the result of a coincidence of several factors. firstly, the late jurassic intracratonic seaway in the north sea region was prone to stratification and the development of oxygen deficiency in bottom waters, probably as a result of regional palaeogeographic and partially related oceanographic factors (tyson et al. 1979; doré 1991). a number of additional factors combined to create conditions particularly favourable for the accumulation of highly organic-rich sediments in the late–middle middle volgian – early late ryazanian. an arid climate resulted in reduced sediment influx and, hypothetically, the development of saline waters in fringing evaporative bays that may have sourced the central graben bottom waters, thus enhancing watermass stratification (miller 1990). a long-term ‘second order’ fall in sea level from the middle volgian to the late ryazanian, in combination with the complex tectonic topography of the north sea, may have contributed to the poor circulatory system. it appears likely, however, that the lower ryazanian ‘hot shales’, represented by the bo member in the danish sector, record a superimposed, short-term transgressive event (or events) that resulted in lateral expansion of the anoxic bottom waters onto the flanks of the central graben and over intra-basinal highs. 432 acknowledgements this study incorporates results from a series of energy research projects (efp 91, efp 92, efp 94), funded in part by the danish ministry of environment and energy. we thank jan andsbjerg, peter n. johannessen, jens jørgen møller and niels e. poulsen for advice and constructive criticism. the paper was greatly improved by the reviews of richard v. tyson and paul b. wignall. references ager, d.v. 1975: the jurassic world ocean (with special reference to the north atlantic). in: finstad, k.g. & selley, r.c. 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(eds): tectonic evolution of the north sea rifts. publication (international lithosphere program) 181, 1–36. new york: oxford university press. manuscript received 1 april 1996; revision accepted 1 november 1997. geological survey of denmark and greenland bulletin 1, 217-230 217 the jurassic of the netherlands g.f. waldemar herngreen, wim f.p. kouwe and theo e.wong a recent revision of the lithostratigraphy of the netherlands has triggered an extensive re-evaluation of existing ideas on the jurassic structural and depositional history. significant advances can be attributed to the incorporation of sequence stratigraphic concepts. in the course of the triassic and jurassic, structural complexity increased progressively. the jurassic sedimentary succession can be subdivided into three depositional megasequences. megasequence i (rhaetian– aalenian) reflects the period between the so-called early and mid-cimmerian tectonic phases. megasequence ii (aalenian – middle callovian) covers the period of activity of the mid-cimmerian phase. megasequence iii (middle callovian – ryazanian) corresponds with the period between the mid-cimmerian and late cimmerian phases (particularly after pulse ii). in this latter megasequence, six stages (iiia–f) are recognised. sediments deposited during the rhaetian and ryazanian bear a stronger affinity with the jurassic succession than with triassic and cretaceous sediments respectively. these stages are thus treated here as an integral part of the jurassic succession. during the rhaetian–bajocian the area subsided relatively uniformly. a sheet of predominantly fine-grained marine sediments of great lateral uniformity was deposited. during the toarcian, in particular, basin circulation was largely restricted. the cooling that followed the thermal central north sea dome uplift triggered an important extensional phase during the aalenian–callovian. the rift phase resulted in the formation of several smaller basins, each with its own characteristic depositional succession. the basins fall into three structural provinces: the eastern province (lower saxony basin, e–w-striking); the northern province (central graben, n–s-striking); and the southern–central system (roer valley graben – broad fourteens, with a strong nw–se strike). the mid-cimmerian event started to affect the dutch basins during the bajocian. sedimentation ceased in the dutch central graben while it persisted in a predominantly coarse-grained, shallow marine facies in the southern basins (roer valley graben, west netherlands basin). extensional tectonics in the central graben were initiated during the middle callovian, with the deposition of continental sediments. during the oxfordian–kimmeridgian, marine incursions gradually became more frequent. marine deposition in the other basins in the south persisted into the oxfordian, at which time deposition became predominantly continental. marine conditions gradually returned in the south during the ryazanian–barremian, with a series of advancing partial transgressions from the north. the present-day distribution of jurassic strata in the netherlands was determined largely by erosion associated with late cretaceous – paleocene uplift. keywords: the netherlands onshore and offshore, jurassic, lithostratigraphy, sequence stratigraphy, tectonics, regional geology g.f.w.h.* & t.e.w., netherlands institute of applied geoscience tno – national geological survey, p.o. box 80015, nl-3508 ta utrecht, the netherlands. *retired. e-mail: g.f.w.herngreen@bio.uu.nl w.f.p.k., wintershall noordzee b.v., eisenhowerlaan 146, nl-2517 jl the hague, the netherlands. geological survey of denmark and greenland bulletin 1, 217–229 (2003) © geus, 2003 the jurassic succession in the netherlands has significant hydrocarbon source rock and reservoir potential and the stratigraphy of the succession is thus a subject of particular interest. the jurassic lithostratigraphic nomenclature in the netherlands has recently been updated in a joint effort by the geological survey of the netherlands (rgd) and nogepa, the organisation of oil companies active in the netherlands. this project has benefited significantly from integration of new knowledge on jurassic biostratigraphy. in addition, sequence stratigraphic concepts have been used to explain the observed distribution of facies in time and space. the results have been published in part in van adrichem boogaert & kouwe (1994–1997). in this study, we treat the most recent ideas about the jurassic geological history of the netherlands. the geological history of the jurassic in the netherlands has been presented previously by haanstra (1963), heybroek (1974) and van wijhe (1987). ziegler (1990) treated the area from a northwest european perspective, whereas burgers & mulder (1991) summarised certain aspects of the late jurassic and cretaceous history. regional stratigraphic overviews of the jurassic in the southern north sea have been presented by brown (1990) and cameron et al. (1992). michelsen & wong (1991) presented a stratigraphic correlation between the dutch, danish and southern norwegian sectors of the central graben. underhill & partington (1993) discussed the effect of middle jurassic thermal doming on regional jurassic stratigraphy in a sequence stratigraphic context. kimmeridgian to ryazanian sequence stratigraphy, biostratigraphy and the distribution of the main reservoir intervals in the north sea were dealt with by partington et al. (1993). during the last two decades, several authors from the geological survey of the netherlands (rgd) have published detailed review papers on the middle–late jurassic history of the dutch central (north sea) graben, the vlieland basin and adjoining onshore areas: herngreen & de boer (1984), herngreen & wong (1989), herngreen et al. (1988, 1991), wong et al. (1989), geological atlas of the subsurface of the netherlands, sheets i–v (rgd 1991a, b, 1993a, b, 1995) and x (nitg–tno 1998; map sheet vi is in press and sheets vii and viii are currently in preparation). the accumulated rgd knowledge, combined with contributions by several oil companies, served as a basis for the revision of the existing lithostratigraphic nomenclature for the netherlands (van adrichem boogaert & kouwe 1994–1997). the revision of the jurassic involved two working groups: permian – middle jurassic and upper jurassic – lower cretaceous. a correlation of the current dutch jurassic – lower cretaceous lithostratigraphy with the stratigraphic subdivisions of the neighbouring countries is presented in figure 1. structural setting during triassic–jurassic times, the structural style of the netherlands gradually changed from the single, extensive southern permian basin into a complex of smaller, largely fault-controlled, highs and lows. this transformation, related to the break-up of pangea (ziegler 1990), took place in several discrete extensional phases: scythian (hardegsen), norian–rhaetian (early cimmerian), aalenian – callovian/oxfordian (mid-cimmerian) and kimmeridgian– valanginian (late cimmerian). the intervening periods were dominated by regular thermal subsidence. the result can be seen by comparing figures 2 and 3, which display the triassic and late jurassic basin configurations, respectively. in the northern half of the netherlands’ offshore territory, the segregation between highs and basins was enhanced by halokinesis in the permian–triassic successions along the structural boundaries. associated salt withdrawal commonly determined the distribution of jurassic depocentres. throughout the jurassic, the area comprised three interactive structural provinces (fig. 3). 1. the lower saxony basin system (previous ems low), extending into central germany. 2. the north sea central graben – vlieland basin system, trending north–south across the mid-north sea high – ringkøbing–fyn high complex. 3. a block-faulted basin system extending nw–se through the netherlands, connecting the roer valley graben, the central netherlands basin, the west netherlands basin and the broad fourteens basin (previous off-holland low), and linked with the sole pit basin in the uk offshore. during the early jurassic, the area subsided relatively uniformly. a sheet of open marine, fine-grained sediments of great lateral uniformity was deposited. structural complexity gradually increased during early and middle jurassic times, and reached a maximum in the callovian. during the middle and late jurassic, in particular, each of the above-mentioned provinces accumulated its own characteristic depositional succession. the impact of the uplift of the central north sea thermal dome during the aalenian–bathonian is most 218 219 w ie he ng eb .qu ar zi t po rt asa nd st ei n (m ac ro ce ph . s st ) r ed c ha lk f m sp ee to n c la y fm sp ils by sa nd st o ne fm k im m er id ge c la y fm c o ra lli an f m o xf o rd c la y fm w in te rt o n fm fl am m en m er ge l cromer knoll group schieland group delfland subgroup rijnland group cromer knoll group scruff group central graben subgroup rijnland group osningsandstein niedersachsen gp breeveertien fm zurich fm humber group west sole group altena group altena group central graben gp keuperliasdoggermalm lias group penarth group h o lla nd f m h o lla nd f m v lie la nd c la ys to ne f m v lie la nd sa nd st o ne fm v lie la nd sa nd st o ne fm sc ru ff g re en sa nd f m k im m er id ge c la y fm fr ie se fr o nt fm s le en f m a al bu rg f m po si do ni a sh al e fm po si do ni a sh al e fm po si do ni en sc hi ef er w er ke nd am f m w er ke nd am f m b ra ba nt f m r ø db y fm so la f m t ux en f m v al ha ll fm fa rs un d fm lo la f m fj er ri ts le v fm w in te rt o n fm sl ee n fm a al bu rg f m m id dl e g ra be n fm lo w er g ra be n fm r hä tk eu pe r v yl fm p o ul fm h en o fm b ry ne f m lo w er g ra be n sa nd fm w ei te ve en f m c o ev o rd en f m v lie la nd c la ys to ne fm m id dl e g ra be n sh al e fm b üc ke be rg f m ( ‘w ea ld en ’) n eo ko m -s ch ie fe rt o n (h ils to n fm ) m in um us to n b en th ei m er sa nd st ei n g ild eh äu se r sa nd st ei n r o th en be rg sa nd st ei n se rp ul it m b m ün de r fm ei m be ck hä us er p la tt en ka lk g ig as sc hi ch te n k im m er id ge ka lk e & m er ge l h ee rs um er s ch ic ht en o rn at en to n m ac ro ce ph al en to n o sn in g gr ø ns an d pu zz le h o le fm u pp er g ra be n fm a sp id o id es sa nd st ei n w ür tt em be rg ic us sa nd st ei n ‘c o rn br as h’ a ge a lb ia n a pt ia n b ar re m ia n h au te ri vi an v al an gi ni an r ya za ni an po rt la nd ia n k im m er id gi an (s en su la to ) o xf o rd ia n c al lo vi an b at ho ni an b aj o ci an a al en ia n t o ar ci an pl ie ns ba ch ia n si ne m ur ia n h et ta ng ia n r ha et ia n u ni te d k in gd o m so ut he rn n o rt h se a so ur ce : r hy s (1 97 4) , c am er o n et a l. (1 99 2) d en m ar k d an is h c en tr al g ra be n so ur ce : j en se n et a l. (1 98 6) , m ic he ls en & w o ng ( 19 91 ) n et he rl an ds co m po si te f o r th e no rt he rn , ce nt ra l a nd w es te rn s ec to rs n et he rl an ds (n o rt h)e as te rn s ec to r g er m an y lo w er s ax o ny b as in (w es te rn p ar t) so ur ce : b ri nk m an n (1 95 9) , c as ey e t al . ( 19 75 ), k em pe r( 19 76 ), k la ss en ( 19 84 ) epoch early cretaceous early jurassic l. triassicmiddle jurassiclate jurassic k o ra lle no o lit h nieuwerkerk fm ? ? = h ia tu s f ig . 1 . r e g io n al l it h o st ra ti g ra p h ic c o rr e la ti o n c h ar t o f th e j u ra ss ic – l o w e r c re ta ce o u s fo r th e n e th e rl an d s an d n e ig h b o u ri n g c o u n tr ie s. k im m e ri d g ia n s en su la to e q u al s k im m e ri d g ia n se n su a n gl ic o . f o r re ce n t re v is io n s o f th e d an is h s ch e m e , se e m ic h e ls e n e t a l. (2 0 0 3 , th is v o lu m e ). m o d if ie d f ro m v an a d ri ch e m b o o g ae rt & k o u w e ( 1 9 9 4 – 1 9 9 7 ). 220 evident in the northern offshore area of the netherlands, where lower jurassic successions are deeply truncated. the combination of initial cooling of the thinned crust under the dome and an overall transtensional tectonic regime triggered callovian–kimmeridgian rifting, resulting in the formation of the north sea central graben rift system. the uplift phase terminated the uniform subsidence and sheet-like deposition that characterised the early and middle jurassic. rifting induced structural differentiation into rapidly subsiding basins with high sediment infill rates and more stable, sediment-starved, platform areas. this differentiation persisted until the early cretaceous. outside the main basins depicted in figure 3, upper jurassic deposits are rare and thin, and associated with salt domes (rim synclines) or transverse fault zones. the north-eastern part of the netherlands formed the western fringe of the german ems low – lower saxony basin system. the ems low, a north–south elongated, 100 km sr o q a b e f g k 1 4 7 10 13 16 2 5 8 11 14 17 3 6 9 12 15 18 l m n p 3°e 5°e 7°e 54°n 52°n mid north sea high elbow spit h igh ringkøbing–fyn high c en tr al g ra be n sole pit basin em s lo w netherlands swell east netherlands high roer valley graben w est netherlands basin south hewett shelf london–brabant massif r he ni sh m as si f off-holland low structural high/subaerial landmass platform/occasionally flooded basin major normal fault (zone) seismic line shown in fig. 6 uk n dk g nl fig. 2. main triassic to early jurassic structural elements in the netherlands. the k-quadrant shows the block numbering system used for the netherlands’ continental shelf. each complete quadrant (1°n x 1°e) is divided into 18 blocks measuring 10´n x 20´e, numbered from nw to se. incomplete quadrants are numbered as if they were complete (e.g. the o-quadrant only comprises blocks 12, 15, 17 and 18). national sectors of the north sea: dk, denmark; g, germany; n, norway; nl, the netherlands; uk, united kingdom. modified from van adrichem boogaert & kouwe (1994–1997). fig. 3. middle–late jurassic to early cretaceous structural elements in the netherlands. for legend, see fig. 2. modified from van adrichem boogaert & kouwe (1994–1997). sr o q a b e f g k l m n p 52°n 54°n c en tr al g ra be n terschelling basin st ep g ra be n ijmuiden high gouwzee trough w est netherlands basin lower saxony basin hantum fault zone lauw erszee trough g roningen high ameland block rifgronden fault zone schill grund high roer valley g raben zandvoort ridge noord–holland platform texel–ijsselmeer high elbow spit h igh k refeld h igh maas bommel high peel block indefatigable fault zone gronau fault zone outer rough basin ringkøbing–fyn high mid north sea high cleaver bank high sole pit basin broad fourteens basin vlieland basin friesland platform winterton high central netherlands basin london–brabant massif rhenish massif vlieland high 3°e 5°e 7°e 100 km fault-bounded basin during carboniferous–triassic times, evolved into the slightly east–west-trending, sag-like lower saxony basin during the middle jurassic. a relatively undisturbed, continuous jurassic succession is found in the central parts of the basin in germany (fig. 1). in the eastern netherlands’ development, a hiatus spanning the aalenian – early kimmeridgian reflects the situation along the western margin of the basin. the west netherlands basin, the roer valley graben and the broad fourteens basin formed a different depositional province, connected with the sole pit basin of the uk sector of the north sea. since permian–triassic salts are largely absent in the subsurface here, these basins demonstrate a pure block-faulted nature. the three mentioned provinces merge in the onshore netherlands, where the central netherlands basin and the vlieland basin (a small pull-apart basin) were positioned. the transitions between these provinces are now obscured as a result of later erosion which has stripped jurassic sediments from most of the country. application of sequence stratigraphy in connection with the revision of the existing lithostratigraphic nomenclature for the netherlands (van adrichem boogaert & kouwe 1994–1997), sequence stratigraphic analysis was seen as a valuable additional tool for a better understanding of the complex geological settings and stratigraphic relationships. the lower and middle jurassic successions in the netherlands are of open marine origin, and developed in regionally uniform facies. depositional cycles are commonly discerned in this interval, and some of these were already incorporated in the old lithostratigraphic subdivision by nam & rgd (1980). in the recent revisions, therefore, it was not considered necessary to improve this scheme by incorporation of results from new biostratigraphic or sequence stratigraphic analyses. in the (middle–)upper jurassic, however, the common intercalation of continental and marine deposits makes sequence stratigraphy especially effective. therefore all available data (well and seismic correlations, biostratigraphic and palynological data) were integrated into a regional sequence stratigraphic framework. this framework was used to select those units which were suitable candidates for lithostratigraphic units. criteria for unit selection included mappability, relevance for exploration geology and the existence of diagnostic lithological and/or biostratigraphical criteria for their recognition. with the available data and time, the construction of a specific, local sequence framework fell outside the scope of the working group. instead, the group tied the recognised transgressive and regressive events to the best-fitting sequences in the cycle chart published by haq et al. (1988). this haq et al. (1988) time-scale has been recalibrated numerically to the scale of harland et al. (1990), which was chosen as the current standard for dutch stratigraphy. for the sake of completeness, figures 4 and 5 (facing pages 226 and 227, respectively) indicate the haq et al. (1988) sequence subdivision for the whole of the jurassic; figure 5 provides an overview of some significant biostratigraphic marker horizons that were used for calibration of dutch lithostratigraphy with the cycle chart. sequence stratigraphic analysis was carried out using concepts defined by the exxon school, viz. sequences are stratal units bounded by unconformities and their correlative conformities (van wagoner et al. 1988). in contrast, concepts of genetic sequence stratigraphy (sensu galloway 1989), in which genetic sequences are bounded by maximum flooding surfaces, are commonly invoked for regional correlation studies. an example of this approach is found in partington et al. (1993), for their regional correlation of the jurassic of the north sea area. it should be noted that their interpretation of dutch jurassic sediments was based on obsolete ideas derived from nam & rgd (1980). figure 4 presents the most modern ideas on the dutch chrono-lithostratigraphic development in the context of the development in the surrounding countries. depositional history the jurassic succession of the netherlands can be subdivided into three depositional megasequences. megasequence i (rhaetian–aalenian) reflects the period between the early and the mid-cimmerian tectonic phases. megasequence ii (aalenian – middle callovian) covers the period of activity of the mid-cimmerian phase. megasequence iii (middle callovian – ryazanian) corresponds to the period between the mid-cimmerian and the late cimmerian (pulse ii) phases (rgd 1991a). rhaetian–aalenian (megasequence i) this period was characterised by the deposition of a very uniform blanket of marine shales across large parts of northwest europe. in the netherlands, these deposits 221 are placed in the altena group. after a long period of restricted marine to continental deposition in the triassic, the last pulse of the early cimmerian extensional phase in the earliest rhaetian caused a marine transgression across large parts of europe. very fine-grained deposits of rhaetian age, containing abundant lacustrine and marine fossils, are placed in the sleen formation. hettangian–pliensbachian or lowermost toarcian sediments, consisting of a uniform succession of dark grey or black silty claystones with abundant pyritised fossil remains, are called the aalburg formation. towards the london–brabant massif (the southern basin fringe during the early jurassic), an increasing number of thin limestone beds are intercalated in this unit. basin circulation became restricted during the toarcian, with anoxic bottom waters and deposition of a bituminous shaly claystone, called the posidonia formation, over large parts of northwest europe. it constitutes the most prominent oil source rock in the netherlands. basin circulation returned to normal during the late toarcian – bajocian, as indicated by the deposition of the werkendam formation, consisting of marine silty mudstones and greensands. aalenian – middle callovian (megasequence ii) this was a period of significant tectonic activity, which caused important structural differentiation (figs 2, 3). the main effect of the tectonic phase traditionally addressed in the netherlands as ‘mid-cimmerian’ was the uplift of the central north sea dome. the deformation front gradually shifted southwards with time, resulting in a considerable delay between the timing of deformation of the dome crest in the central north sea (mid-aalenian) and the southernmost dutch provinces (kimmeridgian). the amount of intra-jurassic truncation decreases away from the dome (underhill & partington 1993), and consequently is most severe within the area of this study in the dutch central graben, the northernmost province of the netherlands, where open marine deposition of the altena group ceased in the bajocian. the dutch part of the central graben remained nondepositional during the bathonian – early callovian. in the middle callovian, deposition gradually resumed, in a continental facies. the uplift event probably also affected the terschelling basin, the dutch lower saxony basin and the central netherlands basin. however, the evidence for the impact of this phase was removed by later, more severe truncation in the jurassic successions of these basins. the impact of the mid-aalenian central north sea uplift is negligible in the southern basins (broad fourteens basin, west netherlands basin, roer valley graben). werkendam formation deposition continued, with an important bajocian influx of marine sandstones along the southern basin margin. depositional facies changed to shallow marine, sandy carbonates and marls during the bathonian (brabant formation, ‘cornbrash facies’). at least three carbonate–marl cycles were deposited in the bathonian to oxfordian, which are at present only preserved as erosional remnants in the southern basins. in the dutch achterhoek (eastern onshore), on the south-western fringe of the lower saxony basin, a special development is found (herngreen et al. 1984). the sedimentary succession up to the middle bathonian shows strong parallels with successions of the roer valley graben and the german lower saxony basin proper (fig. 1). the whole area appears to have been a single depositional province during this period. at the transition to the late bathonian, however, a differentiation occurred. during the late bathonian – callovian, an open marine claystone facies was deposited in germany and the achterhoek (informally termed the klomps member, fig. 4). in contrast, deposition of shallow marine sandy carbonates and marls in the roer valley graben and the west netherlands basin persisted into the oxfordian. middle callovian – ryazanian (megasequence iii) upper jurassic – lower cretaceous deposits in northwest europe demonstrate a step-by-step overall transgression from north to south. periods of marine transgression alternated with phases of short-term progradation of, partly tectonically controlled, continental siliciclastics. the continuous shifting of marine and terrestrial realms in response to syndepositional tectonism and sea-level fluctuations is reflected by the recurrent intertonguing of marine and continental sediments. the predominantly marine scruff group (upper jurassic – ryazanian) and rijnland group (lower cretaceous) interfinger with the mainly continental schieland group (upper jurassic – barremian) and the paralic to restricted marine niedersachsen group (upper jurassic – ryazanian). differential movement of fault blocks was caused by a combination of oblique-slip effects in an overall extensional regime and halokinesis in areas with salts in the subsurface (wong et al. 1989). together with a high sed222 223 iment input, this resulted in complex sediment distribution patterns and continuously shifting depocentres. the cyclic alternation of marine and continental sediments indicates that sediment deposition was also strongly controlled by sea-level changes. middle callovian – oxfordian (stage iiia) in the middle–late callovian, predominantly continental sedimentation (schieland group) resumed along the axis of the northern dutch central graben (fig. 4). the basal alluvial plain deposits are referred to the lower graben formation. this unit displays huge thickness variations due to onlap onto syndepositional topography, and due to differential subsidence. the depositional area gradually extended into the southern dutch central graben in the course of the latest callovian, oxfordian and kimmeridgian. deposition in the latest callovian started with the marginal marine rifgronden member of the friese front formation. it indicates connections to open marine areas in the northern central graben (central north sea), or possible links with the marine realm in the southern and central dutch basins. the shift to deposition of the middle graben formation in the latest callovian – early oxfordian reflects an abrupt change to more fine-grained, lakeand swamp-dominated sedimentation. this shift was accompanied by a short-lived, marine incursion into the whole dutch central graben, which is correlated with the maximum flooding surface of sequence lza4.1 of haq et al. (1988). during the middle oxfordian, lacustrine conditions prevailed throughout the dutch central graben. marine incursions were scarce and restricted to the far north during the rest of the oxfordian. the oxfordian was a period of significant transgression and onlap. areas adjacent to the northern dutch central graben, such as the southern dutch central graben, terschelling basin and step graben were incorporated into the depositional area. simultaneously, the open marine realm started to expand southwards into the dutch central graben, first into block f03 (middle–late oxfordian, sequence lza-4.2 of haq et al. 1988). initially, a stacked prograding coastal-barrier sand complex (upper graben formation) developed, behind which a paralic delta plain formed, represented by the deposits of the puzzle hole formation (blocks f08–f14). north of the barrier complex, the kimmeridge clay formation represents the open marine environment. the coastal sand bodies of the upper graben formation in the area of block f03 drowned at the end of the oxfordian (sequence lza-4.4 of haq et al. 1988). by this time, kimmeridge clay deposition also invaded the step graben, onlapping the upper permian zechstein group. non-marine deposition of the schieland group had already commenced in the dutch central graben during the callovian, but deposition of the marine brabant formation (altena group, oisterwijk limestone member) persisted into the early–middle oxfordian in the southern netherlands (haanstra 1963; nam & rgd 1980). cessation of marine altena group deposition in the roer valley graben, the west netherlands basin, the broad fourteens basin and probably the central netherlands basin – lower saxony basin during the late oxfordian – earliest kimmeridgian was triggered by tectonic pulse i of the late cimmerian. in the roer valley graben and the west netherlands basin, the brabant formation is locally overlain unconformably by erosional remnants of late oxfordian – portlandian deposits in continental floodplain facies (schieland group, nieuwerkerk formation). early–late kimmeridgian (stage iiib) during the kimmeridgian and portlandian, the northern dutch central graben became a major depocentre, accumulating a thick succession of increasingly marine sediments. the area of deposition once more expanded significantly. deposition resumed in continental facies in the broad fourteens basin, the dutch lower saxony basin and the vlieland basin (fig. 4). the depositional style in the broad fourteens and vlieland basins remained continental (floodplain, lacustrine, with occasional sandy fluvial intercalations), with a few marine incursions. the vlieland basin was the site of volcanic activity in the middle–late jurassic, as the zuidwal volcanic dome formed (perrot & van der poel 1987; herngreen et al. 1991). depending on the time-scale used, volcanic activity (dated radiometrically at 155–143 ma) may have taken place somewhere between the callovian and the early ryazanian. in the course of the kimmeridgian, deposition of the paralic puzzle hole formation in the central dutch central graben gradually gave way to the open marine kimmeridge clay formation in the area of blocks f08–f11. thin marine sand bodies are found locally in the uppermost parts of the puzzle hole formation, suggesting the existence of a backstepping coastal-barrier system. however, much of the character of the transgression cannot be reconstructed due to subhercynian 224 and/or laramide erosion (late cretaceous – paleocene). to the south (blocks f15–f17), the paralic puzzle hole formation grades into deposits characterised by continental alluvial plain facies (delfland formation of herngreen & wong, 1989; now called friese front formation). in the southern dutch central graben, alluvial plain deposition replaced the predominantly lacustrine deposition around the end of the oxfordian. during the early kimmeridgian (lza-4.4 of haq et al. 1988), the depositional area in the southern dutch central graben expanded. seismic and palaeogeographic information suggest that the boundaries between the areas of deposition of the puzzle hole formation, the kimmeridge clay formation and the friese front formation were determined by faults. in the broad fourteens basin, widespread deposition commenced in the early kimmeridgian (lza-4.5 of haq et al. 1988), with the accumulation of sandy alluvial plain sediments referred to the aerdenhout member of the breeveertien formation (fig. 4). this member unconformably overlies deposits of the altena group or the upper germanic triassic. the progressive transgression observed in the central graben coincides with a shift from alluvial plain (aerdenhout member) to lacustrine and lagoonal deposition (fourteens claystone member) in the broad fourteens basin (associated with the maximum flooding surface of sequence lza-4.6 of haq et al. (1988). deposition of the basal weiteveen clastic member in the dutch lower saxony basin (= niedersachsen basin) seems to have started close to the end of the early kimmeridgian. the introduction of coarser siliciclastics in the dutch central graben (main friese front member, puzzle hole formation and upper graben formation), the broad fourteens basin (breeveertien formation, aerdenhout member) and the dutch lower saxony basin (weiteveen basal clastics member) coincided with the start of the late cimmerian phase (haanstra 1963; ’t hart 1969; ‘late kimmerian i pulse’ of rgd 1991b). the resulting uplift terminated the first depositional phase of the nieuwerkerk formation in the most rapidly subsiding areas of the roer valley graben and the west netherlands basin. late kimmeridgian – earliest portlandian (stage iiic) in the late kimmeridgian, the ongoing transgression led to the first marine influence on sedimentation in the southern dutch central graben and the terschelling basin. this is witnessed by the deposition of the marineinfluenced oyster ground member (friese front formation, fig. 4). two distinct transgressive phases are identified; in the early late kimmeridgian, the transgression reached block f18, while block l02 became transgressed by the latest kimmeridgian. these events are tentatively correlated with the transgressive systems tracts of sequences lza-4.7 and lzb-1.1 of haq et al. (1988). the latter flooding event is associated with onlap onto exposed triassic and permian rocks in the terschelling basin (oyster ground member in block f15) and the vlieland basin – central netherlands basin area (continental zurich formation). at the same time, tectonic tilting and associated halokinesis caused the depocentre of the dutch central graben to shift from the central–eastern axis (from block f03, extending southwards into blocks l03–f18) to the western graben margin (block f02–l05). the seismic cross-section of the graben system shows this westwards shift (fig. 6). during the late kimmeridgian – portlandian, siliciclastic deposition in the lower saxony basin was periodically replaced by accumulation of evaporites and carbonates (evaporitic and marl members of the weiteveen formation, fig. 4). these cycles may be correlatable with the alternation of coarser clastics and fines with minor evaporites found in the broad fourteens basin (breeveertien formation, several members). the lithofacies (carbonates, marls, evaporites, coals) of the zurich formation in the remnants of the central netherlands basin (‘voorthuizen subbasin’ of haanstra 1963; gouwzee trough of rgd 1993a) are similar to those in the niedersachsen group in the dutch lower saxony basin. in the west netherlands basin and the roer valley graben, lacustrine and alluvial plain deposition was restricted to those fault blocks undergoing strongest subsidence. a progressive depositional onlap is seen in the portlandian–ryazanian section. in each consecutive depositional sequence, higher basin-fringe fault blocks became part of the depositional area. very thick successions of proximal alluvial plain deposits can be found in places. in the portlandian and ryazanian, deposition resumed in the central netherlands basin. the depositional style is transitional between the mainly lacustrine and evaporitic facies of the lower saxony basin and the paralic and restricted marine facies of the central graben – vlieland basin. deposition in the southern province (west netherlands basin and the western roer valley graben) ceased due to uplift in the kimmeridgian (around the lower sequence boundary of lzb-1.1 of haq et al. 1988). non-deposition lasted until the latest portlandian – ryazanian. from then on, continental sediments were deposited; marine conditions did not reach this area until the late hauterivian – barremian. portlandian (stage iiid) during the early portlandian, the ongoing transgression resulted in deposition of the terschelling member of the friese front formation, reflecting coastal deposition along the southern fringe of the dutch central graben (blocks l09–l12, sequences lzb-1.2, -1.3 of haq et al. 1988). to the north, the friese front formation grades into the open marine scruff greensand formation in the southern dutch central graben. thick, sand-dominated successions of portlandian–ryazanian age were deposited here (blocks f15–f18, sequences lzb-1.3 to -1.5 of haq et al. 1988). equivalent, thinner sand tongues are found in the eastern terschelling basin, the vlieland basin and the northern dutch central graben (blocks f03–f05). during this period, the vlieland basin became divided into two subbasins, separated by the zuidwal volcanic dome (herngreen et al. 1991). during the early portlandian, marine conditions only prevailed in the northern subbasin. the southern subbasin was characterised by continental (lacustrine to lagoonal) deposition. the scruff greensand formation grades into the kimmeridge clay formation in the northern dutch central graben. the depocentre of the open marine kimmeridge clay formation, which prior to the portlandian was situated in this northern area, abruptly shifted to the southernmost central graben and the northern vlieland basin. in the southern b-quadrant, basin circulation stagnated during the portlandian. this resulted in deposition of the bituminous claystones of the clay deep member. euxinic marine conditions became more widespread in the northern dutch central graben during the ryazanian (sequence lzb-1.5 and particularly lzb-1.6 of haq et al. 1988). late portlandian – ryazanian (stage iiie) during the late portlandian (sequence lzb-1.5 of haq et al. 1988), marine conditions (scruff greensand formation) briefly reached the entire vlieland basin. in the southern dutch central graben, the marine basin became shallower, inducing the northwards progradation of shallow marine, spiculitic greensands (scruff spiculite member). even the more elevated areas (for example over salt domes) of the dutch lower saxony basin and central netherlands basin, which had thus far remained exposed, became inundated by the sea. in the latter basin, the depositional area expanded to the north-west. in the broad fourteens basin, this overall regressive tendency is reflected by the transition within the breeveertien formation from lacustrine and lagoonal coastal plain fines (fourteens claystone member and driehuis mottled claystone member) to widespread sandy alluvial plain deposits (bloemendaal member). in the dutch lower saxony basin, the late portlandian shoaling trend is demonstrated by the serpulite member of the weiteveen formation. this widespread carbonate deposit marks the culmination of clastic starvation in this area. deposition of evaporites and carbonates with subordinate siliciclastics (weiteveen formation) in the lower saxony basin was replaced by open water lacustrine deposition (coevorden formation) at the beginning of the ryazanian. this event is interpreted as indicative of a flooding phase that correlated with the transition from the sandy fluvial bloemendaal member to the lagoonal neomiodon claystone member (both of the breeveertien formation) in the broad fourteens basin. this period was also marked by widespread deposition of sediments referred to the nieuwerkerk formation in the roer valley graben and west netherlands basin; thick successions of locally coarse alluvial plain sediments were deposited on rapidly subsiding fault blocks along the axes of the basins. the depositional area continued to expand gradually. the basin margins were either covered by a thin, condensed succession (e.g. locally in the province of groningen), or remained exposed and non-depositional. late ryazanian (stage iiif) during the ryazanian (sequence lzb-1.6 of haq et al. 1988), the stagnant marine basin area in the northern dutch central graben expanded southwards into block f05. deposition of the clay deep member completely superseded scruff greensand formation deposition around the mid-ryazanian. this change in depositional style coincided with the first signs of tectonic pulse ii of the late cimmerian (rgd 1991a). this also caused local truncation of the scruff greensand formation and the friese front formation in the southern central graben (parts of blocks l02–05). initially, sedimentation of the scruff greensand formation resumed briefly (stortemelk member, correlated with the lowstand of 225 sequence lzb-1.6 of haq et al. 1988). subsequently, the deep marine basin expanded markedly southwards, depositing kimmeridge clay formation sediments (schill grund member) in the previously shallow marine to continental realm. this marine incursion also reached the vlieland basin, where the stortemelk member is found intercalated with lagoonal–lacustrine deposits of the zurich formation. in the broad fourteens basin, tectonic pulse ii of the late cimmerian is expressed as two minor unconformities (base and intra-neomiodon claystone member, breeveertien formation). in the dutch central graben, large-scale differential subsidence ended with tectonic pulse ii of the late cimmerian (mid-ryazanian and earliest valanginian). from then on (sequence lzb-2.1 of haq et al. 1988), a more uniform sedimentation pattern started, associated with the post-rift thermal sag phase. this is illustrated by the contrast between the highly variable thickness of the succession underlying the stortemelk member and the more uniform development of the post-uplift succession (clay deep member, stortemelk member and schill grund member). in the broad fourteens basin, the west netherlands basin and the roer valley graben, the highly differential subsidence patterns continued at least throughout the valanginian. subsequent history the expansion of the marine sedimentation area continued during the cretaceous, until eventually the london–brabant massif became flooded in the campanian–maastrichtian. the jurassic successions in the dutch subsurface were deformed by several later tectonic phases. the santonian–campanian (subhercynian) and early paleogene (laramide) inversion phases had the most severe impact. during these compressive events, the jurassic depocentres were inverted (van wijhe 1987). practically all jurassic sediments were removed along the inversion axes of these basins. at present, the occurrences of jurassic rocks are restricted to the basinal areas (fig. 3). subsequent tertiary subsidence in the netherlands was more or less evenly distributed. subsidence rates were highest in the northern dutch offshore, however, and tertiary (particularly neogene) sediment distribution patterns are dominated by large-scale progradation in this direction. petroleum geology several jurassic formations have economic significance in the netherlands, either as reservoirs or as oil source rocks. figures 1 and 4 show the stratigraphic positions of the units mentioned in this context below, and their equivalents in neighbouring countries. the toarcian posidonia formation is the most prominent oil and wet gas source rock in the dutch subsurface (bodenhausen & ott 1981), to which the majority of the oil reserves in the country can be attributed. additional oil sourcing potential can be attributed to certain lacustrine strata of the coevorden formation (ryazanian) in the lower saxony basin. this interval is also known to act as an oil source rock in adjacent parts of germany. the highly bituminous clay deep member (ryazanian) of the kimmeridge clay formation in the northern sector of the dutch central graben has oil-sourcing potential. however, the areal distribution and stratigraphic range of this deposit is much smaller than that of equivalent bituminous intervals in the kimmeridge clay formation (and equivalents) in the uk, danish and norwegian offshore, where it constitutes one of the major oil source rocks. coal occurrences in the lower graben formation (middle–upper callovian), the middle graben formation (oxfordian), the puzzle hole formation (mainly kimmeridgian) and the friese front formation (uppermost callovian – portlandian) may locally have sourced wet gas. however, in most areas, burial was insufficient to reach the gas window (wong et al. 1989). on the other hand, gas source rocks of late carboniferous age are more or less ubiquitous throughout the netherlands. the main problem for gas generated from these older rocks is to pass through the cover of permian salts and reach the jurassic. furthermore, the maximum burial depths of the carboniferous strata, for instance in the central graben, may have caused these rocks to become overmature. at present, oil and gas reserves have been discovered in the lower graben formation (middle–upper callovian), upper graben formation (uppermost oxfordian), scruff greensand formation (portlandian) and friese front formation (uppermost callovian – portlandian) in the central graben area. some sandstone members of the breeveertien formation (kimmeridgian– ryazanian) in the broad fourteens basin were found to be oil-bearing. in the west netherlands basin, the ryazanian and younger levels of the nieuwerkerk formation are prospective. the middle werkendam member (bajocian) and carbonate members of the 226 227 f 1 1 -0 3 2 .0 1 .0 twt sec 3 .0 en e a lt e n a g p p u zz le h o le f m . u p p e r g ra b e n f m p u zz le h o le f m l o w e r g ra b e n f m m id d le g ra b e n f m k im m e ri d ge c la y f m sc ru ff g re e n sa n d f m . c la y d e e p m b . l o w e r n o rt h s e a g p z e ch st e in sa lt f m z e ch st e in sa lt f m c h al k g p r ij n la n d g p u p p e r g e rm an ic t ri as g p l o w e r g e rm an ic t ri as g p p o si d o n ia s h al e f m b as e n o rt h se a g ro up s b as e c ha lk g ro up b as e v al an gi ni an b as e sc ru ff g re en sa nd f o rm at io n b as e k im m er id ge c la y fo rm at io n; o ys te r g ro un d m b b as e u pp er g ra be n fo rm at io n b as e m id dl e g ra be n fo rm at io n b as e lo w er g ra be n fo rm at io n b as e lo w er g er m an ic t ri as g ro up ( ba se l o w er b un ts an ds te in f o rm at io n) b as e pu zz le h o le f o rm at io n, f ri es e fr o nt f o rm at io n in tr at ri as si c le ve l i (n ea rba se k eu pe r fo rm at io n) in tr at ri as si c le ve l i i ( m us ch el ka lk e va po ri te m em be r) in tr at ri as si c le ve l i ii (n ea rba se m id dl e b un ts an ds te in s ub gr o up ) b as e/ to p po si do ni a sh al e fo rm at io n b as e a lt en a g ro up ( ba se s le en f o rm at io n) o pe n m ar in e cl ay st o ne ( v lie la nd c la ys to ne f o rm at io n) o pe n m ar in e & la go o na l c la ys to ne ( k im m er id ge c la y fo rm at io n, a lt en a g ro up ) eu xi ni c re st ri ct ed m ar in e cl ay st o ne s (c la y d ee p m b (k im m er id ge c la y fm ), p o si do ni a sh al e fm ) o pe n m ar in e ar gi lla ce o us s an ds to ne /g re en sa nd ( sc ru ff g re en sa nd f o rm at io n) sh al lo w m ar in e/ co as ta l s an ds to ne ( u pp er g ra be n fo rm at io n) c o al -r ic h co as ta l p la in ( pu zz le h o le f o rm at io n) fi ne -g ra in ed f lu vi al p la in , o ve rb an k do m in at ed ( m id dl e g ra be n fo rm at io n) sa nd y flu vi al p la in , c ha nn el d o m in at ed ( lo w er g ra be n fo rm at io n) r e fl e ct o rs d e p o si ti o n a l se tt in g /s e is m ic f a ci e s f 0 8 -0 2 f 0 9 -0 1 w sw en e f ig . 6. s ei sm ic c ro ss -s ec ti o n , ru n n in g w sw –e n e a cr o ss t h e d u tc h s ec to r o f th e c en tr al g ra b en ( f ig . 2) . t h e ju ra ss ic – l o w er c re ta ce o u s se ct io n h as b ee n c o lo u rco d ed a cc o rd in g to t h e m ai n d e p o si ti o n al f ac ie s. brabant formation (callovian–oxfordian) have locally been shown to be oil-bearing in the roer valley graben and the west netherlands basin. exploration of the jurassic in the netherlands has reached a mature stage. the acquisition of high-quality seismic and well data and the good biostratigraphic control obtained in recent years have resulted in a clear regional geological picture. these data also allow, for the first time, the application of sequence stratigraphy. integration of sequence stratigraphic concepts into the revision of dutch lithostratigraphy (van adrichem boogaert & kouwe 1994–1997) has resulted, in particular, in a far better understanding of the upper jurassic stratigraphy of the netherlands. acknowledgements the authors wish to thank the geological survey of the netherlands (rijks geologische dienst – rgd/nitg) for permission to publish the presented data. the authors are indebted to r. rijkers, a. hollen and f. rispens (all rgd) for providing information on the regional distribution and petroleum exploration successes in the dutch jurassic. h.a. van adrichem boogaert and m.c. geluk (rgd) gave valuable comments to the manuscript and its precursors. similarly, the manuscript has benefited significantly from earlier discussions with the various members of the working group on the upper jurassic – lower cretaceous stratigraphy for the new stratigraphic nomenclature of the netherlands. references bodenhausen, j.w.a. & ott, w.f. 1981: habitat of the rijswijk oil province, onshore, the netherlands. in: illing, l.v. & hobson, g.d. 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(eds): sea-level changes – an integrated approach. society of economic paleontologists and mineralogists special publication 42, 71–108. harland, w.b., armstrong, r.l., cox, a.v., craig, l.e., smith, a.g. & smith, d.g. 1990: a geologic time scale 1989, 263 pp. cambridge: cambridge university press. herngreen, g.f.w. & de boer, k.f. 1984: palynology of the ‘upper jurassic’ central graben, scruff and delfland groups in the dutch part of the north sea continental shelf. in: michelsen, o. & zeiss, a. 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(compiler) 1974: a proposed standard lithostratigraphic nomenclature for the southern north sea and an outline structural nomenclature for the whole of the (uk) north sea. institute of geological sciences report 74/8, 14 pp. london: her majesty’s stationery office. ’t hart, b.b. 1969: die oberjuraund unterkreide-sedimentation in den nördlichen und östlichen niederlanden. erdöl und kohle, erdgas, petrochemie 22, 253–261. underhill, j.r. & partington, m.a. 1993: jurassic thermal doming and deflation in the north sea: implications of the sequence stratigraphic evidence. in: parker, j.r. (ed.): petroleum geology of northwest europe: proceedings of the 4th conference, 337–345. london: geological society. van adrichem boogaert, h.a. & kouwe, w.f.p. (compilers) 1994–1997: stratigraphic nomenclature of the netherlands, revision and update by rgd and nogepa. mededelingen rijks geologische dienst 50, sections a–j (sections paginated independently). van wagoner, j.c., posamentier, h.w., mitchum, r.m., vail, p.r., sarg, j.f., loutit, t.s. & hardenbol, j. 1988: an overview of the fundamentals of sequence stratigraphy and key definitions. in: wilgus, c.k. et al. (eds): sea-level changes – an integrated approach. society of economic paleontologists and mineralogists special publication 42, 39–45. van wijhe, d.h. 1987: structural evolution of inverted basins in the dutch offshore. in: ziegler, p.a. (ed.): compressional intraplate deformations in the alpine foreland. tectonophysics 137, 171–219. wong, th.e., van doorn, th.h.m. & schroot, b.m. 1989: ‘late jurassic’ petroleum geology of the dutch north sea central graben. geologische rundschau 78, 319–336. ziegler, p.a. 1990: geological atlas of western and central europe, 2nd edition, 239 pp. amsterdam: elsevier for shell internationale petroleum maatschappij. 229 manuscript received 11 september 1995; revision accepted 17 january 1997. gsb kimmeridge clay fm cft cfr m. graben fm l. graben fm clay deep mb scruff greensand fm friese front fm puzzle hole fm cfo schill grund mbgss gsp gsakim. clay fm zurich fm fourteens claystone mb santpoort mb bloemendaal mb aerdenhout mb coevorden fm a b c e d f n ie de rs ac hs en g p sc hi el an d sc ru ff g ro up kn kn kn neomiodon mb r ya z. valang. k im . k im m er id gi an t it ho ni an po rt la nd ia n b er ri as . m al m t et hy s b o re al d o gg er li as α γ−ζ ζ ε7 ε6 ε5 δ2 δ1 α δ2 β1 β2-4 ζ ε2 δ1 γ3 β3 γ2 β2 γ1 β1 α3 α2 α1 ε1 γ ε1-4 oxford. callov. g lo ba l su bs ta ge s se qu en ce s af te r h aq e t al . (1 98 8) b at ho ni an b aj o ci an a al en ia n t o ar ci an si ne m ur ia n h et ta ng ia n pl ie ns ba ch ia n norian rhaetian 157.1 154.7 152.1 145.6 140.7 147.8 142.8 time (ma) after harland et al. (1990) stratigraphy 203.5 208.0 209.5 194.5 187.0 173.5 178.0 166.1 161.3 weiteveen fm breeveertien fm nieuwerkerk fm nieuwerkerk fm roer valley graben s n west netherlands basin central netherlands basin achterhoek lower saxony basin dutch central grabenbroad fourteens basin aalburg fm sleen fm posidonia shale fm werkendam fm ? ? ? lower werkendam claystone mb upper werkendam claystone mb brabant fm atbr1 atbrl atbr2 atbrm atbr3 atbro klomps mb atbru middle werkendam mb β sc hi el an d g ro up a lt en a g ro up rn u a b -3 u a b -4 lz a -1 lz a -2 lz a -3 lz a -4 lz b -1 uab-2 uab-1 uaa-4 lzb-2.1 sc hi el an d g ro up sc hi el an d g p cms u. graben fm driehuis mb depositional facies marl open marine clay (cretaceous) open marine clay (jurassic) bituminous marine clay/shale open marine argillaceous greensand shallow marine greensand coastal sand coal-rich coastal plain heterolithics sandy coastal/fluvial plain heterolithics fine-grained coastal plain and lacustrine heterolithics lagoonal claystones/siltstones lacustrine/highly restricted marine carbonates highly restricted marine salts highly restricted marine anhydrite/carbonates shallow marine sandy limestone abbreviated stratigraphic terms brabant formation atbro: oisterwijk limestone mb atbru: upper brabant marl mb atbr3: upper brabant limestone mb atbrm: middle brabant marl mb atbr2: middle brabant limestone mb atbrl: lower brabant marl mb atbr1: lower brabant limestone mb middle graben formation cms: middle graben sandstone mb friese front formation cfo: oyster ground claystone mb cft: terschelling sandstone mb cfr: rifgronden claystone mb weiteveen formation f: serpulite mb e: upper marl mb d: upper evaporite mb c: lower marl mb b: lower evaporite mb a: basal clastic mb scruff greensand formation gss: stortemelk mb gsp: scruff spiculite mb gsa: scruff argillaceous mb gsb: scruff basal sandstone mb kn: rijnland gp rn: upper germanic trias gp 1.6 1.5 1.4 1.3 1.2 1.1 4.7 4.6 4.5 4.4 4.2 4.1 3.2 3.1 2.4 2.3 2.2 2.1 1.1 4.6 4.5 4.4 4.3 4.2 4.1 3.4 3.3 3.2 3.1 4.3 fig. 4. litho-chronostratigraphic scheme of the rhaetian–ryazanian succession of the five main jurassic basin systems in the netherlands: (1) roer valley graben – west netherlands basin, (2) off-holland low – broad fourteens basin, (3) central netherlands basin, (4) ems low – lower saxony basin and (5) vlieland basin, terschelling basin and dutch central graben. abbreviated stage names are given in full in fig. 1; berrias., berriasian. compiled and modified from van adrichem boogaert & kouwe (1994–1997, sections f, g). lza-1 uab-4 uab-3 uab-2 u a b -1 u a a -41. 1 4. 6 4. 5 4. 4 4. 3 4. 2 3. 4 3. 3 3. 2 3. 1 2. 1 4. 1 4. 4 lza-3 lza-2 3. 2 3. 1 2. 3 2. 2 2. 1 2. 4 4. 1 4. 2 4. 3 4. 5 el m oxfordian callovian el m sequences (haq et al. 1988) lza-4lzb-1lzb-2 ryazanian valanginian 2. 3 kimm. kimmeridgian s.l. el tithonian portlandian berriasian 4. 6 4. 7 1. 1 1. 2 1. 3 1. 4 1. 5 1. 6 ‘e’e ‘l’l 2. 1 2. 2 el st ra ti gr ap hy 13 5 14 0 14 5 15 0 15 5 16 0 16 5 17 0 17 5 18 0 18 5 19 0 19 5 20 0 20 5 21 0 t im e (m a) doggermalm lias ζ ε δ 2 δ 1 α δ 2 β 2– 4 ζ ε 2 δ 1 γ 3 β 3 γ 2 β 2 γ 1 β 1 α 3 α 2 α 1ε 1γ ε 1– 4 bathonian bajocian aalenian toarcian sinemurian hettangianpliensbachian n o ri an triassicearly jurassicmiddle jurassiclate jurassiccretaceous r ha et ia n β 1 e l e l eml d ic ho to m it es un na m ed n w e ur o pe an st an da rd a m m o ni te z o na ti o n p o ly pt yc hi te s p ar at o lli a al bi d um st en o m ph al us ic en ii ru nc to ni la m pl ug hi pr ep lic o m ph al us pr im it iv us ‘o pp re ss us ’/a ng ui fo rm is ke rb er us o ku se ns is gl au co lit hu s al ba ni fit to ni ro tu nd a pa lla si o id es pe ct in at us hu d le st o ni w he at le ye ns is sc it ul us el eg an s au ti ss io d o re ns is eu d o xu s m ut ab ili s cy m o d o ce ba yl ei se rr at um /g lo se ns e te nu is er ra tu m d en si pl ic at um co rd at um /m ar ia e la m be rt i at hl et a co ro na tu m ja so n ca llo vi en se m ac ro ce ph al us d is cu s o rb is ho d so ni m o rr is i su bc o nt ra ct us pr o gr ac ili s te nu ip lic at us zi gz ag pa rk in so ni ga ra nt ia na ni o rt en se hu m ph ri es ia nu m pr o pi nq ua ns la ev iu sc ul a d is ci te s co nc av um br ad fo rd en si s m ur ch is o na e o pa lin um aa le ns is ps eu d o ra d io sa d is pa ns um th o ua rs en se va ri ab ili s bi fr o ns se rp en ti nu s te nu ic o st at um sp in at um d av o ei ib ex ja m es o ni ra ri co st at um se m ic o st at um bu ck la nd i an gu la ta lia si cu s pl an o rb is m ar sh i su es si m ac er o xy no tu m o bt us um tu rn er i m ar ga ri ta tu s ro se nk ra nt zi /r eg ul ar e ko ch i se le ct ed s po ro m o rp h da tu m s va ri o us t ril ob os po rit es s pp . c la vi fe ra t rip le x a eq ui tr ira di te s; p lic at el la c la ss op ol lis c la ss op ol lis c la ss op ol lis e ch in at us /h am m en ii pl ex us c c ic at ric os is po rit es pr ec ic at ric os is po rit es pr ec ic at ric os is po rit es s pp . c al lia sp or ite s se gm en ta tu s; l yc op od ia ci di te s ru gu la tu s; n eo ra is tr ic ki a tr un ca ta ; u va es po rit es a rg en te ae fo rm is ; c ly co po di um sp or ite s se m im ur is c al lia sp or ite s se gm en ta tu s c ha sm at os po rit es m aj or c irc ul in a m ey er ia na t ril ite s sp p. is ch yo sp or ite s va rie ga tu s; s ta pl in is po rit es (i nc l. c or on at is po rit es ) c r og al sk ai sp or ite s ci ca tr ic os us c al lia sp or ite s sp p. ; n eo ra is tr ic ki a tr un ca ta le pt ol ep id ite s sp p. ; s es tr os po rit es p se ud oa lv eo la tu s c h el io sp or ite s al tm ar ke ns is c on tig ni sp or ite s pr ob le m at ic us c er eb ro po lle ni te s sp p. o va lip ol lis p se ud oa la tu s c in gu liz on at es r ha et ic us ; c or nu tis po rit es s ee be rg en si s; d en so sp or ite s fis su s; l un at is po rit es r ha et ic us ; r ha et ip ol lis g er m an ic us ; s em ire tis po ris s pp .; t ria nc or ae sp or ite s re tic ul at us ; t su ga ep ol le ni te s ps eu do m as su la e; z eb ra sp or ite s la ev ig at us r ic ci is po rit es t ub er cu la tu s; z eb ra sp or ite s in te rs cr ip tu s n eo ra is tr ic ki a gr is th or pe ns is ; u va es po rit es ar ge nt ea ef or m is ; c d en so is po rit es ; se st ro sp or ite s ps eu do al ve ol at us r ai st ric ki sp or ite s br ev itr un ca tu s c c on ca vi ss im is po rit es ; c i m pa rd ec is po ra ; c t ril ob os po rit es ; k ra eu se lis po rit es s p. pa rv is ac ci te s ra di at us k ra eu se lis po rit es tu bb er ge ns is m . e xt en si va se le ct ed d in o fla ge lla te d at um s t . a pa te la e . p ha ro t . d av ey i b . r ad ic ul at um g . v irg ul a c . p an ne um ; g . d im or ph um g . m ut ab ili s; s. ju ra ss ic a c m ud er on gi a sp . a s. in rit ib ilu m a . d ic ty ot a; p . p an no su m p. p an no su m n . p el lu ci da ; s . c ry st al lin um l. s ca rb ur gh en si s li th od in ia ju ra ss ic a; c pa re od in ia p ro lo ng at a n an no ce ra to ps is s pi cu la ta ; n . g ra ci lis l. s ca rb ur gh en si s c r . a em ul a; w an ae a c . c on tin uu m c ar pa th od in iu m p re da e b ej ui a po ly go na lis n an no ce ra to ps is d ic ty am bo ni s; n . t ric er as ; w al lo di ni um c yl in dr ic um sc rin io ca ss is w eb er i lu eh nd ea s pi no sa li as id iu m v ar ia bi le d ap co di ni um p ris cu m r ha et og on ya ul ax s pp . pa rv oc ys ta s pp .; r eu tli ng ia s pp .; su sa di ni um s pp .; c ph al lo cy st a eu m ek es m ei ou ro go ny au la x va le ns ii r hy nc ho di ni op si s re ga lis ; v al va eo di ni um s pi no su m c te ni do di ni um c om ba zi i/o rn at um p le xu s st ep ha ne ly tr on ; s . f as c. /p en ic . c p. p an no su m e . l ur id um r g . j ur as si ca ; r o . p at ul um o . p at ul um c c rib ro pe rid in iu m s p. a /b ; e . p ol yp la co ph or um g on ya ul ac ys ta s p. a ; r . t hu la d . s pi no su m ; e . t or yn um ; k . p or os is pi nu m c p. ‘e op el lif er um ’ s en su r r i (1 98 7) a m m ov er te lla c el le ns is ( f) ; p ro to cy th er e ha nn ov er an a (o ); pr ot oc yt he re p se ud op ro pr ia ( o ) m an de ls ta m ia s ex ti (o ); c yt he ro pt er in a tr ie be li (o ); g al lia ec yt he rid ea t er es ( o ); p ar an ot ac yt he re s pe et on en si s (o ); sc hu le rid ea ju dd i ( o ) c yp rid ea c ar in at a (o ); c . g ra nu lo sa ( o ) g al lia ec yt he rid ea p os ts in ua ta ( o ); k lie an a di ct yo ta ( o ) fa ba ne lla a ns at a (o ); m an te lli an a pu rb ec ke ns is ( o ) pa ra no ta cy th er e el on ga ta ta ( o ); g al lia ec yt he rid ea c om pr es sa ( o ) g al lia ec yt he rid ea p ol ita ( o ); p ar al es le ya p er fo ra ta ( o ) g al lia ec yt he rid ea s pi no sa ( o ); m an de ls ta m ia t um id a (o ); sa ra ce na ria o xf or di an a (f ); a al en ie lla in or na ta ( o ) e oc yt he rid ea e us ar ca ( o ); g al lia ec yt he rid ea v ol ga en si s (o ); m ac ro de nt in a ru gu la ta ( o ); m ac ro de nt in a tr an si en s (o ); e xo ph th al m oc yt he re g ig an te a (o ); k lie an a ca ly pt ro id es ( o ) se le ct ed f o ra m in ife r/ o st ra co d da tu m s m an de ls ta m ia m ac ul at a (o ); e pi st om in a nu da ( f) m an de ls ta m ia r ec til in ea ( o ) v er no ni el la s eq ua na ( o ) lo ph oc yt he re m ul tic os ta ta ( o ) n op hr ec yt he re c ru ci at a ox fo rd ia na ( o ) ps eu do pe ris so cy th er id ea p ar ah ie ro gl yp hi ca ( o ); e uc yt he ru ra c os ta ei rr eg ul ar is ( o ) g al lia ec yt he rid ea p un ct at a (o ); m ac ro de nt in a ci ca tr ic os a (o ); e rip le ur a el ea no ra e (o ); g al lia ec yt he rid ea d is si m ili s (o ) sc hu le rid ea t rie be li (o ); g al lia ec yt he rid ea w ol bu rg i ( o ) e uc yt he ru ra h or rid a (o ) lo ph oc yt he re f le xi co st a (o ); n op hr ec yt he re c ru ci at a cr uc ia ta ( o ); e pi st om in a m os qu en si s (f ) lo ph oc yt he re in te rr up ta in te rr up ta ( o ) lo ph oc yt he re s ca br a sc ab ra ( o ); l . b ip ar tit a (o ); ps eu do hu ts on ia t ub er os a (o ) pr og on oc yt he re s til la ( o ); g ly pt oc yt he re g ue m be lia na ( o ) pr og on oc yt he re p ol on ic a (o ); l op ho cy th er e pl en a (o ) pl eu ro cy th er e co nn ex a (o ); l en tic ul in a qu en st ed ti (f ) g ly pt oc yt he re a ur ic ul a (o ) a m m op al m ul a in fr aj ur en si s (f ); f uh rb er gi el la g ig an te a (o ); pl eu ro cy th er e im pa r (o ); g ly pt oc yt he re t ub er od en tin a (o ) pl eu ro cy th er e re gu la ris ( o ) fu er be rg ie lla p rim iti va ( o ) g ly pt oc yt he re s ci tu la ( o ); f uh rb er gi el la h or rid a ho rr id a (o ); lj ub im ov el la p iri fo rm is ( o ) g ly pt oc yt he re p ol ita ( o ) pr ae sc hu le rid ea d ec or at a (o ); c am pt oc yt he re p us ill a (o ) c am pt oc yt he re m ed ia ( o ) c am pt oc yt he re f ov eo la ta ( o ) o to cy th er e ca llo sa ( o ); a ph el oc yt he re k uh ni ( o ); c am pt oc yt he re p ra ec ox ( o ); l en tic ul in a fo ve ol at a (f ) k in ke lin el la p er si ca ( o ) li ng ul in a te ne ra g ro up ( f) ; m ar gi nu lin a pr im a gr o up ( f) fr on di cu la ria t er qu em i ( f) pl eu rif er a ha rp a (o ); g am m ac yt he re u bi qu ita ( o ); o gm oc on ch el la b is pi no sa ( o ); g ra m an ni cy th er e ba ch i ( o ); o gm oc on ch a am al th ei ( o ); b ai rd ia c lio ( o ); p ol yc op e ci nc in na ta ( o ) k lin gl er el la v ar ia bi lis ( o ) lo ph od en tin a pu m ic os a (o ); e kt yp ho cy th er e be tz i ( o ); e kt yp ho cy th er e tr ie be li (o ); l op ho de nt in a la cu no sa ( o ) o gm oc on ch a ha ge no w i ( o ); n an ac yt he re e le ga ns ( o ) o gm oc on ch el la e lli ps oi de a (o ); c yt he re llo id ea c irc um sc rip ta ( o ); c yt he re llo id ea p ul ch el la ( o ); k lin gl er el la t ra ns lu ce ns ( o ) r ho m bo cy th er e pe na rt he ns is ( o ) c yt he re llo id ea b ui se ns is ( o ); l in gu lin a te ne ra c ol le no ti (f ); lu tk ev ic hi ne lla s p. ( o ) o gm oc on ch a co nt ra ct ul a (o ); t ra ch yc yt he re t ub ul os a (o ); sa ra ce na ria s ub la ev is ( f) ; b ol iv in a lia si ca li as ic a (f ) w ic he re lla s em io ra s em io ra ( o ); g ra m an ne lla a po st ol es cu i ( o ) m ic ro pn eu m at oc yt he re s ub co nc en tr ic a (o ); o lig oc yt he re is f ul lo ni ca ( o ) pl eu ro cy th er e ric ht er i ( o ) to p ac m e ba se a cm e co ns is te nt ra re fo ra m in ife r o st ra co d sp o ro m o rp h ap pe ar an ce s an d di sa pp ea ra nc es a re a pp ro xi m at e to p o cc ur re nc e ba se o cc ur re nc e (f ) (o ) c r f ig . 5 . a s e le ct io n o f d ia g n o st ic b io m ar k e r h o ri zo n s fo r th e r h ae ti an – v al an g in ia n , co rr e la te d w it h t h e n o rt h w e st e u ro p e an s ta n d ar d a m m o n it e z o n at io n . t h e h aq e t a l. ( 1 9 8 8 ) cy cl e c h ar t h as b e e n r e ca li b ra te d t o f it t h e t im e -s ca le o f h ar la n d e t a l. (1 9 8 9 ). k im m e ri d g ia n s .l . e q u al s k im m e ri d g ia n s en su a n gl ic o . t h e t e rm s li as , d o g g e r an d m al m a n d t h e ir c la ss ic r e g io n al s u b d iv is io n s as d e p ic te d i n t h e v ar io u s fi g u re s ar e u se d i n o rd e r to s h o w t h e s tr at ig ra p h ic p o si ti o n o f th e s e d im e n ts f o u n d i n t h e n e th e rl an d s in a e u ro p e an c o n te x t o f w e ll -e st ab li sh e d z o n ati o n s. c o m p il e d a n d m o d if ie d f ro m v an a d ri ch e m b o o g ae rt & k o u w e ( 1 9 9 4 – 1 9 9 7 , se ct io n s f, g ). geological survey of denmark and greenland bulletin 11, 87-99 87 zircon geochronology from the kangaatsiaq– qasigiannguit region, the northern part of the 1.9–1.8 ga nagssugtoqidian orogen, west greenland kristine thrane and james n. connelly the kangaatsiaq–qasigiannguit region in the northern part of the palaeoproterozoic nagssugtoqidian orogen of west greenland consists of poly-deformed orthogneisses and minor occurrences of interleaved, discontinuous supracrustal belts. laser ablation icp-ms 207pb/206pb analyses of detrital zircons from four metasedimentary rocks (supplemented by ion probe analysis of one sample) and igneous zircons from six granitoid rocks cutting metasedimentary units indicate that the supracrustal rocks in the kangaatsiaq–qasigiannguit (christianshåb) region are predominantly archaean in age. four occurrences of metasedimentary rocks are clearly archaean, two have equivocal ages, and only one metasedimentary unit, from within the naternaq (lersletten) supracrustal belt, is demonstrably palaeoproterozoic and readily defines a large fold complex of this age at naternaq. the 2.9–2.8 ga ages of detrital archaean grains are compatible with derivation from the local basement orthogneisses within the nagssugtoqidian orogen. the detrital age patterns are similar to those of metasediments within the central nagssugtoqidian orogen but distinct from age patterns in metasediments of the rinkian belt to the north, where there is an additional component of pre-2.9 ga zircons. synkinematic intrusive granitoid rocks constrain the ages of some archaean deformation at 2748 ± 19 ma and some palaeoproterozoic deformation at 1837 ± 12 ma. keywords: nagssugtoqidian orogen, deformation, la-icp-ms, zircon, metasediment ______________________________________________________________________________________________________________________________________________________________________________________________________ k.t., geological institute, university of copenhagen, øster voldgade 10, dk-1350 copenhagen k, denmark. e-mail: kthrane@geol.ku.dk j.n.c., department of geological science, university of texas at austin, austin, tx 78712, usa. the kangaatsiaq–qasigiannguit area that is the focus of this paper (fig. 1) forms a large part of the northern nagssugtoqidian orogen, which is interpreted as the southern part of a major collisional orogenic system that crops out in central and northern west greenland and adjacent parts of eastern canada (connelly et al. 2006). the northern nagssugtoqidian orogen, which was re-investigated in 2001–2003 by the geological survey of denmark and greenland (geus) in co-operation with external partners, is underlain by poly-deformed, variably reworked grey archaean orthogneiss interleaved with dismembered archaean and palaeoproterozoic supracrustal rocks of volcanic and sedimentary origin. only few significant time marker horizons (such as distinct suites of mafic dykes or one or more groups of characteristic supracrustal rocks with known ages) are present. the primary objectives of this geochronological study were therefore to determine the extent of palaeoproterozoic metasedimentary rocks and attempt to directly date different phases of deformation and metamorphism. a number of lithological, structural and metamorphic features, especially in the kangaatsiaq–aasiaat area (fig. 1), © geus, 2006. geological survey of denmark and greenland bulletin 11, 87–99. available at: www.geus.dk/publications/bull 88 provide some immediate constraints on the archaean and palaeoproterozoic geological evolution of the northern nagssugtoqidian orogen, and are outlined here as an introduction to the geochronological study. the study area may be divided into two different tracts based on metamorphism and structural style (piazolo et al. 2004; mazur et al. 2006, this volume). the tract south-west and southeast of kangaatsiaq is metamorphosed at granulite facies grade and is characterised by a general wsw–ene-trending structural grain with large, moderately to steeply plunging fold structures and undeformed to weakly deformed, synkinematic granitic neosome (van gool et al. 2002; garde 2004). several e–w-trending mafic dykes occur south of kangaatsiaq around 68°n. they are undeformed and discordant to the main structures and lithological boundaries, but variably metamorphosed (glassley & sørensen 1980; árting 2004). these dykes are presumed to be of palaeoproterozoic age and perhaps related to pre-nagssugtoqidian rifting (árting 2004), and if so would constrain the deformation and granulite facies metamorphism south of kangaatsiaq to be archaean in age, whereas the thermal event recorded by the dykes themselves would be palaeoproterozoic. the remainder of the study area, to the north and east of kangaatsiaq, is at amphibolite grade (e.g. hollis et al. 2006, this volume), and does not display any signs of retrogression from granulite facies except within a c. 10 km thick transition zone adjacent to the granulite facies terrain. these northern and eastern areas generally possess a much more intense planar and linear tectonic fabric than in the south, commonly including a strong subhorizontal extension lineation that also penetrates the late granitic neosome. furthermore, a structural discordance occurs in the naternaq area (fig. 1) between wnw–ese-trending amphibolite to the west and the structurally overlying, ne–sw-trending naternaq supracrustal belt in the east, suggesting that the respective structures of the two supracrustal units are unrelated to each other and of different age (mazur et al. 2006, this volume). in addition, the northern and eastern areas also host occasional mafic dykes on islands north-east of aasiaat and on the southern coast of sydostbugten (fig. 1). although these dykes are still largely coherent and unmigmatised, they are intensely deformed, almost concordant with their host rocks, and tectonically thinned to about 1–2 m thick. both the granitic neosome, the naternaq supracrustal rocks, and the deformed dykes provide relative age constraints on the intense deformation in the northern and eastern parts of the study area. if it is again assumed that the deformed dykes in the north are palaeoproterozoic, it would follow 69° 54° 68° inland ice palaeogene basalt quaternary deposits metasedimentary rocks palaeoproterozoic (naternaq supracrustal belt) arfersiorfik quartz diorite amphibolite archaean variably reworked. may include palaeoproterozoic supracrustal components granodioritic and granitic gneiss orthogneiss metasedimentary rocks amphibolite qasigiannguit aasiaat kangaatsiaqkangaatsiaq ka ng er su ne q saqqarputataneq naternaq/ lersletten sydostbugten 20 km amitsoq amitsoq amitsoq kangaatsiaq 5151°°51° 480041 483631 448392 448394 480054 470515 463129 463257 448004 464435 500 km fig. 1. simplified geological map of the kangaatsiaq–qasigiannguit region, with sample locations. 89 448004 metasediment ne of kangaatsiaq 1 22419 0.21046 2909 7.7 2 30428 0.20444 2862 4.9 3 27946 0.20011 2827 5.9 4 41739 0.20405 2859 4.8 5 66864 0.20548 2870 5.8 6 52963 0.20846 2894 4.2 7 70422 0.18216 2673 3.9 8 46147 0.20058 2831 5.2 9 73807 0.20449 2862 3.7 10 41046 0.20919 2899 5.9 11 75396 0.20183 2841 6.5 12 84403 0.20242 2846 4.2 13 27932 0.20390 2858 7.5 14 102678 0.20107 2835 6.0 15 129026 0.18972 2740 6.9 16 46526 0.20716 2883 5.5 17 71802 0.20579 2873 6.3 18 659551 0.20033 2829 4.9 19 165828 0.19242 2763 6.1 20 73874 0.19895 2818 5.4 21 20371 0.18508 2699 5.5 22 21982 0.17386 2595 5.3 23 33164 0.21021 2907 6.4 24 86486 0.18406 2690 5.1 25 99148 0.20434 2861 4.4 26 54554 0.20049 2830 5.6 27 52435 0.17947 2648 3.8 28 45325 0.20018 2828 4.3 29 75391 0.18983 2741 3.0 30 77047 0.20775 2888 4.7 31 32181 0.19856 2814 3.1 32 50218 0.19811 2811 3.3 33 28491 0.20148 2838 4.3 34 21801 0.19768 2807 4.6 35 22466 0.20144 2838 5.9 36 48990 0.20013 2827 3.3 37 26535 0.20445 2862 5.8 38 114112 0.18364 2686 2.1 39 41973 0.20083 2833 3.4 40 57549 0.20210 2843 2.6 41 26869 0.25312 3204 2.7 42 49986 0.19811 2811 3.0 43 20567 0.19924 2820 4.6 44 5467 0.19417 2778 9.2 45 29042 0.20106 2835 4.2 46 9255 0.18565 2704 6.7 47 18597 0.20277 2849 4.3 48 112700 0.17900 2644 2.3 49 84858 0.19285 2767 2.8 50 14867 0.17617 2617 8.2 51 24908 0.19765 2807 3.7 52 11178 0.19419 2778 5.5 53 91255 0.17807 2635 4.3 54 28338 0.20395 2858 4.7 55 24855 0.18937 2737 4.8 56 7761 0.18757 2721 9.0 57 12436 0.19563 2790 6.5 58 12571 0.19849 2814 5.4 448392 granite, kangersuneq 1 318831 0.19069 2748 3.5 2 361175 0.18986 2741 2.7 3 406129 0.19945 2822 3.3 4 163666 0.18800 2725 3.6 5 205935 0.19380 2775 3.1 6 227282 0.19148 2755 3.0 7 123658 0.18830 2727 3.1 8 294942 0.18738 2719 5.1 9 407109 0.19415 2778 5.0 10 481882 0.19342 2771 5.1 11 212302 0.18706 2716 4.7 12 407464 0.19766 2807 3.0 13 491512 0.19950 2822 4.2 14 94032 0.18905 2734 3.0 44 19762 0.19659 2798 6.5 45 36375 0.11197 1832 9.0 46 17548 0.18024 2655 11.7 47 9064 0.19962 2823 10.9 48 11530 0.19199 2759 7.8 49 64234 0.11111 1818 10.3 50 7566 0.16671 2525 11.0 51 38371 0.10619 1735 9.1 52 15464 0.18496 2698 9.1 53 15534 0.14855 2329 9.3 54 27618 0.11461 1874 8.4 55 15853 0.19890 2817 9.4 56 10902 0.18316 2682 11.0 57 8905 0.20952 2902 9.4 58 6493 0.18680 2714 10.5 59 16248 0.19267 2765 8.7 60 43736 0.14480 2285 6.4 61 48133 0.11266 1843 12.3 62 52656 0.12037 1962 10.7 63 88558 0.11566 1890 7.2 64 65717 0.10988 1797 8.8 65 14964 0.15276 2377 8.5 66 59777 0.11635 1901 7.3 67 23849 0.16781 2536 8.6 68 16825 0.19548 2789 12.3 69 17260 0.14321 2266 8.8 70 28538 0.19178 2757 10.3 71 65355 0.11192 1831 8.4 72 58939 0.12654 2050 9.6 73 69509 0.11151 1824 6.8 74 49893 0.13319 2140 8.6 75 76541 0.11448 1872 8.1 76 67611 0.11351 1856 8.0 77 58817 0.10691 1747 8.9 78 69641 0.11468 1875 11.3 79 57943 0.11116 1818 4.7 463129 synkinematic granite, saqqarput 1 2283739 0.18759 2721 3.0 2 1266859 0.19890 2817 3.6 3 344375 0.18904 2734 4.1 4 531257 0.18883 2732 5.5 5 565174 0.19441 2780 4.6 6 247679 0.18844 2729 4.9 7 460352 0.20656 2879 3.8 8 1058356 0.19510 2786 3.2 9 405853 0.18296 2680 6.8 10 554081 0.17660 2621 3.0 11 1363965 0.20876 2896 4.0 12 935603 0.19609 2794 2.7 13 605520 0.18625 2709 2.6 14 516471 0.17880 2642 5.1 15 822166 0.18954 2738 5.5 16 655511 0.20436 2861 4.0 17 755390 0.19587 2792 5.0 18 127005 0.18594 2707 5.9 19 422927 0.19261 2765 4.8 20 653950 0.19183 2758 4.0 21 1135912 0.19679 2800 2.9 22 1096015 0.19497 2785 2.4 23 653314 0.19170 2757 2.6 24 228993 0.20892 2897 7.4 25 221510 0.21878 2972 9.2 26 346159 0.20045 2830 6.6 27 37048 0.16944 2552 11.9 28 97269 0.17974 2650 10.8 29 85210 0.18521 2700 8.7 30 172975 0.18213 2672 8.2 31 171017 0.17446 2601 9.0 32 165639 0.18002 2653 5.5 33 133709 0.18851 2729 7.8 34 182742 0.18315 2682 5.2 35 125199 0.18194 2671 7.0 36 169034 0.19244 2763 7.5 37 85182 0.16778 2536 9.4 15 173984 0.18392 2689 4.9 16 109933 0.18320 2682 5.7 17 50994 0.19030 2745 4.6 18 13465 0.18864 2730 6.2 19 21101 0.17697 2625 6.4 20 99478 0.18431 2692 5.8 21 108982 0.18687 2715 3.9 22 33255 0.18969 2739 5.7 23 192965 0.18985 2741 6.8 24 280376 0.18859 2730 6.1 25 287725 0.18761 2721 5.1 26 101087 0.18975 2740 4.7 27 85412 0.18695 2716 4.3 28 125421 0.18639 2711 6.2 29 45496 0.18854 2730 5.7 30 75470 0.18108 2663 4.9 31 40021 0.18483 2697 4.9 32 48564 0.19087 2750 5.6 33 101631 0.18754 2721 3.2 34 117730 0.18292 2679 2.5 35 49211 0.18807 2725 3.8 36 112930 0.18847 2729 2.9 37 202637 0.18826 2727 2.2 38 102831 0.18893 2733 2.2 39 55266 0.19174 2757 2.8 40 45349 0.18639 2711 4.5 41 104416 0.18742 2720 3.3 42 188642 0.18481 2696 2.2 43 97849 0.18797 2724 2.6 44 145946 0.17859 2640 4.0 448394 metasediment, kangersuneq 1 695411 0.16006 2456 3.6 2 52863 0.20417 2860 5.3 3 443404 0.11180 1829 3.8 4 1104248 0.11717 1913 4.4 5 579803 0.11532 1885 4.7 6 231966 0.12351 2008 4.9 7 362937 0.10979 1796 3.1 8 303451 0.11334 1854 3.9 9 277637 0.11090 1814 3.1 10 380962 0.12251 1993 3.9 11 115636 0.16115 2468 6.0 12 461330 0.11598 1895 3.5 13 493717 0.19532 2787 3.7 14 207687 0.17408 2597 5.3 15 393460 0.11112 1818 2.7 16 242631 0.10929 1788 4.9 17 132013 0.19838 2813 4.9 18 178574 0.10859 1776 6.1 19 303683 0.10774 1762 4.1 20 241139 0.15569 2409 7.4 21 51484 0.12627 2047 5.5 22 53211 0.12080 1968 7.7 23 53531 0.11660 1905 6.9 24 23896 0.19593 2793 6.2 25 79706 0.11458 1873 6.4 26 89308 0.11277 1845 6.3 27 63147 0.11176 1828 8.6 28 12586 0.19431 2779 6.5 29 100961 0.13800 2202 7.0 30 12592 0.16853 2543 9.7 31 57066 0.11124 1820 8.5 32 51764 0.11438 1870 10.1 33 218430 0.11295 1847 7.4 34 78169 0.10868 1777 9.7 35 96773 0.11345 1855 8.4 36 143102 0.11037 1806 6.7 37 33237 0.13986 2225 6.4 38 92186 0.10819 1769 9.7 39 80332 0.12802 2071 8.3 40 35510 0.19386 2775 8.0 41 11684 0.18283 2679 7.4 42 21389 0.19620 2795 8.2 43 14702 0.19528 2787 9.7 table 1. zircon la-icp-ms 207pb-206pb data spot 206pb (cps) 207pb/206pb age (ma) 2σ %spot 206pb (cps) 207pb/206pb age (ma) 2σ % spot 206pb (cps) 207pb/206pb age (ma) 2σ % 90 table 1 (continued) spot 206pb (cps) 207pb/206pb age (ma) 2σ %spot 206pb (cps) 207pb/206pb age (ma) 2σ % spot 206pb (cps) 207pb/206pb age (ma) 2σ % 38 101924 0.18113 2663 7.6 39 178145 0.20233 2845 8.9 40 35771 0.18557 2703 8.3 41 23866 0.19033 2745 10.0 42 78620 0.22740 3034 11.3 43 88660 0.20740 2885 7.8 44 264622 0.18784 2723 6.5 45 219347 0.19029 2745 5.2 46 215885 0.18648 2711 9.4 47 117234 0.17897 2643 9.0 48 29425 0.18849 2729 8.9 49 59458 0.18317 2682 10.0 50 44706 0.19343 2772 11.5 51 47511 0.20920 2899 14.7 52 52220 0.18199 2671 10.6 53 58597 0.17855 2639 12.7 54 47047 0.18403 2690 6.8 55 85100 0.19408 2777 8.0 56 150838 0.18512 2699 9.1 57 42220 0.18152 2667 8.4 58 182300 0.17444 2601 6.3 59 181857 0.19158 2756 5.8 60 656182 0.18446 2693 3.8 61 1625878 0.19433 2779 4.0 62 1033362 0.19004 2742 7.1 463257 metasediment, amitsoq 1 94060 0.20316 2852 4 2 126332 0.19611 2795 4 3 245874 0.21538 2946 4 4 154787 0.20172 2840 4 5 68216 0.19982 2825 4 6 428099 0.18536 2701 4 7 100464 0.18737 2719 4 8 106081 0.19619 2794 4 9 178863 0.20711 2883 4 10 72018 0.19715 2808 4 11 102336 0.18203 2671 4 12 218440 0.21010 2907 4 13 144435 0.20135 2837 4 14 73200 0.20617 2875 4 15 103837 0.17190 2575 4 16 100257 0.15132 2361 4 17 120574 0.20468 2864 4 18 88636 0.20786 2889 4 19 129707 0.20434 2861 4 20 133092 0.21288 2928 4 21 176443 0.20885 2897 4 22 48385 0.19377 2774 5.2 23 61486 0.19210 2760 8.2 24 60275 0.22028 2983 3.6 25 44550 0.20247 2846 6.8 26 30952 0.20191 2842 5.9 27 7392 0.18113 2663 8.0 28 20571 0.19351 2772 8.6 29 15357 0.19909 2819 6.7 30 31747 0.20691 2881 7.0 31 22596 0.20038 2829 8.1 32 35613 0.20326 2853 7.7 33 15204 0.20568 2872 10.5 34 24804 0.19424 2778 8.2 35 17027 0.19728 2804 5.8 36 21866 0.19494 2784 8.4 37 13148 0.20815 2891 9.3 38 27502 0.20821 2892 6.1 39 26648 0.20452 2863 8.3 40 27263 0.18701 2716 10.7 41 46499 0.14869 2331 6.7 42 36471 0.20245 2846 6.7 43 64587 0.20102 2834 8.7 44 31986 0.20332 2853 8.9 45 46174 0.21292 2928 8.9 46 61284 0.20775 2888 6.6 47 41436 0.20439 2862 6.8 48 72510 0.20430 2861 5.1 49 67124 0.20347 2854 7.9 50 37221 0.19866 2815 7.0 14 162431 0.11214 1834 4.2 15 42424 0.11157 1825 5.5 16 109374 0.11367 1859 4.3 17 52552 0.11218 1835 6.4 18 67018 0.11372 1860 5.2 19 38574 0.11173 1828 5.3 20 184531 0.11162 1826 2.5 21 420598 0.11279 1845 2.5 22 675700 0.11206 1833 1.7 480041 quartz diorite, qasigiannguit 1 130744 0.19864 2815 5.2 2 127784 0.19639 2796 4.7 3 30286 0.19684 2800 4.6 4 28769 0.20120 2836 4.7 5 41484 0.19738 2805 4.7 6 19837 0.20222 2844 7.0 7 35270 0.19516 2786 5.5 8 48190 0.20117 2836 5.6 9 35231 0.19155 2756 5.0 10 93023 0.19849 2814 4.8 11 36116 0.19465 2782 4.8 12 82370 0.19490 2784 10.4 13 58322 0.19959 2823 7.2 14 61328 0.19932 2821 6.7 15 58943 0.19951 2822 11.6 16 25024 0.19642 2797 3.7 17 61436 0.19260 2765 5.7 18 56976 0.19778 2808 7.2 19 43379 0.19673 2799 5.3 20 68466 0.19216 2761 7.7 480054 tonalite intruding mafic complex 1 8174 0.20380 2857 10.3 2 10419 0.19353 2772 7.4 3 18592 0.20474 2864 5.5 4 213185 0.15919 2447 5.9 5 17238 0.19681 2800 5.3 6 11204 0.20444 2862 6.4 7 17603 0.20266 2848 7.2 8 36568 0.20791 2889 9.5 9 42107 0.20580 2873 6.5 10 30492 0.19888 2817 7.1 11 25591 0.20251 2847 7.2 12 14106 0.20374 2856 6.4 13 18218 0.20025 2828 4.4 14 20117 0.19869 2816 5.8 15 42704 0.20836 2893 6.8 16 29583 0.20336 2853 7.6 17 23900 0.19738 2805 9.0 483631 granite intruding metasediment 1 259347 0.19195 2759 3.1 2 155094 0.19256 2764 2.4 3 94380 0.19393 2776 3.3 4 33706 0.18539 2702 3.7 5 57040 0.18930 2736 3.2 6 42007 0.19204 2760 3.5 7 71104 0.19592 2793 3.8 8 33803 0.19616 2794 4.1 9 79316 0.19110 2752 3.9 10 13550 0.18486 2697 7.3 11 57313 0.19407 2777 4.3 12 56128 0.19155 2756 3.1 13 56620 0.19591 2792 3.4 14 101430 0.19250 2764 3.6 15 41779 0.19211 2760 3.4 16 367814 0.19593 2793 2.0 17 118779 0.18771 2722 2.7 18 26473 0.16345 2492 13.9 19 45218 0.19626 2795 3.6 20 76399 0.19586 2792 3.6 21 24409 0.18865 2730 4.7 464435 metasediment, naternaq 1 620630 0.12031 1961 4 2 184109 0.14293 2261 4 3 177844 0.12013 1959 4 4 508546 0.12356 2019 4 5 521502 0.11208 1833 4 6 560514 0.11545 1887 4 7 455565 0.10976 1795 4 8 294092 0.11916 1944 4 9 407244 0.12342 2006 4 10 217026 0.11556 1889 4 11 240050 0.11948 1948 4 12 285058 0.12258 1995 4 13 651523 0.11831 1938 4 14 367681 0.12552 2036 4 15 337595 0.12582 2041 4 16 465635 0.11732 1917 4 17 321964 0.12267 1995 4 18 1150971 0.11774 1922 4 19 266990 0.12383 2013 4 20 374761 0.12502 2030 4 21 297903 0.12321 2002 4 22 87395 0.11806 1927 4.3 23 88706 0.12335 2005 6.5 24 53359 0.13734 2194 6.5 25 72472 0.11727 1915 5.8 26 16174 0.13058 2106 4.4 27 125924 0.11860 1935 4.6 28 81398 0.11940 1947 6.3 29 93208 0.11402 1864 6.3 30 131504 0.12001 1956 4.2 31 107212 0.12410 2016 6.6 32 66177 0.12687 2055 7.7 33 72338 0.11608 1897 4.1 34 163168 0.11450 1872 4.4 35 92298 0.12172 1982 5.5 36 220614 0.12305 2001 4.3 37 112247 0.12249 1993 5.7 38 76097 0.11662 1905 4.7 39 76847 0.11907 1942 4.1 40 39338 0.11918 1944 6.8 41 51130 0.11856 1935 6.6 42 86970 0.12690 2055 5.0 43 128237 0.11865 1936 5.3 44 47126 0.12236 1991 5.5 45 84328 0.11894 1940 5.6 46 307611 0.12127 1975 5.0 47 115975 0.11797 1926 6.9 48 149629 0.12005 1957 7.5 49 385671 0.11759 1920 7.7 50 454534 0.12076 1967 6.8 51 245715 0.11875 1937 7.4 52 320479 0.12160 1980 6.4 53 1098422 0.10860 1776 7.8 54 578352 0.12047 1963 4.1 55 186864 0.11804 1927 7.0 56 79299 0.11614 1898 5.5 57 255968 0.10900 1783 3.3 58 707747 0.11876 1938 7.4 59 97872 0.12173 1982 6.5 60 109798 0.11649 1903 5.4 61 489175 0.12003 1957 4.0 470515 pegmatite ne of kangaatsiaq 1 149998 0.11231 1837 3.3 2 114249 0.11111 1818 2.3 3 128681 0.11066 1810 2.5 4 249115 0.11405 1865 2.5 5 174468 0.11307 1849 2.2 6 188664 0.11253 1841 2.7 7 118304 0.11223 1836 3.0 8 69708 0.11414 1866 4.3 9 107108 0.11379 1861 3.5 10 57749 0.11019 1803 5.2 11 255076 0.11091 1814 2.7 12 112190 0.11350 1856 4.7 13 145495 0.11459 1873 3.2 91 that the northern and eastern parts of the study area are strongly reworked by nagssugtoqidian deformation and amphibolite facies metamorphism. geochronological targets and methods both archaean and palaeoproterozoic supracrustal sequences are known to exist within the nagssugtoqidian orogen (marker et al. 1999; nutman et al. 1999). depositional ages of such supracrustal belts may be constrained by the ages of detrital zircons in their sedimentary components, since the youngest grains define their maximum age of deposition; conversely, the age of a magmatic rock that has intruded the supracrustal sequence may serve to define a lower depositional age limit. ideally, both metasediment and cross-cutting magmatic rocks from the same outcrop should be analysed to best constrain the timing of deposition. however, cross-cutting intrusive rocks of appropriate age (i.e. other than late palaeoproterozoic pegmatites) were not generally present. the direct dating of archaean or palaeoproterozoic deformation by dating e.g. synkinematic granitoids requires the rather scarce occurrence of an intrusive rock that unequivocally both cuts and is affected by a single fabric. ten samples from the kangaatsiaq–qasigiannguit area, mainly provided by members of the geus mapping groups in 2001–2002, have been analysed by quadrupole laser ablation inductively coupled mass spectrometry (la-icp-ms) at the university of texas at austin (zircon pb-pb data, table 1); additional ion probe u-pb zircon data from one metasedimentary rock were obtained at the nordsim laboratory, naturhistoriska riksmuseet, stockholm (table 2). analytical details are given in the appendix. the samples were collected from seven different, dismembered metasedimentary sequences (four samples of metasediment and four samples of cross-cutting granitoid rocks), and from intrusive granite and orthogneiss that constrain the timing of deformation (two samples). all ages of rocks presented in this manuscript have been calculated using isoplot/ex (ludwig 1999) and are reported with 2-sigma uncertainties. the main advantage of using the la-icp-ms technique for zircon geochronology is that each analysis only lasts about two minutes, whereas the analytical time on an ion microprobe is typically around 15–20 minutes. this becomes an important factor when analysing detrital rocks, where analysis of a large number of detrital grains is essential to achieve good statistics. the major limitation of the la-icp-ms technique employed is that u-pb ratios could not be measured, and only 207pb/206pb ages are obtained. a direct indication of concordance therefore is not available, and all the ages obtained should be interpreted conservatively to represent minimum ages of crystallisation or metamorphism. furthermore, common pb corrections cannot be carried out due to interference in the plasma of 204hg from the carrier gases. a test of the la-icp-ms instrument used in this study was carried out by connelly et al. (2006), who analysed zircons from the itilli diorite, disko bugt, west greenland using both la-icpms and id-tims methods and found that the 207pb/206pb age of 3019 ± 23 ma obtained with the laser instrument compared well with its id-tims age of 3030 +8/–5 ma. 1 404 161 167 0.40 0.37 0.1160 0.36 5.390 1.81 0.3370 1.77 –1.4 2 384 170 170 0.44 0.02 0.1162 0.33 5.727 1.80 0.3575 1.77 4.4 3 235 121 101 0.51 1.34 0.1159 0.75 5.338 1.93 0.3341 1.78 –2.2 4 411 178 173 0.43 0.24 0.1170 0.33 5.483 1.81 0.3398 1.77 –1.5 5 489 195 208 0.40 0.24 0.1158 0.32 5.534 1.80 0.3466 1.77 1.6 6 360 123 149 0.34 0.02 0.1174 0.33 5.511 1.80 0.3406 1.77 –1.6 7 416 163 176 0.39 0.04 0.1160 0.31 5.537 1.80 0.3463 1.77 1.3 8 413 178 178 0.43 0.03 0.1169 0.31 5.629 1.80 0.3494 1.77 1.4 9 653 281 239 0.43 0.70 0.1137 0.40 4.743 1.82 0.3025 1.77 –9.5 10 237 88 99 0.37 0.04 0.1163 0.39 5.500 1.81 0.3429 1.77 0.0 11 239 108 101 0.45 0.05 0.1174 0.39 5.521 1.81 0.3410 1.77 –1.6 12 448 224 194 0.50 0.03 0.1170 0.39 5.539 1.81 0.3434 1.77 –0.5 13 2192 1713 975 0.78 0.15 0.1165 0.17 5.337 1.78 0.3323 1.77 –3.3 1898 6 1935 16 1970 30 1894 13 1875 17 1858 29 1911 6 1898 16 1886 29 1892 6 1906 16 1918 29 1916 6 1902 16 1890 29 1895 6 1906 16 1917 29 1909 6 1921 16 1932 30 1860 7 1775 15 1704 27 1901 7 1901 16 1900 29 1896 7 1883 16 1872 29 1918 7 1904 16 1891 29 1911 7 1907 16 1903 29 1903 3 1875 15 1849 2 table 2. zircon ion probe u-th-pb data from sample 464435, naternaq spot u th pb th/u f 206 % 207pb σ % 207pb σ % 206pb σ % disc. % # ppm ppm ppm measured 206pb 235u 238u (conv.) 207pb σ 207pb σ 206pb σ 206pb 235u 238u ages (ma) errors on ratios and ages are quoted at 1σ level. f 206 %: the fraction of common 206pb, estimated from the measured 204pb. disc. % (conv.): degree of discordance of the zircon analysis (at the centre of the error ellipse). 92 fig. 2. zircon age data from the kangaatsiaq–qasigiannguit region. a, c, d, g, j, k: weighted average plots of la-icp-ms 207pb/206pb age data of igneous rocks. b, e, h, i: probability density plots of la-icp-ms 207pb/206pb age data of metasediments. f: ion probe u-pb age data (concordia plot), sample 464435. intercepts at 1904 ± 8 and 452 ± 290 ma mswd = 1.9 1740 1780 1820 1860 1900 1980 2020 0.29 0.31 0.33 0.35 0.37 464435 metasediment, naternaq n = 13 464435 metasediment, naternaq n = 61 0 2 4 6 8 10 12 14 16 fr eq ue nc y fe 207pb/206pb age (ma) 20 6 p b/ 23 8 u 207pb/235u 4.64.2 5.0 5.4 5.8 6.21700 2100 2500 2900 3300 0 2 4 6 8 10 12 1700 2100 2500 2900 3300 fr eq ue nc y 448394 metasediment, kangersuneq n = 79 b 207pb/206pb age (ma) 2400 2600 2800 3000 3200 mean age = 2801 ± 34 ma mswd = 0.094 a 20 7 p b/ 20 6 p b ag e (m a) 480041 quartz diorite, qasigiannguit n = 20 2600 2800 3000 3200 480054 tonalite intruding mafic complex n = 16 mean age = 2839 ± 46 ma mswd = 0.117 2500 2600 2700 2800 2900 3000 mean age = 2723 ± 15 ma mswd = 0.33 dc 20 7 p b/ 20 6 p b ag e (m a) 20 7 p b/ 20 6 p b ag e (m a) 448392 granite, kangersuneq n = 41 93 geochronological age constraints of metasedimentary belts the study area contains numerous, dismembered, discontinuous belts of metasedimentary rocks that may be either archaean or palaeoproterozoic in age. while the main focus of this work was to constrain their timing of deposition, provenance information gained through the detrital zircons permits regional correlation of these metasedimentary belts. the analysed samples are presented in tables 1–2 and fig. 2 and discussed below from north to south. sample 480041, quartz diorite intruding metasedimentary and metavolcanic rocks at qasigiannguit sample 480041 of a homogeneous, grey, medium-grained quartz diorite was collected 3 km east of qasigiannguit at 68°48.83′n, 51°08.05′w (fig. 1). the rock consists of plagioclase, quartz, hornblende and biotite and has a strong linear fabric. the quartz diorite forms a 3–4 km long elongate body exposed on the top of the ridge facing qasigiannguit. its contact relationships are generally equivocal due to deformation, but at the south-western margin the contact appears to be intrusive into a metasedimentary-metavolcanic sequence. the zircons from this sample are clear and stubby. twenty grains were analysed, which yield consistent 207pb/ 206pb ratios corresponding to a weighted mean age of 2801 ± 34 ma (mswd = 0.094, fig. 2a). the age is interpreted as the crystallisation age of the quartz diorite, implying that the supracrustal sequence it cuts must also be archaean. samples 448394, metasediment and 448392, intruding granite on the south coast of kangersuneq sample 448394 (68°46.24′n, 50°52.16′w) from a pelitic metasedimentary rock and sample 448392 (68°46.20′n, 50°51.55′w) of a granite that cuts the metasedimentary belt, were collected c. 200 m apart on the south coast of kangersuneq (fig. 1). after the analytical results were obtained, the locality was revisited in 2003 and the previously reported field relations confirmed (jeroen van gool, personal communication 2003). the zircons from the metasediment are brownish, elongate, 100–200 µm long, and in many cases cracked and showing clear signs of dissolution. the least altered and, presumably, least disturbed zircons were chosen for anal1700 2100 2500 2900 3300 fr eq ue nc y 463257 metasediment, amitsoq n = 50 i 207pb/206pb age (ma) 0 2 4 6 8 10 12 14 483631 granite intruding metasediment n = 21 2200 2400 2600 2800 3000 mean age = 2763 ± 20 ma mswd = 0.47 g 20 7 p b/ 20 6 p b ag e (m a) 463129 synkinematic granite, saqqarput n = 62 20 7 p b/ 20 6 p b ag e (m a) mean age = 2748 ± 19 ma mswd = 1.14 j 2300 2500 2700 2900 3100 3300 207pb/206pb age (ma) 1700 2100 2500 2900 3300 fr eq ue nc y 448004 metasediment ne of kangaatsiaq n = 58 h 0 2 4 6 8 10 12 14 470515 pegmatite ne of kangaatsiaq n = 22 mean age = 1837 ± 12 ma mswd = 0.av44 k 20 7 p b/ 20 6 p b ag e (m a) 1720 1760 1800 1840 1880 1920 1960 94 yses. in several cases it was possible to distinguish broad rims containing more u than the cores, and in such cases both core and rim were analysed. seventy-nine spots were analysed and yield an age spectrum with a large peak at 1850 ma and a smaller one at 2800 ma (fig. 2b). a range of intermediate ages (2500–2100 ma) between the two peaks are also present (see below). the archaean peak comprises only analyses from cores, whereas the 1850 ma peak consists of analyses from both cores and rims. the zircons from the granite are typically brown, and larger than those in the metasediment. in size they range from 100–350 µm and occur both as slender and somewhat stubby crystals. core–rim zonation is observed in the majority of the zircons. of 44 grains analysed from the granite, 41 yielded a consistent pattern of 207pb/206pb ratios corresponding to an average age of 2723 ± 15 ma (mswd = 0.33) (fig. 2c); both cores and rims were analysed in several grains without observing any age variations. the remaining three grains yield ages from 2822 to 2807 ma and are most likely inherited. due to the homogeneity of the zircon population it is highly unlikely that the zircons are detrital grains inherited from the metasediment. they are also unlikely to have been inherited from the orthogneisses adjacent to the metasediment, as these do not generally contain such young zircons. therefore, the age of 2723 ± 15 ma is interpreted as the emplacement age of the granite, and the metasediment must also be of archaean age. the 1850 ma peak for the zircons in the metasediment is therefore interpreted to date nagssugtoqidian metamorphism, and the 2500–2100 ma ages most likely represent archaean zircons that have suffered pb-loss; alternatively the latter analyses might represent accidental mixtures of cores and rims. sample 480054, tonalite intruding mafic complex c. 25 km south-east of kangersuneq sample 480054, a biotite-hornblende tonalite, was collected from a relatively undeformed tonalitic body c. 2 km2 in size at 68°35.53′n, 50°30.28′w within a large mafic supracrustal complex near the inland ice about 25 km south-east of kangersuneq (fig. 1). the tonalite is light grey in colour, mediumto coarse-grained, homogeneous, and has a weak linear fabric. it is feldspar-phyric with phenocrysts up to 2 cm in diameter. near the contacts with the surrounding mafic rocks the tonalite contains xenoliths of the mafic supracrustal rocks, and its intrusive nature is unequivocal. dykes of tonalite, 50 cm to 2 m wide, extend from the main tonalite body into rocks of the surrounding large mafic complex. the tonalite sample yielded a population of large, euhedral, mostly prismatic, clear to yellow zircons. seventeen spots on zircon grains were analysed, and sixteen of them generated a consistent spectrum of 207pb/206pb ratios corresponding to an average age of 2839 ± 46 ma (mswd = 0.117) (fig. 2d). the consistent 207pb/206pb ratios indicate that little or no pb-loss has occurred. the age result is therefore interpreted to closely reflect the crystallisation age of the tonalite, and the mafic complex intruded by the tonalite must consequently also be archaean. sample 464435, metasedimentary rock from the naternaq supracrustal belt naternaq (lersletten) is an extensive quaternary outwash plain with scattered outcrops of precambrian basement gneisses and supracrustal rocks (østergaard et al. 2002). a sample of very fine-grained mica schist was collected from the extensive naternaq supracrustal belt at 68°24.10′n, 51°56.70′w (fig. 1). the zircons are elongate, 50–150 µm long, and vary in colour from clear to slightly brown. all 61 analyses carried out yield palaeoproterozoic 207pb/206pb ages ranging from 2261 to 1776 ma, with the main peak of 207pb/206pb ages around 1950 ma (fig. 2e). while it is possible that some of the younger grains may be metamorphic, we interpret the majority of the grains to be detrital because of the igneous appearance of the zircons and because they are older than any metamorphic event so far described in the nagssugtoqidian orogen (e.g. connelly et al. 2000, earliest metamorphism at c. 1870 ma). furthermore, it seems unlikely that a zircon population from a metasedimentary rock would only comprise metamorphic grains and not contain a single detrital grain. consequently this requires a palaeoproterozoic deposition age for the metasedimentary unit at naternaq. in order to confirm the obtained 207pb/206pb la-icpms ages, zircons from this sample were also analysed on the cameca ims 1270 ion microprobe at the nordsim laboratory, swedish museum of natural history, stockholm. the thirteen ion probe analyses yield a cluster of ages on the concordia diagram of fig. 2f (table 2), with an upper intercept isochron age of 1904 ± 8 ma (mswd = 1.9). the ion probe age is thus slightly younger than the c. 1950 ma peak obtained by la-icp-ms, but the two data sets overlap within the large analytical error of the latter method, and the apparent older laicp-ms age could be due to common pb for which we were unable to correct. in conclusion, the ion probe data clearly demonstrate that the zircons are older than any metamorphic ages hitherto obtained from the nagssug95 toqidian orogen. the most likely interpretation is that the sediment at naternaq was derived from the magmatic arc that formed in the central part of the orogen between 1920 and 1870 ma (kalsbeek et al. 1987; kalsbeek & nutman 1996; whitehouse et al. 1998; connelly et al. 2000). the new age data from the naternaq supracrustal belt have important consequences for the structural interpretation of the naternaq area, documenting the existence of large palaeoproterozoic folds. sample 483631, granite vein intruding metasediment on strike with the naternaq supracrustal sequence a sample (483631) of an 8 cm wide vein of muscovitebiotite granite vein was collected east of naternaq at 68°31.04′n, 51°17.87′w (fig. 1). the granite vein is deformed but clearly intrudes mica schist on strike with the eastern part of the naternaq supracrustal belt. most of the zircons in sample 483631 are long, prismatic grains with a distinct core-rim zonation and range from clear to brownish in colour. twenty-two analyses were carried out, mostly on cores, but also on a few rims. all except one analysis yielded consistent 207pb/206pb ratios corresponding to an average age of 2763 ± 20 ma (mswd = 0.47, fig. 2g). one core analysis yielded a 207pb/206pb age of 2467 ± 158 ma, which may be due to pb-loss. the analyses demonstrate that the granite is archaean. the regional basement does not generally contain orthogneisses with such young ages and, therefore, limits the possibility that the zircons in the granite were inherited. it follows that the supracrustal rocks east of naternaq on strike with the naternaq supracrustal belt must also be of archaean age. sample 448004, metasedimentary belt near kangaatsiaq sample 448004 of a quartz-rich metasedimentary rock was collected north-east of kangaatsiaq at 68°21.15′n, 53°13.18′w (fig. 1). the zircons vary from elongate to stubby but all have been rounded during transport. they are clear and between 50 to 200 µm in length. a weak igneous zonation is present in the majority of the grains. fifty-eight spots were analysed, and both core and rim were analysed in several grains. the age population ranges from 2909 to 2595 ma, with a single grain yielding an age of 3200 ma (fig. 2h). a peak is present around 2850 ma, which is a common age for polyphase orthogneisses within the nagssugtoqidian orogen (kalsbeek et al. 1987; kalsbeek & nutman 1996; whitehouse et al. 1998; connelly & mengel 2000; hollis et al. 2006, this volume). the scatter of younger ages from 2800 to 2595 ma most likely results from variable degrees of pb loss. we cannot with certainty assign an age of deposition to this sediment, as the data are compatible with both archaean and palaeoproterozoic sedimentation. sample 463257, quartz-rich metasedimentary sequence at amitsoq sample 463257 of a mediumto fine-grained, quartz-rich metasedimentary rock with abundant small garnets was collected at the head of the fjord amitsoq at 68°05.78′n, 52°30.99′w (fig. 1). it is part of an extensive metasedimentary sequence, which is significantly more quartz-rich than all other metasedimentary rocks reported from the kangaatsiaq map area, although similar rocks have been observed in the central nagssugtoqidian orogen (jeroen van gool, personal communication 2003). the zircons are clear, 50–250 µm in length and vary from elongate to stubby, and have been rounded during transport. most zircons show clear igneous zonation, and some contain a high-u metamorphic rim. this rim was unfortunately too thin to analyse with the la-icp-ms. all except two of the 50 analysed grains yield archaean ages, with two exceptions interpreted to have suffered pbloss. the zircons show very little age variation, with a major peak of 207pb/206pb ages at around 2850 ma (fig. 2i). this age is comparable to that of the surrounding regional orthogneisses, and indicates that the detritus may be locally derived. however, it is only possible to conclude that the sediment was deposited after 2850 ma. dating of deformation using synkinematic granitic rocks sample 463129, synkinematic granite vein at saqqarput a sample of synkinematic granite (463129) was collected at saqqarput at 68°09.22′n, 52°42.65′w (fig. 1). the granite occurs as fineto medium-grained, subconcordant veins in the orthogneiss. sixty-two analyses yielded 207pb/ 206pb ratios corresponding to an average 207pb/206pb age of 2748 ± 19 ma (mswd = 1.14; fig. 2j). this is interpreted to be the crystallisation age of the granite since, as in sample 483631 described above, it is unlikely that zircons 96 of this age are inherited. some of the observed deformation in the host basement orthogneisses must, therefore, also be archaean in age. sample 470515, pegmatite north-east of kangaatsiaq a sample of pegmatite (470515) was collected north-east of kangaatsiaq at 68°20.23′n, 59°00.17′w (fig. 1). the pegmatite forms a 020° trending vertical sheet cutting orthogneiss. the pegmatite is a member of a conjugate set of pegmatites within the kangaatsiaq map area that indicate late, regional n–s orientated compression (ian alsop, personal communication 2002), and itself contains evidence of ductile sinistral shear along its margins; the regional foliation is deflected into sinistral shear fabrics, indicating that the pegmatite emplacement took place later than the foliation formation in the gneisses, but while the host rock was still hot enough to behave in a ductile manner. the sample contains large, brownish, prismatic zircons that vary from slender to short and stubby in shape. twenty-two spots were analysed on thirteen grains. both rims and cores were analysed on several grains, but no age variation was documented between the two. all analyses yield the same result within uncertainties; the average 207pb/ 206pb ratio corresponds to an age of 1837 ± 12 ma (mswd = 0.44) (fig. 2k). this is interpreted to be the emplacement age of the pegmatite, and is considered to date the late nagssugtoqidian n–s compression. discussion and conclusions the zircon ages obtained from this study show that metasedimentary rocks in the kangaatsiaq–qasigiannguit region are predominately archaean in age. the best age constraints come from the four archaean granitoid rocks that cut four different supracrustal belts. only one metasediment was analysed from these belts and yields an archaean detrital peak of c. 2800 ma and a palaeoproterozoic peak of c. 1850 ma. the palaeoproterozoic peak is attributed to the growth of metamorphic zircon during nagssugtoqidian metamorphism. similarly, the occurrences of ages between 2800–1850 ma are attributed to pb-loss from detrital grains and/or mixed analysis of detrital and metamorphic zircon. two of the three remaining metasedimentary rocks yield only archaean detrital ages with peaks between 2800 and 2900 ma, which are similar to the ages of the basement orthogneisses in the nagssugtoqidian orogen (kalsbeek et al. 1987; kalsbeek & nutman 1996; whitehouse et al. 1998; connelly & mengel 2000) and may indicate that the sedimentary sequences were derived from local sources. while it is tempting to conclude that these metasediments might also themselves be of archaean age, the lack of cross-cutting granites from these locations only permits the conclusion that they must be younger than 2850 ma. thus, the sediments could have been deposited either in the archaean at around 2850–2750 ma (i.e., before the regional 2.75 ga metamorphism documented within the nagssugtoqidian orogen), or during the palaeoproterozoic (most likely before the formation of the arfersiorfik–sisimiut arc; kalsbeek et al. 1987; kalsbeek & nutman 1996; whitehouse et al. 1998; connelly et al. 2000). the remaining sample of metasediment (464435), collected from the naternaq supracrustal belt, is the only metasediment in this study which is interpreted to be of palaeoproterozoic age. similar rocks which crop out south of sydostbugten to the north-east have previously been interpreted as along-strike equivalents of the naternaq supracrustal belt, although the intervening area is partly concealed by quaternary deposits (fig. 1). however, the discordant archaean granitic vein (483631) that cuts the metasedimentary rocks south of sydostbugten requires that the two belts contain rocks of different age. it is interesting to note that all the archaean detrital ages obtained match the ages between 2850 and 2800 ma of the archaean basement gneisses in the central nagssugtoqidian orogen. this distinguishes the metasedimentary rocks of the study area from metasedimentary rocks in the rinkian belt to the north, which include detrital zircons that are as old as 3600 ma (thrane et al. 2003). the predominance of archaean metasedimentary rocks unfortunately precludes them from being useful marker horizons to partition archaean and palaeoproterozoic deformation. nevertheless, the 2748 ± 19 ma synkinematic granite (463129) from saqqarput south-east of kangaatsiaq dates large fold structures in the northern nagssugtoqidian basement at around this age, which overlaps with the previously defined age of archaean deformation and metamorphism in the central part of the orogen (e.g. connelly & mengel 2000). the new age data place several constraints on the timing and style of palaeoproterozoic metamorphism and deformation in the region. the palaeoproterozoic sediment at naternaq (sample 464435) was probably metamorphosed and deformed shortly after its deposition, in line with the significant c. 1850 ma metamorphic peak in the archaean sediment from kangersuneq (sample 448394). the metamorphic zircon age from this sample 97 is not very precise, and tims analyses would be necessary to obtain an exact age of the metamorphism. however, it correlates with previous estimates for the timing of deformation and metamorphism both north and south of the study area (kalsbeek et al. 1987; kalsbeek & nutman 1996; whitehouse et al. 1998; connelly et al. 2000; thrane et al. 2003; connelly et al. 2006). furthermore, a late phase of n–s-directed shortening is dated at 1837 ± 12 ma by a synkinematic pegmatite (470515). the age of this pegmatite may correlate with the 1821 ma d2 deformation event defined in the central nagssugtoqidian orogen by connelly et al. (2000), and with 1821–1823 ma deformation east of ilulissat in the north (connelly et al. 2006). acknowledgements funding by the carlsberg foundation (thrane) and the national science foundation (grant ear-0337594 to connelly) is gratefully acknowledged. we thank ian alsop (university of st. andrews), adam a. garde and jeroen van gool (geus) for providing samples. we also thank john lansdown (the university of texas at austin) for assisting in collecting the la-icp-ms data, and julie a. hollis and adam a. garde (geus) for re-analysing sample 464435 zircons on the ion microprobe. allen p. nutman and åke johansson are thanked for their constructive comments, and adam a. garde and a.k. higgins are thanked for help with the geological introduction. references árting, u.e. 2004: a petrological study of basic dykes and sills of assumed palaeoproterozoic age in central western greenland, 122 pp., two appendices. unpublished m.sc. thesis, university of copenhagen, denmark. connelly, j.n. & mengel, f.c. 2000: evolution of archean components in the nagssugtoqidian orogen, west greenland. geological society of america bulletin 112, 747–763. connelly, j.n., van gool, j.a.m. & mengel, f.c. 2000: temporal evolution of a deeply eroded orogen: the nagssugtoqidian orogen, west greenland. canadian journal of earth sciences 37, 1121–1142. connelly, j.n., thrane, k., krawiec, a.w. & garde, a.a. 2006: linking the palaeoproterozoic nagssugtoqidian and rinkian orogens through the disko bugt region of west greenland. journal of the geological society (london) 163, 319–335. garde, a.a. 2004: geological map of greenland, 1:100 000, kangaatsiaq 68 v.1 syd. copenhagen: geological survey of denmark and greenland. glassley, w.e. & sørensen, k. 1980: constant ps-t amphibolite to granulite facies transition in agto (west greenland) metadolerites: implications and applications. journal of petrology 21, 69–105. hollis, j.a., keiding, m., stensgaard, b.m., van gool, j.a.m. & garde, a.a. 2006: evolution of neoarchaean supracrustal belts at the northern margin of the north atlantic craton, west greenland. in: garde, a.a. & kalsbeek, f. (eds): precambrian crustal evolution and cretaceous–palaeogene faulting in west greenland. geological survey of denmark and greenland bulletin 11, 9–31 (this volume). kalsbeek, f. & nutman, a.p. 1996: anatomy of the early proterozoic nagssugtoqidian orogen, west greenland, explored by reconnaissance shrimp u-pb dating. geology 24, 515–518. kalsbeek, f., pidgeon, r.t. & taylor, p.n. 1987: nagssugtoqidian mobile belt of west greenland: a cryptic 1850 ma suture between two archaean continents – chemical and isotopic evidence. earth and planetary science letters 85, 365–385. ludwig, k.r. 1999: isoplot/ex version 2.00 – a geochronological toolkit for microsoft excel. berkeley geochronology center, special publication 2. marker, m., whitehouse, m., scott, d., stecher, o., bridgwater, d. & van gool, j.a.m. 1999: deposition, provenance and tectonic setting for metasediments in the palaeoproterozoic nagssugtoqidian orogen, west greenland: a key for understanding crustal collision. abstracts eug 10, strasbourg, france. mazur, s., piazolo, s. & alsop, g.i. 2006: structural analysis of the northern nagssugtoqidian orogen, west greenland: an example of complex tectonic patterns in reworked high-grade metamorphic terrains. in: garde, a.a. & kalsbeek, f. (eds): precambrian crustal evolution and cretaceous–palaeogene faulting in west greenland. geological survey of denmark and greenland bulletin 11, 163– 178 (this volume). nutman, a.p., kalsbeek, f., marker, m., van gool, j.a.m. & bridgwater, d. 1999: u-pb zircon ages of kangâmiut dykes and detrital zircons in metasediments in the palaeoproterozoic nagssugtoqidian orogen (west greenland): clues to the pre-collisional history of the orogen. precambrian research 93, 87–104. østergaard, c., garde, a.a., nygaard, j., blomsterberg, j., nielsen, b.m., stendal, h. & thomas, c.w. 2002: the precambrian supracrustal rocks in the naternaq (lersletten) and ikamiut areas, central west greenland. geology of greenland survey bulletin 191, 24– 32. piazolo, s., alsop, g.i., van gool, j. & nielsen, b.m. 2004: using gis to unravel high strain patterns in high grade terranes: a case study of indentor tectonics from west greenland. in: alsop, g.i. et al. (eds): flow processes in faults and shear zones. geological society special publication (london) 224, 63–78. schuhmacher, m., de chambost, e., mckeegan, k.d., harrison, t.m. & migeon, h. 1994: in situ dating of zircon with the cameca ims 1270. in: benninghoven, a. (ed.): secondary ion mass spectrometry sims ix, 919–922. chichester: wiley. thrane, k., connelly, j.n., garde, a.a., grocott, j. & krawiec, a. 2003: linking the palaeoproterozoic rinkian and nagssugtoqidian belts of central w. greenland: implications of new u-pb and pb-pb ages. european union of geosciences meeting, geophysical research abstracts, cd 5, abstract # 09275. 98 van gool, j.a.m. et al. 2002: precambrian geology of the northern nagssugtoqidian orogen: mapping in the kangaatsiaq area. geology of greenland survey bulletin 191, 13–23. whitehouse, m.j., claesson, s., sunde, t. & vestin, j. 1997: ion microprobe u-pb zircon geochronology and correlation of archaean gneisses from the lewisian complex of gruinard, north-western scotland. geochimica et cosmochimica acta 61, 4429–4438. whitehouse, m.j., kalsbeek, f. & nutman, a.p. 1998: crustal growth and crustal recycling in the nagssugtoqidian orogen of west green__________________________________________________________________________________________________________________________________________________________________________________ manuscript received 15 october 2004; revision accepted 9 september 2005 land: constraints from radiogenic isotope systematics and u-pb zircon geochronology. precambrian research 91, 365–381. wiedenbeck, m., allé, p., corfu, f., griffin, w.l., meier, m., oberli, f., von quardt, a., roddick, j.c. & spiegel, w. 1995: three natural zircon standards for u-th-pb, lu-hf, trace element and ree analyses. geostandards newsletter 19, 1–23. williams, i.s. 1998: u-th-pb geochronology by ion microprobe. in: mckibben, m.a., shanks iii, w.c. & ridley, w.i. (eds): applications of microanalytical techniques to understanding mineralising processes. reviews in economic geology 7, 1–35. 99 appendix analytical methods rock samples were crushed to mineral size under clean conditions using a jaw crusher and a disc pulveriser, and initial mineral separation was made using a wilfley table at the university of copenhagen or the university of texas at austin. all subsequent procedures, including sieving, heavy liquids and magnetic separation, were conducted at the university of texas at austin. mineral fractions were characterised using a binocular reflected light microscope, a transmitted light petrographic microscope (with condenser lens inserted to minimise edge refraction), and a scanning cathodoluminescence (cl) imaging system on a jeol 730 scanning electron microscope. selected zircons of comparable size were hand picked and placed on two-sided tape, collared, and covered with epoxy. the zircons in the resulting mount were ground to approximately two thirds of their original thickness and polished. cl imaging was used to characterise the zircons before analysis. laser ablation analysis utilised a merchantek 213nm yag-laser connected to a micromass quadrupole mass spectrometer (platform). fractionation and inherent detector non-linearity were accounted for by analysing zircons already well characterised by tims. corrections necessary to obtain the correct 207pb/206pb ratios for these internal laboratory standards, covering a range of intensities and isotopic ratios, were applied to unknowns. standards were run throughout each session. blanks and offpeak baselines were also determined throughout each analytical session. selecting and analysing only the highest quality zircons minimised the need for common pb corrections using measured 204pb, a procedure made impossible by high 204hg counts. a single zircon analysis comprises approximately 450 ten-microsecond scans of 207pb/ 206pb. ratios reflecting the moving average of twenty 207pb and 206pb measurements are first plotted on a graph to check for anomalous ratios throughout a run. those with high ratios at the beginning are presumed to reflect common pb and are removed from further consideration. a jump from one ratio plateau to another during one analysis is interpreted to reflect piercing a core or rim of different age. only data from one plateau at a time were considered. in cases where the beam pierces the grain too deeply and ejecta are not effectively emitted towards the end of an analysis, the signal intensity and commonly also isotope ratios change dramatically. data from the late part of such runs were also rejected. with this first assessment of data complete, the 207pb and 206pb data were then passed through a 4-sigma filter to remove highly anomalous counts before being passed through a more rigorous 2-sigma filter. the averages of the remaining individual measurements (typically < 5% rejection) of 207pb and 206pb provided the final 207pb/206pb ratio and consequent age. given the transient signal inherent in la-icp-ms and sequential acquisition required by the single collector, standard statistics on multiple blocks of scans is not applicable. a major limitation of our la-icp-ms protocol is that u abundances are not measured; instead only 207pb/206pb ratios are obtained. a direct indication of concordance is, therefore, not available and all the ages obtained should conservatively be interpreted to represent minimum ages for crystallisation. a single sample was analysed using the cameca ims 1270 ion microprobe at the nordsim laboratory, naturhistoriska riksmuseet, stockholm. the sample was prepared in the same way as the samples analysed by laicp-ms. reference zircon 91500 from ontario, canada, with a weighted average 207pb/206pb age of 1065 ma (wiedenbeck et al. 1995), was included in the mount and used as standard. analytical procedures and common lead corrections are similar to those described by schuhmacher et al. (1994) and whitehouse et al. (1997). calibrations of pb/u ratios are based on the observed relationship between pb/u and uo 2 /u and follow procedures similar to those used by the shrimp group at the australian national university (williams 1998). 100 geological survey of denmark and greenland bulletin 1, 75-114 75 the upper jurassic of europe: its subdivision and correlation arnold zeiss in the last 40 years, the stratigraphy of the upper jurassic of europe has received much attention and considerable revision; much of the impetus behind this endeavour has stemmed from the work of the international subcommission on jurassic stratigraphy. the upper jurassic series consists of three stages, the oxfordian, kimmeridgian and tithonian which are further subdivided into substages, zones and subzones, primarily on the basis of ammonites. regional variations between the mediterranean, submediterranean and subboreal provinces are discussed and correlation possibilities indicated. the durations of the oxfordian, kimmeridgian and tithonian stages are reported to have been 5.3, 3.4 and 6.5 ma, respectively. this review of the present status of upper jurassic stratigraphy aids identification of a number of problems of subdivision and definition of upper jurassic stages; in particular these include correlation of the base of the kimmeridgian and the top of the tithonian between submediterranean and subboreal europe. although still primarily based on ammonite stratigraphy, subdivision of the upper jurassic is increasingly being refined by the incorporation of other fossil groups; these include both megafossils, such as aptychi, belemnites, bivalves, gastropods, brachiopods, echinoderms, corals, sponges and vertebrates, and microfossils such as foraminifera, radiolaria, ciliata, ostracodes, dinoflagellates, calcareous nannofossils, charophyaceae, dasycladaceae, spores and pollen. important future developments will depend on the detailed integration of these disparate biostratigraphic data and their precise combination with the abundant new data from sequence stratigraphy, utilising the high degree of stratigraphic resolution offered by certain groups of fossils. this article also contains some notes on the recent results of magnetostratigraphy and sequence chronostratigraphy. keywords: europe, upper jurassic, oxfordian, kimmeridgian, tithonian, volgian, ammonite zonal and subzonal biostratigraphy and correlations, subdivision by non-ammonite fossil groups, chronometric data, magnetostratigraphy, sequence stratigraphy institut für paläontologie der universität erlangen-nürnberg, loewenichstr. 28, d-91054 erlangen, germany. present address: albert schweitzer strasse 19, d-91080 uttenreuth, germany. e-mail: arnold.zeiss@t-online.de geological survey of denmark and greenland bulletin 1, 75–114 (2003) © geus, 2003 76 contents subdivision and definition of stages: status and unsolved problems 78 the upper jurassic (malm) series 79 boundaries of the upper jurassic series 79 lower boundary (middle–upper jurassic series boundary) 79 upper boundary (jurassic–cretaceous system boundary) 80 upper jurassic stages – subdivision and correlation 81 oxfordian 81 lower boundary 82 substages 82 zones 84 correlation 85 chronometric data 85 kimmeridgian 85 lower boundary 86 additional remarks on lower kimmeridgian correlation 89 substages 89 zones 90 correlation 91 chronometric data 91 tithonian and volgian 91 lower boundary 92 substages 92 zones and subzones 93 correlation 95 chronometric data 96 biochronological importance of non-ammonite fossil groups: a review 96 invertebrate megafossil groups 96 cephalopods – other than ammonite conchs 96 aptychi 96 belemnites 96 bivalves 97 gastropods 97 brachiopods 97 echinoderms 97 corals (scleractinians) 97 sponges 97 vertebrate megafossils 97 invertebrate microfossils 98 foraminifera 98 radiolaria 98 ciliata 98 ostracodes 99 plant microfossils 99 dinoflagellata 99 calcareous nannofossils (coccoliths, nannolith groups) 99 charophyaceae 100 dasycladaceae 100 spores and pollen 100 magnetostratigraphy 100 sequence chronostratigraphy 100 acknowledgements 101 references 101 the term ‘upper jurassic’ (‘oberer jura’) was introduced by von buch (1839). arkell (1956) revived this name with only minor changes in its chronostratigraphic content. the term ‘upper jurassic’ in the sense of arkell (1956) was accepted by the first and second ‘colloque du jurassique’ at luxembourg in 1962 and 1967; only the stage name ‘purbeckian’ was eliminated, as it was considered to characterise merely a distinct lithofacies. this usage was followed by the five subsequent international symposia on jurassic stratigraphy at erlangen in 1984, lisbon in 1987, poitiers in 1991, mendoza in 1994 and vancouver in 1998. focus on the formal stratigraphic subdivision of the jurassic, and the upper jurassic in particular, is reflected in the series of key meetings since the early 1960’s (table 1). the term ‘malm’ was included in the recommendations of the first luxembourg colloquium in 1962 as an alternative term for the ‘upper jurassic’ (maubeuge 1964). although this term, like the term ‘tithonian’ (see below), is not based on a geographical site, it has been widely used since its introduction by oppel (1858, 1865). referring to the tithonian stage, arkell (1956, p. 8) wrote: “it is too late to abolish it after a hundred years of continuous use”; this also applies to the term ‘malm’. it is important to note that both ‘upper jurassic’ and ‘malm’ are chronostratigraphic terms; the latter, in particular, has frequently been used in a lithostratigraphic sense by some authors. at the first colloquium in luxembourg in 1962, a subdivision of the jurassic system into stages was proposed, the basic framework of which has survived to the present day. the stages were defined by their lower and upper ammonite zones. the recommendations of the first colloquium (maubeuge 1964) were thus a landmark in the history of international agreements concerning the subdivision of the jurassic system into series and stages. after a period of discussion following the publication of the resolutions of the luxembourg colloquia (maubeuge 1964, 1970), these proposals have been accepted 77 table 1. key events in upper jurassic stratigraphy since 1960 date place event reference 1962 luxembourg colloque du jurassique à luxembourg maubeuge 1964 1965 sofia vii congress, carpatho-balkan geological association cbga 1965 1967 luxembourg colloque du jurassique à luxembourg maubeuge 1970; brgm 1974 1967 moscow international symposium on upper jurassic stratigraphy anssr 1974 1969 london william smith symposium on jurassic geology 1969 budapest colloque du jurassique méditerranéen végh-neubrandt 1971 1973 neuchâtel colloque sur la limite jurassique–cretacé, lyon brgm 1975 1975 sofia international symposium on the jurassic–cretaceous boundary in bulgaria nikolov & sapunov 1977 1977 stuttgart international field meeting on the jurassic system of southern germany – this meeting zeiss 1977; ziegler 1977 initiated the reorganisation of the international subcommission on jurassic stratigraphy 1979 novosibirsk international colloquium on the upper jurassic and the jurassic–cretaceous boundary saks 1979 1984 erlangen international symposium on jurassic stratigraphy michelsen & zeiss 1984 1984 sümeg meeting of the working group for the jurassic–cretaceous boundary fülöp 1986 1987 lisbon 2nd international symposium on jurassic stratigraphy rocha & soares 1988 1987 international field meeting on jurassic–cretaceous boundary problems at menner 1990 the northern caucasus 1988 zaragoza 1st oxfordian working group meeting, zaragoza – iberian chain meléndez 1990 1990 basel 2nd oxfordian working group meeting, basel and jura range of northern switzerland gygi 1990b 1991 poitiers 3rd international symposium of jurassic stratigraphy cariou & hantzpergue 1994 1992 warsaw joint meeting of the oxfordian and kimmeridgian working groups atrops et al. 1993a 1993 london w. j. arkell symposium of jurassic geology taylor 1996 1994 mendoza 4th international symposium on jurassic stratigraphy riccardi 1996 1994 lyon 4th oxfordian and kimmeridgian working groups meeting, lyon and atrops & meléndez 1994a south-eastern france basin 1997 warsaw oxfordian (jurassic) meeting in poland glowniak et al. 1997 1998 vancouver 5th international symposium on the jurassic system pálfy 1998, hall & smith 2000 worldwide, the only exception being that in the former soviet union the callovian has been considered to belong to the upper jurassic (see krymholts et al. 1988), while in the rest of the world the callovian is included in the middle jurassic. however, following a decision by the interdepartmental stratigraphic commitee in 1989, the callovian is also now considered in russia to belong to the middle jurassic (zhamojda 1991). according to the most recent estimates, the late jurassic had a duration of a little more than 15 million years according to gradstein et al. (1994, 1995; ogg 1995), or 12 million years (+5.6/-7.3) according to pálfy et al. (1998). the data of gradstein et al. (1995) have been used in figures 2, 4 and 5 of this paper; on this basis each of the three upper jurassic stages has an average length of 5 million years, while zones and subzones have approximate durations of 700 000 and 300 000 years, respectively. each subzone comprises at least three horizons, each of which has an approximate duration of 100 000 years. subdivision and definition of stages: status and unsolved problems on the basis of the recommendations of the first luxembourg colloquium (maubeuge 1964), the upper jurassic series was subdivided into four stages for the boreal and subboreal regions: oxfordian, kimmeridgian (sensu anglico), portlandian (sensu anglico) and volgian, and three for the submediterranean and mediterranean regions: oxfordian, kimmeridgian (sensu gallico equivalent to ‘crussolian’) and tithonian (equivalent to ‘danubian’ and ‘ardescian’). in the following decades, there has been much confusion as the kimmeridgian and portlandian stages have often been used differently in different parts of europe. in 1990, a formal vote of the international subcommission on jurassic stratigraphy (isjs) led to the decision to use stages with approximately the same vertical age ranges and uniform names in both regions: kimmeridgian (sensu gallico) and tithonian (zeiss 1991a). with regard to the still unresolved correlation problems between the boreal and mediterranean provinces, it was agreed that the volgian can be used as an alternative stage for the tithonian in subboreal and boreal regions (fig. 1). the main problem which remained to be solved was the definition of the lower boundary of each stage. to date, no stage has a type locality and a defined lower boundary (global stratotype section and point, or gssp) formally accepted by the international commission on stratigraphy (ics). there are of course a lot of proposals, but they have not been validated according to the guidelines and rules of the ics (cowie et al. 1986; remane et al. 1996). the most intractable problems are to find isochronous levels in submediterranean (and mediterranean) and subboreal (and boreal) europe for the lower boundary of the kimmeridgian stage and for the upper boundary of the tithonian (volgian) stage. as the former is of particular significance for upper jurassic subdivision and correlation, it will be treated here in some detail (see below). other problems are the unification of the differing subdivisions of stages into substages, correlation of the zones of each stage between the different areas of europe and the development of better correlation charts from the boreal regions to the mediterranean areas. provisional correlation charts on a zonal and subzonal level for each stage of the european upper jurassic are presented here (see figs 2–5). zones and subzones are used here as chronozones following the international stratigraphic guide (salvador 1994); originally, many of them were defined as biozones whereas others were used as standard zones, standard chronozones or biochronological standard zones, i.e. only the base is defined while the top is defined by the base of the next overlying unit (callomon 1965, 1984a, 1994). problems arise, however, due to inconsistent usage of the term ‘standard zone’. in northwest europe, standard zones are mostly used following the concept of callomon (1994), whereas in central and southern europe, standard zones are often synonymous with biostratigraphic zones for use in biochronology (cariou & hantzperque 1997). it is often difficult, therefore, to determine in which meaning ‘standard zones’ are used. the problems encountered in moving from biostratigraphic field data to biochronological interpretations have been discussed recently by remane (1991). the term biochronological zone is now used by many authors instead of chronostratigraphic zone, if the zone is based on fossil data. as the ultimate subdivision of biochronology, french authors use the term ‘biohorizon’ (e.g. enay 1997); their concept is therefore ‘sensiblement different’ from the pure biostratigraphic horizon concept of j.h. callomon (dommergues 1997). no attempt has been made here to correlate ammonite faunal horizons due to the variable nature of the published research on the upper jurassic in the various sedimentary basins of europe. where necessary, however, correlations of horizons are discussed in the text. 78 for an example of such horizon correlations, the reader is referred to the work of callomon (1984c) on the upper jurassic of north america (this study also covers the european amoeboceras subdivision). although attempts have been made to generalise horizons for the whole ‘domaine tethysien’ and ‘domaine boréal’ (cariou et al. 1997; hantzperque et al. 1997), these appear premature and of little practical use, given the present state of knowledge. in europe, subdivisions down to the level of ammonite faunal horizons have been proposed for several sedimentary basins. such studies include that of the upper jurassic of east greenland by callomon & birkelund (1980, 1982; birkelund & callomon 1985), the lower kimmeridgian of southern england by birkelund et al. (1983), the kimmeridgian of spitsbergen by wierzbowski (1989), the kimmeridgian of the barents sea by wierzbowski & smelror (1993), the lowermost oxfordian of northern france by vidier et al. (1993), the upper oxfordian, kimmeridgian and lower tithonian of western france by hantzperque (1989), the lowermost oxfordian of south-east france by fortwengler & marchand (1994b), the lower kimmeridgian of south-east france by atrops (1982), the upper oxfordian, upper kimmeridgian and lower tithonian of south-west germany by schweigert (1994, 1995a, b, 1996a, b; schweigert & callomon 1997), the oxfordian– kimmeridgian of poland (matyja & wierzbowski 1997), the middle volgian of central poland (kutek 1994) and the oxfordian of north-east spain by cariou et al. (1991a) and meléndez & fontana (1993). the ‘faunal horizon’ approach clearly represents a method for increasing precision in correlation and dating in the future, when the data from the various sedimentary basins reach the necessary standard. it is already proving useful in deciphering the history of basin deposits at a resolution that was hitherto impossible; such data, in particular, allow us to date events more precisely and to determine the ‘completeness’ of the sedimentary record i.e. to identify accurately the position and duration of hiatuses. a prerequisite is, however, that it is possible to reconstruct the complete succession of faunal horizons by correlating individual local successions. in this context, it is worth mentioning that the methods of jurassic stratigraphy and high-resolution geochronology have been discussed in detail by callomon (1984a, b, 1994, 1995), page (1995), corna et al. (1997), blau (1998) and blau & meister (2000); formal aspects were covered by remane (1996). the upper jurassic (malm) series (fig. 1) in this paper, subdivision and correlation of the upper jurassic series have been carried out mainly using ammonites. other fossil groups are reviewed briefly, however, with request to their biochronologic resolution and correlation potential. many papers have been published on upper jurassic ammonites and their chronostratigraphic resolution (see detailed discussion below). for a broad overview, the reader is referred to the papers of cariou et al. (1997), geyssant (1997) and hantzpergue et al. (1997) for western europe and the mediterranean. other important, partly regional compilations and revisions have been published by sapunov (1979), donovan et al. (1981), krymholts et al. (1988), malinowska et al. (1988), enay et al. (1994) and schlegelmilch (1994). boundaries of the upper jurassic series lower boundary (middle–upper jurassic series boundary) the lower boundary of the oxfordian stage is rather well-defined by ammonite zones and subzones and only requires more precise definition with respect to the lowermost faunal horizon, which then would characterise the beginning of the lowermost subzone (and zone) of the stage. furthermore, it appears that the lower boundary is approximately (on a subzonal level) the same in boreal and mediterranean areas. once the type faunal horizon has been chosen, then the problem of the type locality for the boundary will also have been solved. at present, this boundary lies in france between the uppermost horizon of the quenstedtoceras lamberti zone of the upper callovian substage (the cardioceras paucicostatum horizon) and the lowermost horizon of the q. mariae zone; this was first named in france after peltoceratoides elisabethae (fortwengler & marchand 1994a), but afterwards was changed to hecticoceras (brightia) thuouxense (fortwengler & marchand 1994b, c), a species described only recently (fortwengler et al. 1997). in dorset, however, cardioceras cf. woodhamense and c. woodhamense are found in the lowermost levels of the q. mariae zone (callomon & cope 1996), whereas in north-west france, c. woodhamense has been collected only in the third horizon of the q. mariae zone (vidier et al. 1993). in south-east france, this horizon is only recognised tentatively. these different faunal horizons all lie 79 in the cardioceras scarburgense subzone, the lower subzone of the q. mariae zone, so that the age difference of these horizons (if any) should not be too large. a vote by the callovian/oxfordian boundary working group in 1995 resulted in a preference for a type locality in south-east france, with the consequence that the oxfordian would begin with the h.(b.) thuouxense horizon (see above), but a final decision was not taken (meléndez 1995; meléndez et al. 1998). upper boundary (jurassic–cretaceous system boundary) in accordance with the decision of the isjs (see above), there are two alternative stages for the uppermost part of the jurassic system: tithonian and volgian. as they differ in duration, the boundary may be drawn at two different levels, i.e. there are two variants of the jurassic–cretaceous boundary. accordingly, the members of the former jurassic–cretaceous boundary working group agreed to work provisionally with two boundaries (remane 1986; remane et al. 1986; zeiss 1986). 1. in mediterranean and submediterranean europe, the boundary is placed between the top of the tithonian stage (top of durangites vulgaris zone and/or of calpionellid zone a) and the base of the berriasian stage (base of berriasella jacobi zone s.l. (= berriasella jacobi and pseudosubplanites grandis subzones or pseudosubplanites euxinus zone) and/or base of calpionellid zone b). 2. in subboreal and boreal europe, the boundary lies between the upper volgian (top of craspedites nodiger or chetaites chetae zone) and the ryazanian or ‘boreal berriasian’ (base of chetaites sibericus, rjasanites rjasanensis or runctonia runctoni zone) (rawson et al. 1978; kejsi et al. 1988; sey & kalacheva 1993a). 80 upper upper upper upper upper upperupper upper middle middle middle middle middle middle middle lower lower lower lower lower lower lowerlowerlower abnormis scythicus klimovi autissiodorensis mutabilis baylei glosense plicatilis mariae semiforme hybonotum beckeri acanthicum platynota bimammatum bifurcatus transversarium mariae tithonian kimmeridgian oxfordian tithonian (volgian) stagesstages substagessubstages germany france submediterranean province subboreal province basal zones of substages basal zones of substages kimmeridgian oxfordian fig. 1. subdivision of the upper jurassic series of europe into stages, substages and zones. substage usage varies in the literature, dependent on author; those indicated are only examples. in the first case, the type locality should be best selected in south-eastern france, where the ardescian substage (upper tithonian) and the berriasian stage were originally described. subsequent studies have revealed that the sequences are not complete at the base, however, so that it has been suggested that the best sections illustrating the jurassic–cretaceous boundary beds and their fauna are situated in southern spain (enay & geyssant 1975; tavera 1985; tavera et al. 1994; enay et al. 1998a, b). in the second case, the boundary should correspond to the base of the berriasella boissieri zone in the mediterranean area. thus, the upper volgian substage corresponds to the lower berriasian (zeiss 1974, 1979, 1983, 1986; rawson et al. 1978; hoedemaker 1990; sey & kalacheva 1993a; w.a. wimbledon in: callomon & cope 1996), and is not equivalent to the upper tithonian as mesezhnikov (1988) and other authors have assumed. in a recent review of the berriasian stage, hoedemaker (1994) stated that the jurassic–cretaceous boundary is typically placed at one of two different levels, either at the base or at the top of the jacobi chronozone: “investigators of jurassic stratigraphy prefer the lower of these two boundaries, investigators of the cretaceous stratigraphy the upper” (hoedemaker 1994, p. 12). at the same time, there has also been an attempt to trace the jurassic–cretaceous boundary based on geomagnetic anomalies from the tethys to southern england (ogg et al. 1994). in the tethyan–atlantic faunal realm, the top of magnetic polarity reversal m19r approximately coincides with the tithonian–berriasian boundary in the mediterranean area. this reversal is difficult to place precisely in england, but it seems to be situated in the lowermost purbeck beds. if so, it would demonstrate once again that the ‘upper volgian’ (casey 1973) or ‘upper portlandian’ of england (wimbledon 1980), i.e. the zonal sequence subcraspedites primitivus – subcraspedites lamplughi, overlaps with the lower berriasian. wimbledon (1980) also included the ‘upper volgian’ zones of casey (1973) in the ‘portlandian’ of britain, thus extending the stage upwards by three further zones (termed here ‘upper portlandian’). in a recent compilation chart, w.a. wimbledon (in: callomon & cope 1996) correlated these ‘upper portlandian’ zones and the upper volgian zones of the russian platform with parts of the lower berriasian. in poland, the jurassic–cretaceous boundary has been traced by joint studies of ostracodes and ammonites (marek et al. 1989) whereby the upper tithonian and the lower part of the lower berriasian could be recognised as well as the upper berriasian (= ‘ryazanian’). in a recent paper (marek & shulgina 1996), the ammonites of the berriasian (ryazanian) were considered to belong to the interval upper occitanica – lower boissieri zones. in a recent development, the interdepartmental stratigraphic committee of russia (isc) approved the following resolutions of its commissions on the jurassic and cretaceous systems (rostovtsev & prozorovskiy 1997, p. 48). “1. to draw the jurassic–cretaceous boundary in the boreal realm between the middle and upper substages of the volgian, and not …… as …… earlier adopted in russia (1978). this boundary mainly corresponds to the tithonian/berriasian boundary in tethyan realm (colloque lyon–neuchâtel, 1975). correspondingly, the lower volgian in the whole correlated with the lower and middle tithonian; the middle volgian, with the upper tithonian; the upper volgian, with two lower zones of the berriasian (jacobi/grandis and occitanica). 2. to transfer the volgian stage in its former range to the category of regional stratigraphic units (regional stage). to distinguish as chronostratigraphic units in the boundary part of the jurassic and cretaceous scale of russia only tithonian and berriasian.” these resolutions, which were precipitated by the work of sey & kalacheva (1993a), confirmed the earlier opinions of many authors concerning upper jurassic/lower cretaceous correlations. it is clear that general consensus has not yet been reached; it is assumed, however, that the present tithonian–berriasian boundary is not suitable for global correlation. it may be preferable, therefore, to return to an old proposal: to define the jurassic–cretaceous boundary at the base of the b. boissieri zone, where many guide fossils of different groups are available for correlation. recent studies in the caucasus area by remane (1997) are supportive of this proposal. upper jurassic stages – subdivision and correlation oxfordian (figs 2, 3) the colloquium at luxembourg in 1962 (maubeuge 1964, p. 85) came to the resolution “...... that it seemed necessary to return to the original sense of this stage 81 [the oxfordian] as defined by a. d’orbigny and given precision by w.j. arkell (1956)”. the ‘base’ was indicated to be the ‘zone of quenstedtoceras mariae’ and the ‘top’ the ‘zone of ringsteadia pseudocordata (= zone of idoceras planula), (= zone of epipeltoceras bimammatum)’. it was recommended that other stage and substage names then still in use, e.g. the argovian (marcou 1848), rauracien (greppin 1867), sequanian (marcou 1848) and the lusitanien (choffat 1885; haug 1910) should be abandoned. these stages had been interpreted in different ways so that continued usage would have created only more confusion. subsequent studies (e.g. enay 1980a; gygi & persoz 1986; enay et al. 1988) demonstrated the validity of this resolution. lower boundary see discussion above. substages although the oxfordian has been subdivided into three substages, lower, middle and upper oxfordian, full agreement has not been reached on the zonal content of these substages and the position of their boundaries (callomon 1988, 1990, fig. 10; meléndez & fontana 1993, fig. 5; wright 1996a). the subdivision is thus essentially informal but the substages are capitalised in 82 switzerlandfrance, spain s. germany england greenland, scotland, svalbard galar (gigantoplex, grandiplex) galar planula galar planula (grandiplex) planula proteron pl an ul a pl an ul a luciaeformis (wartae) parandieri parandieri nunningtonense cautisnigrae serratum serratum koldewayense regulare rosenkrantzi variocostatum caledonica pseudoyo parandieri schilli schilli schilli rotoides stenocycloides stenocycloides grossouvrei grossouvrei antecedens antecedens antecedens tenuiserratum glosense (alternoides) glosense ilovaiskyi tenuiserratum blakei pu m ilu s c au ti sn ig ra e antecedens vertebrale vertebrale vertebrale maltonense vertebrale cordatum cordatum cordatum cordatum cordatum costicardia costicardia costicardia costicardia costicardia bukowskii bukowskii bukowskii bukowskii bukowskii praecordatum praecordatum praecordatum praecordatum praecordatum scarburgense scarburgense scarburgense scarburgense scarburgense plicatilis pl ic at il. pl ic at ili s c o rd at um c o rd at um c o rd at um cordatumcordatum m ar ia e m ar ia e m ar ia e mariaemariae a lt er na ns o va le b au hi ni r in gs te ad ia densiplicatum densiplicatum transversarium transversarium tr an sv er sa ri um tr an sv er sa ri um bifurcatus bifurcatus hypsel. hauffianum bimammatum bimammatum bimam-matum bimammatum b im am m at um ps eu do co rd at a b ay le i r av ni (s ub -) b o re al o x. /k i. bo un da ry pseudocordata evoluta densicostata baylei ? ? bauhini (? bayi) bauhini tonnerense praecursor praecursor berrense berrense hauffian. semimammatum b ifu rc at us submediterranean subboreal boreal 15 9. 4 (± 3 .6 ) 15 4. 1 (± 3 .2 ) u pp er m id dl e lo w er o xf o rd ia n fig. 2. a tentative correlation chart for the oxfordian stage in europe (thick lines indicate periods during which correlation is difficult). modified after zeiss (1984), mesezhnikov (1988), cariou et al. (1991b), wright (1996a, b), matyja & wierzbowski (1997, 1998), schweigert & callomon (1997) and gygi (2000a, b). this paper, following common usage. an example of the ongoing debate is the inclusion of the d. bifurcatus zone in the middle or upper oxfordian; this zone was introduced by enay (1966) as the upper subzone of the g. transversarium zone but was later considered as the lowermost zone of the upper oxfordian (cariou et al. 1971). preference is given here to a subdivision in which the d. bifurcatus zone is included in the middle oxfordian (fig. 1) as has also been proposed by meléndez (1989), cariou & meléndez (1990), cariou et al. (1991a) and gygi (2000a) although not followed by cariou et al. (1991b, 1997). while the lower and middle substages have the same lower boundaries in submediterranean and subboreal europe, the position of the lower boundary of the upper substage differs. in boreal europe, it has been drawn at three different levels (wright 1996a, fig. 6). the solution to draw it at the base of the a. glosense zone is well-known (sykes & callomon 1979; wright 1980); it would correspond to the base of the p. luciaeformis subzone in the g. transversarium zone, i.e. the boundary would be drawn around one and a half zones deeper than in the submediterranean subdivision. it seems preferable to draw the boundary at the lower boundary of the a. rosenkrantzi zone, corresponding approximately to the lower boundary of the upper oxfordian both in submediterranean europe (base of e. bimammatum zone) and in subboreal europe (base of r. pseudocordata zone), although the latter lies somewhat deeper (matyja & wierzbowski 1997, fig. 4). additional literature references pertinent to the subdivision of the oxfordian stage are enay (1963, 1966), zeiss (1966), sequeiros (1974), sapunov (1976), gygi (1977, 1986, 1990a, 2000a, b, c), wierzbowski (1978), enay & meléndez (1984), a. zeiss (in: enay & meléndez 1984), cariou & meléndez (1990), malinowska (1991), meléndez & fontana (1993), schweigert (1995a, b), fözy & meléndez (1996), matyja & wierzbowski (1997, 1998), groiss et al. (2000) and schweigert & callomon (1997) for the submediterranean and mediterranean provinces, and sykes & callomon (1979), wright (1980, 1996a, b) and mesezhnikov (1988) for the subboreal and boreal provinces. mönning & bertling (1995), mönning (1998) and gramann et al. (1997) have presented interesting and useful reviews of the ammonite succession in northern germany. 83 submediterranean standard (cariou et al. 1991b) spain – north africa (sequeiros 1974; cariou et al. 1991b) poland (tarkowski 1990; matyja & glowniak 1994) bulgaria (sapunov 1976) transversarium plicatilis riazi antecedens antecedens promiscuus oculatum helenaepaturattensis baccatum spixi wartae antecedens episcopalis renggeri athletoides riazi antecedens cordatum costicardia bukowskii praecordatum scarburgense vertebrale (tenuicostatum) rotoides schilli luciaeformis parandieri paturattensis claromontanus claromontanus paturattensis paturattensis plicatilis minax magnouatius mazuricuscordatum mariae transversarium fig. 3. a tentative correlation chart for some alternative subdivisions of parts of the oxfordian stage in mediterranean and submediterranean europe. zones the zonal and subzonal subdivision of the lower oxfordian substage was established by arkell (1941) using quenstedtoceras mariae and cardioceras cordatum as index species; it can be used over large areas of northern and central europe (fig. 1) and is also applicable in the dauphinois basin of south-east france as recently demonstrated by fortwengler & marchand (1994a; fortwengler et al. 1995). in southern europe, a variety of subdivisions exist; at least three distinct subdivisions testify to the difficulties in erecting a generally accepted zonal scheme if cardioceratids are missing. in such cases, peltoceratids (peltomorphites, peltoceratoides and parawedekindia), oppeliids (taramelliceras, popanites and creniceras) and perisphinctids (otosphinctes, perisphinctes, prososphinctes and properisphinctes) are important guide fossils (see fig. 3), e.g. taramelliceras minax, t. spixi, t. baccatum, t. oculatum, popanites paturattensis in poland (tarkowski 1990), peltomorphites athletoides and creniceras renggeri in bulgaria (sapunov 1976), and prososphinctes mazuricus and p. claromontanus in spain (aurell et al. 1990). from the base of the middle oxfordian, perisphinctids and peltoceratids become the dominant ammonite groups with respect to index fossils at the substage level in the submediterranean and subboreal provinces. the first aulacostephanids (decipia) also appear at this level. the perisphinctes plicatilis, gregoryceras transversarium and dichotomoceras bifurcatum zones make up the middle oxfordian substage in the submediterranean area, the perisphinctes plicatilis, p. pumilum and p. cautisnigrae zones are representative of the subboreal province. boreal indexes are cardioceras tenuicostatum and c. tenuiserratum, amoeboceras glosense and a. serratum. the correlation between subboreal perisphinctid and amoeboceratid zones was well demonstrated by wright (1996b). there is a difference in the usage of the p. plicatilis and g. transversarium zones in submediterranean europe. although gygi & marchand (1982) replaced the basal c. vertebrale subzone with the c. densiplicatum zone and included the p. antecedens subzone in the g. transversarium zone, subsequent authors have not followed the arguments of these authors and have continued to use the p. plicatilis zone in the sense of cariou et al. (1991a, b), i.e. with c. vertebrale and p. antecedens subzones (e.g. meléndez & fontana 1993, fig. 4; cariou et al. 1997). cariou et al. (1991a) defined the g. transversarium zone to contain the p. parandieri, p. luciaeformis, l. schilli and p. rotoides subzones. in a more recent publication, gygi (1995) included in the lower part of the g. transversarium zone not only the p. antecedens subzone but also the c. densiplicatum subzone i.e. the whole p. plicatilis zone (following the original usage of oppel & waagen 1866; r.a. gygi, personal communication 1997). in further contributions to the upper jurassic of switzerland (gygi 2000b, c), the g. transversarium zone is subdivided into the c. densiplicatum, p. antecedens, and p. luciaeformis subzones; the overlying d. bifurcatus zone contains in its lower part the l. schilli subzone, which is considered in spain and france to represent the upper part of the g. transversarium zone (see above). the main reason for these differences is the occurrence of l. schilli in switzerland above the vertical range of g. transversarium. the upper oxfordian substage in submediterranean europe comprises the epipeltoceras bimammatum, idoceras planula and sutneria galar zones. considering the new correlations of wright (1996a), matyja & wierzbowski (1997) and cariou et al. (1997), ringsteadia pseudocordata would be the corresponding index fossil for the subboreal province, whereas amoeboceras rosenkrantzi would be the index fossil for boreal europe. the amoeboceras serratum zone of malinowska (1991) contains epipeltoceras (uhligi group) and ringsteadia salfeldi thus indicating, at least partly, equivalence with the lower e. bimammatum zone (e. hypselum subzone); this demonstrates that the a. serratum zone of this author is younger in age than the a. serratum zone of sykes & callomon (1979). the a. regulare subzone of malinowska (1991) seems to represent the upper e. bimammatum and perhaps the lowermost i. planula zones, while the a. lineatum subzone apparently corresponds to the rest of the i. planula zone and the s. galar zone. the most difficult problems associated with these upper oxfordian zones concern their correlation in the subboreal and submediterranean schemes; this aspect is discussed in detail below. some minor problems may be caused by the different hierarchical status of zones and subzones in the subboreal and boreal provinces. for example, atrops et al. (1993b) recognised the a. regulare, a. rosenkrantzi and a. bauhini zones, whereas malinowska (1991) subdivided the r. pseudocordata zone into the a. regulare and a. lineatum subzones or, in boreal europe, into the a. regulare and a. rosenkrantzi subzones. however, comparing the correlation chart of malinowska (1991, table 3) with that of matyja & wierzbowski (1997, fig. 3), it becomes evi84 dent that the p. pseudocordata zone of malinowska corresponds only to the upper part of the a. regulare, the a. rosenkrantzi and the p. baylei zones. another example is the variable status of a. bauhini as an index species. there is the a. bauhini horizon in the upper e. bimammatum zone equivalent to the p. densicostata horizon (schweigert & callomon 1997), the a. bauhini subzone of the a. rosenkrantzi zone (sykes & callomon 1979; cariou et al. 1997), equivalent to the p. baylei zone of birkelund & callomon (1985), and the a. bauhini zone. although initially equivalent to the p. densicostata horizon (wierzbowski & smelror 1993), the a. bauhini zone was expanded by matyja & wierzbowski (1997, 1998) to correlate with the uppermost p. pseudocordata zone and nearly the whole p. baylei zone on the one hand and with the whole i. planula zone and uppermost e. bimammatum zone on the other; a little more restricted was the a. bauhini zone of schweigert & callomon (1997), who excluded the s. galar subzone of the i. planula zone (see below). correlation there have been many proposals and attempts to correlate the zonal subdivisions of the oxfordian of mediterranean, submediterranean, subboreal and boreal areas of europe; the most important ones have been already discussed in the text above (see figs 2, 3). further informative compilations have been presented by enay & meléndez (1984), mesezhnikov (1988), cariou et al. (1991a, b; 1997), malinowska (1991), aleynikov & meledina (1993), meléndez & fontana (1993), schweigert (1995b), wright (1996a, b) and matyja & wierzbowski (1997). in short, correlation within the lower oxfordian is possible over wide regions of boreal, subboreal and submediterranean europe, but becomes difficult on approaching the mediterranean area. at the base of the middle oxfordian, ammonites of the perisphinctes plicatilis zone provide the last possibility for long-distance correlation. higher up in the middle oxfordian, zonal correlations become more and more difficult, best illustrated by the charts of j.h. callomon (in: wright 1980), enay & meléndez (1984) and cariou et al. (1991b; see also fig. 2). the divergent views are also well-documented by the tables of malinowska (1991), wright (1996a), cariou et al. (1997) and matyja & wierzbowski (1997). the problems of upper oxfordian correlation, concentrated mainly on the correspondence of the e. bimammatum, i. planula and s. galar zones to the r. pseudocordata, p. baylei, a. regulare, a. rosenkrantzi and a. bauhini zones, are under discussion (wierzbowski 1991; atrops et al. 1993b; atrops & meléndez 1994b; schweigert 1995a, b; cariou et al. 1997; matyja & wierzbowski 1997; schweigert & callomon 1997). this aspect is especially relevant to the oxfordian– kimmeridgian boundary problem and is therefore discussed in more detail below. chronometric data the duration of the oxfordian stage is estimated at 5.3 ma (gradstein et al. 1995; ogg 1995; ogg & gutowski 1996); for precise data, see figure 2. kimmeridgian (fig. 4) following the luxembourg recommendations of 1962 and 1967 (maubeuge 1964, 1970), two possibilities existed with respect to usage of the kimmeridgian stage, namely either a long version (‘sensu anglico’) or a short version (‘sensu gallico’), both with differing zonal content and boundaries (see below). use of two different versions of the kimmeridgian evoked much confusion in following years and led to endless discussion. therefore a vote of the international subcommission on jurassic stratigraphy (isjs) on this question was arranged in 1990, simultaneously with the vote on the tithonian stage (see below); the members of the isjs voted for a ‘short’ version of the kimmeridgian stage (i.e. ‘sensu gallico’). this meant that in future the upper boundary of the kimmeridgian stage should be coincident with the lower boundary of the tithonian stage and its boreal equivalent, the volgian (zeiss 1991a). the lower boundary of the stage, however, remained ambiguous (see below). because of the still unresolved problems at the oxfordian–kimmeridgian boundary, the lower boundary of the kimmeridgian stage is drawn in this paper at the base of the sutneria platynota zone, following the above-mentioned adoption of a short kimmeridgian stage (i.e. ‘sensu gallico’ or according to the ‘continental’ concept; enay 1980b). the working group of the oxfordian–kimmeridgian boundary is mandated to finally define the boundary at a level which allows farreaching correlations and corresponds to the resolutions of the international commission on stratigraphy (ics); see also the discussions by wierzbowski (1999, 2001). 85 until such a definition has been taken by the oxfordian–kimmeridgian boundary working group, voted on by the isjs and approved by isc, it seems useful to maintain the traditional boundaries in both biogeographic provinces, and it is premature to draw the oxfordian–kimmeridgian boundary in the submediterranean area in the upper part of the e. bimammatum zone (cf. gygi 2000a, b). lower boundary as the luxembourg recommendations made it possible to select between two distinct versions of the kimmeridgian stage, the lower boundary was also defined twofold. in subboreal regions of europe, the boundary was drawn at the lower boundary of the pictonia baylei zone, whereas in submediterranean regions it was placed at the base of the sutneria platynota zone (maubeuge 1964, p. 85–86). at that time, it was supposed that both boundaries were more or less isochronous (ziegler 1964), although doubts remained (e.g. zeiss 1965; cariou et al. 1971). with the publication of sykes & callomon (1979), new impetus was given to further studies, which have suggested that the assumed time equivalence is erroneous or, at best, only partially true (matyja & wierzbowski 1988; wierzbowski 1991; atrops et al. 1993b; schweigert 1995a, b). the main reasons for this view were the discovery of new amoeboceras faunas by these authors 86 beckeri/ pressulum beckeri eudoxus eudoxus mutabilis cymodoce cymodoce achilles chatelaillonensis cymodoce baylei bayi subkitchini modestum ruepellense mutabilis lallierianum orthocera caletanum contejeani autissiodorensis irius mutabilis autissiodorensis (volgensis) autissiodorensis (taimyrense) elegans kochi k o ch i n o rv egi cu m autissiodorensis eudoxus eudoxuscavouri acanthicum acanthicum divisum hypselocyclum platynota polygyratus desmoides guilheradense hippolytense lothari crusoliense uhlandi balderum linealis attenuatus eulepidus liparum/ schilleri eudoxus caletanum subeumela setatum ulmense submediterranean s. germany mediterranean n. italy (s. alps) biome franco-germanique w. france subboreal great britain boreal n. europe mixed poland herbichi strombecki silenum trenerites raschi stenonis divisum uhlandi fallax subborealis a ut is si o do re ns is m ut ab ili s c ym o do ce k it ch in i acanthicum divisum hypselocyclum platynota u pp er m id dl e k im m er id gi an lo w er 15 0. 7 (± 3. 0) 15 4. 1 (± 3. 2) fig. 4. a tentative correlation chart for the kimmeridgian stage in europe (thick lines as in fig. 2). modified after zeiss (1965), atrops (1982), sarti (1988), hantzpergue et al. (1991), wierzbowski & smelror (1993), kutek & zeiss (1994), schweigert & zeiss (1994) and matyja & wierzbowski (1997, 1998). and a re-evaluation of salfelds (1915) cardioceras paper as well as that of koerner (1963), particularly with respect to their remarks concerning the type locality and possible type horizon of cardioceras (= amoeboceras) bauhini. the discussion of wierzbowski (1991) concerning the range of the genus ringsteadia in poland is also important in this context. it soon became evident that amoeboceras bauhini has its type horizon just below the upper boundary of the e. bimammatum zone, (see a. zeiss in: enay & meléndez 1984). the studies of schweigert (1995a, b; schweigert & callomon 1997) resulted in similar conclusions, but led to a more precise faunal horizon subdivision of the upper oxfordian in württemberg, sw germany and to better correlation possibilities with england, with respect to the a. bauhini and the a. bayi (?= a. subtilicaelatum) horizon. some problems remained unsolved, however: 1. does the a. bauhini horizon of southern germany represent the same time interval as the beds bearing a. bauhini in england, scotland and the barents sea? or is there a difference, and the vertical range of this species is different in these two areas? what is the situation in poland, representing an intermediate region? 2. does the a. subtilicaelatum horizon of southern germany represent the same time interval as the a. bayi horizon in england? or is there also a difference in the vertical range of these species in different parts of europe? 3. which units in the subboreal realm correspond to the succession from the base of the i. planula zone (with three or four faunal horizons) and the top of the lower s. galar zone, which in submediterranean europe occurs between the a. bauhini and the a. subtilicaelatum (?= a. bayi) horizon? it is not easy to answer these questions given the present state of knowledge; the following points are pertinent prior to discussion of these problem areas. the usage of a. bauhini as an index ammonite began with its introduction by sykes & callomon (1979) as a subzone of the a. rosenkrantzi zone (uppermost oxfordian); its stratigraphic position was subsequently revised by birkelund & callomon (1985), who regarded the a. bauhini subzone and the p. baylei zone (lower kimmeridgian) as approximate equivalents. one year prior to this latter publication, a. zeiss (in: enay & meléndez 1984, fig. 6) had used a. bauhini informally as a zonal index in a correlation chart to show its approximate correspondence with the i. planula zone sensu lato; this view was also held by atrops et al. (1993b) and matyja & wierzbowski (1997, 1998). wierzbowski & smelror (1993) established the a. bauhini zone formally and suggested that it was equivalent to only the lower part of the p. baylei zone (the p. densicostata horizon); in more recent papers, matyja & wierzbowski (1994, 1995, 1997, 1998) provided charts showing the correlation between the a. bauhini zone and the i. planula zone sensu lato as well as with the p. baylei zone (with the exception of the uppermost part). finally, in southern germany, an a. bauhini horizon was described by schweigert (1995b; schweigert & callomon 1997) in the upper part of the t. hauffianum subzone (uppermost e. bimammatum zone); the latter authors correlated the boreal a. bauhini zone with the i. planula zone sensu stricto, whereas the s. galar zone was correlated with the amoeboceras kitchini zone. the amoeboceras bayi horizon was introduced by birkelund & callomon (1985) in the upper part of the p. baylei zone, whereas wierzbowski & smelror (1993) reported the species at the base of their a. subkitchini subzone. atrops et al. (1993b) found the species, or closely related forms, in the sutneria platynota zone of the submediterranean area. schweigert (1995b) established an a. subtilicaelatum horizon in the uppermost part of the sutneria galar zone, assuming that a. bayi is only a variant of a. subtilicaelatum, which would then have priority. this conflicts with the opinion of salfeld (1915), that a. lineatum and a. subtilicaelatum are very close and perhaps synonymous. schweigert (1995b) also assumed that many specimens determined earlier as ‘a. bauhini’ belong in reality to a. bayi. to verify these assumptions, a comprehensive re-evaluation of the upper oxfordian – lower kimmeridgian amoeboceras species complex (a. bauhini – a. bayi – a. subtilicaelatum – a. lineatum) would be necessary. such a study should also illustrate the variation within each species in time and space (see, for example, klieber 1981; birkelund & callomon 1985; matyja & wierzbowski 1988, 1994; schweigert & callomon 1997). for the time interval of the i. planula zone, malinowska (1991) established the a. lineatum subzone in poland. it was introduced as the upper subzone of the r. pseudocordata zone, but the precise correlation with other areas is not clear; from the list of fossils one would conclude that the s. galar zone is not present. however, as a sutneria sp. (of the galar/praecursor group?) is mentioned in the text but not figured, a deci87 sion is difficult; its low stratigraphic level in the goldap section would favour the s. praecursor zone. in addition, wierzbowski (1978) has described a. lineatum and a. bauhini together from the lower part of the i. planula zone; thus, the a. lineatum subzone seems to correspond to the lower part of the p. baylei zone rather than to the upper part of the r. pseudocordata zone. malinowska (1988) reported specimens of a. bauhini only from the lower kimmeridgian, but these forms belong to other species such as a. bayi or a. cf. cricki. in the subboreal province, the pictonia baylei zone consists of two or three horizons. the lowermost horizon in great britain and the boulonnais area is the pictonia densicostata horizon; as mentioned above, this probably corresponds to the a. bauhini horizon. in the boulonnais and normandy areas, this is followed by the pictonia baylei horizon sensu stricto, and, more widespread in france, the p. baylei and p. thurmanni horizon. in dorset, the second horizon is apparently missing (hantzpergue 1989), while the third one is represented by the p. baylei and p. normandiana horizon, which can also be observed in east greenland (p. aff. normandiana horizon, birkelund & callomon 1985). p. normandiana is regarded as a synonym of p. thurmanni by hantzpergue (1989). this third horizon also contains a. bayi. what conclusions can be made from all these observations? 1. it seems likely that a. bauhini has a longer range in south germany, as suggested by the many records of this ammonite species from the e. hypselum subzone of the e. bimammatum zone to the i. planula and s. galar zones and even from the s. platynota zone; a number of these determinations, although probably not all, may however be erroneous (schweigert 1995b). data from poland also demonstrate that the range of a. bauhini is not restricted to the upper t. hauffianum zone (= a. bauhini horizon), but extends as in southern germany from the upper e. hypselum subzone of the e. bimammatum zone to the top of the i. planula zone sensu lato (matyja & wierzbowski 1997, 1998). it is likely, therefore, that the a. bauhini zone is of longer duration in the submediterranean area, because it comprises not only the a. bauhini horizon of the upper t. hauffianum subzone, but also three or four horizons of the i. planula zone sensu stricto and at least one horizon of the lower s. galar zone. as mentioned above, malinowska (1991, p.16–17) apparently introduced the term a. lineatum subzone for such an extended a. bauhini zone. approximately the same time interval has been called the a. bauhini subzone (of an unnamed zone) by matyja & wierzbowski (1994, 1995) and subsequently elevated to the a. bauhini zone (matyja & wierzbowski 1997, 1998); this zone is now correlated with the upper e. bimammatum zone and the i. planula zone sensu lato. it should also be noted that there is some evidence, at least in scotland, that above the p. densicostatum bed follows another, younger bed with a. bauhini and pictonia sp. (wright 1989). this could be a hint that there are some more beds with a. bauhini, but without p. densicostata, which could correspond to the higher horizons of the p. baylei zone. in england, in contrast, cox & richardson (1982) observed a. bauhini in the uppermost part of the a. rosenkrantzi (= r. pseudocordata) zone. if these determinations are correct, a. bauhini may occur a little earlier than the p. densicostata horizon. one can conclude from these observations that the range of a. bauhini, even in the subboreal regions, is not restricted to the p. densicostata horizon or the ‘a. bauhini zone’ sensu wierzbowski & smelror (1993). 2. if it can be confirmed that amoeboceras bayi and amoeboceras subtilicaelatum are synonymous, as assumed by schweigert (1995b), then the upper horizon of the sutneria galar zone (a. subtilicaelatum horizon) may correspond to the amoeboceras bayi horizon of the lowermost kimmeridgian amoeboceras kitchini zone. it should be noted, however, that a. bayi has also been reported from the lower (‘orthosphinctes’) horizon of the s. platynota zone (atrops et al. 1993b). 3. (a) it can be concluded from the above that correlation of the a. bauhini and p. densicostata horizon with the a. subtilicaelatum and a. bayi horizon is possible, but the vertical ranges of the former species may be longer and the correlation may thus be only partial. consequently, the position of the upper boundary of the a. bauhini zone and the lower boundary of the a. bayi horizon require more precise definition. (b) in the sequence between the a. bauhini and the a. subtilicaelatum horizons, equivalent to the middle part of the pictonia baylei zone, the p. baylei horizon of normandy and the upper a. bauhini-bearing beds in scotland (e.g. bed 38 with pictonia sp., wright 1989) could be expected. they may have 88 their equivalents anywhere in this succession, whereas other parts of the submediterranean succession are not represented in the subboreal sections or only by gaps. (c) the inclusion of this part of the submediterranean subdivision in an a. lineatum subzone (malinowska 1991) with its unprecise limits (in southern germany, the species is known to occur in the upper oxfordian and lower kimmeridgian) will not help significantly; this subzone can be replaced by the a. bauhini zone, as used by matyja & wierzbowski (1997, 1998). (d) there are apparently different possibilities of correlation and further research is necessary to clarify the situation. (e) the subboreal oxfordian–kimmeridgian boundary (r. pseudocordata/p. baylei zone) can, with a high degree of probability, be positioned within the submediterranean and mediterranean scheme in the uppermost part of the e. bimammatum zone on the basis of the correlation of the a. bauhini horizon with the p. densicostata horizon. the submediterranean oxfordian–kimmeridgian boundary remains at the base of the s. platynota zone. additional remarks on lower kimmeridgian correlation as mentioned above, the upper s. galar zone (a. subtilicaelatum horizon) is probably an equivalent of the amoeboceras bayi horizon (schweigert 1995a), which extends into the lower part of the s. platynota zone (amoeboceras horizon with a. bayi, see atrops et al. 1993b). this contrasts somewhat with the correlation of birkelund et al. (1983, table 1), who considered the pictonia baylei zone and the paraspidoceras rupellense zone of hantzpergue (1979) to be equivalent. hantzpergue (1989), too, correlated the p. baylei zone with the p. rupellense zone (horizons r1 and r2); horizons p1–3 of the i. planula zone sensu lato are considered to be equivalent to the r. pseudocordata zone sensu lato (hantzpergue 1989, tables e, f). in his sections, he found the upper oxfordian sutneria galar in the lithacosphinctes gigantoplex horizon (p3), immediately below his p. rupellense zone (see fig. 2). the p. rupellense zone itself is situated between the gigantoplex horizon (p3) of the uppermost idoceras planula zone sensu lato and the rasenia cymodoce zone (fig. 4); it is therefore considered to be equivalent to the lowermost submediterranean kimmeridgian (s. platynota zone; schairer 1970; atrops 1982; olóriz & rodríguez-tovar 1996); its lower horizon (r1) seems to correspond to the upper part of the lower (‘orthosphinctes’) subzone of the s. platynota zone, whereas the lower part (amoeboceras horizon) of this zone is not represented; its upper horizon (r2) contains the index ‘ardescia virgatoides’, which is similar to forms of the ardescia desmoides horizon of the ardescia desmoides subzone of the middle sutneria platynota zone and is therefore very important for correlation to the submediterranean region. above the p. ruppelense zone, hantzpergue (1989) subdivided the rasenia cymodoce zone into nine horizons (c1–9); the r. cymodoce horizon (c2) could be traced from western france to normandy and the subboreal regions. in northern europe, the r. cymodoce horizon is rather widespread (wierzbowski 1989) and in spitsbergen it represents the only rasenoid horizon within the amoeboceras succession. in east greenland, birkelund & callomon (1985, fig. 5) recognised two other horizons below the horizon of rasenia cymodoce (‘17’), namely the ‘pachypictonia’ horizon (‘16’) and the rasenia inconstans horizon (‘15’). these horizons of the lower r. cymodoce zone were considered to be equivalent to the p. altenense horizon (c1; hantzperque 1989); they are probably equivalent to the lower ataxioceras hippolytense subzone of the lower ataxioceras hypselocyclum zone of south-east france, whereas the r. cymodoce horizon perhaps has its equivalents in the upper part of this subzone. in the middle and upper part of the r. cymodoce zone, only a few possibilities remain for far-reaching correlations in europe, such as the eurasenia aulnisa horizon (c5), which contains the highly characteristic submediterranean subzonal index a. lothari, and the semirasenia askepta horizon (c7), which has been found in scotland, england, normandy, western france (birkelund & callomon 1985; hantzpergue 1989) and southern germany (heller 1964; doben & heller 1968). in northern germany, submediterranean ammonites of early kimmeridgian age have been found in sediments which had earlier been attributed to the upper oxfordian (fischer 1991). substages the kimmeridgian stage has been subdivided into two or three substages; here a subdivision into three sub89 stages is preferred. if the middle kimmeridgian is not recognised, then the middle and the upper part are united as upper kimmeridgian (fig. 4). zones in the mediterranean and submediterranean provinces, the lower kimmeridgian consists of three zones, which can be correlated approximately as follows: (1) sowerbyceras silenum – sutneria platynota, (2) ataxioceras hypselocyclum – taramelliceras strombecki and (3) crussoliceras divisum – mesosimoceras herbichi (fig. 4). their further subdivision into subzones is different in both areas (fig. 4); precise correlation of these units is thus difficult (pavia et al. 1987; sarti 1993). detailed subdivisions into subzones and faunal horizons have been proposed in south-east and western france (atrops 1982; hantzpergue 1989); that of south-east france can also be used with some minor changes in southern germany. the submediterranean zonal subdivision as established by geyer (1961) can be used from the iberian peninsula to bulgaria and turkey (sapunov 1977a; lopez marques 1983; alkaya 1992). in poland, the submediterranean zonal subdivision has been adopted by malinowska (1988) and matyja & wierzbowski (1998). in subboreal and boreal regions, subdivision into two zones is typical (see above): (1) pictonia baylei and (2) rasenia cymodoce. these zones can be replaced by the amoeboceras kitchini zone in areas where no perisphinctids occur (e.g. wierzbowski & smelror 1993); this zone may extend into the lower part of the aulacostephanus mutabilis zone (see below). the middle and upper kimmeridgian substages together consist of three zones in all parts of europe (fig. 4). 1. in mediterranean and submediterranean europe: (1) aspidoceras acanthicum zone, (2) mesosimoceras cavouri or aulacostephanus eudoxus zone and (3) hybonoticeras pressulum/h. beckeri or h. beckeri zone. 2. in boreal and subboreal europe: (1) aulacostephanus mutabilis zone, (2) a. eudoxus zone and (3) a. autissiodorensis zone. in regions where no perisphinctids are present, these latter zones can be replaced in the lowermost parts by the amoeboceras kitchini zone (see above) followed by the a. kochi, a. elegans and suboxydiscites taimyrensis zones (fig. 4). the latter index has been taken from northern siberia charts (birkelund & callomon 1985), but there is no mention of this species in more western regions, with the exception of a determination from the middle kimmeridgian of greenland. therefore, for these boreal regions too, aulacostephanus autissiodorensis seems to represent the more appropriate index species. the middle kimmeridgian zonal and subzonal subdivisions can be applied without great difficulty in boreal, subboreal and submediterranean europe, as there are large regions with overlapping guide fossils, whereas in the mediterranean province, only a zonal subdivision is possible. hantzpergue (1989) established a detailed subdivision in western france, which can also be used in northern france (geyssant et al. 1993; proust et al. 1993) and traced as far as germany (zeiss 1991b; schweigert 1993a, 1996a), england, norway and east greenland (hantzpergue 1989). an unresolved problem is the lower boundary of the a. mutabilis zone; it is drawn at the base of the a. lineatum horizon in western and northern france (hantzpergue 1989; hantzpergue et al. 1997), but in england, following the revisions of birkelund et al. (1983), it is placed four horizons deeper, at the base of the s. askepta horizon. recent investigations in central poland came to similar results (matyja & wierzbowski 1998); these workers traced the boundary to a slightly deeper level in the upper a. hypselocylum zone. in germany and the submediterranean region, the usage from south-east france has been followed (hantzpergue 1989; hantzpergue et al. 1991; zeiss 1991b), which facilitates correlation with the base of the a. acanthicum zone; the lower boundary of this zone in germany is traditionally drawn at the incoming of the first representatives of the genus aulacostephanus (lineatum group). in a recent publication by hantzpergue et al. (1997), the problems of this boundary are well illustrated by their table 12; in the ‘biome franco-germanique’, the lower boundary of the a. mutabilis zone is drawn below its lowermost horizon (linealis horizon), whereas the base of the a. mutabilis subzone, curiously, is placed two horizons higher (attenuatus horizon). it is evident that the new data from poland (matyja & wierzbowski 1998), which place the base of the a. mutabilis zone much deeper, will probably necessitate revision of all these correlations. amoeboceras subdivisions are important from norway to spitsbergen (wierzbowski 1989; wierzbowski & århus 1990; wierzbowski & smelror 1993) and east greenland (birkelund & callomon 1985). 90 in the upper kimmeridgian (upper a. autissiodorensis zone) of poland and the russian platform, a sarmatisphinctes fallax subzone has been established (mesezhnikov 1984, 1988; kutek & zeiss 1994, 1997). for the lower part (lower a. autissiodorensis zone), the discosphinctiodes subborealis subzone is proposed; d. subborealis is a significant index fossil. in poland, aulacostephanus autissiodorensis has been found only in the lower and middle parts of the s. fallax subzone. in western siberia, a zone of virgataxioceras dividuum is the equivalent of the s. fallax subzone (mesezhnikov 1988). in northern germany, schweigert (1996a) stated, based on re-study of previous collections, that the a. autissiodorensis zone is probably present. in southern germany, where subdivision into two subzones was previously adopted, new discoveries of ammonites have made it possible to organise the h. beckeri zone into three subzones: (1) sutneria subeumela, (2) virgataxioceras setatum and (3) lithacoceras ulmense (schweigert & zeiss 1994, 1999); further subdivision into several faunal horizons is possible (schweigert 1996b, 1998). furthermore, schweigert (1993a, b, 1994) discovered ammonites in the upper kimmeridgian of swabia with a subboreal habitus, providing better correlation possibilities between the subboreal a. autissiodorensis and submediterranean h. beckeri zones (see below). for the upper kimmeridgian of western france, a useful subdivision has been proposed by hantzpergue (1989), who subdivided the a. autissiodorensis zone into two subzones, the a. autissiodorensis and the gravesia irius subzones, each with two faunal horizons. the succession in the boulonnais area and farther north has been worked out in detail by geyssant et al. (1993) and geyssant (1994); the succession in southern england was reported by cox & gallois (1981), birkelund et al. (1983) and callomon & cope (1996). correlation many difficulties are encountered in correlating zones (and subzones) of the lower kimmeridgian in europe, mainly between the submediterranean and subboreal regions, but also between the submediterranean and mediterranean areas (fig. 4). many correlations are arbitrary and well-constrained correlation is only possible at certain levels. such correlation possibilities in the lower kimmeridgian substage have already been explained in connection with the problems of the oxfordian–kimmeridgian boundary. some problems exist around the lower–middle kimmeridgian boundary, as the base of the a. mutabilis zone is variably defined in different parts of europe (see above). considering the most recent results from poland (matyja & wierzbowski 1998), the lower boundary of the subboreal a. mutabilis zone lies within the uppermost part of the submediterranean a. hypselocyclum zone, i.e. one zone deeper than previously assumed. in the middle kimmeridgian substage, correlations within the a. acanthicum/a. mutabilis zones and the a. eudoxus zone pose no great problems although the uppermost part of the a. eudoxus zone of western france (a. contejeani subzone) seems to correspond to the lower part of the h. beckeri zone in south germany (schweigert 1993b). correlation of the a. kochi zone with the upper part of the a. mutabilis and/or the lower part of the a. eudoxus zone (wierzbowski & smelror 1993) is still tentative, as is the correlation of the a. elegans zone with most of the a. eudoxus zone. correlation of the upper kimmeridgian substage (submediterranean h. beckeri zone with the subboreal a. autissiodorensis zone) was hitherto only possible by indirect arguments. the elaboration of a new zonal and subzonal subdivision in western france by hantzpergue (1989) and the new discoveries by schweigert (1993a, b, 1994) in germany and by kutek & zeiss (1997) in poland now permit correlation of parts of the upper kimmeridgian of western, central and eastern europe and perhaps also western siberia. chronometric data the duration of the kimmeridgian stage has been estimated to be 3.4 ma (gradstein et al. 1995; ogg 1995; ogg & gutowski 1996); for precise data, see figure 4. tithonian and volgian (fig. 5) the tithonian, and its boreal equivalent the volgian, have been confirmed as stage names by a vote of the international subcommission on jurassic stratigraphy in 1990 (zeiss 1991a). a further stage name ‘bononien’ (for the ‘upper kimmeridgian sensu anglico’, proposed by cope 1993) seems unnecessary and could result in each region with a differing zonal subdivision claiming its own stage name, leading only to more confusion rather than to international agreement concerning uniform nomenclature. furthermore, due to the different meanings of the stage ‘portlandian’ in different 91 countries, it was voted in 1990 that usage of this name should be discontinued. the most recent review of the tithonian stage and its ammonites is that provided by geyssant (1997); for the volgian stage and ammonite biostratigraphy, see gerasimov et al. (1995), callomon & cope (1996) and kutek & zeiss (1997). lower boundary the base of the tithonian stage is defined by the base of the hybonoticeras hybonotum zone. it is generally supposed that the base of the coeval gravesia gigas, virgatosphinctoides elegans and ilowaiskya klimovi zones are drawn at approximately the same time level (see also below). substages the tithonian is subdivided into two or three substages; here preference is given to a tripartite tithonian stage (fig. 5). if only two substages are used, then the lower and middle part are united as the lower substage (‘danubian’), the upper substage corresponds to the ‘ardescian’ substage. type regions for the lower and middle tithonian substages have been proposed by barthel (1975) and zeiss (1975). the type region for the upper tithonian substage, the ardescian, has been revised by cecca et al. (1989a, b). the subdivision of the volgian is threefold, into lower, middle and upper substages. the lower and middle substages (‘gorodishchian’) correspond roughly to the tithonian stage (fig. 5), whereas the upper substage 92 n. italy (s. spain) e. austria, moravia russian platforms. germany central poland england greenland vulgaris (durangites) [crassicollaria] subpalmatus ? palatinus vimineus triplicatus tagmersheimense moernsheimense rueppellianus riedense palmatus glaber ciliata rothpletzi/ penicillatum albertinum (darwini) hybonotum volanense (ponti, ‘burckhardticeras’) transitorius transitorius [crassicollaria] [granulosa p.p.] [dunkeri] pseudoscythica pseudoscythica sokolovi sokolovi klimovi klimovi puschi regularis zarajskensis scythicus quenstedti oppressus nikitini blakei rosanovi virgatus zarajskensis pavlovi (disprosopa, contradictionis) oppressus anguiformis kerberus okusensis glaucolithus albani fittoni rotunda pallasioides elegans scitulus eastlecottensis paravirgatus dorsetensis smedmorensis wheatleyensis reisiformis encombensis scitulus wheatleyensis hudlestoni pectinatus primus iatrensis rugosa communis liostraca gracilis pseudaperta anguinus groenlandicus elegans vogulicus (pseudoscythica) mucronatum lithographicum admirandum/ biruncinatum semiforme/ verruciferum richteri richteri volanense austriacus [rugosa] tenuicostata occidentalis tenuicostata tenuicostata magnum [boneti] scruposus simplisphinctes m ic ra ca nt um u pp er m id dl e t it ho ni an lo w er fa lla ux i fa lla ux i sc yt hi cu s pa nd er i pe ct in at us h ud le st o ni w he at le ye ns is pa ra vi rg at us v ir ga tu s m id dl e vo lg ia n lo w er v o lg ia n n ik it in i h yb o no tu m m uc ro na tu m v im in eu s se m ifo rm e 14 4. 0 (± 2. 5) 15 0. 7 (± 3. 0) mediterranean submediterranean subboreal eastern western boreal fig. 5. a tentative correlation chart for the tithonian and volgian stages in europe (thick lines as in fig. 2). modified after barthel (1964), zeiss (1968, 2001), cope et al. (1980), callomon & birkelund (1982), kutek & zeiss (1988, 1997), mesezhnikov (1988), sarti (1988), zeiss & bachmayer (1989), mitta (1993), kutek (1994) and geyssant (1997). non-ammonite taxa are indicated in square brackets. (‘kashpurian’) belongs to the cretaceous system (sasonova & sasonov 1979; zeiss 1983, 1986; sey & kalacheva 1993a; w.a. wimbledon in: callomon & cope 1996). a type section for the volgian stage has been proposed by gerasimov & mikhailov (1966). zones and subzones whereas the two lower stages of the upper jurassic have two main zonal subdivisions, at least four subdivisions are necessary in the upper stage (fig. 5). this is due to the extreme provincialism of ammonites caused by the increasing isolation of late jurassic marine basins, which seem to have only rarely been directly connected; interbasinal migration was apparently only favoured during the lowermost zone of the stage. the most important lower zone is that of hybonoticeras hybonotum, which can be followed over long distances in mediterranean and submediterranean europe (zeiss 1968; olóriz 1978; sapunov 1979; sarti 1988); in southern germany it is possible to recognise three subzones and seven horizons in the h. hybonotum zone (schweigert & zeiss 1999). in central europe, the latter overlaps with the gravesia gigas zone, which has a rather wide distribution regionally in central and western europe. during the last decades, many new discoveries have been reported and the genus gravesia and the stratigraphy of the beds with gravesia have been revised (hahn 1963; zeiss 1974; hantzpergue 1989; schweigert 1994, 1996a, b; schweigert et al. 1996; zeiss et al. 1996; dimke & zeiss 1997). in the subboreal subprovince, the genus gravesia is also present, but less numerous, so that other index fossils have been given priority, such as virgatosphinctoides elegans in northwestern and ilowaiskya klimovi in eastern europe (cope 1967; cope et al. 1980; kutek & zeiss 1974, 1994, 1997; callomon & birkelund 1982; mesezhnikov 1988). according to callomon & cope (1996), gravesia cf. gravesiana occurs in the lower part of the virgatosphinctoides scitulus zone, thus demonstrating the correlation with the upper h. hybonotum zone (containing g. gravesiana). in northern germany, beds with gravesia gigas intermedia are apparently the youngest beds containing jurassic ammonites (schweigert 1996a) and are succeeded by brackish and freshwater sediments up to the jurassic–cretaceous boundary. in these beds, ostracodes have proved to be the best guide fossil (bischoff & wolburg 1963; schudack 1994, fig. 24), permitting subdivision of the tithonian stage in northwest germany into four zones. in other areas, such as eastern england and denmark, subdivision into nine zones is possible using ostracodes (christensen 1988; schudack 1994, fig. 24). the upper zone of the lower tithonian in mediterranean europe, the zone of semiformiceras darwini (or of virgatosimoceras albertinum), is apparently equivalent to the neochetoceras mucronatum and franconites vimineus zones (each of them with two subzones and some horizons) of submediterranean europe, as they have numerous faunal elements in common (enay & geyssant 1975; olóriz 1978; cecca et al. 1986; sarti 1984, 1988; cecca 1990a, b). precise correlations have still to be worked out, however, and at present this is difficult as no subzones or even horizons have been recognised in the tethyan realm. the submediterranean zones have been traced from south-east france via southern germany to hungary as well as in bulgaria and perhaps also turkey (zeiss 1968; sapunov 1977b, 1979; vigh 1984; fözy 1988, 1993; alkaya 1989; atrops 1994; fözy et al. 1994). correlation with the subboreal regions is only tentative and different proposals have been published (fig. 5; zeiss 1977; mesezhnikov 1988; kutek & zeiss 1997). in subboreal europe, the situation is not much better and correlations between the different subprovinces of northwest and eastern europe are only approximate. consequently, different zonal subdivisions are also applied in these subprovinces. in eastern europe, for example, species of the genus ilowaiskya are used (e.g. the ilowaiskya sokolovi and i. pseudoscythica zones; mesezhnikov 1988; kutek & zeiss 1997), whereas in northwest europe, representatives of the genera virgatosphinctoides, arkellites and pectinatites have been selected (e.g. the virgatosphinctoides scitulus, w. wheatleyensis, arkellites hudlestoni and pectinatites pectinatus zones); each of these latter zones can be subdivided into two subzones (cope et al. 1980; callomon & birkelund 1982; geyssant 1997). for the middle tithonian substage, the subdivisions in mediterranean and submediterranean europe are rather distinct (fig. 5). furthermore, minor faunal differentiations exist within the mediterranean area, and different zonal indexes are used for the same time interval (enay & geyssant 1975; olóriz 1978; cecca & santantonio 1988; sarti 1988): (1) semiformiceras semiforme or haploceras verruciferum, (2) semiformiceras fallauxi or (2a) richteria richteri and (2b) simoceras admirandum/biruncinatum (or s. biruncinatum), and (3) simoceras volanense or ‘burckhardticeras’ peroni or micracanthoceras ponti. note that burckhardticeras olóriz 1978 is a junior homonym of burckhardticeras 93 flores lopez 1967 (schweigert & zeiss 1998). in the submediterranean area of southern germany, the following guiding ammonites have been observed (barthel 1975; zeiss 1986): (1) virgatosimoceras rothpletzi and sublithacoceras penicillatum, (2) lemencia ciliata, (3a) sublithacoceras(?) glaber, (3b) isterites palmatus, and (3c) isterites subpalmatus. according to scherzinger & schweigert (1999), a horizon with sublithacoceras callodiscus has been observed above the level with lemencia ciliata. in eastern europe, the equivalents of the middle tithonian substage are probably the upper part of the lower volgian (upper ilowaiskya pseudoscythica and ilowaiskya tenuicostata zones). the latter unit is discernable in poland but has not been recognised in russia to date (kutek & zeiss 1974, 1988, 1994, 1997; mesezhnikov 1988; kutek 1994). in its upper part, the pseudovirgatites puschi horizon is important due to its mixed fauna (kutek & zeiss 1974, 1988, 1997). a local time equivalent in north-eastern austria is probably the isterites austriacus zone with buchia rugosa as an important guide fossil (fig. 5). a quite different zonal subdivision exists in great britain and the adjoining subboreal and boreal regions as far as greenland (cope 1978, 1980; wimbledon 1980; callomon & birkelund 1982; kejsi et al. 1988); the middle tithonian perhaps corresponds to the main part of the pectinatites pectinatus zone and perhaps to the pavlovia pallasioides zone of england or to the dorsoplanites primus and pavlovia iatrensis zone of east greenland. the upper tithonian substage consists of two or three zones in the mediterranean area. in southern spain, the lowermost zone has been identified as the simplisphinctes zone (tavera 1985). this unit has not been identified in northern italy (sarti 1988), but could be recognised as far as north-eastern austria, where the same ammonite fauna (containing the genus oloriziceras) occurs (zeiss & bachmayer 1989). in the absence of the rather peculiar index genus simplisphinctes, this zone was called the oloriziceras magnum zone for this region (zeiss 2001). above the simplisphinctes (or s. abnormis or o. magnum) zone, the paraulacosphinctes transitorius zone (with the first crassicollaria) occurs. a micracanthoceras micracanthum zone is sometimes adopted instead of the p. transitorius zone; this zone apparently also contains the equivalents of the simplisphinctes (better s. abnormis) zone (enay & geyssant 1975; sarti 1988; geyssant 1997). some authors consider the simplisphinctes and p. transitorius zones as subzones of the m. micracanthum zone (benzaggagh & atrops 1997; geyssant 1997) although the former authors, based on moroccan data, only partially substituted the simplisphinctes subzone, replacing its upper part and the p. transitorius subzone by two new subzones, that of ‘micracanthoceras (corongoceras) spp.’ and that of ‘moravisphinctes spp.’. it is very important that these new subzones can be correlated rather precisely with the calpionellid subdivision; the chitinoidella boneti subzone (of the chitinoidella spp. zone) corresponds to the first two subzones. the base of the crassicollaria spp. zone (zone a) approximately coincides with the base of the moravisphinctes spp. subzone, which corresponds to the lower part of this zone (= subzone a1). the durangites zone follows above the p. transitorius zone. in northern italy, this zone was named the durangites vulgaris zone by sarti (1988); this term has also been adopted by other authors. in some countries, this zone has not been recognised; the equivalents of this zone are then apparently included in the p. transitorius zone, which sometimes even includes parts of the lower cretaceous (e.g. sapunov 1977b). the fauna of this zone has been mainly described by tavera (1985), tavera et al. (1994) and enay et al. (1998a, b). during the middle volgian, central poland belonged to the eastern subboreal subprovince, but only the lowermost unit, the zaraiskites scythicus zone (with the lower z. scythicus and upper z. zarajskensis subzones) is represented (kutek 1994). brackish sediments prevail higher in the polish section and yield ostracodes; the cypridea dunkeri and the cypridea granulosa zones can be recognised. on the russian platform, the lowermost horizon of the z. scythicus subzone (z. quenstedti horizon in poland) is probably represented by beds containing zaraiskites disprosopa and isterites(?) contradictionis (ilovaiskij & florenskij 1941). on the russian platform, a dorsoplanites panderi zone is now used instead of the z. scythicus zone (mesezhnikov 1988; kutek 1994); above follows the virgatites virgatus zone (with three subzones: v. gerasimovi, v. virgatus and c. ivanovi; gerasimov et al. 1995). the v. virgatus zone is succeeded by the epivirgatites nikitini and lomonossovella blakei zone (separated by callomon & birkelund (1982), and, in reverse order, by mesezhnikov (1988) but adopted as a single zone by other russian authors (e.g. gerasimov et al. 1995)). the uppermost middle volgian is represented by the paracraspedites oppressus zone (mesezhnikov 1988). in the baltic area, middle volgian ammonites are rare although a few specimens from lithuania were mentioned by rotkyte . (1976, 1987). in scandinavia, middle volgian ammonites have been found in denmark 94 (birkelund & pedersen 1980) and in norway (birkelund et al. 1978). in england and east greenland, dorsoplanitidae are prevalent, but in both these regions, the subdivisions are distinct; in england, pavlovia pallasioides, pavlovia rotunda and virgatopavlovia fittoni characterise the lower part of the middle volgian whereas progalbanites albani and the giants glaucolithites glaucolithus, galbanites okusensis, kerberites kerberus and titanites anguiformis characterise the upper part (cope 1978; wimbledon & cope 1978). as in russia, the uppermost zone is the paracraspedites oppressus zone (casey 1973; kejsi & mesezhnikov 1986; kejsi et al. 1988), but not all authors adopt this zone. in east greenland, there are some similarities with siberian ammonite successions, but in general the subdivision there has its own character and, with three exceptions, its distinct index species (callomon & birkelund 1982; mesezhnikov 1988): dorsoplanites primus, pavlovia iatrensis, pavlovia rugosa, pavlovia communis and dorsoplanites liostracus characterise the lower part of the middle volgian, whereas dorsoplanites gracilis, epipallasiceras pseudapertum, crendonites anguinus, laugeites groenlandicus and epilaugeites vogulicus are represented in the upper part. the lower part of the upper volgian praechetaites tenuicostatus zone of east greenland may correspond to the uppermost part of the middle volgian, the upper paracraspedites oppressus zone of england and the lower praechetaites exoticus zone (= lowermost craspedites okensis zone sensu lato) of northern siberia. correlation as explained above, the basal zones of the tithonian (and volgian) can be correlated over long distances, but correlation becomes very difficult in the higher parts of these stages. not only is it difficult to correlate between the boreal and mediterranean regions, but also within these regions. distinct lineages of ammonites were evolving throughout the area and consequently it is necessary to develop and apply different ammonite zonal subdivisions; correlation possibilities are thus only few and mostly tentative. many attempts have been made to correlate the different zonal subdivisions of europe (cope & zeiss 1964; zeiss 1965, 1974a, 1979, 1983, 1986; enay 1972; enay & geyssant 1975; olóriz 1978; callomon & birkelund 1982; jeletzky 1984, 1989; tavera 1985; cecca et al. 1986; hoedemaker 1987, 1991; kejsi et al. 1988; kutek & zeiss 1988, 1997; geyssant & enay 1991; sey & kalacheva 1993a; kutek 1994; w.a. wimbledon in: callomon & cope 1996; geyssant 1997). due to problems of provinciality, such correlation schemes are necessarily speculative and ultimately unsatisfactory. a tentative summary correlation scheme is given in figure 5, based on developments since earlier attempts by the author (zeiss 1983, 1986). a similar, although in detail somewhat different, correlation chart has recently been published by hantzpergue et al. (1998). concerning the middle and upper tithonian (upper lower and middle volgian) substages, a number of observations are pertinent. although correlation between the mediterranean and submediterranean area is quite possible in the lowermost middle tithonian substage (s. semiforme/r. richteri – v. rothpletzi/s. pennicilatum zones), a number of different proposals have been made for the higher zones (enay & geyssant 1975; olóriz 1978; jeletzky 1984, 1989; cecca et al. 1986; kutek 1994). a satisfactory answer to this problem requires complete revision of the famous submediterranean neuburg fauna and sections, in which some levels with distinct ammonite faunas have already been recognised by barthel (1964, 1975). in eastern central europe (north-eastern austria, moravia, central and southern poland), some submediterranean and mediterranean ammonites genera of middle and late tithonian age are represented by characteristic forms. they sometimes interfinger with subboreal elements, thus providing good potential for correlation (kutek & wierzbowski 1986; kutek & zeiss 1988, 1997; kutek 1994). the i. tenuicostata and z. scythicus zones of central and southern poland, for example, display interesting forms with affinities to both the submediterranean and subboreal provinces. combined with observations from other localities, this facilitates better correlation between these two regions: (1) the pseuvirgatites puschi horizon of the uppermost ilowaiskya tenuicostata zone contains isterites species described from the higher parts of the neuburg beds, i.e. of late middle tithonian age, and (2) the z. regularis horizon of the lower z. zarajskensis subzone (upper z. scythicus zone) contains pseudovirgatites scruposus and calpionellids indicative of the calpionellid zone a, such that correlation is possible with the lower part of the paraulacosphinctes transitorius zone. in the boreal and subboreal provinces, quite different zonal subdivisions exist, mainly based on different perisphinctid groups, such as the pectinatitinae and dorsoplanitinae in england, denmark, norway and greenland and the ilowaiskyinae, virgatitinae and dorsoplanitinae in poland and russia. the correlation of these zones is rather arbitrary, as demonstrated by callomon & birkelund (1982), mesezhnikov (1988) and 95 w.a. wimbledon (in: callomon & cope 1996), and is based mainly on similar, but non-identical species of dorsoplanitinae. chronometric data the approximate duration of the tithonian has been estimated to be 6.7 ma (gradstein et al. 1995; ogg 1995); for precise data, see figure 5. biochronological importance of nonammonite fossil groups: a review the jurassic system is the classic one for subdivision by ammonites. this fossil group has been used with much success since the pioneering work in the last century by workers such as l. von buch, a. d’orbigny, a. oppel, f.a. quenstedt, k.a. von zittel and s. buckman. indeed, this contribution on the chronological subdivision of the upper jurassic of europe has been compiled primarily using ammonites (see above). however, upper jurassic marine sediments of epicontinental shelves, the habitat of ammonites, are not present everywhere in europe, so that ammonites are not always available. it is often necessary, therefore, to utilise other fossil groups with proven stratigraphic value such as bivalves, brachiopods, foraminifera, ostracodes and distinct plant mega-, microand nannofossil groups. radiolarians, calpionellids, conchostracans, insects and vertebrates should also be added to this list; the first two groups are very useful in pelagic sedimentary basins whereas the last ones are used with much success in the stratigraphic subdivision of continental sediments, such as those of central and eastern asia and of north america. the challenging task of correlating between the different fossil subdivision schemes has been addressed for individual groups (e.g. le hégarat & remane 1968; surlyk & zakharov 1982). multidisciplinary correlation charts, typically for microfossil groups, have only been successfully developed within the last two decades. useful though incomplete examples of such schemes, including microand macrofossils, have recently been published by tavera et al. (1994), r. enay (in: cariou & hantzpergue 1997), gramann et al. (1997) and remane (1997). it remains as one of the more important tasks, however, to establish european multidisciplinary correlation charts that incorporate all fossil groups important for biochronology and also include radiometric ages and palaeomagnetic reversal data. during the editorial work, it was brought to the attention of the author that charts fulfilling many of these expectations have recently been published by hardenbol et al. (1998, charts 6–7); of special interest are the chronometric data for most of the biochronostratigraphic units (see below). invertebrate megafossil groups cephalopods – other than ammonite conchs aptychi in the tethyan regions, aptychi have proven to be a useful addition to ammonites for the subdivision of upper jurassic sediments. following the studies of durand & gąsiorowski (1970) and gąsiorowski (1962, 1985), it is possible to differentiate eleven zones of aptychi using four larger groups of aptychi, the lamellaptychi and laevaptychi and to a lesser degree the laevilamellaptychi and punctaptychi. correlation between aptychi and ammonite zones still poses problems (a. wierzbowski, personal communication 1998). eliás̆ et al. (1996) also used aptychi ranges for biostratigraphy, but without a zonal subdivision; they preferred a multidisciplinary correlation method using the calpionellid subdivision as reference. belemnites the most recent review of this fossil group is that of doyle & bennett (1995) which includes a section on middle and upper jurassic belemnite groups, including those of europe. this publication presents a comprehensive review of the subject, including the work of saks & nalnyaeva (1964, 1966), riegraf (1980, 1981), combémorel & mariotti (1986), and doyle & kelly (1988); a range chart of the most useful taxa for biostratigraphy of the middle and upper jurassic is included by doyle & bennett (1995). the stratigraphic ranges of some more important polish species have been published by pugazewska (1988) and malinowska (1997) and those of sicily by combémorel & mariotti (1990). recently, combémorel (1997) compiled all data available for the tethys and the boreal region of europe and for each of them presented a correlation scheme with the subdivisions based on ammonites and belemnites; see also hardenbol et al. (1998, chart 7). 96 bivalves the most important group of bivalves for biostratigraphic purposes in the upper jurassic of europe is the genus buchia. in the boreal regions of eurasia and north america, it is of particular importance as a supplement to ammonites. the genus has been the focus of many papers in the last decades such as zakharov (1981, 1987, 1990), surlyk & zakharov (1982), jeletzky (1984), kelli (1990), sey & kalacheva (1993b) and sha & fürsich (1994). an interesting interpretation of the different ranges of buchia species in america and eurasia has been presented by hoedemaker (1987). stratigraphic range lists of selected bivalve species from poland have been published by karczewski & pugaczewska (1988) and malinowska (1997). a correlation chart that is mainly based on buchiid bivalves but also includes other bivalve genera (e.g. retroceramus) has been compiled for northern russia and the circum-pacific regions by damborenea et al. (1992). in the upper jurassic, the stratigraphic resolution of bivalve taxa, with the exception of buchiids, seems to be rather limited and/or needs further research (damborena et al. 1992). for some regions, stratigraphic range lists of selected bivalve species have been published, for example for poland (malinowska 1997; karczewski & pugaczewska 1998) and for northern germany by kaever et al. (1976). gastropods the biostratigraphic resolution of this group in the jurassic is not very high, but in special cases, when other guide fossils are not present, some representatives of the group may be used. an example from the upper jurassic of france (nerineaceae) has been published recently by barker (1994). range lists of selected species from poland have been published by karczewski (1988) and malinowska (1997). brachiopods the most recent reviews of this group with respect to upper jurassic brachiopods are those of ager (1994) and alméras et al. (1991, 1994), especially for france and britain, and boullier & laurin (1997) for the tethys and the ‘domaine nw européen français’. ager (1994) considered the group within a global context. alméras et al. (1994) discussed the facies dependence of brachiopods, concluding that distinct zonal species of brachiopods are often necessary for different facies. for biostratigraphical purposes, it is possible to subdivide the upper jurassic of england and north-west france into nine zones and some subunits. the polish species have been figured and described by barczyk (1988); range charts are given in malinowska (1997). prozorovskaja (1993) presented an overview of the brachiopod subdivision of the upper jurassic of the southern part of the former ussr. echinoderms to date, there is no subdivision scheme of the upper jurassic with respect to echinoderms. some genera have biostratigraphic value; saccocoma, for example, has been used in some multidisciplinary schemes. thierry et al. (1997) presented range charts of the upper jurassic regular and irregular echinoid genera and species of france, with the expectation that with detailed research it would be possible to create a subdivision scheme comparable to that developed for the brachiopods of france. corals (scleractinians) this group has poor biostratigraphic resolution. its usefulness for stratigraphic purposes is therefore rather limited, also because of the close dependence of corals on ecological factors (rosendahl 1988). nevertheless, beauvais (1988) subdivided the upper jurassic series (except the lower oxfordian) into six zones based on madreporians (scleractinians). polish species with range charts have been presented by roniewicz & morycowa (1988) and range charts were published by malinowska (1997). sponges this fossil group is poorly suited to regional correlation, but some species may be useful for local subdivision; examples from france have been presented by gaillard (1997). vertebrate megafossils jurassic vertebrate fossils are too scarce to be used as guide fossils. nevertheless, if vertebrate remains are 97 studied thoroughly, they frequently provide valuable biostratigraphic information (e.g. elasmobranchian teeth, gramann et al. 1997). it should be mentioned that the jurassic period in europe saw the early evolution of mammals, the flourishing of the first true birds and the first wave of the acme of the dinosaurs. in other parts of the globe, vertebrates have been used for stratigraphy; in north america, for example, turner & peterson (1998) subdivided the upper jurassic morrison formation into four biozones on the basis of dinosaurs, whereas in china, fish are used for subdivision (chen 1990). invertebrate microfossils foraminifera in the 1950–60s, foraminifera were one of the most important microfossil groups, together with ostracodes, for relative age determinations of marine sediments in boreholes; their importance has decreased in more recent times. studies of foraminifera faunas from outcrops in southern germany were reviewed by groiss (1984). an account of epistominian zonation was given by ascoli (1988), who also presented zonations and correlations between east canadian offshore wells and the east european platform (grigelis & ascoli 1995). foraminifera from northern germany were presented by klingler et al. (1962) and gramann et al. (1997). the guide fossils and characteristic species of the upper jurassic foraminifera of poland have been published by bielecka (1988) and styk (1997), those of the russian platform by a.y. azbel (in: mesezhnikov 1989). foraminifera of sweden were studied by norling (1972) and guy-ohlson & norling (1988). a short compilation of upper jurassic foraminifera in britain has been published by shipp & murray (1981), together with a range chart and figures of index species. the most recent reviews of foraminifera of europe have been compiled by ruget & nicollin (1997) on the small benthic forms, and by bassoulet (1997a) on the large forms; see also hardenbol et al. (1998, chart 7). radiolaria this microfossil group, which has been the subject of much scientific research in recent years in europe, is of particular importance in the tethyan region. a comprehensive monograph was recently published by baumgartner et al. (1995) on the radiolarians of the tethys, including a catalogue of all tethyan species. the biochronological potential for subdividing the upper jurassic series into ‘unitary association zones’ (u.a.z.) is well-demonstrated; there are six such zones covering the whole upper jurassic. they have a duration of between 2–6 ma. this monograph demonstrates the significant advances in research into this group, especially if new quantitative concepts, such as the ‘unitary association zones’, are applied to the biochronological subdivision of the upper jurassic. research into radiolarians and their stratigraphic potential has also been on the increase outside the tethys, as demonstrated by recent publications concerning the submediterranean province (riegraf 1987; kießling 1997; zügel 1997; zügel et al. 1998), and even the subboreal and boreal provinces, including the north sea (dyer & copestake 1989), the russian platform and the barents sea (vishnevskaya 1993, 1997, 1998; kozlova 1994). dyer & copestake (1989) introduced a biozonation based on a succession of ten radiolarian events in the kimmeridgian and tithonian. important attempts are also underway to correlate the new peri-tethyan radiolarian assemblages with different microand macrofossil biozonations (vishnevskaya & de wever 1997); owing to strong provincialism, direct correlation between the peri-tethyan and tethyan zonations is still very difficult, but has been undertaken recently (hardenbol et al. 1998, chart 7). ciliata this group is important only in the tethyan region and the surrounding shelf deposits; the most comprehensive studies of the ciliata in recent years have been published as a result of the sümeg meeting (fülöp 1986; remane et al. 1986). polish forms have been reported by nowak (1988) and those of spain by tavera et al. (1994) and olóriz et al. (1995). remane (1997, 1998) recently published informative reviews of the state-ofthe-art of the group, providing tables which include the stratigraphic succession of calpionellid species and the correlation of calpionellid, nannofossil and ammonite subdivisions with magnetostratigraphic events. nearly simultaneously, blau & grün (1997a, b) and grün & blau (1996, 1997) proposed a revision of the calpionellid zonal and subzonal division. for the tithonian stage, they introduced and formally defined two zones and seven subzones; the duration of zones in the jurassic 98 is less than one million years, that of subzones about 300 000 years. important results from the southern tethyan margin have been contributed by benzaggagh & atrops (1995, 1997). these workers provided precise correlation and species range charts for ammonites and calpionellids for the lower part of the calpionellid succession, which previously was poorly known, and clarified the succession of zones and subzones from the middle tithonian semiformiceras fallauxi/chitinoidella dobeni subzone to the upper tithonian durangites vulgaris/ crassicollaria a3 subzone. an important contribution on the calpionellid faunas of the southern and eastern tethyan region of europe was presented by reháková & michalík (1997); the western carpathians and their foreland in moravia were treated by ̌rehánek (1990) and reháková (1995, 2000). in all these last-mentioned publications, the middle/upper tithonian boundary has apparently been drawn a little too high. following the results of benzaggagh & atrops (1995, 1997), this boundary lies between the dobeni and boneti subzones of the chitinoidella zone and not above this zone. ostracodes this group has a rather high stratigraphic resolution and has therefore been used frequently and successfully for the subdivision of sediments in northern germany, poland, england, the netherlands, the north sea basin, france and russia. in a recent monograph, schudack (1994) revised the ostracodes of the upper jurassic in north-west germany, documenting the correlation possibilities of this group in western, central and northern europe. the upper jurassic of north-west germany was subdivided into nineteen ostracode zones, representing variable durations (0.25–2.5 ma; schudack 1996a; gramann et al. 1997). this study also presents a comprehensive list of all important publications on ostracodes. in northern europe, the papers of herngreen et al. (1988), herngreen & wang (1989) and guy-ohlson & norling (1994) deal with this group in the netherlands and sweden, respectively. in poland, bielecka et al. (1988) treated the group, and range charts have been published by j. szteijn (in: marek & pajchlova 1997); danish faunas were described by christensen (1988). the most recent reviews of european ostracodes are those of bodergat (1997) on marine ostracodes and colin (1997) on non-marine ostracodes; see also hardenbol et al. (1998, chart 7). plant microfossils dinoflagellata dinoflagellate cysts have become a widely used supplement to ammonites and are of particular importance in the subsurface. in a recent study, poulsen (1996) emphasised the important role of dinoflagellates in jurassic stratigraphy while comparing the upper jurassic of denmark and poland. the marine upper jurassic of denmark was divided into seven zones and fifteen subzones whereas that of poland was divided into four zones and twelve subzones (poulsen 1996); the dinoflagellate cyst zonation of the jurassic of subboreal europe is reviewed in poulsen & riding (2003, this volume). in great britain, riding & thomas (1992) have delivered the most recent compilation of dinoflagellates. other important papers are those of sarjeant (1979), riley (1980), riley & fenton (1982) and riding & sarjeant (1984); one concerning russia is that of lentin & vozzhennikova (1990). in the netherlands, herngreen et al. (1988; see also herngreen & wang 1989) presented a report on the stratigraphic bioevents based on the first and last appearance of dinoflagellate cyst species which made possible a subdivision into nine zones. in north-west germany, the oxfordian and kimmeridgian has been subdivided into three dinoflagellate zones and eight subzones (gramann et al. 1997). detailed subdivisions for the boreal and tethyan regions have recently been published by hardenbol et al. (1998, chart 7). calcareous nannofossils (coccoliths, nannolith groups) recent advances in jurassic calcareous nannofossil research have been reviewed by bowen (1996), who dealt with several general aspects of this group, such as evolutionary succession, species diversity and longevity, distribution and provincialism, which are all important when regarding the utility of the group for biostratigraphic purposes. if conditions are favourable, then it is possible to subdivide the upper jurassic into five boreal nannofossil zones (with six subzones) or three submediterranean nannofossil zones (with seven subzones); correlation between these two regions is thus still problematic. the calcareous nannofossil bioevents were recently reviewed by gardin (1997). subdivisions and correlations for the boreal/subboreal 99 and the tethyan/submediterranean provinces can be found in hardenbol et al. (1998, chart 7). charophyaceae this group of calcareous algae has received new impetus with respect to its potential for biostratigraphy. in a recent publication, the results of a local zonal subdivision based on charophytes in the lower saxony basin of north-west germany (schudack 1996b) has been correlated firstly with the new european mesozoic charophyte biozonation (riveline et al. 1996), secondly with the subdivisions of other microfossil groups in north-west germany, such as ostracodes and dinocysts, and thirdly with the old micropalaeontological subdivisions for the upper jurassic (malm) of north-west germany (e.g. klingler et al. 1962; wick & wolburg 1962). in north-west germany, from the upper oxfordian to the top of the tithonian, five charophyte zones are now recognised, whereas in other parts of western europe there are only three (schudack 1991, 1993). the stratigraphic resolution of this group is not very high in the upper jurassic. each biozone represents a duration of between 0.5 and over 2 million years. the charophyaceae of western europe have been revised in detail by schudack (1993), and a useful compilation of all new data in europe has been compiled by riveline et al. (1996); see also hardenbol et al. (1998, chart 7). dasycladaceae this group seems to be only locally important for biostratigraphy (e.g. portugal, italy, dinarids); a short review was presented by bassoulet (1997b). spores and pollen the value of pollen and spore grains for stratigraphic subdivision is not very high in the upper jurassic. the palynostratigraphy of sweden (north-west skåne) was discussed by guy-ohlson & norling (1988) in connection with a study of the microflora of some boreholes. it was revealed that “detailed correlation without the presence of dinoflagellates or other significant taxa appears difficult if not impossible” (guy-ohlson & norling 1988, p. 15). in the central graben of the southern north sea, upper jurassic sediments were subdivided into four zones on the basis of sporomorphs (herngreen et al. 1988; herngreen & wang 1989). in north-west germany, the upper jurassic was divided into four zones using spores and pollen (gramann et al. 1997). the group apparently has its greatest importance at the system boundaries; it has been used successfully at the triassic–jurassic boundary and, to a lesser degree, at the jurassic–cretaceous boundary. magnetostratigraphy this important method has become more directly applicable for stratigraphic purposes in the last few decades, especially when combined with radiometric and biostratigraphic data. some of the more important papers on this topic are: (1) mesozoic in general, harland et al. (1990), gradstein et al. (1995); (2) upper jurassic – lower cretaceous, ogg (1983), ogg et al. (1984), odin et al. (1994); (3) oxfordian, steiner et al. (1985), ogg & steiner (1988a), ogg et al. (1991), ogg & coe (1998); (4) oxfordian – lower kimmeridgian, ogg & gutowski (1996); (5) kimmeridgian–tithonian, ogg et al. (1994), (6) jurassic–cretaceous boundary, ogg et. al. 1984), ogg & lowrie (1986), ogg & steiner (1988b), ogg et al. (1991, 1994). in a recent publication on sequence chronostratigraphy of european mesozoic basins, charts with magnetochronostratigraphic units have been compiled together with sequence chronostratigraphic and biochronostratigraphic data (hardenbol et al. 1998, see below); the time span of the upper jurassic contains polarity chronozones m35 (upper part) – m19. sequence chronostratigraphy sequence stratigraphy is gaining in importance in chronostratigraphic correlation, as illustrated recently by the presentation of a framework for the european mesozoic and cenozoic basins (hardenbol et al. 1998). many data have been used and compiled in charts, two of which are important for the upper jurassic. they demonstrate the sequence chronostratigraphy (sequences, t-r facies cycles, major transgressive–regressive cycles) for the boreal and tethyan realms combined with the ammonite biochronostratigraphy and magnetostratigraphy, plotted against the time scale. the upper jurassic of europe starts in the upper half of the transgressive part of the second major t-r cycle (1st order cycle, named north sea cycle) in the jurassic and ends within the regressive phase of this cycle. a 100 total of 21 sequences (3rd order cycles) have been recognised (ox 0–8, ki 1–7, ti 1–6) and three 2nd order t-r cycles (t8b–r10b) in the boreal area, whereas the number in the tethyan area is somewhat lower. a detailed overview of the north sea cycle in europe (from the north sea to south-east france) has been presented by jacquin et al. (1998); marginal areas have been studied as follows: east greenland (surlyk 1991; 2003, this volume), portugal, lusitanian basin (leinfelder & wilson 1998), portugal and spain, south iberian margin (olóriz et al. 1991), south-east france (jan du chêne et al. 2000), switzerland (gygi et al. 1998), west carpathians (reháková 2000) and russia (sahagian et al. 1996). acknowledgements the author expresses his sincere thanks to jon r. ineson who kindly improved the english text and provided many useful suggestions. two critical readers, beris m. cox and andrzej wierzbowski, contributed much to the advancement of this paper by their useful proposals and comments. many colleagues helped with literature; in particular, i should like to mention jean guex, franç̧ois atrops, elie cariou, raymond enay, reinhart gygi, vassili mitta, zdenek vasicek and andrzej wierzbowski. technical help has been provided by f. boehm, h. forke, w. kießling and e. samankassou at erlangen, and by the staff of the geological survey of denmark and greenland, to whom i express my thanks. references ager, d.v. 1994: brachiopod stratigraphy in the jurassic. in: cariou, e. & hantzpergue, p. 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